一种求解地下结构顶板频率和振型的方法

采用欧拉梁横向自由振动理论,发展了一种求解浅埋地下结构顶板频率和振型的方法.鉴于地下结构顶板频率求解问题的复杂性,首先将该问题假定为平面应变问题求解,推导出浅埋地下结构顶板梁的自由振动方程;然后根据顶板梁的边界条件,得到了顶板梁的频率方程,从而得出了顶板梁的频率和振型;进一步得出了墙体转动刚度对顶板频率影响的规律,即转...     

绕流对称性破缺诱发柔细结构振动研究——以Tacoma大桥风振致毁事故为例

绕流对称性破缺往往对柔细结构产生很大的作用效应,诱发结构振动,严重影响其可靠性和安全性.基于圆柱平面绕流模型,系统分析了实际流体圆柱绕流纵向对称性破缺以及各种情况的横向对称性破缺现象.为了更加深入地理解理论分析的结果,利用Fluent软件对圆柱绕流模型进行了计算机模拟,详细分析了雷诺数为10、20、40、100、200...     

Risk Assessment in the Working Environment in Estonia

The first step to chart hazards in the working environment in Estonia (labour force: 0.65 million) was taken by the National Board of Health Protection in the beginning of 1996.

The existing chemical, physical, and biological agents in the working environment were investigated with the help of local health inspectors in all counties. An identification of hazards and workers at risk was carried out. The results of the analysis showed that 16% of Estonian industrial workers are exposed to different hazards: 20,000 persons are exposed to noise, 11,000 are working in the conditions of vibration, 10,000 are affected by unsatisfactory microclimate, 6,000 complain about long-lasting work in a compulsory posture, the overexertion of eyes is suffered by 5,500 persons, and physical overload by 3,500 workers. In the group of chemical hazards the greatest numbers of workers are exposed to organic dust (6,500) and welding aerosols (5,400), followed by petroleum products (2,700), and oil-shale dust (4,300). The measurements of working conditions showed that an average of 30.3% of the results are above the standards. Proposals for the improvement of the situation in occupational safety and health are presented.     

Evaluation and Optimization of Handle Design Parameters of a Grass Trimming Machine

The grass trimming machine is a widely used agricultural machine for cutting grass by the roadside and in other areas in Malaysia. Hand-arm vibration (HAV) syndrome is very common among workers operating power tools and performing similar work for extended periods. Grass trimming involves the use of a motorized cutter spinning at high speed, resulting in high levels of HAV among its operators. The existing D-shape handle causes HAV-related stress and operational load in operators. This research proposes a new design of a handle of the grass trimming machine. When this new design was compared with the old one, it was found that the new handle resulted in 18% lower HAV. To find the lowest HAV, 3 critical parameters of the new handle (length, angle and material of the cap of the handle) were optimized using the Taguchi quality tool. Appropriately selected parameters of the new handle significantly reduced the occurrence of HAV among grass trimmers.     

A Study on the Combined Effect of Noise and Vibration on Operators’ Performance of a Readability Task in a Mobile Driving Environment

This paper presents a study in which the main objective was to investigate the combined effect of noise and vibration on the performance of a readability task in a mobile driving environment. Subjects performed a readability task on a laptop computer in a sitting posture with their backs supported with a backrest under varying levels of noise and vibration. The data in terms of the mean number of characters read per minute were collected and statistically analyzed. Results showed that the individual effect of noise, vibration, and the operators’ gender as well as the interaction between gender and noise, and gender and vibration were statistically significant. However, the combined effect of noise and vibration was not found to be statistically significant. Results also indicated that gender was statistically significant at all levels of noise as well as vibration, and noise and vibration were statistically significant at both levels of gender.     

天然气增压站噪声和振动治理效果分析

分析了天然气增压站噪声的主要来源,在阐述降噪原理的基础上,根据增压站所在地区实际情况,采用更换消声器、修建减振沟、修建降噪厂房、优化降噪厂房墙体等不同措施,结合治理前后噪声监测数据分析,对不同措施降噪减振的效果进行评价,同时综合了采取不同措施的合理性,为类似增压站噪声和振动治理提供借鉴。     

在噪声治理中二次隔振的应用实例

在噪声治理工程中应用二次隔振降低固体传声,可以起到较理想的隔振效果。二次隔振系统固有频率低,可以隔绝低频振动。对制冷系统的压缩机组进行二次隔振,取得了满意的隔振效果。     

某型飞机进气道在噪声环境中的振动疲劳分析

某型飞机进气道常出现蒙皮裂纹、铆钉松动及掉铆钉头等故障,给飞行安全带来隐患.研究发现,此类故障是进气道在强噪声环境下,噪声脉动压力引起的结构振动疲劳损伤.应用阻尼层可降低强噪声对进气道蒙皮和铆钉的破坏.发动机地面试验结果表明,进气道阻尼层的应用显著降低了蒙皮壁板的振动量级.     

振动离心复合试验系统发展概述

以电动振动台和压电激振器与离心机复合发展为主线,系统总结了以离心机为主体的振动离心复合环境试验系统发展历程以及国内外发展现状,重点介绍了电动振动台与离心机复合的关键技术及难点。最后介绍了振动离心复合环境试验系统发展趋势及展望。     

水泵系统噪声与振动控制

从水泵系统振动噪声传播途径控制的角度,着重分析了水泵机座二次隔振系统、水泵接管隔振、隔振系统位移限制、管道支架减振、管道穿墙隔振、管道阻尼隔声包扎等水泵系统振动固体传递途径的控制,消除与建筑结构之间的刚性连接。分析了振动噪声空气传播的阻隔与吸收。