A NEW APPRAISAL OF STRIP THEORY 



Lyssimachos Vassilopoulos and Philip Mandel 



Massachusetts Institute of Technology 



Cambridge, Massachusetts 



ABSTRACT 



After a brief historical review, this paper presents the results of the 

 broad comparison between experimentally measured and theoretically- 

 computed ship nnotions and phase angles first reported in Ref, [6]. 

 Tank data for a wide range of Series 60 models in regular waves were 

 extracted from N.S.M.B. publications and correlated with model re- 

 sponses calculated by a digital computer program which is based on the 

 Korvin-Kroukovsky linear theory of ship motions in conjunction with 

 Griin's latest results on added mass and damping. Seas from both di- 

 rectly ahead and astern are considered and emphasis is paid to the ef- 

 fects of variations in hull form shape and weight distribution. 



Methods which will improve the applicability of strip theory and ad- 

 vantages to be gained by modifying its analytical description are next 

 presented in anticipation of further development of the theory. New 

 theoretical data on added mass and damping are also discussed. Al- 

 though no definite statements are as yet made with regard to some 

 apparent inconsistencies in the Korvin-Kroukovsky analysis, there is 

 reason to believe that certain modifications and corrections can be 

 miade which will generally imiprove the procedure and render it more 

 useful. 



INTRODUCTION 



About seventy years ago, Captain Kriloff laid the foundation of what today is 

 known to be the strip theory for computing pitching and heaving motions of a 

 ship in regular waves [1,2]. Yet, it was only in 1950 when Weinblum and St. 

 Denis launched a new era in seakeeping research [3] that Kriloff's seldom read 

 paper received the recognition it deserved. During the last decade, Korvin- 

 Kroukovsky addressed himself to the problem of improving and refining the 

 analytical procedure and in this work he was assisted by numerous complemen- 

 tary studies made by other researchers. The culmination of all this activity led 

 to the publication in 1960 of a guide by Jacobs et al. [5] making possible the 

 ready application of strip theory as it was understood at that time. 



In a recent report [6], one of the present authors utilized strip theory es- 

 sentially as it was set forth by Jacobs et al., with a view towards evaluating 

 seawortiiiness performance in random seas along analytical lines. The present 



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