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by rynhardt
Fri May 31, 2019 7:12 am
Forum: Gear Builders
Topic: An object in a fluid
Replies: 23
Views: 1349

Re: An object in a fluid

JakeFarley wrote:
Thu May 30, 2019 2:59 pm
Professor Rynhardt,
You are bringing back memories from my college years 48 years ago. Please, no homework or tests... :D
Great info though. :thumb:
Thanks,
Jake
Hehe.. I'm actually using these diagrams to explain this to my son, which is 6 years old. :-)
by rynhardt
Thu May 30, 2019 11:51 am
Forum: Gear Builders
Topic: An object in a fluid
Replies: 23
Views: 1349

Re: An object in a fluid

Almost there. Let's get rid of the front face, which means we now have a prism with angled bottom and side faces. It starts to look a little bit like a boat now :-) I've inset a little 3D picture to aid the visualisation. Let's also place this prism so that the top face is just above the water surfa...
by rynhardt
Thu May 30, 2019 8:26 am
Forum: Gear Builders
Topic: An object in a fluid
Replies: 23
Views: 1349

Re: An object in a fluid

There is of course a wealth of literature on the subject of fluid dynamics.
We started off with a conceptual cube, and will be moving to a conceptual triangle.
by rynhardt
Thu May 30, 2019 8:09 am
Forum: Gear Builders
Topic: An object in a fluid
Replies: 23
Views: 1349

Re: An object in a fluid

Okay, same scenario as before, except this time the side faces of the prism now also form an angle of attack to the fluid flow. In the sketch below, the red arrows indicate the fluid pressure which is now higher on the sides, but still in balance, so no net lift to either side. But there is still ne...
by rynhardt
Thu May 30, 2019 7:15 am
Forum: Gear Builders
Topic: An object in a fluid
Replies: 23
Views: 1349

Re: An object in a fluid

Whats your point of this thought experiment. Seems you are just openly considering fluid dynamics. But to what end? what do you hope to achieve? Mostly I like the sound of my own voice :D There was a discussion around planing vs displacement hulls. I want to write down my understanding of it and se...
by rynhardt
Wed May 29, 2019 11:02 am
Forum: Gear Builders
Topic: An object in a fluid
Replies: 23
Views: 1349

Re: An object in a fluid

Anyway, back to my little cube, being dragged under water. In the first case, where it is symmetrical in all respects orthogonal to the direction of travel, the net lift forces are zero. I'm using red arrows to indicate the force the water is exerting on the object. In a second case, it's no longer ...
by rynhardt
Wed May 29, 2019 10:50 am
Forum: Gear Builders
Topic: An object in a fluid
Replies: 23
Views: 1349

Re: An object in a fluid

lederhosen wrote:
Wed May 29, 2019 10:26 am
If you dont care about the eddies you can calculate the forces on the object with a random average navier stokes RANS model in steady flow in a fluid solver
Are you volunteering? :naughty:
by rynhardt
Wed May 29, 2019 10:06 am
Forum: Gear Builders
Topic: An object in a fluid
Replies: 23
Views: 1349

Re: An object in a fluid

I do not undertand to which question this message answers, but I like it ! I guess you will speak of the vertical lift induced by a non-symetrical object in the water, caused by a non-zero angle of attack... it is rare that these notions of water displacements are described ; this is great since it...
by rynhardt
Wed May 29, 2019 9:35 am
Forum: Gear Builders
Topic: An object in a fluid
Replies: 23
Views: 1349

Re: An object in a fluid

When the relative velocity between the object and the fluid is non-zero, the object will need to displace water in the direction it is moving, because once again it can't occupy the same space as the water at the same time :-) Displacing the water requires pressure, which, depending on the object's ...
by rynhardt
Wed May 29, 2019 9:04 am
Forum: Hydrofoil
Topic: Hand Shaped Beauty
Replies: 32
Views: 5548

Re: Hand Shaped Beauty

Going off topic here, but the belly bottom got me interested in reading... http://www.surfscience.com/topics/surfboard-design-and-anatomy/bottom-contour/displacement-hulls Seems like they're saying the OPPOSITE of what we have today for kiting small waves -- which seems to be planing hull with doub...

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