PE Pipe Technical Catalogue (PDF) - Pipelife Norge AS

Pipelife Norge ASPE CATALOGUE-SUBMARINE APPLICATIONS, PIPELIFE NORGE AS, December 2002.The breaking depth (h b ) for a wave can roughly be calculated by formula A.4-25)h b = 0.05 ⋅ L o A.4-25)L o = wave length at deep water (ref. A.4-22) and A.4-23))On the following pages we shall deal with some examples where we apply the formulas forcalculation of wave properties and wave forces.Example 5Find the wave height, H o , and wave length, L o , at deep water for a wind speed u = 30 m/s(strong storm) and a fetch length, F = 10 km.Apply both the method with diagrams and the method with formulas.Compare the results. At which depth will the wave break ?Solution :a) Use of wind statistic :First we find the wind speed in miles/hour and the fetch length in miles.30 ⋅ 60 ⋅ 60u = 30 m / s = miles / h = 67 miles / h160910000F = 10 km = miles = 6.21609milesBy use of diagrams in fig. A.4.6.2 and fig. A.4.6.3 we get :H / 3= 7 feet 2.1m5.3 s1 =T 1 / 3 =Maximum wave height is given by formula A.4-19) :H o = 1.8 ⋅ 2.1 m = 3.8 mWavelength can be calculated by formula A.4-23) :L o = 1.56 ⋅ 5.3 2 m = 44 mb) Use of formulas :We apply formulas A.4-21) and –22) :H o = 0.045 ⋅ 30 ⋅L o = 0.56 ⋅ 30 ⋅10 m = 4.2 m10 m = 53 mc) Comparison of results :If we compare the results from a) and b), we find that the formula method gives highervalues than the method applying wind statistics.The differences expressed in percentage are :4.2 − 3.8Wave height ⋅100%= 10 %3.853 − 44Wavelength ⋅100%= 20 %44Side 63 av 84