柱壳有限条元法在预应力U型薄壳渡槽稳定性分析中的应用

本文采用半解析有限元法建立了用于U型薄壳渡槽稳定性分析的柱壳有限条元模型,推导出了稳定性问题的特征方程,确定了渡槽结构失稳的临界应力,编制了相应的计算程序。通过与简支的单向受压板和四边简支单向纯弯板的稳定性问题的理论解的对比,验证了模型的合理性和精确性。计算结果说明,以结构的最大压应力小于失稳临界应力为准则,可对预应力U型薄壳渡槽稳定性进行判断。

加劲柱壳结构外压屈曲问题的柱壳有限条元法

半解析柱壳有限条元法由于采用了解析函数与离散多项式函数相结合的位移模式,不但减少了自由度,提高了计算精度,还能方便地处理各种复杂的结构及其不同的连接方式。考虑加劲环被嵌固的影响,采用该方法对加劲柱壳结构外压作用下的失稳屈曲问题进行了分析研究,并通过算例得出加劲柱壳结构外压失稳的欧拉曲线,验证了半解析柱壳有限条元法的正确性与合理性。

圆柱壳结构外压稳定性的有限条元法分析

圆柱壳结构在外压作用下往往发生失稳屈曲破坏。本文采用半解析柱壳有限条元法 ,从而保证了壳体离散时几何形状表示与实际结构一致 ,并且通过算例分析 。

高层建筑筒体结构三维静力分析的改进条元法

提出了改进条元法,即根据柱壳理论构造了柱壳曲条,结合柱壳曲条和平壳条元对任意平面形状高层筒体结构承受弯曲和扭转作用进行三维静力分析。该方法所用位移基函数能描述剪弯型杆件的变形曲线,克服了传统有限条元法选用纯三角函数作为基函数导致基底剪应力为零的缺点。运用该方法所涉及的未知量少,未知量数目只与划分条元数和所选基函数项数有关,而与结构的层数无关。层数越多,改进条元法与有限元法相比未知量减少越明显。研究结果表明,改进条元法计算结果与试验结果及空间有限元结果较接近,可用于高层建筑筒体结构三维静力分析。

高层筒体结构整体稳定及二阶位移分析的改进条元法

根据柱壳理论,构造了一种柱壳曲条,本文结合柱壳曲条和平壳条元求解高层筒体结构的整体稳定及二阶位移。采用三次H erm ite插值函数模拟条元横截面的翘曲位移变化,能较好地反映筒体受力“剪切滞后”效应;采用一族能较好地逼近弯剪型变形曲线的正交多项式作基函数来描述位移沿竖向变化。用最小势能原理建立稳定及二阶位移分析方程。该方法适用于任意平面形状的高层建筑筒体结构及剪力墙结构的稳定及二阶位移分析。与其它方法相比,该方法具有精度高、通用性强、计算量小等优点。

基于共轭梯度法带隔板连续薄壁直箱位移参数的动态Bayes估计

推导了简支薄壁直箱有限条元控制方程,并结合柔度理论解决了带隔板连续薄壁直箱的超静定问题。基于Bayes定理,建立了带隔板连续薄壁直箱位移参数的动态Bayes误差函数,推导了相应的位移参数计算公式,并应用共轭梯度法研究了带隔板连续薄壁直箱位移参数的动态Bayes估计方法,同时给出了连续薄壁直箱位移参数的具体估计步骤,编制了相应的计算程序。通过典型算例分析可知,联合有限条元法和共轭梯度法进行带隔板连续薄壁直箱位移参数的动态Bayes估计是可行的,只需利用若干测点位移即能同时进行多参数估计,且先验信息合理时,迭代过程稳定地收敛于位移参数实际值。

装配式空心板梁桥铰缝数值分析与试验研究

针对装配式空心板梁桥铰缝的横向抗剪性能进行有限元分析和试验研究。首先,根据空心板梁桥结构形式和受力特点,引入有限条元计算理论,推导装配式空心板梁桥的有限条元计算列式,研究铰缝抗剪性能的计算方法,研制相应的计算程序;其次,结合某装配式空心板梁桥实桥试验,提出铰缝相对位移差来衡量铰缝的抗剪性能,评判铰缝的横向传力性能。实桥试验及数值计算结果表明:铰缝相对位移差为1×10^-3~1×10^-2 mm数量级,是实际可测的,能够用来区分铰缝传力性能的优劣;相比商用软件无法单独处理装配式空心板梁桥的铰缝而言,有限条计算理论能用较少单元进行空心板铰缝的横向抗剪性能分析,计算效率高。

Two-dimensional frequency-domain acoustic fullwaveform inversion with rugged topography

We studied finite-element-method-based two-dimensional frequency-domain acoustic FWI under rugged topography conditions. The exponential attenuation boundary condition suitable for rugged topography is proposed to solve the cutoff botmdary problem as well as to consider the requirement of using the same subdivision grid in joint multifrequency inversion. The proposed method introduces the attenuation factor, and by adjusting it, acoustic waves are sufficiently attenuated in the attenuation layer to minimize the cutoff boundary effect. Based on the law of exponential attenuation, expressions for computing the attenuation factor and the thickness of attenuation layers are derived for different frequencies. In multifrequency-domain FWI, the conjugate gradient method is used to solve equations in the Gauss-Newton algorithm and thus minimize the computation cost in calculating the Hessian matrix. In addition, the effect of initial model selection and frequency combination on FWI is analyzed. Examples using numerical simulations and FWI calculations are used to verify the efficiency of the proposed method.

Modeling Technology in Finite Element Analysis of Electrostatic Proximity Fuze Problem

In order to analyze the electrostatic field concerned with electrostatic proximity fuze problem using the available finite analysis software package, the technology to model the problem with a scale reduction object and boundary was presented. The boundary is determined by the maximum distance the sensor can detect. The object model is obtained by multiplying the terms in Poisson's equation with a scale reduction factor and the real value can be reconstructed with the same reverse process after software calculation. Using the finite element analysis program, the simulation value is close to the theoretical value with a little error. The boundary determination and scale reduction method is suitable to modeling the irregular electrostatic field around air targets, such as airplane, missile and so on, which is based on commonly used personal computer (PC). The technology reduces the calculation and storage cost greatly.

周边缝拱坝应力的弹性有限条元分析

本文应用壳体理论和有限条元法解周边缝拱坝的坝体变位与应力，导得坝体条元的刚度矩阵及等效结线荷载，编制了计算机程序和计算实例。

WAVE TRANSFORMATION AND BREAKING OVER A RECTANGULAR STEP

An idealized numerical wave flume has been established by finite element method on the bases of Navier Stokes equations through prescribing the appropriate boundary conditions for the open boundary,incident boundary,free surface and solid boundary in this paper.The characteristics of waves propagating over a step have been investigated by this numerical model.The breaker wave height is determined depending on the kinetic criterion.The numerical model is verified by laboratory experiments,and the empirical formula for the damping of wave height due to breaking is also given by experiments.

Analysis model for deformation mechanism of strip foundation of building:Considering shear effect of down-crossing tunnel under excavation

When the tunnel underpasses through the building,it will cause deformation and even damage to the buildings above,and the deformation of building foundation is the key to building safety.Based on the engineering case,the theoretical analysis was employed to evaluate the influence of shield tunnel underpass construction on the stability of the building,and the optimal tunneling parameters in the field construction have been obtained through the verified theoretical model and parameter analysis.First,the strip foundation of the building was simplified to the Timoshenko beam,which was taken into account the shear effect,and then the deformation displacement of the soil at the same place of strip foundation was applied to the simplified Timoshenko beam.Finally,the numerical solution of the displacement of the strip foundation was obtained by using the finite element method and verified its reliability using Euler-Bernoulli beam theoretical model,field monitoring data,and numerical simulation.Parameters analysis for the deformation and internal force of strip foundation under different types of shield machine tunneling parameters showed that the influence of the pressure of shield excavation chamber,thrust of shield,and driving speed played an important role in the deformation of the building’s strip foundation and internal force.

Finite element model updating of existing steel bridge based on structural health monitoring

Based on the physical meaning of sensitivity,a new finite element(FE) model updating method was proposed. In this method,a three-dimensional FE model of the Nanjing Yangtze River Bridge(NYRB) with ANSYS program was established and updated by modifying some design parameters. To further validate the updated FE model,the analytical stress-time histories responses of main members induced by a moving train were compared with the measured ones. The results show that the relative error of maximum stress is 2.49% and the minimum relative coefficient of analytical stress-time histories responses is 0.793. The updated model has a good agreement between the calculated data and the tested data,and provides a current baseline FE model for long-term health monitoring and condition assessment of the NYRB. At the same time,the model is validated by stress-time histories responses to be feasible and practical for railway steel bridge model updating.

Prediction of Fluid Velocity Distribution near a Rising Bubble

Flow and concentration fields of liquid phase in a gas-liquid contacting system are simulated to showthe Rayleigh convection by utilizing the finite-element method. The Schlieren images in CO2-ethanol system provided direct visual verification of the present simulation, and the simulated results were well consistent with theexperimental observation. The influence of the Rayleigh convection on mass transfer is analyzed qualitatively andquantitatively based on the simulated and the experimental results.

Simulation of Current Structure Interactions Using Least-Squares Finite Element Method

The objective of this paper is to investigate the condition number of various formulations of LSFEM （least-squares finite element method） for SWE （shallow-water equations）, and develop a better conditioned shallow-water model to simulate current structure interactions. Various formulations of LSFEM for a two-dimensional vertically-averaged non-viscous shallow-water equations can be constructed, depending on the choice of norm, variables, interpolations, and possible treatment of boundary conditions. The condition number of the resulting system of equations is systematically examined and compared. It is found that condition number of the resulting system of equations depends on the choice of variables, interpolations, and size of element （h）. Order reduction （UW） formulations, with introducing auxiliary variables, with low-order interpolation is better conditioned and more efficient than direct （U） formulation with high-order interpolation. However, to resolve large gradients and fine structures of flow filed, high-order methods are generally preferred. The developed shallow-water model is used to simulate flow past an elliptic hump and flow past a cylinder. Computed results are compared with other numerical solutions.

Condition evaluation of a unique mining site

The primary objective of this study was to evaluate the existing conditions and the stability of a mining site in which the unique features of seismicity, mining activity, hydrological conditions, geological conditions, environmental conditions, and future development plans were considered. In particular, the potential subsidence locations near the proposed construction site, the effects of mining boundary profile,and the influence scope of the mining activity on the neighboring areas were investigated using the finite element method. The study results indicate:(1) the overlying sandstone layer to the coal layer is the key to the stability of the mining roof;(2) the broken boundary has the most effect, followed by the arc boundary and linear boundary;(3) the safe distance from the mining boundary should be at least400 m if the proposed structure is to be built near an active mining site. Other relevant engineering recommendations are also proposed. The concluded results from this study may serve as a guide to other similar sites in the world.

Analysis of raft foundation design based on considering influence of superstructure stiffness

The finite element method was used for analysis of raft foundation design in high-rise building.Compared with other conventional methods,this method is more adapted to the practical condition since both superstructure stiffness and soil conditions were considered in calculation.The calculation results by example show that the base reaction is more uniform and the maximum reaction decreases obviously.Accordingly,the raft foundation design is more economic without any loss of security for high-rise building.

Analysis of thin plates by the weak form quadrature element method

The recently proposed weak form quadrature element method （QEM） is applied to flexural and vibrational analysis of thin plates The integrals involved in the variational description of a thin plate are evaluated by an efficient numerical scheme and the par- tial derivatives at the integration sampling points are then approximated using differential quadrature analogs. Neither the grid pattern nor the number of nodes is fixed, being adjustable according to convergence need. The C~ continuity conditions char- acterizing the thin plate theory are discussed and the robustness of the weak form quadrature element for thin plates against shape distortion is examined. Examples are presented and comparisons with analytical solutions and the results of the finite element method are made to demonstrate the convergence and computational efficiency of the weak form quadrature element method. It is shown that the present formulation is applicable to thin plates with varying thickness as well as uniform plates.

Wave propagation of laminated composite plates via GPU-based wavelet finite element method

This paper presents a novel parallel implementation technology for wave-based structural health monitoring (SHM) in laminated composite plates. The wavelet-based B-spline wavelet on he interval (BSWI) element is constructed according to Hamilton’s principle, and the element by element algorithm is parallelly executed on graphics processing unit (GPU) using compute unified device architecture (CUDA) to get the responses in full wave field accurately. By means of the Fourier spectral analysis method,the Mindlin plate theory is selected for wave modeling of laminated composite plates while the Kirchhoff plate theory predicts unreasonably phase and group velocities. Numerical examples involving wave propagation in laminated composite plates without and with crack are performed and discussed in detail. The parallel implementation on GPU is accelerated 146 times comparing with the same wave motion problem executed on central processing unit (CPU). The validity and accuracy of the proposed parallel implementation are also demonstrated by comparing with conventional finite element method (FEM) and the computation time has been reduced from hours to minutes. The damage size and location have been successfully determined according to wave propagation results based on delay-and-sum (DAS). The results show that the proposed parallel implementation of wavelet finite element method (WFEM) is very appropriate and efficient for wave-based SHM in laminated composite plates.

On the Existence for Some Special Primitive Elements in Finite Fields

Let F_q be a finite field of characteristic p. In this paper, by using the index sum method the authors obtain a sufficient condition for the existence of a primitive elementα∈ F_(q^n) such that α + α^(-1)is also primitive or α + α^(-1)is primitive and α is a normal element of F_(q^n) over F_q.