Critical Top Tension for Static Equilibrium Configuration of A Steel Catenary Riser

This paper aims to present the critical top tension for static equilibrium configurations of a steel catenary riser（SCR） by using the finite element method. The critical top tension is the minimum top tension that can maintain the equilibrium of the SCR. If the top tension is smaller than the critical value, the equilibrium of the SCR does not exist. If the top tension is larger than the critical value, there are two possible equilibrium configurations. These two configurations exhibit the nonlinear large displacement. The configuration with the smaller displacement is stable, while the one with larger displacement is unstable. The numerical results show that the increases in the riser＇s vertical distances, horizontal offsets, riser＇s weights, internal flow velocities, and current velocities increase the critical top tensions of the SCR. In addition, the parametric studies are also performed in order to investigate the limit states for the analysis and design of the SCR.

GaN-based heterostructures： electric-static equilibrium and boundary conditions

In the GaN-based heterostructures, this paper reports that the strong electric fields induced by polarization effects at the structure boundaries complicate the electric-static equilibrium and the boundary conditions. The basic requirements of electric-static equilibrium for the heterostructure systems are discussed first, and it is deduced that in the application of the coupled Schroedinger-Poisson model to the heterostructures of electric static equilibrium state, zero external electric field guarantees the overall electric neutrality, and there is no need to introduce the charge balance equation. Then the relation between the screening of the polar charges in GaN-based heterostructures and the possible boundary conditions of the Poisson equation is analysed, it is shown that the various boundary conditions are equivalent to each other, and the surface charge, which can be used in studying the screening of the polar charges, can be precisely solved even if only the conduction band energy is correctly known at the surface. Finally, through the calculations on an AlGaN/GaN heterostructure with typical structure parameters by the coupled Schroedinger-Poisson model under the various boundary conditions, the correctness of the above analyses are validated.

Static equilibrium model for the bead formation in high speed gas metal arc welding

On the basis of the Young-Laplace Equation that describes the pressure difference between each side of a curved liquid surface, a static equilibrium model is established to describe the surface shape of the weld bead. The geometrical model for the molten pool is included, which is essential to explain the undercut phenomenon during high speed bead-on-plate welding. The results got from an iteration algorithm show that it is the force balance on the liquid mixture of the deposited metal and the molten base metal that causes the undercut. Some factors and their effects are also analyzed.

Reaction Forces on a Fixed Ladder in Static Equilibrium: Analysis and Definitive Experimental Test of the Ladder Problem

The development of a theoretical model to predict the four equilibrium forces of reaction on a simple ladder of non-adjustable length leaning against a wall has long remained an unresolved matter. The difficulty is that the problem is statically indeterminate and therefore requires complementary information to obtain a unique solution. This paper reports 1) a comprehensive theoretical analysis of the three fundamental models based on treating the ladder as a single Euler-Bernoulli beam, and 2) a detailed experimental investigation of the forces of reaction as a function of applied load and location of load. In contrast to previous untested proposals that the solution to the ladder problem lay in the axial constraint on compression or the transverse constraint on flexure, the experimental outcome of the present work showed unambiguously that 1) the ladder could be modeled the best by a pinned support at the base (on the ground) and a roller support at the top (at the wall), and 2) the only complementary relation needed to resolve the static indeterminacy is the force of friction at the wall. Measurements were also made on the impact loading of a ladder by rapid ascent and descent of a climber. The results obtained were consistent with a simple dynamical model of the ladder as a linear elastic medium subject to a pulse perturbation. The solution to the ladder problem herein presented provides a basis for theoretical extension to other types of ladders. Of particular importance, given that accidents involving ladders in the workplace comprise a significant fraction of all industrial accidents, the theoretical relations reported here can help determine whether a collapsed structure, against which a ladder was applied, met regulatory safety limits or not.

The Role of Friction in the Static Equilibrium of a Fixed Ladder: Theoretical Analysis and Experimental Test

In a recent publication the author derived and experimentally tested several theoretical models, distinguished by different boundary conditions at the contacts with horizontal and vertical supports, that predicted the forces of reaction on a fixed (i.e. inextensible) ladder. This problem is statically indeterminate since there are 4 forces of reaction and only 3 equations of static equilibrium. The model that predicted the empirical reactions correctly used a law of static friction to complement the equations of static equilibrium. The present paper examines in greater theoretical and experimental detail the role of friction in accounting for the forces of reaction on a fixed ladder. The reported measurements confirm that forces parallel and normal to the support at the top of the ladder are linearly proportional with a constant coefficient of friction irrespective of the magnitude or location of the load, as assumed in the theoretical model. However, measurements of forces parallel and normal to the support at the base of the ladder are linearly proportional with coefficients that depend sensitively on the location (although not the magnitude) of the load. This paper accounts quantitatively for the different effects of friction at the top and base of the ladder under conditions of usual use whereby friction at the vertical support alone is insufficient to keep the ladder from sliding. A theoretical model is also proposed for the unusual circumstance in which friction at the vertical support can keep the ladder from sliding.

A Geometrical Theorem about the Static Equilibrium of a Common-point-force System and its Application

A geometrical theorem for the static equilibrium of a common-point-force system has been proven by means of virtual-work principle: The equilibrium point of a common-point force system has a minimal weighted distance summation to every fixed point arbitrarily given on each force line with a weighing factor proportional to corresponding force value. Especially the mechanical simulating technique for its inverse problem has been realized by means of pulley block. The conclusions for the inverse problem derived from mechanic method are in accordance with that given by the pure mathematical method, and the self-consistence of the theorem and its inverse problem has been demonstrated. Some application examples in engineering, economy and mathematics have been discussed, especially the possible application in the research of molecular structure, has also been predicted.

Distribution of static equilibrium points in static electric field produced by fixed electrons

Fix n electrons on the disk ｜z｜≤R. They generate a static electric field. Let a be an electron located in the disk ｜z｜≤R sin π/n. It shows that the closed disk with center a and radius R contains at least one static equilibrium point.

An Engineering Application Tool for Visual Assessment of the Equilibrium Beach

An engineering application tool for prediction of the static equilibrium bay （ Beach Mod） is established to describe two bay shape formulas by use of the programming software ＂MATLAB＂ with a graphic user interface （ GUI）. The tool is user-friendly for engineering students for the design of beach shapes. This tool was tested through application on three types of beaches in Taiwan and Australia. By implementing the concept of Headland Control, the Beach Mod program allows users to draw a structure and create an ＇artificial headland. The results indicate that Beach Mod can efficiently forecast beach changes as well as MEPBAY, a competing software package, while boasting a better user interface.

Buckling and Multiple Equilibrium States ofViscoelastic Rectangular Plates

On the basis of Karman's theory of thin plates with large deflection, the Boltzmann law on linear viscoelastic materials and the mathematical model of dynamic analysis on viscoelastic thin plates, a set of nonlinear integro partial differential equations is first presented by means of a structural function introduced in this paper. Then, by using the Galerkin technique in spatial field and a backward difference scheme in temporal field, the set of nonlinear integro partial differential equations reduces to a system of nonlinear algebraic equations. After solving the algebraic equations, the buckling behavior and multiple equilibrium states can be obtained.

BUBBLE POINT PRESSURE MEASUREMENT FOR ISOTHERMAL QUATERNARY SYSTEM AND PREDICTION OF VAPOR-LIQUID EQUILIBRIUM

1 INTRODUCTIONVapor-liquid equilibrium(VLE)relations are required for practical use,such as in the designand operation of disitillation equipment.In the conventional experimental methods of vapor-liquid equilibria,some analytical instruments are applied.They are time-consuming and dif-ficult for multicomponent system because the proper method for the composition analysis isnot easy to be set up.

基于不完全信息静态博弈的工控系统风险评估方法

针对目前大多数工业控制系统风险评估方法未思考防御者策略以及攻防两者之间的对抗问题,提出一种基于博弈模型的风险评估方法。通过攻击防御图模型,计算攻击收益和防御收益;建立静态贝叶斯攻防博弈模型,计算混合策略贝叶斯纳什均衡,获得攻防两者最优策略概率分布。根据信息安全风险评估的计算方法,以防御者收益和攻击者最优策略选择概率分布为基础进行风险评估计算。通过一个实例证明了该方法的可行性和有用性。

并网逆变器LVRT同步稳定性分析及其优化策略

针对现有低电压穿越(LVRT)研究难以准确全面评估变流器同步运行能力的问题,首先结合LVRT特性和电网侧特性定量研究不同因素对准静态平衡点的影响,揭示系统准静态平衡点的存在条件。其次,分析LVRT特性对并网逆变器暂态稳定性和小信号稳定性的影响,明晰电网故障期间系统不仅存在暂态失步的风险,而且难以在准静态平衡点稳定运行。基于以上理论分析,提出一种提高并网逆变器LVRT同步运行能力的优化策略。该策略在LVRT期间根据电网运行状态自适应调整锁相环参数,不仅可降低系统暂态失步的风险,还可增强其小信号稳定裕度。最后,通过仿真和实验验证了理论分析的正确性和优化策略的有效性。

任意静定桁架内力分析仿真实验设计

提出了描述桁架几何结构、载荷和支座约束的平衡方程,构建了桁架系统平衡方程的统一矩阵形式,基于MATLAB开发了静定桁架内力分析仿真实验软件。通过该软件,学生可以自主搭建任意静定平面桁架和空间桁架,并完成结构的内力分析实验。实践表明,将仿真实验引入理论力学课程教学,不仅激发了学生的学习兴趣,加深了学生对基本概念的理解;而且培养了学生的高阶思维,提升了学生利用计算机求解问题的能力。

碰撞测试假人在儿童生活领域的应用

针对市面上广泛存在的儿童生活领域消费品安全稳定性问题,将目前成熟的人体假人技术应用于安全稳定性分析,借助L S-Dyna与HyperMesh有限元软件,选择碰撞测试P系列假人,搭建假人与消费品的虚拟场景,进行过程模拟与稳定性分析。从仿真动画与数据可知,仿真结果与试验数据保持一致,证明碰撞测试假人应用于消费品稳定性分析的可信性。此外,对儿童攀爬柜类家具的物理模型进行公式推导与静力平衡分析,得出重心与倾覆力矩,对比仿真分析,验证了碰撞测试假人应用于消费品安全稳定性分析的可信性。

基于动静平衡理念髌骨骨折术后康复量化方案临床观察

目的基于“动静平衡”理念的髌骨骨折术后不同康复量对患者膝关节活动度及相关功能的影响。方法选取山东省中医院骨科收治的90例髌骨骨折手术治疗后患者,按照随机数字表法将患者分为观察组A组、观察组B组和对照组C组,每组30例,观察组分别以不同的康复量进行功能锻炼,对照组以传统的“无痛”康复方法进行锻炼。观察A、B、C三组患者膝关节主动屈伸角度、WOMAC骨关节炎指数评分和临床疗效。结果①A组、B组膝关节主动屈伸角度均大于对照组C,且差异具有统计学意义(P<0.05);②A组、B组的疼痛、僵硬、关节功能评分及WOMAC总分均低于对照组C,差异有统计学意义(P<0.05);③A组的优良率为93.33%,B组为90.00%,对照组C为70.00%,三组比较差异有统计学意义(P<0.05);④A组与B组间疗效比较无显著性差异(P>0.05)。结论髌骨骨折术后采用“量化控制”康复方法治疗,可提高膝关节活动度,减少膝关节疼痛僵硬,恢复膝关节正常生理功能,疗效优于传统无痛康复方法,值得推广。

梁板融合预制装配式双拼槽钢-混组合楼板试验

为充分发挥装配式工业化程度高和钢-混组合结构优良力学性能的优势,提出一种装配式双拼槽钢-混凝土组合楼板,对3组简支组合楼板试件进行了四点加载试验,研究了该组合楼板的竖向静载下力学性能。分析了楼板裂缝、挠度、应变(钢筋、钢梁、混凝土板)随荷载发展规律;基于极限平衡法,提出了考虑受拉薄膜效应和刚度强化系数的承载力计算公式。结果表明:组合楼板的变形呈双向板特征,试件破坏时均出现板顶角部裂缝和弧形裂缝,混凝土板底中心区域为网状裂缝和向角部延伸的斜裂缝,双拼主梁发生塑性弯曲;在楼板的中心挠度达到l 0/40时,试件荷载分别为327.63 kN、436.92 kN和406.12 kN,组合楼板承载力较高;钢筋的应变发展在垂直钢梁方向较大,沿着塑性铰线屈服;考虑受拉薄膜效应和刚度强化系数的计算公式与试验结果吻合良好,准确地预测了楼板荷载-挠度全过程曲线。

基于极限平衡法的挡土墙设计理论

本文针对嵌入式挡土墙进行拟静力极限平衡设计,采用Blum法计算动力条件下的内力和临界加速度,讨论该方法的主要缺陷,并基于真正动态二维有限差分分析的结果,提出一种新的极限平衡方法。研究表明:在水平接触应力和弯矩分布方面,拟静力预测法结果与真正的动态二维有限差分分析法获得结果以及相关文献研究结果高度吻合。随着土-墙体系强度增加,土-墙体系的临界加速度和最大弯矩均增大。土-墙系统强度越大,在振动中产生位移越小,但这一目标实现需要增加墙体内力。Blum方法仅为中等地震提供了对墙体最大内力的可靠估计,并且显著低估了临界加速度和相应的最大弯矩。相反,本文所提出的方法与数值数据吻合较好,并始终给出保守估计的最大弯矩值。

高功率微波加热三维温度模型仿真与验证

微波加热不均匀性一直以来都是从事微波加热控制方向研究人员心目中的热点问题。根据微波加热装置的物理结构建立了炉内各层表面的温度静态差分模型结合实验以求得微波加热的实际功率。再基于传热学的有限差分法建立三维空间中的温度分布模型,利用MATLAB以及COMSOL仿真对比验证了模型的有效性。假定微波均匀加热求得被加热介质的平衡温度与不均匀加热时的温度进行比对以找出微波加热过程中介质的部分温升平衡点,最后互相比对找出最优点为控制对象进行专家PID(proportion-integral-derivative)微波加热。实验结果表明,该方法能较为精确地测量出被加热介质任何时刻的平衡温度,使得微波加热在工业生产上有着更加广泛的应用。

基于博弈论的高校学生教育管理研究

高校学生教育管理是我国高等教育工作的重要组成部分。随着我国高等教育改革的不断深化和教育管理对象的时代性变化,高校学生教育管理工作不断面临新的挑战。因此,不断改进高校学生教育管理,是我国高等教育进一步发展的必然选择。根据博弈论的分析框架,分析了高校学生和思想政治辅导员老师之间的博弈行为,通过构建博弈模型并对其进行推导分析,得出符合博弈主体利益要求的主要途径,以便为学生学习成长提供更好的育人环境,同时为高校思想政治教育工作者提供教育管理创新理念和决策思路。

基桩自平衡静载试验中平衡点问题研究

基桩自平衡静载试验是一种被广泛采用的单桩竖向承载力测试方法,平衡点位置的确定是保证试验成功的重要条件。相关规范采用竖向力平衡条件确定平衡点,在多个现场试验中发现以此条件确定的平衡点位置上下位移差异较大,极易造成荷载箱达到最大行程时某段桩承载力尚未充分发挥的状况。本文针对试验中位移差异问题,提出用桩土界面刚度平衡确定位移协调平衡点位置,以达到试验过程中位移协调的目的。为此,采用实测数据结合有限元数值计算,对平衡点位置上下位移差异较大的原因进行分析,提出刚度平衡条件,建立位移协调平衡点的经验计算公式,并采用数值计算及实测数据对经验公式进行验证,结果表明经验公式具有较好的效果,对确保试验成功具有重要意义。