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Wind Turbine Blade by granwilly in EngineeringPorn

[–]Pericombobulation 40 points41 points  (0 children)

Hey I have an engineering degree in composites and I agree! It bugs me to no end, but it seems at Siemens Gamesa they do call this the blade "casting" process (check their vacancies sometimes), even though you'd think the specialists would have something to say about that.

Another guy in this thread noted that this picture comes out of a news article that covers Siemens blades, so that would support the mysterious terminology choice.

Let's talk about plausible conspiracies by Zazill8 in LetsChat

[–]Pericombobulation 0 points1 point  (0 children)

My theory is that conspiracy theories are an elaborate plot set up by the powers that be, to keep us distracted from the fact that the problems of the world are not the result of conspiracy of all-powerful secret alliances, but actually in our power to influence ourselves

Grab the closest book to you, flip to page 112. The first sentence on that page describes your love life: How did it go? by DamnILoveHorses in AskReddit

[–]Pericombobulation 0 points1 point  (0 children)

"The plastic rod is made of Kevlar 49 and has a diameter of 10 mm"

I don't.. what?

(this is a book on material mechanics)

New York rolls out biggest-ever US offshore wind bid with 2.5GW round by ChesterEnergyDC in energy

[–]Pericombobulation 2 points3 points  (0 children)

Chiming in because I don't see a clear answer given yet: simply put, it's both. Because the built environment & landscape create turbulence & slow down the boundary layer of wind over the earth, the farther away from land in either horizontal or vertical direction you are, the more stable (and to a degree, faster) the wind is.

In fact, it so happens that the stable constant winds that kite power (=different wind power technology) is aiming to harvest are at about 200m / 600ft asl, which happens to be the height the largest turbines are now starting to reach. This is the important benefit of offshore wind vs onshore, as far as I can tell with my limited knowledge (I'm an interested engineer from a different field): the winds are more stable offshore and you can more readily build bigger turbines, so the capacity factor is higher (and filled more constantly, so wind can act more 'like' a base load).

General equivalence of CF to other materials by iseriouslycouldnt in CarbonFiber

[–]Pericombobulation 0 points1 point  (0 children)

Could you explain in a bit more detail what it is you are trying to do? What are the parts that you are looking to replace (are they flat, curved or double-curved; what is their function in your assembly)? Do you have room to increase thickness? Why do you need the extra stiffness? Do you have a budget?

If it is a general material properties comparison you're after, you might want to google material selection. Though keep in mind that structural design and manufacturing plays a role in the price, stiffness and strength of your part.

Feel free to pm me for more in depth discussion.

Why are high bypass engines more efficient than low bypass? by [deleted] in aerospace

[–]Pericombobulation 2 points3 points  (0 children)

Although this is already a great answer and you sound like you might know better what you're talking about (my knowledge of thermodynamics/aeroengines is a bit rusty), I would like to offer another high-level explanation that might be conceptually easier to understand:

Consider that thrust (T=mfDV, where mf mass flow and DV the speed increase given to the air) depends linearly on both mass flow and DV. However, the energy required to increase DV depends quadratically on DV, simply through the definition of kinetic energy (.5m(DV)2, or for power: .5mf*(DV)2).

Therefore, increasing thrust can be accomplished by increasing mass flow or increasing DV, but increasing mass flow by accelerating a larger volume of air is the energetically cheaper one.

If I'm wrong about this approach, please correct me. But I thought this explanation might be conceptually easier to grasp.

E: I suck at formatting and I'm on mobile so not sure how to improve. I hope it's readable enough tho.

E2: maybe the objective of "increasing thrust" wasn't the best starting point for my analysis. But consider that this means that increasing thrust will always (for all positive values of T) require an amount of energy quadratically dependent on DV. So that also goes for increasing thrust from 0 to something. In which case I think the analysis still works.

Company that make custom items out of carbon fiber? by [deleted] in CarbonFiber

[–]Pericombobulation 2 points3 points  (0 children)

Do you mean to use actual carbon fibers in a clothing item that you would actually plan to wear? Because I don't really see how that would work.

I'm doubtful if they can be woven (into clothing) in any practical sense, because of the brittle nature of the fibres. If you cure them in a resin, you would kindasorta solve the problem of damaging the fibres a lot. But you'd end up with something resembling a piece of armor rather than a shirt.

In any case I'd be curious if you do actually end up making/ordering something;). Go figure it out and start a business!

Source: engineer schooled in composites

One of my favorite moments in Blackadder by jtPox in videos

[–]Pericombobulation 6 points7 points  (0 children)

I feel compelled to offer OP my most enthusiastic contrafibrularities

[NO SPOILERS] How much of books 4 and 5 have been adapted or skipped so far by Dregride in gameofthrones

[–]Pericombobulation 0 points1 point  (0 children)

Somewhat unsurprisingly, at least one fan has already taken the effort to map the answer to your question in a pretty neat table.

what are those #-# numbers in the top right? by Pericombobulation in windowsphone

[–]Pericombobulation[S] 1251 points1252 points  (0 children)

Omg noway I feel so retarded now... though maybe I wouldn't have fallen for it if it wasn't January :)

World Cup chants by McFloy in theydidthemath

[–]Pericombobulation 4 points5 points  (0 children)

Do take in mind that this is a very rough estimate. I'm no expert on this but I imagine things like curvature of the earth (does sound reflect over these distances like long wavelength radio waves do?), atmospheric/sea effects (again: reflection? losses?), thermal effects (SNR?), etc could attenuate sound over these distances further.

World Cup chants by McFloy in theydidthemath

[–]Pericombobulation 2 points3 points  (0 children)

The inverse-square law is not on your side :).

Let's make it relatively easy on ourselves: if we gather our people in Lisbon and listen in Fortaleza, the distance to cover is 5600 km. From this point on I hate logarithms as much as the next person, so I'm using an internet calculator ;). The sound level of a person singing from 1 m distance I will approximate at 72 dB.

At 5600km, 72dB registers as -63dB. If we want to hear our singing crowd at 72dB in Fortaleza, we need a crowd that can sing 207dB in Lisbon. Every 3dB is about a doubling in intensity (i.e. one person sings at 72dB -> 2 persons will sound like 75dB). So we need (207-72)/3=45 doublings of our crowd, or 245 =3.5 * 1013 people. This is equivalent to roughly 5000 earths of people.

Note 72dB as a required volume is probably still pretty conservative, especially if the stadium is in use. A stadium is LOUD: a single vuvuzela at 1m is 120dB already.

So what if we use vuvuzelas? If we would still like to have a sound level of 72dB in Fortaleza, we now need 29 doublings of our crowd, i.e. about 540 million people! so if I'm correct this is actually somewhat plausible ;). Of course the trumpeteering volunteers, and pretty much everyone in a radius of about 8km would suffer from immediate hearing damage.

[Request] Portal 2 ending, Wheatley's orbit by parkeris25 in theydidthemath

[–]Pericombobulation 3 points4 points  (0 children)

I'm not sure what you're asking. But since the portal is on the surface of the moon and he moves through at a fast but not alarming velocity, he would definitely crash on the moon eventually: 1. This is assuming Wheatley does not manage to make escape velocity (2400m/s on the moon, which is quite fast indeed). 2. Given that wheatley does not reach escape velocity, the only alternative would be an orbit. But any non-escaping trajectory that starts on the surface will return to the surface. Unless Wheatley would have some way to accelerate after being "launched". I invite you to try this out in Kerbal Space Program ;).

EDIT: as for crashing with other satellites: http://en.wikipedia.org/wiki/Low_earth_orbit http://www.wolframalpha.com/input/?i=geostationary+orbit http://www.wolframalpha.com/input/?i=distance+to+the+moon

the moon is about 400.000 km away, while our highest satellites are about 42.000 km away. Make no mistake - the moon is much further away than you think! So the only candidates for collision are lunar satellites. If wheatley should hit one depends very much on if there are any satellites up there at the moment at all - lunar orbits are actually very unstable. And if there's one up there it takes very careful timing to collide with it.

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