振动插板法在塑料排水板软基处理施工的应用

随着塑料排水板施工工艺的不断提高,振动插板法越来越普遍应用到塑料排水板施工中.笔者以珠海十字门、中央商务区横琴片区市政基础设施(道路)一期工程五标段的塑料排水板施工为例,阐述了振动插板法的施工工艺及施工中存在问题,并分析和提出了解决的措施.     

Evaluating worker vibration exposures using self-reported and direct observation estimates of exposure duration

The objective of this study was to compare objective and subjective methods of collecting exposure time data for hand arm vibration (HAV) and whole-body vibration (WBV), and to evaluate the impact of inaccurate exposure times’ on the calculation of the average vibration exposure over an 8 h working day A(8).The study was carried out in the engineering services and maintenance departments of a construction and property management company. Worker exposure time data was collected using three methods, questionnaire surveys, daily worker interviews and 8 h direct workplace observations. Vibration magnitudes (m/s²) were measured for a range of hand tools and vehicles, and daily vibration exposure estimates A(8) were calculated using exposure times observed, reported in interview and self reported in the questionnaire.Results from the study showed that self-reported exposure time estimates from the questionnaire survey were a factor of 9.0 (median value) times greater for HAV and a factor of 6.0 (median value) times greater for WBV when compared with direct observation estimates. Exposure times reported in interview were higher, than those observed, but more reliable than those self reported in the questionnaire; a factor of 2.1 (median value) times greater for HAV and a factor of 1.4 (median value) times greater for WBV. A(8) values calculated using questionnaire exposure times were up to 66% and 75% greater for sources of HAV and WBV respectively when compared to A(8) values calculated using observed exposure times.For the purposes of carrying out a reliable risk assessment, results from this study indicate that direct measurements of worker exposure time are not recommended over questionnaires especially where work is highly variable for example in construction and property management. Worker interviews or direct workplace observation methods were found to be reliable alternative methods for collecting exposure time.     

Exact closed form solutions for free vibration of non-uniform annular plates

Presented herein are exact solutions for the free vibration problems of a class of annular plates with parabolically varying rigidity and for a sandwiched non-uniform annular plate. These exact solutions are useful for verifying numerical methods and algorithms.     

半波整流线路在电振给料机中的改进与试验

为减少电振给料机余振对铁合金生产中配料精确性的影响,利用续流二极管的半波整流控制电路对控制电振给料机的余振进行了改进。实验结果表明：制动效果良好,提高了配料的精确性,减少了成本损失,节约了能源,为生产运行提供了保障。     

Three-dimensional free vibration of variable thickness thick circular and annular isotropic and functionally graded plates on Pasternak foundation

This paper describes a study of three-dimensional free vibration analysis of thick circular and annular isotropic and functionally graded (FG) plates with variable thickness along the radial direction, resting on Pasternak foundation. The formulation is based on the linear, small strain and exact elasticity theory. Plates with different boundary conditions are considered and the material properties of the FG plate are assumed to vary continuously through the thickness according to power law. The kinematic and the potential energy of the plate-foundation system are formulated and the polynomial-Ritz method is used to solve the eigenvalue problem. Convergence and comparison studies are done to demonstrate the correctness and accuracy of the present method. With respect to geometric parameters, elastic coefficients of foundation and different boundary conditions some new results are reported which may be used as benchmark solutions for future researches.     

The coupled vibration in a rotating multi-disk rotor system

The influence on coupling vibrations among shaft-torsion and blade-bending coupling vibrations of a multi-disk rotor system was investigated analytically. The natural frequencies and the mode shapes of the system were solved for one- to three-disk cases as examples. First, numerical results showed how the natural frequencies varied with blades in a disk unit. The diagrams of the coupling mode shapes were drawn. From the results, it was found that the inter-blade (BB) modes were of repeated frequencies of (N_b-1) multiplicity for number blades. At multi-disk unit, the shaft-blade (SB) modes added to N_d modes for number disks. The BB modes were of repeated frequencies of [N_d×(N_b-1)] multiplicity for number disks. Numerical calculations also revealed that the natural frequencies were affected by disk distance. In the rotation effect, the times of instability will due to the number of disk. And, the more disk rotor causes instability earlier than the less disk case.     

湛江发电厂4号机抗燃油泵的振动测试与分析

湛江发电厂4号机在调试期间进行抗燃油泵的首次试运，发现B，C泵振动大，停泵进行体查，复测轴的晃动度，找平衡后再次试转，振动仍无改善，技术人员对抗燃油泵进行了振动测试和分析，得出此振动属于拍振的结论，针对拍振的产生原因，提出可采取更换马达使两泵转速相同和在两泵间构筑隔离带等措施来解决此振动问题。     

上海世博会中国馆国家馆结构设计与研究

2010年上海世博会中国馆的国家馆造型独特,其底部架空,展区部分层叠出挑,呈四棱台斗冠状。屋面由混凝土筒体出挑34.75m,不但使得竖向质量分布不均匀,还使得楼盖的转动惯量大,导致结构的扭转周期成为第一周期。介绍了国家馆的结构体系、结构布置、结构分析以及主要的构造加强措施。利用楼、电梯间设置四个落地的混凝土筒体作为承重和抗侧力结构,利用建筑的倒梯形造型设置斜柱来支承楼盖大跨度钢梁,在确保结构安全的前提下,最大限度地满足了建筑使用功能的要求。分析了扭转周期为第一自振周期对结构的影响以及底部挑空对结构竖向侧向刚度分布的影响。详细的计算分析及模拟振动台试验结果表明,虽然扭转周期为第一周期,但结构的扭转反应并不严重,对结构的抗震性能影响不大,结构具有良好的抗震性能,可达到预定的抗震性能目标。     

Effect of vibration extrusion on the structure and properties of high‐density polyethylene pipes

BACKGROUND: The axial strength of a plastic pipe is much higher than its circumferential strength due to the macromolecular orientation during extrusion. In this work, a custom‐made electromagnetic dynamic plasticating extruder was adopted to extrude high‐density polyethylene (HDPE) pipes. A vibration force field was introduced into the whole plasticating and extrusion process by axial vibration of the screw. The aim of superimposing a vibration force field was to change the crystalline structure of HDPE and improve the molecular orientation in the circumferential direction to obtain high‐circumferential‐strength pipes. RESULTS: Through vibration extrusion, the circumferential strength of HDPE pipes increased significantly, and biaxial self‐reinforcement pipes could be obtained. The maximum increase of bursting pressure and tensile yield strength was 34.2 and 5.3%, respectively. According to differential scanning calorimetry and wide‐angle X‐ray diffraction measurements, the HDPE pipes prepared by vibration extrusion had higher crystallinity, higher melting temperature, larger crystal sizes and more perfect crystals. CONCLUSION: Vibration extrusion can effectively enhance the mechanical properties of HDPE pipes, especially the circumferential strength. The improvement of mechanical properties of HDPE pipes obtained by vibration extrusion can be attributed to the higher degree of crystallinity and the improvement of the molecular orientation and of the crystalline morphology. Copyright © 2008 Society of Chemical Industry     

Beam to String Transition of Vibrating Carbon Nanotubes Under Axial Tension

State‐of‐the‐art nanoelectromechanical systems have been demonstrated in recent years using carbon nanotube (CNT) based devices, where the vibration of CNTs is tuned by tension induced through external electrical fields. However, the vibration properties of CNTs under axial tension have not been quantitatively determined in experiments. Here, a novel in situ method for precise and simultaneous measurement of the resonance frequency, the axial tension applied to individual CNTs and the tube geometry is demonstrated. A gradual beam‐to‐string transition from multi‐walled CNTs to single‐walled CNTs is observed with the crossover from bending rigidity dominant regime to extensional rigidity dominant regime occur much larger than that expected by previous theoretical work. Both the tube resonance frequency under tension and transition of vibration behavior from beam to string are surprisingly well fitted by the continuum beam theory. In the limit of a string, the vibration of a CNT is independent of its own stiffness, and a force sensitivity as large as 0.25 MHz (pN)^?1 is demonstrated using a 2.2 nm diameter single‐walled CNT. These results will allow for the designs of CNT resonators with tailored properties.