New & Noteworthy

1. General information

  • Version no. 5.0.0

2. RIFLEX

2.1. Static loading

2.1.1. Automatic static loading sequence

A new option to automatically create loading sequence is added to static calculation. The model will be inspected and the required load groups will be constructed.

It is also possible to use Create initial loading sequence action to populate the table manually to use as a start.

sima500 automatic loading
Figure 1. Automatic loading sequence
sima500 create init loading seq
Figure 2. Create initial loading sequence

2.1.2. Illustration of static loading groups

Illustration of common configuration and suggested order of static loads are added in the user manual.

See user manual Load sequency for typical configurations

2.2. Absolute convergence criterion

If the current is set to zero or a very low value, the static loading process in may not succeed due to the relative convergence criterion. To address this, an absolute convergence limit has been introduced in addition to the displacement and energy convergence norms.

The absolute convergence limit is determined based on an estimated equivalent diameter multiplied by a small factor.

No new input is required.

2.3. Export of static convergence information

Information about the static convergence is now written to the <*>_stamod.mpf file. The following information is now available:

  • the number of iterations performed at each static load step

  • the development of the relative Displacement norm during the iterations at each step

  • the development of the relative Energy norm during the iterations at each step is available if the energy norm is specified

2.4. Matrix storage format

The default matrix storage is changed to AUTOMATIC.

The matrix storage format will be automatically set to Sparse or Skyline in the static analysis depending on the finite element model.

2.5. Rope/Wire cross section wizard​

A new wizard is added in the new menu for cross sections to help creating Axisymmetric cross sections representing steel wire or nylon/polyester rope​. The different options are - Steel wire​ - Nylon rope​ - Polyester rope

2.6. Steel catenary and lazy wave wizards

To help user start modelling, a wizard for creating two typical configuration are added.

The wizard is launched when you create a new Riflex task or by creating a new line, in the Slender system.

The different options are

After the configurations are created, the cross sections and line types can be modified and adjusted.
sima500 wizard rif task
Figure 3. Create a new task
sima500 wizard slender system
Figure 4. Create line
sima500 wizard scr
Figure 5. Catenary
sima500 wizard lazy
Figure 6. Lazy wave

2.7. Wind turbine controller

2.7.1. Overview of the signals in the controller log file

A table with an overview of the contents in the wind turbine log file printed by SIMA is added to the user manual, see Log file (external controller).

2.7.2. Accelerations exported to external wind turbine controller

The original acceleration signals exported are a result of the time integration algorithm, and may not represent values the user expects.

For example, using the Newmark procedure with beta = 0.25, acceleration values correspond to an average value during each time step.

To improve this, a new option to calculate the accelerations from displacements is added.

This option is available for the external controller only.
sima500 log acc
Figure 7. Calculate acceleration signals from displacements

2.8. Ramping of wind velocity

The wind velocity can now be ramped using a predefined clutch.

The wind will be gradually scaled from an initial ramp value up to the full value at the specified ramp duration. If the wind ramp is delayed, the ramp will be equal to the ramp start value until 50% of the specified ramp duration is reached and then scaled up to the full value at the specified ramp duration, see Wind ramp.

A comparison of the incoming wind speed in the x-direction with no wind ramp, wind ramp and delayed wind ramp is shown in Incoming wind speed.

sima500 windramp
Figure 8. Wind ramp input
sima500 wramp res
Figure 9. Incoming wind speed

2.9. IEA 22 MW turbine model available

A model of the IEA 22 MW reference wind turbine is available as an example in SIMA. The model is created according to the How-to model a wind turbine guide.

2.10. Marine growth scaling for individual lines

The scaling factor for marine growth can now be specified for individual lines in addition to an overall scaling factor. This will allow the user to switch between no marine growth, partly accumulated marine growth and fully developed marine growth on selected lines.

sima500 margrowth
Figure 10. Marine growth scaling for individual lines

2.11. Deactivate current in static parameter variation

If current is specified but not activated in the static loading sequence, the current will be activated if static parameter variation is specified. The current will then be added in the first load step.

An new option to deactivate the current is added, see Deactivate current. For details see Load groups and Parameter variation definition.

This only affects the lines in the slender system.
sima500 stapar current deactivate
Figure 11. Deactivate current

2.12. Include slug loads from angles between elements end

Loads from the internal fluid are applied if a slug is specified or varying internal content is read from a flow import file.

Previously, only the change in flow direction given by curvature over the individual elements have given loads on the system. For example, a main riser line consisting of two lines with an angle between their stress-free orientations, would not have had a load contribution from this angle.

The loads from the angles between the element ends are now included. For each element, nodal loads corresponding to half of the angle between the element ends and the neighbouring element ends are applied.

The change will normally be negligible unless there are angles between neighbouring element in the stress-free configuration.

2.13. Matrix plot improvements

It is now possible to view multiple matrix plots together (mpf-files in the results)

sima500 mpf
Figure 12. View and select matrix plot

2.14. Current profile from file

The current profile can now be defined in a separate file and given as input.

sima500 current from file
Figure 13. Current profile from file

2.15. User defined elements

The user defined element can now be connected to either end 1, end 2 or both of the reference element, see Input and Element End drop down menu.

Currently, only single node elements are available. The element is primarily intended for modelling seafloor contact, anchor modelling, additional loads or other type of contact problems but may be used for other purposes.

The external dll interfaces is the same choosing element end Both, One or Two .
sima500 userdef
Figure 14. Input

2.16. T-N fatigue calculation

Fatigue damage may be calculated from tension time series and a T-N curve. The T-N can be used to calculate the nominal tension fatigue lives of mooring components

\[NR^M=K\]

where

  • N = number of cycles

  • R = ratio of tension range

A table of M and K values can be found in the API standard Design and Analysis of Stationkeeping Systems for Floating Structures, API Recommended Practice 2SK, Third Edition, OCTOBER 2005.

The functionality is available for beam and bar elements using the forces stored in the OUTMOD format.

sima500 TN fig1
Figure 15. Storage of forces
sima500 TN fig2
Figure 16. T-N fatigue analysis

2.17. Mooring line capacity check

Mooring line capacity check is added according to the DNV offshore standard Position mooring, DNV-OS-E301 Capacity Check (2021).

sima500 E301 fig1
Figure 17. Code check DNV-OS-E301 for mooring lines
sima500 E301 fig2
Figure 18. Input

2.18. Tension and curvature capacity check

Perform a capacity check for a combination of curvature and tension. The capacity can be expressed by a utilization factor, \(u\), given as

\[u = \frac{S_{t,d}\cdot\gamma_{t,f}}{\frac{R_{t,k}}{\gamma_{t,m}}} +\frac{S_{c,d}\cdot\gamma_{c,f}}{\frac{R_{c,k}}{\gamma_{c,m}}} \text{ where } u < 1\]

where

  • \(S_{t,d}\), is the characteristic environmental tension

  • \(S_{c,d}\), is the characteristic environmental curvature

  • \(\gamma_{t,f}\), is the load factor for tension

  • \(\gamma_{t,m}\), is the material factor for tension

  • \(\gamma_{c,f}\), is the load factor for curvature

  • \(\gamma_{c,m}\), is the material factor for curvature

  • \(R_{t,k}\), is the tension capacity

  • \(R_{c,k}\), is the maximum curvature

sima500 tens curv fig1
Figure 19. Tension and curvature capacity check
sima500 tens curv fig2
Figure 20. Input

3. SIMO

3.1. New implementation of difference frequency QTF

From SIMA 5.0, the Difference Frequency QTF model is changed. The legacy QTF model from SIMA version <= 4.8 continues to be supported for backwards compatibility. Users can choose to convert to the new model by right-clicking the QTF model in the model tree and choosing Export/Convert QTF. You will see a warning message in the model tree if you have a legacy QTF model in your SIMA workspace.

The new QTF model refers to QTF data stored on an external file, which can drastically reduce the size of the SIMA workspace. The QTF file is optimized for efficient access by both SIMA (for plotting) and SIMO (for simulation). The overhead in the communication between SIMA and SIMO is therefore greatly reduced by the new model.

When hydrodynamic data is imported from a SIF file, a new model and associated QTF file is created automatically. However, when hydrodynamic data is imported from WAMIT files, the legacy model is currently created, and it is thus recommended to convert to the new model after importing.

In addition to changing the storage method, the new model corresponds to a new implementation in SIMO. The new implementation will give slightly different results for the following reasons:

  • Different interpolation methods

    • The new implementation uses a combination of linear (close to the main-diagonal) and bi-linear interpolation in the bi-frequency domain

    • The legacy implementation uses a two-step interpolation where step 1 creates a dense QTF by resampling the QTF data with bi-linear interpolation, and step 2 use "nearest neighbor" interpolation on the dense QTF

  • The new implementation applies forces in the low-pass filtered body-related coordinate system (following low-frequency yaw motions), while the legacy implementation applies forces in the body-related coordinate system (following total yaw motion). Note that both implementations does heading correction based on the low-pass filtered yaw motion.

Reflecting the difference in coordinate system, the new implementation creates a new result type Difference frequency wave force with force components XBRLF Force, YBRLF Force, ZBRLF Force, Moment XBRLF axis, Moment YBRLF axis and Moment ZBRLF axis. Storing the new result type is optional (default is to not store QTF forces).

The new implementation also comes with other improvements:

  • The mean wave drift force is now included in static analysis (STAMOD)

  • Body symmetry is now utilized to reduce the number of relative wave headings required in the QTF, and reduce the number of pregenerated time series accordingly

  • The new model avoids generation of forces for vessel headings never experienced ("on-demand" pre-generation)

  • General efficiency improvements

Due to the efficiency improvements, simulations with a full QTF now has approximately the same running time as simulations with wave drift force coefficients (using Newman’s approximation).

Now, it will also be possible to use sum- and difference frequency QTFs at the same time by using the new difference frequency model in combination with the existing sum-frequency model.

3.2. A new hydrostatic force model containing submerged volume and center of buoyancy

A new hydrostatic force model have been added which explicitly includes the mean buoyancy force in the centre of buoyancy. The change in buoyancy due to non-zero position and rotation is included via linear restoring coefficients. When the new hydrostatics model is used, the gravity force will always be included, regardless of the "Apply gravity force" flag.

The new model is particularily useful for bodies where bouyancy and gravity forces are not in balance, for example for floating wind turbines where the gravity force from the tower and nacelle is included via RIFLEX elements or separate SIMO bodies.

3.3. Current profile from file

The current profile can now be defined in a separate file and given as input, see Current profile from file.