Foil for current-driven propulsion?

Bravo !!! Now, if you can find what energy is consummed in order for the system to operate, you will win a clue about how the fundamental thermodynamics can be applied to any device converting energy from moving mass and water, or whatever... (even thermoelectric coupling). And so discovering that it has, effectively, everything to do with the subject.

 

I don't know the velocity polar of Arthemis foiler, 2 times the TWS @ 135° is just an assumption , I think it is more 3 times for a foiler (you can see the america's cup foilers jybing downwind with wings sheeted nearly in the axe of the boat, doing several time the tws at course angles more than 135°) . In this particular case, for an observer attached with the mass of water the TWS (motion of air / water) is the opposite of the current velocity / shore, so the vmg upstream should be 3.v.cos(45°) relative to this observer and 3.V.cos(45°) - v for an observer on the shore. Which gives about 11 kt of Vmg / shore for a 10 kt river flow. All you need to have more exact figure is the velocity polar of Arthemis foiler at different TWS. My reasoning has nothing particular, it is amost simple reasoning accessible to any physic student !

 

Great !!! As you have demonstrated to understand the subject at hand both from a practical and highly theoretical level perhaps we can try to find an answer to @MacktheYounger 's original question.

 

Here is my best shot for now (first shot), Flotation. I keep trying hard, believe me... It's harder to make true geometry and mathematical analyses than saying that because 1 + 1 = 2, Artemis may have a chance to realize what they have said., you know. Have you find what energy is consummed ?

Foil for current-driven propulsion? https://www.boatdesign.net/threads/foil-for-current-driven-propulsion.67320/#post-934109

 

Okay Patzefran, as you can see, there is quite a number of solutions to your problem of vector addition. I represent some of them using RMLOCK inputs. Unfortunately, not all of them or perhaps none of them can be realize by the boat we are talking about, with the given inputs. You speak about "any physic student", but what you are doing here is only pure mathematics. If you want to give it a physical meaning, you have to verify the known physical principle, or invent new ones.

-sorry for the missing arrows, I hope you that "any physic student" will understand the meaning of my lines. -

 

Like i said before: ""energy from masses of water and air moving at relative speeds".

As also implied in my first response in this thread, explaining how Artemis sails upriver "Using the current going downriver at speed of 10 mph."

Or like Skyak said ""To generate power, a craft must tap two masses with a usable relative velocity."

And as i again implied the energy comes from moving masses by saying "A sailboat extracts energy (i hope this wording is correct) from the speed difference between water and air."

And how also tried to make clear with this example demonstrating there is energy in moving masses: "We let the trucks move away from each other at a speed of 10 mph. Will Charlie notice a force being exerted?".

And as implied by this statement: "You can only understand the answer to this question when you realise there is energy potential between air and water moving at different speeds relative to each other."

e.t.c. e.t.c.

To spend some more words:

The energy comes from a moving mass, and can only be tapped by making use of another mass with a different relative speed.

 

And FYI, Doug made a comment on my view that is absolutely relevant. I took account into his remark when making aaaaaallllll the force equilibrium representation that you see in my post. I recall in the post Foil for current-driven propulsion? https://www.boatdesign.net/threads/foil-for-current-driven-propulsion.67320/page-4#post-934370 that there is known errors in this representation and invite everyone to find them. Have you made any answer to this question ? If your head would be in play with the question : Can Artemis do what they have explained in their video, will you rely on your own believe ? Even if it is me, handling the axe ?

In my post Foil for current-driven propulsion? https://www.boatdesign.net/threads/foil-for-current-driven-propulsion.67320/page-3#post-934293 I show you a way to decipher the question by yourself. Have you got any remark about this representation ? Have you tried yourself to do some physics instead of pure mathematics and rethoric ?

In my post Foil for current-driven propulsion? https://www.boatdesign.net/threads/foil-for-current-driven-propulsion.67320/page-2#post-934271 , I asked you if the given representation was correct, with your "Gibraltar Inputs". As far as I know, I just got nothing from you, besides something like this :



Are you really serious ?

 

Just repeating an infinite amount of time the same thing does not count for a proof. I've already answered your objection, and showed you some already existing way to "tap", in the post Foil for current-driven propulsion? https://www.boatdesign.net/threads/foil-for-current-driven-propulsion.67320/#post-934220

 

I was reluctant to do that to Charlie, but here it is... Poor Charlie.... Science means so much sacrifice !!! Ok, I believe that Charlie will have great pain. But may I make the remark that, even is the trucks are moving away from Charlie at a speed of 10 mph ( 5 + 5 = 4 + 6 = 3 + 7 = 2 + 8 =....... whichever sum is ten .... ), the pain will be the same for Charlie. The problem of Artemis is to find which of the vector composition will be physically relevant, due to the aerodynamic efficiency of the boat !

Tap... you mean ????



You give an impulse and Woooooaaahhh !!!! Here is energy transfer ! It's coming....It's coming... Be ready to catch the train, little Artemis, or you won't ride the river !

 

Anyone, anything can fly... their flight time depends on the aerodynamic efficiency and the initial potential energy. The sum of the potential energy and of the kinetic energy remains constant, if no "tapping" is done, ie if no other energy is introduced in the system.

Even with an "infinite" energy tank at our disposal, and "tapping" technics, involving the wind and the fan, helicopters cannot use their weight and the motorless fan thrust to got up at an higher altitude. So tapping, here, gives no solution for an helicopter, even with the great amount of aerodynamicist that have worked on the problem. Sometimes, the solution is trivial, and only show a total impossibilty (again, without any new physical principle) . The autogyration flight, with motor transmission disengaged, (safe flight mode of helicopter) serves only as parachute, minimizing the impact energy when propulsion lost, for instance, and is required by the particular domain of flight of the helicopters. Compared to the one of the airplanes, with their greater aerodynamic efficiency, you have to use a maximum thrust power when landing an helicopter. The autogyration mode is mandatory for helicopters to be certified. But again, no miracles.

A glider can fly higher than his take-off point if pumps effects due to certain thermodynamic gradients, or can use the dynamic soaring, with some configurations of the ground relief. Without these tapping opportunities, it is not possible, also for a glider, to go upper than is take-off point.If we replace the river by a canyon, and Artemis by glider, can the glider fly higher than is entry point ? The answer depends :
- on its aerodynamic efficiency
- on the wind profile in the edge's vincinity
- on the profile of the canyon

The same goes for Artemis. Without estimating the aerodynamic efficiency of the boat, ( and taking into account the energy loss when jibbing or tacking), ie without knowing the "magic angles", we cannot predict if Artemis can effectively sails counter to the current. But given the examples and the different representation of mechanical systems, I'm sure we will find the answer. That said, I'm not sure that the solution found will be accepted. I will do the exercice for myself. You are absolutely free of your opinions.

 

Which, by the way, is what's happening in the "dynamic soaring" video you posted.

"Dynamic soaring is a flying technique used to gain energy by repeatedly crossing the boundary between air masses of different velocity."


All your other airborne examples cannot be compared to Artemis.

Edit: @MacktheYounger, sorry if this conversation is derailing your original question. I do think these are things relevant to finding an answer though. The other examples all rely on a power source other than the moving medium (air or water).

 

@Skyak
Thank you for reframing my understanding and clarifying exactly what I was trying to say. Though it seems obvious now, I hadn't realized that the crucial aspect is two fluids with different relative velocities.
I had been imagining a craft (for example) moving east, and 'tapping' a current flowing from north to south with a winglike hydrofoil to produce thrust perpendicular to that flow. You've helped me realize that drag would gradually accelerate the craft to the same speed as the current, and eliminate apparent current, making this impossible. If you cut a kite string, it accelerates to the same velocity as the wind, sees zero apparent wind, therefore can't produce any lift, and falls out of the sky.
You cut right to the heart of my misunderstanding, and I appreciate it, though it seems the thread has moved in a different direction in discussing the Artemis technology video.

 

Good philosophy !

 

It's a well known principle in physics that you can use any "inertial" frame of reference. That means it's not accelerating or rotating. A steady current counts at the size and timescale we're working at here. As it happens, that's a very convenient frame of reference in this case, because we're all used to thinking about sailing. If a boat can sail downwind, faster then the wind, it will do so here. The "true" wind, in this case, relative to the water in the current, is at the same velocity that the land is, relative to the water. Therefore, if the boat can sail faster than the wind, downwind, it will do so here, and in that case, it's making progress over the bottom, up-current.

No need for any confusing diagrams or math beyond simple addition and subtraction.

I've studied Newtonian physics, but I really don't understand the extra lines in post 65.

As far as sailplanes going up, it's usually because they're flying through air that's rising. If they're circling, it's to stay in that same column of rising air. Dynamic soaring is an exception. I think I might have as many as 5 seconds of inadvertent dynamic soaring in my RC glider flying experience, compared to many hours in thermals (i.e. rising air). I've tried dynamic soaring at other times, but have not succeeded.
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It's entirely possible to have currents be at different velocities, in different directions, in the ocean. If one had a very low drag cable, it might be possible to use this to propel a boat or submarine. I'm not sure such differences are as common as wind is, though. For the patient, in tidal areas, one could just anchor whenever the current was going the wrong way, and wait a few hours, though moving across a current might not be as easy. Unless you could string out another anchor a long way. I'm not sure, but I think one could work out a method with a dinghy that has a daggerboard, working with the restraint of the anchor rode. A SLOW way to get around, though.

 

Thanks, rnlock, it is exactly what I already said. Looks some educated looking people ignore the fundaments of Newtonian physics and relativity, i.e. the law of physics are the same in any inertial frames (as well in general relativity where inertial frames are free fall frames). Nevertheless I remark he his doing some progress toward the thruth, his objection now are left with the efficiency of the foiler and the lost induced by Jybing !