Comment by ZYbCRq22HbJ2y7 | Hacker News Reader

Comment by ZYbCRq22HbJ2y7 | Hacker News Reader

> We propose novel urinal designs that were generated by solving differential equations derived from the isogonal curve problem to ensure the urine stream impacts at or below this critical angle. Experiments validate that these designs can substantially reduce splashback to only 1.4% of the splash of a common contemporary commercial urinal. The widespread adoption of the urinal designs described in this work would result in considerable conservation of human resources, cost, cleaning chemicals, and water usage, rendering large-scale impacts on modern society by improving sustainability, hygiene, and accessibility.

https://academic.oup.com/pnasnexus/article/4/4/pgaf087/80987...

The experiments aren't in real world scenarios or with real urethrae excreting urine.

> A pseudo-urethra nozzle matching the internal geometry of a human urethra was used to “urinate” a controlled jet of dyed water onto urinals and the subsequent splash was caught on a large paper on the floor.

Anyone else here appreciate that this article appeared in a journal called 'PNAS Nexus'?

It's nut lost on me.

I'm glad you put your head out there and had the balls to say it.

> The experiments aren't in real world scenarios or with real urethrae excreting urine.

Physics is physics though. Urine is not a magical substance that can violate conservation of momentum or the law of gravity.

> Urine is not a magical substance

No, but people do have urine (specific gravity, consistency, etc), physical (flow rate differences, penile dimensional differences, urinary meatus differences, etc), and behavioral differences (unkempt urinary meatus, different holding patterns, shaking, shy bladder, etc) which would affect those ideal scenarios.

No, it wouldn't. This is just angles. Angles don't change. Gravity is stable and points roughly to the center of the planet. Viscosity changes won't change the angle of anything. That's the entire point.

From the supplementary materials:

> Importantly, the dynamic viscosity µ and surface tension γ do not change across our experiments, nor in the context of human urination.

From the paper:

> Splash generated from a jet or droplet train impinging on a flat surface is a complex phenomenon depending on many factors, including the impact speed (U), impinging angle (θ), dynamic viscosity (μ), density (ρ), diameter of the jet or droplet (D), surface tension (γ) of the liquid, ambient pressure (P), as well as the wettability, contact angle, and roughness of the surface. ... In the context of urination, most of these factors cannot be changed. However, the impinging angle can be controlled to reduce or eliminate splash.

I think you misread that. That all says the general case might be more complex, but this specific subset of the problem isn't.

I didn't misread anything. I was replying to your claim with statements, from the paper itself, that invalidate your statement.

The study used an experimental design that ignores those variables, because, they claim, they do not apply to human urination, without citing any resources.

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