Staff

Abstract:
Despite the prevalence of well-established and explored navigation systems, alternative localization methods are currently the focus of intensive research. This interest is driven by geopolitical challenges and increasingly sophisticated applications of mobile robots and uncrewed aerial vehicles. This study investigates the problem of real-time positioning in GPS-denied environments. Based on the mapped magnetic anomaly field and using Bayesian formalism for data fusion, the localization obtained from embedded sensors is corrected to reduce cumulative errors. The proposed method has minimal computational cost and a minimal number of tunable parameters. The paper introduces it and demonstrates its effectiveness in a laboratory study. Experimental tests, using a system equipped with an Inertial Measurement Unit, demonstrated a significant reduction in localization uncertainty. The improvement was especially notable in areas with large, smooth variations in the magnetic field. Finally, the accuracy of the method is analyzed, and its performance is compared to a particle filter.

Keywords:
Sensor fusion, Bayesian inference, Real-time positioning, Magnetic anomaly, Intelligent navigation system

Abstract:
The paper presents the concept of equivalent parameter predictive control (EPPC) elaborated for semi-active fluid-based (hydraulic and pneumatic) shock absorbers equipped with controllable valves and subjected to impact excitation. The undertaken problem concerns the absorption and dissipation of the impact energy with the requirement to minimize the generated reaction force and corresponding impacting object deceleration. The development of a control strategy for a challenging problem with unknown impacting object mass and unknown changes of external and disturbance forces is proposed and discussed in detail. The innovative solution utilizes the paradigm of model predictive control supplemented by the novel concept of equivalent system parameters identification. The EPPC is based on the online measurement of system response, the computation of the equivalent mass of the impacting object, and the repetitive solution of the optimal control problem with various prediction intervals and constraints imposed on valve opening. The presented method is proven to operate robustly for unknown excitations, including double-impact conditions, and it has similar efficiency to control methods developed previously for known impact parameters.

Keywords:
adaptive impact absorption,semi-active control,self-adaptive shock absorber,adaptive model predictive control,model identification adaptive control,model predictive control

Abstract:
The paper introduces Extended Identification-Based Predictive Control (EIPC), which is a novel control method developed for the problem of adaptive impact mitigation. The model-based approach utilizing the paradigm of Model Predictive Control is combined with sequential identification of selected system parameters and process disturbances. The elaborated method is implemented in the shock-absorber control system and tested under impact loading conditions. The presented numerical study proves the successful and efficient adaptation of the absorber to unknown excitation conditions as well as to unknown force and leakage disturbances appearing during the process. The EIPC is used for both semi-active and active control of the impact mitigation process, which are compared in detail. In addition, the influence of selected control parameters and disturbance identification on the efficiency of the impact absorption process is assessed. As a result, it can be concluded that an efficient and robust control method was developed and successfully applied to the problem of adaptive impact mitigation.

Keywords:
adaptive control,optimal control,predictive control,impact mitigation,shock absorber

Abstract:
This short communication is aimed at indication of a significant problem to be solved by researchers working in the field of engineering structures. The contribution concerns a very important application of a rescue cushion, which is an airbag system devoted to the impact mitigation appearing during evacuation of people from heights. Although, a very similar in the principle of their operation, car airbags have been thoroughly tested, rescue cushions have not received sufficient attention. It should be emphasized that the performance of the actually operated devices is far from sufficient and even fatal accidents occur. The authors identified the problem and have initiated a study, which includes numerical simulation and experimental validation of the impact absorption process, as well as the elaboration of a suitable adaptive solution.

Keywords:
adaptive airbag, Adaptive Impact Absorption, inflatable structure, pneumatic absorber, rescue air cushion

Abstract:
The paper is aimed at detailed discussion of the Identification-based Predictive Control (IPC) developed for semi-active fluid-based shock-absorbers which protect structures and machines against impact excitations. The problem addressed is the optimal impact absorption providing adaptive mitigation of dynamic response of the mechanical system. The goal of applied control is dissipation of the entire impact energy and minimization of the impacting object deceleration during the process. Three proposed implementations of the IPC are based on sequentially repeated procedures, which include identification of excitation parameters and calculation of the valve opening providing minimization of tracking error of the optimal path. The presented numerical examples concerning mitigation of the dynamic excitation acting on the double-chamber pneumatic shock-absorber reveal high efficiency and prove robustness of the proposed control methods. The developed algorithms are compared against each other in terms of path-tracking efficiency and character of required control actions. The most important challenges in practical implementation of the proposed methods are indicated.

Keywords:
adaptive control, adaptive impact absorption, identification-based predictive control, model predictive control, self-adaptive shock-absorber, semi-active control

Abstract:
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.

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

Abstract:
The paper covers detailed discussion on novel control system developed for adaptive fluidbased shock-absorbers serving for mitigation of unknown impact excitations. In order to provide complete independence of the control system from the loading conditions, the Hybrid Prediction Control (HPC) was elaborated. The proposed method is an extension of previously introduced kinematic feedback control which ensures optimal path finding, tracking and path update in case of high disturbance or sudden change of loading conditions. Implementation of the presented control system allows to obtain self-adaptive fluid-based absorbers providing robust impact mitigation. In contrast to previously developed methods of Adaptive Impact Absorption, the proposed control strategy does not require prior knowledge of impact excitation or its preliminary identification. The independence of applied control system from parameters of impact loading results in the capability of automatic path correction in the case of disturbance occurrence and readaptation to a number of subsequent impacts. The successful operation of the selfadaptive system is investigated with the use of numerical examples involving doublechamber pneumatic shock-absorber equipped with controllable valve. Efficiency of the HPC is proved by comparison with passive absorber as well as device equipped with adaptive and optimal control modules.

Keywords:
hybrid prediction control, kinematic feedback control, adaptive impact absorption, unknown impact mitigation, self-adaptive system

Abstract:
The paper presents development, evaluation and comparison of various control systems for adaptive fluid-based absorbers serving for absorption of the impact loading. The investigations concern two competitive approaches: i) standard control systems with single determination of the optimal system path based on identified impact conditions, and ii) newly-developed control systems with on-line determination and update of the system path during the process. It is revealed that low robustness of the standard control systems to imprecise impact identification and unknown disturbances results from the assumed path-determination approach and utilized simple path-tracking methods. The proposed solution to this problem is application of the innovative control systems, which utilize Automatic Path Finding and Automatic Path Update algorithms based on full kinematic feedback as well as Hybrid Path Tracking method dedicated for fluid-based absorbers. The introduced approach to absorber control is used to develop three different self-adaptive systems of increasing complexity and robustness. The favourable capabilities of proposed systems including no need for impact identification, high robustness against force disturbances and reduction of leakages influence are proved. Detailed discussion is presented using the illustrative example of single-chamber adaptive pneumatic shock-absorber mitigating impact loading.

Keywords:
adaptive impact absorption, automatic path finding, automatic path update, full kinematic feedback, hybrid path tracking, self-adaptive system, pneumatic shock-absorber

Abstract:
This paper investigates an application of a ball-screw inerter for mitigation of impact loadings. The problem of impact absorption is to provide a minimum reaction force that optimally decelerates and eventually stops an impacting object within the available absorber stroke. It significantly differs from vibration mitigation problems which are typical application of inerters. The paper demonstrates that the optimum absorption can be achieved by fully passive means. For known values of the object mass and inerter parameters, the obtained solution is independent of the impact velocity. The optimum passive absorption is achieved by employing a variable thread lead. As a result, two force components emerge, the typical inertance-related force and a damping-like term, and sum up to provide the optimum constant deceleration force. This result is relatively unique: conventional absorbers do not provide a constant force even with complex active control systems. Finally, an optimization problem is formulated to reduce the influence of process uncertainties (range of possible mass values, unknown friction). The results are verified and analyzed in a numerical example.

Abstract:
Recent progress in the field of sensors, actuators, and smart materials allows the construction of more and more efficient controllable pneumatic dampers for shock absorption. Typically, such devices apply online semi-active control techniques, which utilize electromagnetic, piezoelectric, or magnetostrictive valves. As a result, they are characterized by a high efficiency of impact absorption, but simultaneously by a complicated construction and a specialized electronic system. The alternative solutions are semi-passive absorbers that ensure a similar performance by using a much simpler, low-cost construction and a less complicated adaptation mechanism. This paper introduces an adaptable semi-passive single-chamber pneumatic shock absorber, SOFT-DROP, which provides the optimal impact absorption and energy dissipation after a single reconfiguration performed at the beginning of the process. The high effectiveness of the proposed concept is proved in numerical and experimental investigations of the device. Moreover, the proposed semi-passive damper is also compared against already known pneumatic absorbers that utilize semi-active control methods. Ultimately, the device might be used in an airdrop system for delivery of light packages.

Keywords:
adaptable, semi-passive, impact absorption, optimal design, pneumatic shock absorber

Abstract:
This paper introduces and discusses a new concept of impact absorption by means of impact energy management and storage in dedicated rotating inertial discs. The effectiveness of the concept is demonstrated in a selected case-study involving spinning management, a recently developed novel impact-absorber. A specific control technique performed on this device is demonstrated to be the main source of significant improvement in the overall efficiency of impact damping process. The influence of various parameters on the performance of the shock-absorber is investigated. Design and manufacturing challenges and directions of further research are formulated.

Keywords:
adaptive impact absorption, adaptive inerter, semi-active control, shock-absorber

Abstract:
Our study presents the research on elaboration of a novel type of the rescue air cushion, which is an inflatable structure used by fire brigades for evacuation of people at heights. The goal of our work is to increase its injury prevention capabilities. We consider the system based on an airframe filled with a compressed gas and a double-chamber airbag, which exchanges the air with environment. Discussed research includes modelling of the system, numerical simulations of its dynamic behavior and description of the dedicated adaptive solution. Practical implementations of the original ideas are conducted using the rescue cushion in 1:2 scale and a full-scale demonstrator of semi-passive valves. According to the already obtained results it is experimentally proven that a significant improvement of the system’s characteristics can be achieved by introducing valves of simple construction [1]. In this study the influence of a delayed start of the adaptation procedure is investigated in detail. Obtained conclusions are used in order to indicate directions of further system development, which will concern, among others, estimation of the impacting body trajectory and identification of the impact position.

Keywords:
Adaptive Impact Absorption, Airbag system, Dynamic characteristics optimization, Impact mitigation, Rescue cushion, Pneumatic shock-absorber.

Abstract:
Within this contribution a challenging problem of adaptive impact absorption is considered and studied in detail. The paper is focused on practical implementation of the self-adaptive system and experimental assessment of its performance. For this purpose a novel kinematics feedback control method is applied and used to adjust in real-time the opening of piezo-electric valve, which is an important part of the smart pneumatic shock-absorber devel-oped in the Institute of Fundamental Technological Research Polish Academy of Sciences (IPPT PAN). As a result, an outstanding shock-absorbing system, capable to adaptively mitigate the impact, is obtained and decelerations acting on the amortized object are significantly reduced for varying parameters of the dynamical excitation. Within the paper the control system im-provement based on proportional control of the piezo-electric valve opening is considered. This improvement may provide much better response of the system in terms of reaction force, which is transferred to the amortized object. Indeed, such control in real-time is very hard to be realized in practice. Nevertheless, the authors make an effort to develop the electronic system allowing for proportional adjustment of the valve opening and replacing the on-off control, which gives worse performance and higher control cost.

Keywords:
self-adaptive impact absorber, adaptive control system, real-time control, pneu-matic absorber, drop tests, piezo-electric valve, braking system

Abstract:
The contribution describes three innovative external airbag systems developed by the
authors for the protection of flying objects during emergency landings. The first one is the
AdBag system dedicated for small drones, which is designed to protect the carried equipment
and prevent damages to objects or injuries to people at the crash location. The second system
is external airbag designed for ultralight aircraft Skyleader 600, which provides significant
reduction of touchdown velocity and deceleration levels during emergency landings, thereby
improving protection of the pilot and the passengers. Finally, the last presented solution is the
Spring-Drop system with specialized airbag deployment technique, which is dedicated for
specialised airdrop operations where the touchdown conditions can be extremely harsh and
unexpected, while protection of transported cargo is of crucial importance. Both conceptual
studies, numerical simulations and experimental tests of the three proposed systems are
presented and discussed.

Keywords:
External airbags, adaptive system, emergency landing, human safety

Abstract:
The paper is aimed at modelling and optimization of a rescue cushion system, which is a device used by fire brigades for evacuation of people from buildings. The goal of the study is an improvement of the system response under various operational conditions. For faster and cheaper analysis of the system performance and further development of the complex structure of the rescue cushion system, a dedicated dynamical model is elaborated. Implemented numerical model is further applied for the parametric study in order to evaluate the influence of selected airbag parameters on the effectiveness of impact mitigation process and to determine possible improvements of the actual system design. In particular, adaptation of the rescue cushion to the mass of landing person, as well as to the initial velocity, is analyzed. Simultaneously, the necessity of meeting all the functional and operational requirements is taken into account. The most promising directions of further research are indicated.

Abstract:
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.

Abstract:
For over two decades, inerter-based devices are a subject of research papers, patents and engineering reports. Since 2002, when the inerter was introduced as the missing element of mechanical networks, various applications of the inerter have been proposed. They include solutions for earthquake engineering, suspensions of vehicles, aircraft landing gears and even systems improving walking performance of humanoid robots. In contrast to majority of the inerter-based systems, which are mainly developed for vibration mitigation problems, this paper concerns the inerter as the shock-absorber protecting objects excited by the impact. In particular, adaptive performance of the ball-screw inerter with variable moment of the flywheel inertia is investigated. In order to ensure efficient adaptation of the inerter to various excitation conditions, the single reconfiguration technique, which was successfully applied for pneumatic absorber, is now adjusted and implemented in the proposed inertial system. The contribution consists of the concept introduction, discussion of the mathematical model of the system, theoretical as well as numerical analyses. Results of the presented study show that optimal impact absorption can be obtained in semi-passive manner. The properly adjusted geometry of the surface guides for the inertial elements ensure appropriate variability of the flywheel moment of inertia. Variable moment of the flywheel inertia provides optimal deceleration of the amortized object. The calculated moment of inertia depends on the mass of amortized object and friction but it is independent of the impact velocity.

Keywords:
ball-screw inerter, impact absorption, passive absorber, variable inertance, variable moment of inertia, inertial damping

Abstract:
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.

Abstract:
The paper presents development of innovative, self-adaptive, fluid-based absorbers and investigation of their application for mitigation of impacts and forced vibrations. The considered absorbers are composed of two chambers filled with fluid and separated by a piston equipped with a controllable valve. The valve enables control of the fluid flow between the chambers and adjustment of the actual value of force generated by the absorber. The aim of the research is to develop the strategy of valve control providing self-adaptive operation of the absorber ensuring dissipation of submitted energy by using minimal value of generated force. The paper includes description of self-adaptive impact absorber, presentation of the control system and numerical simulation of its effectiveness in the case of impact excitation and harmonic loading. It is concluded that self-adaptive system provides optimal mitigation of impact excitation, but its response in the case of harmonic loading is not always optimal and requires further improvement.

Abstract:
The paper is aimed at development of high performance shock-absorbers for aeronautical applications. This contribution concerns pneumatic dampers because of their lightweight, technical simplicity and low manufacturing costs. The concept of semi-passive devices is introduced and single reconfiguration technique is discussed for both single- and double-chamber shock-absorber. Presented general approach to optimal design of the semi-passive devices can be applied for design of different types of fluid-based absorbers, e.g. hydraulic or oleo-pneumatic dampers. The absorbers can be used as a suspension of light airdrop system as well as a part of landing gear of small UAV.

Abstract:
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.

Keywords:
Adaptive Impact Absorption, adaptive control, adaptable system, damper

Abstract:
Pneumatic dampers are still an attractive subject of research in both modelling and experimental testing. Progress in the field of sensors and actuators allows to construct more and more efficient absorbers and dampers based on active or semi-active control algorithms. However, passive and semi-passive solutions are also developed because of their lower costs and simplicity. This paper presents adaptable pneumatic shock-absorber that allows to obtain optimal impact absorption and energy dissipation by a single reconfiguration performed at the beginning of the process. The absorber is composed of two cylinders including at least one narrow rectangular slot and adequate number of outflow vents precisely shaped for certain impact scenarios. During operation of the device the air is released through overlapping slots and selected vents, which provides constant value of the generated force. As a result, the shock-absorber works as a passive device but provides minimal value of the reaction force in similar manner as semi-active system equipped with fully controllable mechanical valve. The paper presents the results of numerical simulations of adaptable shock-absorber operation and attempts of demonstrator construction aimed at conducting experimental verification of the concept.

Keywords:
Adaptable, Semi-passive, Impact Absorption, Pneumatic Shock-absorber

Abstract:
This paper discusses passive and semi-active techniques of structural control by means of smart joints, and then it proposes a specific smart joints system for frame structures and tests its capability in mitigation of free vibrations. Basically, the proposed solution modifies frame beams by addition of truss-type hinges, and its effectiveness relies on the softening effect that occurs in compression due to geometric nonlinearities and which triggers the highly-damped high-frequency response modes of the structure. First, the finite element (FE) model of the specific frame structure with geometrical nonlinearities is derived, and the proposed passive joints are described and incorporated into the model. Then, their principle of operation and effectiveness is examined numerically for the first two natural modes of vibrations with various initial displacement amplitudes. An objective function is proposed to assess joints placement, based on the efficiency in mitigation of the excited vibrations.

Keywords:
Vibration Damping, Structure Response, Smart Structure, Structural Control

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

Abstract:
The contribution presents recent progress in development of the control systems for
semi-active fluid-based dampers equipped with fast-operating valves. The attention is focused
on the case when the damper is subjected to impact of mass moving with initial velocity and
additional excitation force acting during the process. The objective of the corresponding control
problem is to find the change of valve opening which provides absorption of the entire impact
energy with minimal value of generated reaction force. The contribution presents two different
approaches to solution of the challenging control problem with unknown excitations and disturbance
forces, which are based on the concept of Model Predictive Control.

Keywords:
fluid-based dampers, semi-active dampers, Hybrid Prediction Control, Identification-based Predictive Control

Abstract:
Despite the fact that airbag systems are well-known and used in safety engineering for many years the growth of research and development activities and increasing number of new applications of airbags are observed. Advances in the field includes among others: development of advanced car airbags, analyses of airbag cushioning for landing on Mars, elaboration of emergency landing system for drones. Another field of airbags application and simultaneously the main motivation for the study presented in the paper is the evacuation of people conducted by the fire brigade. When people are forced to leave the building by jump from the window or roof the rescue cushion is placed on the ground in order to mitigate the impact and safe life of evacuated people. The aim of the study is to develop the relevant adaptation strategy for the system and provide efficient operation of the airbag in case of different impact velocities and different masses of the landing person. Several approaches to the system adaptation are analyzed and they include semi-active as well as semi-passive solutions. Also possibility of implementing the concept of self-adaptive impact absorption is assessed. Technical and operational requirements for the rescue cushion are considered and based on them the final adaptation principles are selected. Evaluation of the system performance is conducted with the use of numerical models of dummies provided in the LS Dyna software environment. In Fig. 1. the overloads acting on pelvis of three different dummies dropped from assumed height are shown. The obtained mitigation of the impact loading is significant for all considered cases.

Abstract:
The current progress in the field of sensors and actuators has triggered increasing application of semi-active shock-absorbers for mitigation of dynamic excitations in car suspensions, aircrafts landing gears and buildings seismic protection systems [1]. The problems related to design of semi-active shock-absorbers include not only their proper construction providing reliable operation, but also elaboration of control strategies ensuring optimal mitigation of dynamic excitations of various kinds [2,3]. Development of optimal control strategies is especially difficult because of limitations of applied actuators, e.g. their finite stroke and speed, which are often critical for system operation and strongly influence efficiency of the shock-absorbing device. The contribution concerns the fundamental problem of mitigation of the rigid object’s impact using fluid-based shock-absorber equipped with a controllable valve with predefined performance limitations. The problem of impact mitigation is formulated as optimal control problem aimed at dissipation of the entire impact energy and minimization of the global deviation of generated force and corresponding impacting object's deceleration from the theoretical optimal values [4]. The considered limitations of valve operation cause that solution of the control problem is no longer intuitive and sophisticated mathematical tools have to be applied. First, the application of Pontryagin's maximum principle to impact mitigation problem is analyzed and the difficulties in obtaining final solution are discussed. Secondly, the possibilities of solving the problem using gradient-based methods of variational calculus are considered and the influence of initially assumed control scenario is investigated. Eventually, the solution of impact mitigation problem is obtained using direct methods with various discretization and schemes of numerical integration. The
obtained solutions are thoroughly analyzed and compared against each other, which allows to draw general conclusions about application of optimal control methods for semi-active shock-absorbers subjected to impact loads and to evaluate the influence of valves limitations on the efficiency of impact absorption process.

Abstract:
Novel semi-active shock-absorbers dedicated to impact absorption utilize high-performance valves to control actual flow of the fluid between absorber chambers, modify generated reaction force and obtain optimal process of energy dissipation. Although various control strategies providing optimal impact mitigation were elaborated, they were based on strict assumptions such as apriori knowledge of impact loading and lack of system disturbances. In contrast, more challenging objective is to develop control systems maintaining efficient and robust operation in the case of incomplete information about system excitation and disturbances in the process. The possible solution is application of self-adaptive systems based on sequential measurements of system state, such as elaborated by authors Hybrid Prediction Control involving bang-bang and continuous valve actions. In this contribution improvement of self-adaptive system is achieved by introduction of the online identification of system parameters and its application to compute optimal control.

Keywords:
impact mitigation, fluid-based shock-absorber, Model Identification Adaptive Control, semi-active control

Abstract:
The inerter is a subject of intensive research in the field of structural dynamics and control since 2002, when it was introduced by Malcolm Smith. Inerter-based devices are implemented in various practical applications, which include protective systems in earthquake engineering, suspensions of trains, road vehicles and aircraft landing gears. The majority of inerter applications proposed in the literature concerns vibration mitigation problems, e.g., implementation of the inerter in tuned mass dampers. In contrast, this contribution discusses an application of the inerter for solving the problem of impact absorption. The inerter was previously considered as a shock-absorber in [Ref.] but optimal impact mitigation was not provided. Recently, the authors have studied a simple inerter device based on the ball-screw mechanism with a variable thread lead, which ensures minimization of the generated reaction force and the optimal impact absorption. This contribution sums up the results obtained in the full-length journal paper, currently under review.

Keywords:
ball-screw inerter, impact absorption, passive absorber, variable inertance, variable moment of inertia, inertial damping

Abstract:
Pneumatic dampers are still an attractive subject of research in both modelling and experimental testing. Progress in the field of sensors and actuators allows to construct more and more efficient absorbers and dampers based on active or semi-active control algorithms. However, passive and semi-passive solutions are also developed because of their lower costs and simplicity. This paper presents adaptable pneumatic shock-absorber that allows to obtain optimal impact absorption and energy dissipation by a single reconfiguration performed at the beginning of the process. The absorber is composed of two cylinders including at least one narrow rectangular slot and adequate number of outflow vents precisely shaped for certain impact scenarios. During operation of the device the air is released through overlapping slots and selected vents, which provides constant value of the generated force. As a result, the shock-absorber works as a passive device but provides minimal value of the reaction force in similar manner as semi-active system equipped with fully controllable mechanical valve. The paper presents the results of numerical simulations of adaptable shock-absorber operation and attempts of demonstrator construction aimed at conducting experimental verification of the concept.

Keywords:
Adaptable, Semi-passive, Impact Absorption, Pneumatic Shock-absorber.

Abstract:
The goal of this paper is to present further development of the inertial shock-absorber called SPINMAN. Application of the device in mitigation of structures response is investigated and selected case study is discussed. The specific construction and operation of the device is introduced and explained. In reference to the impact absorption problems, the SPIN-MAN is a concept of adaptive inerter device with two phases of operation. The first of them includes energy absorption and accumulation. External energy of the load is converted to kinetic energy of rotational motion of the mass. During the second phase, accumulated energy is dissipated by inverse spinning of the second mass powered by the remaining part of the impact energy. To obtain this type of operation, special switchable actuators are used. Applicability of the device in mitigation of impact-born structure response, especially in case of space systems, is investigated. General concept of the device construction and operation is adjusted to meet the requirements for space systems. This results in a fluidless, passive-like solution but adaptable to the load conditions. Tuning of the shock-absorber may be realized by manual or easily automated mechanical adjustments. Effectiveness of the solution is based on the specific on/off type of control, which is responsible for the optimal energy flow in the system and efficient dissipation of impact energy inside the SPIN-MAN. Results of numerical simulations confirmed quick and effective operation of this device.

Keywords:
structure response mitigation, adaptive impact absorption, adaptive inerter, semi-active control, shock-absorber

Keywords:
Adaptive Impact Absorption, shock-absorber, vibration damping

Keywords:
Smart And Adaptive Structures, Adaptive Impact Absorption, Safety Engineering