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A Space-Time Conservative Method for Hyperbolic Systems with Stiff and Non Stiff Source Terms

Communications in Computational Physics 2006年第3期1卷 449-478页

作者： shamsul qamar Gerald Warnecke Institute for Analysis and Numerics Otto-von-Guericke UniversityPSF 4120D-39106 MagdeburgGermany

In this article we propose a higher-order space-time conservative method for hyperbolic systems with stiff and non stiff source terms as well as relaxation systems.We call the scheme a slope propagation(SP)method.It is an extension of our scheme derived for homogeneous hyperbolic systems[1].In the present inhomogeneous systems the relaxation time may vary from order of one to a very small value.These small values make the relaxation term stronger and highly stiff.In such situations underresolved numerical schemes may produce spurious numerical results.However,our present scheme has the capability to correctly capture the behavior of the physical phenomena with high order accuracy even if the initial layer and the small relaxation time are not numerically resolved.The scheme treats the space and time in a unified manner.The flow variables and their slopes are the basic unknowns in the scheme.The source term is treated by its volumetric integration over the space-time control volume and is a direct part of the overall space-time flux balance.We use two approaches for the slope calculations of the flow variables,the first one results directly from the flux balance over the control volumes,while in the second one we use a finite difference approach.The main features of the scheme are its simplicity,its Jacobian-free and Riemann solver-free recipe,as well as its efficiency and high of order accuracy.In particular we show that the scheme has a discrete analog of the continuous asymptotic limit.We have implemented our scheme for various test models available in the literature such as the Broadwell model,the extended thermodynamics equations,the shallow water equations,traffic flow and the Euler equations with heat transfer.The numerical results validate the accuracy,versatility and robustness of the present scheme.

关键词： Hyperbolic systems with relaxation stiff systems space-time conservative and Jacobian-free method high order accuracy discontinuous solutions

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The Space-Time CE/SE Method for Solving Reduced Two-Fluid Flow Model

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Communications in Computational Physics 2012年第9期12卷 1070-1095页

作者： shamsul qamar Munshoor Ahmed Ishtiaq Ali Department of Mathematics COMSATS Institute of Information TechnologyPark RoadChak Shahzad IslamabadPakistan Max Planck Institute for Dynamics of Complex Technical Systems Sandtorstr.139106 MagdeburgGermany

The space-time conservation element and solution element(CE/SE)method is proposed for solving a conservative interface-capturing reducedmodel of compressible two-fluid flows.The flow equations are the bulk equations,combined with mass and energy equations for one of the two fluids.The latter equation contains a source term for accounting the energy exchange.The one and two-dimensional flow models are numerically investigated in this manuscript.The CE/SE method is capable to accurately capture the sharp propagating wavefronts of the fluids without excessive numerical diffusion or spurious oscillations.In contrast to the existing upwind finite volume schemes,the Riemann solver and reconstruction procedure are not the building block of the suggested method.The method differs from the previous techniques because of global and local flux conservation in a space-time domain without resorting to interpolation or extrapolation.In order to reveal the efficiency and performance of the approach,several numerical test cases are presented.For validation,the results of the current method are compared with other finite volume schemes.

关键词： Reduced model space-time CE/SE method central schemes conservation laws hyperbolic systems shock solutions

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用时空CE/SE方法求解微溶一维间歇结晶模型(英文)

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Chinese Journal of Chemical Engineering 2015年第2期23卷 337-341页

作者： Saima Noor shamsul qamar Department of Mathematics COMSATS Institute of Information Technology

This article is concerned with the numerical investigation of one-dimensional population balance models for batch crystallization process with fines dissolution.In batch crystallization,dissolution of smaller unwanted nuclei below some critical size is of vital importance as it improves the quality of product.The crystal growth rates for both size-independent and size-dependent cases are considered.A delay in recycle pipe is also included in the model.The space–time conservation element and solution element method,originally derived for non-reacting flows,is used to solve the model.This scheme has already been applied to a range of PDEs,mainly in the area of fluid mechanics.The numerical results are compared with those obtained from the Koren scheme,showing that the proposed scheme is more efficient.

关键词：间歇结晶平衡模型一维空时求解晶体生长速率临界尺寸数值结果

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Application of the Method of Characteristics to Population Balance Models Considering Growth and Nucleation Phenomena

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Applied Mathematics 2014年第13期5卷 1853-1862页

作者： Shahzadi Mubeen ur Rehman shamsul qamar Department of Mathematics COMSATS Institute of Information Technology Islamabad Pakistan

The population balance modeling is regarded as a universally accepted mathematical framework for dynamic simulation of various particulate processes, such as crystallization, granulation and polymerization. This article is concerned with the application of the method of characteristics (MOC) for solving population balance models describing batch crystallization process. The growth and nucleation are considered as dominant phenomena, while the breakage and aggregation are neglected. The numerical solutions of such PBEs require high order accuracy due to the occurrence of steep moving fronts and narrow peaks in the solutions. The MOC has been found to be a very effective technique for resolving sharp discontinuities. Different case studies are carried out to analyze the accuracy of proposed algorithm. For validation, the results of MOC are compared with the available analytical solutions and the results of finite volume schemes. The results of MOC were found to be in good agreement with analytical solutions and superior than those obtained by finite volume schemes.

关键词： Population Balance Modeling Batch Crystallization Method of Characteristics Nucleation and Growth

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A Gas-Kinetic Scheme for Six-Equation Two-Phase Flow Model

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Applied Mathematics 2014年第3期5卷 453-465页

作者： Saqib Zia Munshoor Ahmed shamsul qamar Department of Mathematics COMSATS Institute of Information Technology Islamabad Pakistan

A kinetic flux-vector splitting (KFVS) scheme is applied for solving a reduced six-equation two-phase flow model of Saurel et al. [1]. The model incorporates single velocity, two pressures and relaxation terms. An additional seventh equation, describing the total mixture energy, is added to the model to guarantee the correct treatment of shocks in the single phase limit. Some salient features of the model are that it is hyperbolic with only three wave propagation speeds and the volume fraction remains positive. The proposed numerical scheme is based on the direct splitting of macroscopic flux functions of the system of equations. The second order accuracy of the scheme is achieved by using MUSCL-type initial reconstruction and Runge-Kutta time stepping method. Moreover, a pressure relaxation procedure is used to fulfill the interface conditions. For validation, the results of suggested scheme are compared with those from the high resolution central upwind and HLLC schemes. The central upwind scheme is also applied for the first time to this model. The accuracy, efficiency and simplicity of the KFVS scheme demonstrate its potential for modeling two-phase flows.

关键词： Six-Equation Model Kinetic Flux-Vector Splitting Scheme Central Upwind Scheme Non-Conservative System Shock Solution

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High Order Central Schemes Applied to Relativistic Multi-Component Flow Models

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Applied Mathematics 2014年第8期5卷 1169-1186页

作者： Tayabia Ghaffar Muhammad Yousaf Saira Sultan shamsul qamar Department of Mathematics COMSATS Institute of Information Technology Islamabad Pakistan Department of Mathematics Quaid-i-Azam University Islamabad Pakistan

The dynamics of inviscid multi-component relativistic fluids may be modeled by the relativistic Euler equations, augmented by one (or more) additional species equation(s). We use the high-resolution staggered central schemes to solve these equations. The equilibrium states for each component are coupled in space and time to have a common temperature and velocity. The current schemes can handle strong shocks and the oscillations near the interfaces are negligible, which usually happens in the multi-component flows. The schemes also guarantee the exact mass conservation for each component, the exact conservation of total momentum, and energy in the whole particle system. The central schemes are robust, reliable, compact and easy to implement. Several one- and two-dimensional numerical test cases are included in this paper, which validate the application of these schemes to relativistic multi-component flows.

关键词： Multi-Component Flows Relativistic Euler Equations Central Schemes Higher Order Accuracy

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Central Upwind Scheme for Solving Multivariate Cell Population Balance Models

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Applied Mathematics 2014年第8期5卷 1187-1201页

作者： Shahzadi Mubeen ur Rehman Nadia Kiran shamsul qamar Department of Mathematics COMSATS Institute of Information Technology Islamabad Pakistan

Microbial cultures are comprised of heterogeneous cells that differ according to their size and intracellular concentrations of DNA, proteins and other constituents. Because of the included level of details, multi-variable cell population balance models (PBMs) offer the most general way to describe the complicated phenomena associated with cell growth, substrate consumption and product formation. For that reason, solving and understanding of such models are essential to predict and control cell growth in the processes of biotechnological interest. Such models typically consist of a partial integro-differential equation for describing cell growth and an ordinary integro-differential equation for representing substrate consumption. However, the involved mathematical complexities make their numerical solutions challenging for the given numerical scheme. In this article, the central upwind scheme is applied to solve the single-variate and bivariate cell population balance models considering equal and unequal partitioning of cellular materials. The validity of the developed algorithms is verified through several case studies. It was found that the suggested scheme is more reliable and effective.

关键词： Cell Population Balance Cell Growth Substrate Consumption Central Upwind Scheme Equal and Unequal Partitioning of Cells

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