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I normally wear shorts in the summer, at which point I become very aware of the problem every man knows about - splashback of pee from urinals. No matter how you stand or aim, the inherent splashing effect of a stream of liquid hitting a surface will tend to distribute some of it around the environment. Also the curved shape of urinals, like a concave mirror, will always bounce those splashes back towards you regardless of where on the urinal you direct your flow. (Yes, ladies, it's not just about the aim!) If your legs are covered then those small splashes may not be noticeable, and they'll dry very quickly, but if you're wearing shorts then you can definitely feel those droplets hitting your legs.

Over the last decade or so, deodorising urinal blocks which dissolve are tending to be replaced by scented plastic urinal mats. With plastic mats though, more interesting designs are possible - some manufacturers have designed urinal mats with textured surfaces which attempt to prevent splashback. As a user of urinals, this seems like an obvious win for both the person peeing and the person who has to keep the place clean.

As an engineer, I would have thought that the design of structures which limit the effect of liquids splashing off a surface should be a well-researched subject. It has clear applications in civil engineering for roofs and other surfaces which catch rainfall, for instance, or dam spillways. And yet every urinal mat manufacturer seems to have different designs, with varying degrees of success.

Who researches the effect of splashing liquids? Is there a "best" design for this? And why is it that the multi-billion-dollar hygiene products industry appears unaware of whatever this "best" design is?

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    $\begingroup$ Definitely needs to spawn research that will get an IgNobel award! $\endgroup$ Jun 29 at 12:47
  • $\begingroup$ I assume you are quite tall. I want to see research on the worst case retroreflective urinal. $\endgroup$
    – DKNguyen
    Jun 29 at 13:31
  • $\begingroup$ @CarlWitthoft Quite possibly! It's primeIgNobel territory - urinals are just one of many places where controlling unwanted splashes of liquid would be a good thing, so it feels like it's one of those bizarre subjects which relates to real science/engineering progress. The fact I thought it up after a couple of pints in the pub is just a bonus. :) $\endgroup$
    – Graham
    Jun 29 at 15:38
  • $\begingroup$ @DKNguyen I'm only regular height (5'10", 178cm). The issue is that the backs of most urinals are sections of an oval both horizontally and vertically, so there's a natural "focal point" from both axes. $\endgroup$
    – Graham
    Jun 29 at 15:48
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    $\begingroup$ There has been some previous research: phys.org/news/… $\endgroup$
    – hazzey
    Jun 30 at 1:57

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I'm not sure about research but as a civil engineering fan I am guessing that designing a shape that diminishes kinetic energy of fluid flow would be a great start. An inverse cyclonic funnel would seem the obvious design choice. In addition, a spiral flow deceleration into a gradually increasing volume would reduce velocity. Just a thought...

Imagine the shape of water flowing down a plughole and imagine the inverse shape with "screwthread" spiralling around the outside. There is more to the design in my head but I'm not going to give that away for nothing.

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  • $\begingroup$ As a user, the problem is splashing. You have to have a serious "angle of attack" problem before the main flow hits the bowl, runs round it, and leaves on the other side. So it's not fluid flow exactly that's the problem. $\endgroup$
    – Graham
    Jun 30 at 10:14

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