# mooring lines parameters

Hi,
I’m doing research on the 5MW NREL OC3 Hywind turbine.
I want to change the angle of the wind inflow relative to the location of the three anchors in the xy plan eg. wind blowing from 15 degrees relative to the anchor mooring line.
I believe this is easiest achieved by shifting angles of the anchors, but how do I do this?
In NRELOffshrBsline5MW_Platform_OC3Hywind3.dat:
what is LAngAnch?
what is LAngFair?

Regards
Søren Christiansen
PhD student
Aalborg University

Dear Søren,

The mooring line fairlead and anchor locations in FAST’s platform input file are defined in a cylindrical coordinate system. Three parameters are needed to define a point location: the depth, radius, and angle. To locate the anchor, LAngAnch is the angle about the positive zi-axis from the positive xi-axis of the inertial frame. To locate the fairlead, LAngFair is the angle about the positive zt-axis from the positive xt-axis of the tower frame. The inertial frame is defined with the xi-axis directed downwind (given a zero degree wind direction), the yi-axis transverse directed to the left when looking downwind, and the zi-axis vertically upward opposite gravity. The tower frame is a body-fixed frame in the floating platform that is coincident with the inertial frame when the platform is undisplaced.

The OC3-Hywind spar buoy has three mooring lines with anchor and fairlead angles of 0 deg, 120 deg, and 240 deg. This means that one line is directed nominally downwind and the remaining two are 120 deg apart.

I hope that helps.

Best regards,

Dear Jason,
Thank you for the reply. I am trying to think of a case where LAngAnch would be different from LAngFair? The only case I can think of is if you want to have asymmetric distribution of angles? Otherwise if a symetric distribution as on hywind is desired, LAngAnch and LAngFair should be the same. Is this the inttention?

Regards
Søren

Dear Søren,

If the mooring lines are not directed radially from the platform centerline, than LAngAnch and LAngFair would be different. We’ve needed this when modeling the mooring lines of a rectangular barge. For spar buoys and tension-leg platforms, your correct that LAngAnch and LAngFair are likely to be identical.

Best regards,