SPH模拟螺杆挤出的粒子穿透边界问题研究

采用光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)模拟双螺杆挤出时,常会出现粒子穿透边界的问题,这是由于螺杆挤出过程存在“挤压流”这一特殊流动现象而造成的。过去的“人工声速判据”不适用于解决“挤压流”这类问题。为了修正“人工声速判据”的缺陷,针对挤压过程进行推算,提出了一种理论计算“特征速度”的方法。为了验证该方法的有效性,对SPH的模拟结果与传统商业软件POLYFLOW的模拟结果进行了比较。结果显示,新计算方案的运用可以有效避免粒子穿透边界的问题。这种计算方案可为其他存在“挤压流”现象的复杂加工模拟解决粒子穿透边界问题提供参考。

考虑强度速率衰减效应的地震滑坡SPH-FEM模拟

基于SPH和FEM耦合的数值计算方法,引入滑动面摩擦强度的速率衰减模型,提出了一种能够模拟地震诱发滑坡破坏过程的数值模拟方法。基于所提数值方法模拟了唐家山地震滑坡,模拟结果与现场勘查结果及室内试验现象较为一致。基于模拟的滑动面上摩擦系数的演化过程,将唐家山滑坡的发生分为4个阶段:启动阶段、摩擦衰减阶段、低摩擦滑移阶段和逐步稳定阶段。模拟结果表明速度增加和摩擦强度衰减的相互促进,是触发滑体的高速运动的根本原因。提出采用滑体上作用的动摩擦力fd和动下滑力Td的比值R作为判别指标用于判断大型滑坡的启动,当首次出现R小于1时认为滑动面发生整体贯通并出现失稳启动。基于滑动面不同位置摩擦系数的演化,揭示了滑坡启动中滑动面摩擦强度衰减和滑动面的渐进贯通过程,解释了地震作用与滑动面摩擦参数速率衰减效应共同作用触发大型滑坡发生破坏的内在机理。

Effects of hydrodynamics processes on phosphorus fluxes from sediment in large,shallow Taihu Lake

The turnover of phosphorus （P） in lake sediments, a major cause of eutrophication and subsequent deterioration of water quality, is in need of deep understanding. In this study, effects of resuspension on P release were studied in cylindrical microcosms with Yshape apparatus. The results indicated that there was a positive correlation between flux of suspended substance across sediment-water interface （Fss） and the wind speed, and an increasing Fss during each wind process followed by a steady state. The maximal Fss under fight, moderate, and strong wind conditions were 299.9±41.1,573.4±61.7, and 2093.8±215.7 g/m^2, respectively. However, flux of P across sediment-water interface （Fp） did not follow a similar pattern as Fss responding to wind intensity, which increased and reached the maximum in initial 120 rain for fight wind, then decreased gradually, with maximal flux of 9.4±1.9 mg/m^2. A rapid increase of Fp at the first 30 rain was observed under moderate wind, with maximal flux of 11.2±0.6 mg/m^2. Surprisingly, strong wind caused less Fp than under light and moderate wind conditions with maximal flux of 3.5±0.9 mg/m^2. Fss in water column declined obviously during the sedimentation process after winds, but Fp varied with wind regime. No obvious difference was detected on Fp after 8 h sedimentation process, compared with the initial value, which means little redundant P left in the water column after winds.

基于SPH露天台阶的爆破优化

针对露天深孔台阶爆破容易出现块度不均匀、大块率高等问题,运用经验公式法对台阶爆破参数进行计算并确定爆破方案,建立基于光滑粒子流体动力学(SPH)的台阶数值模型,对深孔台阶爆破孔排距共同作用下的岩体损伤情况及孔间应力大小进行研究。结果表明:孔排距会影响炮孔间的应力叠加作用,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和岩石损伤范围,当孔间距为8.5 m、排间距为5.0 m,爆破效果最佳。将模拟结果应用于现场试验,大块率较优化前降低了10.3%,块度平均合格率提高了5.2%,现场试验与模拟结果最优爆破方案效果高度一致,说明利用SPH的数值模拟方法研究台阶爆破是合理可行的。研究结果可为相关台阶爆破孔排距选择提供依据和参考。

基于SPH算法的热仿真系统开发

随着电子设备日益微型化和集成化,热仿真已成为其设计中的关键因素。电子封装模块的热仿真通常使用传统的有限元法FEM(finite element method),存在计算效率和精度之间的矛盾,在处理大变形问题和网格畸变方面也容易造成计算不收敛,从而导致结果错误。针对该问题,提出一种基于光滑粒子动力学SPH(smoothed particle hydrodynamics)算法的电子封装模块热仿真系统。该算法基于无网格拉格朗日数值方法,通过将热仿真对象离散为1组粒子的方式求解热传导方程,从而准确地预测电子封装模块的传热与散热,无需生成并处理大量的微小网格,不用担心网格失真等问题。SPH相对于FEM,仿真精度误差保持在1%~2%,仿真效率可提升近30倍,适合用于复杂和动态系统的模拟仿真。

基于SPH方法的二维液舱晃荡特性研究

本文基于流固耦合动力学理论,建立二维液舱晃荡的光滑粒子流体动力学模型,并引入Dummy边界处理固定边界问题。首先,与实验结果对比验证模型的有效性;随后,分析不同横摇激励、多种载液率下自由液面的运动规律,研究液体抨击舱壁产生的压力特性;在此基础上,设计单一隔板和组合隔板等不同制荡结构,探究共振频率、30%载液率下,自由液面形态和壁面冲击压力的特性。结果表明:在共振频率下,横摇幅值对压力峰值的影响最大;随着载液率的增加,壁面抨击压力双峰特性逐渐消失;当隔板尺度较小时,T型隔板更有利于降低压力的整体水平;双T型隔板可有效降低舱底冲击。

三维FEM与SPH结合算法在穿燃弹侵彻靶板中的应用研究

三维FEM与SPH粒子相结合的仿真算法在子弹侵彻靶板的研究中发挥了重要的作用,可以避免在强冲击计算中FEM网格出现大变形的问题,为了掌握三维FEM/SPH算法的优缺点,开展12.7 mm穿燃弹弹芯侵彻Q235靶板的数值仿真研究,选择二维FEM算法和三维FEM算法与其进行对比,通过分析侵彻深度、压力和塑性应变的影响范围、计算效率等,得到了以下结论:3种算法在计算侵彻深度方面相差无几,三维FEM算法相比其他算法计算的压力更加准确,而SPH粒子法不擅长计算靶板压力;子弹侵彻靶板过程中的侵蚀范围不超过5倍弹芯半径;二维FEM算法计算效率最高,适合用于调整模型和材料参数,而三维FEM/SPH结合的算法则更适合输出计算效果图。

一维理想弹塑性体的SPH-HLLC耦合算法

通过弹塑性波分析求得HLLC(Harten-Lax-van Leer-contact)近似黎曼解,提出了SPH(smoothed particle hydrodynamics)与一维理想弹塑性体模型下近似的HLLC黎曼求解器耦合的一种构造简单的算法。在SPH计算中,支持域内每个粒子对都存在一个黎曼间断问题,它的黎曼解被代入控制方程中计算。其中一维理想弹塑性体的HLLC近似黎曼解的思想是:先假设整体处于弹性状态计算黎曼解,然后对计算结果进行塑性条件修正,最后用修正后的物理变量计算HLLC近似黎曼解。将提出的SPH-HLLC耦合算法与传统SPH算法在一维算例下的计算结果进行对比,结果表明,该算法能有效模拟一维理想弹塑性体材料的碰撞,并能有效抑制在不同材料之间的压强和偏应力震荡,这是传统SPH方法很难做到的。

基于SPH-FEM耦合算法的台阶精准爆破延期时间研究及应用

电子雷管在大型露天矿爆破中广泛使用,利用其精准起爆特性通过设置合理延期时间可有效改善爆破质量,对矿山生产降本增效具有重要意义。基于光滑粒子流体动力学—有限单元(SPH-FEM)耦合算法,利用LS-Dyna软件建立了多个巴润矿常规台阶尺寸的三维数值模型。针对电子雷管起爆条件下不同孔间和排间延时分别建立双孔、三孔SPH-FEM三维模型,从矿岩体SPH粒子应力和移动2个维度研究了被爆矿岩体的受力破碎、抛掷位移特征,并重点分析了不同排间延时下后排炮孔爆破漏斗的偏移角度。据此确定了最佳孔间、排间延期时间范围,并通过现场验证对比试验,选出了适合该爆区的最优延时。研究结果表明:在巴润矿现行孔排距条件下利用电子雷管精准起爆,孔间延时在20~30 ms内可达到较好的破碎效果;排间延时大于35 ms时,先爆炮孔为后续炮孔提供新的自由面和抛掷空间,且大于40 ms时应力趋于稳定;在现场验证试验中,试验区内边长1 m以下的破碎矿岩体占比达91%,较非试验爆区中同尺寸岩块占比提高了14%,破碎效果得到有效改善。

基于SPH-FEM耦合方法的泥石流冲击输电塔基础的动力分析

泥石流是我国西南山区常见的地质灾害。架空输电杆塔在泥石流的冲击下往往发生基础破坏甚至会造成杆塔倒塌。首先采用光滑粒子流体动力学(smoothed particle hydrodynamics,简称SPH)方法和有限元方法(finite element method,简称FEM)相耦合的三维数值方法模拟了泥石流对杆塔基础的冲击作用;在与相关模型试验结果验证的基础上,开展了不同泥石流密度、黏度系数及初始速度条件下对输电塔基础的冲击力作用的参数分析;研究结果表明:随着泥石流初始速度的增加,冲击力峰值会随之增大;前排基础的冲击力峰值均大于后排基础;泥石流冲击过程特性受到泥石流密度和黏度系数影响。与稀性泥石流相比:黏性泥石流冲击基础后,基础下游真空区相对要小;此外,将数值模拟结果与Kwan冲击力公式及铁二院推荐的冲击压力设计公式预测值进行对比分析可以发现:Kwan冲击力公式能较好地预测出基础所受泥石流冲击力的平均趋势,最大预测误差低于30%,铁二院公式预测的稀性和黏性泥石流的冲击压力平均偏低分别约17%和28%。相关研究结果有望为泥石流频发区域输电塔基础的设计和风险评估提供一定的参考依据。

基于SPH方法的孤立波数值模拟

文中应用DualSPHysics开源代码平台,基于Goring理论采用推板造波方法构建二维数值造孤立波水槽,探究粒子间距D p对数值模拟孤立波的影响.采用6种粒子间距D p分别对2种波高的孤立波进行了数值模拟,显示了2个监测点处数值模拟与解析解的波形对比,计算和分析了不同D p下、4个监测点处的波高与理论波高的误差.结果表明:粒子间距D p=0.01 m时数值模拟精度较高同时计算耗时较少,并将此种粒子间距D p的数值模拟结果与物理试验测量结果进行了对比,二者吻合程度好.

基于SPH方法的空调进气口进水量分析及优化

由于雨刮臂摆动频次与导水槽及空调外循环进风口结构不匹配等因素,部分车型在淋雨工况下,有水滴甚至水流沿空调进风口进入空调系统,导致空调出现异味,甚至有水渗漏进入乘客舱,出现严重的感知质量问题。采用SPH方法,考虑雨刮臂运动、车身姿态及气流效应工况下,借助PreonLab软件仿真,复现某车型淋雨场景下的水管理质量问题,通过在空调外循环进风口位置增加挡板,显著减少了溅入空调箱的雨水量,并在实车淋雨试验中得到验证。方法能在车辆开发阶段发现并整改车辆在淋雨场景下的流通路径设计不合理等问题,可改变目前车辆淋雨场景水管理质量控制主要依托实车测试的现状,也可应用于车辆水管理的其他性能质量的控制,如涉水、雨污等。

颗粒流运动SPH方法及滑坡破碎效应研究

山体滑坡是全球范围内多发的一种地质灾害。由于滑坡具有突发性和破坏性强的特点,建立有效的数值分析模型将有助于制定针对性的防治策略。本文针对滑坡运动过程中表现出的颗粒流特性,基于μ(I)模型提出了针对浅层滑坡的动态摩擦系数表达式,并构建了对应的光滑粒子流体动力学(SPH)方法求解框架。考虑到颗粒破碎对滑坡运动性的显著影响,结合基于破坏势能的颗粒破碎法则,建立μ(I)模型中基底摩擦力与颗粒分布之间的关系。通过两个经典的三维斜面模型试验,验证了μ(I)模型在滑坡运动分析中的应用价值,并进行了颗粒破碎效应参数敏感性分析,为后续滑坡灾害的防治工作提供参考。

基于SPH方法的船体海洋飞沫生成形态模拟

为了研究海洋飞沫的生成形态,采用光滑粒子法(SPH)的粒子捕捉技术,分析4种常见的船首特征对海洋飞沫轨迹的影响。研究发现,船首的设计在飞沫的生成和运动特性上起着决定性作用。球鼻艏和破冰艏通过镇压波浪减少飞沫的覆盖范围,而飞剪艏和前倾艏则利用其独特的流线型设计有效地对飞沫进行引流,但却导致飞沫的生成高度较高,覆盖范围较广。此外,研究还揭示了不同类型的飞沫(如崩波破碎、卷波和激散波破碎)在船首附近的工况和轨迹模式。研究结果可为船舶设计优化及防除冰技术提供重要理论支持。

A flexible multiscale algorithm based on an improved smoothed particle hydrodynamics method for complex viscoelastic flows

Viscoelastic flows play an important role in numerous engineering fields,and the multiscale algorithms for simulating viscoelastic flows have received significant attention in order to deepen our understanding of the nonlinear dynamic behaviors of viscoelastic fluids.However,traditional grid-based multiscale methods are confined to simple viscoelastic flows with short relaxation time,and there is a lack of uniform multiscale scheme available for coupling different solvers in the simulations of viscoelastic fluids.In this paper,a universal multiscale method coupling an improved smoothed particle hydrodynamics(SPH)and multiscale universal interface(MUI)library is presented for viscoelastic flows.The proposed multiscale method builds on an improved SPH method and leverages the MUI library to facilitate the exchange of information among different solvers in the overlapping domain.We test the capability and flexibility of the presented multiscale method to deal with complex viscoelastic flows by solving different multiscale problems of viscoelastic flows.In the first example,the simulation of a viscoelastic Poiseuille flow is carried out by two coupled improved SPH methods with different spatial resolutions.The effects of exchanging different physical quantities on the numerical results in both the upper and lower domains are also investigated as well as the absolute errors in the overlapping domain.In the second example,the complex Wannier flow with different Weissenberg numbers is further simulated by two improved SPH methods and coupling the improved SPH method and the dissipative particle dynamics(DPD)method.The numerical results show that the physical quantities for viscoelastic flows obtained by the presented multiscale method are in consistence with those obtained by a single solver in the overlapping domain.Moreover,transferring different physical quantities has an important effect on the numerical results.

Multimoment Hydrodynamics in Problem on Flow around a Sphere: Entropy Interpretation of the Appearance and Development of Instability

Multimoment hydrodynamics equations are applied to investigate the phenomena of appearance and development of instability in problem on a flow around a solid sphere at rest. The simplest solution to the multimoment hydrodynamics equations coincides with the Stokes solution to the classic hydrodynamics equations in the limit of small Reynolds number values, . Solution ?to the multimoment hydrodynamics equations reproduces recirculating zone in the wake behind the sphere having the form of an axisymmetric toroidal vortex ring. The ?solution remains stable while the entropy production in the system exceeds the entropy outflow through the surface confining the system. The passage of the first critical value ?is accompanied by the ?solution stability loss. The ?solution, when loses its stability, reproduces periodic pulsations of the periphery of the recirculating zone in the wake behind the sphere. The ?and ?solutions to the multimoment hydrodynamics equations interpret a vortex shedding. After the second critical value ?is reached, the ?solution at the periphery of the recirculating zone and in the far wake is replaced by the ?solution. In accordance with the ?solution, the periphery of the recirculating zone periodically detached from the core and moves downstream in the form of a vortex ring. After the attainment of the third critical value , the ?solution at the periphery of the recirculating zone and in the far wake is replaced by the ?solution. In accordance with the ?solution, vortex rings penetrate into each other and form the continuous vortex sheet in the wake behind the sphere. The replacement of one unstable flow regime by another unstable regime is governed the tendency of the system to discover the fastest path to depart from the state of statistical equilibrium. Having lost the stability, the system does not reach a new stable position. Such a scenario differs from the ideas of classic hydrodynamics, which interprets the development of instability in terms of bifurcations from one stable state to another stable state. Solutions to the multimoment hydrodynamics equations indicate the direction of instability development, which qualitatively reproduces the experimental data in a wide range of Re values. The problems encountered by classic hydrodynamics when interpreting the observed instability development process are solved on the way toward an increase in the number of principle hydrodynamic values.

Smoothed-Particle Hydrodynamics Simulation of Ship Motion and Tank Sloshing under the Effect of Regular Waves

Predicting the response of liquefied natural gas(LNG)contained in vessels subjected to external waves is extremely important to ensure the safety of the transportation process.In this study,the coupled behavior due to ship motion and liquid tank sloshing has been simulated by the Smoothed-Particle Hydrodynamics(SPH)method.Firstly,the sloshing flow in a rectangular tank was simulated and the related loads were analyzed to verify and validate the accuracy of the present SPH solver.Then,a three-dimensional simplified LNG carrier model,including two prismatic liquid tanks and a wave tank,was introduced.Different conditions were examined corresponding to different wave lengths,wave heights,wave heading angles,and tank loading rates.Finally,the effects of liquid tank loading rate on LNG ship motions and sloshing loading were analyzed,thereby showing that the SPH method can effectively provide useful indications for the design of liquid cargo ships.

基于SPH粒子法的汽车高压油箱碰撞CAE计算分析

文章基于汽车车体结构、高压燃油箱及其周围零部件组成的子模型,采用LS-DYNA显式求解器,利用SPH 粒子技术,针对整车正面碰撞、侧面碰撞以及后面碰撞过程中,高压油箱周围变形以及其内部油液的晃动对油箱壳体的影响进行有限元模拟和研究。通过碰撞CAE计算分析,得出碰撞过程中油液晃动对油箱的撞击而产生的应力分布及变化过程,分析油箱的变形、应力、应变分布等情况,可以评估汽车在发生高速碰撞时油箱损伤、破坏情况。最终通过在某整车高速追尾CAE模拟中的应用,再现了油液SPH 粒子的有效作用。

Improved Model for Soil as a Two-Phase Mixture Based on Smoothed Particle Hydrodynamics (SPH)

It is desired to resolve soil contamination with reduced costs. “Insoluble treatment” is a soil improvement method for heavy metal containing soil, which uses soil mixers to mix soil and soil improvement liquid agents. To reduce the costs of this method, soil mixers have to be optimized. However, it is not achieved due to the lack of theoretical knowledge on mixing solid with liquid. Therefore, a numerical model to simulate the dynamic behavior of solid and liquid is on the development in this study using Smoothed Particle Hydrodynamics (SPH) method. To validate the numerical model, several experiments were carried out and numerically reproduced. The comparisons of the results showed that the numerical model replicated a liquid flow with an error rate of 2.1% and a seepage flow with an error rate up to 26.1%. Especially, the water distribution in the soil pores was highly improved with absolute gaps in volumetric water content up to 4.4% in the porosity range of 10% - 90%. For the water absorption into dry sand, the simulation result became more realistic by concerning soil suction.

Extension of Smoothed Particle Hydrodynamics (SPH), Mathematical Background of Vortex Blob Method (VBM) and Moving Particle Semi-Implicit (MPS)

SPH has a reasonable mathematical background. Although VBM and MPS are similar to SPH, their ma-thematical backgrounds seem fragile. VBM has some problems in treating the viscous diffusion of vortices but is known as a practical method for calculating viscous flows. The mathematical background of MPS is also not sufficient. Not with standing, the numerical results seem reasonable in many cases. The problem common in both VBM and MPS is that the space derivatives necessary for calculating viscous diffusion are not estimated reasonably, although the treatment of advection is mathematically correct. This paper discusses a method to estimate the above mentioned problem of how to treat the space derivatives. The numerical results show the comparison among FDM (Finite Difference Method), SPH and MPS in detail. In some cases, there are big differences among them. An extension of SPH is also given.