Choice of a dangerous wave direction

Assignment

Methodical recommendations are prepared in compliance with "Shelf and Port Equipment" and "Shelf and Coastal Construction" disciplines program developed as per the instructions of Federal State Educational Institution of Higher Professional Training majoring 08.04.01 Construction (Magistracy). Methodical recommendations include basic definitions on wind waves and its particulars, brief description of wave’s formation factors and its definitions, calculations of wind wave’s elements for open and closed water areas.

Methodical recommendations are intended for bachelors, masters, postgraduate students studying the construction of marine hydrotechnical structures and continental shelf structures, inclusive of teachers and designers, technologists, constructors and operators.

Key words: waves; wind; water area; deep water area; shallow area; coastal area; refraction; diffraction; transformation; probability.

Introduction

Wind waves within seas and water-storage reservoirs are formed due to friction force and complex interaction between air flow (wind) and water. Heights and lengths of waves can be significant; force impact of waves for several types of hydrotechnical structures (protective; beaching) can prevail upon the other types of load. So, any knowledge on wind waves and its impact is necessary for development of hydrotechnical structures.

In order to define wave impact upon structures and to evaluate the protection level for water areas, it is necessary to obtain the calculating values for basic wave’s elements, i.e. height, length and period.

The process of formation and development of wind waves is rather complicated. There are a lot of factors influencing wave’s parameters and type inclusive of velocity, direction and evenness of wind, size and configuration of water surface, water depth, bottom configuration, etc.

General part

Choice of a dangerous wave direction

We make a choice on the rose of winds, with the gradation of the rumba and speed. To do this, combine the north-south direction on the plan of the water area with the wind rose and choose the most unfavorable wind direction in terms of frequency and speed.

In my case, the three most dangerous areas are the following: WNW, NW, NNW.

Wind characteristics are graphically represented as a wind rose.

The wind rose is a polar diagram of the frequency and speed of winds from different directions for a given place for a certain period of time, the most complete is with a gradation of speed.

Table 1 Determination of the scale of the wind rose

N	NNE	NE	ENE	E	ESE	SE	SSE	S	SSW	SW	WSW	W	WNW	NW	NNW	м/с
1.6	0.5	0.3	0.2	0.5	0.6	1.7	0.6	3.2	1.2	1	0.9	2	1	1.1	1.2	0-5
0	0.2	0.3	0.5	0.5	0.1	1	0.9	0.5	0.6	0.4	0.4	2	1.6	0.9	0.5	5-10
0	0.2	0.3	0.3	0.2	0.1	0.5	0.8	0.3	0.8	0.6	0.7	0.1	0	0	0.3	10-15
0	0	0	0	0	0	0	0	0	0	0	0	4.1	2.4	0.5	0.5	15-20
0	0	0	0	0	0	0	0	0	0	0	0	1	0.8	0.1	0	>20

1.6	0.9	0.8	1	1.1	0.8	2.3	2.3	4	2.6	2	2.2	9.2	5.9	2.6	2.5	S
41.8

Table 2. Distribution of wind frequency in wave directions

	ЗСЗ	СЗ	ССЗ
Calm	1.0	1.0	1.0
0-5	2.2	2.2	2.4
5-10	3.2	1.8	1
10-15	0	0	0.6
15-20	4.8	1.0	1.0
>20	1.6	0.2	0
Sum	12.8%	6.2%	7%
	0.128	0.062	0.07

Table 3. Wind speed repeatability in wave-safe directions

	WNW	NW	NNW
>0	11.8	5.2	6.0
>5	9.6	3.0	3.6
>10	6.4	1.2	2.6
>15	6.4	1.2	2.0
>20	1.6	0.2	1.6

Table 4. Integral repeatability of wind speed in wave-dangerous directions

	ЗСЗ	СЗ	ССЗ
>0	28.2	12.4	14.4
>5	23	7.2	8.6
>10	15.3	2.9	6.2
>15	15.3	2.9	4.9
>20	3.8	0.5	3.8

Determination of wave elements in the surf zone

Hкр.п<Н£Нкр

Table 16. Wave elements in the surf zone

	H’кр	i	H’кр/lr	hпр1%/gt²	hпр1%	lпр/lr	lпр	hс/ hпр1%	hс
WNW	9.4	0.011	0.05	0.006	7.1	0.65	122.7	0.86	6.1
NW	3.12	0.014	0.08	0.009	2.2	0.8	31.2	0.82	1.8
NNW	9.8	0.017	0.055	0.0065	7.3	0.73	130	0.858	6.3

Assessment of the protection of the water area

Table 17. Defining the diffraction boundaries

#	Breakwater 1j=60				#	Breakwater 2j=120
#	r	r/l	l/l	l	#	r	r/l	l/l	l
1	160	0.9	2.5	447	6	270	1.5	2.2	393
2	370	2.1	2.8	500	7	490	2.7	3	536
3	490	2.7	3	536	8	370	2.1	2.8	500
4	670	3.8	3.2	572	9	560	3.1	3.1	554
5	745	4.2	3.4	607	10

Table 18. Construction of the main ray

r1	r2	#	b	l1	l2	la1	la2	x
150	300	1	200	160	95	178.6	268	138
370	510	2		340	230	268	286	68
480	620	3		350	300	286	304	132

Conclusion

Literature

SNiP 206.04-82*. Loads and impacts on hydraulic structures (wave, ice and navigational). - М.: “Strroyizdat”, 1989. - 40 pages
Recommendations for identification of loads and impacts on hydraulic structures (wave, ice and navigational). P58-76/VNIIG. - L.: VNIIG Publishing House named after Vedeneyev B. E., 1977 - page
USSR Climate Guide. C. Z. Veter. - L.: HydroMeteoIzdat, -1968. - pages
Smirnov G. N. Oceanology - М.: "Vysshaya Shkola" Publishing house, 1974. - pages
SNiP 2.01.07-85. Loads and Impacts - М.: StroyIzdat, 1986 - pages