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*YAWDAMPMOL,NAME=name_of_floater

Data format:

One line with four values

LFORE LAFT Cyaw Np

Status:

Optional

Purpose:

To define an additional yaw damping moment

Restriction:

The floater named NAME_OF_FLOATER must have been previously defined.

Details: :

Parameter	Description
Lfore	algebraic distance of the fore end of the
vessel from centre of motions
Laft	algebraic distance of the aft end of the vessel from the centre of motions
Cyaw	a damping coefficient used in eq.[1] below.
Np	number of points regularly distributed for the integration of eq.[1] with the Trapeze method (Default=100).

Note

The yaw damping moment is calculated as such:

\(M_{yawdamping} = \frac{1}{2}\rho C_{yaw} \int_{Xaf}^{Xfave} (V_{\perp}(\xi, \dot{\Psi}) V(\xi, \dot{\Psi}) - V_{\perp}(\xi, 0) V(\xi, 0))\xi d \xi\) eq.[1]

\(V_{\perp}(\xi, \dot{\Psi})\) is the transverse component of the relative fluid velocity at the algebraic distance \(\xi\) from the centre of motions: \(V_{\perp}(\xi, \dot{\Psi}) = -(\nu + \xi \dot{\Psi})\)

\(V(\xi, \dot{\Psi})\) is the total relative fluid velocity at the algebraic distance x rom the centre of motions: \(V_{\perp}(\xi, \dot{\Psi}) = \sqrt{u'^2 + (\nu + \xi \dot{\Psi})^2}\)

\(u'\) and \(v'\) are the relative velocity projected on the vessel axis system (respectively surge and sway) and \(\dot{\Psi}\) the floater yaw velocity.

\(C_{yaw}\) is usually taken as: \(C_{yaw} = 130\%C_{cur}(90°) * S_{ref}\) where

\(C_{cur}(90°)\) is the current polar coefficient for a heading of 90°,

\(S_{ref}\) the reference surface for the current loads evaluation,