Contour plots can be generated if a RAO database has been generated for multiple headings. If multiple databases are selected, all must contain multiple headings to allow contour plots.

RAO

By selecting one or multiple channels, a contour plot of the RAO amplitude appears. The x-axis is by default in wave frequencies and the y-axis is the heading. If relevant, a line will show the 0 encounter frequency, the natural roll frequency, natural pitch frequency and natural heave frequency. The lines can be hidden by selecting them and un-checking the line in the menu. If the natural frequencies are not found in the file, these lines will not be shown.

The user can choose to show the data as function of period, in polar coordinates or with line contours using the different option buttons in the bottom right of the GUI. A contour containing the phases of the RAO can also be shown. By default the phases are wrapped between -180 and 180 degrees, but this can be turned off with the wrap button. Finaly, the polar plot can be extended to 360 degrees with simple mirorring.

The mirror option does not take into account the type of signal to apply symmetry or anti-symmetry. The data is simply mirrored.

In contour line mode (full button is off), the user can choose between a colorbar and/or labels. This is done by changing the options in Help>Preferences:

contour.colorbar = False # Add a colorbar

contour.clabel = False # Use value labels along the contour lines


Both options can have the same value. When contour.clabel is True, the user can choose a series of additional options:

contour.clabel.colors = None

contour.clabel.inline = True

contour.clabel.inline_spacing = 5

contour.clabel.fmt = %.5g

contour.clabel.rightside_up = True

see https://matplotlib.org/stable/api/contour_api.html#matplotlib.contour.ContourLabeler.clabel for more information.

Contour with inline labels


Contour with colorbar

RMS, SDA and Mean

RAOViewer can present the first order signals as RMS or SDA values based on a given long-crested or short-crested irregular wave spectrum. The spectrum used is a JONSWAP one with a user defined Hs, Tp and gamma. This is only valid for first order signals. For second order signals, the mean value is computed by selecting the SDA (or Mean) button, the RMS button is disabled for second order signals.

A cos^2 or cos^2s spreading function can be added. When short-crested spectra are used, the data is still presented for all headings, these are then the principal headings.

The data should contain sufficient headings to compute short-crested responses.

The data can be presented in several different ways by selecting an option from the Variation drop-down menu. This defines the X axis of the contour plot. The Y axis is always the heading. The options are:

  • Peak period: use a range of Tp with a fixed Hs, depth, roll damping linearisation and speed

  • Wave height: use a range of Hs with a fixed Tp, depth, roll damping linearisation and speed

  • Speed: use all speeds availbale with a fixed Hs, Tp, depth and roll damping linearisation

  • Roll amplitude: use all roll amplitudes available with a fixed Hs, Tp, depth and speed. This can be usefull to check non-linear roll damping effects.

The range of Hs or Tp is chosen by specifying a start, step and stop value. The depth, speed, heading and roll amplitude ranges are defined by the content of the database. If multiple files are selected, the choices are limited to the overlapping conditions.

The roll amplitude parameter is the roll damping linearisation angle and is described further in Roll damping.

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