对称区域边界处理方法及基于表面粒子提取的表面张力计算

流固边界处理一直是流体模拟的研究重点,边界力法和虚粒子法是研究流固边界 的常用方法。边界力法通过对铺设在边界上的粒子施加排斥力防止粒子穿透,但边界力的计算 限制了模拟速度。虚粒子法在边界处生成虚粒子,随着粒子数的增加所需的虚粒子数也随之增 加,导致计算速度下降,且会出现流体与边界分离的现象。为此,提出一种对称区域边界处理 方法,在保证逼真度的前提下满足实时性要求,随着粒子数的增加,其耗时增长也明显比其他 传统方法慢,更适合对复杂场景的模拟,同时避免了边界处流体与边界分离的现象。CSF 方法 是处理表面张力常用的方法,可将表面张力看作体积力进行计算,大大减弱了表面形状对曲率 计算的影响,而事实上曲率的计算只与表面的形状有关。为此,对CSF 方法进行了改进,提出 了一种基于表面粒子提取的表面张力计算方法,减小了传统CSF 方法计算曲率的误差,提高了 计算速度。模拟仿真的效果验证了该方法的有效性。     

高可扩展可容错的无网格/粒子程序petaPar及其测试

petaPar 粒子模拟程序面向千万亿次级计算,在统一框架下实现两种广受关注的粒子模拟算法：光滑粒子流体动力学（Smoothed Particle Hydrodynamics,SPH）和物质点法（Material Point Method,MPM)。代码支持多种材料模型、强度模型和失效模型,适合模拟大变形、高应变率和流固耦合问题。支持纯 MPI 和 MPI+X 混合两种并行模型。系统具有可容错性,支持无人值守变进程重启。在Titan 上测试表明,petaPar 可线性扩展到 26 万 CPU 核,SPH 和 MPM 算法并行效率相对 8 192 核分别为 87% 和 90%。     

Modelling elastoplastic frictional collisions of ellipsoidal granules with collisional-SPH

The Collisional-SPH method models the combined evolution of deformation and frictional contact forces in elastoplastic granular collisions. However, there are many applications in which the granules are not spherical. In this paper, CSPH is extended to model an impact of an ellipsoidal granule on a flat deformable substrate. The CSPH spring-stiffness formulation is developed to account for the contact area eccentricity. Validation for different granule orientations and aspect-ratios are presented. The combined effect of substrate deformation and non-spherical granule shape on the contact-zone mechanics is investigated for different granule orientations and aspect ratios. It is found that the granule’s orientation and aspect ratio influences the interdependence between substrate deformation and contact-force distribution and should be accounted for in collision models.     

Resonance Treatment Based on Ultra-fine-group Spectrum Calculation in the AEGIS Code

The resonance calculation method using the ultra-fine-group spectrum calculations in the AEGIS code is explained in detail. By a simple benchmark problem, it is verified that the effect of anisotropic scattering on effective cross-sections is not very large and the isotropic scattering source approximation is adequate in practical resonance calculations in LWRs. Furthermore, some efficient numerical algorithms in the ultra-fine-group calculations to reduce the computation time without large degeneration of accuracy are presented. In addition, the SPH method for energy collapsing of cross-sections is adopted in the AEGIS code to reduce the error of energy collapsing.

Through the comparison with continuous-energy Monte-Calro calculation in the pin-cell geometry, the validity of the resonance treatment in the AEGIS code is verified.     

基于SPH粒子法的盲天井掏槽爆破数值模拟

针对上向盲天井掏槽孔爆破效果,运用补偿系数法对周边大空孔孔间距进行计算并进行方案制定,利用光滑粒子流体动力学方法(SPH粒子法)进行数值模拟计算,开展盲天井掏槽爆破周边空孔作用以及补偿系数对爆腔及岩石损伤范围影响研究。研究结果表明:在孔间距一定时,爆腔面积随补偿系数增大呈增加趋势;当补偿系数达到2.42时爆破效果最佳且达到峰值0.54 m²,而后爆破效果作用达到极限,爆腔面积变化趋于稳定;岩石损伤范围因炸药作用效果有限,总体变化范围在10%以内;模拟过程中SPH粒子能良好地模拟出爆破过程中岩石运动状态、空孔填充情况以及岩石损伤范围。所得模拟结果与现场试验爆腔断面面积吻合度高,说明数值模拟计算具有一定的准确性。     

A thermo-visco-plastic damage model and SPH simulations of plugging failure

ABSTRACT

A thermo-visco-plasticity model, recently developed based on a microinertia driven dynamic flow rule, is exploited to account for damage due to fracture. This is accomplished by adjoining the equations for thermo-visco-plasticity, herein discretized through the smooth particle hydrodynamics (SPH), with a “pseudospring” based discrete damage model. In treating ductile fractures, this coupled material model accounts for the inertia associated with moving microstructural defects and time lags for the dissipative fluxes to attain the steady state. In this approach, while the microinertia-driven flow rule provides a vehicle to evolve plastic strain, pseudosprings are exploited to treat material damage and the resulting reduced force transfer. The current scheme does not necessitate the introduction of a yield or damage surface in evolving the plastic-strain/damage parameters, and thus the numerical implementation avoids a computationally intensive return mapping. We demonstrate the performance of the proposed model through SPH-based numerical simulations and also undertake a validation exercise against experimental observations from gas-gun penetration tests on an 8-mm thick Weldox 460 E steel plate.     

基于SPH结合FEM的喷丸残余应力数值模拟

针对以往有限元模型中弹丸数量较少且为规则阵列排布的缺陷,采用光滑粒子流体动力学法(Smoothed particle hydrodynamics,SPH)与有限元法(Finite element method,FEM)相结合的方法,对喷丸过程进行数值模拟;使用MATLAB对弹丸空间位置坐标进行随机化处理,形成了大量丸粒冲击工件表面的随机喷丸仿真模型。通过分析确定了喷丸饱和时间,研究了喷射角度、弹丸流量对残余应力场的影响。结果表明:在喷丸参数一定的条件下,存在相应的饱和喷丸时间;研究喷丸参数对残余应力的影响时,应在喷丸达到饱和时间之后提取残余应力值;喷射角度增大,残余压应力增大;开始时弹丸流量增大,残余压应力会有所增大,但当其达到饱和值后,残余压应力不再变化。     

磨粒叶序排布砂轮磨削的磨削力模拟分析

为了改善超硬磨料砂轮的磨削能力,基于生物学的叶序排布理论,提出了一种新型有序化排布磨料的超硬磨料砂轮。利用Ls—dyna仿真软件的光滑粒子法（SPH）,对叶序排布砂轮进行了磨削力的分析研究,得出了叶序参数和磨削用量对磨粒叶序排布外圆砂轮磨削力的影响规律。仿真结果表明,合理地选择叶序系数忌和磨料半径r,可以使叶序排布砂轮在磨削过程中获得较低的磨削力。     

非均质煤层瓦斯渗流的SPH方法模拟研究

应用光滑粒子流体动力学（smoothed particle hydrodynamics,SPH）方法对煤层瓦斯渗流进行模拟研究。针对非均质煤层瓦斯瞬态渗流问题,利用Fortran语言编制了变系数瓦斯渗流偏微分方程的求解程序,通过虚粒子法处理边界条件,构建了无网格性质的SPH瓦斯渗流模型。进行了不同原始瓦斯压力和透气性系数时常系数渗流方法下结果的误差分析,同时考虑透气性系数受矿山压力及Weibull分布影响的非均质煤层,分析了非均质煤层中瓦斯压力及涌出量的变化规律。模拟结果表明：应用SPH方法能很好的模拟煤层的瓦斯渗流;矿山压力影响以及透气性系数按Weibull分布赋值的非均质煤层都会导致瓦斯渗流的非线性。     

基于SPH方法的大块煤冲击破碎数值模拟

为研究大块煤在钎杆冲击下的破碎效果,引入RHT混凝土本构模型材料来模拟大块硬煤（压缩强度35 MPa）,并基于光滑质点流体动力学（SPH）方法建立了钎杆冲击大块煤的三维仿真模型。分析比较了大块在静压、纯冲击和冲压组合作用下的破坏程度,以及平头和圆锥形钎杆冲击效果的差异。仿真结果表明：平头钎杆在30 MPa压力、15 m/s速度或是其组合作用下,均无法使大块产生有效破坏;平头钎杆在200 m/s的超高速下可使大块产生彻体破坏,但实现钎杆高速运动困难;圆锥钎杆在30 MPa压力和15 m/s速度的冲压作用下,使大块产生了较大范围的锥形失效,远高于常规液压破碎锤的单次冲击破坏程度。锥形钎杆、高压高速是破碎硬质大块煤的一种有效方法,可在较少作用次数下实现破碎,验证了低频重载破碎大块的可行性。