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Issue with radiation wave elevation (probably related to phases) #431
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Thank you for reporting this. I don't have the time to look in depth into it right now, but here are some comments:
But there has been some reports of suspicious results (such as #191 and #387) so there might be a bug somewhere in there. Footnotes
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Your comments solved the entire issue ;) Your last comment is a copy & paste error from here: https://github.com/capytaine/capytaine/blob/v2.0/docs/user_manual/examples/boat_animation.py#L44 So the example should be corrected. For the sake of completeness, here's the adjusted code:
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Ah, yes indeed. Would you like to submit a PR with the correction? |
Yes, will do (I have not done this befoe, so I probably need some time to dig in the github details ;)) |
Dear all,
I have a question regarding the free surface elevation of radiated waves. I computed them based on the cookbook examples using the new
compute_free_surface_elevation
in version 2.0 (source: here) andget_free_surface_elevation
in version 1.5 and 2.0 (source: here and here)Each function yields different wave elevations (code to generate the plots is at the end of this issue):
2.
3.
4.
5.
6.
The results of
get_free_surface_elevation
(plots 1. and 2. as well as plots 4. and 5.) seem to differ in phase only. The results ofcompute_free_surface_elevation
look very different.With motion RAOs for a wave direction equaledit: Since the radiated waves due to roll and sway cannot be symmetrical (opposite phases on port and starboard side) for a given time instant, the total radiated wave pattern for a certain time instant cannot be symmetrical either. Only heave radiated waves are symmetric to the x axis. This can be seen in the plots 7., 8. and 9. For 90°, roll and sway contributions are cancelled out by the heave contribution on the side where x is positive.pi/2
, I would consider the results of the new function in 2.0 (plot 3.) to be correct, since the radiation should be in both directions. ButI would expect plot 6. (motion RAOs for 270° wave direction) to be symmetric to plot 3. (90°).
8.
9.
Additionally, results obtained with version 1.5 show a better agreement with tank tests (really small 1:144 model in a narrow tank, so I consider the agreement acceptable) compared to
compute_free_surface_elevation
results (plots consider incident, radiated and diffracted waves):Here's the code to produce the first six plots in this issue
Summarizing my questions:
get_free_surface_elevation
is deprecated in 2.0, the results should be that same in 1.5 and 2.0, shouldn't they?compute_free_surface_elevation
differ for 90° and 270°? This is not due to the instant of time, see following plots which show the absolute values:Any hint for further investigation is appreciated!
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