Learning Forum

[Sellera]

Hello, I'm trying to observate the roll motion of a hull(2D case). I've tried to simulate using a setup(without 6DOF-I accept tutorials for it) but I'cant found a way to plot the degree x time grafic for the decay.

Any tips for the case general or to help me with the problem above is welcome ?.

[Rob]

You'll need a surface facet (post processing points don't move with the mesh) and monitor the x, y & z coordinates on that facet with time. Assuming that point is directly below the centre of rotation (I'd pick a facet on the keel) you can use Excel and trigonometry to figure out the roll angle. You could use an Expression, but if you retain the raw data you can also use it to calculate the pitch (lengthways motion) too.

[Sellera]

I see, I noticed that is possible monitore the coordinates but for that it's necessary to use a Dinamic Mesh, and set up it for the hull right?(I can't plot using the actual configuration because it's not especified the point I want to monitore, right?)
I've tried but its necessary to use a doc.txt for that setup, how can I prepare that doc?

Thanks for your answer

[Rob]

If you want the ship to roll you need the 6DOF solver on a rigid body. What doc.txt? We use .c files to define things, but rigid body may not need that: check the manual (click on Help) and review the examples and tutorials.

[Rahul C R]

Hello Rob,

I am also trying to do a roll decay. I use dynamic mesh, but how do I give an initial roll displacement for the decay process to start? 

[Rob]

You'll need to move the hull to the starting point and then start the motion. So rather than upright you need to be at the tip angle you want to damp from. 

[Rahul C R]

Thanks Rob, 

Where do I define the free surface ? My domain is a square box of height 100m. I want my watersurface at 50m. I have placed my body at an intial roll displacement of 5 degrees. Since I am not using open channel flow or waves, in which boundary condition can I set the water free surface?

 

 

[Rob]

Have a look at "patch". Ideally you will want a pressure boundary at the sky to help with stability, and potentially monitor the water level to make sure you're not losing too much when remeshing. 

[Rahul C R]

Thanks a lot Rob.

It appears to be working properly.