Abstract:To enhance the isolation performance of the current three-parameter isolators, a prototype of broadband fluid damping strut has been designed. The damping strut features several frequency selective valves to adjust its damping characteristics at the low-frequency range, and a machined spring with a clearance element to act as a secondary stiffness. A dynamic mathematical model and a simulation model of a vibration isolation system using the designed fluid damping strut for a spacecraft control moment gyroscope have been established, followed simulation results indicate that compared to current three-parameter dampers the designed damping strut has achieved adaptive outer characteristics of high damping in the low-frequency range and low damping in the high-frequency range, it has obtained a significant suppressive effect on low-frequency vibrations, especially those near the resonance peak, its statistical vibration isolation effect is also better than that of the current dampers in the mid and high frequency bands, thus, the designed fluid damping strut has obtained excellent vibration isolation characteristics in a broad frequency band.

Abstract:Most of the current research methods use the prediction correction method, but other numerical methods are less frequently used. In this paper, a numerical method for computing fractional-order dynamical systems is elaborated using Lagrange polynomial interpolation. And this is used to successfully obtain an effective numerical solution for a new fractional-order jerk chaotic system. The results obtained are compared with those of the prediction correction method and found to be in good agreement with each other, verifying the validity of this method. The maximum Lyapunov exponent of the new fractional-order jerk chaotic system is further explored for different system orders, and it is concluded that the system exhibits instability when the system order α=0.85, α=0.95, and the phase diagram of the system in Caputo’s sense is further demonstrated.The results show that different system order α have a significant effect on the dynamical behaviour of new fractionalorder jerk chaotic system.

Abstract:On the basis of the two-component coupled Hirota equation, the higher-order solitons solution of the equation is investigated, and dynamical characteristics is analyzed. Based on the Lax pair and generalized Darboux transformation, the Taylor expansion of the characteristic function is carried out, and the expressions of the second-order and third-order soliton solutions of Hirota equation are derived. The real and imaginary parts of spectral parameter λ are discussed in different cases. Under the influence of the value of different free parameters, the evolution graphs of soliton interaction are obtained via numerical simulation. The effects of different parameters on the amplitude change and propagation direction of solitons are analyzed. The results show that different values of parameters affect the interaction and propagation direction of solitons.

Abstract:For vibration and noise reduction of the most railway wheels, corresponding dampers are generally installed to increase the structural damping of wheels, so as to reduce vibration and noise. Wheel-damper system was a wheel system with multilayer damper installed. The dynamic model of wheel-damper system of railway vehicle was established, and the equivalent ratio model of wheel-damper system was derived. A method for obtaining the modal damping ratio of structures based on theoretical model and simulation and independent of modal test was presented. Combined with abaqus modal superposition method, the vibration frequency response function(FRF) of the wheel-damper system was calculated. Finally, the vibration frequency response function of the wheel-damper system was tested, and the simulation results are in good agreement with the text results, which shows that the method is an important means to qualitatively compare the damping performance of different wheel damper devices in the design stage.

Abstract:This study proposes a ROV-based deep-sea mining system to overcome the stability issues of tracked vehicles in the traditional deep-sea mining system. The ROV-based deep-sea mining vehicle replaces the traditional tracked deep-sea mining vehicle. The ROV-based deep-sea mining vehicle consists of a remote operated vehicle (ROV) and a mining robot (MRT). First, this paper investigates the dynamic model of the ROV-based mining vehicle, assuming that the ROV maintains a fixed depth while towing the MRT. By analogy with a bicycle model, the dynamic model of the ROV-based mining vehicle is established. Subsequently, a hierarchical path tracking control strategy is introduced. Based on the kinematic model of the ROV-type mining vehicle, a linear model predictive control (LMPC) controller is designed to calculate a virtual control law for converging MRT path tracking deviations. A lower-level PID controller computes the ROV control input in response to the virtual control law. Finally, the feasibility of the hierarchical path tracking control strategy is preliminarily validated through numerical simulations.

Abstract:As the deployment of low-orbit large constellations reaching its peak with rapidly expanding scales, this study investigates the internal collision risks during the deployment of large low-Earth orbit (LEO) satellite constellations. A constructed constellation is used as an example to analyze the effect of phase parameters and orbital inclination on internal collision risk. Two methods are employed: the spherical geometry method, which does not consider perturbation effects, and the collision probability method, which does consider perturbation effects, to calculate the constellation's minimum distance and collision probability. Collision analysis reveals that the overall minimum distances decrease when perturbations are considered. Moreover, consistency is observed between the optimal configurations for minimum distance and collision probability indices when perturbations are taken into account. The study also discovers that the minimum distances of the constellation fluctuate periodically by 2° to 6° as orbital inclination increases. Based on these findings, an optimization strategy is proposed that involves fine-tuning the orbital inclination to reduce collision risks. Additionally, a configuration design strategy is designed to improve the computation precision with limited computational resources, namely the “initial screening of inclination by geometric method followed by detailed phase parameter screening with perturbation”

Abstract:Aiming at the problem of fuel-optimal control of hypersonic vehicles (HSV) in the ascending stage, a trigonometric regularization method is introduced based on the optimal control indirect method. This method makes up for the shortcoming of the indirect method: The derivation of the first-order optimal necessary condition for complex optimal control problems is cumbersome, singular optimal problem is difficult to solve and the optimal control is unsmooth. Aiming at the problem of divergence due to the improper initial costate variables guess in the two-point boundary value problem(TPBVP) transformed the indirect method, the continuation method is introduced and improved. The method uses the solution of the simplified problem as the initial value of the continuation, and through solving a series of TPBVP, approximates to the solution of the original problems. The simulation results show that through the above methods, the fuel-optimal control problem of HSV in the ascending stage under the complex model can be solved reliably.

Abstract:Dynamic models serve as effective tools for simulating physical systems, facilitating a deeper understanding of the operational principles governing systems. They provide theoretical underpinnings for prediction, optimization, and control system development. In recent years, data-driven approaches for dynamic modeling have garnered widespread attention in academia. While significant progress has been made, there remain limitations. This paper delves into the data-driven modeling of planar articulated multibody systems and proposes an improved neural network framework, termed Topological Lagrangian Neural Network (TLNN), building upon the foundation of Lagrangian Neural Networks (LNN). Compared to LNN, TLNN leverages topological information embedded within multibody systems, enhancing the learning performance of neural networks. Prediction results demonstrate that TLNN establishes higher-precision dynamic proxy models for articulated multibody dynamics compared to LNN, Hamiltonian Neural Networks (HNN), and Neural Ordinary Differential Equations (NODE) when trained on the same dataset. Furthermore, this paper discusses the generalized coordinate selection issue in the data-driven modeling process. Both training and prediction results indicate that utilizing rigid body absolute angles for modeling yields dynamic proxy models with higher precision compared to modeling based on joint relative angles in data-driven modeling of articulated multibody systems.

Abstract:The phenomenon of vibrational resonance holds significant application value in weak signal detection and energy harvesting. However, existing studies predominantly focus on symmetric bistable systems or linear dissipation scenarios. To address this gap, this paper investigates vibrational resonance (VR) in an asymmetric bistable system with nonlinear dissipation,driven by biharmonic forces at two different frequencies. The fast and slow variable separation method is applied to derive the response amplitude of the system at low frequencies. Moreover,based on the analytical expression of the response amplitude,the effects of the dual-frequency periodic signal,the nonlinear dissipation and the asymmetric parameter on the VR are investigated. The results indicate that,first,the larger the nonlinear dissipation factor,the weaker the VR of the system occurs. Second,for the systems with nonlinear dissipative term,tuning the asymmetric parameter can change the shape of the VR,that is,the symmetric bistable systems emerge the double resonance,and the asymmetric bistable systems have the single resonance. Third,the asymmetric parameter does not influence the location of the VR,but it can weaken the response amplitude. Finally,the theoretical predictions are in good agreement with the numerical simulation results,verifying the validity of the theoretical analysis.

Abstract:Gap junctions play an important role in the transmission of information between neurons, the development of neural circuits, and the understanding of the working mechanism of the nervous system. The direct coupling between neurons connected by gap junctions may contribute to the synchronization of neuronal firing and the emergence of sharp wave-ripples(SWR), which affect brain functions such as memory consolidation. Because gap junctions are so few in the mature brain, they have been ignored in earlier studies. Considering the heterogeneous characteristics of excitatory and inhibitory neurons, it is unclear whether gap junctions in different neuronal types can provide a corresponding compensatory mechanism for SWR in abnormal networks. In order to explore the above problems, a network of neurons in CA1 region of hippocampus with introduction of gap junctions was constructed, which consisted pyramidal cells, parvalbumin-positive basket cells, and axon-axonic cells. The results show that when the chemical synapses in CA1 are weakened and cannot generate SWR synchronous discharge, gap junctions in pyramidal cells and parvalbumin-positive basket cells can promote SWR. The SWR compensation was most effective when gap junctions in pyramidal neurons and in both types of neurons were present.

Abstract:Appling pre-defined-time stability theory, three controllers were designed to achieve synchronization between Chen-Qi-like four-dimension hyper-chaotic driving systems and response systems of the same type with unknown parameters within a pre-defined time based on tangent function, hyperbolic tangent function, or exponential function. Theoretical proofs were provided. Its’effectiveness were testified with state time history diagrams and synchronous error curves via numerical simulation. The results indicated that controllers designed can achieve to synchronize to chaotic motion while the driving system in chaotic motion, and with a small convergence time difference among the four state synchronization errors. But there was a significant convergence time difference in the four state synchronization errors while driving system in periodic motion. That was induced by the imbalance and mismatch of the state cubic nonlinear term essentially. The results also indicated that adaptive controller and parameter correction law based on tangent function had a larger range of adaptability to initial state values and system parameters comparing to the other two controllers and parameter adaptive laws, thus it hold a better universality.

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