New Particle Collision Model 0penLB 1.6
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Dear OpenLB community,
I have tried the new particle collision model but I failed in validating the model with experimental studies (Single spherical Particle-wall Collision). The snippet of the code:
// Discretization Settings
int res = 50;
T const charLatticeVelocity = 0.03;// Time Settings
T const maxPhysT = 0.45; // max. simulation time in s
T const iTwrite = 1E-3; // write out intervall in s// Domain Settings
T const lengthX = 0.11;
T const lengthY = 0.11;
T const lengthZ = 0.20;// Fluid Settings
T const physDensity = 1141.;
T const physViscosity = 0.008/1141.;//Particle Settings
T Radius = 10.0/1000.0;
T const SphereDensity = 2170.;
T const PositionX = 0.055;
T const Positiony = 0.055;
T const PositionZ = 0.16;Vector<T,3> SpherePosition = {PositionX,PositionX,PositionZ};
Vector<T,3> SphereVelocity = {0.,0.,0.};
Vector<T,3> externalAcceleration = {.0, .0, -9.81 * (1. – physDensity / SphereDensity)};// Characteristic Quantities
T const charPhysLength = lengthX;
T const charPhysVelocity = 0.66; // Assumed maximal velocityunsigned contactBoxResolutionPerDirection = 16;
unsigned particleContactMaterial = 0;
unsigned wallContactMaterial = 0;
T youngsModulus = 575e6;
T poissonRatio = 0.25;
T dampingConstant = 0.1;
T coefficientStaticFriction = 0.02;
T coefficientKineticFriction = 0.3;/// End of the code
The rest is similar to the settlingcube3D example. I do not see any rebound of the particle even if I increase the time step or the grid size. I read the published paper but I could not fix the issue. Any help here?
Regards,
Dear Jijo,
as stated in [1], it is necessary to enlarge the particle for the consideration of the contact. You can do this using
particle.setField<NUMERICPROPERTIES, ENLARGEMENT_FOR_CONTACT>( /* choose a value */ );. Otherwise it is to be expected that the incompressible fluid slows down the particle so that there is no contact with the wall, especially for high resolutions.Kind regards,
Jan[1]: 10.1016/j.partic.2022.12.005
Dear Jijo,
I agree, that part is advanced. Let me break it down:
1.solidBoundariesis an std::vector of solid boundaries (walls). In this case we only have one, but we can have as many as we like. This can be useful if the walls are made of different materials, or if we want to make sure that contacts in a corner or on an edge are detected separately.
2. In the call of thepush_backmethod, we create an instance of aSolidBoundaryand add it to the above mentioned vector.
3. TheSolidBoundaryis created from a unique pointer of anIndicatorF, alatticeMaterial, acontactMaterialand an optional enlargement solely for the contact treatment.With this in mind, it may be a little easier to understand. The last two entries are the material numbers. The
2is the one used on the lattice, e.g. inprepareLatticeto set the fluid boundary conditions. The second, thewallContactMaterial, is used to identify the wall properties during the contact treatment. As indicated above. Walls can be of different materials but you are likely to use the same boundary condition for the fluid interaction. Therefore thelatticeMaterialcould be the same but thecontactMaterialis different.The first parameter, which is probably the most complex looking one, is a simple unique pointer to an indicator that describes the geometry of the wall. Here we use the inverse of a cuboid, which describes the fluid domain. This means that the wall contains everything except the fluid. This is done by the first argument of
IndicInverse. The other two arguments take the new min and max values. If we didn’t set them manually and just used the min and max of the fluid, the wall would have a thickness of 0, which would probably cause problems with the distance calculations during the contact treatment.Kind regards,
JanDear Jijo,
I’m not sure what I’m seeing in the pictures. Are the particles passing through the wall or are they bouncing back off it?
If they are passing through it:
– Most likely the contact force is too low, perhaps because the Young’s modulus is too low.
– It could also be that the contact handling in your case is not configured correctly. To debug this, I suggest you check if contacts are detected in your case. If they are detected, then theparticleContactsorwallContactsof thecontactContainer(see https://www.openlb.net/DoxyGen/html/db/d56/structolb_1_1particles_1_1contact_1_1ContactContainer.html) should contain at least one object. You can add this check aftercoupleResolvedParticlesToLattice.If they bounce and you’re wondering about the artifact:
If the “automatic” porosity reset doesn’t work for you, you can try to reset the fields manually withresetSuperParticleField(see https://www.openlb.net/DoxyGen/html/da/d81/namespaceolb_1_1particles.html#a9f93e2392819fc95fc4dc52e282893e0) before writing the VTKs.Best regards,
Jan
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