Wind Speed and Wave Height
Predicting the height of the waves depending on the wind strength. It's time to tell you about forecasting wave height depending on the wind speed. the relationship between the dimensionless parameters of the waves obey universal laws. A statistical comparison of wind speed, wave height, and wave period derived wave period using the altimeter-derived wind speed and wave height are found to . over time or space through the temporal and spatial de-correlation analyses . Yes, there is a high degree of correlation between wind speed and significant wave height in the images. Simultaneous observations of wind speed and wave.
Three main types of breaking waves are identified by surfers or surf lifesavers. Their varying characteristics make them more or less suitable for surfing, and present different dangers.
Wind wave - Wikipedia
They can be found in most areas with relatively flat shorelines. They are the most common type of shorebreak. The deceleration of the wave base is gradual, and the velocity of the upper parts does not differ much with height. Breaking occurs mainly when the steepness ratio exceeds the stability limit. These are the preferred waves for experienced surfers. Strong offshore winds and long wave periods can cause dumpers.
They are often found where there is a sudden rise in the sea floor, such as a reef or sandbar. Deceleration of the wave base is sufficient to cause upward acceleration and a significant forward velocity excess of the upper part of the crest. The peak rises and overtakes the forward face, forming a "barrel" or "tube" as it collapses.
They tend to form on steep shorelines. These waves can knock swimmers over and drag them back into deeper water. When the shoreline is near vertical, waves do not break, but are reflected.
Most of the energy is retained in the wave as it returns to seaward. This law states that at constant wind speed and direction over a fixed distance fetchit can be expected that the waves will reach a stationary state, depending on the length of the acceleration fetch-limited state of development. In such a situation, the wave height will be constant in a statistical sense over time, but will vary along the acceleration.
The waves and the wind. Wave height statistical forecasting
Acceleration - is a term used in Russian literature. The length of the body of water, where the wind affects the surface of the sea in a constant direction is understood as the acceleration of wind. I found this term here. It would seem, that with an increase of time and length of the wind acceleration, the wave can grow indefinitely, but that doesn't occur.
In the s, researchers have found that the formation of waves is best described by the wave spectrum distribution of wave energy depending on frequency and the transfer of energy from the wind to the wave there is some info about it in the first article. And, as mentioned above, the wave ceases to grow, reaching a steady state, energy balance, and it becomes fully developed sea. The empirical relation for the fully formed waves height, which can serve as the upper limit of assessment of wave height for any wind speed has been derived.
Everything got more complicated. At the place of the wave prediction models of the first generation came second-generation model using the energy spectrum.
In the early s, there were wave models of the third-generation 3G. Actually, we hadn't reached the fourth-generation models yet, but the most commonly used model is the third generation WAM model Hasselmann, S. Of course, there are still shortcomings, for example, these models can not predict the waves in a rapidly changing wind situations, but still 3G models provide a good result.
In the pre-computer era, you could use a model built on the nomogram for wave heights forecasting in relatively simple situations, such as pre-assessment or for small projects which have been given, for example, in Shore Protection Manual. There are 3 situations possible when the simplified prediction will give quite an exact estimation. The wind is blowing in a constant direction over some distance and not limited by time enough time - then the growth of the wave is determined and limited by the length of acceleration fetch-limited.
The wind rapidly increases within a short period of time and not limited by distance enough distance - then the growth of the wave is determined and limited by elapsed time duration-limited. This occurs very rarely in nature. The wind is blowing in a constant direction at a sufficient distance and for a sufficient time so the wave will be fully formed fully developed wave under these conditions.
Note that even in the open ocean waves rarely reach the limit values at wind speeds greater than 50 knots.
Empirically, we obtained the following dependence for the case when wave growth is limited by the length of the acceleration. The time waves require under the wind influence at the velocity on the distance to achieve the maximum possible for a given distance heights. The relationship between the significant wave height and the distance The relationship between the period of the wave and the distance The drag coefficient For a fully developed waves Also the transition from the duration of the wind to the length of the acceleration i.
Thus, if the duration of action and length of the acceleration of the wind is known, it is necessary to select the most restrictive value. If the wave generation height is limited by the time it is necessary to replace it by an equivalent distance and calculate the wave height based on it. In case of shallow water equations remain valid except for the additional limitations under which the wave period can not exceed the following ratiosThen the order of the wave height prediction for the shallow water is as follows: Assess the wave period for a given distance and wind speed using conventional formula.
In the case of shallow water verify the conditions of the period and depth.