Roll damping for barges !!

[thomasjo87]

I'm sure anyone who has done vessel motion analysis has come across this dilemma about the roll prediction for barges with rectangular cross sections and no bilge keels....

in my case im using a program based on 2d strip theory with possibilities of empirically calculating roll damping using IKEDA's method [not specifically for barges] and hence resulting in very high value of roll motion...I believe this is due to the fact that it is based potential theory and hence no viscous effects are considered and since for rectangular barge sections with sharp edges, the value of roll eddy damping [ which actually should be quite high] is not estimated correctly...

how have you the designers/engineers dealt with this problem and how have you validated the results from such programs for rectangular cross-sectioned barges ??

which roll damping formulations do you use ?? which software's ??

could be an interesting topic for discussion

 

[NavalSArtichoke]

I'm sure anyone who has done vessel motion analysis has come across this dilemma about the roll prediction for barges with rectangular cross sections and no bilge keels....

in my case im using a program based on 2d strip theory with possibilities of empirically calculating roll damping using IKEDA's method [not specifically for barges] and hence resulting in very high value of roll motion...I believe this is due to the fact that it is based potential theory and hence no viscous effects are considered and since for rectangular barge sections with sharp edges, the value of roll eddy damping [ which actually should be quite high] is not estimated correctly...

how have you the designers/engineers dealt with this problem and how have you validated the results from such programs for rectangular cross-sectioned barges ??

which roll damping formulations do you use ?? which software's ??

could be an interesting topic for discussion

Roll motions are tricky for any vessel motions program to model accurately because roll response is essentially non-linear. The early 2-D strip theory programs got around this problem by incorporating results of various model tests into their code for analyzing vessels with and without bilge keel.

Most of the data used came from Vugts in the Netherlands and from various Japanese research done in the 1960s and 1970s.

Transport barges are going to show high roll accelerations because these vessels typically are operated with large GMs.

A lot of transport analysis was done using the MOSES software developed by Ultramarine in Houston, Texas. This software has now been acquired by Bentley Systems:

http://www.ultramarine.com/

The basic MOSES package was a 2-D strip theory analysis, with the option of using a 3-D diffraction analysis (at a higher cost for the lease).

 

[thomasjo87]

I see...since MOSES is using a 3d diffraction/radiation model, I believe it would have a better prediction of the exciting wave forces and radiation/diffracion response of the vessel resulting in more accurate values than 2D strip theory, but on the matter of eddy damping is it not still handicapped , since a RANS code is required to accurate predict eddy damping ?

 

[NavalSArtichoke]

I see...since MOSES is using a 3d diffraction/radiation model, I believe it would have a better prediction of the exciting wave forces and radiation/diffracion response of the vessel resulting in more accurate values than 2D strip theory, but on the matter of eddy damping is it not still handicapped , since a RANS code is required to accurate predict eddy damping ?

You can get lost in the thicket of hydrodynamic theories playing these "what if?" games. That's why safety factors were invented, to cover the uncertainty inherent in most modeling processes. Most transportation studies also specify that a certain level of response is to be used for design, beyond the significant response, say the average of the highest 1/10 or highest 1/100 responses.

In most cases, for single hull vessels, it's a toss-up whether to use strip theory or 3-D Diffraction. For multi-hulled vessels, or vessels with complex geometry, 3-D Diffraction is better suited to account for interaction between multiple immersed bodies or pieces of bodies.

 

[thomasjo87]

You can get lost in the thicket of hydrodynamic theories playing these "what if?" games. That's why safety factors were invented, to cover the uncertainty inherent in most modeling processes. Most transportation studies also specify that a certain level of response is to be used for design, beyond the significant response, say the average of the highest 1/10 or highest 1/100 responses.

In most cases, for single hull vessels, it's a toss-up whether to use strip theory or 3-D Diffraction. For multi-hulled vessels, or vessels with complex geometry, 3-D Diffraction is better suited to account for interaction between multiple immersed bodies or pieces of bodies.

true..I get your point....After all there are some elements of uncertainties involved in every design process and we should work with what is feasible and workable...very true what u said

 

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thomasjo87

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