求解超静定刚架的一种新方法

通过满足基本方程和边界条件去确定系数,得到确定的挠度曲线方程,进而求得内力图.     

带弹簧支撑超静定结构位移的简化计算方法

针对带有弹性支撑的超静定结构的位移计算问题, 对利用虚功原理得到的位移计算一般公式进行了进一步推导, 提出了该类结构位移的简化计算方法. 文中计算公式表达形式简洁, 且与一般刚性支撑超静定结构的位移计算方法一致. 通过与有限元分析结果的对比,证明了该公式的正确性.     

含有无穷大弯曲刚度段变截面刚架的求解

采用扩大平衡隔离体范围的方法, 直接由平衡方程求得位移法典型方程系数, 解决了难以写出转角位移方程等困难, 方便地求解了含有无穷大弯曲刚度段的变截面刚架.     

单跨超静定梁在非线性分布温度作用下的载常数

现有结构力学教材中, 一般只给出沿梁截面高度方向线性分布温度变化时的载常数. 而工程上更常见的是非线性分布的温度变化. 本文根据弹性理论首先推出了静定梁在温度变化作用下的杆端位移. 在此基础上, 用力法导出了单跨超静定梁在非线性温度作用下的载常数, 并给出了温度沿截面高度按照指数规律变化时的杆端力, 可供混凝土梁设计参考.     

带弹簧支撑结构的计算方法

针对工程中一类带弹簧支撑结构的静力分析,运用结构分析中的虚功原理推导该类结构位移计算的一般公式,介绍了带弹簧支撑超静定结构的静力分析方法. 经验证,其计算结果与有限元分析结果一致,证明该公式的正确性.     

关于“用过渡法计算超静定结构”论述的商榷

本文指出“基本结构”与“基本体系”是两个不同的概念,在论述“用过渡法计算超静定结构”时,二者应同时给出．     

超静定梁变形计算的积分法

从线性化弯矩和曲率关系出发,将超静定梁多余反力的弯矩叠加到梁截面弯矩中去,经两次积分得到了包括积分常数和多余反力的分段转角方程和挠曲线方程,利用边界条件和连续条件确定积分常数和多余反力,进而确定了转角方程和挠曲线方程.文中工作扩大了积分法的应用范围. 教学实践表明,用积分法解超静定梁的变形能够起到帮助学生学习和掌握固体力学的边值问题解题思想的作用.     

用等效弹簧--质量体系确定单自由度结构的自振频率

基于虚功原理, 将不符合单自由度杆系结构自振频率计算公式的单自由度结构, 转化为一个等效弹簧-质量体系, 从而可用该公式计算其自振频率, 扩大了公式的适用范围. 由于用本文方法计算自振频率, 不必建立动平衡方程, 所以较为简便. 本文结果与按照建立运动微分方程得到的结果完全相同.     

巧解铅球最佳出手角

利用运动叠加原理通过对铅球运动的恰当分解, 提出了一种计算最佳出 手角的新方法, 并与传统方法就两种不同情形进行了对比, 说明了新方法的物理思想.     

具有半刚性节点性质的平面刚架弹簧单元的研究

联合应用力法与逐段刚化法推导出具有半刚性节点性质的弹簧节点梁单元和平面刚架弹簧单元的单元刚度方程. 该方法具有物理概念清楚,推导过程简便、巧妙的特点. 本文所建立的弹簧节点梁单元和平面刚架弹簧单元可以应用在具有半刚性节点性质的工程结构的承载力分析与计算中.     

On an attempt to simplify the Quartapelle–Napolitano approach to computation of hydrodynamic forces in open flows

In this paper we are interested in the Quartapelle–Napolitano approach to calculation of forces in viscous incompressible flows in exterior domains. We study the possibility of deriving a simpler formulation of this approach which might lead to a more convenient expression for the hydrodynamic force, but conclude that such a simplification is, within the family of approaches considered, impossible. This shows that the original Quartapelle–Napolitano formula is in fact “optimal” within this class of approaches.     

Differential quadrature method to stability analysis of pipes conveying fluid with spring support

It is a new attempt to extend the differential quadrature method (DQM) to stability analysis of the straight and curved centerline pipes conveying fluid. Emphasis is placed on the study of the influences of several parameters on the critical flow velocity. Compared to other methods, this method can more easily deal with the pipe with spring support at its boundaries and asks for much less computing effort while giving aceptable precision in the numerical results. Supported by National Key Project of China (No. PD9521907) and the National Science Foundation of China (No. 19872025).     

Effect of static loading on the nonlinear vibrations of a three-time redundant portal frame: Analytical and numerical studies

An analytical study of the nonlinear vibrations in a three-time redundant portal frame is presented herewith, considering the effect of the axial forces caused by the static loading upon the first anti-symmetrical mode (sway) and the first symmetrical mode natural frequencies. It is seen that the axial forces may play an important role in tuning the sway mode and the first symmetrical mode into a 1:2 internal resonance. Harmonic support excitations resonant with the first symmetrical mode are then introduced and the amplitudes of nonlinear steady states are computed based upon a multiple scales solution. Comparisons with numerical analyses using a finite-element program developed by the authors show good qualitative agreement.     

A method to simplify the strength design of bolted joints—Case of connecting-rod bolts

This study shows the development of the strength-design system for general bolted joints. Specifically, a simplified method of the strength design for the connectingrod bolts is proposed. The connecting-rod joint is transformed into a single-bolted-joint model by using the ring model. The axial stress on the bolt and separation behavior at the contact plane are discussed. The strength design of the connecting-rod joint can be performed by applying the unified procedure to the single-bolted-joint model. The local deformation of the connecting-rod joint and the stress on the bolt were measured and the analytical results are compared with the experimental results. Both results show fairly good agreement.     

Stability and bifurcations of an axially moving beam with an intermediate spring support

The forced non-linear vibrations of an axially moving beam fitted with an intra-span spring-support are investigated numerically in this paper. The equation of motion is obtained via Hamilton??s principle and constitutive relations. This equation is then discretized via the Galerkin method using the eigenfunctions of a hinged-hinged beam as appropriate basis functions. The resultant non-linear ordinary differential equations are then solved via either the pseudo-arclength continuation technique or direct time integration. The sub-critical response is examined when the excitation frequency is set near the first natural frequency for both the systems with and without internal resonances. Bifurcation diagrams of Poincaré maps obtained from direct time integration are presented as either the forcing amplitude or the axial speed is varied; as we shall see, a sequence of higher-order bifurcations ensues, involving periodic, quasi-periodic, periodic-doubling, and chaotic motions.     

Non-conservative stability of intermediate spring supported columns with an elastically restrained end support

The non-conservative stability of an intermediate spring supported uniform column clastically restrained at one end and subjected to a follower force at the other unsupported end is studied. It is found that when the intermediate spring support is far from the unsupported end, the instability mechanism is flutter. As the intermediate spring support approaches the unsupported end, the instability mechanism is changed from flutter to divergence with the increase of intermediate spring stiffness. For the hinged-intermediate and guided-intermediatc spring supported columns, the critical buckling load of flutter instability will first decrease, then increase as the intermediate spring stiffness is increased. Nevertheless, when the instability mechanism is divergence, the critical buckling load depends on the location of the intermediate spring support only, whereas for the clamped-intermediate spring supported column the critical buckling load of divergence instability decreases monotonically to a fixed value as the intermediate spring stiffness is increased. Finally, the influence of elastic end restraints on the stability of the column is also investigated.     

微分求积法分析具有弹性支承输液管的临界流速

将微分求积方法推广到分析输液管的临界流速,这是一个新的尝试,与其它数值方法相比,该法极易处理具有弹性边界的输液管,另外,由于避免了一系列数值积分的计算,且最终须求解的方程的阶数较低,故计算量较少,精度令人满意,在此基础上,本文还研究了各参数对临界流速的影响。     

The dynamics of two-dimensional cantilevered plates with an additional spring support in axial flow

In this paper, the dynamics of two-dimensional cantilevered flexible plates in axial flow is investigated using a fluid–structure interaction model. An additional spring support of either linear or cubic type is installed at various locations on the plate; its presence qualitatively affects the dynamics of the fluid–structure system. Without the spring, the cantilevered plate loses stability by flutter when the flow velocity exceeds a critical value; as the flow velocity increases further, the system dynamics is qualitatively the same: the plate undergoes symmetric limit cycle oscillations with increasing amplitude. With a linear spring, a state of static buckling is added to the dynamics. Rich nonlinear dynamics can be observed when a cubic spring is considered; the plate may be stable and buckled, and it may undergo either symmetric or asymmetric limit cycle oscillations. Moreover, when the flow velocity is sufficiently high, the plate may exhibit chaotic motions via a period-doubling route.     

Dynamics of cantilevered pipes conveying fluid. Part 2: Dynamics of the system with intermediate spring support

This paper, the second in a three-part series, deals with the three-dimensional (3-D) nonlinear dynamics of a vertical cantilevered pipe conveying fluid, additionally constrained by arrays of four or two springs or a single spring at a point along its length. Theoretical calculations are presented for the same pipe but different spring configurations, points of attachment and stiffnesses, the main generic difference being this: in some cases, the system loses stability by planar flutter, and thereafter performs two-dimensional (2-D) or 3-D periodic, quasiperiodic and chaotic oscillations; in other cases, the system loses stability by divergence, followed at higher flows by oscillations in the plane of divergence or perpendicular to it, again periodic, quasiperiodic or chaotic. Experiments were conducted for some of the systems studied theoretically, and agreement is found to be generally good, although some open questions remain.     

A method for transforming a full computation of the effects of a complex-explosion scenario to a simple computation by ConWep

When a large amount of explosive that is stored inside a structure explodes, a blast wave is generated. The strength of the blast depends on both the explosive (type and weight) and the properties of the storing structure, since part of the blast energy is needed to destroy the structure. If one is to determine the dynamic load (e.g., pressure and impulse) that is exerted by the blast on a neighboring structure, he needs to conduct a full numerical simulation with a validated numerical code. If the amount of the stored explosive changes while the storing structure remains the same a new full hydrodynamic computation is required. In the present study, we present a method by which, for a given structure inside which explosive is stored, only a few full hydrodynamic computations with different amounts of explosive are required in order to obtain the resulted blast wave load on a neighboring structure that is located at different distances from the exploding structure for any amount of explosive between the minimal and the maximal amounts that were used in the full hydrodynamic computations. By means of the proposed method, the problem, which as mentioned above needs a full hydrodynamic computation, is replaced by an equivalent problem of the explosion of a bare hemispherical charge. The equivalent problem can be solved by means of an empirical model such as ConWep, which is very simple to apply. The solution of the equivalent problem results in identical peak pressure and peak impulse at close and far ranges from the explosion source and very similar pressure and impulse profiles at far ranges. The proposed method is demonstrated by an explanatory example in which the effect of an explosion inside an ammunition magazine on the surroundings is studied.