微重环境下Cassini贮液腔中液体晃动特性研究

针对我国某一型号大型卫星液体燃料Cassini贮箱（腰为圆柱,两底为半球）,应用有限元方法研究了微重环境下液体的小幅晃动问题和横向受迫晃动问题,采用Galerkin方法得到了系统的有限元离散方程；得到了晃动固有频率和等效力学模型参数.针对周期脉冲激励,推导了液体作用于贮箱壁的晃动力和晃动力矩计算公式并给出了数值计算结果和分析结论.     

挠性加速度计石英摆片的微运动仿真分析

加速度计石英摆片的微运动仿真分析可以获取帮助提高石英挠性加速度计生产质量的技术手段和途径。从加速度计石英摆片的物理模型入手,用有限元方法对摆式加速度计的关键部件石英摆片进行静力计算与模态分析,直观地显示了石英摆片结构的应力场与形变场,获得了各阶自然频率和阵型。结果表明：采用有限元分析的方法能够辅助提高加速计的性能。     

Numerical Modeling and Experimental Validation of Free Surface Flow Problems

In this paper we present a summary of numerical methods for solving free surface and two fluid flow problems. We will focus the attention on level set formulations extensively used in the context of the finite element method. In particular, numerical developments to achieve accurate solutions are described. Specific topics of the algorithms, like mass preservation and interface redefinition, are evaluated. To illustrate these aspects, numerical strategies previously developed are applied to the solution of a sloshing and a water column collapse problems. To assess the capabilities of these techniques, the numerical results are compared against each other and with experimental data. Considering these aspects, the present work is aimed to outline some well reported aspects of level set-like formulations.     

Spar平台月池水晃动的等效力学模型及模型参数研究

研究深海Spar平台月池水晃动的等效力学模型,确定模型参数.基于势流理论推导了月池内水体运动的动力学方程,建立了月池内水体晃动的等效单摆模型.采用ANSYS软件建立模型并进行网格划分,采用Matlab软件进行数值计算.运用Galerkin方法求解水体晃动的固有频率、模态函数以及势函数离散解,确定等效单摆模型的模型参数.对比分析了数值模拟结果与解析解,验证了本文计算方法的正确性.建立了不同月池水高度的等效力学模型参数库,为进一步研究平台-月池内流体的耦合运动奠定了基础.     

Frameworks for finite strain viscoelastic-plasticity based on multiplicative decompositions. Part I: Continuum formulations

The present work deals with studies on viscoelastic-plasticity at finite strains. Different forms can be proposed for the combination of plasticity and viscoelasticity mechanisms. In the present work, we propose two different formulations, each of them is motivated by a distinct simple one-dimensional rheological model. These different rheological models suggest different kinematic assumptions at finite strains which in turn lead to different local governing equations issued from thermodynamically consistent frameworks. However, one of the common features characterizing the two formulations is the use of local multiplicative decompositions of the deformation gradient. Model examples issued from these formulations are proposed. They are suitable for the simulation of filled rubbers, polymers and polymeric foams. Computational aspects and numerical examples within the framework of the finite element method are addressed in detail in Part II of this work.     

On various formulations of large amplitude free vibrations of beams

Various finite element formulations of large amplitude free vibrations of beams with immovably supported ends are discussed in this paper. Analytical formulation based on the Rayleigh-Ritz method is also presented. Numerical results of the analytical approach are seen to be in good agreement with some of these finite element formulations. Mixed finite element formulations based on two methods are derived to study the large amplitude free vibrations of beams. The mixed finite element methods also show good agreement with the analytical and the above finite element formulations. Various points of view raised from time to time on the applicability of these formulations can now be clarified through these formulations and the numerical results. The weakness of the so-called improved Ritz-type finite element model in predicting the nonlinear frequency ratio is highlighted through various results of the above formulations. As a typical example, a hinged-hinged beam on immovable ends is considered for all the above formulations and the nonlinear frequencies show a good agreement amongst themselves at all amplitude levels.     

基于射频技术的油罐车在途状态监测系统设计

针对油罐车罐体温度过高、罐体倾斜、阀门漏油等问题,文章设计了基于射频一体化芯片SI1000的油罐车罐体状态监测系统,车载终端控制单元以S3C2440A为主控制器,SI1000芯片为从控制器,设计了主从结构的片上系统(SOC)方案,提出了各个模块的硬件设计和软件流程;该罐体状态监测系统应用GPRS技术、GPS技术以及温度传感器、倾角传感器、铅封锁能够对车辆位置、罐壁温度、罐体倾角、油阀状态等参数进行远程在线监测;通过实验测试,各个参数的测量误差值在5%以内,且系统运行情况良好,符合系统设计需求。     

FEM considering local bending effects for flat sliding isolators

Presented in this paper are an advanced analytical model and finite element formulations including the local bending moment effect for the flat sliding system. This study reveals that the local bending effect is a very important factor. The results presented in this paper show that the design of the isolation without considering this effect may endanger structures during earthquakes. The new formulations taking into consideration the local effect provide an effective tool for the more realistic simulation of the behavior of flat-sliding-isolated structures subjected to earthquake loadings. The proposed finite element formulations can be applied directly for both two- and three-dimensional analyses without any further assumption, and can generally be placed at any location in the structure. The implementation of the proposed techniques in existing finite element computer codes is a simple task. Examples of structures equipped with flat-sliding isolators is also given to demonstrate the paramount findings through the proposed formulations. Results obtained from the numerical analyses suggest that the local bending moment effects are extremely important, and should be taken into account to assure the safety of isolated-structures during earthquakes.     

Parallel 3D computation of unsteady flows around circular cylinders

In this article we present parallel 3D finite element computation of unsteady incompressible flows around circular cylinders. We employ stabilized finite element formulations to solve the Navier-Stokes equations on a thinking machine CM-5 supercomputer. The time integration is based on an implicit method, and the coupled, nonlinear equations generated every time step are solved iteratively, with an element-vector based evaluation technique. This strategy enables us to carry out these computations with millions of coupled, nonlinear equations, and thus resolve the flow features in great detail. At Reynolds number 300 and 800, our results indicate strong 3D features arising from the instability of the columnar vortices forming the Karman street. At Re = 10 000 we employ a large eddy simulation (LES) turbulence model.     

The Data Analyses of a Vertical Storage Tank Using Finite Element SOFT Computing

With the rapid development of the petrochemical industry, the number of largescale oil storage tanks has increased significantly, and many storage tanks are located in potential seismic regions. It is very necessary to analyze seismic response of oil storage tanks since their damage in an earthquake can lead to serious disasters and losses. In this paper, three models of vertical cylindrical oil storage tank in different sizes, which are commonly used in practical engineering are established. The dynamic characteristics, sloshing wave height and hydrodynamic pressure of the oil tank considering the liquid-structure coupling effect are analyzed by using ADINA finite element software, which are compared with the result of the standard method. The close numerical values of both results have verified the correctness and reliability of finite element model. The analytic results show that liquid sloshing wave height is basically in direct proportion to ground motion peak acceleration, the standard method of portion sloshing wave height calculation is not conservative. The hydrodynamic pressure generated by liquid sloshing caused by ground motion is not negligible compared with the hydrostatic pressure. The tank radius and oil height have a significant effect on the numerical value of hydrodynamic pressure. The ratio of the hydrodynamic pressure and hydrostatic pressure, which is named hydraulic pressure increase coefficients, is related to the height, which given by the GB 50341-2014 code in China have a high reliability. The seismic performances of tank wall near the bottom needs to be enhanced and improved in the seismic design of the oil tank.     

输入饱和的充液航天器抗干扰有限时间滑模控制

研究三轴稳定充液航天器姿态控制过程中存在外部未知干扰、参数不确定和输入饱和的问题,提出一种抗干扰有限时间滑模控制的姿态机动控制方法.将部分充液贮箱内液体燃料晃动等效为球摆模型,采用动量矩守恒定律推导出充液航天器耦合动力学方程.首先,设计有限时间积分滑模干扰观测器,保证控制系统中集总干扰可以在有限时间内被估计;然后,基于所设计的干扰观测器,提出一种抗干扰有限时间快速终端滑模控制策略,并且证明在该控制律的作用下闭环系统的状态是有限时间稳定的,而且收敛到指定的快速终端滑模面上.此外,通过引入辅助变量补偿控制输入超调量,克服输入饱和的约束.仿真结果验证了该控制策略的有效性和鲁棒性.     

Object-Oriented Symbolic Derivation and Automatic Programming of Finite Elements in Mechanics

Symbolic approaches to assist in the development of finite element formulations have been used since the late 1970s. Today, symbolic mathematical software such as Mathematica, Maple, etc., has proved to be helpful when testing formulations. In earlier work, the authors introduced a new way of integrating naturally symbolic concepts in numerical finite element codes, taking advantage of an objectoriented code organization. In this paper, we wish to prove on practical examples that the proposed approach is very attractive and promising today, leading to an alternative way of conceiving finite element codes. After presenting a state-of- the-art of symbolic approaches for finite element developments, we first give a practical application of symbolic developments (for discontinuous space-time formulations), and then examples of Computer Aided Software Engineering tools that can be introduced into such a finite element environment.     

圆柱形贮箱液晃系统稳定性边界分析

本文研究了纵向激励下液晃系统的稳定性边界.首先利用等效摆模型获得纵向激励下液体晃动的等效动力学Mathieu方程,然后利用摄动法得到随阻尼、储液高度及贮箱直径变化时的液晃系统的稳定区域.结果表明,液体晃动阻尼、储液量及贮箱尺寸对晃动稳定性具有显著影响.     

Discontinuous subgrid formulations for transport problems

In this paper we develop two discontinuous Galerkin formulations within the framework of the two-scale subgrid method for solving advection–diffusion-reaction equations. We reformulate, using broken spaces, the nonlinear subgrid scale (NSGS) finite element model in which a nonlinear eddy viscosity term is introduced only to the subgrid scales of a finite element mesh. Here, two new subgrid formulations are built by introducing subgrid stabilized terms either at the element level or on the edges by means of the residual of the approximated resolved scale solution inside each element and the jump of the subgrid solution across interelement edges. The amount of subgrid viscosity is scaled by the resolved scale solution at the element level, yielding a self adaptive method so that no additional stabilization parameter is required. Numerical experiments are conducted in order to demonstrate the behavior of the proposed methodology in comparison with some discontinuous Galerkin methods.     

An extended residual-based variational multiscale method for two-phase flow including surface tension

In this study, an extended residual-based variational multiscale method is proposed for two-phase flow including surface tension. The extended residual-based variational multiscale method combines a residual-based form of the variational multiscale method and the extended finite element method (XFEM). By extending the solution spaces, it is possible to reproduce discontinuities of the solution fields inside elements intersected by the interface. In particular, we propose a quasi-static enrichment to reproduce time-dependent discontinuities. Kink enrichments of both velocity and pressure as well as kink enrichments of velocity combined with jump enrichments of pressure are considered here. To capture the interface between the phases on a fixed grid, a level-set approach is used. A residual-based variational multiscale method is employed for computing both flow and interface motion. The presented method is tested for various two-phase flow examples exhibiting small and large density and viscosity ratios, with and without surface tension: a two-phase Couette flow, a Rayleigh–Taylor instability, a sloshing tank and a three-dimensional rising bubble. To the best of our knowledge, these are the first simulation results for representative time-dependent three-dimensional two-phase flow problems using an extended finite element method. Stable and accurate results are obtained for all test examples.     

基于流固耦合的非满载液罐车制动性能分析

为研究非满载充液罐车紧急制动过程中液体晃动剧烈程度,采用有限单元法对液罐车减速过程中液体晃动进行模拟.分析了相同充液比下全防波板的数量差异、相同表面积的部分防波板安装位置对液体冲击力的影响,同时,将液体压力作为负载加载到防波板上研究防波板应力变化.仿真结果得出：纵向布置的全防波板随数量的增加,可以明显降低减速过程中液体对前封头的冲击力；与相同表面积的下端防波板相比,上端防波板对降低冲击力的影响较小；将液体晃动得到的压力作为防波板载荷输入,应力最大值出现在第二块防波板处.     

Finite element analysis of viscous fluid flow

A finite element model for the analysis of two dimensional viscous flows is formulated using the virtual work method. The model is in part based on a finite element shell model, using the same reduced integration of quadratic interpolations for all variables[1]. Differences from preceding formulations are that integration by parts is applied to the continuity equation, yielding different loading terms which are more easily defined in some problems, and a new approach is used for the convective inertia terms, giving a clearer interpretation of their effects which are distributed to both sides of the nonlinear recurrence relation. In the case of compressible flow, for which comparatively few formulations have been proposed to date, the thermal energy equation is used to form a two stage solution and here this seems the most natural and economical approach.     

Boundary Element Simulation of Thermal Waves

In this paper we survey computational techniques based on boundary integral formulations for the simulation of thermal waves. Time-harmonic solutions to diffusion problems appear in many physical situations of interest and give rise to many interesting problems related to material characterization, parameter assessment or detection of defects. We review the main direct, indirect and mixed integral numerical methods for a model of scattering of thermal waves by many obstacles and discuss how multiple scattering techniques and other physical tools can be understood as iterative methods or used as preconditioners. We also deal with some transient problems that can be solved with boundary element methods using the Laplace transform and with coupled finite and boundary element schemes for non-homogeneous obstacles.