Scientists at the University of Waterloo have determined the optimal design for a splash-free urinal: a tall, slender porcelain structure with curves reminiscent of a nautilus shell, playfully dubbed the “Nauti-loo.” That’s good news for men tired of having urine splash onto their pants and shoes—and for the poor souls who have to regularly clean up all the splatter. Bonus: It’s quite an aesthetically appealing design, giving this workhorse of the public restroom a touch of class.

“The idea originated exactly where you think it did,” Waterloo’s Zhao Pan told New Scientist. “I think most of us have been a little inattentive at our post and looked down to find we were wearing speckled pants. Nobody likes having pee everywhere, so why not just create a urinal where splatter is extremely unlikely?” His graduate student, Kaveeshan Thurairajah, presented the results of this research during last week’s American Physical Society (APS) meeting on fluid dynamics in Indianapolis.

It’s not the first time scientists have attempted to address this issue. Pan is a former graduate student of Tadd Truscott, a mechanical engineer who founded the so-called “Splash Lab” at Utah State University. In 2013, the Splash Lab (then at Brigham Young University) offered a few handy tips on how men could avoid staining their khaki pants with urine splashback while relieving themselves in restrooms. “Sitting on the toilet is the best technique, since there’s less distance for the pee to cover on its journey to the bowl,” I wrote previously at Gizmodo. “If you opt for the classic standing technique, the scientists advised standing as close to the urinal as possible, and trying to direct the stream at a downward angle toward the back of the urinal.”

For those who lack optimal anti-splash technique, another of Truscott’s graduate students, Randy Hurd, presented an optimal design for a splash-free urinal insert at the 2015 APS fluid dynamics meeting. There are three basic types of inserts. One employs absorbent cloth to keep splashing to a minimum; another uses a honeycomb structure—a raised layer (held up by little pillars) with holes—so urine droplets pass through but splash doesn’t come out; and a third type featuring an array of pillars. However, absorbent fabrics can’t absorb liquid quickly enough and soon become saturated, while the honeycomb and arrayed pillar structures don’t prevent urine pools from gradually forming.

Hurd and Truscott’s insert design drew inspiration from a type of super-absorbent moss (Syntrichia caninervis) that thrives in very dry climates and thus is very good at collecting and storing as much water as possible. And they found that the manmade material called “VantaBlack” mimicked the moss’ absorbent properties. They copied that material’s structure for their urinal insert and found it successfully blocked droplets of pee from escaping—effectively acting as a “urinal black hole.”

Nor have the ladies been left out of this scientific (ahem) pissing contest. Women, too, suffer from urine spillage, most notably when required to pee into a cup for medical testing purposes. In 2018, the Splash Lab conducted a series of experiments involving a model of an anatomically correct female urethra. (They used a soft polymer to model the labia.) The results inspired the (patented) design of the “Orchid,” a funnel-shaped attachment for urine cups that reduces spillage. The research could lead to devices that allow women to pee standing up, which would be a boon to women in the military or female academics working in the field.

According to Pan, the key to optimal splash-free urinal design is the angle at which the pee stream strikes the porcelain surface; get a small enough angle, and there won’t be any splashback. Instead, you get a smooth flow across the surface, preventing droplets from flying out. (And yes, there is a critical threshold at which the urine stream switches from splashing to flowing smoothly, because phase transitions are everywhere—even in our public restrooms.) It turns out that dogs have already figured out the optimal angle as they lift their legs to pee, and when Pan et al. modeled this on a computer, they pegged the optimal angle for humans at 30 degrees.

Pan and his team also conducted a series of experiments with dyed fluids sprayed in jets of varying speeds into a range of faux-urinal designs (see top photo) made of dense, epoxy-covered foam—including the standard commercial shape and a urinal similar to the one Marcel Duchamp used in his famous (and controversial) 1917 art installation “La Fontaine.” All produced varying degrees of splashback, which the scientists wiped up with paper towels. They weighed the wet towels and compared that to how much the paper towels weighed when dry to quantify the amount of splash. The more the wet towels weighed, the bigger the splashback.

The next step was to figure out a design that would offer that optimal urine stream angle for men across a wide range of heights. Instead of the usual shallow box shaped like a rectangle, they landed on the curved structure of the nautilus shell. They repeated the simulated urine stream experiments with the prototypes, et voila! They didn’t observe a single droplet splashing back. By comparison, the other urinal designs produced as much as 50 times more splashback. There was one round design with an opening shaped like a triangle that performed even better than the Nauti-loo in the experiments, but Pan et al. rejected it because it wouldn’t work across a wide range of heights.

https://arstechnica.com/?p=1900256