Track-position and vibration control simulation for strut of the Stewart platform

Vibrations inherently generated by on-board disturbance sources degrade the performance of the instruments in an on-orbit spacecraft, which have stringent accuracy requirements. The Stewart platform enables both track-positioning and vibration control. The strut of the Stewart platform is designed as a piezoelectric (PZT) element in series with a voice coil motor (VCM) element and a viscoelastic element. The track-positioning system uses a VCM as the main positioning control driver and a PZT as the positioning compensator. The vibration control system uses the characteristics of struts including active and passive control elements to attenuate the vibration. Simulation results indicate that the Stewart platform with the designed struts has good performance in tracking and vibration attenuation with different interference waves.     

Fused empirical mode decomposition and wavelets for locating combined damage in a truss-type structure through vibration analysis

Structural health monitoring （SHM） is a relevant topic for civil systems and involves the monitoring, data processing and interpretation to evaluate the condition of a structure, in order to detect damage. In real structures, two or more sites or types of damage can be present at the same time. It has been shown that one kind of damaged condition can interfere with the detection of another kind of damage, leading to an incorrect assessment about the structure condition. Identifying combined damage on struc- tures still represents a challenge for condition monitoring, because the reliable identification of a combined damaged condition is a difficult task. Thus, this work presents a fusion of methodologies, where a single wavelet-packet and the empirical mode decom- position （EMD） method are combined with artificial neural networks （ANNs） for the automated and online identification-location of single or multiple-combined damage in a scaled model of a five-bay truss-type structure. Results showed that the proposed methodology is very efficient and reliable for identifying and locating the three kinds of damage, as well as their combinations. Therefore, this methodology could be applied to detection-location of damage in real truss-type structures, which would help to improve the characteristics and life span of real structures.     

Vertical whole-body vibrations improve the total volume of a biceps curl set to failure

Abstract

The purpose of this study was to examine the acute effects of using whole-body vibrations exposure during a biceps curl set to failure (70% one-repetition maximum load) on number of repetitions performed, perceived exertion, as well as velocity- and acceleration-related parameters. Twenty-three recreationally active students (19 males and 4 females) completed one set of the biceps curl exercise with and without vibration applied. Results indicate that the vibration platform provides additional stimulus for biceps curl performance, enhancing the number of maximal repetitions achieved throughout a set to volitional exhaustion at 70% one-repetition maximum. These findings suggest that vibration can have a significant influence on exercise performance, even when the stimulus is not applied directly to the muscle group being stressed.     

基于HP35670A的皮带通廊振动测试系统

根据某焦化厂输煤皮带通廊的工作振动情况,建立了基于HP35670A的相应振动测试系统,并通过对该振动测试系统的相应标定,实现了对该皮带通廊的准确测试.     

频段内汽车悬架时滞反馈控制参数优化

对有限频段内汽车悬架系统的时滞反馈控制参数优化问题进行研究。首先,建立时滞加速度反馈控制下 1/4 汽车悬架系统力学模型,推导出车身和车轮加速度幅值的解析表达式;其次,通过对系统稳定性分析,得到关于反馈增益系数和时滞的稳定性分区图,以数值计算验证稳定性分析的正确性;最后,在有限频段内以最大车身加速度变化的百分比为优化目标,以反馈增益系数和时滞为优化参数,利用粒子群优化算法获得有限频段内最优反馈增益系数和时滞。实验结果表明,与被动汽车悬架系统相比较,最优时滞反馈控制下汽车悬架系统的隔振性能获得了明显提高,在最优时滞反馈控制参数取值下,有限频段内车身加速度幅值至少降低37.27%。     

评定波纹度的一个新参数——波形系数

本文从波纹度对轴承振动影响的角度,提出了一个能够用来评定波纹度波形特征的新参数:波形系数Sc,并对其含义和计算方法作了详尽的讨论。     

声乐学习过程中各器官的作用和关系

本篇文章以翔实的理论和生动的语言描述了歌唱过程中身体机能的运动过程。从声音物理学的角度阐述了身体的发声器官、共鸣器官、语言器官和动力系统的相互关系。文章既强调了歌唱过程中声情并茂的基本原则 ,又强调了发声器官各自独力的重要性。文章既重视理论性又强调实用性 ,用大量篇幅叙述了歌唱器官的功能和具体训练手段。阅读本篇文章 ,对声乐的学习和提高会产生积极而深远的影响     

Studies on vibration characteristics of a pear using finite element method

The variation of the vibration characteristics of a Huanghua pear was investigated using finite element simulations. A new image processing technique was used to obtain the unsymmetrical and un-spherical geometrical model of a pear. The vibration characteristics of this type of pear with the correlation of its behavior with geometrical configurations and material characteristics were investigated using numerical modal analysis. The results showed that the eigenfrequency increased with the increasing pear Young＇s modulus, while decreased with increasing pear density, and decreased with increasing pear volume. The results of this study provided foundation for further investigations of the physical characteristics of fruits and vegetables by using finite element simulations.     

交变负荷对机体影响的机制研究

运用文献资料调研、归纳分析等方法,根据近年来对交变负荷力量训练的实证研究,综述交变负荷力量训练及其特点;研究机体承受交变负荷的神经科学基础,交变负荷的动态适应性,机体承受交变负荷的生理组织变化等。研究发现,机体承受交变负荷刺激可引起中枢神经功能加强、协调性改善,突触的可塑性是极限力量突破的神经生物学基础,交变负荷引起脑功能的自组织适应;交变负荷引起生物有机体突破力量极限的点、线、面适应原理,可减少或避免运动损伤的发生;交变负荷引起组织细胞结构与代谢的改善。     

振动力量训练与核心力量训练模式探讨

目前,我国竞技体育发展中对力量训练重视不够,对力量训练理论和应用的研究不够,对力量训练发展的新动向缺乏深入了解,训练理念和方法陈旧,影响了力量训练的质量和效果。为此,通过查阅CNKI、Elsevier,对振动力量训练与核心力量训练的概念、发展历程、作用及生理学机理以及影响训练效果的因素进行了综述,并总结了两种训练模式的区别、联系及局限性,以期为竞技体育发展提供技术支持。