Determination of the wind speed of the design storm

 

Rated storm – is a storm with intensive wind heave once per defined number of years n_t. The intensity of heave is assumed by the average height of waves . Structure permanentness class depends upon the structure responsibility, i.e. the highest rated storm shall be considered (with less repeatability).

Repeatability of calculated storm – means the value that is inversive to the defined number of years n_{t ,} subject to one rated storm for this period. The higher structure permanentness class, the smaller repeatability of rated storm.

 

Table 5. Calculated values of repeatability and cumulative probability of rated storm

Structure class	nt, years	Repeatability of rated storm	Cumulative probability of rated storm, %
I and II	50	0.02	2
III and IV	25	0.04	4

 

Points for development of line on the probability paper shall be identified as follows. Several points of wind velocity shall be marked on abscissa axis subject to the defined velocity. Than according to defined points the line shall be constructed within the probability table; rated storm wind velocity W shall be defined as an abscissa of point at the line subject to the integral wind repeatability, i.e. [1]:

 

(%),      

where t – time of rated storm activity, hour. (see below); N - number of measuring for ice free year; n_t – rated number of years; р – the repeatability of this wave-hazard direction of wind among the other directions shown as fractions.

Data on wind measurement for most areas of our country inclusive of coastal line is given in USSR Climate Reference Book [3].

Wind velocity data given in [3] was obtained via measurement of wind velocity using wind vane. Anemometer data (wind velocity W) are used for calculation of wave elements.

 

 

 

Wave acceleration D. D value shall be defined using maps for each wave course as a distance from the opposite coast, ice area or storm zone border up to this point. Acceleration shall be defined against wind. Different acceleration shall be assumed for each wave dangerous direction.

For the further identification of wave elements, an average value of acceleration (m) for defined rated wind velocity W, m/s, shall be calculated as follows:

,

where k – coefficient equal to 5*10¹¹ ;  - kinematic viscosity equal to 10^-5 m²/s.

Value of maximum acceleration D_n , m, shall be defined for assigned rated wind velocity W, m/s.

 

 Table 6 Maximum acceleration D_n subject to defined rated wind velocity W, m/s

Wind velocity W, m/s	20	25	30	40	50
Maximum acceleration Dn 10-3, m	1600	1200	600	200	100

 

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