海洋波に及ぼす風の統合作用と最も頻度の多い波の性質に就て

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There are many waves in the confused, fully arizen sea surface, which have various periods and different heights. But there may exist a groupe of waves whose period prevail and are most frequently observed. These waves can be determined analytically by applying the theory of Sverdrup-Munk to the sea surface under varying wind velocity : (βu)^5δ^2=(β_mu_m)^5δ_m^2,where : u is wind velocity, β is wave age, and δ is wave steepness, The suffix m denotes the maximum values in the centre of storm. This relation is shown in Fig. 1 which is calculated for every β_m=0.3,0.4,……, 1.4 at u/um=1. The state of every stage of β at every moment in the storm can be analysed graphically by the equation (5+2β/δ(dδ)/(dβ))u(t)(dβ)/(dt)+5β(du(t))/(dt)=0.2237(1±2.5(1-β)^2)/(β^2) The distribution of integrated β-t curves for every 3 hours are given in Figs. 2 and 3,wherein the observed values of β areplotted. These two graphs show that ocean winds have some agency of unification on waves. Observers on board of ship usually point out and record the waves which have the most regular time interval, or in other words, which have the maximum frequency of wave period and its wave height from over the confused sea. This wave will have originated at many different places and also have various phases over the wide area of sea surface, then we can readily acknowledge the Longuet-Higgins' theory, which have cited the statistical distribution of wave heights.The wave age which observed most frequently is indicated in the waving, concentrated narrow bands which issue from the places of the minimum values where the wind velocity have reached at the maximum value. Before this period, wind velocity are always increasing, so waves which have larger ages are all suppressed, but waves with shorter ages are forced to grow up. Thus swells and seas coincide in the centre of storm. After the centre have passed, wind velocity decreases gradually, then ages of these unified waves increase.The larger becomes the rate of increase of wind velocity, the minimum value of the wave age reaches to the smaller value. The above cited β_m is thus defined : (dβ)/(dt)|<u=u_m>=0,or (du)/(dt)|<u=u_m>=0.0447(1+2.5(1-β_m)^2)/(β_m^3) The fact that the average value of this wind velocity gradient is about 2 m/sec. hour as is shown in Fig. 4,then β_m lies usually between 0.3〜0.4. Observed values at X-ray are plotled in Fig. 5,also wave period is constant at every moment in the region of storm ; in Fig. 1 dotted lines show β_mu_m=βu, which are almost equal to (β_mu_m)^5δ_m=(βu)^5δ^3.From the state of concentration of β, the statistical distribution of β. or wave period seem to be more narrow than that of Longuett-Higgins' wave height. distribution or we may take practically, unique, which justifies ard agrees with their assumptions.
社団法人日本船舶海洋工学会の論文

海洋波に及ぼす風の統合作用と最も頻度の多い波の性質に就て

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