碟形封头有限元应力分析及水压试验破坏原因研究

对按常规方法设计的受内压碟形封头进行了有限元应力计算。通过对计算结果的分析，讨论了碟形封头的应力状态和失效形式，对液压试验情况下按常规方法设计的碟形封头容易发生破坏的原因进行了研究。     

谈谈对锅筒封头设计计算时的几点认识

锅炉锅筒封头的强度计算按GB／T9222标准,球冠形封头国内从88年起就不用了,主要原因是受力情况较差,但ASME规范允许使用。笔者主要介绍在选用封头强度计算时,应加强对封头结构要求的理解,同时选用合理的计算结果。下文主要介绍GB／T9222标准和ASME范围对凸形封头计算和标注的结构要求的分析。     

椭圆形封头的参数计算

根据椭球的体积计算公式导出十分有用的椭圆形封头表面积的精确计算公式，并顺便给出椭圆形封头其他的参数计算公式，以供设计者参考。     

仿形旋压封头液压活动模板的设计研究

对仿形旋压封头的液压活动模板的设计理论进行了研究和探索，首次得出了渐开线型活动模板有关参娄物确定方法，据之设计出了φ２０００×１５ｍｍ封头的仿形活动模板，可为其它旋压件旋轮运动轨迹的确定提供参考。     

凸形封头壁厚计算公式的分析

通过弹性力学分析,采用抛物线插值公式,得到了旧标准JB2194—77与新标准GB9222—88中的凸形封头强度计算公式。对按两个公式计算的凸形封头计算壁厚作了比较,认为按新标准设计的封头较旧标准安全。     

锅炉汽包封头的制造工艺

根据锅炉汽包热压封头的制造工艺顺序,详细论述了常用热压封头的展开尺寸的计算、划线、气割、热压以及成形后封头的划线加工和封头管接头管孔的加工及装配等工序,指出了相关工序的关键技术和经验数据,为相似锅炉汽包热压封头的制造工艺提供了可以借鉴的方法。     

锅筒封头壁厚公式的力学分析

对常用的封头壁厚公式进行了力学分析，并对两种类型锅炉的封头壁厚公式进行比较。     

油田火筒加热炉大开孔封头强度研究

油田火筒加热炉密集大开孔封头的设计计算,因没有相应的强度计算标准在一定程度上限制了我国油田火筒加热炉技术的发展。本文利用板壳元模型分别对无任何加强的大开孔封头,有火筒加强的大开孔封头和有十字加强筋的大开孔封头,进行了有限元强度分析计算。理论与实验研究结果表明,本文建立的有限元模型用于大开孔封头强度分析是可行的,计算结果与实测吻合较好,实际应力没有超过材料的许用应力。     

人孔封头的热冲压工艺探讨

封头是锅简和受压容器的重要承压零件之一,对于人孔封头可利用液压机在其顶出缸的配合下,一次冲压成形。我厂生产的人孔封头如图1所示。由于原有的1200t液压机顶出缸损坏,我们设计了一种经济实用的新工艺装备,一次热冲压成形,取得了良好的效益,现介绍如下。     

普通碳素钢椭圆形封头压制工艺的探讨

封头是锅炉、化工设备上的重要部件，在锅炉压力容器中所见的椭圆形封头、半球形封头、碟形封头和拱形盖中，以椭圆形封头最为常见。封头的制造方法有很多种，但在工业生产中主要采用在液压机上冲压和在旋压机上滚压两种方法。在液压机上冲压封     

弹性和柔性地基上动力人工边界及地震动输入方法

为完善粘弹性边界在弹性地基地震动输入中的应用,并实现柔性地基的地震动输入,系统研究了弹性和柔性地基上动力人工边界及其地震动输入方法,对均质弹性地基,分析了弹簧刚度系数不同取值方法、网格尺寸和模型截断边界范围的影响,在将底边界和侧边界均设置为粘弹性边界时,现行弹簧刚度系数的不同取值方法均可行,网格尺寸应小于波长的1/20,截断边界范围不需考虑上部结构尺寸;对规则水平成层柔性地基,底边界可设置为粘弹性边界,当侧边界设置为截断自由边界时截断边界宽度应不小于地基高度的15倍,当侧边界设置为粘弹性边界时截断边界宽度应不小于地基高度的2倍。对不规则成层柔性地基,底边界可设置为粘性边界,侧边界可设置为截断自由边界,其宽度应不小于地基高度的10倍。分析表明,这些动力人工边界的设置方法可将最大相对误差控制在5%左右,满足实际工程的精度要求。     

Experimental Confirmation on the Calibration Curves for Preston＇s Method

The Preston＇s method is considered as one of the most commonly employed methods to measure the wall shear stress. However, it is only possible to determine the wall shear stress from measured pressure differences of the Preston tube and undisturbed static pressure, combined with calibration curves, which depend on the Preston tube diameter, fluid density, and viscosity. Since its invention, no significant advancement in theory has been made, and calibration curves proposed by Preston, Patel and Bechert are still in use. In the present study, a need to measure surface shear stress over a circular cylinder prompted us to develop our original Preston tube system. The developed system has been calibrated by measuring the wall shear stress in the fully developed turbulent flow regime in a circular pipe. The present results generally confirm the previously reported calibration curves. A slight modification of the coefficients in the calibration equation shows further improvement.     

具有辐射边界的三维非规则域内稳态温度场分析

研究了具有辐射边界的空间非规则域内稳态导热问题,求解方法为在球极坐标系内分离变量,获得级数形式的解后,采用边界离散法确定级数项的待定系数,算例表明,边界离形方法不仅可以解决非正交边界问题,而且也可以处理诸如辐射边界的非线性边值问题。     

Improved velocity and temperature profiles for integral solution in the laminar boundary layer flow on a semi‐infinite flat plate

One of the most important problems in Mechanical Engineering is the determination of laminar boundary layer thickness over a flat plate. Integral solution and similarity solutions are two well‐known methods for calculation of boundary layer thickness. However, integral solution method is a computational cost‐effective method rather than the similarity solution method. Velocity and temperature profiles must be determined for the integral solution method. Velocity boundary layer thickness can be determined by the velocity profile whereas for determination of thermal boundary layer thickness both velocity and temperature profiles must be used. Available velocity profiles do not give an exact value for velocity boundary layer thickness, while the Nusselt number is affected by these profiles. In this study, a new velocity profile is proposed which gives an exact value for laminar boundary layer thickness on a flat plate. In addition, two temperature profiles are proposed that give the exact values of the Nusselt number over a flat plate for uniform temperature and uniform heat flux boundary conditions. The calculated constants in the velocity boundary layer thickness equation and the Nusselt relations are validated with the results of the similarity solution method. Excellent agreement between the results of the two methods is observed.     

Thermoelasticity problem for a multilayer coating/half-space assembly with undercoat crack subjected to convective thermal loading

The transient thermal stress crack problem for a half-space with a multilayer coating under thermal surface loading containing an undercoat crack, perpendicular to the interface, is considered. The problem is solved using the principle of superposition and uncoupled quasi-static thermoelasticity. Transient temperature distribution and corresponding thermal stresses for the uncracked multilayer assembly are obtained in a closed analytical form using the model with generalized thermal boundary conditions of heat exchange of a half-space with ambient media via the coating. The crack problem is formulated as a perturbation mixed boundary value problem, in which the crack surface loading should be equal and opposite to the thermal stresses obtained for the uncracked medium, and is reduced to a singular integral equation and solved numerically. Numerical computations are performed for the analysis of influence of the coating upon thermal stresses and thermal stress intensity factor.     

边界点法在传热问题数值分析中的应用

将一种新的数值分析方法-边界点法应用于传热问题的研究，对无内热源稳态热传导问题，通过传统边界元法将边界积分方程离散化，发现可以不直接求解影响系数矩阵，而是通过对偶关系，由域外虚源构造方程组的特解场形成边界已知和未知温度，热流密度的系数矩阵，而且域内温度和热流密度的求解将不依赖于边界未知参数的求解，对于有内热源的问题，可以将非齐次方程的解转换为齐次方程的解和某一确定解的叠加，对于非线性问题，可以通过基尔霍夫变换，将非线性问题转化为线性问题求解，这种边界点方法不但具有边界元法降维的优势，而且不须求解奇异积分，大大节约了计算时间，计算精度极高，以有内热源非线性稳态热传导问题的实例印证了这种方法的高效性。     

Application of differential transform method to unsteady free convective heat transfer of a couple stress fluid over a stretching sheet

In the present article, the transient rheological boundary layer flow over a stretching sheet with heat transfer is investigated, a topic of relevance to non‐Newtonian thermal materials processing. Stokes couple stress model is deployed to simulate non‐Newtonian characteristics. Similarity transformations are utilized to convert the governing partial differential equations into nonlinear ordinary differential equations with appropriate wall and free stream boundary conditions. The nondimensional boundary value problem emerging is shown to be controlled by a number of key thermophysical and rheological parameters, namely the rheological couple stress parameter (), unsteadiness parameter (), Prandtl number (Pr), buoyancy parameter . The semi‐analytical differential transform method (DTM) is used to solve the reduced nonlinear coupled ordinary differential boundary value problem. A numerical solution is also obtained via the MATLAB built‐in solver “bvp4c” to validate the results. Further validation with published results from the literature is included. Fluid velocity is enhanced with increasing couple stress parameter, whereas it is decreased with unsteadiness parameter. Temperature is elevated with couple stress parameter, whereas it is initially reduced with unsteadiness parameter. The flow is accelerated with increasing positive buoyancy parameter (for heating of the fluid), whereas it is decelerated with increasing negative buoyancy parameter (cooling of the fluid). Temperature and thermal boundary layer thickness are boosted with increasing positive values of buoyancy parameter. Increasing Prandtl number decelerates the flow, reduces temperatures, increases momentum boundary layer thickness, and decreases thermal boundary layer thickness. Excellent accuracy is achieved with the DTM approach.     

Solution of steady-state thermoelastic problems using a scaled boundary representation based on nonuniform rational B-splines

This work explores the application of isogeometric scaled boundary method in the two-dimensional thermoelastic problems of irregular geometry. The proposed method inherits the advantages of both isogeometric analysis and scaled boundary finite element method and overcomes their respective disadvantages. In the proposed approach, the boundaries of the problem domain are discretized with nonuniform rational B-splines (NURBS) basis functions, while the temperature distributions inside the domain are represented by a sequence of power functions in terms of radial coordinate within the framework of scaled boundary finite element method. The resulting solution of the stress in radial direction can be computed analytically for the temperature changes. The construction of tensor product structure is circumvented for the two-dimensional problems as only the boundary information of the problem domain is required. Hence, the flexibility to represent the complex geometry can be significantly improved in the proposed method. Numerical examples are presented to validate the performance of the proposed method where it is seen that superior accuracy, e?ciency, and convergence behavior can be achieved over the conventional scaled boundary finite element method.     

Hamiltonian Approach to Analytical Thermal Stress Intensity Factors—Part 2 Thermal Stress Intensity Factor

The equations of thermoelasticity are first rewritten in Hamiltonian form where the variables are separable in spatial coordinates. The symplectic eigensolutions satisfying the boundary conditions along the crack faces are solved analytically from the homogeneous equations. The loading and the particular integral are expanded in the eigensolutions and the coefficients are determined by the geometric boundary conditions excluding the crack. The thermal stress intensity factors are obtained and the behavior of the thermal stress intensity factors under arbitrary thermal loading is investigated.     

炉膛中间截面边界条件对双切圆锅炉空气动力场计算的影响

大容量超超临界锅炉广泛采用单炉膛双切圆的空气动力组织方式,在计算流体力学软件FLUENT平台上,针对1GW超超临界单炉膛双切圆锅炉,计算了全炉膛和炉膛中间截面边界条件设为对称面和边壁条件的炉内空气动力场。计算表明,与标准κ-ε双方程模型相比雷诺应力模型(RSM)具有更高的计算精度;中间截面采用对称边界条件时,其流场分布规律与全炉膛模拟结果相似;中间截面为边壁条件时炉膛中间截面附近流速降低,但对整个炉膛流场影响较小;中间截面采用这两种边界条件均会导致1#、6#角射流衰减缓慢而冲刷炉膛前墙中间水冷壁。