# Preprocessing Hydrodynamic Properties for BModesJJ / OpenFAST of a floating substructure

**URL:** <https://forums.nlr.gov/t/preprocessing-hydrodynamic-properties-for-bmodesjj-openfast-of-a-floating-substructure/1975>\
**Category:** Computer-Aided Engineering Software Tools\
**Created:** [January 30, 2019, 4:25pm UTC](https://forums.nlr.gov/t/preprocessing-hydrodynamic-properties-for-bmodesjj-openfast-of-a-floating-substructure/1975 "2019-01-30T16:25:27Z")\
**Posts on this page:** 1\
**Showing post:** 12

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**Author:** ![Jason.Jonkman](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/jason.jonkman/32/3086_2.png) [@Jason.Jonkman](https://forums.nlr.gov/u/Jason.Jonkman)\
**Post date:** [August 30, 2019, 1:51am UTC](https://forums.nlr.gov/t/preprocessing-hydrodynamic-properties-for-bmodesjj-openfast-of-a-floating-substructure/1975/12 "2019-08-30T01:51:19Z")

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Dear Daniel,

Your overall approach sounds reasonable. Just a few comments:

- Your hydro\_k and hydro\_m matrices seem to match those from your WAMIT output in the attachments. However, the WAMIT output is nondimensional whereas BModes is expecting the data to be dimensional. See the following forum post for information on how to dimensionalize the WAMIT output: [WAMIT - #4 by Jason.Jonkman](http://forums.nlr.gov/t/wamit/373/4).
- For your body weight term, it looks like your z is positive valued i.e. the center of mass is above MSL; is that correct?
- I would expect the unstretched length of the tendons of a TLP to have a significant effect on the tendon tensions/stiffness and resulting natural frequencies.

Best regards,

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