Newman 



DISCUSSION 



SOME DEVELOPMENTS IN SHIP WAVE PATTERN RESEARCH 



N. Hogben 



National Physical Laboratory ^ Ship Division 

 Felthanij Middlesex, England 



I. INTRODUCTION 



This note briefly reports two developments in ship wave 

 pattern research. The first concerns progress in application of the 

 'Equivalent Source Array' concept described in Ref. 1; the second is 

 the development of a fully automated system of recording and 

 analyzing the waves, a more detailed account of which is being 

 prepared as Ref. 2. 



II. EQUIVALENT SOURCE ARRAYS 



An 'Equivalent Source Array' means for the present purpose, 

 a source distribution which according to linear theory would generate 

 a given wave pattern. It can be used for evaluating and interpreting 

 the correlation between wave theory and experiment and also for 

 predicting the effects of wavemaking on changing tank width and depth. 



In Ref. 1 , this concept was invoked to interpret wave pattern 

 measurements behind -■. series of 3 models with parabolic hull forms 

 and systematically varied beam. More recently, a similar investi- 

 gation has been made of the wave patterns behind 3 trawler type hull 

 forms (aparent and 2 derivatives) tested by Everest (Ref. 3). In the 

 case of these more realistic models, the 'equivalent source arrays' 

 were found to vary significantly with speed as indicated by the sample 

 results for one of the models shown in Fig. 1, It may be seen that 

 sources and sinks appear at a distance ahead of the bow which in- 

 creased with increasing Froude number. This effective lengthening 

 of the array may be explained in terms of 2nd order increases of 

 wave phase velocity due to nonlinearity of the waves generated in the 

 bow regions . 



III. AUTOMATED RECORDING AND ANALYSIS 



A prototype for a fully automated recording and analysis 

 system has now been developed and operated. It comprises a station- 

 ary array of 4 capacitance probes with paper tape output and a com- 



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