Transmission of whole body vibration to the lower body in static and dynamic half-squat exercises

Whole body vibration (WBV) is used as a training method but its physical risk is not yet clear. Hence, the aim of this study is to assess the exposure to WBV by a measure of acceleration at the lower limb under dynamic and static postural conditions. The hypothesis of this paper is that this assessment is influenced by the frequency, position, and movement of the body. Fifteen healthy males are exposed to vertical sinusoidal vibration at different frequencies (20–60 Hz), while adopting three different static postures (knee extension angle: 180°, 120° and 90°) or performing a dynamic half-squat exercise. Accelerations at input source and at three joints of the lower limb (ankle, knee, and hip) are measured using skin-mounted accelerometers. Acceleration values (g) in static conditions show a decrease in the vibrational dose when it is measured at a more proximal location in the lower extremity. The results of the performed statistical test show statistically significant differences (p < 0.05) in the transmissibility values caused by the frequency, the position, and to the presence of the movement and its direction at the different conditions. The results confirm the initial hypothesis and justify the importance of a vibration assessment in dynamic conditions.     

基于能量法的梁的非线性振动解法

本文首先由能量法推导出了大挠度梁的振动运动方程 ,然后研究了等截面简支梁大挠度自由振动的各种解法     

Beam-stabilized optical switch using a voice-coil motor actuator

This paper presents the design, analysis, and implementation of a beam-stabilized optical switch using a voice-coil motor actuator. A closed-loop control system using a proportional-integral-derivative (PID) controller is developed to stabilize the beam at the desired angle to maximize the optical power detected by a photodiode. Experimental results show a good performance with 17 ms switching speed and a maximum overshoot of only 3%.     

一种两自由度的压电-电磁复合能量收集器

研究目的：对一种两自由度的压电-电磁复合能量收集器进行发电性能研究。创新要点：建立了一种两自由度压电-电磁复合能量收集器发电性能的数学模型,该数学模型可以评估两自由度压电-电磁复合能量收集器中压电元件、电磁元件以及系统总输出功率。研究方法：对一种两自由度的压电-电磁复合能量收集器进行数学建模,并实验验证数学模型的正确性。基于实验测试得到的系统参数值,理论研究压电元件和电磁元件的机电耦合系数对不同能量收集器发电性能的影响关系,并对几种能量收集器的发电能力进行对比分析。重要结论：对于非强耦合（弱或中间耦合）的两自由度机电转换器,复合能量收集器（压电＋电磁）具有比单一能量收集器（压电或电磁）更高的发电能力。     

航空机载电子设备可靠性强化试验方法研究

本文介绍了可靠性强化试验的原理和特点,提出在航空机载电子设备研制早期应用可靠性强化试验的方法可以快速暴露设备本身的缺陷和薄弱环节从而提高设备的可靠性,并通过实例进行了阐述。     

单自由度振动系统对任意激励响应的仿真分析

根据单自由度振动系统对单位脉冲激励的响应,利用杜哈梅积分公式可以求出系统对任意激励的响应,再用计算机对其进行仿真分析,结果直观明了,是一种非常有效的振动分析工具。     

爆破地震安全判据探讨

本文对现行爆破地震安全判据中的合理性及某些局限和不足进行探讨,着重分析了综合考虑强度因子、频率和时间等因素对建立多参数地震安全判据的重要性,并就完善现有爆破地震安全判据提出了建议。     

振动测试中加速度计与被测对象连接方式的研究

在机械振动测试中，加速度计与被测对象之间连接方式的不同，对测试结果有不同程度的影响。本简要介绍了常用的连接方式及特点应用，并对一简谐振动进行实测，给出了测试结果及简要分析。     

隔振垫层对桥上轨道结构减振的影响分析

首先介绍了桥上轨道结构的减振及隔振垫层原理,然后利用ansys建立在移动荷载作用下桥上轨道结构振动模型,并以外部激励的形式输入轨道不平顺。然后分析了有碴轨道结构在混凝土桥梁上的竖向动力特性,研究不同隔振垫层及参数的情况下,轨道结构的动力响应和加速度频谱,最后对桥上轨道结构的减振设计提出了建议。     

Free vibration of pre-tensioned nanobeams based on nonlocal stress theory

The transverse free vibration of nanobeams subjected to an initial axial tension based on nonlocal stress theory is presented. It considers the effects of nonlocal stress field on the natural frequencies and vibration modes. The effects of a small scale parameter at molecular level unavailable in classical macro-beams are investigated for three different types of boundary conditions： simple supports, clamped supports and elastically-constrained supports. Analytical solutions for transverse deforma- tion and vibration modes are derived. Through numerical examples, effects of the dimensionless nanoscale parameter and pre-tension on natural frequencies are presented and discussed.