3D buoys: Data


Used to refer to the 3D buoy.

Included in static analysis

Determines whether the equilibrium position of the buoy is calculated by the static analysis. This property is only available if the buoy's connection is free.

Wave calculation method

The wave calculation method to be used when computing the buoy's wave kinematics. The default value is specified by environment, meaning that the method specified on the environment form will be used; you can override that (for this buoy) by selecting a different method here if you wish.

Disturbance vessel

Determines whether the buoy will experience sea state disturbance generated by a particular vessel.


A 3D buoy can be free, fixed, anchored or connected to another object.

Initial position

$x$, $y$ and $z$ connection coordinates that determine the initial position of the buoy origin. If the buoy's connection is free and it is not included in the static analysis, then this initial position is taken to be the static position of the buoy. If the buoy's connection is free and it is included in the static analysis, then this initial position is used as an initial estimate of the buoy position and the statics calculation will move the buoy from this position iteratively until an equilibrium position is found.


The mass of the buoy.


Used to calculate buoyancy and added mass.

Bulk modulus

Defines the compressibility of the buoy. A value of infinity represents a buoy which is not significantly compressible.


Used to model floating buoys correctly, where the buoyancy, drag etc. vary according to the depth of immersion, and to draw the buoy. The buoy height is the vertical distance over which the fluid-related forces change from zero to full force as the buoy pierces the surface. It is taken to be symmetrical about the buoy's origin.

Seabed friction coefficient

OrcaFlex applies Coulomb friction between the buoy and the seabed. The friction force applied never exceeds $\mu R$, where $\mu$ is the friction coefficient and $R$ the seabed reaction force.

Note: The friction coefficient for contact with elastic solids is specified on the friction coefficients data form.

Contact area

This is used to determine contact forces when the buoy comes into contact with the seabed and with elastic solids. If the value is '~', then OrcaFlex calculates the contact area as $\text{volume} / \text{height}$.

A value of zero disables contact forces for the buoy.


Drag forces are calculated in each of the global axes directions $G\urm{X}$, $G\urm{Y}$ and $G\urm{Z}$. For each direction you define a drag coefficient and drag area.

Added mass

Fluid inertia effects are calculated in each global axes direction, based on the added mass coefficients $\Ca$ for each direction. The inertia coefficient $\Cm$ is implicitly defined as $1{+}\Ca$ in this calculation.

Characteristic scales

For some models it may be desirable to explicitly set a characteristic length and characteristic force for the 3D buoy. These characteristic scales directly affect the convergence criteria of the iterative solvers employed in the analysis. The data does not appear on the 3D buoy data form but can be found on the all objects data form.