Changing Geometry

[ivan]

Hello, everybody,rnrnI’m quite new at OpenLB and I was gives the task of simulate a flow in a channel with a spheric obstacle. For this I thought about editing the bstep2d example, removing the step and adding the obstacle. Initially I just set the step dimensions as zero, so it was removed, and right now I am trying to figure out how I can add the obstacle itself. What I am supposed to change? Only the bstep2d.cpp code or any of the functions?rnrnAtt.

[mathias]

Hi,rnrnwe have an example cylinder2d that is very close to what you want. Please, have a look at it.rnrnBestrnMathias

[ivan]

Yes, thank you! That’s exactly what I was looking for. Still, is there any way I can also move the step in the “”bstep2d”” example and not only changing its dimensions?

[mathias]

Hi,rnrnYes, you can change it easily. Look at this line in the beginning of the exmape code:rnrn// Parameters for the simulation setuprnconst T lx1 = 5.0; // length of steprnconst T ly1 = 0.75; // height of steprnconst T lx0 = 20.0; // length of channelrnconst T ly0 = 1.5; // height of channel rnrnBest Mathias

[ivan]

Yes, I was able to change the dimensions of the step but I wanted to move it, to make is further from the channel inlet.

[ivan]

But right now I’m dealing with the cylinder2d example, in which I have to add more obstacles. Any tips of how to start it?

[robin.trunk]

Hi ivan,rnrnincreasing the value for lx1 inrnconst T lx1 = 5.0; // length of steprnshould move the step further from the inlet, or did you mean something else?rnrnFor the cylinder2d example it is possible to add more obstacles by creating more IndicatorCylinder2D objects. At line 84 of the example the existing obstacle is defined. You can add more round obstacles by insertingrnVector<T,2> center1(0.2,0.2); rnIndicatorCircle2D<T> circle(center1, 0.1);,rnjust change the values for the center and the radius (here 0.1). It is also possible to define rectangular obstacles byrnVector<T,2> center2(0.1,0.1); rnVector<T,2> extend1(0.2,0.14);rnIndicatorCuboid2D<T> cube(extend1,center2);.rnThis gives gives a cube 0.2 by 0.14. To apply the constructed obstacle for the simulation addrnsuperGeometry.rename(1,5,cube);rnas for the original obstacle in line 101 of the example. In this case the material numbers 1 will be set to 5 at every node occupied by the obstacle cube. The material numbers are used to assign e.g. boundary conditions to certain areas of the geometry. In cylinder2d everything with material number 5 is treated as obstacle.rnrnbestrnrobin

[ivan]

Oh, wow, that was really helpfull! Thank you very much for that, Robin!rnrnSo, basically I was able o insert some more obstacles ( for now Im only interested in the round ones, but I really appreciate your extra tips for the square ones as well ) but it seems like I’m missing something because I’m getting some ERROR messages regarding the boundary conditions. Let me get everything here:rnrnOn // Parameters for the simulation setup// I added:rnconst T secondcenterCylinderX = 0.2;rnconst T secondcenterCylinderY = 0.2+L/2;rnconst T secondradiusCylinder = 0.035;rnrnOn /// Stores geometry information in form of material numbers/// I added:rn Vector<T,2> secondcenter(secondcenterCylinderX,secondcenterCylinderY);rn IndicatorCircle2D<T> secondcircle(secondcenter, secondradiusCylinder);rnrnThen, on /// Set material number for cylinder/// I added:rnsuperGeometry.rename(1,5,secondcircle);rnrnAnd finally, on /// Material=5 –>bouzidi, which seems to be part of /// Setting of the boundary conditions, I added:rn Vector<T,2> secondcenter(secondcenterCylinderX,secondcenterCylinderY);rn IndicatorCircle2D<T> secondcircle(secondcenter, secondradiusCylinder);rnrn and after sLattice.defineDynamics(superGeometry, 5, &instances::getNoDynamics<T,DESCRIPTOR>()); I addedrn offBc.addZeroVelocityBoundary(superGeometry, 5, secondcircle);rnrnThen when running it I get a lot of those:rnrn[BoundaryConditionInstantiator2D] ERROR: no boundary found at (17,19) ~ (1.65,0.295), in direction 3rn[BoundaryConditionInstantiator2D] ERROR: no boundary found at (17,18) ~ (1.65,0.29), in direction 1rn[BoundaryConditionInstantiator2D] ERROR: no boundary found at (17,19) ~ (1.65,0.295), in direction 2rn[BoundaryConditionInstantiator2D] ERROR: no boundary found at (17,20) ~ (1.65,0.3), in direction 3rn[BoundaryConditionInstantiator2D] ERROR: no boundary found at (17,19) ~ (1.65,0.295), in direction 1rn[BoundaryConditionInstantiator2D] ERROR: no boundary found at (17,20) ~ (1.65,0.3), in direction 2rnrnBut still, it runs. What could it be?rnrn[ And by the way, I made versions with 2, 5 and 30 obstacles, and I get more repetitions of those ERROR messages the more obstacles I have ]rnrnAtt.rn

[robin.trunk]

Hi Ivan,rnrnit seems that some error checks for the Bouzidi boundary can’t handle multiple obstacles with the same material number. However, the later performed computations and the solution should not be affected by this. If you want to get rid of the error messages, you could assign a different material number to each object. I think that would be the fastest workaround.rnAlternatively you could try to construct an IndicatorF2D object from the circles, since for this object other functions are called, that maybe work better in the case of multiple objects.rnrnBestrnRobinrnrn

[ivan]

Thank you for that Robin, it really helped! 🙂

[LaurentDelaon]

Hi
when you do this :

Code:

IndicatorCircle2D<T> circle(center1, 0.1);

Is it possible (so far in the code ) to modify circle to ajust radius after it’s definition ?
like :

Code:

circle(center1, 0.5)

Is it possible to realise a change like this ?
Regards.

[mjk]

No, please see Dogygen or read directly our implementation and a basic c++ book for more information!

[LaurentDelaon]

hi thank’s for your response.
I have look at documentation but I have think that I can miss a specific move function.
I not expert in C++. I am just using the code to try to simulate air flow.
My objectives are not to rewrite your code but to use it as it…

Regards.

[Author]

Posts