Simulation urinal

How CFD simulation can solve real everyday problems.

Created by Dipl.-Ing. (TU) Stefan Merkle

01/26/2023

[Translate to English:] Pissoir Merkle Simulation

The motivation

Sometimes people work simultaneously on a solution to the same problem. Thus, the telephone was invented four times, Philip Reis, Antonio Meucci, Elisha Gray in the end, however, Alexander Graham Bell in 1876 takes the credit, the patent was attributed to him.

Much like Rice, Meucci and Gray, I felt like someone snatched an important issue out from under my nose! But in order:

The topic of "urinals" has been on the Merkle CAE Solutions blog list for quite some time, as I have been asking myself for quite some time why the floor in the FCH men's restroom should only be walked on with rubber boots after the halftime break. Unfortunately, the floor under the urinals is clean only in Croatian 5-star campsites, because here a cleaning lady wipes felt after each visit. Otherwise, the problem runs like a wet trail through human history since the invention of the urinal in 1882.

Dogs seem to have a better handle on the problem than their masters, as long as they don't pee in the apartment. Maybe it's because of the skillfully set 30 degrees, maybe because they rarely pee on a tiled floor, but rather in the grass.

Bild_1_Albstueble_web — [Translate to English:] Abbildung 1: Die Motivation

Unfortunately, on November 22, 2022, the American Society beat us to the scientific solution to this problem at its 75th Annual Meeting of the Division of Fluid Dynamics with a presentation from the Indiana Convention Center, Indianapolis entitled: "Splash-free Urinals Inspired by Nautilus Shells and Dogs."

Geo magazine took up the topic immediately and also reported on it.

Besides nice scientific and not-so-scientific texts, however, there is one thing I have missed: a simulation video that shows the physics to the average Joe and helps him to do better without having to install a $10,000 - $16,000 urinal (that's how much some designer urinals cost, like the one in picture 2). Here, Merkle CAE Solutions is first to market to close that gap once and for all.

Bild_2_Dekadenz_web — Figure 2: The decadence

Since we are in prudish Germany, I now ask all sensitive readers to close the blog article immediately. Because in the following things are shown, which are not youth-friendly, although to my knowledge even small boys pee already standing.

I showed one of the first videos to my Skat brothers in advance. The majority of them called it tasteless. All the more an incentive for me, since I basically do not do what they think is right. Probably it is rather the bad conscience that makes the topic taboo for older gentlemen.

So please only read on and especially look if you have strong nerves. Unfortunately, I have had bad experiences in the past with my bra blog, where I was accused of showmanship and sexism. And I am very sensitive!

The model

The way to the video is through the simulation.

For a good simulation, you need reasonable geometry data and physical boundary conditions. In addition, I think the whole thing should look good. I find the men from the CAD tools rather unrealistic and boring, and you can't use the water jet in the air. So a penis definitely has to be used.

My son Julian, who works in game design, understands better than anyone else when I describe to him what I want him to do. His first geometry suggestion for the protagonist of our blog therefore met my ambitious requirements right away.

In order not to offend the older gentlemen with recriminations, we placed a younger to middle-aged man in front of the basin, who you can see has already had something to drink. However, we have disregarded swaying movements.

Since hair makes a simulation model unnecessarily complicated, we have given him a clean-shaven skull. For this, note the drape of the shirt and pants, a master of his craft was at work here 😊!

Bild_3_Randbedingungen_web — Figure 3: The boundary conditions

The boundary conditions

Volume flow and time course of the same can be found for the simulation in medical journals. Even if the appearance of our hero may seem suspicious, we have set normal conditions at the source. However, I can tell you one thing for sure: With age or reduced volume flows, the result on the ground does not get better.

The software

Carsten, who drew my attention to the article at the American Society, carried out initial flow investigations with Star CCM+ in order to work out influences such as position, volume flow and jet angle. We are on the same level of knowledge as the dog. 30 degrees to the surface is not bad.

The final tests were then performed by Oli in PreonLab.

The result

The simulation explains a lot, including the fact that our clothes probably get quite a bit, but the splashes on the floor are all too explainable.

Video 1: The simulation

Especially at the end of the small store it drips on the edge and no design in the world will save the floor if we stand too far away from the pool.

However, this does not mean that the design does not play an equally important role. If you see a need here and perhaps even build urinal basins, Merkle CAE Solutions will provide you with the necessary optimization basics. We could now provide those with well-founded, simulative arguments who categorically forbid standing peeing at the home toilet, but I believe that the CFD simulation shown here should open the eyes of notorious sit pee refusers and bring them to their knees.