Wikipedia:Reference desk/Archives/Miscellaneous/2019 December 31

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December 31

You don't notice what you don't notice

Curious whether there's a name for this fallacy. Say you're a Sneetch, and you think you can tell intuitively whether another Sneetch is a star-bellied Sneetch or a non-star-bellied Sneetch, even though everyone's wearing a shirt and you can't see whether they have a star. Sometimes you guess someone is star-bellied, then later you find out that they in fact are. But much of the time, you don't even find out for sure, and just become more confident in your nonscientific judgement of it, since your judgement is rarely disproven. Temerarius (talk) 00:06, 31 December 2019 (UTC)

Does intuition stand up to scientific rigor? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:58, 31 December 2019 (UTC)

Confirmation bias? Mitch Ames (talk) 03:14, 31 December 2019 (UTC)

@Temerarius: What you named "you don't notice what you don't notice" is not a fallacy itself, but rather just a state of unnoticed lack of knowledge, common in beginners in all areas of knowlegde. Some detailed examples can be found e.g. at Quora “You don’t know what you don’t know”, what does that even mean?.

What you describe as a result of the state is an example of Inductive reasoning: you get some specific, detailed observation (a sample of verified guesses, all of which appear correct) and make a general conclusion (all guesses are correct).

The unnoticed fallacy in this reasoning is described in Inductive reasoning#Generalization and linked as a hasty generalization and a biased sample there. --CiaPan (talk) 09:24, 31 December 2019 (UTC)

you don't notice what you don't notice – also known (or not) as unknown unknowns. Mitch Ames (talk) 02:10, 1 January 2020 (UTC)

The concept of Confirmation bias probably applies to this scenario. {The poster formerly known as 87.81.30.195} 90.204.182.54 (talk) 16:03, 31 December 2019 (UTC)

Also related to the taxicab problem/taxicab fallacy. (And is anyone else really grossed out by the phrase "star-bellied Sneetch"?) 93.136.90.120 (talk) 19:26, 31 December 2019 (UTC)

Well, Dr. Seuss wasn't.[1] ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:35, 31 December 2019 (UTC)

Wikipedia:Wikipedia has an article on everything!, including Sneetches – The Sneetches and Other Stories § The Sneetches. Mitch Ames (talk) 02:01, 1 January 2020 (UTC)

Another related concept is the Dunning–Kruger effect. This might even be what Temerarius was asking for. --142.112.159.101 (talk) 20:52, 31 December 2019 (UTC)

Such an overestimate of one's capabilties might fall into the "stupid but industrious" category attributed to Kurt von Hammerstein-Equord. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:38, 1 January 2020 (UTC)

• Accidental logician Donald Rumsfeld famously posited the concept of the unknown unknown, which seems germane to the current discussion. --Jayron32 13:43, 2 January 2020 (UTC)
  • That even made it into a CD of art songs called “The poetry of Donald Rumsfeld”. (See NPR story.)

    As we know,
    There are known knowns.
    There are things we know we know.
    We also know
    There are known unknowns.
    That is to say
    We know there are some things
    We do not know.
    But there are also unknown unknowns,
    The ones we don't know
    We don't know.

    ◄ Sebastian 14:47, 2 January 2020 (UTC)

Maybe your star-belly spider sense is better than random chance, maybe not, you would have to test to find out. Star-belly detection sounds something like gaydar and there is apparently evidence that gaydar is actually a thing. 67.164.113.165 (talk) 02:36, 5 January 2020 (UTC)

Falling windmills

A junk windmill that was supposed to power up our entire neighborhood fell and did a lot of damage. It fell away from my apartment, which was good even though I doubt it would do damage from that far away. I doubt this is a one-off thing. So, I've been Googling. I can't find cases of windmills falling and damaging buildings and cars (the one here took out a billboard and fell on a parked car). Perhaps it is because most people aren't dumb enough to put one on top of an apartment or retail building. Are there references of similar situations that I just can't find? 135.84.167.41 (talk) 13:44, 31 December 2019 (UTC)

• Windmills are rarely placed on or near buildings because the disturbed airflow around a building is hard to extract useful wind energy from. Also it's known that such airflow often involves resonances which can put cyclic bending forces into the turbine mast, leading to failures. So it's just a bad idea and no-one does it.

In the euphoria of 2000 (and in London, again around 2012) there was a brief fashion for erecting urban windmills. These were mostly of the vertical axis design. The Gorlov helical design was favoured, as this reduces the cyclical loading problem, especially in urban wind conditions. And yet they have still been a great disappointment.

Most "worked" (but a £50,000 asset generating £5 / month was one example) and didn't fall down. But economic breakeven was almost unheard of, and reliability was generally awful. I know one locally which hasn't turned in five years and is mostly enjoyed by its roosting starlings.

It's rare for them to fail. Either by the mast failing, or by them shedding blades. I know of one urban turbine (5kW horizontal axis) which shed its blades, but that was during a severe storm and it may have been hit by other debris. It's such an undesirable accident that maintenance works hard to avoid this ever happening, and a dubious turbine will probably be removed before it's dangerous. An accident is probably predictable, and so would have more to do with lack of maintenance (i.e. removing it before real hazard) than inherent risk of windmills. But as they're just not a success as turbines, and they're now clearly yesterday's embarassing bad idea, we're going to see many more removed in the future, or left until they do become dangerous. Some are pretty well known for shedding small parts in high winds. At present though? It's still a pretty rare event. The riskiest size are probably 5-10kW machines on remote farms, where the wind can (sometimes) just get to crazy levels. People in those areas generally recognise that.

Was your example the one in the Bronx? AIUI, that one was still being erected and wasn't yet regarded as commissioned and installed. It's not clear to me why it failed, but there are several possibilities. Firstly, if it was allowed to free-spin and it had a wind of >20mph on it, then it _might_ overspeed (The control system should have set the blade pitch to avoid this, but it wouldn't be the first where the control system wasn't yet in service, and the blades were left in the wrong state. You don't ever erect wind turbines in Winter with no control system!) Also the mast failed at the base. Now maybe the head loads went excessive and that will then always destroy the mast, or maybe the mast mount simply failed because someone didn't mount it properly - you'd have to check the wreckage. Maybe it was an airflow problem, and strong wind in one direction just set up the wrong resonance. But still, this is a rare accident. Andy Dingley (talk) 14:54, 31 December 2019 (UTC)

A bit out of date but Factcheck: How often do wind turbines break? (2015), but it's UK focussed and by Greenpeace who may not be entirely motiveless.

I also found on YouTube; Germany: Wind turbine blade flies crushing lorry on the autobahn and GIANT wind turbine collapses in Northern Ireland.

The German Windmill in the Video is a transport incident. It fell from the trailer during transport. Best regards -- Neozoon 16:32, 6 January 2020 (UTC)

Alansplodge (talk) 19:02, 31 December 2019 (UTC)

Those are large turbines though, maybe 2MW, so several hundred times the power we're talking about here. Andy Dingley (talk) 19:25, 31 December 2019 (UTC)

True. Smaller falling turbines seem to be un-newsworthy. Alansplodge (talk) 16:18, 3 January 2020 (UTC)

One would think that there should be some sort of viscous coupling (or fluid coupling?) device that would limit RPMs and/or torque to the shaft. 2606:A000:1126:28D:80CC:FB4F:9449:9FB1 (talk) 06:42, 6 January 2020 (UTC)

• There's no need to limit the shaft speed. The main problem is limiting vibration at speed, as that causes tower failures, and most of all it's about limiting the forces on the blades. This is partly the radial force on the blade, but that's actually fairly easy to resist (the blades will never fail from this, but the hub attachment will). Mostly, AIUI these days, the limit is a bending or twisting force on the blade, as the aerodynamic forces (inevitably, on any propeller) aren't constant along the blade length.

So limiting speeds at the shaft wouldn't really help. What we need is to make the blades less efficient, by turning them out of the wind. Either by turning the pitch of each blade, or else by turning the head to a deliberately inefficient heading. Although most large turbines have a shaft brake, this is quite limited in its power and it can only hold the turbine, not slow it or absorb energy long term.

If the pitch control mechanism fails, the turbine will self destruct. This is how almost all turbine failures of large turbines have happened. It's also an almost deliberate thing, in an incredibly high wind: it becomes very expensive to build a hurricane-proof large turbine and it's cheaper to lose one or two cheaper turbines rarely, than it is to try and make them indestructible. But that's not an option open for urban turbines. Andy Dingley (talk) 17:07, 6 January 2020 (UTC)