Irregularity of seas and swells in typhoon area

DOI Web Site

Bibliographic Information

Other Title
  • 暴風海面に於ける波群の解析(十三) : スペクトルの分布と波高の分布
  • 暴風海面に於ける波群の解析-13-
  • ボウフウ カイメン ニ オケル ハグン ノ カイセキ 13

Search this article

Description

Randomness of sea waves is closely related to the spectral distribution of energy. So if we know the wave spectrum, we can estimate statistically their probability distribution of heights of sea waves. According to Rice's theory of noise current, if wave height is analysed into Fourier series: [numerical formula] where ξ_N is supposed to be distributed according to normal law, and letting w(f) be spectral distribution and ψ_0 mean square, [numerical formula] then for velocity and acceleration: [numerical formula],[numerical formula] So that if there is any other regular wave [numerical formula] index number of irregularity is expressed as follows: (i) Theory of maxima: [numerical formula] (ii) Theory of envelope: [numerical formula] Theory of maxima is applicable to sea state before typhoon centre approaches and theory of envelope is effective after it has passed away. According to Neumann's theory, wave energy density between T and T+dT is [numerical formula]. C=8.27×10^<-4>sec^<-1> where T is wave period, u is wind velocity. Then [numerical formula]・[numerical formula], [numerical formula]. [numerical formula] where β is wave age and δ is wave steepness. This result shows that at the beginning of storm, x is large, so [numerical formula], but at the centre x is small, then [numerical formula]. and that at the centre again β is small, so [numerical formula] but at the end of storm β is large, then [numerical formula]. The state ε^2=1 is Gauss' distribution, which corresponds to perfect seas, ε^2=0 and a=0 is Rayleigh's distribution, which is mixed and jointed state of seas and swells, and, excepting wave height, both wave periods are equal; and that a=∞ is perfect regular swells both in wave height and wave period. So that above eqation expresses whole process of sea state in typhoon area. Neumann's spectrum and Rayleigh's distribution are approximately corresponds to eachother in the vicinity of typhoon center for moderately rough seasurface.

Journal

Details 詳細情報について

Report a problem

Back to top