Three-dimensional forward modeling for magnetotelluric sounding by finite element method

A finite element algorithm combined with divergence condition was presented for computing three-dimensional(3D) magnetotelluric forward modeling. The finite element equation of three-dimensional magnetotelluric forward modeling was derived from Maxwell's equations using general variation principle. The divergence condition was added forcedly to the electric field boundary value problem, which made the solution correct. The system of equation of the finite element algorithm was a large sparse, banded, symmetric, ill-conditioned, non-Hermitian complex matrix equation, which can be solved using the Bi-CGSTAB method. In order to prove correctness of the three-dimensional magnetotelluric forward algorithm, the computed results and analytic results of one-dimensional geo-electrical model were compared. In addition, the three-dimensional magnetotelluric forward algorithm is given a further evaluation by computing COMMEMI model. The forward modeling results show that the algorithm is very efficient, and it has a lot of advantages, such as the high precision, the canonical process of solving problem, meeting the internal boundary condition automatically and adapting to all kinds of distribution of multi-substances.

Three-Dimensional Simulations of RESET Operation in Phase-Change Random Access Memory with Blade-Type Like Phase Change Layer by Finite Element Modeling

An optimized device structure for reducing the RESET current of phase-change random access memory （PCRAM） with blade-type like （BTL） phase change layer is proposed. The electrical thermal analysis of the BTL cell and the blade heater contactor structure by three-dimensional finite element modeling are compared with each other during RESET operation. The simulation results show that the programming region of the phase change layer in the BTL cell is much smaller, and thermal electrical distributions of the BTL cell are more concentrated on the TiN/GST interface. The results indicate that the BTL cell has the superiorities of increasing the heating efficiency, decreasing the power consumption and reducing the RESET current from 0.67mA to 0.32mA. Therefore, the BTL cell will be appropriate for high performance PCRAM device with lower power consumption and lower RESET current.

Autologous nerve graft repair of different degrees of sciatic nerve defect:stress and displacement at the anastomosis in a three-dimensional finite element simulation model

In the repair of peripheral nerve injury using autologous or synthetic nerve grafting, the mag- nitude of tensile forces at the anastomosis affects its response to physiological stress and the ultimate success of the treatment. One-dimensional stretching is commonly used to measure changes in tensile stress and strain; however, the accuracy of this simple method is limited. There- fore, in the present study, we established three-dimensional finite element models of sciatic nerve defects repaired by autologous nerve grafts. Using PRO E 5.0 finite element simulation software, we calculated the maximum stress and displacement of an anastomosis under a 5 N load in 10-, 20-, 30-, 40-mm long autologous nerve grafts. We found that maximum displacement increased with graft length, consistent with specimen force. These findings indicate that three-dimensional finite element simulation is a feasible method for analyzing stress and displacement at the anas- tomosis after autologous nerve grafting.

Evaluation value of three-dimensional finite element model analysis for bone mineral density and bone metabolism activity in patients with osteoporosis

Objective: To study the evaluation value of three-dimensional finite element model analysis for bone mineral density (BMD) and bone metabolism activity in patients with osteoporosis. Methods: A total of 218 patients who were diagnosed with osteoporosis in the hospital between February 2014 and January 2017 were collected as observation group, and 100 healthy volunteers who received physical examination in the hospital during the same period were selected as normal control group. The femoral head of the two groups was analyzed by three-dimensional finite element model, and the femoral head BMD levels and serum bone metabolism index contents were measured. Pearson test was used to evaluate the evaluation value of femoral head three-dimensional finite element model for osteoporosis. Results: The cancellous bone and cortical bone Von Mises stress value of observation group were lower than those of normal control group, and femoral neck BMD value of observation group was lower than that of normal control group;serum bone metabolism index BGP content was lower than that of normal control group while NBAP, TRACP-5b and CTX-1 contents were higher than those of normal control group. Pearson test showed that the cancellous bone and cortical bone Von Mises stress value of patients with osteoporosis were directly correlated with BMD value and bone metabolism index contents. Conclusion: The three-dimensional finite element model analysis resultsof patients with osteoporosis can objectively reflect the femoral headBMD value and bone metabolism activity, and is a reliable way to evaluate the risk of long-term fractures.

Three-dimensional finite element analysis on effects of tunnel construction on nearby pile foundation

A three-dimensional finite element simulation was carried out to investigate the effects of tunnel construction on nearby pile foundation.The displacement controlled model (DCM) was used to simulate the tunneling-induced volume loss effects.The numerical model was verified based on the results of a centrifuge test and a set of parametric studies was implemented based on this model.There is good agreement between the trend of the results of the centrifuge test and the present model.The results of parametric studies show that the tunnelling-induced pile internal force and deformation depend mainly on the pile?tunnel distance,the pile length to tunnel depth ratio and the volume loss.Two different zones are separated by a 45° line projected from the tunnel springline.Within the zone of influence,the pile is subjected to tensile force and large settlement;whereas outside the zone of influence,dragload and small settlement are induced.It is also established that the impact of tunnelling on a pile group is substantially smaller as compared with a single pile in the same location with the rear pile in a group,demonstrating a positive pile group effect.

Simulation-Based Construction of Three-Dimensional Process Model for Punching Cartridge Cases

A method of constructing three-dimensional process model for the punching cartridge cases is presented based on DEFORM simulation analysis. Using DEFORM software,the finite element simulation models for the punching and forming process of cartridge cases are established,and the corresponding simulation result model of each intermediate procedure is obtained by continuously performing the forming process simulation. The simulation model cannot annotate size and process information due to poor interface between DEFORM software and CAD software. Thus,a 3D annotation module is developed with secondary development technology of UG NX software. Consequently,the final process model with dimension and process information is obtained. Then,with the current 3D process management system,the 3D punching and forming process design of cartridge cases can be completed further. An example is also provided to illustrate that the relative error between the simulation process model and the physical model is less than 2%,which proves the validity and reliability of the proposed method in this study.

Implementation of a particle-in-cell method for the energy solver in 3D spherical geodynamic modeling

The thermal evolution of the Earth’s interior and its dynamic effects are the focus of Earth sciences.However,the commonly adopted grid-based temperature solver is usually prone to numerical oscillations,especially in the presence of sharp thermal gradients,such as when modeling subducting slabs and rising plumes.This phenomenon prohibits the correct representation of thermal evolution and may cause incorrect implications of geodynamic processes.After examining several approaches for removing these numerical oscillations,we show that the Lagrangian method provides an ideal way to solve this problem.In this study,we propose a particle-in-cell method as a strategy for improving the solution to the energy equation and demonstrate its effectiveness in both one-dimensional and three-dimensional thermal problems,as well as in a global spherical simulation with data assimilation.We have implemented this method in the open-source finite-element code CitcomS,which features a spherical coordinate system,distributed memory parallel computing,and data assimilation algorithms.

Microstructure-based three-dimensional characterization of chip formation and surface generation in the machining of particulate-reinforced metal matrix composites

Particulate-reinforced metal matrix composites(PRMMCs)are difficult to machine due to the inclusion of hard,brittle reinforcing particles.Existing experimental investigations rarely reveal the complex material removal mechanisms(MRMs)involved in the machining of PRMMCs.This paper develops a three-dimensional(3D)microstructure-based model for investigating the MRM and surface integrity of machined PRMMCs.To accurately mimic the actual microstructure of a PRMMC,polyhedrons were randomly distributed inside the matrix to represent irregular SiC particles.Particle fracture and matrix deformation and failure were taken into account.For the model’s capability comparison,a two-dimensional(2D)analysis was also conducted.Relevant cutting experiments showed that the established 3D model accurately predicted the material removal,chip morphology,machined surface finish,and cutting forces.It was found that the matrix-particle-tool interactions led to particle fractures,mainly in the primary shear and secondary deformation zones along the cutting path and beneath the machined surface.Particle fracture and dilodegment greatly influences the quality of a machined surface.It was also found that although a 2D model can reflect certain material removal features,its ability to predict microstructural variation is limited.

3D finite element analysis of a two-surface wear model in fretting tests

This article aims at developing a computationally efficient framework to simulate the erosion of two contact surfaces in three-dimensional(3D),depending on the body resistance.The framework involves finite element(FE)resolution of a fretting problem,wear computation via a non-local criterion including a wear distribution parameter(WDP),as well as updating of the geometry and automatic remeshing.Its originality is based on the capability to capture the damage on each surface and obtain local and global results for a quantitative and qualitative analysis.Numerical simulations are carried out for two 3D contact specimens with different values of WDP.The results highlight the importance of correctly modelling wear:One-surface wear model is sufficient from a global point of view(wear volume),or whenever the wear resistance for a body is much higher than that of another one,whereas a 3D two-surface wear model is essential to capturing local effects(contact pressure,wear footprint,etc.)related to the difference in wear resistance of the bodies.

Anybody仿真太极不同步法时股骨及下肢骨主要关节的应力特征

背景:Anybody骨肌建模系统,使用数学建模技术模拟人体骨骼、肌肉和环境的关系,可对人体的逆向动力学进行研究,得出下肢关节力等指标。目的:分析练习太极拳动作时下肢骨主要关节的应力分布规律,为其科学训练和锻炼价值提供依据。方法:在北京体育大学武术学院选取8名太极拳健将级运动员进行7组步法动作和右腿股骨CT的数据采集。使用BTS红外捕捉系统、Kistler三维测力台采集太极(八法五步)7组步法动作的运动和力学数据,利用Anybody 7.2骨肌模型的多体动力学仿真技术计算下肢关节动力学参数,结合Workbench 19.2对股骨进行应力计算分析。结果与结论:①利用Workbench软件分析得出了7组步法动作的股骨应力结果,7组动作的应力峰值由大至小顺序是:退步捋势(22.00 MPa)、退步採势(19.379 MPa)、左右移步挤按(9.35 MPa)、左右移步肘靠(6.30 MPa)、进步掤势(4.68 MPa)、进步挒势(2.57 MPa)、中定独立势(0.31 MPa)。②在7组步法动作中2种向后退步动作股骨应力最大(P<0.05),且在7组动作运动过程中的股骨最大应力位置均不同。③上述结果证实,在太极(八法五步)7种步法动作练习时,股骨应力阈值和最大应力位置会随着5种方向(7组动作)运动不同而变化,通过连续训练能够全面地刺激股骨体,进步动作对于股骨体正面和外侧上端影响较大,退步动作对股骨体后面和内侧影响较大,左右横向步法动作主要是股骨体两侧对称受力。④初学者要根据不同步法动作的受力特点来进行针对训练,进步动作和退步动作训练时要注重太极拳的旋转用力以及左右横移步法动作训练时的内侧对抗用力,根据自身薄弱问题,对太极拳训练步法有所侧重,进而达到更好的锻炼效果。

基于肌骨动力学与有限元耦合模型的脊柱生物力学研究应用进展

由于现代生活方式的改变与人口老龄化,近年来脊柱疾病发病率急剧升高。生物力学研究是评估脊柱相关疾病的重要内容,通过建模仿真的方法探究脊柱生物力学一直是重要的手段之一。目前,结合肌骨模型与有限元的方法成为脊柱生物力学的研究热点,因此,本研究对国内外使用肌骨模型与有限元相结合的方法探究脊柱生物力学特征的文章进行调研,系统阐述了该方法在脊柱相关疾病方面的临床应用进展,总结基于这种方法的建模方式,包括加载方法、杨氏模量、泊松比等参数设置,以及使用该方法在脊柱相关疾病上的评估应用。结果表明:基于肌骨动力学与有限元的方法,对探究人体在体运动时脊柱组织层面的应力应变、椎间盘内压力(intervertebral disc pressure, IDP)等情况,提供了一种多尺度评估方法,但该种方法目前存在模型构建时间长、研究动作单一、需要验证模型有效性不足等问题,是未来脊柱生物力学领域研究需要研究的方向。

人工颞下颌关节窝假体固定的有限元研究

以一款标准型人工颞下颌关节假体为对象,建立下颌骨骨肌模型,计算获得颞下颌假体关节载荷力,然后基于骨肌模型建立有限元接触力学模型,对关节窝假体进行界面力学分析,揭示可能影响假体固定的主要因素。结果表明,关节窝整体固定能够满足所需的机械强度,当骨质较弱时会产生较大的骨应变,从而影响假体的固定。研究成果不仅能为关节窝假体设计提供分析方法及理论依据,还能为颞下颌关节置换术的固定技术提供参考依据。

FINITE ELEMENT MODELLING OF COMPLEX 3D STATIC AND DYNAMIC CRACK PROPAGATION BY EMBEDDING COHESIVE ELEMENTS IN ABAQUS

This study proposes an algorithm of embedding cohesive elements in Abaqus and develops the computer code to model 3D complex cragk propagation in quasi-brittle materials in a relatively easy and efficient manner. The cohesive elements with softening traction-separation relations and damage initiation and evolution laws are embedded between solid elements in regions of interest in the initial mesh to model potential cracks. The initial mesh can consist of tetrahedrons, wedges, bricks or a mixture of these elements. Neither remeshing nor objective crack propagation criteria are needed. Four examples of concrete specimens, including a wedgesplitting test, a notched beam under torsion, a pull-out test of an anchored cylinder and a notched beam under impact, were modelled and analysed. The simulated crack propagation processes and load-displacement curves agreed well with test results or other numerical simulations for all the examples using initial meshes with reasonable densities. Making use of Abaqus＇s rich pre/post- processing functionalities and powerful standard/explicit solvers, the developed method offers a practical tool for engineering analysts to model complex 3D fracture problems.

Experimental and numerical evaluation of multidirectional compressive and flexure behavior of three-dimensional printed concrete

Three-dimensional concrete printing(3DCP)can proliferate the industrialization of the construction sector,which is notoriously conservative and indolent toward changes.However,the mechanical behavior of 3DCP should be characterized and modeled considering the interfaces when its performance is thoroughly compared to that of the existing concrete construction methods.This study presents an experimental and numerical investigation of uniaxial compression and three-point bending(TPB)tests on extruded 3DCP beams in different loading directions.The orientation of translational and depositional interfaces with respect to the direction of loading influenced the strength.Both the elastic and post-damage behavior of the 3DCP specimens were compared with those of the conventionally cast specimen under quasi-static loading conditions.Despite the higher compressive strength of the casted specimen,the flexural strength of the 3DCP specimens was higher.This study employed the finite element and cohesive zone models of the appropriate calibrated traction-separation law to model fracture in the notched TPB specimens.Furthermore,the real-time acoustic emission test revealed the nature of failure phenomenon of three-dimensional-printed specimens under flexion,and accordingly,the cohesive law was chosen.The predicted load-displacement responses are in good agreement with the experimental results.Finally,the effects of cohesive thickness and notch shape on the performance under bending were explored through parametric studies.

Stochastic analysis of excavation-induced wall deflection and box culvert settlement considering spatial variability of soil stiffness

In this study, a three-dimensional (3D) finite element modelling (FEM) analysis is carried out to investigate the effects of soil spatial variability on the response of retaining walls and an adjacent box culvert due to a braced excavation. The spatial variability of soil stiffness is modelled using a variogram and calibrated by high-quality experimental data. Multiple random field samples (RFSs) of soil stiffness are generated using geostatistical analysis and mapped onto a finite element mesh for stochastic analysis of excavation-induced structural responses by Monte Carlo simulation. It is found that the spatial variability of soil stiffness can be described by an exponential variogram, and the associated vertical correlation length is varied from 1.3 m to 1.6 m. It also reveals that the spatial variability of soil stiffness has a significant effect on the variations of retaining wall deflections and box culvert settlements. The ignorance of spatial variability in 3D FEM can result in an underestimation of lateral wall deflections and culvert settlements. Thus, the stochastic structural responses obtained from the 3D analysis could serve as an effective aid for probabilistic design and analysis of excavations.

肌骨系统生物力学建模2021年研究进展

肌骨系统生物力学模型具有精确的人体解剖结构和良好的生物逼真度,能够较为精准有效地描述肌骨生物力学状态、预测肌骨内部力学响应,故被广泛应用于人体肌骨系统生物力学研究、骨科疾病诊断和治疗、植入体优化设计及术前规划。2021年国内外关于肌骨系统生物力学建模方法的最新进展主要体现在个体化有限元建模、统计模型建模和肌骨系统建模3个方面。基于此,本文结合最新相关文献,总结上述建模方法的研究进展和主要应用,并探讨肌骨建模未来的发展方向。

股骨粗隆间骨折术后步行状态的生物力学特性

目的:研究单臂外固定架治疗股骨粗隆间骨折术后步行状态的生物力学特性。方法:将CT数据文件经Simpleware软件进行三维重建处理,得到股骨及外固定架的三维几何模型。在Anybody软件中建立正常人体股骨模型,并与股骨外固定架模型(stl几何模型)一同导入Geomagic Studio软件中,将两组模型进行比对配准。将配准好的股骨外固定架模型导入Anybody软件中,通过Simpleware得到的网格模型(inp格式)导入到Abaqus软件中,分析1个步态周期的应力分布情况。结果:以左侧为例,术后在行走过程中较大应力发生在不锈钢钉与股骨的连接处以及不锈钢钉与固定架的连接处,整体未见明显应力集中现象,在典型步态右足趾离地和左全足底着地中产生较大应力,在左足跟着地、右足跟着地产生一定应力集中现象,左足趾离地时应力最小。结论:单臂外固定架治疗股骨粗隆间骨折,安全、有效,符合人体步行状态的生物力学要求。

不同负重方式对腰椎生物力学的影响

目的结合骨骼肌肉模型及腰椎有限元模型研究直立状态下不同背包方式对椎旁肌收缩和腰椎各节段椎间盘应力分布的影响。方法建立无负重和使用双肩包、单肩包和手提包的4种骨骼肌肉模型以及腰椎的有限元模型。使用骨骼肌肉模型分析站立位下使用3种负重方式时的肌肉收缩力和腰椎椎间压力,并将其施加在腰椎有限元模型中来分析腰椎椎体、间盘和韧带的应力分布。结果与无负重模型相比,双肩包、单肩包和手提包的平均椎旁肌收缩力增加了31.0%、43.4%和105.1%。双肩包模型的椎旁肌收缩力左右均衡,单肩包模型中负重侧的总体椎旁肌收缩力较大,而在手提包模型中非负重侧的椎旁肌收缩力较大。多裂肌在不同负重条件下的收缩力均有统计学差异(P<0.05)。与无负重模型相比,双肩包、单肩包和手提包模型中T12~S1平均椎间压力分别增加了37%、45%和64%。双肩包、单肩包及手提包模型的椎体平均峰值应力分别增加了71.6%、122.3%和146.6%。双肩包、单肩包及手提包模型的纤维环峰值应力分别增加了155.6%、183.4%、195.8%;髓核峰值应力分别增加了95.2%、146.9%、161.5%。结论左右平衡的负重方式对肌肉和腰椎间盘的产生负荷最小。当使用非平衡负重方式时,肌肉的收缩使得躯体保持平衡,但同时也使得腰椎应力增加。

股骨粗隆间骨折单臂外固定术后站立状态肌骨有限元模型的建立及其应力分析

目的:研究股骨粗隆间骨折单臂外固定术后站立状态的生物力学特性,为临床治疗提供理论依据。方法:将CT数据文件经Simpleware软件进行三维重建处理得到股骨及外固定架的三维几何模型。在Anybody软件中建立正常人体股骨模型,并与股骨外固定架模型(stl几何模型)一同导入Geomagic Studio软件中,将两组模型进行比对配准,将配准好的股骨外固定架模型导入Anybody软件中,通过Simpleware得到的网格模型(inp格式)导入到Abaqus软件中,分析站立状态的应力分布情况。结果:在不锈钢钉与股骨的连接处以及不锈钢钉与固定架的连接处产生较大应力,整体未出现明显应力集中现象。结论:单臂外固定架治疗股骨粗隆间骨折安全、有效,其治疗骨折符合中医伤科"筋骨并重"理论,符合生物力学要求。

Numerical simulation of mechanisms of deformation,failure and energy dissipation in porous rock media subjected to wave stresses

The pore characteristics,mineral compositions,physical and mechanical properties of the subarkose sandstones were acquired by means of CT scan,X-ray diffraction and physical tests.A few physical models possessing the same pore characteristics and matrix properties but different porosities compared to the natural sandstones were developed.The 3D finite element models of the rock media with varied porosities were established based on the CT image processing of the physical models and the MIMICS software platform.The failure processes of the porous rock media loaded by the split Hopkinson pressure bar(SHPB) were simulated by satisfying the elastic wave propagation theory.The dynamic responses,stress transition,deformation and failure mechanisms of the porous rock media subjected to the wave stresses were analyzed.It is shown that an explicit and quantitative analysis of the stress,strain and deformation and failure mechanisms of porous rocks under the wave stresses can be achieved by using the developed 3D finite element models.With applied wave stresses of certain amplitude and velocity,no evident pore deformation was observed for the rock media with a porosity less than 15%.The deformation is dominantly the combination of microplasticity(shear strain),cracking(tensile strain) of matrix and coalescence of the cracked regions around pores.Shear stresses lead to microplasticity,while tensile stresses result in cracking of the matrix.Cracking and coalescence of the matrix elements in the neighborhood of pores resulted from the high transverse tensile stress or tensile strain which exceeded the threshold values.The simulation results of stress wave propagation,deformation and failure mechanisms and energy dissipation in porous rock media were in good agreement with the physical tests.The present study provides a reference for analyzing the intrinsic mechanisms of the complex dynamic response,stress transit mode,deformation and failure mechanisms and the disaster mechanisms of rock media.