连铸坯在保温坑内的保温过程和效果分析

建立了保温坑内连铸坯保温过程数学模型及在线控制数学模型,并讨论了保温坑的保温效果。     

Analysis of Non-Fourier Conduction-Radiation Heat Transfer in a Cylindrical Enclosure

This article deals with the analysis of non-Fourier conduction and radiation heat transfer in a participating medium contained between 1-D concentric cylinders. The conducting-radiating medium is radiatively absorbing, emitting, and scattering. The non-Fourier effect is analyzed by suddenly perturbing the temperatures of the concentric cylinders. With radiative information computed using the finite volume method, the finite difference method is used to solve the hyperbolic energy equation. Effects of various parameters such as the extinction coefficient, the scattering albedo, the conduction-radiation parameter, the emissivity and the radius ratio are studied on the temporal evolution of temperature field in the medium. These parameters have been found to significantly influence the temporal temperature field, and non-Fourier effects are captured well. For non-Fourier conduction and Fourier conduction–radiation cases, results have been benchmarked against those available in the literature. A good comparison has been observed. In case of non-Fourier conduction-radiation, for some sample cases, the steady-state temperature distributions have been compared against those available in the literature. Results have been found to agree well.     

Influence of Aiding Buoyancy on the Suppression of Flow Separation for Power-Law Fluids Around a Circular Object

Numerical computations are performed to analyze the influence of aiding thermal buoyancy on the phenomenon of suppression of flow separation in power-law fluids around a circular object. The idea has been borrowed from some recent similar works in Newtonian fluids. Owing to the contradictory behavior of shear-thinning and shear-thickening fluids in regard to the separation mechanism, we intend to understand the role of superimposed thermal buoyancy on the suppression phenomena in non-Newtonian power-law fluids, for which a range of power-law indices (0.4 to 1.8) is considered. The Reynolds numbers are kept intentionally low, within 10 to 40, such that the isothermal flow remains steady and separated without imposition of thermal buoyancy. The buoyancy causes a delay in the separation, thereby affecting the suppression phenomena. We determine the critical heating parameter (Richardson number) for the complete suppression of the flow separation and from there we construct a bifurcation diagram to show the typical flow regime evolved due to the complex interplay between the aiding thermal buoyancy and fluid rheology. The Richardson number in the simulation lies in the range 0 to 0.35, keeping the Prandtl number fixed at 50. The heat transfer rates from the object are also obtained and important inferences are drawn in regard to the inhibition/augmentation of heat transfer due to fluid rheology.     

Dispersion Analysis of Generalized Magneto-Thermoelastic Waves in a Transversely Isotropic Cylindrical Panel

In this article the three-dimensional dispersion analysis of a homogeneous transversely isotropic magneto generalized thermoelastic cylindrical panel is discussed in the context of the linear theory of generalized thermoelasticity. Three displacement potential functions are introduced to uncouple the equations of motion. A Bessel function solutions with complex argument is used directly to analyze the frequency equations with traction-free boundary conditions and the special cases have also been deduced for magneto-elastic, thermoelastic and elasto-kinetic at various levels from the present analysis. Finally the numerical example demonstrates the present method and is studied for the material magnetostrictive cobalt iron oxide (CoFe₂O₄). The computed non-dimensional phase velocity, attenuation coefficient, specific loss and thermo-mechanical coupling factor are plotted in the form of dispersion curves with the support of MATLAB.     

一次筒节整体脆断的原因分析

介绍一次锅炉汽包筒节卷制整体脆断的现象,通过金相实验分析找出原因,改进工艺方案杜绝汽包筒节脆断的现象.     

某型燃气轮机圆柱滚子轴承失效原因分析

某型燃气轮机圆柱滚子轴承在加速寿命试验时发生了外圈滚道承载区域疲劳剥落现象。为查明失 效原因,针对轴承试验件开展了尺寸精度、径向游隙、滚动表面轮廓、材料化学成分、显微组织等9项检测工 作,并复查了试验系统和设备的工装尺寸和加载头设计原理。经综合分析,判断轴承试验件的失效原因为： 加载套内径尺寸偏小,且选用材料硬度偏低,在使用紧固螺栓拉紧固定时,加载套导致自身及试验轴承的椭 圆变形,进而引起轴承外圈的提前疲劳剥落。上述分析工作准确地定位了轴承失效原因,改进试验系统,有 力地保证了某型燃气轮机圆柱滚子轴承加速寿命试验的顺利开展。     

离心铸造铁素体基球墨铸铁燃烧环的研制

阐述了铁素体基体球墨铸铁燃烧环的生产工艺,通过对原材料的选择和化学成分的控制．可以离心铸造生产铁素体基球墨铸铁。结果表明,选择合适的球化剂加入量,合理的冷却工艺参数,优化孕育方法,简便有效的退火方式,其球化性能、基体组织、力学性能都能达到或超过了国家标准。     

三种基流分割方法在黄河源区应用中的对比分析

基于黄河源区唐乃亥水文站1961~2004年的实测逐日径流量资料,分析基流年内分配规律,分别选取典型年径流量过程单峰型(2003年)、双峰型(1963年)、多峰型(1967年)进行标准化处理,运用数字滤波法、加里宁试算法和改进的经验斜割法计算基流过程和基流指数(BFI),并对比分析了气候、冰川(积融雪)和冻土过程对各种方法分割结果的影响。结果表明,黄河源区径流年内分配规律受自然条件的影响不同于其他流域;基流计算中数字滤波法计算结果稳定,加里宁试算法更贴合实测径流过程,经验斜割法在枯水年份基流分割中更为简便,应根据不同的年内径流过程及基流计算目的选择合适的基流分割方法。     

O_2/CO_2气氛下电站锅炉汽水系统仿真模型研究

基于O2/CO2气氛下烟气侧换热特点,建立了电站锅炉汽水系统整体动态数学模型。以某300 MW O2/CO2煤粉燃烧锅炉为仿真对象进行仿真试验,仿真结果表明,燃料量、O2/CO2容积比的增加可导致燃烧速率和燃烧温度迅速升高,进一步引起工质参数不同程度的变化。     

变频器谐波分析与抑制对策

变频设备中的变频器产生大量6k±1次谐波,此特征谐波使电网电流波形严重畸变,THD超过国标（GB/T14549-93）限值。对此本文提出有效的谐波抑制方案,并给出了单调谐滤波器的详细设计过程,同时通过仿真分析验证了谐波抑制效果的明显性。     

Analysis of Radiative Transport in a 2-D Cylindrical Participating Medium Subjected to Collimated Radiation

This article deals with the numerical analysis of radiative transport in a 2-D axisymmetric cylindrical enclosure containing absorbing, emitting, and scattering medium. The participating medium receives collimated radiation from the top boundary of the enclosure. Attenuation of the collimated radiation in the medium gives rise to the diffuse radiation. Thus, the governing radiative transfer equation accounts for both collimated and diffuse radiation. The radiative transfer equation is solved using the modified discrete ordinate method. Effects of extinction coefficient, scattering albedo, and aspect ratio on radial and axial distributions of heat flux and incident radiation are studied. In all cases, results are validated against those available in the literature. Modified discrete ordinate method has been found to provide accurate results.     

浅析离心铸造镶圈分层问题

镶圈加工后出现明显痕迹而报废,致使有两三批次的镶圈的废品率达到了30%,造成了很大的浪费.通过分析,断定该废品形式是分层而不是裂纹,初步确定是铸造的问题.又进一步分析,找出了产生该问题的根本原因,是随流孕育的时机掌握不好,孕育剂没充分熔化好就随液流进入了模具型腔所致,从而找出了正确的随流孕育的时机.降低了缸套及镶圈铸造废品损失,为其他同行厂在降低铸造废品方面具有借鉴意义.     

柴油机迷宫式油气分离器分离效率数值模拟

应用商用CFD软件AVL-FIRE对某三缸柴油机迷宫式油气分离器进行CFD分析,模拟迷宫内的流速与压力分布;采用离散模型模拟油滴粒子喷射,假定油滴粒子与壁面碰撞后即被捕捉,进而得出不同直径的油滴分离效率;对比了几种迷宫结构方案的进出口压降以及油气分离效率。结果显示:计算结果虽偏高,但趋势与试验值较吻合,证明了采用CFD技术对油气分离器进行模拟的可行性。     

DQM-Based Thermal Stresses Analysis of a Functionally Graded Cylindrical Shell Under Thermal Shock

The transient thermal stresses of a functionally graded (FG) cylindrical shell subjected to a thermal shock are investigated. The dynamic temperature fields of FG shells are obtained by using the Laplace transform and power series method. The differential quadrature method is developed to obtain the transient thermal stresses by solving dynamic governing equations in terms of displacements. The effects of the material constitutions on the transient temperature and the thermal stresses are analyzed in the cases of obverse thermal shock and reverse thermal shock. It turns out that the thermal stresses could be alleviated by means of changing the volume fractions of the constituents.     

Performance of a Circular Fin in a Cylindrical Porous Enclosure

The problem of natural convection heat transfer from a vertical cylindrical fin to a saturated porous medium in a cylindrical enclosure is solved numerically. A conjugate conduction-convection analysis is accomplished by solving the equation of heat conduction in the fin together with the mass, momentum and energy balance equations in the porous medium. Numerical results are obtained by using ADI method. The effects of the conduction-convection ratio parameter, aspect ratio and Darcy number on local heat transfer coefficients and fin efficiency are discussed. Comparison of the local heat transfer coefficients and fin efficiency is shown with those for non-porous medium.     

Numerical Analysis of Natural Convection in a Cylindrical Envelope with an Internal Concentric Cylinder with Slots

Detailed numerical analysis is presented for natural convection heat transfer in a cylindrical envelope with an internal concentric cylinder with slots. Governing equations are discretized using the finite volume method, and solved using SIMPLE algorithm with QUICK scheme. The results show that the system can reach steady state and be symmetric when the Rayleigh number is below 4 × 10⁵. When the Rayleigh number is greater than 6 × 10⁵, an asymmetric periodical solution is obtained although the initial field and boundary conditions were symmetric. As the Rayleigh numbers increase further, a quasi-periodic solution of the system is achieved at Ra = 2 × 10⁶, and the periodicity is lost at Ra = 6 × 10⁶. It is ascertained that the oscillatory flow undergoes several bifurcations and ultimately evolves to a chaotic flow.     

简体非径向大开孔的有限元分析

本文采用有限元分析技术,对开孔大小超过GB150限制范围的非径向大开孔进行了数值模拟计算,有限元模型采用参数化建模,对参数化建模的优点进行了介绍。结合应力分布云图对结构危险位置进行了应力线性化处理并根据应力分类图对危险路径进行了应力评定。最后,就改善结构受力给出了建议和措施。     

钢锭冷凝过程仿真及试验研究

提出了直接对凝固潜热进行差分计算的一套计算方法，在此基础上开发了三维非稳态凝固传热的计算程序。应用该程序计算了包钢Ｂ９６钢锭模内２０钢钢锭冷却的温度分布和凝固率随时间的变化规律。根据理论计算的预报情况，进行现场工业试验。理论和现场两者相结合确定了最佳的镇静时间和开脱时间。     

Analysis of Conduction and Radiation Heat Transfer in a 2-D Cylindrical Medium Using the Modified Discrete Ordinate Method and the Lattice Boltzmann Method

This article deals with the analysis of radiative transport with and without conduction in a finite concentric cylindrical enclosure containing absorbing, emitting, and scattering medium. Isothermal medium as the radiation source confined between the cold cylinders and a nonisothermal medium with the inner cylinder as the radiation source are the two nonradiative and radiative equilibrium problems. They involve only calculation of radiative information. In the third problem, a conducting-radiating medium is thermally perturbed by raising the temperature of the inner cylinder. In all problems, radiative information is computed using the modified discrete ordinate method (MDOM), and in the third problem, the lattice Boltzmann method (LBM) is used to formulate and solve the energy equation. Depending on the problems, effects of various parameters such as the extinction coefficient, the scattering albedo, the boundary emissivity, the conduction-radiation parameter, and the radius ratio are studied on temperature and heat flux distributions. The MDOM and the LBM-MDOM results are compared with those available in the literature. To further establish the accuracy of the MDOM and the LBM-MDOM results, in all problems, comparisons are made with the results obtained from the finite volume method (FVM) and the finite difference method-FVM approach, in which FVM provides the radiative information. The selection of the FDM-FVM for the third problem is also with the objective that for this problem, not much work is reported in which the FVM is used to calculate the radiative information. MDOM and LBM-MDOM results are found to compare well with those available in the literature, and in all cases they are in excellent agreement with FVM and FDM-FVM approaches.     

Comparison of the Discrete-Ordinates Method and the Finite-Volume Method for Steady-State and Ultrafast Radiative Transfer Analysis in Cylindrical Coordinates

The time-dependent equation of radiative transfer is solved for an axisymmetric cylindrical medium using both the discrete-ordinates method and the finite-volume method. Steady and transient flux profiles are determined for absorbing and scattering media. Results for each solution method are compared and shown for various grid numbers, scattering albedos, and optical thicknesses. A comparison of computational time and memory usage between the methods is presented. It is found that the finite-volume method uses more memory and has a longer convergence time than the discrete-ordinates method for all cases, due to the difference in angular treatment.