共查询到20条相似文献,搜索用时 171 毫秒
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结合人工神经网络建立裂缝介质多尺度深度学习流动模型.基于一套粗网格和一套细网格,通过在粗网格上训练数据,多尺度神经网络能够以较少的自由度训练出准确的神经网络.并在粗网格上通过求解局部流动问题获得多尺度基函数,结合神经网络进一步得到精细网格的解.基于离散裂缝的流动方程可视为多层网络,网络层数依赖于求解时间步数.阐述裂缝介质多尺度机器学习数值计算格式的建立,介绍如何使用多尺度算法构建离散裂缝模型的多尺度基函数,并采用超样本技术进一步提高计算准确性.数值结果表明,多尺度有限元算法与机器学习结合是一种有效的流体流动模拟算法. 相似文献
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在用拉格朗日方法模拟二维多介质可压缩流体的运动时,网格发生大变形往往是模拟不能正常进行下去的重要原因。网格动态局域重分可以有效改善网格的畸变程度,使计算得以持续。针对三角形计算网格提出了一种新的动态局域重分方法,包含"对角线交换""长边劈裂""短边融合"和"帽子戏法"4种基本操作,其中前3种操作不仅作用于同种介质内部,还可将其拓展到多介质界面处,与"帽子戏法"一起处理界面附近的大变形网格。在网格动态局域重分后,将旧网格上的物理量映射到新网格上,先计算出新三角形的质量和内能,再根据动量守恒和能量守恒对新三角形的格点速度及内能进行修正。利用该方法对冲击波与气泡相互作用和R-T不稳定性问题进行了数值模拟,取得了良好的效果。在R-T不稳定性算例中,采用同种介质和不同介质两种模型进行对比,模拟结果验证了该方法的有效性。 相似文献
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研究可压缩多介质流场的激波和多介质界面相互作用问题.在Descartes固定网格采用level-set方法追踪界面,气/气界面边界条件处理采用OGFM方法,采用修正的rGFM方法提高气/水和气/固界面处构造Riemann问题精度,将Riemann近似解得到的界面参数外推到两侧真实和虚拟流体,采用五阶WENO方法求解流场Euler方程和界面level-set方程,给出不同时刻流场数值纹影图像.结果表明:在可压缩流场嵌入固体和水、气体等目标,本文方法可较精确地分辨平面运动激波和单列水柱及包含气/气、气/水和气/固等界面作用后产生的复杂激波结构.和传统的分区与贴体变换方法不同,为Descartes网格包含多介质界面复杂流场计算提供新途径. 相似文献
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本文在VOF方法的基础上,采用粗细两套网格对高密度和高粘度比率下的气液两相流动模拟进行了研究分析.在细网格中求解流体体积函数方程,在粗网格中采用交错网格求解动量方程和压力修正方程,通过粗细网格间的数据传递获得求解动量方程时需要的准确的界面密度和粘度及控制体密度,克服了高密度和高粘度比率下通过插值方法计算界面密度和粘度及控制体密度带来较大误差的困难,保证了质量和动量同时守恒.高密度和高粘度比率下气液两相流动中气液交界面处密度、速度和压力急剧变化,为了保证格式的有界性和稳定性,采用稳定的有界高阶组合格式STOIC.最后模拟了不同工况下气泡在液体中的运动,并通过实验和模拟结果验证了方法的可行性及准确性. 相似文献
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热传导方程的一类无网格方法 总被引:1,自引:0,他引:1
构造求解热传导方程的一类无网格方法,只要选择好每个节点的适当的邻点集合,便可利用节点信息顺利进行计算.作为特殊情形,也可在各种结构或非结构网格上进行计算.在矩形或均匀平行四边形网格上进行计算时具有二阶精度,当在任意的不规则四边形或三角形网格上计算时仍然是守恒的和相容的,且至少具有一阶精度.作为数值试验,将该方法用于在不规则四边形网格上及四边形与三角形混合网格上求解二维非线性抛物型方程,并在不规则四边形网格上求解二维三温辐射热传导方程,均获得了较为理想的数值结果. 相似文献
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Ghost Fluid方法与双介质可压缩流动计算 总被引:1,自引:1,他引:0
应用带有Isobaric修正的GhostFluid方法配合LevelSet方法计算可压缩双介质无粘流动.该方法可以消除计算流体界面时所产生的数值跳动和耗散,且编程上比界面跟踪法简单.应用WENO格式数值求解欧拉方程和LevelSet方程,对由刚性气体状态方程所支配的一二维双介质流动进行数值计算,得到了分辨率较高的计算结果. 相似文献
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With the intermediate flow states predicted by local two phase Riemann problem,the modified ghost fluid method(MGFM)and its variant(r GFM)have been widely employed to resolve the interface condition in the simulation of compressible multi-medium flows.In this work,the drawback of the construction procedure of local two phase Riemann problem in r GFM was investigated in detail,and a refined version of the construction procedure was specially developed to make the simulation of underwater explosion bubbles more accurate and robust.Beside the refined r GFM,the fast and accurate particle level set method was also adopted to achieve a more effective and computationally efficient capture of the evolving multi-medium interfaces during the simulation.To demonstrate the improvement brought by current refinement,several typical numerical examples of underwater explosion bubbles were performed with original r GFM and refined r GFM,respectively.The results indicate that,when compared with original r GFM,numerical oscillations were effectively removed with the proposed refinement.Accordingly,with present refined treatment of interface condition,a more accurate and robust simulation of underwater explosion bubbles was accomplished in this work. 相似文献
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The modified ghost fluid method (MGFM) provides a robust and
efficient interface treatment for various multi-medium flow
simulations and some particular fluid-structure interaction (FSI)
simulations. However, this methodology for one specific class of FSI
problems, where the structure is plate, remains to be developed.
This work is devoted to extending the MGFM to treat compressible
fluid coupled with a thin elastic plate. In order to take into account
the influence of simultaneous interaction at the interface, a
fluid-plate coupling system is constructed at each time step and
solved approximately to predict the interfacial states. Then,
ghost fluid states and plate load can be defined by utilizing
the obtained interfacial states. A type of acceleration strategy in
the coupling process is presented to pursue higher efficiency.
Several one-dimensional examples are used to highlight the utility
of this method over loosely-coupled method and validate the
acceleration techniques. Especially, this method is applied to
compute the underwater explosions (UNDEX) near thin elastic plates.
Evolution of strong shock impacting on the thin elastic plate and
dynamic response of the plate are investigated. Numerical results
disclose that this methodology for treatment of the fluid-plate
coupling indeed works conveniently and accurately for different
structural flexibilities and is capable of efficiently simulating
the processes of UNDEX with the employment of the acceleration
strategy. 相似文献
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A RKDG finite element method for the one-dimensional inviscid compressible gas dynamics equations in Lagrangian coordinate 下载免费PDF全文
In this paper, Runge-Kutta Discontinuous Galerkin (RKDG) finite element method is presented to solve the one-dimensional inviscid compressible gas dynamic equations in Lagrangian coordinate. The equations are discretized by the DG method in space and the temporal discretization is accomplished by the total variation diminishing Runge-Kutta method. A limiter based on the characteristic field decomposition is applied to maintain stability and non-oscillatory property of the RKDG method. For multi-medium fluid simulation, the two cells adjacent to the interface are treated differently from other cells. At first, a linear Riemann solver is applied to calculate the numerical flux at the interface. Numerical examples show that there is some oscillation in the vicinity of the interface. Then a nonlinear Riemann solver based on the characteristic formulation of the equation and the discontinuity relations is adopted to calculate the numerical flux at the interface, which suppress the oscillation successfully. Several single-medium and multi-medium fluid examples are given to demonstrate the reliability and efficiency of the algorithm. 相似文献
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An RKDG finite element method for the one-dimensional inviscid compressible gas dynamics equations in a Lagrangian coordinate 下载免费PDF全文
In this paper,Runge-Kutta Discontinuous Galerkin(RKDG) finite element method is presented to solve the onedimensional inviscid compressible gas dynamic equations in a Lagrangian coordinate.The equations are discretized by the DG method in space and the temporal discretization is accomplished by the total variation diminishing Runge-Kutta method.A limiter based on the characteristic field decomposition is applied to maintain stability and non-oscillatory property of the RKDG method.For multi-medium fluid simulation,the two cells adjacent to the interface are treated differently from other cells.At first,a linear Riemann solver is applied to calculate the numerical ?ux at the interface.Numerical examples show that there is some oscillation in the vicinity of the interface.Then a nonlinear Riemann solver based on the characteristic formulation of the equation and the discontinuity relations is adopted to calculate the numerical ?ux at the interface,which suppresses the oscillation successfully.Several single-medium and multi-medium fluid examples are given to demonstrate the reliability and efficiency of the algorithm. 相似文献
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虚拟流体方法为模拟具有清晰物质界面的多介质流动问题提供了一种简便途径.尤其基于多介质Riemann问题解的修正虚拟流体方法及其变体,能够真实考虑到界面附近非线性波的相互作用和物质性质的影响,可以有效解决各种界面强间断等挑战性难题,具有巨大的工程应用潜力.文章重点回顾了虚拟流体方法的发展历史,总结和对比了各种代表性版本在模拟可压缩多介质流时的界面条件定义方式和多维推广方式,并介绍了该方法的设计原则和精度分析方面的研究进展.文章还回顾了该方法在其他更广泛和更具挑战性典型科学问题中的最新应用进展,并对方法的优势和特点进行了总结. 相似文献
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The high-order accurate Runge–Kutta discontinuous Galerkin (RKDG) method is applied to the simulation of compressible multi-medium flow, generalizing the interface treating method given in Chertock et al. (2008) [9]. In mixed cells, where the interface is located, Riemann problems are solved to define the states on both sides of the interface. The input states to the Riemann problem are obtained by extrapolation to the cell boundary from solution polynomials in the neighbors of the mixed cell. The level set equation is solved by using a high-order accurate RKDG method for Hamilton–Jacobi equations, resulting in a unified DG solver for the coupled problem. The method is conservative if we include the states in the mixed cells, which are however not used in the updating of the numerical solution in other cells. The states in the mixed cells are plotted to better evaluate the conservation errors, manifested by overshoots/undershoots when compared with states in neighboring cells. These overshoots/undershoots in mixed cells are problem dependent and change with time. Numerical examples show that the results of our scheme compare well with other methods for one and two-dimensional problems. In particular, the algorithm can capture well complex flow features of the one-dimensional shock entropy wave interaction problem and two-dimensional shock–bubble interaction problem. 相似文献
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对于粘性绕流的数值模拟,在自适应直角网格基础上,结合三角形非结构网格和结构化网格,利用其各自的优势和特点,提出一种生成混合杂交网格的思路和方法.在物面附近生成适合粘性流计算的大长宽比结构化网格,在远场分布自适应直角网格,快速离散计算空间.对于复杂的多体问题,采用三角形网格来连接各体网格,并运用网格合并的方法,保证各网格之间的光滑过渡与连接,提高网格质量.针对一些二维、三维外形的绕流问题,在上述网格基础上,采用B-L代数湍流模型和中心有限体积法,完成Navier-Stokes和Euler方程数值模拟的对比计算,结果表明网格生成和流场计算是正确的. 相似文献