6D buoys: Wing data

6D buoys can have a number of wings attached, each having its own data and type.

Name

Used to refer to the wing.

Span

The length of the wing, in the local $W\urm{z}$ direction.

Chord

The width of the wing, in the local $W\urm{x}$ direction.

Centre of wing

The position of the wing origin, relative to buoy axes. The wing is drawn as a simple rectangle centred on this origin, the rectangle's dimensions being the specified chord and span.

This origin is the point at which the relative velocity is calculated and at which the resulting wing lift and drag forces are applied. It should therefore normally be at the centre of pressure, which may not be at the centre of area (even though OrcaFlex draws the wing as being centred at this point).

Orientation

The orientation of the wing is given by the three angles azimuth, declination and gamma, relative to the buoy axes. These angles can be fixed, can vary with simulation time, or can be given by an external function.

The angles define the orientation of the local wing axes relative to the buoy axes as follows:

1. Start with the wing axes $\Wxyz$ aligned with the buoy axes $\Bxyz$.
2. Rotate $\Wxyz$ about $B\urm{z}$ by the azimuth angle. This leaves $W\urm{z}$ aligned with $B\urm{z}$, but $W\urm{x}$ now points in the direction towards which the declination is to be made.
3. Now rotate by the declination angle about the new direction of $W\urm{y}$. This declines $W\urm{z}$ to its final direction: $W\urm{z}$ now points along the direction specified by the given azimuth and declination angles.
4. Finally rotate by the gamma angle about this final $W\urm{z}$ direction. This is a rotation about the principal wing axis, so it allows you to adjust the pitch of the wing.

For each of these rotations, positive angles mean clockwise rotation and negative angles mean anti-clockwise rotation, looking along the axis of rotation.

When setting these orientation angles, it is easiest to first set the azimuth and declination values to give the desired $W\urm{z}$-direction. This is the direction of the axis about which the wing pitch is set. Then set gamma to give the correct pitch of the wing. This process is best done with local axes enabled to confirm that the resulting orientation is as you expect.

Wing type

Determines the properties of the wing. You can define a number of wing types – click the wing types button to open the wing types data form.