# comparison of results. relaxation time

Hi everyone,

Im trying to compare the results of my LB simulation to some already published results. However, my simulations runs for around 5 seconds but the published results are shown at t=50secs. My tutor has told me that this is to do with the time scaling used in the different programs but i am unsure how to work out the appropriate scales so i can determined what time in my program would be the equivalent time for these other published results. I presume it is something to do with the relaxation time or something else? Could anybody explain to me how i can go about figuring this problem out?

Thanks. James.

Can you be a little more specific? What are your parameters? Which paper are you talking about?

Timm

I am investigating dam break problems and trying to compare my results to those shown in he following:

Non-oscillatory relaxation methods for the shallow-water equations in one and two space dimensions, Seaid M - INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS
Int. J. Numer. Meth. Fluids 2004; 46:457–484 (DOI: 10.1002/d.766)

In this paper, the plots of water height and velocity are shown at time t=50seconds. However, in the program i have, the simulation only runs for around 5 seconds before the water level settles to a uniform height.

My parameters are:

M = 50; % Mesh size
N = 125gridscale+1; %
dx = 25/(N-1); %length of link
e = 15.0; % lattice link velocity
dt = dx/e; % LBM time step
rho_l = +2.0/dx;
rho_r = +2.0/dx;
g = 9.81
dt^2/dx; % gravitational acceleration
eta = 0.012dx^(1/3)/dt; % Manning’s coefficient [s/m^(1/3)]
qx_l = dx
10dt/dx^2;
qy_l = 0;
q0 = 4.42
dt/dx^2; %discharge

maybe the reason is that the simulation is not the same.