Pracownicy

Streszczenie:
This paper proposes and tests a semi-active method for mitigation of random and harmonic forced vibrations of frame structures. The method is based on the Prestress Accumulation-Release (PAR) strategy, and it stimulates the transfer of vibration energy from low-order into high-order natural modes of vibration. Due to their high-frequency, the target high-order modes are efficiently mitigated by standard material damping mechanisms. The control is based on local reconfiguration of nodal ability to transfer moments between adjacent beams, which might be momentarily suppressed for selected nodes: performed at the maximum of the local bending strain, such a suppression stimulates a sudden release of the accumulated strain energy into high-frequency local and global vibrations. The effectiveness of the approach is confirmed numerically and experimentally in mitigation of low-frequency vibrations, including resonance conditions, of a slender planar frame structure subjected to harmonic, sweep and random forced excitations.

Słowa kluczowe:
damping of vibrations, smart structures, semi-active control, decentralized control, truss–frame nodes

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 presents an experimental approach to assessment of semi-active vibration control systems based on the Prestress-Accumulation Release concept. The objectives are threefold: 1) to introduce an experimental validation method for control algorithms based on switchable transfer of moments, 2) to propose a method to assess experimentally the control effects on structural dynamic response under several types of excitation, and 3) to propose an approach for adequate sensor placement. A laboratory frame demonstrator equipped with dedicated semi-active nodes is used. The proposed approach is based on spectral responses and modal analysis. According to the presented findings, the investigated control is effective in reducing the vibration level while keeping the structural dynamic stiffness at a proper level. The investigation is conducted in the case of free response, as well as responses to impact loading and random excitation. The results confirm the accuracy of the adopted algorithm parameters and reveal the sensor locations that provide the best control effectiveness.

Streszczenie:
The paper presents an analysis of the state-dependent path-tracking method devoted to mitigation of dynamic response of systems and structures under impact excitations. The objective of the study is an evaluation of the adaptive performance and robustness of the novel control method. Robust and adaptive control methods are intensively developed by researchers and control engineers. Progress in the field influences various areas including mechanical engineering, within which these methods are applied for control of industrial processes as well as mitigation of structure dynamic response. Commonly solved problems relate especially to mitigation of vibrations, e.g. for protection of seismically excited structures. Another closely related area is the field of impact absorption, which is still challenging because of short time periods of energy absorption and number of process uncertainties. Nevertheless, due to higher and higher performance of smart sensors and actuators, as well as increasing efficiency of data processing systems, novel high- performance solutions also for impact mitigation problems can be proposed. This fact is reflected in the paper and important contribution to the field of Adaptive Impact Absorption is demonstrated. The importance of presented study results from the fact that applied smart absorber controlled with the use of kinematics-based approach ensures efficient mitigation of the impact excitation and automatic adaptation to various loading conditions. In contrast to shock-absorbers developed so far, the system implemented in laboratory provides adaptation to unknown impact conditions and compensates the influence of unpredictable perturbations. Within the paper an experimental validation of the novel control method is discussed and the system robustness to contact conditions, as well as to different values of operational medium parameters, is demonstrated. Possible extension of the method is analyzed and directions of further research are indicated.

Słowa kluczowe:
adaptive impact absorption, experimental study, kinematic feedback control, pneumatic absorber, self-adaptive system, smart shock-absorber

Streszczenie:
This paper proposes an on/off semi-active control approach for mitigation of free structural vibrations, designed for application in 2D smart frame structures. The approach is rooted in the Prestress-Accumulation Release (PAR) control strategies. The feedback signal is the global strain energy of the structure, or its approximation in the experimental setup. The actuators take the form of on/off nodes with a controllable ability to transfer moments (blockable hinges). Effectiveness of the approach is confirmed in a numerical simulation, as well as using a laboratory experimental test stand.

Słowa kluczowe:
structural reconfiguration, structural control, semi-active control, frame structures, controllable nodes‎

Streszczenie:
This paper proposes a quantitative criterion for optimization of actuator placement for the Prestress–Accumulation Release (PAR) strategy of mitigation of vibrations. The PAR strategy is a recently developed semi-active control approach that relies on controlled redistribution of vibration energy into high-order modes, which are high-frequency and thus effectively dissipated by means of the natural mechanisms of material damping. The energy transfer is achieved by a controlled temporary removal of selected structural constraints. This paper considers a short-time decoupling of rotational degrees of freedom in a frame node so that the bending moments temporarily cease to be transferred between the involved beams. We propose and test a quantitative criterion for placement of such actuators. The criterion is based on local modal strain energy that can be released into high-order modes. The numerical time complexity is linear with respect to the number of actuators and potential placements, which facilitates quick analysis in case of large structures.

Słowa kluczowe:
semi-active control, damping of vibrations, actuator placement, smart structures, prestress-accumulation release (PAR)

Streszczenie:
This paper proposes, tests numerically and verifies experimentally a decentralized control algorithm with local feedback for semi-active mitigation of free vibrations in frame structures. The algorithm aims at transferring the vibration energy of low-order, lightly-damped structural modes into high-frequency modes of vibration, where it is quickly damped by natural mechanisms of material damping. Such an approach to mitigation of vibrations, known as the prestress-accumulation release (PAR) strategy, has been earlier applied only in global control schemes to the fundamental vibration mode of a cantilever beam. In contrast, the decentralization and local feedback allows the approach proposed here to be applied to more complex frame structures and vibration patterns, where the global control ceases to be intuitively obvious. The actuators (truss–frame nodes with controllable ability to transmit moments) are essentially unblockable hinges that become unblocked only for very short time periods in order to trigger local modal transfer of energy. The paper proposes a computationally simple model of the controllable nodes, specifies the control performance measure, yields basic characteristics of the optimum control, proposes the control algorithm and then tests it in numerical and experimental examples.

Słowa kluczowe:
Damping of vibrations, Smart structures, Semi-active control, Decentralized control, Truss-frame nodes

Streszczenie:
BACKGROUND: Electrospun nanofibers have widespread putative applications in the field of regenerative medicine and tissue engineering. When compared to naturally occurring collagen matrices, electrospun nanofiber scaffolds have two distinct advantages: they do not induce a foreign body reaction and they are not at risk for biological contamination. However, the exact substrate, structure, and production methods have yet to be defined. MATERIAL AND METHODS: In the current study, tubular-shaped poly(L-lactide-co-caprolactone) (PLCL) constructs produced using electrospinning technology were evaluated for their potential application in the field of tissue regeneration in two separate anatomic locations: the skin and the abdomen. The constructs were designed to have an internal diameter of 3 mm and thickness of 200 μm. Using a rodent model, 20 PLCL tubular constructs were surgically implanted in the abdominal cavity and subcutaneously. The constructs were then evaluated histologically using electron microscopy at 6 weeks post-implantation. RESULTS: Histological evaluation and analysis using scanning electron microscopy showed that pure scaffolds by themselves were able to induce angiogenesis after implantation in the rat model. Vascularization was observed in both tested groups; however, better results were obtained after intraperitoneal implantation. Formation of more and larger vessels that migrated inside the scaffold was observed after implantation into the peritoneum. In this group no evidence of inflammation and better integration of scaffold with host tissue were noticed. Subcutaneous implantation resulted in more fibrotic reaction, and differences in cell morphology were also observed between the two tested groups. CONCLUSIONS: This study provides a standardized evaluation of a PLCL conduit structure in two different anatomic locations, demonstrating the excellent ability of the structure to achieve vascularization. Functional, histological, and mechanical data clearly indicate prospective clinical utilization of PLCL in critical size defect regeneration.

Słowa kluczowe:
Polymers, Regenerative medicine, Tissue Engineering, Tissue Scaffolds, Urinary Diversion

Streszczenie:
Many of mechanical energy absorbers utilized in engineering structures are hydraulic dampers, since they are simple and highly efficient and have favourable volume to load capacity ratio. However, there exist fields of applications where a threat of toxic contamination with the hydraulic fluid contents must be avoided, for example, food or pharmacy industries. A solution here can be a Pneumatic Adaptive Absorber (PAA), which is characterized by a high dissipation efficiency and an inactive medium. In order to properly analyse the characteristics of a PAA, an adequate mathematical model is required. This paper proposes a concept for mathematical modelling of a PAA with experimental verification. The PAA is considered as a piston-cylinder device with a controllable valve incorporated inside the piston. The objective of this paper is to describe a thermodynamic model of a double chamber cylinder with gas migration between the inner volumes of the device. The specific situation considered here is that the process cannot be defined as polytropic, characterized by constant in time thermodynamic coefficients. Instead, the coefficients of the proposed model are updated during the analysis. The results of the experimental research reveal that the proposed mathematical model is able to accurately reflect the physical behaviour of the fabricated demonstrator of the shock absorber.

Streszczenie:
The critical monotonic strain of Ni-W and MoS2(Ti,W) coatings on steel substrates was studied. The idea of axisymmetric bending test (called here as coin bending test) limited to monitoring of the coating failure was used. Experiments revealed mechanism of the coating failure, as cracking initiated from coating surface defects and/or substrate was demonstrated using indentation technique. By pushing the center of the uncoated side of a circular plate, the axisymmetric stress state was generated in the coating. The stress components varied gradually from the greatest value in the center to the smallest value at the edge of the specimen. The changes of the sample surface as a result of loading were monitored step by step via optical microscopy.

Słowa kluczowe:
Ni-W coating, MoS2(Ti.W) coating, steel substrate, fracture, coatings strength, axisymmetric bending test

Streszczenie:
Albumin is rarely used for electrospinning because it does not form fibres in its native globular form. This paper presents a novel method for electrospinning human albumin from a solution containing pharmaceutical grade protein and 25% polyethylene oxide (PEO) used as the fibre-forming agent. After spontaneous cross-linking at body temperature, with no further chemicals added, the fibres become insoluble and the excess PEO can be washed out. Albumin deposited along the fibres retains its native characteristics, such as its non-adhesiveness to cells and its susceptibility for degradation by macrophages. To demonstrate this we evaluated the mechanical properties, biocompatibility and biodegradability of this novel product. After subcutaneous implantation in mice, albumin mats were completely resorbable within six days and elicited only a limited local inflammatory response. In vitro, the mats suppressed cell attachment and migration. As this product is inexpensive, produced from human pharmaceutical grade albumin without chemical modifications, retains its native protein properties and fulfils the specific requirements for anti-adhesive dressings, its clinical use can be expedited. We believe that it could specifically be used when treating paediatric patients with epidermolysis bullosa, in whom non-healing wounds occur after minor hand injuries which lead to rapid adhesions and devastating contractures.

Słowa kluczowe:
albumin, nanofibers, wound dressing, biocompatibility, bioresorption

Streszczenie:
Adaptive Impact Absorption focuses on adaptation of energy absorbing structures to actual dynamic loading by using system of sensors detecting and identifying impact in advance and embedded semi-active dissipaters with controllable mechanical properties. Application of such devices allows to modify dynamic characteristics of the structure during the period of impact and to precisely control the process of energy dissipation. The paper presents an overview of research conducted at the Department of Intelligent Technologies of the Institute of Fundamental Technological Research dedicated to design and applications of various systems of Adaptive Impact Absorption. Wide range of presented examples covers adaptive hydraulic and pneumatic landing gears, skeletal systems equipped with controllable elements and detachable joints as well as adaptive inflatable structures.

Słowa kluczowe:
adaptive impact absorption, safety engineering, smart structures, optimal control

Streszczenie:
The purpose of this study was to compare: a new five-layered poly (L–lactide–co–caprolactone) (PLC) membrane and small intestinal submucosa (SIS) as a control in rat urinary bladder wall regeneration. The five-layered poly (L–lactide–co–caprolactone) membrane was prepared by an electrospinning process. Adipose tissue was harvested from five 8-week old male Wistar rats. Adipose derived stem cells (ADSCs) were seeded in a density of 3×106 cells/cm2 onto PLC membrane and SIS scaffolds, and cultured for 5-7 days in the stem cell culture medium. Twenty male Wistar rats were randomly divided into five equal groups. Augmentation cystoplasty was performed in a previously created dome defect. Groups: (I) PLC+ 3×106ADSCs; (II) SIS+ 3×106ADSCs; (III) PLC; (IV) SIS; (V) control. Cystography was performed after three months. The reconstructed urinary bladders were evaluated in H&E and Masson's trichrome staining. Regeneration of all components of the normal urinary bladder wall was observed in bladders augmented with cell-seeded SIS matrices. The urinary bladders augmented with SIS matrices without cells showed fibrosis and graft contraction. Bladder augmentation with the PLC membrane led to numerous undesirable events including: bladder wall perforation, fistula or diverticula formation, and incorporation of the reconstructed wall into the bladder lumen. The new five-layered poly (L–lactide–co–caprolactone) membrane possesses poorer potential for regenerating the urinary bladder wall compared with SIS scaffold.

Słowa kluczowe:
urinary bladder regeneration, electrospinning

Streszczenie:
This paper describes a pneumatic valve based on a multilayer piezoelectric actuator and Hörbiger plates. The device was designed to operate in an adaptive pneumatic shock absorber. The adaptive pneumatic shock absorber was considered as a piston–cylinder device and the valve was intended to be installed inside the piston. The main objective for the valve application was regulating the gas flow between the cylinder's chambers in order to maintain the desired value of the reaction force generated by the shock absorber. The paper describes the design constraints and requirements, together with results of analytical modelling of fluid flow verified versus experimentally obtained data. The presented results indicate that the desired performance characteristics of the valve were obtained. The geometrical constraints of the flow ducts were studied and the actuator's functional features analysed.

Streszczenie:
Auxetic materials exhibit counterintuitive and interesting properties, which can be utilized to develop new families of products, which can meet sophisticated needs. Study presented within this paper is focused on manufacturing and testing auxetic polyurethane foams for potential introduction for seats in military helicopters. Firstly, a manufacturing process was developed which benefits from the well-known methods of processing conventional foams and allows preparing necessary test specimens for further tests. Secondly, a series of static and dynamic tests was performed during which the market available conventional foams used in transport are compared with processed auxetic foams.

Streszczenie:
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.

Słowa kluczowe:
Adaptive landing gear, adaptive impact absorption, shock absorber, load mitigation

Streszczenie:
The article presents a review of recent research carried out in the Department of Intelligent Technologies of Institute of Fundamental Technological Research, dedicated to application of systems for adaptive impact absorption to adaptive aircraft landing gears, novel concept of protective MFM structures, flow-control based airbags, maritime applications of inflatable structures, and development of adaptive wind turbine blade – hub connections.

Słowa kluczowe:
Adaptive Impact Absorption, Adaptive Structure, Optimal Control

Streszczenie:
Podwozia lotnicze są traktowane przez konstruktorów samolotów jako elementy konieczne, ale z wielu względów mające negatywny wpływ na projekt. Z punktu widzenia aerodynamiki podwozia w trakcie lotu, stawiają dodatkowy opór aerodynamiczny (mniejszy w przypadku podwozi chowanych), a z punktu widzenia możliwości przewożenia ładunków, pochłaniają część masy startowej samolotu, która mogłaby być wykorzystana na transport towarów lub pasażerów. Biorąc pod uwagę takie uwarunkowania, idealne podwozie lotnicze powinno ważyć jak najmniej i zajmować minimalną ilość miejsca.
Obecnie najpopularniejszym rodzajem podwozia stosowanego w lotnictwie jest typ olejowo-gazowy, który charakteryzuje się najkorzystniejszym stosunkiem sprawności do wagi. Sprawność obecnie stosowanych podwozi lotniczych dochodzi do 80%. Aczkolwiek jest to wartość, która jest uzyskiwana dla jednego predefiniowanego przypadku lądowania z określoną energią uderzenia samolotu o pas startowy. Praktyka pokazuje, że w rzeczywistości zmienność warunków lądowania jest dużo większa niż zakres, na jaki można zaprojektować klasyczne podwozie pasywne. Najczęściej energia uderzenia przy lądowaniu jest znacząco mniejsza od tej, jaką konstruktorzy zakładają do obliczeń w procesie projektowania.
Dwa przedstawione problemy w projektowaniu podwozi lotniczych mogą zostać rozwiązane dzięki koncepcji nowego podwozia gazowego przedstawionego w tym artykule. Po pierwsze, dzięki zastosowaniu technologii inteligentnych i wykorzystaniu materiału funkcjonalnego stało się możliwe zaprojektowanie amortyzatorów czysto gazowych w podwoziach do aparatów latających, dzięki czemu możliwe jest wyeliminowanie oleju hydraulicznego o znacznie większej gęstości od gazu i efektywne obniżenie ciężaru podwozia samolotu. Po drugie dzięki wprowadzeniu inteligentnego sterowania przepływem gazu w amortyzatorze, stała się możliwa adaptacja rzeczywistych charakterystyk pracy amortyzatora do aktualnej wartości energii uderzenia samolotu o pas startowy.
Artykuł przedstawia wstępną fazę badań koncepcyjnych nad gazowym absorberem uderzeń przeznaczonym od zastosowania w podwoziu aparatu latającego, sterowanym przy pomocy zaworu piezoelektrycznego. W trakcie badań wykonano serię prób na modelu numerycznym, która została zweryfikowana przy pomocy badań eksperymentalnych, do których zaprojektowano i zrealizowano sterowanie w pętli zamkniętej dla szybkiego zaworu piezo elektrycznego zintegrowanego z absorberem gazowym.

Słowa kluczowe:
podwozia lotnicze, podwozie adaptacyjne, adaptacyjna dyssypacja energii

Streszczenie:
The objective of this paper is to present an integrated feedback control concept for adaptive landing gears (ALG) and its experimental validation. Aeroplanes are subjected to high dynamic loads as a result of the impact during each landing. Classical landing gears, which are in common use, are designed in accordance with official regulations in a way that ensures the optimal energy dissipation for the critical (maximum) sink speed. The regulations were formulated in order to ensure the functional capability of the landing gears during an emergency landing. However, the landing gears, whose characteristics are optimized for these critical conditions, do not perform well under normal impact conditions. For that situation it is reasonable to introduce a system that would adapt the characteristics of the landing gears according to the sink speed of landing. The considered system assumes adaptation of the damping force generated by the landing gear, which would perform optimally in an emergency situation and would adapt itself for regular landings as well. This research covers the formulation and design of the control algorithms for an adaptive landing gear based on MR fluid, implementation of the algorithms on an FPGA platform and experimental verification on a lab-scale landing gear device. The main challenge of the research was to develop a control methodology that could operate effectively within 50 ms, which is assumed to be the total duration of the phenomenon. The control algorithm proposed in this research was able to control the energy dissipation process on the experimental stand.

Streszczenie:
Podczas każdego lądowania samoloty są narażone na duże przeciążenia dynamiczne mające zdecydowany wpływ na trwałość i niezawodność konstrukcji nośnej. Wielkość przeciążeń, jakim poddawany jest kadłub samolotu, zależy w dużej mierze od poprawnej pracy podwozia lotniczego. Głównym elementem podwozia, który pochłania największą ilość energii kinetycznej związanej z momentem przyziemienia jest amortyzator. Optymalne działanie amortyzatora lotniczego ma decydujący wpływ na zużycie zmęczeniowe materiałów konstrukcyjnych oraz na bezpieczeństwo lądowania.
Wprowadzenie systemu adaptacyjnego, który będzie w stanie modelować charakterystykę dyssypacji po przeprowadzeniu diagnozowania energii kinetycznej związanej z prędkością przyziemienia i ciężarem samolotu, znacznie poprawi efektywność działania amortyzatora lotniczego, zwiększając niezawodność eksploatacyjną konstrukcji i bezpieczeństwo lotu.

Słowa kluczowe:
podwozia lotnicze, podwozie adaptacyjne, adaptacyjna dyssypacja energii

Streszczenie:
Adaptive impact absorption is a modern control problem being solved nowadays for several transportation and industry branches. The objective of the impact absorption process is dissipation of the impact energy by means of generation the minimal interface forces and minimal decelerations acting on the protected structure. One of the possibilities for minimization of the impact forces is using of an adaptive actuator that enables adjusting its characteristics to the actual impact energy. The presented research was focused on development of the adaptive impact absorption procedurę and as an example of the adaptive actuator an MR damper was used. The MR damper ensured the convenient rangę of the damping forces to provide the proper controllability of the process. However, sińce impact is a very short phenomenon the performance of the device must have met very strict reąuirements in the field of time delays. High ąuality of the driving electronics is the emphasized factor influencing the system performance. The paper presents the controller for the MR damper and control algorithms with experimental verification.

Słowa kluczowe:
MR damper, vibrations, damping

Streszczenie:
The discussed study is focused on implementation of a novel kinematics-based control technique. Presented results are based on theoretical and numerical analyses as well as on experimental investigations, which are focused on elaboration of the efficient self-adaptive energy absorption system. The developed control method has been originally dedicated to the impact mitigation problem, but it can be adjusted to other types of dynamic excitations. Superior performance of the method results from the fact that proposed system adapts automatically to unidentified dynamic excitations and compensates possible unexpected disturbances during the impact absorption process. The analyzed self-adaptive impact absorption system is based on the pneumatic shock-absorber with piezoelectric valve and real-time control system. This contribution is focused on chosen factors which can lead to undesired imperfections in practical implementation of the control method.

Streszczenie:
This contribution presents an experimental analysis of the control system configuration for a semi-active frame structure. The structure is equipped with a system that implements a Prestress Accumulation Release strategy for mitigation of vibration. A proper distribution of the sensors for monitoring the actual state of the structure is the key factor that determines the overall effectiveness of the applied strategy. The results and findings presented here reveal a set of basic rules dedicated to solving this crucial issue.

Słowa kluczowe:
Prestress Accumulation Release, Vibration control, Sensor placement, Semi-active structures, Piezoelectric actuation

Streszczenie:
Semi-active control systems are investigated for more than 40 years, and despite the great progress in this research area, they are still considered to be a complex topic in both theoretical and technical terms. However, their advantages ensure that these control systems remain an extremely attractive subject of scientific and technological development.
In this contribution, we present a semi-active strategy for mitigation of vibration, which utilizes an energy management approach called Prestress-Accumulation Release and is based on controllable activation and removal of selected structural constraints. Here, it is implemented by means of controllable structural nodes of a specific design that allow the transmission of moments between adjacent structural elements to be controlled in an on/off manner. The developed control strategy turned out to be very effective in damping of free structural vibrations of planar frame structures. Extension of the research to other types of vibrations has shown that the proposed control algorithm is versatile and stays efficient in a range of applications and different configurations of the investigated structures. This work is focused on mitigation of vibrations excited by a randomly generated force load.
Decentralization, understood here as controlling the employed actuators based on locally measured structural response, results in a decisive reduction of the complexity of the data acquisition and control systems, which is crucial for actual implementations in real structures, and which facilitates an ad hoc reconfiguration and expansion of the control system if necessary. It also provides the possibility of considering selected structural elements as separate energy dissipative devices, which in our approach act effectively as vibration dampers. This feature, provided by the decentralization, enables to take the advantage of two complementary, interrelated mechanisms of material damping: global dissipation of vibration energy by the PAR and local dissipation in single involved elements.
Numerical and experimental analyses indicate a high degree of effectiveness in alleviation of the amplitude of vibrations induced by a random transient force excitation. The proposed control strategy can be thus utilized not only in the case of momentary impulsive loads that result in predominantly free vibrations, but also in the case of transient random force excitation. It significantly extends the range of possible modes of operation of a structure equipped with the proposed damping system.

Słowa kluczowe:
Semi-active damping, Vibration damping, Random vibration, Forced vibration

Streszczenie:
Vibration mitigation and vibration isolation are problems existing in a variety of industry branches. Pneumatic suspensions and isolators are a widely utilized technology, and in many applications they need to adapt their properties to a varying mass of the supported object, e.g., loaded or unloaded lorries. However, the pneumatic solutions posses limitations in the field of adequate damping. The change in mass results in a change in the required level of damping. This contribution presents and verifies a concept of an enhanced damping pneumatic device using an example of a Pneumatic Adaptive Absorber (PAA) adapted to the task of mitigation of forced vibrations. The investigation presents a concise introduction to the concept, as well as analytical and numerical modelling of the conceptual device. The contribution proposes a control algorithm based on performed analysis of mechanical energy dissipation process. The concept is verified experimentally in a laboratory. The proposed modelling seems to be in agreement with the demonstrator response.

Streszczenie:
Vibration mitigation in space structures creates a unique class of a technical problem where resistant for outgassing and non-fluidic solutions are preferable. Additionaly, a vibration induced by time-varying excitations needs to be effectively reduced. The vibration mitigation task is speciffically difficult in the case of light, slender and inherently flexible structures of various types, such as supporting structures, deployable structures, modular structures or wide-span skeletal roofing structures. This study presents a concept of a vibration attenuation method based on semi-active joints and dedicated to frame structures under forced vibration excitation. The presented investigation contains an analysis of the problem of the optimal control of a structure fitted with semi-active structural members. Furthermore, an adequate model of the semi-active joints is developed and a numerical example is presented. Finally, the research provides an experimental verification of the developed control algorithms, which is conducted on a test stand in a laboratory environment.

Streszczenie:
Small drones with total mass of a few kilograms are becoming more and more popular in many applications increasing the probability of occurrence of emergency situations caused by an equipment failure or a human error. In case of a fall from a high altitude very often it is possible to use parachute rescue systems, which however require relatively long time for deployment and development of braking forces. The touchdown velocity may be large enough to exceed limit accelerations for UAV equipment. The paper presents the concept of deployable airbag systems, in particular with adaptive flow control, which provides a possible solution to the above-mentioned problems. The paper discusses the overall control and adaptation strategy. Simplified methods for mathematical modeling are proposed and formulated for an example on a cylindrical airbag. The conceptual part is concluded with the presentation of the methodology of experimental verification and results of initial tests of the integrated airbag system.

Streszczenie:
This contribution proposes a quantitative criterion for optimization of actuator placement for the Prestress–Accumulation Release (PAR) strategy of mitigation of vibrations. The PAR strategy is a semi-active control approach that relies on controlled redistribution of modal energy into high-frequency high-order modes, where it is effectively dissipated by means of the natural mechanisms of material damping. The energy transfer is achieved by a controlled temporary removal of selected structural constraints. An example is a short-time decoupling of rotational degrees of freedom in a frame node, so that the bending moments are no longer transferred between the involved beams. If it such a decoupling is performed at the maximum of the shear/bending strain energy of adjacent beams, it results in an almost instantaneous energy release into high-frequency local vibrations and quick dissipation of energy. We propose and test a quantitative criterion for placement of such actuators. The criterion is based on local modal strain energy that can be released into high-order modes. The numerical time complexity is linear with respect to the number of actuators, which facilitates quick selection of placements in large structures.

Słowa kluczowe:
semi-active control, damping of vibrations, actuator placement, smart structures, Prestress-Accumulation Release (PAR)

Streszczenie:
Semi-active systems for mitigation of vibrations proved to be effective in many applications. Their prominent advantage is that they combine strong points of passive and active damping systems. Proper design can ensure their reliability, which is what passive systems are praised for. A high effectiveness in vibration damping links them with active systems. At the same time they do not have many deficiencies of active systems. They are adaptive, so they can stay effective in different environmental conditions, which is the factor that eliminates passive systems from many implementations. Their mass and energy consumption is very low, and the controlled structure can stay in the safe configuration even in case of power supply failure, which puts them in contrast to many active systems. The mentioned attributes make them a good choice for many structures subjected to vibrations, especially when there is a strong emphasis on maximization of the efficiency/mass ratio of the damping system.
This contribution presents a decentralized closed-loop control strategy and applies it in a frame structure equipped with controllable truss-frame nodes. Such nodes can be switched between frame-like and truss-like states in a controllable manner. In the frame-like state the node transmits all forces and moments, while in the truss-like state only axial and shearing forces are transmitted. These nodes allow for structural reconfiguration, which can be utilized by semi-active control strategies for the purpose of vibration damping. The implemented control algorithm applies the Prestress-Accumulation Release (PAR) strategy based on the transmission of the accumulated potential energy to high modes of vibration, which are highly dissipative. Strain measurements are conducted locally on selected elements. A similar strategy proved its effectiveness in mitigation of free structural vibrations. This research studies the concept of its application to mitigation of forced structural vibrations, caused by variable external conditions.

Słowa kluczowe:
Semi-active damping, Truss-frame nodes, Prestress-Accumulation Release (PAR), Decentralized control

Streszczenie:
The paper is aimed at discussion of various control techniques developed for adaptive impact-absorbers protecting structures and machines. Different approaches to the problem of optimal damper design are presented and systems comparison is provided with the example of pneu-matic shock-absorber. The influences of selected control strategy on the absorber characteris-tics, its efficiency and adaptation capabilities are shown. The contribution includes both numerical and experimental examples. The authors highlight the fact that the final design of the device should be elaborated simultaneously with the development of dedicated control system. In some cases properly assumed architecture of the control system enables significant simplifi-cation of the absorber. The paper covers analyses of semi-passive devices with single reconfig-uration to identified excitation conditions and semi-active absorbers capable of adaptation to unknown impact loading. Adaptation mechanisms of such devices and their robustness are com-pared in reference to volatility of system parameters and variety of loading conditions. Limita-tions of smart devices (e.g. piezo-electric valve in pneumatic absorbers) used in practice for absorbers' control are described in relevant mathematical models. Technological challenges in the design and manufacturing of absorbers are identified and methods of their overcoming are proposed.

Słowa kluczowe:
Adaptive Impact Absorption, adaptive control, adaptable system, damper

Streszczenie:
This contribution proposes a decentralized closed-loop control algorithm for semi-active mitigation of free vibrations in frame structures. The control uses dedicated dissipative devices, which consist of two controllable structural nodes placed pairwise in both ends of selected structural beams. The nodes are capable of a controlled transition between the standard frame mode of operation (full moment-bearing ability) and the truss mode in which they do not bear any moments and constitute in fact structural hinges. Synchronous switching is equivalent to reconfiguration of the global structure by (dis)allowing the involved beams to transmit moments and to accumulate vibration energy in the form of their bending strain. Upon switching to the truss mode, the accumulated energy is released into high-frequency local vibrations, which undergo quick dissipation by standard mechanisms of material damping. The approach is illustrated in a numerical example and verified in a preliminary experimental test.

Słowa kluczowe:
Mitigation of vibrations, Semi-active control, Decentralized control, Structural reconfiguration

Streszczenie:
Extensive research efforts have been recently devoted to semi-active structural control with its paradigms of smart self-adaptivity and low consumption of energy, which is used for local adaptation rather than to generate external control forces. Considered application areas include adaptive landing gears, seismic isolation systems, vehicle-track/span systems, power train electro-mechanical systems, damping of flexible space structures, vehicle crashworthiness, arctic engineering, wind turbines, etc. A part of the research concerns semi-active management of strain energy for damping of structural vibrations. Early works considered truss structures with stiffness-switched bars. They later evolved into either standalone one degree of freedom stiffness-switched dampers and isolators or investigations in triggering modal energy transfer to highly-damped high-order modes. The latter researches seem all to study the fundamental vibration mode of a cantilever beam with two detachable layers and differ mainly in the actuator technologies; the main idea is to employ actuators for a quick release of the vibration-related strain energy. This research extends the problem to general 2D frames. Controllable truss-frame nodes are incorporated into the structure. Thanks to their controllable ability to transmit moments, they allow for a quick transition between truss and frame modes. We propose a new, decentralized, closed-loop control strategy based on local energy measures. Vibration damping is more effective than in the previously studied control scheme based on a global energy measure, especially for higher vibration modes. Mitigation of vibrations will be presented in representative numerical examples, including a comparison to the global energy-based control strategy. Finally, results of experimental study, conducted on a structure analogous to the one from numerical simulations, will be demonstrated.

Słowa kluczowe:
Vibration damping, Smart structures, Semi-active control, PAR strategy, Decentralized damping strategy

Streszczenie:
Adaptive structures, equipped with so-called structural fuses (based on fast responding piezo-devices), able to connect/disconnect instantly selected structural interface, allows effective protection against resonance induction via externally forced vibrations. The presented case study demonstrates haw forced vibrations with modifiable frequencies can be smoothly received, if structural fuses are properly activated/deactivated when the external excitation approaches the structural eigen frequencies.

Słowa kluczowe:
Adaptive structures, forced vibrations, avoiding resonance, structural fuses

Streszczenie:
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.

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

Streszczenie:
The objective of this paper is to provide results of an experimental and analytical investigation of Amplified Piezoelectric Actuators (APA) as vibrational isolator in a configuration of a mechanical Single Degree of Freedom system. The investigation is aimed at assessment of the mechanical properties modification ability via shunting techniques. The investigation consist of a phenomenological modelling of the APAs considered as generators and experimental verification of the vibrational energy dissipation ability in frequency domain. The results obtained during this investigation reveal that it is feasible to receive more than 20 dB reduction of the displacement amplification in the resonant range. Moreover, three tested examples of APA reveal up to 9 % of resonant frequency shift due to proper adjustment of the electronic shunting circuit, which is an encouragement for further analyses towards application of the APAs in semi-passive vibration control applications.

Słowa kluczowe:
Vibration, Dissipation, Adaptive, Piezoelectric

Streszczenie:
This paper presents experimental and numerical studies of magnetorheological (MR) fluids. Experimental studies have been focused on the investigation of MR fluid flow in the valve mode. An experimental device operating in the valve mode has been built and used for testing. Numerical investigations h ave included analysis of magnetic field, continuum based analytical modelling of the valve mode as well as micromechanical discrete element simulation of MR fluid. Analytical studies of the MR flow have been carried out using the conventional Buckingham equation with constant yield stress across the valve gap and the modified Buckingham equation with nonlinear yield stress distribution across the channel according to the magnetic field distributionm determined numerically. The analytical results have been compared with experimental data. A better performance of the modified Buckingham model has been observed. A micromechanical model of MR fluids has been developed within the discrete element framework. The DEM model has been verified qualitatively on a test example of forming chains by magnetized particles after application of an external magnetic field.

Streszczenie:
The objective of this work was to develop a mathematical model of coupled thermodynamic and mechanical processes proceeding in pneumatic, adaptive absorbers under cyclic loadings. The results of the modelling were to be verified versus experimentally obtained data. The analysis was divided into sections devoted to: forces acting on the piston, thermodynamics of the gas in the absorber’s chambers, gas flow through the piezoelectric valve. Three control volumes were distinguished within the absorber’s structure in order to analyze the thermodynamic processes. For each control volume analysis of energy balance, thermodynamic state parameters and heat transfer were performed. A set of equations was formulated for each control volume in order to determine: (1) motion of the piston in relation to the acting forces, (2) the gas state evolution, (3) energy balance within each control volume and (4) heat transfer to the surroundings. The obtained results revealed that the proposed approach to modeling was in good agreement with the data obtained experimentally. The controllability of the absorber was successfully reflected by means of the numerical model outcome.

Streszczenie:
Adaptive Impact Absorption focuses on adaptation of energy absorbing structures to actual dynamic loading by using system of sensors detecting and identifying impact in advance and semi -active dissipaters with controllable mechanical properties which enable change of system dynamic characteristics in real time. The article present s a review of research conducted at the Department of Intelligent Technologies of the Institute of Fundamental Technological Research dedicated to applications of systems for Adaptive Impact Absorption. Wide range of presented examples covers pneumatic landing gears, bumpers for offshore towers, wind turbine blade-hub connections and d protective barriers for automotive applications.

Słowa kluczowe:
adaptive impact absorption, safety engineering, smart structures, optimal control

Streszczenie:
This paper describes concepts of two different technologies developed for control of gas flow in High Performance Actuator (HPA) and control of gas discharge from airbag system through High Performance Valve (HPV). The HPA technology utilizes piezoelectric valve to govern flow in the pneumatic cylinder, used as an impact absorber or smart damper, while the HPV uses membrane surfaces driven by flow and controlled by explosive rings to mode discharge of an airbag system. Both techniques, different in their nature realizes comparatively similar function in flow different scales but similar time scale, where each cycle of operation is near single milliseconds. The paper also covers experimental results and a simple numerical study on the High Performance Valve (HPV) concept developed for a control of an adaptive inflatable impact energy absorber (gas-bag). Patent pending concept of the HPV is utilizing a flow energy drive method, using the flow energy to move and seal working parts of the valve.

Słowa kluczowe:
Adaptive devices, Piezo-valve, Airbag, Valve, Explosion, Control

Streszczenie:
An adaptive pneumatic shock absorber with a piezo-valve was designed for real-time impact energy dissipation. The device was a piston-cylinder type with a fast actuated (less than 2 ms) piezo-valve positioned inside the piston. The principle of operation of the device was to keep the reaction force on a predefined level by means of managing of the gas flow between the internal chambers of the shock absorber. The internal chambers were defined by spaces in the cylinder on both sides of the piston. The proper control of the valve, which connected the two chambers, allowed to adjust the instantaneous pressure drop between them. The pressure drop was a decisive factor that influenced the total reaction force of the shock absorber.
The presented investigation was conducted using the MTS Test System experimental setup in order to perform measurements of stiffness and viscous effects in the domain of frequency of excitation. The shock absorber under investigation was fixed between a stiff base and a piston rod of the hydraulic actuator that was used for the mechanical excitation.
The conducted set of experimental tests included measuring of the following set of quantities: frequency of harmonic excitation, reaction force of the absorber, displacement of the piston, velocity of the piston, gas pressure in both chambers.
The presented research was focused on characterization of the response of the device to harmonic excitation. The study was aimed at identification of limits of the device in terms of its controllability and adaptability.

Słowa kluczowe:
adaptive devices, Adaptive Impact Absorption, AIA, pneumatic shock-absorbers, piezo stack, piezo-valve

Streszczenie:
Adaptive Impact Absorption focuses on active adaptation of energy absorbing structures to actual dynamic loading by using system of sensors detecting and identifying impact in advance and controllable semi-active dissipaters with high ability of adaptation. The article presents a review of research carried out in the Department of Intelligent Technologies of Institute of Fundamental Technological Research dedicated to applications of systems for adaptive impact absorption. Wide range of presented examples covers pneumatic landing gears, adaptive crashworthy structures, wind turbine blade-hub connections and flow control based airbags for maritime and aeronautical applications.

Słowa kluczowe:
smart structures, adaptive structures, Adaptive Impact Absorption, crashworthiness, safety engineering

Streszczenie:
This paper proposes a benchmark for conceptual devices dedicated to adaptive impact absorption (AIA) and protection against shock excitations. The problem of the exploitation impacts is present in a wide class of applications, and particularly where direction of the object’s movement is well-defined, for example: precise docking systems, rail car buffers or landing gear shock absorbers. In those applications the objective is to equalize the values of velocities of the bodies in order to minimize the deceleration peak. The proposed benchmark establishes a comparing procedure for materials or devices in the field of AIA in a simplified regime in order to improve the comparability of the solutions. A drop test device is proposed to be used for testing the proposed devices in the predefined experimental regime. Besides, an example of the adaptive absorber is presented.

Słowa kluczowe:
Adaptive structures, Shock absorption, Impact energy absorption, Piezoelectric valve

Streszczenie:
The class of ultra-light aircraft becomes more and more popular among the enthusiasts of aviation due to low formal requirements of getting the pilot license and low costs of the equipment. Therefore, the training of the pilots starts to be a large-scale task. One of the most difficult operation for the inexperienced pilots is touch-down and it often happens to strike the ground with a high sink speed. In consequence the training machines are endangered of fast structural damage. A potential solution would be to mount a system of adaptive landing gear for light aircraft with a capability of recognition of the actual landing impact and tuning the landing struts in order to conduct the smoothest landing operation possible. In the case of the ultra-light aircraft class the weight of the components is the crucial task and therefore the low-weight pneumatic system is proposed for these application.
The paper presents a concept of an adaptive landing system and adequate control strategy for a small aerial vehicle. The objective of the work was to develop a fully functional model of the landing system and experimental verification of it. The system is based on the new pneumatic impact absorbers actuated via piezo-stacks. The concept assumes designing of the system with the capability of adaptation to actual energy of impact scenario identified by a dedicated sensing system for impact energy recognition.
The designed control system was dedicated to process the data from the system of impact energy recognition in order to perform the optimal landing scenario. The objective of the control strategy was minimization of the structure’s deceleration peaks during the touchdown.
The presented results consist of numerical analysis of the adopted strategy of control and experimental verification of the concept on the dedicated experimental device. The results proved that the proposed method allowed minimization of the maximal deceleration level acting on the demonstrator.

Streszczenie:
In the recent decades, a significant stream of research in structural control has focused on semi-active control approaches. The two constitutive characteristics of a semi-active system are its low consumption of energy and the capability of smart self-adaptation. The inspiration can be traced back to Nature, where dynamic and energy-efficient self-adaptation to varying external conditions is a ubiquitous mode of operation. These ideas are fundamentally different from the paradigms behind the active control (active counteraction) and the passive approaches (passive absorption). In applications to mitigation of vibrations in structural control, within the spectrum of the semi-active techniques, there are two basic approaches that can be identified as: 1) stimulation of local dissipation in actuators, which basically amounts to maximization of the local force--displacement loops, and 2) local triggering of the global material dissipation mechanisms, which is called the prestress accumulation--release (PAR) control strategy. This contribution reports on a specific control technique from the second group.

Streszczenie:
Almost all man-made structures are exposed to vibration. Regardless of whether these are large structures such as bridges or skyscrapers, machines with rotating parts such as engine shafts, frame structures or vehicle suspensions, excessive vibrations can be very harmful. From the perspective of their effects they can be seen as very spectacular (e.g., a collapse of a bridge) or not worth much attention (e.g., a failure of a motor shaft), but in each of these cases, the effect is the destruction of the structure and a negative impact on the users of these devices.
Several approaches can be used by the designers to overcome this phenomenon. The most basic, but often sufficient, method is to introduce changes in the mechanical parameters of the system affecting the severity of vibration in operational conditions, i.e., its mass or stiffness. If such design changes cannot be realized, or if vibration problems are detected after the system is manufactured, or if a vibration suppression system must be used for other reasons, one of the three basic types of such systems can be used.
The primary choice is usually a passive vibration damping system. These are relatively simple systems whose mode of operation is the passive dissipation of the energy of structural vibrations. Their design and simple functionality ensures that they are highly reliable, but their simplicity is reflected, unfortunately, in their limited efficiency. Their flexibility may be also considered as insufficient: once configured, even a small change in the specific operating conditions can result in a drastic loss of performance. This indicates a rather narrow spectrum (frequency range) of correct system operation.
Active systems constitute a much more effective damping approach. In this case, vibration attenuation is achieved not by means of dampers, but by actuators integrated into the structure. This approach allows to achieve very good results of vibration mitigation over a wide range of excitation frequencies. High efficiency, however, is burdened with a much higher degree of complexity of such a system as compared to the passive systems. In order to develop such a system, it is necessary to design the controller and install actuators that implement the control algorithm. During the vibration suppression, the actuators themselves require a large energy supply, which can be troublesome in some cases.
The compromise between these damping systems are semi-active systems, where the actuators are used to affect structural properties instead of exerting large external forces. In terms of reliability, semi-active systems can be compared with passive systems, while in terms of the efficiency of damping with active ones. They also do not require large amounts of electric energy to implement the control algorithm. Despite being a relatively new research area with less established design and development procedures, their advantages seem to be large enough to attract a growing number of scientists and engineers.
This contribution presents a strategy for semi-active reduction of forced vibrations in frame structures. Analogous damping technique proved to be effective in damping of free vibrations. The control strategy is based on the Prestress Accumulation–Release (PAR) concept and uses specially designed semi-active rotational nodes. Successive decentralization of the damping system demonstrates that apart from the global mechanism of the energy dissipation based on the PAR, it is also possible to disperse it locally to individual beams that are separate elements of the damping system.

Słowa kluczowe:
Smart And Adaptive Structures, Adaptive Impact Absorption, Safety Engineering

Streszczenie:
Results of numerical simulations for transonic flow in control valve are presented. The valve is the main part of an adaptive pneumatic shock absorber. Flow structure in the valve domain and the influence of the flow non-uniformity in the valve on a mass flow rate is investigated. Numerical simulation results are compared with experimental data.

Słowa kluczowe:
pneumatic valve, transonic flow, numerical simulations