结构动力优化设计述评与展望

结构动力优化设计是当前工程结构设计研究领域中的前沿性课题。文中着重从结构动力特性优化、结构动力响应设计、结构动力灵敏度分析和基于可靠性的结构动力优化设计等四个专题方面对结构动力优化设计研究的发展与现状进行了述评,并粗略地展望了结构动力优化研究未来的发展趋势。      

船舶动力定位系统

随着深海技术的不断发展,动力定位系统的在海洋工程上得到广泛应用。动力定位系统通过其控制系统驱动船舶推进器来抵消风、浪、流等作用于船上的环境外力,从而使船舶保持在确定的位置上或沿预期的航迹航行。本文在分析了国际海事组织和国际海洋工程承包商协会对动力定位系统定义及分级要求的基础上,阐述了国外船舶动力定位系统的发展及其应用状况,分析了动力定位系统的组成和工作原理,研究了动力定位系统的各种约束、控制策略、控制技术、推力分配等关键技术,指出动力定位系统精度取决于控制系统和测量系统性能,并提出了发展国产动力定位系统应采用的途径。     

节理岩体边坡的动力稳定性分析

阐述了动力离散元的原理及计算方法, 并将其用于一个受高烈度地震威胁的滑节理岩体边坡的动力响应分析与动力稳定性评价, 阐明了滑坡动力稳定性分析的必要性。     

结构随机动力稳定性的定量分析方法

提出了结构随机动力稳定性的定量分析方法,讨论了经典的随机动力稳定性概念,指出结构动力稳定性不仅与结构参数有关,也与作用在结构上的外部载荷密切相关,据此引入了一种判定结构动力稳定性的新准则,明确了结构随机动力稳定性的基本涵义.在概率守恒原理基础上,推导了概率耗散系统的广义概率密度演化方程.引入结构动力失稳的物理机制作为引起概率耗散的驱动力,利用概率耗散系统概率密度演化方程、可以方便获得结构响应的概率密度演化过程,从而定量求解结构的动力稳定概率.据此,可以定量评价结构系统依概率为1或依给定概率意义上的结构随机动力稳定性.采用本文所建议方法对典型结构动力系统进行了随机动力稳定性分析,并与蒙特卡洛方法计算结果进行对比.数值结果表明了所建议方法的有效性.      

动力猫道提升过程动力学建模与分析

举升式动力猫道在提升过程中,拉力的变化较大,设计时需要确定提升过程中拉力的变化规律以及所需的最大拉力值.基于此,结合动力猫道提升过程的边界条件,推导了动力猫道提升各阶段的几何方程,应用达朗贝尔原理建立了4个阶段的动力学方程.通过建立的4个阶段的动力学模型,采用C#软件调用Matlab程序求解方程,编写了动力猫道提升动力学的软件.应用该软件分析了所设计动力猫道提升过程中拉力的变化规律,并对其规律进行了分析,相关计算结果表明所设计的动力猫道满足现场使用的要求,为动力猫道的现场使用提供了重要的参考,为动力猫道进一步的优化、性能提升奠定了基础.     

动力损伤后的脆性岩石静力蠕变断裂模型研究

应力波动力扰动下脆性岩石的静力蠕变特性,对深部地下工程围岩变形的评价有重要的实践意义.动力载荷作用导致的局部细观裂纹损伤严重影响脆性岩石蠕变力学行为.基于细观裂纹扩展与应力关系模型、动力扰动损伤演化函数、静动力载荷演化路径函数与黏弹性本构模型,提出一种应力波动力扰动下脆性岩石蠕变断裂特性的宏细观力学模型.其中动力损伤通过控制岩石内部细观裂纹数量变化实现.模型描述了应力波动力扰动下岩石的应变时间演化曲线,解释了岩石动力扰动下蠕变失效特性.研究了不同应力波幅值及周期影响下的脆性岩石应变-时间关系曲线,并通过试验结果验证了模型的合理性.讨论了动力损伤变化形式,突变发生时刻,突变量的大小对岩石蠕变失效特性的影响.分析了应力波幅值、周期对岩石动态动力损伤效应以及蠕变失效特性的影响.主要研究结果:动力损伤的变化值越大,岩石蠕变失效发生时间越短.冲击载荷扰动期间,动力损伤发生的时刻及增加的形式,对动力扰动后的岩石应变及蠕变破坏时间影响很小.动力损伤变化量随应力波幅值增加、周期减小而加速增大.应力波幅值越大、周期越小,岩石发生蠕变失效时间越短.     

结构-地基系统静-动力联合分析模型

以有限区域模拟无限区域的动力计算必须考虑边界上波的传播效应,应不使波在边界上发生反射再返回到计算域中,并且应考虑初始静力场对其动力反应的影响。因此,基于无限元的静、动力特性提出静-动力统一无限元,通过算例验证无限元静-动力统一人工边界在静-动力联合分析模型中的精度和稳定性。结果表明:无限元静-动力统一人工边界在静力、动力及静-动力联合分析模型中具有很高的精度和良好的稳定性,突破了传统动力人工边界不能兼顾静力效应的局限。     

固定式海洋平台结构分析程序——DASOS-J(D)的动力分析策略

本文简述了在固定式海洋平台动力分析程序DASOS-J(D)中发展及使用的各种动力分析策略。它以结构分析通用程序JIGFEX为基础,全部动力分析都可采用三维多层子结构模型。在自振特性计算、确定性或随机性动力响应分析等一系列模块中,不但考虑了我国规范和国际惯例的要求,而且发展了一些新的有效方法,使动力分析更为准确、方便与经济。     

基础振动动力响应的边界单元分析

本文应用边界单元法对基础振动的动力响应进行了数值求解。结构的弹性动力微分方程在通过Laplace积分变换后,可以得到弹性动力的基本边界积分方程。然后在变换空间内划分边界单元进行数值求解。最后通过Laplace的数值逆变换求得时间域内的动力响应值。文中对刚性的动力基础,在简谐荷载的作用下,对于不同频率、不同压缩层厚度和基础埋深等动力响应进行了计算与探讨。     

非线性碟簧动力吸振器的宽带数值优化设计及其应用

提出了非线性碟簧动力吸振器的宽带数值优化设计,推广了前人在非线性动力吸振器领域的研究．首先提出了计算耦合非线性动力吸振器的主系统的稳态响应的平均法,然后采用数值优化法详细的研究了非线性动力吸振器的宽带优化设计,系统讨论了质量比、主系统阻尼比、吸振器阻尼比、系统频率比、激励频率比、位移比、吸振器刚度非线性系数和吸振器阻尼非线性系数与抑振带宽的关系;最后考虑了非线性动力吸振器的应用实例,指出非线性动力吸振器可以显著拓宽抑振频带．     

Comparison of methods for calculating the shock hugoniot of mixtures

Various methods used to determine the shock Hugoniot of condensed phase multi-component mixtures are reviewed and compared to available experimental data. The assumptions inherent in the different models are presented in this overview and their implications are discussed. The comparisons of the various models demonstrate that the predicted shock Hugoniots are in good agreement with published data despite the simplifying assumptions that are associated with the models. Averaging models are shown to be among the simplest methods to implement and result in the closest agreement with experimental data.     

Natural harmonic oscillations of a heavy fluid in basins of complex shape

The natural harmonic oscillations of a heavy fluid in uniform-depth basins of complex shape, including those with three or more symmetry axes, are investigated within the shallow-water approximation. The waves are assumed to be gently sloping. The modes found are compared with the similar modes in an elliptic basin representing the class of basins with two symmetry axes. The mode characteristics associated with the number of basin symmetry axes and the basin shape are explored. Basins with two symmetry axes whose shape differs considerably from the elliptic, in particular, nonconvex basins, are considered. Both rotating and non-rotating basins are studied. The possibility of approximating the amplitudes of certain rotating-basin mode classes by Bessel functions is discussed.     

Experimental Validation of Reduction Methods for Nonlinear Vibrations of Distributed-Parameter Systems: Analysis of a Buckled Beam

An experimental validation of the suitability of reduction methods for studying nonlinear vibrations of distributed-parameter systems is attempted. Nonlinear planar vibrations of a clamped-clamped buckled beam about its first post-buckling configuration are analyzed. The case of primary resonance of the nth mode of the beam, when no internal resonances involving this mode are active, is investigated. Approximate solutions are obtained by applying the method of multiple scales to a single-mode model discretized via the Galerkin procedure and by directly attacking the governing integro-partial-differential equation and boundary conditions with the method of multiple scales. Frequency-response curves for the case of primary resonance of the first mode are generated using both approaches for several buckling levels and are contrasted with experimentally obtained frequency-response curves for two test beams. For high buckling levels above the first crossover point of the beam, the computed frequency-response curves are qualitatively as well as quantitatively different. The experimentally obtained frequency-response curves for the directly excited first mode are in agreement with those obtained with the direct approach and in disagreement with those obtained with the single-mode discretization approach.     

Visualization of flow boiling of liquid nitrogen in a vertical mini-tube

The flow boiling patterns of liquid nitrogen in a vertical mini-tube with an inner diameter of 1.931 mm are visualized with a high-speed digital camera. The superficial gas and liquid velocities are in the ranges of 0.01–26.5 m/s and 0.01–1.2 m/s, respectively. Four typical flow patterns, namely, bubbly, slug, churn and annular flow are observed. Some interesting scenes about the entrainment and liquid droplet deposition in the churn and annular flow, and the flow reversal with the indication of negative pressure drop, are also presented. Based on the visualization, the two-phase flow regime maps are obtained. Compared with the flow regime maps for gas–water flow in tubes with similar hydraulic diameters, the region of slug flow in the present study reduces significantly. Correspondingly, the transition boundary from the bubbly flow to slug flow shifts to higher superficial gas velocity, and that of churn to annular flow moves to lower superficial gas velocity. Moreover, time-averaged void fraction is calculated by quantitative image-digitizing technique and compared with various prediction models. Finally, three kinds of oscillations with long-period and large-amplitude are found, possible explanation for the oscillations is given by comparing the instantaneous flow images with the data of pressure, mass flux and temperature recorded synchronously.     

Application of streamwise diffusion to time-dependent free convection of liquid metals

A numerical analysis is given for the application of streamwise diffusion to high-intensity flows with marginal spatial resolution. Terms are added to the momentum equation which are similar to those used in the Petrov-Galerkin, Taylor-Galerkin and balancing tensor diffusivity methods. Values for the streamwise viscosity are obtained from mesh refinement studies. An illustration is given for the time-dependent free convection of a liquid metal in a cavity with differentially heated sided walls. The spatial problem is solved with the Galerkin finite element method and the time integration is performed with the backward Euler method. Solution quality and computation time are compared for results with and without added streamwise diffusion. For the cases presented, streamwise diffusion eliminates spurious oscillations and saves computation time without compromising the solution.     

Simulation of impacts of fluid free surfaces with solid boundaries

Deficiencies associated with the simulation of impacts of fluid free surfaces with solid boundaries by use of marker-and-cell methods are identified and addressed. New procedures are introduced that affect the movement of markers in cells adjacent to a solid boundary, the flags of the cells that comprise a solid boundary and the pressure boundary condition for a cell in which impact occurs. Combined with fundamental changes in the sequence of steps in the computational cycle, these new procedures allow the intentional treatment of impact. As a result, improved estimates are obtained of the pressure associated with the cells adjacent to a boundary along which impact occurs. Consequently, more appropriate adjustments are made of the tentative internal velocities associated with such cells. In addition, a special procedure is presented for the adjustment of the tentative internal velocity between two surface cells. Finally, a new cell type termed a corner cell is defined and a procedure for its treatment is presented. Numerical examples are included to illustrate the previous deficiencies associated with the simulation of impact as well as the effectiveness of the new methods presented in this paper. Validation of the new methods is achieved by comparison with experimental results for spillage over a containment dike.     

Experimental investigation of slosh dynamics of liquid-filled containers

This paper is concerned with the experimental studies on the sloshing response of liquid-filled containers. A three-dimensional finite element analysis is carried out for the numerical simulation of this problem. The effects of sloshing are computed in the time domain using Newmark's time integration scheme. A simple experimental setup is designed and fabricated in-house to conduct experiments for measuring some of the basic parameters of sloshing. A sensor device is especially developed to record the free-surface wave heights. Each wave height sensor is a capacitance probe that detects the change in level of liquid (water) precisely with no time lag. The sensors are used in conjunction with a signal-processing unit in which the capacitance values are transduced to a voltage signal between 0 V and 10 V. These wave height sensors simultaneously record the slosh wave height near the periphery of the container wall from 16 predetermined locations to give the free-surface profiles of liquid at desired time steps. The experimental results are compared with those obtained from the present theoretical analysis, and good agreements are observed.     

Experimental Study of the Dynamic Flexural Strength of Concrete

In this paper, we analyze the increase in the dynamic flexural strength of concrete according to strain rate. A simple beam with center-point loading and a classical electro-mechanical testing machine are used to determine the static flexural strength. The dynamic measurements are conducted using a split Hopkinson pressure bar (SHPB) device in the same three-point bending configuration. The outer faces of the beams are instrumented with strain gauges to record the extreme tensile strains. Moreover, full-field displacement measurements are obtained using digital image correlation (DIC) on images recorded by a very high-speed camera. The strain gauge and DIC measurements are compared and used to determine the onset of failure and to evaluate the rate-related tensile strength. Several tests are performed at strain rates in the range from 1/s to 15/s. As expected, a significant increase in the flexural tensile strength with strain-rate is observed, which is consistent with results from the literature.     

Effects of multiple structural nonlinearities on limit cycle oscillation of missile control fin

Aeroelastic analyses are performed for a 2-D typical section model with multiple nonlinearities. The differences between a system with multiple nonlinearities in its pitch and plunge spring and a system with a single nonlinearity in its pitch are thoroughly investigated. The unsteady supersonic aerodynamic forces are calculated by the doublet point method (DPM). The iterative V-g method is used for a multiple-nonlinear aeroelastic analysis in the frequency domain and the freeplay nonlinearity is linearized using a describing function method. In the time domain, the DPM unsteady aerodynamic forces, which are based on a function of the reduced frequency, are approximated by the minimum state approximation method. Consequently, multiple structural nonlinearities in the 2-D typical wing section model are influenced by the pitch to plunge frequency ratio. This result is important in that it demonstrates that the flutter speed is closely connected with the frequency ratio, considering that both pitch and plunge nonlinearities result in a higher flutter speed boundary than a conventional aeroelastic system with only one pitch nonlinearity. Furthermore, the gap size of the freeplay affects the amplitude of the limit cycle oscillation (LCO) to gap size ratio.     

Elastic analyses of heterogeneous hollow cylinders

Two different kinds of heterogeneous elastic hollow cylinders are studied in the present paper. One is a multi-layered cylinder with different values in different layers for both elastic modulus and Poisson’s ratio. Another is an elastic hollow cylinder with continuously graded material properties. By introducing two recursive algorithms, the extrusion stresses between two neighbor layers in the multi-layered cylinder submitted to uniform pressures on the inner and outer surfaces can be simply determined. Then the exact solutions of the multi-layered structure can be found based on Lamé’s solution. For the hollow cylinder with continuously graded properties, the displacement method is used. Both Whittaker equation and hyper-geometric equation are derived and successfully solved, and then the exact solutions are found. The results obtained in the present paper are compared with the numerical solutions and good agreements are found. At the end of the present paper, some inherent properties of these two different kinds of heterogeneous elastic hollow cylinders are presented and discussed. The results obtained in the present paper are useful in the design and analysis for composites reinforced by unidirectional fiber layers.