锥体差压式流量传感器流出系数的预测

利用RNG k-ε模型,对100 mm口径锥体差压式流量传感器进行了CFD数值模拟实验,其等效直径比β值分别为0.50、0.65、0.85,前锥角分别为40°、45°、50°,后锥角分别为120°、130°、140°,共27种锥体组合.实验结果表明:β值越大,流出系数越小,且流出系数更易受雷诺数的影响;β值相同时,前锥角对流出系数具有较大影响,且较大的前锥角可减弱雷诺数对流出系数的影响;后锥角对流出系数的线性度具有一定程度的影响.数值模拟实验于实流物理实验结果相比,平均误差约5%,最大值小于9.1%.     

尾气再热器大开孔区域基于ANSYS软件在壳程和夹套压力共同作用下的校核评定

通过有限单元法,对尾气再热器大开孔区域在壳程和夹套压力共同作用下进行应力计算和强度分析。根据计算结果,判定该设备在该处的安全性,也为此类超标准设计的校核评定提供了新的方法和新思路。     

基于PCL的带开孔翼梁腹板参数化建模和分析

针对带开孔翼梁腹板的结构稳定性,利用PCL编写带开孔的复合材料翼梁结构的参数化建模程序,分析2种开孔位置对结构稳定性的影响.结果表明圆形开孔与翼梁根部的距离以及水滴形孔与圆形开孔的距离对结构稳定性影响明显:屈曲因子随圆形开孔离翼梁根部距离的增大先增大、后减小;屈曲因子随着水滴形孔与圆形孔距离的增大而单调减小;水滴形孔与下壁板的距离对结构稳定性影响不大.在保证结构稳定性和最大应变小于设计值的前提下,确定水滴形孔与下壁板之间的最小距离.     

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．     

周期轴向力作用下旋转圆锥薄壳动力稳定性研究

本文开展了周期轴向力作用下旋转圆锥薄壳动力稳定性研究.基于Donnell薄壳理论推导了旋转锥壳的动力学方程,采用广义微分求积法和Hill法分析了系统在周期轴向载荷作用下的参数不稳定性,讨论了多个不稳定区随工况和几何参数的变化规律.结果表明:提高转速会导致不稳定区沿频率轴移动,但对不稳定宽度影响不大.增加恒定拉伸轴向载荷,不仅会显著增加失稳宽度,而且会导致失稳区域向更高的频率范围移动.锥角、厚径比或长径比的变化都会导致不稳定区沿频率轴移动.锥角和厚径比会增大失稳宽度(长径比会减小).随着周向波个数的增加,锥角对失稳区的影响逐渐减弱,而厚径比的影响则基本保持不变.     

滴灌覆膜开孔蒸发三维空间水盐运移实验研究

通过滴灌入渗结束的覆膜开孔蒸发实验,分析了土表覆膜开孔率对累积蒸发量随时间变化趋势的影响。累积蒸发量与时间平方根的线性关系符合Gardner的理论关系,而两者关系的系数又与覆膜开孔率之间存在良好的对数关系,从而得出了累积蒸发量的两因素函数关系。这一结果发展了Gardner的理论关系并将其应用于覆膜开孔蒸发的实践上。对相对累积蒸发量和单位膜孔面积的累积蒸发量随开孔率变化的函数特征进行了定量分析,并分析比较了全覆膜和不覆膜蒸发条件下含水率、含盐率和盐分浓度特征,做出了相应水盐特征的等值线图。     

利用激光光源实现镍网开孔率的检测

分析了用光通量测量法镍网开孔率的理论依据和现有技术的缺点,采用激光二极管作为光电探头光源,使用四个光电二极管获取开孔率采样值,通过计算机软件校正光电二极管的非线性,采用多重数字滤波技术提高仪器的精度和的稳定性,实现自动测量、自动校准,同时还提供了与上位机通信的Max232接口.     

基于超声波原理的开孔参数标定系统研究

针对传统的人工丈量方法标定开孔方位角和倾斜角存在操作程序繁琐、稳钻时间长、精度低等问题,设计了基于超声波原理的钻孔开孔参数标定系统。该系统采用超声波渡越时间检测法测量参考点之间的距离,并由单片机解算出钻杆的方位角,选用微机械三轴加速度计测量倾斜角,实现了全自动化的实时跟踪测量及智能化的钻机姿态调整语音指导操作;在误差允许范围内,可快速标定所需开孔参数。该系统提高了开孔参数标定精度、标定效率及煤矿管理水平,降低了矿工劳动强度和煤矿管理成本。     

基于超声波原理的开孔参数标定系统研究

针对传统的人工丈量方法标定开孔方位角和倾斜角存在操作程序繁琐、稳钻时间长、精度低等问题,设计了基于超声波原理的钻孔开孔参数标定系统。该系统采用超声波渡越时间检测法测量参考点之间的距离,并由单片机解算出钻杆的方位角,选用微机械三轴加速度计测量倾斜角,实现了全自动化的实时跟踪测量及智能化的钻机姿态调整语音指导操作;在误差允许范围内,可快速标定所需开孔参数。该系统提高了开孔参数标定精度、标定效率及煤矿管理水平,降低了矿工劳动强度和煤矿管理成本。     

利用激光光源实现镍网开孔率的检测

分析了用光通量测量法镍网开孔率的理论依据和现有技术的缺点,采用激光二极管作为光电探头光源,使用四个光电二极管获取开孔率采样值,通过计算机软件校正光电二极管的非线性,采用多重数字滤波技术提高仪器的精度和的稳定性,实现自动测量、自动校准,同时还提供了与上位机通信的Max232接口。     

材料塑性应变对某钢制车轮残余应力测试的影响

针对车轮轮辋与轮辐组合焊缝附近结构的残余应力测试通常采用盲孔法,孔边由于应力集中易产生塑性变形的问题,采用有限元仿真与测试相结合的方法分析在钢制车轮加工的不同阶段,轮辋焊缝区残余应力测试时材料塑性变形对应变释放因数和残余应力测试结果的影响,并分析由Kirsch解析解确定的应变释放因数A和B计算车轮焊缝区残余应力测试所带来的误差.发现当孔边塑性变形较大时,用Kirsch解析解确定的应变释放因数计算残余应力会产生很大误差.     

基于FLAC~(3D)的引水隧洞主、支洞交叉部位的围岩变形分析

圆形洞室开挖后,岩体中形成一个自由空间,使原来处于挤压状态的围岩,由于失去了支撑而发生向洞内松动变形;如果这种变形超过了围岩本身所能承受的能力,则围岩就会发生破坏。本文应用有限差分法数值模拟软件FLAC3D对主、支洞交叉部位的隧洞围岩变形进行模拟分析。模拟结果表明,隧洞开挖后,围岩各部分的位移量较大,围岩应力集中在主、支洞交叉部位。     

Design study of hole positions and hole shapes for crack tip stress releasing

The method of hole drilling near or at the crack tip is often used in fatigue damage repair. From a design optimization point of view, two questions are posed: Where should the hole(s) be drilled? And is there a better shape of the hole than a circular one? For the first question, we extend earlier results for isotropic material and in general study the influence of having orthotropic material. Optimal shapes are by no means circular, and we focus on the shape of a single hole centered at (or in front of) the crack tip. It is shown that the stress field at the crack boundary can be significantly improved by noncircular shapes. As a byproduct, an alternative method for extracting the stress intensity factor from a finite element analysis is presented.     

Optimum cone angles in aeroelastic flutter

The determination of flutter frequencies and flutter boundary pressures of conical shells is carried out using finite element analysis. Static condensation procedure with Q.R. algorithm is used for the extraction of eigen values of the system. An empirical relation for determining the values of flutter boundary pressures of clamped-clamped conical shells is proposed. It is seen that there is an optimum semivertex angle at which a given conical shell of prescribed length and initial radius offers maximum resistance for flutter.     

Finite element analysis of static and dynamic stresses around suddenly punched holes in plates and shells

The magnitude and distribution of stresses around suddenly punched holes in initially stressed plates and shells is of interest to insure that cracks will not precipitate from stress concentration. This problem is of practical interest to pressure vessel designers to preclude catastrophic failure when holes are punched in vessels to release gas. This paper presents a finite element analysis of several problems investigating static and dynamic stress fields around suddenly punched circular holes.

The first problem deals with the investigation of the radial and tangential stress fields in the vicinity of a suddenly punched hole in a stretched, elastic, isotropic plate subjected to an initial hydrostatic stress field. The wave propagation from a punched hole in the plate under a hydrostatic state of stress was solved analytically, using transform techniques, by Miklowitz; the finite element analysis of this problem presented in this paper confirms the analytical solution. Two grid meshes were investigated and results are presented to show the effect of grid mesh on solution accuracy and the power of finite element techniques for solving stress unloading problems. A formula for determining integration step size is found to be a function of the minimum element length and the wave propagation velocity. A similar investigation into the stress effects around a suddenly punched hole in the plate subjected to an initial uniaxial state of stress was also carried out as a prerequisite for the final problem studied.

The last problem is an anisotropic composite shell of varying thickness under an initial stress field due to internal pressure. The static and dynamic stress fields are computed from an unloading wave that radiates outward from a reinforced circular hole that is cut in the shell in 20 μs. A finite-element model of the shell is developed using quadrilateral and triangular plate elements and both in-plane and bending stiffness is included in the analysis as is nonlinear differential stiffening incorporated into the analysis as a single step approximation. Both bending and in-plane waves radiate outward from the cut hole and the dynamic stresses around the hole edge are computed for both unloading waves. The effects of the unloading waves are temporally spaced due to different wave velocities.

The paper demonstrates that fast response stress problems are readily amenable to finite-element analysis. For holes other than circular, the power of finite-element methods is apparent since these shapes lead to mathematically intractable problems if closed form solutions are attempted.     

发动机缸体线性与非线性对比分析

采用线性分析发动机缸体时,在螺栓接触和绑定的位置会出现明显的应力集中点,且计算得到疲劳安全因数远远低于合理值.在考虑材料非线性的基础上对发动机缸体进行非线性分析,发现在螺栓接触和绑定位置处的应力明显降低,计算得到的疲劳安全因数也趋于合理.通过汽油机缸体线性与非线性对比分析可以发现,缸体非线性模型的计算结果更合理.若要改善螺栓孔周边的安全因数,一定要保证螺栓绑定和接触位置接近实际情况,特别在2个面过渡的位置不能绑定,这样可以避免造成应力集中.     

本质安全型无线压力传感器天线设计

提出了一种煤矿井下本质安全型无线压力传感器天线结构的设计方案,研究了金属外壳一侧开口时其参数及天线位置对天线增益的影响。仿真与实测结果表明,天线增益随金属外壳的开口长度和宽度的增大而增加,且增加幅度逐渐减小;天线增益随天线距开口的距离减少而增加;开口侧的金属外壳厚度每减少1mm,天线增益增加约2dB;金属外壳空间高度毫米级变化引起的天线增益变化基本可以忽略;当金属外壳的开口长度和宽度分别为天线波长的1/4与1/8,厚度为2mm,空间高度为41mm,天线位置距开口为1.4mm时,天线辐射增益达到最佳,天线的传播距离约为14m。     

基于属性开运算的汽车牌照区域定位算法

现有的复杂背景下汽车牌照定位算法,大都是基于牌照水平或者近似水平的前提,如何处理倾斜情况下牌照定位是一个尚待解决的问题。本文提出了一种基于属性开运算的汽车牌照定位算法,其处理结果与牌照的倾斜角度无关,并成功地应用于交通监控系统中     

Studies on stress concentration in tensile strips with large circular holes

The stress concentration factor K in a tensile strip with large circular hole is accurately determined using a high precision, plane stress, triangular element. The values of a/w where a is the diameter of the hole and w is the width of the strip, considered range from 0.99 to 0.999. The values of K obtained found to be very near to but greater than 2.0, when linear analysis is performed. Some discrepancies in the stress values at the outer free edge observed in the present linear analysis compared to the well documented experimental values prompted the authors to go for geometrically nonlinear analysis gave a K value which is a function of the load applied, less than 2.0 and for sufficiently large loads this value is very near but slightly greater than 1.0.     

Learning nonlinear dynamics with behavior ordinary/partial/system of the differential equations: looking through the lens of orthogonal neural networks

In this paper, size-dependent dynamic stability of axially loaded functionally graded (FG) composite truncated conical microshells with magnetostrictive facesheets surrounded by nonlinear viscoelastic foundations including a two-parameter Winkler–Pasternak medium augmented via a Kelvin–Voigt viscoelastic approach is analyzed considering nonlinear cubic stiffness. To this purpose, von Karman-type kinematic nonlinearity along with modified couple stress theory of elasticity was applied to third-order shear deformation conical shell theory in the presence of magnetic permeability tensor and magnetic fluxes. The numerical technique of generalized differential quadrature (GDQ) was used for the solution of microstructural-dependent dynamic stability responses of FG composite truncated conical microshells. It was seen that moving from prebuckling to postbuckling domain somehow increased the significance of couple stress type of size dependency on frequency. In addition, within both prebuckling and postbuckling regimes, an increase of material gradient index decreased the importance of couple stress type of size dependency on the frequency of an axially loaded FG composite truncated conical microshell. Furthermore, it was revealed that by applying a positive magnetic field to an axially loaded truncated conical microshell with magnetostrictive facesheets, its frequency at a specific axial load value was increased in prebuckling domain and decreased in postbuckling domain. However, this pattern was reversed by applying a negative magnetic field.