3.3 WA\"E FIELD 



3.31 DBTLOPMEJiT OF k MkVE FIELD 



Various descriptions of the aechanisa of wave g^ieratioo by vind have 

 been given, and significant progress in explaining the aechanisa nas re- 

 ported by Miles C1957) and Phillips (19S7) . Inteir^r-: : ' ; cnssions of the 

 results of aany of the aore pr«»inrait descripticr.s :f i -er.eraticHi by 

 wind are given by Kinsaan (1965), Phillips (1966), "i I 1971). 





Laboratory studies, (Hidy and Plate, 1966^ ^-i S-tzci:. i 

 1966), carefully designed to Batch the assusipti:-.5 r=.de by Miles and by 

 Phillips show reasonably good arrTe-^-" -:'- -'- z - rtretical rrefirtir::- . 

 SusBaries of various filed studies .- . -i 1> . ->^7) deacr^trate "ir.a": 

 theory provides a reasonable frirt-:r- f:r -.r liI sis of observations. 



The Nliles-Riillips theor>- as t -.ttiti ^- i i:m.-.i- :. t;;-eriBental 

 data pemits the foiBulation of a. differential equzticfa governing tie 

 growth of wave energ>-. This equat::- e written in a variety of ways. 

 (Inoue, 1966, 1967) and Bamett , 1.-: is approadi will cot be disr^s: 

 in detail because it requires = itrzi lii^zity co^pater i- i -:rT i-i.rz- 

 logical data than is likely to :e f:_-z r ztt": i- = -a;;r f:rT:iit :e--er. 



A brief discussion of the physical concepi; tiloj-ed in tie ci-r-ter 

 wave forecast, however, is presented to show tT rtcfings a- i -Trits 

 of simpler procedures that can be used in wave irT.asting. 



Growth and dissipation of wave energ)- are very sensitive to wave 

 frequency and wave direction relative to the wind direction. Ihus it is 

 desirable to consider each narrow band of directi(ms and frequencies 

 separately. A change in wave energy depends on the advecticn of energy 

 into and out of a region; trans forBatioo of the wind's kinetic energy 

 into the energ>- of water waves; dissipation of wave energy into tmbaleiice 

 and by fricticm, \-iscosity and breaking; and trans foraatirr. cf vave energy 

 at one frequency into wave energ>- at other frequencies. 



Mave energy- is discussed in Section 2.258. Wave Energj- and Power. 

 -Althou^ it is known that ener5>' transfers from one band of wave frequen- 

 cies to another do take place, this trocess is secondary- to the transfer 

 of energ>- froa the atBosx)here to the sea, and is not yet well enon^ onder- 

 stood to justify its consideration in a practical wave prediction sdieae. 



Riillips (1957) shewed that the turbulence assrciated with thf fl:- 

 of wind near the water v.c>uld create traveling pressure pulses. Thtir 

 pulses generate waves traveling at a speed appropriate to the diaensirn; 

 of the pressure pulse. Wave grc«t;h ry t-i5 7r::e55 i; - - f- 

 the waves are short and ^liien their speed is luenticu. _i-. : . .;: t " 

 of the wind velocity in the directirn cf wave travel. The err in; 1 ii:a 

 analyzed by Inoue (1966, 1967) indicate- -.'- \' - r effect of : r: lei 

 pressure pulses is real, but is only ii:_i ;r. -i eniieth as _^rge ^s t^ie 

 original theor>' indicated. 



3-15 



