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Q: What is the basis for the suggested added mass and damping for launch barges? REV 7.04 A: Originally these numbers were based on the high frequency results in a frequency domain analysis for nominal launch barge in a nominal launch position. These…

Q: How can I remove all viscous damping terms in the damping matrix when computing RAOs? REV 5.03 A: Do not include any Morrison elements, #PLATE or #AREA commands. Also, the Tanaka damping must be turned off using the A_TANAKA BNAME NONE command, and…

Q: Should I alter the default damping values for really large structures, such as big TLPs? REV 5.10 A: You should turn off the Tanaka damping and use -cs_curr 1 1 1 on PGEN or &describe piece. This adds some viscous damping to the problem, which is…

Q: How can I add a damping of some percentage of critical? REV 6.01 A: A problem here is the definition of critical damping. Critical damping is defined in terms of the natural period, but there is no "natural period". There is another FAQ on natural…

Q: How does MOSES get low frequency damping? REV 7.00 A: SRESPONSE does not include low frequency damping. The only damping here is due to viscous effect, so you can claim that this is conservative. In time domain, there is ample damping from all the…

Q: How can I input a 6x6 damping matrix? REV 7.00 A: In MOSES you model physical things. Thus, there is no need to input a 6x6 matrix. Consider for example, a single dashpot. This can be modeled as either damping added to a GSPR connector or one term…

Q: Why does the model of the BALDER have #TUBEs added for viscous damping when your answer to a FAQ says to use -CS_CURR 1 1 1? REV 7.04 A: The #TUBEs are included in the model so that we can show the effects of using them. See Section XIII of the verification…

Q: What is the difference between damping, drag, drag caused by current, and drag caused by waves? REV 7.04 A: First let's us agree that drag and damping are considered the same. Now, divide damping into radiation damping and viscous damping. The first…

This section contains frequently asked questions on the subject of damping and/or drag.

Q: What does the message "*** WARNING: Negative On Diagonal Of Damping" mean? REV 5.10 A: It means you have negative values in either your damping values and/or your added mass values resulting from the hydrodynamic pressure computation. We discovered…

Q: Do the damping matrices obtained using the v_matrices command include both linear radiation damping and viscous damping coefficients? REV 7.01 A: No, what you get with MATRICES in FREQ_RESP contains both, what you get with V_MATRICES in HYDRODYNAMICS…

Q: Is the viscous damping linearized stochastically or harmonically? REV 7.02 A: By default, MOSES linearizes harmonically via a "equivalent linearization". If you tell it to, MOSES will perform a spectral linearization. Remember that the viscous forces…

Q: How can I include damping in a cable? REV 7.04 A: Use the -DAMPING option on the class definition command.