A comprehensive study on the parameters setting in smoothed particle hydrodynamics (SPH) method applied to hydrodynamics problems

Smoothed particle hydrodynamics (SPH) is a meshfree, Lagrangian particle method which has advantages in handling solids with extremely large deformation. Like any other numerical methods, cares must be taken to ensure its desirable accuracy and stability through considering several correction techniques in calculation. The selection of values for parameters in those correction approaches is a key step in SPH simulation, which is always difficult for new beginners to deal well with effectively. This paper examines the common inconsistency and instability problems in SPH method and studies its computational efficiency when applied to hydrodynamics problems with material strength like soil column collapse. We analyzed in detail how the correction techniques mitigate these inconsistency and instability problems. Also, the numerical testing results associate with different values for the parameters used in the correction techniques are provided for better understanding the influence of these parameters and for finding out the desirable values. It is found that (1) the SPH method is easily subjected to an inconsistency problem in the boundary area due to the boundary deficiency, and it can be treated well by adopting “virtual particles” contributing to the particle summations. (2) The numerical oscillation in SPH simulation can be mitigated effectively by artificial viscosity with the suggested parameter values. (3) The tension cracking treatment, artificial viscosity and artificial stress work well in removing the tensile instability problem in SPH method. In addition, the nearest neighboring particle searching (NNPS) algorithm, spacing ratio, smoothing length and time step influence the efficiency and accuracy of SPH method significantly. It is shown that SPH method with suggested parameters values can produce a very good result compared with the experimental result.     

高温高盐高黏油藏缔合聚合物-表面活性剂二元驱技术

针对大港油田孔南地区高温、高盐、中低渗、稠油等制约化学驱提高采收率的瓶颈技术问题,以官109 1断块枣Ⅴ油组为目标油藏,在优选适合缔合聚合物和表面活性剂基础上,进行聚合物-表面活性剂二元驱技术室内实验和现场应用研究。通过室内实验优选,缔合聚合物AP P7和表面活性剂BHS 01二元体系溶液与常规体系相比,具有较好的耐温抗盐性,拓展了常规二元驱适用油藏的温度和矿化度范围;缔合聚合物经过岩心剪切后仍能够有效建立阻力系数和残余阻力系数;通过岩心驱替实验,体系能有效提高稠油油藏的采收率,拓宽了聚合物驱适用的原油黏度范围;矿场单井试注后,注入井注入压力和启动压力升高,纵向吸水剖面得到改善,说明该体系在高温高盐条件下仍能保持较高黏度,能够有效改善水油流度比,效果明显。     

基于粘弹性球体地球模型的震后位移与重力变化计算软件

在考虑地球曲率、成层结构、可压缩性与自重的前提下,Tanaka等［1-2］提出一套较为完备的粘弹性球体位错理论,可计算全球任意位置由地震产生的同震与震后形变（含位移、重力变化、大地水准面变化）。Gao等［3］给出了与上述理论相匹配、界面友好的计算软件,能计算30个震后时间点对应的震后形变。本研究针对Gao等的软件进行改进,可计算震后任意时间点对应的震后形变。新软件由3个部分组成：1）与32个震后时间点相对应的32套离散格林函数数值框架;2）格林函数插值计算程序,可针对上述32套格林函数数值框架进行插值运算,输出任意震后时间点对应的格林函数数值结果;3）积分计算程序,调用上述格林函数数值结果,计算任意类型地震在地表任意位置产生的同震与震后形变。一般情况下,使用者只需按要求准备辅助文件,提供发震断层模型和观测站位置信息,以及震中周围地区地幔粘滞性因子,先后运行格林函数插值计算程序和积分计算程序,即可计算出目标地震在地表任意位置产生的同震与震后形变。本文基于粘弹球体位错理论与弹性球体位错理论,分别计算2011年日本MW9.0地震引起的远场同震位移,2套结果的高度一致性证明了新程序的正确性。最后,介绍需要注意的若干事项,便于使用者掌握该软件。     

一维问题的等效远置动力人工边界条件

在土-结构动力相互作用分析中,黏性人工边界条件和黏弹性人工边界条件虽具有计算效率和精度较高的优点,但施加边界单元的工作量较大;远置边界虽然具有处理技术简单、精度高等优点,但又存在计算成本高的问题。为克服黏性人工边界和黏弹性人工边界施加边界黏弹性单元工作量大、远置边界计算成本高的缺点,基于波的传播理论和波在介质交界面上的反射、透射原理,通过设置完全透射层并大大降低波在透射层的传播速度的方法,提出了一种等效远置动力人工边界条件并对其进行数值验证分析。研究结果表明,所提出的等效远置动力人工边界条件仅需通过合理选取透射层的参数,即可实现反射波向无限地基传播的模拟,具有精度和效率较好、不需施加边界单元工作量等优点,可应用到土-结构动力相互作用分析当中。     

大陆造山带岩石圈拆沉过程的数值模拟

岩石圈拆沉作用是指部分岩石圈由于重力不稳定性而沉入软流圈中的过程,与造山带的演化密切相关.本文基于非牛顿流体近似的有效黏度模型对岩石圈拆沉的过程进行了数值模拟,着重分析了岩石圈的黏度结构对拆沉作用的影响.数值模拟显示,下地壳控制着地壳与岩石圈地幔的耦合程度,对拆沉作用的过程和形态有很大的影响;在一定的初始重力不稳定性条...     

A dimensional analysis of scaling viscosity and velocity in DEM of constant strain rate tests on asphalt

This paper presents the results from discrete element modelling (DEM) of an idealised (sand) asphalt mixture under constant strain rate (velocity) compressive loading using the Burgers viscoelastic model. Using dimensional analysis it is shown that the effect of scaling applied velocity is the same as that of scaling both viscosities in the Burgers model by the same factor. This has been shown to be the case for a bonded aggregate, and it also has been shown to be applicable even when bond breakage occurs within the sample. This scaling method will be of great benefit in modelling tests on asphalt under different constant strain rates, simply by scaling both viscosities to minimise computational time.     

Experimental Study Optimizing Hole Cleaning-Cuttings Transport in Oil Drilling Engineering

With a clear understanding of the drilling fluid techniques and the cutting-taking mechanism, a new advanced model is set up for analyzing field data and quantitative forecast of cutting-taking mechanism. Therefore, a number of values affecting the drilling rate and the hole cleaning are studied over a wide range of parameters. Drilling data obtained under high-borehole-pressure conditions are analyzed to determine the causes of the reduction in rate of penetration (ROP) as the borehole pressure increases, which in some cases is caused by the buildup of rock debris under the bit. The theoretical achievement and testing conclusions can be very instructional for horizontal well drilling. Much higher annular velocities are required for effective hole cleaning in directional wells than in vertical wells. Highviscosity muds are observed to provide better transport than low-viscosity muds.     

不稳定边界层下地形重力内波

水槽实验及线性理论研究表明,当低层大气处于近中性或不稳定时,如果地形引起的动力扰动足够强,地形扰动可在上部稳定层结中激发出重力内波,波动反过来影响低层流场,引起动量输送。低层大气处于近中性或不稳定时,地形波同样对大气运动可产生波阻,这应引起模式工作者的重视。最后讨论了大气粘性对中性或不稳定层结下地形波的影响。