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.

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).

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 frst.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.

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.

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.

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.

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。

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。

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。

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。

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。

基于有限元分析的冷冻干燥机矩形干燥舱结构优化

由于冷冻干燥机矩形干燥舱结构设计采用简化计算与经验设计相结合,为了满足其工作需求,在设计过程中确保安全性,常会出现过度设计的问题。针对该问题,本次研究采用迭代设计优化结构,使其既能满足抽真空阶段干燥舱变形量不得高于3 mm的要求,又能降低干燥舱自重、减少材料浪费以此降低成本,提升竞争力。优化过程中,将干燥舱三维模型进行优化,利用有限元分析法,对工作过程中抽真空阶段以及预冷却阶段干燥舱变形情况进行分析,明确后续优化只要满足抽真空阶段箱体所受应力即可满足冷却阶段工作需求。经多次迭代优化结构,其变形量最终降到2.951 mm,质量减少417 kg。该研究结果对设计人员进行冷冻干燥机矩形干燥舱强度结构设计时,提供加强筋排布参考依据。

基于板-梁理论的FGM矩形截面杆扭转振动的理论研究

基于板-梁理论和Saint-Venant扭转理论的研究成果,将纵向位移假设为含有待定系数的表达式,通过几何方程推导了功能梯度材料矩形截面杆的总应变能方程,并利用最小应变能原理确定待定系数,得到自由扭转刚度的理论公式。在此基础上对矩形截面杆的自由振动出现纯扭转模态时的动能进行研究,求出在夹支条件下的扭转振动时的动能表达式、总势能的表达式及频率表达式。利用有限元软件ANSYS建立具有功能梯度材料特性的矩形截面杆的扭转振动的有限元模型,通过后处理命令查看对应边界条件的振动频率。通过有限元软件验证表明:基于板-梁理论推导得出的理论解与有限元解吻合较好,最大误差在4%以内。

某型航空用矩形截面弹簧逆止器设计

传统的防逆转装置存在体积与质量大的缺点,不适用于对质量指标极度敏感的航空类产品。为此,提出一种小巧轻便的新型矩形截面弹簧逆止器设计方法,通过对逆止器中矩形截面弹簧进行力学分析,明确矩形截面弹簧的受力与变形关系,分析矩形截面弹簧尺寸、配合套筒过盈量与逆止性能的变化特性。推导矩形截面弹簧逆止器逆止有效条件,并引入遗传算法进行求解;根据求得的结构参数,运用CATIA软件建立矩形截面弹簧逆止器结构模型,并导入HyperWorks软件进行校核分析。结合样件试制及测试,结果表明:所提方法与传统摩擦盘式方法相比同负载条件下质量可降低约61%,仿真与实验对照验证所提方法的有效性。

基于热弹塑性有限元法的船体板极限强度研究

利用Abaqus软件,分析了热弹塑性有限元法在对接焊船体矩形板极限强度评估中的应用。首先,基于热弹塑性有限元法,直接获取船体板焊接残余应力与变形。进而采用非线性有限元法,评估了2块不同板厚(9.5 mm、11 mm)对接焊船体矩形板在轴向压缩载荷下的极限强度。研究表明,壳单元与实体单元计算所得温度场、残余应力场、变形结果相近,但前者计算效率显著提高。不同矩形板厚度对矩形板纵向残余应力的分布影响较小,但对其垂向挠度峰值影响较大。不同厚度矩形板通过数值模拟得到的极限强度值与Faulkner简化公式计算值误差分别为4.2%和5.1%,因此数值模拟值与公式计算值较吻合。

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.