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Parallel Numerical Implementation of Mathematical Wave Hydrodynamics Models Taking into Account the Features of the Vertical Turbulent Exchange Using Remote Sensing Data 利用遥感数据并行数值实现考虑到垂直湍流交换特征的数学波浪流体力学模型
Q3 Mathematics Pub Date : 2024-04-01 DOI: 10.1134/s2070048224020170
A. Sukhinov, E. Protsenko, S. Protsenko, N. D. Panasenko
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引用次数: 0
On the Accuracy of Finite-Difference Schemes in Calculations of Centered Rarefaction Waves 论有限差分方案在计算居中稀释波中的准确性
Q3 Mathematics Pub Date : 2023-12-26 DOI: 10.1134/s2070048223070104
O. A. Kovyrkina, V. V. Ostapenko

Abstract

A comparative accuracy analysis of three finite-difference schemes (the first order UpWind (UW), the second order TVD, and the third order in time WENO5 schemes) is carried out when calculating the nonlinear transport equation of the Cauchy problem with piecewise linear discontinuous periodic initial data. We show that in the case of stable initial discontinuities from which a sequence of shocks is formed, the convergence order of all three schemes between the shocks coincides with their formal accuracy. In the case of unstable initial discontinuities, when a sequence of centered rarefaction waves is formed, all three schemes have the first order of convergence within these waves. We obtain an explicit formula for the disbalances of the difference solutions in a centered rarefaction wave. This formula agrees closely with the numerical calculations in the case of high-order accurate schemes, does not depend on the scheme type, and is determined by the error in approximating the initial data in the vicinity of an unstable strong discontinuity.

摘要 在计算具有片断线性不连续周期性初始数据的 Cauchy 问题非线性输运方程时,对三种有限差分方案(一阶 UpWind (UW)、二阶 TVD 和三阶 WENO5 方案)进行了精度比较分析。我们的研究表明,在稳定的初始不连续处形成一连串冲击的情况下,这三种方案在冲击之间的收敛阶数与它们的形式精度相吻合。在初始不连续性不稳定的情况下,当形成一连串居中的稀释波时,所有三种方案在这些波内的收敛阶次都是第一阶次。我们得到了中心稀释波中差分解不平衡的明确公式。该公式与高阶精确方案情况下的数值计算结果非常吻合,不依赖于方案类型,由不稳定强不连续性附近的初始数据近似误差决定。
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引用次数: 0
Generalized Model Representation of the Thermal Shock Theory 热冲击理论的广义模型表示法
Q3 Mathematics Pub Date : 2023-12-26 DOI: 10.1134/s2070048223070062
E. M. Kartashov

Abstract

This article considers the open problem of the thermal shock theory in terms of a generalized model of dynamic thermoelasticity under conditions of a locally nonequilibrium heat transfer process. The model is used for a massive body in the cases of three coordinate systems: Cartesian coordinates for a body bounded by a flat surface; spherical coordinates for a body with an internal spherical cavity; and cylindrical coordinates for a body with an internal cylindrical cavity. Three types of intensive heating and cooling are considered: temperature, thermal, and heating by the medium. The task is set to obtain an analytical solution, to carry out numerical experiments, and to give their physical analysis. As a result, generalized model representations of a thermal shock in terms of dynamic thermoelasticity are developed for locally nonequilibrium heat transfer processes simultaneously in three coordinate systems: Cartesian, spherical, and cylindrical. The presence of a curvature of the boundary surface of the thermal shock area substantiates the initial statement of the dynamic problem in displacements using the proposed corresponding compatibility equation. The latter made it possible to propose a generalized dynamic model of the thermal reaction of massive bodies with internal cavities simultaneously in Cartesian, spherical, and cylindrical coordinate systems under conditions of intense thermal heating and cooling, thermal heating and cooling, and heating and cooling by the medium. The model is considered in displacements on the basis of a local nonequilibrium heat transfer. An analytical solution for stresses is obtained and a numerical experiment is carried out; the wave nature of the propagation of a thermoelastic wave is described. A comparison is made with the classical solution without taking into account the local non-equilibrium. Based on the operational solution of the problem, design engineering relations that are important in practical terms for the upper estimate of the maximum thermal stresses are proposed.

摘要 本文从局部非平衡传热过程条件下动态热弹性广义模型的角度,探讨了热冲击理论的未决问题。该模型用于三个坐标系情况下的大质量体:笛卡尔坐标系适用于以平面为边界的物体;球面坐标系适用于内部有球面空腔的物体;圆柱坐标系适用于内部有圆柱空腔的物体。考虑了三种密集加热和冷却方式:温度加热、热加热和介质加热。我们的任务是获得解析解,进行数值实验,并对其进行物理分析。因此,在三个坐标系中同时为局部非平衡传热过程开发了动态热弹性热冲击的广义模型表示法:笛卡尔坐标系、球面坐标系和圆柱坐标系。热冲击区域边界表面曲率的存在,证实了利用所提出的相应相容方程对位移动态问题的初步阐述。后者使我们有可能在笛卡尔、球面和圆柱坐标系中同时提出带有内腔的大质量体在强烈热加热和冷却、热加热和冷却以及介质加热和冷却条件下的热反应的广义动态模型。该模型在局部非平衡传热的基础上考虑了位移问题。获得了应力的解析解,并进行了数值实验;描述了热弹性波传播的波性质。与不考虑局部非平衡的经典解法进行了比较。根据问题的实际解法,提出了对最大热应力上限估算具有重要实际意义的设计工程关系。
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引用次数: 0
Direct Numerical Simulation Method of Turbulence Taking the History of the Process into Account 考虑过程历史的湍流直接数值模拟法
Q3 Mathematics Pub Date : 2023-12-26 DOI: 10.1134/s2070048223070165
Yu. V. Yanilkin, A. R. Guzhova, L. I. Degtyarenko, V. Yu. Kolobyanin, V. A. Shmelev

Abstract

A new approach to the direct numerical modeling (DNM) of the turbulent mixing of miscible and immiscible materials of different densities is proposed. The idea of the approach is to separate the states of homogeneous mixtures from heterogeneous ones, consisting of fragments with interfaces, in mixed cells containing mixing substances. This article describes a 2D technique developed in the Euler gas dynamics with concentrations (EGAK) code to realize the approach described above. The method is verified using a classical problem of turbulent mixing arising due to the Rayleigh–Taylor instability at the constant acceleration of the interface between two gases of different densities.

摘要 针对不同密度的可混合物和不可混合物的湍流混合,提出了一种直接数值建模(DNM)的新方法。该方法的思路是在包含混合物质的混合单元中,将均相混合物状态与由带界面的碎片组成的异相混合物状态分开。本文介绍了为实现上述方法而在带浓度的欧拉气体动力学(EGAK)代码中开发的二维技术。该方法使用了一个经典的湍流混合问题进行验证,该问题是由于两种不同密度气体之间的界面恒定加速度处的瑞利-泰勒不稳定性引起的。
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引用次数: 0
Optimally Controlled Turbulent Boundary Layers in Supersonic Gas Flows 超音速气体流动中的优化控制湍流边界层
Q3 Mathematics Pub Date : 2023-12-26 DOI: 10.1134/s2070048223070049
K. G. Garaev, I. R. Mukhametzyanov

Abstract

A variational problem for a conditional extremum of the Mayer type on the construction of the distribution law of the normal component of the velocity of injection of a cooled gas into a turbulent boundary layer under a supersonic flow regime that provides the minimum value of the convective heat flux transmitted from the hot gas to the streamlined surface is considered. The isoperimetric condition is the power of the injection control system, calculated taking into account Darcy’s filtration law. To solve the optimal problem, we use the first integral for the conjugate system with respect to Lagrange multipliers, obtained earlier by the authors using the classical theorem of E. Noether on invariant variational problems and the Lie-Ovsyannikov infinitesimal apparatus. A.A. Dorodnitsyn’s method of generalized integral relations, which has proven itself well in calculating the characteristics of boundary layers under various flow regimes, is used for the calculations. A computational experiment conducted for the case of a flow around a sphere shows the effectiveness of the optimal control law found in comparison with a uniform injection: the gain in the value of the minimized functional is 16.8%. The novelty of the study lies in the development of a method for solving the variational problem using the first integral for the conjugate system, as well as the Dorodnitsyn’s method of generalized integral relations. The scientific significance of the study lies in the development of the theory of an optimally controlled boundary layer under a turbulent flow regime in supersonic gas flows. The results obtained may be of interest in the design of systems for the active thermal protection of surfaces in high-velocity gas flows.

摘要 研究了在超音速流动状态下,冷却气体注入湍流边界层的速度法向分量分布规律的构建问题,该问题是一个梅耶型条件极值的变分问题,它提供了从热气体传输到流线型表面的对流热通量的最小值。等周条件是喷射控制系统的功率,计算时考虑了达西过滤定律。为了解决最优问题,我们使用了共轭系统关于拉格朗日乘法器的第一积分,这是作者早先利用 E. Noether 关于不变变异问题的经典定理和 Lie-Ovsyannikov 无穷小装置获得的。计算中使用了 A.A. Dorodnitsyn 的广义积分关系方法,该方法在计算各种流动状态下的边界层特性时证明了自己的优越性。对球体周围的流动进行的计算实验表明,与均匀注入法相比,所发现的最佳控制法非常有效:最小化函数值的增益为 16.8%。该研究的新颖之处在于开发了一种利用共轭体系的第一积分以及多罗尼琴的广义积分关系法来解决变分问题的方法。这项研究的科学意义在于发展了超音速气体流动中湍流状态下的最佳控制边界层理论。获得的结果可能对高速气流中表面主动热保护系统的设计有意义。
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引用次数: 0
Modeling the Nearest Neighbor Graphs to Estimate the Probability of the Independence of Data 建立近邻图模型以估算数据独立性的概率
Q3 Mathematics Pub Date : 2023-12-26 DOI: 10.1134/s2070048223070086
A. A. Kislitsyn

Abstract

The proposed method is based on calculations of the statistics of the nearest neighbor graph (NNG) structures, which are presented as a benchmark of the probabilities of the distribution of graphs by the number of disconnected fragments. The deviation of the actually observed occurrence of connectivity from the calculated one will allow us to determine the probability that this sample can be considered a set of statistically independent variables. The statements about the independence of the NNG statistics from the distribution of distances and from the triangle inequality are proved, which allows the numerical modeling of such structures. Estimates of the accuracy of the calculated statistics for graphs and their comparison with estimates obtained by modeling random coordinates of points in d-dimensional space are carried out. It is shown that the model of the NNGs without taking into account the dimension of the space leads to fairly accurate estimates of the statistics of graph structures in spaces of dimensionality higher than five. For spaces of smaller dimensionality, the benchmark can be obtained by directly calculating the distances between points with random coordinates in a unit cube. The proposed method is applied to the problem of analyzing the level of unsteadiness of the earthquake catalog in the Kuril–Kamchatka region. The lengths of samples of time intervals between neighboring events are analyzed. It is shown that the analyzed system as a whole is interconnected with a probability of 0.91, and this dependence is fundamentally different from the lag correlation between the sample elements.

摘要 本文提出的方法基于对近邻图(NNG)结构统计量的计算,并将其作为按断开片段数量计算图分布概率的基准。根据实际观测到的连通性与计算结果的偏差,我们可以确定该样本被视为一组统计上独立变量的概率。我们证明了 NNG 统计量与距离分布和三角形不等式的独立性,从而可以对此类结构进行数值建模。对图形计算统计量的准确性进行了估算,并将其与 d 维空间中点的随机坐标建模所获得的估算值进行了比较。结果表明,在不考虑空间维度的情况下,NNG 模型可以对维度大于 5 的空间中的图形结构的统计量进行相当精确的估计。对于维度较小的空间,可以通过直接计算单位立方体中随机坐标点之间的距离来获得基准。所提出的方法被应用于分析千岛-堪察加地区地震目录的不稳定性程度。对相邻事件之间的时间间隔样本长度进行了分析。结果表明,所分析的系统作为一个整体以 0.91 的概率相互关联,这种依赖性与样本元素之间的滞后相关性有着本质区别。
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引用次数: 0
Application of the Local Discontinuous Galerkin Method to the Solution of the Quasi-Gas Dynamic System of Equations 应用局部非连续伽勒金方法求解准气体动态方程组
Q3 Mathematics Pub Date : 2023-12-26 DOI: 10.1134/s207004822307013x
E. V. Shilnikov, I. R. Khaytaliev

Abstract

The solution of a quasi-gas dynamic (QGD) system of equations using the local discontinuous Galerkin method (LDG) is considered. One-dimensional Riemann discontinuity problems with known exact solutions are solved. Strong discontinuities are present in the solutions of the problems. Therefore, to ensure the monotonicity of the solution obtained by the LDG method, the so-called slope limiters, or limiters, are introduced. A “moment” limiter is chosen that preserves as high an order as possible. The limiter is modified to smooth the oscillations in the areas where the solution is constant.

摘要 研究了利用局部不连续伽勒金方法(LDG)求解准气体动力学(QGD)方程组的问题。求解了已知精确解的一维黎曼不连续问题。问题的解中存在强不连续性。因此,为了确保 LDG 方法求解的单调性,引入了所谓的斜率限制器或限制器。我们选择了一个 "矩 "限制器,以尽可能保留高阶。对限制器进行修改,以平滑解恒定区域的振荡。
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引用次数: 0
Modeling the Elastic-Diffusion Vibrations of a Hinged Timoshenko Plate under the Action of a Distributed Surface Load 铰链式季莫申科板在分布式表面载荷作用下的弹性-扩散振动建模
Q3 Mathematics Pub Date : 2023-12-26 DOI: 10.1134/s2070048223070050
N. V. Grigorevskiy, A. V. Zemskov, A. V. Malashkin

Abstract

We consider the unsteady problem of bending a homogeneous orthotropic hinged Timoshenko elastic-diffusion plate under the action of a mechanical load distributed over the surface. The initial mathematical formulation of the problem includes the system of elastic-diffusion equations for a continuum, which takes into account the finite propagation velocity of diffusion perturbations. The equations of unsteady elastic-diffusion vibrations of the plate are obtained from the equations for a continuum using the generalized principle of virtual displacements and hypotheses of Timoshenko’s theory. The solution is sought using the Laplace transform and expansion into Fourier series. The originals are found analytically using residues and tables of operational calculus.

摘要 我们考虑了在分布于表面的机械载荷作用下均质正交铰链季莫申科弹性扩散板弯曲的非稳态问题。问题的初始数学公式包括连续体的弹性扩散方程系统,其中考虑了扩散扰动的有限传播速度。利用虚拟位移的广义原理和季莫申科理论的假设,从连续体方程求得板的非稳态弹性扩散振动方程。利用拉普拉斯变换和傅里叶级数展开求解。利用运算微积分的残差和表格分析求得原点。
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引用次数: 0
Numerical Simulation of Dynamic Processes in the Medium of Fine-Grained Solid Particles 细粒固体颗粒介质中动态过程的数值模拟
Q3 Mathematics Pub Date : 2023-12-26 DOI: 10.1134/s2070048223070128
M. Y. Nemtsev

Abstract

A mathematical model and numerical method for solving problems of the flow of two-phase mixtures of gas and fine solid particles are considered. The particles are assumed to be absolutely rigid, incompressible, and nondeformable. As the initial model, the continuum model of R.I. Nigmatulin is considered. The model has two drawbacks: it is not strictly hyperbolic (i.e., it degenerates into an elliptical one under certain flow regimes) and has a nonconservative form, which makes it difficult to solve numerically. This paper proposes a method for regularizing Nigmatulin’s model at a discrete level, which makes it possible to eliminate these shortcomings and develop a numerical model that is well-conditioned for evolutionary problems of the flow of gas-dispersed mixtures with nondeformable solid particles. The regularization method is based on splitting the original system into two subsystems, each of which is strictly hyperbolic and has a conservative form. Difference schemes of the Godunov type are developed for the numerical solution of these subsystems. Testing of the proposed model and implemented methods includes checking the preservation of a homogeneous solution and the formation of shock waves and rarefaction waves in a gas, as well as compaction and decompaction waves in the particle phase. The results of the numerical simulation of the interaction of a shock wave in a gas with a near-wall layer of particles are also presented.

摘要 研究了解决气体和细小固体颗粒两相混合物流动问题的数学模型和数值方法。假设颗粒是绝对刚性、不可压缩和不可变形的。作为初始模型,考虑了 R.I. Nigmatulin 的连续模型。该模型有两个缺点:它不是严格的双曲模型(即在某些流动状态下会退化为椭圆模型),而且具有非守恒形式,因此难以进行数值求解。本文提出了一种在离散水平上对 Nigmatulin 模型进行正则化的方法,从而有可能消除这些缺点,并为含有不可变形固体颗粒的气体分散混合物的流动演化问题建立一个条件良好的数值模型。正则化方法的基础是将原始系统拆分为两个子系统,每个子系统都是严格双曲的,并具有保守形式。为这些子系统的数值求解开发了戈杜诺夫类型的差分方案。对提出的模型和实施的方法进行的测试包括检查均匀解的保持情况、气体中冲击波和稀释波的形成情况,以及粒子相中压实波和解压实波的形成情况。此外,还介绍了气体中冲击波与近壁颗粒层相互作用的数值模拟结果。
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引用次数: 0
BlackOilFoam: Modelling Multiphase Flow from Laboratory Cells to Unconventional Reservoirs 黑油泡沫:从实验室细胞到非常规储层的多相流建模
Q3 Mathematics Pub Date : 2023-12-01 DOI: 10.1134/s2070048223070141
Soledad Fioroni, A. Larreteguy, G. Savioli
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引用次数: 0
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