对流换热边界下梯度功能材料板瞬态热传导有限元分析

用有限元法与有限差分法相结合的方法 ,对处在对流换热边界条件下的梯度功能材料板的瞬态热传导问题进行了分析 ,并且通过由ZrO2 和Ti 6A1 4V组成的梯度功能材料板对本方法的正确性进行了检验 ,最后给出了对流换热边界下的瞬态温度场分布。数值计算结果表明 :材料组分的分布形状系数M、环境介质温度和对流换热系数的变化对梯度功能材料板的瞬态温度场分布均有明显的影响。本文结果为梯度功能材料的优化设计和进一步的热应力分析提供了理论计算依据。     

对流换热边界下梯度功能材料板瞬态热传导有限元分析

用有限元法与有限差分法相结合的方法，对处在对流换热边界条件下的梯度功能材料板的瞬态热传导问题进行了分析，并且通过对ZrO2和Ti－6Al-4V组成的梯度功能材料板对本方法的正确性进行了检验，最后给出了对流换热边界下的瞬态温度场分布。数值计算结果表明：材料组成的分布形状系数M、环境介质温度和对流换热系数的变化对梯度功能材料板的瞬态温度场分布有明显的影响。本文结果为梯度功能材料的优化设计和进一步的热应力分析提供了理论计算依据。     

不同变形状态下变物性梯度功能材料板瞬态热应力

用非线性有限元法分析了由ZrO2和Ti-6Al-4V组成的变物性梯度功能材料板的对流换热瞬态热应力问题,与已有文献比较检验了方法的正确性,给出了该材料板在不同变形状态下的瞬态热应力分布,并与常物性时的结果进行了比较。结果表明:无限自由长板内的热应力最小;当无限长板只能伸长、不能弯曲时,板内瞬态拉应力最大;当无限长板伸长、弯曲受限时,板内的瞬态压应力最大;考虑变物性时的最大拉应力比常物性减小48.9%,最大压应力减小39.6%;此外,对流换热系数的变化对不同变形状态下该变物性材料板瞬态热应力场的影响显著。此结果为该材料的设计和应用提供了准确的理论计算依据。     

换热边界下变物性梯度功能材料板稳态热应力

用非线性有限元法分析了由ZrO2和Ti-6Al-4V组成的变物性梯度功能材料无限自由长板在对流换热边界下的稳态热应力问题,检验了方法的正确性,给出了该材料板的稳态热应力场分布,并与不考虑变物性时的结果进行了比较.结果表明当M=1.0时,考虑变物性的最大拉应力比不考虑变物性减小70.5%,最大压应力减小62.5%;此外,材料组分的分布形状系数M、环境介质温度、对流换热系数和孔隙度P的变化对变物性梯度功能材料板的稳态热应力场分布均有明显的影响;在本研究相同条件下,当孔隙度系数A=3.99时,陶瓷侧拉应力最大.此结果为梯度功能材料的设计制备提供了准确的理论计算依据.     

换热边界下梯度功能材料板瞬态热应力研究

用有限元和辛普生法,研究了由ZrO2和Ti-6Al-4V组成的梯度功能材料板的瞬态热应力问题,检验了方法的正确性,给出了对流换热边界下的瞬态热应力场分布.结果表明:材料组分的分布形状系数M、对流换热系数和环境介质温度的变化对该材料板的瞬态热应力场分布均有明显的影响;在本研究相同条件下,该材料无限自由长板在金属和陶瓷附近板内为压应力,而在板中部为拉应力.此结果为该材料的设计制备提供了准确的理论计算依据.     

孔隙率对金属-FGM-陶瓷复合ECBF板冷却变物性瞬态热应力的影响

功能梯度材料(简称FGM)是一种材料性质非均匀变化的特殊材料。根据热传导问题的基本方程,采用变分有限元法、有限差分法,结合算例,通过数值计算,最终得到冷却边界条件下夹FGM复合板瞬态热应力的分布规律,并主要研究孔隙率变化对FGM复合板瞬态热应力的影响。结果表明:当无限长板不能伸长、只能弯曲时,孔隙率对该变物性材料板瞬态热应力的影响比较显著。     

蜂窝夹层复合材料结构非线性传热分析

考虑材料热物性随温度变化的影响,针对蜂窝夹层复合材料结构的特点,假定其内部的瞬态温度场的分布状况,并在此假定的基础上基于三维各向异性热传导理论及复合材料层合结构传热分析的热叠层方法,提出一种针对蜂窝夹层复合材料结构的改进的计算方法,并推导出蜂窝夹层复合材料结构瞬态温度场分析的有限元方程。应用这种方法对热物性非线性蜂窝夹层复合材料板的瞬态温度场进行分析,数值算例结果显示了材料特性的非线性对蜂窝夹层复合材料板热传导的影响,只有非线性程度很小时忽略非线性因素导致的误差才可被忽略;当非线性程度较强烈时,考虑非线性因素的计算结果与忽略非线性因素的计算结果就会产生很大偏差。      

梯度功能材料板瞬态温度场有限元分析

采用有限元法与有限差分法相结合的方法,对梯度功能材料板的瞬态温度场进行了分析,并且通过ＺｒＯ２和Ｔｉ－６Ａｌ－４Ｖ组成的梯度功能材料对本方法的正确性进行了检验,最后给出了加热、冷却过程的瞬态温度场分布。     

SiCP/Al功能梯度装甲板抗侵彻性能的试验与数值模拟

采用粉末冶金方法制备碳化硅陶瓷颗粒(SiC_P)增强金属铝基复合材料板(MMCs), 并采用热压扩散法制备功能梯度装甲板(FGM)。利用高速冲击空气炮系统, 对纯铝靶板和两种不同铺层结构的功能梯度装甲靶板进行侵彻试验, 并利用LS-DYNA软件对侵彻试验过程进行数值模拟分析, 同时考察等厚、 等面密度下SiC颗粒分布对抗侵彻性能的影响。研究结果表明, 功能梯度板的抗侵彻性能比纯铝板好, 而两种不同铺层结构功能梯度板的抗侵彻性能相差不大。数值计算结果与现有试验结果取得了较好的一致, 说明了数值模拟的有效性。从数值计算结果可以看出, 层状功能梯度板比等厚、 等面密度均质复合材料靶板的抗侵彻能力好, 并可近似地认为等厚、 等面密度下多层功能梯度板的抗侵彻性能对颗粒分布不敏感。     

基于样条无网格法的厚/薄压电功能梯度板动力分析

在将板的挠度和剪切应变作为场变量的基础上增加考虑面内位移,采用样条无网格法建立了热环境下厚/薄压电功能梯度板动力分析新的计算格式。考虑功能梯度材料的物性参数随温度改变以及温度变化引起的面内力,讨论了压电FGM板在不同边界约束下材料梯度指数变化时,面内位移及面内力对热环境下压电功能梯度板的动力特性和动力响应的影响。分析结果表明,新建立的模型对厚/薄压电功能梯度板动力分析具有通用性和有效性,没有剪切闭锁现象,且计算效率和计算精度较高。     

Transient mixed convective heat transfer with melting effect from the vertical plate in a liquid saturated porous medium

This paper aims to numerically analyze the melting effect on transient mixed convective heat transfer from a vertical plate in a liquid saturated porous medium. The Darcy’s flow with the Boussinesq approximation and energy equations for this study is transformed into the non-dimensional equations by using pseudo-similarity coordinate (ζ) and dimensionless time (ξ). The resulting the boundary value problem is solved by the method of lines (MOLs) with central finite difference and Newton’s iteration to completely obtain the solutions for the whole transient mixed convective heat transfer from transient heat conduction to steady mixed convection in porous medium with melting effect in the presence of aiding and opposing external flows. As shown in the results, it is both found that the rate of dynamic heat transfer is reduced with increasing melting strength and the response time from transient heat conduction to steady mixed convection in porous medium for aiding external flow is shorter than that for opposing external flow in the presence of melting effect. Additionally, the melting effect may be reduced with increasing mixed convective strength Gr/Re^1/2 during transient mixed convective heat transfer in porous medium with aiding external flow.     

Transient thermoelastic deformations of 2-D functionally graded beams under nonuniformly convective heat supply

Numerical solutions obtained by the meshless local Petrov–Galerkin (MLPG) method are presented for transient thermoelastic deformations of functionally graded (FG) beams. The MLPG method is a truly meshless approach, and neither the nodal connectivity nor the background mesh is required for solving the initial-boundary-value problem. In this study, the MLPG weak formulations associated with the governing equations of the transient-state thermal equilibrium and quasi-static mechanical equilibrium are given. The penalty method is adopted to efficiently enforce the essential boundary conditions, and the test function is chosen to equal the weight function of the moving least squares approximation. An example is demonstrated for an FG beam with thermoelastic moduli varying exponentially through the thickness direction under a nonuniformly convective heat supply. Results obtained from the MLPG method are found to agree well with those by the analytical solution. The nonhomogeneity of the material properties on the thermo-mechanical response of the FG beam is investigated. It is shown that temperature and deformation fields of FG beams in a transient state differ substantially from those at the steady state. Besides that, the rate of change of the heat supply on the transient responses is also delineated.     

Transient free convection flow past an impulsively started isothermal vertical cylinder with mass flux

This paper concern with the laminar flows, which arise in fluids due to the interaction of the force of gravity and density differences, caused by temperature differences and material or phase constitution for both air and water. A solution of laminar boundary layer equations has been obtained for the transient free convective flow past an impulsively started semi-infinite isothermal vertical cylinder with uniform mass flux. The solutions of the dimensionless, unsteady, coupled and non-linear governing partial differential equations are obtained by a more accurate, unconditionally stable and fast converging implicit finite difference scheme. The results show many interesting effects on velocity, temperature and concentration profiles and local as well as average shear stress, rate of heat and mass transfer. It is observed that there is a rise in the velocity due to the presence of mass diffusion.     

对流边界条件下竖板降膜除湿过程中传热传质的数值模拟

针对竖板降膜(层流)溶液除湿空调系统,建立了溶液降膜过程传热传质的数学模型,给出了对流换热边界条件下过程的数值解.模拟了三种不同冷却条件下的降膜除湿过程.结果表明,当对流换热系数较小时,与绝热边界有相似的发展趋势;而当对流换热系数较大时,则接近于等温条件下的规律.同时,模拟结果还给出了不同的无量纲吸收热λv和刘易斯Le对降膜内Nusselt数和Sherwood数的影响,表明无量纲吸收热的改变不影响Nu数和Sh数在流动方向上的最终渐近值.     

多孔介质材料在低温下的传热特性实验研究

对多孔介质材料在低温下的传热特性进行了实验研究,在填充液氮以后其低温维持时间明显增加,主要原因是由于多孔材料的参与改变了传热特性;采用连续介质管束模型,用有限元分析软件对其整体温度场分布进行了数值模拟计算,计算结果和实验数据吻合。     

Numerical investigation of nanofluid heat transfer in helically coiled tubes using the four-equation model

Helical coils and nanofluids are among efficient methods for heat transfer augmentation. The present study numerically investigates convective heat transfer with nanofluids in helically coiled tubes. Two boundary conditions are applied to the coil walls; constant temperature and constant heat flux. Heat transfer in nanofluids are mainly investigated using either the homogeneous model or the two-phase model. However, in the present numerical solution, the four-equation model is applied, using slip mechanisms for the base fluid and nanoparticles. Considering that the proposed model is simplified compared to the two-phase model, it can be regarded as an efficient model for numerical solution of heat transfer in nanofluids. Governing equations are solved in the non-dimensional form using the projection algorithm of finite difference method. Water/CuO with a 0.2% volume fraction and water/Ag with a 0.03% volume fraction are examined for validation of numerical results in case of constant temperature and constant heat flux boundary conditions, respectively. The obtained results show a better agreement of this model with respect to experimental data, compared to the homogeneous model.