public void CalculateDensity(List <Particle> plst, float smoothing_radius)
{
int pindex, nindex;
float density, near_density, distance_squared, distance, smoothing_kernel, smoothing_kernel_squared, smoothing_kernel_cubic;
Vector2 vector_between_particle_neighbour;
pindex = 0;
foreach (Particle p in plst)
{
p.Density = 0.0f;
p.Neardensity = 0.0f;
p.Neighbourlist.Clear();
density = 0.0f;
near_density = 0.0f;
for (nindex = pindex + 1; nindex < plst.Count; nindex++)
{
vector_between_particle_neighbour.X = plst.ElementAt(nindex).Position.X - plst.ElementAt(pindex).Position.X;
vector_between_particle_neighbour.Y = plst.ElementAt(nindex).Position.Y - plst.ElementAt(pindex).Position.Y;
distance_squared = vector_between_particle_neighbour.LengthSquared();
distance = (float)Math.Sqrt(distance_squared);
if (distance_squared < smoothing_radius * smoothing_radius)
{
N_Particle nparticle = new N_Particle();
smoothing_kernel = 1 - distance / smoothing_radius;
//smoothing_kernel_squared = (smoothing_kernel * smoothing_kernel);
smoothing_kernel_squared = (float)(6 / (smoothing_radius * Math.PI * smoothing_radius)) * (smoothing_kernel * smoothing_kernel);
//smoothing_kernel_cubic = smoothing_kernel_squared * smoothing_kernel;
smoothing_kernel_cubic = (float)(10 / (Math.PI * smoothing_radius * smoothing_radius)) * (smoothing_kernel * smoothing_kernel * smoothing_kernel);
density += smoothing_kernel_squared;
near_density += smoothing_kernel_cubic;
plst.ElementAt(nindex).Density += smoothing_kernel_squared;
plst.ElementAt(nindex).Neardensity += smoothing_kernel_cubic;
nparticle.Particleindex = nindex;
nparticle.Smoothingkernel = smoothing_kernel;
nparticle.Smoothingkernelsquared = smoothing_kernel_squared;
nparticle.Distance = distance;
nparticle.Ismovingboundary = plst.ElementAt(nindex).Ismovingboundary;
nparticle.Isstationaryboundary = plst.ElementAt(nindex).Isstationaryboundary;
plst.ElementAt(pindex).Neighbourlist.Add(nparticle);
}
}
p.Density += density;
p.Neardensity += near_density;
pindex++;
}
}
public void CalculateViscosity(List <Particle> plst, float smoothing_radius, float dt)
{
int pindex, nindex;
float length, q, inward_radial_vel;
N_Particle nparticle = new N_Particle();
Vector2 vector_between_neighbour_particle;
Vector2 normalised_vector_between_neighbour_particle;
Vector2 impulse;
pindex = 0;
foreach (Particle p in plst)
{
foreach (N_Particle n in p.Neighbourlist)
{
nparticle = n;
nindex = nparticle.Particleindex;
vector_between_neighbour_particle = plst.ElementAt(nindex).Position - plst.ElementAt(pindex).Position;
length = nparticle.Distance;
q = length / smoothing_radius;
normalised_vector_between_neighbour_particle = vector_between_neighbour_particle / length;
//calculate inward radial velocity
Vector2 temp = new Vector2();
temp.X = plst.ElementAt(pindex).Velocity.X - plst.ElementAt(nindex).Velocity.X;
temp.Y = plst.ElementAt(pindex).Velocity.Y - plst.ElementAt(nindex).Velocity.Y;
inward_radial_vel = Vector2.Dot(temp, normalised_vector_between_neighbour_particle);
if (inward_radial_vel > 0.0f)
{
impulse = normalised_vector_between_neighbour_particle * (plst.ElementAt(nindex).Vsigma *inward_radial_vel + plst.ElementAt(nindex).Vbeta *inward_radial_vel *inward_radial_vel) * (1 - q);
impulse *= dt * dt_scalefactor;
if (plst.ElementAt(pindex).Ismovingboundary == false && plst.ElementAt(pindex).Isstationaryboundary == false)
{
plst.ElementAt(pindex).Velocity -= impulse;
}
if (plst.ElementAt(pindex).Ismovingboundary == false && plst.ElementAt(pindex).Isstationaryboundary == false)
{
plst.ElementAt(nindex).Velocity += impulse;
}
}
}
pindex++;
}
}
public void CalculatePressure(List <Particle> plst, float stiffness, float near_stiffness, float rest_density, float dt, float smoothing_radius)
{
int pindex, nindex;
float pressure, near_pressure, smoothing_kernel, smoothing_kernel_squared, scalar_pressure;
Vector2 particle_pressure;
Vector2 vector_between_particle_neighbour;
Vector2 neighbour_pressure;
N_Particle nparticle = new N_Particle();
pindex = 0;
foreach (Particle p in plst)
{
pressure = stiffness * (p.Density - rest_density);
near_pressure = near_stiffness * p.Neardensity;
particle_pressure.X = particle_pressure.Y = 0; //reset particle pressure vector to 0
foreach (N_Particle n in p.Neighbourlist)
{
nindex = n.Particleindex;
//smoothing_kernel = n.Smoothingkernel;
smoothing_kernel = (float)(n.Smoothingkernel * (3 / (Math.PI * smoothing_radius * smoothing_radius)));
smoothing_kernel_squared = n.Smoothingkernelsquared;
vector_between_particle_neighbour.X = plst.ElementAt(nindex).Position.X - plst.ElementAt(pindex).Position.X;
vector_between_particle_neighbour.Y = plst.ElementAt(nindex).Position.Y - plst.ElementAt(pindex).Position.Y;
scalar_pressure = pressure * smoothing_kernel + near_pressure * smoothing_kernel_squared;
scalar_pressure *= dt * dt * dt_scalefactor * dt_scalefactor;
if (n.Distance != 0)
{
neighbour_pressure = vector_between_particle_neighbour / n.Distance * scalar_pressure;
}
else
{
neighbour_pressure.X = neighbour_pressure.Y = 0;
}
plst.ElementAt(nindex).AccumulateForce(neighbour_pressure);
particle_pressure -= neighbour_pressure;
}
p.Pressure = (float)(Math.Sqrt(particle_pressure.X * particle_pressure.X + particle_pressure.Y * particle_pressure.Y));
p.AccumulateForce(particle_pressure);
pindex++;
}
}
public void CalculateViscoElasticity(List <Particle> plst, float smoothing_radius, float k, float yield_ratio, float pconst, float dt)
{
int pindex, sindex, sp1index, sp2index;
float restlength, tolerable_def, distance_between_neighbour_particle, tempfloat;
Vector2 sdisplacement;
Vector2 temp;
//create springs
pindex = 0;
foreach (Particle p in plst)
{
foreach (N_Particle n in p.Neighbourlist)
{
N_Particle nparticle = new N_Particle();
Spring spring = new Spring();
nparticle = n;
if (!SpringArray.Springarray[pindex, nparticle.Particleindex])
{
SpringArray.Springarray[pindex, nparticle.Particleindex] = true;
spring.Point1 = pindex;
spring.Point2 = nparticle.Particleindex;
spring.Restlength = smoothing_radius;
tempfloat = rand.Next((int)(k * 10), (int)(k * 10 + 3));
spring.Coefficient = tempfloat / 10;
//spring.Coefficient = k;
SpringArray.Springlst.Add(spring);
}
}
pindex++;
}
//Alter the rest length of springs
sindex = 0;
foreach (Spring s in SpringArray.Springlst.ToList())
{
sp1index = s.Point1;
sp2index = s.Point2;
restlength = s.Restlength;
tolerable_def = yield_ratio * restlength;
temp.X = plst.ElementAt(sp2index).Position.X - plst.ElementAt(sp1index).Position.X;
temp.Y = plst.ElementAt(sp2index).Position.Y - plst.ElementAt(sp1index).Position.Y;
distance_between_neighbour_particle = temp.Length();
if (distance_between_neighbour_particle > (restlength + tolerable_def))
{
s.Restlength += dt * dt_scalefactor * pconst * (distance_between_neighbour_particle - restlength - tolerable_def);
}
else if (distance_between_neighbour_particle < (restlength - tolerable_def))
{
s.Restlength -= dt * dt_scalefactor * pconst * (restlength - tolerable_def - distance_between_neighbour_particle);
}
if (s.Restlength > smoothing_radius && sindex < plst.Count)
{
SpringArray.Springarray[sindex, sindex] = false;
SpringArray.Springlst.RemoveAt(sindex);
sindex--;
}
sindex++;
}
//update position of particle due to spring forces
sindex = 0;
foreach (Spring s in SpringArray.Springlst)
{
Vector2 sforce = new Vector2(0, 0);
sp1index = s.Point1;
sp2index = s.Point2;
restlength = s.Restlength;
sforce = s.CalculateForce(sforce, s, plst.ElementAt(sp1index), plst.ElementAt(sp2index));
sdisplacement = sforce * (1.0f - restlength / smoothing_radius) * dt * dt_scalefactor * dt * dt_scalefactor;
if (plst.ElementAt(sp1index).Ismovingboundary == false && plst.ElementAt(sp1index).Isstationaryboundary == false)
{
plst.ElementAt(sp1index).Position -= sdisplacement;
}
if (plst.ElementAt(sp2index).Ismovingboundary == false && plst.ElementAt(sp2index).Isstationaryboundary == false)
{
plst.ElementAt(sp2index).Position += sdisplacement;
}
sindex++;
}
}