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AQWA - An
Integrated System
AQWA is a fully integrated system consisting of
modules for diffraction/radiation (AQWA-LINE), static and dynamic
initial stability including mooring lines (AQWA-LIBRIUM), frequency
domain with irregular waves (AQWA-FER), time domain with irregular
waves including slow drift (AQWA-DRIFT) and non-linear time domain
with regular or irregular waves (AQWA-NAUT)
These modules are
encapsulated in the powerful AQWA-Graphical Supervisor
In
addition an optional integrated module for coupled Cable Dynamics is
available with frequency and time domain modules as well as stands
alone within the AQWA-Graphical Supervisor.
Other optional Modules include AQWA-LAUNCH and
AQWA-FLOAT. These perform the simulation of jacket launch and float
operations during installation. The AQWA Graphical Supervisor can
present results from the programs and perform animations.
Hydrodynamic
Interaction between floating bodies
AQWA can take account of hydrodynamic
interaction between adjacent structures. Thus the motions of one
structure can affect the motions of another. The structures can be
articulated, connected by cables or independent. A typical
application would be shielding effects. Note that hydrodynamic
interaction with forward speed is currently not
available.
The colored lines between these two vessels will
help to tell the user what percentage they have moved during an
analysis. Brown is under 30% and yellow between 50% and 30%.
Multiple Body
Articulations
AQWA has the ability to handle articulated
structures. Up to 10 of these structures can be
diffracting/radiating structures. Up to a further 40 can be
mechanical structures such as cranes and other rigid connects etc.
This permits the modeling of combined hydrodynamic and mechanical
dynamic configurations. Articulations can have 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 calculated.
Powerful modeling
and results interrogation
The AQWA-Graphical Supervisor is the key module
within the suite. It can perform a range of tasks including:
Data Editing
Automatic Mesh
Generation
On-Line Help
On-Line Reference
Manual
On-Line Tutorial/Demos
Control and
Monitoring of
Analyses
Bending Moment/Shear
Force Calculation including
Forward
Speed
Splitting Force
Calculation
Scaling of existing Models
Results
Presentation
Powerful graphing facilities
Export
to spreadsheets
Function processing e.g. Nodal
RAOs
Transformation analysis e.g. time domain to
frequency domain
Display of wave height
elevation |
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Total
Capability for all Hydrodynamic Applications
AQWA is not just for moorings or diffraction
radiation but is a general purpose hydrodynamics analysis suite
providing enormous flexibility to address most types of problem.
Examples of its use include:
- Design and analysis of mooring systems
- Motions analysis of FPSOs
- Determination of Air Gaps
- Calculation of Shielding Effects of ships and
barriers
- Multiple Body Interactions during LNG transfer
- Coupled mooring line-structure interaction
- Cable Dynamics with intermediate buoys
- Splitting Force calculations for
Semi-Submersibles
- TLP concept design
- TLP tether analysis
- Dropped object trajectory calculations
- Concept design and analysis of Wave 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
- Motions analysis of Spar vessels
Coupled
Cable Dynamics
As an optional extra it is possible for AQWA to
perform both stand alone and coupled cable dynamics analyses. The
capability is available within both the frequency domain (AQWA-FER)
and time domain modules (AQWA-DRIFT and AQWA-NAUT). Frequency domain
solutions are very fast and can help determine whether cable
dynamics needs to be considered as part of the analysis. Accuracy
however can only be about 90%. Time domain solutions can provide
much greater accuracy but of course take longer to run.
Some
organizations also insist on a stand alone cable dynamics analysis
being performed and this is achieved directly within the AQWA
Graphical Supervisor.
Other features of Coupled Cable
Dynamics include:
- Intermediate Buoys
- Intermediate clump weights
- Buoyant catenaries
- Cables between vessels
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This screen shows the difference which can
occur between including and excluding the effects of coupled
cable dynamics. Also shown is the distribution of energy dying
the analysis.
The Cable Dynamics capabilities have been
verified against both software and experimental
data
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External Force
Dynamic Link Libraries
AQWA 5.5 has an ability to add a force history
via a dynamic link library (DLL). This feature permits the user to
create his or her own .dll in 'C++' or FORTRAN to calculate a force
based on the time, the position and/or the velocity of a structure.
A mass matrix can also be defined 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 be passed to the external force routine.
This facility
could be used to model, for example:
- a dynamic positioning system
- a steering system
- the towing force provided by a tug
- a damping system with unusual characteristics
- the suction force between two ships close
together, or between a ship and the sea-bed.
Comprehensive
Verification and Validation
AQWA has been developed over a period of almost
30 years. Initially it was employed as a tool to predict the
launching and floating of large jacket structures as the North Sea
started to become a major oil producing area. Experience from actual
launches proved that AQWA was able to predict the jacket motions
with great accuracy. This evidence served to establish the
LAUNCH/FLOAT programs as de facto standard and subsequently was
incorporated in other third party software including Exxon, DNV and
Bureau Veritas. Subsequently the capability was extended to become a
more general purpose program and AQWA-FER, AQWA-NAUT and AQWA-DRIFT
came about. Again these programs have been extensively validated
against tests and other comparisons.
A verification
document is available to licensees but the following gives a list of
some documents used for AQWA Verification:
An engineering
assessment of the role of non-linearities in transportation barge
roll response; Robinson and Stoddart. Proc RINA Vol 129
1986.
Experience in analysis of SPM system; Rainey, Cash and
Withee OTC 4346 1982
Ship stability based on chaotic
transients from incursive fractals; Thompson, Rainey and Soliman.
Phil. Trans. R. Soc vol 332 1990.
Practical problems with
computer simulation of SPM systems; Rainey and MacFarlane. 2nd
Offshore Mechanics/Arctic Engineering Symposium, ASME 1983.
A
new theory and its application for stability criteria covering
wave-induced tilt phenomena on semi-submersibles; Rainey. Advances
in Underwater Technology, Ocean Science and Offshore Engineering,
Graham and Trotman 1986.
Measurement of full scale barge
motions and comparison with model test and mathematical mode
predictions; DeBord et al.
Results comparison of computer
simulation, model test and offshore installation for Wandoo
integrated deck float over installation; Chu, Cochrane, Mobbs, and
Mitchell. OTC 8614 1998.
Prediction of the sea keeping
performance of small craft; Khattab. 1st European Symposium on Yacht
and small craft design.
Comparative study on mooring line
dynamic loading; Brown and Mavrakos. Marine Structures 12
(1999).
Design aspects of SPM LNG terminals in shallow
water; Naciri and Poldervaart. OTC 16424 2004.
AQWA-FER,
AQWA-LINE and AQWA-LIBRIUM have been approved by the Norwegian
Maritime Directorate for mooring analysis. AQWA was used in the FPS
2000 comparison tests within the NTNF research program along with 23
other international organizations. Results can be made available to
licensees.
Transfer of
Results to for Stress Analysis
AQWA-WAVE is a linking program between
AQWA-LINE and ASAS. It takes the results in the form of pressures
and motions for given wave directions, period and frequency and
automatically applies them as pressures and accelerations to an ASAS
finite element model. Differences in nodal coordinated between the
two models is automatically accounted for.
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