SIMO Standalone Release Notes

Fixed a bug which caused a crash when reading wind timeseries from file.

Error since version 4.18.0.

SIMO Inpmod is no longer a part of the installation package.

SIMO Outmod is no longer a part of the installation package.

For quadratic transfer functions where NDQTF2=1 SIMO did previously require IDQTF2 = 1 for all coefficients. This has been changed so that now IDQTF2 must always be equal to IDQTF1.

To use old input files, the values for IDQTF2 must be updated accordingly.

The tools simo.sh and simo.exe has new names. They are now called simo-tui.sh and simo-tui.exe respectively.

An error resulted in airfoils with user-specified stall points always operating in dynamic stall. This has been corrected.

Error since SIMO version 4.6.0

When the body geometry is symmetric about the X=0 and/or Y=0 planes, SIMO offers the possibility to mirror wave drift damping coefficients to wave headings not present in the input based on symmtry relations. These symmtry relations was wrongly implemented resulting in wrong sign on some of the damping matrix entries. The error has now been corrected.

Longstanding error

Previously, it was not allowed to provide frequency dependent wave drift damping coefficients (Newmans method) when wave drift coefficients was not provided. This is relevant in cases where wave drift damping coefficients is used in combination with a full QTF. This restriction has now been removed.

Longstanding error

Fixed an issue related to the initial yaw angle of a turret body. Before the fix, the initial angle was interpreted as a relative angle (relative to the master) in the static analysis, and as a global yaw angle in the dynamic analysis. Now, the intial angle is interpreted as a global yaw angle in both static and dynamic analysis. The documentation has also been clarified. In relation to this, a modification of the static analysis is implemented such that the friction of the turret is turned off during the search for static equilibrium.

Another issue related to the turret body has also been fixed. Before, the turret body could have sudden "jumps" in yaw angle when the yaw angle of the master body crosses the angle (+/-) 180 degrees. These jumps are now avoided.

Error since SIMO version 4.12.0

The sign of the products of inertia as documented in the user manual was not consistent with the implementation. Moreover, the sign of the products of inertia in the mass mastrix as written to the prs.lis file was not consistent with the implementation. Now, the sign is flipped in the documentation and in the mass matrix written to the prs.lis file. The simulation results are not affected.

The maximum length of airfoil identifiers was not consistent in code and documentation. The maximum length was 8 characters and not 64 as described in the airfoil library file description. Long identifiers were truncated to 8 characters. This could result in the wrong airfoil being used in the analyses.

The length is now increased and standardized to 32 characters in both SIMO and RIFLEX.

Also, a potential error that could cause data to be overwritten when reading the airfoil library file has been corrected. This error has not been observed.

A new option to specify a vertical domain for computing wind velocity in has been added to account for vertical variation spectral density when computing wind velocity at multiple locations during timedomain simulation.

This option should be considered when using parametric wind spectra and the following features:

See the section Environment specification in the Userguide and the section Wind in the theory manual for further details.

Airfoil coefficients may now be given for a single Reynolds number. They will then be used for all Reynolds numbers.

Extrapolation outside the range of Reynolds values given will now be allowed. The value for the closest Reynolds number will be used; i.e. flat extrapolation.

The import of the airfoil library for foil load coefficients has been improved. This will reduce the analysis time for both static and dynamic analysis. The reduction will be most noticeable in static analysis.

The issues with parameterized wind spectra has now been resolved (see previous release notes).

See also release note for the new functionality Computation of wind velocity from parametric wind spectra at multiple locations.

Error since SIMO version 4.2.

A bug has been fixed in the DP system guidance mode. Previously the initial reference position was set at global origin which meant that vessels starting guidance mode outside global origin would not follow the desired path.

Longstanding error.

Allow SIMO to read airfoil library files that include airfoil geometry. This has previously caused SIMO to fail.

Longstanding error.

Incorrect naming of rotational accelerations in result presentations have been corrected. It is rotational accelerations that are presented and not double derivative of Euler angles as was incorrectly reported in previous versions.

Longstanding error.

A bug has been fixed in the DP system guidance mode. Previously the initial reference position was set at global origin which meant that vessels starting guidance mode outside global origin would not follow the desired path.

Longstanding error.

Allow SIMO to read airfoil library files that include airfoil geometry. This has previously caused SIMO to fail.

Longstanding error.

Airfoil coefficients may now be given for a single Reynolds number. They will then be used for all Reynolds numbers.

Extrapolation outside the range of Reynolds values given will now be allowed. The value for the closest Reynolds number will be used; i.e. flat extrapolation.

The import of the airfoil library for foil load coefficients has been improved. This will reduce the analysis time for both static and dynamic analysis. The reduction will be most noticeable in static analysis.

Simulations where multiple bodies had quadratic transfer functions (QTFs) would previously yield incorrect results. This has now been resolved.

Longstanding error.

The default value for viscosity in air is set to 1.516E-5, air temperature 20 degree centigrades.

A constant tension control mode has been added to the Simple Wire Coupling. It is intended to simulate tugger wires with constant tension winches and can limit the winch run velocity.

The internal control system for vertical axis wind turbines was updated: the low-pass filter was removed, and a 2np filter was added (in addition to improving the existing np filter).

Previously the winch in SIMO could get stuck if all of the wire initially on the drum was payed out. The algorithm has now been improved so that this does not happen anymore.

A bug in the initialization of rotation angle for articulated structure was fixed.

The internal control system for vertical axis wind turbines was updated: the low-pass filter was removed, and a 2np filter was added (in addition to improving the existing np filter).

The aerodynamic loads on vertical axis wind turbines during iteration steps are now maintained from the previous step when the aerodynamic code was run.

The state space wind model now supports using the Simiu wind spectrum for simulating wind with gusts normal to the main wind direction.

Wind type 14, stationary uniform wind with shear, has been added. A power or logarithmic shear profile may be specified.

This wind type differs from wind type 10, stationary uniform wind with shear, values interpolated at grid points, in that the shear profile is used directly.

A new turret model is implemented in SIMO. The functionality enables modeling of a turret as an articulated structure with free-rotation around vertical axis (Z). The vessel is considered as the master and turret as the slave. The model also provides simple locking and sliding through "maximum lock angle" and "slip angle" options. See Articulated Structures section in user manual for more details.”

A bug has been fixed where the wind speed used to calculate force from quadratic wind coefficients was incorrect. This applies when the following wind types was used in combination with quadratic wind coefficients:

Previously the body z-position was used to determine the wind speed used in the force calculation while the reference height for the wind coefficient should have been used.

Corrected in SIMO 4.10.1.

A bug has been fixed where the notch filter gave incorrect large differences between estimated and real heading when the real heading passed +-180 deg.

When giving input to fixed direction thrusters the NDIR parameter would have to be given, even though the manual states that this parameter is intended for rotatable thrusters. This has now been fixed. As a result, old input files using fixed direction thrusters need to be updated by removing this parameter.

An error correction has been done to SIMO wind turbine to prevent program termination if the turbine is only equipped with one blade.

Corrected in SIMO 4.10.4.

Avoid possible overflow during calculation of the optimal division of time series into sequences. The error was observed for very large systems with long time series and could cause incorrect array dimensions and error termination before the dynamic simulation in SIMO or in RIFLEX for coupled analysis.

Corrected in SIMO 4.10.2.

SIMO will in some situations calculate wind speed based on an incorrect wind spectrum for bodies with wind coefficients. This depends on the choice of wind spectrum type, the wind spectrum reference height and the wind coefficients reference height.

If default values are used for both wind coefficients and spectrum reference heights (both default values are 10 m) the calculated wind speed will always be correct.

If non-default values are used some spectra will give incorrect wind speeds:

*) ONLY if wind spectrum reference height is 10 m (default)

**) unless wind spectrum reference height is set to the same value as the wind coefficients reference height

SIMO will in some situations calculate wind speed based on an incorrect wind spectrum for bodies that has slender elements with wind drag coefficients. This depends on the choice of wind spectrum type, the wind spectrum reference height and the vertical position of the slender elements:

*) ONLY if wind spectrum reference height is 10 m (default)

**) unless wind spectrum reference height is set to the same z-value

An error in load moments caused by wind forces acting on slender elements and fixed bodies has been corrected. The error has been present since 4.2.0. In addition, the wind drag force has been calculated from the wind velocity only. The relative velocity is now used in the wind drag calculation.

A bug has been fixed where the program would crash during reading of large QTF data sets from WAMIT.

The calculation of wind velocity could fail if all resulting wind components at a point and time were exactly zero. Scaling of the components resulted in a division by zero and an illegal number (NaN) was returned. This has been corrected.

A method for estimating wave frequency and low frequency motions when using body type 1 (wave force transfer functions) has been added. This is in particular important to consider when using cosine series waves and when simulating a turrent moored ships.

The method utilises a 2nd order Butterworth low pass filter in order to estimate the low frequency motion from the total motion during simulation. For more details see Separation of wave frequency and low frequency motions for body type 1 in the user guide.

The following change break compatibility with macro files used by older versions of DYNMOD, S2XMOD and OUTMOD. Macro files need to be updated in order to be used with new versions of SIMO.

Time series of total and low frequent position are now always stored for bodies of body type 1 (wave force transfer functions) and body type 2 (wave motion transfer functions). This means that DYNMOD macro files that specify storage of results must be updated before they can be run in newer versions.

Users of S2XMOD and/or OUTMOD should note that the content of responses 29 and 33 has changed and macro files need to be updated to accomodate this change. Starting with version 4.10.0 the content of these responses are the same for all bodies regardless of type. The table below summarises the content of the relevant responses before and after this change.

It is now possible to compute the static equilibrium of a SIMO system by using a Newton-Raphson algorithm. The method used in the previous SIMO versions is now referred to as "Transient".

Some remarks when using the Newton-Raphson method: - the Newton-Raphson method is generally faster when considering a system with only one body - the "transient" method still remains the most robust method, especially in case of systems with several bodies, and/or with strong non-linearities (like fenders, DP systems, …).

It is recommended to use the "transient" method as the default method.

When using the Newton-Raphson method, the user can choose to restrain the "global" degrees of freedom of one or several bodies during the static equilibrium calculation. By "global" degrees of freedom, we refer here to the translations and rotations about the axes of the XGB coordinate system.

When using the Newton-Raphson method, it is possible to use the "multiple equilibrium calculation" option on one specified body. This allows the user to define a grid of roll and pitch values. For each point of the grid, the equilibrium position will be computed, restraining the roll and pitch rotations. This means that the equilibrium is solved for the other degrees of freedom.

Note that in the present version, the results are stored in the prs.lis file but are not available directly in SIMA. This will be updated in a future version of SIMO/SIMA.

It is now possible to model the quadratic current coefficients as a function of: - relative current direction - body vertical position - body roll angle - body pitch angle

It is now possible to model the wind coefficients as a function of: - relative wind direction - body vertical position - body roll angle - body pitch angle

It is now possible to model the non-linear buoyancy force by means of volume integration, by using the new Hydrostatic Stiffness option Non-linear hydrostatic stiffness. The geometry of the hull is given as a STL file (mesh of triangular panels) allowing the definition of complex geometries.

It is now possible to model a ballast system made of an unlimited number of ballast tanks by using the TDM new option BALLAST SYSTEM. The geometry of each tank is described by a STL file (mesh of triangular panels) allowing the definition of complex geometries.

Functionality is added for changing the wave, wind, and current over the course of a simulation. The program fades from one environment to the next defined environment at the prescribed time over the specified fade-in period.

A new option has been added that allows the SIMO DP system to receive line tension measurements from RIFLEX lines in a coupled simulation. Previously this has only been possible for SIMO catenary lines. See the the section on Dynamic positioning in the userguide for more details.

In certain cases when using the new thruster model and specifying thruster blackout the simulation would fail unexpectedly. This has now been fixed.

Corrected in SIMO 4.8.0.

Some models using the time dependent mass functionality will cause SIMO to crash. This has now been fixed.

Corrected in SIMO 4.8.0.

In certain models including slender elements with and without aerodynamic drag coefficients simulations would fail with NaN (not a number) results. This has now been fixed.

Corrected in SIMO 4.8.0.

The underlying linear algebra routine in eigenmode calculations has been replaced. The new routine gives improved accuracy, especially for longer eigenperiods. Note that this means slightly modified results.

The MTDP functionality for external DP systems have been changed so that SIMO is now the server in the TCP/IP communication. As a result any external DP systems using the MTDP protocol must be changed from being a TCP/IP server to a TCP/IP client. The input of MTDP hostname have been removed from the SIMO sys-file as it is no longer needed.

Controling thrusters using the new thruster model is now supported through the MTDP interface.

The new Linux release of SIMO, RIFLEX and VIVANA is 64-bit and solves several issues. Unfortunately, this means that 32-bit Linux operating systems are no longer supported.

The package has been tested on the following Linux distributions:

Stiffness forces are now presented in body related coordinate system. In previous SIMO versions they were presented in body fixed system.

Corrected in SIMO 4.6.2.

In previous SIMO versions the thruster dynamic was not calculated correctly when using formulation 4.1, which could lead to numerical problems. This error has now been fixed. Simulations using thrusters and DP controller with formulation 4.1 should be rerun.

Corrected in SIMO 4.6.1.

In previous SIMO versions, an error prevented time series generation using the summation of harmonic components (cosine series) in the time domain for environments with swell waves. This error has now been fixed.

In previous SIMO versions, a certain combination of visualization and catenary lines with the line failure option enabled would cause the program to crash. This error has now been fixed.

The wave forces are now applied in body-related reference system instead of the fixed initial reference system. This ensures that the wave forces and corresponding reaction forces now act in the same system for non-zero yaw angles, which in turn leads to a more numerically robust solution of the system of equations. This correction is expected to give insignificant changes to results for normal analysis with small yaw motions. However, the changes in results will become larger with larger yaw motions.

In previous SIMO versions the nonlinear buoyancy correction was not calculated correctly when used for bodies which also had wave drift force coefficients. This error has now been fixed. Simulations using the Nonlinear Buoyancy Correction feature along with wave drift force coefficients should be rerun.

Corrected in SIMO 4.4.2.

A potential infinite loop in error reporting of wind termination is eliminated.

Corrected in SIMO 4.4.1.

A bug has been fixed where SIMO failed to initialize an interactive simulations using HLA.

Corrected in SIMO 4.4.1.

TurbSim 3D wind files may now be read by SIMO.

Possible problem with numerical precision when using TIME DEPENDENT MASS. This has been counteracted by increasing the numerical precision during accumulation of the time dependent mass.

The bumper formulation has been improved when contact occurs at the end of a bumper. The mathematical model can be regarded as if there are half-spheres at the end of all bumper elements. For more details see `Bumpers' in `Station-keeping forces' in `Force models' in the SIMO Theory Manual.

Improved in SIMO 4.4.1.

Vertical axis wind turbine functionality is added. The aerodynamic loads are computed using the double-multiple streamtube method.

Added in 4.4.1.

The use of an external control system (Java) for horizontal axis wind turbines in SIMO is now possible.

Added in 4.4.1.

Windows versions 4.4 and higher are 64 bit executables and therefore require different Fortran and Java DLLs than earlier version. The necessary DLLs are included in the download package. The preformance is improved.

If depth dependent current was applied and wind also was specified in the environmental condition, the computed current drag forces on slender elements were in error. This was due to an incorrect z-position being used to interpolate the shear profile. The error has been present since version 4.2.0. The consequence is incorrect drag forces on the slender elements. Analysis done with this combination by version 4.2.0 should be re-run! The error has been corrected.

Corrected in SIMO 4.2.1.

The formulation is corrected so that no modification to drift forces is made if no waves are active. Normally of no consequence to results.

Corrected in SIMO 4.2.1.

To be in accordance with the old deprecated thruster force model the thrust forces from the "new thruster" model (THRUSTER SYSTEM DATA) are updated at each main time step and kept constant during substepping. This will give insignificant consequence to the results.

Corrected in SIMO 4.2.1.

The applied models for wave- and hydrostatic stiffness loading acting on a "large volume" body are based on a hydrodynamic input description pre-calculated for a certain draught assuming constant geometry of the intersection between the hull and the mean water level. This means that the body fixed coordinate system has to coincide with the system used for computation of the hydrodynamic potential flow solution and that the load model for nonlinear modification of buoyancy and wave forces has to be initialized at the appropriate draught.

Originally the load model was initialized at the initial position of the body. This created unwanted requirements to the initial position which had to coincide with the origin of the system used for hydrodynamic calculations.

In the improved version the load model is initialized at the reference position for hydrostatic stiffness forces. As a consequence the reference position has to coincide with the origin of the system used for hydrodynamic calculations. This implies that the reference position can not be used to introduce specified force in global Z-direction, nor moments for roll or pitch.

Improved in SIMO 4.2.1.

The "old" thruster model (THRUSTER DATA) can still be used in the current version of SIMO, but is marked as "deprecated", meaning that it will be removed in the next release version. The new thruster model has two main additional features compared to the "old" one:

Note 1: for a given body, all thrusters have to be modelled with the same model (all with the "old" one or all with the "new" one).

Note 2: the new thruster model cannot be used with the "old" DP model (DYNAMIC POSITIONING SYSTEM)

The "old" DP model (DYNAMIC POSITIONING SYSTEM) can still be used in the current version of SIMO, but cannot be used with the new thruster model (see section above). It is marked as "deprecated", meaning that it will be removed in the next release version. The new DP model has one main additional feature compared to the "old" one: the thruster data used by the DP system has to be given separately from the physical thruster data. The DP model does no longer "know" everything about the physical thruster, and can now be provided with wrong or inaccurate information if one wants to do error analysis or check robustness. Further, the DP system does not have to use all thrusters, but only those assigned to it.

Note: the new DP model can only be used with the "new" thruster model (THRUSTER SYSTEM DATA)

In data group DISTRIBUTED ELEMENT FORCE it is now possible to include wind drag forces on slender elements. Quadratic wind drag coefficients in x-, y- and z-direction are then given in data group AERODYNAMIC DESCRIPTION.

In the new version it is possible to account for non-linear buoyancy due to the variation in vessel geometry above and below the still-water plane.

The basic first order wave forces and wave-drift forces are computed as before using transfer functions and wave-drift coefficients. Then the non-linear correction is obtained by integrating pressure forces on the instantaneously additional wet/dry surface. New input is a file in so-called (.gdf) format, containing the hull geometry in the splash zone.

A new feature Generic External Control System has been added to enable SIMO simulations with user developed control systems. External control systems are developed using a Java interface defined in HLAlib.jar. Currently the system supports controlling SIMO winches.

The included Java folder and the HLALIB.jar file have been updated in the Windows installation .zip file.