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Artificial stiffness in Vessel data may help to optattin Static equilibrium.

If there are convergence problems in the static solution, the user should add artificial stiffness to the vessel. Although it has no physical meaning, it is required in the Static analysis. Because at the beginning of the Static analysis, the mooring system might not be able to provide sufficient restoring force, then the artificial stiffness will help the calculation to get converged. And it will be reduced step by step, so not to affect the result if it has been defined with a proper value.

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DeepC generating empty dynmod.inp

Possible reason:  T1.FEM (geometry file) is missing. Riflex requires this to create dynmod inp.

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Does DeepC support wave drift damping for Simo?

There is a misunderstanding here that DeepC or Simo cannot set up the parameters for calculation of wave drift damping. From DeepC, it is not directly supported to set up these parameters. It can however be edited in the Simo input files (by running DeepC and locking the input file).

There is an ongoing discussion wether it is numerically correct when Simo calculates this wave drift damping. The main focus is on, when Simo calculate the drift damping force, a relative velocity (directly calculated from the vessel motion time series and current velocity) is multiplied by the drift damping coefficient. However, the theory of wave drift damping assumes that the vessel velocity is small compared to the wave speed; if it is not then these formulae can result in unreasonable encounter effects. Strictly, the slow motion should be time independent.

If checked with the Simo TM, it indicates how Simo calculates using Newman’s method. But the question here is that, when calculating Vir (=Vic – Vib), Simo uses the full vessel velocity (Vib), instead of the low frequency part (which can be derived by filtering the full motion time series). And this may arouse arguments since damping coefficients are calculated based on slow motions.

The reason Mimosa does not have this problem, is because Mimosa calculates wave frequency motion and low frequency motion separately, thus when it calculates the drift damping, it uses the low frequency motion.

A reference is found to the document DNV GL RP-F205, which indicates that the wave drift damping is proportional to the forward velocity. Numerically the terms proportional to the time deviation of slow motion has been neglected. Finne’s paper, as referred in the RP, is enclosed.

Our conclusion to this is that the calculation of drift damping force in Simo is not consistent and it is up to our client’s own discretion to use this function. This is also the reason we did not implement this function from Simo to DeepC.  On the other hand, the solution in frequency-domain is more consistent.

Please see the attached document ISOPE2000 - Prediction of the Complete Second Order Wave Drift Damping Force for Offshore Structures.

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ERROR during time domain simulation, heading outside range (from Simo 4.0 / DeepC 4.8)

Version: From 4.8

If the following error message is encountered (example):

     *** ERROR during time domain simulation, heading
               of body outside range defined when
               generating responses.

The reason for your error is that the vessel is performing a yaw motion outside the allowable heading range, which has a default value of 45 degrees.

THE FOLLOWING SOLUTION APPLIES TO DeepC from version 4.8 and Simo version 4.0 and above:

To allow for a larger heading change than default (45 degrees) you have to modify the Simo input file manually:

The following line in DYN.MAC in the analysis folder:

**y                     ' Default method parameters ? (N)    **

**                
**

should be replaced by the following sequence of lines (the name OOB must be replaced by the name of the floater in your model):

** ' *** VVVVVVVVVVVVV Changes from next line *** VVVVVVVVVVVVVVVVVVVVVVVVVVVVV
 N                     ' Default method parameters ? (N)
 Interpolation in time domain  ' Heading changes 1st order wave force, OOB
 180                                  ' Max heading change (deg)
 Newman model - pregeneration  ' 2nd order wave drift force - pregenerate, OOB
 Interpolation in time domain  ' Heading changes 2nd order wave drift, OOB
 180                                  ' Max heading change (deg)
 Resultant, ie. sum of all dir ' Storing of wave elevation, OOB
 Resultant, ie. sum of all dir ' Storing of wave elevation , ORIGO
 ' *** AAAAAAAAAAAAA Changes until previous line *** AAAAAAAAAAAAAAAAAAAAAAAA**

Please make sure that the edited DYN.MAC  is not overwritten by DeepC.

This can be done by NOT ticking the tick mark “Automatically regenerate input files” in the Analysis Control window, or use lock settings in the Export Model / Generate Input files.

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How is Fatigue damage computed in DeepC?

Fatigue damage is computed in DeepC using the modules Riserlife and Accdam.

Riserlife computes the damage for one seastate for a pipe section.

Accdam is used to add up all partial damages for all seastates and associanted probablilities from the scatter discretization.

Further details on Riserlife can be found in the attached document.

Please see the attached document Riserlife_Erica.

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How to do fatigue analysis for mooring lines with zero bending stiffness

The fatigue calculations in DeepC are designed for Steel Catenary Risers (SCR) using S/N-curves, and not for mooring lines. The method may however be adapted to use with T/N-curves (tension vs. number of cycles) for mooring lines by the following settings:

  • The S/N curve for fatigue analysis must be replaced by T/N curve.
  • Set the cross sectional area to 1
  • Use a very low bending stiffness (close to zero, but not zero)
  • Give a huge moment of inertia to the line to reduce the contribution from bending stiffness even more.

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Min. and max. for envelope curves show deviation from static solution

When the envelope curves for minimum and maximum (or other statistical) values are plotted along a line, the values shown are the deviations from the static solution for the line.

If the real values are wanted, the static values must be added manually (or in Excel)

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Not able to obtain Static Equilibrium Solution in DeepC

The reason for not getting a static equilibrium solution in DeepC is often a combination of:

  1. The compensating force for extra buoyancy (due to riser and mooring line tension) is too low.
  2. The stress free length of the tendons is too long.

To mitigate the problem, you must look at the Wadam results (WADAM1.LIS) to see the difference between the gravity and the buoyancy forces. The compensating force must be equal to this extra buoyancy (directed upwards). Secondly you must compare the wanted tension from the tendons to the axial stiffness. The stress free length must be shorter than the actual length for the tendons, so they acquire the correct tension when they are stretched to the actual length. When looking at the Static Configuration step by step, you may see that the tendons have negative tension, i.e. they go into compression, and hence it may not be possible to obtain a proper solution.

HINT: To view the static configuration, do the following: Right-click on the analysis and select "Read Static Results" Select the "Static View" view option Right-click on the analysis and select "View Static Configurations ..." In the pop-up window "Static Results" you can step either forwards or backwards.

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Quadratic Transfer Function (QTF) Wadam analysis Wadam (All to 9.1-02) + DeepC (SIMO/RIFLEX)

This FAQ gives information regarding some limitations and workarounds when applying HydroD/Wadam to calculate QTFs and then using the QTFs in DeepC (SIMO/Riflex).

The current limitation of Wadam on this: even though the user does not request second-order pressures, these are still computed and processed by Wadam during the calculation of QTFs. And this limitation will greatly increase the computation time.

Thus we have proposed the following workaround as attached. Also in the attachment it is described how you can apply the QTFs successfully in DeepC.

Newer versions of Wadam, 9.2-03 and later, avoids this issue. Especially version 9.4-03 has significant updates regarding 2nd order analysis.

Please see the attached document 2nd order Wadam analysis + DeepC (SIMORIFLEX).

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Recovering from workspace crash

The following error message shows that the workspace file has become corrupt, probably by one of the last commands you entered:

*CMofaMainApp: Exception caught*

*Unknown Exception caught *

To recover from the error you should do the following:

Create a new workspace in DeepC, and save the workspace.

In the old workspace folder you have JS files with names like “_yyyymmdd_hhmmss.js”, where yyyy is year, mm is month, dd is date, hh is hour, mm is minute and ss is second. These are so-called sequential

Copy the file with the time stamp closest before the error happened the first time, to the new workspace folder. Also copy the necessary data files (T-files for vessel geometry, G-files for Wadam global response, other input files) to the new folder.

In the new workspace, try to read the JS file referred to above, to see if it is OK, or if DeepC crashes again.

If DeepC still crashes, it may be one of the last commands in the JS file that causes the error. Then do as follows:

Close DeepC. Answer NO if DeepC asks if you want to save the workspace. We do not want to save a corrupt workspace.

Edit the JS file (referred to above) and deactivate the last JS command by inserting the string “//  “ in the beginning of the line. This will make DeepC to interpret the line as a comment and not a command.

Start DeepC again. Select the menu File -> Recent Workspaces, and select the workspace you are working on, it is probably on the top of the list.

Read the same JS file again. 

If DeepC still crashes, repeat the steps in this paragraph by deactivating one more command etc., until the problem is solved. If this needs to be repeated more than 5-8 times, the error is probably so serious that this procedure does not help.

When the error is solved by this method, you should save a “Clean JS file” in order to have a point of recovery. 

HINT: It is a good idea to save a clean JS file now and then, especially before you start experimenting with different parameter settings for analyses etc. In this case it is good to have a “safe haven” to return to, in case the experimentation is going wrong (this is from my personal experience).

PS:  It is also possible to make a new workspace in the same folder as the original workspace, but it is more risky, you may risk to overwrite the sequential JS files. Please make sure you have a backup of all JS files in this folder stored in another folder. The method is to delete the *.ddb file and then create a new workspace with the same name and location as the original one.  If you are asked by DeepC if you want to regenerate the workspace, answer NO, and proceed as explained in the beginning of the email, by saving the (empty) workspace and then read in the sequential JS file.

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Recovering lost panes (GUI, CLI etc.) by resetting registry.

Another attempt you can try is to delete the information about DeepC in the registry.

Here is the method, repeated:

The user has to have admin rights to do this. Her is the process:

First close all instances of DeepC

Start a Command Prompt Window (DOS-window) and type the command regedit

A new window called “Registry Editor” will open:

Go through the following folders to find the settings for DeepC 4.6-08  (change the corresponding number for different versions):

HKEY_CURRENT_USER

                Software

                                DNVS

                                                DeepC

                                                                4.6.08

Right-click on “4.6.08” (see above). A pop-up menu opens, and select “Delete” in this menu.

Confirm deletion in the following window:

Close the Registry Editor window.

Start DeepC again (it may take a little longer time the first time). I do not think it is necessary to log out or restart the computer.

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Send a command to the operating system from a Sesam journal file (DOS Windows)

For classic Sesam you may send a command to the operating system ( DOS Windows) from a Sesam journal file by typing a ! before the command. E.g. ! copy FileA FileB ! C:"Program Files"\DNVS\SESAM\Bin\Installjac.exe

Remenber to quote blanks in DOS. E.g. "Program Files"

Can be used in Manager to start a non supported program

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Wind and current loads in DeepC

DeepC does not print the time series of wind and current loads.

In order to print the loads, one needs to manually modify DYN.MAC file in the analysis folder. One should make a manual revision every time if he or she has a different DeepC model.

As an example, a revised DYN.MAC file is attached. The example is a two body model and the below parts have been revised manually:

/                     ' Default storage parameters ? (N)

 y                     ' Store WIND FORCE ? (N)

 1 1 1 1 1 1                          ' Specify storage for VESSEL1 (6 DOF)

 1 1 1 1 1 1                          ' Specify storage for VESSEL2 (6 DOF)

 y                     ' Store TOTAL FORCE ? (N)

 1 1 1 1 1 1                          ' Specify storage for VESSEL1 (6 DOF)

 1 1 1 1 1 1                          ' Specify storage for VESSEL2 (6 DOF)

 /                     ' Store RETARDATION FORCE ? (N)

 /                     ' Store HYDROSTATIC STIFFNESS FORCE ? (N)

 /                     ' Store LINEAR DAMPING FORCE ? (N)

 /                     ' Store QUADRATIC DAMPING FORCE ? (N)

 y                     ' Store QUADRATIC CURRENT DRAG FORCE ? (N)

 1 1 1 1 1 1                          ' Specify storage for VESSEL1 (6 DOF)

 /                     ' Store SPECIFIED FORCE for any body ? (N)

 /                     ' Store GLOBAL POSITION ? (Y)

 1 1 1 1 1 1                          ' Specify storage for VESSEL1 (6 DOF)

 1 1 1 1 1 1                          ' Specify storage for VESSEL2 (6 DOF)

 /                     ' Store GLOBAL ACCELERATION ? (N)

 /                     ' Store LOCAL VELOCITY ? (N)

The manual procedure is as follows:

  1. Run DeepC(Input and Static analysis) with default option.
  2. Copy the analysis folder to a new folder.
  3. Run Simo in DOS mode in the new folder.     a. Start Dynamic mode.     b. Record all commands by typing @create my_macro        i. Then my_macro.MAC will be created in the new folder and all commands you make will be recorded.        ii. For more details, please see the SIMO user manual (e.g. ver. 4.8), sec. 2.1.1 Macro System(pp.3-4).     c.Input commands properly.     d. Stop recording by typing @close
  4. Open the my_macro.MAC file and compare with the original DYN.MAC that was automatically generated by DeepC with default options.
  5. Edit the DYN.MAC file by updating the necessary parts recorded in the my_macro.MAC file.
  6. Copy the revised DYN.MAC file to the analysis folder.
  7. Run the dynamic analysis in DeepC. Don’t forget to switch **OFF **the ‘Automatically regenerate input files’ not to overwrite it.
  8. After finishing the dynamic analysis, read all results.
  9. Go to the ‘Vessel Time Series’ folder and you will find time series of wind and current forces.

Please see the attached document DYN.

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