二维非均匀多孔介质中不可压两相驱替的有限分析算法

为提高油藏数值模拟算法的计算效率,在求解单向稳态渗流的有限分析算法基础上,构建二维非均匀多孔介质中不可压两相渗流的有限分析算法.算法中,网格界面上的平均渗透率不是简单地取为相邻网格渗透率的调和平均值,而是通过奇点邻域解析解积分求得.相比于传统的数值算法,有限分析算法随着网格的加密,能够很快地收敛(仅需将原始网格细分至2×2或3×3),并且其计算精度和收敛性不依赖于介质的非均匀强度,从而计算效率得到提高.

板片空间结构关键理论及软件开发综述

结合SPSA软件剖析板片空间结构体系的有限元分析核心算法、共同工作问题、结构稳定问题、结构优化的关键理论问题。

3D FEM analysis for layered rock considering anisotropy of shear strength

An empirical expression of cohesion （C） and friction angle （Ф） for layered rock was suggested. This expression was compared with a test result made by the former researchers. The constitutive relationship of a transversely isotropic medium and Mohr-Coulomb criterion in which C and Ф vary with directions were employed, and a relative 3D elasto-plastic FEM code was developed, in which the important thing was to adopt a search-trial method to find the orientation angle （p） of shear failure plane （or weakest shear plane） with respect to the major principal stress as well as the corresponding C and Ф Taking an underground opening as the calculation object, the numerical analyses were carried out by using the FEM code for two cases of transversely isotropic rock and isotropic rock, respectively, and the computation results were compared. The results show that when the rock is a transversely isotropic one, the distributions of displacements, plastic zones and stress contours in the surrounding rock will be non-axisymmetric along the tunnel＇s vertical axis, which is very different from that of isotropic rock. The stability of the tunnel in transversely isotropic rock is relatively low.

Bending behaviour of lightweight aggregate concrete-filled steel tube spatial truss beam

A lightweight aggregate concrete-filled steel tube(LACFST) spatial truss beam was tested under bending load. The performance was studied by the analysis of the beam deflection and strains in its chords and webs. According to the test results, several assumptions were made to deduce the bearing capacity calculation method based on the force balance of the whole section. An optimal dimension relationship for the truss beam chords was proposed and verified by finite element analysis. Results show that the LACFST spatial truss beam failed after excessive deflection. The strain distribution agreed with Bernoulli-Euler theoretical prediction. The truss beam flexural bearing capacity calculation results matched test evidence with only a 3% difference between the two. Finite element analyses with different chord dimensions show that the ultimate bearing capacity increases as the chord dimensions increase when the chords have a diameter smaller than optimal one; otherwise, it remains almost unchanged as the chord dimensions increase.

Experimental and Numerical Investigations on Vibration Characteristics of a Loaded Ship Model

In this paper, the vibration characteristics of the structure in the finite fluid domain are analyzed using a coupled finite element method. The added mass matrix is calculated with finite element method （FEM） by 8-node acoustic fluid elements. The vibration characteristics of the structure in the finite fluid domain are calculated combining structure FEM mass matrix. By writing relevant programs, the numerical analysis on vibration characteristics of a submerged cantilever rectangular plate in finite fluid domain and loaded ship model is performed. A modal identification experiment for the loaded ship model in air and in water is conducted and the experiment results verify the reliability of the numerical analysis. The numerical method can be used for further research on vibration characteristics and acoustic radiation problems of the structure in the finite fluid domain.

Mapping relationship analysis of welding assembly properties for thin-walled parts with finite element and machine learning algorithm

The finite element(FE)-based simulation of welding characteristics was carried out to explore the relationship among welding assembly properties for the parallel T-shaped thin-walled parts of an antenna structure.The effects of welding direction,clamping,fixture release time,fixed constraints,and welding sequences on these properties were analyzed,and the mapping relationship among welding characteristics was thoroughly examined.Different machine learning algorithms,including the generalized regression neural network(GRNN),wavelet neural network(WNN),and fuzzy neural network(FNN),are used to predict the multiple welding properties of thin-walled parts to mirror their variation trend and verify the correctness of the mapping relationship.Compared with those from GRNN and WNN,the maximum mean relative errors for the predicted values of deformation,temperature,and residual stress with FNN were less than 4.8%,1.4%,and 4.4%,respectively.These results indicate that FNN generated the best predicted welding characteristics.Analysis under various welding conditions also shows a mapping relationship among welding deformation,temperature,and residual stress over a period of time.This finding further provides a paramount basis for the control of welding assembly errors of an antenna structure in the future.

Analytical Solution of Helmholtz Equation in Anisotropic and Nonhomogeneous Region

The analytical solution of Helmholtz equation for magnetic vector potential in anisotropic and nonhomogeneous region is presented. The solution is built of a combination of both Bessel and power functions. There are developed two examples that proof the accuracy of the proposed analytical solution. First example is showing the electromagnetic field analysis in slot of ferromagnetic rotor of electrical induction machine. The second example approaches electromagnetic field wave in resonator of the form of rectangular cavity The analytical solution presented is treated as an exact one and is being compared with the numerical solution, e.g., given by finite element method. The analytical solution can be used as a benchmark test for numerical algorithms,

On the Set of Common Consequent Indices of a Class of Binary Relations

Let V = {a1,a2 ,...,an} be a finite set with n ≥ 2 and Pn（V） the set of all primitive binary relations on V. For Q E Pn（V）, denote by G（Q） the directed graph corresponding to Q. For positive integer d ≤ n, let Pn（V, d） = {Q ： Q ∈ Pn（V） and G（Q） contains exactly d loops}. In this paper, it is proved that the set of common consequent indices of binary relations in Pn （V, d） is {1, 2,..., n -[d/2] }. Furthermore, the minimal extremal binary relations are described.

Resonant frequencies of a piezoelectric drum transducer

This paper presents a piezoelectric-metal structure called a drum transducer. An equation for calculating the resonance frequency of the drum transducer is obtained based on thin plate elastic theory of piezoelectric and metal material combined with the Rayleigh-Ritz method. The finite element method (FEM) was used to predict the excitation frequency of the drum transducer. To verify the theoretical analysis, the input impedance characteristic of the drum transducer was measured using an experimental method. The results obtained from theoretical analysis were in very good agreement with those from the FEM and experimental results. The effect of geometrical changes to the thick-walled steel ring of the drum transducer at the first resonance frequency is also described. The calculated results were found to be in good agreement with the FEM results. The results indicate that the first resonance frequency of the drum decreases with the increasing inner diameter of the thick-walled steel ring.

Load-carrying capacity and practical calculation method for hollow cylinder joints connected with H-shaped beams

A type of hollow cylinder joints connected with H-shaped beams is proposed for spatial structures. Based on von Mises yield criterion and perfect elasto-plasticity model, a series of finite element models of the joints is established, in which the effect of geometric nonlinearity is taken into account. Then mechanical behavior and load-carrying capacity of the joints were investigated, which were subjected to axial load, in- and out-plane bending moments, and their combinations. The results show that the ultimate loads of the joints are determined by the maximum displacement. Furthermore, the case of one joint connected with multiple beams was discussed. Experiments on a set of typical full-scale joints were conducted to understand the structural behavior and the failure mechanism of joint, and also to validate the finite element models. Finally, the practical calculation method was established through finite elements analysis (FEA) results and numerical fitting. The results show that the joints are more ductile and materially economical than welded hollow spherical joints, and the practical calculation method can provide a reference for direct design and the revision of relevant design codes.