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Dynfloat runs

For Dynfloat runs the following tabs are available:

  • Run definition
  • Signal selection
  • Statistics
  • Time traces
  • Visualizer
  • Output files
  • View line shapes

 

Run definition

In the tab Run definition the scenario of the run is defined. 

First, a configuration has to be selected. This is done by means of a pull-down menu showing all the available configurations in the project. Second, an environment has to be selected. Again, this is done by means of a pull-down menu showing all the available environments in the project.

Normally, the time simulation step is 0.5 seconds. By choosing the skip factor of 1, the logging interval is the same as the simulation time step. If the simulation time step is small, a logging file will be large. To reduce the file size, the logging skipping factor can be increased.

 

Start-off and swell up periods

The total simulation time can be subdivided into four periods:

  1. Start-up time for constant environmental forces (T1)
  2. Simulation time with constant forces (T2)
  3. Start-up time with dynamic forces (T3)
  4. Simulation time with dynamic forces (T4

In the first period, only constant environmental forces are applied. The forces are gradually applied with a start-up function such that they slowly increase from zero towards their maximum value at the end of the start-up period. The use of constant forces implies that:

  • Wind gust is not applied (only mean wind force based on mean wind speed)
  • The first-order wave forces and varying wave drift forces are not applied (only the mean wave drift forces)

The length of this period can be zero.

In the second period, other constant forces are applied. The length of this period can be zero.

In the third and fourth period, the dynamic forces are included (wind gust, first-order wave forces and slowly varying wave drift forces). However, during the third period, the dynamic part of the force is gradually applied again with a start-up function. The length of the third period can be zero.

Below, an example of the build-up of a typical force is shown.

SwellUp.gif

The first three periods T1, T2 and T3 of the simulation are excluded from the statistics. The statistics are calculated during the fourth period T4, when all forces are fully applied.

 

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Mooring line dynamics

When the mooring line dynamics is checked, the dynamic properties of the defined legs are taken into account during the simulation. When  "Generate element node signals" is checked, every x,y,z position of each node is generated as signal for review.

By default the ground absorption is set at 0.25m.

If too many nodes are defined, it will take a lot of CPU capacity.

In case the following message is shown in the message-window "Maximum time step reduction is reached in the dynamic anchor line computation, solving is aborted", then most probably one or more elements of the indicated anchor lines are compressed instead of strained, due to large motions at the fairleads or at the seabed. This can cause numerical instabilities when the compressions are too large. Please contact MARIN at support@marin.nl for assistance.

 

 

Static calculation

In a static calculation the equilibrium position of the vessel, with or without the environment, is determined with an iteration procedure. In this case there are no timetraces. The results of the calculation can be found in the <run name>.sta file.

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Signal selection

In the signal selection tab the signals for the post-processing are defined.

Before signals can be selected, a configuration in the Run definition tab has to be defined.

By selecting the signals with the mouse and shift or ctrl held down, signals can be quickly selected and deselected with the "Use selected" or "Do not use selected" buttons. A number of basic signals are permanently selected: vessel position and motions, line tensions, wind and waves.
Because the number of current layers can vary from run to run the current signals are not present in the list. When they need to be generated, the check box "Current layer signals to be generated by the model" must be selected. For each current layer the current speed and direction will be reported.

 

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Statistics

The statistics tab shows a table with the following statistics per signal:

  • mean value
  • standard deviation
  • maximum
  • minimum.

These statistics are copied from the <run name>.rep file. The top part of the table is shown in blue. This part contains a fixed selection of sgnals.The naming of these signals is also fixed: a moored vessel is named "Body 1" and an approaching vessel is named "Body 2". These signals comprise the body's position, motions, total forces and the forces of each excitation source, like current, damping, hydrostatics, lines, fenders, etc.

In the lower, white part of the table the user's selected signals are shown with the actual names of the vessels.

 

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Time traces

In the Time traces tab time traces can be plotted of the selected signals. A pull-down menu shows the available signals. The signal list contains a basic data set and an extended data set. The basic data set contains vessel position, motions, line forces and fender forces. When the check box "Use extended dataset" is selected the environmental signals are added to the list: wave height and direction, wind speed and direction and current layer speed and direction.

When in a Dynfloat run line dynamics are applied and the check box "Generate element node signals" is selected, the extended data set contains also for each node in the mooring legs the X-Y-Z position and tension.

The lower and upper boundaries of the time and Y-axes can be adjusted to zoom-in at the graph. Multiple lines can be plotted in one plot. When a signal is selected and plotted it is removed from the pull-down list. After clearing the plot with the "Clear" button all signals are put back in the list.

The plot can be saved as a png-file with the "Save As" button.

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Visualizer

In this tab the simulation can be viewed as a 2D animation.

Above the plot there are options to manipulate the animation:

  • Play ratio: this sets which frames are plotted. If it's 1 then each time step of the simulation is plotted, if it's 2 every second time step is plotted, etc.
  • Generate echoes: when selected the contour of the vessel remains visible at the selected time rate. This helps viewing the envelope of the vessel's motions.
  • Echo update rate: this sets the time rate at which the echoes are plotted. 

At the centre bottom of the plot there are small buttons with which the view can be manipulated: zoom-in and -out (magnifying glass buttons), restore initial view (home button), panning  (hand button) and rubber band zooming (rectangular-with-arrow button). Note that when the panning button is selected it replaces the rubber band zooming button and vice versa: only one of the two buttons is visible.
To the right of these buttons there is also a button with a camera: it allows saving the current view to a jpg-file.

In the bottom left corner of the panel there are the standard video playing buttons: start playing, pause and stop playing.

 

Output files

At the Output files tab all files are shown which were used and generated by the run. All files are in ASCII and can be opened by double-clicking with the mouse. When the "Remove output" button is pressed all files will be deleted.
  

File name Description 
<run name>.ini aNySim input file with the complete model description
<run name>.rep aNySim output file with input review and run statistics
WindCoef_<vessel name>.ini

file with wind coefficients, present when wind is applied

CurrentCoef_<vessel name>.ini file with current coefficients, present when current is applied
samples.txt  ASCII file with signal time traces
f900.log log file
messages.txt log file
status.txt file with run status (i.e. success, failed) and messages of signal level exceedences
StaticShapes_Mooring_1.txt file with node positions and tensions of all anchor lines in the mooring system
DesignShape_Line_#.shp file with line node positions and water depth

 

 

Depending on the file, the following names are used (see Known bugs):

  • Moored vessel, buoy: either body 1 or FPSO
  • Approaching vessels: either body 2 or shuttle 

 

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