Minimizing the makespan in open‐shop scheduling problems with a convex resource consumption function

We consider open‐shop scheduling problems where operation‐processing times are a convex decreasing function of a common limited nonrenewable resource. The scheduler's objective is to determine the optimal job sequence on each machine and the optimal resource allocation for each operation in order to minimize the makespan. We prove that this problem is NP‐hard, but for the special case of the two‐machine problem we provide an efficient optimization algorithm. We also provide a fully polynomial approximation scheme for solving the preemptive case. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2006     

非线性随机动态响应的高效模拟方法

提出了一种分析多自由度非线性系统在随机激励下响应的高效模拟方法。该方法以蒙特卡罗方法为基础,针对动态问题,建立了有效的重要性判别准则,采用俄罗斯轮盘赌与分裂方法来处理响应样本,增加了样本在低失效概率区域出现的几率,提高了模拟效率。通过两个算例表明,该方法操作简单,可以大大地减少计算量,能够适用于实际的工程问题。     

强侧风作用下棚车气动外形优化

铁路通用车型中,强侧风作用下棚车的气动性能最差。利用二维定常不可压缩N-S方程、k-ε两方程紊流模型,采用有限体积法对强侧风作用下棚车气动外形进行了优化研究。结果表明,棚车车顶形状对强侧风作用下棚车气动性能有较大影响,圆弧型车顶的P65型棚车气动性优于“人”字型车顶P64型棚车;棚车侧壁和车顶圆弧采用圆弧过渡比直接连接的效果好,综合考虑棚车气动性能和有效容量两方面因素,建议车顶圆弧和过渡圆弧半径分别取2692mm和500mm。     

基于移动Agent的特定数值求解算法研究

在分布式环境下,运用移动Agent技术实现大型复杂系统研究中经常使用的特定数值算法求解,可显著提高计算效率。以分支定界法为例,介绍了其设计思想和实践步骤,并对算法的时间复杂度进行了分析。     

带壳体云爆弹药液体燃料抛撒的数值模拟

建立了带壳体云爆弹药数值模拟模型,分析了圆柱壳体的断裂准则。壳体材料采用Johnson-Cook热粘性本构方程,断裂准则采用Taylor断裂应力准则,应用Autodyn软件进行了数值模拟,给出了内部爆炸载荷下液体燃料的压力曲线和速度曲线,并进行了分析。     

数值模拟气液针栓式火箭发动机喷雾燃烧对声学激励的响应

为研究气液针栓式火箭发动机的声学振荡特性并为其优化设计提供指导,加工了具有矩形燃烧室的LOX/GCH₄针栓式发动机,采用Euler-Lagrange方法仿真横向速度扰动产生的声学响应,以期在热试前了解声学激励频率对非稳态喷雾燃烧过程的影响。仿真结果表明,采用的横向速度扰动能在燃烧室内产生同频率的一阶横向声学振荡响应。喷雾燃烧对声学激励的响应强弱受扰动频率与燃烧室一阶横向振荡模态固有频率的相对大小影响较大。当扰动频率与该固有频率相等时,压力和燃烧释热随速度扰动出现同相振荡,压力振荡幅值显著增高导致燃烧室前半段的喷雾和火焰同步摆动;同时,燃烧室内存在扩散燃烧变为预混燃烧的趋势,甲烷在更短的距离内燃烧完全且燃烧室温度趋于均匀。     

复合固体推进剂颗粒填充模型及其统计特性分析

复合固体推进剂属于高填充比颗粒类复合材料,氧化剂和金属颗粒在基体中的随机分布使其在细观尺度具有非均质的特点。从细观尺度研究固体推进剂燃烧及力学性能时,必须考虑颗粒级配、空间分布和种类等因素的影响。采用分子动力学方法,以硝酸酯增塑聚醚高能复合固体推进剂为研究对象,将固体颗粒模型化为球形,生成其在基体内随机分布的颗粒填充模型。利用Monte-Carlo算法模拟计算颗粒填充模型细观结构的两点概率函数,并研究了颗粒填充体积分数、尺寸与级配等参数对其的影响规律。从统计意义上给出具有各态历经性、统计均匀性和各向同性特点的颗粒填充构型最小周期性代表体元尺寸,可有效减小后续研究的计算量,节约计算成本。所构建的推进剂细观几何构型及对最小周期性代表体元尺寸的计算为后续开展复合固体推进剂细观尺度燃烧、燃面处铝团聚及力学性能数值研究奠定了基础。     

An efficient and modular modeling for launch dynamics of tubed rockets on a moving launcher

This paper develops a modular modeling and efficient formulation of launch dynamics with marching fire (LDMF) using a mixed formulation of the transfer matrix method for multibody systems (MSTMM) and Newton-Euler formulation. Taking a ground-borne multiple launch rocket systems (MLRS), the focus is on the launching subsystem comprising the rocket, flexible tube, and tube tail. The launching subsystem is treated as a coupled rigid-flexible multibody system, where the rocket and tube tail are treated as rigid bodies while the flexible tube as a beam with large motion. Firstly, the tube and tube tail can be elegantly handled by the MSTMM, a computationally efficient order-N formulation. Then, the equation of motion of the in-bore rocket with relative kinematics w.r.t. the tube using the Newton-Euler method is derived. Finally, the rocket, tube, and tube tail dynamics are coupled, yielding the equation of motion of the launching subsystem that can be regarded as a building block and further integrated with other subsystems. The deduced dynamics equation of the launching subsystem is not limited to ground-borne MLRS but also fits for tanks, self-propelled artilleries, and other air-borne and naval-borne weapons undergoing large motion. Numerical simulation results of LDMF are given and partially verified by the experiment.     

Static and free vibration analyses of functionally graded porous variable-thickness plates using an edge-based smoothed finite element method

The main purpose of this paper is to present numerical results of static bending and free vibration of functionally graded porous (FGP) variable-thickness plates by using an edge-based smoothed finite element method (ES-FEM) associate with the mixed interpolation of tensorial components technique for the three-node triangular element (MITC3), so-called ES-MITC3. This ES-MITC3 element is performed to eliminate the shear locking problem and to enhance the accuracy of the existing MITC3 element. In the ES-MITC3 element, the stiffness matrices are obtained by using the strain smoothing technique over the smoothing domains formed by two adjacent MITC3 triangular elements sharing an edge. Materials of the plate are FGP with a power-law index (k) and maximum porosity distributions (Ω) in the forms of cosine functions. The influences of some geometric parameters, material properties on static bending, and natural frequency of the FGP variable-thickness plates are examined in detail.     

Formation and characterization of core-shell CL-20/TNT composite prepared by spray-drying technique

The core-shell 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane/2,4,6-Trinitrotoluene (CL-20/TNT) composite was prepared by spray-drying method in which sensitive high energy explosive (CL-20) was coated with insensitive explosive (TNT). The structure and properties of different formulations of CL-20/TNT composite and CL-20/TNT mixture were characterized by scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Laser particle size analyzer, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), differential scanning calorimetry (DSC), impact sensitivity test and detonation performance. The results of SEM, TEM, XPS and XRD show that ϵ-CL-20 particles are coated by TNT. When the ratio of CL-20/TNT is 75/25, core-shell structure is well formed, and thickness of the shell is about 20–30 nm. And the analysis of heat and impact show that with the increase of TNT content, the TNT coating on the core-shell composite material can not only catalyze the thermal decomposition of core material (CL-20), but also greatly reduce the impact sensitivity. Compared with the CL-20/TNT mixture (75/25) at the same ratio, the characteristic drop height of core-shell CL-20/TNT composite (75/25) increased by 47.6% and the TNT coating can accelerate the nuclear decomposition in the CL-20/TNT composites. Therefore, the preparation of the core-shell composites can be regarded as a unique means, by which the composites are characterized by controllable decomposition rate, high energy and excellent mechanical sensitivity and could be applied to propellants and other fields.