Directional Waves in the Nearshore Coastal Region of Perth ...

More documents

Recommendations

Info

Directional waves in the nearshore coastal region of Perth, Western AustraliaHuey Jean TanFigure 2.5: The surface elevation time series and spectrum of an irregular wave (USACE 2002)2.2.3 Significant Wave Height and Peak PeriodThe concept of significant wave heightH or H1 3is a very useful and important index toscharacterise the heights of the surface waves on the sea. It is defined as the mean of the onethirdhighest waves in a sample record (Kinsman 1965), or in terms of the total energy of thewave system (Tucker and Pitt 2001):H= Hm0 4 m 0Equation 2-2s=where m 0 is the spectral moment or variance (‘energy’) of sea surface elevation given bym ! " 0= S( f )df Equation 2-30It is conventional to denote significant wave height H s as H 1/3 when it is measured directly viathe wave-by-wave analysis and H m0 when it has been estimated from the variance of therecord or the integral of the variance in the spectrum. Both are good estimates of H s and aregenerally very close in value, and it is typical forH to exceed H1 3by 5-10% (Lemm 1996).The mean period of these ‘significant’ waves is termed as the significant wave periodAccording to Kinsman (1965), visual observations of wave heights and periods are goodapproximations ofHsand Ts.sTs.Peak period T p is the reciprocal of the frequency at which the peak of the spectrum occurs(Tucker & Pitt 2001). T p is associated with the largest wave energy and is only obtainablethrough spectral analysis. An example of peak period for natural ocean waves is shown inFigure 2.5b. The spectral representation of swell waves will display a single value of peakperiod and wave energy decays at frequencies on either side. The spectra of storm waves ismulti-peaked, with one peak (although not always the highest) corresponding to swelloccurring at lower frequencies. One or more peaks are associated with storm waves occurringat higher frequencies.2.2.4 Spectral Wave PowerWave power (or wave energy flux) is defined as the rate of energy transmission in thedirection of wave travel across a vertical plane that is perpendicular to the direction of waveLiterature Review 11
Directional waves in the nearshore coastal region of Perth, Western AustraliaHuey Jean Tanpropagation and extending down the entire depth (USACE 2002). For a unidirectional wavespectrum, the power transported per metre of the crest length can be derived using spectralenergy defined in Equation 2-5 (Tucker and Pitt 2001):!( f ) S( f )P = ECn = " g C df Equation 2-4gwhere C g is the group velocity, which is defined as the rate of transmission of waveenergy:C g= CnE is termed the specific energy or energy density and is the total average wave energyper unit surface area:E =! gH82shallow water.n = 0.5 in deep water, increases in value in the transition zone to become n = 1 in12 Literature Review
Page 1 and 2: Directional Waves in the NearshoreC
Page 3 and 4: m, and a maximum H s of 2.75 m was
Page 5 and 6: Directional waves in the nearshore
Page 70 and 71:
Directional waves in the nearshore
Page 72 and 73:
Page 74 and 75:
Page 76 and 77:
Page 78 and 79:
Page 80 and 81:
Page 82 and 83:
Page 84 and 85:
Page 86 and 87:
Page 88 and 89:
Page 90 and 91:
Page 92 and 93:
Page 94:
show all

Directional Waves in the Nearshore Coastal Region of Perth ...

Create successful ePaper yourself

Delete template?

Save as template?