Pracownicy

Streszczenie:
In this study, a novel modal control strategy by means of semi-actively lockable joints is proposed. The control strategy allows for a directed flow of energy between vibrational modes, which makes it suitable not only for vibration attenuation purposes but also for energy scavenging driven by electromechanical energy harvesters. The proposed control strategy is an extension of the prestress-accumulation release (PAR) technique; however, it introduces also new concepts that increase the efficiency of the overall control system. Contrary to the PAR, the proposed method requires measurement of both strains in the vicinity of the semi-active joints and translational velocities that provide global information about system behavior. The latter aspect requires the control system to be organized within a hierarchical feedback architecture. The benefit from this higher complexity of the control system is its better performance compared to the PAR. The proposed semi-active modal control not only attenuates structural vibration faster, but it also achieves this goal with a smaller number of switches implemented in the joints. The effectiveness of the proposed methodology has been demonstrated on structures equipped with two lockable joints. Two practical examples have been investigated: one employs the concept of vibration-based energy harvesting for a two-story frame structure, while the second one reduces vibration of an eight-story frame structure subjected to kinematic excitation.

Słowa kluczowe:
energy harvesting, lockable joint, modal coupling, semi-active control, vibration attenuation

Streszczenie:
This paper proposes a computationally effective framework for load‐dependent optimal sensor placement in large‐scale civil engineering structures subjected to moving loads. Two common problems are addressed: selection of modes to be monitored and computational effectiveness. Typical sensor placement methods assume that the set of modes to be monitored is known. In practice, determination of such modes of interest is not straightforward. A practical approach is proposed that facilitates the selection of modes in a quasi‐automatic way based on the structural response at the candidate sensor locations to typical operational loads. The criterion used to assess sensor placement is based on Kammer's Effective Independence (EFI). However, in contrast to typical implementations of EFI, which treat the problem as a computationally demanding discrete problem and use greedy optimization, an approach based on convex relaxation is proposed. A notion of sensor density is applied, which converts the original combinatorial problem into a computationally tractable continuous optimization problem. The proposed framework is tested in application to a real tied‐arch railway bridge located in central Poland.

Słowa kluczowe:
optimal sensor placement, effective independence method, Fisher information matrix

Streszczenie:
The main drawback of vibration-based energy harvesting is its poor efficiency due to small amplitudes of vibration and low sensitivity at frequencies far from resonant frequency. The performance of electromagnetic energy harvester can be improved by using mechanical enhancements such as mechanical amplifiers or spring bumpers. The mechanical amplifiers increase range of movement and velocity, improving also significantly harvester efficiency for the same level of excitation. As a result of this amplitude of motion is much larger comparing to the size of the electromagnetic coil. This in turn imposes the need for modelling of electromagnetic circuit parameters as the function of the moving magnet displacement. Moreover, high velocities achieved by the moving magnet reveal nonlinear dynamics in the electromagnetic circuit of the energy harvester. Another source of nonlinearity is the collision effect between magnet and spring bumpers. It has been shown that this effect should be carefully considered during design process of the energy harvesting device. The present paper investigates the influence of the above-mentioned nonlinearities on power level generated by the energy harvester. A rigorous model of the electromagnetic circuit, derived with aid of the Hamilton's principle of the least action, has been proposed. It includes inductance of the electromagnetic coil as the function of the moving magnet position. Additionally, nonlinear behaviour of the overall electromagnetic device has been tested numerically for the case of energy harvester attached to the quarter car model moving on random road profiles. Such a source of excitation provides wide band of excitation frequencies, which occur in variety of real-life applications.

Słowa kluczowe:
energy harvesting, velocity amplification, nonlinear electromagnetic circuit, spring bumper, quarter car model

Streszczenie:
This paper describes a semi-active control strategy that allows to transfer the vibration energy from an arbitrarily induced to a selected structural mode. The intended aim of the proposed control strategy is energy harvesting from structural vibrations. Another potential application is related to structural safety. In the paper, a mathematical model is first introduced to describe the phenomenon of vibrational energy transfer, and then, based on this model, an efficient semi-active control strategy is proposed. Finally, some problems related to measurement techniques are discussed. The effectiveness of the proposed methodology is demonstrated in an example of energy transfer between vibrational modes of a three-bar planar frame structure.

Słowa kluczowe:
vibration energy, modal control, lockable joint, modal coupling

Streszczenie:
The success of virtually all structural health monitoring (SHM) methods depends on the information content of the measurements, and thus on the placement of the available sensors. This paper presents an efficient method for finding optimal sensor distribution over structural system with many degrees of freedom (DOFs). The objective function is based on the classical Fisher information matrix. Originally, this yields a computationally hard discrete optimization problem. However, the proposed numerical solution method is based on a concept taken from structural topology optimization, where a discrete optimization problem is replaced with a continuous one. Two numerical examples demonstrate the effectiveness of the proposed methodology. These are a 5-bay truss with 24 DOFs and a two-story frame structure whose finite element model has been condensed to 14 DOFs.

Słowa kluczowe:
optimal sensor placement, structural damage identification, topology optimization

Streszczenie:
The paper presents application of the MFC actuator and selected control algorithms to the suppression of the composite cantilever beam vibrations. The first part concentrates on the identification of the real structure’s parameters. The numerical model is based on the Euler-Bernoulli beam theory with a nonlinear curvature component. The second part draws on numerical simulations and leads to the identification of optimal control parameters. Finally, the determined parameters are examined in an experimental laboratory system equipped with a DSP controller.

Słowa kluczowe:
MFC actuator, control algorithm, active beam, DSP controller

Streszczenie:
A method for a sizing of an electromechanical battery for electrical go-kart was presented in the paper. The main goal of this research was to replace the internal combustion (IC) engine by an electric drive system taking into account the traction properties, on the one hand and the duration of operation on a single charge and the number of the battery life cycles on the other. The proposed method permits an entire depreciation of the price of the vehicle before the degradation of the battery occurs. The results of the study have been used to adjust the source for electric go-karts that will be mass produced.

Słowa kluczowe:
electrical vehicle, go-kart, optimal battery sizing, traction simulation

Streszczenie:
W artykule zaprezentowano metodę adaptacji algorytmu sterowania aktuatorem MFC służącym do redukcji drgań nieliniowych belki wysięgnikowej. Zastosowany opis matematyczny regulatora PD zaprojektowano jako strukturę MRAS, a algorytm adaptacji oparty jest o zasadę Lapunowa. Przeprowadzone badania symulacyjne określiły odporność algorytmu na błędy modelowania oraz na występujące w rzeczywistych systemach opóźnienia sprzętowe.

Słowa kluczowe:
regulacja adaptacyjna, algorytm adaptacji Lapunowa, drgania belki wysięgnikowej, aktuator MFC

Streszczenie:
Performance of any Structural Health Monitoring (SHM) system strongly depends on a set of sensors which are distributed over the structure under investigation. Optimal deployment of sensors on large scale structures such as tied-arch bridges is quite a challenging problem. Moreover, deployment of a sensor network consisting of different types of sensors (accelerometers, inclinometers or strain gauges) over a large scale bridge renders the task of optimization even more demanding. In the present study, a conventional sensor placement method for distribution of a homogenous sensor network is expanded to the heterogeneous case. First, the basic equations governing the estimation error will be recalled. Then, the Fisher information matrix is assembled using normalized translational and rotational mode shapes. Finally, a computational procedure is proposed which allows optimal sensor positions to be selected among thousands candidate locations. The effectiveness of the proposed strategy is demonstrated using a realistic example of a tied-arch bridge located in Poland.

Słowa kluczowe:
optimal sensor placement, structural health monitoring, tied-arch bridges, multi-type sensor network

Streszczenie:
This contribution proposes a semi-active control approach for a directed energy transfer between structural vibrational modes. The motivation is the intended localization of the vibration energy in a selected mode for the purpose of energy harvesting and mitigation of structural vibrations. The proposed control strategy aims at the instantaneous maximization of the energy transfer to the target mode. It is based on an untypical approach of dynamic structural reconfiguration and implemented using a semi-actively controllable node: a lockable joint. Such a joint, depending on the control signal, can act as a hinge or as a typical frame node. Effectively, it provides thus an on/off ability to control the transfer of bending moments between the adjacent structural elements. The effectiveness of the approach is demonstrated in a numerical example of a plane frame structure.

Słowa kluczowe:
Modal control, Semi-active control, Lockable joints, Energy harvesting

Streszczenie:
W ostatnim czasie wiele prac naukowych poświęcono problemom półaktywnego sterowania drganiami układów mechanicznych. Większość tych prac jednak dotyczy zagadnienia tłumienia drgań, natomiast znacznie mniej z nich obejmuje strategie sterowania na potrzeby odzyskiwania energii z drgających układów. Celem niniejszej pracy jest opracowanie strategii półaktywnego sterowania drganiami, mającej za zadanie przenosić energię drgań wzbudzanych losowo do jednej wybranej postaci drgań własnych. Sterowanie takie realizowane jest przy pomocy dynamicznie rozłączanych węzłów konstrukcyjnych. Węzły w zależności od sygnału sterowania mogą być blokowane w celu przenoszenia momentu zginającego pomiędzy łączonym członami konstrukcji lub odblokowywane, aby pracować jak połączenie przegubowe. Prowadzone badania podstawowe mają wiele potencjalnych zastosowań. Wraz ze zmianą postaci drgań, istnieje możliwość zmiany amplitudy w miejscach, w których zainstalowany jest tłumik lub urządzenie odzyskujące energię (ang. energy-harvester). Możliwe jest również szybkie przeniesienie energii mechanicznej do postaci drgań, która nie zakłóca funkcjonalności konstrukcji lub nie powoduje jej uszkodzenia bądź zmęczenia. W porównaniu do sterowania aktywnego stosowanie sterowania półaktywnego pozwala obniżyć koszty układu, dodatkowo nie powodując destabilizacji konstrukcji [1]. Sterowanie takie może z powodzeniem znaleźć zastosowanie w konstrukcjach o wielu stopniach swobody [2]. Strategia półaktywnego sterowania z użyciem blokowalnych węzłów pierwotnie została opracowana w celu przeniesienia energii drgań do wyższych postaci własnych w celu skutecznej ich redukcji przez tłumienie materiałowe [3]. W niniejszej pracy zaprezentowany zostanie model matematyczny transferu energii oraz oparte na nim prawo sterowania. Dodatkowo przedstawiony zostanie przykład numeryczny pokazujący, że transfer energii mechanicznej jest możliwy nawet wtedy, gdy mierzone są tylko pierwsze – podstawowe – postacie drgań własnych. Prowadzone badania zostały wsparte przez Narodowe Centrum Nauki w ramach projektu Re-Conf (DEC-2017/25/B/ST8/01800).

Słowa kluczowe:
sterowanie półaktywne, analiza modalna, blokowane węzły

Streszczenie:
The present study provides a comprehensive framework for sensor layout optimization aiming at accurate estimation of the modal coordinates coming from the structural response. The proposed procedure consists of two steps briefly described below. The first step is a selection of vibrational modes taking part in the motion of structures during their normal operation – in this case subjected to traveling load. Among these structures there are various types of bridges especially railway bridges. In the case of present study structural responses are obtained from rigorous finite element (FE) model of the bridge. The FE model is calibrated with measured response of real bridge located in Huta Zawadzka. The calibration process is based on the displacement signals of the bridge under the traveling load. In the second step modes of interest are selected and a set of candidate sensor locations is proposed. It is a subset of all degrees of freedom (DOFs) of the FE model from which several locations are chosen as best possible locations for the displacement sensors. The above sensor placement problem is a combinatorial task. Many methods for solving such problems have been developed previously, but in the case of large scale structures they require tremendous computational effort. To reduce this effort the so-called convex relaxation is incorporated into optimization process. The technique consists in reformulation of combinatorial problem into continuous convex one. Then, the convex relaxation is achieved by introducing the so-called sensor density function, which assigns a certain metric for individual candidate sensor location. Next, the value of this function is optimized in such a way that it maximize determinant of the Fisher Information Matrix. It has been shown that above algorithm is very effective and is distributing a number of sensors in several iterations only. Finally, it is worth noting that presented method can be used to distribute sensors for structural health monitoring. Moreover, it can be also applied in modal control strategies in vibration suppression.

Streszczenie:
The vibration attenuation problem has been solved using many different methods, some of which involve the use of advanced control algorithms. The topic of harvesting the energy of structural vibrations is less explored. For that reason, this contribution studies the problem of conversion of mechanical energy of vibrations. The paper presents a method of semi-active control, which is applied to dynamically transfer the vibration energy into a selected vibration mode. The target mode is selected in such a way that the amount of energy that can be recovered during the vibration process is maximized. In other words, switching between two modes is not intended to dissipate the energy of vibrations, but rather to maximize the energy-harvesting potential of the overall system. The concept will be illustrated using an example of a simple frame structure, in which semi-actively controlled lockable joints modify the modal properties of the structure.

Słowa kluczowe:
semi-active control, lockable joints, energy-harvesting