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Improving the control performance of dynamic vibration absorbers has recently been effective by introducing a grounded negative stiffness device. However, the negative stiffness structure is unstable and difficult to achieve in engineering practice , and its major drawback is that it amplif ies the vibration response of the primary system at low frequency region. Meanwhile, some mechanical devices can be combined to make the DVA work even better with a grounded positive stiffness. For this purpose, this paper combines for the first time the control effect of the inerter device and grounded positive stiffness into a three-element DVA model in order to better improve vibration reduction of an undamped primary system under excitation. First, the dynamic equation of motion of the system is written according to Newton 's second law. Then, the steady-state displacement response of the primary system under harmonic excitation is calculated. In order to minimize the resonant response of the primary system around its natural frequency, the extended fixed point theory is applied. Thus, the optimized parameters such as the tuning frequency ratio, the stiffness ratio , and the approximate damping ratio are determined as a function of mass ratio and inerter – mass ratio. From the results analysis, it was found that the inerter – mass ratio has a better working range to guarantee the stability of the coupled system. Then , study on the effect of inerter – mass ratio on the primary system response is carried out. It can be seen that increasing the inerter – mass ratio in the optimal working range can reduce the response of the primary system beyond its uncontrolled static response. However, it is necessary to avoid the situation where the inerter – mass ratio is very large because it can lead to unrealistic optimal parameters. Finally, comparison with other DVA models is show n under harmonic and random excitation of the primary system. It is found that the proposed DVA model in this paper has high control performance and can be used in many engineering practice s. [ABSTRACT FROM AUTHOR]

The dynamics and vibration reduction performance of bistable nonlinear energy sink (BNES) are studied in this paper. First, the negative stiffness of BNES is realized by geometric nonlinearity, and the dynamics model of the system is established. The slow flow equation of the system under 1:1 main resonance is analyzed based on the complexification-averaging (CX-A) method, and the boundary conditions of saddle node bifurcation and Hopf bifurcation are analyzed. Second, the slow invariant manifold (SIM) of the BNES is studied based on multiscale analysis, and the excitation threshold of strongly modulated response (SMR) is analyzed; the analysis results are verified by the numerical method. The results show that the analytical solution is highly consistent with the numerical solution, and the error is less than 1%. Finally, the influence of structural parameters on the vibration reduction performance is analyzed and optimized. The vibration reduction performance of BNES and CNES is compared, and the results show that the BNES has better vibration reduction performance in the full frequency band. [ABSTRACT FROM AUTHOR]

Vibration-driven robots are innovative mechanical systems that exhibit a wide range of capabilities and applications due to their simple propellers. The applications of these robots span from clearing debris after an incident, traversing pipelines for inspection and maintenance, or medical purposes. In this paper, optimization and motion control of an energy-efficient two-module vibration-driven robot are investigated. The robot contains two blocks connected by a spring as its main body, and an unbalanced rotating mass to drive the robot rectilinearly. At first, the governing dynamic equations of the robot are derived and solved using MATLAB/Simulink. Then, the dynamic model of the robot is verified by comparing the obtained results with the simulation results from MSC Adams. Subsequently, a parametric study is conducted to investigate the effect of various physical parameters of the robot on its average velocity and consumed energy. Afterward, optimization variables are determined and a proper objective function is considered. By performing an optimization process using a genetic algorithm (NSGA-II), optimal parameters of the robot are obtained. Moreover, for motion control of the optimized robot, two control schemes, PID and Fractional Order PID, are designed. To evaluate and compare the performance of the proposed controllers, parameters of both controllers are optimized using a genetic algorithm in which both tracking error and control input are minimized, simultaneously. Finally, tracking error and control effort of the mentioned controllers for motion control of the robot are compared and discussed. [ABSTRACT FROM AUTHOR]

This paper presents a novel method for efficiently solving a trajectory planning problem for swarm robotics in cluttered environments. Recent research has demonstrated high success rates in real-time local trajectory planning for swarm robotics in cluttered environments, but optimizing trajectories for each robot is still computationally expensive, with a computational complexity from O (k (n t , ε) n t 2) to O (k (n t , ε) n t 3) where n t is the number of parameters in the parameterized trajectory, ε is precision, and k (n t , ε) is the number of iterations with respect to n t and ε. Furthermore, the swarm is difficult to move as a group. To address this issue, we define and then construct the optimal virtual tube, which includes infinite optimal trajectories. Under certain conditions, any optimal trajectory in the optimal virtual tube can be expressed as a convex combination of a finite number of optimal trajectories, with a computational complexity of O (n t) . Afterward, a hierarchical approach including a planning method of the optimal virtual tube with minimizing energy and distributed model predictive control is proposed. In simulations and experiments, the proposed approach is validated and its effectiveness over other methods is demonstrated through comparison. [ABSTRACT FROM AUTHOR]

Regarding the low machining efficiency and poor surface quality in micro-electrical discharge machining (μ-EDM) of large depth-to-diameter ratio micro-holes, this paper focuses on ultrasonic vibration–assisted multi-objective optimization in μ-EDM to achieve high material removal rate (MRR) and low tool wear rate (TWR). In this work, second-order quadratic models were developed for MRR and TWR, considering the peak voltage (U p), peak current (I p), pulse width (Width), frequency (Freq.), ultrasonic amplitude (UA), and rotation speed (Rot.) as the machining parameters, using the Plackett–Burman design and Box–Behnken design. The developed models were used for multi-objective optimization by desirability function approach to determine the optimum machining parameters. The optimized parameters were processed for micro-holes, and it was found that the surface quality of the micro-holes was significantly improved. [ABSTRACT FROM AUTHOR]

A theoretical model of the normal sound insulation of a rectangular locally resonant (LR) plate with simply supported boundary conditions is established. The accuracy of the model is verified through comparison with finite element simulation results. Considering a 1-m2 aluminum plate as the research object, a non-dominated genetic algorithm is introduced. The algorithm optimizes the lightweight sound insulation of an LR finite plate with a center frequency band of 20–800 Hz as the optimization objective of maximum average sound insulation and minimum mass. The optimization parameters are substrate thickness and local resonance parameters (including resonator target frequency (f obj), number of resonators, additional mass ratio, and resonator damping). Optimization results indicate that the average sound insulation fluctuates at approximately 2 dB due to changes in f obj. The results also provide an optimal solution to the algorithm. The optimal sound insulation value curve of LR plates corresponding to different surface densities of intermediate improved cases is fitted and compared with the sound insulation value of an equal-mass bare plate. Under lightweight optimization, the resonators are deemed capable of improving the local frequency band sound insulation. In contrast, the wideband average sound insulation can approximate but not surpass the insulation provided by the equal-mass bare plate. In practical applications, an LR plate that can improve the local frequency band sound insulation and ensure the overall lightweight sound insulation performance of the wide frequency band can be obtained. This can be achieved by analyzing the frequency spectrum of optimal points in the lightweight sound insulation optimization process. Relevant research can provide a basis for the evaluation and design of the low-frequency sound insulation of plates for transportation equipment, such as airplanes, high-speed trains, and cars. [ABSTRACT FROM AUTHOR]

Nonlinear factors exist in electro-hydraulic shaking table and may distort the response signal when a sinusoidal acceleration is inputted. To obtain accurate harmonics, a harmonic identification strategy for the acceleration of the electro-hydraulic shaking table based on the SA-PSO (Simulated Annealing-Particle Swarm Optimization) algorithm was proposed. First, the criterion function of harmonic identification was built with the least square method. Then, the PSO algorithm was introduced into the internal circulations of the SA algorithm to speed up the local search speed to construct the harmonic identification strategy. To verify the performance of the identification strategy, the SA algorithm, PSO algorithm, and SA-PSO algorithm were successively used to identify the response signal. And the convergence rate, accuracy, and stability of the three algorithms were compared. Finally, the harmonic regeneration was carried out after the amplitude and phase of each harmonic were obtained. Experimental results show that the harmonic identification strategy has fast identification speed and high identification accuracy. [ABSTRACT FROM AUTHOR]