Wind Power B/C

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Re: Wind Power B/C

Post by maxxxxx » February 13th, 2017, 6:11 am

RestingDoll wrote:
maxxxxx wrote:
kenniky wrote: Last year had a bit in the rules that stated minimum distance; since that isn't there anymore, I think it's safe to assume that there is no minimum distance
That's what I thought, but on Saturday at a comp they used a minimum of 5cm rule and since that was the State ES I wanted to make sure. If I want an official answer should I submit this as a FAQ? I don't want to get to States and have the same problem.
I don't think 1 cm vs 5 cm would decrease wind speed by that much. In any case, everyone would be affected the same amount.
I don't think it's fair to assume that everyone would be impacted the same, as there were other discussions earlier in this thread about some turbines not starting because they were positioned too far away. And besides, don't you want the State Supervisor to be following the most current rules? They also didn't tell us our voltage after the testing on each speed(which is bold in the rules) so I think they just need to take another look through the rules. That last sentence may have sounded a little harsh but the people running it were really nice and I don't mean any disrespect, just that it would be beneficial for Supervisors to be more familiar with the rules, which is also why I wanted the distance issue clarified.
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Re: Wind Power B/C

Post by Alex-RCHS » February 13th, 2017, 6:52 am

I agree with maxxxxx. It wouldn't affect all teams equally because some teams may have spent some time deciding what distance generates the most voltage for each speed. If a team figures out that their turbine runs best at 3 cm, they should be rewarded for that.
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Re: Wind Power B/C

Post by RestingDoll » February 13th, 2017, 10:01 am

maxxxxx wrote:
RestingDoll wrote:
maxxxxx wrote:
That's what I thought, but on Saturday at a comp they used a minimum of 5cm rule and since that was the State ES I wanted to make sure. If I want an official answer should I submit this as a FAQ? I don't want to get to States and have the same problem.
I don't think 1 cm vs 5 cm would decrease wind speed by that much. In any case, everyone would be affected the same amount.
I don't think it's fair to assume that everyone would be impacted the same, as there were other discussions earlier in this thread about some turbines not starting because they were positioned too far away. And besides, don't you want the State Supervisor to be following the most current rules? They also didn't tell us our voltage after the testing on each speed(which is bold in the rules) so I think they just need to take another look through the rules. That last sentence may have sounded a little harsh but the people running it were really nice and I don't mean any disrespect, just that it would be beneficial for Supervisors to be more familiar with the rules, which is also why I wanted the distance issue clarified.
Conversely, a set distance would give equal power available to be captured regardless if the turbine started or not; similarly, 5 cm does not seem like an outlandish distance. I agree though, event supervisors should be well-versed in the current iteration of the rules, and that probably shouldn't've happened.

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Re: Wind Power B/C

Post by ashmmohan » February 14th, 2017, 5:22 am

RestingDoll wrote:
maxxxxx wrote:
RestingDoll wrote:
I don't think 1 cm vs 5 cm would decrease wind speed by that much. In any case, everyone would be affected the same amount.
I don't think it's fair to assume that everyone would be impacted the same, as there were other discussions earlier in this thread about some turbines not starting because they were positioned too far away. And besides, don't you want the State Supervisor to be following the most current rules? They also didn't tell us our voltage after the testing on each speed(which is bold in the rules) so I think they just need to take another look through the rules. That last sentence may have sounded a little harsh but the people running it were really nice and I don't mean any disrespect, just that it would be beneficial for Supervisors to be more familiar with the rules, which is also why I wanted the distance issue clarified.
Conversely, a set distance would give equal power available to be captured regardless if the turbine started or not; similarly, 5 cm does not seem like an outlandish distance. I agree though, event supervisors should be well-versed in the current iteration of the rules, and that probably shouldn't've happened.
1 cm vs 5 cm definitely makes a difference; it ups my voltage by about 10 or 20 mV. For high speed, the supervisor at Golden Gate did not let us come within like 3 centimeters, but on low speed we could move it as close as we wanted; it was pretty weird how they facilitated things.
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Re: Wind Power B/C

Post by maxxxxx » February 14th, 2017, 8:26 am

So at an invite, the test had the following question:
Invitational wrote:Water is stored in a vertical cylinder shaped container on top of a 35 meter tower. The cylinder has a radius

of 12 m and a height of 18 m. The density of water is (1000 kg / m^3). What is the potential energy of the

water stored in the tower?
I did:

U = mgh, m = DV, V = pi*r^2*H

U = (1000*pi*12*12*18)*9.81*35

and ended up with U = 2.8GJ, which was one the multiple choice answers.

The key said the answer was 3.5GJ. Did I do something wrong, or was it a mistake on the answer key?
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Re: Wind Power B/C

Post by P2P » February 14th, 2017, 8:37 am

Water is stored ON TOP of the 35 m tower. So the center of mass of the water is 35 m + 18/2 m (which is 44 m) above the ground. Therefore the height is 44 m instead of 35. Honestly it's a weird question but that's how you get 3.5 I guess...

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Re: Wind Power B/C

Post by Alex-RCHS » February 14th, 2017, 2:43 pm

P2P wrote:Water is stored ON TOP of the 35 m tower. So the center of mass of the water is 35 m + 18/2 m (which is 44 m) above the ground. Therefore the height is 44 m instead of 35. Honestly it's a weird question but that's how you get 3.5 I guess...
This.

When you have h = 44 you get 3.52GJ.
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Re: Wind Power B/C

Post by maxxxxx » February 14th, 2017, 7:00 pm

Thanks for the help. Can anyone help me with this question?
Test wrote:The power generated by a turbine is 18,000 Watts. If the wind speed, which is initially 30 m/s decreases by 25%, what must the lift force be in order to generate the same amount of power?
My memory of AP Physics is failing me and I don't know how to start this. The answer is 800N but I have no clue how to get it.
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Re: Wind Power B/C

Post by Alex-RCHS » February 14th, 2017, 8:46 pm

Woahhhh

That's a really tough question. Unless I'm overlooking something, there's no way to answer that. You can't find the radius of the blade without knowing the efficiency constant for that turbine. And I think you need the radius to find the force needed.

Also, those numbers seem weird to me. Even with a low efficiency constant (like .3, half of betz' limit) your blade radius would be just above 1m.

I'm totally stumped by this.
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Re: Wind Power B/C

Post by RestingDoll » February 15th, 2017, 6:11 am

maxxxxx wrote:Thanks for the help. Can anyone help me with this question?
Test wrote:The power generated by a turbine is 18,000 Watts. If the wind speed, which is initially 30 m/s decreases by 25%, what must the lift force be in order to generate the same amount of power?
My memory of AP Physics is failing me and I don't know how to start this. The answer is 800N but I have no clue how to get it.
I think what they want you to do is P=F*v, and then plug and solve for F. However, this wouldn't actually work since wind speed is cubed proportionally to velocity. They'd probably want to say "linear velocity of the blade" in the question instead.

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