Floating Hull FEA Analysis

[LNGuy]

Hi,
I am doing my first academic project using Abaqus. I am trying to model a floating box hull with water pressure acting from the bottom and the sides. I am trying to follow the paper attached here. I am having problem setting the boundary conditions even though I am setting it up as per the paper's instructions. I am trying to study the box hull deformation. I would then take it forward to an actual ship's hull.
Kindly advise as to how do I go ahead with this.

Thank you.

 

[StefCon]

Hello,
What problems are you having? Convergence issues? If so, please write the error messages and maybe we can find out.

Best regards,

 

[LNGuy]

I am trying to simulate what has been done in the paper. The paper shows the longitudinal bending of the hull. However, when I apply the same boundary conditions as prescribed, I am getting the bottom plating caving in (which is expected as the pressure is acting from below). So, I am not sure how do I get to the paper's results.
Thanks.

 

[StefCon]

Hi,
It is hard to tell what has been done exactly. There is no elastic-plastic material data in the paper. What material did you use? Does it cave in with purely elastic material properties? NLGEOM is on, right?

It seems like the author in the paper is using a riks step.

If you attach the input file, maybe I can take a look to see if I see anything strange.

Cheers!

 

[LNGuy]

I have used purely elastic material with E=210000 and mu=0.3 as prescribed by the paper. Yes it caves in but I want to focus on the bending. I have used static,Riks step to deal with bending. I am applying the tie constraint on the MPC point.
Kindly find attached the input file.
Thanks.

 

[LNGuy]

And the figure showing the MPC point is as shown here.

 

[StefCon]

Hi,
The paper you attached shows what it calls "Flange of stiffener" and "Side of stiffener" in figure 1 (I think).
I only have a preprocessorthatwedonottalkabout right now and I am a bit unfamiliar with how it displays loads. Are your loads applied on the "right side" of the shells?

Are you applying the bending as rotation (measuring the reaction moment)? I am not sure if that works. Link

Cheers!

 

[LNGuy]

How do we apply the self load of a beam?

 

[LNGuy]

As regards the modelling of the boundary condition I adopted the following conditionssort of pinned ends)
Left node => Ux=Uy=Uz=URy=URz=0
Right node => Ux=Uy=URy=URz=0, where x=transverse axis, y= vertical axis, z=longitudinal axis, The box cross-section lying in the X-Y plane. It seems to be working now though I will have to calculate and verify the results as per theoretical formulas.
For the self-weight I took Gravity load and applied a vertically downward factor CFy= -9810 mm/sec2 (as all my length units are in mm).
If someone has any advise or notices any mistake, feedbacks are highly welcome. Will keep updating this post as the results come. Thanks.