A couple of questions

Hi

I have a few question relating to trnasportation analysis, seastate and wave response modules:

1. Transportation (tow) Analysis: How to determine centre of roll of structure (option within 'weight' in precede) is it something SACS gives you when reporting CoG? That is, structure rolls about an axis through CoG?

2. Seatate: What is SEAS line. Please would you provide a practical description (I have already read it within SACS manual but there is still some confusion).

3. Wave response: What is SEED? Again please provide a practical description.

Many thanks.

Parents
  • 1. The center of roll depends on the properties of the vessel as well as the cargo. You will need to perform a hydrodynamic analysis in order to find the center of roll. Typically you will get this information from your Naval Architect. MOSES can be used to generate this information.

    2. The SEAS line allows you to define the waves used to generate the transfer function in the seastate input file so that you don't have to define the transfer function in the fatigue input file. Sample08 is a good example of the SEAS line in action. Also, section 3.4.1.4 has a good explanation of the SEAS line as well as the alternative options for defining transfer functions in spectral fatigue analyses.

    3. A SEED is simply input for a random number generator. You can read more about seeds on Wikipedia.

    Regards,

    Geoff

  • Many thanks Geoff, as always!
    Just an other minor point on transportation analysis: How is this analysis performed? Is it responsibility of naval architect to analyse for the fatigue through MOSES and pass the cumulative damage to structural engineer for him to add this to his in-place analysis fatigue and pile driving damage fatigue OR naval architect will only pass info like wave and centre of roll data etc. and structural egineer will need to complete transportatio fatigue analysis himself.

    On the same token, who's generally responsible for completing fatigue analysis during fabrication, when structure is sitting in fabrication yard and subject to wind fatigue, possibly!

    Thanks.
  • In the case of tow fatigue, the naval architect would typically provide the structural engineer with response amplitude operators (RAO's) which are calculated using their hydrodynamic analysis in MOSES. The structural engineer would then calculate the fatigue data using the RAO's provided.

    I've never seen any fatigue analyses performed for fabrication yard scenarios, probably because the structures typically are not there long enough and the loads are typically low enough that there is not appreciable amount of damage accumulated. I would imagine that the structural engineer would be responsible for performing the fatigue analysis, but these are questions outside the technical scope of SACS.

    Regards,

    Geoff

  • Many thanks Geoff.
    I asked the question while feeling that the forum being 'Offshore Structural Analysis', specific to SACS issues.

    Cheers
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