Buoy Properties

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Buoy Properties

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Theory

The specified buoy properties include:

(i)The mass of the buoy, and its inertia in yaw, roll and pitch

(ii)The buoy added mass matrix

(iii)The buoy stiffness (due to buoyancy) in heave, roll and pitch

(iv)The buoy radiation damping matrix

(v)Hydrodynamic force terms in heave, surge and pitch, appropriate to the dynamic analysis regular wave period

Properties (i) to (iv) must be supplied in an initial static analysis, along with the geometry and properties of the rest of the model. The load terms in (v) would normally be supplied with the rest of the regular wave dynamic analysis data. All of the inputs would typically be generated using a standard radiation/diffraction program.

There is one final important point to note. The initial draft of the CALM buoy, as reflected by the locations of the nodes and elements of the CALM buoy assemblage, should be at the level where the weight and buoyancy of the buoy are in equilibrium (the buoy is floating). This is implicitly assumed by Flexcom, so that changes in the buoyancy loads due to relative buoy/surface elevation changes are accounted for by the buoyancy terms in the stiffness matrix from (iii) above.

The buoy mass and inertia matrix is defined in the following format:

where:

M11 = M22 = M33 is the mass of the buoy

I11 is the roll inertia of the buoy

I22 is the pitch inertia of the buoy

I33 is the yaw inertia of the buoy

The added mass matrix is defined in the following format:

where:

A11 is the surge added mass

A33 is the heave added mass

A55 is the pitch added mass

A15 is the coupled surge pitch added mass

The buoyancy stiffness matrix is defined in the following format:

where:

K33 is the heave stiffness

K44 is the roll stiffness

K55 is the pitch stiffness

The radiation damping matrix is defined in the following format:

where:

D11 is the surge damping

D33 is the heave damping

D55 is the pitch damping

D15 is the coupled surge pitch damping

 

Relevant Keywords

*CALM MODEL is used to specify the properties of calm buoys.

If you would like to see an example of how this keyword is used in practice, refer to E01 - CALM Buoy - Simple.