基于消息传递接口的空中爆炸问题的并行计算

研究了用于处理三维多物质欧拉网格的模糊界面技术以及算法存在的数据相关性问题,提出了解决数据相关性的方法。采用基于消息传递接口(MPI)模式,设计出了相应的MMIC-3D并行程序,得到了无限空气介质中爆炸的三维数值模拟结果,计算结果与实际的实验现象及规律基本吻合。在共享存储的全对称多处理机(SMP)上进行了测试,得到了理想的加速比。     

A two-stage hybrid optimization for honeycomb-type cellular structures under out-of-plane dynamic impact

Honeycomb structures with better balance between lightweight and crashworthiness have aroused growing attentions. However, structural parameters design by traditional optimization algorithm in small design space is not sufficient to significantly enhance the specific energy absorption (SEA) with the lower peak acceleration (a_max). In this paper, a two-stage hybrid optimization for honeycomb-type cellular parameters is proposed to achieve rapid positioning of design space and significantly increase crashworthiness in a larger variable domain under out-of-plane dynamic impact. In stage I, a Taguchi-based grey correlation discrete optimization, combining Taguchi analysis, grey relational analysis, analysis of variance (ANOVA) with grey entropy measurement, is performed to determine the initial optimal value with a higher robustness and the significant influence variables. In stage II, a multi-objective design technique, namely non-nominated sorting genetic algorithm II based on surrogated model, is adopted to maximize the SEA and minimize the a_max in a relatively small design domain. And it is found that the proposed two-stage hybrid method can broaden the optimal design space compared to that of traditional method attributable to its center point positioned by stage I. And the final optimization based on the proposed strategy is superior to the original structure, i.e., the SEA is increased by 47.55% and the a_max is decreased by 80.8%. Therefore, the proposed algorithm can also be used to solve other more complicated engineering problems in a large design space with insightful design data.     

爆炸成型弹丸对Al2O3装甲陶瓷材料的侵彻实验研究

用爆炸成型弹丸(explosively formed projectile, EFP)对Al2O3装甲陶瓷材料进行了侵彻（depth of penetration, DOP）实验,得到了99Al2O3装甲陶瓷对模拟EFP的质量防护因数和差分防护因数及他们随陶瓷块厚度的变化规律,初步评估了99Al2O3装甲陶瓷对EFP的抗侵彻性能,解释了装甲陶瓷对EFP的抗侵彻过程和机理。研究结果表明,增加约束可以提高陶瓷的抗侵彻性能。     

深水域近水面水下爆炸水柱形态及演变实验研究

 为研究不同起爆深度的水下爆炸水柱形态及演变特征,进行了1 kg球形RDX装药在不同起爆深度下的海上爆炸实验,通过高速摄像机记录装药起爆后水柱的形成和成长过程,获得了喷射水柱形态的演变特征以及水柱高度、直径、水柱突出水面时间等参数的变化规律,并与Cole、Hole和Swisdak等人的研究结果进行对比分析。研究结果表明：对于深水域近水面水下爆炸,水柱以垂直喷射形态为主,当气泡在膨胀阶段到达水面时水柱存在微弱的径向飞散现象;水柱最大高度随起爆深度呈脉动变化,水柱直径随起爆深度线性减小;Swisdak关于水柱最大高度的计算公式不适用深水域近水面水下爆炸情况。     

激光作用铝靶爆轰波流场观测与理论分析

进行了强激光作用铝靶实验,采用纹影照相法,观察爆轰波流场演化过程,分析了爆轰波衰减规律。根据冲击波运动的自相似性,采用点爆炸模型描述了激光作用下爆轰波流场的演化,计算了波阵面速度、压力和温度。结果显示:爆轰波阵面沿迎着激光光源方向较快传播,波阵面形状由最初的半椭球形逐渐向半球形转变,在演化过程中扰动区结构复杂,存在多个密度间断层。在爆轰波开始传播阶段,波阵面的压力和温度较高但下降很快。     

A p-channel SMC poly-Si thin film-transistor with a GOLDD structure

We have developed a silicide-mediated crystallization (SMC) polycrystalline silicon (poly-Si) thin film transistor (TFT) with a gate overlapped lightly doped drain (GOLDD) structure. Applying a GOLDD structure to the SMC poly-Si TFT, the off-state leakage current of coplanar TFT is reduced, while the reduction of the on-state current is relatively small. The p-channel poly-Si TFT with a GOLDD structure exhibited a field effect mobility of 50 cm²/V s and an off-state leakage current of 3.8×10⁻¹¹ A/μm at the drain voltage of −5 V and the gate voltage of 10 V.     

A new membrane model for the ballistic impact response and V50 performance of multi-ply fibrous systems

This paper develops an analytical model for the ballistic impact response of fibrous materials of interest in body armor applications. It focuses on an un-tensioned 2D membrane impacted transversely by a blunt-nosed projectile, a problem that has remained unsolved for a half a century. Membrane properties are assumed characteristic of the best current body armor materials (Kevlar^®, Spectra^®, Zylon^®, S2 glass), which have very high stiffness and strength per unit weight, and low strain-to-failure. Successful comparisons will be made with extensive experimental data on such material systems as reported by Cunniff [Decoupled response of textile body armor. Proc. 18th Int. Symp. of Ballistics, San Antonio, Texas, 1999a, pp. 814–821; V_s–V_r relationships in textile system impact. Proc. 18th Int. Symp. of Ballistics, San Antonio, Texas, 1999b; Dimensional parameters for optimization of textile-based body armor systems, Proc. 18th Int. Symp. of Ballistics, San Antonio, Texas, 1999c, pp. 1303–1310]. Our mathematical formulation draws on the seminal work of Rakhmatulin and Dem’yanov [Strength Under High Transient Loads, 1961, pp. 94–152]. Under constant projectile velocity we first develop self-similar solution forms for the tensile ‘implosion’ wave and the curved cone wave that develops in its wake. Through matching boundary conditions at the cone wave front, we obtain an accurate approximate solution for the membrane response including cone wave speed and strain distribution. We then consider projectile deceleration due to membrane reactive forces, and obtain results on cone velocity, displacement and strain concentration versus time. Other results obtained are the membrane ballistic limit, or V₅₀ velocity, and the residual velocity when penetrated above this limit. We then derive an exact functional representation of a V₅₀ ‘master curve’ found empirically by Cunniff [ibid] to reduce data for a wide variety of fabric systems impacted by blunt cylindrical projectiles. This curve is given in terms two dimensionless parameters based only on fiber mechanical properties and the ratio of the fabric areal density to the projectile mass divided by its area of fabric contact. Our functional representation has no fitting parameters beyond one reflecting uncertainty in the effective diameter of the impact zone relative to the projectile diameter, and even then the values are consistent across several experimental systems. The extremely successful comparison of our analytical model to experimental results in the literature raises fundamental questions about many long-held views on fabric system impact behavior and parameters thought to be important.     

A unified periodical boundary conditions for representative volume elements of composites and applications

An explicit unified form of boundary conditions for a periodic representative volume element (RVE) is presented which satisfies the periodicity conditions, and is suitable for any combination of multiaxial loads. Starting from a simple 2-D example, we demonstrate that the “homogeneous boundary conditions” are not only over-constrained but they may also violate the boundary traction periodicity conditions. Subsequently, the proposed method is applied to: (a) the simultaneous prediction of nine elastic constants of a unidirectional laminate by applying multiaxial loads to a cubic unit cell model; (b) the prediction of in-plane elastic moduli for [±θ]_n angle-ply laminates. To facilitate the analysis, a meso/micro rhombohedral RVE model has been developed for the [±θ]_n angle-ply laminates. The results obtained are in good agreement with the available theoretical and experimental results.     

The effects of the no-touch gap on the no-touch bipolar radiofrequency ablation treatment of liver cancer: A numerical study using a two compartment model

The no-touch bipolar radiofrequency ablation (RFA) for cancer treatment is advantageous primarily because of its capability to prevent tumour track seeding (TTS). In this technique, the RF probes are placed at a distance (no-touch gap) away from the tumour boundary. Ideally, the RF probes should be placed sufficiently far from the tumour in order to avoid TTS. However, having a gap that is too large can lead to ineffective ablation. This paper investigates how the selection of the no-touch gap can affect the tissue electrical and thermal responses during the no-touch bipolar RFA treatment. Simulations were carried out on a two compartment model using the finite element method. Results obtained indicated that a gap that is too large may lead to incomplete ablation and failure to achieve significant ablation margin. However, keeping the gap to be too small may not be clinically practical. It was suggested that the incomplete ablation and the insufficient ablation margin observed in some of the cases may require the placement of additional probes around the tumour. The present study stresses on the importance of identifying the optimal no-touch gap that can avoid TTS without compromising the treatment outcome.     

The continuation and stability analysis methods for quasi-periodic solutions of nonlinear systems

Nonlinear Dynamics - The continuation and stability analysis methods for quasi-periodic solutions of nonlinear systems are proposed. The proposed continuation method advances the...