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1.
The Locally Conservative Galerkin (LCG) Method — a Discontinuous Methodology Applied to a Continuous Framework
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Rhodri L. T. Bevan Raoul vanLoon & Perumal Nithiarasu 《advances in applied mathematics and mechanics.》2009,1(3):319-340
This paper presents a comprehensive overview of the element-wise
locally conservative Galerkin (LCG) method. The LCG method was
developed to find a method that had the advantages of the
discontinuous Galerkin methods, without the large computational and
memory requirements. The initial application of the method is
discussed, to the simple scalar transient convection-diffusion
equation, along with its extension to the Navier-Stokes equations
utilising the Characteristic Based Split (CBS) scheme. The
element-by-element solution approach removes the standard finite
element assembly necessity, with an face flux providing continuity
between these elemental subdomains. This face flux provides explicit
local conservation and can be determined via a simple small
post-processing calculation. The LCG method obtains a unique
solution from the elemental contributions through the use of simple
averaging. It is shown within this paper that the LCG method
provides equivalent solutions to the continuous (global) Galerkin
method for both steady state and transient solutions. Several
numerical examples are provided to demonstrate the abilities of the
LCG method. 相似文献
2.
A method is developed for obtaining transient temperature distribution in a cooling semitransparent layer of ceramic. The layer is emitting, absorbing, isotropically scattering and heat conducting with a refractive index ranging from 1 to 2. The solution involves solving simultaneously the energy equation and the integral equation for the radiative flux gradient. The energy equation is solved using an implicit finite volume scheme and the integral equation of radiative heat transfer is solved using the singularity technique and Gaussian integration. The effects of scattering are investigated. It is shown that scattering has a significant effect on the transient temperature distribution and the transient mean temperature of the layer. 相似文献
3.
含对流与蒸发表面的有限厚度材料的双曲型热传导分析 总被引:3,自引:0,他引:3
本文对于含有对流与蒸发表面的有限厚度材料,在遭受一脉冲表面热流作用时的双曲型热传导进行了分析,采用热势函数描述的双曲型热传导方程来描述该问题,并用有限差分法进行数值求解.同时,本文还就表面对流与蒸发对材料表面与内部瞬态温度变化的影响以及材料双曲型热传导对表面蒸发的影响进行了分析. 相似文献
4.
Natural convection flows of an incompressible Newtonian fluid inside a circular cylinder are studied. The heat transfer process is described by a generalized fractional constitutive equation for the thermal flux-temperature gradient. Caputo time-fractional derivative operator, which provides the damping of thermal flux, is considered into the studied model.Analytical solutions to the fluid temperature, thermal flux, fluid velocity and volume flow rate are obtained with the integral transforms method (Laplace transform and finite Hankel transform).Temperature behaviors for small and large values of the time t, as well as the post-transient and transient velocity components are determined. The influence of the memory parameter (the order of the time-fractional derivative) on the temperature, thermal flux, velocity and the volume flow rate is numerically and graphically studied. 相似文献
5.
Three Boundary Meshless Methods for Heat Conduction Analysis in Nonlinear FGMs with Kirchhoff and Laplace Transformation
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Zhuo-Jia Fu Wen Chen & Qing-Hua Qin 《advances in applied mathematics and mechanics.》2012,4(5):519-542
This paper presents three boundary meshless methods for solving problems of steady-state and transient heat conduction in nonlinear functionally graded materials (FGMs). The three methods are, respectively, the method of fundamental solution (MFS), the boundary knot method (BKM), and the collocation Trefftz method (CTM) in conjunction with Kirchhoff transformation and various variable transformations. In the analysis, Laplace transform technique is employed to handle the time variable in transient heat conduction problem and the Stehfest numerical Laplace inversion is applied to retrieve the corresponding time-dependent solutions. The proposed MFS, BKM and CTM are mathematically simple, easy-to-programming, meshless, highly accurate and integration-free. Three numerical examples of steady state and transient heat conduction in nonlinear FGMs are considered, and the results are compared with those from meshless local boundary integral equation method (LBIEM) and analytical solutions to demonstrate the efficiency of the present schemes. 相似文献
6.
Vincent P. Gutschick Frederick W. Wiegel 《Journal of Quantitative Spectroscopy & Radiative Transfer》1984,31(1):71-82
We develop an exact integral equation for the angle-integrated flux interception by a leaf or a volume element in a layered medium. Iterative numerical solutions converge well. Any converged solution can be simply integrated to give the exact, angle-dependent flux at any depth. The method is presented for an axially symmetric input and an isotropic canopy, with results indicating quantitative significance in photosynthetic modeling and remote sensing. The generalization to arbitrary canopy anisotropy is developed without numerical results. 相似文献
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大平板瞬态热传导问题的一种新的近似解法 总被引:1,自引:0,他引:1
1引言大平板瞬态热传导问题有着广泛的工程应用背景。对于复杂的初边值条件或含内热源问题,以及工程上常见的多层复合平壁对象,分析求解难度很大甚至无法求解。在此类情况下往往采用数值方法。但是单纯的数值解不便于理解影响该问题的各种参数的物理意义。因此,各种近似分析方法得到了发展[1,2]。但在近似精度上,往往难以对整个时间坐标范围都达到较高的精度,这就使得近似解更多地局限于定性分析。此外,对于不同的初边值条件或含内热源问题,近似解的形式相异,降低了解的通用性。增加了求解的工作量。本文提出一种基于矩阵理论… 相似文献
9.
W.F. Breig A.L. Crosbie 《Journal of Quantitative Spectroscopy & Radiative Transfer》1974,14(3):189-209
Exact numerical results are presented for the emissive power and radiative flux at the boundary of a two-dimensional, absorbing-emitting, semi-infinite medium bounded by (1) a strip of collimated radiation and (2) a constant temperature black strip. The method of super-position is used to obtain the finite strip solutions in terms of cosine varying solutions. The infinite integrals arising in the solutions are converted to an alternating series of finite integrals. The Euler transformation is then applied to speed up convergence. Error bounds are determined whereby the two-dimensional finite strip analysis can be approximated by the simpler one-dimensional solution. 相似文献
10.
Gert Eilenberger 《Zeitschrift für Physik A Hadrons and Nuclei》1964,180(1):32-42
Abrikosov's method to get periodic solutions of the GL-equations for superconductors of type II is reformulated in order to make higher approximations possible. It is shown that instead of the external magnetic field, the average field in the superconductor must be used as fixed quantity in the approximations; then the method can be extended to a general iteration procedure with a fixed period-parallelogram for the solution. In the first approximation every periodic solution is given by a simple product of ?-functions; among those solutions which possess one flux quantum per period-parallelogram only, the hexagonal modification has the lowest free energy as already proposed byKleiner et al. 相似文献
11.
An anode heat flux model has been developed for pulsed high-intensity dc arcs. The model is based on temperature-time-history measurements of the rear face of a very thin plane anode and high-speed streak photographs of the arc. The arc heat flux model is derived from a comparison of experimental data with an analytical solution of the one-dimensional heat conduction equation and the arc intensity and timing information obtained from high-speed photographs. A simplified input heat flux model consisting of connected segments of linearly varying heat fluxes with respect to time is used. Duration of the individual segments is determined from the streak photographs and the graphical match of measured rear-face temperature history and the numerical solution. Results using argon gas at atmospheric pressure indicate an initial transient heat flux regime of 100-?s duration with a peak heat flux of 2 × 109 W/m2 followed by a quasi-steady heat flux regime with a heat flux of 1 × 108 W/m2. 相似文献
12.
线性瞬态涡流电磁场定解问题的主要特点是边界条件使用磁感应强度的法向分量边界条件代替了电场强度的切向分量边界条件,约束方程中忽略了位移电流.这种具有特殊性的定解问题的解是否唯一和稳定对于求解瞬态涡流电磁场而言是一个基本问题.本文在非涡流区引入标量位函数,证明了在推导过程中起重要作用的辅助函数的存在性.通过推导线性瞬态涡流电磁场定解问题的能量估计式,证明了该定解问题的解是唯一的,并且关于初始条件和外源项是稳定的.本结果对于线性瞬态涡流电磁场的求解有一定的指导意义.作为应用,给出了通有单脉冲电流的单匝圆环线圈与球形导体共轴的涡流问题的解析解.
关键词:
瞬态涡流电磁场
能量估计式
唯一性
稳定性 相似文献
13.
溶液的微观结构对溶液的宏观性质具有决定性影响,团簇的存在和溶液不均性的认知是该领域研究的重要进展之一,也是关注的热点.为了考察溶液的微观结构,本文采用分子动力学方法对浓度适中的氯化钠水溶液进行了模拟,获得了各原子(离子)间的径向分布函数和溶液的瞬态图像.通过对比分析Na~+-Cl~-和Cl~--Na~+的径向分布函数,并结合已有研究结果,表明该径向分布函数上第三峰也来源于离子对,发现氯化钠水溶液存在着第三种离子对;上述径向分布函数上的三个峰分别与直接接触离子对、部分间隔离子对和完全间隔离子对相对应,并给出了这三种离子对的瞬态图像.三个时刻下系统瞬态图像的分析结果表明,溶液中存在水分子连续分布的区域和由离子与水分子共同构成的离子团簇.各瞬态图像中水分子连续分布的最大区域的平均尺寸至少为1.43 nm,溶液中部分间隔离子对的比例最大,约为0.68.在同时考虑直接接触离子对和部分间隔离子对时,三个时刻中最大团簇尺度的平均值为1.44 nm,该值约为部分间隔离子对最概然尺寸的3倍;团簇尺寸随团簇中离子数的增加而增大,在团簇中离子数较大时,满足无规行走(自由连接链)模型的结果.这些说明氯化钠水溶... 相似文献
14.
The multiscale finite volume (MsFV) method has been developed to efficiently solve large heterogeneous problems (elliptic or parabolic); it is usually employed for pressure equations and delivers conservative flux fields to be used in transport problems. The method essentially relies on the hypothesis that the (fine-scale) problem can be reasonably described by a set of local solutions coupled by a conservative global (coarse-scale) problem. In most cases, the boundary conditions assigned for the local problems are satisfactory and the approximate conservative fluxes provided by the method are accurate. In numerically challenging cases, however, a more accurate localization is required to obtain a good approximation of the fine-scale solution. In this paper we develop a procedure to iteratively improve the boundary conditions of the local problems. The algorithm relies on the data structure of the MsFV method and employs a Krylov-subspace projection method to obtain an unconditionally stable scheme and accelerate convergence. Two variants are considered: in the first, only the MsFV operator is used; in the second, the MsFV operator is combined in a two-step method with an operator derived from the problem solved to construct the conservative flux field. The resulting iterative MsFV algorithms allow arbitrary reduction of the solution error without compromising the construction of a conservative flux field, which is guaranteed at any iteration. Since it converges to the exact solution, the method can be regarded as a linear solver. In this context, the schemes proposed here can be viewed as preconditioned versions of the Generalized Minimal Residual method (GMRES), with a very peculiar characteristic that the residual on the coarse grid is zero at any iteration (thus conservative fluxes can be obtained). 相似文献
15.
We give the general solution of Liouville's equation in Robertson-Walker space-times, and use this to find exact inhomogeneous Einstein-Liouville solutions, using the covariant harmonic method of Ellis, Matravers and Treciokas [1]. The average four-velocity of the gas is tilted, and the gas has nonzero acceleration, shear, energy flux, and anisotropic stress. 相似文献
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We introduce a multidimensional peridynamic formulation for transient heat-transfer. The model does not contain spatial derivatives and uses instead an integral over a region around a material point. By construction, the formulation converges to the classical heat transfer equations in the limit of the horizon (the nonlocal region around a point) going to zero. The new model, however, is suitable for modeling, for example, heat flow in bodies with evolving discontinuities such as growing insulated cracks. We introduce the peridynamic heat flux which exists even at sharp corners or when the isotherms are not smooth surfaces. The peridynamic heat flux coincides with the classical one in simple cases and, in general, it converges to it in the limit of the peridynamic horizon going to zero. We solve test problems and compare results with analytical solutions of the classical model or with other numerical solutions. Convergence to the classical solutions is seen in the limit of the horizon going to zero. We then solve the problem of transient heat flow in a plate in which insulated cracks grow and intersect thus changing the heat flow patterns. We also model heat transfer in a fiber-reinforced composite and observe transient but steep thermal gradients at the interfaces between the highly conductive fibers and the low conductivity matrix. Such thermal gradients can lead to delamination cracks in composites from thermal fatigue. The formulation may be used to, for example, evaluate effective thermal conductivities in bodies with an evolving distribution of insulating or permeable, possibly intersecting, cracks of arbitrary shapes. 相似文献
18.
Torsional guided waves are often used to detect the defects in a hollow cylinder. To realize the excitation of the torsional guided waves with high efficiency, the transient vibration responses of finite, semi-infinite and infinite hollow cylinders to external torsional forces must be clarified theoretically. In this study, the method of eigenfunction expansion is employed to solve the above problems. The exact analytical solutions derived by this method are not only explicit but also concise. Furthermore, the analytical solution of the transient torsional vibration of the finite hollow cylinder is numerically evaluated. The results obtained agree well with those simulated by the finite element method. 相似文献
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采用解析方法对双导传输线Taylor模型和Agrawal模型进行研究,获得了这两个模型基于平面电磁波激励下的终端负载响应的频域解析解,并证明它们的解析解是相同的,从而得到双导传输线基于平面电磁波激励的终端负载响应的频域解析解公式。Taylor模型和Agrawal模型其实是对同一个解的不同描述,由于Agrawal模型比Taylor模型相对简单,因此在实际应用时可以采用Agrawal模型或频域解析解公式进行求解。应用频域解析解公式和Fourier变换与逆变换技术,可以求得终端电压或电流的瞬时响应解。 相似文献