Float design under laminar conditions

[Nidhi]

Hi all
i am an Agricultural engineering student working on the "design of float for rice transplanter". To tell you, transplanter is self-propelled one which is run in water logged fields (depth of water about 4inches above soil surface) in order to plant rice seedlings.the sp.gravity of the puddle is about 1.2 .this transplanter is having two parallel wooden floats placed 24cm apart and have lengh of 100cm.i am working to sort out the problem of soil flow in front of the transplanter. and also to reduce wave formation on the sides which is caused due to the splashing when transplanter is working in the field this splashing uproots the already transplanted rice seedlings which adversely affects the number of plants per hill and hence reduce the yeild of the crop. I need to experiment with different float design and at different speeds of the transplanter (o.8kmph to 1.2kmph).
To be frank I have very little idea of Hydrodynamics and only elementry idea of fluid mechanics. Can you please suggest me some help in design of these floats or related websites. Thanks again.
nidhichandu@rediffmail.com

[Karsten]

Very interesting problem. I'm not quite sure if anybody has researched the hydromechanics of mud yet but I guess it might be still a Newton fluid. Anyway.

Guess your requirements are that the transplanter floats and doesn't splash. things like drag are not a problem because you probably have plenty of power. Therefore do not even look at boundary layer theories.

Since the density of the mud is 1.2, each cubic centrimeter of submerged volume is able to support 1.2 grams of weight. So you have to work out what the weight of the machine is and make sure there is enough volume in the floats. To prevent splashing I would make the thing pointy at the front and back and the sides vertical.

Good luck,
Karsten

[Ilan Voyager]

Karsten has already answered. Theory will be of little help.


An idea is to add to the piece of wood parallel flat steels (see drawing) so the mud stays trapped under the piece of wood and won't splash. The steels will generate very small waves. You have to make trials with the shape of the bow.

Good luck.

[Nidhi]

Thank you Voyager and Karsten! :)
Your ideas are really commendable. Once I decide the pressure above the float, I can design the bottom of the float such that it retains required volume of water below it.
However, I have got one more question. If the front of the float has to be of specific shape like a curved one as you suggested that it should be pointed at front, then how can one design curvature at the front? Please help me in designing this curvature. :(
If Voyager can help me with the top view of the float also, that could be really helpful.

[Ilan Voyager]

The top of the float is simply rectangular.

The curve of the bow has to be found by trials. A simple curve to get the mud trapped under the float and not splashing on the sides. A pointed bow will make a "wave" and possibility of splashing. It's a little similar to a sled.

It's impossible (or at least useless complicated) to mathematize the problem: the speed is very low (and the reynolds number), the medium (mud) has unknown characteristics and you won't find data.

On a such "design" and because of the very low cost of floats the "trial" method is the most effective.Take the simpler method to solve this (small) problem; try different floats.

[Daniel Wolf]

Wow, V & K, I am really impressed by how you helped Nidhi. Good on you!
Dan