MODEL B-I FOR MACRO RECTANGULAR ELEMENT AND PROBLEMS OF INFLUENCE SURFACE FOR PLATE STRUCTURES

Model B-I for marco rectangular element is presented for the first time in this paper. To establish the influence surf ace for resultant R of bending plates, a number of generalized distributive loads q are defined. It is shown by numerical examples that Model B-I and the formula for the generalized distributive loads advanced in this paper are featured by high accuracy, low memory space and flexibility in practical application, and that they are especially effective for plate structures subject to moving loads, such as the two-dimensional continuous plates of highway bridges and the flat stabs in piled jetty engineering.

A RECTANGULAR ELEMENT OF THIN PLATES BASED UPON THE GENERALIZED VARIATIONAL PRINCIPLES

Based on generalized variational principles, an element called MR-12 was constructed for the static and dynamic analysis of thin plates with orthogonal anisotropy. Numerical results showed that this incompatible element converges very rapidly and has good accuracy. It was demonstrated that generalized varialional principles arc useful and effective in founding incompatible clement.Moreover, element MR-12 is easy for implementation since it does not differ very much from the common rectangular element R-12 of thin plate.

Uniformly convergent H(div)-conforming rectangular elements for Darcy-Stokes problem

We consider a singular perturbation problem which describes 2D Darcy-Stokes flow. An H（div）- conforming rectangular element, DS-R14, is proposed and analyzed first. This element has 14 degrees of freedom for velocity and is proved to be uniformly convergent with respect to perturbation constant. We then simplify this element to get another H（div）-conforming rectangular element, DS-R12, which has 12 degrees of freedom for velocity. The uniform convergence is also obtained for this element. Finally, we construct a de Rham complex corresponding to DS-R12 element.

A Generalized Point Conforming Rectangular Plate Element

A generalized point conforming rectangular element for plate bending is proposed. The present element displacement field can not only satisfy the continuity of normal displacement and its derivative at the element node, but also satisfy the generalized continuity at the middle point of each element boundary, where the generalized conforming condition is to make the non-conforming residual to be minimum. Numerical results show that the proposed element is more accurate than the ordinary 4-node non-conforming rectangular plate element (ACM element).

Multiresolution Finite Element Method Based on a New Locking-Free Rectangular Mindlin Plate Element

A locking-free rectangular Mindlin plate element with a new multi-resolution analysis (MRA) is proposed and a new finite element method is hence presented. The MRA framework is formulated out of a mutually nesting displacement subspace sequence whose basis functions are constructed of scaling and shifting on the element domain of basic full node shape function. The basic full node shape function is constructed by extending the split node shape function of a traditional Mindlin plate element to other three quadrants around the coordinate zero point. As a result, a new rational MRA concept together with the resolution level (RL) is constituted for the element. The traditional 4-node rectangular Mindlin plate element and method is a mono-resolution one and also a special case of the proposed element and method. The meshing for the monoresolution plate element model is based on the empiricism while the RL adjusting for the multiresolution is laid on the rigorous mathematical basis. The analysis clarity of a plate structure is actually determined by the RL, not by the mesh. Thus, the accuracy of a plate structural analysis is replaced by the clarity, the irrational MRA by the rational and the mesh model by the RL that is the discretized model by the integrated.

Element-free Galerkin method for free vibration of rectangular plates with interior elastic point supports and elastically restrained edges

The element-free Galerkin method is proposed to solve free vibration of rectangular plates with finite interior elastic point supports and elastically restrained edges.Based on the extended Hamilton＇s principle for the elastic dynamics system,the dimensionless equations of motion of rectangular plates with finite interior elastic point supports and the edge elastically restrained are established using the element-free Galerkin method.Through numerical calculation,curves of the natural frequency of thin plates with three edges simply supported and one edge elastically restrained,and three edges clamped and the other edge elastically restrained versus the spring constant,locations of elastic point support and the elastic stiffness of edge elastically restrained are obtained.Effects of elastic point supports and edge elastically restrained on the free vibration characteristics of the thin plates are analyzed.

BOUNDARY ELEMENT ANALYSIS OF INTERACTION BETWEEN AN ELASTIC RECTANGULAR INCLUSION AND A CRACK

The interaction between an elastic rectangular inclusion and a kinked crack in an infinite elastic body was considered by using boundary element method.The new complex boundary integral equations were derived.By introducing a complex unknown function H(t) related to the interface displacement density and traction and applying integration by parts,the traction continuous condition was satisfied automatically.Only one complex boundary integral equation was obtained on interface and involves only singularity of order l/r.To verify the validity and effectiveness of the present boundary element method,some typical examples were calculated.The obtained results show that the crack stress intensity factors decrease as the shear modulus of inclusion increases.Thus,the crack propagation is easier near a softer inclusion and the harder inclusion is helpful for crack arrest.

Mixed finite element and differential quadrature method for free and forced vibration and buckling analysis of rectangular plates

This paper presents a combined application of the finite element method （FEM） and the differential quadrature method （DQM） to vibration and buckling problems of rectangular plates. The proposed scheme combines the geometry flexibility of the FEM and the high accuracy and efficiency of the DQM. The accuracy of the present method is demonstrated by comparing the obtained results with those available in the literature. It is shown that highly accurate results can be obtained by using a small number of finite elements and DQM sample points. The proposed method is suitable for the problems considered due to its simplicity and potential for further development.

Isoparametric Boundary Element Method Applied to the Rectangular and Delta Hydrofoils near the Free Surface

In this paper, the hydrodynamic characteristics and flow field around rectangular and delta hydrofoils, moving with a constant speed beneath the free surface are numerically studied by means of isoparametric boundary element method （IBEM）. The quantities （source and dipole strengths） and the geometry of the dements are represented by a linear distribution. Two types of three-dimensional hydrofoils （rectangular and delta） are selected with NACA4412 and symmetric Joukowski sections. Some numerical results of pressure distribution, lift, wave-making drag coefficients and velocity field around the hydrofoils are presented. Also, the wave pattern due to moving hydrofoil is predicted at different operational conditions. Comparisons are made between computational results obtained through this method and those from the experimental measurements and other numerical results which reveal good agreement.

Formation of internal cracks during soft reduction in rectangular bloom continuous casting

To investigate the formation of internal cracks in GCrl 5 bearing steels during the soft reduction process in rectangular bloom con- tinuous casting, fully coupled thermomechanieal finite element models were developed using the commercial software MSC.MARC, and microstructures and fractographs were also observed. With the finite element models, the contours of temperature, equivalent plastic strain, and equivalent vun Mises stress were simulated. It is observed that the fracture surfaces of internal cracks are covered by cleavage or quasi-cleavage facets. The region of internal cracks in the intergranular brittle fracture mode is in the mushy zone between the zero ductility temperature （ZDT） and the zero strength temperature （ZST）. The simulated equivalent plastic strain in the crack region is 2.34%-2.45%, which is larger than the critical strain （0.4%-1.5%）, and the equivalent von Mises stress is 1.84-5.05 MPa, which is within the range of criti- cal stress （3.9-7.2 MPa）, thus resulting in the occurrence of internal cracks. Reducing the soft reduction amount from 3 to 2 mm can lower the stress under the critical value.

新型空心管状翼缘钢板组合梁设计理念与力学性能

工字钢组合梁桥正朝着少主梁、精简横向联系的方向发展。与传统多主梁复杂横向联系组合梁桥相比,双主梁桥由于采用了开口截面的结构形式,极大地削弱了其抗扭能力,在偏载作用下会产生较大的变形及翘曲应力,使钢主梁处于弯扭耦合的受力状态。空心管状翼缘钢板组合梁采用空心钢管取代传统的平板上翼缘,提升了稳定性,改善了结构性能。本文通过理论分析和实体有限元法的计算,研究了单梁在自重与横向风荷载作用下的稳定性;对非组合截面的组合体系下的稳定性能进行了分析与比较,并分离出扭转翘曲应力和纵向正应力,研究了不同跨径下扭转效应的影响。最后,对横向联系、加劲肋的影响进行了分析。研究结果表明,空心管状翼缘钢板组合梁桥扭转刚度大于传统工字形截面组合梁扭转刚度,自身横向稳定性好,并且需要较少的横向联系与加劲肋,可实现单梁吊装,避免采用过多临时加固及支撑措施,提高施工效率。

Grating Lobe Suppression with Element Count Optimization in Planar Antenna Array

The novel approach of this paper describes the suppression of grating lobe level with the element count optimization in planar antenna array. Rectangular lattice (RL) and triangular lattice (TL) structures are chosen for determining the achievable array element patterns (EP) and further suppressing the grating lobe level. The element spacing and number of elements (10 × 20 array) are taken into account for particular lattice. Grating lobe peaks are observed for the 200-element planar array at maximum scan angle (θ) with the set frequency of 3 GHz. Further, it is found that 14°;bore sight elevation of rectangular lattice produces a transformed field of view, which permits a reduction in element count of 20.39% compared with 10° bore sight elevation. Finally, the typical values of elevation, element count and array size (25 cm2) are trained using artificial neural network (ANN) algorithm and element count is predicted after testing the network. The network shows a high success rate.

狭窄空间内矩形导体电流测量装置设计与优化

针对狭窄空间内矩形导体电流测量,提出了一种基于霍尔元件椭圆阵列的电流测量装置,通过理论计算和有限元仿真分析确定了相对最优的阵列分布,搭建实验平台并通过实验验证了该方法的可行性,以及导体偏心状态下电流测量的有效性,同时分析了导体偏心状态下的电流测量偏心误差。仿真和实验结果表明,椭圆阵列电流测量装置在行业允许的±1%误差限内,允许导线X轴偏心-4.1~4.1 mm,Y轴无限制;且与传统电流测量装置相比,重量减轻82.9%,安装占用面积减小72.4%,对狭窄空间的适用性更强,为新能源产品轻量化、小型化、持续降本提供了技术支持。

思政元素融入混凝土结构课程的教学设计--以单筋矩形截面梁承载力设计为例

土木工程专业的课程思政设计是实现专业课程与思政课同步前行的重要举措,也是培养社会主义合格建设者和可靠接班人的重要途径。混凝土结构系列课程在土木工程专业课程体系中占据重要的地位,因此,在对课程教学背景和学情分析的基础上,以单筋矩形截面梁承载力设计知识单元为例,基于OBE理念,将思政元素融入教学设计,从课程目标、课程内容、教学过程设计、教学方法设计及教学实施方面,探讨如何合理、科学地将思政元素引入课程教学设计的各个环节,不仅解决专业教育和思政教育“两张皮”问题,且对学生的自主学习能力和学习热情起到积极的促进作用,另外对其他专业课具有引领和示范作用。

平面矩形单元及其在结构拓扑优化中的应用

在结构拓扑优化研究领域,越来越多的研究提供了简短的程序代码以验证所提方法或算法的有效性,其中应用较多的单元是平面矩形单元或更为特殊的正方形单元,但其解析公式均没有明确给出。基于此,本文以在结构拓扑优化中惯常使用的矩形单元为研究对象,推导其单元刚度矩阵、单元应力矩阵和单元质量矩阵的解析表达式,采用Matlab软件编写相关矩阵的计算代码,并通过结构拓扑优化方面的应用算例对代码进行了验证。结果表明,所给出的代码可直接使用,给出的单元矩阵的解析公式有助于更好地理解和使用相关结构拓扑优化程序。

硅油介质中矩形电容式微机械超声换能器发射与接收声场特性研究

与传统压电式超声换能器相比,基于微机电系统微加工技术制备的电容式微机械超声换能器(CMUT)具有频带宽、灵敏度高、一致性好、易于集成等优势,在医学超声成像中具有广阔的应用前景。该文针对研制的矩形CMUT器件,开展硅油介质中CMUT发射、接收声场特性的理论分析及实验验证研究。首先,针对CMUT阵元结构特征和工作原理,根据指向性函数理论和Bridge乘积原理,建立了矩形CMUT阵元指向性函数分析模型。此基础上,分析微元数目以及谐振频率对CMUT指向性的影响规律。最后,针对7 mm×7 mm二维矩形CMUT在硅油介质中的发射和接收特性进行了实验验证,测试表明发射指向性曲线与仿真理论曲线基本吻合;此外,CMUT接收与发射指向性的测试表明,收发指向性具有一致性,从而验证了声场的互易性。该文的研究对CMUT器件的封装设计以及基于CMUT阵列的乳腺超声CT成像系统的研制具有重要参考价值。

MS1180方管连续辊弯成形角部开裂机理

方矩形管在辊弯成形中会产生角部开裂现象,这已成为严重制约方矩形管质量的关键问题,为解决其角部开裂缺陷展开深入研究,寻找控制开裂缺陷的方法。首先通过对MS1180进行单轴拉伸、缺口拉伸和平面应变实验得到了材料的力学特性,并分别利用3种拉伸试验将Ayada、Rice-Tracey和标准化Cockroft-Latham准则进行校准,得到了预测误差最小的一种断裂准则,并以此构建了方矩管辊弯开裂模型。其次利用辊弯成形COPRA RF设计软件和有限元MARC仿真专业软件,结合生产实际条件建立了方矩形管连续辊弯成形三维有限元模型,并进行辊弯实验验证模型的准确性。最后采用扫描电镜和金相显微镜对方矩形管开裂件以及断口进行微观观察,针对性的利用有限元模型探究了方矩形管连续辊弯成形时应力-应变分布规律,并分析了道次数量、角部成形半径和机架间距对方矩管角部应力-应变分布的影响。结果表明:发现材料起裂点位于角部近外层,对开裂断口进行分析,得到其开裂方式为准解理开裂,角部剪切面上所受的主应力过大导致其开裂;增加辊弯道次数量、方矩形管角部成形半径以及机架之间的间距能有效减少开裂问题的出现,为以后解决方矩形管角部开裂问题提供了理论基础。

矩形截面组合柱-钢梁节点数值模拟分析

针对矩形截面组合柱-钢梁节点,结合广东某实际工程,对节点进行有限元数值模拟分析。结果表明,组合节点受力合理,混凝土和型钢能够协同工作,该节点在大震工况下,混凝土局部出现受压损伤,集中在内置型钢交接位置以及柱脚位置;混凝土内钢筋Von-Mises等效应力最大位置集中在柱脚受压侧,绝大部分钢筋尚未进入屈服阶段,节点区域钢材均未达到屈服强度,处于弹性范围内,满足设计要求。此研究能为类似设计提供参考价值。

基于NSGA-Ⅱ算法的阵元间距多目标优化

针对定向扬声器换能器阵列设计的复杂性与不确定性问题,提出了一种基于NSGA-Ⅱ算法的矩形换能器阵元间距多目标优化方法。基于矩形换能器主要结构参数与阵元间距之间的动态性能分析,建立了以方向锐度角、主瓣波束宽度以及旁瓣级为协同优化目标的阵元间距解析函数和约束条件;在此基础上,采用NSGA-Ⅱ算法对所构建的多目标模型进行优化,由此获取矩形换能器阵元间距的最优可选集。仿真结果表明:在满足各项目标协同优化以及约束条件的情况下,所提出的矩形换能器阵元间距设计方法可实现换能器阵列旁瓣级较小且阵列指向性较好的定向扬声器。

容器矩形大开孔补强结构优化设计

为保证充足的换热面积与换热效率,矩形冷却器是内冷碳化塔一个重要组成部分,碳化塔塔体与矩形冷却器的连接可视为圆筒体上带有矩形大开孔的结构,本文以实际工程案例中某一碳化塔水箱矩形大开孔为例,回顾一种安全可靠且经济有效的容器矩形大开孔补强结构的设计及优化过程。通过ANSYS数值模拟方法对容器矩形大开孔进行结构应力计算,采用分析设计方法对应力进行分析和评定,对不同的结构形式进行对比分析,最终确定一种纵向加环向筋板整体加强方案的典型结构,该结构可以根据非标结构和强度设计的需要灵活调整,实现结构强度设计安全可靠且经济合理,可为工程实践中容器的矩形大开孔结构设计和优化提供有益参考。