Łukasz Jankowski, Ph.D., Dr. Habil., Eng.

Department of Intelligent Technologies (ZTI)
Division of Safety Engineering (PIB)
position: professor IPPT
telephone: (+48) 22 826 12 81 ext.: 428
room: 432
e-mail: ljank
personal site: http://bluebox.ippt.pan.pl/~ljank/

Doctoral thesis
2004-10-29Modelling and simulation of light propagation in non-aged and aged step-index polymer optical fibres  (UP)
supervisor -- Prof. Markus Klein, Ph.D., UP
1062
 
Habilitation thesis
2014-03-06Dynamic load identification for structural health monitoring 
Supervision of doctoral theses
1.2015-10-29Suwała Grzegorz  Nieparametryczna metoda identyfikacji zmian masy i sztywności konstrukcji670
 

Recent publications
1.Suwała G., Jankowski Ł., Nonparametric identification of structural modifications in Laplace domain, MECHANICAL SYSTEMS AND SIGNAL PROCESSING, ISSN: 0888-3270, DOI: 10.1016/j.ymssp.2016.09.018, Vol.18, pp.867-878, 2017
Abstract:

This paper proposes and experimentally verifies a Laplace-domain method for identification of structural modifications, which (1) unlike time-domain formulations, allows the identification to be focused on these parts of the frequency spectrum that have a high signal-to-noise ratio, and (2) unlike frequency-domain formulations, decreases the influence of numerical artifacts related to the particular choice of the FFT exponential window decay. In comparison to the time-domain approach proposed earlier, advantages of the proposed method are smaller computational cost and higher accuracy, which leads to reliable performance in more difficult identification cases. Analytical formulas for the first- and second-order sensitivity analysis are derived. The approach is based on a reduced nonparametric model, which has the form of a set of selected structural impulse responses. Such a model can be collected purely experimentally, which obviates the need for design and laborious updating of a parametric model, such as a finite element model. The approach is verified experimentally using a 26-node lab 3D truss structure and 30 identification cases of a single mass modification or two concurrent mass modifications.

Keywords:

Structural health monitoring (SHM), Nonparametric model, Inverse problem, Virtual distortion method (VDM), Structural reanalysis, Sensitivity analysis, Laplace domain

Affiliations:
Suwała G.-IPPT PAN
Jankowski Ł.-IPPT PAN
2.Michajłow M., Jankowski Ł., Szolc T., Konowrocki R., Semi-active reduction of vibrations in the mechanical system driven by an electric motor, OPTIMAL CONTROL APPLICATIONS & METHODS, ISSN: 0143-2087, DOI: 10.1002/oca.2297, pp.1-12, 2017
Abstract:

In this paper, a semi-active damping approach is used for reduction of vibrations in a laboratory drivetrain system. The considered drivetrain system is powered by an electric, asynchronous motor at the one side and loaded with a harmonically varying torque on the other side. Here, an influence of electromechanical interaction, i.e., an electromechanical coupling, between the electric motor and the mechanical system has been taken into consideration. The harmonic load signal induces torsional vibrations in the system, which in the steady-state phase of motion become periodic. The aim of the work is to determine the optimal control function for a semi-active damping element, leading to vibration reduction and considering only the steady-state phase of system motion. The optimal control is derived by using a semi-analytical approach based on the optimal control theory aided with supplementary numerical computations. The proposed methodology is fully general, and it can be directly applied to any type of a periodically oscillating system.

Keywords:

electric motor, electromechanical coupling, optimal control, periodic torsional vibrations, semi-active damping

Affiliations:
Michajłow M.-IPPT PAN
Jankowski Ł.-IPPT PAN
Szolc T.-IPPT PAN
Konowrocki R.-IPPT PAN
3.Zhang Q., Jankowski Ł., Damage identification using structural modes based on substructure virtual distortion method, ADVANCES IN STRUCTURAL ENGINEERING, ISSN: 1369-4332, DOI: 10.1177/1369433216660018, Vol.20, No.2, pp.257-271, 2017
Abstract:

A damage identification approach is presented using substructure virtual distortion method which takes the advantage of the fast structural reanalysis technique of virtual distortion method. The formulas of substructure virtual distortion method are deduced in frequency domain, and then the frequency response function of the damaged structure is constructed quickly via the superposition of the frequency response function of the intact structure and the frequency responses caused by the damage-coupling virtual distortions of the substructures. The structural damage extents are identified using the measured modal parameters. Two steps are adopted to increase the efficiency of optimization: the modals of finite element model are estimated quickly from the fast constructed frequency response function during the optimization and the primary distortions of the substructures are extracted by contribution analysis to further reduce the computational work. A six-story frame numerical model and an experiment of a cantilever beam are carried out, respectively, to verify the efficiency and accuracy of the proposed method.

Keywords:

damage identification, frequency domain, structural health monitoring, substructure, virtual distortion method

Affiliations:
Zhang Q.-IPPT PAN
Jankowski Ł.-IPPT PAN
4.Holnicki-Szulc J., Ichchou M., Duan Z., Jankowski Ł., Adaptive Impact Absorption, MATHEMATICAL PROBLEMS IN ENGINEERING, ISSN: 1024-123X, DOI: 10.1155/2016/4871549, Vol.2016, pp.4871549-1-2, 2016
Abstract:

The surging quest for safety is a clearly visible trend in modern societies. One of the related areas of research is the design of systems protecting against heavy dynamic loads such as low and medium velocity traffic-related impacts and environmental loadings. Commonly applied passive systems are typically designed to withstand a specified, well-defined heavy load scenario, which limits their performance over any wider range of loads, including the less heavy loads that are encountered in the lifetime of a typical structure much more often than the maximum limiting loads.

Affiliations:
Holnicki-Szulc J.-IPPT PAN
Ichchou M.-École Centrale de Lyon (FR)
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
Jankowski Ł.-IPPT PAN
5.Michajłow M., Szolc T., Jankowski Ł., Konowrocki R., Semi-Active Reduction of Vibrations of Periodically Oscillating System, Solid State Phenomena, ISSN: 1662-9779, DOI: 10.4028/www.scientific.net/SSP.248.111, Vol.248, pp.111-118, 2016
Abstract:

Periodical vibrations are common phenomenon affecting a wide range of mechanical systems. Most frequently it affects machines designed to work in a steady-state conditions like: turbine, pump, rail vehicle, etc. In those kinds of machines it is always possible to decompose the system motion to basic average-speed constant component and oscillatory component. Usually the second term is treated as undesirable and various techniques are applied in order to minimize it as far as it is possible. These techniques refers to both the hardware selection – meaning the type of damping system (active, semi-active, passive) and the control method selection – meaning the damping system control method. Concerning the control methods, there are many algorithms available in literature devoted to transient systems. One of typical application is to use them in systems experiencing sudden, external force excitation. After destabilization of the system, caused by excitation, the role of the control algorithm is to restore the system stable position and additionally to reach the extreme of some additional criterion. Typical criterions are minimization of the time, of restoring the stable position, minimizing the consumed control energy, etc. On the other hand, considering the steady-state systems, especially based on semi-active damping elements, there are not so many control methods available.This paper focuses on developing the proper methodology for deriving the optimal control strategy of semi-active damping element, to be used in periodically vibrating mechanical system. The control strategy is developed on the basis of the Optimal Control Theory. Numerical computations are involved in order to solve the optimal control problem for the considered test system. Problem solution reveals the periodical nature of optimal control function.

Keywords:

Optimal Control Theory, Periodical Vibrations, Vibration Reduction

Affiliations:
Michajłow M.-IPPT PAN
Szolc T.-IPPT PAN
Jankowski Ł.-IPPT PAN
Konowrocki R.-IPPT PAN
6.Hou J., Jankowski Ł., Ou J., Frequency-domain substructure isolation for local damage, ADVANCES IN STRUCTURAL ENGINEERING, ISSN: 1369-4332, DOI: 10.1260/1369-4332.18.1.137, Vol.18, pp.137-154, 2015
Abstract:

This paper proposes a frequency-domain method of substructure identification for local health monitoring using substructure isolation method (SIM). The first key step of SIM is the numerical construction of the isolated substructure, which is a virtual and independent structure that has the same physical parameters as the real substructure. Damage identification and local monitoring can be then performed using the responses of the simple isolated substructure and any of the classical methods aimed originally at global structural analysis. This paper extends the SIM to frequency domain, which allows the computational efficiency of the method to be significantly increased in comparison to time domain. The mass-spring numerical model is used to introduce the method. Two aluminum beams with the same substructure are then used in experimental verification. In both cases the method performs efficiently and accurately.

Keywords:

structural health monitoring (SHM), damage identification, substructuring frequency domain, boundary

Affiliations:
Hou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
7.Chen G.Y., Codemard C.A., Lewis R.J., Jankowski Ł., Chan J.S., Gorman P.M, Zervas M.N., Enhanced responsivity with skew ray excitation of reflection- and transmission-type refractometric sensors, OPTICS LETTERS, ISSN: 0146-9592, DOI: 10.1364/OL.39.003822, Vol.39, No.13, pp.3822-3825, 2014
Abstract:

The responsivity of optical fibers to refractive index can be enhanced using high-order skew rays compared with using meridional rays. Skew rays can have a much higher number of reflections with increased interaction length along the core–cladding interface, which gives rise to stronger interactions with the external medium. Reflection/transmission-type refractometric sensors based on twin-coupled-core and multimode fibers showed one/two orders of magnitude increase in responsivity with skew ray excitation. The responsivity and sensitivity for the two types are ∼2000%/RIU, ∼1400%/RIU, and 4.9×10−5  RIU, 7.0×10−5  RIU, respectively.

Keywords:

Fiber optics sensors, Fiber properties, Remote sensing and sensors, Propagation, Biological sensing and sensors

Affiliations:
Chen G.Y.-University of Southampton (GB)
Codemard C.A.-Advanced Laser Laboratory SPI Lasers (GB)
Lewis R.J.-Cardiff University (GB)
Jankowski Ł.-IPPT PAN
Chan J.S.-University of Southampton (GB)
Gorman P.M-Advanced Laser Laboratory SPI Lasers (GB)
Zervas M.N.-University of Southampton (GB)
8.Hou J., Jankowski Ł., Ou J., Substructure isolation and damage identification using free responses, Science China Technological Sciences, ISSN: 1674-7321, DOI: 10.1007/s11431-014-5622-1, Vol.57, No.9, pp.1698-1706, 2014
Abstract:

Structural health monitoring (SHM) has become a hot and intensively researched field in civil engineering. Thereinto, damage identification play an important role in maintaining structural integrity and safety. Many effective methods have been proposed for damage identification. However, accurate global identification of large real-world structures is not easy due to their complex and often unknown boundary conditions, nonlinear components, insensitivity of global response to localized damages, etc. Furthermore, global identification often requires lots of sensors and involves large number of unknowns. This is costly, rarely feasible in practice, and usually yields severely ill-conditioned identification problems. Substructuring approach is a possible solution: substructuring methods can focus on local small substructures; they need only a few sensors placed on the substructure and yield smaller and numerically much more feasible identification problems. This paper proposed an improved substructure method using local free response for substructure damage identification. The virtual supports are constructed by Substructure Isolation Method (SIM) using the linear combination of the substructural responses. The influence of the global errors is isolated by adding the virtual supports on the main degree of freedoms (DOFs) of the substructure. Through the correlation analysis, the substructural modes are selected and used for damage identification of the substructure. A plain model of cable stayed bridge is used for the verification of the proposed method.

Keywords:

structural health monitoring (SHM), damage identification, substructure, cable stayed bridge, free response

Affiliations:
Hou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
9.Hou J., Jankowski Ł., Ou J., Structural health monitoring based on combined structural global and local frequencies, MATHEMATICAL PROBLEMS IN ENGINEERING, ISSN: 1024-123X, DOI: 10.1155/2014/405784, Vol.2014, pp.405784-1-13, 2014
Abstract:

This paper presents a parameter estimation method for Structural Health Monitoring based on the combined measured structural global frequencies and structural local frequencies. First, the global test is experimented to obtain the low order modes which can reflect the global information of the structure. Secondly, the mass is added on the member of structure to increase the local dynamic characteristic and to make the member have local primary frequency, which belongs to structural local frequency and is sensitive to local parameters. Then the parameters of the structure can be optimized accurately using the combined structural global frequencies and structural local frequencies. The effectiveness and accuracy of the proposed method are verified by the experiment of a space truss.

Affiliations:
Hou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
10.Zhang Q., Duan Z., Jankowski Ł., Substructure damages and excitations identification using measured response, APPLIED MECHANICS AND MATERIALS, ISSN: 1662-7482, DOI: 10.4028/www.scientific.net/AMM.501-504.843, Vol.501-504, pp.843-846, 2014
Abstract:

This paper proposes a methodology on simultaneous identification of substructure excitation and damage. Structural damages are simulated by virtual distortions which are computed together with unknown excitations using the measured responses through the intact isolated substructure model; the damage extent and type is then recovered by a comparison of the virtual and actual distortions. Unknown factors are reduced greatly which allows the method to be applied on practical complex structure. The computational cost is cutoff sharply. A damaged nonlinearity aluminum beam is used in the experimental verification. Both load and damage are successfully identified.

Keywords:

Damage Identification, Load Identification, Structural Health Monitoring (SHM), Substructure

Affiliations:
Zhang Q.-IPPT PAN
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
Jankowski Ł.-IPPT PAN
11.Hou J., Jankowski Ł., Ou J., An online substructure identification method for local structural health monitoring, SMART MATERIALS AND STRUCTURES, ISSN: 0964-1726, DOI: 10.1088/0964-1726/22/9/095017, Vol.22, No.9, pp.095017-1-11, 2013
Abstract:

This paper proposes a substructure isolation method, which uses time series of measured local response for online monitoring of substructures. The proposed monitoring process consists of two key steps: construction of the isolated substructure, and its identification. The isolated substructure is an independent virtual structure, which is numerically isolated from the global structure by placing virtual supports on the interface. First, the isolated substructure is constructed by a specific linear combination of time series of its measured local responses. Then, the isolated substructure is identified using its local natural frequencies extracted from the combined responses. The substructure is assumed to be linear; the outside part of the global structure can have any characteristics. The method has no requirements on the initial state of the structure, and so the process can be carried out repetitively for online monitoring. Online isolation and monitoring is illustrated in a numerical example with a frame model, and then verified in a cantilever beam experiment.

Affiliations:
Hou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
12.Zhang Q., Jankowski Ł., Duan Z., Simultaneous identification of moving vehicles and bridge damages considering road rough surface, MATHEMATICAL PROBLEMS IN ENGINEERING, ISSN: 1024-123X, DOI: 10.1155/2013/963424, Vol.2013, pp.963424-1-12, 2013
Abstract:

A method for the simultaneous identification of moving vehicles and the damages of the supporting structure from measured responses is presented. A two-axle vehicle model with two degrees of freedom (DOF) is adopted. The extent of the damage and the vehicle parameters were chosen as the optimisation variables, which allow ill conditioning to be avoided and decrease the number of sensors required. The identification is performed by minimising the distance between the measured responses and the computed responses to given optimisation variables. The virtual distortion method (VDM) was used, such that the response of the damaged structure can be computed from comparison with the intact structure subjected to the same vehicle excitation and to the response-coupled virtual distortions. These are related to the optimisation variables by the system impulse response matrix and are expressed by a linear system, which allowed both types of optimisation variables to be treated in a unified way. The numerical cost is reduced by using a moving influence matrix. The adjoint variable method is used for fast sensitivity analysis. A three-span bridge numerical example is presented, where the identification was verified with 5% root mean square (RMS) measurement, and model, error whilst also considering the surface roughness of the road.

Affiliations:
Zhang Q.-IPPT PAN
Jankowski Ł.-IPPT PAN
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
13.Hou J., Jankowski Ł., Ou J., Structural damage identification by adding virtual masses, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-012-0879-0, Vol.48, No.1, pp.59-72, 2013
Abstract:

This paper presents a method for damage identification by adding virtual masses to the structure in order to increase its sensitivity to local damages. The main concept is based on the Virtual Distortion Method (VDM), which is a fast structural reanalysis method that employs virtual distortions or pseudo loads to simulate structural modifications. In this paper, the structure with an added virtual mass is called the virtual structure. First, the acceleration frequency response of the virtual structure is constructed numerically by the VDM using local dynamic data measured only by a single excitation sensor and a single acceleration sensor. Second, the value of the additional mass is determined via sensitivity analysis of the constructed frequency responses of the virtual structure with respect to damage parameters; only the natural frequencies with high sensitivity are selected. This process is repeated for all the considered placements of the virtual mass. At last, the selected natural frequencies of all the virtual structures are used together for damage identification of the real structure. A finite element (FE) model of a plane frame is used to introduce and verify the proposed method. The damage can be identified precisely and effectively even under simulated 5 % Gaussian noise pollution.

Keywords:

Structural health monitoring (SHM), Damage identification, Virtual distortion method (VDM), Virtual mass, Sensitivity analysis

Affiliations:
Hou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
14.Hou J., Ou J., Jankowski Ł., Structural damage identification using additional virtual supports, JOURNAL OF VIBRATION AND SHOCK, ISSN: 1000-3835, Vol.32, No.10, pp.118-129, 2013
Abstract:

针对土木工程中实测模态相对较少,很难进行大型结构的损伤识别的困难,提出附加虚拟支座的损伤识别方法。该方法利用约束子结构方法在结构上附加虚拟支座来增加结构形式的方法,增加识别模态的数量,从而实现结构的准确损伤识别。约束子结构方法的基本思想是通过响应的卷积组合为零将传感器转化为虚拟支座。将附加虚拟支座后的结构定义为虚拟结构,每个虚拟支座对应一个虚拟结构,那么在结构上不同位置附加虚拟支座,则可以获得多个虚拟结构的模态;联合所有虚拟结构和对应的频率即可准确快速的识别出整体结构的损伤。最后通过三层空间框架模型验证方法的有效性。

Keywords:

结构健康监测, 损伤识别, 约束子结构方法, 灵敏度分析, 频率

Affiliations:
Hou J.-Dalian University of Technology (CN)
Ou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
15.Zhang Q., Duan Z., Jankowski Ł., Fast simultaneous identification of structural damages and loads, JOURNAL OF VIBRATION AND SHOCK, ISSN: 1000-3835, Vol.32, No.2, pp.33-38, 2013
Abstract:

本文仅以损伤因子为优化变量,提出一种结构损伤和荷载同步识别的方法。首先通过时域荷载识别的方法将未知荷载转化为损伤因子的函数,将近似荷载作用下的结构响应和实测响应的平方距离作为目标函数,从而降低了需要识别未知参数的数目;然后在目标函数的计算过程中,利用虚拟变形法(VDM)可进行结构快速重分析的思想,快速构造给定损伤因子下系统的脉冲响应,避免每步迭代重新集装系统矩阵,并通过荷载形函数方法进一步提高荷载识别的效率;最后利用二次多项式插值近似结构每个时刻的响应方法和推导对应目标函数的梯度表达式来提高优化搜索的速度。本文利用刚架模型进行数值模拟,准确识别了结构中柱子单元刚度损伤、附加质量以及梁上的未知移动荷载,并通过一个悬臂梁试验进一步验证所提出方法的准确性和可行性。

Keywords:

结构健康监测, 荷载识别, 损伤识别, 虚拟变形法(VDM)

Affiliations:
Zhang Q.-IPPT PAN
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
Jankowski Ł.-IPPT PAN
16.Hou J., Ou J., Jankowski Ł., Model updating experiment of space truss using global and local dynamic information, JOURNAL OF VIBRATION AND SHOCK, ISSN: 1000-3835, Vol.32, No.16, pp.100-105, 2013
Abstract:

由于土木工程结构的复杂性、传感器测点的有限性以及局部损伤的不敏感性等问题,大型结构的模型修正存在一定困难。针对空间桁架结构,为克服上述问题,对其进行整体和局部的动力测试试验,然后联合实测的结构整体和局部动态信息进行模型修正:首先进行空间桁架整体的动力测试试验,获得反应整体特性的低阶模态;然后为了提高局部杆件的动态特性,在杆件上附加一定质量,获得附加质量后杆件的局部主频率,并在各类杆件中选取一定数目进行动态测试;最后联合所有实测结构整体的低阶模态和杆件的局部主频率,对空间桁架结构进行模型修正。修正后的模态参数与实测模态吻合良好,验证了方法的有效性。

Keywords:

结构健康监测, 模型修正, 桁架, 频率, 振型

Affiliations:
Hou J.-Dalian University of Technology (CN)
Ou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
17.Zhang Q., Hou J., Duan Z., Jankowski Ł., Substructural virtual distortion method for damage identification, Engineering Mechanics, ISSN: 1000-4750, DOI: 10.6052/j.issn.1000-4750.2012.08.0613, Vol.30, No.12, pp.176-182, 2013
Abstract:

针对大型土木结构损伤识别优化效率低的问题,提出了子结构虚拟变形方法。虚拟变形方法是一种结构
快速重分析的方法,该方法利用单元的虚拟变形模拟结构的损伤,可以在不重新建立有限元模型的情况下,快速
计算出结构参数改变后的结构响应。该文基于虚拟变形法的基本思想,对子结构的刚度矩阵进行分解和对损伤后
结构运动方程进行整理,推导出利用子结构的虚拟变形刻画损伤的方法,扩展了虚拟变形方法的适用范围;并且
给出了虚拟变形和结构响应的相关性计算公式,通过相关性分析提取主要的虚拟变形,减少参与计算的子结构虚
拟变形的数目,提高计算效率;最后利用一个五十层框架的数值仿真验证方法的有效性

Affiliations:
Zhang Q.-IPPT PAN
Hou J.-Dalian University of Technology (CN)
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
Jankowski Ł.-IPPT PAN
18.Hou J., Ou J., Jankowski Ł., The experiment of substructure isolation and identification using local time series, Engineering Mechanics, ISSN: 1000-4750, DOI: 10.6052/j.issn.1000-4750.2011.10.0722, Vol.30, No.4, pp.129-135, 2013
Abstract:

针对大型复杂结构的整体监测常常面临测量信息不足等困难,提出只利用局部动态响应进行子结构损伤识别的约束子结构方法。约束子结构方法是通过子结构响应的卷积组合限制子结构边界的响应为零,来实现施加虚拟支座,从而将子结构分离出整体,然后利用构造的相应子结构内部响应,进行子结构损伤识别。该文利用先分段提取结构响应的子时间序列,再延时排列Toeplitz矩阵的方式,使基于不同响应的构造约束子结构的方程具有相同表达式,统一了约束子结构方法的基本思想。通过测量悬臂梁的局部动力响应,利用局部响应的时间序列实现了子结构的快速准确地分离和识别,验证了方法的实用性和有效性。

Keywords:

结构健康监测, 损伤识别, 子结构, 时间序列, 脉冲响应

Affiliations:
Hou J.-Dalian University of Technology (CN)
Ou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
19.Suwała G., Biczyk J., Jankowski Ł., Nonparametric identification of added masses in frequency domain: a numerical study, IPPT REPORTS, ISSN: 2299-3657, Vol.4f, pp.1-6, 2013
Abstract:

This paper presents a theoretical derivation and reports on a numerical verification of a model-free method for identification of added masses in truss structures. No parametric numerical model of the monitored structure is required, so that there is no need for initial model updating and fine tuning. This is a continuation and an improvement of a previous research that resulted in a time-domain identification method, which was tested to be accurate but very time-consuming. A general methodology is briefly introduced, including the inverse problem, and a numerical verification is reported. The aim of the numerical study is to test the accuracy of the proposed method and its sensitivity to various parameters (such as simulated measurement noise and decay rate of the exponential FFT window) in a numerically controlled environment. The verification uses a finite element model of the same real structure that was tested with the time-domain version of the approach. A natural further step is a lab verification based on experimental data.

Affiliations:
Suwała G.-IPPT PAN
Biczyk J.-Adaptronica Sp. z o. o. (PL)
Jankowski Ł.-IPPT PAN
20.Zhang Q., Jankowski Ł., Duan Z., Simultaneous identification of excitation time histories and parametrized structural damages, MECHANICAL SYSTEMS AND SIGNAL PROCESSING, ISSN: 0888-3270, DOI: 10.1016/j.ymssp.2012.06.018, Vol.33, pp.56-68, 2012
Abstract:

This paper presents and experimentally verifies an effective method for simultaneous identification of excitations and damages, which are two crucial factors in structural health monitoring and which often coexist in practice. The unknowns are identified by minimizing a time-domain square distance between the measured and the computed responses. Even though both damage and excitation are unknown, only damage parameters are treated here as the optimization variables: given the damage, the excitation is uniquely determined from the measured responses. As a result, all unknowns are of the same type, which allows standard optimization algorithms to be used and obviates the need for two-step procedures. The sensitivity analysis is facilitated by interpolating in each iteration the relation between structural responses and damage parameters. The numerical costs are further decreased by the fast reanalysis approach of the virtual distortion method (VDM), which is used to compute exact impulse responses of the damaged structure. The proposed methodology is verified both numerically (using a multi-span frame) and experimentally (using a cantilever beam). Stiffness-related damages and mass-related modifications are identified successfully together with the three tested types of external excitation.

Keywords:

Structural health monitoring, Load identification, Damage identification, Virtual distortion method (VDM)

Affiliations:
Zhang Q.-IPPT PAN
Jankowski Ł.-IPPT PAN
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
21.Suwała G., Jankowski Ł., A model-free method for identification of mass modifications, STRUCTURAL CONTROL AND HEALTH MONITORING, ISSN: 1545-2255, DOI: 10.1002/stc.417, Vol.19, No.2, pp.216-230, 2012
Abstract:

In this paper, a model-free methodology for off-line identification of modifications of structural mass is proposed and verified experimentally. The methodology of the virtual distortion method is used: the modifications are modeled by the equivalent pseudo-loads that act in the related degrees of freedom of the unmodified structure; their influence on the response is computed using a convolution of the pseudo-loads with the experimentally obtained local impulse responses. As a result, experimentally measured data are directly used to model the response of the modified structure in a non-parametric way. The approach obviates the need for a parametric numerical model of the structure and for laborious initial updating of its parameters. Moreover, no topological information about the structure is required, besides potential locations of the modifications. The identification is stated as a problem of minimization of the discrepancy between the measured and the modeled responses of the modified structure. The formulation allows the adjoint variable method to be used for a quick first- and second-order sensitivity analysis, so that Hessian-based optimization algorithms can be used for fast convergence. The proposed methodology was experimentally verified using a 3D truss structure with 70 elements. Mass modifications in a single node and in two nodes were considered. Given the initially measured local impulse responses, a single sensor and single excitation were sufficient for the identification.

Keywords:

mass identification, structural health monitoring (SHM), virtual distortion method (VDM), model-free, non-parametric modeling, adjoint variable method

Affiliations:
Suwała G.-IPPT PAN
Jankowski Ł.-IPPT PAN
22.Hou J., Jankowski Ł., Ou J., Experimental study of the substructure isolation method for local health monitoring, STRUCTURAL CONTROL AND HEALTH MONITORING, ISSN: 1545-2255, DOI: 10.1002/stc.443, Vol.19, No.4, pp.491-510, 2012
Abstract:

This paper extends and studies experimentally the substructure isolation method. Local health monitoring is significant for large and complex structures, since it costs less and can be easily implemented compared with global analysis. In contrast to other substructuring methods, in which the substructure is separated from the global structure, but coupled to it via the interface forces, the substructure isolation method isolates the substructure into an independent structure by placing virtual fixed supports on the interface. Model updating or damage identification can be then performed locally and precisely using the constructed responses of the isolated substructure and any of the existing methods aimed originally at global identification. This paper discusses and further extends the approach to improve its performance in real applications. A new type of virtual interface support (free support) is proposed for isolation. Relaxation of the original requirements concerning the type and placement of the isolating excitations is discussed. Previously, the method relied on the linearity of the global structure; here, only the substructure is required to be linear, the global structure besides the substructure can be non-linear, yielding, changing or unknown. A damaged cantilever beam is used in the experimental study. Up to three modified global structures with the same substructure are used to test the robustness of the isolation with respect to unknown modifications and non-linearities of the outside structure. Two typical global health monitoring methods are applied at the substructural level. A comparison with the results obtained from a generic substructure separation method is offered.

Keywords:

Structural Health Monitoring (SHM), substructure isolation method, substructural identification, virtual distortion method (VDM), local monitoring, virtual supports

Affiliations:
Hou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
23.Hou J., Ou J., Jankowski Ł., The study and experiment of substructure damage identification based on local primary frequency, Engineering Mechanics, ISSN: 1000-4750, DOI: 10.6052/j.issn.1000-4750.2010.12.0928, Vol.29, No.9, pp.99-105, 2012
Abstract:

针对大型复杂结构的整体监测常常面临测量信息不足等困难,提出只利用局部动态响应进行子结构损伤识别的局部主频率方法.子结构的局部主频率指:如果整体模态中含有以局部子结构位移为主的模态,即等价于在局部激励作用下,整体结构的振动主要体现为子结构的振动,并且主要以这阶局部模态振动为主,那么对应的该阶频率即定义为子结构的局部主频率.局部主频率主要反映子结构的局部特性,对子结构损伤的灵敏度高,所以只利用局部主频率就可以识别子结构.当子结构特征不明显时,提出通过附加质量使子结构具有局部主频率的有效方法.该文进行了大型空间桁架的局部动力测试试验,试验中通过附加质量使杆件子结构具有局部主频率,并能准确地识别出杆件损伤的位置和程度.

Keywords:

结构健康监测, 损伤识别, 子结构, 模态分析, 频率响应

Affiliations:
Hou J.-Dalian University of Technology (CN)
Ou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
24.Zhang Q., Duan Z., Jankowski Ł., The study on simultaneous identification of structural damages and loads, Engineering Mechanics, ISSN: 1000-4750, DOI: 10.6052/j.issn.1000-4750.2011.05.0275, Vol.29, No.12, pp.316-321, 2012
Abstract:

针对结构中同时存在未知损伤和荷载的情况,基于虚拟变形法(VDM)发展一种两者共同识别的时域方法。VDM方法利用虚拟变形模拟结构损伤,可快速计算模型改变后的响应。该文首先结合有限元理论把VDM方法拓展到具有多个单元变形的结构中;然后考虑结构存在未知荷载时,利用未损伤理论模型同时识别荷载和虚拟变形,继而由虚拟变形和单元实际变形的关系来识别判断损伤类型和识别损伤大小;最后通过一个悬臂梁的试验进行方法验证,试验中未知荷载和损伤(包括其类型和大小)均能够被有效识别,并利用提出的移动时间窗和荷载形函数方法实现损伤与荷载的在线识别。

Keywords:

结构健康监测, 虚拟变形法(VDM), 荷载识别, 损伤识别, 荷载形函数

Affiliations:
Zhang Q.-IPPT PAN
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
Jankowski Ł.-IPPT PAN
25.Zhang Q., Duan Z., Jankowski Ł., Parameter identification of moving vehicles considering road roughness of bridge, Journal of Vibration Engineering, ISSN: 1004-4523, Vol.25, No.2, pp.146-153, 2012
Abstract:

基于虚拟变形(VDM)方法中移动动态影响矩阵的概念,利用双自由度质量-弹簧阻尼模型模拟移动车辆,系统推导和阐述了车-桥耦合系统中粗糙路面上移动体参数的识别方法。以移动体参数的修正因子为优化变量,通过最小化桥体结构实测响应和计算响应的平方距离进行识别,识别精度高,对噪声鲁棒性强,且较少的传感器就能识别多个移动体参数。利用移动动态影响矩阵,每步优化中无需时时重构系统参数矩阵,计算效率高。利用一个三跨连续梁模型验证该方法的有效性,在5%的噪声影响下,利用一个传感器可以准确地识别多个移动体参数和移动荷载。此外,通过比较平坦路面与粗糙路面上的移动体参数的识别方法和结果,结合车体参数的灵敏度分析,说明了路面粗糙度、移动体参数对结构响应的影响及不同情况下参数识别中优化变量的选取原则。

Keywords:

结构健康监测, 移动车辆(荷载)识别, 虚拟变形法(VDM), 影响矩阵, 粗糙路面

Affiliations:
Zhang Q.-IPPT PAN
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
Jankowski Ł.-IPPT PAN
26.Jilin Hou, Jankowski Ł., Jinping Ou, A substructure isolation method for local structural health monitoring, STRUCTURAL CONTROL AND HEALTH MONITORING, ISSN: 1545-2255, DOI: 10.1002/stc.389, Vol.18, pp.601-618, 2011
Abstract:

This paper describes an effective method of substructure isolation for local structural health monitoring (SHM). In practice, often only a small part of a larger structure is critical and needs monitoring. However, typical low-frequency SHM methods require modeling and analysis of the global structure, which can be costly, time-consuming and error-prone. The proposed approach is based on the virtual distortion method (VDM) and uses force distortions to model fixed supports in the boundary nodes to isolate the considered substructure from influences of the rest of the structure. Therefore, given an excitation of the substructure and the measured response of the global structure, the response of the substructure treated as fixed supported can be computed. Local-only monitoring is then possible using virtually any of the existing methods. However, consistently with the isolation methodology, strain distortions are used here for modeling of damages of the isolated substructure. The discrete adjoint variable method is used for the first time within the framework of the VDM in order to perform fast analytical sensitivity analysis and improve the computational effectiveness of the damage identification by one order of magnitude. A numerical example of a frame-truss with 5 and 10% noise level and an experiment of a cantilever beam are presented to validate the isolation methodology.

Keywords:

substructure isolation, damage identification, virtual distortion method (VDM), structural health monitoring, adjoint variable method

Affiliations:
Jilin Hou-other affiliation
Jankowski Ł.-IPPT PAN
Jinping Ou-other affiliation
27.Zhang Q., Duan Z., Jankowski Ł., Wang F., Experimental validation of a fast dynamic load identification method based on load shape function, JOURNAL OF VIBRATION AND SHOCK, ISSN: 1000-3835, Vol.30, No.9, pp.98-102, 154, 2011
Abstract:

在动态荷载识别中常常由于矩阵的病态性影响识别的精度,利用有限元理论中的形函数逼近荷载曲线,将识别离散的荷载历程转化为计算有限的形函数权重,从而显著改善反卷积法识别荷载中存在的采样时间长或采样频率高时数值求解困难的问题;并能改善反问题的病态性,提高对噪音的鲁棒性。一个连续梁的数值算例比较验证了该方法在5%的高斯噪声影响下能精确地识别未知荷载。悬臂梁试验中,通过实测的结构动态响应,在移动时间窗内利用荷载形函数方法可以实现激励的在线识别。

Keywords:

结构健康监测, 荷载识别, 在线识别, 反卷积法, 形函数

Affiliations:
Zhang Q.-IPPT PAN
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
Jankowski Ł.-IPPT PAN
Wang F.-Dalian University of Technology (CN)
28.Zhang Q., Duan Z., Jankowski Ł., Moving mass identification of vehicle-bridge coupled system based on virtual distortion method, Chinese Journal of Theoretical and Applied Mechanics, ISSN: 0459-1879, DOI: 10.6052/0459-1879-2011-3-lxxb2009-481, Vol.43, No.3, pp.598-610, 2011
Abstract:

利用双自由度质量-弹簧阻尼模型模拟移动车辆, 并基于虚拟变形(VDM)方法的结构快速重分 析思想, 提出一种车-桥耦合系统的移动质量快速识别的有效方法. 该方法以双自由度车体模 型的质量为变量, 通过最小化桥体结构实测响应和计算响应的平方距离来识别移动质量 (载荷), 避免了识别载荷时常遇到的病态问题, 对噪声鲁棒性强, 且需要传感器信息少. 每步优化 中, 利用在VDM方法基础上提出的移动动态影响矩阵概念, 无需时时重构车-桥耦合系统的时 变系统参数矩阵, 显著提高了计算效率. 利用数值框架梁模型, 通过比较不同车辆简化模型 对移动体质量及等效移动载荷的识别效果, 验证了该方法的可行性和有效性, 即使在5% 的噪声影响下, 利用一个传感器可以准确地识别多个移动体的质量.

Keywords:

结构健康监测, 移动车辆识别, 结构重分析, 虚拟变形法, 影响矩阵

Affiliations:
Zhang Q.-IPPT PAN
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
Jankowski Ł.-IPPT PAN
29.Zhang Q., Jankowski Ł., Duan Z., Identification of coexistent load and damage, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-009-0421-1, Vol.41, pp.243-253, 2010
Abstract:

Load reconstruction and damage identification are crucial problems in structural health monitoring. However, it seems there is not much investigation on identification of coexistent load and damage, although in practice they usually exist together. This paper presents a methodology to solve this problem based on the Virtual Distortion Method. A damaged structure is modeled by an equivalent intact structure subjected to the same loads and to virtual distortions which model the damages. The measured structural response is used to identify the loads, the distortions and to recover the stress-strain relationship of the damaged elements. This way both the damage type and extent are identified. The approach can be used off-line and online by repetitive applications in a moving time window. A numerical experiment of a truss with 5% measurement error validates that the two tested damage types (constant stiffness reduction and breathing crack) can be identified along with the loads.

Keywords:

Structural health monitoring, Load identification, Damage identification, Virtual Distortion Method (VDM)

Affiliations:
Zhang Q.-IPPT PAN
Jankowski Ł.-IPPT PAN
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
30.Zhang Q., Jankowski Ł., Duan Z., Simultaneous identification of moving masses and structural damage, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-010-0528-4, Vol.42, pp.907-922, 2010
Abstract:

A method for simultaneous identification of moving masses and damages of the supporting structure from measured responses is presented. The interaction forces between the masses and the structure are used as excitation. Masses and damage extents are used as the optimization variables; compared to the approaches based on identification of the interaction forces, it allows ill-conditioning to be avoided and decreases the number of required sensors. The virtual distortion method is used; the damaged structure is modeled by the intact structure subjected to response-coupled virtual distortions and moving forces. These are related to the optimization variables via a linear system, which allows the optimization variables of both kinds to be treated in a unified way. A moving dynamic influence matrix is introduced to reduce the numerical costs. The adjoint variable method is used for fast sensitivity analysis. A numerical experiment of a three-span beam with 10% rms measurement error and three types of model errors is presented.

Keywords:

Moving load identification, Damage identification, Mass identification, Virtual distortion method (VDM), Structural health monitoring (SHM)

Affiliations:
Zhang Q.-IPPT PAN
Jankowski Ł.-IPPT PAN
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
31.Zhang Q., Duan Z., Jankowski Ł., Moving mass identification based on Virtual Distortion Method, Journal of Vibration Engineering, ISSN: 1004-4523, Vol.23, No.5, pp.494-501, 2010
Abstract:

在车-桥耦合系统的移动质量(荷载)识别反问题中,识别移动质量会面临重构系统、优化缓慢的问题;而若直接识别移动荷载常常会遇到病态问题且对噪音敏感。针对这些缺陷,根据虚拟变形法(VDM)的结构快速重分析思想,提出移动动态影响矩阵,实现利用较少的传感器即可快速而准确地识别移动质量(荷载)。以移动质量为优化变量,避免了识别荷载常遇到的病态问题,对噪音鲁棒性强;且需要传感器信息少。每步优化中,利用移动动态影响矩阵,无需时时重构车-桥耦合系统的时变系统参数矩阵,优化效率高。VDM方法的思想是将实际结构的响应计算转化为初始结构模型在相同外荷载作用下的响应,与在结构模型发生改变的位置施加相关的虚拟变形或虚拟力引起的响应的线性叠加。通过简支梁模型和框架梁模型验证了该方法的可行性和有效性,即使在5%的噪声影响下,利用一个传感器就可以很好地识别多个移动质量。

Keywords:

结构健康监测, 结构重分析, 影响矩阵

Affiliations:
Zhang Q.-IPPT PAN
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
Jankowski Ł.-IPPT PAN
32.Jankowski Ł., Off-line identification of dynamic loads, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-008-0249-0, Vol.37, No.6, pp.609-623, 2009
Abstract:

This paper considers off-line identification of spatial and temporal characteristics of a dynamic load, and is focused on the case of a limited number of sensors. Both elastic and elasto-plastic structural behaviours are taken into account. The identification is performed off-line, based on optimisation of modelled local structural responses, and—in the case of limited number of sensors—identifies an observationally equivalent load, which in a given sense optimally approximates the actual load. Compared to previous researches this approach allows to identify general dynamic loads of unknown locations, including multiple impacts and moving loads, and gives more insight into the identification process by distinguishing between the reconstructible and unreconstructible load components. Additionally, the problem of optimum sensor location is discussed.

Keywords:

Load identification, Inverse dynamics, Elasto-plastic structures, Black box, Forensic engineering

Affiliations:
Jankowski Ł.-IPPT PAN
33.Mikułowski G., Jankowski Ł., Adaptive Landing Gear: optimum control strategy and potential for improvement, SHOCK AND VIBRATION, ISSN: 1070-9622, DOI: 10.3233/SAV-2009-0460, Vol.16, No.2, pp.175-194, 2009
Abstract:

An adaptive landing gear is a landing gear (LG) capable of active adaptation to particular landing conditions by means of controlled hydraulic force. The objective of the adaptive control is to mitigate the peak force transferred to the aircraft structure during touch-down, and thus to limit the structural fatigue factor. This paper investigates the ultimate limits for improvement due to various strategies of active control. Five strategies are proposed and investigated numerically using a~validated model of a real, passive landing gear as a reference. Potential for improvement is estimated statistically in terms of the mean and median (significant) peak strut forces as well as in terms of the extended safe sinking velocity range. Three control strategies are verified experimentally using a laboratory test stand.

Keywords:

Adaptive landing gear, adaptive impact absorption, shock absorber, load mitigation

Affiliations:
Mikułowski G.-IPPT PAN
Jankowski Ł.-IPPT PAN
34.Suwała G., Jankowski Ł., A model-less method for added mass identification, SOLID STATE PHENOMENA, ISSN: 1012-0394, DOI: 10.4028/www.scientific.net/SSP.147-149.570, Vol.147-149, pp.570-575, 2009
Abstract:

This paper present and validates experimentally a model-less methodology for off-line identification of modifications of nodal masses. The proposed approach is entirely based on experimentally measured data; hence no numerical modeling and tedious fine-tuning of the model are necessary. The influence of the added mass is modeled using virtual distortion forces and experimentally obtained system transfer matrices. The identification amounts to solving an optimization problem of minimizing the mean square distance between measured and modeled structural responses, the latter is based on previously recorded responses of the unaffected structure.

Keywords:

mass identification, model-less SHM, virtual distortion method (VDM), inverse dynamics

Affiliations:
Suwała G.-IPPT PAN
Jankowski Ł.-IPPT PAN
35.Szolc T., Jankowski Ł., Active control of transient torsional vibrations due to run-up of a rotor machine driven by the electric motor, VIBRATIONS IN PHYSICAL SYSTEMS, ISSN: 0860-6897, Vol.23, pp.341-346, 2008
Abstract:

In the paper active control of transient torsional vibrations induced by the electric motor during run-ups of the radial compressor drive system is performed by means of couplings with the magneto-rheological fluid. The main purpose of these studies is a minimisation of vibration amplitudes in order to increase the fatigue durability of the most responsible elements. The theoretical investigations are based on a hybrid structural model of the vibrating mechanical system and sensitivity analysis of the response with respect to the damping characteristics of the control couplings.

Keywords:

active control, transient vibrations, drive system, electric motor

Affiliations:
Szolc T.-IPPT PAN
Jankowski Ł.-IPPT PAN
36.Jankowski Ł., Wikło M., Holnicki-Szulc J., Robust post-accident reconstruction of loading forces, KEY ENGINEERING MATERIALS, ISSN: 1662-9795, DOI: 10.4028/www.scientific.net/KEM.347.659, Vol.347, pp.659-664, 2007
Abstract:

The paper presents a novel methodology for robust post-accident reconstruction of spatial and temporal characteristics of the load. The methodology is based on analysis of local structural response, and identifies an observationally equivalent load, which in a given sense optimally approximates the real load. Compared to previous researches this approach allows to use a limited number of sensors to reconstruct general dynamic loads of unknown location including multiple impacts and moving loads. Additionally, the problem of optimum sensor location is studied.

Keywords:

impact identification, inverse dynamics, smart systems, structural health monitoring

Affiliations:
Jankowski Ł.-IPPT PAN
Wikło M.-IPPT PAN
Holnicki-Szulc J.-IPPT PAN

List of recent monographs
1.
323
Jankowski Ł., Dynamic load identification for structural health monitoring, Rozprawa habilitacyjna, IPPT Reports on Fundamental Technological Research, pp.1-280, 2013
2.
73
Jankowski Ł., Modelling and simulation of light propagation in non-aged and aged step-index polymer optical fibres, Wirtschaftsverlag NW Verlag für Neue Wissenschaft, pp.1-137, 2005
List of chapters in recent monographs
1.
349
Jankowski Ł., Holnicki-Szulc J., Świercz A., Mróz M., Kołakowski P., Monitorowanie obciążeń i stanu technicznego konstrukcji mostowych, rozdział: Numeryczne metody identyfikacji parametrów konstrukcji, IPPT Reports on Fundamental Technological Research, pp.109-159, 2014
2.
166
Jankowski Ł., Bednarek T., Sosnowski W., Knowledge acquisition for hybrid systems of risk assessment and critical machinery diagnosis, rozdział: Selected topics in identification of dynamic loads, Silesian University of Technology (Gliwice), Moczulski W., Ciupke K. (Eds.), pp.357-404, 2008
3.
196
Pawłowski P.K., Mikułowski G., Graczykowski C., Ostrowski M., Jankowski Ł., Holnicki-Szulc J., Smart technologies for safety engineering, rozdział: Adaptive impact absorption, Wiley, Holnicki-Szulc J. (Ed.), pp.153-213, 2008
4.
197
Jankowski Ł., Sekuła K., Błachowski B.D., Wikło M., Holnicki-Szulc J., Smart technologies for safety engineering, rozdział: Dynamic load monitoring, Wiley, Holnicki-Szulc J. (Ed.), pp.105-151, 2008
5.
202
Wikło M., Jankowski Ł., Mróz M., Holnicki-Szulc J., Smart technologies for safety engineering, rozdział: VDM-Based remodeling of adaptive structures exposed to impact loads, Wiley, Holnicki-Szulc J. (Ed.), pp.215-249, 2008

Conference papers
1.Popławski B., Graczykowski C., Jankowski Ł., Controllable Truss-Frame Nodes in Semi-Active Damping of Vibrations, Advances in Science and Technology, ISSN: 1662-0356, DOI: 10.4028/www.scientific.net/AST.101.89, Vol.101, pp.89-94, 2017
Abstract:

In recent years, vibration damping strategies based on semi-active management of strain energy have attracted a large interest and were proven highly effective. However, most of published research considers simple one degree of freedom systems or study the same basic example (the first vibration mode of a cantilever beam) with the same control strategy. This contribution focuses on truss-frame nodes with controllable moment-bearing ability. It proposes and tests an approach that allows the control strategy to be extended to more complex structures and vibration patterns.

Keywords:

adaptive impact absorption, smart structures, semi-active control, safety engineering

Affiliations:
Popławski B.-IPPT PAN
Graczykowski C.-IPPT PAN
Jankowski Ł.-IPPT PAN
2.Jankowski Ł., Graczykowski C., Pawłowski P., Mikułowski G., Ostrowski M., Popławski B., Faraj R., Suwała G., Holnicki-Szulc J., Adaptive Self-Protection against Shock and Vibration, Advances in Science and Technology, ISSN: 1662-0356, DOI: 10.4028/www.scientific.net/AST.101.133, Vol.101, pp.133-142, 2017
Abstract:

This contribution reviews the challenges in adaptive self-protection of structures. A proper semi-active control strategy can significantly increase structural ability to absorb impact-type loads and damp the resulting vibrations. Discussed systems constitute a new class of smart structures capable of a real-time identification of loads and vibration patterns, followed by a low-cost optimum absorption of the energy by structural adaptation. Given the always surging quest for safety, such systems have a great potential for practical applications (in landing gears, road barriers, space structures, etc.). Compared to passive systems, their better performance can be attributed to the paradigm of self-adaptivity, which is ubiquitous in nature, but still sparsely applied in structural engineering. Being in the early stages of development, their ultimate success depends on a concerted effort in facing a number of challenges. This contribution discusses some of the important problems, including these of a conceptual, technological, methodological and software engineering nature.

Keywords:

adaptive impact absorption, smart structures, semi-active control, safety engineering

Affiliations:
Jankowski Ł.-IPPT PAN
Graczykowski C.-IPPT PAN
Pawłowski P.-IPPT PAN
Mikułowski G.-IPPT PAN
Ostrowski M.-IPPT PAN
Popławski B.-IPPT PAN
Faraj R.-IPPT PAN
Suwała G.-IPPT PAN
Holnicki-Szulc J.-IPPT PAN
3.Jankowski Ł., Holnicki-Szulc J., Mróz A., A new strategy for adaptive impact absorption (AIA), SMART 2015, 7th ECCOMAS Thematic Conference on Smart Structures and Materials, 2015-06-03/06-05, Ponta Delgada (PT), pp.1-17, 2015
Abstract:

This contribution presents and overviews a new class of strategies for Adaptive Impact Absorption (AIA) and illustrates a selected strategy in a numerical example. The proposed strategies are based on a challenging approach of a semi-active management and dissipation of structural kinetic and potential energy. The entire process of AIA is considered, including its two main phases: semi-actively controlled reception of an impact and semi-actively controlled damping of the resulting structural vibrations. Management and redistribution of impact energy seems to be one of the most promising and challenging problems in the field of AIA, which requires a substantial theoretical progress in semi-active control strategies and in structural optimization, besides a technological progress in semi-active actuators.

Keywords:

Adaptive impact absorption, smart structures, adaptive structures, impact energy management, bilinear control, switched systems

Affiliations:
Jankowski Ł.-IPPT PAN
Holnicki-Szulc J.-IPPT PAN
Mróz A.-IPPT PAN
4.Suwała G., Jankowski Ł., Nonparametric identification of added masses in frequency domain, 6WCSCM, 6th World Conference on Structural Control and Monitoring, 2014-07-15/07-17, Barcelona (ES), pp.2358-2366, 2014
Abstract:

This paper presents a frequency-domain, nonparametric method for identification of added masses, and reports on its experimental verification. The identification is directly based on experimentally collected characteristics of the unmodified structure, so that no parametric numerical model of the monitored structure is required. Consequently, there is no need for the initial stage of model updating. This is a continuation of and an improvement over a previous research that resulted in a time-domain identification method, which was tested to be accurate but significantly time-consuming. For the experimental verification, a 4~m long 3D truss structure with 26 nodes and 70 elements is used. A total of 12 modification cases is tested: in each of 3~selected nodes, 4~additional masses are separately added and successfully identified.

Affiliations:
Suwała G.-IPPT PAN
Jankowski Ł.-IPPT PAN
5.Zhang Q., Jankowski Ł., Duan Z., Structural damage identification using random response based on Virtual Distortion Method, 6WCSCM, 6th World Conference on Structural Control and Monitoring, 2014-07-15/07-17, Barcelona (ES), pp.740-745, 2014
Abstract:

Structural damage identification plays a critical role in structural health monitoring on evaluating structural safety and maintaining structural integrity. This paper presents a damage identification approach based on Virtual Distortion Method (VDM) using random response. VDM is a fast structural reanalysis method in which virtual distortions are introduced to simulate structural damages or modifications. Via VDM, responses of damaged structure can be computed quickly without reanalysis of the whole structure. In this paper, firstly the frequency response of damaged structure is constructed efficiently using VDM, and then damage extents are optimized using the objective function which is computed using the MAC (modal assurance criterion) of the power spectrum of theoretical response and measured responses. At last, a plane truss is proposed to verify the proposed method.

Affiliations:
Zhang Q.-IPPT PAN
Jankowski Ł.-IPPT PAN
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
6.Hou J., Jankowski Ł., Ou J., Construction of Virtual Structure for Damage Identification, 6WCSCM, 6th World Conference on Structural Control and Monitoring, 2014-07-15/07-17, Barcelona (ES), pp.732-739, 2014
Abstract:

This paper presents a damage identification method using virtual structure. The main concept is based on Virtual Distortion method (VDM), which belongs to a fast structural reanalysis method and employs the virtual distortions or virtual forces to simulate the structural modifications. In this paper, the structure with virtual mass, damping or stiffness is defined as virtual structure. Firstly, the frequency response of the virtual structure is constructed by VDM method; Secondly, the natural frequencies of virtual structure with additional masses or stiffness are estimated; At last, the estimated natural frequencies of the virtual structure are used for damage optimization of the structure. A numerical beam model is used to describe and verify the proposed method.

Affiliations:
Hou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
7.Hou J., Jankowski Ł., Ou J., The substructure isolation method for local analysis at the substructural level, SMART2013, 6th ECCOMAS Thematic Conference on Smart Structures and Materials, 2013-09-03/09-06, Turyn (IT), pp.1-20, 2013
Abstract:

This paper presents the substructure isolation method, which a novel method for substructural analysis and structural health monitoring (SHM) at the local level. The motivation behind it are the facts that global SHM of large and complex structures is generally difficult and that often only small substructures are crucial and require monitoring. These facts suggest that there is a need for ways of applying global SHM approaches locally, which is impossible with typical substructuring methods. The paper offers an overview of the common substructuring approaches and describes the substructure isolation method. The method splits the task of local monitoring into two stages: (1) Isolation; the outside influences are numerically eliminated from the measured response of the substructure. (2) Local SHM; all methods aimed originally at global SHM can be used with the constructed response of the isolated substructure. Local analysis is possible in time domain as well as in frequency domain; in offline and in online time regimes. The method is illustrated in a numerical example and substantiated in an experimental study using a damaged cantilever beam; the robustness of the isolation with respect to unknown modifications of the outside structure is tested.

Keywords:

Substructuring, Structural Health Monitoring, SHM, Damage identification, Local analysis

Affiliations:
Hou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
8.Hou J., Jankowski Ł., Ou J., Large substructure identification using substructure isolation method, Conference on Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems, 2012-03-12/03-15, San Diego (US), DOI: 10.1117/12.915102, Vol.8345, pp.83453V-1-7, 2012
Abstract:

Substructure Isolation Method (SIM) is used for large substructure identification. It utilizes the responses of global structure to construct the responses of the isolated substructure, which is a virtual and independent structure with the same system parameters as the real substructure. Then, the substructure identification is carried out equivalently via the isolated substructure and flexibly by some of the existing identification methods which aim originally at the large structure. Therefore, the performance of the SIM offers the possibility that the large substructure can be identified. A numerical bridge model is used to verify the proposed method, which preforms efficiently and accurately.

Keywords:

Structural Health Monitoring (SHM), Damage identification, Substructure, Interface force

Affiliations:
Hou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
9.Zhang Q., Jankowski Ł., Duan Z., Damage identification using Substructural Virtual Distortion Method, Conference on Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems, 2012-03-12/03-15, San Diego (US), DOI: 10.1117/12.915126, Vol.8345, pp.83453X-1-7, 2012
Abstract:

This paper presents a Substructure Virtual Distortion Method (SVDM) for damage identification based on Virtual Distortion Method (VDM). VDM is a fast structural reanalysis method by introducing virtual distortions to simulate structural damages. SVDM extends the virtual distortions regard to the damaged elements to the related substructures. Such that the required number of virtual distortions depends on the substructure other than the elements, which reduces the computational work a lot. In addition, for a structure under a certain external force, the dynamic responses may be reflected by a few of main eigenvectors, and thus it only needs to compute the virtual distortions which are relative with these main eigenvectors. This further reduces the computational work. In this paper, first the relation among the virtual distortions of the substructure, actual distortions, and the substructure damage extents are derived; then the main distortions of the substructure are chosen by the contribution analysis of the distortions to the structural responses. In this way, the damages are optimized and identified by minimizing the least square distance between the measured response and the estimated response. A numerical frame model is used to verify the proposed method.

Keywords:

structural health monitoring (SHM), damage identification, Virtual Distortion Method, substructure

Affiliations:
Zhang Q.-IPPT PAN
Jankowski Ł.-IPPT PAN
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
10.Suwała G., Jankowski Ł., Experimental study of a model-free method for identification of stiffness-related structural damages, EWSHM 2012, 6th European workshop on Structural Health Monitoring, 2012-07-03/07-06, Dresden (GE), pp.714-721, 2012
Abstract:

This paper presents a theoretical derivation and an experimental verification of a model-free method for identification of stiffness-related damages. The proposed method requires no parametric numerical model of the monitored structure, which obviates the need for initial model updating and fine tuning. The paper introduces the general methodology, including the inverse problem, focuses it on stiffness-related damages, and reports on an experimental verification. A 4-meter-long, 70-element truss steel structure made of a commercially available system of nodes and connecting tubes is used for that purpose. Damage is simulated by an intentional replacement of a structural element.

Affiliations:
Suwała G.-IPPT PAN
Jankowski Ł.-IPPT PAN
11.Hou J., Jankowski Ł., Ou J., Substructure Isolation Method for online local damage identification using time series, EWSHM 2012, 6th European workshop on Structural Health Monitoring, 2012-07-03/07-06, Dresden (GE), pp.1631-1638, 2012
Abstract:

This paper proposes a Substructure Isolation Method based on time series (SIM-TM) of measured local response and intended for local online monitoring of substructures. The method consists of two key steps: (numerical) construction of the isolated substructure, and local identification. The isolated substructure is an independent virtual structure, which is separated from the global structure with virtual supports placed in their interface. In the first step, the response of the isolated substructure is constructed by linear combinations of sub-time series of the measured local responses. Then, natural frequencies of the isolated substructure are identified based on the constructed response and used for local identification. The method has no requirements on the initial state of the structure. The isolation can be carried out time section by time section using the successive fragments of the measured responses, so that the approach can be used for online monitoring. A numerical frame model is used to verify the proposed online monitoring method.

Affiliations:
Hou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
12.Hou J., Jankowski Ł., Ou J., Local damage identification in frequency domain based on substructure isolation method, ANCRiSST2011, 6th International Workshop on Advanced Smart Materials and Smart Structures Technology, 2011-07-25/07-26, Dalian (CN), pp.1-9, 2011
Abstract:

This paper proposed a frequency domain method of substructure identification for local health monitoring. The substructure isolation method (SIM) consists of two steps: the first is the construction of isolated substructure which is the key of the method, and the second is damage identification of substructure. The isolated substructure is a virtual and independent structure, and it have the same physical parameters of the real substructure with the additional virtual supports on boundary, which is realized by operating the measured response. This paper extends the SIM method to frequency domain, which could make the method employ more measured response and compute more efficiently. A mass-spring numerical model is used to verify the theory of the SIM method, and a cantilever beam is experimented to test the method. The method preformed efficiently and accurately in the both numerical model and experiment.

Affiliations:
Hou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
13.Qingxia Z., Jankowski Ł., Zhongdong D., Experimental verification of a methodology for simultaneous identification of coexistent loads and damages, CM/MFPT 2011, 8th International Conference on Condition Monitoring and Machinery Failure Prevention Technologies, 2011-06-20/06-22, Cardiff (GB), pp.1-12, 2011
Abstract:

This paper presents the concept of smart structures dedicated to improving structural safety in case of unpredictable impact loadings. The concept is developed by bringing together two different ideas: adaptive impact absorption (AIA) and structural health monitoring (SHM). The potential for safe energy dissipation is maximized by optimum structural adaptation to impact loading parameters, for which the AIA subsystem is responsible. The SHM subsystem is used for on-line identification of impact type loadings, which is necessary in order to trigger optimum adaptation, as well as for post-impact damage assessment. Both subsystems depend on smart material technologies: optimum adaptation can be implemented through a small number of optimally distributed structural fuses, that is elements with controllable yield stresses, which can be implemented using magneto-rheological fluids, while the health and loading monitoring require a reliable sensing system, e.g. based on piezo-materials. The paper presents the general concept, provides a literature review and discusses in detail the challenges related to the SHM part.

Affiliations:
Qingxia Z.-other affiliation
Jankowski Ł.-IPPT PAN
Zhongdong D.-other affiliation
14.Holnicki-Szulc J., Jankowski Ł., Smart technologies for structural safety, CMM 2011, 19th International Conference on Computer Methods in Mechanics, 2011-05-09/05-12, Warszawa (PL), pp.057-1-7, 2011
Abstract:

This paper presents the concept of smart structures dedicated to improving structural safety in case of unpredictable impact loadings. The concept is developed by bringing together two different ideas: adaptive impact absorption (AIA) and structural health monitoring (SHM). The potential for safe energy dissipation is maximized by optimum structural adaptation to impact loading parameters, for which the AIA subsystem is responsible. The SHM subsystem is used for on-line identification of impact type loadings, which is necessary in order to trigger optimum adaptation, as well as for post-impact damage assessment. Both subsystems depend on smart material technologies: optimum adaptation can be implemented through a small number of optimally distributed structural fuses, that is elements with controllable yield stresses, which can be implemented using magneto-rheological fluids, while the health and loading monitoring require a reliable sensing system, e.g. based on piezo-materials. The paper presents the general concept, provides a literature review and discusses in detail the challenges related to the SHM part.

Keywords:

adaptivity, crashworthiness, inverse problems, structural monitoring, smart materials

Affiliations:
Holnicki-Szulc J.-IPPT PAN
Jankowski Ł.-IPPT PAN
15.Szolc T., Jankowski Ł., Pochanke A., Michajłow M., Vibration control of the coal pulverizer geared drive system using linear actuators with the magneto-rheological fluid, SIRM 2011, 9th International Conference on Vibrations in Rotating Machines, 2011-02-21/02-23, Darmstadt (GE), pp.1-10, 2011
Abstract:

Torsional vibrations are in general rather troublesome to control from the viewpoint of proper control torque generation as well as because of difficulties of imposing the control torques on quickly rotating parts of the drive- or rotor-shaft systems. In this paper there is proposed an active control technique based on the linear actuators with the magneto-rheological fluid (MRF) connecting the drive system planetary gear housing with the immovable rigid support. Here, by means of the magneto-rheological fluid of adjustable viscosity control damping torques are generated. Such actuators can effectively suppress amplitudes of severe transient and steady-state rotational fluctuations of the gear housing position and in this way they are able to minimize dangerous oscillations of dynamic torques transmitted by successive shaft segments in the entire drive system. The general purpose of the considerations is to control torsional vibrations of the power-station coal-pulverizer drive system driven by means of the asynchronous motor and the single stage planetary gear. In the computational examples drive system transient torsional vibrations induced by the electromagnetic motor torques during start-ups as well as steady-state vibrations excited by the variable dynamic retarding torques generated by the coal pulverizer during nominal operation have been significantly attenuated.

Keywords:

Torsional vibrations, rotational fluctuation, magneto-rheological fluid

Affiliations:
Szolc T.-IPPT PAN
Jankowski Ł.-IPPT PAN
Pochanke A.-other affiliation
Michajłow M.-IPPT PAN
16.Suwała G., Jankowski Ł., A benchmark for identification of structural modifications and inelastic impacts: the structure, test data and an example solution, SMART2011, 5th ECCOMAS Thematic Conference on Smart Structures and Materials, 2011-07-06/07-08, Saarbrücken (DE), pp.1-11, 2011
Abstract:

This paper proposes a simple lab-size benchmark for testing algorithms in two identification problems related to global structural health monitoring (SHM): identification of structural modifications and identification of inelastic impacts. A 3D truss-like structure, constructed of a commercial tube/node system, is used. Structural modifications are implemented by attaching additional nodal masses or by cutting a selected element to reduce its stiffness. Inelastic impact is simulated by an impulsive excitation of an additional nodal mass. Technical specification and experimental characteristics of the unmodified structure are provided for model updating. Several modification and impact cases are experimentally tested. All the data and measurements are freely accessible in Internet. An evaluation system is proposed for assessing the solutions, based on identification accuracy, instrumentation and source lines of code. The authors encourage the readers to test their approaches on the provided data. With each solution received, the evaluations will be calculated and published online.

Affiliations:
Suwała G.-IPPT PAN
Jankowski Ł.-IPPT PAN
17.Hou J., Jankowski Ł., Ou J., Substructural damage identification using time series of local measured response, 5WCSCM 2010, 5th World Conference on Structural Control and Monitoring, 2010-07-12/07-14, Tokyo (JP), pp.1-10, 2010
Abstract:

This paper presents a Substructure Isolation method for substructural damage identification using time series of local measured response. Isolated Substructure is a virtual and independent structure which is numerically separated from the global structure by adding virtual supports on the substructure interface. The basic concept of the isolation method is that: first time series of substructural responses are divided into several sub-series with overlap; through the linear combination of all the sub-series, when the boundary response are constrained to zeros, the corresponding inner responses are the constructed responses of the Isolated Substructure; then the substructural damage identification can be performed equivalently by the modes of the Isolated Substructure which are identified from the constructed inner responses. Numerical model of a six-span truss and an experiment of a cantilever beam are used to validate the method. Both the isolation and damage identification are preformed very well using local measured responses.

Affiliations:
Hou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
18.Mróz M., Jankowski Ł., Holnicki-Szulc J., VDM-based identification of localized, damage induced damping, EWSHM 2010, 5th European workshop on Structural Health Monitoring, 2010-06-29/07-02, Sorrento (IT), pp.988-993, 2010
Abstract:

This paper presents and experimentally verifies a method for identification of structural damage. The work is focused on such damage types as cracks, delamination or excessive allowances, which may not cause significant stiffness degradation but induce noticeable additional damping. Damaged elements are located and the damage is assessed in terms of the damage-induced damping and also the stiffness degradation. The Virtual Distortion Method (VDM) is used for modeling of the modifications.

Affiliations:
Mróz M.-other affiliation
Jankowski Ł.-IPPT PAN
Holnicki-Szulc J.-IPPT PAN
19.Suwała G., Jankowski Ł., Model-free damage identification of skeletal structures, EWSHM 2010, 5th European workshop on Structural Health Monitoring, 2010-06-29/07-02, Sorrento (IT), pp.925-930, 2010
Abstract:

This paper presents and verifies experimentally a model-free methodology for off-line damage identification of truss structures. The Virtual Distortion Method (VDM) is used, which allows the approach to be based entirely on experimentally obtained non-parametric characteristics of the monitored structure, so that no parametric numerical modeling is necessary. The damage is modeled using certain damage-equivalent pseudo-loads, which are convolved with experimentally obtained local responses of the original structure to compute the response of the damaged structure. An effective sensitivity analysis is possible via the adjoint variable method.

Affiliations:
Suwała G.-IPPT PAN
Jankowski Ł.-IPPT PAN
20.Hou J., Jankowski Ł., Ou J., Substructure isolation and identification using FFT of measured local responses, EWSHM 2010, 5th European workshop on Structural Health Monitoring, 2010-06-29/07-02, Sorrento (IT), pp.913-918, 2010
Abstract:

A substructuring method is presented for substructure identification and local health monitoring. The concerned substructure is numerically separated from the global structure to be a so-called Isolated Substructure by adding virtual supports on the substructure interface. The isolated substructure is a small and independent structure; its virtual supports are constructed using the FFT of measured local responses of the global structure. The damage of the substructure can be then identified easily by any of the classical methods which perform well on global structures. An experiment of a cantilever beam, of which the upper part is chosen as the substructure, is used to validate the method.

Affiliations:
Hou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
21.Zhang Q., Jankowski Ł., Duan Z., Fast identification of loads and damages using a limited number of sensors, EWSHM 2010, 5th European workshop on Structural Health Monitoring, 2010-06-29/07-02, Sorrento (IT), pp.1039-1044, 2010
Abstract:

This paper presents a method for fast identification of coexistent loads and damages, in which the number of sensors is mainly decided by the number of unknown loads.The computational efficiency is improved by Virtual Distortion Method (VDM), with which the repeated estimation of system impulse response is performed efficiently and by a local interpolation of perturbations of the structural response with respect to damage parameters. The proposed methodology is verified by a numerical example of a multi-span frame.

Affiliations:
Zhang Q.-IPPT PAN
Jankowski Ł.-IPPT PAN
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
22.Szolc T., Jankowski Ł., Pochanke A., Magdziak A., An application of the magneto-rheological actuators to torsional vibration control of the rotating electro-mechanical systems, IFToMM, 8th International Conference on Rotor Dynamics, 2010-09-12/09-15, Seoul (KR), pp.488-495, 2010
Abstract:

In the paper control of transient and steady-state torsional vibrations of the driven by the asynchronous motor laboratory drive system of the imitated coal pulverizer is performed by means of actuators with the magneto-rheological fluid. The main purpose of these studies is a minimisation of vibration amplitudes in order to increase the fatigue durability of the most responsible elements. The theoretical investigations are based on a hybrid and finite element structural model of the vibrating mechanical system as well as on sensitivity analysis of the response with respect to the actuator damping characteristics. For suppression of transient torsional vibrations excited by electro-magnetic torques generated by the motor and by the coal pulverizer tool there is proposed a control strategy based on actuators in the form of rotary control dampers.

Keywords:

Semi-active control, torsional vibrations, electro-mechanical drive system, control dampers, magneto-rheological fluid

Affiliations:
Szolc T.-IPPT PAN
Jankowski Ł.-IPPT PAN
Pochanke A.-other affiliation
Magdziak A.-other affiliation
23.Hou J., Jankowski Ł., Ou J., Substructural damage identification using Local Primary Frequency, ISSE11, 11th International Symposium on Structural Engineering, 2010-12-18/12-20, Guangzhou (CN), pp.1-6, 2010
Abstract:

This paper presents a substructuring method on damage identification using Local Primary Frequency (LPF).When a local excitation is applied on a concerned substructure, if the caused vibration mainly consists of only one single modal which represents most of the substructural distortion, then the corresponding frequency is defined as the substructural LPF. LPF reflects more information of the substructure and hence is more sensitivity to the substructural damage. Therefore, LPF can be used for substructural model updating and identification. However, generally substructures don’t own LPF. In this case, virtual supports constructed by Substructure Isolation Method are applied on the substructural boundary, such that it can enhance the constraint on the boundary, and decrease the influence from elements outside the substructure. In this way, the substructure sensitivity is enhanced and correspondingly the LPF of the substructure can be constructed. Numerical simulation of a three-story space frame structure testifies that substructural damages are identified effectively by this method.

Keywords:

Structure Health Monitoring (SHM), Damage Identification, substructuring method, Substructure Isolation Method, Local Primary Frequency (LPF), Virtual Supports

Affiliations:
Hou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
24.Hou J., Jankowski Ł., Ou J., Substructure isolation for local structural health monitoring, ECCOMAS Thematic Conference: International Symposium on Inverse Problems in Mechanics of Structures and Materials, 2009-04-23/04-25, Łańcut (PL), pp.33-34, 2009
Abstract:

This paper describes an effective method of substructure isolation for local structural health monitoring (SHM). In practice, often only a small part of a larger structure is critical and needs monitoring [1]. However, typical SHM methods require modeling or analysis of the global structure, which can be costly, time-consuming and error-prone. The proposed approach is based on the virtual distortion method [2]; the substructure is isolated from the entire structure by placing modeled fixed supports in all nodes of their mutual boundary. Therefore, given an excitation of the substructure and a measured response, the response of the substructure treated as fixed supported can be computed. Only experimental data are used for isolation, and no numerical modeling is required. A numerical experiment of damage identification in a frame-truss will be presented during the talk to validate the methodology at 5% rms measurement error level. It is omitted here due to space constraints.

Affiliations:
Hou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
25.Mróz M., Jankowski Ł., Holnicki-Szulc J., A VDM-based method for fast reanalysis and identification of structural damping, WCSMO-8, 8th World Congress on Structural and Multidisciplinary Optimization, 2009-06-01/06-05, Lisbon (PT), pp.1-9, 2009
Abstract:

This paper proposes a new approach for modeling and identification of damping in linear structures. The approach is based on the Virtual Distortion Method (VDM), which is a reanalysis methodology for fast modeling and identification of structural parameters. The VDM is extended in the sense of considering structural damping in frequency domain. The assumed damping model is a modified version of the proportional damping, which allows to distinguish between and to modify independently the damping properties of each element and in each degree of freedom. In this way, a precise formulation of the task of remodeling of damping is possible. Moreover, the proposed approach is used to state and solve the (basically nonlinear) inverse problem of identification of material damping by decomposing it into two linear subproblems.

Keywords:

damping identification, structural reanalysis, Virtual Distortion Method (VDM)

Affiliations:
Mróz M.-other affiliation
Jankowski Ł.-IPPT PAN
Holnicki-Szulc J.-IPPT PAN
26.Zhang Q., Jankowski Ł., Duan Z., Simultaneous identification of moving mass and structural damage, WCSMO-8, 8th World Congress on Structural and Multidisciplinary Optimization, 2009-06-01/06-05, Lisbon (PT), pp.1-10, 2009
Abstract:

Identification of damage and moving load (or mass) are crucial problems in structural health monitoring (SHM). However, it seems there is not much investigation on simultaneous identification of the two factors, although in practice they usually exist together. This paper proposes a methodology to solve the coupled problem based on the Virtual Distortion Method (VDM): the damaged structure is modeled by an equivalent intact structure (called the distorted structure) subjected to the same moving mass (or in fact to the equivalent response-coupled moving load) and to certain virtual distortions which model the damage. The measured structural response is used to identify the moving mass and the damage; unknown mass and damage extents are used as the optimization variables instead of the usually chosen moving mass-equivalent force. In this way well-conditioning of the identification is ensured and the number of the necessary sensors is decreased. The numerical costs are considerably reduced by using the introduced concept of the moving dynamic influence matrix. The proposed identification method can be used both off-line and online by a repetitive application in a moving time window. A numerical experiment of a beam with 5% measurement error demonstrates that the moving masses can be identified along with the damage extents.

Keywords:

Structural health monitoring (SHM), Moving mass (load) identification, Damage identification, Virtual distortion method (VDM)

Affiliations:
Zhang Q.-IPPT PAN
Jankowski Ł.-IPPT PAN
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
27.Suwała G., Jankowski Ł., Model-free identification of added mass, WCSMO-8, 8th World Congress on Structural and Multidisciplinary Optimization, 2009-06-01/06-05, Lisbon (PT), pp.1-10, 2009
Abstract:

This paper presents and experimentally validates a model-free methodology for off-line identification of modifications of structural mass. The proposed approach makes use of the Virtual Distortion Method (VDM) and is based entirely on experimentally measured data of the original unmodified structure, which is a significant advantage: no numerical modeling of the structure and tedious updating of the model are necessary. The mass modification is modeled using equivalent virtual distortion forces and experimentally obtained local impulse-responses of the unmodified structure. The identification amounts to solving an optimization problem of minimizing the mean-square distance between measured and modeled responses of the modified structure; a quick first- and second-order sensitivity analysis using the adjoint variable method is proposed. The method is validated experimentally using a 4-meter-long 70-element truss structure.

Keywords:

mass identification, model-free SHM, virtual distortion method (VDM), adjoint variable method

Affiliations:
Suwała G.-IPPT PAN
Jankowski Ł.-IPPT PAN
28.Kołakowski P., Jankowski Ł., Świercz A., Wikło M., Time-domain identification of damage in skeletal structures using strain measurements and gradient-based optimization, ISMA 2008, International Conference on Noise and Vibration Engineering, 2008-09-15/09-17, Louvain (BE), pp.3257-3266, 2008
Abstract:

This paper presents an improved numerical tool for identification of damage in skeletal structures. The problem of identification has been formulated in the time domain within the framework of the Virtual Distortion Method (VDM). VDM generally belongs to fast structural reanalysis methods and can be applied to Structural Health Monitoring problems, among others. The major computational asset of VDM is the influence matrix, containing all the local-global inter-relations for a structure due to given perturbations e.g. initial strain or external force. A non-linear least squares problem with strains, entering the objective function, is the subject of consideration. Strains are used in order to have relatively smooth variations (compared to accelerations) of the analyzed signal in time. The change of stiffness is the design variable. Analytical gradients are implemented in the optimization code based on the Levenberg-Marquardt algorithm with some penalty function terms. The efficiency of the software tool is demonstrated for a numerical example of a 2D truss structure. A breakthrough in terms of computational time reduction has been observed compared to the previously used steepest-descent optimization. The presented software assumes the feasibility of reliable measurements of strains in time for real skeletal structures (e.g. truss bridges). Future research will include experimental verification of the idea with piezoelectric sensors acting as tensometers.

Affiliations:
Kołakowski P.-IPPT PAN
Jankowski Ł.-IPPT PAN
Świercz A.-IPPT PAN
Wikło M.-IPPT PAN
29.Zhang Q., Jankowski Ł., Duan Z., Identification of coexistent load and damage based on virtual distortion method, EWSHM 2008, 4th European workshop on Structural Health Monitoring, 2008-07-02/07-04, Kraków (PL), pp.1124-1131, 2008
Abstract:

This paper presents a novel method to identify coexistent load and damage based on the idea of Virtual Distortion Method (VDM), which is significant for structural healthy monitoring. This method models a system with unknown damage and load by an equivalent undamaged system with the same load and certain virtual distortions, which are estimated stepwise via measured response. Then damage size can be computed by the estimated virtual distortions. It could be used for both off-line and online identification. A numerical experiment validates that two kinds of damage sizes can be identified as well as coexistent continuous and triangular loads. Moreover two methods (load shape function and initial system iterates) are proposed and incorporated to improve the computational accuracy and to reduce the numerical effort.

Affiliations:
Zhang Q.-IPPT PAN
Jankowski Ł.-IPPT PAN
Duan Z.-Shenzhen Graduate School of Harbin Institute of Technology (CN)
30.Suwała G., Jankowski Ł., Model-less impact mass identification, EWSHM 2008, 4th European workshop on Structural Health Monitoring, 2008-07-02/07-04, Kraków (PL), pp.374-381, 2008
Abstract:

This paper proposes a new model-less method for off-line identification of a mass impacting an elastic structure. The method is aimed at the identification of both mass and its velocity, makes use of the Virtual Distortion Method (VDM) and assumes the inelastic impact case, i.e. permanent modification of structural properties. Since the proposed approach is completely based on experimentally measured data, no numerical modeling and tedious fine-tuning of the model are necessary. The impacting mass is modeled using virtual distortion forces and an experimentally obtained system transfer matrix. The identification amounts to solving an optimization problem of minimizing the mean-square distance between measured and modeled structural responses, the latter is based on previously recorded responses of the unaffected structure.

Affiliations:
Suwała G.-IPPT PAN
Jankowski Ł.-IPPT PAN

Conference abstracts
1.Popławski B., Mikułowski G., Jankowski Ł., On-off damping of free vibrations and optimum actuator placement, SolMech 2016, 40th Solid Mechanics Conference, 2016-08-29/09-02, Warszawa (PL), pp.1-2, 2016
2.Hou J., Su L., Jankowski Ł., Cable force identification based on substructure isolation method, Structures16, The 2016 Structures Congress, 2016-08-28/09-01, Jeju Island (KR), pp.1-6, 2016
Abstract:

Aiming at this characteristic that the cable force identification precision is influenced by factors such as stiffness, boundary conditions and length, especially when the length of cable is short, boundary conditions cannot be simplified as fixed or pinned directly. Therefore, the method of adding virtual supports on the structure was proposed for cable force identification. The method of adding virtual supports on cable is based on the Substructure Isolation, through the change rule of natural frequency realize the structure damage identification. The virtual supports were constructed by the Substructure Isolation method using the liner combination of responses. By adding virtual supports realized that the substructures of cable were constructed, using the method can be additional virtual support in different position of the cable and get more virtual structures, combined with the frequency variation law of all virtual structures, the damage identification of cable can be carried out quickly and accurately.

Affiliations:
Hou J.-Dalian University of Technology (CN)
Su L.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
3.Holnicki-Szulc J., Jankowski Ł., Mróz A., Mitigation of impact-born vibrations, Euromech Colloquium [562] – Stability and Control of Nonlinear Vibrating Systems, 2015-05-24/05-28, Sperlonga (IT), pp.28-29, 2015
4.Holnicki-Szulc J., Faraj R., Graczykowski C., Jankowski Ł., Mikułowski G., Mróz A., Ostrowski M., Pawłowski P., Wiszowaty R., Adaptive impact absorption - potential applications for safety engineering, SMART 2015, 7th ECCOMAS Thematic Conference on Smart Structures and Materials, 2015-06-03/06-05, Ponta Delgada (PT), pp.1-2, 2015
Keywords:

Smart And Adaptive Structures, Adaptive Impact Absorption, Safety Engineering

Affiliations:
Holnicki-Szulc J.-IPPT PAN
Faraj R.-IPPT PAN
Graczykowski C.-IPPT PAN
Jankowski Ł.-IPPT PAN
Mikułowski G.-IPPT PAN
Mróz A.-IPPT PAN
Ostrowski M.-IPPT PAN
Pawłowski P.-IPPT PAN
Wiszowaty R.-IPPT PAN
5.Suwała G., Jankowski Ł., Effective numerical techniques for identification of structural mass modifications, TKI 2014, XIII Konferencja Naukowo-Techniczna , 2014-05-06/05-09, Licheń Stary k. Konina (PL), pp.1-2, 2014
Abstract:

This contribution focuses on effective numerical techniques used in a nonparametric method for identification of structural mass modifications. The approach utilizes the Virtual Distortion Method (VDM), which allows experimentally measured data to be directly used in the modeling process. As a result, experimentally obtained characteristics of the involved structure are used directly, so that no parametric modeling and time-consuming fine-tuning of the parameters are necessary. On the other hand, there are significant computational costs related to the need of direct processing of the measured time series, which require effective numerical techniques. Mass identification is formulated as an optimization problem of minimizing the mean square distance between the measured and the computed structural responses, where the optimization variables are mass-related parameters. Given the testing excitation (which can be unknown but should be reproducible) and the measured response of the original undamaged structure, the corresponding response of the structural mass modifications is computed by using certain mass-equivalent pseudo loads, which are convolved with experimentally obtained local impulse responses of the unaffected structure. The methodology is validated numerically and experimentally using a 4-meter-long, 70-element truss.

Keywords:

mass identification, virtual distortion method (VDM), conjugate gradient least squares, FFT, nonparametric

Affiliations:
Suwała G.-IPPT PAN
Jankowski Ł.-IPPT PAN
6.Holnicki-Szulc J., Jankowski Ł., VDM in inverse problems of safety engineering, IPM 2013, ECCOMAS Thematic Conference: International Conference IPM 2013 on Inverse Problems in Mechanics of Structures and Materials, 2013-04-24/04-27, Baranów Sandomierski (PL), pp.21-22, 2013
Abstract:

The virtual distortion method (VDM) [1] is a quick reanalysis method developed in the Institute of Fundamental Technological Research (IPPT PAN). Earlier related work includes the research of professors Nowacki, Eshelby, Kroener, Argyris, Maier, Majid and Celik, and others; for references see [1, 2]. The term virtual distrotion has been coined in 1989 [3], and the concept of the influence matrix has been proposed, which is the distinguishing factor of the VDM that provides for its effectiveness. This contribution presents the background and formulation of the method and reviews its applications in safety engineering.

Affiliations:
Holnicki-Szulc J.-IPPT PAN
Jankowski Ł.-IPPT PAN
7.Suwała G., Jankowski Ł., Model-free monitoring of structures, IPM 2013, ECCOMAS Thematic Conference: International Conference IPM 2013 on Inverse Problems in Mechanics of Structures and Materials, 2013-04-24/04-27, Baranów Sandomierski (PL), pp.61-62, 2013
Abstract:

This contribution presents the model-free approach to structural identification and monitoring, which has recently been developed in IPPT PAN [1–3]. The approach adapts the essentially nonparametric methodology of the virtual distortion method (VDM, [4]). Monitored structure is characterized in a purely experimental way, so that no parametric numerical modelling is required: the monitoring process is based directly on experimentally measured local impulse response functions. Even though, the approach can be used for identification of parametrized modifications of mass and stiffness or inelastic impacts. In comparison to other monitoring methods, it is characteristic enough to warrant the name of a model-free approach.

Most of the low-frequency methods used for global structural health monitoring (SHM, see the references in [1]) can be classified into two general groups:
1. Model-based methods, which rely on a parametric numerical model of the monitored structure. An appealing feature of these methods is the physicality of the model and identified damages; however, an accurate parametric model is often not easy to obtain.
2. Pattern recognition methods rely on a database of numerical fingerprints extracted from the experimentally measured responses. No parametric modeling is required, but at the cost of the physicality of the model. The identification rarely goes beyond damage detection or approximate localization.

The developed approach is aimed at exploiting the advantages of both groups of methods: it makes use of a nonparametric model of the monitored structure composed of experimentally measured data, but it enables full identification of parametrically expressed modifications and inelastic impacts.

Affiliations:
Suwała G.-IPPT PAN
Jankowski Ł.-IPPT PAN
8.Hou J., Jankowski Ł., Ou J., Online local structural health monitoring using the substructure isolation method, SolMech 2012, 38th Solid Mechanics Conference, 2012-08-27/08-31, Warszawa (PL), pp.306-307, 2012
Abstract:

This paper proposes a Substructure Isolation Method (SIM) for online local health monitoring at the substructural level. The SIM [1] includes two key steps: isolation of the substructure, and its local identification. Isolated substructure is an independent virtual structure, which is isolated from the global structure with virtual supports placed in the interface DOFs. Its response is constructed by such a linear combination of time series of measured local responses that the desired boundary conditions are satisfied and all outside influences are removed. Given the combined response, the substructure is locally identified using any of the standard methods aimed originally at global analysis. This is unlike other substructuring methods, see e.g. [2,3], which require dedicated methods in order to deal simultaneously with structural damages and generalized interface forces.

The SIM has been originally [1] used in off-line analysis and required zero initial conditions. Here, it is used for local online monitoring by a repeated application to successively extracted measurement time series. Non-zero initial conditions are allowed; they are reflected in a free vibration component of the constructed responses of the isolated substructure.

Affiliations:
Hou J.-Dalian University of Technology (CN)
Jankowski Ł.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
9.Suwała G., Jankowski Ł., Model-free identification of structural damages, SolMech 2010, 37th Solid Mechanics Conference, 2010-09-06/09-10, Warszawa (PL), pp.288-289, 2010
Abstract:

This work presents and verifies experimentally a model-free methodology for off-line identification of structural damages. The Virtual Distortion Method (VDM) [1] is used, which allows the structure to be modeled locally in an essentially non-parametric way, so that no error-prone parametric modeling is necessary. The damage is modeled using damage-equivalent pseudo-loads, which are convolved with the experimentally obtained responses of the original structure to compute the response of the damaged structure. A related approach has been earlier used for model-free impact and mass identification [2,3]. An effective sensitivity analysis is possible via the adjoint variable method.

Affiliations:
Suwała G.-IPPT PAN
Jankowski Ł.-IPPT PAN
10.Zhang Q., Jankowski Ł., Off-line reconstruction of dynamic loads, SolMech 2008, 36th Solid Mechanics Conference, 2008-09-09/09-12, Gdańsk (PL), pp.392-393, 2008