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Old 01-06-2015, 15:34   #1
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Wave and Currents at a detached breakwater

I'm not a mathematician but I'm curious how waves and currents act around a detached breakwater; specifically when the incoming wave direction is more or less perpendicular to the structure.

I assume there is some amount of flow back but direction, magnitude, and distance back out to sea is a mystery to me. Is it significant?

Any analysis of this for dummies?

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Old 02-06-2015, 13:06   #2
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Re: Wave and Currents at a detached breakwater

When sea waves reach an obstacle, a very small part of the incoming energy is dissipated in heat through viscous effects. In certain conditions (breaking), another part is dissipated in spray. If the obstacle is fitted with openings, another part is transmitted through them. The remainder of the energy is reflected. The direction of reflection depends on the incidence and on the slope of the bottom, because the wave celerity is linked to the water depth as well as to the wave period.

The superposition of incoming and reflected waves creates "standing waves" in front of the obstacle. The analysis is made more complex by the fact that natural waves are irregular: a sea state can be described as the superposition of an infinite number of individual regular waves, each with its own direction, period, height and phase.

A more detailed description would not fit the "for dummies" requirement. For pictures, see for example www.csun.edu/~aes15831/subjects/Oceanography/unit8/powerpoints/L09_Waves.ppt

Describing the flow of current around an obstacle is another matter.

Alain
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Old 02-06-2015, 14:15   #3
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Re: Wave and Currents at a detached breakwater

Quote:
Originally Posted by Hydra View Post
The superposition of incoming and reflected waves creates "standing waves" in front of the obstacle. The analysis is made more complex by the fact that natural waves are irregular: a sea state can be described as the superposition of an infinite number of individual regular waves, each with its own direction, period, height and phase.

Alain
Thank you for responding.

I think what I'm interested in are the "standing waves" or chop as well as changes in current that are created.

What magnitude and how far out to sea away from the breakwater does the phenomenon carry - is it significant?
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Old 02-06-2015, 14:35   #4
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Re: Wave and Currents at a detached breakwater

Yes, the chop in front of a breakwater can be significant. It's the same at the foot of a cliff: not a good place to be. If the reflection were perfect, the wave height would be twice the incoming one.

I will not try to go in a more detailed discussion. You will have to dive in technical publications: Google is your friend, the key words are "sea", "waves", "reflection".

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