Fluid velocity at defined point

[pk-guest]

Dear users,

how to get the fluid velocity as a vector(xyz) at a defined point in main setup when the coordinates of point are known? Nearest velocity or average velocity would be also fine.

How to get access to one of them in "setup.cpp":

from "kernel.cpp"
)+R(float3 closest_u(const float3 p, const global float* u) { // return velocity of closest lattice point to point p
return load3(index(closest_coordinates(p)), u);
}
)+R(float3 interpolate_u(const float3 p, const global float* u) { // trilinear interpolation of velocity at point p

lbm.u???????

Many thanks for your help
Peter

[ProjectPhysX]

Hi @pk-guest,

all the functions in src/kernel.cpp are OpenCL C code that runs on the GPU. This code is compeltely separate from C++ host code, yet mostly compatible so it's possible to port functions over. But here you don't need this, it's much simpler.

Here is how to get one 3D velocity vector at specific 3D space + time coordinates in the main_setup() function:

	const uint probe_x = 25u;
	const uint probe_y = 36u;
	const uint probe_z = 47u;
	const ulong probe_t = 123ull;
	float3 probe_u; // velocity to be read at x/y/z/t

	lbm.run(probe_t); // run probe_t time steps
	lbm.u.read_from_device(); // copy velocity field from device memory (GPU VRAM) to host memory (CPU RAM)
	const ulong probe_index = lbm.index(probe_x, probe_y, probe_z); // convert x/y/z coordinates to linear index suitable for array access
	probe_u = float3(lbm.u.x[probe_index], lbm.u.y[probe_index], lbm.u.z[probe_index]); // copy x/y/z components of velocity from CPU RAM to probe_u variable

	print_info("velocity at probe point = "+to_string(probe_u.x)+", "+to_string(probe_u.y)+", "+to_string(probe_u.z));

	wait(); // so that console doesn't immediately close on Windows

Kind regards,
Moritz

[pk-guest]

Hello Moritz,

many thanks for your answer, it helped a lot.

Regards,
Peter