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The operation disturbance induced by the solar array drive system (SADS) and the residual vibration of solar array following the attitude adjustment of the spacecraft obviously affect the dynamics environment, quick stabilization, and attitude stability of the high-precision spacecraft. However, these two kinds of vibration disturbance are characterized by distinct vibration categories, direction of vibration, and modal shapes. A multi-degree-of-freedom vibration reduction strategy (VRS) was presented to improve the dynamic characteristics of SADS and then to weaken these disturbances synthetically in this paper. SADS applying this VRS was modeled based on the virtual work principle, and the influence of the stiffness and damping parameters of this VRS on the SADS dynamic characteristics was analyzed. Then a prototype of vibration reduction device (VRD) was designed and verified by disturbance characteristic and modal experiments. The results indicate that the equivalent stiffness of VRD is critical to the natural frequency of SADS and thus should be carefully deliberated to avoid resonance. The equivalent damping of VRD always has positive correlation with modal damping. A good performance up to 40% in terms of operation disturbance suppression and a greater than 56% decrease of the damping time for 99% residual vibration have been obtained.

There are few methods for detecting abnormal behaviors of crowd massing in public places, and they have the following problem; most of the detection methods are performed after the crowd has gathered abnormally, and the detection accuracy is not high, and the timeliness is not good enough. Therefore, a crowd massing anomaly prediction model based on multi-scale convolutional neural network (MCNN) is proposed. Firstly, a crowd counting model is built through MCNN for testing the video of crowd massing anomaly. In the test, the number of crowd and the coordinate points of their heads are acquired. Secondly, the crowd density, crowd distance potential energy and crowd distribution entropy are calculated. Finally, the predictive model is built through the eigenvalues of three crowd motion state by PSO-ELM. Through the change of characteristic data, the prediction is completed. The experimental results show that, compared with the existing algorithms, the proposed algorithm can effectively achieve the early warning and detection of abnormal behaviors in crowd massing. With a prediction accuracy rate of 97.17%, it's more time-sensitive and provides more time for taking corresponding emergency measures. [ABSTRACT FROM AUTHOR]

Solar Array Drive System (SADS) is characterized by rigid-flexible coupling and electromechanical coupling, thus the influence regulation for the dynamic characteristic of SADS becomes to be very complicated. Based on the motion particularity of solar array, the mechatronics model of SADS was simplified to an equivalent structural dynamics model sharing the same dynamic characteristic with SADS in this paper. This model was validated by comparing with dynamic characteristic identified from system simulation results, and the influence analysis on system dynamic characteristic parameters was also implemented. The results indicate that the effect of drive assembly on system dynamic characteristics is in accord with that of a kind of elastic boundary on structure dynamic characteristics of solar array. The system dynamic characteristic could be impacted by rated torque amplitude, number of teeth in motors, reduction gear ratio, transmission efficiency of the gearing chain, lubrication performance between brushes and slip rings, drive speed and so on, among these reduction gear ratio and viscous friction ratio have the widest impact range to equivalent stiffness and damping, respectively. The dynamic characteristic of SADS with large reduction gear ratio approximates to the structure dynamic characteristic of solar array with cantilever boundary condition. [ABSTRACT FROM AUTHOR]

The multi-direction impact loads imposed on the crewman maybe exceed the head-pelvis acceleration limit. According to the vertical attenuation seat, a new directional attenuation seat system is designed for absorbing the horizontal and vertical landing impact energy. A dynamic model of this buffer system is presented via the Lagrange equations. Numerical simulations of the analytic model are consistent with that of the Adams software. The effects of reducing impact loads between the vertical attenuation seat and the bidirectional one are compared. And the response characteristics of the head and the turn center are also presented. Numerical results show that the bidirectional attenuation seat reduces the head-pelvis acceleration markedly, and has little influence on vertical attenuation pole and chest-back acceleration. [ABSTRACT FROM AUTHOR]