检索结果-内蒙古大学图书馆

Calculation of the stationary flame propagation velocity by the variational principle of irreversible thermodynamics

引用

CASE STUDIES IN THERMAL ENGINEERING 2022年 30卷

作者： Karpov, Alexander, I Kudrin, Alexei, V Alies, Michael Y. Russian Acad Sci Udmurt Fed Res Ctr Ural Branch Izhevsk 426067 Russia

numerical algorithm for the prediction of the stationary flame propagation velocity over premixed gas mixture has been formulated by using the foundations of non-equilibrium thermodynamics. Considering the combustion as a set of irreversible processes, the steady-state regime of flame propagation is identified with the stationary state of the non-equilibrium thermodynamic system. The generalized form of functional has been stated allowing its minimization relatively to the sought stationary flame propagation velocity treated as additional variable. Based on this variational statement an integral relationship for the flame propagation velocity has been obtained. The calculations of the stationary flame propagation velocity over model premixed gas mixture performed by proposed algorithm showed a faster convergence at the initial steps of iteration process in comparison with the commonly used approach based on the mass conservation of combustion chemical traction. The combined algorithm has been formulated, which benefits from the proposed 'thermodynamic' approach at the initial steps and converges to final solution satisfying the general mass balance.

关键词： Flame propagation Stationary state numerical algorithm Variational principle Irreversible thermodynamics Entropy production

来源：评论

学校读者我要写书评

暂无评论

numerical Technologies for Investigating Optimal Control Problems with Free Right-Hand End of Trajectories 6th

Numerical Technologies for Investigating Optimal Control Pro...

引用

6th International Conference on Computer Science, Applied Mathematics and Applications (ICCSAMA)

作者： Zarodnyuk, Tatiana Gornov, Alexander Anikin, Anton Sorokovikov, Pavel Matrosov Inst Syst Dynam & Control Theory SB RAS Irkutsk Russia

ISBN: (纸本)9783030383640;9783030383633

The paper considers numerical approaches for solving optimal control problems with free trajectories at the end of the time interval. A modification of the algorithm of the conjugate gradient for studying the controlled dynamic problem is presented. The proposed technique has been tested by using the test optimal control problems. We describe the results of solving an applied problem of nanophysics. It is considered two cells of a quantum computer which are based on four tunnel-coupled semiconductor quantum dots. The multistage series of computations for investigation of system dependence from changes of the model parameters values are carried out and allowed to demonstrate the effectiveness of the proposed approach.

关键词： numerical algorithm Optimal control Applied problem

来源：评论

学校读者我要写书评

暂无评论

Time-scale investigation with the modified phase field crystal method

引用

MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING 2022年第6期30卷 064001-064001页

作者： Burns, Duncan Provatas, Nikolas Grant, Martin McGill Univ Dept Phys Montreal PQ H3A 2T8 Canada

This paper extends the two time-scale modified phase-field crystal model to examine crystal plasticity. Two non-linear density dependent functions are constructed to effectively represent hydrostatic strain and dislocation density. The functions are then used to develop a new modified phase field crystal model, which accounts for strain and strain-rate couplings on density dynamics. The non-linear additions provide tunable parameters for controlling dislocation climb versus glide, as well as phonon softening mechanisms. A short-wavelength dampening is also introduced to account for phonon scattering and thermoelastic dissipation processes. Finally, a novel semi-implicit numeric scheme for efficient simulations of this model is presented, which also serves as a generalization of the commonly used Fourier pseudo-spectral method. The technique gives rise to unconditionally stable dynamics with simple numeric implementation requirements.

关键词： plasticity phase field crystal strain strain-rate numerical algorithm dislocations

来源：评论

学校读者我要写书评

暂无评论

DIFFERENTIAL QUADRATURE METHOD FOR SOME DIFFUSION-REACTION PROBLEMS

引用

CHEMICAL AND PROCESS ENGINEERING-INZYNIERIA CHEMICZNA I PROCESOWA 2020年第1期41卷 3-11页

作者： Szukiewicz, Miroslaw K. Rzeszow Univ Technol Dept Chem & Proc Engn Al Powstancow Warszawy 6 PL-35959 Rzeszow Poland

In the paper, differential quadrature method (DQM) is used to find numerical solutions of reaction-diffusion equations with different boundary conditions. The DQM-method changes the reaction-diffusion equation (ordinary differential equation) into a system of algebraic equations. The obtained system is solved using built-in procedures of Maple (R)(Computer Algebra System-type program). Calculations were performed with Maple (R) program. The test problems include reaction-diffusion equation applied in heterogeneous catalysis. The method can be employed even in relatively hard tasks (e.g. ill-conditioned, free boundary problems).

关键词： numerical algorithm boundary value problem reaction-diffusion equation

来源：评论

学校读者我要写书评

暂无评论

A SIMPLE SCALAR DIRECTIONAL HARDENING MODEL FOR THE BAUSCHINGER EFFECT COMPARED WITH A TENSORIAL MODEL

引用

JOURNAL OF MECHANICS OF MATERIALS AND STRUCTURES 2020年第4期15卷 511-537页

作者： Kroon, Martin Rubin, M. B. Linnaeus Univ Dept Mech Engn Vaxjo Sweden Technion Israel Inst Technol Fac Mech Engn Haifa Israel

Modeling the Bauschinger effect is usually accomplished by introducing a second-order back-stress or directional hardening tensor. The objective of this paper is to propose a simpler scalar model of the Bauschinger effect based on a scalar directional hardening parameter that is determined by integration of an evolution equation. The behavior of this scalar model is compared to a tensorial model for a number of load cases. Strongly objective numerical algorithms are developed for integrating the evolution equations for both the tensorial and scalar models. Also, a consistent tangent is developed for both models. Obviously, the numerical implementation of the scalar model is significantly less complicated than for the tensorial model. Examples show that the tensorial and scalar models predict the same results for cyclic proportional triaxial extension and triaxial compression loadings. In contrast, the tensorial model predicts a Bauschinger effect for cyclic proportional pure torsion loading which is not predicted by the scalar model. More complicated examples with nonproportional loading paths and inhomogeneous deformations indicate that, relative to the tensorial model, the scalar model accounts for directional hardening fairly well and the simplicity of the model makes it an attractive option to add to isotropic hardening models.

关键词： Bauschinger effect finite deformation isotropic elastic-inelastic response numerical algorithm scalar directional hardening

来源：评论

学校读者我要写书评

暂无评论

Closed-Form Expressions for the Quantile Function of the Chi Square Distribution Using the Hybrid of Quantile Mechanics and Spline Interpolation

引用

WIRELESS PERSONAL COMMUNICATIONS 2020年第3期115卷 2093-2112页

作者： Okagbue, Hilary I. Adamu, Muminu O. Anake, Timothy A. Covenant Univ Dept Math Ota Nigeria Univ Lagos Dept Math Lagos Nigeria

Chi square distribution is a continuous probability distribution primarily used in hypothesis testing, contingency analysis, and construction of confidence limits in inferential statistics but not necessarily in the modeling of real-life phenomena. The closed-form expression for the quantile function (QF) of Chi square is not available because the cumulative distribution function cannot be transformed to yield the QF and consequently places limitations on the use of the QF. Researchers have over the years proposed approximations that improve over time in terms of speed, computational efficiency, and precision, and so on. However, most of the available closed-form expressions (quantile approximation) fail at the extreme tails of the distribution. This paper used the Quantile mechanics approach to obtain second-order nonlinear ordinary differential equations whose solutions using the power series method yielded initial approximates in form of series for different values of the degrees of freedom. The initial approximate varies with the exact (R software) values which serve as the reference and the error between them was minimized by the natural cubic spline interpolation. The final approximates are correct up to an average of 8 decimal places, have small error, and is closer to the exact when compared with some other results from other researchers. The upper tail of the distribution was considered and excellent results were obtained which is a major improvement over the existing results in the literature. The approach used in this work is a hybrid of series expansions and numerical algorithms. Computer codes can be written for the application.

关键词： Chi square Quantile function numerical algorithm Quantile mechanics Cubic spline Approximation

来源：评论

学校读者我要写书评

暂无评论

A Crank-Nicolson-type finite-difference scheme and its algorithm implementation for a nonlinear partial integro-differential equation arising from viscoelasticity

引用

COMPUTATIONAL & APPLIED MATHEMATICS 2020年第4期39卷 1-23页

作者： Zheng, Xuan Chen, Hongbin Qiu, Wenlin Cent South Univ Forestry & Technol Inst Math & Phys Coll Sci Changsha 410004 Hunan Peoples R China Hunan Normal Univ Key Lab Comp & Stochast Math Sch Math & Stat Minist Educ Changsha 410081 Hunan Peoples R China

A Crank-Nicolson-type finite-difference scheme is proposed and analyzed for a nonlinear partial integro-differential equation arising from viscoelasticity. The time derivative is approximated by the Crank-Nicolson scheme and the Riemann-Liouville fractional integral term is treated by means of the trapezoidal convolution quadrature rule. To construct a fully discrete difference scheme, the standard centered difference formula is utilized to approximate the second-order spatial derivative and the Galerkin method based on piecewise linear test functions is used to discrete the nonlinear convection term. Theoretical results of stability and convergence are derived using the non-negative character of the real quadratic form associated with the convolution quadrature, and combining with the discrete Gronwall inequality. Besides, a fixed point iterative numerical algorithm, which fills the gap that the existed numerical schemes have only theoretical analysis but no numerical results, is presented. numerical results show the efficiency and feasibility of our scheme, and the orders of convergence are in good agreement with the theoretical results.

关键词： Nonlinear partial integro-differential equation Crank-Nicolson-type finite-difference scheme Convolution quadrature Stability and convergence numerical algorithm numerical experiment

来源：评论

学校读者我要写书评

暂无评论

Sector bounds in stability analysis and control design

引用

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL 2020年第18期30卷 7857-7882页

作者： Xia, Meng Gahinet, Pascal Abroug, Neil Buhr, Craig Laroche, Edouard MathWorks Natick MA 01760 USA CEA LIST Gif Sur Yvette France Univ Strasbourg ICube Lab Illkirch Graffenstaden France

The sector stability theorem is an intuitive condition for the stability of feedback loops that unifies many lines of research including robust control and the theory of passive and dissipative systems. Applying this theorem typically requires checking or enforcing sector bounds on linear time-invariant systems. This article discusses practical and efficient numerical methods for performing these tasks. We derive a frequency-domain test for sector boundedness and use it to developO(n(3))numerical algorithms for computing the relative or directional indices of sector bounds. We also discuss how such algorithms can be combined with nonsmooth optimization techniques to enforce sector bounds while designing and tuning controllers. Several application examples illustrate the potential of these tools and techniques.

关键词： numerical algorithm passivity index sector bound

来源：评论

学校读者我要写书评

暂无评论

Cost minimization of real-time mission for software systems with rejuvenation

引用

RELIABILITY ENGINEERING & SYSTEM SAFETY 2020年 193卷 106593-000页

作者： Levitin, Gregory Xing, Liudong Xiang, Yanping Univ Elect Sci & Technol China Sch Comp Sci Collaborat Auton Comp Lab Chengdu Sichuan Peoples R China Israel Elect Corp Ltd POB 10 IL-31000 Haifa Israel Univ Elect Sci & Technol China Sch Mech & Elect Engn Chengdu Sichuan Peoples R China Univ Massachusetts Dartmouth MA 02747 USA

This paper considers the optimal rejuvenation policy problem for software systems performing real-time tasks. Due to software aging, the system performance deteriorates with time eventually leading to the system crash, which can be catastrophic for critical applications. To prevent the system crash or minimize its occurrence probability, software rejuvenation has been widely adopted for counteracting the software aging effect but at the cost of extra system overhead and downtime. We derive the optimal state-based rejuvenation policy minimizing the total expected mission cost for software aging systems subject to multiple performance degradation states. The solution encompasses an event transition-based numerical method that assesses the total expected mission cost of a real-time task, covering penalty cost from the mission failure, operation cost of running the mission software and the expected rejuvenation cost. The proposed cost evaluation model can accommodate arbitrary types of state transition time distributions. The suggested model also allows simultaneous evaluations of other system performance metrics including the probability of the successful task completion (i.e., mission reliability) and conditional expected mission completion time given a successful mission task. Examples are presented to demonstrate the proposed methodology and optimizations. Effects of different parameters on the rejuvenation optimization solution are also investigated.

关键词： Event transition Mission cost Mission reliability Optimization Real-time task Software aging Software rejuvenation numerical algorithm

来源：评论

学校读者我要写书评

暂无评论

Elliptical fibre dielectric waveguides: a transverse transmission line analysis

引用

IET OPTOELECTRONICS 2020年第1期14卷 1-9页

作者： Boucouvalas, Anthony C. Papageorgiou, Christos Georgantzos, Euripides Univ Peloponnese Dept Informat & Telecommun Arcadia 22100 Greece Natl Tech Univ Athens Dept Elect Engn Iroon Politech 9 Athens 16121 Greece

The authors present a new method for determining the optical properties of arbitrary refractive index elliptical core fibres. The method applies the elliptic cylindrical coordinate system to Maxwell's equations and appropriately, using Fourier Transforms, operated on an elliptical core optical fibre waveguide, derives a flexible algorithm, which can be used to determine the optical properties of elliptical fibre waveguides. By dividing the fibre into a series of uniform consecutive thin dielectric layers transversely across the elliptical cross section with suitable transforming functions representing voltage and current themselves based on the electromagnetic field components, leads to transverse transmission line equations. The resonance frequencies of the cascaded matrices determine the mode propagation constants. The analysis leads to a numerical algorithm for calculating the exact modes of propagation constants. The method is analytically exact and computationally accurate, leading to algorithmic implementation, without making use of Mathieu functions which are solutions for step index waveguide. The advantage of this work is also the fact that it can be applied to arbitrary refractive index profiles. They present results of modal $\bar b - V$b over bar -V diagrams for various fibre ellipticities and also apply this method to determine the birefringence of graded index profile fibres and mode cut-off frequencies.

关键词： Maxwell equations electromagnetic fields optical fibres gradient index optics dielectric waveguides birefringence refractive index uniform consecutive thin dielectric layers elliptical cross section suitable transforming functions transmission line equations mode propagation constants numerical algorithm algorithmic implementation step index waveguide arbitrary refractive index profiles fibre ellipticities graded index profile fibres elliptical fibre dielectric waveguides transverse transmission line analysis optical properties arbitrary refractive index elliptical core fibres elliptic cylindrical coordinate system Maxwell's equations Fourier Transforms elliptical core optical fibre waveguide flexible algorithm elliptical fibre waveguides

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：