应用三维光弹性分析轧辊的接触应力

对有限长，外载荷又集中作用的轧辊，当其母线接触压靠性，接触面上的应力分布是不均匀的。于是，根据弹性力学理论推导的无限长辊子相互压靠的接触应力“赫芝”解法无法得到充分应用。由于这个原因。该文提出了一个辊子接触应力非均匀分布模型假设，它是在横向满足半椭圆分布，而纵向为未可知的曲线分布，根据这个假设应用三维光弹性的应力切片法及有限元数值计算概念。导出了这类辊子接触应力的混合计算方法。作为一个应用实例，该文讨论了宝钢1420双平整轧机轧辊的接触问题，该轧机有六个辊子组成，上下三三对称，其中最外层为支承辊，中间是中间辊，下层是工作辊，工作辊与轧件接触，钢厂在板形控制研究中，十分需了解各辊子之间的接触应力，应用该文分析方法。可以得到接触面上理想的三向接触应力值。为厂方的板形控制工艺改进提供了极有用的参数。     

有限长圆柱体接触应力的光弹性解法

对两个有限长，外载荷又集中作用的圆拄体，在接触面上的应力分布是不均匀的．为了获得接触应力，本文应用弹性力学的理论、光弹性应力分析方法和有限元计算概念，提出了一种混合计算法．最后给出一个应用实例，讨论了某轧机轧辊的接触问题．     

基于分形理论的双渐开线齿轮接触应力研究

综合考虑接触面粗糙度、材料特性等因素对齿轮接触应力的影响，基于分形理论和经典Hertz接触理论建立双渐开线齿轮分形接触模型. 该模型中，影响载荷和实际接触面积的主要因素包括分形维数、粗糙度幅值和材料特性参数. 理论分析表明:分形维数一定时，真实接触面积随着载荷的增大而增大；载荷一定时，接触面积随着粗糙度幅值的增大而减小；随着材料特性参数值的增加，在一定程度上加强了软材料轮齿承载能力，同时会使得微凸体由弹性变形到塑性变形的临界面积减小. 对比分形接触模型和有限元模型两种计算双渐开线齿轮轮齿接触应力方法，结果证明了分形接触模型计算双渐开线齿轮接触应力的有效性.      

大型三排滚柱回转支承承载能力和寿命分析

针对两种不同类型的滚子，研究了大型三排滚柱回转支承承载能力和疲劳寿命．首先，通过理论推导滚子和滚道之间的变形量，并数值模拟轴承滚子和滚道之间的接触应力分布，从而推导滚子的寿命．计算结果显示，圆柱滚子的端部应力较大，而异形修正滚子最大应力出现在接触中心处，端部应力在数值上远小于圆柱滚子．通过等效应力的计算，在载荷较低时，圆柱滚子的疲劳寿命高于修正滚子；当载荷较大时，异形修正滚子的疲劳寿命明显高于圆柱滚子．     

基于数字图像相关方法的矿用扁平接链环模型接触变形实验研究

采用分割辅助数字图像相关方法,针对矿用扁平接链环模型在多齿啮合状态下的接触变形进行了实验分析,测量了该结构在承受拉伸载荷时的全场变形分布,并对其接触面附近区域的应变集中现象进行定性与定量分析。实验以Φ26mm×92mm规格的梯齿型接链环模型为研究对象,提出了相应的多分辨率方法进行接触变形场测量。方法中仅采用单个相机实现多分辨率测试,从而避免了传统多分辨率方法中的图像修正误差。采用降采样后的图像计算试件的全场变形,以实现高效的应变分布分析以及应变集中区域定位;采用高分辨率图像进行局部变形计算,以分析应变集中区域的变形分布。实验结果表明,接链环第Ⅱ对和第Ⅲ对啮合齿的齿根部发生的变形最大,是接链环的薄弱部位。该实验结果为梯齿型接链环的变形规律分析和结构设计提供了有效的实验依据。     

考虑接触应力非线性分布的接触力元模式及其验证分析

在作者提出的非连续变形计算力学模型中,采用接触力元模型描述多体接触界面上的接触特性．由于这种模型中假定接触应力沿接触界面为线性分布,从而得到的接触界面应力分布往往出现跳跃等非光滑性特征,该文对此进行了改进,采用具有高阶光滑性的非线性函数建立了能够考虑界面上接触应力非线性分布的接触力元模式,以期合理地揭示多体系统中界面的接触特性．对某一典型算例进行了数值计算,通过与大型通用非线性有限元结构分析软件ABASQUS的计算结果对比,验证了所建议计算模型的合理性与有效性．两种方法计算得到的界面接触对上的接触力基本相同;而由于采用的应力分布模式的假定不同,接触应力有所差别,由于在该文计算模型中接触对上的接触应力是按照未知量直接求得的,因此按照所建议的非线性接触力元模式所得到的接触应力更为合理．     

完整齿轮副的三维有限元应力分析

本文分析的三维有限元模型是一完整的齿轮副,不必假设切开表面上的力与位移边界条件,也不必在进行齿轮的应力分析前预估齿牙上作用的载荷。为了减少数据准备及计算工作量,用接触线代替了啮合齿间的接触面,把非线性接触问题简化为线性接触问题。利用这里所介绍的办法,可以得到齿向载荷分布结果、齿间载荷分配结果、以及完整齿轮副任一区域内的位移及应力结果。     

钢筋混凝土斜交刚构连续梁桥的实验与数值分析

本文利用三维光弹性法和ANSYS软件分析了铁路斜交刚构连续梁桥在一期、二期自重载荷和两种不同工作载荷下的梁体应力分布，数值研究中分别针对实验模型和建筑实物建立计算模型，并将计算结果与实验结果进行了比较，结果表明，桥梁的应力分布呈明显的不对称特征，有其自身的独到之处。     

轴流泵参数化设计及应力与模态特征分析

以船用轴流式喷水推进泵为对象,探索了轴流泵参数化设计、水动力性能、静强度和结构声学特征分析的数值途径。轴流泵叶轮采用升力法设计,导叶采用流线法设计,叶片三维造型在NUMECA参数化设计平台中完成。轴流泵水动力性能校核由粘性CFD计算完成,CFD计算同时提取得到叶片分布式水动力载荷。叶片静强度校核由ANSYS有限元计算叶片应力和应变特征完成,应力分析时同时考虑水动力载荷、重力载荷和离心力载荷。叶片结构声学特征分析由NASTRAN有限元计算叶片模态振型和振型频率完成。计算结果表明,轴流泵扬程和功率满足设计指标,效率达87.13%;叶轮叶片形变相对于叶顶间隙来说为极小量,可忽略不计,叶片存在局部应力集中现象,最大应力小于许用应力,满足静强度要求;叶片前四阶振型特征与分析经验一致,且振型频率远离轴频、叶频及其谐频特征频率,能够避免共振产生。     

用焦散线方法测量集中载荷的误差分析

在实验应力应变分析中，焦散线方法是研究奇异应力场的有效方法．本文以半无限平面受边界压缩载荷作用的问题为例，对集中力作用下的焦散线与分布力作用下的焦散线作了比较，分析了由分布载荷得到的焦散线而计算得到的载荷与施加到试件上的实际载荷之间的误差，并提出了减小误差的措施．     

接触状态对叶根轮槽应力分布影响的研究

汽轮机叶片叶根、轮槽连接区域常因加工误差及磨损等原因导致接触状态的改变,从而改变整个区域应力分布并大大降低汽轮机的使用寿命。本文运用数字光弹性技术实验测试了长叶片叶根、轮槽在不同接触状态下的应力分布情况,同时结合有限元进行了仿真计算。结果表明,叶根、轮槽对称接触时,全部齿同时接触的应力集中系数最小且分布较均匀;而当部分接触齿产生间隙时,接触状态发生显著变化,应力集中系数明显增大;尤其是当左右齿非对称接触时,最大应力集中系数明显增大且应力分布不均匀。本文研究可为叶根、轮槽的优化设计、加工以及叶片的装配、维护提供实验依据。     

Load and Boundary Condition Calibration Using Full-field Strain Measurement

For critical load bearing structures, it is often necessary to experimentally determine the load distribution on the structure so that accurate finite element models can be developed for stress and fatigue life predictions. An inverse problem approach is presented here for computing or calibrating the loads and boundary conditions acting on a structure. This enables the creation of more accurate finite element models, especially for structures that have complicated load distribution and compliant boundary conditions. The method presented here involves minimizing the least square error between the strains computed using the finite element model and the strains and displacements obtained experimentally. The nodal loads and the compliance at fixed boundaries are treated as the variables in the optimization problem. The compliance is modeled as springs attached at the nodes that are on the boundary where the structure is restrained. The method is verified by computing the loads and boundary conditions when displacements, maximum shear strain or both are available at large number of points on the surface of the structure. The experimental data set was generated using the luminescent photoelastic coating (LPC) technique.     

鸟撞击叶片时载荷因素的数值模拟分析

鸟与叶片的撞击过程是一个复杂的加载过程。为了将其简化,以建立一个简单且合理的鸟撞击载荷模型,需要分析鸟撞击载荷的各种因素对叶片响应的影响。本文通过计算机数值模拟进行上述工作。以矩形悬臂板模拟实际叶片,以冲击载荷模拟鸟撞击载荷,采用有限元法计算悬臂板在冲击载荷下的非线性瞬态响应。从鸟撞击载荷的冲量、时间因索、空间因素三个方面分析了冲量、加载持续时间、力-时间函数、初始冲击压力、加载位置、载荷的空间分布以及载荷类型等七种因素对叶片响应的影响。本文得出的结论为合理简化鸟撞击加载过程及建立鸟撞击载荷模型提供了参考与依据。     

正交各向异性地基平面问题动力响应研究

以位移分量为基本未知量,在直角坐标系下建立正交各向异性地基的平面应变问题动力偏微分方程．采用Laplace-Fourier变换和逆变换方法,引入初始条件和边界条件,推导了任意形式表面动荷载作用下正交各向异性地基平面问题在时域内动力反应的积分形式解．基于理论解,编制了相应的计算程序,并对正交各向异性土
体表面作用线性移动谐振荷载进行了算例分析,研究了土体参数、荷载移动速度、荷载频率不同而导致的土体表面各点竖向位移幅值的变化规律,以及荷载速度对竖向应力分量的影响规律．数值分析结果表明：土体的各向异性、荷载频率和移动速度对表面位移幅值有较大影响,土体阻尼比对于荷载中心点附近的位移幅值影响较小;荷载移动速度对于竖向应力分量有较大影响,这对工程实践具有重要指导意义．     

Stress calculations for lifetime prediction in turbine blades

In order to predict fatigue lifetime in cooled turbine blades it is necessary to know stabilized cyclic stress and strain fields for typical ground-to-ground cycle.Previous works permit to obtain the viscoplastic temperature dependent behavior and the classical one-dimensional plane cross-section method gives the stress and strain fields on the blade.However this classical method does not take into account the restraining effects of moments due to action of centrifugal forces on the deflected blade. This paper presents an extension of the plane cross-section method in which the coupled problem induced by these restraining effects is solved without iteration. p]Results are given for a turbine blade made of a refractory alloy and compared with the case in which restraining effects are neglected.     

On indentation of a pair of rigid punches connected by an elastic beam into an elastic half-plane with regard to the friction and adhesion forces in the contact region

The contact problem of indentation of a pair of rigid punches with plane bases connected by an elastic beam into the boundary of an elastic half-plane is considered under the conditions of plane strain state. The external load is generated by lumped forces applied to the punches and a uniformly distributed normal load acting on the beam.It is assumed that the contact between the punch and the elastic half-plane can be described by L. A. Galin’s statement, i.e., it is assumed that the adhesion acts in the interior part of each of the contact regions and the tangential stresses obeying the Coulomb law act on their boundaries.With the symmetry taken into account, the problem is stated only for a single punch, and solving this problem is reduced to a system of four singular integral equations for the tangential and normal stresses in the adhesion region and the contact pressure in the sliding zones. The solution of the constitutive system together with three conditions of equilibrium of the system of punches connected by a beam is constructed by direct numerical integration by the method of mechanical quadratures.As a result of the numerical analysis, the contact stress distribution functions were constructed and the values of the sliding zones and the punch rotation angle were determined for various values of the geometric, elastic, and force characteristics.     

Investigation of horizontal-axis wind turbine (HAWT) blade threedimensional rotational effect based on field experiments

Field experiments are performed on a two-bladed 33 kW horizontal-axis wind turbine (HAWT). The pressures are measured with 191 pressure sensors positioned around the surfaces of seven spanwise section airfoils on one of the two blades. Three-dimensional (3D) and two-dimensional (2D) numerical simulations are performed, respectively, on the rotor and the seven airfoils of the blade. The results are compared with the experimental results of the pressure distribution on the seven airfoils and the lift coefficients. The 3D rotational effect on the blade aerodynamic characteristics is then studied with a numerical approach. Finally, some conclusions are drawn as follows. From the tip to the root of the blade, the experimental differential pressure of the blade section airfoil increases at first and then decreases gradually. The calculated 3D result of the pressure distribution on the blade surface is closer to that of the experiment than the 2D result. The 3D rotational effect has a significant impact on the blade surface flow and the aerodynamic load, leading to an increase of the differential pressure on the airfoils and their lift coefficient than that with the 2D one because of the stall delay. The influence of the 3D rotational effect on the wind turbine blade especially takes place on the sections with flow separation.     

基于SWT方法的钢绞线索微动疲劳特性分析

为得到钢绞线索丝间接触区的应力场分布并预测微动疲劳裂纹萌生位置和微动疲劳寿命，本文利用参数化方法建立了精细化的钢绞线拉索有限元模型，包括整索模型和不同层丝间接触区域的局部精细化子模型．分析了钢绞线索在两种交变荷载工况下的应力场变化情况，并基于多轴疲劳SWT(Smith-Watson-Topper)临界平面法进行了疲劳特性分析和疲劳寿命预测．主要结论如下：钢绞线索内接触区边缘处的微动幅值较大，中心处几乎没有相对滑动，微动疲劳的初始裂纹萌生点位于接触区域边缘；经不同区域子模型分析比较，在轴向循环荷载作用下，外层钢丝的接触区域比内层钢丝更易发生微动疲劳损伤；在横向位移循环荷载作用下，同层钢丝因位置角度不同而产生了较大的疲劳特性差异，且相比轴向循环拉伸，该工况下最不利单丝的微动疲劳寿命更低；与非接触区域相比，接触区的疲劳寿命大幅降低，微动现象对钢绞线索的抗疲劳性能有明显降低作用．     

A friction contact stiffness model of fractal geometry in forced response analysis of a shrouded blade

To investigate the nonlinear vibration behavior of a shrouded blade with friction dynamic contact interface, a friction contact stiffness model is proposed to describe the friction force at different rough interfaces and different normal loads. In the proposed model, the friction contact interface is discretized to a series of friction contact pairs and each of them can experience stick, slip, or separate states. Fractal geometry is used to simulate the topography of contact surfaces. The contact stiffness is calculated using the Hertz contact theory and fractal geometry, which is related to contact interfaces parameters including normal load, roughness, Young??s modulus, and Poisson??s ratio. The trajectory tracking method is used to predict the friction force and it is not necessary to judge the transition condition among stick, slip, and separate states. It is suitable for complicated periodic motion of the contact interfaces. The forced response of a real shrouded blade is predicted using the proposed model and the multi-harmonic balance method. The effect of surface roughness, initial normal load, and contact area on the forced response of a shrouded blade is studied. It is shown that contact stiffness increases with normal load and fractal dimension. The resonant amplitude is sensitive to the initial normal load and contact surface roughness. The response can be influenced by the contact area, which is an important parameter for blade designers.