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
•*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.