Technology

WAve Load Interface System (WALIS) for Ship Structural Design

Classification rules have been the mainstay of ship structural design. The advantage of these rules is the simplicity provided by their semi-empirical nature. But modern ships continue to increase in size and exceed the traditional limits of operational experience. For such new designs, a clear disadvantage of the semi-empirical approach lies in its inability to extrapolate confidently to new technology and new designs. To account for this major shortcoming, ship designers have sought an alternative method based on direct engineering analysis to reflect the emerging trends in ship design. WALIS   Hyundai Maritime Research Institute (HMRI) has developed an integrated analysis procedure directly using wave loads acting on ships in the entire-ship structural analysis: WAve Load Interface System (WALIS). WALIS provides ship designers and engineers with a robust interface between hydrodynamic models and finite element structural models used in well-known structural analysis tools, such as the NASTRAN solver. Although some features are still under development, the following are its primary functions: Hydrodynamic and finite element modeling Wave loads and ship behavior at sea Statistical analysis for various responses Load transfer to FEA model Finite element analysis for entire-ship structural models Seakeeping analysis   For predicting ship behavior and dynamic loads for design and analysis, the linear strip theory has been widely used as a practical analysis tool. WALIS uses a modified strip theory that partially accounts for non-linear effects. Vessel responses in regular and irregular waves are calculated in the frequency domain, and extreme values during the whole lifetime of ships are obtained through WALIS. The outcome of WALIS seakeeping analysis includes: Rigid body responses in six-degree-of-freedom motion Sectional loads in longitudinal cuts Relative motion between vessel and free surface at specified points Pressure distribution on the hull Wave loads and ship behavior in irregular waves Extreme values during the whole lifetime Fully integrated with FEA   Pressure load on the wet surface of the hull, internal pressure acting on cargo holds and/or ballast tanks, and inertia loads throughout the vessel can be automatically transferred to the finite element program of NASTRAN. This automatic transfer saves time and improves quality. The FEA model can be automatically adjusted to displacement and center of gravity. Force equilibrium is checked to minimize rigid-body motion caused by the unbalance forces acting on the FEA model in entire-ship structural analysis.   End-users of WALIS can improve their knowledge about ship performance and strength both in the design phase and in the operation of the vessel.