Mechanisms of fracture propagation from multi-cluster using a phase field based HMD coupling model in fractured reservoir

Natural fractures(NFs)are common in shale and tight reservoirs,where staged multi-cluster fracturing of horizontal wells is a prevalent technique for reservoir stimulation.While NFs and stress interference are recognized as significant factors affecting hydraulic fracture(HF)propagation,the combined influence of these factors remains poorly understood.To address this knowledge gap,a novel coupled hydromechanical-damage(HMD)model based on the phase field method is developed to investigate the propagation of multi-cluster HFs in fractured reservoirs.The comprehensive energy functional and control functions are established,while incorporating dynamic fluid distribution between multiple perforation clusters and refined changes in rock mechanical parameters during hydraulic fracturing.The HMD coupled multi-cluster HF propagation model investigates various scenarios,including single HF and single NF,reservoir heterogeneity,single HF and NF clusters,and multi-cluster HFs with NF clusters.The results show that the HMD coupling model can accurately capture the impact of approach angle(θ),stress difference and cementation strength on the interaction of HF and NF.The criterion of the open and cross zones is not fixed.The NF angle(a)is not a decisive parameter to discriminate the interaction.According to the relationship between approach angle(θ)and NF angle(a),the contact relationship of HF can be divided into three categories(θ=a,θ<a,andθ>a).The connected NF can increase the complexity of HF by inducing it to form branch fracture,resulting in a fractal dimension of HF as high as2.1280 at angles of±45°.Inter-fracture interference from the heel to the toe of HF shows the phenomenon of no,strong and weak interference.Interestingly,under the influence of NFs,distant HFs from the injection can become dominant fractures.However,as a gradually increases,inter-fracture stress interference becomes the primary factor influencing HF propagation,gradually superseding the dominance of NF induced fractures.

COUPLED SIMULATION OF 3D ELECTRO-MAGNETO-FLOW FIELD IN HALL-HEROULT CELLS USING FINITE ELEMENT METHOD

Two full 3D steady mathematical models are developed by finite element method （FEM） to calcalate coupled physics fields. the electro-magnetic model is built and solved first and so is the fluid motion model with the acquired electromagnetic force as source body forces in Navier-Stokes equations. Effects caused by the ferromagnetic shell, busbar system around, and open boundary problem as well as inside induced current were considered in terms of the magnetic field. Furthermore, a new modeling method is found to set up solid models and then mesh them entirely with so-called structuralized grids, namely hex-mesh. Examples of 75kA prebaked cell with two kinds of busbar arrangements are presented. Results agree with those disclosed in the literature and confirm that the coupled simulation is valid. It is also concluded that the usage of these models facilitates the consistent analysis of the electric field to magnetic field and then flow motion to the greater extent, local distributions of current density and magnetic flux density are very much dependent on the cell structure, the steel shell is a shield to reduce the magnetic field and flow pattern is two dimensional in the main body of the metal pad.

Numerical Investigation on the Flow and Temperature Fields in an Inductively Coupled Plasma Reactor

This paper gives a numerical study on the flow and temperature fields in an induced plasma reactor, which worked in 0.5 ATM with air as a working gas. We employed a two-dimensional mode of an inductively coupled plasma to calculate the temperature and flow field of the reactor as well as the generator. The algorithm is based on the solutions of the two-dimensional continuity, momentum, and energy equations in term of vorticity, stream function and enthalpy. An upwind finite-difference scheme was adopted to solve those equations with appropriate boundary conditions. The computed results show that there is a flat region with little parameter change in the reactor, that the diameter of the region is not much larger than that of the generator and that a deep change of parameter exists in the outer side of the region.

Fluid Flow and Solidification Simulation in Beam Blank Continuous Casting Process With 3D Coupled Model

Based on turbulent theory, a 3D coupled model of fluid flow and solidification was built using finite difference method and used to study the influence of superheating degree and casting speed on fluid flow and solidification, analyze the interaction between shell and molten steel, and compare the temperature distribution under different technological conditions. The results indicate that high superheating degree can lengthen the liquid-core depth and make the crack and breakout possible, so suitable superheating should be controlled within 35℃ according to the simulation results. Casting speed which is one of the most important technological parameters of improving production rate, should be controlled between 0. 85 m/min and 1.05 m/min and the caster has great potential in the improvement of blank quality.

Development and application of coupling model of aluminum thin-gauge high-speed casting

Based on the analyses of aluminum melt flow, solidification, heat transfer during the process of twin-roll casting, a coupling mathematical model of aluminum thin-gauge high-speed casting was developed, which included the casting roller shell. At the same time, Galerkin method was adopted to solve the coupling model. The fluid field and temperature field of aluminum melt in casting zone, the temperature field and thermal stress field of roller shells were simulated by the coupling model. When the casting velocity is 7m/min, and the thickness of strip is 2mm, the circumfluent area comes into being in the casting zone, and the mushy zone dominates the casting zone, while the temperature of melt decreases rapidly as it approaches the rollers. The temperature of the roller shell varies periodically with the rotation of roller, and reaches the highest temperature in the casting zone, while the temperature of roller shell decreases gradually as it leaves the casting zone. The difference of thermal stress between the inner surface and outer surface of the roller shell is very large, and the outer surface suffers tensile-compressive stress.

Coupled Modeling of Electromagnetic Fleld,Fluid Flow,Heat Transfer and Solidification During Conventional DC Casting and Low Ftequency Electrmagnetic Casting of 7xxx Aluminum Alloys

A comprehensive mathematical model has been developed to describe the interaction of the multiple physics fields during the conventional DC casting and LFEC (low frequency electromagnetic casting) process. The model is based on a combination of the commercial finite element package ANSYS and the commercial finite volume package FLUENT, with the former for the calculation of the electromagnetic field and the latter for the calculation of the magnetic driven fluid flow, heat transfer and solidification. Moreover, the model has been verified against the temperature measurements obtained from two 7XXX aluminum alloy billets of 200mm diameter, cast during the conventional DC casting and the LFEC casting processes. In addition, a measurement of the sump shape of the billets were carried out by using addition melting metal of Al-30%Cu alloy into the billets during casting process. There was a good agreement between the calculated results and the measured results. Further, comparison of the calculated results during the LFEC process with that during the conventional DC casting process indicated that velocity patterns, temperature profiles and the sump depth are strongly modified by the application of a low frequency electromagnetic field during the DC casting.

超深层裂缝性致密砂岩气藏多尺度耦合流动数值模拟

塔里木盆地克拉苏气田白垩系气藏是罕见的超深层裂缝性致密砂岩气藏,该类气藏的储渗空间具有显著的多尺度特征,基质与多尺度裂缝、断层介质的渗透率级差相差5~6个数量级,常规渗流理论难以准确描述其流动规律和开发机理。为此,基于单裂缝流动物理实验结果及流体力学理论,结合多尺度裂缝几何信息,应用均化理论和体积平均尺度升级方法,将多尺度介质划分为5个流动系统,建立了考虑介质间的非稳态窜流多尺度耦合流动数学模型,并应用有限体积法对耦合流动模型进行了数值求解和数值试井分析。研究结果表明:(1)不同尺度裂缝中具有不同的流动特征,随缝宽增加流速加快,流动模态发生变化;(2)多尺度耦合流动模型与双重介质模型结果存在较大差异,导数曲线具有不同趋势特征;(3)应用所建立的多尺度耦合流动模型成功解释了气藏实际试井数据,模型能够反映实际地层中的流动过程。结论认为,超深层裂缝性致密砂岩气藏多尺度耦合流动模型揭示了多尺度裂缝以及致密基质间逐级动用、协同供气的开发机理,可为类似气藏制订合理开发技术政策及气藏提高采收率提供理论和技术支撑。

球状风化花岗岩类土质边坡土-岩界面优势流潜蚀特性研究

受降雨作用,球状风化花岗岩类土质边坡的土-岩差异风化界面极易演化为优势渗流通道而发生渗流潜蚀,进而加速该类边坡的变形失稳,然而当前有关其渗流潜蚀作用特征、细颗粒迁移规律等的研究仍鲜见开展。基于多孔介质非饱和渗流理论,综合考虑细颗粒运移、潜蚀启动响应与非饱和渗流的耦合关系,提出一种可准确描述土-岩界面渗流潜蚀过程的数值计算框架。采用有限元方法,构建优势流作用下非饱和花岗岩残积土的渗流潜蚀模型,并以均质土柱的渗流潜蚀过程为参考,系统研究3种典型土-岩界面埋藏状态下的优势流潜蚀特性。结果表明:球状风化花岗岩类土质边坡的土-岩界面与基质渗透性存在高度差异性,湿润锋形成向下凹陷的渗透漏斗,且随着降雨的持续,湿润锋的凹陷程度愈发明显;细颗粒流失程度与土-岩界面的埋藏状态相关,其中下填土体工况的优势流潜蚀最为显著,其界面处甚至出现超孔隙水压力,最不利于该类边坡的稳定性。研究成果可为降雨条件下球状风化花岗岩类土质边坡稳定性的准确评价提供科学依据。

螺杆泵转速对油水旋流分离管流场特性的影响

旋流分离器在井下采油螺杆泵作用下会发生复杂的振动现象,对旋流分离器内部流场造成一定影响。为研究螺杆泵不同转速下旋流分离器内部流场的变化规律,以同井注采工艺中螺杆泵作用下的旋流分离管柱为研究对象,针对振动壁面旋流分离管柱结构及工作特点,基于计算流体动力学方法、计算固体力学方法以及流固耦合理论,建立流固耦合力学模型;利用流固耦合分析方法,对双螺杆泵转动条件下井下旋流分离管柱内速度场、油相分布、涡量及湍动能等流场特性进行分析。分析结果表明:随着螺杆泵转速升高,分离器内切向速度和轴向速度强度逐渐减弱,径向速度的不对称性逐渐加剧,转速的周期性变化还会造成径向速度场分布的偏移;螺杆泵不同转速下旋流分离器内部涡量分布不同,随着转速升高,溢流管以及锥段部分附近相关流场的涡旋明显增强;旋流器溢流口附近油相体积分数会随着螺杆泵转速的升高而减小;不同螺杆泵转动状态下,大颗粒油滴的分布不同。所得结果可为螺杆泵井下旋流分离同井注采系统的设计及螺杆泵的转速设定提供参考。

一种基于线性零磁场的动脉血管扫描成像方法仿真

基于磁电耦合效应的血流检测及血管成像是实现心血管疾病早期诊疗的有效方法之一。该文基于磁场与血流耦合电效应,设计一种用于动脉血管扫描成像的组合线圈结构,产生带有零磁场线(FFL)区域的线性梯度磁场;在此结构的基础上,通过控制激励电流驱动FFL实现成像区域双向扫描;结合卷积神经网络(CNN)实现磁电耦合信号与血管信息的非线性映射,进而提出一种基于线性零磁场的动脉血管扫描成像新方法。采用多物理场仿真软件COMSOL对基于线性零磁场的血管扫描成像方法进行建模,求解磁电耦合信号,验证了所提出方法的合理性和有效性。结果表明,线性梯度磁场模式下的磁电耦合信号含有血管位置、半径等信息;CNN重建血管位置误差平均值为1.5694 mm,重建血管半径的方均误差(MSE)和相关系数(CC)平均值分别为0.0548和0.9870。研究结果可用于血管成像装置设计及后续相关临床应用提供研究支撑。

基于电-热流场双向耦合的直流继电器温升特性仿真研究

高压直流继电器体积小、散热能力有限,长期工作下存在局部过热的风险,发热严重时甚至影响到接触稳定性和继电器工作寿命。针对200 A直流继电器,综合考虑导体回路通电下欧姆损耗发热,在大空间的自然热对流、热传导以及热辐射、材料电阻率随温度变化等因素,建立继电器在额定工况下电-热流场双向耦合模型,设置电阻率随温度变化函数,进行耦合计算。最后,搭建对应的样机测温平台,对仿真正确性进行验证。结果表明双向耦合结果比单向耦合结果高约5.1%,与实验测量值误差小于6.2%,验证了电热流场双向耦合的有效性。

电场耦合垂直流人工湿地对农村污水的净化效果及细菌群落结构变化特征

为进一步提高人工湿地处理农村污水效果,构建了耦合电场垂直流人工湿地系统(E-VFCW系统),以昆明市盘龙区长地梗城中村东干渠的原水为处理对象,探究其稳定性及净化效果,通过微生物群落演变特征,揭示其污染物去除的生物学化学机制.结果表明:①与垂直流人工湿地系统(VFCW系统)相比,E-VFCW系统对农村污水的净化效果更高,化学需氧量(COD)、总磷(TP)、氨氮(NH_(4)^(+)-N)、总氮(TN)处理效果分别提高了7.94%、5.67%、51.14%、27.54%,其中NH_(4)^(+)-N去除率存在显著差异(P<0.05).②E-VFCW系统中,相对丰度排序前三的优势菌门为变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)和放线菌门(Actinobacteria),其相对丰度之和约为80%;优势菌属包括脱氯单胞菌属(Dechloromonas)、黄杆菌属(Flavobacterium)和假单胞菌属(Pseudomonas)等.③冗余分析表明,E-VFCW系统中变形菌门(Proteobacteria)、酸杆菌门(Acidobacteria)、绿菌门(Chlorobi)、放线菌门(Actinobacteria)、硝化螺旋菌门(Nitrospirae)是COD、TN、TP、NH_(4)^(+)-N净化的主要驱动因素.④秩相关分析表明,电场施加能促进E-VFCW系统中产电细菌假单胞菌(增加4.76%)、氢噬胞菌(增加2.02%)、黄杆菌(增加12.54%)等的富集和积累.研究显示,将电场与垂直流人工湿地进行耦合后,可使产电细菌相对丰度显著增加,可为农村污水治理提供理论指导和科学依据.

高过载软回收系统内弹道双向耦合特性分析

为探究高过载软回收系统中弹前压力对内弹道的影响,在20000 g过载指标要求下,建立了弹前具有高压缓冲气体作用下的双向耦合内弹道仿真模型,采用FLUENT软件计算弹前压力,并利用UDF将弹前压力与经典内弹道进行双向耦合仿真分析。在5.51 kg装药情况下,对质量为90 kg的弹仓进行高过载仿真,结果表明:2 MPa的弹前预充气体压力会造成膛内最大压力增大2.32%;预充气体为5、8、10 MPa的情况下,弹仓的最大速度分别降低7.32%、12.36%和15.61%;弹仓质量为70 kg和80 kg时,弹仓最大速度分别增大9.63%和4.56%;气体介质种类不同对弹前压力造成影响较小,选择空气作为缓冲介质最优。以弹前压力与内弹道之间的双向耦合模型为基础,分析预充气压、弹仓质量、预充气体介质对内弹道特性的影响,为空气阻尼软回收试验的内弹道研究提供了理论参考。

直通调节阀内流场流道分析

随着油田的大量开发,油气井的工作情况更加复杂,一些出砂井常用螺杆泵,为了满足不同井深和产液量的需求,需要对压力调节阀进行检测。此次设计一种直通调节阀,在进出口压力一定的情况下,模拟仿真所设计的调节阀是否具有一定的稳定调节性能。调节阀又称控制阀,基于SOLIDWORKS三维模型,利用Fluent软件对其进行数值模拟,通过不同开度下的阀芯进行对比,通过分析压力云图、速度云图和流线图分析其流动规律。结果表明:(1)随着阀门开度的增大,阀芯阀座间流通面积变大,流速随着阀门开度的增加而减小。(2)随着阀门开度的不断增大,内流场压力会出现明显的变化。(3)随着阀门开度的增加,调节阀内流场会出现明显的漩涡。利用ANASYS软件进行流-固耦合,联合使用流场模块、静力场模块和温度场模块对调节阀内流场进行应力形变,当流体进入时,调节阀内流场发生应力形变比较稳定。以上所有模拟结果均符合实际情况,具有良好的稳定调节性能。

华龙一号反应堆上腔室及热段流-热耦合场数值模拟

压水型反应堆(pressurized water reactor,PWR)系统主管道热段内冷却剂的温度和流量,直接反映了核功率和堆芯换热状态,是反应堆功率控制和安全保护的核心参数。为全面掌握华龙一号反应堆上腔室及热段内冷却剂流-热耦合场分布及演变规律,为核心参数测控提供参考,基于有限元分析(finite element method,FEA)方法,对上腔室及热段冷却剂流域进行了计算流体力学(computational fluid dynamics,CFD)数值模拟。首先建立了合理简化后的华龙一号(Hualong One)反应堆上腔室及相连热段的3D几何结构模型。随后对模型计算域进行了离散化网格划分和网格敏感性分析。最后通过计算,获得了冷却剂非等温流动的稳态特性解,流量、温度与相关设计估算值、实际测量值的相对误差均小于2%。对稳态特性研究表明,高、低温冷却剂在上腔室垂直内壁附近的不充分换热导致热段入口冷却剂温度分布不均,存在14.0~16.3℃的温差。随冷却剂沿轴向流动,冷却剂温度场分布和流场分布均逐渐趋于均匀和稳定,且是热段内低温冷却剂的流动主导了冷却剂温度分布的变化。

海域天然气水合物储层的多场耦合模式及研究进展

海域天然气水合物是重要的清洁能源,实现其安全高效开采战略意义重大。受海域天然气水合物储层非成岩、弱固结、埋藏浅等特征的影响,水合物开采过程中储层处于强烈的多场耦合状态。复杂的多场耦合行为给开采产能和安全风险演化规律预测及其调控方案的制定均带来了巨大挑战。本文围绕南海天然气水合物储层特征并结合降压法开采工程需求,论证了在多场耦合行为分析中考虑固相传质过程的必要性和重要性,提出将传统热(T)-流(H)-固(M)-化(C)四场耦合升级为热(T)-流(H)-固(M)-化(C)-砂(S)五场耦合的新模式,并概述了实现多场耦合行为模拟的基本方法。在此基础上,分别综述了目前在水合物储层流体传质行为、固相传质行为、传热行为、力学变形行为等方面的主要研究进展,梳理了目前天然气水合物开采储层多场耦合基础研究领域的主要瓶颈与发展方向。可为海域天然气水合物开采工程-地质-环境一体化调控实践提供有益的参考。

小型垂直轴风力机叶片流固耦合分析

这里选取旋转直径为2m的垂直轴风力机叶片为研究对象,该研究对象为参考某1000W垂直轴风力机叶片,叶片翼型为NACA0021,采用数值模拟计算与实验相互验证的方法。对垂直轴风力机叶片进行实验位移测试分析,并使用ANSYS Workbench对叶片进行流固耦合分析,调用系统耦合器实现数据的相互传递,完成对叶片的双向耦合计算。研究风力机叶片在不同工况下的位移、应力应变。研究结果表明:风载使叶片产生变形,且沿叶片展向有较大幅度的位移;随着风速的增加,叶片位移增加明显。叶片来流方向压力大于背流方向压力,沿叶片展向叶片位移变形曲线上下波动。

电流体雾化双液滴电聚结行为研究

电流体喷印技术具有分辨率高,溶液参数适应性广等优点,是新型显示制造工艺创新突破的重要载体之一,可用于OLED微米厚度有机TFE膜高效制造。为深入探索电流体雾化技术制备微纳液膜过程,解决现阶段对液膜制备过程中各因素作用机理了解不清的问题,基于相场方法建立了液滴电聚结两相流耦合模型,分析了制备过程中“双液滴电聚结”单元。研究外加电压、基板接触角、液滴间隙和直径对液滴聚结的影响,并总结了液滴可聚结工艺参数相图。研究结果表明,外加电压越大、液滴隙径比越小,聚结后液滴高径比越大,聚结越快;基板接触角越大,聚结后高径比越大,聚结越慢,甚至可能使液滴无法聚结。在亲水基板上外加适当电压或增加液滴密度缩短液滴间隙有助于促成基板上液滴电聚结.该研究结论和工艺相图可应用与电流体雾化制膜时工艺参数调控。

基于声学层析成像的温度场和流速场重构

为有效重构三维管道内液体的温度场和流速场,提出了一种超声飞渡时间计算表征,并基于此求解温度场和流速场反演模型。同时考虑温度梯度导致的声线弯曲效应,采用正四面体前向展开法,追踪超声弯曲路径;开展“华龙一号”反应堆主管道冷却剂温度场和流速场重构实验。实验结果表明,所提方法能有效重构管道冷却剂温度场和流速场,且考虑弯曲效应能进一步提高重构精度。

镍电沉积界面层流/气泡-形核生长模拟研究

为探明镍电沉积过程中电沉积基体/电沉积液界面低流速层流场内电沉积副反应产生的气泡演变规律、Ni^(2+)浓度场变化和镍晶体形核及生长特点,建立了电场、低流速层流场、浓度场、气泡/沉积液/镍晶体多相场的气泡/层流-镍晶体形核生长模型,并利用有限元方法计算该模型。结果表明,当形核前的气泡从镍基体脱附到浓度扩散层边界时,在气泡脱附位置周围气泡迎流区和背流区的基体表面镍以瞬时形核方式形核,当离开Ni^(2+)浓度扩散层后,其产生的低Ni^(2+)浓度区与层流对流和Ni^(2+)扩散作用使镍晶体沿Ni^(2+)流动最大方向择优生长,在气泡迎流区的枝晶高度最高。与此不同,形核后的气泡从镍基体脱附到浓度扩散层边界时,气泡产生的涡流只能使已经形核的晶体不均匀生长;当离开Ni^(2+)浓度扩散层后,随后镍晶体以枝晶形式生长,沿Ni^(2+)流动最大方向枝晶的生长速度最快。