Advances in Applied Nonlinear Dynamics, Vibration and Control -2021

Autonomous and Electrical Vehicles are two development trends for automobile industry. Plenty of sensors are demanded to monitor the traffic condition in autonomous vehicle, hence sustainable and reliable power supply for these sensors is a key issue. For the Electrical Vehicles (EVs), the range extension is a core issue, while energy harvesting approach can solve this problem properly. Therefore, the smart shock absorber is proposed with capacity of both road condition monitoring and energy harvesting. The road condition module is based on a rotation triboelectric nanogenerator, voltage signal is utilized to characterize the smooth, pothole or bump road condition by different amplitudes, and finally upload to the big data cloud to support the intelligence transportation systems (ITS). The energy harvesting module is based on an overrun clutch, which drives the generator rotation along one direction, a speed-increasing gearbox ensures that the generator works under high efficiency domain. Damping force can be adjusted by varying the value of external resistor; therefore, stiffness of the whole suspension can be controlled by external circuit to improve the vehicle handling and ride comfort performances. This smart shock absorber has the potential to popularize the Autonomous Vehicle, Internet of Vehicle as well as Electrical Vehicles.

In this paper, the dynamic damping performance of energy harvesting shock absorber (EHSA) with overrun clutch under open circuit condition is investigated by experiment. Force-displacement loops under harmonic excitation with different frequency and amplitude are test and analysed. Results shows that there exists a faint disengagement phenomenon introduced by overrun clutch and a dynamic response caused by the transmission chain in EHSA at the beginning of each stroke under the low frequency and small amplitude excitation condition. In this condition, the damping force produced by the internal friction is about 29.0 N, and the equivalent damping coefficient is 1176 Ns/m. Then, the disengagement phenomenon and dynamic response will intensity with the increase of frequency and amplitude of excitation. Furthermore, the equivalent friction force increases as the result of the enhanced disengagement phenomenon and dynamic response. However, the equivalent damping coefficient is dropped to 200 Ns/m with the increase of frequency and amplitude of excitation.

In this work, a game theory in security problem of cyber-physical systems is studied. A class of malicious attacks can be adopted simultaneously by sensible attacker to undermine performance of systems, meanwhile, defender cloud also take different actions to respond. In the case that both defender and attacker all possess numerous strategies to select to confront each other in an action. Both sides all make efforts to maximize their own payoffs. To investigate the optimal actions for both sides, a game framework is build. And we transform the problem of finding equilibrium solutions to the game into a Multi-objective optimization problem where the resources constraints are removed to ensure the effectiveness of the defensive or offensive behavior. Then, a modified nondominated sorting genetic algorithm II (NSGA-II) is introduced to solve the corresponding problem. By forming Pareto front, optimal action sets can be obtained to help both sides to make decisions. Numerical example is proposed to illustrate our main results.

As an important industrial transportation tool, the shipboard rotary crane is widely used in marine environment to accomplish transportation tasks between a single ship and the harbor, or between different ships. Most exsisting control methods for shipboard rotary crane is developed on linearized/approximated dynamics, and most of them require exact velocity measurement signals. However, practical shipboard cranes systems inevitably suffer from many complex interferences, such as sea wind, sea wave as well as system uncertainties (e.g. unknown payload mass and boom mass). To deal with thess problems, in this paper, a nonlinear output feedback antiswing controller for Three-dimensional (3D) shipboard rotary crane systems is developed under the situations when the velocity signals are unmeasurable. Specifically, an energy storage function which consists of kinetic and potential energies is constructed, on the basis of that, the accurate rotation positioning and load swing suppression are achieved simultaneously without any approximation or linearization for the nonlinear dynamics. The Lyapunov’s theorem and LaSalle’s invariance principle are utilized to verify the asymptotic stability of the closed-loop system. Finally, numerical simulations are implemented to further prove the effectiveness of the proposed output feedback controller.

A novel sliding mode control method, as is shown in this paper, is proposed for the 4-DOF tower crane system by employing beneficial disturbance effects to enhance the transient control performance as well as to ensure the strong robustness simultaneously. More precisely, we deliberately construct a nonlinear disturbance observer, and then, the advantages and disadvantages of the disturbance influence on the 4-DOF tower crane system are described by a constructed disturbance effect indicator (DEI) based on the observation information. Subsequently, the novel sliding model control method is designed in the light of the estimated disturbance and the introduced DEI. Additionally, the stability of the closed-loop system is demonstrated by Lyapunov techniques. It should be pointed out that the designed method points out that besides bad effects, disturbance has the desirable side-effect of transient control performance improvement, and as a result, introducing desirable side-effect into the controller design is of great importance. The effectiveness and robustness of the designed sliding model control method can be demonstrated by simulation results.

In recent years, in order to exploit beneficial nonlinearities, an X-shaped supporting structure with helpful nonlinear stiffness and damping characteristics has been developed and deliberately introduced to improve the energy harvesting performances. In this paper, the Volterra series-based frequency domain method is utilized to achieve a systematic analysis and design of the present X-structured nonlinear system. The generalized frequency response functions (GFRFs) and the output frequency response function (OFRF) of the system are theoretically derived using the recursive algorithm. Importantly, analytical relationships between the power generation function (PGF) of the harvesting system and the structural parameters of the X-structure would be derived, to show how the power generation is affected by the structural parameters of the system. The results indicate that, the present study could provide an effective and efficient way to characterize the nonlinear effects on the proposed energy harvesting system.

Aimed at the typical annular flat connection structure in the heavy-duty gas turbine, based on the Archard wear theory and finite element method, the influences of tie rod parameters and material properties on the fretting damage characteristics of the annular flat contact interface are studied. The results show that the preload mistuning of tie rod will result in the uneven distribution of fretting characteristics in the circumferential direction. With the tie rod approaches to the annular flat, the relative slip distance and shear stress decrease, while the contact pressure increases at the inner side of annular flat and decreases at the outer side of the annular flat. The material properties have little effect on contact pressure. When friction coefficient, elastic modulus and Poisson’s ratio of annular flat increase, the shear stress, slip distance and wear depth decrease. The researches can provide a reference for the mechanism design and engineering application of the annular flat connection structure.

Fault diagnosis of shaft cracks plays an important role for the safety and reliability of rotating machineries such as aero-engine, turbopump, wind power generator and internal combustion turbine in modern industrial applications. In this paper, a novel method for diagnosing shaft cracks of rotating machineries based on nonlinear transmissibility function is proposed. In the new method, a nonlinear dynamic model is built to describe the nonlinear behavior of a simply supported rotor with breathing cracks and nonlinear supports (nonlinear bearing damping and stiffness coefficients). Damage features for benchmark and cracked structures are derived respectively, and damage indicator for crack diagnosis is defined as the relative change between damage features. Through two numerical studies simulated by the Matlab software, procedures of proposed method are demonstrated and method’s effectiveness and availability are verified. In the future study, the proposed nonlinear transmissibility function-based crack diagnosis method could be extended and applied for other faults in rotating machineries like unbalance, misalignment, stator-to-rotor rub and support structure looseness and so forth.

For the application and research of the nonlinear energy sink (NES), the vibration of the NES is generally not restricted. However, the vibration amplitude of the NES may be greatly excited, which is unacceptable in engineering. A limited NES consisting of a conventional NES and a piecewise spring is investigated to restrict the vibration of the NES. The effects of the piecewise stiffness and the gap on the dynamic response of the primary system and the NES are considered in forced vibration. The piecewise function is fitted into a continuous function to obtain the nonlinear vibration responses with harmonic balance method. Then the results are verified wtih the Runge-Kutta method. The results show that the piecewise stiffness has a good performance on limiting the NES. Although the introduction of the piecewise spring will weaken the damping effect of the NES on the primary system, the NES obtain a considerable damping effect with proper parameters. In a word, this work provides a simple and reliable method to restrict the NES, which is beneficial to the design of the NES and broadening the application of the NES in engineering.

Disc-shaped triboelectric energy harvesters can harvest kinetic energy from two kinds of sources: continuous rotation and vibration. A majority of studies about disc-shaped triboelectric energy harvesters focus on scavenging energy in continuous rotation, and only several of them deal with vibration energy. In this work, a new disc-shaped triboelectric energy harvester consisting of a stationary disc, a rotating disc having an eccentric mass with a magnet, and a separate magnet fixed to the harvester base is developed. The pair of repulsive magnets are utilized for the first time in a disc-shaped triboelectric energy harvester for efficiency enhancement. One of the discs is covered with a metal film and the other one is covered with a metal films on top of a dielectric film. Several alternating sectors of equal size are cut away from each piece of film. A comprehensive theoretical model coupling both structural dynamic and electric dynamic domains is established. Numerical simulations are carried out to investigate the effect of the potential well due to the two magnets on both structural and electrical behaviours, basins of attractors and the influence of the number of sectors. The results indicate that the magnetic bistable mechanism is able to enhance the power of the harvester considerably, compared with conventional disc-shaped triboelectric harvesters without bistable mechanism. Additionally, increasing the number of sectors also improves the output efficiency of the harvester.

This paper proposes a scaled model to investigate the dynamic characteristics of suspension string and LMS adaptive control of hoop flexible structure. Firstly, the lateral vibration equation of micro segment string is established, along with the vibration frequency calculated. Also, the state space equation is theoretically obtained when the LMS adaptive algorithm is used to calculate the control force. Then, the scaled model is established by the finite element method before and after suspension, and there exist shaking mode and nodding mode. With this, a vibration control simulation is conducted for the hoop flexible structure to obtain the effect of LMS adaptive control. In the program, fixed step and variable step solvers are used to solve the state space equation, and Pulse, Square, Sawtooth and Random signals are applied as excitations. The simulation results show that the response curves are all obviously decreased after suspension. Moreover, the LMS adaptive control has a significant effect on steady-state response. It is concluded that the control results can be used as a reference for the large hoop truss antenna structure.

In this paper, the neural-based adaptive asymptotic tracking control problem is considered for a class of multiple-input multiple-output (MIMO) stochastic non-strict-feedback nonlinear systems with unknown control gains and full state constraints. A barrier Lyapunov function (BLF) is designed to avoid the violation of state constraints, and the problem of the unknown control gains is solved by introducing an auxiliary virtual controller. Besides, a new control scheme is proposed, which can not only realize the asymptotic tracking control in probability but also meet the requirement of the full state constraints imposed on the system. Eventually, the simulation results verify the feasibility of the scheme.

Fast and accurate positioning while suppressing swing is pivotal to efficient and safe operation for the rotary cranes. The problem becomes more complicated when a double-pendulum effect exists for some certain payloads. This paper proposes a nonlinear coupling-based motion trajectory planning method for double-pendulum rotary crane subject to state constraints. The proposed control method consists of two parts: a positioning reference component and a swing-eliminating component. The positioning reference angular acceleration trajectory is derived from a trapezoid-like function with suitable duration, which considers state constraints. The swing-eliminating angular acceleration trajectory is designed based on the nonlinear coupling relationship among the boom luffing motion, the hook swing and the payload swing. State constraints can be guaranteed by adjusting angular acceleration (deceleration) change duration, hold duration and constant velocity duration. The Lyapunov technique and LaSalle’s invariance theorem are used for stability analysis. Simulation results verify the control performance of the proposed nonlinear coupling-based motion trajectory planning method.

This paper investigates an adaptive neural network (NN) optimal control problem for stochastic nonlinear systems. The stochastic systems under consideration contain unknown nonlinearities, immeasurable states and state constraints. The NNs are utilized to approximate the unknown nonlinearities, and a nonlinear state observer is designed and thus the unmeasured states are estimated via it. In the framework of observer-based output feedback control and the backstepping technique, the virtual and actual optimal controllers are developed based on the actor-critic architecture. All the states are confined within the preselected compact sets by developing the tan-type Barrier optimal performance index functions. Furthermore, the stability of the closed-loop systems is proved by using Lyapunov function theory. The simulation results demonstrate the effectiveness of the presented scheme.

This article presents a novel control strategy based on dual-loop adaptive dynamic programming (ADP) to optimize the tracking performance and ensure the security of autonomous vehicles when actuator faults occur. The proposed dual-loop ADP of controller, composed of two online policy iteration algorithms and an adaptive observer for fault-tolerant control (FTC), guarantees the online tracking accuracy of underactuated systems with uncertain faults, which is difficult to control by single ADP. In addition to actuator faults, the proposed controller can also address the external disturbances such as icy roads and uncertainty of wheel cornering stiffness, which means the controller possesses better robustness. The autonomous vehicle is simulated in multiple driving scenarios with different types of faults, demonstrating the effectiveness of the control strategy.

As a tool for transporting goods, three-dimensional bridge cranes are widely used in many industrial sites, such as workshops, warehouses, docks and so on. The main control objective is to transport goods to the designated position smoothly and quickly while restraining load swing angles. However, the influence of external disturbances and the uncertainty of the system model parameters increase the difficulty of designing the controller. In the first step, we constructed a composite signal to increase the coupling relationship of the state vectors, and then designed an adaptive tracking controller, which can achieve a satisfactory tracking effect while completing the estimations of the uncertain model parameters. In the second step, considering the fact that the velocity signals are not measurable in actual situations, we replace the velocity feedback with velocity-like signals, and then propose an improved adaptive tracking control strategy. Use Matlab as a simulation platform to complete comparative simulation and robustness verification. A series of simulation results shows that the designed controller can complete the control goal and its control performance is significantly better than the other two controllers in the comparative simulation.

In this paper, the principal-internal resonance produced by the principal resonance and the 1:3 internal resonance for an axially moving thin plate with clamped and hinged supports under periodic line load is studied. Based on Kirchhoff’s basic assumption and large deflection theory, the expressions of kinetic energy and potential energy of thin plate are given, the nonlinear vibration differential equation of axially moving thin strip plate is achieved by means of Hamiltonian variational principle. By using Galerkin discretization method, the ordinary differential vibration equations with respect to time variables are derived. The multi-scale method is used to obtain the approximate solution, and the characteristic equation for the steady-state amplitude of the system is obtained. The effects of axial velocity, external excitation position, external excitation amplitude and external excitation frequency on the resonance amplitude are analyzed. The results show that the amplitude of the system may increase with the increase of the axial velocity, excitation amplitude and frequency of the external excitation, respectively.

With the continuous improvement of high-speed railway train operation speed, the problems of train operation safety and wheel rail wear are increasingly prominent. Improving train safety and reducing wheel rail wear can reduce operation and maintenance costs and bring greater economic benefits. In this context, a new semi-active control strategy applied in a Magnetorheological damper (MRD) is proposed to improve train safety and reduce wheel rail wear. Firstly, the transmission characteristics of the vehicle are analyzed according to the lateral vibration model of one quarter of two degrees of freedom. Then, the co-simulation model of Universal Mechanism (UM) and MATLAB is established, and the proposed control strategy is applied to the model to study its impact on the dynamic performance of the train. At the same time, the paper analyzes the influence of the control strategy on the dynamic performance of the train under different wearing levels. The results show that the control strategy can reduce the derailment coefficient of the train and the lateral force of the wheel axle, and improve the safety of the train greatly. At the same time, the wheel rail wear is reduced, the wheel wear degree is reduced, and the lathing cycle is prolonged. In addition, the control strategy can take into account the ride comfort of the train and maintain the good operation quality of the train.

The maglev trains suffer from various control complexities such as strong nonlinearity, open-loop instability, disturbances and parameter perturbations in the long-term operation of trains, which make the control of magnetic levitation system very challenging. In this paper, an airgap robust control strategy is proposed for a maglev trains. Specifically, the developed controller utilizes backstepping method in conjunction with sliding mode control technology to asymptotically regulate the airgap to a desired trajectory despite parameter perturbations and external disturbance. The nonlinear dynamic model of magnetic suspension system is derived and analyzed. Then, the system is decomposed into two sub-systems. For the first subsystem, the Lyapunov function and inter virtual control variables are designed. The sliding mode surface is constructed in the second subsystem to complete the design of the whole robust control law. The stability of the presented controller is proven by Lyapunov techniques. Finally, results of simulation show the superiority of the proposed control algorithm tackling parameters change and disturbances.

The integration and transcendence control among disciplines is gradually becoming a consensus in the academic field. Domik and Fischer (2010: 90) contended that as the integration and transcendence control among disciplines, trans-disciplinarity has significant theoretical and practical values under the current era of constantly overlapping information. Language, as a tool of interpersonal communication control, is the carrier of culture. Language application ability involves not only language and pragmatic knowledge, but also cultural knowledge relevant to target language control. This paper will focus on intercultural communication control from the perspective of trans-disciplinarity, with the aim of effectively improving students’ awareness of intercultural communication control and cultivating their intercultural communication skills so as to satisfy the needs of the society for high-quality international human resources in the new era.

This paper investigates the identification problem on the delay parameter for time-delay Boolean networks (TBNs). First, the observability of TBNs is proposed, and some observation conditions are obtained. Then the relation between observability and identifiability is discussed. Using the results of observability, some criteria for the identifiability of the delay parameter are derived. Finally, the paper shows an important result that the delay parameter can be identified if structure matrices are known. Moreover, two examples are given to show the feasibility of the proposed method.

As one of the most important parts of the heating, ventilation and air conditioning (HVAC) system, the performance of air-handling units (AHU) which is a typically multi-input multi-output (MIMO) nonlinear complex system will directly affect the indoor air quality (IAQ), environmental comfort and system energy consumption, etc. Hence, it is essential to dynamically analyze the AHU system and to design an advanced nonlinear multivariable controller, in order to achieve aforementioned goals. In this paper, for such MIMO nonlinear complex system, the nonlinear multivariable dynamic model is detailed analyzed and carefully built firstly. And then, the backstepping based nonlinear multivariable controller, in which the air and cool water flow rates are taken as input variables and the relative humidity and indoor temperature are considered as control targets, is designed step by step. Finally, both different types targets control of indoor temperature and humidity ratio demonstrated the superior performance of the designed controller, no matter the response time or the control errors.

Energy harvesting technologies motivated researchers and manufacturers to develop a sustainable and eco-friendly power supply to drive low-power electronics. In electrified vehicles, regenerative automobile shock absorbers are currently receiving focus to harvest a part of the dissipated suspension’s kinetic energy. Despite other energy harvesting applications in automobiles, the car’s suspension works and dissipates kinetic energy as much as the vehicle moves on the road, which can be used in continuous vibration-to-electricity energy harvesting applications. This paper provides a full characterization of an arm-toothed rotary electromagnetic regenerative damper. The arm-toothed/flywheel mechanism converts the linear shock absorber’s motion to a rotational motion during both the compression and expansion strokes. The flywheel’s inertia helps to amplify the input speed to enhance the harvested power and provide smooth operation during random non-periodic excitations. A 2-DOF quarter model equipped with the arm-toothed energy-harvesting damper was built. The arm-toothed energy-harvester model is verified through test-bench results. The car regenerative suspension model has been entirely characterized concerning both the harvester and suspension parameters during simulations. To mimic a real-car traveling on roads, the regenerative suspension model was simulated under non-periodic ISO 8606 roads with different qualities and speeds. The results indicated that traveling on a Grade-C road with speeds between 20–100 km/h, the average power and voltage RMS outputs ranged between 5–24 mW and 0.75–1.65 V, respectively.

In actual engineering application, Quasi-zero-stiffness (QZS) vibration isolation systems may not achieve expected low-frequency isolation effect. In this study, a QZS system with nonlinear hysteretic damping was investigated to discuss the reasons for failure of isolation performance. The results indicate there are two main reasons for the above failure phenomenon: a) the nonlinearity of the system and b) the stiffness error in actual structure. The latter includes two cases of the system is at equilibrium position and disequilibrium position. The dynamic behavior of the system under above situation are analyzed. By using the harmonic balance method (HBM) to discuss the primary and secondary harmonic transmissibility responses, the methods to avoid the effect of nonlinearity are provided. The results were verified by numerical simulations.

This paper proposes a novel mixed H∞/passive vibration control approach for active suspension of in-wheel motor electric vehicles. To mitigate the negative effects caused by the electromagnetic excitation of the switched reluctance motor and the shock road disturbance, a robust controller with a mixed H∞/passive performance is developed based on finite-time stability method. A stabilization condition is given in terms of Bilinear Matrix Inequalities (BMIs) based on Lyapunov method. Then, some decoupling methods are utilized to cast the nonlinear feasibility problem into a linear feasibility problem with the framework of Linear Matrix Inequalities (LMIs). Finally, the proposed active control method is compared with a traditional passive control method. The comparison results indicate that all the concerned requirements are improved by the proposed active suspension.

Engineering structures are usually subjected to random excitation, which may cause nonlinear dynamic behavior. The random excitation can be modeled as Gaussian or non-Gaussian white noise stochastic process. Thus, it is of important significance to efficiently obtain the structural stochastic responses under various kinds of random excitations, including the simultaneous action of Gaussian and Poisson white noises. In this paper, a novel direct probability integral method (DPIM) is developed to address the stochastic dynamic analysis of nonlinear multi-degree-of-freedom (MDOF) systems subjected to combined Gaussian and Poisson white noises. Firstly, the probability density integral equation (PDIE) of stochastic dynamic MDOF system is derived accounting for the principle of probability conservation. The compound Poisson process is simulated by using the stochastic harmonic function method, and the techniques of probability space partition and smoothing Dirac function in DPIM are proposed to solve the PDIE effectively. Comparing with Monte Carlo simulation and path integral solutions, the probability density function results of stochastic responses of nonlinear MDOF systems under combined Gaussian and Poisson white noises indicate the high efficiency and accuracy of the proposed DPIM.

In this paper, a new method for optimal phasor measurement unit (PMU) placements is proposed when considering system change. In the method, PMU, zero injection buses (ZIBs) and flow measurements are all considered. When the system changes, there are unobservable buses and new PMUs are needed to guarantee the observability of the system. However, it is not easy as a result of the application of ZIBs and flow measurements, as well as existing PMU and observable buses. In order to obtain PMU placements, all observable buses by not only PMU but also ZIBs and flow metableasurements are obtained. In addition, all ZIBs and flow measurements, which can be used in the new system, are also obtained to reduce the number of new PMU. After that, the model considering observable buses, PMU, ZIBs and flow measurements is modified to obtain optimal PMU placements in the new system. The correctness and validity of the method are verified by the IEEE test system simulation.

In this paper, a method based on the convolutional neural network (CNN) is proposed to effectively identify the crack location in the rotor system. Firstly, a dual-disks hollow shaft rotor system model with a breathing crack is established based on the finite element method. Then the dynamic response of the cracked rotor system is obtained by the 4th harmonic balance method (HBM) and the analysis results show that the super-harmonic resonance of the rotor system is closely related to the depth and location of the crack. Finally, the CNN is adopted to identify the crack position in the rotor system and it can achieve high accuracy. To understand the CNN, we visualize the features space and try to explain the reasons of the great performance of the CNN.

A quasi-zero-stiffness isolator is proposed via oblique beams, and negative stiffness is derived from the post-buckling effects. The restoring forces of the oblique beams are characterized based on a beam constraint model and verified by a finite element analysis. The negative-stiffness stroke and the maximum stress during deformation are calculated. Dynamic responses of the nonlinear isolator are analyzed based on a harmonic balance method and verified by a Runge-Kutta method. The proposed isolator works effectively with the excitation frequency beyond a threshold. The frequency threshold is either the frequency with displacement transmissibility equaling to 1 or the jump-down frequency. The isolator design is optimized to achieve the largest negative-stiffness stroke with an optimized oblique angle. Compared with the initially straight beam, a small curvature can increase the largest stroke dramatically due to the multi-stable characteristic of the oblique beams in post-buckling states. The isolator design is also optimized to achieve the lowest frequency threshold. Regardless of the existence of a jump phenomenon, the frequency threshold decreases with the decreasing cubic stiffness. For the proposed isolator via oblique beams, the optimizations for the largest negative-stiffness stroke, the smallest cubic stiffness and the lowest frequency threshold are equivalent.

The output performance of an electromagnetic inductive energy harvester under Gaussian white noise excitations is investigated in this paper. Equivalent linearization method is applied to derive the statistical moment of the system with symmetric quartic potential functions, including the mean square value of displacement and output current. According to the theoretical results, the influence of noise intensity and internal system parameters on the response of the generators subject to Gaussian white noise excitations is emphasized. In order to consider the asymmetric and higher-order potentials, the Fokker-Plank-Kolmogorov (FPK) equation is solved based on the theory of detailed balance, and it is indicated that the mean square value of output current is independent of the shape of potential energy function.

The operational disturbance induced by the solar array drive system (SADS) is a crucial factor affecting the imaging quality and pointing accuracy of spacecraft. A precise system dynamics model of the SADS was proposed and verified by a test in a laboratory environment. The effect of nonlinear factors, such as the current subdivision of the drive controller, varying gear-meshing parameters of the gear reducer, sliding friction between the brush and slip ring and the clearance between the gear teeth, on the SADS’s disturbance characteristics were analyzed in the time and frequency domains. The results show that the current subdivision of the drive controller and varying gear-meshing parameters of the gear reducer can directly cause disturbances, which vary periodically and occur near excitation frequencies and high-order harmonic frequencies. The amplitude of the disturbance increases with a decrease in the number of current subdivisions and an increase in the fluctuation of the gear-meshing parameters. The sliding friction between the brush and slip ring and the clearance between the gear teeth does not change the characteristic frequency of the disturbance but can affect its profile and spectrum distribution.

In this paper, we study the adaptive fuzzy decentralized control problem for the fractional-order nonlinear large-scale systems in strict-feedback form. The controlled systems contain unknown nonlinearities. In the process of recursive design, the global approximation ability of fuzzy logic systems (FLSs) are utilized to cope with the unknown nonlinear continuous functions of the considered systems. In addition, in order to avoid the issue of “explosion of complexity” inherent in the traditional backstepping control design technique, the dynamic surface control (DSC) technique is introduced into the control design. Under the frameworks of the backstepping control design technique, DSC technique and adaptive fuzzy decentralized control theory, an adaptive fuzzy decentralized DSC scheme is put forward. On the basis of the fractional-order Lyapunov stability theory, it is confirmed that all the signals in the controlled systems are bounded and the tracking errors are able to converge to a small neighborhood of the origin.

In this paper, the low-pressure rotor of the typical high bypass ratio turbofan engine is taken as the model, and the dynamic model of the two disk rotor with casing is taken as the basis. Through the finite element numerical simulation, the influence of the vector angle between the unbalanced eccentricity of the fan disk and the turbine disk on the dynamic characteristics of the rotor system wind-impact of the rotor system is emphatically analyzed. The numerical simulation results show that with the increase of the vector angle between unbalanced eccentricity, the rotor system first moves from P-1 periodic motion to P-2 periodic motion, and then enters into the quasi-periodic motion and finally enters into the chaotic motion state.

Most of the previous shell elements based on the classic geometrically exact shell theory focused on the quadrilateral meshes. However, shell elements with quadrilateral meshes are difficult to model shell structures with arbitrary geometry. In this paper, a novel six-node triangular shell with five degrees of freedom per node based on the local frame approach is presented on the special Euclidean group SE(3), which is an extension of our recent work [1]. Considering the classic Mindlin–Ressiner hypothesis, the total Lagrangian method and Green–Lagrange strain tensor are employed for shells with large displacements and large rotations. To ensure the objectivity of the discretized strain measures, the rigid-body motion of the reference point within an element is removed and the relative motion is interpolated. To improve element solution accuracy, the strain interpolation schemes based on the assumed strain method are used to eliminate membrane and shear locking. The effectiveness of the presented novel triangular shell is demonstrated by several popular geometrically nonlinear benchmark examples.

Electrical impedance Tomography (EIT) is a newly developed nondestructive testing technology in recent decades. It can reconstruct the internal image of the measured body according to the measured voltage obtained from the electrode array on the surface of the measured body. EIT has attracted wide attention from all walks of life because of its advantages such as non-damage and simple system. In this paper, the forward and inverse problems of EIT imaging as well as the hardware are introduced, including the advantages and disadvantages of the algorithm, the existing problems and the current research level, etc. At the same time, the factors affecting the imaging quality of each part are analyzed in detail. EIT has been applied in many directions, especially in the medical field, which has a high research value and significance. It is hoped that readers can have a certain understanding of the concept of EIT imaging and the overall process of image reconstruction through reading this article.

The band structure (BS) and the transmission loss (TL) of a two-dimensional (2D) solid/liquid phononic crystal (PnC), which is composed of cylinder water immersed in steel matrix, are investigated by the finite element method (FEM). Meanwhile the effects of various factors on the BS of two-dimensional solid/liquid phononic crystals (PnCs) are analyzed. Unlike other literature, this paper first compares the advantages of steel/water phonon crystals over other solid/rope crystals. The effects of lattice constant, filling rate and the number of sides of regular polygon on the band gap characteristics of 2-D steel/water phonon crystals are investigated. At the same time, it is found that the shape of scatterer has little influence on the band gap, which is beneficial to the design of simple scatterer shape. It is revealed that the model has the advantages of forming band gaps at low frequency and larger bandwidth comparing with other structures. Moreover, the results show that the band gaps (BGs) move to low frequency as the lattice constant increase. Meanwhile, there is a linear relationship between the change of the first complete BG and the lattice constant and the first complete BG bandwidth decreases gradually with the increase of the filling rate of the scatterer. However, the shape of the scatterer has little effect on the BGs. The designed model will bring convenience to low-frequency vibration isolation and noise reduction. The investigation in this paper can be expected to utilize in the design of noise insulators or vibration isolation facility in the large engineering projects.

Model uncertainties, system time-delay, and strong coupling strongly impact the all-clamped plate (ACP) structure. Therefore, linear active disturbance rejection control (LADRC) as controller and inertial actuator (IA) as actuator are used to deal with these problems. However, the complex characteristics of the all-clamped plate with inertial actuator (IA_ACP) still make LADRC difficult to design and analyze. In this work, the frequency characteristics of LADRC are derived, and then it is applied to the vibration suppression system of IA_ACP. According to the frequency response of the system, the identification model of IA_ACP is established to provide the frequency characteristics of the system, and the LADRC parameters are adjusted according to the relationship between the two-degree-of-freedom (2 DOF) PID and LADRC in the frequency domain. Finally, on the hardware in the loop simulation platform based on NI PCIe-6343 acquisition card, it is verified that LADRC can effectively suppress the vibration of ACP. The frequency domain analysis of the experimental results shows that the proposed method is feasible.

According to the structure features and assembly process of an aero-engine, a stiffness characteristic analysis model for aero-engine inter-shaft cylindrical roller bearing was set up. The comprehensive influence of the structure of inter-shaft support, the relative rotational direction of inner and outer ring, the inner and outer ring fit tolerance, the inner and outer ring lock nuts tightening torque, the aero-engine rotating speed, the bearing working temperature, the radial load and the elastohydrodynamic lubrication were considered in this model. The variation laws of the inter-shaft bearing radial stiffness which are changed with the above parameters were analyzed. The results showed that, the inter-shaft bearing stiffness was lack of sensitivity to the inner and outer ring lock nuts tightening torque. The inner and outer ring fit tolerance and the aero-engine operating mode had a great influence on inter-shaft bearing stiffness. The change of the bearing stiffness may have a significant impact on rotor-bearing system vibration features, and attentions should be paid during the design stage. In addition, the inter-shaft bearing stiffness was closely related to the structure of inter-shaft support and the relative rotational direction of inner and outer ring. The structure of inter-shaft support and the relative rotational direction of inner and outer ring should be selected reasonably by reference to the aerodynamic performance and dynamic characteristic requests of aero-engine, in order to make sure that the change of inter-shaft bearing stiffness would not bring negative influence on the reliability of the engine.

Jittering vibration at a robot arm-tip is unavoidable and is one of the key factors affecting its trajectory accuracy. Because a robot arm is a high-dimensional complex system, the actual causes for the vibration at the robot of the arm-tip are very complicated, and very difficult to identify, if it is not impossible. This work presents a novel and practical device for mitigating such vibrations. The present vibration-mitigator consists mounting box with a plate spring carefully designed based on the frequency of the arm-tip vibration. It can be conveniently mounted on the arm-tip. The key idea is to transmit the jittering at the arm-tip to the vibration of an oscillator nested inside the jittering-mitigator box, so that the vibration of jittering-mitigator box can be reduced. The jittering-mitigator box can in turn serve as the working end for the robot arm. The present device requires only the knowledge of the frequency of the jittering vibration at the arm-tip, without the need to explore the underlying causes of the vibration. An actual device is made and it is mounted on a six-axis tandem robot. A systematic study is conducted to examine the effectiveness of the device, by numerical modeling and simulations. The jittering at the arm-tip of the robot is firstly measured under the working conditions using accelerometers connected to LMS Test Lab. Through FFT analysis, the dominating frequency is identified. The parameters of the jittering-mitigator are then calculated theoretically. A finite element model is next established to simulate the reduction effect of the jittering mitigator. The results show that the average amplitude of the jittering vibration at the arm-tip is significantly reduced by as much as 65%.

This study proposes a novel zero-stiffness vibration isolator and investigates its dynamic responses under micro-oscillation with a friction consideration. The novel vibration isolator is based on the mechanism of a cam-roller Quasi-Zero-Stiffness (QZS) system while with improvement by reducing its system components. The proposed vibration isolator consists of a designed bearing, which can provide stiffness responses in the radial direction, and an inserted rod with curved surface. Without the precise cooperation between the positive and negative stiffness systems required in a typical QZS isolator, the designed single stiffness system can provide the high-static-low-dynamic stiffness characteristic directly. The static characteristics of the stiffness performance are numerically confirmed, and then the dynamic responses with friction consideration at the contact surfaces are discussed. The displacement transmissibility in low frequency range is numerically validated when applying harmonic excitation on the base. The analysis results of this study reveal a unique vibration isolating performance of the zero-stiffness system under frication consideration.

The nonlinear multi-stable piezoelectric energy harvesters have attracted a great quantity attention for the performance enhancement. Due to the fact that the nonlinear restoring force plays an important role in dynamic behavior, it is necessary to model the nonlinear restoring force accurately. However, previous models mainly focus on the symmetric system, but the influencing mechanism of widely used asymmetric systems has not been discussed. Therefore, this paper presents an enhanced modelling method of nonlinear restoring force for asymmetric multi-stable energy harvesters. The magnetic charge method is applied to deduce the theoretical expression of magnetic force between the tip magnet and the rotatable magnets. Then, numerical results of magnetic force have verified the effectiveness of proposed method for asymmetric multi-stable energy harvesters. The influence of different structural position parameters of rotatable magnets on nonlinear magnetic force is analyzed. Moreover, the dynamic responses of asymmetric multi-stable energy harvesters with different potential well shapes are compared by directly changing structural parameters.

The parametric instability of an electromechanically coupled single-span rotor-bearing system subjected to periodic axial loads is studied. Here, the rotor system is equipped with two piezoelectric dampers, which has been developed in our previous work. The so-called electromechanically coupled characteristic is namely derived from that damper. By using assumed mode method and Lagrange equation, the equations of motion are derived. The multiple scales method is utilized to obtain the analytical instability boundaries. Numerical simulations based on the discrete state transition matrix method (DSTM) are conducted to verify the analytical results. With the comparison between analytical results and simulated results, we find that the additional combination instability regions are created due to the usage of piezoelectric dampers.

Nonlinear piezoelectric structures have attracted great attention in energy harvesting, vibration control, and morphing structures recently. The most important design and dynamic analysis parameters in a nonlinear piezoelectric structure is the nonlinear stiffness force. However, the nonlinear stiffness force is difficult to calculate analytically or measure statically under complicated practical engineering conditions. Therefore, this paper utilizes signal decomposition and the Hilbert transform-based method for the precise identification of stiffness force of a class of typical nonlinear piezoelectric structures. The quasi-zero stiffness, bistable stiffness, and tristable stiffness structures are designed in the magnetic coupled piezoelectric cantilever beam system. The identification process and the applicability based on free vibration and forced frequency-swept response for different nonlinear structures will be discussed. Numerical examples of quasi-zero stiffness, bistable stiffness, and tristable stiffness nonlinear piezoelectric structures show the necessity to choose the reasonable free decay and the forced frequency-swept response for accurate identification. In the experimental condition, the identified nonlinear stiffness force keeps in good agreement with the measurement by the dynamometer.

Curved beams which have advantages of excellent bearing capacity and beautiful appearance are diffusely applied in various engineering constructions. This paper derives the closed-formed analytical solutions of the steady-state forced vibration of the multi-cracked Euler-Bernoulli curved beam with damping effects by means of Green’s functions. Separate variable method, Laplace transform method and matrix transfer method are successively used to obtain the corresponding Green’s functions for Euler-Bernoulli curved beam with one-crack and multi-crack. The multi-cracked Euler Bernoulli curved beam model can be degenerated into the curved beam when the depth of these cracks to be zero. On this basis, it can be reduced to straight beam vibration model by setting the radius R to infinity. The present analytical solution can be verified through FEM results and solutions in references. Effects of various important physical parameters on curved beams are investigated, such as the influence of geometrical parameters (depth and locations) and the interaction between two cracks in the curved beam. The influence of damping on forced vibration is considered by introducing characteristic parameters.

The energy harvesting backpack has a promising potential in the biomechanical energy harvesting field. However, for the linear harvesting structure, a little deviation of the optimal carried mass will cause a dramatic decline in output power. To address this issue, inspired by the centrifugal governor, centrifugal inertia is designed for sensitivity reduction of energy harvesting backpack performance to carried mass. The dynamics of the traditional linear vibration energy harvesting backpack are analyzed to show the narrow energy harvesting bandwidth of the carried mass. Then, the centrifugal inertia is designed based on the rotation system. The Lagrange equation is used to establish the dynamic model of the harvesting system. The mass sweep analysis is applied to excite the nonlinear dynamic characteristics of the harvesting system. The dynamic analysis shows that the harvesting system has an approximately bi-stable characteristic which is dependent on time. The harvesting system with centrifugal inertia has a high-energy-harvesting orbit and a strong anti-interference capability from the simulation if the rotational damping is large enough. An appropriate perturbation could change the vibration state from low-energy-harvesting orbit to high-energy-harvesting orbit. The performance simulation proves that the centrifugal inertia can broaden the energy harvesting bandwidth of the carried mass.

In a microgravity field, the surface tension is dominant and the liquid restoring force is small. Therefore, the nonlinear large-amplitude liquid sloshing is even more likely to take place, which will negatively affect the attitude stability of the spacecraft. The numerical model for the liquid-filled coupling dynamics of spacecraft was established based on the Arbitrary Lagrangian-Eulerian finite element (ALE) method. The coupling effect is realized by exerting inertia forces to the liquid and sloshing forces and moments to the rigid body. The staggered algorithm is adopted to solve the liquid-sloshing module and the rigid body module in an iterative way. The numerical results of the rigid-liquid coupling system are compared with the analytical results, and the proposed methods in this dissertation are proved to be applicable and accurate. The high-order mode of the liquid is observed in the numerical simulations successfully during the rotation of the spacecraft. Meanwhile, the influences of the liquid sloshing on the coupling system are analyzed.

As key mechanical components, hydrodynamic sliding bearings widely used in rotating machinery can significantly affect the running state, reliability, and life of the rotor system. Bearing static characteristics are required for the determination of the dynamic characteristics. In the present study, the static characteristics of the five-pad tilting-pad journal bearing and the five-lobe journal bearing have been comparatively analyzed.The main difference be-tween these two kinds of bearings is that the pads of the former can tilt freely around their pivots.The numerical results indicate that the former owes the excellent stability due to pads tilting freely around the pivot in comparison with the latter. Further research shows that the characteristics of the tilting-pad journal bearing can be improved by increasing the preload factor and length-to-diameter ratio, which has a certain practical significance for the application of tilting-pad journal bearings.

It is difficult to improve the time and frequency resolution at the same time using traditional time-frequency analysis methods, such as Short Time Fourier Transform (STFT) and Wavelet Transform (WT), when processing non-stationary random signals of suspension systems. Meanwhile, it is also hard to obtain the accurate time-frequency characteristics of the systems. This paper proposes a new type of non-uniform modulation function by employing non-stationary Pseudo Excitation Method (PEM) to improve the precision of analyzing vertical vibration responses of suspension systems which are subjected to non-stationary random excitations. A general model of non-stationary pseudo excitation is then generated by using this new method. A quarter vehicle model is subsequently established and the response power spectrum with a high-precision time-frequency resolution of the vertical acceleration is obtained. Simulation examples are given to illustrate the vibration characteristics of the suspension systems of vehicle under two conditions, constant speed and varying speeds. It is found that when the vehicle travels at varying speeds, the higher the speed is, the wider the resonant frequency band of the suspension will be. Finally, the $${H}_{\infty }$$ H ∞ control method of the active suspension system is used for suspension control in finite frequency domain according to the varying resonant frequency bands. Results show that control in the varying resonant frequency bands can improve the damping performance of suspension systems.

The magnetic focusing effect of Halbach array has a wide range of applications in many areas. In this paper, based on the general theory of static magnetic field, various factors affecting the energy harvesting output voltage of Halbach array are analyzed. After that, according to the simulation carried out by Comsol, the magnetic field distribution of the four module Halbach array with different numbers of magnets was obtained, which verified that the shape of the magnetic field was a periodic sinusoidal distribution converging on one side. Then a Halbach array rotor was designed, and the output voltage of the Halbach array energy harvesting structure with different numbers of magnets under the influence of different factors was simulated, and the optimal Halbach array energy harvesting structure was obtained. At the same time, the halbach array composed of 12 magnets was verified through experiments. The experimental results are consistent with the simulation results, and higher voltage and higher power can be obtained. The designed Halbach array with simple structure and small size, can be more suitable to the lower frequency vibration or motion.

The vibration characteristics of a rotating tapered beam under the excitation of wake flows are considered. The governing equation of the beam is obtained and discretized to a set of ordinary differential equations by using the Galerkin’s method. The coupled vibrations for the first two modes of the beam are investigated. The effects of system parameters such as the taper ratio, the non-dimensional frequency ratio and radius on the first two natural frequencies of the vibrations are studied. Moreover, the vibration responses and stabilities of the coupled system are studied under the 1:1 primary resonance. And the relations between the amplitude of the vibration for the first mode and the parameters including the detuning parameter, the non-dimensional frequency ratio as well as the damping coefficient are investigated for different taper ratios.

In this paper, the problem of consensus tracking control for a class of distributed nonlinear multiagent systems is studied. Considering the system with nonstrict-feedback structure and sensor faults, an adaptive neural network control scheme is proposed, which combines backstepping technique with radial basis function neural network. In the process of control design, neural network approximation technique and its structural characteristics are used to overcome the control design obstacles caused by unknown nonlinear function and nonstrict-feedback structure. A controller is constructed for the system considering the sensor faults, which can not only realize the consensus tracking control of the system, but also ensure that all signals of the closed-loop system are bounded. Finally, an example is given to show the effectiveness of the proposed scheme.

In the practical applications of tower cranes, to improve work efficiency, it is needed to simultaneously rotate the jib, move the trolley, and change the rope length during transportation; however, there exist few control methods for such 5-DOF tower crane systems. In addition, it is still open how to find a balance among reducing the transportation time, saving the energy consumption, and guaranteeing satisfactory transient performance at the same time. Therefore, to address the above issues, in this paper, a multi-objective trajectory planning strategy with state constraints is proposed for 5-DOF tower cranes, which is the first solution that can achieve Pareto optimality of the transportation time and energy consumption, and can simultaneously satisfy all the practical constraints of the state variables and their corresponding velocities. The positioning and anti-swing performance of the planned trajectories are realized by differential flat outputs construction and B-spline curves design; also the multi-objective optimization problem is solved by the improved nondominated neighbor immune algorithm (NNIA). Finally, simulations are carried out for effectiveness verification.

The large-amplitude sloshing of propellant is a widely concerned problem in aerospace engineering. Computational fluid dynamics methods have been proposed to simulate large-amplitude liquid sloshing for decades, with several meshed or meshless methods. This paper proposes an isogeometric analysis (IGA) method for sloshing simulation. The main challenges are tracking liquid free surface and time step convergence. Level Set method is combined with IGA with fixed grids to track free surface moving, also can be used to track liquid separateness which is quite common in large-amplitude sloshing. As IGA can provide numerically accurate solution at any location in computational domain, the mesh of Level Set can be different with IGA mesh without losing accuracy. Characteristic-Based Split (CBS) method is used to control divergence of each time step. The numerical results are compared to published numerical results and Flow3D software results for validation, and good agreement is observed.

Particle Impact Damping (PID) technology shows huge potential in passive vibration control applications. PID is mostly used in aerospace and machinery applications. The working principle of PID is based on the energy dissipation through the impact generated by the collision of particles with particles and with the container walls. The impacts induce harmful stresses to the primary structure in most cases. Particle impact damping is a highly non-linear phenomenon and theoretical models are not well developed. This study presents an approximate theoretical model of particle impact dampers for low natural frequency structures. The vibrating structures are modeled as a simple pendulum oscillating with low frequency. The bob of the pendulum is replaced with an enclosure carrying a particle. Only one particle is used for the analysis to not make the model very complicated. The specific condition for the working of such damper is derived. A detailed theoretical model of the particle impact damper is presented through simple pendulum motion. A soft impact is modeled to reduce the induced stresses to the primary structure by using a smaller value of the coefficient of restitution. The model is then simulated to foresee the oscillations of the pendulum with a particle impact damper.

In this article, an event-triggered adaptive fuzzy control scheme is devised for ship steering autopilot with the unknown dynamics. Considering the mechanical wear of ship rudder, we adopt the event-triggered control manner in the design process. Meanwhile, the unknown dynamics are efficiently addressed with the aid of fuzzy logic systems. The developed method can achieve the expected control performance while it significantly decrease the rudder acting frequency. Finally, the efficiency of the constructed event-triggered strategy is explained by a simulation example.

This paper deals with the problems of the admissibility analysis and control synthesis for polynomial fuzzy singular systems. By the help of the line integral Lyapunov function and an equivalent condition for a matrix inequality, a sufficient admissibility criterion of the polynomial fuzzy singular system is obtained. Furthermore, using a simple technique, the desired controller design method is presented in terms of sum-of-squares to avoid solving complex inequalities. Simulation examples are also provided to illustrate the effectiveness of the proposed methods.

In recent years, reinforcement learning has been widely concerned in the field of adaptive optimal control. In this paper, a reinforcement learning-based output-feedback control scheme is presented for a class of discrete-time strict-feedback systems. Firstly, a novel adaptive neural network-based state observer is constructed and the boundedness of the state estimation errors as well as the weight errors of observer neural networks are guaranteed. Then, a design of critic-action-based controller is implemented. To be specific, critic and action neural networks are adopted to obtain the optimal update law for the controller in a online manner. Variable substitution technique and estimated states are employed in the backstepping procedure instead of the n-step ahead predictor. Therefore, the n-step time delays are avoided during controller implementation. The proposed scheme ensure all the signals of the closed-loop system are uniformly ultimately bounded. Finally, simulation studies are provided to demonstrate the presented scheme.

In the flexible robot domain, due to the high nonlinear characteristics of flexible robot actuators, infinite degrees of freedom in theory, and multidisciplinary integration of mechanics, electricity, chemistry, etc., the establishment of its kinematics model is pretty difficult and imprecise. This paper analyzes the kinematics of a flexible manipulator driven by SMA spring. In the process of forward kinematics, based on Jacobian matrix, use both Newton-Raphson iteration method and Vpasolve function to solve and simulate the position of the end of the robot arm. In the process of inverse kinematics, use the SMA constitutive knowledge and genetic algorithm with nonlinear programming fusion to solve the posture of each joint. The simulation is carried out on Matlab platform, and the motion of the flexible robot arm can be well simulated. The kinematics analysis based on this paper provides a theoretical basis for the dynamic modeling, chaos analysis and nonlinear control of the flexible manipulator in the future.

This paper focuses on the $$H_{\infty }$$ H ∞ memory sample-data (MSD) control issue of T-S fuzzy network control system (TSFNCS) with multiple asynchronous deception attacks (MADAs), which has strong application background in the network information security field. Firstly, an improved Lyapunov-Krasovskii functional (LKF) $$V_{1}(x(t))$$ V 1 ( x ( t ) ) based on fuzzy weight membership function (FWMF) is constructed, which takes into account the nonlinear problem in LKF. Secondly, a novel two-side delay-dependent looped-functional (TSDDLF) is developed, that fully considers time varying delay (TVD) information and sampling delay information enormously enhances the information content of LKF. Then, a new criterion is developed, and a new MSD controller under MADAs is designed, to ensure that TSFNCS is asymptotically stable (AS). Finally, a numerical simulation is carried out based on the dynamic equation of the inverted pendulum system, which verifies the feasibility and effectiveness of the obtained theory.

Autism is a pervasive severe developmental disorder that includes some typical symptoms as interpersonal communication disorders, speech development disorders, language communication skills defects, and it is also with stereotyped behaviour. In the rehabilitation training of autistic children, effective treatment techniques can improve rehabilitation training effectiveness and help develop autistic children’s social skills. The effective treatment methods for treating autistic children are mainly conventional treatment as DIR concept guidance, floor time, sandbox games, and the brain-computer interface technology treatment, which develops in artificial intelligence. The DIR concept is utilized to guide and train the emotional interaction ability of children with autism, and floor time is applied to promote functionally emotional skills in children with autism. Sandbox games treatment can help the self-expression of children with autism, create a safe and accepting environment, and eliminate children’s tension and anxiety with autism. The adoption of new brain-computer interface technology can enhance the exchange and communication ability of autistic children with the outside world, and provide a new and innovative way for the rehabilitation of autistic children.

This paper is concerned with the problem of reliable $$\mathrm H_2$$ H 2 control for discrete-time T-S fuzzy bilinear systems with actuator faults and infinite-distributed delays. A discrete-time homogeneous Markov chain is used to represent the stochastic behavior of actuator faults. Based on a stochastic fuzzy Lyapunov function, the fuzzy observer-based controllers are designed for T-S fuzzy bilinear delay systems, two improved stability conditions are proposed to ensure that the resultant closed-loop system is exponentially stable in the mean-square sense with an $$\mathrm H_2$$ H 2 performance index. It is shown the fuzzy observer-based controller can be obtained by solving a set of nonlinear minimization problem involving linear matrix inequalities (LMIs) constraints. An iterative algorithm making use of sequential linear programming matrix method (SLPMM) to derive a single-step LMI condition for fuzzy observer-based control design. Finally, an illustrative example is provided to demonstrate the effectiveness of the results proposed in this paper.

In this paper, the nonlinear vibration characteristics and optimization analysis of the diaphragm pump valves are studied. Considering the coupling effect between the fluid and structures, the dynamic equations of the quality valve for the diaphragm pump is established by analyzing the force equilibrium of the quality valves. The spring preload can be obtained through analyze fluid flow between the alve lift and the structural parameters. The key parameters of quality valve for the diaphragm pump are obtained by the experimental testing data. The dynamic equation of quality valve is solved by using the fourth-order Runge-Kutta method. The nonlinear vibration characteristics of the quality valve are analyzed, and the influences of the valve clearance circumference and other structure parameters on the nonlinear vibration characteristics are also discussed. Moreover, the optimization analysis of the structural parameters for the quality valve for the diaphragm pump is conducted in order to reduce the vibration of the quality valves. The analysis model and method proposed in this article provide a new design process for quality valves of the diaphragm pump.

Stochastic dynamic analysis of structures aims to explore the propagation of uncertainty in dynamic structures, referring to stochastic response and dynamic reliability analyses. For large-scale nonlinear structures, stochastic dynamic analysis is a challenging issue. In this study, a novel direct probability integral method (DPIM) is proposed to synchronously attack the problem of structural stochastic response and dynamic reliability analyses in an efficient and accurate way. The theoretical foundation of DPIM is the probability density integral equation (PDIE), an integral description of probability conservation, which decouples the evolution of probability density from the physical evolution of structure. Firstly, the PDIEs of static and dynamic structures are uniformly derived based on the principle of probability conservation, and then the equivalent differential equations are also highlighted. Then, the formula with Heaviside function for structural reliability estimation is advanced. Moreover, numerical procedures for structural stochastic responses, dynamic reliability and system reliability analyses based on DPIM are demonstrated. Finally, an example of 15-story hysteretic frame building illustrates the high efficiency and accuracy of DPIM for stochastic dynamic analysis.

In this paper, a multi-step Q-learning (MsQL) method is employed to design an image-based visual servoing controller of the quadrotor, where image moment of the target image is used as the image feature for information extraction. The virtual camera and virtual image plane are introduced to construct the image dynamics model to realize the decoupling of the quadrotor. Combined with the quadrotor dynamics model, the quadrotor-image dynamics is proposed. The MsQL method is used to design the optimal control law for the horizontal motion of quadrotor. The control policy is updated through the dataset, such that the control gain can be solved and the desired trajectory of roll angle and pitch angle can be calculated. Simulation studies are conducted on the Matlab platform and good results are obtained.

The quadrotor transportation system has attracted numerous attention on different occasions due to its broad adaptability. Nevertheless, the “double” underactuated property of the system brings various challenges in practical control, which is caused by the underactuation of the quadrotor and that the suspended payload cannot be controller directly. In addition, most existing methods are designed based on the hypothesis of neglecting the hook’s motion. In fact, the quadrotors translation will also cause the hook’s relative motion with respect to the payload. In this paper, a trajectory generation method for the precise positioning of the quadrotor and the suppression of the double-pendulum swing motion is proposed. By injecting the artificially constructed swing elimination term into the basic positioning reference trajectory, a novel anti-swing trajectory is designed. Lyapunov based stability analysis is provided to prove the performance of the trajectory. Simulation results are concluded to validate the effectiveness of the planning scheme.

A bio-inspired ceil-like structure which can be considered as a pentagon-shaped structure is investigated for understanding and exploring its nonlinearity to achieve vibration isolation in multi-direction. Firstly, the model of low dynamic and high static vibration isolator is established, and the relevant system parameters are designed based on the equations of equivalent restoring force and stiffness of the system. Then the dynamic equations of the system are deduced and established. The natural frequencies of configurations with different connections of spring are studied and the dynamic response harmonic base excitation is derived. And finally, the isolation performance is evaluated by deducing the displacement transmissibility of the system. Several configurations of the pentagon shaped structure are designed for different working environments. The analysis shows that the structure can present flexible stiffness and have good vibration isolation characteristics in both vertical and horizontal directions. The result will provide a novel bio-inspired solution which can potentially be employed in different engineering practices for much better vibration isolation and control for multi-direction vibration isolation.

Similitude laws for the structural response under impact loading are proposed and analyzed in this paper. The scaling process is promoted from analytical, experimental, and numerical perspective. It is demonstrated that impact cases in different structures will be dynamically similar, having the same vibration response despite being different with respect to their size, impact time, and amplitude. In cases of simple structures, acceleration response and shock response spectrum, measured in an impact test on a set of plates, are successfully scaled to extrapolate the behavior of the complete or incomplete similarity of the prototype. Similarity conditions are presented for more precise re-modulating. In cases of complex structures, spacecraft are discussed to validate the similarity conditions and scaling laws. It is expected that the proposed similitude laws will help researchers to reduce costs and risks for experimental studies.

To analyze the speed and phase synchronization control problems of three homodromy exciters in nonlinear vibration system of machinery-material (NVS-MM), the nonlinear vibration system dynamics model under the excitation of three exciters considering the nonlinear support and the influence of the material is derived. Aiming at the synchronous control problem of NVS-MM, a controller based on radial basis function network global sliding mode control (RBFN-GSMC) algorithm and adjacent cross-coupling control (ACCC) strategy is established. Using RBFN to adaptively approximate the total uncertainty of NVS-MM including nonlinear support and material nonlinear force can effectively reduce the estimation error. Using the RBFN method instead of the symbol function can suppress the chattering of the system and stabilized the response of the system. Stability of the controller proposed for NVS-MM is proved by Lyapunov theory. Performance of the proposed RBFN-GSMC algorithm is further analyzed and verified by numerical simulation. Results show that compared with other control methods, the effectiveness of the proposed ACCC strategy combined with RBFN-GSMC algorithm is verified. ACCC strategy considers the coupling between two adjacent exciters, which can improve phase and speed synchronization control accuracy of three homodromy exciters in the NVS-MM. Finally, by studying the influence of parameter disturbances in the NVS-MM on the performance of controller, it is proved that the proposed controller is robust to external loads or parameter disturbances.

A nonlinear energy sink (NES) is studied for reducing the vibration of piecewise structures for the first time. The dynamic model of the piecewise structure coupled with the NES is established. A hyperbolic tangent function is introduced to fit the piecewise restoring force, and thus a piecewise nonlinear model is replaced by an approximate continuous model. Therefore, the resonance response of the coupled piecewise system can be analyzed with the harmonic balance method (HBM). The stability of the steady-state response is determined and numerically verified. Compared with the response of the piecewise system without the NES, the NES has a significant damping performance for the piecewise structures. Moreover, based on the effect of damping, the NES parameters can be optimized. For a given piecewise system, the optimal values of the NES cubic nonlinear stiffness, damping and mass are determined.

This paper studies the adaptive event-triggered consensus problem for the multi-agent systems with disturbance. Moreover, an event-triggered mechanism is proposed by the state sampling method, which the communication burden can be reduced. Based on the neural networks technique, the unknown function is processed. On the basis of impulsive dynamical theory and the Lyapunov theorem, it is testified that all the signals is bounded. Lastly, a simulation example is proposed to prove the validity of the control strategy.

The correction system of a double wheel trench cutter with the multi-laying winding hose system is studied. The dynamic model of a valve-controlled correction system with input delay is established. An adaptive sliding mode controller based on neural network is proposed to solve the problem of angle tracking control of the correction system under the influences of input delay, unknown/mismatched parameter dynamic and random disturbances. Auxiliary signals with input delay information are introduced in the controller to compensate the input delay when constructing the manifold surface. The unknown dynamics are approximated by using neural network and adaptive law. Based on the Lyapunov method, the asymptotic stability of the closed-loop system in finite time is proved theoretically. Finally, the simulation and experiments show that the proposed method has better control performance in terms of correction accuracy, time delay compensation, response speed and robustness.

Recently, phononic crystals have attracted a wide attention. Many potential existences of phononic bandgaps have been investigated, which can be used to manipulate the propagation of acoustic/elastic waves. In the current work, a two-dimensional (2D) phononic diamond crystal is proposed, with a hierarchical periodicities and two-stage band-gaps. The proposed structure is modeled by the finite element method and calculated by the COMSOL Multiphysics software. According to the Bloch theory, the band-gaps of the structure are calculated by applying the Floquet boundary conditions. This structure represents full and directional band-gaps which is different from the one-dimensional periodic structure.

This paper presents the concept of the variable admittance network (VAN) with indirect energy supply for semiactively controlled systems and the admittance analysis of three basic VANs with indirect energy supply in resonance vibration control. A mechanical network is describable with the admittance, which includes the damping, stiffness, and inertance information. The VAN with variable admittance parameters is beneficial for the resonance vibration control of the suspension. However, according to the energy analysis, the variation of inertance and stiffness parameters without direct energy supply to compensate kinetic energy will cause the mechanical itemsʼ physical discontinuity as the inerter and spring can store kinetic energy. The variable damping (VD) device applies the indirect energy supply that is only related to the damping control but not to the exchange with kinetic energy. This paper proposes the VAN with indirect energy supply to achieve the VD, variable equivalent inertance (VEI), and variable equivalent stiffness (VES) characteristics by controlling a VAN with only the VD device in it. The vibration transmissibility of a suspension equipped with VD, VEI, and VES devices is investigated, respectively, to verify their effectiveness in resonance vibration control. The VAN with indirect energy supply is realizable in different applications; the admittance analysis method can facilitate the VAN design and optimization in practice.

Recently, linear magnetorheological (MR) dampers have been widely utilised for impact protection of seat suspensions. However, the viscous force of the linear MR damper increases seriously with the increase of impact velocity. This results in a sharp increase of the total output force of the seat suspension, which may damage the suspension structure and lead to occupant injuries. To address this issue, the performance of a seat suspension installed with a rotary MR damper to improve the impact protection performance is investigated in this paper. Specifically, the mathematical models for the linear MR seat suspension and the rotary MR seat suspension are established. The impact protection performance of these two suspensions are numerically compared by the transient analysis and the dynamic impact simulation. Both the transient analysis and the dynamic simulation indicate that the rotary MR damper seat suspension is less sensitive to the impact velocity and can provide better impact protection performance.

Engine mount is an essential component to support the vehicle engine and to determine the vehicle dynamic property in terms of noise, vibration, and harshness (NVH). It works as the important interface between the engine and the chassis to reduce the bad impact of the engine-induced vibrations on the car body. To this end, this paper proposed a new semi-active engine mount capable of variable stiffness as an attempt to further improve the vibration reduction capability of the current semi-active engine mount which is only capable of varying damping. This study completed the characterization test of the proposed semi-active engine mount and evaluated its capability of stiffness variability. Then a test of an engine mounted with the new mount was performed to evaluate the vibration reduction capability. The experimental results demonstrate that this proposed engine mount show variable stiffness in response to the varied magnetic field, and that it performed well in protecting the chassis from the engine-induced vibration by reducing the vibration transmissibility.

This paper proposes an adaptive estimation and control method for vehicle active suspension systems with unknown time-varying parameter. Unlike the conventional methods that rely on polynomial-based parameter estimation framework, a novel parameter estimation algorithm is developed to achieve the accurate estimation of unknown time-varying parameter (e.g., vehicle mass). To realize this purpose, low-pass filter operation is imposed on system dynamics, by which the auxiliary variables can be constructed to extract the parameter estimation error information. With this method, a novel adaptive parameter estimation algorithm can be designed to online update the unknown time-varying parameter. Then, the estimated parameter is incorporated into an adaptive controller to regulate the vehicle motion. Theoretical analysis is conducted via the Lyapunov theorem to prove the convergence of both control error and parameter estimation error. Comparative simulation is carried out to demonstrate the effectiveness of the proposed method.

Internal friction may induce instability of a high-speed turbine rotor-bearing system. The effects of relative slippage between the inner ring of a ball bearing and the shaft on the vibration and stability of a practical high-speed turbine are experimentally studied. The features of the rotor include a cantilevered large mass and the rigid body mode of the first order critical speed. Clearance and transition fits of the bearing and the shaft are considered, together with the variations of tightening torque acted on the locking nut. The dynamic features of vibrations under each condition are analyzed in detail. For clearance fit with standard tightening torque, a “switch” rotating speed is observed at which both the dominant vibration frequency and amplitude change dramatically. Half-frequency whirl entrainment is captured. The “switch” speed and predominate subharmonic frequency induced by internal friction are all increased with amplified tightening torque. For transition fit, instability is also observed for standard tightening torque. In such case, vibrations are always dominated by the fundamental frequency component, however, two “switch” speeds are captured in terms of vibration amplitudes. The time waveforms, spectrums and orbits vary significantly within the range of the two “switch” speeds. With speed increasing above the second “switch” speed, the rotor becomes stable again. Using larger tightening torque is able to suppress the internal friction. The present studies provide elaborated features of internal friction induced vibration, which are highly potentially useful for rotor fault diagnosis.

In many applications, installing an absorber/tuned mass damper (TMD) is an effective method of vibration control. To overcome the drawbacks of traditional TMDs and improve the overall performance, a bio-inspired structure (X-shaped structure) is used for a tunable and nonlinear TMD (X-absorber). In this study, multi-variable optimization, tunable stiffness and damping properties, nonlinear influence and vibration suppression performance of this novel X-absorber are systematically studied. Compared with traditional absorbers this X-absorber can provide beneficial nonlinear damping which can significantly improve system parametric robustness, tunable quasi-zero stiffness for a widen vibration suppression bandwidth with a widened anti-resonance, effectively suppress resonant peaks of ultra-low frequencies, and eliminate potential instabilities (e.g., bifurcation, detached resonance curves) inherently existing in Duffing oscillators. In the experimental testing, the robustness and effectiveness of the optimized X-absorber with different excitations are validated with comparison of a traditional spring-mass absorber. The X-absorber would provide a more reliable and flexible solution to many vibration suppression applications.

In this paper, the effects of the coil thickness on output voltage and power of the electromagnetic energy harvesters are investigated. A configuration which is mainly comprised of two coil arrays, a pair of restoration springs and a magnet array is designed. The coil arrays are symmetrically distributed on both sides of the magnet array. Ten kinds of coil thicknesses are selected to examine how they influence the electric responses. Based on a series of fabricated prototypes, four experimental studies from the following aspects for comparison purposes: frequency sweep, constant frequency, impedance matching and charging capacitors are conducted. The results show that the resonant frequency of the prototypes is 20 Hz, well agreeing with the theoretical one of 19.7 Hz. The case of h = 5.7 mm (h is coil thickness) reaches the maximum voltage (26.61 V) at the excitation of 1.0 g, 20 Hz. The maximum peak-to-peak power (312.05 mW) and the power density (2.56 mW/cm3) come from the case of h = 4.7 mm at the excitation of 1.0 g, 20 Hz. The case of h = 4.7 mm displays the best charging performance for the capacitor of 220 μF. It is also one of the best cases regarding the charging rates for 680 µF, 1000 µF, 2200 µF and 6800 µF capacitors.

Recently rotary energy harvester, which can replace traditional batteries to power small electronic devices in the rotary system has been proposed. However, most of the proposed rotary energy harvesters are only can be installed concentrically in rotary system, cannot work in the need of eccentric installation. This paper presents a novel electromagnetic energy harvester that can be used in a rotary system where the energy harvester is required to be installed eccentrically. The rotation mechanical energy is converted into electrical energy through a structure of a cylindrical shell, a magnetic ball and coil, which is based on the principle of electromagnetic induction. A protype of proposed energy harvester and corresponding measurement setup has been built for concept verification. The performance of the proposed energy harvester including open-circuit voltage and output power for resistive load have been preliminarily studied at different rotational speed, eccentric distance and diameter of the magnetic ball. The results reveal that the proposed energy harvester is very promising in the application of self-powered system which requires to be installed eccentrically in rotary system.

This paper proposed a diagnosis method for planet gear with local defects using selected features. The features are selected according to the signal model and the sideband variation from influence of local defect. Thus, this method includes the gear mechanics and considering sidebands sensitivity in real application. As verification, experiments are made on a single-stage planetary gearbox test rig. The result shows that the proposed method can be used in planet gear diagnosis, overcoming the difficulties of applying all features from spectrum. Besides, by setting different test conditions, generalization ability was evaluated. All the states were correctly estimated with limited healthy data. These results reveal the correctness and the effectiveness of the proposed method.

The problem of aero-engine vibration has always been the focus and difficulty of many scholars at home and abroad. Vibration control is an important research direction in the field of aeroengine vibration engineering. In order to solve the problems of poor adaptability to passive vibration isolation and insufficient control effect of aero-engines, this article intends to install an actuator at the engine casing, design an active vibration reduction system, and use the “geometric design” control method to design a feedback control system to achieve vibration reduction purpose.

The remaining useful life prediction of the aircraft engine is getting more difficult for its complex structure. Although the prediction methods have achieved certain success in practical application, there are some problems in the GM(1,1) model, such as model method biased, transformation inconsistent and first number of the initial sequence not functioning high precision prediction in model after an accumulated generating operation. Based on the grey prediction theory and with an analysis of the disadvantages of the GM(1,1) model, the improved GM(1,1) model is proposed by introducing linear time-vary terms. The model has been used for prediction and analysis with data of the aircraft engine system, the result shows that the proposed model has largely improves fitting and predicting precision, and widens the adaptation range.

We consider the problem of robot global path planning using traditional A* algorithm based on ROS. By means of an improved A* algorithm, we are able to solve the safety problem of robots. The algorithm calculates the threat value of obstacles to the robot and adds it to the evaluation function. During the execution of the algorithm, the security threat value of the node is calculated according to the shortest distance between the node and obstacle, adding the value to the corresponding node evaluation, finding the best path through the evaluation function. The generated path is smoothed with the two-order Bezier curve. This algorithm improves the safety performance and the optimality of the path.

A fast human–computer interaction dynamic modeling method for transmission towers based on space colonization algorithm is proposed in this paper. The 3D model of transmission towers can be generated only through the 3D coordinates of key points in CAD drawings. First, according to the coordinates of point calculate out the growth direction of the tower rod, and points are sampled along this direction, which are used as attraction points in the space colonization algorithm. The space colonization algorithm generates branches in the process of constructing the 3D skeleton of transmission towers. We give the convention relation between the attraction points and the branch nodes, forming a visual dynamic growth model of transmission towers by introducing interpolation time factor. The effectiveness of this method in the generation of transmission tower model is verified in the unity engine, and the model of a transmission tower which is higher than hundreds of meters is generated in seconds only by inputting the key coordinates in the human–computer interaction system of smart grid.

In this paper, we analyze the control effects of two active primary suspension schemes on improving the lateral stability of a high-speed power bogie. They exert an active yaw torque between the wheelset and frame based on the feedback state of wheelset lateral displacement or velocity. The control effectiveness is verified through the linear and nonlinear stability analysis for a simplified lateral bogie dynamic model. The time delay in the control system is introduced and its effect on bogie dynamics performance is assessed by the continuous time approximation method. In order to study the effect mechanisms of the active controls and time delay, the speed root locus analysis is performed. The analysis results show that the two control cases could improve the bogie lateral stability effectively. In addition, active yaw damping control requires more control energy consumption while achieving the same stability margin as active yaw stiffness, but it has better control robustness. The system stability of active yaw stiffness continues to worsen with the increase of time delay. While a delay less than 55 ms is beneficial to bogie stability for the active yaw damping system. Besides the robustness to time delay, active yaw damping also has better adaptability to tracks and system stability is insensitive to wheel-rail interface parameters.

With the scale of power system increasing, the problem of low efficiency and poor reliability of centralized state estimation becomes more and more prominent. In this paper, we propose a multi-area parallel state estimation method with information exchange based on the zookeeper system. Firstly, by analyzing the structure of power system’s gain matrix, the solution process is carried out parallelly; Secondly, the power system is divided into several areas, and the gain matrix is divided into several blocks correspondingly; After that, according to the calculation factor digraph, the data to be exchanged between areas is determined and the corresponding zookeeper storage nodes are configured; Finally, the simulation results are provided to verify the correctness and effectiveness of this method.

Fracture detection based on deep learning is an interdisciplinary attempt of medicine and computer vision. The existing deep learning framework for object detection is applied to wrist Fracture detection, and its performance still needs to be improved. The main reason is that wrist fracture often appears as small target in X-ray image, and small target is difficulty to be detected in object detection. An effective method to solve this problem is data enhancement. This paper proposes a data enhancement method based on image mosaic. According to the characteristics of X-ray image with many black invalid areas, the mosaic part only focuses on the black area and does not affect the effective data area. At the same time, the proposed data enhancement method is embedded into several existing deep learning frameworks for verification. The experimental results show that the data enhancement method is universal to the existing deep learning frameworks, and the AP value will be improved by 3%.