How to model U-Section with varying thickness in Abaqus?

 

   Dear All, I want to model a U-section (open thin-walled) in Abaqus. I am not able to find a way to model it in the beam profiles. I tried alot using Arbitary section but I am not able to produce this section. I have done it as a solid but I prefer using Beam with warping (B**OS). Or is it better to use shell? If so, how do I do it in Shell? This is to carry out FSI using CFD and coupling mainly focusing on torsional loads. 
Could you please give some guidance? 
Regards, Arun
The beam is shown in https://www.dropbox.com/home?preview=U-section.jpg