# OC3-Hywind RAOs **URL:** \ **Category:** Computer-Aided Engineering Software Tools\ **Created:** [March 3, 2015, 9:36am UTC](https://forums.nlr.gov/t/oc3-hywind-raos/1085 "2015-03-03T09:36:22Z")\ **Posts on this page:** 1\ **Showing post:** 17
**Author:** ![Joeri.Haaker](https://avatars.discourse-cdn.com/v4/letter/j/ea5d25/32.png) [@Joeri.Haaker](https://forums.nlr.gov/u/Joeri.Haaker)\ **Post date:** [January 25, 2018, 9:16am UTC](https://forums.nlr.gov/t/oc3-hywind-raos/1085/17 "2018-01-25T09:16:34Z")
Dear all, I hope that it’s not a problem that I post in this old topic, but since I have a similar problem, and most of the relevant information is within this topic I took the liberty of posting here. I’m also trying to recreate the OC3-Hywind within (Ansys) AQWA. I found the information about the mass/inertia of the total system in this old forum post: [Inertial Moments of OC3-Hywind Components](http://forums.nlr.gov/t/inertial-moments-of-oc3-hywind-components/610/1) I’m also trying to transform the mass matrix and I’m also fail to achieve a diagonal matrix. But maybe I’m doing something wrong? If I do the transformation as mentioned in the topic (M\_cg = TransMat^T_M\_swl_TransMat) I get the following mass matrix: 1.0e+10 \* 0.000806604815450 0 0 0 0.062916225372230 0.000008979927815 0 0.000806604815450 0 -0.062916225372230 0 0.000011226426962 0 0 0.000806604815450 -0.000008979927815 -0.000011226426962 0 0 -0.062916225372230 -0.000008979927815 5.587772915049737 0.000991477122271 -0.001744457491839 0.062916225372230 0 -0.000011226426962 0.000991477122271 5.587772971327059 0.001397033728988 0.000008979927815 0.000011226426962 0 -0.001744457491839 0.001397033728988 0.019157556316314 My second question is a question regarding the provided moments of inertia. I found a paper called ‘Wave- and Wind-Induced Dynamic Response of a Spar-Type Offshore Wind Turbine’ by Madjid Karimirad and Torgeir Moan in which they used the NREL 5mw wind turbine mounted on a spar platform, similar to the hywind platform. Although their platform looks similar, for some reason it is slightly heavier. These are the properties they described in their paper: Total draft 120 m Diameter above taper 6.5 m Diameter below taper 9.4 m Spar mass including ballast 7,593,000 kg Total mass 8,329,230 kg Center of gravity -78.61 m Pitch inertia about the center of gravity 2:20E + 10 kg·m2 Yaw inertia about the centerline 1:68E + 08 kg·m2 Rating 5 MW Rotor configuration 3 blades Rotor and hub diameter 126 and 3 m Hub height 90 m Cut-in, rated, and cut-out wind speed 3, 11.4, and 25 m/s Rotor mass 110,000 kg Nacelle mass 240,000 kg Tower mass 347,460 kg The first thing I noticed is their Pitch inertia about the CM, which is way lower than yours? When I transform the values you provided I have a pitch about the cm of 5.58E + 10 , but if I just make a quick hand calculation where I take the moment of inertia of the floater about the cm and see the tower and nacelle+ rotor as 2 point masses and add them times the length between the cm and the points squared . I 'm also in the region of 2.0E + 10. As you may understand I’m somewhat confused and I hope that someone may have an answer. With regards, Joeri --- _[View the full topic](https://forums.nlr.gov/t/oc3-hywind-raos/1085)._