煤微观结构三维表征及其孔–渗时空演化模式数值分析

 探讨煤岩微观孔隙结构统计意义上的等效构建方法,并于孔隙尺度下模拟流体运移行为的时空演化过程。首先,结合煤岩孔隙结构的各向异性及非线性特征,采用修正的四参数随机生长(QSGS)算法构建煤岩多孔介质模型。随后,采用格子Boltzmann方法(LBM)模拟孔隙中气体单相流的运移过程,并基于数值试验结果,分析煤岩介质中影响渗透率的主要因素及流体运移达到平衡态前的演化模式。分析结果表明：(1) 多孔介质的渗透性能受控于少量、连通性好的大孔所形成的通道,而小孔及微孔中气体的行为基本属于浓度扩散过程;(2) 孔隙属性空间变异条件相同情况下,孔隙度同渗透率之间满足乘幂关系,但幂率系数随孔隙属性变异因子的降低而增加;(3) 渗透率随时间呈减少趋势,自运移开始达到动态平衡的耗时量同孔隙度之间是一种负相关的幂率关系。     

LBM simulation of forced convective channel flow containing multiple obstacles: Effects of obstacles height and position

We examine the effects of the obstacles, height, and position on the forced convective flow in a channel having three obstacles on the lower wall of the channel. All the walls of the channel and obstacles are retained at a constant temperature while the fluid with temperature more than the walls are entered into the channel. The flow governing equations, vorticity equation, and energy equation are solved numerically by using the lattice Boltzmann method (LBM) together with the finite difference successive over relaxation method (SOR). The effects of obstacles height, h, and distance, d, between the obstacles on the streamlines and isotherms are presented. To investigate the heat transfer rate for changing the height and position of the obstacles, local Nusselt number distribution and the mean Nusselt number distribution are also presented. It is observed that vortices, produced backward to each obstacle, increase axially with increasing the height of each obstacle. Also vortices, produced between obstacles, change its shape with decreasing the distance between obstacles. It is asserted that heat transfer rate can be increased by extending only the height of first obstacle.     

地应力作用下水力裂缝中支撑剂导流能力的数值模拟研究

目前,对水力裂缝内支撑剂的运移及其导流能力的研究主要通过实验进行,而完全基于数值模拟的研究不多。基于颗粒离散元对水力裂缝中支撑剂数值模拟的结果,通过数字重构方法,得到了水力裂缝内支撑剂堆积结构的数字模型;在重构的数字模型基础上,采用格子玻尔兹曼方法(LBM),模拟了单相流体在支撑剂孔隙结构内的流动过程,进而得到了不同地应力水平下不同支撑剂的绝对渗透率,且数值计算结果与Kozeny-Carman经验公式吻合。研究结果发现,地应力作用下,裂缝张开度减少,支撑剂颗粒更加密实,可能出现支撑剂嵌入到岩石中的现象;随着地应力的增加,裂缝内支撑剂堆积体的孔隙度减少,比表面积增大,渗透率减少;相同地应力作用下,支撑剂粒径越大,其孔隙度越低,比表面积越小,越易出现支撑剂嵌入现象,渗透率减少越大,但其值一般总大于小粒径支撑剂的渗透率。     

单裂缝中携砂液流动规律研究

水力压裂中,裂缝壁面对支撑剂团在狭窄裂缝中输送沉降时的受力有重要影响。该文基于LBM建立颗粒流动数值模型,构建星型、三棱柱型、长方体型颗粒团簇模型,研究颗粒团簇在不同雷诺数Re、颗粒团簇与壁面相对距离H/d下的升阻力变化规律。结果表明：壁面影响下,随Re的增大,颗粒团簇的曳力系数、升力系数均减小,且壁面方向升力系数总小于无壁面方向的结果;单颗粒曳力系数与团簇平均曳力系数的比值随Re的增加而减小,随壁面边界效应的影响而增大;不同位置的颗粒曳力系数比值表现为前排颗粒减小、中间颗粒先增大后减小、近壁面颗粒逐渐增大。随H/d的增大,颗粒团簇远离壁面,边界影响减弱,曳力系数减小程度逐渐减弱;前排及近壁面颗粒曳力系数比值与升力系数随之减小;远壁面颗粒逐渐靠近壁面,曳力系数比值增大。壁面边界效应会加剧近壁面颗粒受力,且外侧颗粒对内部颗粒受力有屏蔽作用。

     

A review of modeling and simulation of laser beam machining

Laser beam machining (LBM) is a widely used thermal advance machining process capable of high accuracy machining of almost any material with complex geometries. CO₂ and Nd:YAG lasers are mostly used for industrial purposes. Drilling, cutting, grooving, turning and milling are the applications of LBM with different material removal mechanisms. Modeling and simulation of the LBM process is indispensable for optimization purposes. Modeling can be done by implementing analytical, numerical, experimental and artificial intelligence-based methods. This paper provides a review of the various methods used for modeling and simulation of the laser beam machining process as well as key researches done in this field so far.     

LATTICE BOLTZMANN METHOD WITH DOUBLE MESHES

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＩｎｒｅｃｅｎｔ ｙｅａｒｓ ,ｔｈｅｏｒｙａｎｄａｐｐｌｉｃａｔｉｏｎｓｏｆＬａｔｔｉｃｅＢｏｌｔｚｍａｎｎｍｅｔｈｏｄ (ＬＢＭ )ｈａｖｅｍａｄｅｒａｐｉｄ ｐｒｏｇｒｅｓｓ ,ｍａｋｉｎｇＬＢＭｃｏｍｐｅｔｉｔｉｖｅｔｏｔｈｅｃｏｎｖｅｎｔｉｏｎａｌａｐｐｒｏａｃｈｅｓｉｎＣｏｍｐｕｔａｔｉｏｎａｌＦｌｕｉｄＤｙｎａｍｉｃｓ (ＣＦＤ )ａｎｄａｎａｌｔｅｒｎａｔｉｖｅｗａｙｔｏｓｉｍｕ ｌａｔｅｔｈｅｆｌｕｉｄｆｌｅｌｄ[1] .ＴｈｅｋｅｙｉｄｅａｂｅｈｉｎｄＬＢＭｉｓｔｈ…     

WALL EFFECTS ON FLOWS PAST TWO TANDEM CYLINDERS OF DIFFERENT DIAMETERS

Flows past two tandem cylinders of different diameters placed centrally in a channel with fixed centre-to-centre spacing 6D and diameter ratio are simulated based on the Lattice Boltzmann Method(LBM).In all the simulations,the diameter of the smaller cylinder is chosen as the characteristic length.The Reynolds number based on the average inflow velocity is 20-120 and studies are over the range of blockage ratio 2-8.In both Small-Big Arrangement(SBA)and Big-Small Arrangement(BSA),the effects of the channel width and Reynolds number on the flow structures and force coefficients are studied.Results show that the flows in BSA are more regular than those in SBA for the same flow fields.In BSA with and,the force coefficients all fluctuate with constant amplitudes and a coupled frequency,the coupled frequency becomes small as the blockage ratio decreases and by an exact test we give out the relation of the blockage ratio and Strouhal number.As the blockage ratio decreases to 2,there exist pitchfork bifurcations in both SBA and BSA,and results show that the critical Reynolds numbers of pitchfork bifurcations for SBA and BSA are both between 60 and 80.In SBA with,the flow structure has a static asymmetric mode.It is found that the channel width has also an effect on the critical spacing where the flow changes from single body mode into co-shedding mode.By an accurate survey on flows past two cylinders with equal diameters placed inside a channel with the width,the relation between channel width and the critical spacing is given and results show that the critical spacing increases as the channel width increases.     

SIMULATION OF THE TWO PHASE FLOW OF DROPLET IMPINGEMENT ON LIQUID FILM BY THE LATTICE BOLTZMANN METHOD

A Lattice Boltzmann Method (LBM) with two-distribution functions is employed for simulating the two-phase flow induced by a liquid droplet impinging onto the film of the same liquid on solid surface.The model is suitable for solution of twophase flow problem at high density and viscosity ratios of liquid to vapor and phase transition between liquid and its vapor.The roles of the vapor flow,the density ratio of liquid to vapor and the surface tension of the droplet in the splashing formation are discussed.It is concluded that the vapour flow induced by the droplet fall and splash in the whole impinging process may affect remarkably the splash behaviour.For the case of large density ratio of liquid to vapor a crown may engender after the droplet collides with the film.However,for the case of small density ratio of liquid to vapor a "bell" like splash may be observed.     

基于格子Boltzmann方法和大涡模拟的颈动脉分叉狭窄流动并行计算

颈动脉斑块的形成与复杂的血流动力学因素密切相关,血液流动状况的精确模拟对颈动脉斑块的临床诊断具有重要意义。为了精确模拟脉动流场,在格子Boltzmann方法（LBM）的基础上,添加大涡模拟（LES）模型,建立了LBM-LES颈动脉模拟算法。利用医学图像重构软件,建立颈动脉狭窄真实几何模型,对颈动脉狭窄脉动流动进行了数值模拟,通过计算血液流动速度、壁面剪切应力（WSS）等,得出了有意义的流动结果,验证了LBM-LES对颈动脉狭窄后段血液流动研究的有效性。基于OpenMP编程环境,在高性能集群机全互联胖节点上进行了千万量级网格的并行计算,结果表明LBM-LES颈动脉模拟算法具有较好的并行性能。     

Association between novel indices of malnutrition-inflammation complex syndrome and cardiovascular disease in hemodialysis patients

Background: Inflammation and malnutrition are recognized as important risk factors for cardiovascular disease (CVD) in hemodialysis (HD) patients. Owing to substantial short‐term variability of serum C‐reactive protein (CRP), more reliable markers of malnutrition–inflammation complex syndrome should be sought with stronger associations with the risk of CVD in HD patients. We therefore explored the clinical relevance of a composite inflammatory index (prognostic inflammatory and nutritional index [PINI]) and of muscle protein mass indicators, derived from creatinine kinetics. Methods: This cross‐sectional study included 177 HD patients (89 women and 88 men; median age, 67.73 years). CVD and risk factors were assessed using medical charts, clinical examination, and biochemical measurements performed at inclusion. Lean body mass (LBM) was derived from creatinine kinetic modeling, whereas PINI was calculated as the ratio (CRP ×α1‐acid‐glycoprotein)/(albumin × transthyretin). Patients were divided according to the presence or absence of established CVD. Results: The traditional risk factors diabetes (odds ratio [OR], 5.83; p = 0.0045) and smoking (OR, 3.50; p < 0.02) were associated with an increase in prevalent CVD. Low transthyretin (OR, 3.79; p < 0.02) and high levels of CRP (OR, 2.70; p < 0.05), PINI (OR, 3.44; p < 0.02), observed LBM (OR, 3.01; p < 0.05), and the ratio of observed/expected LBM (OR, 4.24; p < 0.01) were associated with CVD after adjustment for age, sex, dialysis center, and dialysis vintage. After additional adjustment for diabetes and smoking, only PINI (OR, 2.85; p = 0.0446) and observed/expected LBM (OR, 2.96; p = 0.0361) were still significant. Conclusion: PINI and LBM are associated with increased relative risk for having CVD and could be used routinely to examine the degree of severity of malnutrition inflammation complex syndrome.