Orcina news

OrcaFlex has two objects whose motion can be imposed rather than calculated:

• The vessel object through displacement RAOs, harmonic motion, time history or externally calculated motion.
• The constraint object (added in version 10.1) through motion time histories in the constraint’s imposed displacement mode.

In addition to these more well-known methods of imposing motion, the constraint object has another mechanism that allows motion to be imposed.

Continue reading “Using curvilinear constraints to impose motion”

We have just released a minor upgrade to OrcaFlex, version 10.2b. This minor upgrade fixes the following bugs:

• The following features may not have worked correctly for lines that have inactive parts: line profile graphs; fatigue analysis; splined lines in line contact relationships; penetrating lines that are around splined lines in a line contact relationships.
• The following features may not have worked correctly for lines that use line feeding: slamming; variable added mass; rolling contact for penetrating lines that include torsion in a line contact relationship; inner lines with containment enabled in a line contact relationship.
• Lines that use line feeding were not compatible with the following features: sea state disturbance for vessels whose sea state RAO data is interpolated on direction and period only; the Static Position (interpolated) wave calculation method; hysteretic bend stiffness; bend stiffness external results; fatigue analysis. The combination of these features with line feeding should have been blocked in version 10.2a, but was not: some combinations failed to run and others gave unexpected results.
• The Calculate Line Lengths mode of the Line Setup Wizard was not compatible with lines that have inactive parts. This combination of features should have been blocked in version 10.2a.
• OrcaFlex sometimes failed to run beyond statics if a line’s End A and End B initial arc lengths were both ‘~’ and the payout rate was non-zero at one or both ends. Cases that failed include lines whose Step 1 Statics Method is Quick, and models in which a static state or instantaneous value range graph is visible.
• The assignment of sea state disturbance vessels to nodes of a line that lie exactly at section boundaries was potentially inconsistent between nodes that are initially active and those that are initially inactive.
• Validation of contents flow and sea state disturbance vessel data was not carried out for the inactive parts of any line. It was therefore possible to run a model containing data that would otherwise have been disallowed if the line were fully active.
• Modal analysis modes graphs, loads graphs and loads tables were reported incorrectly for lines with inactive parts.
• OrcaFlex’s SHEAR7 and VIVA interfaces were not working correctly for lines with inactive parts.
• A line’s actual arc length result could have been reported incorrectly if its payout rate was specified by a variable data table that truncates to zero before the end of the simulation. This only happened once the truncation to zero had occurred, and then only for lines that used smooth growth to control their payout rate. This bug could also have affected instantaneous value range graphs because the actual arc length values of the nodes are the abscissae on these graphs.
• If an uncoupled, single-line modal analysis were performed immediately after loading up a static state simulation file, then it would have failed if the line being analysed was a penetrating line inside an outer splined line in a line contact relationship.
• The MATLAB interface to OrcaFlex was installed incorrectly by the 10.2a installation program. Two source code files, ofx6DBuoyObject.m and ofxWaveScatter.m were missing from the installation. Scripts that depend upon these files would fail to run.

A patch to upgrade from earlier releases of 10.2 is available.

This is a minor update release which fixes a few bugs that have come to light since the 6.0b release. The new release is available here: Distributed OrcaFlex 6.0c

The changes include:

• Bug fix: Sometimes, in the event of an error, the DOF Server would produce a cascade of error report files that caused the DOF Server to become unresponsive for a while. The DOF Server now only logs error details to the DOFServer.log file without generating any further error reports.
• Bug fix: When using the command line tool ‘dofcmd’ to submit jobs, specifying an auto-save interval of 0 was not allowed. This is in fact a valid interval used to disable the auto-save.
• Bug fix: If the DOF Server Service was restarted while jobs were still running on clients, then those jobs could end up being cancelled by the restarted DOF Server rather than re-added to the job list to continue as normal.
• Bug fix: If jobs were submitted whilst the DOF Server was already distributing jobs to DOF Clients then the scheduler’s ramping feature was re-initiated unnecessarily. Now, the ramping feature only starts if the jobs are added and the DOF Server is idle.
• In the client list view of the DOF Viewer, the list columns can now be resized.

It’s been over a year since OrcaFlex 10.1 was released, which means it is time for the 2017 major release, version 10.2. The software was finalised and built on 24^th November. All clients with up-to-date MUS contracts should receive the new version by early December.

We have been blogging regularly through the development process and these posts give a good overview of the more significant enhancements in 10.2. For convenience, here are links to each of those posts:

• Line feeding
• New line clearance results
• Coupled object modal analysis
• Vessels and 3D buoys can be slave objects
• Line statics policy
• Support and constraint release
• Vessel calculation mode
• Text labels on 3D views
• Undo
• Compound properties report
• Documentation

These are the most important developments, in our opinion. As always there are a great many more enhancements which are documented in the What’s New topic for 10.2. Any known bugs will be listed at the support page for the 10.2 release.

For the final post in our series on upcoming developments for version 10.2, we look at line feeding. Line feeding allows line to be dynamically fed into, or out of, the active model.

OrcaFlex 10.2 is very nearly ready to be released and we expect this to happen in the next fortnight. In the meantime, we hope that this article whets your appetite!

Continue reading “Upcoming in OrcaFlex 10.2: Line feeding”

It’s been a little while since we posted in our series on upcoming developments for version 10.2. We’ve been busy finishing off development for the release, and hosting our annual series of user group meetings.

OrcaFlex 10.2 is very nearly ready to be released and we expect this to happen in the next fortnight. In the meantime this post introduces two new features that enable text labels to be displayed in 3D views.

Continue reading “Upcoming in OrcaFlex 10.2: Text labels on 3D views”

We have just released a minor upgrade to OrcaFlex, version 10.1e. This minor upgrade fixes the following bugs:

• In earlier OrcaFlex versions, when importing vessel type data from AQWA, both difference frequency QTFs and sum frequency QTFs were conjugated upon import. After feedback from users, we now have a more complete understanding of the AQWA QTF output conventions and load calculation. With this release, OrcaFlex no longer conjugates the sum frequency QTF values. We believe that this change ensures that the QTF load calculations performed by OrcaFlex match those performed by AQWA. If existing simulations need to be run again because of this issue, note that OrcaFlex sum frequency QTF load will only change if the AQWA QTF data are first re-imported into OrcaFlex.
• For frequency domain analysis, the ZZ Stress process reported through the API, could be 180° out of phase. The error only arises when using a nonlinear Young’s modulus, and for sections of line in mean compressive stress.
• The Line Type Wizard for Umbilicals calculated EA and EI incorrectly if the model force units were not set to kN.
• Previously, when conducting a frequency domain solve, at low or combined solution frequencies, the analysis could fail and present an Argument out of range error message. This affected models containing vessel types with no wave drift QTF data present.
• The bulk modulus data for 3D buoys, 6D buoys and lines specifies the compressibility of the object. When the fluid pressure exceeds the bulk modulus, the formula for compressed volume breaks down and OrcaFlex uses a value of zero. Unfortunately, the related code that calculates variation of compressed volume with depth does not handle this case correctly which in turn leads to statics and dynamics calculations failing. This problem affected line objects from 9.1a, and buoy objects from 10.0a.
• For frequency domain analysis, the external load on 6D lumped buoys associated with a dynamic change in the proportion wet was 180° out of phase. This only affected 6D lumped buoys that were partially submerged, i.e. surface piercing, in the static state.
• Fatigue analysis based on frequency domain simulations did not take account of stress loading factors.
• The extreme statistics results diagnostic quantile plots were not being drawn correctly for the Weibull distribution. Specifically, the fitted model quantiles (along the x-axis) were calculated incorrectly. These plots are intended to provide support (or otherwise) for your choice of fitted distribution, so this bug might have influenced your interpretation of the validity of this choice.

A patch to upgrade from earlier releases of 10.1 is available. If you would prefer to receive version 10.1e on CD please contact us.

Continuing our series of posts on upcoming developments for version 10.2, we consider a number of enhancements to the line clearance results.

Historically, OrcaFlex has offered results reporting the clearance between lines. These results report the shortest distance, in 3D space, between lines. Results are available for clearance between centrelines or between contact surfaces. Some OrcaFlex applications, for example riser / pipeline crossing analysis, call for clearance distances measured horizontally or vertically. A number of new results variables have been introduced in 10.2 to address these requirements.

Continue reading “Upcoming in OrcaFlex 10.2: New line clearance results”

Continuing our series of posts on upcoming developments for version 10.2, we consider a couple of enhancements to the support and constraint objects.

OrcaFlex objects can be connected to each other, so that the connected objects move together. In addition, certain types of connections can be released at defined points in the simulation. For example, line, link and winch connections can all be configured to release at the beginning of a specified stage in the simulation. Version 10.2 introduces the same capability for supports and constraints.

Continue reading “Upcoming in OrcaFlex 10.2: Support and constraint release”

Continuing our series of posts on upcoming developments for version 10.2, let’s now look at a further relaxation of the rules relating to object connectivity.

In version 10.0 we made it possible to connect lines to lines and to form chains of connections, e.g. 6D buoy1 is connected to 6D buoy2, which in turn is connected to 6D buoy3 etc. In version 10.1 the constraint object was introduced, and mid-line connections were enabled.

In version 10.2 it will be possible to connect both vessels and 3D buoy objects as slaves of other objects.

Continue reading “Upcoming in OrcaFlex 10.2: Vessels and 3D buoys can be slave objects”