FEA for Structure Foundations
2015-Nov-13
Why Catamarans are Awesome
2017-Jun-05
A global finite element analysis (FEA) checks the global structural response. This is a fairly big analysis. Simply because all of the structure is modeled. All the stiffeners. All the bulkheads. All the shell plating. That makes a lot of components to mesh. What do you get out of it? A much more precise understanding of the stress distributions as the hull bends. Why does this matter? Because then you can reduce the hull scantlings where they are not needed. And strengthen them in areas where they are. When hull plates are stronger in the right regions, you get longer life out of the hull. Longer service life for the ship.
A global FEA involves a fair amount of computing effort. These are large FEA meshes. You should talk with your engineer and ask how they plan to simplify the structure. What mesh sizes do they plan to use? Do they have any previous experience with global FEA? Ask what loading conditions they are planning to consider. A global FEA should address the following loading conditions in some way.
- Fully loaded in calm water
- Fully loaded with waves at vessel ends
- Fully loaded with waves at midships
- Light loaded in calm water
- Light loaded with waves at vessel ends
- Light loaded with waves at midships
You may not need to analyse all these conditions. The specifics always depend on your situation. But the engineer should be prepared to address them and show they have considered them.
Finally, the global FEA should be checked after you have completed all your other general structural design. Complete all the scantling designs first. Complete all the local strength checks. Check all of that first. The global FEA gets expensive very quickly if you get the wrong scantlings and need to repeat the analysis several times.
Also show interest in how the engineer will derive the wave loads. There are multiple methods, ranging from a quasi-static wave to a full CFD seakeeping analysis. The scale completely depends on your specific situation and how much you want to optimize your design to reduce steel weight.
Deliverables
The final deliverable will be a report. This will identify any stress concentrations or regions of concern. It will also identify any critical loading conditions. This report should be prepared for submission to your class society for review. Also expect the engineer to reserve some time for discussing the report with you. And some time for the engineer to address any comments from the class society.
Budget
Expect 3 – 6 weeks to complete the global FEA, plus another week to write the report. Then there are also the fees for submission to the class society.
Schedule
This should take some time to complete. The analysis time will take 1 – 2 months. And then another month at least for class society review.
Client Input
You will need to provide full structural scantling drawings of the vessel. Small items like foundations are not necessary. The focus here is global structure. Also clarify to the engineer what your goal is for the FEA. Do you just want something to submit to the class society? Did you want to optimize and reduce the vessel weight? How much? Try to quantify how much improvement is worth to you.
