Three-Degree-of-Freedom Rigid Model for Seismic Analysis of Cracked Concrete Gravity Dams

A rigid model with three-degrees-of-freedom is proposed for the purpose of seismic analysis of cracked concrete gravity dams. The model considers the geometry of the dam and all its possible modes of motion: sliding, rocking, rock-sliding, and drifting. The governing equations for all the modes are derived with the Mohr-Coulomb friction assumption at the crack, and corresponding conditions to initiate and maintain the modes are also given. For impact that follows rocking and drifting modes, postimpact velocities of the model are explicitly determined according to the momentum principle and the concept of restitution from classical point collision. Studies with the proposed model on rectangular blocks demonstrate two different types of rocking according to the slenderness. Applications to dams indicate that a large coefficient of friction does not necessarily prevent sliding, and rocking and drifting modes should not be neglected in estimating the stability of concrete gravity dams cracked at the base or at a height.     

边坡最危险滑动面的自动搜索

边坡的稳定性分析计算目前仍大量地依靠对边坡的滑移模式进行假设和简化 ,由此得到的边坡安全系数精度较低且误差难以估计。利用计算机实现边坡最危险滑动面或潜在最危险滑动面的搜索求解是目前边坡稳定性分析的重要研究领域。本文在简述边坡稳定性分析方法的基础上 ,对边坡圆弧滑动面的自动搜索、最危险滑动面搜索的变分法和边坡稳定性分析的运动单元技术进行了论述。     

提高R-170电动轮自动熄火后的制动安全措施

根据R-170(329)电动轮汽车一起发动机自动熄火后溜车的安全事故,对电动轮汽车的制动安全性以及事故的原因进行分析,提出了保证汽车制动安全性的根本措施。     

Earthquake Safety Evaluation of Gravity Dams Considering Aftershocks and Reduced Drainage Efficiency

This paper develops a methodology to perform seismic response analyses of concrete gravity dams considering aftershocks, and reduced drainage efficiency due to disruption of the drainage system. A database of earthquake records has been assembled to characterize main shocks and aftershocks. A drain finite difference hydraulic model considering laminar or turbulent two-dimensional flow in connecting cracks, geometrical distortions due to joint dilatancy while sliding, and misaligned drain segments is developed and validated. Coupled-hydromechanical analyses on the seismic response of a drained 90?m gravity dam are used to show the importance of cumulative displacements on the increase in uplift pressures, drain flow, and reduced sliding safety factors. Aftershock response is especially sensitive to the drainage system dimensions and model parameters, such as the foundation stiffness, and the number of potentially sliding joints. The proposed methodology forms the basis to develop displacement based performance criteria in stability evaluation of existing dams reevaluated for much higher ground motions intensities that they have been designed for many years ago.     

轮式机器人滑模轨迹跟踪控制器设计

轮式机器人是一个典型的非完整性系统.由于非线性和非完整特性,很难为移动机器人系统的轨迹跟踪建立一个合适的模型.介绍了一种轮式机器人滑模轨迹跟踪控制方法.滑模控制是一个鲁棒的控制方法,能渐近的按一条所期望的轨迹稳定移动机器人.以之为基础,描述了轮式机器人的动力学模型并在二维坐标下建立了运动学方程,根据运动学方程设计滑模控制器,该控制器使得机器人的位置误差收敛到零.     

大跨度梯形屋架的一种滑移施工方法

介绍了大跨度钢结构梯形屋架一种滑移施工方法,在狭窄且复杂场地内,采用胎架进行滑移施工,论述了实际施工过程的几个关键技术,且取得很好的经济效益,为类似工程施工提供参考。     

DN2200管架桥结构设计实例

本文为某市输水管线跨越水库溢洪道的工程设计实例。结合工程中管壳结构、橡胶垫板滑动支座和支承环等的具体设计、计算情况,较全面地介绍了该类工程的设计情况,可供相关设计人员参考     

近壁滑移汽泡沸腾换热机理研究进展

在沸腾换热机理研究中,近壁滑移汽泡的研究日益受到广泛的重视.但是,近壁滑移汽泡的研究还远未成熟.本文探讨了近些年来滑移汽泡换热机理方面的最新研究进展.论述了滑移汽泡的动力特性和换热机制;总结了近壁滑移汽泡的换热机理模型及其计算方法.指出了近壁滑移汽泡动力特性所需要继续深入研究的内容,初步构建了近壁滑移汽泡换热机理模型.最后对近壁滑移汽泡的研究方向提出了建议.     

Finite element analysis on local yield map and critical maximum contact pressure for yielding in hard coating with an interlayer under sliding contact

Micro-crack in the hard coating initiates usually from the local yield position. To prevent the crack to occur, the most important criterion is to satisfy the condition that the von Mises stress is less than the yield strength of material. In this paper, the local yield map showing the yielding position are introduced by using the finite element method and the criterion. The critical maximum contact pressures for yielding at the different positions were calculated by using the coating thickness, friction coefficient and the yield strength, where a critical range of yield strength ratio for the transition of yielding positions was found for 0.40.5. When the yield strength ratio is less than the range, yielding initiates from the interlayer and when the ratio is larger than the range, yielding initiates at the surface for high friction coefficient and in the base for low friction coefficient.     

润滑油中磨屑尺寸对滑动摩擦副咬死性能影响的试验研究

在ＭＨＫ－５００型环块式磨损试验机上,对含不同尺寸磨屑润滑油润滑的４５＾＃淬火屑试环,试块组成的滑动摩擦副进行了抗咬死性能试验研究,试验结果表明,润滑油中磨屑尺寸对滑劝摩擦副抗咬伤性能有很大的影响,改善润滑油清洁度的显著提高摩擦副的抗咬死承载能力,滑动摩擦副的抗咬死能力随润滑油中磨屑含量的增中减小很快,观察咬死后试件上的磨痕,表明滑动摩擦副的咬死是由于局部高温引起的接触区熔焊所致。