OrcaFlex 8.6

The latest release of OrcaFlex 8.6 is OrcaFlex 8.6d. To upgrade to OrcaFlex 8.6d, download the following zip file:
OrcaFlex-Patch-8.6a-or-8.6b-or-8.6c-to-8.6d.zip (1.9 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 8.6.

The new features introduced in OrcaFlex 8.6 are described below. For full details please download the following zip file: FlexHelp.zip (1.3 MB) 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 8.6d (released August 2005)

Groups of objects in the Model Browser can now be referred to in batch scripts. The properties of a group which can be modified are Name and Hidden.

Bug Fixes

Earlier versions of 8.6 had a reporting error for lines with zero bend moment and zero connection stiffness. In earlier versions of 8.6 such lines were reporting non-zero bend moments at the line end. Note that this problem only affected the reported values of bend moment - the program correctly used a value of zero internally to calculate the line's motion.
In certain situations the line clashing calculation was not working properly. This problem only arose for cases where a segment was involved in a clash and the following segment did not have clash checking enabled. In turn, this only arises for segments at a section boundary and where the second section has clash checking disabled. In this situation the effect was that the clash force on the node at the section boundary was applied after the original clash had ended. This is easily detected in problem cases because the erroneous force applied to the node leads to the line assuming a quite unrealistic shape. In fact a model with these characteristics almost certainly should have clash checking enabled for both sections in question - if a clash occurs in the final segment of one section then it is very likely that one would occur in the first segment of the following section. Because of this we expect that it is unlikely that this bug will affect many previously run simulations.

Both these problems have now been fixed.

New in Version 8.6c (released July 2005)

Bug fix

In some circumstances, vessel RAOs and QTFs were not being interpolated correctly. This problem could only arise if both of the following conditions apply:

there are at least two wave components, with different directions; and
the difference between these wave directions is smaller than the minimum difference between RAO directions;

and additionally one or more of the following also applies:

the vessel turns about its primary Z axis either during the statics calculation or in dynamics; or
wave heading minus initial vessel heading is < 0 or > 360 degrees for at least one wave component.

Under these circumstances, the interpolation of displacement RAOs, first order wave load RAOs, and second order wave drift QTFs may have been incorrect. This problem has been fixed in OrcaFlex 8.6c.

As it is not straightforward to determine whether or not a particular simulation has been affected by this bug, we have produced a utility which will do this for you. This utility, called RAOBugCheck, can be run by downloading the following zip file:
RAOBugCheck.zip (1.6 MB)
and then running the program that the zip file contains.

New in Version 8.6b (released April 2005)

Pressure effects on Lines

OrcaFlex 8.6b reverts to using the stress diameters to calculate the difference between effective tension and wall tension, as was done by OrcaFlex 8.5 and earlier. OrcaFlex 8.6a (only) used the outer and inner diameters for this purpose, but we have concluded that the approach used by OrcaFlex 8.5 (and earlier) was better for most cases. So OrcaFlex 8.6b onwards use the same method as OrcaFlex 8.5 and earlier, i.e. uses the stress diameters.

As a result of this change, the stress diameters can no longer be edited when a calculation is active. You must reset the model first.

This change only affects cases where the stress diameters differ from the ordinary diameters. In such cases the wall tension reported by OrcaFlex 8.6a (only) effectively assumed that the annulus between the stress OD and the full outer diameter carried zero wall tension and the whole of the axial force was carried by the stress annulus. In OrcaFlex 8.6b we have reverted to the model used in OrcaFlex 8.5 and earlier, which effectively assumed that the annulus between the stress OD and full outer diameter carries an axial load which matches the ambient external pressure.

This is a more suitable model for the majority of cases, for example attached buoyancy modules, since such modules are in compression due to the external water pressure. However note that there could be cases where this model is less suitable. In such cases the wall tension, and hence stress results, reported by OrcaFlex may not be suitable and we recommend users then take the effective tension reported by OrcaFlex and do their own separate wall tension and stress analysis.

The same applies to cases where the stress ID differs from the inner diameter. OrcaFlex 8.6a used the inner diameter for this purpose, which corresponds to assuming that the annulus between the two diameters carried zero tension. In OrcaFlex 8.6b we have reverted to the same as OrcaFlex 8.5 and earlier, i.e. that the stress ID is used when calculating the difference between effective tension and wall tension. This is equivalent to assuming that the annulus between the two diameters is at the ambient internal pressure in the line. We believe this is a better model for most cases, for example non-structural pipe linings.

For cases where the stress diameters differ from the outer and inner diameters you should consider whether the model used by OrcaFlex is suitable. If not you should do your own calculation of wall tension and stress results. See the warning in the Line Pressure Effects section.

For more details contact Orcina.

VIV Toolbox

New commands have been added to the batch script facility to allow the export of SHEAR7 data and Mds files.

New in Version 8.6a (released February 2005)

Pre-processing

A new feature called Wave Scatter Conversion has been added. This tool converts a scatter table of sea states to a scatter table of regular (i.e. individual) waves. The tool can be opened from the OrcaFlex Calculation menu.

Pressure effects on Lines

OrcaFlex now uses the ordinary outer and inner diameters to calculate the difference between effective tension and wall tension. Previous versions (OrcaFlex 8.5 and earlier) used the stress diameters for this purpose. This change therefore only affects cases where the stress diameters differ from the ordinary diameters. In such cases the wall tension reported now includes the pressure contribution on the whole annulus (i.e. between the inner and outer diameter) whereas previously it only included the pressure contribution on the stress annulus.

We have also improved the way OrcaFlex handles the small length changes to lines caused by internal and external pressure. The changes to the program, which are described below, mean that the old and new versions give different results for lines (the new version being the more correct). For most cases the differences are not significant, since length changes due to pressure are very small. But the differences can be significant for length-sensitive cases, such as a stiff straight pipe connected between fixed points. For such a case small length changes can cause significant changes in tension.

These improvements enable OrcaFlex to model cases like pipe buckling due to pressure effects. OrcaFlex has been validated against the experimental results for such a case obtained by Palmer and Baldry.

The changes are:

OrcaFlex now allows for the small length changes due to internal and external pressure. In previous versions (OrcaFlex 8.5 and earlier) the user had to allow for such length changes by specifying the unstretched length in the pressured state, and further length changes due to changes in pressure during the simulation were not allowed for. Now the unstretched length is the unstressed length at atmospheric pressure (both inside and out) and length changes due to pressure are calculated and allowed for by OrcaFlex.
OrcaFlex also now allows for length changes from the Poisson ratio effect from radial and circumferential stress due to internal and external pressure. OrcaFlex release 8.5 (and earlier) did not allow for the Poisson ratio effect, so it effectively took the Poisson ratio to be zero.
The contents pressure is now the internal pressure at a fixed specified reference Z level. Previously it was the internal pressure at end A of the line, even if the Z level of end A changed during the simulation.
Because of these changes, it is no longer possible to edit the contents pressure (or the reference Z level) when a simulation is active.
For further details of these pressure effects changes and the validation case contact Orcina.

Other changes to Lines

The Line Setup Wizard now includes the option of varying anchor position to achieve specified top tension or top declination. Note that the Line Setup Wizard was previously known as the Line Length Wizard.
OrcaFlex now automatically checks for unstable statics configurations.
New results variables Max Bending Strain, Max Axial Strain and Acceleration including g have been added. The acceleration including g results can be used to compare against accelerometer measurements.
The allowable bend moment curve is now shown on range graphs when bend stiffness is variable.
Node axes drawing can now be controlled independently from local axes drawing.
In previous versions Lines which included torsion were forced to use the Full Statics option. This restriction has been lifted, mainly to help analyse cases which use the prescribed starting shape option. However, we still recommend that you use the Full Statics option where possible because this is the only statics option in OrcaFlex which includes the effects of torsion.
The Pre-tension data item on the Line data form is now called As Laid Tension.

Vessels

Several improvements have been made to vessels that affect results. In most case the changes are not significant, but the effect could be more significant for cases with non-zero heel or trim combined with superimposed RAOs or rotational harmonic motion. The details are as follows.

Superimposed roll, pitch and yaw rotations (from displacement RAOs, harmonic motions or a superimposed time history) are now applied in the 'reverse' order, i.e. yaw, then pitch, then roll. Previous versions (OrcaFlex 8.5 and earlier) applied them in the 'forward' order (roll, then pitch, then yaw). This change does affect results. The effect is small in most cases but may be significant for cases involving large rotation angles. For further details see order of application of vessel rotations.
Displacement RAOs, harmonic motion, the stiffness, damping & added mass matrices, and the wind and hydrodynamic drag loads, are all now applied with respect to the primary heading axes. In previous versions (OrcaFlex 8.5 and earlier) these effects were all applied with respect to the instantaneous vessel axes directions. This change has been made so that these effects are applied with respect to a frame of reference with z vertical, in order to better match the frame of reference used by diffraction programs from which this data is normally obtained. This change will affect results, but the effect is only significant for vessels with significant heel or trim angles.
The results variables Heel, Trim and Heading have been renamed as Primary Rotation 1, Primary Rotation 2 and Primary Rotation 3 respectively.
Vessel displacement RAOs are now applied at the RAO origin. Previously (OrcaFlex 8.5 and earlier) the RAOs were transformed to be RAOs about the vessel origin and then applied at that vessel origin. This RAO transformation used a small angle approximation, so to avoid that small angle approximation the RAOs are no longer transformed and are applied at the user-specified RAO origin. Because the new method avoids the small angle assumption it gives slightly different results if the RAO origin is not at the vessel origin. The differences are unlikely to be significant, unless the RAO origin is a long way from the vessel origin and some of the RAO rotation angles are large.
Vessel harmonic motion is also now applied at the RAO origin. Previously (OrcaFlex 8.5 and earlier) harmonic motion was applied at the vessel origin.
The Check RAOs facility now plots graphs of RAO amplitude and phase in addition to the existing complex value graphs.
The RAO phase conventions have been extended to allow you to specify that phases are relative to zero up-crossings or zero down-crossings.

Environment

The program now allows you to define multiple sets of current data in a single data file. Only one set of current data is active at any one time. This is intended to help when you are analysing a series of load cases with differing current data. You can set up all the different current data sets in the base file. Then, in the batch script which generates the load case simulations, you simply select from the pre-defined current data sets.
The View Wave Components report now includes the first 3 spectral moments m0, m1 and m2.
The Seabed Grid Density can now be modified.

Modal Analysis

The modal analysis facility now reports mode type and offset distribution. This allows you to identify whether particular modes are inline, axial or transverse.

Shapes

The Grid Drawing Density can now be modified for plane shapes.

Interface

Object names in OrcaFlex are not case sensitive. This is a change from older versions of OrcaFlex.
The Move Selected Objects Wizard now has the ability to rotate objects.
In previous versions range graphs were plotted for the entire arc length range of a line. There are now additional options of plotting the graph for a selected arc length range or for a selected line section.
Custom Replays are replays in which each frame can be from one or more OrcaFlex files. In previous versions of OrcaFlex these replays were known as Multiple File Replays. We have added a Custom Replay Wizard which greatly simplifies the process of specifying a custom replay.
Exported video files now optionally include details of each frame (e.g. simulation time). This helps relate the events in the video to the OrcaFlex simulation.
A new command line switch has been added called ThickLines which is intended for use when projecting OrcaFlex onto a large screen.

Object Connections

When 2 objects are connected to each other in OrcaFlex (e.g. connecting a line to a vessel) the program changes the object relative position of the slave object (e.g. the line in the earlier example). The change is made so that the slave's position relative to global axes is preserved.

A similar change is now made to the slave's object relative orientation. When a slave object is connected to another object the slave's object relative orientation is changed so as to preserve the orientation relative to global axes. This preservation of slave object orientation was not performed in previous versions of the program.

In order to understand better the effect of this change you should experiment with object connections in OrcaFlex. For example, take an empty model and add to it a Vessel and a 6D Buoy. Set the Vessel's Initial Orientation to be non-zero; for example Heel: 10deg, Trim: 20deg, Heading: 30deg. Now open the 6D Buoy's data form. The buoy's initial attitude is Rotation 1: 0deg, Rotation 2: 0deg, Rotation 3: 0deg. If you now connect the buoy to the vessel by setting the Connection data item to "Vessel1" you will see the buoy's initial attitude change to -10, -20, -30. But if you look in the 3D view you will see that the buoy's orientation relative to global axes remains unchanged.

VIV Toolbox

The VIV Toolbox has a new facility for exporting the SHEAR7 data file. This is in addition to the existing facility for exporting the SHEAR 7 Mds file.
The Wake Oscillator models now start up better at the beginning of a simulation.
A VIV Diameter data item has been added for both the VIVA interface and the Time Domain VIV Models.
If the default value of '~' is specified then the buoyancy diameter is used.
The value '~' can now be specified for the VIVA Z axis direction. This is interpreted to mean the current direction at the sea surface.
In older versions of OrcaFlex a VIV Toolbox licence was required in order to load simulation files which used any of the VIV models. This restriction has now been lifted.

Automation

The Instructions Wizard in the OrcaFlex spreadsheet now allows you to get results for Drag Chains, Flex Joints and attached 6D Buoys. These were not available in older versions of the spreadsheet.

External Functions

The OrcaFlex external function mechanism now includes the facility for external functions to store state information to the simulation file. Some external functions have state information (e.g. the integrator of a PID controller). This new facility allows for simulations which use such external functions to be restarted and continued. For details please refer to the OrcFxAPI help file.

OrcaFlex Programming Interface

A new function called C_GetFileCreatorVersion has been added to the OrcaFlex Programming Interface. For details please refer to the OrcFxAPI help file.

Bug Fixes

Inserting and deleting rows in SN curve table data on the fatigue form was not working properly. This is now fixed.
Clump type drawing data can now be edited while a simulation is active. This is the case for other drawing data in OrcaFlex.
The Ramberg-Osgood profile graph on the Plasticity Wizard was displaying strain values incorrectly. They are labelled as % strain but older versions of the program actually displayed fractional strain. The correct values were used for the calculation; the error only affected the values displayed on the profile graph. This problem is now fixed.
There was a bug which occurred when reloading and restarting partially complete simulations with tension controlled winches. If the winch was in a tension controlled mode when the simulation restarted then the winch would restart with the wrong tension. The problem only occurred if a partially completed simulation was saved, reloaded and then restarted. This bug is now fixed.
Minor corrections have been made to the way prescribed rate of turn and yaw rate drag moment are calculated for vessels with non-zero heel or trim. The changes only affects vessels with non-zero heel or trim, and the effects are not significant unless the heel or trim is large. The changes are therefore very unlikely to be significant.