An MPI parallel DEM-IMB-LBM framework for simulating fluid-solid interaction problems

The high-resolution DEM-IMB-LBM model can accurately describe pore-scale fluid-solid interactions,but its potential for use in geotechnical engineering analysis has not been fully unleashed due to its prohibitive computational costs.To overcome this limitation,a message passing interface(MPI)parallel DEM-IMB-LBM framework is proposed aimed at enhancing computation efficiency.This framework utilises a static domain decomposition scheme,with the entire computation domain being decomposed into multiple subdomains according to predefined processors.A detailed parallel strategy is employed for both contact detection and hydrodynamic force calculation.In particular,a particle ID re-numbering scheme is proposed to handle particle transitions across sub-domain interfaces.Two benchmarks are conducted to validate the accuracy and overall performance of the proposed framework.Subsequently,the framework is applied to simulate scenarios involving multi-particle sedimentation and submarine landslides.The numerical examples effectively demonstrate the robustness and applicability of the MPI parallel DEM-IMB-LBM framework.

A particle-resolved heat-particle-fluid coupling model by DEM-IMB-LBM

Multifield coupling is frequently encountered and also an active area of research in geotechnical engineering.In this work,a particle-resolved direct numerical simulation(PR-DNS)technique is extended to simulate particle-fluid interaction problems involving heat transfer at the grain level.In this extended technique,an immersed moving boundary(IMB)scheme is used to couple the discrete element method(DEM)and lattice Boltzmann method(LBM),while a recently proposed Dirichlet-type thermal boundary condition is also adapted to account for heat transfer between fluid phase and solid particles.The resulting DEM-IBM-LBM model is robust to simulate moving curved boundaries with constant temperature in thermal flows.To facilitate the understanding and implementation of this coupled model for non-isothermal problems,a complete list is given for the conversion of relevant physical variables to lattice units.Then,benchmark tests,including a single-particle sedimentation and a two-particle drafting-kissing-tumbling(DKT)simulation with heat transfer,are carried out to validate the accuracy of our coupled technique.To further investigate the role of heat transfer in particle-laden flows,two multiple-particle problems with heat transfer are performed.Numerical examples demonstrate that the proposed coupling model is a promising high-resolution approach for simulating the heat-particle-fluid coupling at the grain level.

Experimental investigation on the relevance of mechanical properties and porosity of sandstone after hydrochemical erosion

Under the effect of chemical etching,the macroscopic mechanical properties,mesoscopic structure,mineral content,and porosity of rocks undergo significant changes,which can lead to the geological disasters; thus,an understanding of changes in the microscopic and macroscopic structure of rocks after chemical etching is crucial.In this study,uniaxial mechanical tests and nuclear magnetic resonance(NMR) spectroscopy were carried out on sandstone samples that had been previously subjected to chemical erosion under different p H values.The aim was to study changes in properties and mechanical characteristics,including deformation and strength characteristics,of the rock,and microscopic pore variation characteristics,and to perform preliminary studies of the chemical corrosion mechanism.Results show that different chemical solutions have a significant influence on the uniaxial compressive strength,the axial strain corresponding to the peak axial stress,elastic modulus,etc.With the passage of time,porosity increases gradually with exposure to different chemical solutions,and exposure to chemical solutions results in large changes in the NMR T2 curve and T2 spectrum area.Sandstone exposed to different chemical solutions exhibits different corrosion mechanisms; the root cause is the change of mineral.

Mechanical properties and energy mechanism of saturated sandstones

本文研究了饱水对粗砂岩峰后力学特性及能量机制的影响。为了获得这些重要的属性,采用RMT-150B型岩石力学试验系统对自然与饱水状态的粗砂岩岩样进行峰后循环加、卸载试验。在对这些试验进行成功处理后,对比研究自然与饱水状态下粗砂岩的应力–应变、强度、变形、损伤及劣化力学特性和波速、能量特性。试验结果表明:饱水对峰后破裂粗砂岩单轴循环加、卸载强度和弹性模量具有明显的弱化作用;随着峰后循环加、卸载周期的增加,自然状态下,峰值轴向、侧向和体积应变增幅均近似为等速率增加,饱水状态下,轴向峰值应变增幅近似等速率增加,而侧向、体积应变增幅均显著增加;饱水后粗砂岩试样峰值侧向应变、体积应变相对自然状态下的增幅与峰后循环加、卸载周期之间均符合线性函数递增关系;在自然与饱水状态下,各岩样的损伤因子(塑性剪切应变)随着峰后循环加、卸载周期的增加而逐渐增加,各岩样裂隙损伤应力随其塑性剪切应变的增加先期快速衰减,之后裂隙损伤应力近似趋于某一恒定值;随着峰后循环加、卸载周期的增加,岩样承载结构累计损伤程度不断提高,相应地其力学参数不断劣化衰减;自然与饱水状态岩样在峰后循环加、卸载过程中的波速均随着塑性剪切应变的增加而减小,两者之间均符合带有常数项的指数函数关系。饱水降低了岩样的总吸收能量、耗散能及弹性应变能。

Cyclic constitutive equations of rock with coupled damage induced by compaction and cracking

In this paper,the cyclic constitutive equations were proposed to describe the constitutive behavior of cyclic loading and unloading.Firstly,a coupled damage variable was derived,which contains two parts,i.e.,the compaction-induced damage and the cracking-induced damage.The compaction-induced damage variable was derived from a nonlinear stress–strain relation of the initial compaction stage,and the cracking-induced damage variable was established based on the statistical damage theory.Secondly,based on the total damage variable,a damage constitutive equation was proposed to describe the constitutive relation of rock under the monotonic uniaxial compression conditions,whereafter,the application of this model is extended to cyclic loading and unloading conditions.To validate the proposed monotonic and cyclic constitutive equations,a series of mechanical tests for marble specimens were carried out,which contained the monotonic uniaxial compression(MUC)experiment,cyclic uniaxial compression experiments under the variable amplitude(CUC-VA)and constant amplitude(CUC-CA)conditions.The results show that the proposed total damage variable comprehensively reflects the damage evolution characteristic,i.e.,the damage variable firstly decreases,then increases no matter under the conditions of MUC,CUC-VA or CUC-CA.Then a reasonable consistency is observed between the experimental and theoretical curves.The proposed cyclic constitutive equations can simulate the whole cyclic loading and unloading behaviors,such as the initial compaction,the strain hardening and the strain softening.Furthermore,the shapes of the theoretical curves are controlled by the modified coefficient,compaction sensitivity coefficient and two Weibull distributed parameters.

黄原胶生物聚合物固化红黏土力学行为及强化机制

红黏土不良的岩土特性会诱发工程病害,而大量使用水泥、石灰等传统无机固化材料处理红黏土会对生态环境造成不可逆的影响,有必要探索低环境影响材料用以提升红黏土的工程力学性能,经固化的红黏土既可充当工程材料运用,又满足绿色可持续发展需求。目前,黄原胶(XG)生物聚合物被视为一种极具挖掘潜力的环境友好型土壤稳定材料,具有优异的假塑性、安全性和稳定性等特性。本文为了系统地探究黄原胶生物聚合物对红黏土的固化效用及强化机制,在不同黄原胶掺量和养护龄期条件下,对固化后的红黏土开展了无侧限抗压强度试验、不固结不排水剪切试验、扫描电镜-能谱(SEM-EDS)及X射线衍射(XRD)测试。结果表明,在1.5%最佳掺量和28 d标养下,XG有效提升了红黏土的宏观力学性能,固化体的抗压强度和粘聚力分别提高了93.31%和79.47%;引入Duncan-Chang本构模型并进行修正,建立了适用于描述黄原胶生物聚合物固化红黏土应力-应变关系的数学模型,计算结果与试验结果一致性较好;黄原胶生物聚合物通过与红黏土和水分子之间的离子键作用,在固化体微观结构演化过程中产生显著的胶结和充填效应,最终形成致密的复合材料基体。

围压卸载条件下岩石的变形特性及渗透演化的试验研究（英文）

在应力释放条件下岩石的变形行为及水力性质是影响岩石工程开挖及使用安全的两个主要因素,鉴于此,本文以探寻卸荷条件下岩石的变形行为和渗透特性并提供一些表征岩石卸荷性质的参数为研究目标。首先,进行了一组加载路径为应力峰值前卸载围压的三轴试验,在试验中进行渗透率测试及声发射实时信号监测。然后,基于试验结果对整个应力–应变过程中岩石的变形行为及渗透演化情况作了深入分析。结果表明:在围压卸载条件下,岩石的应力–轴向应变曲线、渗透率–轴向应变曲线以及声发射事件分布情况具有很好的对应关系;在围压卸载之后,径向应变发展速率较轴向应变快,从而导致体积应变也迅速增大;所有的卸围压破坏均表现为具有一个宏观破裂面的剪切破坏;随着围压卸载过程中变形模量的不断降低,损伤变量呈不断增加趋势,表明围压卸载过程是一个累积损伤及强度劣化的过程;从整个加载和卸载过程来看,渗透率与体积应变存在一定的正相关关系。

Investigation on the physical mechanism of cavity percentage dependent shear strength for rock joints considering the real contact joint surface

To explain the effect of joint roughness on joint peak shear strength(JPSS)and investigate the effect of different contact states of joint surface on JPSS,we try to clarify the physical mechanism of the effect of joint cavity percentage(JCP)on JPSS from the perspective of the three-dimensional(3D)distribution characteristics of the actual contact joint surface,and propose a JPSS model considering the JCP.Shear tests for red sandstone joints with three different surface morphologies and three different JCPs were performed under constant normal load condition.Based on test fitting results,the reduction effect of the JCP on JPSS is investigated,and a JPSS model for cavity-containing joints is obtained.However,the above model only considers the influence of JCP by fitting test data,and does not reveal the physical mechanism of JCP affecting the JPSS.Based on the peak dilation angle model for consideration of the actual contact joint morphology,and the influence of JCP on the roughness of the actual contact joint surface,a theoretical model of the JPSS considering the JCP is proposed.The derivation process does not depend on the test fitting,but is entirely based on the joint mechanical law,and its physical significance is clear.It is proposed that the essence of the influence of the JCP on JPSS is that the JCP first affects the normal stress of the actual contact joints,further affects the roughness of actual contact joints,and then affects the shear strength.