A POD-Based Solver for the Advection-Diffusion Equation

2011 ◽  
Author(s):  
Elia Merzari ◽  
W. David Pointer ◽  
Paul Fischer
Keyword(s):  
Diffusion Equation ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Galerkin Projection ◽  
Test Problems ◽  
Simulation Code ◽  
Dimensional Flow ◽  
Advection Diffusion Equation ◽  
Advection Diffusion ◽  
Two Dimensional Flow

We present a methodology based on proper orthogonal decomposition (POD). We have implemented the POD-based solver in the large eddy simulation code Nek5000 and used it to solve the advection-diffusion equation for temperature in cases where buoyancy is not present. POD allows for the identification of the most energetic modes of turbulence when applied to a sufficient set of snapshots generated through Nek5000. The Navier-Stokes equations are then reduced to a set of ordinary differential equations by Galerkin projection. The flow field is reconstructed and used to advect the temperature on longer time scales and potentially coarser grids. The methodology is validated and tested on two problems: two-dimensional flow past a cylinder and three-dimensional flow in T-junctions. For the latter case, the benchmark chosen corresponds to the experiments of Hirota et al., who performed particle image velocimetry on the flow in a counterflow T-junction. In both test problems the dynamics of the reduced-order model reproduce well the history of the projected modes when a sufficient number of equations are considered. The dynamics of flow evolution and the interaction of different modes are also studied in detail for the T-junction.

scholarly journals NUMERICAL MODEL OF 3D MORPHODYNAMIC AFTER OFFSHORE NOURISHMENT

2011 ◽  
Vol 1 (32) ◽  
pp. 55 ◽  
Author(s):  
Masamitsu Kuroiwa ◽  
Yoko Shibutani ◽  
Yuhei Matsubara ◽  
Takayuki Kuchiishi ◽  
Mazen Abualtyef
Keyword(s):  
Numerical Model ◽  
Diffusion Equation ◽  
Suspended Sediment Concentration ◽  
Three Dimensional ◽  
Sediment Concentration ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Advection Diffusion Equation ◽  
Advection Diffusion ◽  
Sand Material

A three-dimensional model of morphodynamics after offshore nourishment was developed. In the presented model, the 3D beach evolution model that is not only after nourishment but also taking into account the nourishment process of injected sand material. In order to consider the injected process of sand, the computation using the advection-diffusion equation for suspended sediment concentration was adapted in the model. The presented model was applied to an idealized beach with two groins in order to investigate the performance of the model, and then, the model was applied to a field observation result for shoreface nourishment carried out at the Egmond aan Zee in the Netherlands. Finally, the applicability of the presented model was discussed from the computed results.

An Analytical Methodology to Air Pollution Modelling in Atmosphere

2019 ◽  
Vol 396 ◽  
pp. 91-98 ◽  
Author(s):  
Régis S. Quadros ◽  
Glênio A. Gonçalves ◽  
Daniela Buske ◽  
Guilherme J. Weymar
Keyword(s):  
Analytical Solution ◽  
Diffusion Equation ◽  
Separation Of Variables ◽  
Three Dimensional ◽  
Numerical Inversion ◽  
Analytical Methodology ◽  
Air Pollution Modelling ◽  
Advection Diffusion Equation ◽  
Advection Diffusion ◽  
Using Data

This work presents an analytical solution for the transient three-dimensional advection-diffusion equation to simulate the dispersion of pollutants in the atmosphere. The solution of the advection-diffusion equation is obtained analytically using a combination of the methods of separation of variables and GILTT. The main advantage is that the presented solution avoids a numerical inversion carried out in previous works of the literature, being by this way a totally analytical solution, less than a summation truncation. Initial numerical simulations and statistical comparisons using data from the Copenhagen experiment are presented and prove the good performance of the model.

Hybrid Hermite polynomial chaos SBP-SAT technique for stochastic advection-diffusion equations

2020 ◽  
Vol 31 (09) ◽  
pp. 2050128
Author(s):  
Navjot Kaur ◽  
Kavita Goyal
Keyword(s):  
Diffusion Equation ◽  
Hermite Polynomial ◽  
Polynomial Chaos ◽  
Real Life ◽  
Computational Effort ◽  
Dirichlet Boundary Conditions ◽  
Diffusion Equations ◽  
Test Problems ◽  
Advection Diffusion Equation ◽  
Advection Diffusion

The study of advection–diffusion equation has relatively became an active research topic in the field of uncertainty quantification (UQ) due to its numerous real life applications. In this paper, Hermite polynomial chaos is united with summation-by-parts (SBP) – simultaneous approximation terms (SATs) technique to solve the advection–diffusion equations with random Dirichlet boundary conditions (BCs). Polynomial chaos expansion (PCE) with Hermite basis is employed to separate the randomness, then SBP operators are used to approximate the differential operators and SATs are used to enforce BCs by ensuring the stability. For each chaos coefficient, time integration is performed using Runge–Kutta method of fourth order (RK4). Statistical moments namely mean and variance are computed using polynomial chaos coefficients without any extra computational effort. The method is applied on three test problems for validation. The first two test problems are stochastic advection equations on [Formula: see text] without any boundary and third problem is stochastic advection–diffusion equation on [0,2] with Dirichlet BCs. In case of third problem, we have obtained a range of permissible parameters for a stable numerical solution.

scholarly journals SOLUÇÃO DA EQUAÇÃO DE ADVECÇÃO-DIFUSÃO TRIDIMENSIONAL PELO MÉTODO GIADMT PARA DOIS TERMOS DE CONTRAGRADIENTE

2016 ◽  
Vol 38 ◽  
pp. 53
Author(s):  
Karine Rui ◽  
Camila Pinto da Costa
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Equation ◽  
Turbulent Flow ◽  
Turbulent Diffusion ◽  
Three Dimensional ◽  
Turbulent Diffusion Coefficient ◽  
Advection Diffusion Equation ◽  
Advection Diffusion

In this work, we present the resolution of the three-dimensional stationary advection-diffusion equation, through the GIADMT technique, considering the nonlocal closure for turbulent flow, using two different parameterization for the countergradient, one proposal by Cuijpers e Holtslag (1998) and another proposed by Roberti et al. (2004). The concentration of pollutants is estimated and compared with the observed data in Copenhagen experiment using different parameterization for the vertical turbulent diffusion coefficient.

A Comparison of Forces in Two- and Three-Dimensional Flow Past an Oscillating Cylinder

2015 ◽  
Author(s):  
Sofia Peppa ◽  
Lambros Kaiktsis ◽  
Christos Frouzakis ◽  
George Triantafyllou
Keyword(s):  
Stokes Equations ◽  
Oscillation Amplitude ◽  
Three Dimensional ◽  
Oscillation Mode ◽  
Transverse Oscillation ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Flow Past ◽  
Two Dimensional Flow

DNS results are presented for three-dimensional flow past a circular cylinder forced to oscillate both in the transverse and in-line direction with respect to a uniform stream, at Reynolds number equal to 400, and are compared against simulation results for two-dimensional flow. The cylinder follows a figure-eight motion, traversed either counter-clockwise or clockwise in the upper half-plane for a flow stream from left to right. The transverse oscillation frequency is equal to the natural frequency of the Kármán vortex street. The Navier-Stokes equations are solved using a spectral element code, and the forces acting on the cylinder are computed for both three- and two-dimensional flow. The results demonstrate that the effect of cylinder oscillation on the flow structure and forces differs substantially between the counter-clockwise and the clockwise oscillation mode. For the counter-clockwise mode, forcing at low amplitude decreases the flow three-dimensionality, with the wake becoming increasingly three-dimensional for transverse oscillation amplitudes higher than 0.25–0.30 cylinder diameters, with corresponding discrepancies in forces with respect to two-dimensional flow. For the case of clockwise mode, a strong stabilizing effect is found: the wake becomes two-dimensional for a transverse oscillation amplitude of 0.20 cylinder diameters, and remains so at higher amplitudes, resulting in nearly equal values of the force coefficients for three- and two-dimensional flow.

scholarly journals A hybrid method for solving time fractional advection–diffusion equation on unbounded space domain

2020 ◽  
Vol 2020 (1) ◽  
Author(s):  
H. Azin ◽  
F. Mohammadi ◽  
M. H. Heydari
Keyword(s):  
Diffusion Equation ◽  
Hybrid Method ◽  
Hybrid Approach ◽  
Test Problems ◽  
Legendre Functions ◽  
Space Domain ◽  
Advection Diffusion Equation ◽  
Advection Diffusion ◽  
Derivative Matrix ◽  
Cardinal Functions

Abstract In this article, a hybrid method is developed for solving the time fractional advection–diffusion equation on an unbounded space domain. More precisely, the Chebyshev cardinal functions are used to approximate the solution of the problem over a bounded time domain, and the modified Legendre functions are utilized to approximate the solution on an unbounded space domain with vanishing boundary conditions. The presented method converts solving this equation into solving a system of algebraic equations by employing the fractional derivative matrix of the Chebyshev cardinal functions and the classical derivative matrix of the modified Legendre functions together with the collocation technique. The accuracy of the presented hybrid approach is investigated on some test problems.

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