scholarly journals Particle method of characteristics (PMOC) for unsteady pipe flow

2012 ◽  
Vol 15 (3) ◽  
pp. 780-797 ◽  
Author(s):  
Yao-Hsin Hwang ◽  
Ho-Shuenn Huang ◽  
Nien-Mien Chung ◽  
Pai-Yi Wang
Keyword(s):  
Method Of Characteristics ◽  
Particle Method ◽  
Benchmark Problems ◽  
Present Formulation ◽  
Transient Effects ◽  
Piezometric Head ◽  
Transient Phenomena ◽  
Pipe Flows ◽  
Characteristic Lines ◽  
The Right

A novel particle method of characteristics (PMOC) to simulate unsteady pipe flows is introduced and validated in the present study. Contrary to the conventional method of characteristics (MOC), the present formulation is built by reallocating the computational nodes along the characteristic lines. Both the right- and left-running characteristics are accurately traced and imitated with their associated computational particles. The annoying numerical inconveniences in the fixed-grid arrangement due to incompatible Courant–Friedrichs–Lewy (CFL) condition by repeating solution interpolations is effectively eliminated. Special particles with dual states satisfying the Rankine–Hugoniot relations are deliberately imposed to emulate the shock structure. Efficacy of this formulation is verified by solving some benchmark problems with significant transient effects in pipe flows. Computational results of piezometric head and flow velocity are meticulously compared with available analytical solutions. It is concluded that the proposed PMOC will be a useful tool to replicate transient phenomena in pipe flows.

Broadband Combustion Noise Prediction With the Fast Random Particle Method

2014 ◽  
Author(s):  
Felix Grimm ◽  
Roland Ewert ◽  
Jürgen Dierke ◽  
Berthold Noll ◽  
Manfred Aigner
Keyword(s):  
Scaling Law ◽  
Particle Method ◽  
Reconstruction Algorithm ◽  
Combustion Noise ◽  
Frequency Noise ◽  
Noise Prediction ◽  
Data Set ◽  
Jet Flame ◽  
The Right ◽  
Random Particle

A new highly efficient, hybrid CFD/CAA approach for broadband combustion noise modeling is introduced. The inherent sound source generation mechanism is based on turbulent flow field statistics, which are determined from reacting RANS calculations. The generated sources form the right-hand side of the linearized Euler equations for the calculation of sound fields. The stochastic time-domain source reconstruction algorithm is briefly described with emphasis on two different ways of spatial discretization, RPM (Random Particle Method) and the newly developed FRPM (Fast RPM). The application of mainly the latter technique to combustion noise (CN) prediction and several methodical progressions are presented in the paper. (F)RPM-CN is verified in terms of its ability to accurately reproduce prescribed turbulence-induced one- and two-point statistics for a generic test and the DLR-A jet flame validation case. Former works on RPM-CN have been revised and as a consequence methodical improvements are introduced along with the progression to FRPM-CN: A canonical CAA setup for the applications DLR-A, -B and H3 flame is used. Furthermore, a second order Langevin decorrelation model is introduced for FRPM-CN, to avoid spurious high frequency noise. A new calibration parameter set for reacting jet noise prediction with (F)RPM-CN is proposed. The analysis shows the universality of the data set for 2D jet flame applications and furthermore the method’s accountance for Reynolds scalability. In this context, a Mach number scaling law is used to conserve Strouhal similarity of the jet flame spectra. Finally, the numerical results are compared to suitable similarity spectra.

Influence of velocity head on filling transients in a branched pipeline

2018 ◽  
Vol 35 (7) ◽  
pp. 2502-2513 ◽  
Author(s):  
Ling Wang ◽  
Fujun Wang ◽  
Bryan William Karney ◽  
Ahmad Malekpour ◽  
Zhengwei Wang
Keyword(s):  
Method Of Characteristics ◽  
Energy Equation ◽  
Transient Flow ◽  
Numerical Results ◽  
Velocity Head ◽  
Piezometric Head ◽  
Content Type ◽  
High Point ◽  
Hydraulic Transient ◽  
Column Separation

Purpose The velocity head is usually neglected in the energy equation for a pipeline junction when one-dimensional (1D) hydraulic transient flow is solved by method of characteristics. The purpose of this paper is to investigate the effect of velocity head on filling transients in a branched pipeline by an energy equation considering velocity head. Design/methodology/approach An interface tracking method is used to locate the air–water interface during pipeline filling. The pressured pipe flow is solved by a method of characteristics. A discrete gas cavity model is included to permit the occurrence of column separation. A universal energy equation is built by considering the velocity head. The numerical method is provisionally verified in a series pipeline and the numerical results and experimental data accord well with each other. Findings The numerical results show that some differences in filling velocity and piezometric head occur in the branched pipeline. These differences arise because the velocity head in the energy equation can become an important contributor to the hydraulic response of the system. It is also confirmed that a local high point in the profile is apt to experience column separation during rapid filling. Significantly, the magnitude of overpressure and cavity volume induced by filling transients at the local high point is predicted to increase with the velocity in the pipes. Originality/value The velocity head in the energy equation for a pipeline junction could play an important role in the prediction of filling velocity, piezometric head and column separation phenomenon, which should be given more attention in 1D hydraulic transient analysis.

scholarly journals Performance Comparison of OpenMP, MPI, and MapReduce in Practical Problems

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Sol Ji Kang ◽  
Sang Yeon Lee ◽  
Keon Myung Lee
Keyword(s):  
Parallel Programming ◽  
Large Scale ◽  
Memory Systems ◽  
Performance Comparison ◽  
Benchmark Problems ◽  
Distributed Programming ◽  
Problem Size ◽  
Good Picture ◽  
Data Intensive ◽  
The Right

With problem size and complexity increasing, several parallel and distributed programming models and frameworks have been developed to efficiently handle such problems. This paper briefly reviews the parallel computing models and describes three widely recognized parallel programming frameworks: OpenMP, MPI, and MapReduce. OpenMP is the de facto standard for parallel programming on shared memory systems. MPI is the de facto industry standard for distributed memory systems. MapReduce framework has become the de facto standard for large scale data-intensive applications. Qualitative pros and cons of each framework are known, but quantitative performance indexes help get a good picture of which framework to use for the applications. As benchmark problems to compare those frameworks, two problems are chosen: all-pairs-shortest-path problem and data join problem. This paper presents the parallel programs for the problems implemented on the three frameworks, respectively. It shows the experiment results on a cluster of computers. It also discusses which is the right tool for the jobs by analyzing the characteristics and performance of the paradigms.

scholarly journals On the Quasi-monotone Modified Method of Characteristics for Transport-diffusion Problems with Reactive Sources

2001 ◽  
Vol 2 (2) ◽  
pp. 186-210 ◽  
Author(s):  
Mohammed Seaïd
Keyword(s):  
Method Of Characteristics ◽  
Explicit Scheme ◽  
Diffusion Reaction ◽  
Benchmark Problems ◽  
Modified Method ◽  
Nonlinear Reaction ◽  
Modified Method Of Characteristics ◽  
Transport Diffusion ◽  
Real Stability ◽  
Diffusion Problems

AbstractThis is an attempt to construct a strong numerical method for transportdiffusion equations with nonlinear reaction terms, which relies on the idea of the Modified Method of Characteristics that is explicit but stable and is second-order accurate in time. The method consists in convective-diffusive splitting of the equations along the characteristics. The convective stage of the splitting is straightforwardly treated by a quasi-monotone and conservative modified method of characteristics, while the diffusive-reactive stage can be approximated by an explicit scheme with an extended real stability interval. A numerical comparative study of the new method with Characteristics Crank-Nicholson and Classical Characteristics Runge-Kutta schemes, which are used in many transport-diffusion models, is carried out for several benchmark problems, whose solutions represent relevant transport-diffusion-reaction features. Experiments for transport-diffusion equations with linear and nonlinear reactive sources demonstrate the ability of our new algorithm to better maintain the shape of the solution in the presence of shocks and discontinuities.

scholarly journals Using Genetic Programming with Prior Formula Knowledge to Solve Symbolic Regression Problem

2016 ◽  
Vol 2016 ◽  
pp. 1-17 ◽  
Author(s):  
Qiang Lu ◽  
Jun Ren ◽  
Zhiguang Wang
Keyword(s):  
Experimental Data ◽  
Evolutionary Algorithms ◽  
Genetic Programming ◽  
Search Space ◽  
Research Field ◽  
Benchmark Problems ◽  
Regression Problem ◽  
Mathematical Expressions ◽  
The Right

A researcher can infer mathematical expressions of functions quickly by using his professional knowledge (called Prior Knowledge). But the results he finds may be biased and restricted to his research field due to limitation of his knowledge. In contrast, Genetic Programming method can discover fitted mathematical expressions from the huge search space through running evolutionary algorithms. And its results can be generalized to accommodate different fields of knowledge. However, sinceGPhas to search a huge space, its speed of finding the results is rather slow. Therefore, in this paper, a framework of connection between Prior Formula Knowledge andGP(PFK-GP) is proposed to reduce the space ofGPsearching. The PFK is built based on the Deep Belief Network (DBN) which can identify candidate formulas that are consistent with the features of experimental data. By using these candidate formulas as the seed of a randomly generated population,PFK-GPfinds the right formulas quickly by exploring the search space of data features. We have comparedPFK-GPwith ParetoGPon regression of eight benchmark problems. The experimental results confirm that thePFK-GPcan reduce the search space and obtain the significant improvement in the quality of SR.

Propagation of Continuum Damage in a Viscoelastic Ice Bar

1994 ◽  
Vol 116 (2) ◽  
pp. 109-113
Author(s):  
J. G. Shin ◽  
D. G. Karr
Keyword(s):  
Method Of Characteristics ◽  
Stable Solution ◽  
Continuum Damage ◽  
Governing Equations ◽  
Initial Value ◽  
Nonlinear Viscoelastic ◽  
Characteristic Lines ◽  
Polycrystalline Ice ◽  
Speed Of Propagation ◽  
The Continuum

An initial value problem of a semi-infinite nonlinear viscoelastic bar is solved with continuum damage evolution. The evolution law of the continuum damage for a viscoelastic material is used in order to explore the propagation of two crushing mechanisms: grain boundary cracking and transgranular cracking. Using the method of characteristics, the speed of propagation is found to be dependent on the continuum damage. On the wave front, the delayed elastic strain is zero, and only the continuum damage due to the transgranular cracking evolves. A finite difference method is developed to solve the governing equations on the obtained characteristic lines, and gives a stable solution of the propagation of the stress, strain, and damage. Numerical results are obtained and discussed using the material properties of polycrystalline ice.

UNIVERSALITY ASPECTS OF SELF-ORGANIZATION MODELS

Fractals ◽  
2004 ◽  
Vol 12 (03) ◽  
pp. 303-310 ◽  
Author(s):  
A. MALAKIS ◽  
F. K. DIAKONOS
Keyword(s):  
Order Parameter ◽  
Critical Density ◽  
Universality Class ◽  
Variable Density ◽  
Square Lattice ◽  
Sudden Increase ◽  
Transient Effects ◽  
Directed Flow ◽  
Universality Classes ◽  
The Right

A sandpile model on the square lattice with periodic boundary conditions is studied as a problem of variable density of grains per site. We define an order parameter and we show the existence of a critical density. This model is the closed version of the deterministic BTW model and belongs to the "Fixed Energy Sandpiles" class. An algorithm identifying the periodic states of the system permits us to have a good estimation of the order parameter, which is free from transient effects. The universality of the model with respect to two different forms of oriented flows is studied and compared with that of the isotropic flow. We find two universality classes characterized by different critical exponents. The Manhattan flow appears to belong to the same universality class as the isotropic flow. However, the directed flow gives a completely different critical behavior. The complexity of the model for densities larger than the critical is also studied. It is observed that, both the Manhattan model and the isotropic model have an interesting structure characterized by several plateaus. The right edges of these plateaus are characterized by a sudden increase of the order parameter, giving rise to new critical points. The directed flow model has a simple structure without plateaus.

Improving Zielke’s Method of Simulating Frequency-Dependent Friction in Laminar Liquid Pipe Flow

1991 ◽  
Vol 113 (4) ◽  
pp. 569-573 ◽  
Author(s):  
Katsumasa Suzuki ◽  
Takayuki Taketomi ◽  
Sanroku Sato
Keyword(s):  
Method Of Characteristics ◽  
Weighting Function ◽  
Block Diagram ◽  
Computation Time ◽  
Dimensionless Time ◽  
Frequency Dependent ◽  
Transient Phenomena ◽  
Computer Storage ◽  
Calculation Process ◽  
Visual Understanding

Zielke’s technique of using a method of characteristics to simulate transient phenomena of a liquid transmission line is accurate, easy to apply to complicated systems and therefore, frequently used. However, it requires a very large amount of computation time and computer storage to simulate frequency-dependent friction in a transient liquid flow. Searching for a way to counteract these disadvantages, the authors took note of the fact that the weighting function, which is the root of the above problems, is given by exponential functions or other functions depending on dimensionless time. In order to perform mathematically equivalent calculation without approximations, they have developed a new method which requires much less computation time and computer storage than Zielke’s method. The calculation process is shown by a block diagram to facilitate visual understanding of the method.

scholarly journals On new properties of heat, as exhibited in its propagation along plates of glass. By David Brewster, LL. D. F. R. S. Lond. and Edinb. In a letter addressed to the Right Hon. Sir Joseph Banks, Bart. G. C. B. P. R. S

1833 ◽  
Vol 2 ◽  
pp. 33-35
Keyword(s):  
Optical Properties ◽  
High Temperature ◽  
Transient Effects ◽  
The Subject ◽  
The Right

In a paper communicated to the Society in May 1814, Dr. Brewster observed that glass, when raised to a high temperature, had the property of depolarizing light, and in this respect resembled crystallized substances; but he did not at that time succeed in tracing a resemblance in other points, which he left for future investigation. On resuming this inquiry in the present paper, the subject is divided into two parts; in the former of which he describes the transient effects exhibited during the propagation of heat along plates of glass, whether received from adjacent bodies or communicated to them; and in the latter he describes the permanent optical properties produced in glass by being suddenly and partially cooled when red hot.

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