Integrated process simulation of primary shaping: multi scale approaches

We investigate simulation approaches for the modelling of the primary shaping processes micro powder injection moulding and micro casting. We could reproduce the segregation during micro powder injection moulding (MicroPIM) with a simulation using particle methods. The phase field method allows for accurate prediction of the dynamics of solidification of a melt, whereby model order reduction is used to limit the computational effort. The results give valuable advice for the process conduct and the dimensioning of the micro parts.     

Multiphase Reactor Database Interrogation and Computing at the Finger Tip

A learning approach is proposed to critically evaluate the hydrodynamic, heat and mass transfer parameters for multiphase reactors. Packaged as interactive software, this learning approach exposes students, engineers and researchers to a range of reactor features. It allows gaining insights in computing reactor characteristics, sifting through databases, choosing the fittest correlations, embedding proprietary models and databanks for critical analysis. The software developed at Laval University integrates comprehensive databanks and correlations on gas-liquid co- and counter-current packed beds.     

Testing and numerical simulation of a medium strength rock material under unconfined compression loading

This study aims to numerically and experimentally investigate the response of a medium strength rock material under unconfined compression loading up to failure. The unconfined compressive strength (UCS) is one of the most important parameters in characterising rock material behaviour. Hence the UCS is crucial in understanding the failure mechanism of fractured rocks. An effective approach to determine the UCS and to investigate the behaviours of rock materials under unconfined compression is essential in the majority of research fields of rock mechanics. The experimental configuration for the unconfined compression test, suggested by the protocols of the ASTM standard, has some limitations which affect the accuracy in determination of the real UCS. Among several alternative configurations proposed, the Mogi's configuration seems to be the most appropriate one. Therefore, the ASTM and Mogi's configurations were used to perform the tests on a medium strength rock material, i.e. Pietra Serena sandstone. The results using two configurations were discussed in terms of the differences. The tests were also replicated in LS-DYNA using a finite element method (FEM) coupled smooth particle hydrodynamics (SPH) technique. This technique is employed in this study due to its capabilities to cope with large deformation issues related to the rocks. An advanced material model, called the Karagozian and Case Concrete (KCC) model, is implemented in the numerical simulations. The KCC model consists of three independent fixed failure surfaces and it can consider the damage accumulation based on the current state of stress among these failure surfaces. An equation-of-state (EOS) is used in conjunction with KCC material model for decoupling the volumetric and deviatoric responses. The numerical and experimental results were finally compared with the focus on the stress–strain diagram and the failure patterns. The comparison shows that the numerical results are in good agreement with the experimental results.     

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。     

Hydrodynamic characteristics of gas–solid fluidization at high temperature

Effect of temperature on the hydrodynamics of bubbling gas–solid fluidized beds was investigated in this work. Experiments were carried out at different temperatures ranged of 25–600°C and different superficial gas velocities in the range of 0.17–0.78 m/s with sand particles. The time‐position trajectory of particles was obtained by the radioactive particle tracking technique at elevated temperature. These data were used for determination of some hydrodynamic parameters (mean velocity of upward and downward‐moving particles, jump frequency, cycle frequency, and axial/radial diffusivities) which are representative to solids mixing through the bed. It was shown that solids mixing and diffusivity of particles increases by increasing temperature up to around 300°C. However, these parameters decrease by further increasing the temperature to higher than 300°C. This could be attributed to the properties of bubble and emulsion phases. Results of this study indicated that the bubbles grow up to a maximum diameter by increasing the temperature up to 300°C, after which the bubbles become smaller. The results showed that due to the wall effect, there is no significant change in the mean velocity of downward‐moving clusters. In order to explain these trends, surface tension of emulsion between the rising bubble and the emulsion phase was introduced and evaluated in the bubbling fluidized bed. The results showed that surface tension between bubble and emulsion is increased by increasing temperature up to 300°C, however, after that it acts in oppositely.     

汽车暖通空调气动噪声仿真

为研究汽车暖通空调气动噪声特性,以某车型汽车暖通空调为研究对象,通过风阻试验对滤清器和蒸发器进行等效处理,建立仿真模型;基于流体动力学和气动声学理论,结合宽频带噪声源模型和FW-H模型,预测声源分布和噪声特性;将仿真结果与试验结果进行对标验证,出风口风量最大误差为6.7%,最小为2.1%,噪声频谱特性具有较高的一致性。结果表明,Curle噪声源主要分布在鼓风机和空调箱壁面,近场以旋转噪声为主,远场宽频噪声占主导。可适当通过减小叶片与空气接触面积、增加叶片数量、调整蜗舍角度和间隙、增加导流装置等措施降低暖通空调工作时产生的噪声,为汽车暖通空调前期开发提供一种研究方法。     

Monte-Carlo方法求解水动力学方程的原理及实践

介绍Monte Carlo方法的基本思想及求解Poisson方程的原理 ;利用Monte Carlo方法及图论建立河网计算的随机游动模型 ,并应用于实际的大型河网中 ,取得了较好的结果 .利用Monte Carlo方法计算河网可以避免解大型的稀疏矩阵 ,计算简单、灵活     

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消力池内陡坡水跃的数值模拟

为了满足明渠水流入流的边界条件,扩展SPH方法在明渠恒定流模拟中的应用,本文建立SPH方法的出入流模型,通过设置相应的出入流边界条件,研究不同坡度下消力池内陡坡水跃特性。针对两种不同流量,对斜坡坡角θ分别在20°、30°、45°条件下的陡坡水跃进行数值模拟。模拟结果与文献中的实验结果进行对比分析,结果表明:出入流模型能为陡坡水跃的数值模拟提供稳定的水流。各陡坡不同流量下水面线的变化趋势基本相同,误差均在±10%内;相同坡角时,单宽流量为0.063 m~2/s的消能效果均大于单宽流量为0.105 m~2/s的消能效果。该方法处理出入流边界简单,合理准确,能够较好地模拟不同坡度下消力池内陡坡水跃,得到陡坡水跃特性,具有一定的可行性和可靠性。     

Density functional modelling in multiphase compositional hydrodynamics

This work is essentially a review of a density functional approach in multiphase hydrodynamics developed by the authors during the last 15 years [Dinariev, J Appl Math Mech 1995;59(5):745–752; Dinariev, J Appl Math Mech 1998;62(3):397–405; Demyanov and Dinariev, Fluid Dynam 2004;39(6):933–944; Demianov et al., “Basics of the Density Functional Theory in Hydrodynamics,” Fizmatlit, Moscow; 2009 (in Russian); Dinariev and Evseev, Fluid Dynam 2010;45(1):85–95]. The basic assumption is a representation of the entropy or the Helmholtz energy of the mixture as a functional that is dependent upon chemical component densities. The hydrodynamic system of equations (local conservation laws for chemical components, momentum, and energy) is used to describe multiphase processes, and the constitutive relations (expressions for stresses, diffusion, and heat fluxes) are derived from entropy growth requirement. The authors present the results of numerical simulations describing static and dynamic multiphase systems.