Evaluation of Motions of Marine Craft in Irregular Seas 



Fig. 11 - Impulsive response function for 

 heave motion of hydrofoil craft in head seas 



CONCLUSIONS 



Time histories of the motions of marine vehicles in irregular seas can be 

 reliably calculated by employing the technique of the impulsive response function. 



The impulsive response functions of hydrodynamic systems depend on both 

 wave input exciting forces, which are frequency dependent, and upon the calm 

 water frequency characteristics of the marine craft. In addition, the wave sur- 

 face profile is commonly used as a representation of the exciting forces and the 

 length of the vehicle is usually large relative to discrete wave lengths. Conse- 

 quently, the impulsive response properties of these hydrodynamic systems are 

 distinct from the usual electrical or mechanical systems. 



Theory provides a method for shifting either the system impulsive response 

 function or the irregular wave record from one spatial reference point to an- 

 other. This shifting can lead either to increasing or decreasing the amount of 

 wave information required in future time. 



491 



