基于材料非线性的海洋柔性立管防弯器有限元分析

建立海洋柔性立管防弯器三维有限元模型,研究聚氨酯材料非线性对防弯器弯曲性能的影响．通过算例对比不同材料属性的计算结果,发现不考虑材料非线性的计算结果与理论分析结果吻合较好．试验结果表明考虑防弯器材料非线性的立管最大曲率比不考虑材料非线性的小10％．因此,在防弯器详细分析时很有必要考虑材料非线性．     

钢管脐带缆弯曲刚度有限元分析

为评价钢管脐带缆的弯曲性能,用ANSYS建立高效的钢管脐带缆三维有限元模型,采用梁单元模拟其中所有构件,在相互接触的构件之间设置线线接触模拟其相互作用,并采用库伦摩擦模拟构件间的摩擦行为.将弯曲刚度的分析结果与经典的理论分析结果进行对比,验证有限元模型的正确性.基于此模型,分析不同螺旋角度以及不同摩擦因数对脐带缆弯曲刚...     

谱元法在求解刚架结构动力学问题中的应用

把谱元法应用于刚架结构的动力学响应计算和分析中.建立了杆和梁的谱单元动力学刚度阵,针对刚架结构组装了整体动力学刚度阵,建立了整体结构的运动方程,计算了结构的固有频率和时域响应,并与采用有限元方法得到的结果进行了对比.从结果中可以看出谱元法在数值模拟中的独特优势.     

Euler梁弯曲分析的无网格高阶曲率光顺方案

针对Euler梁弯曲问题的无网格法数值求解,提出与挠度近似相一致的高阶曲率光顺方案。采用耦合权函数方法准确施加固定挠度边界条件,并在曲率光顺过程中引入转角边界条件。数值计算结果表明:该方案能精确反映纯弯曲模式和线性弯曲模式;与标准的高斯积分及现有的常曲率光顺方案相比,该高阶曲率光顺方法可显著改善该类问题的数值求解精度。     

大展弦比板弯扭耦合受迫振动分析

对于工程广泛存在的大展弦比结构,首次研究了大展弦比板弯扭耦合受迫振动响应.考虑弦向相对弯曲刚度远大于展向弯曲刚度,将弦向截面等效为刚体,考虑其绕展向轴线的扭转,应用Hamilton原理分别计算大展弦比板的势能与动能,建立两端简支的大展弦比板弯扭耦合受迫振动的动力学控制方程.将动力学控制方程进行Galerkin截断后,通过谐波平衡法和微分求积法/微分求积单元法,计算得到了大展弦比模型弯扭耦合受迫振动稳态响应的解析解及数值解,同时验证了解的截断收敛性及谐波收敛性.最后研究了外激励幅值对结构受迫振动响应的影响.结果将为工程中广泛存在的大展弦比结构设计提供指导.     

空间薄壁梁单元面向对象程序的实现

针对传统有限元分析软件主要面向过程设计,其可维护性和可扩展性等较差的问题,基于面向对象程序设计方法,建立具有内部节点的空间薄壁截面梁单元模型,给出线弹性空间薄壁梁单元的UML类图,介绍矩阵类、截面类、材料类、节点类、单元类和结构类等6种类成员的主要属性和方法.用C#编制相应的有限元程序,通过T形框架算例比较和验证其位移和弯曲转角计算值、理论解和ANSYS的BEAM 189梁单元的数值解,结果表明该程序精度良好,可用于空间薄壁结构的有限元分析.     

弯曲刚度对织物膜材褶皱特性影响仿真分析

薄膜结构弯曲刚度很低,在外力作用下容易出现褶皱,薄膜弯曲刚度影响着膜材褶皱的几何参数.与一般匀质薄膜相比,织物膜材具有更小的弯曲刚度,弯曲刚度对褶皱半波长与幅值影响很大.引入织物弯曲刚度系数,采用非线性屈曲分析方法得到织物膜材的褶皱参数,与数值仿真计算结果进行对比验证.利用非线性屈曲理论方法研究了弯曲刚度对织物膜材褶皱几何参数的影响,并且与数值仿真计算结果进行对比分析,两者结果一致.研究表明织物膜材的弯曲刚度越小,褶皱波长越小,褶皱幅值越小,弯曲刚度系数不影响褶皱区域分布.     

Duabechies小波基梁单元的构造及应用研究

以Daubechies小波尺度函数作为单元插值函数，构造了一类小波基梁单元，由于采用节点挠度和转角作为单元自由度，单元连接和约束条件处理能够像传统单元一样方便地进行，从而使该小波基梁单元可有效地用于变截面、局部承载等复杂梁弯曲问题分析，数值算例表明，本文构造的小波基梁单元对不同约束条件、不同结构形式梁弯曲问题均有较高分析精度，为有限元方法提出了一种新的研究途径．     

斜拉桥中拉索对桥面动力特性的影响

将斜拉桥的拉索和桥面抽象为带弹性支承的压弯弹性梁模型,并根据轴向受力梁的弯曲振动方程和哈密尔顿原理,建立了考虑拉索索力影响的单梁多索索梁结构-梁的动力学控制方程,应用传递矩阵法进行求解,并编制了求解程序.通过算例对影响桥面动力学特性的索的刚度、张拉力和桥面裂纹等因素进行了数值分析.分析结果表明,在斜拉桥的施工阶段,随着梁的长度的改变,梁的刚度讯速下降,由于索对梁的支承作用使结构的刚度有一定的提高,而索的拉力对桥面作用的压力越来越大,轴向压力使结构的刚度降低越来越明显,另一方面轴向压力对桥面裂纹引起的刚度降低有一定的抑制作用.由此,在桥梁的建设中应重视索力对桥面动力特性的影响.     

悬索桥主缆初应力对桥梁动力特性的影响

为掌握主缆初应力对桥梁动力特性的影响,以悬索桥为例,采用静力非线性分析方法计算应力变化过程中悬索桥的跨中挠度、缆索轴力及加劲梁的轴力变化;将得到的内力作为结构的预加应力进行有预应力的模态分析. 应用ANSYS软件进行分析,其中有限元建模时采用4种单元类型:空间梁单元BEAM4用于模拟加劲梁和塔;空间杆单元LINK10用于模拟主缆及吊杆;通过设定BEAM4和LINK10单元初应变进行有预应力的模态分析;采用MASS21单元模拟横隔板、吊杆锚固装置和桥面上的栏杆,并分别考虑质量和质量惯性矩的作用. 分析表明,悬索桥主梁竖弯振动频率受主缆初应力的影响较大,而侧弯振动频率和扭转振动频率受此影响较小. 该结果为同类桥梁的动力特性分析提供参考.     

Finite element analysis of stiffened plates

A finite element method is presented in which the constraint between stiffener and member is imposed by means of Lagrange multipliers. This is performed on the functional level, forming augmented variational principles. In order to simplify the initial development and implementation of the proposed method, two-dimensional stiffened beam finite elements are developed. Several such elements are formulated, each showing monotonic convergence in numerical tests. In the development of stiffened plate finite elements, the bending and membrane behaviors are treated seperately. For each, the stiffness matrix of a standard plate element is modified to account for an added beam element (representing the stiffener) and additional terms imposing the constraint between the two. The resulting stiffened plate element was implemented in the SAPIV finite element code. Exact solutions are not known for rib-reinforced plated structures, but results of numerical tests converge monotonically to a value in the vicinity of an approximate “smeared” series solution.     

Springback equation of small curvature plane bending

A new analytical method for springback of small curvature plane bending is addressed with unloading rule of classical elastic-plastic theory and principle of strain superposition.We start from strain analysis of plane bending which has initial curvature,and the theoretic derivation is on the widely applicable basic hypotheses.The results are unified to geometry constraint equations and springback equation of plane bending,which can be evolved to straight beam plane bending and pure bending.The expanding and...     

钢管弯制过程有限元仿真及断裂原因分析

针对某金属结构公司在钢管弯制过程中出现的个别钢管断裂现象进行研究,根据现场钢管弯制工艺和工序的情况描述,采用非线性有限元软件Marc对钢管的多工位弯制过程进行模拟仿真.以最恶劣的情况即曲率最大的胎具进行多工位弯制,仿真结果显示6个工位的连续弯制过程最大应力为552 MPa,没有达到材料的抗拉极限626 MPa,该弯制过程不会引起钢管强度失效.模拟钢管多种曲率胎具弯制下的应力应变分布情况和回弹后残余应力应变情况.仿真结果表明,弯制此种钢管最大曲率的圆弧时,钢管上的最大应力为542 MPa,小于材料的抗拉强度626 MPa;最大塑性应变为0.031,小于材料允许的最大伸长应变0.2.经过模拟仿真分析,该公司采用的弯制工艺不会引起材料强度失效断裂.引起钢管弯制断裂的原因为个别材料夹杂或气孔造成的小概率事件.     

Finite element modelling of cable networks with flexible supports

The objective of the paper is to present a mathematical model for analysis of prestressed cable structures with flexible contour beam. The proposed numerical procedures are based on a discrete scheme according to the finite element method. A reliable model of the interaction of the flexible contour beam with the cable network enables the achievement of more efficient solutions in the design analysis. Geometrical nonlinearity is accounted for in the cable net substructure and the contour beam is modelled by linear beam elements. Equations are solved by iterative methods and explicit time integration. The described numerical technique has been employed to model prestressing, static and dynamic behaviour. Theoretical results have been compared to experimental data and used in practical applications.     

单侧主缆刚度损伤悬索桥的模态分析及1∶1内共振

悬索桥缆索在长期服役状态下损伤很难避免,单侧主缆刚度损伤会使系统出现主梁竖弯与扭转自由度间的耦合,这可能会进一步对悬索桥的模态和大振幅下的非线性响应造成影响.为此,建立了考虑单侧主缆刚度受损的七自由度悬索桥横截面模型,模态分析发现单侧主缆刚度损伤会使得系统前两阶固有频率曲线由交叉变为跃迁,导致两个本身相互独立的模态发生耦合.以此为基础,考虑悬索桥主缆刚度有损伤和未损伤两种工况,运用拓展的增量谐波平衡法(EIHB)计算系统在内共振条件下的非线性振动.研究结果表明：单侧主缆刚度有损伤的悬索桥在外部简谐激励下发生1:1内共振,系统能量表现出明显的转移现象;竖向和扭转简谐激励下,有损伤的悬索桥较未损伤工况响应幅值有所减小,但出现了两个共振响应峰值,对激励频率更为敏感.数值结果与利用Runge-Kutta法计算得到的结果吻合一致,验证了EIHB法的准确性.     

An improved formulation of space stiffeners

This paper presents a displacement based finite element model for predicting the constraint torsion effect of stiffeners. In structural modelling, the plate/shell and the stiffeners are treated as separate elements where the displacement compatibility transformation between these two types of elements takes into account the constraint torsional warping effect in the stiffeners. The development is based on a general beam theory which includes flexural-torsion coupling, constrained torsion warping, and shear-centre location. The virtual work principle includes the second order terms of finite beam rotations. For finite element analysis, cubic Hermitian polynomials are used as shape functions of the straight space frame element with two nodes. Elastic stiffness and geometric stiffness matrices for an arbitrary cross-section are evaluated in a closed form, and load correction stiffness for eccentric stiffener loads are considered. To demonstrate the importance of torsion warping constraints and to illustrate the accuracy of this formulation, finite element solutions are presented and compared with available solutions.     

Post-buckling behavior of cold-formed thin-walled stainless steel beams

A numerical approach for predicting the post-buckling responses of cold-formed thin-walled stainless steel beams is presented. In the analysis, the nonlinear and unsymmetrical stress-strain relations in tension and compression for both flat and corner materials are considered. The effective width concept is used to account for the post-buckling strength of the thin compression flange of the beam. Using this concept, the value of the effective width varies with the stress borne by the flange edge. In view of the nonlinearities introduced by considering the material characteristics and the post-buckling behavior of the individual elements, an iterative procedure is employed to establish the nonlinear moment-curvature relation of a section. In a beam subjected to bending, the effective moment of inertia of the section varies from point to point along the length of the beam depending upon the magnitude of the moment at the point considered. In this analysis, the continuously flexible beam is replaced with a finite number of discrete rigid elements connected by flexible joints at which the continuously varied curvature is lumped through numerical integration. In the case of a continuous beam, it is further complicated by the fact that the bending moment distribution along the beam is not known a priori and its determination is part of the solution to the problem. An iterative algorithm is developed to obtain the approximate true moment distribution considering the compatibility conditions at the support. A computer program following th e above solution scheine has been developed and is capable of predicting the nonlinear responses of most of the common thin-walled sections encountered in light-gage steel design. Comparisons with some available experimental data are provided.