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	tChanged simulation parameter values - lbm-d3q19 - 3D lattice-Boltzmann code to…
	git clone git://src.adamsgaard.dk/lbm-d3q19
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	---
	commit cf9d6d652d870a84c7e3b3961f48518573d3a7ab
	parent c9c44e772c0500baf8132d28ffc37cd928902390
	Author: Anders Damsgaard Christensen <[email protected]>
	Date: Mon, 20 May 2013 21:46:37 +0200

	Changed simulation parameter values

	Diffstat:
	M lbm.c \| 56 +++++++++++++++++++++--------…

	1 file changed, 38 insertions(+), 18 deletions(-)
	---
	diff --git a/lbm.c b/lbm.c
	t@@ -21,12 +21,12 @@ typedef struct {
	const int n = 3;

	// Grid dims
	-const unsigned int nx = 4;
	-const unsigned int ny = 6;
	+const unsigned int nx = 3;
	+const unsigned int ny = 4;
	const unsigned int nz = 2;

	// Grid cell width
	-const Float dx = 0.1;
	+const Float dx = 2.0;

	// Number of flow vectors in each cell
	const int m = 19;
	t@@ -36,17 +36,20 @@ const int m = 19;
	const Float dt = 1.0e-4;

	// Simulation end time
	-const Float t_end = 10.1;
	-//const Float t_end = 1.0;
	+//const Float t_end = 2.0e-4;
	+const Float t_end = 1.0;

	// Fluid dynamic viscosity
	const Float nu = 8.9e-4;
	+//const Float nu = 8.9e-0;


	// Gravitational acceleration
	-//const Float3 g = {0.0, 0.0, -10.0};
	-const Float3 g = {0.0, 0.0, 0.0};
	+const Float3 g = {0.0, 0.0, -10.0};
	+//const Float3 g = {0.0, 0.0, 0.0};

	+// Lattice speed of sound for D2Q9 and D3Q19 (1.0/sqrt(3.0))
	+const Float c2_s = 1.0/1.7320508075688772;


	//// FUNCTION DEFINITIONS
	t@@ -64,9 +67,21 @@ Float dot(Float3 a, Float3 b)
	return a.xb.x + a.yb.y + a.z*b.z;
	}

	-// Viscosity parameter
	+// Relaxation parameter, linked to fluid dynamic viscosity
	Float tau(void) {
	- return (6.0nudt/(dx*dx) + 1.0)/2.0;
	+
	+ //Float tau = (6.0nudt/(dx*dx) + 1.0)/2.0;
	+
	+ Float tau = nu/c2_s + 0.5;
	+ if (tau < 0.5) {
	+ fprintf(stderr, "Error: For positive viscosity: tau >= 0.5, ");
	+ fprintf(stderr, "but tau = %f.\n Increase the dynamic viscosity ", tau…
	+ fprintf(stderr, "(nu).\n");
	+ exit(1);
	+ } else
	+ return tau;
	+ //Float c2_s = 1.0/sqrtf(3.0); // for D2Q9 and D3Q19
	+ //return nu/c2_s + 1.0/2.0;
	}

	// Get i-th value from cell x,y,z
	t@@ -153,20 +168,24 @@ void init_fluid(Float* f, Float* rho, Float3* v)
	}
	}

	-// Equilibrium distribution along flow vector e
	+// Equilibrium distribution along flow vector e,
	+// Obtained from the local Maxwell-Boltzmann SPDF
	+// He and Luo, 1997
	Float feq(
	Float rho,
	Float w,
	Float3 e,
	Float3 u)
	{
	+ // Propagation speed on the lattice, squared
	Float c2 = dx/dt;
	- return rhow (1.0 + 3.0/c2*dot(e,u)
	- + 9.0/(2.0c2c2)dot(e,u)dot(e,u)
	- - 3.0/(2.0c2)dot(u,u)*dot(u,u));
	+ return rhow (1.0 + 3.0*dot(e,u)/c2
	+ + 9.0/2.0dot(e,u)dot(e,u)/(c2*c2)
	+ - 3.0/2.0*dot(u,u)/c2);
	}

	-// Bhatnagar-Gross-Kroop approximation collision operator
	+// Bhatnagar-Gross-Kroop approximation collision operator,
	+// Bhatnagar et al., 1954
	Float bgk(
	Float f,
	Float tau,
	t@@ -483,18 +502,19 @@ void print_v(Float3* v, FILE* stream)

	int main(int argc, char** argv)
	{
	- //printf("### Lattice-Boltzman D%dQ%d test ###\n", n, m);
	+ printf("### Lattice-Boltzman D%dQ%d test ###\n", n, m);


	// Print parameter vals
	- //printf("Grid dims: nx = %d, ny = %d, nz = %d: %d cells\n",
	- //nx, ny, nz, ncells);
	+ unsigned int ncells = nxnynz;
	+ printf("Grid dims: nx = %d, ny = %d, nz = %d: %d cells\n",
	+ nx, ny, nz, ncells);
	+ printf("tau = %f\n", tau());

	// Set cell flow vector values
	Float3 e[m]; set_e_values(e);

	// Particle distributions
	- unsigned int ncells = nxnynz;
	Float* f = malloc(ncellsmsizeof(Float));
	Float* f_new = malloc(ncellsmsizeof(Float));