Multi-scale Modeling and Finite Element Analyses of Thermal Conductivity of 3D C/SiC Composites Fabricating by Flexible-Oriented Woven Process

Thermal conductivity is one of the most significant criterion of three-dimensional carbon fiber-reinforced SiC matrix composites(3D C/SiC).Represent volume element(RVE)models of microscale,void/matrix and mesoscale proposed in this work are used to simulate the thermal conductivity behaviors of the 3D C/SiC composites.An entirely new process is introduced to weave the preform with three-dimensional orthogonal architecture.The 3D steady-state analysis step is created for assessing the thermal conductivity behaviors of the composites by applying periodic temperature boundary conditions.Three RVE models of cuboid,hexagonal and fiber random distribution are respectively developed to comparatively study the influence of fiber package pattern on the thermal conductivities at the microscale.Besides,the effect of void morphology on the thermal conductivity of the matrix is analyzed by the void/matrix models.The prediction results at the mesoscale correspond closely to the experimental values.The effect of the porosities and fiber volume fractions on the thermal conductivities is also taken into consideration.The multi-scale models mentioned in this paper can be used to predict the thermal conductivity behaviors of other composites with complex structures.

Contribution to the Full 3D Finite Element Modelling of a Hybrid Stepping Motor with and without Current in the Coils

The paper presents our contribution to the full 3D finite element modelling of a hybrid stepping motor using COMSOL Multiphysics software. This type of four-phase motor has a permanent magnet interposed between the two identical and coaxial half stators. The calculation of the field with or without current in the windings (respectively with or without permanent magnet) is done using a mixed formulation with strong coupling. In addition, the local high saturation of the ferromagnetic material and the radial and axial components of the magnetic flux are taken into account. The results obtained make it possible to clearly observe, as a function of the intensity of the bus current or the remanent induction, the saturation zones, the lines, the orientations and the magnetic flux densities. 3D finite element modelling provide more accurate numerical data on the magnetic field through multiphysics analysis. This analysis considers the actual operating conditions and leads to the design of an optimized machine structure, with or without current in the windings and/or permanent magnet.

Analysis of ground vibrations due to underground trains by 2.5D finite/infinite element approach

The 2.5D finite/infinite element approach is adopted to study wave propagation problems caused by underground moving trains. The irregularities of the near field, including the tunnel structure and parts of the soil, are modeled by the finite elements, and the wave propagation properties of the far field extending to infinity are modeled by the infinite elements. One particular feature of the 2.5D approach is that it enables the computation of the three-dimensional response of the half-space, taking into account the load-moving effect, using only a two-dimensional profile. Although the 2.5D finite/infinite element approach shows a great advantage in studying the wave propagation caused by moving trains, attention should be given to the calculation aspects, such as the rules for mesh establishment, in order to avoid producing inaccurate or erroneous results. In this paper, some essential points for consideration in analysis are highlighted, along with techniques to enhance the speed of the calculations. All these observations should prove useful in making the 2.5D finite/infinite element approach an effective one.

3D Finite Elements Technique for Collapse Causes of the Pylons in Egyptian Temples: A Study of the Great Pylon of Ramesseum Temple, Luxor, Egypt

This research presents damage causes of the pylons in the ancient Egyptian temples based on 3D finite elements analysis. The main purpose of the research determines the failure causes of the first pylon of the Ramessium temple, which is situated in Upper Egypt, at Luxor “Thebes” on the west bank of the Nile River. The first pylon of Ramessium temple subjected to seismic activity effects on long term, combined with several structural damage factors such as the defects resulting from the construction technique, where the builder used the poor quality of stones in foundations of the pylon, the building materials residue was used as filler for the core of the pylon walls, and it lacked vertical joints between the courses. In addition to it founded on alluvial soil that is vulnerable to contaminated water, it is still suffering damage factors and urban trespasses at the moment. All of the former factors helped the pylon to be affected by the earthquakes loads that occurred on it. The structural behavior of the pylon under self-weight and earthquakes loads were carried out by Numerical analysis to find out the loads and stresses which caused collapsing of the pylon. Results of the study indicated that the pylon subjected to a horizontal displacement due to old earthquakes force, led to collapse of the pylon. Finally, the study represents use of modern technique to study the structural behavior of the most important architectural units in ancient Egyptian temples to identify the causes of its collapse.

带式输送机不停机托辊更换车结构设计及特性分析

为提高煤矿带式输送机在更换损坏托辊时的维护效率,减小人工更换产生的安全风险,文中设计了一种可在带式输送机不停机状态下进行托辊更换的更换车。针对不停机更换托辊的工作要求,确定更换车的更换方案,并建立三维模型。采用D-H参数法建立更换车机械手的连杆坐标系,通过MATLAB软件机器人工具箱建立机械手模型,并用蒙特卡洛法确定机械手的工作空间,结果表明,其运动范围满足槽型托辊组3个托辊的更换。采用ADAMS软件对机械手拆卸和安装托辊过程进行仿真,得到损坏托辊和备用托辊的位移曲线,结合夹取结构的运动曲线和运行轨迹,结果表明,机械手的工作过程平稳流畅。采用ANSYS软件对更换车工作中关键受力部件支撑臂和支撑托辊架进行有限元分析,结果表明:两部件强度满足工作要求,保证更换车工作的可靠性。

降雨作用下抗滑桩与三维土工网垫植草护坡坡体的稳定分析

针对抗滑桩与三维土工网垫植草护坡在降雨作用下的稳定性问题,采用有限元强度折减法,利用ABAQUS建立抗滑桩与三维土工网垫植草护坡坡体的三维有限元模型,以坡底水平位移突变情况作为边坡失稳的判断标准,分别比较了不同工况下护坡安全系数随降雨时长的变化规律,以及降雨作用下抗滑桩桩位、桩长对抗滑桩与三维土工网垫植草护坡坡体的稳定性影响,并与未考虑降雨时的影响规律进行对比。结果表明:降雨时长对三维土工网垫植草工况的边坡稳定性影响较为明显;抗滑桩桩长对边坡稳定性影响较大,桩长宜取8 m;无降雨作用下将桩位置于坡中时边坡整体获得最大安全系数,降雨作用下将抗滑桩置于相对位置(L 0.4=4.8 m)时能够起到更好的抗滑效果;抗滑桩与三维土工网垫植草在降雨作用时加固护坡的效果比无降雨时更好,且优于原边坡。

基于ABAQUS的平纹织物同面对向弯曲有限元模拟

为明晰织物结构对其弯曲性能的影响机制,对织物弯曲过程进行了有限元模拟和实验验证。以涤纶织物为例,通过VHX-5000型超景深数码显微镜观测织物,得到纱线几何参数;根据纱线实际尺寸,利用SolidWorks专业建模软件构建涤纶平纹织物的三维几何模型;基于有限元分析软件ABAQUS研究织物同面对向弯曲性能,分析纱线弹性模量、摩擦因数、泊松比等参数对弯曲实验的影响,并将有限元仿真结果与实验结果进行对比。结果表明:模拟所得抗弯力-位移曲线与实验曲线在0.01水平上呈显著相关,模拟结果与实验结果一致,证明用有限元模拟弯曲织物模型的有效性。

基于各向异性和极化介质的2.5维CSAMT正演数值模拟

传统的CSAMT在进行正、反演数值模拟时通常假设地下介质为电各向同性且无IP效应的介质,而实际的地下介质往往同时存在电各向异性和IP效应,因此开展各向异性和IP效应共同作用下的CSAMT电磁场响应特征的研究势在必行。文中基于含源的Maxwell方程组,推导了2.5维各向异性介质的电磁场偏微分方程,采用伽辽金有限元法实现了各向异性的2.5维CSAMT数值模拟,进而讨论了欧拉角和各向异性系数对2.5维CSAMT响应的影响。通过引入Cole-Cole模型分别研究了不同极化参数对CSAMT响应的影响,最后讨论了各向异性和IP效应同时存在时的电磁场响应特征。研究结果表明,各向异性和IP效应均会对CSAMT的响应结果产生较为严重的影响。当各向异性和IP效应同时存在时,根据欧拉角和主轴电阻率的取值,二者的效果将相互叠加或抵消。文中的研究结果对于提高CSAMT资料处理与解释精度具有重要的理论意义。

基于非结构化网格的2.5D直流电阻率模拟

结合大型通用有限元软件ANSYS所提供的强大网格剖分功能，实现了2D地质模型的非结构化三角形网格剖分，并编写了2．5D直流电阻率有限元法FORTRAN语言计算程序。经计算对比表明，在节点数基本相同时，非结构化三角形网格比传统的矩形网格、矩形-三角形网格具有更高的计算精度，可以很好地拟合复杂地形和地质体边界。在此基础上，采用非结构化三角形网格，计算了起伏地形下2．5D地电模型的视电阻率异常，并利用比较法进行了地形改正。与水平地形时的结果对比表明，比较法可以较好地消除地形影响，突出局部地质体的异常。

高铁荷载下路堤和路堑段地面振动特性现场测试与数值分析

对巴黎-布鲁塞尔高速铁路地面振动开展现场测试,对比分析了高铁运行引起的路堤和路堑段地面振动特性以及传播衰减规律。基于2.5维有限元法基本原理,推导并建立了高铁荷载下路堤和路堑段2.5维有限元动力计算模型,详细讨论了路堤和路堑设计参数对地面振动特性的影响。结果表明:距轨道较近处的地面振动幅值主要受列车轴重影响,而距轨道较远处则由中间车相邻转向架轮对的叠加效应主导。高铁运行引起的路堤和路堑段地面振动随与轨道距离增加而减小,中高频成分振动的衰减速率显著大于其他频段。路堤和路堑段地面振动1阶主频主要由列车荷载的基频f_1主导,随车速提高逐渐向高频方向移动。路堤和路堑对地面振动的衰减规律有重要影响,路堤段地面振动随与轨道间距的衰减过程可分为两个阶段,而路堑段地面振动衰减过程则可分为三个阶段,且振动在堑顶处有较为明显的局部放大现象。当与路堤段轨道间距≥19.0 m(路堑段≥23.0 m)后,地面振动Z振级VL_Z均小于80.0 dB。同时,高铁荷载下地面振动随路堤高度或路堑深度的增加而减小,当超过某一限值时,继续增加路堤高度或路堑深度难以有效减小地面振动。路堤段地面振动随路堤弹性模量的增大而减小。此外,在确保稳定性的前提下,较陡的路堑边坡更有利于减小高铁运行引起的地面振动。

磁矢量势的全球电磁感应时间域三维有限元正演计算方法

全球电磁感应测深方法能获得地球深部电导率结构分布,目前被广泛应用于地球内部结构与热状态研究.地磁台站与地磁卫星观测的电磁感应数据为时间序列信号,在时间域分析全球电磁感应数据,特别是分析频谱极宽的磁暴脉冲响应,具有天然的优势.然而,当前的全球电磁感应数据解释技术一般在频率域进行,缺少时间域中的研究成果.为了弥补缺少时间域全球电磁感应数据解释方法的问题,本文开发了一种基于磁场矢量势的全球电磁感应时间域三维有限元并行正演求解方法,具备高精度快速计算源于地球外部时变电流源的地球感应电磁场时间序列的能力,特别适合于计算与分析频谱极宽的磁暴脉冲电磁感应时变响应.首先,建立基于磁场矢量势的全球电磁感应时间域微分控制方程,结合磁层外部电流源的物理属性建立边界条件和初始条件,从而构建出全球电磁感应时间域初始边界值问题.然后,利用四面体矢量有限元技术和无条件稳定的隐式后退欧拉公式,分别实现磁场矢量势的空间域和时间域离散,进而获得不同时刻的实系数大型有限元线性方程组,借助于高性能并行直接求解器,快速高精度地求解不同时刻的磁场矢量势与感应磁场.最后,利用理论模型验证本文算法的正确性.利用Dst磁暴环电流指数建立的时间域电流源与真实地球三维电性模型,研究"澳科一号"后续卫星200 km轨道对中国和澳大利亚下方地幔转换带高导体的探测能力,结果表明这些地幔转换带异常体在200 km卫星轨道高度能产生明显异常.综上所述,本文开发的时间域全球电磁感应方法不仅具备精确快速计算全球感应电磁场时间序列响应的能力,还能为反演与解释"澳科一号"等我国地磁卫星观测数据提供技术支持.

Grain refinement of Mg-Al alloys by optimization of process parameters based on three-dimensional finite element modeling of roll casting

To study the influence of roll casting process parameters on temperature and thermal-stress fields for the AZ31 magnesium alloy sheets,three-dimensional geometric and 3D finite element models for roll casting were established based on the symmetry of roll casting by ANSYS software.Meshing method and smart-sizing algorithm were used to divide finite element mesh in ANSYS software.A series of researches on the temperature and stress distributions during solidification process with different process parameters were done by 3D finite element method.The temperatures of both the liquid-solid two-phase zone and liquid phase zone were elevated with increasing pouring temperature.With the heat transfer coefficient increasing,the two-phase region for liquid-solid becomes smaller.With the pouring temperature increasing and the increase of casting speed,the length of two-phase zone rises.The optimized of process parameters（casting speed 2 m/min,pouring temperature 640 ℃ and heat transfer coefficient 15 kW/（m2·℃） with the water pouring at roller exit was used to produce magnesium alloy AZ31 sheet,and equiaxed grains with the average grain size of 50 μm were achieved after roll casting.The simulation results give better understanding of the temperature variation in phase transformation zone and the formation mechanism of hot cracks in plates during roll casting and help to design the optimized process parameters of roll casting for Mg alloy.

某抽水蓄能电站地下厂房洞室群三维有限元稳定性分析

为了了解抽水蓄能电站地下厂房洞室群开挖支护后围岩的稳定性,以某抽水蓄能电站地下厂房洞室群为例,采用隐式弹粘塑性本构关系,建立三维有限元模型,对比分析地下洞室群毛洞工况、锚杆+锚索+衬砌联合支护工况及支护参数优化后围岩的变形、应力场分布及D-P点安全系数。结果表明:采用锚杆+锚索+衬砌联合支护的方式可以有效减小地下洞室群围岩的位移量,提高D-P点安全系数,使应力分布更为均匀,围岩的稳定性更好。锚杆长度在6m~8m范围变化及锚索预应力变化对围岩的变形、应力以及D-P点安全系数的影响不显著,但是对围岩局部有一定的影响,施工过程中应动态优化调整。

Numerical Study of the Biomechanical Behavior of a 3D Printed Polymer Esophageal Stent in the Esophagus by BP Neural Network Algorithm

Esophageal disease is a common disorder of the digestive system that can severely affect the quality of life andprognosis of patients. Esophageal stenting is an effective treatment that has been widely used in clinical practice.However, esophageal stents of different types and parameters have varying adaptability and effectiveness forpatients, and they need to be individually selected according to the patient’s specific situation. The purposeof this study was to provide a reference for clinical doctors to choose suitable esophageal stents. We used 3Dprinting technology to fabricate esophageal stents with different ratios of thermoplastic polyurethane (TPU)/(Poly-ε-caprolactone) PCL polymer, and established an artificial neural network model that could predict the radial forceof esophageal stents based on the content of TPU, PCL and print parameter. We selected three optimal ratios formechanical performance tests and evaluated the biomechanical effects of different ratios of stents on esophagealimplantation, swallowing, and stent migration processes through finite element numerical simulation and in vitrosimulation tests. The results showed that different ratios of polymer stents had different mechanical properties,affecting the effectiveness of stent expansion treatment and the possibility of postoperative complications of stentimplantation.

Biomechanical analysis of an absorbable material for treating fractures of the inferior orbital wall

AIM:To investigate the biomechanical properties and practical application of absorbable materials in orbital fracture repair.METHODS:The three-dimensional(3D)model of orbital blowout fractures was reconstructed using Mimics21.0 software.The repair guide plate model for inferior orbital wall fracture was designed using 3-matic13.0 and Geomagic wrap 21.0 software.The finite element model of orbital blowout fracture and absorbable repair plate was established using 3-matic13.0 and ANSYS Workbench 21.0 software.The mechanical response of absorbable plates,with thicknesses of 0.6 and 1.2 mm,was modeled after their placement in the orbit.Two patients with inferior orbital wall fractures volunteered to receive single-layer and double-layer absorbable plates combined with 3D printing technology to facilitate surgical treatment of orbital wall fractures.RESULTS:The finite element models of orbital blowout fracture and absorbable plate were successfully established.Finite element analysis(FEA)showed that when the Young’s modulus of the absorbable plate decreases to 3.15 MPa,the repair material with a thickness of 0.6 mm was influenced by the gravitational forces of the orbital contents,resulting in a maximum total deformation of approximately 3.3 mm.Conversely,when the absorbable plate was 1.2 mm thick,the overall maximum total deformation was around 0.4 mm.The half-year follow-up results of the clinical cases confirmed that the absorbable plate with a thickness of 1.2 mm had smaller maximum total deformation and better clinical efficacy.CONCLUSION:The biomechanical analysis observations in this study are largely consistent with the clinical situation.The use of double-layer absorbable plates in conjunction with 3D printing technology is recommended to support surgical treatment of infraorbital wall blowout fractures.

Rectangular tunnel heading stability in three dimensions and its predictive machine learning models

Tunnel heading stability in two dimensions(2D)has been extensively investigated by numerous scholars in the past decade.One significant limitation of 2D analysis is the absence of actual tunnel geometry modeling with a considerable degree of idealization.Nevertheless,it is possible to study the stability of tunnels in three dimensions(3D)with a rectangular shape using finite element limit analysis(FELA)and a nonlinear programming technique.This paper employs 3D FELA to generate rigorous solutions for stability numbers,failure mechanisms,and safety factors for rectangular-shaped tunnels.To further explore the usefulness of the produced results,multivariate adaptive regression spline(MARS)is used for machine learning of big dataset and development of design equations for practical design applications.The study should be of great benefit to tunnel design practices using the developed equations provided in the paper.

2.5D forward modeling and inversion of frequency-domain airborne electromagnetic data

Frequency-domain airborne electromagnetics is a proven geophysical exploration method.Presently,the interpretation is mainly based on resistivity-depth imaging and onedimensional layered inversion;nevertheless,it is difficult to obtain satisfactory results for two- or three-dimensional complex earth structures using 1D methods.3D forward modeling and inversion can be used but are hampered by computational limitations because of the large number of data.Thus,we developed a 2.5D frequency-domain airborne electromagnetic forward modeling and inversion algorithm.To eliminate the source singularities in the numerical simulations,we split the fields into primary and secondary fields.The primary fields are calculated using homogeneous or layered models with analytical solutions,and the secondary（scattered） fields are solved by the finite-element method.The linear system of equations is solved by using the large-scale sparse matrix parallel direct solver,which greatly improves the computational efficiency.The inversion algorithm was based on damping leastsquares and singular value decomposition and combined the pseudo forward modeling and reciprocity principle to compute the Jacobian matrix.Synthetic and field data were used to test the effectiveness of the proposed method.

3-D finite element modeling for evolution of stress field and interaction among strong earthquakes in Sichuan-Yunnan region

Based on the latest achievement about activities of geological structure, a 3-D finite-element model containing four layers of upper crust, lower crust (two layers) and upper mantle is established in the paper. By repeated tests and revisions, the boundary conditions of the model are determined. And then the background stress field, the stress field caused by fault creep and the stress field triggered by strong earthquake in Sichuan-Yunnan region, as well as their dynamic variations are calculated. The results indicate that the latter earthquake often occurs in the area with positive Coulomb rupture stress change associated with the former one, the former earthquake has a triggering effect on the latter one to a certain extent, and strong earthquake often occur in groups under the background of high stress, which is of great significance for distinguishing seismic anomalies, as well as for improving the level of earthquake prediction.

3D finite element analysis on pile-soil interaction of passive pile group

The interaction between pile and soft soil of the passive pile group subjected to soil movement was analyzed with three-dimensional finite element model by using ANSYS software. The soil was assumed to be elastic-plastic complying with the Drucker-Prager yield criterion in the analysis. The large displacement of soil was considered and contact elements were used to evaluate the interaction between pile and soil. The influences of soil depth of layer and number of piles on the lateral pressure of the pile were investigated, and the lateral pressure distributions on the (2×1) pile group and on the (2×2) pile group were compared. The results show that the adjacent surcharge may result in significant lateral movement of the soft soil and considerable pressure on the pile. The pressure acting on the row near the surcharge is higher than that on the other row, due to the "barrier" and arching effects in pile groups. The passive load and its distribution should be taken into account in the design of the passive piles.

3D Finite Element Simulation of Tunnel Boring Machine Construction Processes in Deep Water Conveyance Tunnel

Applying stiffness migration method,a 3D finite element mechanical model is established to simulate the excavation and advance processes.By using 3D nonlinear finite element method,the tunnel boring machine(TBM) excavation process is dynamically simulated to analyze the stress and strain field status of surrounding rock and segment.The maximum tensile stress of segment ring caused by tunnel construction mainly lies in arch bottom and presents zonal distribution.The stress increases slightly and limitedly in the course of excavation.The maximum and minimum displacements of segment,manifesting as zonal distribution,distribute in arch bottom and vault respectively.The displacements slightly increase with the advance of TBM and gradually tend to stability.