THE FLOW RESISTANCE CHARACTERISTICS OF PERFORATED LINER DUCTS

利用计算流体力学方法对穿孔壁面通道内部流动进行了数值模拟,分析了其流动沿程摩擦阻力特性。计算中,假设流体不通过小孔进出穿孔壁面背后的吸声材料。经实验对比,采用Realizable k--" 湍流模型结合增强型壁面函数,可获得比较理想的计算结果,数值模拟与实验测量的压损值相对偏差在10% 以内。对于穿孔壁面通道流动阻力计算,提出了等效粗糙度概念,结合达西公式、克罗布鲁克公式计算获得了等效粗糙度数值。研究了穿孔板小孔孔径、穿孔率对等效粗糙度的影响,发现等效粗糙度与孔径成二次方关系、与穿孔率成线性关系。     

A computational homogenization approach for the yield design of periodic thin plates. Part I: Construction of the macroscopic strength criterion

The purpose of this paper is to propose numerical methods to determine the macroscopic bending strength criterion of periodically heterogeneous thin plates in the framework of yield design (or limit analysis) theory. The macroscopic strength criterion of the heterogeneous plate is obtained by solving an auxiliary yield design problem formulated on the unit cell, that is the elementary domain reproducing the plate strength properties by periodicity. In the present work, it is assumed that the plate thickness is small compared to the unit cell characteristic length, so that the unit cell can still be considered as a thin plate itself. Yield design static and kinematic approaches for solving the auxiliary problem are, therefore, formulated with a Love–Kirchhoff plate model. Finite elements consistent with this model are proposed to solve both approaches and it is shown that the corresponding optimization problems belong to the class of second-order cone programming (SOCP), for which very efficient solvers are available. Macroscopic strength criteria are computed for different type of heterogeneous plates (reinforced, perforated plates,…) by comparing the results of the static and the kinematic approaches. Information on the unit cell failure modes can also be obtained by representing the optimal failure mechanisms. In a companion paper, the so-obtained homogenized strength criteria will be used to compute ultimate loads of global plate structures.     

三维自适应FE-SPH耦合算法在多层间隔金属靶侵彻问题中的应用

鉴于有限元算法不能有效地模拟侵彻过程所产生的金属碎片, 本文中基于三维自适应FE-SPH耦合算法的基本理论, 自主开发了模拟多层间隔金属靶侵彻问题的三维FE-SPH耦合计算程序。该程序采用四面体单元对多层间隔金属靶侵彻模型进行初始离散, 计算过程中, 当四面体单元等效塑性应变超过某一设定值时, 单元自动转化为SPH粒子, 并引入有限单元-粒子接触算法和耦合算法, 实现大变形和破碎区域采用SPH方法计算, 克服有限元法单元畸变存在的问题。多层间隔靶侵彻算例分析表明, 三维FE-SPH耦合计算程序采用等效塑性应变作为转化判据计算结果较稳定, 并且能够有效地再现侵彻过程中所产生的碎片, 能够模拟侵彻碎片对后层靶的毁伤效应。     

爆炸载荷作用下铀气溶胶形成机理研究

针对铀材料在爆炸载荷作用下形成放射性气溶胶的过程,采用光滑粒子流体动力学方法开展了数值模拟和实验研究。通过将颗粒动力学和SPH方法结合,建立了炸药爆轰作用于铀金属壳的数值模拟模型,以铀材料比内能为气溶胶转化判据,获得了铀材料转化为气溶胶的物理过程,得到了在相同爆炸当量下,不同质量铀材料的气溶胶转化效率,并与实验结果进行了对比分析。结果显示,铀材料在爆炸载荷作用下,当其比内能达到1.9 MJ/kg时,即可认为完全转变为气溶胶,对于本文中的爆炸装置结构形式,当炸药质量为铀材料质量的6倍时,转化率超过90%。实验验证了数值模拟结果,表明该方法能够对铀材料的气溶胶转化过程进行准确描述。     

Parameter determination and response analysis of viscoelastic material

The parameter determination of viscoelastic material is a multi-variable, multi-aim nonlinear optimization problem, which made the optimization process very complicated. In this paper a hybrid optimal algorithm was proposed to determine the viscoelastic parameters in the constitutive relation according to the experimentally obtained mechanical properties. This algorithm merges the Broydon–Fletcher–Goldfarb–Shanno search into a genetic algorithm framework as a basic operator in order to enhance the local search capability. The proposed hybrid algorithm not only can reduce the iterative times greatly but can abolish the limitation of initial parameter values. Nonlinear material characteristic curve-fitting was carried out using the proposed algorithm and other existing approaches. And the comparison results show this algorithm is accurate and effective. The numerical simulation and experimental study of viscoelastic cantilever beam also indicates that the finite element formulation and the calculative viscoelastic model parameters are reliable. The proposed optimization method can be extended to further complex parameter estimation researches.     

复合材料扭转轴截面微结构拓扑优化设计

提出复合材料扭转轴截面微结构拓扑优化设计新模型，模型的优化目标是获得具有最大宏观剪切特性加权和的单胞形式．通过模型和均匀化方法及优化技术可以获得优化的微结构单胞，进而改善或者得到最优宏观弹性特性的复合材料．为了便于制造和应用，胞体材料用来获得复合材料的极值剪切模量．最后的优化结果表明，该模型连同数值处理技巧可以非常有效地实现微结构的拓扑优化设计．     

有压管道双孔板水流流场的数值模拟

利用数值计算的方法对多级孔板消能器内湍流流场进行模拟，并将所得的结果与实验进行了比较。这些比较表明，数值计算的方法是可靠的。     

基于力热耦合材料模型的Steven试验数值模拟方法

在力热耦合材料模型中，增加炸药自热放能模型，建立了Steven试验的力-热-化耦合的数值模拟方法。数值计算模型中，应力应变关系采用双线性硬化弹塑性模型，炸药受力后的热作用采用各向同性热材料模型，炸药的化学反应采用Arrhenius反应率函数，同时还考虑了升温和熔化对材料力学、热学性能的影响。针对标准Steven试验，通过数值分析得到了靶板的变形情况和炸药点火的速度阈值，将计算结果与实验数据进行了比较，两者符合较好。表明该方法可以较好地模拟Steven试验，而且与以往的分析模型和方法相比，本文的方法不需要增加经验性的点火准则和判据，具有更广泛的适用性，可以为研究低速撞击条件下炸药的力热响应和局域化点火问题提供参考。     

复合材料波纹梁盒段耐撞性的数值模拟

运用MSC/DYTRAN有限元软件,结合参数等效的方法对复合材料波纹梁盒段的碰撞过程进行了数值模拟,获得了波纹梁盒段碰撞时的破坏过程、载荷-时间曲线、能量吸收能力等数据,将计算结果与M.A.McCarthy的试验结果进行对比,可以发现两者比较吻合。从而说明采用参数等效的方法可以得到复合材料结构耐坠撞性设计中需要的数据。     

复合材料周期性线弹性微结构的拓扑优化设计

提出复合材料周期性线弹性微结构拓扑优化设计的模型，模型1设计具有极值弹性特性的复合材料，模型2设计工况最刚微结构单胞。通过该模型和均匀化技术可以获得优化的微结构单胞，进而改善或者得到最优宏观特性的复合材料。为了便于制造和应用，用胞体材料而不是多相材料来得到复合材料的极值弹性特性和最大刚度。优化结果表明，该模型与数值方法相结合可以有效地实现微结构的拓扑优化设计。