LEVEL SET输运方程的求解方法及其对气-液两相流运动界面数值模拟的影响

用数值模拟方法来研究气-液两相流动与传热现象是当今多相流领域的一个热门课题.由于两相流固有的复杂性,气-液两相流界面迁移现象的数值模拟一直是两相流研究中的一大难点.本文介绍了捕捉气-液两相流相界面运动的水平集方法(Level Set)及其研究进展,介绍了求解Level Set输运方程的3种方法,即一般差分格式、Superbee-TVD格式和Runge-Kutta法-5阶WENO组合格式.结合主流场的求解,分别用这3种方法对4种典型相界面在5种流场中的迁移特性进行了模拟计算,并对计算结果进行了比较和分析.结果表明,Runge-Kutta法-5阶WENO组合格式求解Level Set输运方程的效果最好,在以后的计算中将主要采用这种组合格式来进行气-液相界面输运方程的求解.

连续移动三维瞬态激光熔池温度场数值模拟

详细介绍了在ANSYS软件平台上，建立连续移动三维瞬态激光熔池温度场计算模型的方法，计算模型中考虑了材料表面温度对激光吸收率的影响及材料相变过程对激光熔池温度场的影响。系统分析了连续移动三维激光熔池温度场随时间的变化规律。通过该计算模型，可以掌握激光加工过程中连续移动激光熔池的加热和冷却规律。计算结果表明，当激光沿45#钢基板表面由一端向另一端沿直线扫描时，由于热传导的作用，激光熔池温度随时间增加而升高，同时连续移动熔池表面温度最高点不在激光束中心，而是稍稍偏后于激光束中心。在相同激光工艺参数下，计算熔池横截面尺寸与实验所测熔池横截面尺寸相吻合，表明所建立的连续移动熔池温度场计算模型是正确和可靠的。

Wave Propagation Analysis in a Pressure-Wave-Refrigerator

Pressure wave refrigerators (PWR) refrigerate the gas through periodical expansion waves. Due to its simple structure and robustness, PWR may have many potential applications if the efficiency becomes competitive with existing alternative devices. In order to improve the efficiency, the characteristics of wave propagation in a PWR are studied by experiment, numerical simulation and theoretical analysis. Based on the experimental results and numerical simulation, a simplified model is suggested, which includes the assumptions of flux-equilibrium and conservation of the free energy. This allows the independent analysis of the operation parameters and design specifics. Furthermore, the optimum operation condition can be deduced. Some considerations to improve the PWR efficiency are also given.

车辆与弯道混凝土护栏碰撞的动态数值模拟及试验

对车辆与弯道混凝土护栏碰撞动态数值模拟结果和实车足尺碰撞试验结果进行对比分析，从车辆行驶轨迹、乘员冲击加速度以及车辆损伤形态3个方面，验证了动态数值模拟的准确性，并分析了弯道混凝土护栏曲线半径对乘员碰撞过程中所承受冲击加速度的影响；得到乘员风险的最不利护栏半径。结果表明：有限元仿真是进行汽车护栏碰撞研究的有效方法；弯道处护栏的形式对碰撞时乘员的安全有很大影响。

Forebody Compressibility Research of Hypersonic Vehicle

Three kinds of forebody model of hypersonic vehicles were studied with numerical simulation method. It shows that the two- order compressive ramp model is the best selection among the three for its good evaluative parameters value at the cowl of the inlet . This model can provide higher value of flux coefficient and total pressure recovery coefficient and lower average Mach number compared with those of the other two models . Simultaneously different compressive angles may have different effects . The configuration which the firstorder of compressive angle is 4°and the second 5°is the optimum combination. Furthermore factors such as attack angle were concerned. Better result may be obtained with a range of attack angles . Based on the work above the integrated design for forebodyPinlet of a hypersonic vehicle was performed. The numerical result shows that this integrated model provides good flow field quality for inlet and engine work.

爆轰波在楔面上反射数值分析

应用基元反应模型和频散可控耗散格式(DCD)对氢氧爆轰波在楔面反射进行了数值模拟.计算中氢氧混合物的化学反应采用了8种组分20个反应方程式.在处理化学反应引起的刚性问题时采用了时间算子分裂的方法.模拟了爆轰波在楔面反射由马赫反射向规则反射转变的过程,得到了反射转变临界角,同时考虑了初始压力和组分的影响,并和实验及理论分析结果进行了比较,结果是令人满意的.

Effect of non-uniform magnetic field on crystal growth by floating-zone method in microgravity

The magnetic damping effect of the non-uniform magnetic field on the floating-zone crystal growth process in microgravity is studied by numerical simulation. The results show that the non-uniform magnetic field with designed configuration can effectively reduce the flow near the free surface and then in the melt zone. At the same time, the designed magnetic field can improve the impurity concentration non-uniformity along the solidification interface. The primary principles of the magnetic field configuration design are also discussed.

Study of Gas Combustion in a Vented Cylindrical Vessel

Complicated interaction of a flame front with a turbulent flow induced by venting is studied during combustion of the stoichiometric propane/air mixture in a relatively large vented cylindrical vessel. Flame position, its shape, and combustion pressure were measured as a function of time and vent parameters. The experimental data were used to verify numerical simulation of the combustion process. The proposed numerical model satisfactorily simulates the main features of combustion in a closed and vented vessel such as flame configuration, flow and temperature fields, and pressure variation pattern. Simulated velocity and temperature distribution are very useful pieces of information because they are not available from experiments.

Source Model for Blasting Vibration

By analyzing and comparing the experimental data, the point source moment theory and the cavity theory, it is concluded that the vibrating signals away from the blasting explosive come mainly from the natural vibrations of the geological structures near the broken blasting area. The source impulses are not spread mainly by the inelastic properties (such as through media damping, as believed to be the case by many researchers) of the medium in the propagation pass, but by this structure. Then an equivalent source model for the blasting vibrations of a fragmenting blasting is proposed, which shows the important role of the impulse of the source's time function under certain conditions. For the purpose of numerical simulation, the model is realized in FEM, The finite element results are in good agreement with the experimental data.

The Interaction Between Shock Waves and Foam in a Shock Tube

An experimental study and a numerical simulation were conducted to investigate the mechanical and thermodynamic processes involved in the interaction between shock waves and low density foam. The experiment was done in a stainless shock tube (80mm in inner diameter, 10mm in wall thickness and 5360mm in length). The velocities of the incident and reflected compression waves in the foam were measured by using piezo-ceramic pressure sensors. The end-wall peak pressure behind the reflected wave in the foam was measured by using a crystal piezoelectric sensor. It is suggested that the high end-wall pressure may be caused by a rapid contact between the foam and the end-wall surface. Both open-cell and closed-cell foams with different length and density were tested. Through comparing the numerical and experimental end-wall pressure, the permeability coefficients a and 0 are quantitatively determined.

双层堤基管涌动态发展的有限元模拟

提出了模拟堤基管涌动态发展的概化模型，编制了相应的计算程序，用砂槽模型试验结果进行了验证，并对双层堤基管涌发展过程中的渗流场特点进行了计算分析，对有限元计算中的参数取值进行了探讨。

Optical Diagnostic and Modeling Solution Growth Process of Sodium Chlorate Crystals

Both a real time optical interferometric experiment and a numerical simulation of two-dimension non-steady state model were employed to study the growth process of aqueous sodium chlorate crystals. The parameters such as solution concentration distribution, crystal dimensions, growth rate and velocity field were obtained by both experiment and numerical simulation. The influence of earth gravity during crystal growth process was analyzed. A reasonable theory model corresponding to the present experiment is advanced. The thickness of concentration boundary layer was investigated especially. The results from the experiment and numerical simulation match well.

3D Anisotropic Elastoplastic-Damage Model and its Application in Simulating the Behavior of Rock Materials

A 3D anisotropic elastoplastic-damage model was presented based on continuum damage mechanics theory. In this model, the tensor decomposition technique is employed. Combined with the plastic yield rule and damage evolution, the stress tensor in incremental format is obtained. The derivate eigenmodes in the proposed model are assumed to be related with the uniaxial behavior of the rock material. Each eigenmode has a corresponding damage variable due to the fact that damage is a function of the magnitude of the eigenstrain. Within an eigenmodes, different damage evolution can be used for tensile and compressive loadings. This model was also developed into finite element code in explicit format, and the code was integrated into the well-known computational environment ABAQUS using the ABAQUS/Explicit Solver. Numerical simulation of an uniaxial compressive test for a rock sample is used to examine the performance of the proposed model, and the progressive failure process of the rock sample is unveiled.

Study on Mechanical Properties of Nanocrystal Surface Layer of an Aluminum Alloy

The nanocrystal surface layer of an aluminum alloy induced by High Speed Shot Peening (HSSP) was investigated in this paper. The results of nanoindentation experiment show that the elastic modulus and the hardness of nanocrystal surface layer increased,by 8% and 20%, respectively. The elastic modulus and the hardness appear to be independent of the distance from nanocrystalized surface and the process time.

Depth dependence of nanohardness in a CuAlNi single crystal shape memory alloy

Instrumented nanoindentation was employed to study the depth dependence of nanohardness in a CuAlNi single crystal shape memory alloy that exhibits shape memory effect (SME). A Berkovich indenter and a cube comer indenter were used in this study, and the