tailieunhanh - BASIC COASTAL ENGINEERING Part 6

Tham khảo tài liệu 'basic coastal engineering part 6', kỹ thuật - công nghệ, kiến trúc - xây dựng phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 162 Basic Coastal Engineering two ways 1 by identifying individual waves in the record and statistically analyzing the heights and periods of these individual waves and 2 by conducting a Fourier analysis of the wave record to develop the wave spectrum. The former will be discussed in this section and the latter in the next two sections. Wave Height Distribution Figure shows a short segment of a typical wave record. A question arises as to which undulations of the water surface should be considered as waves and what are the individual heights and periods of these waves. The analysis procedure must be statistically reasonable and consistent. The most commonly used analysis procedure is the zero-upcrossing method Pierson 1954 . A mean water surface elevation is determined and each point where the water surface crosses this mean elevation in the upward direction is noted see Figure . The time elapsed between consecutive points is a wave period and the maximum vertical distance between crest and trough is a wave height. Note that some small surface undulations are not counted as waves so that some higher frequency components in the wave record are filtered out. This is not of major concern since for engineering purposes our focus is primarily on the larger waves in the spectrum. A primary concern is the distribution of wave heights in the record. If the wave heights are plotted as a height-frequency distribution the result would typically be like Figure where p H is the frequency or probability of occurrence of the height H. The shaded area in this figure is the upper third of the wave heights and the related significant wave height is shown. For engineering purposes it is desirable to have a model for the distribution of wave heights generated by a storm. Longuet-Higgins 1952 demonstrated that this distribution is best defined by a Rayleigh probability distribution. Use of this distribution requires that the wave spectrum has a single narrow band of .

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