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Discussion in 'Volkswagen AG Hybrids and EVs' started by JK919, Feb 11, 2020.

  1. Air_Boss

    Air_Boss Senior Member

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    Measured where? With the rotational inertia of a wind turbine blade set?
     
  2. Lee Jay

    Lee Jay Senior Member

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    On the low-speed shaft, obviously.

    I know it's not intuitive.
     
  3. Air_Boss

    Air_Boss Senior Member

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    Not at all, given rotor blade set moment of inertia, from the perspective of helicopter experience.
     
  4. Lee Jay

    Lee Jay Senior Member

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    Inertia doesn't dampen torque changes, it dampens speed changes. T = J × omega dot (the rotational analogy of F=ma). Torque can change instantaneously regardless of inertia just like force can.
     
  5. Air_Boss

    Air_Boss Senior Member

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    Understood, yet it doesn't, appreciably, on a high (or even a low) inertia helicopter rotor/blade set. Going back to the beginning premise, it is non-intuitive that purposeful, maximum performance shifting/driving produces less transient (in a percentage of maximum) transmission shock loading than the various induced loads on a wind machine transmission.
     
    #25 Air_Boss, Feb 13, 2020
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  6. Lee Jay

    Lee Jay Senior Member

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    I'd bet sliding your food off the clutch would, but in regular operation you're limited by the power the engine can produce. Mother nature can produce almost unlimited power, and the power in the wind goes with the wind speed cubed. If your rated wind speed is 11 m/s and your cutout wind speed (the speed at which the turbine shuts down to protect itself) is 25 m/s, you can see that the maximum power in the wind is (25/11)^3 = 11.7 times rated. That's steady-state. A 25 m/s cutout can take seconds to trip so turbines can ride through a 35 m/s gust - 32.2 times as much power in the wind as the rating of the turbine's drive train. I've seen gusts from 2 - 25 m/s in 0.6 seconds and from 3-35 m/s in 3 seconds. These are often combined with coherent vorticity in the wind making loads extreme.

    As I said, modern wind turbines control most of this away. For torque that's done by not reacting it - just let the gust accelerate the rotor and let all that inertia work for you. Then, use blade pitch to keep the speed under control. We also use active pitch to control blade and tower loads.

    I know they look like enormous, slow, lumbering machines but they're actually more complex to understand that helicopters which are themselves more complex to understand than airplanes. The reason for the complexity is that not only are they rotating like helicopters but they are also existing in the Earth's turbulent boundary layer all the time and their slow rotation speed makes that turbulence highly important for loads. Wind turbines regularly see turbulence levels of 10%-25% (standard deviation / mean) persistently, meaning all the time - 5,500 hours a year for 20-30 years. That's a heck of a beating.
     
    #26 Lee Jay, Feb 13, 2020
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  7. Prashanta

    Prashanta Active Member

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    Companies build niches. Usually companies succeed by being very good at a select few things. No reason to think that car manufacturers should also build charging infrastructure. They certainly didn't build the fueling infrastructure. Heck, they even outsource much of their manufacturing now.
     
  8. Trollbait

    Trollbait It's a D&D thing

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    Gasoline was available in cans from the local general store when ICE cars car out. It wasn't the infrastructure as we think of it, but it pre-existed for the cars.

    When a car company wants to sell a car that uses a fuel currently unavailable to the public, they should be the ones that at least start providing the infrastructure. Tesla doing so is part of the reason they dominate the plug in segment now.

    Now, plug ins really don't need public charging to start off. They have the equivalent "can of gas at the store". But some car companies aren't pushing plug ins. They are pushing hydrogen, and had hoped to get someone else to build the required infrastructure so that they could sell their cars.
     
  9. Prashanta

    Prashanta Active Member

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    There are already multiple companies dedicated to providing public chargers in every continent. EV development and charging infrastructure development are both moving forward. You can already drive any non-Tesla from any major city to any other major city in North America. Same goes for Europe. Every year, the network is expanding as well. Same goes for Tesla, I know. But the idea that you must buy a Tesla because others don't have their own proprietary network of chargers is frankly silly.
     
  10. Air_Boss

    Air_Boss Senior Member

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    You were talking torque and jerk, earlier, but whatever. A 'heck of a beating' can happen pretty much anywhere transients occur, albeit the wind machine duty cycle is higher.
     
  11. Trollbait

    Trollbait It's a D&D thing

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    At this point, if you want a BEV that can be used regularly for your long trips, you are better off with a Tesla in the US. The fees will be lower, because Tesla doesn't need the network to provide a profit; they are happy with it just paying for itself and its expansion. Then most of the other fast DCs currently available are slower than even Tesla's old Superchargers. Going by comments here, the Superchargers are more likely to be trouble free, or at least working.
     
  12. Lee Jay

    Lee Jay Senior Member

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    Right, and the difference is how we fixed this issue. Older turbines were constant-speed - directly coupled to the power grid. Thus, aerodynamic torque (Power / Rotational speed) and shaft torque were the same. Now we run them variable speed, and thus decouple aerodynamic torque from shaft torque, with the difference going into rotational inertia.

    Yeah...we usually say that an average year for a wind turbine is like 150,000 miles on your car. We want them to last at least 20 years (3 million miles equivalent), and we change the oil every 3-5 years (450,000 - 750,000 miles equivalent). It's a challenging environment, especially when you consider that the blades are bigger than A380 wings and are doing axial rolls their entire lifetime. Gravity cycles are full reversing cycles and you might get 30 million of them in the life of the blades, plus the wind loads (out-of-plane loads). And the blades have to cost 1/100th the cost of helicopter blades per unit of mass (on the order of $10 a pound instead of $1,000 a pound).
     
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  13. Air_Boss

    Air_Boss Senior Member

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    And if it's not bang-shifting shock loads on the transmission, it's breaking half-shafts under load...