Modify gravity via UDF
 

Hello, i need some help.

I am going to simulate a braking process in a tank, filled with water.

so, therefore i do like to modify the x-gravity in udf. z-gravity is const = -9.81 m/s².

has anyone an idea how to adress the x-gravity component in the udf?
this is my attempt for the udf:

DEFINE_SOURCE(gx_source, c, t, dS, eqn)
{
real gx_source;
real time = RP_Get_Real("flow-time");

if (time <= 0.4)
{
gx_source = 2 * pow(10,-9) * pow(time,4) +
296.74 * pow(time,3) -
178.05 * pow(time,2) +
2.6377 * time -
0.0296;
}

else if(time <= 3.1)
{
gx_source = -8.5;
}

else if(time <= 3.5)
{
gx_source = -2 * pow(10,-9) * pow(time,4) -
296.74 * pow(time,3) +
2937.8 * pow(time,2) -
9661.7 * pow(time,1) +
10551;
}

return (gx_source);

}

many thanks for your help!

Hi

The way you are incorportaing gx is correct. It will be body force/source in x momentum equaion. Please check on units of gx. It should be N/m^3.

Best luck
Vaze

Hello vaze, first of all: thank you for your reply.

I found something like -> C_R(c,t) and C_P(C,t).

How do i have to use it now? I mean, do i have to multiplicate or to divide the gx-source with the C_R(C,t)/C_P(C,t)?
For a testrun i multiplicated it, the visiualisation looked similar to the case, as if i use constant gravity in x direction.

Furthermore, do C_R/C_P depend on the solver i use (pressure-based/density-based)?

Hi

static pressure = rho * gx * z or x distance
Check that C_P corresponds to static pressure or not. if not then deduce it.

all the best,
Vaze