What is fetch in waves

Cavaleri , , M. Donelan , , K. Hasselmann , , S. Hasselmann , , and P. Janssen , Eds. Lamont-Smith , T. Waseda , : Wind wave growth at short fetch. Fuchs , , and M. Tulin , : Laboratory investigation of LGA scattering from wind-generated waves and wave groups. Landrini , M. Colagrossi , , M. Greco , , and M. Tulin , : Gridless simulations of splashing processes and near-shore bore propagation. Liu , P. Schwab , , and R. Jensen , : Has wind-wave modelling reached its limit?

Ocean Eng. Longuet-Higgins , M. I: A numerical method of computation. Miles , J. Peirson , W. Garcia , : On the wind-induced growth of slow water waves of finite steepness. Phillips , O. Plant , W. Smith , M. Poulter , , and J. McGregor , : Doppler radar measurements of wave groups and breaking waves. Snyder , R. Dobson , , J. Elliott , , and R. Long , : Array measurement of atmospheric pressure fluctuations above surface gravity waves.

Stevenson , T. Black, pp. Tian , Z. Perlin , , and W. Choi , : Energy dissipation in two-dimensional unsteady plunging breakers and an eddy viscosity model. Toba , Y.

On the growth process of wind waves. Japan , 28 , — Tulin , M. Waves and Nonlinear Processes in Hydrodynamics, J. Grue, B. Gjevik, and J. Weber, Eds. Li , : On the breaking of energetic waves. Offshore Polar Eng. Waseda , : Laboratory observations of wave group evolution including breaking effects. Army Corps of Engineers , cited : Coastal engineering manual. Vinje , T. Brevig , : Breaking waves on finite water depths: A numerical study.

Ship Research Institute of Norway Tech. Waseda , T. Tulin , : Experimental study of the stability of deep-water wave trains including wind effects. Werle , B. IEEE Int. Radar Conf. Young , I. Ocean Engineering Book Series, Vol. Zakharov , V. White caps, blue water, and a sunny sky. You will have to imagine the wind, salt spray, and motion of the ocean. Trajectories in the phase space for the dynamical system in Eqs. The evolution of wind-induced ocean waves is studied theoretically.

The modeling assumes that wave groups evolve independently of each other in a state of local equilibrium between wind-pumping- and wave-breaking-induced dissipation. The well-known fetch and duration laws appear as natural solutions of the model in the case of a constant wind speed. The link between the fetch and duration laws is explained, and the results are successfully validated against various experimental data.

The methodology proposed here is mainly meant to describe how the average wave energy develops over time and space when the sea surface is forced by the wind. Wind-wave evolution has been described in major monographs Kinsman ; Phillips updated from ; Donelan ; Komen et al. Army Corps of Engineers , as well as major journal articles describing the key processes discussed e.

A concise description of the various wave prediction models is provided in Liu et al. The results by Liu et al. The fact that differences between the model results are often similar in magnitude to the differences between model results and observations, implies that the more advanced models, which involve more complex physical interactions between waves, do not necessarily provide more accurate predictions compared to those obtained with a simpler model.

Liu et al. The wind-wave community seems to have accepted as an explanation of downshifting the process of multiwave interactions incorporated in the kinematic equations pioneered by Hasselmann and Zakharov On the other hand, Tulin , and in his later work, has focused attention on wave group evolution equations. The present study follows this latter route as it is an attempt to develop an integral approach that is consistent with the evolution equations of wave trains proposed by Waseda and Tulin and Tulin and Waseda Some novelties have been introduced with respect to the previous integral-modeling approaches, in particular in the group velocity equation.

It is also understood that the proposed theory has its own intrinsic limitations essentially because of its analytical nature. More complicated source functions and wave evolution schemes are available, but such schemes cannot be solved analytically, whereas this is the strength of the present approach.

It gives an approximate solution and it is partially based on empirical dependences, but it also provides insights into the evolution of integral wave properties and provides the means for fast practical estimates, instead of running unnecessarily complicated models if only integral estimates are needed.

The fact that energy increases with fetch or duration is intuitive since energy is transferred from the wind to the waves. The shift of the peak of the spectrum to lower frequency, also called downshifting, reflects clearly the existence of nonlinear phenomena.

It is quite remarkable to see that the relations between , , , and can be expressed as simple power laws involving fractions of whole numbers. This is typically the sign of a strong physics underlining the nonlinear energy transfer that occurs. Also, the relation between the fetch and the duration law has not yet been clearly established despite experimental results by Hwang and Wangfield providing strong support for the relation of space—time conversion for rendering the fetch limited growth functions to duration-limited growth functions.

The surface of sea is conceptualized as a superposition of multiple wave groups, which evolve under the influence of wind. Winds that blow along the shoreline—longshore winds—affect waves and, therefore, currents. Before one can understand any type of surface current, one must understand how wind and waves operate. Wave height is affected by wind speed, wind duration or how long the wind blows , and fetch, which is the distance over water that the wind blows in a single direction.

The importance of the fetch , hence the length of the wind area, consists in that it enables the generated waves to remain under the wind's action and, in doing so, to accumulate additional energy. As sea waves develop with increasing fetch , a balance is continuously maintained among the enegy increase in waves , the rate of energy received from the wind, and the rate of the energy dissipated in water. The paper treats the rather complex conditions that may lead to the occurrence of swell at a fixed observation pointA when the wave generating fetch though approaching pointA passes it at some distance.

Typically, physical erosion proceeds fastest on steeply sloping surfaces, and rates may also be sensitive to some climatically-controlled properties including amounts of water supplied e. Wave records obtained from the Smith's Knoll and Morecambe Bay light vessels are used to obtain relationships between wind speed and wave height and period in shallow water conditions for various lengths of fetch.

A 2ft wave at 5 seconds will most likely result in small and weak waves. Swells that have a wave height of 8ft and a swell period of 22 seconds are going to be huge! However, an average swell report of 4ft at 12 seconds in Polzeath should result in chest to head high wave faces once they reach the shore. Waves are generated by wind moving over water; they indicate the speed of the wind in that area.

Swell are waves usually with smooth tops that have moved beyond the area where they were generated. The ideal wind direction for this spot is easterly, and Polzeath is best surfed an hour before or after the low tide and avoided at high tide.

Fewer than 8 seconds and the waves will be disjointed and broken up. Over 15 seconds and the swell should be powerful. Rolling waves 1 are the most familiar waves, and the type most surfers prefer because they break in a stable pattern. Dumping waves 2 are more unpredictable and are usually limited to experienced surfers.