I am currently trying to validate DualSPHysics' ComputeForces tool vs. empirical results as well as results attained from ANSYS-Fluent regarding drag forces. My simulations include simulating a submarine moving with a constant velocity in the x-direction while it is submerged but near the surface (about 1 meter below). I understand that DSPH takes free-surface dynamics into account whereas the empirical and Fluent results do not but the discrepancy in the value is about a 500% difference - Empirical and Fluent values = ~60 N, DSPH values = ~330 N and I do not think free-surface dynamics can account for that much of a difference. I was wondering if anyone can shed light on how DSPH computes forces in the x-direction and why there could be such a divergence in values? I have run simulations using 20-55 million particles in these simulations and still find around the same values by a difference of only ~1-5 %.
To test out the values I could get from ComputeForces by running a simple case where the submarine just sits motionless on top of the water and used the CF tool to attain the forces in the z-direction, i.e. the total vertical force, which in this case should = the buoyant force. Even in this simulation I got a difference between empirical and DSPH results of 9-13%. So I am wondering if I am using this tool wrong or if it takes into account something that I am unaware of.
PLEASE HELP! I am supposed to include DSPH results in a final technical paper with NASA and do not want to show this much of a discrepancy in results attained by different tools.