A finite element model for unbonded flexible pipe under combined axisymmetric and bending loads

Flexible pipes are key equipment for offshore oil and gas production systems, conveying fluids between the platform and subsea wells. The structural arrangement of unbonded flexible pipes is quite complex, encompassing several layers with polymeric, metallic and textile materials. Different topologies and a large amount of intricate nonlinear contact interactions between and within their components, especially because of the relative stick-slip mechanism during bending, makes numerical analysis challenging. This paper presents an alternative three-dimensional nonlinear finite element model that describes the response of flexible pipes subjected to combined axisymmetric and bending loads. To simulate the response of a flexible pipe under axial tension or compression combined with uniform curvature, an equivalent thermal loading is employed on the external sheath, which is modelled as an orthotropic thermal expansion material with temperature-independent mechanical properties. To assess the feasibility of the proposed model, the bending moment versus curvature of the finite element solution is compared with experimental results obtained in literature and good agreements are found between them. Detailed finite element results such as contact pressures, armour wire slip displacements and friction, normal and transverse bending stresses are also shown and compared with available analytical models.     

汽车转向器齿条齿扇传动副的几何和啮合计算（续1）

为便于研究变厚渐开线齿轮在循环球齿条齿扇式转向器中的应用,文章介绍了变厚渐开线式齿扇在设计过程中相关参数的选择方法,并通过大量计算得到转向器变齿厚齿扇齿条传动参数匹配表方便设计师的查阅使用;还介绍了齿扇大端单边转角计算方法和齿条齿根圆角干涉验算方法,通过实例计算验算其正确性.结果表明,通过合理地选择变位系数、齿顶高及齿根高,可以确保齿扇大端面齿顶圆齿厚达到0.3～0.5个模数,大端截面重合度达到1.0.     

Understanding ship-grounding events

The paper presents a simple procedure to estimate the damage to a ship bottom and the associated seabed topology that results from a dynamic grounding event. The seabed is modeled as a rigid body and parameterized by a quadratic surface, i.e., a paraboloid, which can in principle model a wide range of seabed topologies. A nonlinear finite element program (LS-DYNA) is used to simulate the contact force versus the lateral penetration, from which the horizontal force component of powered grounding is estimated. The simplified procedure for analyzing dynamic and static grounding events is outlined. Simulations are performed for different ship speeds and for different initial levels of obstruction over the keel. It is shown that a static approach may replace the dynamic grounding simulation, thereby considerably reducing the computational work. The static approach allows for the quick estimation of the energy absorption during powered grounding, which is imperative for decision making during critical situations. The ultimate goal of the study is to provide a near real-time prediction of the risk of rupture of the cargo tanks and hull girder failure. Moreover, the residual strength of damaged ships is an important issue that is related to operations involved in the salvage of wrecked vessels, such as re-floatation and towing.     

Prediction of residual stresses induced by low transformation temperature weld wires and its validation using the contour method

Welding residual stresses are one of the main factors influencing the engineering properties of welded structures, and should be taken into account during designing and manufacturing products such as ships, bridges, etc. Recently, both computational and experimental methods play a significant role for providing residual stresses. The contour method (CM) became one of the most powerful techniques that can provide measurement of residual stresses normal to a plane of interest. In this method a component is cut at any plane of interest. Displacements normal to the cut surface are measured and then processed. Using the Thermal–Elastic–Plastic Finite Element Method (TEP-FEM), residual stresses after welding can be predicted. As well as, the elastic FEM can be used to reproduce residual stresses from measured longitudinal displacements in the CM.The main objective of this paper is to evaluate the effectiveness of different low transformation temperature (LTT) weld wires using TEP-FEM and the CM. In the simulation part, a computational approach is developed to numerically simulate both of welding and the CM. In the TEP-FEM, phase transformation is considered for LTT welds, additionally volume change and variation of mechanical properties with temperature are considered. In the simulated CM, welded specimens to be measured are replaced by TEP-FE models. Then the procedure of the CM is examined before applying it to real measurements. The simulated CM successfully predicted how the CM would reconstruct the residual stresses if applied experimentally. In the experimental part, welding is conducted using conventional and various LTT weld wires. Longitudinal residual stresses produced due to welding are measured using the CM. The results of TEP-FE simulation and the CM show the effectiveness of the different LTT weld wires in introducing compressive stresses in the weld. It is also observed that the applied LTT weld wires, which have almost the same martensitic transformation start temperatures, do not show big difference in the induced compressive residual stresses in the weld metal.     

板架弯曲二次应力对纵骨疲劳评估影响的研究

为了验证散货船、油船协调共同规范(HCSR)中在计算纵骨疲劳寿命时不考虑板架弯曲纵骨二次应力的合理性,讨论两种二次应力的计算方法,分别对散货船和油船板架的纵骨的二次应力进行计算,通过对是否考虑纵骨二次应力计算得到的疲劳寿命进行对比,验证HCSR中简化算法计算纵骨疲劳寿命的合理性。     

基于直接积分法的弓网耦合系统动态性能仿真分析

针对提速铁路采用的弹性链型悬挂接触网及受电弓结构,建立包含承力索、辅助线、接触线和吊弦4个部件的接触网模型、以及简化为弹簧阻尼机构的受电弓模型。通过接触单元将接触网和受电弓直接耦合起来得到弓网系统的整体模型,进而构建弓网耦合系统的动力学平衡方程。采用直接积分法对建立的平衡方程进行求解,得到反映弓网系统动态性能的抬升位移、接触压力以及应力等数据。与先前研究的参考数据比对结果表明,采用接触单元和直接积分法分析弓网耦合系统的动态性能,切实可行。     

新型货车转向架螺旋弹簧三维有限元分析与疲劳寿命估算

基于三维有限元法建模,对转向架弹簧的刚度和支撑圈接触条件下的应力进行计算分析.结果表明分析结果与静应力测试结果相近,转K2外簧静强度满足设计要求;支撑圈与相邻工作圈接触不仅使弹簧的最大应力有所增大,而且在加载过程中接触应力和最大应力随着支撑圈接触面积的变化而变化,因此在制造过程中应控制支撑圈的间隙.采用有限元法可快速获得弹簧的刚度和弹性特性曲线,克服了以往通过试验测试弹簧刚度所带来的周期长、费用高等缺点.弹簧疲劳寿命初步估算表明不考虑弹簧强化处理的影响,弹簧的疲劳寿命约为2.55×106次;采用喷丸等强化处理工艺并在提高弹簧20%的疲劳强度情况下,弹簧的疲劳寿命为8.9×106次.     

多弹性体接触问题的数值算法

提出一种新的求解带摩擦的接触问题的数值算法,即拟高斯迭代法。它对法向接触力和切向接触力进行交替迭代,并利用高斯迭代法求解法向接触力,利用分块高斯迭代法求解切向接触力。同其它的数值算法相比,该算法保留了关于接触力的柔度矩阵的稀疏性和对称性,利用矩阵乘向量可以分步进行的技巧,该算法只需存储关于接触力的柔度矩阵的下三角形矩阵的非零元和对角矩阵。根据可能接触边界的分布特点,将区域分解成不同的子区域,引进拉格朗日乘子表示接触力,保证了各子区域的网格剖分和位移求解是完全独立的。基于上述算法和有限元程序自动生成系统开发了相应的求解带摩擦接触问题的软件,数值实验表明,程序是正确的,算法是高效的。     

非接触IC卡及其管理软件系统探讨

首先展示高速公路电脑收费系统中各种通行券的价格及使用效益的分析比较 ,肯定非接触 IC卡的普遍使用势在必行 ,然后介绍非接触 IC卡作为通行券的收费管理过程 ,简述非接触 IC卡管理软件系统的设计 ,最后提出使用非接触 IC卡时必须注意的几个问题。     

重载列车车辆轮轨作用研究

通过对不同轴重、不同踏面外形和不同钢轨的轮轨接触最大应力的计算,得出轮轨接触应力随轴重、踏面和钢轨的变化情况。分析比较理论计算和试验结果,验证理论研究方法的正确性。研究表明:轮轨接触应力随着轴重的提高而增加;在运用初期轮轨磨耗量随运行里程增加急剧上升;随着轮轨间的进一步磨合,轮轨接触应力和磨耗量将稳定在一定水平;轴重从21 t提高到23 t,轮轨磨耗量增加80%左右;轴重从21 t提高到25 t,轮轨磨耗量增加150%左右;提高钢轨的重量等级,可以在增加车辆轴重的同时有效地降低轮轨接触应力及减少轮轨磨耗。