单双跨梁对平移力与平移质量的响应仿真分析

在仿真分析高速磁悬浮列车悬浮在柔性轨道梁上的动力学行为时 ,一般直观地有两个密切相关的问题 :一是悬浮力是恒定的情况 ,即平移力问题 ;二是气隙是恒定的情况 ,即平移质量问题 .采用模态叠加技术来描述变参数系统 ,给出了将车辆等效为平移力和平移质量两种情况时 。

力的平移定理在塔设备设计中的应用

利用力的平移定理,将作用在塔底引出管法兰面上的管道外载荷转化到接管根部,以符合核算局部应力的要求;将安装垂直度超标的塔器重量载荷转化为垂直状态的重量载荷和偏心载荷,在操作工况和水压试验工况下,分别与风载荷、地震载荷组合,计算各危险截面最大弯矩。

力的平移定理教学方法探讨

力的平移定理是力系等效的重要方法,其目的是将复杂力系进行等效和简化,从而建立复杂力系的静力平衡关系。本文通过"三幅图、三过程",使力的平移定理的全部过程更加清晰,有利于学生对这一定理的掌握和应用。

力的平移定理在塔设备设计中的应用

塔设备,顾名思义是一种形似高塔的装置设备,常在石油、化工等工业生产领域被大量的使用。目前,石油化工等工业生产所必须的冷却、吸收、精馏、解析,以及增湿等操作工序,均由相关的塔设备来完成。因此,塔设备在相关的工业生产中起到了不可替代的作用。完整的塔设备是由多个部件组成的设备,其结构较为复杂,不同功能的塔设备有着不同的结构设计。由于工业生产过程中的不同需求,塔设备上通常会设计一定数量的管口。在设计塔设备管口时,为了确保塔设备管口的使用效果和使用安全性,通常会用到设计力学的相关知识。本文便主要介绍了力的平移定理,并重点分析了力的平移定理在塔设备的设计工作中应用情况。

金属节育器在常规医用磁共振检查时的受力检测

目的通过建立实验模型,测试宫内节育器(IUD)与常规医用磁共振(MR)的相互影响,以期确定使用IUD的对象能否进行MRI检查。方法将磁性与非磁性纯铜IUD,分别放置于测试模型上,在0.4 T、1.0 T、1.5 T、3.0 T MR机上测试IUD各点的平移力和扭力。结果磁性金属IUD在0.4 T永磁MR圈内中心磁力最强,平移力最强,力的方向指向圈内中心,与机器是否扫描无关,未能测到扭力。在1.0 T、1.5 T、3.0 T超导型MR外圈平移力明显,近圈缘最高,未测到扭力,圈内保持磁性平衡,合力为零,平移力与扭力为零。非磁性金属铜IUD不存在平移力和扭力。以上数据与机器是否扫描无关。结论金属磁性IUD的位置变化是在进入检查室及进入检查腔的过程中产生,并不是在扫描中产生,在扫描中并无扭力产生;非磁性纯铜IUD在常规医用MR测试无平移力和扭力,检查时不存在受磁力牵拉引起的移位、出血。

压力容器弯头引出接管管道外荷载转化

压力容器除了承受介质内压外,在接管上还承受着由管道传递过来的外部载荷。由于接管和壳体连接结构的不连续,这些外部载荷通常在接管根部产生较高的局部应力,叠加在由内压产生的薄膜应力之上,影响着压力容器的安全。因此,设计时需要对这些外载荷进行核算。对于径向接管,可以根据力学模型直接确定载荷数据,但是对带有弯头的非径向接管,应通过力的平移定理将载荷转化,以保证力学模型中设计输入的准确性。

教学过程中的“启发”

在教学过程中,我们总是力求采用“启发式”,什么是“启发”,怎样去”启发”,笔者就这个问题谈些想法。

弯管内表面加工装置中圆弧导轨基座的结构设计

圆弧导轨基座是弯管内表面加工装置的主要承力部件,其结构和刚性决定着装置加工管道内表面时的尺寸和形状精度。考虑到圆弧导轨基座结构的特殊性以及所受的复杂空间外载荷力系,采用基于单纯扭转理论的曲线梁结构力学解法对圆弧导轨基座进行刚度设计,从而得出满足要求的基座截面尺寸与形状;针对其所受的复杂的空间外载荷力系使基座产生弯、扭、剪综合效应从而用理论公式难以校核的问题,利用力平移定理进行简化并建立装置的静力学模型,再用有限元软件Workbench进行极限外载荷工况下刚度与强度校核。经过静力学分析,用上述方法设计出的圆弧导轨基座在极限工况下的刚度与强度均符合要求。

Numerical Simulation of Coal Floor Fault Activation Influenced by Mining

By means of the numerical simulation software ANSYS, the activation regularity of coal floor faults caused by mining is simulated. The results indicate that the variation in horizontal, vertical and shear stresses, as well as the horizontal and vertical displacements in the upper and the lower fault blocks at the workface are almost identical. Influ- enced by mining of the floor rock, there are stress releasing and stress rising areas at the upper part and at the footwall of the fault. The distribution of stress is influenced by the fault so that the stress isolines are staggered by the fault face and the stress is focused on the rock seam around the two ends of the fault. But the influence in fault activation on the upper or the lower fault blocks of the workface is markedly different. When the workface is on the footwall of the fault, there is a horizontal tension stress area on the upper part of the fault; when the workface is on the upper part of the fault, it has a horizontal compressive stress area on the lower fault block. When the workface is at the lower fault block, the maximum vertical displacement is 5 times larger then when the workface is on the upper fault block, which greatly in- creases the chance of a fatal inrush of water from the coal floor.

Classification of Teleparallel Homothetic Vector Fields in Cylindrically Symmetric Static Space-Times in Teleparallel Theory of Gravitation

In this paper we classify cylindrically symmetric static space-times according to their teleparallel homothetic vector fields using direct integration technique. It turns out that the dimensions of the teleparallel homothetic vector fields are 4, 5, 7 or 11, which are the same in numbers as in general relativity. In case of 4, 5 or 7 proper teleparallel homothetic vector fields exist for the special choice to the space-times. In the case of 11 teleparallel homothetic vector fields the space-time becomes Minkowski with all the zero torsion components. Teleparallel homothetic vector fields in this case are exactly the same as in general relativity. It is important to note that this classification also covers the plane symmetric static space-times.

Research on Modified Shifting Balance Genetic Algorithms

The increasing overlap of core and colony populations during the anaphase of evolution may limit the performance of shifting balance genetic algorithms. To decrease such overlapping,so as to increase the local search capability of the core population,the sub-space method was used to generate uniformly distributed initial colony populations over the decision variable space. The core population was also dynamically divided,making simultaneous searching in several local spaces possible. The algorithm proposed in this paper was compared to the original one by searching for the optimum of a complicated multi-modal function. The results indicate that the solutions obtained by the modified algorithm are better than those of the original algorithm.

Coupled pile soil interaction analysis in undrained condition

The effective stress method is developed to predict the axial capacity of piles in clay. The effective stress state changes due to the resulting pore pressure change and therefore, the strength and stiffness of the soil will change. In this work, the finite element method is utilized as a tool for the analysis of pile-soil systems in undrained condition. The computer program CRISP was developed to suit the problem requirements. CRISP uses the finite element technique and allows predictions to be made of ground deformation using critical state theories. Eight-node isoparametric element was added to the program in addition to the slip element. A pile loading problem was solved in which the pile-soil system is analyzed in undrained condition. The pile is modelled as elastic-plastic material, while the soil is assumed to follow the modified Cam clay model. During undrained loading condition, the settlement values increase by 22% when slip elements are used. The surface settlement increases by about three times when the load is doubled and the surface settlement at all points increases when using slip elements due to the mode of motion which allows smooth movement of the adjacent soil with respect to the pile. The vertical displacement increases as the distance decreases from the pile and negligible values are obtained beyond 10D (where D is the pile diameter) from the center of the pile and these values are slightly increased when slip elements are used. The vertical effective stress along a section at a distance D from the pile center is approximately the same for all load increments and lower values of effective vertical stress can be obtained when slip elements are used.

Classification of Kantowski-Sachs and Bianchi Type Ⅲ Space-Times According to Their Killing Vector Fields in Teleparallel Theory of Gravitation

In this paper we classify Kantowski-Sachs and Bianchi type Ⅲ space-times according to their teleparallel Killing vector fields using direct integration technique. It turns out that the dimension of the telepaxallel Killing vector fields are 4 or 6, which are the same in numbers as in general relativity. In case of 4 the teleparallel Killing vector fields are multiple of the corresponding Killing vector fields in general relativity by some function of t. In the case of 6 Killing vector fields the metric functions become constants and the Killing vector fields in this case are exactly the same as in general relativity. Here we also discuss the Lie algebra in each case.

Characteristics of deformation and stress distribution of small coa pillars under leading abutment pressure

Based on the engineering project on a small coal pillar of 12,521 working face roadway in Xieqiao Coalmine, data regarding surface displacements of the coal pillar, deep displacements and mining stress have been collected and analyzed. The results show that macroscopic transverse fractures of the inner coal pillar are developed within 2–4 m of the roadway surface, which is located outside the coal pillar anchorage zone. There is a displacement of 530 mm at the monitoring point in the 6 m deep zone of the pillar. Transfer of the fracture zone is found in a small coal pillar and the fractures within 3–4 m of the coal-rock zone from the roadway surface undergo propagation and closure of cracks which means this fracture zone is transferred from 3–4 m outside the roadway to only 2–3 m from the roadway surface. In the monitoring zone, vertical and horizontal stresses increase with a feature that shows that acceleration in the deep zone of the pillar is greater than that in the shallow zone. Furthermore, the acceleration of vertical stress is also greater than that of horizontal stress with a peak value in the 4 m zone.The research findings provide a reference for the regulation of a reasonable width of coal pillar in coalmines and optimal control design of surrounding rock.

A new method to calculate lateral force acting on stabilizing piles based on multi-wedge translation mechanism

A new method based on the multi-wedge translation mechanism is presented to calculate the lateral force acting on the stabilizing piles. At first, there is no assumption for the shape of potential sliding surface, it is just considered that the potential sliding surface is a composite of a number of straight lines. And then, the potential sliding mass is divided into a number of triangular wedges take with these straight lines as its base. The kinematic theorem of limit analysis is adopted to calculate the rate of external work and the rate of energy dissipation for each triangular wedge, respectively. Furthermore, the multivariate functions are established to calculate the lateral force acting on the stabilizing piles. The lateral force and the corresponding potential sliding surfaces can be obtained by an optimizational technique. At last, an example is taken to illustrate the method. The effect of soil strength parameters, slope angle and pile roughness on the lateral force and the corresponding potential sliding surface are analyzed.The result are compared with those obtained using other methods.

新型冷凝水疏水阀原理及应用

介绍了一种新型蒸汽、压缩空气疏水阀。冷凝水对蒸汽和压缩空气管道影响较大,若不及时把积水排除就会造成管道输送异常,出现压力波动或用户端含水量大,冷凝水疏水阀是实现管道疏水的关键元件。蒸汽、压缩空气疏水阀目前存在的主要缺陷是卡阻、泄漏和堵塞,使用寿命短,维护困难,经济性差。针对传统蒸汽、压缩空气疏水阀存在的弊端,通过技术攻关改造,实现了对传统疏水阀的改进,改进后使用效果较好。

A Note on Classification of Spatially Homogeneous Rotating Space-Times According to Their Teleparallel Killing Vector Fields in Teleparallel Theory of Gravitation

In this paper we classify spatially homogeneous rotating space-times according to their teleparallel Killing vector fields using direct integration technique.It turns out that the dimension of the teleparallel Killing vector fields is 5 or 10.In the case of 10 teleparallel Killing vector fields the space-time becomes Minkowski and all the torsion components are zero.Teleparallel Killing vector fields in this case are exactly the same as in general relativity.In the cases of 5 teleparallel Killing vector fields we get two more conservation laws in the teleparallel theory of gravitation.Here we also discuss some well-known examples of spatially homogeneous rotating space-times according to their teleparallel Killing vector fields.

Dynamic Interaction of Parallel Moving Ships in Close Proximity

Nowadays,there are many studies conducted in the field of marine hydrodynamics which focus on two vessels traveling and floating in sufficiently close proximity to experience significant interactions.The hydrodynamic behavior of parallel moving ships in waves is an interesting and important topic of late.A numerical investigation has been carried out for the prediction of wave exciting forces and motion responses of parallel moving ships in regular waves.The numerical solution was based on 3D distribution technique and using the linear wave theory to determine the exciting forces and ship＇s motion.The speed effects have been considered in the Green function for more realistic results.The numerical computations of wave exciting forces and motion responses were carried out for a Mariner and Series 60 for the purpose of discovering different Froude numbers and different separation distances in head sea conditions.Based on the numerical computations,it was revealed that the sway,roll and yaw have a significant effect due to hydrodynamic interaction.

水雷冲击掩埋的一维-三维模型预测

当圆柱体或非圆柱体海军水雷通过空气、水和沉积物下落时,水雷冲击掩埋状态预测模型建立了一段时间历程.模型的输出是预测水雷在空气和水柱中的运动轨迹、在沉积物中的掩埋深度和方向,以及雷体在掩埋物中凸出部分的高度、面积和体积.模型的输入包括环境、水雷特征和初始释放状态等参数.综述近30年来水雷冲击掩埋预测模型从一维到三维的发展情况:(1)一维模型预测了在水雷降落角度恒定时的水雷质心的垂向位置;(2)二维模型预测了水雷质心在(x,z)二维平面中的位置以及绕y轴的旋转情况;(3)三维模型预测了水雷质心在(x,y,z)三维空间里的位置以及绕x,y和z轴的旋转情况.这些模型均通过从水雷冲击掩埋试验中获得的实验数据进行了验证.一维模型只求解了在沿z轴方向运动的一个动量方程,它不能很好地预测水雷的运动轨迹和掩埋深度.二维模型仅限于水雷在(x,z)平面中的运动状态预测,而且要求雷体周围的流体是静止的,另外,使用了不准确的阻尼系数和不精确的沉积物动力学.因此,二维模型在水雷的运动轨迹和埋藏深度的预测上误差很大(比在Monterey湾砂底观察的深度大6～10倍).三维模型能很好地预测圆柱体、近圆柱体以及实验用的Manta和Rockan等水雷的运动轨迹和掩埋深度.

Ground movement mechanism in tectonic stress metal mines with steep structure planes

When mining metal mines with steep structure planes by the caving method,there is a mechanical model in which the horizontal stress on the rock mass is simplified as a column before surface subsidence.The model is used to deduce critical support load and limiting column length for a given horizontal stress and support pressure.Considering the impact of the column effect,a method is proposed to determine the movement of the ground and caving area in a mine.After surface subsidence,the horizontal stress on a surrounding rock mass can be simplified to a cantilever beam mechanical model.Expressions for its bending fracture length are deduced,and a method is given to determine its stability.On this basis,an explanation for the large ground movement and subsidence scope was given.A case study shows that the damage effect of column and cantilever beam is significant for ground movement in metal-ore mine,and an appropriate correction value should be applied when designing for its angle of ground movements.