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Vessel Offsets

Large Angle Theory

The Flexcom inputs in this case are three translations and three rotations. The three translations are the components in the global axes of the vessel translational offset. The three rotations are termed the yaw offset, the roll offset and the pitch offset. The yaw offset rotates the vessel and local vessel axes about the vertical or global X direction. See figure below, where the yaw offset is denoted ψ. The orientation of the yawed axes relative to the global axes is simply the sum of θ and ψ.

 

Vessel Axes following Yaw Offset – Large Angles

The roll offset and the pitch offset define rotations about this yawed vessel axis system. Specifically, the roll offset defines a rotation about the yawed axis in the figure above, while the pitch represents a rotation about the axis. In practice these two rotations define two components of a rotation vector in the standard Flexcom kinematics formulation (the third component being zero). Transformations from the vessel yawed axes back to the global axes are then handled in standard Flexcom fashion.

Small Angle Theory

The handling of the three static offset displacements is naturally unaffected by the choice of large or small angles, which affects only vessel rotations. However in the small angle case the three rotation offsets, yaw, roll and pitch, define individual rotations about the undisplaced vessel axes.

Relevant Keywords

•*VESSEL,INTEGRATED is used to specify all information pertaining to a vessel or vessels. Specifically, the ANGLES= input is used to specify the theory used to combine vessel rotations.

•*OFFSET is used to specify an offset of an attached vessel from its initial position.