Q: How can I specify different added mass and damping coeficents for different plates?

A: You can use either #PLATEs or #AREAs, and specify the added mass multiplier with -AMASS and the drag multiplier with -DRAG.

Q: How does MOSES compute the added mass on a plate?

A: The added mass for plates and #PLATES is computed as defined in DNV Classification Notes 30.5; i.e. the added mass depends on the aspect ratio of the submerged portion of the plate. For #AREAs, it is computed as outlined in the DNV notes except that the coefficient is the one for an aspect ratio of 1.

Q: Is there a way to scale the drag loads on a beam to check for slamming?

A: The during a time domain, the slam loads are automatically included in the loads on a beam. If you do anything, they will be accounted for twice.

Q: can I input directionally dependent Cd / Cm coefficients for a beam?

A: Not directly. MOSES treats all Morrisons equation members as equivalent tubes. If you feel that if this matters then you should not model them as beams but as "pieces" or as a set of #PLATES.

Q: How is the current/wave drag force on an area computed?

A: See Chapter XII of: http://www.ultramarine.com/hdesk/document/verify.pdf

Q: How is the wind force on an area computed?

A: The basic equation is:

 
    F = A * Ch * Cs * Rho * v **2 /2
 

• A is an area,
• Ch is the height coefficient
• Cs is the shape coefficient
• Rho is the density of air, and
• v is the wind speed.

Q: How can I find out the drag force on a tendon?

A: There is no direct way to get this result because it is not really useful except for checking. Thus, you can:

• Turn off the environment,
• Issue the command &STATUS F_ROD,
• Turn on the environment with the current, and
• Again issue the command &STATUS F_ROD.

Q: What is the meaning of the "wave force" I get when I issue the &STATUS FORCE command?

A: The result of all &STATUS command are applicable to the current, static, condition. As a result, the "wave force" is the mean drift force and the "drag" force is that due to current alone. There is no way to get the time variation of the wave force.

Q: Why does the ST_EXFORCE command report drift forces which do not look correct?

A: What you are getting with ST_EXFORCE is not wave drift, but first order wave excitation. You can look at wave drift raos in the Hydrodynamics Menu with V_MDRIFT. To see the results in an irregular sea, do:

       &ENV -SEA .....
       &STATUS FORCE

Q: Can you define your own spectral force in MOSES?

A: I am not sure what you mean by spectral force, but you can define a force and define a time variation to the force and bind them together. Click here for the Reference Manual and here for a test.

Q: Does MOSES use shielding effects when computing the drag force on a tubular structure?

A: Drag force is computed for all members, no shielding is assumed.

Q: When I issue the command &STATUS FORCE, I get a several different types of forces listed, what are these?

A: This is actually more of a genealogy question than a MOSES one and as always, gemology is tricky. Also, the following applied to what is reported when one issues either ELMFORCE or LDGFORCE. Here is our best explanation:

• Weight is the total force due to weight.
• Contents is the force due to contents in compartments or elements.
• Buoyancy is the net force due to water pressure.
• Wind is the force due to wind.
• Drag is the "v squared" force due to water. It is due to both the body having a velocity, the wave velocity, and a current.
• Wave is the Mean Drift Force due to waves and the force due to wave acceleration. With &STATUS, it is only static forces and hence, only the Mean Drift is reported.
• Slam is the force due to the change in added mass.
• Coriolis is the force due the Coriolis acceleration.
• Deformation is the force due to the deformation of the body. This will be zero unless generalized degrees of freedom are used.
• Extra is the "extra" force computed to put the system in equilibrium when one used &INSTATE -C_FORCE.
• Applied is the total force due to any "load sets" which have been defined and applied.
• Inertia is the force on the body due to its acceleration. This is normally zero.
• A_inertia is the force due for the acceleration of the body and its added inertia
• C_inertia is the force due the the acceleration of a body and the inertia of its "contents"; i.e. ballast water.
• Flex. Connectors is the force due to flexible connectors.
• Rigid Connectors is the force due to rigid connectors.
• Total is the new force on the body.