2022年泸定地震某隔震建筑内非结构构件震害模拟分析

在2022年9月5日四川泸定地震中，位于震中近断层场地的一栋采用隔震设计的建筑内部非结构构件发生不同程度的破坏。非结构构件作为整体结构经济价值占比重要组成部分，减小其地震损伤对于建筑震后功能恢复至关重要。为此，本文在介绍该建筑内部非结构构件主要震害的基础上，采用二阶段级联分析方法。第一阶段在Etabs中建立一8层框架-剪力墙结构有限元模型，基于实测邻近台站近断层强震记录的非线性地震反应分析，模拟该建筑各楼层地震响应。第二阶段以建筑内部文件柜等常见浮放式非结构构件为原型，在OpenSees中建立零长度转角弹簧模型，基于上一阶段的结构楼面加速度响应作为输入，模拟建筑内部不同尺寸高宽比非结构构件的摇晃与倾覆响应，并同时考虑水平单向输入与水平-竖向双向输入两种方式，以重点考察近断层地震强竖向分量的影响。结果表明，隔震层能有效降低上部结构的水平楼面加速度响应，但竖向楼面峰值加速度相比竖向地面峰值加速度被显著放大；水平与竖向激励同时输入下浮放式设备的摇晃角度与倾覆概率大于水平单向激励输入的情况，考虑竖向激励的作用后会增大浮放式设备的破坏风险。因此，在近断层场地进行建筑抗震设计时，强竖向地面运动对内部非结构构件的影响不容忽视。     

Turbulence and mixing across gravitationally unstable interface by tank-overturn experiment

Turbulence and mixing across gravitationally unstable interface were studied in the laboratory by overturning a tank of two-layer fluids initially of stable stratification. As the dense fluid fell under gravity to mix with the lighter fluid from below, highly unsteady exchange of fluids across the unstable interface was produced by the buoyancy force. The exchange was captured in the experiment by a video camera using dye in the dense fluid as tracer. Absorption of light by the dye determined the excess mass at every pixel of the digitized images. The position of the excess-mass center and the speed of the center were computed from the excess-mass profiles as parameters to characterize the mixing across the unstable interface. With positive feedback by the buoyancy force, mixing across the interface rapidly intensified. It increased linearly from zero to a maximum in an acceleration regime and then asymptotically toward a terminal state, as the total buoyancy in the layer stayed constant. In the terminal state, the excess-mass center advanced at a terminal speed in proportion to the square root of the layer's total buoyancy.     

侧风对储物箱的安全性影响分析与试验

针对一种大尺寸储物箱在大风速侧风作用下装卸时存在滑移甚至倾覆风险的安全性问题,采用数值分析方法,分析不同风速作用下储物箱受到的侧向力和倾覆力矩,数值分析计算结果表明：在平均风速15 m/s和瞬时风速25 m/s的情况下,储物箱不会发生滑移和倾覆;针对该储物箱开展加载试验验证,试验结果表明：在3.193 N侧向拉力作用下储物箱未发生滑移和倾覆,佐证了数值分析结果的准确性,证明该储物箱在平均风速15 m/s和瞬时风速25 m/s的情况下装卸是安全的。     

对框架与剪力墙协同工作结构体系的界定与设计建议

结合某工程实例,探讨了对于框架地震倾覆力矩比大于0.5的框架-剪力墙结构体系的设计方法与建议,并拓展分析了框架与剪力墙协同工作结构体系的界定,抗震等级及适用高度的确定,并给出相应的设计方法和抗震构造措施。阐明了目前规范与规程中存在的不明确问题,为结构设计提供必要的合理建议。     

增加挡墙稳定的措施

针对挡墙抗滑、抗倾、基底应力及偏心难以满足规范要求的情况，介绍几种增加挡墙稳定的措施。     

A new method for determining the preload in a wire race ball bearing

This paper explores a numerical method to calculate the frictionless three-dimensional non-conforming contact problem associated with a wire race ball bearing used in a certain aircraft simulating rotary table, for challenging the conventional method on the determination of the preload magnitude. A computer program based on the Hertz elastic contact theory and a mathematical model of two critical loading conditions was performed in MATLAB^® by using an example of a wire race ball bearing having an approximately 900 mm diameter. The normal contact forces, the contact deformation, the maximum contact pressure, the semi-major axes and the semi-minor axes of contact ellipses of the ball-wire race were computed. The analytic results show that the overturning moment, the pitting corrosion and the shear failure due to combined stresses can be avoided by controlling preload values in the range 11.3–169.9 μm. The experimental results are closely in agreement with the theoretical results, and verify the availability of the numerical method. The research provides theoretical support for the development and further application of wire race ball bearings with large diameters.     

挟沙强横风对高速列车气动特性的影响研究

为了研究强风沙环境下高速列车运行的安全性能和气动性能,基于空气动力学理论,运用Navier-Stokes方程、标准k-ε湍流模型对气流进行连续化处理,应用DPM模型对沙粒进行离散化。算例采用欧拉 拉格朗日方法进行求解。研究结果表明：随着挟沙风速的增大,列车背风侧的涡流强度有所降低,但在背风侧的近地面,列车的流线越来越不规则;除此之外,列车车身的压力会随着挟沙风速的增大而增大,会随着沙粒直径的增大而有所降低;随着挟沙风速的增大,列车的阻力、侧力、升力均增大。随着沙粒直径的增大,列车的升力、侧力、阻力、倾覆力矩均有所降低,但比净风情况下要大。研究结果对强风沙地区合理设计高铁线路具有一定的参考价值。     

Estimating the relationship between measured wind speed and overturning truck crashes using a binary logit model

This paper develops a quantitative model that correlates overturning freight vehicle crash records in Wyoming to measured wind speeds at nearby weather stations. The database consists of 14,700 truck crashes from 1994 to 2003 and wind speed and gust information from 21 weather stations. A binary logit model was estimated from the data to determine if there was significant correlation between weather station wind data and the likelihood that the crash was of the overturning type. While it is reasonably known that local wind speeds at the crash location are critical in predicting overturning truck crash likelihood, it was not known if distant weather station data were an adequate predictor of these crash types. The results from this work indicate that weather station data can be used as a predictor of overturning crashes. This work provides the necessary first step for the development of operational rules for roadway sections that run high risk of overturning truck crashes in high wind conditions.     

Optimal load of elastic joint mobile manipulators imposing an overturning stability constraint

Full load motion of mobile manipulators while carrying a load with pre-defined motion precision is an important consideration in their application. Therefore, in this paper a general formulation for finding the maximum load-carrying capacity of compliant joint mobile manipulators is presented. The overturning stability of the system and the precision of the motion on the given end effector trajectory are taken into account. The main constraints used for the algorithm presented are the actuator torque capacity, the limited error bound for the end effector and the overturning stability during motion on the given trajectory. This paper presents a strategy for determining the dynamic load-carrying capacity (DLCC), subject to overturning stability, accuracy and actuator constraints, in which a series of ball-type bounds centred at the desired trajectory is used in the end effector oscillation constraint, while a typical d.c. motor speed-torque characteristics curve is used in the actuator constraint. The technique, which considers the full nonlinear mobile manipulator dynamics, actuator constraint, overturning stability constraint, and accuracy constraint, permits the user to specify the trajectory completely. In order to verify the effectiveness of the algorithm presented, a simulation study considering a compliant joint two-link planar manipulator mounted on a differentially driven mobile base is given with details.     

推进剂贮箱金属膜片的变形模拟及参数分析

航天推进剂金属膜片贮箱是航天运载器的重要部件,贮箱膜片能否有效稳定地翻转是影响贮箱性能的关键因素.使用MSC.marc软件,采用大变形弹塑性有限元法对膜片的翻转变形过程进行模拟,并分析其翻转失效状态及翻转失效原因,总结出膜片各参数对翻转效果的影响,为金属膜片的设计及控制膜片的失效提供参考依据.