基于SPH方法的射孔枪设计及射孔过程研究

基于SPH方法对射孔枪射孔过程进行了模拟,并实现高速射流情况下的射孔过程仿真.计算了射孔弹弹型不变的情况下以40CrNiMo为材料的枪筒,在不同射流速度下盲孔毛刺高度值,不同射流速度和不同盲孔深度下的穿孔直径以及不同材料下毛刺高度值.通过计算发现,盲孔毛刺高度随射孔速度的增加而降低,且高度值变化幅度越来越小;射孔枪的穿...     

NUMERICAL SIMULATIONS OF WATER WAVE DYNAMICS BASED ON SPH METHODS

A numerical model was established for simulating water wave dynamic problems by adopting the Smoothed Particle Hydrodynamics (SPH) methods of iterative solution of Poisson's equation for pressure field, and meanwhile the sub-grid turbulence model was applied in the simulation so as to more accurately describe the turbulence characteristics at the time of wave breaking. In this article, simulation of the problem of the dam collapsing verifies the compoting accuracy of this method, and its results can be identical with the results of VOF method and the experimental results by comparison. Numerical simulations of the course of solitary wave and cnoidal wave run-up breaking on beaches were conducted, and the results are basically consistent with experimental results. This indicates that the SPH method is effective for the numerical simulation of the complex problems of water wave dynamics.     

WATER ENTRY OF A WEDGE BASED ON SPH MODEL WITH AN IMPROVED BOUNDARY TREATMENT

The hydrodynamic problem of a two-dimensional wedge entering water is studied based on Smoothed Particle Hydrodynamics (SPH) model. A non-reflection boundary treatment for SPH method is proposed to reduce the reflection of sound waves. The boundary pressure is obtained using an improved coupling boundary treatment approach, which is validated by comparing the simulation results with experimental and analytical results in literature. A series of cases with different initial entering velocities are simulated. The maximum force on the wedge and the corresponding time required to reach it for the different cases of initial entering velocities of the wedge are obained and fitted into formulas against the initial entering velocity of the wedge. The maximum drag coefficients of the wedge for the different cases with Froude number greater than 2 are all near the value of 0.91.     

Processing capabilities of micro ultrasonic machining for hard and brittle materials: SPH analysis and experimental verification

Micro ultrasonic machining (micro-USM) is an unconventional micromachining technology that has capability to fabricate high aspect ratio micro-holes, intricate shapes and features on various hard and brittle materials. The material removal in USM is based on brittle fracture of work materials. The mechanical properties and fracture behaviour are different for varied hard and brittle materials, which would make a big difference in the processing capability of micro-USM. To study the processing capability of USM and exploit its potential, the material removal of work materials, wear of abrasive particles and wear of machining tools in USM of three typical hard and brittle materials including float glass, alumina, and silicon carbide were investigated in this work. Both smoothed particle hydrodynamics (SPH) simulations and verification experiments were conducted. The material removal rate is found to decrease in the order of glass, alumina, and silicon carbide, which can be well explained by the simulation results that cracking of glass is faster and larger compared to the other materials. Correspondingly, the tool wear rate also dropped significantly thanks to the faster material removal, and a formation of concavity on the tool tip center due to intensive wear was prevented. The SPH model is proved useful for studying USM of different hard and brittle materials, and capable of predicting the machining performance.     

液固交互过程中固体破碎现象的实时模拟

提出一种适用于液固交互过程中的固体破碎模拟方法.针对传统液固交互边界处理算法复杂,难以实时模拟固体破碎的缺陷,本文基于SPH算法,提出对液体与固体使用统一的粒子表示,将预测校正方案应用于处理液固交互过程中固体之间的碰撞问题,从而将固体破碎过程简化为固体碎片边界粒子生成的过程,并使用形状匹配算法对固体碎片进行形状约束.实验结果证明,采用文中方法能够实时模拟出液固交互过程中,细节丰富的固体破碎现象,效果真实.     

WCSPH方法模拟三角形底板水跃特性

使用弱可压光滑粒子动力学（weakly compressible smoothed particle hydrodynamics,WCSPH）方法,对弗劳德数Fr=1.68～6.08和不同波长与波高(S/t）之比的三角形波状底板上的水流流态、流速云图以及流速矢量图、共轭水深、消能率等水跃特性进行模拟研究。经对比分析：数值模拟结果与试验结果吻合较好;三角形波状底板表面会产生顺时针漩涡增加能量耗散,提高消能率,其水跃长度比光滑底板的小,且消能效果优于光滑底板。通过分析不同工况的水跃特性,确定了最佳三角形波状底板,其可使共轭水深和相对水跃长度分别降低14.15%和24.83%,而消能率比光滑底板提高48.52%。     

基于SPH法的正弦形消力池底板水跃现象数值模拟

利用光滑质点水动力学法(SPH方法)对正弦形消力池底板上的水跃现象进行数值建模,共模拟2种波形5种工况。将SPH方法的模拟值与已有文献的试验值作对比,验证数值模型及数值方法研究此类问题的可行性和适用性,并分析水面线、流速分布、跃长、共轭水深、消能率等水跃特性的变化规律。结果表明:SPH方法模拟结果与试验结果吻合度较高;水跃段流速分布不均匀、自由表面波动较大,且流层间存在相对运动从而形成旋滚,同等条件下随着弗劳德数的递增,掺气量和自由表面破碎现象越来越剧烈,旋滚的影响范围逐渐变大;正弦形底板消能率较光滑底板提高10%左右且所有工况消能率均在47%以上。     

基于周期性校正神经网络的血流血管壁耦合

针对传统的血流血管壁耦合难以兼顾计算效率和视觉真实感的问题,提出了一种基于周期性校正神经网络（Periodic-corrected Network,PcNet）的血流血管壁耦合数据驱动仿真方法。设计基于平滑粒子流体动力学（SPH）的血流粒子状态特征向量,对邻域血流粒子和血管壁代理粒子的混合贡献进行建模。提出一种半监督的神经网络--改进的周期性校正神经网络,预测每个粒子在下一帧的加速度。实验结果表明该仿真方法实现了快速、稳定、逼真的血流血管壁耦合。     

A skewed kernel approach for the simulation of shocks using SPH

A wide variety of jump discontinuities, such as shock fronts, are abound in high‐speed flows. An accurate approximation of these fronts may require higher order techniques either under mesh‐based methods or mesh‐free methods. In the latter class, the smoothed particle hydrodynamics (SPH) is becoming popular as a promising method. However, the standard approach in SPH (like any other discrete methods) can result in highly diffusive solutions because of the inevitable use of artificial viscosity to suppress numerical oscillations. On the other hand, the SPH formulation allows innovative ways to model complicated phenomena. In this paper, we introduce the novel idea of a skewed Gaussian kernel, to improve the shock capturing capability in high speed flows. Here, the standard Gaussian kernel function is modified, and its ‘shape’ is altered with a predesigned tunable skewness parameter, while the basic unity property of the kernel function is still preserved. The SPH with the proposed skewed Gaussian kernel is then applied on a number of benchmark problems in computational fluid dynamics, featuring shocks. The simulations have shown significantly better shock capture through the skewed kernel approach as against the standard techniques, with almost no increase in computational time. Copyright © 2016 John Wiley & Sons, Ltd.     

High-speed water impacts of flat plates in different ditching configuration through a Riemann--ALE SPH model

The violent water entry of flat plates is investigated using a Riemann-arbitrary Eulerian-Lagrangian(ALE) smoothed particle hydrodynamics(SPH) model. The test conditions are of interest for problems related to aircraft and helicopter emergency landing in water. Three main parameters are considered: the horizontal velocity, the approach angle(i.e., vertical to horizontal velocity ratio) and the pitch angle, a. Regarding the latter, small angles are considered in this study. As described in the theoretical work by Zhao and Faltinsen(1993), for small a a very thin, high-speed jet of water is formed, and the time-spatial gradients of the pressure field are extremely high. These test conditions are very challenging for numerical solvers. In the present study an enhanced SPH model is firstly tested on a purely vertical impact with deadrise angle α=4°. An in-depth validation against analytical solutions and experimental results is carried out, highlighting the several critical aspects of the numerical modelling of this kind of flow, especially when pressure peaks are to be captured. A discussion on the main difficulties when comparing to model scale experiments is also provided. Then, the more realistic case of a plate with both horizontal and vertical velocity components is discussed and compared to ditching experiments recently carried out at CNR-INSEAN. In the latter case both 2-D and 3-D simulations are considered and the importance of 3-D effects on the pressure peak is discussed for α=4° and α=10°.