IndicatorCuboid2D : Need extra Explanation
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Hello,
New user of OpenLB here. I am trying to use galliumMelting2D example of OpenLB to simulate a problem of mine. I have read userguide till chapter 7 and I feel like, I should be able to write the a simple
program. I want to learn OpenLB in Depth if possible ( new c++ user as well).
In Gallium example a cuboid is defined like this: IndicatorCuboid2D<T> cuboid(extend, origin).`void prepareGeometry(SuperGeometry2D<T>& superGeometry,
ThermalUnitConverter<T, NSDESCRIPTOR, TDESCRIPTOR> const& converter)
{OstreamManager clout(std::cout,”prepareGeometry”);
clout << “Prepare Geometry …” << std::endl;superGeometry.rename(0,4); // turn geometry from out of geometry to constant pressure or outflow
std::vector<T> extend(2,T()); // create a vector and first element of it is lx and second
extend[0] = lx; // ly . Cuboid extends till here in x and y directions .
extend[1] = ly;
std::vector<T> origin(2,T()); //create origin vector. first element is physical
origin[0] = converter.getPhysLength(1); //length of a 1 lattice and second element is half of
origin[1] = 0.5* converter.getPhysLength(1); // it.
clout << “origin ” << origin[0] << “,” << origin[1] << std::endl; // I added these to see if I
clout << “extend ” << extend[0] << “,” << extend[1] << std::endl;// could make sense of origin if
IndicatorCuboid2D<T> cuboid2(extend, origin); // I saw the numbers.superGeometry.rename(4,1,cuboid2); // change the cells on cuboid2 from 4 to fluid.
‘
I did go and take a look at indicatorF2d.h file but I guess my lack of knowledge in c++ is the heart of the problem. I could not figure out what was going on in there.Second part : for my own problem I need to create a circle which I did with IndicatorCircle2D
and after I need to rename the cells ofc. Now for a bounce back boundary all around the circle:
1-Is there a specific method that I can use ?
2- What I wanted to do is create another circle indicator with a radios just one lattice smaller than
the original and subtract the smaller from main and rename the resulting indicator using the material numbers. (seems feasible based on the userguide)
3- (Should not be necessarily answered – trivial question) I do want to add a specific model to OpenLB . But based on a week long study, I feel like my c++ knowledge is lacking . Which one is better add it to OpenLB or just use Fortran and be done with it?Dear at8i,
in case you are not yet familiar with the C++ syntax standardly used in OpenLB, please have a look at introductory books/tutorials for C++ programming and our User Guide.
Then start with compiling, and running the most simplified examples (e.g. laminar, single-phase flows in simple geometries) offered in the latest OpenLB release.The Example section in the current User Guide should help you with understanding the purpose of each sample code (e.g.: geometry primitives, which are necessary for your code snippet above).
You could then identify the example which is most suitable as a basis for extension towards your own application and have a detailed look on that.Please note, that we unfortunately cannot debug your code within this forum, but we can however assist you in doing that by yourself.
In that sense, I’ll provide hints and try to answer your questions below.
– The .rename function is simply “renaming” the material numbers assigned to the voxels in your geometry, under (if any are specified) certain indicator constraints. These material numbers are then used as specifiers to be assigned with e.g. different boundary or initial conditions.
– Please use the doxygen documentation to double-check the arguments for renaming and indicator functions.
– First part (origin): Let me explain that via perceiving the 2D cuboid as a planar rectangle. The origin vector comprises the location of the lower left corner of the cuboid. The extend in turn is then the vector which is added to the origin to obtain the upper right corner of the cuboid. The center of the rectangle is then subsequently defined as “origin + 1/2 * extend”, and the angle theta is the rotation (counter-clockwise) which can addtionally be specified.
– Circular boundary: (1) Yes, please have a look at an example with a circular geometry. An incremental search in the olb folder for indicatorCircle2D / 3D should lead you to the specific sections. Copy or code along the syntax of your geometry and boundary conditions from that application after you made sure that it does what you want. (2) That should work, yes, however make sure to hit the nodes correctly with your indicator function (i.e. maybe you should consider a larger distance between the circles than one lattice unit or add a buffer distance e.g. half a lattice unit). (3) You can add multiphysics models in OpenLB in the same manner as the dynamics which are currently implemented. This of course requires knowledge in: C++, LBM for the actual model, and OpenLB in terms of code structure. From my point of view (I am not an expert in Fortran) realizing the same LB algorithm from scratch in Fortran should take you way longer than implementing it in OpenLB.Hopefully, I could help you a bit.
In case you have further questions, please let me know.BR
StephanDear Amir,
thanks for your reply.
Please continue posting in case you need further help with the implementation, and use the “CODE” macro in the text field to highlight the snippets you include.Your questions are absolutely not redundant, this is the right place to ask them.
We are always glad to help you with realizing your project.BR
StephanThis is an oversight in the documentation. Functor and indicator arithmetic use
std::shared_ptrsince version 1.3. See section 10.3.2 of the userguide for an introduction.Basically you can write any indicator as
`
std::shared_ptr<IndicatorF2D<T>> box1 = std::make_shared<IndicatorCuboid2D<T>>(extend1, origin1);
std::shared_ptr<IndicatorF2D<T>> box2 = std::make_shared<IndicatorCuboid2D<T>>(extend2, origin2);
auto unified_box = box1 + box2;
`and so on. This also works for functors.
Sure, fur functions that are not yet converted to using FunctorPtr arguments such as
renameyou can dereference the shared_ptr using the “*” operator:`
superGeometry.rename(4,1,*unified_box);
`Any external force has to be added manually in OpenLB using forced dynamics. So if you currently use e.g. a normal BGK collision you already model a “weightless” system.
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