起重机上翼缘仿生简支板的局部稳定性分析

研究面内荷载作用下起重机上翼缘仿生简支板的局部稳定性分析问题。针对起重机箱梁结构轻量化设计,上翼缘板厚度变薄导致的局部稳定性改进。借鉴与起重机上翼缘板存在相似结构、受力和功能特性的生物叶脉结构,模仿叶脉倾斜、交错等结构特征提出了叶脉斜向肋箱梁结构设计。鉴于斜板屈曲稳定性数值求解的复杂性,给出仿生简支板结构模型分析,给出约束边界条件和加载的具体实现方法。利用有限元软件结合实例分析表明,仿生简支板结构局部稳定性大大提高。简支斜板底边和高度不变时,屈曲临界载荷随倾角增大而减小;斜板底边长和倾角不变时,屈曲临界载荷随高度增大而减小。简支加劲斜板倾角θ=45°较90°时屈曲临界载荷提高较大。     

复合材料细长柱受冲击荷载动力屈曲研究

对复合材料细长柱在轴向冲击荷载下的动力屈曲问题进行了研究.基于单层材料本构方程及D'Alembert原理,建立了结构轴向及横向耦合振动方程.用Laplace变换得到轴向运动解析解,并用Galerkin法对结构横向振动进行求解.用数值方法讨论了冲击质量、冲击速度,复合材料铺层角等对结构临界动力屈曲时间及冲击物与结构接触时间的影响.结果表明随着冲击质量、冲击速度,复合材料铺层角增大,结构动力屈曲时间减小;冲击速度,铺层角对冲击块与结构的接触时间无影响.     

低速轴向气流中曲壁板的稳定性及分岔分析

本文研究了带有初始曲率的二维曲壁板在低速轴向气流中的稳定性及分岔问题.基于薄翼理论获得了作用在曲壁板上的气动力,并设计了风洞实验以验证该理论气动力的准确性.采用Galerkin方法将非线性运动方程离散成常微分方程组;利用牛顿迭代法求解壁板的静变形;在参数区间内分析了系统的分叉结构.结果表明：本文给出的气动力理论计算结果与实验吻合良好;静态气动力会破坏系统的对称性;在来流动压超过临界值后,曲壁板会发生非对称的静态分岔并出现新的稳定及不稳定的平衡态;系统临界来流动压随面内拉力(压力)的增加而增加(减小),而随初始曲率的增加呈现先增大后减小的规律;系统在不同参数区域内存在四种典型的分岔行为;系统的响应与来流动压及初值有关.     

铝合金整体壁板填料滚弯成型有限元仿真

提出整体壁板填料滚弯成型工艺,建立填料滚弯成型过程的有限元模型.仿真分析填料和工艺参数对滚弯成型壁板的等效应力、剪切应力、等效应变和回弹等的影响规律.结果表明：壁板滚弯成型时纵向筋条的等效应力和应变最大,填料填充滚弯提高壁板等效应力和塑性应变的均匀性,改善壁板弯曲半径的均匀性,提高弯曲件的几何精度;随着压下量的增大,壁板回弹率减小.     

潜艇流水孔流噪声特性研究

潜艇流水孔流场产生流噪声,影响隐身性,威胁潜艇的生存安全.针对降噪问题,为了研究潜艇流水孔参数对艇体流噪声特性的影响,提出了流水孔形状、尺寸、数量以及流速对流噪声特性的影响建模.根据大涡仿真(LES),Lighthill理论和FW-H方程对流水孔三维模型进行数值计算,结果表明,流水孔参数的改变会直接影响流噪声的水平.比较四种形状流水孔流噪声以正方形流水孔最低,随后依次为圆形、菱形、长方形.随着流水孔尺寸的增大,流噪声变化趋势为先增大后减小,存在一个声压级峰值.流噪声与流水孔数量的关系呈现正比例关系.以上结果可为潜艇流水孔的降噪设计提供参考.     

机身壁板稳定性显式非线性分析

对6种不同构型的飞机机身下壁板薄壁结构试验件,进行显示有限元非线性屈曲分析,并与工程方法及试验得到的结果进行对比分析,可知有限元法比工程方法更精确,且与试验相比,误差更稳定.     

叶片-轮盘榫联结构的接触分析

叶片与轮盘之间的榫联结构存在接触和摩擦组合运动,在较高的热-机械载荷作用下容易发生微动磨损并导致疲劳破坏.本文采用有限元法对叶片-轮盘榫联结构进行接触分析,计算不同摩擦系数和不同转速情况下的叶片榫头和轮盘榫槽之间的接触压力、接触滑动距离.结果表明,摩擦系数增大,榫联结构接触面上的接触压力和滑动距离减小;转速增加,则接触压力和滑动距离增大.     

基于MSC Nastran的机身壁板剪切试验件屈曲分析

对机身壁板剪切稳定性试验件进行初步强度分析,利用MSC Nastran的屈曲求解器对试验件进行屈曲载荷的计算,将计算出的屈曲载荷施加在试验件上,然后用MSC Nastran的静力求解器分析试验件应力,得出试验件考核部位的应力云图,为后续试验设计提供参考.     

基于MSC Nastran的发动机盖支撑杆屈曲分析

用MSC Nastran对2种发动机盖支撑杆结构进行屈曲分析.计算结果表明,2种结构支撑杆的屈曲临界载荷均未超过稳定性要求,不同的结构形式具有不同的屈曲临界载荷和屈曲模态,撑杆结构是影响支撑杆稳定性的重要因素.第二种结构方案的屈曲临界载荷大于第一种方案,为设计部门选取更适合的方案提供参考.     

在裂纹尖端引入奇异单元的偶应力有限元法

针对在微观状态下结构力学行为会受尺度效应影响的问题,在偶应力理论中考虑微观结构的旋转梯度可以较好解释结构的尺度效应.建立基于一般偶应力理论的有限元法的基本方程,并在裂纹尖端引入奇异单元,计算受单向拉伸的中心斜裂纹板裂纹尖端场的应力强度因子(Stress Intensity Factor,SIF),分析特征长度变化对SIF的影响,对比偶应力理论下的结果与经典理论下的结果.结果表明：在裂纹尖端引入奇异单元可以提高计算精度和稳定性;偶应力使得裂纹尖端SIF比经典理论下的值小,并且SIF随着特征长度增大而减小.     

Buckling and postbuckling of composite panels with cutouts subjected to combined edge shear and temperature change

The results of a detailed study of the buckling and postbuckling responses of composite panels with central circular cutouts are presented. The panels are subjected to combined edge shear and temperature change. The panels are discretized by using a two-field degenerate solid element with each of the displacement components having a linear variation throughout the thickness of the panel. The fundamental unknowns consist of the average mechanical strains through the thickness and the displacement components. The effects of geometric nonlinearities and laminated anisotropic material behavior are included.The stability boundary, postbuckling response and hierarchical sensitivity coefficients are evaluated. The hierarchical sensitivity coefficients measure the sensitivity of the buckling and postbuckling responses to variations in the panel stiffnesses, and the material properties of both the individual layers and the constituents (fibers and matrix). Numerical results are presented for composite panels with central circular cutouts subjected to combined edge shear and temperature change, showing the effects of variations in the hole diameter, laminate stacking sequence and fiber orientation, on the stability boundary and postbuckling response and their sensitivity to changes in the various panel parameters.     

Nonlinear and postbuckling analyses of curved composite panels subjected to combined temperature change and edge shear

The results of a detailed study of the nonlinear and postbuckling responses of curved unstiffened composite panels with central circular cutouts are presented. The panels are subjected to uniform temperature change and an applied in-plane edge shear loading. The analysis is based on a first-order shear-deformation Sanders-Budiansky type theory with the effects of large displacements, moderate rotations, transverse shear deformation and laminated anisotropic material behavior included. A mixed formulation is used with the fundamental unknowns consisting of the generalized displacements and the stress resultants of the panel. The nonlinear displacements, strain energy, transverse shear stresses, transverse shear strain energy density, and their hierarchical sensitivity coefficients are evaluated. Numerical results are presented for cylindrical panels with central circular cutouts and are subjected to uniform temperature change and an applied in-plane edge shear loading. The results show the effects of variations in the panel curvature, hole diameter, laminate stacking sequence and fiber orientation, on the nonlinear and postbuckling panel responses, and their sensitivity to changes in the various panel, layer and micromechanical parameters.     

Optimized design of sandwich panels for integral thermal protection systems

This paper proposes a new ITPS panel with special corrugated-core webs which are designed with cutouts for weight saving. The structural design problem was formulated with mass per unit area of the ITPS as the objective function and some functional requirements as constraints. We developed the optimizer fulfilling both thermal and structural functions for minimal areal density. The optimization problem was solved by interpolating the residual error of response surface approximation (RSA) with Radial Basis Function (RBF) to establish the improved RSA (IRSA). The 400 preliminary design points were obtained using Latin Hypercube Sampling method. The quadratic polynomial RSA of the ITPS sandwich panel performance was generated by the least squares method (LSM) based on finite element results and IRSA was used to optimize the constraints. Transient heat transfer, stress and buckling analyses were conducted using finite element method (FEM). Finally, a new ITPS panel with optimal dimensions was obtained. The optimization results show that the areal density of the new ITPS panel decreases by 26.27 % compared with the previous research, which proves the potential of this new design optimization method for the future spacecraft vehicles.     

Stenciling: Designing Structurally‐Sound Surfaces with Decorative Patterns

We present a novel method to design shells with artistic cutouts in a manner that produces a stable final result. The process of stenciling, removing material with a fixed shape, is a particularly appealing way to introduce a decorative pattern into the design of architectural structures, furniture, or household objects. However, removing material can easily weaken an object to the point where its integrity is compromised, while purely functional distributions of cutouts lack the desired aesthetic component. We tackle this problem by combining aesthetics, stability, and material efficiency in an optimization that determines the distribution and scaling of these stencils in a way that complies as much as possible with both pattern and stability objectives. We demonstrate the capabilities of our system on examples from architecture, furniture design, and decorative items, and show how user interaction can be integrated to guide the aesthetics of the final result.     

Structural optimization of lifting surfaces with divergence and control reversal constraints

In this paper, the static aeroplastic characteristics, divergence velocity, control effectiveness and lift effectiveness are considered in obtaining an optimum weight structure. Swept wing structures are used with upper and lower skins, spar and rib thicknesses, and spar cap and vertical post cross-sectional areas as the design parameters. The aerodynamic strip theory is used to derive the constraint formulations and aerodynamic load matrices. A Sequential Unconstrained Minimization Technique (SUMT) algorithm is used to optimize the wing structure to meet the desired aeroelastic constraints.     

非概率可靠性理论在机械臂架设计中的应用分析

以轮式起重机六边形箱形截面臂架为对象,对1 0 0吨汽车起重机椭圆截面臂架进行非概率可靠性优化,使其强度、刚度和稳定性满足非概率可靠度的条件下,重量最轻;并对椭圆截面中的大圆直径、顶边长度和圆心到顶边距离三者关系进行了分析,得出三者协同变化及独自变化时对臂架重量和可靠度的影响,为设计者提供了有力的参考依据。     

基于Modem的返回重发式ARQ协议的设计与实现

在无人值守机站及远程监控的应用中，通常利用Modem进行数据传输。文章分析 了停等式ARQ协议和返回重发式ARQ协议的原理及其传输效率，提出了一种用单片机实现的适 合于无人值守采气站的返回重发式ARQ数据传输协议及其编码方式。采用了类似TCP/IP的流 量控制机制，在实际应用中取得了较好的传输效率。     

含双圆孔Mindlin板弹性波散射与动应力集中

基于Mindlin平板理论，采用波函数展开法和局部坐标系方法，对含双圆孔平板结构中弹性波散射与动应力集中问题进行了研究．文中对Mindlin板含双圆孔时的开孔动弯矩集中系数做了数值计算，并分析了开孔间距对动弯矩分布的影响．结果表明：与单圆孔情况相比，由于开孔之间的相互影响，双圆孔间的动弯矩分布会发生比较复杂的变化．孔间距相互作用有时会使动应力集中得到缓解，而有时会使动应力集中加剧．在低频和平板较薄的情况下，平板开孔动弯矩互不影响间距较小；在较高频率和平板较厚的情况下，平板开孔动弯矩互不影响间距较大．所有这些现象都与入射波波长与孔径等特征尺度有关．因此，在工程结构动力学分析与强度设计中，应对不同波长和特征尺度下的动应力作具体的分析计算，而不是简单地套用静载强度设计标准或规范．     

圆的整数反走样生成算法

针对现有圆的反走样生成算法计算复杂,反走样效果一般的缺点,提出一种基于中点画圆法的整数反走样生成算法。该算法根据像素中心到理想圆弧的距离来分配灰度,生成64级灰度的反走样圆弧。通过省略二次项来简化计算,并用简单的计算修正省略带来的误差以保证精度。为了简化计算,提出相邻像素的灰度递推方法,利用整数移位、加法、比较来实现反走样。该算法结构简单,反走样效果较好,由于避免了浮点和除法运算,便于硬件实现。     

喷射距离对喷射冷板散热性能影响的实验研究

为了增强对喷射冷板散热性能影响因素的了解,通过实验研究了喷射距离对喷射冷板散热性能与阻力值的影响,并对喷射冷板散热性能的均匀性进行了分析。实验结果表明,在流量相同的情况下,现有结构喷射冷板的总热阻随喷射距离的增大先减小后增大,在喷射距离为1.5 mm时存在一个最小值;喷射冷板的阻力值随喷射距离的增大而降低,但喷射距离对喷射冷板的阻力影响较小;喷射冷板在水流方向的散热性能存在一定不均匀性,喷射冷板进水侧散热能力要略高于出水侧。