Ship motions computation available in PIAS

Motions is a program for predicting the ship motions in the frequency domain. As of now it uses a semi-analytical method for quick calculations in the concept design phase which can calculate the transfer functions for the heave, roll and pitch motions of the vessel, using only the main parameters of a vessel together with its speed, heading and the wave frequency. The method makes it possible to calculate the vertical motion, velocity and accelerations on any point on vessel on the longitudinal axis of the vessel.

Motions is a module within the PIAS software but can be used on its own. If a PIAS hullform is available, the right parameters can be derived from it and will save the user time. Some parameters also have the possibility to be estimated when the user doesn’t have a fixed number.

The output is designed to make it as easy as possible to responses for certain locations on the hull. This can be easily imported to text editors or spreadsheets for further processing.

To expand the new motion module SARC is currently working on implementing a strip theory method, which will be made available later this year. The strip theory based method is capable of computing the transfer functions for all six ship motions (surge, sway, heave, roll, pitch and yaw), and will be able to calculate the motion, velocity and acceleration of any point on the vessel.

Six sea spectra have been programmed: JONSWAP, one-parameter Pierson-Moskowitz, two-parameter Pierson-Moskowitz, ISSC, ITTC and Liu. These can be used to analyse the ships behaviour in irregular seas.