| This suite of programs, developed by WS Atkins is used for motions responses and mooring analysis of single or coupled floating structures, dynamic analysis of offshore heavy lifts and integrated deck mating, hydrodynamic loading analysis of large gravity base structures and vessel hulls. We have built up an extensive library of analysis models. These include FPSO tankers, semi-submersibles, transportation barges, crane vessels, supply boats, tugs and concrete gravity base structures. We have also developed techniques for highly non linear applications such as heavy lift, docking, mating and fender loads and extreme analysis of moorings. The suite comprises:- AQWA LINE: Used for modelling and generation of hydrodynamic and hydrostatic properties of floating structures. A full 3D diffraction radiation analysis is performed based on a flat plate element mesh model of the vessel hull. Water depth is included as a boundary condition allowing the incorporation of shallow water effects on vessel responses. Similarly a quay wall in close proximity to the vessel can be modelled for interaction effects. Frequency dependent wave exciting forces, reactive added mass and damping, free floating linear stiffness matrix, mean second order wave drift forces and first order response amplitude operators (RAO) are produced for subsequent motions, moorings or hydrodynamic loading analyses.
AQWA LIBRIUM:
Used for calculating the initial equilibrium conditions of analysis models prior to dynamic analysis. Mean forces are applied, being self weight, hydrostatic, second order wave drift, wind, current and mooring restraint.
AQWA FER:
Used for linear frequency domain spectral analysis of structure motions, excursion and mooring loads with allowance for slowly varying second order wave drift effects. Irregular seastates are defined using standard Pierson-Moskowitz, JONSWAP or arbitrary user defined spectra. Vessel RAOs may be modified for the effects of mooring stiffness, coupling with other structures and viscous damping of roll motions.
AQWA DRIFT:
Used for time domain simulation of vessel motions, moorings, heavy lift, docking and mating where highly non-linear characteristics preclude the use of linear frequency domain methods. Direct time integration of vessel motions and excursions allows for non-linearities such as composite mooring effects (e.g. clump weight lift off or buoy submergence), single point mooring fishtailing motions and snatch loading, transitions from weight to elastic stiffness properties in catenaries, interaction between coupled structures, docking and mating impact loads and fender loads. Selection of suitable integration time step length and duration of the simulation in conjunction with a synthesised irregular wave time history, ensures stability and adequate resolution for subsequent statistical post processing. Multiple restarts of simulations may be required to eliminate startup transient effects and to ensure adequate duration of the record. Multiple independent simulations may be used for the analysis of extremes or Monte Carlo type studies.
AQWA NAUT:
Also a time domain simulation program, but using regular waves only. It is used for detailed studies of particular conditions such as extreme design wave loading. Non-linearities are accounted for as in AQWA DRIFT above, with additional features such as full non-linear hydrostatic stiffness where the relative position of wave surface and the vessel is calculated to allow for such things as keel emergence, deck wetness or change of shape. Fluid loading calculations are enhanced by the use of a non-linear wave theory, plus Morison’s equation for small diameter tubular members.
AQWA GS:
Is the graphics program used for 3D plotting of plate element and tubular models for plots of any analysis parameter, such as RAOs hydrodynamic coefficients, motions responses, loads and time series results from AQWA DRIFT and NAUT. |