混凝土损伤组合模型

在AUTODYN软件中成功嵌入了TCK模型,并总结了TCK模型中各参数的确定方法.结合TCK模型的嵌入,对AUTODYN中材料模型的二次开发进行了简要的介绍.应用AUTODYN中二次开发文件的调用规则,实现了TCK模型和RHT模型的组合,得到了组合模型,并指出了组合模型中TCK部分发生的一些变化和组合模型存在的一些问题.应用该组合模型对高速动能杆侵彻混凝土进行了仿真研究,仿真结果与试验结果符合的很好,说明该模型在高速冲击领域有很好的应用前景.     

The two‐dimensional streamline upwind scheme for the convection–reaction equation

This paper is concerned with the development of the finite element method in simulating scalar transport, governed by the convection–reaction (CR) equation. A feature of the proposed finite element model is its ability to provide nodally exact solutions in the one‐dimensional case. Details of the derivation of the upwind scheme on quadratic elements are given. Extension of the one‐dimensional nodally exact scheme to the two‐dimensional model equation involves the use of a streamline upwind operator. As the modified equations show in the four types of element, physically relevant discretization error terms are added to the flow direction and help stabilize the discrete system. The proposed method is referred to as the streamline upwind Petrov–Galerkin finite element model. This model has been validated against test problems that are amenable to analytical solutions. In addition to a fundamental study of the scheme, numerical results that demonstrate the validity of the method are presented. Copyright © 2001 John Wiley & Sons, Ltd.     

复合材料胶接结构有限元分析方法研究进展

胶接结构的强度分析方法可以分为解析法和数值法两类,数值法主要是有限元方法.本文综述了复合材料胶接结构的有限元分析方法,按照胶接结构有限元模型建立的物理机理,将胶接结构力学分析模型分为基于有限元应力分析模型、基于断裂力学模型和基于损伤力学模型3类.详细介绍了这3类模型中的主要有限元建模分析方法:三维应力分析方法、虚拟裂纹闭合技术方法和内聚力模型方法,介绍了每种方法的基本思想、适用范围、优缺点、改进和扩展、有限元建模的实施步骤,以及有限元分析中应用该方法所取得的成果.第五部分从适用范围、应力奇异和破坏判据3个方面对这几种分析模型进行了对比分析.最后,对该领域发展趋势进行了展望.      

Characterization of hole-diameter in thin metallic plates perforated by spherical projectiles using genetic algorithms

The empirical and semi-empirical models available in literature for the estimation of hole-diameter in thin metallic plates by the strike of spherical projectile are mostly valid for the data for which these have been developed. This may be partly attributed to the form of the model employed for their development. The behavioural constraints and the limiting conditions are not satisfied by these models. In the present paper, some of the non-dimensional models have been developed that satisfy the behavioural constraints and limiting conditions. The data used in the development of earlier statistical models has been reanalyzed for the development of new models for the characterization of hole-diameter with a view towards seeing whether better characterization is possible. The genetic algorithm coupled with the penalty function method has been used for the constrained optimization of model parameters that result in low errors and high correlation coefficients.     

Comparison of residual-stress variation with depth-analysis techniques for the hole-drilling method

Numerous data-analysis techniques have been developed to determine residual-stress information from strain data obtained from the hole-drilling method. The most commonly used technique for data analysis was developed by Rendler and Vigness (which forms the basis of the standard described in ASTM E837-85). A numerical development which was a model of the hole-drilling procedure has been used to determine stress variation with depth. A rigorous finite-element method to specifically analyze stresses in discrete hole increments has been developed. To evaluate these data-analysis techniques, three different computer-simulated stress fields are compared. The stress fields include a uniaxial stress that is constant with depth, a bending stress that varies linearly with depth, and a subsurface stress reversal. (The basis for this comparison is a finite-element developed technique. Its accuracy will be discussed later.) All data-analysis techniques showed excellent agreement for the uniaxial stress constant with depth test case. However, for the other two stress fields, significant discrepancies were apparent. Results are compared and discussed.     

The reduced detailed configuration accounting (RDCA) model for NLTE plasma spectral calculations

The purpose of this work is to continue development of a model to provide a fast and accurate in-line NLTE capability for calculating plasma spectral properties in large-scale radiation-transport hydrodynamic simulations. A method has recently been developed to transform the large detailed atomic models into very small models that can be used for fast in-line calculations. The reduced model is more accurate than the average-atom models conventionally used in such simulations. In the present work, spectra calculated with the reduced model are compared to the original detailed model and the average-atom model. The spectra of iron and gold plasmas under various plasma conditions are compared.     

A DEPTH-INTEGRATED 2D COASTAL AND ESTUARINE MODEL WITH CONFORMAL BOUNDARY-FITTED MESH GENERATION

Details are given of the development and application of a 2D depth-integrated, conformal boundary-fitted, curvilinear model for predicting the depth-mean velocity field and the spatial concentration distribution in estuarine and coastal waters. A numerical method for conformal mesh generation, based on a boundary integral equation formulation, has been developed. By this method a general polygonal region with curved edges can be mapped onto a regular polygonal region with the same number of horizontal and vertical straight edges and a multiply connected region can be mapped onto a regular region with the same connectivity. A stretching transformation on the conformally generated mesh has also been used to provide greater detail where it is needed close to the coast, with larger mesh sizes further offshore, thereby minimizing the computing effort whilst maximizing accuracy. The curvilinear hydrodynamic and solute model has been developed based on a robust rectilinear model. The hydrodynamic equations are approximated using the ADI finite difference scheme with a staggered grid and the solute transport equation is approximated using a modified QUICK scheme. Three numerical examples have been chosen to test the curvilinear model, with an emphasis placed on complex practical applications.     

Modeling of the metal powder compaction process using the cap model. Part I. Experimental material characterization and validation

In order to produce crack free metal powder compacts that respect both the dimensional tolerances and the mechanical strength requirements, both tooling design and compaction sequence have to be adequately determined. The finite element method, through the use of an appropriate constitutive model of the powder medium, has recently been used as an efficient design tool. The accuracy of this method highly depends on the faithfulness of the constitutive model and the quality of the material parameter set. Furthermore, in order for the simulation results to be reliable, they should be experimentally validated on real parts featuring density variations. Hence, the main concerns of this paper are the development of a standard calibration procedure for the cap material model as well as the development of a reliable technique for the experimental validation of the powder compaction simulation results.The developed calibration procedure, applied for the case of 316L stainless steel powders, is based on a series of isostatic, triaxial and uniaxial compaction tests as well as resonant frequency tests. In addition, a sensitivity study was performed in order to determine the relative importance of each factor and basic simulations served to validate the parameter set extraction procedure.On the other hand, a local density measurement technique was developed for the experimental validation of the model results. This technique is based on correlation with Vickers macro-hardness. Finally, an application featuring the compaction of a 316L stainless steel cylindrical component is presented to illustrate the predictive capabilities of the cap material model as well as the accuracy of the acquired material parameter set.     

人工黏性增强三维移动粒子半隐算法稳定性

通过综合比较移动粒子半隐方法(moving-particle semi-implicitmethod, MPS)各种稳定性计算方法, 考虑了多种可能导致计算不稳定的因素, 并首次提出加入人工黏性来抑制非物理压力振荡, 得到了较为稳定的三维MPS算法.采用各种稳定性方案对比模拟了三维立方流体旋转状态下的变形及三维静水压问题, 并进一步与商业软件的流体体积函数方法(volumeof fluid, VOF)模型计算结果对比, 验证了其正确性.结果表明:对三维情形, 单纯应用已有的稳定性算法仍难以满足MPS计算稳定性的要求, 而进一步辅以该文提出的人工黏性方法则可以在准确性及稳定性方面均取得较好的效果, 且计算结果显示, 通过该文提出的开关模式增加人工黏性并不影响压强泊松方程的求解精度, 因而不会对流场的求解产生负面作用.     

多尺度材料模拟的自适应有限元方法研究

研究了材料模拟中一类新型耦合多尺度的自适应有限元方法. 采用微观分子动力学耦合宏观有限元的桥尺度方法来模拟材料破坏的前期行为,其中宏观有限元计算推广到了一般非结构三角形网格. 材料破坏形成后,停止微观尺度的计算,它的进一步发展和演化通过一个宏观模型来描述,采用自适应有限元方法来求解这一宏观模型. 其中,后验误差估计的基础是变分多尺度理论,即自适应网格加密是基于粗尺度上残差分布和细尺度上单元Green's函数. 计算中采用了破坏准则来模拟材料的断裂. 数值实验表明了方法的有效性.      

Proper Generalized Decomposition (PGD) for the numerical simulation of polycrystalline aggregates under cyclic loading

The numerical modelling of the behaviour of materials at the microstructural scale has been greatly developed over the last two decades. Unfortunately, conventional resolution methods cannot simulate polycrystalline aggregates beyond tens of loading cycles, and they do not remain quantitative due to the plasticity behaviour. This work presents the development of a numerical solver for the resolution of the Finite Element modelling of polycrystalline aggregates subjected to cyclic mechanical loading. The method is based on two concepts. The first one consists in maintaining a constant stiffness matrix. The second uses a time/space model reduction method. In order to analyse the applicability and the performance of the use of a space–time separated representation, the simulations are carried out on a three-dimensional polycrystalline aggregate under cyclic loading. Different numbers of elements per grain and two time increments per cycle are investigated. The results show a significant CPU time saving while maintaining good precision. Moreover, increasing the number of elements and the number of time increments per cycle, the model reduction method is faster than the standard solver.     

Development of a PLIC-VOF method for the dynamic simulation of entry region flow in a laminar falling film

The present work describes a numerical procedure to simulate the development of hydrodynamic entry region in a gravity-driven laminar liquid film flow over an inclined plane. It provides a better insight into the physics of developing film in entry region. A novel numerical approach is proposed which has the potential to provide solutions for the complex physics of liquid film spreading on solid walls. The method employs an incompressible flow algorithm to solve the governing equations, a PLIC-VOF method to capture the free surface evolution and a continuum surface force (CSF) model to include the effect of surface tension. To account for the moving contact line on the solid substrate, a precursor film model based wall treatment is implemented. Liquid film flow has been simulated for the Reynolds number range of 5 ≤ Re ≤ 37.5, and the predicted results are found to agree well with the available analytical and experimental data.     

Methodology for the Stress Measurement of Ferromagnetic Materials by Using Magneto Acoustic Emission

Magneto acoustic emission (MAE) is a magnetic nondestructive testing (NDT) method that has been used in different fields for 30 years. MAE is a promising method for the early characterization of damage and the evaluation of the residual stress of ferromagnetic materials. However, this technique is still in its early stage and requires further development. The mechanism and influence factors of MAE are still under investigation. Quantitative NDT is difficult because of the lack of robust theoretical bases and models. In this study, we investigated the influence factors of MAE signals systematically and established a mathematical model to describe these influences. The special design of the specimen and the precise control of experimental conditions are the key points for obtaining reasonable experimental results and for developing the model. A methodology for stress assessment was developed on the basis of the proposed model and was verified by using the pure bending test. Results show that stresses within a measureable depth of 4 mm can be evaluated and that the maximum testing error is 30 %.     

光测力学技术：连接虚拟空间和现实世界的纽带

在轿车的整个开发过程中，零部件、总成和整车产品都必须根据试验结果验证和优化，在轿车开发的过程中测试技术是连接设计师思维空间和现实空间的纽带，现代光学测试技术以数字图象数据处理技术为基础，融汇贯通高速宽带数字采样、数据库和数据自动分析以及计算机智能工程及专家系统等最新技术，巧妙应用于轿车开发过程，在满足计算机虚拟开发工程对测试技术新要求的同时，还可以优化轿车开发程序，提高开发质量，本文以作者多年来在德国轿车开发部门主持的现代测试技术项目的实例介绍采用光测技术解决开发程序中的问题的构想，方法和手段。     

FE Formulation of Detonation Important by the Stabilized Galerkin Method

We introduce a finite element formulation of Detonation problems. The detonation involves supersonic combustion waves which emanate from an exothermic chemical reaction occurring behind propagating shock waves. The development of geometrically versatile schemes is required to meet practical needs. The Galerkin/Least-squares method with entropy variables possesses good accuracy and stability properties. As a first attempt to handle chemical reaction model, we use a simple two front model which has a good performance and a flexibility in adapting to the experimental data. It is emphasized that the process of generation and propagation of the shock triple points has been demonstrated.     

基于深度学习的超高速碰撞碎片云生成模型

数据驱动的模型已经被广泛研究,并成功应用到了计算力学。基于深度学习技术,提出一种新的采用数据驱动的碎片云生成模型。此模型可以学习SPH数值模拟结果,然后在多种控制条件下快速生成碎片云。在模型训练前的数据预处理阶段,对SPH模拟结果进行空间网格划分和质量聚合,实现了改善数据分布规律、加速模型训练和提升模型泛化性的目的。以高速靶球撞击薄壁圆筒后的碎片云质量分布为例,模拟并测试了多种控制条件下深度学习模型计算结果的正确性和稳定性,以及计算速度的高效性。实验证明,深度学习模型可以从训练集学习碎片云的物理规律,然后在训练集控制参数范围内进行良好的推理及插值;并且可以在训练数据集控制参数范围外,进行小范围推理预测;同时深度学习模型的计算速度远快于SPH方法。通过深度学习方法建立碎片云模型,可能是一种在空间飞行器防护结构原型设计阶段,实现碎片云实时生成的潜在方案。     

基于深度学习的超高速碰撞碎片云生成模型

数据驱动的模型已经被广泛研究,并成功应用到了计算力学。基于深度学习技术,提出一种新的采用数据驱动的碎片云生成模型。此模型可以学习SPH数值模拟结果,然后在多种控制条件下快速生成碎片云。在模型训练前的数据预处理阶段,对SPH模拟结果进行空间网格划分和质量聚合,实现了改善数据分布规律、加速模型训练和提升模型泛化性的目的。以高速靶球撞击薄壁圆筒后的碎片云质量分布为例,模拟并测试了多种控制条件下深度学习模型计算结果的正确性和稳定性,以及计算速度的高效性。实验证明,深度学习模型可以从训练集学习碎片云的物理规律,然后在训练集控制参数范围内进行良好的推理及插值;并且可以在训练数据集控制参数范围外,进行小范围推理预测;同时深度学习模型的计算速度远快于SPH方法。通过深度学习方法建立碎片云模型,可能是一种在空间飞行器防护结构原型设计阶段,实现碎片云实时生成的潜在方案。     

An implicit numerical algorithm for solving non‐hydrostatic free‐surface flow problems

Details are given of the development of a two‐dimensional vertical numerical model for simulating unsteady free‐surface flows, using a non‐hydrostatic pressure distribution. In this model, the Reynolds equations and the kinematic free‐surface boundary condition are solved simultaneously, so that the water surface elevation can be integrated into the solution and solved for, together with the velocity and pressure fields. An efficient numerical algorithm has been developed, deploying implicit parameters similar to those used in the Crank–Nicholson method, and generating a block tri‐diagonal algebraic system of equations. The model has been applied to simulate a range of unsteady flow problems involving relatively strong vertical accelerations. The results show that the numerical algorithm described is able to produce accurate predictions and is also easy to apply. Copyright © 2001 John Wiley & Sons, Ltd.