ComputeForces Issue
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.
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.
Comments
Regards
Altomare C, Domínguez JM, Crespo AJC, González-Cao J, Suzuki T, Gómez-Gesteira M, Troch P. 2017. Long-crested wave generation and absorption for SPH-based DualSPHysics model. Coastal Engineering, 127: 37-54 doi: 10.1016/j.coastaleng.2017.06.004.
Altomare C, Crespo AJC, Domínguez JM, Gómez-Gesteira M, Suzuki T, Verwaest T. 2015. Applicability of Smoothed Particle Hydrodynamics for estimation of sea wave impact on coastal structures. Coastal Engineering, 96: 1-12. doi:10.1016/j.coastaleng.2014.11.001.
We will try to check why the discrepancy
Alex
How can I assign different mk's to 4 different walls in CaseSloshing example?
Thank you!
What was the final verdict on this discrepancy reported by ShaneCM? I am also getting higher forces than the experimental value.
Regards.
setmkbound mk="10" />
drawbox>
boxfill>left
point x="0.9" y="0.24" z="0" />
size x="0.12" y="0.12" z="0.45" />
/drawbox>
shapeout file="Building"/>
if [ $errcode -eq 0 ]; then
$computeforces -dirin $dirout -filexml $dirout/${name}.xml -onlymk:21 -savecsv $dirout/WallForce
errcode=$?
fi
Why -onlymk:21 ?
Note that values of the final mk are different to
mkfluid, mkbound and mkvoid following the rules:
mk for boundaries = mkbound + 11
mk for fluid particles = mkfluid + 1
I don't know the historical reasons why 11 and not some other number, but all that matters is that we use the correct number for any given particle type.
Many thanks
we use initially mkbound and mkfluid but these are later converted to a unique list of mk values... so the first 11 are booked for fluid and then we have boundaries. on the other hand the first mk should be 1 and not zero... then:
mk for fluid = mkfluid +1
mk for boundaries = makbound + 11
Alex
I performed several simulations where use ComputeForces tool and compare results with MPS method. The results are in good agreement but there are some questions. Who from DualSPHysics developer can comment ?