Palabos2.0原始基礎案例tutorial_1_5.cpp
文件位置:\palabos-v2.0r0\examples\tutorial\tutorial_1/tutorial_1_5.cpp
注:Just1ceOne同學的所有問題都標註在源代碼當中,答案寫在源代碼後面。
/* This file is part of the Palabos library.
*
* Copyright (C) 2011-2017 FlowKit Sarl
* Route d'Oron 2
* 1010 Lausanne, Switzerland
* E-mail contact: [email protected]
*
* The most recent release of Palabos can be downloaded at
* <http://www.palabos.org/>
*
* The library Palabos is free software: you can redistribute it and/or
* modify it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* The library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "palabos2D.h"
#include "palabos2D.hh"
#include <vector>
#include <iostream>
#include <iomanip>
/* Code 1.5 in the Palabos tutorial
*/
using namespace plb;
using namespace std;
typedef double T;
#define DESCRIPTOR plb::descriptors::D2Q9Descriptor
/// Velocity on the parabolic Poiseuille profile
T poiseuilleVelocity(plint iY, IncomprFlowParam<T> const& parameters) {
T y = (T)iY / parameters.getResolution();
return 4.*parameters.getLatticeU() * (y-y*y);
//////Q1:getLatticeU是讀取parameter中的哪一個值呀?
}
/// A functional, used to initialize the velocity for the boundary conditions
template<typename T>
class PoiseuilleVelocity {
public:
PoiseuilleVelocity(IncomprFlowParam<T> parameters_)
: parameters(parameters_)
{ }
/// This version of the operator returns the velocity only,
/// to instantiate the boundary condition.
void operator()(plint iX, plint iY, Array<T,2>& u) const {
u[0] = poiseuilleVelocity(iY, parameters);
u[1] = T();
///////Q2:這兩個運算符重載中u[1]是什麼意思呀?
}
/// This version of the operator returns also a constant value for
/// the density, to create the initial condition.
void operator()(plint iX, plint iY, T& rho, Array<T,2>& u) const {
u[0] = poiseuilleVelocity(iY, parameters);
u[1] = T();
rho = (T)1;
}
private:
IncomprFlowParam<T> parameters;
};
void channelSetup (
MultiBlockLattice2D<T,DESCRIPTOR>& lattice,
IncomprFlowParam<T> const& parameters,
OnLatticeBoundaryCondition2D<T,DESCRIPTOR>& boundaryCondition )
{
// Create Velocity boundary conditions.
boundaryCondition.setVelocityConditionOnBlockBoundaries(lattice);
// Specify the boundary velocity.
setBoundaryVelocity (
lattice, lattice.getBoundingBox(),
////////Q3:經常看到lattice中的getBoundingBox函數,它和另一個常出現getBounding分別是什麼意思呢?
PoiseuilleVelocity<T>(parameters) );
// Create the initial condition.
initializeAtEquilibrium (
lattice, lattice.getBoundingBox(), PoiseuilleVelocity<T>(parameters) );
lattice.initialize();
}
void writeGifs(MultiBlockLattice2D<T,DESCRIPTOR>& lattice, plint iter)
{
const plint imSize = 600;
ImageWriter<T> imageWriter("leeloo");
imageWriter.writeScaledGif(createFileName("u", iter, 6),
*computeVelocityNorm(lattice),
imSize, imSize );
/////////Q4:imSize是什麼用途呢?
}
int main(int argc, char* argv[]) {
plbInit(&argc, &argv);
global::directories().setOutputDir("./tmp/");
// Use the class IncomprFlowParam to convert from
// dimensionless variables to lattice units, in the
// context of incompressible flows.
IncomprFlowParam<T> parameters(
(T) 1e-2, // Reference velocity (the maximum velocity
///////Q5:parameter中的參數單位是什麼呢?存在實際尺寸與晶格的換算關係嗎?
//////////下面116行的imSave和maxT的單位是什麼呢?
// in the Poiseuille profile) in lattice units.
(T) 100., // Reynolds number
100, // Resolution of the reference length (channel height).
2., // Channel length in dimensionless variables
1. // Channel height in dimensionless variables
);
const T imSave = (T)0.1; // Time intervals at which to save GIF
// images, in dimensionless time units.
const T maxT = (T)3.1; // Total simulation time, in dimensionless
// time units.
writeLogFile(parameters, "Poiseuille flow");
/////Q6:這一行不是很明白,但經常看到類似代碼,求解......
MultiBlockLattice2D<T, DESCRIPTOR> lattice (
parameters.getNx(), parameters.getNy(),
new BGKdynamics<T,DESCRIPTOR>(parameters.getOmega()) );
OnLatticeBoundaryCondition2D<T,DESCRIPTOR>*
boundaryCondition = createLocalBoundaryCondition2D<T,DESCRIPTOR>();
channelSetup(lattice, parameters, *boundaryCondition);
// Main loop over time iterations.
for (plint iT=0; iT*parameters.getDeltaT()<maxT; ++iT) {
if (iT%parameters.nStep(imSave)==0 && iT>0) {
pcout << "Saving Gif at time step " << iT << endl;
writeGifs(lattice, iT);
}
// Execute lattice Boltzmann iteration.
lattice.collideAndStream();
}
delete boundaryCondition;
}
Q1:getLatticeU是讀取parameter中的哪一個值呀?
答:在本代碼中,parameter是IncomprFlowParam類的一個實例對象,用於統一配置不可壓縮流動相關參數,從而可以統一參數的調用,getLatticeU沒記錯的話應該就是取的其實就是格子速度,也就是你輸入的第一個參數值,這個類主要就是爲了統一調配參數,並不太涉及任何計算,實現目的主要是爲了統一代碼寫作,防止在需要改某一參數時滿篇找對應參數位置修改。在源代碼文件units.h文件中有這個類的明確定義,可以打開看一下,註釋寫的挺明白的。
Q2:這兩個運算符重載中u[1]是什麼意思呀?
答:u[1]=0,只不過按照規範這麼寫比較好,寫成T(),實際上就是0,u[0]對應x,u[1]對應y,就是配置好一個用來初始化速度密度的對象,在調用setBoundaryVelocity()當中使用函數指針作爲參數,函數指針的使用,主要是爲了可以重載一些函數,這個位置只要按格式即接口寫好相應的函數,就可以簡易的設置某些值,是數據處理器類的一個簡便使用方法。
Q3:經常看到lattice中的getBoundingBox函數,它和另一個常出現getBounding分別是什麼意思呢?
答:getBoundingBox()是獲得整個計算域的計算範圍,返回一個BoxXD對象,整個Palabos中並不存在getBounding對應的函數,你可能看錯了,或者和OpenLB混淆了。
Q4:imSize是什麼用途呢?
答:這個是圖像輸出的一個參數,好像是像素值,圖片輸出需要多少像素。具體請看源代碼包裏的io文件夾內的文件。
Q5:parameter中的參數單位是什麼呢?存在實際尺寸與晶格的換算關係嗎?下面的imSave和maxT的單位是什麼呢?
答:得到的是格子速度和對應參數,單位就是格子單位。imSave和maxT是用來控制文件輸出和總計算時間步的,imSave是多少步存一次圖片數據,maxT是總共計算多少時間步,沒有單位。
Q6:這一行不是很明白,但經常看到類似代碼,求解…writeLogFile(parameters, “Poiseuille flow”);
答:這個是配套的一套將輸入參數輸出爲固定格式log記錄文件的一個函數調用,配套IncomprFlowParam類而存在,同樣在units.h文件當中。