Wikipedia:Reference desk/Archives/Science/2015 July 23

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July 23

Differences between industrial electricity prices from different sources

According to the Energy Information Administration, Washington state had the lowest industrial electricity prices in 2014[1]. But this site[2], citing the Edison Electric Institute, says differently. I believe both sources are correct, they're simply measuring (slightly) different things. So where is the discrepancy coming from? My other car is a cadr (talk) 14:00, 23 July 2015 (UTC)

At least one of the sources - EIA - provides more details at no cost: here's the 221 page EIA report, Electric Power Monthly. It has an appendix with algorithms and methodology. Edison Electric Institute sells access to their reports: available products. A subset of analysis and reporte are available on their data and analysis website at no cost. Nimur (talk) 14:30, 23 July 2015 (UTC)

The Edison report is the 12-month average ending in June 2014. The EIA link shows April 2014 only. Rmhermen (talk) 14:33, 23 July 2015 (UTC)

Thanks a lot. My other car is a cadr (talk) 03:26, 24 July 2015 (UTC)

Resolved

Small wind turbine blade design

I'm getting a stepper motor from someone's broken printer and I'm going to use that to generate power from the wind to charge a USB battery. [The wind is a lot more reliable in Scotland than the sun and piezoelectric shoes generate too little power]. I want to buy the blades because I think they'll work better (more accurate shape and balance) than homemade ones. My question is which blades should I buy? There's thin and fat ones. They're not designed with this purpose in mind but I don't think that matters too much. Thin Fat Also fat ----Seans Potato Business 15:46, 23 July 2015 (UTC)

Considering your application (for camping), I'd think you would want the lightest weight blades you can find, which would mean lower width and thickness). The downside of such blades is that they are more fragile, but if they are protected inside a housing, that won't be as much of a concern. Of course, the housing will add to the bulk and weight considerably. If you have a "naked blade" design in mind, then you will need to be careful to protect the blades. If they are removable, that would allow you to pack them more carefully and compactly. StuRat (talk) 16:09, 23 July 2015 (UTC)

Wind turbine design might be of interest. In particular it discusses why commercial wind turbines (of which there are many in Scotland) typically use only three blades, whereas one might naively think "the more the better" (from my brief reading it seems that the gain in "drive" from adding blades doesn't compensate for the extra weight and drag). AndrewWTaylor (talk) 16:18, 23 July 2015 (UTC)

Long thin ones are more efficient. It is to do with the characteristics of the aspect ratio (aerodynamics). Fat blades are popular in domestic applications only because the generate less noise. However the drag/air friction is greater. Hence less efficient. Thats why helicopters have thin blades. Cheaper still would be to place a live haggis in a tread mill. One doesn't then need to rely on the wind. Just show it a gravy-boat of redcurrant-horseradish-and-whisky haggis source and it will brake into a gallop, powering the whole village ;¬)--Aspro (talk) 17:03, 23 July 2015 (UTC)

It is worth bearing in mind that a blade designed for use in a fan (i.e. to create an airflow as a result of being turned by power) may not be the best shape for use as a turbine (i.e. to generate power from a moving airflow). In particular, if the blades aren't symmetrical in cross section (which they shouldn't be for maximum efficiency - they should be cambered like an aircraft wing aerofoil) they will be 'the wrong way up' if you use a fan blade in a turbine. AndyTheGrump (talk) 17:14, 23 July 2015 (UTC)

As I said: domestic fans are designed to be quiet. The hurricane blowers used in films to create a hurricane on set are aircraft screws. They make a hell of a racket, which is why the actors lips are always out of sync with their voices which have to be dubbed on in post-production. Whether the screw is driven by shaft power or wind is nether here nor there. The physics aero dynamic doesn’t care. That is not to say a quiet narrow bladed domestic fan can't be made. They would look a bit like the complex-curve blades of a nuclear-sub and high-performance Russian military turbo-prop aircraft. However, that technology is still classified so the OP is unlike to find them on eBay. Also,I don't get the "'the wrong way up'" bit. Just turn it the other way round on the shaft! I still think a nice round plump haggis is the better option--Aspro (talk) 17:54, 23 July 2015 (UTC)

'Turning it the other way round on the shaft' doesn't work. To appreciate why, think of an aeroplane wing - the top surface is generally more curved than the bottom surface, for maximum efficiency (a symmetrical aerofoil will still give lift but the lift/drag ratio is lower). A propeller has the higher-cambered side of the blade facing forwards into the airstream, whereas a turbine blade will have the higher-cambered side at the back - and you can't simply turn it round as this then results in the (rounded) leading edge becoming the (sharp) trailing edge. AndyTheGrump (talk) 18:29, 23 July 2015 (UTC)

That would only apply if the OP was going to use it as a motor. He clearly states that he intends to use it as a generator. So by reversing the prop the 'wind' drives it – all be it backwards (and SM will generate regardless). Yet thin long bladed air-screws are nearly all 'pullers' so the OP will probably not have to turn it around anyway. Thats the bit I don't understand and you haven't answered yet. --Aspro (talk) 19:32, 23 July 2015 (UTC)

I am fully aware of what the OP is trying to do, and your response has no relevance to my comment on the differences between a propeller and a turbine with regards to optimal aerofoil camber. Frankly though, I think the OP might do better to seek advice somewhere else, since nobody here has even bothered to comment on the need to match the characteristics of the turbine to the generator - you can't just stick any old set of blades on an electric motor and expect it to generate useful power. AndyTheGrump (talk) 19:49, 23 July 2015 (UTC)

You said “they will be 'the wrong way up'” which you haven't explained but instead now give a tangential reply to the OP suggesting every other editor here (save for you) are out of their depth. (COI disclaimer. I am a qualified engineer).--Aspro (talk) 20:21, 23 July 2015 (UTC)

I have given an explanation - your inability to understand it isn't my problem. And your qualifications, since they self-evidently don't include aerodynamics, aren't relevant. AndyTheGrump (talk) 20:39, 23 July 2015 (UTC)

Hi Andy. I've got motors from a broken Epson printer. I was hoping they would turn out to be stepper motors because for some reason they're the ones many websites advise to use (possibly because they're slow?). These are regular motors (RS445PA14233R, specifically) but at least I know they're low speed motors. I'll continue to look out for broken printers on Freegle/Freecycle but maybe these will work. Do you know whether the propeller I will want would be a push or pull prop? I figure it should be push (relatively unusual for an aircraft) but figure I should check my logic. ---Seans Potato Business 20:09, 23 July 2015 (UTC)

Whether the generator is mounted in front of or behind the turbine will only affect the direction the generator is turned - it won't have any other consequences beyond the fact that having the turbine 'downwind' will reduce the airflow, and add turbulence. The direction the turbine revolves is solely dependent on whether it is a 'clockwise' or 'anticlockwise' helix, and reversing the way it faces on the generator shaft doesn't reverse the helix. As I have stated above though , a propeller is designed to generate thrust, and thus may not be optimal for use as a turbine. Not only is the camber likely to be wrong (if it doesn't use a symmetrical aerofoil) but you may find that the pitch is too fine - a very fine pitch may result in the turbine not turning at all under load. As I have stated above though, you might do better to ask questions at a specialist website - this website [3] looks as if it might be useful. AndyTheGrump (talk) 20:52, 23 July 2015 (UTC)

Okay, thanks. I'll ask for advice at a more specialist site. Before I go, could I ask you to clarify a "fine pitch"? These propellers are defined in the format 16" x 10" or 16" x 8" for example, where the second number is the pitch. Is a greater or smaller number a finer pitch? Thanks again. --Seans Potato Business 21:06, 23 July 2015 (UTC)

The pitch is the theoretical distance the propeller/turbine would move relative to the air mass per revolution, if there was no slip. A coarse pitch is larger than a fine one. AndyTheGrump (talk) 21:11, 23 July 2015 (UTC)

Incidentally, you should possibly consider alternatives to a horizontal-axis turbine. As our article shows, there are vertical-axis designs which may better suit your needs - they don't need to be pointed into wind, and might be more practical as a portable device. They aren't generally as efficient (in terms of generating power for a given size and windspeed) but some designs at least look as if they might be more robust. AndyTheGrump (talk) 21:38, 23 July 2015 (UTC)

Hi. The problem is that VAWT blades don't seem to be cheaply available so I'd have to make one myself to keep the project economical. I was hoping that a manufactured plane propeller would be superior to anything I could make myself even if the specifics were suboptimal for the application. There's also these large plastic garden windmill blades but I wonder if they would be worse than the the RC propellers... --Seans Potato Business 22:00, 23 July 2015 (UTC)

Good luck. Make sure your USB device isn't driving the motor. You'll probably need a charge pump or switching network based on turbine speed and a regulator. --DHeyward (talk) 21:51, 23 July 2015 (UTC)

Multiple ring systems around planets

Is it possible for a planet to have multiple ring systems moving in different orbits such as this — Preceding unsigned comment added by Malamockq (talk • contribs) 16:55, 23 July 2015‎

No - or at least, it won't be stable in the long term. The objects in each ring will be gravitationally attracted towards the objects in the other, causing the two rings to gradually drift into a common alignment. It is this tendency for multiple small objects in orbit around a common larger one to align their orbits in a common plane that is responsible for the formation of rings in the first place. AndyTheGrump (talk) 17:25, 23 July 2015 (UTC)

Maybe, if the two rings have enough distance between them. After all, the solar system is also a "ring system", but not all of objects orbit in exactly the same plane. Then there's the Oort Cloud, where there is no single orbital plane at all at that distance. I agree that eventually everything would theoretically fall into a single plane, but that may very well take longer than the age of the universe to happen. Now, as for planets, the problem with a ring system being far enough out to not interfere with an inner ring system on a short time scale would be that, at those distances, it would come too close to other planets, etc. But, if you had a planet without a solar system, say one that had been ejected from it's own system, then this configuration might be possible, and stable for millions or billions of years. StuRat (talk) 17:45, 23 July 2015 (UTC)

A single object is not a ring. Can't you find some way to resist giving answers to questions you don't know anything about? Looie496 (talk) 19:43, 23 July 2015 (UTC)

No, it's not a single object, it's a massive number of single objects. I never stated it was a single object, so I have no idea where that straw man came from. (The solar system being a ring system refers to the asteroid belt, Kuiper belt, etc.) Also note that SemanticMantis' and DHeyward's comments and links below supports my assertion. StuRat (talk) 17:13, 24 July 2015 (UTC)

Hear hear! Fgf10 (talk) 21:09, 23 July 2015 (UTC)

The problem with the diagram is not that it shows multiple ring systems in different orbits, but that it shows multiple ring systems in non-coplanar orbits. Saturn can be said to have multiple ring systems in coplanar orbits, depending on what you mean by a ring system as opposed to a ring. I think that an earlier editor is right that the objects in the two rings, due to gravitational attraction, will gradually drift into a common alignment. Has there been any computer simulation of the formation and behavior of rings and ring systems? Robert McClenon (talk) 19:47, 23 July 2015 (UTC)

If the two rings are made up of very small particles (dust), and are some distance apart, the interaction between them will be negligible. Amount of light reflected by a visible object is proportional to the area (cross-section) of the object, for any object substantially larger than the wavelength of reflected light. The gravitational interaction of the object, on the other hand, is proportional to its mass, which scales with volume rather than area. Thus, for a given total reflective area, the smaller the particles making up the rings are, the weaker the gravitational interaction between the rings will be. Dr Dima (talk) 19:48, 23 July 2015 (UTC)

I feel like somebody should link Ring_system_(astronomy), and point out that we have articles for many specific systems, like Rings of Saturn. One interesting thing mentioned in the article is the notion of a "shepherd moon". Here is one article I found that addresses stability of ring systems [4]. This work looks at equilibria of a "ring configuration", but I think it may have some application to continuous rings [5] Here's another work on the stability of ring systems [6]. Here's a paper on numeric simulations of planetary rings with focus on collisions [7]. Here's an older (1984) paper about then-current unsolved problems in ring dynamics [8]. I suspect looking at recent citations to that article could be fruitful. SemanticMantis (talk) 21:27, 23 July 2015 (UTC)

Hey, look what a few minutes with google scholar a can find! Here [9] is an article presenting information on Beta_Pictoris. They say in the abstract "A deconvolved image strongly suggests that the newly detected features arise from a system of four noncoplanar rings", emphasis mine. So at least some researchers think that there are noncoplanar rings around things in space, though they do not comment on long-term stability. SemanticMantis (talk) 21:33, 23 July 2015 (UTC)

I believe it's Tidal locking related. Are the planes of the rings of Saturn and the orbits of moons in the plane of orbit around the sun or the rotation plane of the planet? I don't see why a small rock vs. large moon would be different with respect to tidal locking other than time. Saturn does have the Phoebe ring which is inclined and retrograde. The Phoebe ring is near the ecliptic plane while the other rings and moons are equatorial with Saturn's rotation. Saturn is inclined similar to earth I believe. See Laplace plane and it seems far away rings could exist in the ecliptic plane and near rings would be equatorial. --DHeyward (talk) 22:01, 23 July 2015 (UTC)

That optical illusion

We have an article on this but I forget what the name is. There are a bunch of great images at commons that could use a proper category. Thanks for any help you can offer. Anna Frodesiak (talk) 22:10, 23 July 2015 (UTC)

Moiré pattern. Found it ten minutes after looking and two seconds after posting here. :) Anna Frodesiak (talk) 22:14, 23 July 2015 (UTC)

Hey, a blast from the past! We discussed something rather similar a few years ago here. At that time, I think you added a section to Moiré pattern as I recall. I wonder if maybe a DAB or redirect for kinegram is warranted. SemanticMantis (talk) 22:33, 23 July 2015 (UTC)

You have a great memory. I remembered posting somewhere about it, but couldn't figure out where.

Not sure if these all fit Fresnel lens of if they are related to Zone plates . --DHeyward (talk) 22:38, 23 July 2015 (UTC)

Those seem different. Anna Frodesiak (talk) 22:43, 23 July 2015 (UTC)

I agree they are different, but part of the problem is that the OP link sort of conflates two things - one of them has to do with Lenticular_printing and lenticular lens (and that's what reminds you of Fresnel), while the other thing with the grid screens is rather different. SemanticMantis (talk) 23:02, 23 July 2015 (UTC)

Anyhow, check the commonscat now. Not sure if it's sorted out properly. I just added a few images and gave Moire a parent cat and that's it.. Anna Frodesiak (talk) 22:42, 23 July 2015 (UTC)

Looks good. Someone removed your animation section [10] in april. This is a tricky thing to get WP:RS for. This guy [11] says a kinegram is a combination of Moire pattern and Zoetrope. Last time we discussed it, Steve Baker was adamant that kinegrams were not Moire patterns (though I still disagree), and I also don't think that it's all that similar to a zoetrope - as I pointed out before, each image in zoetrope is a complete image, and then some shuttering mechanism is used to expose them sequentially. Here, there are no "frames" and the image is only formed after the screen is overlaid. Perhaps the best thing to do is to make a stub for kinegram, and include links to zoetrope and moire pattern. You could fill it with refs from this thread and the one I linked above, I'd help if you got it started :) SemanticMantis (talk) 22:57, 23 July 2015 (UTC)

Now this is extra cool: when I go to your new category commons:Category:Moiré and scroll, I see animation effects on several of the thumbnails as I scroll. (It's probably wicked browser- and screen-dependent, though.) —Steve Summit (talk) 23:15, 23 July 2015 (UTC)

WP:OR- I saw it too! Only on the simpler geometric ones, not the more complicated animations. It was much more apparent on my iPhone 5. On my larger Apple_Thunderbolt_Display and Firefox, I had to make the browser window and thumbnails both rather large before I got the effect, and it was still less apparent. Do you agree a new stub for 'Kinegram' is warranted, or do you think this notion of using periodic banded screen overlays to produce an animation fits better with 'Moire pattern'? Or perhaps somewhere else? SemanticMantis (talk) 00:26, 24 July 2015 (UTC)

Hardware assisted anti-aliasing, plus hardware-accelerated scrolling, in WebKit, CoreText, and ... everywhere else! The antialiasing strength can be dynamically scaled to ensure smoother performance. Nimur (talk) 15:59, 24 July 2015 (UTC)

Okay. I started Kinegram. Now to find some way to get an ogv in there. Thanks all. Oh, and please copy edit it. It is not pretty right now. :) Oh, and one more thing. We need to sort out the Commonscats. Any thoughts on how to do that? I also wish to upload the overlays from here. There's no way they're copyrightable, right? I tried to convert them from pdf to pgn and they came out all skewomp. I could make some more, but I do not know the measurements. Anna Frodesiak (talk) 02:18, 24 July 2015 (UTC)

"When two grids intersect with a patterned effect — that's a Moiré." {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:10, 24 July 2015 (UTC)

"When the interference hits your eye, and your brain it does fry, that's a Moiré." StuRat (talk) 16:44, 24 July 2015 (UTC)

• "When the lines of a screen make some lines in between, that's a Moiré." —Tamfang (talk) 06:26, 25 July 2015 (UTC)

@DHeyward, Scs, SemanticMantis, and Nimur: Thank you all for input. Please, please give it a copy edit. I am terrible at describing such things. And, if you are so inclined, make a short ogv that is better than my bit of rubbish. All the best, Anna Frodesiak (talk) 00:12, 25 July 2015 (UTC)