This allows you to define their shape by building up a number of cylinders of appriopriate lengths and diameters. Spar buoys are modelled as a series of co-axial cylinders placed end to end along the local $z$-axis (see spar buoy and towed fish properties).

These are intended for modelling axisymmetric buoys whose axis is normally vertical and where surface-piercing effects are important (such as for a CALM buoy). See lumped buoy properties for more details of this buoy type. Its buoyancy therefore changes linearly with vertical position, without regard to orientation, neglecting the rotational stiffness that would be experienced by most surface-piercing buoys. When a lumped buoy pierces the surface it is treated for buoyancy purposes as a simple vertical stick with a length equal to its specified height. This necessarily restricts the accuracy with which interactions with the water surface are modelled. These are the simplest type, and have an abstract geometry: their shape is not defined. These share some common data, but they differ in the ways in which the buoy geometry is defined and the fluid loads and surface-piercing effects are calculated. Three types of 6D buoy are available: lumped buoys, spar buoys and towed fish. Lines can be connected to an offset position on a buoy – this allows the direct study of line clashing, including the separation introduced by spaced connection points. Lines connected to a 6D buoy can experience both moment effects and translations as the buoy rotates.

Contact loads, including friction, from the vertices of the buoy contacting the seabed or elastic solids.

Applied loads, which may be used to model thrusters for instance.

Wing loads: a wing is a rectangular surface attached to the buoy at a specified position and orientation, which experiences lift and drag forces and a moment, due to the relative flow of the sea past the wing.

Connection loads from parent objects to which the buoy is connected (e.g.

Slam forces as the buoy passes through the sea surface.

Buoyancy, added mass, damping and drag, proportioned appropriately for a surface-piercing buoy.Broadly speaking, buoys are intended for use in the drag/inertia regime in which Morison's equation applies, requiring that their diameter be much smaller than the wavelength they experience if this is not the case, then diffraction effects tend to dominate and an OrcaFlex vessel object may be more suitable (though spar buoys do have some limited diffraction capability).īuoys have both mass and moments of inertia, and forces and moments from many different effects can be modelled, including: 6D buoys are rigid bodies having all six degrees of freedom – three translational $(X, Y, Z)$ and three rotational $( ext 1, 2, 3)$.

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