Strange behavior of water surface near solid body

JBrake · January 14, 2019, 14:57

I am experiencing strange initial behavior of my water surface near a solid body at the beginning of my simulation.

The water level starts out flat from setFields, and I took away the waves that I will eventually be including. Even with calm initial conditions, the water level dips near the solid flap (the flap is hinged at the bottom so that it may rotate).

My boundary conditions on the flap are movingWallVelocity for U, and similar to a normal wall for all others.

I am using rigidBodyMotion solver to generate movement of the flap, and an AMI patch rotates a cylindrical portion of the mesh surrounding the flap. In previous simulations, I used a prescribed motion of the flap (with constant rotational velocity) and did not experience the strange initial water surface behavior.

vatavuk · January 15, 2019, 09:18

Hi Justine,

See the link below for instructions on how to include an image in a post:
Picture doesn't appear

Best Regards,
Paulo

JBrake · January 15, 2019, 19:07

Thanks, I have posted an image. As an update, this water surface issue occurs even when I go back to a prescribed flap motion and set the angular velocity to zero (so indeed there is no flap motion, yet still a disturbance near the flap). I am trying to retrace my steps and determine what is causing this issue. Any help would be greatly appreciated.

pete20r2 · January 16, 2019, 06:37

Why movingWallVelocity? Seems wrong to me.

JBrake · January 16, 2019, 14:14

I used movingWallVelocity based on a tutorial case that had a floating object or something of that nature (it might have been the propeller case). Like everything I try to do with OpenFOAM, I find examples and work from there.

The flap is a moving solid body and needs to rotate about a "hinge" point, which happens to be the origin in my model.

JBrake · January 16, 2019, 17:12

I have removed the flap entirely and found that the behavior continues. It is likely due to the circular AMI. If I plot velocity, there is definitely something going on around the AMI when it shouldn't be.

JBrake · January 16, 2019, 18:51

Additional information: when I run checkMesh, it "Failed 1 mesh checks" but it doesn't say which check it failed. Does it have to do with "***Number of edges not aligned with or perpendicular to non-empty directions: 24057"? Here is a picture of the circular/cylindrical part of the mesh:

Could it be it simply needs more refinement, or is something else possible going wrong with the AMI?

January 14, 2019, 14:57	Strange behavior of water surface near solid body	#1
JBrake Member Justine Join Date: Nov 2018 Posts: 30 Rep Power: 8	I am experiencing strange initial behavior of my water surface near a solid body at the beginning of my simulation. The water level starts out flat from setFields, and I took away the waves that I will eventually be including. Even with calm initial conditions, the water level dips near the solid flap (the flap is hinged at the bottom so that it may rotate). My boundary conditions on the flap are movingWallVelocity for U, and similar to a normal wall for all others. I am using rigidBodyMotion solver to generate movement of the flap, and an AMI patch rotates a cylindrical portion of the mesh surrounding the flap. In previous simulations, I used a prescribed motion of the flap (with constant rotational velocity) and did not experience the strange initial water surface behavior. Last edited by JBrake; January 15, 2019 at 15:19.

January 15, 2019, 09:18		#2
vatavuk Senior Member Paulo Vatavuk Join Date: Mar 2009 Location: Campinas, Brasil Posts: 200 Rep Power: 18	Hi Justine, See the link below for instructions on how to include an image in a post: Picture doesn't appear Best Regards, Paulo JBrake likes this. Last edited by vatavuk; January 16, 2019 at 07:33.

January 16, 2019, 18:51	checkMesh	#7
JBrake Member Justine Join Date: Nov 2018 Posts: 30 Rep Power: 8	Additional information: when I run checkMesh, it "Failed 1 mesh checks" but it doesn't say which check it failed. Does it have to do with "***Number of edges not aligned with or perpendicular to non-empty directions: 24057"? Here is a picture of the circular/cylindrical part of the mesh: Could it be it simply needs more refinement, or is something else possible going wrong with the AMI?

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January 15, 2019, 19:07		#3
JBrake Member Justine Join Date: Nov 2018 Posts: 30 Rep Power: 8	Thanks, I have posted an image. As an update, this water surface issue occurs even when I go back to a prescribed flap motion and set the angular velocity to zero (so indeed there is no flap motion, yet still a disturbance near the flap). I am trying to retrace my steps and determine what is causing this issue. Any help would be greatly appreciated.

January 16, 2019, 06:37		#4
pete20r2 Senior Member Peter Baskovich Join Date: Jul 2014 Posts: 127 Rep Power: 12	Why movingWallVelocity? Seems wrong to me.

January 16, 2019, 14:14		#5
JBrake Member Justine Join Date: Nov 2018 Posts: 30 Rep Power: 8	I used movingWallVelocity based on a tutorial case that had a floating object or something of that nature (it might have been the propeller case). Like everything I try to do with OpenFOAM, I find examples and work from there. The flap is a moving solid body and needs to rotate about a "hinge" point, which happens to be the origin in my model.

January 16, 2019, 17:12		#6
JBrake Member Justine Join Date: Nov 2018 Posts: 30 Rep Power: 8	I have removed the flap entirely and found that the behavior continues. It is likely due to the circular AMI. If I plot velocity, there is definitely something going on around the AMI when it shouldn't be.