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Brain teaser: the shell game.


ArthurSmith
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There's no topic thread for teasers that I can see so I'll put this here.

I'm going to give you the chance to win some virtual money. Here on the table in front of you I have three half-walnut shells and a pea. Now, watch carefully! I place the pea under one shell and shuffle the shells around with amazing and professional dexterity. Now, your turn! Choose a shell, the one you think the pea is under. If you choose the one with the pea, you win virtual ten dollars. OK, you keep that near you - no, don't turn it over yet. Let me show you something. Here are the two shells you didn't choose and I'm going to turn one over. Ah, no pea! Now, are you still happy with your choice? Because, if you like, I'm going to let you swap to the other unturned shell. Would you like to swap?

(Hint: as a professional shell game player, I can keep track of the hidden pea)

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OK another teaser.

The sail has contributed to civilization, trade and conflict since before the Phoenicians and Greeks. The Portuguese, Dutch, British have at different times dominated the seas with their wind-powered navies. Yet there are physical limits to using the power of the wind. You can't outrun the wind. The fastest you can go downwind (if there were no drag) would be no faster than the wind. And you can't sail directly upwind at all. You can make progress by sailing at an angle and tacking but there is no way you can sail directly upwind.

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23 hours ago, ArthurSmith said:

OK another teaser.

The sail has contributed to civilization, trade and conflict since before the Phoenicians and Greeks. The Portuguese, Dutch, British have at different times dominated the seas with their wind-powered navies. Yet there are physical limits to using the power of the wind. You can't outrun the wind. The fastest you can go downwind (if there were no drag) would be no faster than the wind. And you can't sail directly upwind at all. You can make progress by sailing at an angle and tacking but there is no way you can sail directly upwind.

I got the solution, link = https://en.wikipedia.org/wiki/Nimitz-class_aircraft_carrier 

Then laugh at how stupid ancient peoples were.

Edited by VictorMedvil
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19 minutes ago, VictorMedvil said:

the limit is surface area of the sail or windmill or whatever.

Well maybe we agree. The limit to using wind power is how much wind you can interact with and how efficiently you can harvest it. Is there an avenue to harvesting and storing energy and storing it, then using it as needed? Of course, yes, in the general case. That's why Elon Musk is focused on battery technology. But can you redirect the wind to sidestep the limits of fixed sails? Can you sail directly upwind using the power of the wind if you adapt a sail?

Edited by ArthurSmith
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23 minutes ago, ArthurSmith said:

Well maybe we agree. The limit to using wind power is how much wind you can interact with and how efficiently you can harvest it. Is there an avenue to harvesting and storing energy and storing it, then using it as needed? Of course, yes, in the general case. That's why Elon Musk is focused on battery technology. But can you redirect the wind to sidestep the limits of fixed sails? Can you sail directly upwind using the power of the wind if you adapt a sail?

Honestly, Wind power is not something I have researched a great deal so I am uncertain but I don't think that you can sail directly upwind. I am uncertain to whether or not you can sidestep the limits of fixed sails by redirecting the wind. This is definitely not something I am a expert in.

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Regarding the limits of fixed sail.

I've seen video of recent America's Cup racing where the yachts are up on hydrofoils. According to impressive graphic overlay, they are approaching 4x true wind speed at times.

Ice yachts have gone beyond 8x true wind speed.

There's a land yacht, Greenbird, that holds the world record for speed Vs ground that achieves similar leverage.

I could dig up links if of interest.

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Or we could cut to the chase and consider the downwind case. I hope nobody disputes it is physically impossible to sail precisely upwind using fixed leverage of the wind against any other medium: water, ice, solid ground.

And of course there's no question a turbine arrangement would not work, contrary to the direct upwind example (storage on board such as batteries is ruled out).

So is there a way to operate a wind-powered vehicle directly downwind and achieve sustained speed in excess of the wind?

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13 hours ago, ArthurSmith said:

No problem. It's just a teaser. One solution is to mount a turbine on the vehicle and drive the wheels with it. Practical tests have achieved twice windspeed upwind.

Legitimate, (not crackpot) turbine cart racing teams such as AEOLUS in the Netherlands, established a world record of 101,76% and a Canadian team that of 102,45%. These are very high tech vehicles and the speed records are official.

QUOTE

RACING AEOLUS - ROTARY SAIL DRAG RACE 2014

A rather unconventional race is held once a year in Den Helder in the North of the Netherlands. In the Racing Aeolus seven student teams compete to drive as fast as possible on headwind. Last year’s record of 101,76% efficiency was broken yesterday by a Canadian team that realised an efficiency of 102,45%.

Seven student teams from the Netherlands, Turkey, Germany, Denmark and Canada arrived in Den Helder this week for a new round in the annual Racing Aeolus, one of the four large sustainability races in the world along with the World Solar Challenge in Australia, the Dong Energy Solar Challenge Boat race in Friesland, and the Shell Eco Marathon.

 

2014 - The Chinook ETS scientific club’s purpose is to design a wind propelled vehicle with the ability to drive into a headwind. Based at École de technologie supérieure University, in Montreal, Canada, the Chinook team competes each year at the international event Racing Aeolus in Holland. Teams from all over the world meet at Racing Aeolus to match designs for wind turbine vehicles.

In 2012, Chinook ETS were the champions at Racing Aeolus. in 2013, they set the record with a vehicle speed of 82.6% of the wind speed while heading into the wind. This last August was even better.

As Alexandre Lupien-Bédard says: “We broke the world record for this type of wind turbine car as the vehicle was going at 96.91% of the wind speed towards the wind.”

UNQUOTE

Source: http://www.change-climate.com/Transport_Land_Sea_Sustainable/Assisted_Ships_Sails_Solar_Projects_Marine_Pollution/Rotary_Sails_Powered_Sailing_Boats_Ships_Turbines_Wind_Cars.htm

 

On the other hand, there is a crackpot claim made by one individual with a poorly designed cart, of achieving over 2 times wind speed, both upwind and down wind. There is no scientific evidence for this, no peer reviewed journal has ever touched it, and no math or logic supports it. We had a thread about this and when the crackpot became hostile, I closed it, and I am not going to allow another one on the same topic.

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That's a shame. If the claim (the possibility to exceed windspeed when travelling directly downwind powered only by the wind) is crackpot and/or its chief proponent is a crackpot, wouldn't it be better to address and expose the claim scientifically rather than hide it?

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11 minutes ago, ArthurSmith said:

That's a shame. If the claim (the possibility to exceed windspeed when travelling directly downwind powered only by the wind) is crackpot and/or its chief proponent is a crackpot, wouldn't it be better to address and expose the claim scientifically rather than hide it?

It has been addressed. Read this post: https://www.scienceforums.com/topic/38721-the-1969-blackbird-wind-turbine-sailing-craft-concept/?do=findComment&comment=396519

The crackpots have no answer for that.

That is the end of discussion on that subject on this forum.

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