Three-dimensional numerical simulation of detonations in coaxial tubes

Three-dimensional numerical simulation of detonations in both a circular tube and a coaxial tube are simulated to reveal characteristics of single spinning and two-headed detonations. The numerical results show a feature of a single spinning detonation which was discovered in 1926. Transverse detonations are observed in both tubes, however, the single spinning mode maintains the complex Mach reflection whereas the two-headed mode develops periodically from the single Mach reflection to the complex one. The calculated cell aspect ratio for the two-headed mode changes from 1.09 to 1.34 as the radius of axial insert increases from r ₁/R = 0.1 to 0.9. The calculated cell aspect ratio for r ₁/R = 0.1 is close to the experimental results without an axial insert. The formation of an unreacted gas pocket behind the detonation front was not observed in the single spinning mode; however, the two-headed mode has unreacted gas pocket behind the front near the axial insert.      

曲线公路隧道交通风力非稳态模拟研究

为分析小半径曲线隧道对交通风力的影响,采用移动网格和滑移交界面技术对半径600 m的曲线隧道和直线隧道进行三维非稳态数值计算.结果表明,采用动网格技术进行直线隧道交通风力计算结果与实验吻合;曲线隧道中,隧道断面风速分布表现出极不对称性,外侧风速较大,内侧较小;曲线隧道交通风力较直线隧道明显增大,汽车内车道行驶交通风力大于外车道行驶;曲线隧道中,汽车头部侧面出现了负压峰值,与直线隧道相比,该值较低,车身侧面压力沿纵向逐渐增大,汽车尾部背风面存在较低的负压区.     

A numerical simulation of reflection processes of a detonation wave on a wedge

Abstract. A two dimensional numerical simulation has been performed to study reflection processes of detonation waves on a wedge. The numerical scheme adopted is the flux corrected transport scheme and a two-step chemical reaction is assumed for a stoichiometric oxyhydrogen mixture diluted with argon. Transverse wave structures of the detonation are produced by artificial disturbances situated in front of a one-dimensional Chapman-Jouguet detonation wave. Numerical grids are generated by solving a Laplace equation. Results show that in the case where Mach reflection occurs, the cells in the Mach stem are smaller than those in the incident wave and are distorted in shape. There is also an initiating stage during which the cells in the Mach stem are created. The critical angle beyond which Mach reflection cannot occur is discussed. Received 15 October 1999 / Accepted 27 March 2000     

New strategy of solid/fluid coupling during numerical simulation of thermo-mechanical processes

In this study, numerical methods are developed to simulate thermomechanical processes, taking into account both the fluid flows in the molten pool and the deformations of the solid parts. The methods are based on a new strategy of solid/fluid coupling. They allow to simulate the formation of the molten pool by taking into account the fluid flows through both effects of the surface tension (“curvature effect” and “Marangoni effect”) and the buoyancy. An ALE approach is used to follow the evolution of the free surface. The effects of the deformations in the base metal on the fluid flows in the molten pool (solid/fluid interaction) is ensured by imposing the velocities of the solid nodes during the thermo-fluid simulation. As an application, a thermo-fluid-mechanical simulation of laser welding is carried out. It is found that the solid/fluid interaction has a minor effect on simulation results.     

一维溃坝洪水波的高精度数值模拟

将ENO(Essentially Non-Oscillatory)格式和Runge-Kutta时间离散的思想应用于一维Saint-Venant方程组的求解,数值模拟溃坝洪水,得出了水位和流速的沿程分布。经与理论解比较可见,数值解在间断波附近没有出现数值振荡,水位和流速大小均符合较好,表明ENO格式是一类新的高精度无振荡差分格式,采用ENO格式所建立的高分辨率模型能够很好地模拟溃坝波的演进过程。     

Structural layout assessment by orthogonal array based simulation

A common simulation approach, widely employed in industry for optimal process/product design, is applied in this paper to the sensitivity analysis of structural systems. It is shown how orthogonal array based technique, once suitably customized, may result in a valuable piece of information for the design process. Based on a limited number of numerical experiments properly arranged, structural layout assessment—a typical decision making task with its potential benefits for safety and/or functional performance—is investigated in the light of both analysis of variance and Taguchi method. A specific computer model is implemented for operation and a 3D truss structure is tested for discussion of attainable results.     

泥水平衡盾构机掘进并行数值模拟方法研究

以某大型越江隧道工程为背景,建立该工程场地土层的大规模三维非线性数值模型。同时基于共享内存式并行计算平台(SMP),利用刚度迁移法,完成了泥水平衡盾构机逐步掘进百米长距离,并穿越大堤这一复杂力学过程的大规模数值模拟。为模拟泥水平衡盾构机掘进各施工阶段,不同施工因素之间的复杂力学作用关系,提出了对各施工因素模拟的简化方法。具体包括:开挖面泥水压力对前方土体的作用、盾构机机头的超挖、盾构机机身对土体的作用、盾尾注浆材料的时空变化特性、盾构机后方百米长拖车对已铺成隧道的作用等施工因素。通过对计算结果与工程试验段实测数据对比验证的基础上,预测了地表沉降在盾构机掘进过程中的变化规律。通过对SMP并行计算平台下盾构法施工数值模型之并行计算效率的对比研究,给出了各并行算法的加速比、计算效率以及接触模型对并行计算效率的影响关系。     

Plastic multipliers as driving variables of numerical simulation in elastoplasticity

Statics of elasto-plastic media is stated in terms of eigenstrains acting upon a background elastic problem with fixed (initial) stiffness. In order to minimize the number of unknowns and to provide computationally cheap algorithms plastic multipliers are used as main driving variables. Fixed-point type iterations are suggested for computing plastic multipliers within the load increment. Numerical experiments results are shown to be in good correlation with other software results. A range of problems is outlined where the usage of the proposed algorithms can be advantageous.     

Full-wave numerical simulation of nonlinear dissipative acoustic standing waves in wind instruments

A finite volume full-wave method is used to simulate nonlinear dissipative acoustic propagation in ducts with a circular cross-section. Thermoviscous dissipative effects, due to bulk viscosity and shear viscosity in the boundary layer adjacent to the duct walls, are also considered. The propagation is assumed to be axisymmetric, and two different geometries are considered: a straight cylindrical tube, and a cylindrical tube joined smoothly to a slowly-flaring bell. Of special interest is the study of the onset of standing waves in the nonlinear regime. The full-wave numerical scheme is particularly well-adapted for this purpose, as it is not necessary to impose boundary conditions at the open end of the duct. A simplified model of excitation is adopted, where the lips are replaced by a spring–mass system which behaves like a pressure valve with a single degree of freedom. The full system behaves as expected, with a feedback cycle established between the pressure valve and the air column. The simulation is validated successfully in the linear regime using a theoretical solution. It is shown that increasing the stiffness of the lips leads to discrete jumps in playing frequency, which is behaviour typical of brass instruments. In the nonlinear regime, shock formation is observed for sufficiently high amplitudes of oscillation, and the radiation of these shock waves by the open end of the ducts can be visualised in the time-domain, along with edge-diffraction effects. The formation and evolution of standing waves in the nonlinear regime, where the effect of these shocks is very noticeable, is also examined.     

岩石弹塑性破裂过程的数值模拟研究

分析了对于非均质、非连续且材料参数分布具有分散性和随机性的岩体介质,采用传统有限元法解决其工程问题的局限性．阐述了用岩石力学性质的分布特性来描述岩石材料不均匀性,并用蒙特卡洛模拟方法,将符合Weibull分布规律的材料参数赋予岩体结构中的各个单元体,进而用计算机进行数值模拟的研究方法．应用了在Windows95环境下利用FORTRAN Power Station4．0平台开发的具有可视性的“岩石弹塑性破裂过程分析”软件——REPFPA软件,对典型的岩石试样和巷道模型的弹塑性破裂过程进行数值模拟研究,得到了有价值的实验结果．证明把材料参数随机赋值方法引入到岩土类材料的弹塑性破裂过程分析中去,并用计算机进行数值模拟是研究岩石弹塑性破裂过程的一种有效方法。     

Validation of a numerical model for the simulation of an electrostatic powder coating process

Numerical modeling of a complete powder coating process is carried out to understand the gas-particle two-phase flow field inside a powder coating booth and results of the numerical simulations are compared with experimental data to validate the numerical results. The flow inside the coating booth is modeled as a three-dimensional turbulent continuous gas flow with solid powder particles as a discrete phase. The continuous gas flow is predicted by solving Navier–Stokes equations using a standard k–ε turbulence model with non-equilibrium wall functions. The discrete phase is modeled based on a Lagrangian approach. In the calculation of particle propagation, a particle size distribution obtained through experiments is applied. The electrostatic field, including the effect of space charge due to free ions, is calculated with the use of the user defined scalar transport equations and user defined scalar functions in the software package, FLUENT, for the electrostatic potential and charge density.     

Metal matrix composite solidification in the presence of cooled fibers: numerical simulation and experimental observation

Attempts have been made to alter the solidification microstructures of fiber reinforced aluminum composites by cooling the ends of the fibers extending out of the mold. Experimental observations indicate that cooling the extended ends of the reinforcement results in finer microstructures in the matrix and changes the nature of the interface. In this paper, numerical simulation is performed on a two-dimensional axi-symmetric model to investigate the solidification process of metal matrix composite (MMC) with the extended ends of the fibers cooled by a heat sink. The numerical simulation is based on the source-based enthalpy method with finite volume discretization. The temperature profiles obtained by simulation are compared to the cooling curves measured experimentally in order to validate the current mathematical model. It is found that the simulation result matches the experimental data with reasonable agreement.     

基于砼SHPB试验数值分析的HJC模型参数研究

为了研究混凝土HJC本构模型的参数取值及其参数对混凝土动态性能的影响,本文基于HJC模型原始参数,运用有限元软件ANSYS/LS-DYNA对混凝土SHPB试验进行了数值模拟,结果显示数值计算结果与试验结果存在一定的差异。据此根据模型中参数的物理意义确定出可能影响混凝土动态性能的关键参数,通过保持其他参数不变、改变关键参数的方法对混凝土SHPB试验进行数值分析,得到了各关键参数对混凝土动态性能的影响规律,并基于该分析结果对HJC模型的原始参数进行了修正。数值模拟结果表明,采用本文修正参数的计算结果与试验结果吻合良好,能较准确地反映混凝土的动态性能。     

基于离散缝洞网络模型的缝洞型油藏混合多尺度有限元数值模拟

针对缝洞型油藏具有多尺度特征,基于离散缝洞网络模型,建立了Darcy/Stokes-Brinkman多尺度耦合数学模型,采用多尺度混合有限元方法,对缝洞型油藏的流体流动问题进行了研究。阐述了多尺度混合有限元方法的基本原理,推导得到了Darcy/Stokes-Brinkman多尺度模型的多尺度混合有限元计算格式。数值计算结果表明,在大尺度模型上进行计算能够捕捉到小尺度上的流动特征;相对于传统有限元,多尺度混合有限元能够捕捉小尺度上的非均质特征而具有更高的计算精度,在保证计算精度的同时能够减少计算量。     

Region dependent fracture resistance behavior of human dentin based on numerical simulation简

Dentin has a hierarchical structure and is composed of numerous tubules whose diameters and densities vary with the distances to the dentin-enamel junction. The unique structure determines the mechanical performance of dentin. In this study, a multiscale model, which is based on the combination of the virtual multidimensional internal bond (VMIB) theory and the Monte Carlo method, is used to simulate the fracture behavior of human dentin. Numerical simulations reveal that human dentin exhibits a graded resistance curve (R-curve). Among the three regions of dentin, superficial dentin shows the strongest resistance to crack propagation, and deep dentin has the weakest resistance. In addition, the predictions of fracture toughness of middle dentin agree well with the experimentally reported values, suggesting that the proposed model can be used to characterize the fracture behavior of human dentin comprehensively and properly.     

A note on numerical simulation of vortical structures in shock diffraction

In numerical simulation of the Euler equations, the slipstream or shear layer that appears behind a diffracted shock wave may develop small discrete vortices using fine computational meshes. Similar phenomena were also observed in the simulation of a Mach reflection that is accompanied by a shear layer. However, these small vortices have never been observed in any shock-tube experiment, although the wave pattern and the shape of the main vortex agree very well with visualization results. Numerical solutions obtained with coarse grids may agree better with experimental photos than those with very fine grids because of the pollution of the small vortices. This note tries to investigate the effect of viscosity on the small vortices by comparing the solutions of the laminar Navier-Stokes equations and the turbulence model. It is found that the small vortices are still observed in the solution of the laminar Navier-Stokes equations, although they can be suppressed by using the turbulence model. Numerical and experimental factors that are responsible for the deviation of the laminar solutions from experimental results are discussed. The secondary vortex in shock diffraction is successfully simulated by solving the Navier-Stokes equations.Received: 28 March 2003, Accepted: 6 May 2003, Published online: 11 June 2003     

Numerical simulation of blood flow and interstitial fluid pressure in solid tumor microcirculation based on tumor-induced angiogenesis

A coupled intravascular–transvascular–interstitial fluid flow model is developed to study the distributions of blood flow and interstitial fluid pressure in solid tumor microcirculation based on a tumor-induced microvascular network. This is generated from a 2D nine-point discrete mathematical model of tumor angiogenesis and contains two parent vessels. Blood flow through the microvascular network and interstitial fluid flow in tumor tissues are performed by the extended Poiseuille’s law and Darcy’s law, respectively, transvascular flow is described by Starling’s law; effects of the vascular permeability and the interstitial hydraulic conductivity are also considered. The simulation results predict the heterogeneous blood supply, interstitial hypertension and low convection on the inside of the tumor, which are consistent with physiological observed facts. These results may provide beneficial information for anti-angiogenesis treatment of tumor and further clinical research. The project supported by the National Natural Science Foundation of China (10372026).     

Two-dimensional nonlinear dynamic system model of interspecific interaction and numerical simulation research on it

IntroductionInbiomechanics,interspecificinteractioncanbereducedtodynamicsystem ,andwecanusetwo_dimensionalnonlineardynamicsystemmodelstodescribethemechanismandthecourseofinteractionbetweentwopopulations[1,2 ,3 ] .Interspecificinteractioninvolvesnotonlyonepopulation’sefforttotheother,butalsoothereffortsfromenvironment.Accordingtointeractiomechanism ,thesedynamicsystemscanbedividedintopredator_preysystem ,competitionsystem ,beneficialsymbiosissystemandsoon ,andpredator_preysystemisalwaysvaluedm…     

混凝土中爆炸数值仿真算法研究

用AUTODYN动力学软件对装药在混凝土介质靶中爆炸作数值仿真,研究了不同的网格描述方法,以及网格划分方法对计算结果的影响。通过实际算例比较了Lagrange算法和SPH算法以及不同的网格划分细度对靶径向、轴向不同距离的最大冲击压力、靶背过载以及损伤区、炸坑大小的模拟计算结果。分析得到了混凝土介质靶中爆炸问题数值仿真的合适算法,即拉氏算法对炸点近处的较高的最大冲击压力有较好的敏感能力,SPH算法对仿真计算爆坑形态以及抛掷体速度等具有明显的优势。对于算例问题,拉氏算法10 mm网格和SPH算法3 mm粒子即可满足一定的计算精度。     

爆炸冲击波在长直坑道和复杂坑道内传播规律的对比研究

利用非线性动力分析软件LS-DYNA,对炸药在坑道入口处爆炸情况下,爆炸流场在长直坑道、＂L＂形坑道、＂S＂形坑道内的变化过程进行了数值仿真,得到了爆炸冲击波在不同形状坑道中的传播规律。研究结果表明：带弯道设计的坑道可以有效地削弱冲击波强度,提高坑道的抗破坏能力;弯道外侧峰值压力比同位置长直坑道中的峰值压力大,因此在进行带弯道的坑道设计时,应相应地加强弯道外侧坑道壁的强度。该方法适合于解决爆炸冲击波在复杂弯曲坑道内传播的问题,为今后的坑道防护设计提供了参考和依据。