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Q&A forum: Vessel Motions
(displacements, velocities and accelerations)

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Trying to use Vessacc and RAO we found that applying the DVN rules was giving lower results than the harmonic for small waves.

We bought another version through one of my young engineers (Vasilis Papadopoulos) and then we found that there was a problem in the previous editions of Vessacc and RAO which I got.

We check also the waves but we found no problem between the 2 editions.

I am sending you, for your consideration, the slides with the comparison, together with the excel file of the data. The results are for a specific angle μ (angle of wave direction in respect to vessel direction), and a specific angle θ (angle through the wave). For different angles you get bigger or smaller x,y,z components for acceleration.

Your customer has indeed recognised an error in the earlier version (1.0) of Vessac
It is a coding error that was corrected in the later version (1.2)
... this was the only correction made to the calculator
The latest version is correct and the earlier version is not correct.
The issue raised by your customer only applied to the Classical Harmonic calculation option of version 1.0, it did not apply to the DnV Rules for Ships calculation option.

Any customer running version 1.0 of this calculator may contact CalQlata direct for a free copy of version 1.2 in which the above error has been corrected.

Having read the technical help, I would like to ask you the following:
Input zᴿᴬ is defined as heave RA in m. In the technical help doc you say that you must enter the amplified response itself, and the amplified response operator (RAO).
Output zᴳ is defined as heave in m @ CoG

I would expect output zᴳ to have the same value with input zᴿᴬ, which is not the case when I run the analysis.

Is it possible to give me some insight?
zᴿᴬ is the RA (in metres) at the vessel's centre of gravity
zᴳ is the actual movement of the vessel at the CofG taking acceleration and velocity and phase angles into account

The maximum heave at the vessel's centre of gravity will not necessarily occur at the peak of the wave and accelerations and velocities will cause the vessel to move independently of the water in which it sits.

(No relevant questions have been issued for this program to date)

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