OrcaFlex 8.5

The latest release of OrcaFlex 8.5 is OrcaFlex 8.5d. To upgrade to OrcaFlex 8.5d, download the following zip file:
  OrcaFlex-Patch-8.5a-or-8.5b-or-8.5c-to-8.5d.zip (2.1 MB)
and then run the program that the zip file contains.

This patch can only be applied if you are currently using an earlier release of version 8.5.

The new features introduced in OrcaFlex 8.5 are described below. For full details please download the following zip file: FlexHelp.zip and save the files it contains. You can then open the saved .hlp file and open the What's New topic in the Introduction chapter of the contents, and follow the links from there to other parts of the help file.

New in Version 8.5d (released September 2004)

Improvement and bug fix in calculation of wave drift load applied to vessels

  • OrcaFlex now uses the formula given in the paper by Standing, Brendling and Wilson (1987), rather than the formula given by Newman (1974), to calculate the wave drift load. The Standing, Brendling, Wilson formula has the advantage that it avoids the spurious high-frequency terms generated by the Newman formula.
  • In previous versions of OrcaFlex there was a sign error in the wave component phases used when calculating the oscillatory parts of the wave drift loads. This bug has now been corrected. The effect of the bug was that the oscillatory parts of the wave drift load were incorrectly phased. In a typical random sea application of wave drift loads, the wave component phases are random, so the phasing of the wave drift load is random and so not significant. However the bug caused the oscillatory parts of the wave drift loads to be incorrectly phased relative to the 1st order wave loads and vessel motion.

New in Version 8.5c (released September 2004)

Bug fixes

  • Saving simulation files for models which use external functions for vessel applied loads was causing errors to be reported and the simulation file to be corrupted.
  • The drawing for attached 6D Buoys with wings was incorrect when the model was in the Reset state.
  • Some simulation files which modelled line clashing could not be opened with versions 8.5a or 8.5b.
  • In some circumstances the Cancel button for the Line Type Wizard was failing to cancel changes.

New in Version 8.5b (released July 2004)

Spreadsheet output of tabular results

OrcaFlex displays tabular results in a spreadsheet window. This spreadsheet window has a maximum number of rows that it can display. If you attempt to display tabular results with more rows than this you are given the options of either truncating or sub-sampling the table before it is displayed in the spreadsheet. You are now offered the additional option of exporting the results to a tab-delimited text file which gives you access to the entire results table.


  • We have decided to change the way the added mass, damping and stiffness matrices of a vessel type are specified. For details, see the note in the added mass, damping and stiffness topic. When reading old files (written by previous releases) OrcaFlex automatically handles for you any data changes needed, so there should be no need for you to take any action. However OrcaFlex will tell you if it needed to make any data changes, in which case we recommend that you check the data. When entering new data, remember to specify these matrices with respect to the conventions directions.
  • We have also changed how the damping matrix is applied. Previously the damping load was calculated as the damping matrix multiplied by the vessel velocity relative to the earth, but this meant that the damping load tended to restrain a free floating vessel from moving with the current. The damping matrix is now multiplied by the vessel velocity relative to the current.

Bug fix

The Stress Outer and Inner Diameter data items can be modified after a simulation has been run. This is because they only affect the wall tension results, stress results and fatigue analyses. In version 8.5a, if you did modify these data items after a simulation had been run then the wall tension results and stress results were not updated accordingly. This problem has been fixed in version 8.5b.

New in Version 8.5a (released June 2004)

Distributed OrcaFlex

Distributed OrcaFlex is a suite of programs that enables a collection of networked, OrcaFlex licensed computers to run OrcaFlex jobs, transparently, using spare processor time. More information can be found here.

Spectral Response Analysis

A new facility for calculating RAOs for any OrcaFlex results variable has been added. The method uses a fully non-linear random wave simulation together with the Fourier transform to generate the RAOs. Full details of the method can be found in the Spectral Response Analysis topic.

Fatigue Analysis

  • A spectral fatigue analysis capability has been added which makes use of the new Spectral Response Analysis feature. This fatigue analysis method is in addition to the existing regular and rainflow fatigue analysis methods.
  • The load case damage results are now reported as damage per hour. In previous versions of the software they were reported as damage per cycle (for regular analysis) and damage accrued over the analysed simulation period (for rainflow analysis). The change has been made for the sake of consistency between the different fatigue analysis methods.
  • Fatigue Analysis results now includes details of where on the line the worst damage occurred. This is reported both for individual load cases and for overall total damage.
  • The Fatigue Analysis now allows you to specify which stresses are to be calculated. The fatigue calculation is quicker if fewer stress components are analysed so this feature can help you to reduce calculation times. For example, in cases where pressure effects are not significant for damage you may choose only to analyse ZZ stress.


  • Several new (optional) facilities have been added which enable coupled analyses, i.e. where the motion of a vessel is calculated allowing for the effects of not only waves but also other loads, such as those from attached lines or other objects, applied loads, etc. First, you can now specify 1st order wave load RAOs for a vessel type and include the resulting wave loads on a vessel. Second, you can now specify the added mass, damping and hydrostatic stiffness matrices for a vessel type in full 6 degrees of freedom. Third, you can now set a vessel's Primary Motion to a new option, called Calculated (6 DOF), in which OrcaFlex calculates the motion of the vessel in full 6 degrees of freedom. Together, these 3 new facilities enable coupled analyses, which is useful for systems where the vessel motion is significantly affected by other loads, e.g. from attached lines or other objects. With this approach no superimposed motion would normally be applied (since the wave induced motion is already being calculated and included in the primary motion). Note that in this release only a single pair of added mass and damping matrices can be specified and these are used for all frequencies; in a future release we intend to allow these matrices to be frequency-dependent.
  • Vessel applied loads may now be set for all 6 degrees of freedom.
  • You may now more easily specify which loads are included for the vessel. Ticking a check box means that load will be applied to the vessel. If the vessel primary motion is set to be calculated then the vessel motion will allow for the included loads.
  • Individual results are now available for those loads which have been included.


  • The OrcaFlex spreadsheet now has an Instructions Wizard which helps you to create OrcaFlex spreadsheet instructions interactively. It can be thought of as the equivalent of the Select Results form in OrcaFlex.
  • The OrcaFlex spreadsheet has a new Duplicate Instructions feature which allows you to duplicate sets of OrcaFlex spreadsheet instructions for multiple load cases. Suppose you are analysing a number of different load cases for a variety of environmental conditions. Once you have built the spreadsheet instructions for a single load case you typically want to generate the same instructions for each other load case. This Duplicate Instructions feature automates the procedure.
  • A new command called Spectral Response Graph has been added to the OrcaFlex spreadsheet.
  • A new command called Working Directory has been added to the OrcaFlex spreadsheet. It outputs the directory where the spreadsheet is stored. If you are using relative paths then this command helps keep track of the base path for QA purposes.


  • OrcaFlex allows you to specify non-linear bend stiffnesses for Line Types by defining a table of bend moment against curvature. To help create this table we have added a Plasticity Wizard. This asks you to specify the relationship between material stress and strain and then derives the table of bend moment against curvature. The stress/strain relationship can be specified either as a table or by a Ramberg-Osgood curve.
  • Torsional stiffness can now be non-linear, by specifying variable data.
  • When torsion is included, lines with zero twist stiffness at each end can now be analysed. In previous versions of OrcaFlex the program refused to analyse such lines.
  • Pre-bend can now be modelled for lines when torsion is modelled. Pre-bend is provided for modelling lines which are not straight when unstressed, e.g. spool pieces.
  • Node axis directions (x, y, z) can now be drawn in different colours (previously each node axis was drawn in the node pen colour). This helps distinguish between x and y directions thus making component results easier to interpret. The node axes directions are drawn optionally and can be controlled by the Draw Local Axes preference or by pressing CTRL+Y.
  • The Line Clashing Report, which was added in version 8.3, has been improved slightly. In the previous version the reported values of Peak Clash Energy did not allow for contact damping. This has now been changed and the reported values do indeed allow for contact damping. Note that you will need to re-run any old simulations to take advantage of this change. This is because the values reported in the Line Clashing Report are calculated during the simulation and saved in the simulation file.
  • Range graphs of component stress results (i.e. ZZ stress, von Mises stress etc.) are now available.
  • A new Line Clash Energy results variable has been added.
  • A new Mean Axial Strain results variable is available.
  • A new Sea Surface Clearance results variable is available which reports vertical clearance from node centre to the instantaneous sea surface. Negative values mean that the node is submerged.

Line attachments

  • Summary and Full Results tables are now available for flex joints.
  • In previous versions of OrcaFlex line clumps which are net heavy in water were treated differently from those which are buoyant. These net heavy clumps were intended to be used to represent drag chains and modelled the supported weight and friction effects of drag chains contacting the seabed. The drag chain object is available to perform this function and does so rather better.
  • To simplify the program we have decided to treat all line clumps the same irrespective of whether they are net heavy or buoyant. This means that if you load an old file which used the drag chain line clump feature the new program will treat such clumps differently. The program will warn you of this should you load such a file.

Connection arclengths

  • Line attachment z position specifies the arclength at which the attachment is connected. In previous versions of OrcaFlex this arclength was always measured relative to End A of the Line. This arclength can now optionally be specified relative to End B.
  • Links, Winches and 6D Buoys can now be connected to lines with connection arclength specified relative to either End A or End B. In previous versions of OrcaFlex this arclength was always measured relative to End A of the Line.


Position, velocity and acceleration results are now available for shapes.


  • The program is now more helpful if the maximum number of iterations for Buoy and Vessel Statics is reached. In previous versions the model would be reset when this occurred. Now you have the extra options of either increasing the maximum number of iterations and continuing the static calculation or to call the Use Calculated Positions feature.
  • Lines can now be excluded from the statics calculation. This can be done on the Line Data form and the All Lines Data Form. Results are not available for such lines and dynamics is disabled if you have any lines which are excluded from statics.
  • This is mainly useful when building a model and a particular line is not converging. In this situation you could exclude all other lines from from statics (this is easiest from the All Lines Data Form). This would allow you to experiment with different statics convergence parameters for the problematic line without having to wait for all the other lines to converge each time you tried a new set of convergence parameters.

User Interface

  • The batch processing form now has a check box allowing you to request that OrcaFlex be closed once the batch of runs is complete. This feature is intended principally for users with networked licences. It allows you to release your claim on an OrcaFlex licence as soon as the batch of runs is complete.
  • The Use Calculated Positions and Use Static Line End Orientations functions can now be accessed from the main Model menu.
  • A Lengths page has been added to the All Lines Data Form which shows total line lengths for all lines in the model.

VIV Toolbox

  • An Area per Unit Strength data item has been added which gives you more control over the drawing of Vortex Tracking models.
  • The time domain VIV models now allow more control over their model parameters. For details see the relevant topics for the Milan Wake Oscillator model, the Iwan and Blevins Wake Oscillator model and the Vortex Tracking models.

Bug fixes

  • Data files which use Vortex Tracking Models with non-default smear factor values were being read incorrectly in previous versions of OrcaFlex. The smear factor was being reset to the default value.
  • Simulations using time domain VIV models were sometimes giving different results if you restarted a partially run simulation. This affected the Wake oscillator models and the Vortex Tracking (2) model. With this version the problem has now been fixed and simulations can be paused and restarted without affecting results.
  • Offset graphs for multiple statics were not offering the user the option of choosing the offset direction in version 8.4 of OrcaFlex.
  • Printing, copying and exporting of the attachments data form was not working in previous versions of OrcaFlex. In addition, the Compare Data feature was not reporting any differences between attachment type data.
  • The OrcaFlex spreadsheet includes a function called OffsetCell. For users of Excel 97 this function would intermittently fail to work resulting in cells containing '#VALUE!'. This problem has been fixed in the spreadsheet distributed with this version of OrcaFlex.