Analysis settings for the Hydrodynamic Response analysis system depend on the Computation Type field. This field can be set to for the calculation of static equilibrium starting conditions for a subsequent Hydrodynamic Response analysis, for a calculation in the time domain, or for a calculation in the frequency domain.
By default, a Hydrodynamic Response system connected to a Hydrodynamic Diffraction system has the Computation Type of . A Hydrodynamic Response system connected to another Hydrodynamic Response system has a default Computation Type of . See Hydrodynamic Response System for a table of valid system connections.
- Parallel Processing
Time response analyses can take advantage of parallel processing for any of the following cases:
Multiple dynamic cables are defined
Multiple tether/risers are defined
One or more quasi-static composite cable(s) that touch down on a sloped seabed are defined
Analysis Type in Time Response Specific Options is set to Irregular Wave Response
Calculation of time domain pressure
Other Computation Types of Hydrodynamic Response analysis without quasi-static composite cables that touch down do not make use of parallel processing. For these cases, if Parallel Processing is set to Manual Definition and anything other than 1 is set for Number of Requested Cores, an information message is displayed and only one core is used.
For more information, see Aqwa Parallel Processing Calculation in the Aqwa Theory Manual.
- Use Cable Dynamics
If Yes, enables cable dynamics to be used (can be set per cable). If Cable Dynamics is disabled, then regardless of the selection in the individual cable, it is not used during the analysis.
The following analysis settings are specific to a Stability Response analysis.
- Output Global Stiffness Matrix
If Yes, output the global stiffness matrix.
- Require Convergence for Subsequent Analysis
If Yes, prevent any analysis dependent upon results from the current Stability Response analysis from running if convergence is not achieved.
- Maximum Number of Iterations
Defines the maximum number of iterations to perform in the stability analysis. If convergence has not occurred after the maximum number of iterations has been reached, the simulation stops.
- Movement Limitations per Iteration Step
Defines the maximum amount a structure can move in the X, Y, Z, RX, RY, and RZ directions in a single time step. When set to Program Controlled, the values for each maximum are 2 m, 2 m, 0.5 m, 0.573°, 0.573°, 1.432° respectively. When set to Manual Definition, the following additional options appear:
- Movement Limitations Applied to
Defines the structure to apply manual movement limitations to. When defined, additional Max Movement/Step fields appear for the X, Y, Z, RX, RY, RZ directions. You can define up to 5 sets of movement limitations.
- Maximum Error in Equilibrium Position
Defines the convergence criteria. When the movement per iteration drops below the values set in this field (in all six freedoms), the solution is considered converged and the simulation stops. When set to Program Controlled, the values for X, Y, Z, RX, RY, and RZ are 0.02 m, 0.02 m, 0.02 m, 0.057°, 0.057°, 0.143° respectively.
- Use Linear Stiffness Matrix to Calculate Hydrostatics
If Yes, uses the linear stiffness matrix and Froude-Krylov forces from the Hydrodynamic Diffraction calculation instead of re-calculating using the individual elements. This normally will reduce the time to run the program substantially.
These analysis settings control what is written to the Aqwa output text file. For more information, see the Aqwa Reference Manual.
- Axes System for Joint Reactions
Defines the axis system for the output of joint reaction forces.
- Fixed Reference Axes
Joint reactions are output using axes parallel to the global axes.
- Local Structure Axes
Joint reactions are output using axes parallel to the local structure axes.
- Local Articulation Axes
Joint reactions are output using the individual local joint axes.
- Data List
If Yes, include all extended data output in the .LIS file.
- Element Properties
If Yes, output complete details of each element used in the body modeling to the *.LIS file. All important details of the body elements are output together with the resultant properties of the bodies.
- Dynamic Cable/Tether Drag
If Yes, the drag force acting on each dynamic cable or tether connection at each iterative step will be output in the *.LIS file.
The following analysis settings are specific to a Time Response analysis.
- Analysis Type
Select one of the analysis types listed. Depending upon the type selected, either a Regular or Irregular Wave object must be defined for the analysis. Available settings are:
Irregular Wave Response With Slow Drift (Irregular Wave)
Irregular Wave Response (Irregular Wave)
Regular Wave Response (Regular Wave)
Slow Drift Only (Irregular Wave)
- Start Time, Duration
Set the Start Time and Duration for the Time Response simulation. The Finish Time is updated automatically. If there is an upstream Hydrodynamic Response system the Start Time must be within the range of the Start Time and the Finish Time of the upstream system.
- Output Step
The length of time between outputs to the plotting and text files. The Output Step will default to 0.1s, and will always be equal to the nearest whole number of time step intervals. Enter 0 to reset the Output Step to the Time Step value.
Note: In order to limit the size of the hydrodynamic output files, the maximum number of output time steps accepted by Aqwa Workbench is 1,000,000. If this is exceeded, the program will set Output Step to the minimum permissible for the defined Time Step.
- Time Step
Set the length of time simulated at each time step. The Number of Steps is calculated from the Time Step and Duration, and is updated automatically.
- Starting Position
If a Time Response Analysis is preceded by a Stability Analysis, the equilibrium position from the Stability Analysis is used and the (read-only) Starting Position is set to . This also applies if there is an upstream Time Response Analysis, where the Starting Position is determined by the position at the corresponding time in the upstream system.
If a Time Response Analysis is linked directly to a Hydrodynamic Diffraction/Radiation Analysis and Starting Position is set to Program Controlled, the equilibrium position will be automatically determined before the Time Response Analysis is started and used as the starting position. If Starting Position is set to , the current geometry determines the starting position. Note that when the model includes one or more Joints, the option is replaced by .
- X- and Y-Position for Wave Surface Elevation Output
Define a Fixed Position at which the Wave Surface Elevation will be available as a result.
When the Time Response Analysis Type is set to Irregular Wave Response or Regular Wave Response, the Time Response Pressure Output options can be used to set up the generation of instantaneous pressure results for one or more structures in the analysis. The options are:
- Output for Structure
Select a structure for which instantaneous time domain pressures will be output; or, in an analysis with multiple structures, you may choose All Structures.
- Output Start Time
Set the time at which pressures will start to be recorded. The Output Start Time cannot be less than the analysis Start Time, and is automatically adjusted to the nearest whole number of Output Step intervals.
- Output Time Step
Set the length of time between pressure records. The Output Start Time is automatically adjusted to the nearest whole number of Output Step intervals.
- Output Finish Time
Set the time at which pressures will stop being recorded. The Output Finish Time cannot be greater than the analysis Finish Time, and is automatically adjusted to the nearest whole number of Output Step intervals.
Note: For a workflow which includes time domain Hydrodynamic Response pressure mapping to a Static Structural finite element analysis using the Aqwa Hydrodynamic Pressure Mapping Add-on, the structures and time steps available for pressure mapping in the Static Structural system are defined by the Time Response Pressure Output options. Time domain pressure mapping will not be possible while the Output for Structure option is set to None.
These analysis settings control how the Time Response Analysis is performed. In normal circumstances they will not need adjusting. For more information, see the Aqwa Reference Manual.
Time Response analyses with the Use Cable Dynamics option set to Yes can take advantage of parallel processing with the proper licenses. For more information, see Setting Aqwa Parallel Processing Options.
- Convolution
If Yes, specifies that convolution method is used in radiation force calculation. This is a more rigorous approach to the radiation force calculation in time domain and will enhance the capability of handling nonlinear response of structures. Convolution requires that a Hydrodynamic Diffraction/Radiation analysis has been performed for at least 5 wave frequencies.
- Call Routine "user_force"
If Yes, calls a routine called "user_force" at each stage of the calculation. This routine can be used to add externally calculated forces to the simulation. See External Force Calculation in the Aqwa Reference Manual for more information.
- Connect to Server for External "user_force" Calculation
If Yes, uses a process running on an external server for the user-force calculation. See External Server for User-Defined Force Calculation in the Aqwa Reference Manual for more information.
- Calculate Motions Using RAOs Only
If Yes, calculates motions using RAOs only. Note that this option suppresses all motion except that defined by the RAOs. In particular current, wind, drift forces, moorings etc. have no effect on the motions of the structure.
- Account for Current Phase Shift
If No, switches off the wave phase shift due to a current speed.
- Apply Mean Drift Force with Multi-Directional Wave Interaction
If Yes, utilize the drift coefficients which include interactions between different wave directions that have been calculated in the preceding Hydrodynamic Diffraction analysis. This option is invalid if the Include Multi-Directional Wave Interaction option in the preceding Hydrodynamic Diffraction analysis is set to No.
- Calculate Wave Drift Damping
If No, stops the automatic calculation of wave drift damping for a floating structure. Note that the wave drift damping calculated by the program is only for the floating structure, damping from risers, etc. is not included.
- Include Yaw Wave Drift Damping
If No, suppresses the calculation of wave drift damping for yaw motion. To prevent the calculation of all wave drift damping use the No Automatic Wave Drift Damping Calculation option.
- Use Slow Velocity for Hull Drag Calculation
If Yes, uses the slow velocity (drift frequency velocity) for the hull drag calculation, instead of the total velocity (drift frequency velocity + wave frequency velocity) which is the default.
- Use Linear Starting Conditions
If Yes, starts a simulation with the motions and velocities derived from the Hydrodynamic Diffraction system results. This can be used to limit the transient at the start of a simulation.
- Use Linear Stiffness Matrix to Calculate Hydrostatics
If Yes, uses the linear stiffness matrix and Froude-Krylov forces from the Hydrodynamic Diffraction calculation instead of re-calculating using the individual elements. This normally will reduce the time to run the program substantially.
- Include Maneuvering Force
If Yes, adds the maneuvering loads due to the low frequency ship maneuvering motions, as described in Low Frequency Maneuvering Loads in the Aqwa Theory Manual, to the total structure forces/moments.
- Use Wheeler Stretching
The functionality of this option depends on the context in which it is used.
If the Analysis Type is set to Regular Wave Response: Use Wheeler Stretching = Yes turns on Wheeler stretching when calculating the Froude-Krylov force over the instantaneous wave surface.
If the Analysis Type is set to Irregular Wave Response, Wheeler Stretching is always used. The Use Wheeler Stretching field can be used to specify:
With Linear Wave Theory - calculation will only use linear wave theory.
With Second Order Correction - calculation will add a second order correction on wave elevation, pressure, and fluid particle velocity/acceleration in addition to the linear wave theory.
These analysis settings control the use of the QTF matrix for Time Response Analyses. For more information, see the Aqwa Reference Manual.
- Use Full QTF Matrix
If Yes, specifies that the full matrix of difference frequency QTFs is to be used when calculating slowly varying drift forces.
- Use Sum Frequency QTFs
If Yes, specifies that the full matrix of sum frequency QTFs is to be used when calculating slowly varying drift forces, in addition to using the full matrix of difference frequency QTFs. You must also have Use Full QTF Matrix set to Yes to use this feature.
These analysis settings control what is written to the Aqwa output text file. For more information, see the Aqwa Reference Manual.
- Axis System for Joint Reactions
Defines the axis system for the output of joint reaction forces.
- Fixed Reference Axes
Joint reactions are output using axes parallel to the global axes.
- Local Structure Axes
Joint reactions are output using axes parallel to the local structure axes.
- Local Articulation Axes
Joint reactions are output using the individual local joint axes.
- Data List
If Yes, include all extended data output in the *.LIS file.
- Element Properties
If Yes, writes complete details of each element used in the body modeling to the *.LIS file. All important details of the body elements are output together with the resultant properties of the bodies.
- Dynamic Cable/Tether Drag
If Yes, the drag force acting on each dynamic cable or tether connection at each time step will be output in the *.LIS file.
When the Hydrodynamic Response Settings is set to Irregular Wave Response or Regular Wave Response, the Co-simulation FMU Package options become available to set up the generation of the Aqwa Functional Mock-Up Unit (FMU) package. This Aqwa FMU package contains the information of the current Aqwa model, and it is used for the co-simulation analysis. The inputs for this Aqwa FMU package need to be the displacement, velocity, and acceleration at the center of gravity of each Aqwa structure. The outputs of this Aqwa FMU package are the total forces and moments of hydrostatic, hydrodynamic, and mooring loads at each Aqwa structure's center of gravity. More information about Aqwa co-simulation is elaborated in The Aqwa Co-simulation Add-on section. The following are the available options for the generation of the Aqwa FMU package:
- Output FMU Package
Select whether to output an Aqwa FMU package for the current analysis. Select Yes if the co-simulation analysis is required. The solver input files of the current analysis and FMI supporting file are contained within the Aqwa FMU package.
- FMU Export Version
Select the FMU version for the output Aqwa FMU package file. The selection must be based on the FMU versions supported by the co-simulation platform.
- Co-simulation Partner's Unit
Select the unit system used by the co-simulation partner, which is planned to be connected to the Aqwa FMU package. The available selections follow the Mechanical application interface unit options and their converting relationships with the Mechanical solver units. During the co-simulation, the unit transformation will be conducted according to the selected units.
- Co-simulation Coordinate System Offsets
Select whether there are differences between the coordinate system of the current Aqwa model and the co-simulation partner. If Yes is selected, the offsets between the two coordinate systems can be defined by X Offset, Y Offset, Z Offset, Rotational Offset X, Rotational Offset Y, and Rotational Offset Z options. The application of the offsets on the Aqwa coordinate values should be equal to the coordinate values of the co-simulation partner.
The following analysis settings are specific to a Frequency Statistical analysis.
- Analysis Type
Select one of the analysis types listed. Available settings are:
Wave and Drift Frequencies
Wave Frequencies Only
Drift Frequencies Only
- Direction of Output for RAOs
Allows you to change the direction in which some of the Graphical Results (Motion RAOs, Cable Tension and Fender Force RAOs, and Transfer Functions) are given. When there is more than one direction available, the entries in the menu are the unsuppressed waves contained in the analysis. When Direction of Output for RAOs is set to Program Controlled, the output is given in the direction of the spectrum that has the largest significant wave height.
- Spectrum Sub-Direction of Output for RAOs
Only editable if Direction of Output for RAOs has a Cross Swell defined, or is configured with a Number of Sub-Spectra greater than 1 (Wave Spreading is not None (Long Crested Waves)).
- Axis System for Significant Motions and Nodal Response
Sets the (global or local) axis system in which significant motions and nodal response spectra are reported.
- Starting Position
If a Frequency Statistical Analysis is preceded by a Stability Analysis, the equilibrium position from the Stability Analysis is used and the (read-only) Starting Position is set to Determined by Upstream System.
If a Frequency Statistical Analysis is linked directly to a Hydrodynamic Diffraction/Radiation Analysis and Starting Position is set to , the equilibrium position is automatically determined before the Frequency Statistical Analysis starts and is used as the starting position. If Starting Position is set to , the current geometry determines the starting position. Note that when the model contains one or more Joints, the option is replaced by .
Caution: The Based on Geometry option should be used with care, as a Frequency Statistical Analysis of any system containing connections or articulations is unlikely to be correct if the tensions and reactions at those connections or articulations are not calculated first. Linking a Frequency Statistical Analysis to a Stability Analysis, or setting Starting Position to Program Controlled, ensures that the forces acting on connections and articulations are determined before the Frequency Statistical Analysis is performed.
These analysis settings control how the Frequency Statistical analysis is performed. In normal circumstances they will not need adjusting. For more information, see the Aqwa Reference Manual.
- Calculate RAOs with Mooring Lines
If Yes, allows access to the CRAO option in the input file.
- Apply Drift Force with Multi-Directional Wave Interaction
If Yes, utilize the drift coefficients which include interactions between different wave directions that have been calculated in the preceding Hydrodynamic Diffraction analysis. This option is invalid if the Include Multi-Directional Wave Interaction option in the preceding Hydrodynamic Diffraction analysis is set to No.
- Linearized Morison Drag
If Yes, computes linearized Morison drag for tube, disc, and slender tube elements, and for wind and current drag forces.
The analysis settings control the use of the QTF matrix for Frequency Statistical analyses. For more information, see the Aqwa Reference Manual.
- Use Full QTF Matrix
If Yes, specifies that the full matrix of difference frequency QTFs is to be used when calculating slowly varying drift forces.
These analysis settings control what is written to the Aqwa output text file. For more information, see the Aqwa Reference Manual.
- Axes System for Joint Reactions
Defines the axis system for the output of joint reaction forces.
Fixed Reference Axes - Joint reactions are output using axes parallel to the global axes.
Local Structure Axes - Joint reactions are output using axes parallel to the local structure axes.
Local Articulation Axes - Joint reactions are output using the individual joint axes.
- Data List
If Yes, output all extended data output in the *.LIS file.
- Output Element Properties
If Yes, writes complete details of each element used in the body modeling to the *.LIS file. All important details of the body elements are output together with the resultant properties of the bodies.