HYBRID FEM WITH FUNDAMENTAL SOLUTIONS AS TRIAL FUNCTIONS FOR HEAT CONDUCTION SIMULATION

A new type of hybrid finite element formulation with fundamental solutions as internal interpolation functions, named as HFS-FEM, is presented in this paper and used for solving two dimensional heat conduction problems in single and multi-layer materials. In the proposed approach, a new variational functional is firstly constructed for the proposed HFS-FE model and the related existence of extremum is presented. Then, the assumed internal potential field constructed by the linear combination of fundamental solutions at points outside the elemental domain under consideration is used as the internal interpolation function, which analytically satisfies the governing equation within each element. As a result, the domain integrals in the variational functional formulation can be converted into the boundary integrals which can significantly simplify the calculation of the element stiffness matrix. The independent frame field is also introduced to guarantee the inter-element continuity and the stationary condition of the new variational functional is used to obtain the final stiffness equations. The proposed method inherits the advantages of the hybrid Trefftz finite element method （HT-FEM） over the conventional finite element method （FEM） and boundary element method （BEM）, and avoids the difficulty in selecting appropriate terms of T-complete functions used in HT-FEM, as the fundamental solutions contain usually one term only, rather than a series containing infinitely many terms. Further, the fundamental solutions of a problem are, in general, easier to derive than the T-complete functions of that problem. Finally, several examples are presented to assess the performance of the proposed method, and the obtained numerical results show good numerical accuracy and remarkable insensitivity to mesh distortion.

A HYBRID FEM ALGORTHM FOR FLUID FLOW IN A VISCO-ELASTIC PIPE

A variational principle of hybrid FEM is proposed to solve the flow in a visco-elaslic pipe. As an example, the influence of an axisymmetrical stenosis on an artery vibrating flow with a single frequency is calculated.

基于FEM-IE混合算法的电火工品安全性仿真分析

论文针对电火工品在电磁环境中的安全性问题,基于FEM-IE混合算法,利用ANSYS HFSS电磁仿真软件,研究分析了电磁能对电火工品的作用机理,通过对电火工品在不同频率、不同距离和不同角度条件下安全性仿真分析,获得了电磁场对电火工品的作用规律,为分析电火工品在电磁场中的安全性提供理论支撑。

基于第一类Whitney基函数的三维FEM/BEM混合方法中积分的计算

给出了一种坐标变换方法,使基于第一类Whitney基函数的三维矢量有限元/边界元混合方法中积分的数值计算方便易行。利用三次坐标变换,将积分区域由任意的三角形区域变换成单位正方形区域,或由任意的四面体区域变换成单位正方体区域,从而混合方法中的积分可以方便地使用高斯-勒让德求积公式计算。通过数值实验对这种方法进行了检验。

斑马鱼fem-1c cDNA克隆与表达分析

为进一步探究鱼类性别决定的相关机理,增加对鱼类性控基因表达和功能的认识,克隆斑马鱼fem-1c基因并对其进行表达分析。研究采用RACE-PCR方法从斑马鱼卵巢组织c DNA中克隆了fem-1c的c DNA全长序列,其大小为2701 bp,编码618个氨基酸。生物信息学分析显示,斑马鱼FEM-1C蛋白包含9个ANK结构域、2个TPR结构域和2个低复杂性区域,与其他脊椎动物的FEM-1C蛋白序列保守性较高。脊椎动物的fem-1c与tmed7、trim36等邻近的4—5个基因具有保守的同线性关系。半定量RT-PCR实验结果显示斑马鱼fem-1c在受精后17d开始表达,并特异地表达于成体卵巢组织中。RNA原位杂交结果显示,fem-1c基因m RNA定位于卵巢组织的Ⅰ期和Ⅱ期卵母细胞胞质中。fem-1c的时空表达特征暗示其在斑马鱼卵巢分化中具有重要作用。

A hybrid finite-element and integral-equation method for forward modeling of 3D controlled-source electromagnetic induction

We have developed a hybrid solver that combines the finite-element and integralequation method for 3D CSEM modeling based on unstructured meshes. To avoid the source singularity, the secondary field is used in the modeling framework. The primary electromagnetic field from an electric dipole source in a layered medium is calculated based on the magnetic vector potential method. The inhomogeneities of the computational region are discretized by a vector-based finite-element mesh with boundaries at finite distance from the inhomogeneities by using the dyadic Green's function, reducing the truncation boundary effect and the solution region. The electric and magnetic Green's function is used in data postprocessing to reduce the numerical errors owing to inaccurate gradients because of unstructured meshes; thus, the electromagnetic field is more accurately calculated. Finally, the proposed algorithm is applied to a block and a disc model, and we assess the topography effect on the field components.

Hybrid graded element model for transient heat conduction in functionally graded materials

This paper presents a hybrid graded element model for the transient heat conduction problem in functionally graded materials （FGMs）. First, a Laplace transform approach is used to handle the time variable. Then, a fundamental solution in Laplace space for FGMs is constructed. Next, a hybrid graded element is formulated based on the obtained fundamental solution and a frame field. As a result, the graded properties of FGMs are naturally reflected by using the fundamental solution to interpolate the intra-element field. Further, Stefest＇s algorithm is employed to convert the results in Laplace space back into the time-space domain. Finally, the performance of the proposed method is assessed by several benchmark examples. The results demonstrate well the efficiency and accuracy of the proposed method.

FEM Simulation of Distortion and Residual Stress Generated by High Energy Beam Welding with Considering Phase Transformation

A series of experiments was carried out so as to elucidate the effect of the phase transformation in the cooling process on welding distortion and residual stress generated by laser beam welding (LBW) and laser-arc hybrid welding (HYBW) on the high strength steel (HT780). Then, the experiments were simulated by 3D thermal elasticplastic analysis with FEM (Finite Element Method) which was performed with using the idealized mechanical properties considering the transformation superplasticity. From the results, the effects of the phase transformation on welding distortion and residual stress generated by LBW and HYBW were elucidated. Furthermore, the generality of the idealization of the mechanical properties was verified.

Electromagnetic Performance Analysis of Flux-Switching Permanent Magnet Tubular Machine with Hybrid Cores

The performance of traditional flux switching permanent magnet tubular machine(FSPMTM)are improved by using new material and structure in this paper.The existing silicon steel sheet making for all mover cores or part of stator cores are replaced by soft magnetic composite(SMC)cores,and the lamination direction of the silicon steel sheet in stator cores have be changed.The eddy current loss of the machine with hybrid cores will be reduced greatly as the magnetic flux will not pass through the silicon steel sheet vertically.In order to reduce the influence of end effect,the unequal stator width design method is proposed.With the new design,the symmetry of the permanent magnet flux linkage has been improved greatly and the cogging force caused by the end effect has been reduced.Both 2-D and 3-D finite element methods(FEM)are applied for the quantitative analysis.

Conjugate natural convection of non-Newtonian hybrid nanofluid in wavy-shaped enclosure

The present study concerns the modelization and numerical simulation for the heat and flow exchange characteristics in a novel configuration saturated with a nonNewtonian Ag-MgO hybrid nanofluid.The wavy shaped enclosure is equipped with onequarter of a conducting solid cylinder.The system of equations resulting from the mathematical modeling of the physical problem in its dimensionless form is discretized via the higher-order Galerkin-based finite element method(GFEM).The dependency of various factors and their interrelationships affecting the hydro-thermal behavior and heat exchange rate are delineated.The numerical experiments reveal that the best heat transfer rate is achieved for the pseudo-plastic hybrid nanoliquid with high Rayleigh number and thermal conductivity ratio and low Hartmann number.Besides,the power-law index has a major effect in deteriorating the heat convection at high Rayleigh number.

Hybrid domain multipactor prediction algorithm and its CUDA parallel implementation

Based on the finite element method(FEM)in the frequency domain and particle-in-cell approach in the time domain,a hybrid domain multipactor threshold prediction algorithm is proposed in this paper.The proposed algorithm has the advantages of the frequency domain and the time domain algorithms at the same time in terms of high computational accuracy and considerable computational efficiency.In addition,the compute unified device architecture(CUDA)acceleration technique also can be employed to further enhance its simulation efficiency.Numerical examples are carried out to demonstrate the effectiveness of the proposed algorithm.The results indicate that the multipactor threshold can be accurately predicted and the computational efficiency can be improved.

A Study on the Initial Fracture Behavior of CF/GF Intra-Hybrid Woven Fabric Reinforced Composites

In this paper, woven fabrics of glass fiber/carbon fiber intra-hybrid in plain structure were used to fabricate fiber reinforced plastic (FRP) composite by hand lay-up method. The investigation on tensile property was carried out on specimens in 7 orientations including 0°/5°/15°/75°/85°/90° in previous works. With the specimen parameters and experimental data, FEM model was built by the software of Marc. By combining the experimental results and finite element analysis, the modulus was simulated and calculated at the first stage. Then interfacial stress of the 0 degree and 90 degree was also calculated. By the initial fracture stress data from experiment as well as the simulation value of interfacial strength of 0 and 90 degree, the initial fracture stress of the off-axial specimens wascalculated and predicted. The result shows that the interfacial strength of the glass fiber bundle is higher than that of the carbon fiber bundle in transverse direction. By using the interfacial strength and according to the Von Mises yielding criterion, the initial fracture stress was predicted, which can be a contribution to the design or predict of the material properties.

基于重叠边界的有限元与离散元耦合异步长并行计算方法

为了减少有限元和离散元耦合领域问题的计算时间,本文建立了有限元-离散元耦合异步长并行计算方法。整个计算模型分为有限元和离散元两类计算区域,根据每个子域单元特性选择合适的积分时间步长。每个子分区均采用显式时间积分格式进行求解,采用重叠边界法处理边界耦合问题,不涉及子循环过程的插值和截断过程。数值算例表明该方法在保证高精度的同时有效降低了计算时间。

磁芯探头涡流检测信号数值模拟方法研究

提出了一种基于退磁场理论的磁芯探头涡流检测信号简化数值模拟方法,基于已有FEM-BEM涡流检测数值方法开发了计算程序,通过与商用软件比较验证了其有效性。首先,分析了磁芯磁化过程中内部退磁场的特点,提出了磁芯退磁场和磁化场的计算方法;其次,提出了磁芯线圈激励磁场计算方法,考虑了激励线圈传导电流和磁芯等效磁流,利用磁流环电流模型和毕奥萨法尔定律进行激励磁场计算;最后,采用和激励磁场计算类似的思路进行了检测信号分析,即用感生涡流二次磁场替代激励线圈磁场来计算检测线圈磁芯的退磁场和磁化场,并基于磁芯内部磁通变化计算检测电压信号。基于所提理论,本研究在已有FEM-BEM混合法涡流检测数值模拟软件的基础上,开发了可考虑磁芯影响的涡流检测数值计算程序。对于不同参数条件下的磁芯探头涡流检测问题,本研究方法与全域有限元商用软件计算结果一致,但本研究方法原理更为直观,验证了方法和程序的有效性。

生物组织热传导问题的数值仿真

针对生物组织热传导方程解析解无法获得的问题,提出了将Laplace变换与杂交有限元相结合的数值求解算法。首先,利用Lapace变换对生物组织热传导方程进行处理,将时间域内的边值问题转化为Laplace空间内;接着,利用杂交元方法在Laplace空间对此新的边值问题进行求解;然后,通过Stehfest算法进行Laplace反变换,将结果变换会时间域中,从而得到生物组织的温度分布。最后,以皮肤组织的热传导问题为例,利用Matlab编制程序对其温度场分布进行数值仿真,算例结果表明肿瘤病变会改变皮肤组织的温度分布,即肿瘤处的温度较周围组织明显升高。仿真结果表明LT和HFEM相结合算法的正确性和有效性,为非入侵式医疗诊断提供了依据。

混合硬化弹塑性本构关系及其在环件冷辗扩模拟中的应用

采用数值模拟方法和混合硬化弹塑性本构关系,提出了基于弹性张量的应力补偿更新算法,引入等向强化系数,给出了有限元计算步骤,基于ABAQUS/Explicit平台开发了子程序VUMAT,并在单个单元模型中验证了其可靠性。将其应用于环件冷辗扩过程模拟中,着重研究了等向强化系数对环件冷辗扩成形的影响规律。结果表明,随着等向强化系数的增大,辗扩力、辗扩力矩增大,鱼尾形状系数减小,环件外圈金属受各向异性硬化影响较大,进而从理论上进行了解释。研究结论指出该研究对环件冷辗扩成形工艺具有指导意义。

定子分割式轴向磁通切换混合励磁同步电机三维有限元分析与实验研究

提出一种定子分割式轴向磁通切换型混合励磁同步电机,分析电机的工作机理和电磁特性,制作样机进行实验验证。基于三维有限元方法,建立了电机的有限元分析模型,获得了电枢绕组磁链、空载电动势及绕组电感等电磁特性;分析了不同励磁电流下的气隙磁场分布和调磁特性;根据理论分析结果试制了一台样机,测试了电机的空载电动势和调磁特性等。分析结果表明:通过调节励磁电流,线圈磁通变化明显,调磁效果较好;实验结果验证了理论分析的正确性。

混杂纤维布加固钢/聚丙烯短纤维增强混凝土构件技术研究

对采用杜拉纤维和钢纤维混杂改性的混凝土梁外贴碳纤维布和玻璃纤维布(CFSG/FS)进行混杂加固抗弯试验与有限元对比研究,并对构件加固后刚度变化进行对比分析,结果表明,掺入杜拉纤维和钢纤维,可以延缓混凝土构件微裂缝的出现,有效地控制裂纹扩展,提高混凝土材料的强度,这种混杂纤维混凝土梁表现出比单一纤维混凝土梁更优良的材料性能。

颗粒和纤维混杂增强复合材料力学性能的三维有限元模拟

为了研究原位合成TiB纤维和TiC颗粒混杂增强的钛基复合材料的力学性能与微观结构的关系,根据其微观结构特点,并基于随机序列吸附(RSA:Random Sequential Adsorption)方法,提出了短纤维和颗粒混杂增强的三维有限元模型。该模型可以生成位置及取向随机分布的多纤维多颗粒的代表体积单元,同时纤维的长径比、取向分布规律可以任意调整,适合各种不同的混杂增强复合材料微观结构的模拟。对比实验测试结果,证明该模型对混杂增强的复合材料的模拟较为精确。模拟结果显示:在纤维状增强体中,平行于加载方向的增强体承载了最大的应力,而与加载方向约呈45°角的增强体承受的应力最小;颗粒状增强体承受的应力相比平行于加载方向的纤维状增强体要小很多;基体中应力在加载方向上靠很近的增强体之间较高。