ANSYS Aqwa Features

ANSYS Aqwa software addresses the vast majority of analysis requirements associated with hydrodynamic assessment of all types of offshore and marine structures.

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Integrated System Integrated System

ANSYS AQWA software is an integrated system for undertaking hydrodynamic and mooring analyses. Functionally is split into six operations:

  • Diffraction/radiation
  • Static and dynamic initial stability including the effects of mooring systems and other physical connections
  • Frequency domain dynamic analysis
  • Time domain with irregular waves including slow drift
  • Nonlinear time domain with large-amplitude regular or irregular waves
  • Hydrodynamic load transfer to a structural finite element analysis 

A graphical interface provides a common tool to facilitate visualization and results processing for the ANSYS AQWA system.

An optional facility for coupled cable dynamics is available with the static and dynamic solvers (in both frequency and time domain) to provide more rigorous modeling of mooring system loading and response, especially in deep waters.

Modeling Flexibility Modeling Flexibility

For large floating bodies, ANSYS AQWA requires a description of the hull form. A standard panel discretization of the hull is utilized in the radiation/diffraction stage of the simulation (and may be used in subsequent solvers, such as static and dynamic time domain solutions). This can be achieved in one of several ways.

For ship-form shaped vessels, there is an automated mesh generator that works from the ship's lines plan (or offsets).

For more general vessel forms, the ANSYS DesignModeler tool may be utilized either to generate the geometry directly or to import geometry from a wide range of CAD systems. This geometry can then be imported into the new ANSYS AQWA hydrodynamic diffraction analysis system that includes its own meshing capabilities. Alternatively, suitably defined external CAD geometry may be directly imported into ANSYS AQWA hydrodynamic diffraction.


Total Capability for All Hydrodynamic Applications Total Capability for All Hydrodynamic Applications

ANSYS AQWA is not just for moorings or diffraction/radiation. It is a general-purpose hydrodynamics analysis tool that provides enormous flexibility to address most types of problems. Examples of its use include:

  • Design and analysis of mooring systems, including intermediate buoys and clump weights
  • Motions analysis of FPSOs
  • Determination of air gaps
  • Calculation of shielding effects of ships and barriers
  • Multiple body interactions during LNG transfer
  • Coupled cable dynamics
  • Sectional force calculations
  • TLP tether analysis
  • Dropped object trajectory calculations
  • Concept design and analysis of wave and wind energy systems
  • Simulation of lifting operations between floating vessels
  • Discharging landing craft from mother ships
  • Transportation of large offshore structures using barges/ships
  • Float over analyses
  • Motion analysis of spar vessels

Stress Analysis Results Transfer Stress Analysis Results Transfer

ANSYS AQWA WAVE is a linking program between the ANSYS AQWA diffraction calculation and a finite element model. It takes results in the form of pressures and motions for given wave directions and frequencies and automatically applies them as pressures and accelerations to an ANSYS structural mechanics or ANSYS ASAS finite element model. Differences in mesh density between the two models are accounted for automatically.

Functional Interface to Microsoft Excel Functional Interface to Microsoft Excel

When ANSYS AQWA is installed, a Microsoft® Excel® add-in is made available to permit direct interrogation of the ANSYS AQWA database via the insert function facility. This allows for custom report generation, plotting and additional post-processing that can be defined by the user.

The extraction of response amplitude operator information from a diffraction analysis

 

Available Functions

FUNCTIONS

DESCRIPTION

Aqlcogcoord

Returns x, y or z coordinate of a structure center of gravity

Aqlcoord

Returns x, y or z coordinate of a node

Aqlelcent

Returns x, y or z coordinate of a diffracting element' centroid

Aqlelpres

Returns pressure at element centroid

Aqlfrequency

Returns wave frequencies analyzed in ANSYS AQWA LINE

Aqlglobals

Returns global parameters

Aqlmessage

Returns error message for a given aql error flag number

Aqlndirns

Returns number of wave directions for structure

Aqlnfreqs

Returns number of wave frequencies for structure

Aqlnlines

Returns number of mooring lines in model

Aqlnstructs

Returns number of structures in model

Aqlposition

Returns position of a structure for time history analysis

Aqlrao

Returns RAO information from hydrodynamic database

Aqlrao2

Returns interpolated RAO information from hydrodynamic database

Aqlstatmooring

Returns mooring line information for static (ANSYS AQWA LIBRIUM) analysis

Aqlstatposcog

Returns position of CoG for static (ANSYS AQWA LIBRIUM) analysis

Aqlstatposnod

Returns position of specified node for static (ANSYS AQWA LIBRIUM) analysis

Aqlthacccog

Returns acceleration of cog for time history analysis

Aqltharticulation

Returns articulation reactions for time history analysis

Aqlthfender

Returns fender information for time history analysis

Aqlthmooring

Returns mooring line information for time history analysis

Aqlthnumsteps

Returns number of time steps for time history analysis

Aqlthposcog

Returns position of CoG for time history analysis

Aqlthtime

Returns time associated with time step in time history analysis

Aqlthvelcog

Returns velocity of cog for time history analysis

Aqlwavedirn

Returns wave directions analyzed in ANSYS AQWA LINE

Aqlzcge

Returns ZCGE parameter for structure in ANSYS AQWA LINE analysis

 

External Force Dynamic Link Libraries External Force Dynamic Link Libraries

ANSYS AQWA has the ability to include a user-defined external force algorithm via a dynamic link library (DLL). A DLL can be created to calculate a force based on time, position and/or velocity of a structure. Example interfaces are provided for C or FORTRAN™, but any programming language that can produce a DLL can be employed. An added mass matrix can be computed at each time step to simulate inertia forces. The calculation can be controlled by a set of up to 100 integer parameters and 100 real parameters that may be input and then passed to the external force routine.

This facility can be used to model:

  • Dynamic positioning system
  • Steering system
  • Towing force provided by a tug
  • Damping system with unusual characteristics
  • Suction force between two ships close together, or between a ship and the sea bed
  • Fluid transfer between vessels
  • Calculated energy extracted from a wave-power device

Coupled Cable Dynamics Coupled Cable Dynamics

As an option, ANSYS AQWA software can include the effects of line dynamics by modeling the mooring lines as a series of rod elements. This has the added benefit of including drag loads and added mass effects of the line, which can be significant for the long lengths of line encountered in deep-water applications. The feature is available for both static (drag effects) and dynamic analyses. For the dynamic response, the capability is available within both the frequency and time domains. Frequency domain solutions are very fast and can help determine whether cable dynamics need to be considered as part of the analysis. Time domain solutions can provide much greater accuracy, but they take longer to run.

As a further level of investigation, individual lines may be processed through the graphical supervisor, providing detailed information about tensions and motions along the line.

Differences can occur between including and excluding the effects
of coupled cable dynamics. The distribution of energy during the analysis is also illustrated.

Powerful Modeling & Results Interrogation Powerful Modeling & Results Interrogation

The ANSYS AQWA graphical supervisor is the key module within the suite. It can perform a wide range of tasks.

  • Data review
  • Automatic mesh generation
  • Scaling of existing models
  • Results presentation
  • Powerful graphing facilities
  • Export to spreadsheets
  • Function processing (for example, nodal RAOs)
  • Transformation analysis (for example, time domain to frequency domain)
  • Bending moment/shear force calculation including forward speed
  • Sectional force calculation
  • Online tutorials/demos
  • Control and monitoring of analyses

Multiple Body Articulations Multiple Body Articulations

ANSYS AQWA software has the ability to handle articulated structures, up to a maximum of 50 structures and 50 articulations. This permits modeling of combined hydrodynamic and mechanical dynamic configurations. Articulations can have stiffness, friction and damping included. If the mechanical connections are represented as tubes, these are allowed to become wholly or partially submerged and Morison-types forces are calculated.

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Hydrodynamic Interaction between Bodies Hydrodynamic Interaction between Bodies

ANSYS AQWA software can take into account the hydrodynamic interaction between adjacent vessels and structures, since the motions of one structure can affect the motions of another. These structures can be articulated, connected by cables or independent. A typical application is shielding effects. Forward speed effects can be included in the interaction.

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 Shielding effects of a pier adjacent to a ship, an important aspect in the design of breakwaters and how they affect mooring systems

 

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