Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Fatigue from platform motion

Fatigue from platform motion

Fatigue from platform motion

Haven't done this in a while. I have 10-year and 100-year accelerations and wind loads, but I'm not sure how to translate that into cycles or account for cumulative damage from cycles at lower accelerations. In other words, should I be using some sort of statistical distribution (I have a dim memory of having done something like that for a client like 10 years ago). I know how to build a FAT text file and pull it into Caesar, I just need a little direction on what to use as a basis for the cycle distribution.

RE: Fatigue from platform motion

If you are doing a fatigue analysis in accordance with ASME VIII Div 2 (as probably you should be) then Caesar does not perform the calculations strictly in accordance with ASME VIII Div 2 even though the documentation says otherwise. On the statistical point, sometimes a weibul distribution is used but I would have thought that the number of platform motions(i.e wave height distribution) would have been specified in the Clients documentation.

RE: Fatigue from platform motion

Hi Crusader911,

I'm actually don't use the ASME standards for doing my job, so I'm going to answer you how I would deal with this issue without using a standard, although I find important to use it.

I imagine you're doing a fatigue analysis. Basically, there are 2 ways to do it: A) fatigue analysis in time domain; and (B) fatigue analysis in frequency domain.

Marine loading are random by nature. So, the most time-saving way to do it is to do a fatigue analysis in frequency domain. First, you have to do a FFT on each wind turbine loading and apply this loading in your component/system. After that, you should do FEA using this loading. The results will be the stresses measured in the frequency domain. After that, you should perform a frequency-based fatigue analysis. The results of it is the life of the structure, measured in each surface node.

frequency-based FEA and Fatigue analyses are complex subjects. So, I recommend to read some texts. For fatigue, I recommend chapter 10 of the book Fatigue Testing and Analysis: Theory and Practice of Yung-Li Lee.

If you have any other question, please let me know.


Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close