Postresp

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Can short term response be calculated from individual wave spectra?

Regarding the short term response calculation, the Postresp user manual (page 5-39) says the following:

The wave spectra to be used have to be generated by the FULL-RANGE alternative.

Thus, we do not recommend using other solutions. It is however possible, at your own discretion, to define single wave spectra and use these for this calculation. The important part is that the naming of the wave spectra must follow the same syntax as for the Full-range option. This is a name (prefix) and a sequential number (eg. UM page 5-47).

The commands may be on the following form:

CREATE WAVE-SPECTRUM JONS1 test JONSWAP SINGLE HS-TZ 7.14 7 3.3 0.07 0.09
CREATE WAVE-SPECTRUM JONS2 test JONSWAP SINGLE HS-TZ 10.42 9 3.3 0.07 0.09
CREATE WAVE-SPECTRUM JONS3 test JONSWAP SINGLE HS-TZ 17.3 13 3.3 0.07 0.09
CREATE WAVE-SPECTRUM JONS4 test JONSWAP SINGLE HS-TZ 16.0 14.5 3.3 0.07 0.09
CREATE WAVE-SPECTRUM JONS5 test JONSWAP SINGLE HS-TZ 11.5 17.5 3.3 0.07 0.09
CREATE SHORT-TERM-RESPONSE ( ONLY SECL3011 ) ( ONLY 0. 90. 180.0 ) JONS 1 5 NONE

Please do verify that the results are as expected.

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Compare results from different runs

How to display and compare results from different result files simultaneously?

Read two or more result files. Select 'All' (bodies) in Define Presentation options.

The bodies will be avaliable in Display Response Variables etc.

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Create Specific Point

In which coordinate system is a specific point defined in Postresp?

Postresp specific points should be defined with respect to Global origin of Wadam and Wasim. 

Please see SpecificPoint_referencePosition.pdf

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Does Postresp have a Slamming option?

The Slamming feature was removed from Postresp.

The option that exists in Postresp is to use the offbody point results directly to evaluate the possibilities for slamming. When an offbody point is defined in the still water line, the calculated wave elevation will be available in Postresp together with the wave particle velocities in this point. These results may be used to evaluate submergence of a point on the vessel and the velocity of the wave at this point.

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Handling of offbody points from different data sets (G-files) in one session

Offbody points will not be updated when reading a new data set (G-file) into Postresp. The coordinates will remain as defined in the first data set. The results (response values) will of course be updated.

This because the intention of reading more data sets is to compare results from different runs of the similar analysis. The response names are handled as 'global' responses, as for other response names (heave etc.).

Also, if there are more offbody points in data set no. 2 than in no. 1, the new points will be added to the complete list of points. The complete list may thus have points from both data set 1 and 2.

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How does Postresp perform the non-Weibull long term computation?

“Non-Weibull” probability.

Given a response level x, the Rayleigh distribution provides an extreme-value distribution giving the probability fi (x) for each sea-state (cell) I, in the scatter diagram.

With the probability of occurrence,  pi of each cell, the total probability of x is p = SUM( pi* fi (x)), where the sum is taken over all cells in the scatter diagram.  

This way, we have a map, x -> p, without fitting it to a Weibull distribution.

What we are interested in is the map p -> x, giving  the response extreme for a given probability.

This is accomplished numerically, by calculating p for a set of x-values and establish the

inverse map for any given p on interpolation between these p-values.

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How does Postresp perform the weibull fit?

A least square approximation is adopted for the Weibull-fit in the log-log space where the Weibull distribution is a straight line. The residuals of the approximation are printed by Postresp. The residuals of 10e-2 and lower is regarded OK.

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How to create acceleration in Postresp

There are (at least) two ways of computing the accelerations from the motions:

Create a specific point in Postresp, then use the command Create Response-Variable Combined-Motion --- Acceleration ---- to compute the acceleration in this point based on the motions. This command is described in page 5-34 of the Postresp user manual

Use the command Create Response-Variable Second-Derivated ---, described in page 5-37 of the user manual.

When the new response variable is computed, it can be displayed, printed and used as the other responses (Display Response-Variable etc.).

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How to define off body points for Postresp in a HydroD and Wadam analysis?

To use off body point results in Postresp, specific off body points must be defined in HydroD, using coordinates given in the Global coordinate system, i.e. having the origin in the still water line.

Further calculations can be done in Postresp on the results in these off body points.

The off body point grid is used for visualization & animation in Xtract only.

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How to export pictures from Framework, Profast, Stofat, Postresp?

Update November 2017:As Office has been more restrictive to Postscript due to a security vulnerability in EPS please try this workaround:select "Microsoft print to PDF" or a similar PDF printer driver as default printer on your computerinside Postresp set the Plot to Format Windows-printersWhen you Plot the image, this will be saved in a pdf file

Please note that the file will not be properly saved until you close Postresp.

It was possible to import CGM files directly into MS Office in the past. However, a Windows update rendered MS Office uncapable of recognizing this file format.

In order to export pictures from the software it is recommended to export as Postscript format and change the file extension from .ps to .eps.

Then it is possible to import into MS Office.

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How to generate a PDF file for a plot from Framework, Profast, Stofat, Postresp

User can follow the below steps to create a PDF file for a Framework plot.

  • After a desired plot displayed on the screen, on **Set **tab select **Plot **and then choose Postscript. Click Apply or OK to save the selection.
  • Click Plot, the file with the defined name, such as FrameworkActivity1.PS, is created in the analysis folder. Now exit Framework.
  • In the analysis folder, double click the generated postscript file FrameworkActivity1.PS to open Acrobat, click YES to generate the PDF file.

See also the attached document for details.

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How to understand Panel pressure naming and symmetry

This is described to some extent in the Postresp User Manual, section 3.11, page 3-11.

PS&P* Panel pressure, alt. 1, for panel indexes less than 1000. ‘&’ is the section or symmetry plane number and ‘*’ the internal panel index or pressure point number.

The correspondence between the external element number and the panel index (internal number) is found in the list of panels in Wadam.lis. See the attached PDF.

P&P* Panel pressure, alt. 2, for panel indexes larger than 999. ‘&’ is the section or symmetry plane number and ‘*’ the internal panel index.

In a double symmetry model from Wadam, the sequence of the reflections (symmetry plane number) will be as follows:

4 | 1
-------x
3 | 2

In a simple symmetry model nos. 1 and 2 will be used.

Please see the attached document WadamPanelNumber.

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Read jnl file (Postresp, Stofat, Framework)

A JNL command file cannot be read from within Postresp (or Stofat, Framework) when it is located in a folder using blanks (spaces) in the name or path. Workaround: copy the file to another folder, e.g. C:\DNV\workspaces

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Use of CREATE HYDRODYNAMIC-INTERFACE (Prepost)

Prepost can convert results from a structural results file R#.SIN, based on frequency domain wave loads, to a hydrodynamic type of results file, like G1.SIF, for use in Postresp.

This is for example relevant if statistical calculations are needed for structural responses of stresses or displacements, because Postresp cannot read the R file directly. The command syntax is typically:

 OPEN, SIN-DIRECT-ACCESS, ' ' R100, OLD, READ-ONLY
 CREATE HYDRODYNAMIC-INTERFACE, ' ', G1, 1 NODAL-DISPLACEMENTS 1 X END

Please see the user manual for Prepost for details.

Notice that this command is only available if the S#.FEM file is available when running Sestra, together with the T#.FEM and L#.FEM files.

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Use of units

Postresp is using the units defined in the model and in HydroD.

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