履带车辆路面激励响应的简化计算

为了快速计算履带车辆在路面不平度激励下的动力学响应,基于合理假设采用理论力学方法建立了某履带车辆的简化动力学模型,用ADAMS 软件建立了同种工况下的履带车辆动力学模型,并把两种模型的求解结果进行了对比,验证了简化模型的合理性. 研究结果为基于简化模型的动力学方程对车辆悬挂系统进行优化和逆动力学分析奠定了基础.     

基于离散模型的混凝土构件破坏过程研究

刚体-弹簧元模型是一种离散化分析模型,可以反映连续体从开裂到破坏不连续过程的真实裂缝形态.论文在总结既有相关研究的基础上,引入并程序化刚体-弹簧元模型用于混凝土构件开裂破坏行为研究,特别是有关混凝土构件开裂后直至破坏的裂缝真实形态研究.首先确定了三维刚体-弹簧元模型中刚体单元的划分、弹簧元的特性(混凝土材料本构关系施加于弹簧元)、刚体单元与弹簧元装配方式、钢筋本构关系及其与混凝土相互作用,然后实现了刚体-弹簧元模型用于混凝土构件开裂破坏行为研究的程序化,并以剪切破坏的钢筋混凝土构件进行实例验证.结果表明,基于刚体-弹簧元模型的程序可以较为准确地反映该钢筋混凝土构件从开裂到破坏真实裂缝形态.     

后加混凝土-砌体组合结构简化计算模型研究

后加混凝土构件的加固方法是在原有砌体结构外部新增钢筋混凝土构件,形成一种新型的组合结构．本文提出了考虑连接节点的后加混凝土构件-砌体组合结构的简化理论计算模型,并推导了不同构件的等效计算公式．考虑均布分布荷载和倒三角分布荷载作用,对组合结构的变形、剪力分配进行计算分析．计算结果从定性方面验证了本文提出的简化计算模型的可行性和有效性．同时针对某实际工程进行理论计算,与三维空间模型在弹性阶段的计算结果进行对比,从定量方面验证了本文提出的简化计算模型的准确性．     

小行星进入与撞击效应评估模型敏感性研究

近地小行星对地球的撞击是人类生存和发展面临的潜在威胁之一.当前小行星进入与撞击效应评估模型输入参数不确定度大,给模型的使用带来困扰,也较大地影响了危害评估结果.本文分析了输入参数的取值范围,以范围中概率最大或文献的推荐值作为敏感性研究的基准值,利用所发展的小行星进入与撞击效应分析评估软件AICA,通过改变一个或多个输入...     

梁格法计算双室箱梁剪力滞效应的精度研究

为研究梁格法计算双室箱梁剪力滞效应的精度,采用梁格法建立单箱双室简支箱梁的梁格分析模型,研究了单箱双室箱梁在竖向集中力以及均布荷载作用下的弯曲效应。采用有机玻璃模型进行实测研究,并建立基于板壳有限元的数值计算模型。将梁格解的剪力滞系数与板壳数值解、实验实测的剪力滞系数进行比较,得出的结论主要有:1采用梁格法计算单箱双室箱梁的剪力滞效应时,横截面的剪力滞系数呈台阶状分布,由于台阶数量过少,使得梁格法很难真实反映单箱双室箱梁的剪力滞效应;2集中荷载作用下,梁格法计算的峰值剪力滞系数偏小,跨中顶板截面与实验值最大相差10.5%;3均布荷载作用下,梁格解与板壳数值解的剪力滞系数在跨中顶板截面最大相差20.7%,峰值剪力滞系数的最大差率为-12.9%,且随着宽跨比的减小,梁格解的剪力滞系数逐渐增大。     

考虑车辆随机停放的停车楼减震设计与可靠度分析

在停车楼的设计中通常将车辆荷载以活荷载的方式均匀分布到结构上,实际上受车辆随机停放的影响,停车楼结构整体质量中心偏移,一旦结构遭遇罕遇地震时,车辆的随机停放可能造成停车楼结构发生扭转破坏.本文在传统减震设计方法的基础上考虑车辆活荷载的随机性,并从可靠度的角度验算减震结构在大震作用下的倒塌概率.结果表明,相同的减震设计布...     

基于机械振动理论的垂直侵彻弹靶作用模型

为了给侵彻引信抗高过载优化设计提供准确的力学输入,将机械振动理论引入侵彻过程建模领域,提出了一种侵彻战斗部刚体运动与一阶轴向振动相结合的垂直侵彻弹靶作用模型。在垂直侵彻过程受力分析的基础上,基于牛顿第二定律建立了战斗部刚体运动模型,基于单自由度弹簧-质量-阻尼系统建立了战斗部一阶轴向振动模型,并采用数值积分的方法获得了垂直侵彻过程中各物理量的变化规律。和火炮试验实测加速度信号的对比分析结果表明:考虑战斗部一阶轴向振动后的垂直侵彻弹靶作用模型能更准确地描述侵彻过程,能更有效地指导侵彻引信的抗高过载优化设计。     

超高层钢筋混凝土结构不同强度等级混凝土梁柱节点的模型实验与有限元分析

本文应用环氧树脂加添加剂的高分子材料模拟不同强度等级的混凝土，用特制的合金材料模拟钢筋，做成带有复杂多层钢筋笼和钢筋箍的梁柱节点模型。在模型内部钢筋和模型表面上粘贴了应变片，进行了模型实验。在考虑复杂钢筋配置的情况下，应用多重多枝子结构方法，在微机上进行了具有十万多个自由度的有限元分析。并将实验与有限元分析结果进行了比较，为梁柱节点的合理设计提供了重要的参考依据。     

竖向载荷作用下框架结构力学模型的简化与计算

针对结构力学与工程结构设计中力学模型和载荷作用方式的简化,分别采用一次性加载法、模拟施工三加载法和分层法,研究了竖向载荷作用下框架结构力学模型的简化与计算,分析了三种方法的计算假定和计算结果,给出了合理适用范围。一次性加载法更适用于抗连续性倒塌分析和建筑结构改造设计计算,模拟施工三加载法更适用于新建工程的设计计算,分层法作为一种简化的手算方法可作为理解结构力学原理的基本方法。     

竖向载荷作用下框架结构力学模型的简化与计算

针对结构力学与工程结构设计中力学模型和载荷作用方式的简化,分别采用一次性加载法、模拟施工三加载法和分层法,研究了竖向载荷作用下框架结构力学模型的简化与计算,分析了三种方法的计算假定和计算结果,给出了合理适用范围。一次性加载法更适用于抗连续性倒塌分析和建筑结构改造设计计算,模拟施工三加载法更适用于新建工程的设计计算,分层法作为一种简化的手算方法可作为理解结构力学原理的基本方法。     

Emulation system for assessment of human-robot collision

The research described is focused on cooperation of a small industrial robot and human operator where collision is expected only between the robot end-effector and the lower arm of the human worker. To study the effect of the impact between the robot and man, a passive mechanical lower arm (PMLA) was developed. The investigation presented in this paper evaluates whether the PMLA is a sufficiently accurate emulation system of a passive human lower arm. The same experiments were performed with the PMLA and with human volunteers. The results of both investigations were compared and evaluated in order to determine whether the PMLA can competently replace human volunteers in more dangerous investigations.     

Analytical track models for ride dynamic simulation of tracked vehicles

This paper presents various modelling strategies to account for track in the ride dynamic simulation of high mobility tracked vehicles negotiating rough off-road terrains. Four analytical track representations of varying complexities are formulated in conjuction with an in-plane ride dynamic model of a typical tracked vehicle. These track models are conceived in view of the tracked vehicle kinematics while ignoring the track belt vibrations. The ride dynamic response of a conventional armoured personnel carrier is evaluated in conjunction with different track methods, and validated against field-measured ride data. The relative performances of these track models are thus assessed based on the accuracy of response predictions, and associated computational time.     

The process of front-to-side collision of motor vehicles in terms of energy balance

Nonlinear Dynamics - The reconstruction of a road accident can be treated as the resolution of an “inverse problem” in mechanics using analytical or numerical models. In the road...     

Rheological models for unified curves for simplified design calculations in polymer processing

A method has been proposed earlier by Shenoy et al. to estimate complete flow curves depicting the variation of melt viscosity over industrially relevant range of shear rate and temperature through the use of unified curves characteristic of each generic type of polymer. In the present paper, the unified curves have been fitted through modified forms of already known generalized Newtonian models. The advantage of fitting such rheological models to unified curves lies in the fact that calculations involving entrance length estimates, heat transfer, die design, mold design, etc. are greatly simplified. Knowing the model parameters, one needs to know only the melt flow index, which is a relatively easy parameter to obtain, to make any engineering design calculations. The modified generalized Newtonian models have been fitted to a number of polymers covering one or more from each group of olefinics, styrenics, cellulosics, vinyls and engineering thermoplastics.NCL-Communication No. 3108     

Analysis of self-excited forces for a box-girder bridge deck through unsteady RANS simulations

This paper presents the results of two-dimensional numerical simulations of the flow field around a trapezoidal box-girder bridge section with later cantilevers, experiencing small-amplitude heaving or pitching harmonic oscillations. Unsteady Reynolds-averaged Navier–Stokes equations are solved in conjunction with an eddy-viscosity and an explicit algebraic Reynolds stress model. Flutter derivatives are determined and compared with wind tunnel results, showing fairly good agreement. The degree of sharpness of the deck lower edges is found to play a key role in the aeroelastic behavior of the profile. In particular, the bridge section fully behaves as a bluff body and is prone to low-reduced-wind-speed torsional galloping in the case of perfectly sharp edges. By contrast, the presence of a small radius of curvature in the section lower corners changes the nature of the instability to coupled flutter and significantly postpones the stability threshold, in line with a quasi-streamlined body behavior. Moreover, a wide sensitivity study is carried out, investigating the influence on the self-excited forces of the amplitude of oscillation, mean angle of attack and Reynolds number. In particular, the numerical simulations for the geometry with smooth lower edges highlight the regime transition occurring when the Reynolds number is varied, with significant effects on the flutter derivatives. Finally, the numerical flow visualizations provide a physical explanation of some phenomena observed in the wind tunnel experiments.     

波形钢腹板PC组合箱梁纯扭作用下抗扭承载力计算模型

以扭转理论和固定角软化桁架模型为基础,推导了纯扭作用下波形钢腹板PC组合箱梁的抗扭承载力计算模型.该模型针对组合箱梁极限状态时,波形钢腹板处于屈服和未屈服状态两种情况,分别建立了剪应交连续与剪力流连续方程,模型同时考虑了不同位置预应力筋对抗扭承载力的不同作用.通过四根试验梁抗扭承载力理论计算结果与试验数据的对比分析,结果表明本文提出的计算模型不仅能够有效的计算抗扭承载力,还能计算出混凝土开裂后的扭矩-扭率曲线.     

气体模型对再入飞行器气动力热环境影响的数值研究

复杂外形再入飞行器的设计,需对气动力热环境进行预测,由于不同的气体模型会对预测的结果产生影响,所以气动设计时就必须考虑这一影响.采用热化学平衡气体模型和双温度热化学非平衡气体模型对复杂外形再入飞行器的气动力热环境进行了数值计算;分析了气体模型对气动力、壁面热流等值线、驻点线平动温度、振动温度、组分质量分数等特征量的影响...