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Free trim and sinkage ship hull simulation - bow sinks

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Old   August 16, 2019, 02:49
Default Free trim and sinkage ship hull simulation - bow sinks
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Paul Renaud
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Hello everyone,

I am currently working on OFv1806 and interFoam to simulate a (full scale) boat in calm waters with dynamic trim and sinkage. I am able to reproduce the simulation from this post for a planing hull Planing boat simulation with InterDyMFoam and force ramp for make it stable

, but I can not get a good result for displacement hull.

Indeed, the bow sinks in the water until the crash of the simulation. I do not understand why. Whether taking the parameters of the DTCHull or simulation with planing hull (boundary conditions, fvSchemes, fvSchemes ...), I always get the same trend.

I tried initializing with dynamic mesh (LTS), adding a ramp force, modifying accelerationRelaxation, passing from rigidibodyMotion to sixDofRigidBodyMotion without success. In DynamicMeshDict, I put the centerOfMass as the center of gravity, momentOfInertia and the mass of the half hull (because of the symmetry).

Some data :
L = 6.4 m
Draft = 0.484 m
Displacement 2.707 m3
U = 2.57 m/s
k = 0.0003566 m2/s2
nut = 5e-07 m2/s
omega = 495 /s

Time step = 0.001 and Courant number max = 0.5 before the crash

Mesh = 0.5M cells with layers
Has anyone ever faced this problem?

Kind regards

boat_sinks.jpg

mesh.jpg

dynamicMeshDict.zip

fvSchemes.zip

fvSolution.zip
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Old   August 16, 2019, 06:40
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Yann
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Hello Paul,



The first picture shows a quite distorted mesh with cells which could cause a crash. Have you tried increasing the outerDistance parameter? It could help to smooth the mesh deformation.


Yann
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Old   August 16, 2019, 07:12
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Paul Renaud
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Hello Yann,

Yes I have already tried to increase this parameter. And it was actually the cause of the crash in another simulation where the (positive) trim could not increase more because of the ¨compression¨ of the mesh.

Paul
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Old   August 16, 2019, 07:24
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Paul Renaud
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My best simulation on that hull has been quiet stable but the trim should be positive and not negative. On all the other hulls, the simulation has the same behavior as before with the bow that sinks.

Paul

trim_monitoring.png
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