PIAS Manual
2021
Program for the Integral Approach of Shipdesign

This method is based on Jensen, J. J., Mansour, A. E., & Olsen, A. S. (2004). Estimation of ship motions using closedform expressions. Ocean Engineering, 31(1), 6185. They developed closedform semianalytical expressions for the frequency response function for heave, pitch and roll and the vertical (relative) motion, velocity and acceleration of monohull ships. The formulas predict the variation of the motions and accelerations with the main dimensions, frequency, heading and speed fairly accurately, with the exceptions of:
A strip theory method will be implemented in the summer of 2021.
In order to calculate the probability of exceedance of a motion, a wave spectrum is required. Six wave spectra have been preprogrammed, according to the formulation in Stansberg, C. T., Contento, G., Hong, S. W., Irani, M., Ishida, S., Mercier, R., ... & Kriebel, D. (2002). The specialist committee on waves final report and recommendations to the 23rd ITTC. Proceedings of the 23rd ITTC, 2, 505551. These spectra are discussed below.
The JONSWAP spectrum defines seas with finite fetch. It requires input of a peak frequency and a peak enhancement factor. The approximations for this spectrum are believed to be correct for a range of the peak enhancement factor between 1 and 7. When the wind speed U and the fetch F are known, the peak frequency of the spectrum can be calculated according to \(f_p=\frac{g\hat{F}^{1/3}}{U}\) where \(\hat{F}=\frac{gF}{U^2}\).
The other spectra are of the generalized Pierson Moskowitz or Bretschneider form. These spectra define fully developed seas. The spectra and their required input are listed below:
In this window the parameters which are needed for the various methods are given. The list below now only lists those for the Jensen et al method. For additional detail it is advised to consult the source publication.
In these menus the points of interest and the specific output can be specified.
In this menu the socalled ‘points of interest’ can be defined. These are the points that output can be specified for in the next menu. A point is defined by a name, abbreviation and location coordinates. For the limited Jensen method, this location is only defined by a longitudinal position, the transverse position is always on the centerline and the vertical position is always on the waterline. For the strip theory based method all three coordinates are required.
In this menu the output for a point of interest is specified. First, after a new line has been created, a point of interest must be selected from a popup menu containing all of the points of interest defined in the previous menu. Alternatively, in the second column an abbreviation of one of the points of interest can be manually entered.
The third column opens a menu to select all the output for the point of interest. The heave, pitch and roll transfer function are always around the center of gravity of the vessel., which for the Jensen et al method is always at 0.5Lwl. The (relative) motions, velocities and accelerations are at the location specified for the point of interest.
As only three of the six motion transfer function can be calculated using the Jensen method, and information about the phase angles of these motions are not calculated, only vertical motions on the centerline of the vessel can be calculated. A more complete calculation, where also the transverse and longitudinal motions, velocities and accelerations are calculated will be introduced with the strip theory method.
If a wave spectrum is defined in menu /secref{motions,motions_main_input_vessel}, and only a single type of output is selected, then a probability of exceedance of a defined threshold value of the output type against the wave spectrum can be calculated. When this option is selected, a threshold value must be defined. An acceptable probability of exceedance can optionally be defined, which is used to clarify the graph output. The unit of the threshold value naturally depends on the selected type of output, and is shown in the cell comment when the cell is selected. The acceptable probability is given in percentages (0%100%).
Using the parameters given in the first menu option, the output specified in the second menu option is calculated and printed as specified.
With this option design versions can be managed, with a mechanism as described in Data storage and backups.