|Home||Compare with Obs*||Data Assim*||Monitor*||RTOFS & WOCE*||Graphics Viewer||Data Access||About the Model|
|* -- MMAB internal use only|
If you have a small lake nearby (a few hundred yards to a couple of miles across), this would be easiest and give the best data. The thing to do is measure the wind speed (science fair books at the library often have directions for build-your-own anemometers, or you can use your local weather reports) and then measure the wave heights as you move away from the shore in the direction the wind is blowing. Very near shore, the waves will be small. As you go off shore (but in the wind's direction) the waves will build up, even though the wind is no faster than before. On a lake I regularly visit, it is easy to see this effect across the half mile of the lake's length. There may even be no apparent waves for the first 100 yards, if the wind speed is low enough. The distance from shore is called the 'fetch'. If your lake is small, then you may find that you're 'fetch-limited' -- that is, the waves are continuing to get taller even at the far shore.
The harder method is to build a combination wave tank/wind tunnel. Since you probably can't build a wave tank a half mile long, you won't be able to explore the fetch effects. But what you should be able to examine is the wind speeds for the start of wave growth and what effect the initial state of the water has. Wave tanks can be interesting to study in their own rights (wave shadows behind pillars, waves meeting other waves and interfering or reinforcing each other).
The best wave tank is one made with see-through sides. Plexiglass is good for this. You'll want to be able to change the depth of water in the tank (this may have an effect on your results, I don't know so it is good to test) so ideally the tank should be a foot or two tall. For wave generation by wind, you don't need a very wide tank, a foot should be enough (to do other wave experiments, you would make a tank that was only a few inches deep, but was easily two feet wide, and preferably three). For wave generation, you'll need some length to the tank, at least 3-4 feet. This gets to be a lot of water, which will weigh a lot and take a fair amount of time to fill. The ends of the tank, you'll need to make a fair amount of time to fill. The ends of the tank, you'll need to make in such a way (hinges? I'm not the best hands-on construction person so find someone who is good to figure out the best way) that the tank ends don't block the entry of air to the tank. You want the end the air starts from to be barely above the water level of the tank. (The far end doesn't have to match so well.)
The wind speed is a bit of a problem. A home built wind tunnel may not be able to reach a high enough speed to build good waves. What you may find easier, if you have a fairly unobstructed place to set up the wave tank, is to build the wind tunnel-like cover and then let the natural wind funnel in through that. What you'll want is a cover that does funnel, the wider the open end is, the better, the wind in to your wave tank. Then keep a constant size to the chamber over the tank. The funnel will speed up the wind (by making the same amount of air pass through a smaller channel) in proportion to the area ratio. That is, if the big end facing in to the wind is 10 times the area of the channel over the water, then the wind in your tunnel should be about 10 times faster than the outside world.
To work with a wind tunnel that you control the whole way, what you'll need is a strong fan to _pull_ the air in to the tunnel. Ideally, the fan will be about the size of the tunnel where the tunnel is over the wave tank. If you have to widen out to reach the fan, then you'll lose some of the area effect for making the winds faster. But you do have to make the covering extend out to the fan, or you won't pull air through the tunnel. You'll also need an anemometer to tell how fast the wind is moving.
There is room for a lot of experimentation on how to construct this, and on what to measure. The above are just some starting points.
About the MMAB - Mission - Other NCEP Centers - MMAB Personnel - NOAA Locator
is the U.S. government's official web portal to all federal,
state and local government web resources and services.
National Weather Service
National Centers for Environmental Prediction
Environmental Modeling Center
Marine Modeling and Analysis Branch
5200 Auth Road
Camp Springs, Maryland 20746-4304 USA
Page last modified: Monday, 17-Dec-2012 19:48:48 UTC