# Residual value Oscillations

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December 7, 2017, 11:30
Residual value Oscillations
#1
New Member

Siddhartha Desu
Join Date: Dec 2017
Posts: 3
Rep Power: 2
All,

I am simulating a box barge in head waves condition (first order waves) to study the forces, and wave profiles in the wake.

I am simulaiting fixed barge of L=2m, B=1m, T=0.5m in a tank of (L,W,H = 30,30,20). Using first order waves (wavelength= L). I am using wave damping length of 2L from the boundaries. My BC's are Velocity inlet for
Inlet, Bottom, Top , Pressure outlet for Outlet, Symmetry for sides. I am using about 4.8m cells for this condition.

My problem is with the residuals, They are dying down as more physical time passes but the oscillations are not. Is this acceptable? Could anyone suggest what the problems might be?

Attached Images
 Residual.jpg (76.5 KB, 10 views)

 December 7, 2017, 13:34 #2 Member     André Join Date: Mar 2016 Posts: 53 Rep Power: 3 I believe the residuals may oscillate however they still appear rather high. They should drop 3 to 4 orders of magnitude. Have you tried reducing the cell size? __________________ Sapere aude!

 December 7, 2017, 15:41 #3 New Member   Siddhartha Desu Join Date: Dec 2017 Posts: 3 Rep Power: 2 Can you recommend me what the best size for the tank is ? Right know my tank is 15 times the length of the barge. Thus I am not able to reduce the cell size much (current cell size = 0.07m). If I reduce further I am getting too many cells to compute effectively (about 15m or more cells). On the other hand when I was working in a reduced tank size (10 times the length of the barge), I am getting so much reflections from the boundaries and the waves are dying down before the simulation is ending.

December 8, 2017, 03:58
#4
Senior Member

Ashok Chaudhari
Join Date: Aug 2016
Location: Pune, India
Posts: 109
Rep Power: 3
Quote:
 Originally Posted by Siddhartha1993 Can you recommend me what the best size for the tank is ? Right know my tank is 15 times the length of the barge. Thus I am not able to reduce the cell size much (current cell size = 0.07m). If I reduce further I am getting too many cells to compute effectively (about 15m or more cells). On the other hand when I was working in a reduced tank size (10 times the length of the barge), I am getting so much reflections from the boundaries and the waves are dying down before the simulation is ending.
Which mesher are you using? also physics models?

 December 8, 2017, 04:10 #5 New Member   Siddhartha Desu Join Date: Dec 2017 Posts: 3 Rep Power: 2 Trimmed cell mesher and prsim layer mesher and surface remesher. Models: Implicit Unsteady, Eulerian Multiphase, K-Epsilon Turbulence, Volume of Fluid (VOF), VOF Waves, Gravity,Cell Quality Remediation.

 Tags residuals, vof damping, wave boundary conditions

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