OpenLB – Open Source Lattice Boltzmann Code Forums on OpenLB General Topics Geometry – Example “MultiComponentXd”

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• #1827
ivan
Member

Hello, everybody,rnrnI am trying to change the geometry of the example “”MultiComponentXd”” and have been facing a couple problems, which are described below:

#2394
ivan
Member

Hello, everybody,rnrnInitially, I just wanted to change its length, for which I thought of editing the number of horizontal nodes nx.rnrn

Code:
[quote]// Parameters for the simulation setuprnconst int nx = 400;rnconst int ny = 200;rnconst int maxIter = 20000;[/quote]

rnrnOnce nx was changed from 400 to 30 I got a simulation in which the fluids don’t move, so I decided to analyse the material numbers to understand the reason of it. Above there is the original code and a few pictures for showing what I understood from it so far (which I assume is wrong).rnrn

Code:
[quote]rn // Sets material number for fluid and boundaryrn superGeometry.rename(0,1);rnrn std::vector<T> origin1(2,T());rn origin1[0] = -2.;rn origin1[1] = -2.;rn std::vector<T> origin2(2,T());rn origin2[0] = -2.;rn origin2[1] = ny/2.;rn std::vector<T> origin3(2,T());rn origin3[0] = -2.;rn origin3[1] = ny-1.;rnrn std::vector<T> extend1(2,T());rn extend1[0] = nx+3.;rn extend1[1] = 2.;rn std::vector<T> extend2(2,T());rn extend2[0] = nx+3.;rn extend2[1] = ny/2.+2.;rnrn IndicatorCuboid2D<T> bottom(extend1, origin1);rn IndicatorCuboid2D<T> upper(extend2, origin2);rn IndicatorCuboid2D<T> top(extend1, origin3);rnrn superGeometry.rename(1,2,upper);rn superGeometry.rename(1,3,bottom);rn superGeometry.rename(2,4,top);[/quote]

rnrnObservation: Instead of 400×200, I used 40×20 cells for the representation just to make it simpler, but I am still talking about the original dimensions. rnrnInitially, we have 40×20 nodes, represented by the yellow cells, which material numbers were renamed from 0 to 1rnrn[img]https://postimg.org/image/hlzuqgiip/[/img]rnrnIt was inserted a Cuboid called Bottom, represented by the orange cellsrnrn[img]https://postimg.org/image/lweim1nlt/[/img]rnrnThe Upper Cuboid was inserted and its represented by the green cellsrnrn[img]https://postimg.org/image/so4xowcld/[/img]rnrnThe Top Cuboid was inserted and its represented by the blue cellsrnrn[img]https://postimg.org/image/60poiqx1d/[/img]rnrnThe material numbers were changed according to the following imagesrnrn[img]https://postimg.org/image/md4bm80qp/[/img]rnrn[img]https://postimg.org/image/sfbycpp6p/[/img]rnrn[img]https://postimg.org/image/5rwp6k9mp/[/img]rnrnrnIf I understood correctly, changing nx from 400 to 30 would not change the interactions between the fluids/the simulation itself, since the horizontal dimension of the the cuboids are given in function of it (nx). Then why doesn’t it work?rnrnExtra questionsrnrnWhen a 400×200 nodes Lattice is set, what does it mean to have something like “”origin1[0]=-2″”? Does it mean this node is two nodes left distant the first one (which I assume is on the left bottom of the lattice)?rnrnIf so, why was used -2 instead of -1 or 0? And why nx+3 instead of nx-origin (in this example, nx+2)?Why do we need those extra nodes before and after the lattice which don not seem to be part of it?rnrnI hope I have made myself clear enough ( I assume there must be a couple mistakes with the vocabulary ) for you guys to understand my point.rnrnBest regards,rnrnIvanrnrnrn

#2338
mlm
Participant

Hello Ivan,rnrnThe SuperGeometry of the problem is the original geometry extended with an overlap of 2. So the cuboid with material number 1 is larger than you assume. Use a visualization software as for exampleparaview (www.paraview.com) and visualize the geometry to see the material numbers.rnIf you do so, you see, material numbers are set correctly for nx = 30. rnThere is no “”fluid flow”” as you call it, because of the physical properties of the problem. There are periodic boundary conditions and therefore depending of the length of nx, the periodicity keeps the solution kind of stationary.rnrn>>> When a 400×200 nodes Lattice is set, what does it mean to have something like “”origin1[0]=-2″”? Does it mean this node is two nodes left distant the first one (which I assume is on the left bottom of the lattice)?rnrnThis is because of the overlap (=2) set for the SuperGeometry generation. The given origin for the original CuboidGeometry is (0,0,1).rnrn>> If so, why was used -2 instead of -1 or 0? rnrnThe overlap is 2.rnrn>> And why nx+3 instead of nx-origin (in this example, nx+2)?Why do we need those extra nodes before and after the lattice which don not seem to be part of it?rnrnThe extend is added to the origin, therefore the complete length is nx=4.rnrnI hope I could help you! rnrnmlm

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