Recent content by Arjan82

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    Difficulty Understanding 'Drag Crisis' (transitionary period from laminar to turbulent flow)

    You conglomerate several concepts that shouldn't be conglomerated. Let's untangle a few concepts first: Laminar/Turbulent flow in this application refers to the state of the boundary layer around an object. The boundary layer is a thin layer adjacent to the surface from which the flow velocity...
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    News Weird News Compilation

    Just in case you're wondering, he wasn't defying....
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    Wing Sails on modern ships

    A leeboard does nothing for stability, if anything they decrease it because together with the sail they form the heeling moment. Removing the leeboard actually reduces the heeling moment because the lateral resistance point moves upward (although I wouldn't use that as a method to prevent...
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    Wing Sails on modern ships

    I think you are underestimating how stable a flat bottomed ship actually is, just as an example, this is fine: These ships have no keel, to be clear. Also, the height of the center of mass isn't as high as it looks. That there is a lot of volume high up doesn't mean the mass is as well. I...
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    Wing Sails on modern ships

    Yeah, purely sail powered is not gonna fly, I agree with that. There is indeed some over ambitious, economically naive and ridiculously fantastical things going on there...
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    Wing Sails on modern ships

    There is a lot happening in the field for wind assist ships at commercial scale: There are several attempts for commercialization: https://www.bbc.com/news/technology-66543643 https://www.econowind.nl/ https://bound4blue.com/ http://www.dealfeng.com/ There are research initiatives with...
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    Wing Sails on modern ships

    It said 2 millibars, 2 millibars is 200 Pascals...
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    Collection of Lame Jokes

    Low speed stealth northern subsurface unicorn
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    Great one-liners from PF members

    I think what he meant a word of caution: "please constrain your problem well enough or engineers will run with it in the direction they think is fun, rather than useful" Because hey, if you can make a trebuchet within the given specs, that's just way more fun :cool:.
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    Pyramids built along dry river bed

    The latter have to be the Tau aliens, they are better!
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    Pyramids built along dry river bed

    There is a new paper in Nature saying that a now vanished branch of the Nile river (dubbed the Ahramat Branch) was much closer to where the Pyramids were build. The branch dried probably thousands of years ago. So... It wasn't aliens after all...
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    Collection of Lame Jokes

    At my work there was a special room that you could use either to relax in or for new mothers to express milk. The sign said in Dutch: "kolf ruimte / rust ruimte" ('kolven' meaning 'to express milk', 'ruimte' means 'room' and 'rust' means 'rest', i.e. 'rust ruimte' is a room to rest/relax in)...
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    B Too much energy -- thought experiment

    I think your reasoning is that the difference in density causes a larger difference in pressure if you increase the height. So (rho_hot*g*h1 - rho_cold*g*h1) < (rho_hot*g*2*h1 - rho_cold*g*2*h1), which on itself is true of course. The thing is that for equal P0 the temperature and therefore...
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    B Too much energy -- thought experiment

    The Cp for cooling is exactly equal to the Cp for heating at the same pressure and temperature, I don't know how you got two different answers....
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    B Too much energy -- thought experiment

    You cannot use the full dp due to difference in rho for the turbune power. Because the system has to overcome a small amount of friction as well. If you don't include that friction it becomes a problem where you do not need any energy at all to keep the flow going (Newton's first). In that...
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