Purpose

The structural design and general performance of a ship requires the evaluation of its motions and wave induced pressure distributions over the hull in severe sea states. In order to estimate the importance of extreme events, a nonlinear sea keeping solution must simulate, with sufficient accuracy and efficiency, the sea keeping behavior of a ship in steep random wave trains that may be several hours long in duration. With this goal in mind, the development of WASIM was initiated and carried out.

Benefits

Improved understanding of structural behavior in various sea states leads to more optimal designs and safer ship operation. Ships can be operated more safely by providing ship's Masters with the necessary information for selecting speed and heading in rough seas. Fuel consumption can be reduced by comparing design alternatives and thereby optimize wave resistance. Passenger comfort may be improved through better understanding of a ship's motion characteristics.

Features

The present version of WASIM enables the user to evaluate the performance of a vessel with respect to both structural strength and motion characteristics. The following non linear effects can be included in the simulations:

• Integration of Froude-Krylov force and hydrostatics over exact wetted surfaces

• Finite rotation angles in equations of motion

• Quadratic pressure terms

• Quadratic roll damping

• Slamming pressures

• Pressures due to water on deck

• Flexibility of the hull

The motion control in sway and yaw can be done by active rudders controlled by an auto-pilot, or alternatively by an artificial spring system. Jobs are created and maintained in the Graphical User Interface (GUI) of WASIM The time domain output can be processed statistically by the SESAM post-processor Postresp_time.

Animation of vessel motions, wave elevation and pressure distribution can be made by the SESAM program module Xtract.

One of the important features is that WASIM is a part of the SESAM software package: This makes it easy to transfer data from WASIM to the structural analysis program SESTRA.

When the excitation due to slamming is included in the simulation, the whipping response can be simulated. Whipping may, for flexible hulls, lead to a significant increase in the vertical bending moment.