# Changing wave direction

Dear Dr.Jonkman

Greetings for the day!I have a quick question in OC3 Hydrodyn module. When we say the wave direction is in zero degree , is it modeled as the waves hitting at center of the spar i.e. x=0,y=o. If we imagine spar as circle with center (0,0). [Below are the corresponding lines from hydrodyn]
JointID Jointxi Jointyi Jointzi JointAxID JointOvrlp [JointOvrlp= 0: do nothing at joint, 1: eliminate overlaps by calculating super member]
(-) (m) (m) (m) (-) (switch)
1 0.00000 0.00000 -120.00000 1 0
2 0.00000 0.00000 -12.00000 1 0
3 0.00000 0.00000 -4.00000 1 0
4 0.00000 0.00000 10.00000 1 0
---------------------- MEMBER CROSS-SECTION PROPERTIES -------------------------
2 NPropSets - Number of member property sets (-)
PropSetID PropD PropThck
(-) (m) (m)
1 9.40000 0.00010
2 6.50000 0.00010

If is it so ,this point of reference considered for the waves to hit does not change when the wave direction is changed say for 30 ,60deg,… , I request you to correct me if am wrong in understanding this .

Thanks
Krishnaveni

Dear Krishnaveni,

Correct, the location on the platform where the waves hit does not change with the wave direction (WaveDir) in HydroDyn. However, WaveDir will impact the direction of the hydrodynamic loads, e.g., for an axisymmetric structure the hydrodynamic loads will act in the surge and pitch directions when WaveDir = 0, but when WaveDir = 90deg, the hydrodynamic loads will act in the sway and roll directions.

Best regards,

Thanks for your quick response Dr.Jonkman.

Having said that, I would be unable to rotate the spar say for 90 degrees as the point of reference is center(0,0) always.I will have to achieve it only by doing WaveDir 90 degrees.

Krishnaveni

Dear Krishnaveni,

I’m not sure what you mean by “rotate the spar”, but you can introduce platform rotation via the structural degrees of freedom in ElastoDyn. However, ElastoDyn limits the platform rotations to small angles (so, you can’t set them to 90 degrees).

Best regards,