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Flexcom 2026.1.1

Overview

The following faults are present in Flexcom 2026.1.1. More detailed information on each fault is provided in the following sections.

Detailed Information

Issue 1: Responsiveness of Flexcom GUI

•Related Topics: User Interface

•Description: Responsiveness of the Flexcom user interface can deteriorate if the program has been running continuously for some time. Whenever you open a keyword file, Flexcom loads the data into memory, so that it can display the model in in the Model View for example. Due to a bug in the code, that memory which should become free when the keyword file is closed, is retained. This behaviour is known as a memory leak, meaning that the amount RAM used by the Flexcom GUI tends to grow continuously.

•Workaround: Close and relaunch the GUI if you feel it is not responding as quickly as you might expect.

Issue 2: User-defined Flexcom GUI settings not being saved

•Related Topics: Flexcom Settings Dialog

•Description: User defined settings for the Flexcom GUI (e.g. to enable Licence Monitoring) are not always saved correctly. Although rare, the issue can occur when the Flexcom Configuration File is malformed. We do not know how this occurs on a user machine, but sometimes this file can exist but have zero size. In this case, Flexcom fails to load or save the config file. The next version will check for a zero size file and delete it rather than attempting to load it, resetting all options to their default values.

•Workaround: Manually delete the configuation file if you are experiencing any save issues with the Flexcom Settings dialog. The file is called FlexcomGlobal.config and is located in the C:\ProgramData\Wood\Flexcom\Version 2026.1.1.

Issue 3: Hydrodynamic Data Importer does not read QTF data from ANSYS Aqwa files

•Related Topics: Hydrodynamic Data Importer

•Description: Any QTF data contained in .LIS files generated by ANSYS Aqwa is ignored during the data importation process.

•Workaround: Manually import the relevant QTF data. Contact Wood Group if you need assistance.

Issue 4: Floating feedback control for FOWTs

•Related Topics: Coupling between Flexcom and ServoDyn

•Description: There are actually two issues here, but as they are so closely related, they are grouped together under the same fault heading. 

ServoDyn provides three options for modelling floating feedback in the controller, namely: Fl_Mode = 0 (no nacelle velocity feedback), Fl_Mode = 1 (translational velocity feedback), and Fl_Mode = 2 (rotational velocity feedback). The relevant OpenFAST axis systems are as follows:

i.Tower-Top/Base-Plate Coordinate System: Fixed to the top of the tower. It translates and rotates as the platform moves and the tower bends, but it does not yaw with the nacelle.

ii.Nacelle/Yaw Coordinate System: Translates and rotates with the top of the tower, plus it yaws with the nacelle.

Issue A: Translational velocities of the tower top node are supplied by Flexcom to ServoDyn in the tower system. This is consistent with the internal workings of OpenFAST, and while it is not necessarily incorrect, it is somewhat restrictive. Starting from Flexcom 2026.1.2, the translational velocities of the tower top node are supplied by Flexcom to ServoDyn in the nacelle system by default, but you may also select the tower system if you wish. Refer to *SERVODYN for further information and discussion.

Issue B: Rotational accelerations of the nacelle (roll, pitch/nodding, and yaw) are passed as zero values from Flexcom to ServoDyn. This means that floating feedback is not captured by the controller. The issue may not be obvious for all turbine models but typically seems to manifest itself in unstable blade pitch for wind speeds above rated, even if the applied wind has constant speed. Starting from Flexcom 2026.1.2, the rotational velocities of the nacelle CoG node are supplied by Flexcom to ServoDyn (in the Nacelle/Yaw Coordinate System), and this corrects the issue.

Note that these issues relate specifically to floating wind turbine models only. Fixed base models are unaffected as floating feedback is disabled (Fl_Mode = 0).

•Workaround: Issue A may not necessarily represent a problem, depending on your perspective. Issue B may be circumvented by using translational velocity feedback (Fl_Mode = 1) rather than rotational velocity feedback.

Issue 5: Database write error where motion database storage is disabled

•Related Topics: Data Storage Files

•Description: The vast majority of Flexcom models create a motion database (DBM) file. However you may disable the DBM file completely if wish, by specifying *DATABASE CONTENT -> EXCLUDE=1, 2, 3. If you invoke this option in Flexcom 2026.1.1, you will receive an error message stating "Error: Unable to write to direct access database file. system error number is 37. Error may be caused by a lack of disk space".

•Workaround: Retain at least one parameter from motion/velocity/acceleration to enable DBM file creation. For example, specify *DATABASE CONTENT -> EXCLUDE=2, 3 instead.

Issue 6: QTF data reading error

•Related Topics: Floating Body

•Description: If your Flexcom model contains more than one floating body, and you have specified a different number of QTF frequencies for each body, you will receive an error message stating "QTF data must be specified at the same headings for each frequency used".

•Workaround: Specify the same number of QTF frequencies for both floating bodies in your model.

Issue 7: Aerodynamic forces on wind turbine blade applied at structural centre rather than aerodynamic centre

•Related Topics: Wind Turbine Modelling

•Description: The application of aerodynamic forces and moments in the flexible blade model are not taking into account the spatial offset between the structural centre and the aerodynamic centre on the blade cross section. A similar limitation applies to the application of mass terms at the centre of gravity, although this is likely to be less significant. So, although the blade structural properties are correctly represented by the relevant stiffness terms, the twisting moment induced by the spatial offset is neglected. This could lead to some inaccuracy in deformational blade twist induced by the wind loads, particularly near rated wind speed where the forces are largest. Notwithstanding this limitation, the structural twist due the physical shape of the blade, and the rigid body twist imparted by the control system, are both correct. As these terms account for the majority of the overall twist angle, the local angle of attack and the corresponding aerodynamic forces should be quite close to their theoretical values.

•Workaround: There is no workaround, so you are advised to upgrade to Flexcom 2026.1.2 or later.