I don't know who you are. I don't know what you want...

Before I saw his name printed on screen, I heard "Emmanuel Bernoulli", and I thought, "well, no wonder he's good at this stuff!!" :))

"Imagine it's a spreadsheet. It probably isn't..." Um, you've known Matt Parker for _how_ long?

I first heard you say "Vanoli" as "Bernoulli" and thought that was a suspiciously serendipitious name for an expert in fluid dynamics.

"All models are wrong. Some models are useful." -My professor on biological modeling

That is a worryingly good Liam Neeson impression.

In college I did some work with modeling wildlife populations. The rule that all models follow: you don't need to be accurate, just accurate enough to be useful. The useful metric is determined by running the model and comparing the result to historic/real world data. The more dynamic the system, the worse all models are at peering into the future.

Hey I've seen a lot of interesting videos from you. As a German with only basic English knowledge i can say: You are one of the best international artists on KZfaq. I love scientific content from a lot of KZfaq producers, but you manage to explain that I understand every word without a lot of pictures. Even though it's a foreign language for me. Because of your videos, I first dared to watch English content and now, after years, I no longer shy away from seeing every video in English. Thank you for the good content and the great pronunciation so that people who speak other languages ​​understand it well.

We used a teen's vape to visualise airflows around an external supermarket queue with a 90 degree bend in it - proving 50% of all possible wind directions can cause particulate transfer, and you're never too old to be barred from Waitrose. Old uk duffer here :)

Air curtains are underutilized. One of the easiest ways to isolate an area with very little construction.

Like comedian Pete Holmes says, the best way to do a good impression is to insist that it was good

I think the lattice model needs to use hexagons, because they are the bestagons.

So did anyone measure the actual airflow at sample points in the hospital to check the accuracy of the model?

The research institute i worked at had 2 corridors with rooms in between in a building, the clean corridor was slightly positive pressure, the room was neutral, the dirty corridor was negative, this meant air could only go from clean to dirty (clean and dirty related to diseases)

"Emmanuel Vanoli has a very particular set of skills... skills that he acquired using today's sponsor, Skillshare!"

Come to think of it... I've never seen Steve and Liam Neeson pictured together. Are we sure they're two different people?

So... fluid flow is basically like a big game of chess... where it's just Kings... but they can occupy the same square? sometimes. it's nothing like chess. This is a dreadful analogy

when working on the design of a hospital many years ago. there is a lot of thought put into which spaces are positively and negatively presurised. it's not as simple as spaces only having extraction. sany sensitive spaces like an operating theatre, ICU etc are positively presurised, so they dont get any nasties into them, things will tend to flow outwards, quarantine wards would be the reverse. the challenge is often getting spaces next to each other that work well like this, you cant have every room negatively pressurised, so it works really well to alternate them. The surprising thing here is having opening windows, you wont see that on many newer hospitals, precisely because it can screw a lot of this up.

As a game developer who makes a lot of particle systems, I learnt some cool new stuff watching this, so really appreciate the content.

Steve you can really explain complex topics to the common people. Thank you for making every topic interesting.

Hahaha man 0:41 exactly what I was thinking when you said "particular set of skills"

Fluid dynamics is the dark sorcery of engineering. Thank you for a peek into the grimoire!

Steve: "and they have a chance to be convected upwards, away from the people around you" Overhead fan: are you sure that's a good thing?

"The artist formerly known as particle" Is that what they call that guy with the peculiar skill set?

Fun fact: The lattice at 8:55 works like pixels in an image or monitor. This allows developers to abuse the existing drawing functions in graphics cards to simulate fluids & gases using the same technology used for Textures in 2D/3D graphics. Each new image you draw is essentially a new time step in the simulation. The colors of the R G B pixels can be (ab-)used to represent 3d coordinates for position or speed

5:43 Matt Parker Loves Tau lol

My dad was in a neg-pressure room in hospital which were positioned at the end of hallways. They replaced one window in each room with plywood and a circular vent connection and placed the portable A/C unit's exhaust air hose but used it only in fan mode to pump air outside so that room air would not seep back out into the hallway. It was a cheap and easy fix to protect the staff and limit spread.

*Steve:* _"How many lives could you save....."_ *My idiot brain for no reason:* _"Twelve."_

"It's actually really good." Classic phrase of an expert mimic.

"That will be the final word of the video; You saying that.", he says, stealing the final word.

Have been watching and liking your channel for years. This is the first time you are touching fields that are surprisingly close to my heart: I did tons of Lattice Boltzmann simulations coupled with Lagrangian Particle Tracking in my PhD thesis, and I now actually work for Dassault System (even though it is in the Electromagnetism department). You did an amazing job explaining these issues, and that is high praise from someone who worked "in the field"...

Before covid outbreak: How to put spoilers on my car. During covid outbreak: How to put spoilers on my mask.

I found it particularly amazing how probability in the fluid simulation represents real world fluid physics so well because it seems to reinforce the notion that comes from quantum physics that everything is at its core based on probability. We are random chance. Crazy to think about.

Hi Steve, I just wanted to thank you. I received and still receving a lot of kind messages from your community since this video! Thank you so much! If someone is interested, we published some papers in Scientic Report & Environment International on this very topic! Happy new year to you and your community & stay safe

The great thing about Steve Mould is the very diverse range of topics he covers and the fact that he somehow manages to explain complex science and engineering in a way that non-specialists can understand. My own field is electronics and I've watched a few of his videos on electronics and they're always spot on.

Steve has interest in all fields n thats what makes him my favourite.

When I saw the lattice and the particle with the 8 arrows, I immediately thought of Mine Sweeper.

How robust is the solution though? If someone has a fever, or turns an extra computer on, will it break everything?

I worked for a year as a tech for a company that installed special filters for clean rooms. After installation, we would balance the air thus so when entering an air lock between the dirty and clean spaces, the air would pull in and not escape from the dirty spaces. Fascinating physics and fun models

Steve mate, isn't it Das- oh as in Ren-oh? Delt a lot with Das-oh Falcon 20s in me time. Great vid.

Just a note: the most common CFD applications use the Finite Volume Method for discretization (and I'd say the great majority of simulations aren't even dealing with transient problems). The Lattice Bolzmann Method, though cool and powerful (and currently a little hyped) has quite a few limitations. At the end of the day CFD is still a decent guess, at best. It is quite useful and, if you use the correctly, can have a huge impact in several areas (assuming proper verification and validation of your models isn't skipped, which I'd say is a problem in most cases you see). And I make a living out of it, so I guess I can talk sh*t about it every now and then. But like all computer simulations EVER, people tend to think all colorful images are automatically correct, and oh boy they are not.

This type of air management becomes far more critical when viral load is factored into the equation. Managing airflow in a pandemic saves lives by reducing new infectios but more so in the severely infected by reducing viral load. Putting sick people together just increases deaths. No govts consider these dynamics & few humans think this deep so thanks for surfacing this content.

That simulation reminded me of the Ph D my old Industrial Placement Tutor was doing in the 80s, but he was trying to control fires in copper mines, to allow some attempt at evacuations. I don't know if he ever completed it. He was using a BBC B to preprocess the matrix work, then loading the data into the mainframe

Steve, your content just keeps getting better and better.

Steve, thanks for making fascinating content that I can use to engage my 8-year-old son in the sciences. Thanks for being a science communicator.

The Lattice Boltzmann Method bares some striking resemblance to quantum field theory.

I just realized that code I wrote at ~16 is exactly like the particle simulator shown here. Nothing like these videos was available to me then, so I _never_ put together that they were the same...and today those kinds of connections are _easy_. I hope this gets in front of more eyes.

Thank you Steve Mould for actaully disclousing you were paid by this company. Veratasium rubbed me the wrong way a few years ago because he did not mention (or did so at the very end) he was sponsored by a company. Glad you have some integrity.

What can we say about that Liam Neeson impression?

Particle McParticle Face, yes of course one of my favourite airborne particles 👍

5:42 I LOVE that particles 18 & 19 are called "Particle McParticle Face" & "The artist formally known as particle"

I just found your channel. Really enjoying it. I appreciate the way that you don't talk down your audience like some of the more saucy channels out there. One thing I notice that other channels do to help keep attention that you don't do id to keep changing the set throughout the video. Your background gets boring to look at after a while. Just filming in other rooms or your garden would help I think. Just my two cents

This is amazing! There’s just something about the physics of flow, whether it’s in the form of heat, liquids or gases etc. that’s just so satisfying. Is this reason enough to finally decide what region of physics I wish to pursue as a career? I think so

The man's a genius. He got a hospital to pay him for the expert advice of "Open the window"

I just realised why youtubers put their face on the thumbnail, as I've avoided this video for two weeks thinking it was something clickbaity or boring, until I realised it was from this channel and then realised it would be interesting and clicked immediately.

I dont know why I'm here and I have no idea what your talking about but, I'm completely invested in this video.

Wouldn't "closing the wrong window" mean it should have been open?

Very Cool! And a good description of how to make a simulation... must have taken hours of compute time to create those animations... This is such a complex thing to model, because you have so many confounders such as people moving in and around the building, they will open doors/windows at various times, outdoor weather patterns, maybe barometric pressure and temperature changing atmospheric density... all those things perturbing the air flow, but don't get me wrong... it's really good work, just super hard to nail down the real-world! and finally what if Air flow is not the only vector this virus spreads? The simulation can only account for what we assume are the relevant facts.

Content of this video I didn’t find as elegant and thrilling as Steve's other videos. The reason obviously is the constraints due to sponsorship. Still, I appreciate how STEVE cleverly MOULD it to maintain the quality. Limited numbers of sponsored videos are necessary for the financial stability of an independent youtuber and It's absolutely justified. I am glad Steve did not became like Johnny Harris (in his China video sponsored by WEF).

This might be my fave Steve Mould video... a lot of unexpected angles, intuitive, informative, relevant... just damn crackin' over all.

I've found the last part with the convection through your body heat very interesting. Is there less convection in the winter, when we are thermally isolated (clothing) then in the summer? Or is the difference in temperature high enough? And could it provide to the higher spreading of the common cold during winter times?

I'm jealous, your Liam is spotless, I was really Taken by it.

Great info! And as an FYI from a licensed building engineer, in the US, code bodies such as the International Mechanical Code set requirements for hospital HVAC design, such as pressurized buildings, all air returned from rooms in ducts, and patient rooms specifically being positively or negatively pressurized, amung many many other requirements.

Interesting video. Its amazing how Florence Nightingale came to the same conclusion, with regard to ventilating wards, without a computer :-) Her 'Notes on Hospitals' is well worth reading.

The Liam Neeson impression was sick!

That’s some serious Testing Adjusting and Balancing. Did he consult with T.A.B.B. to figure out all of the airflow specifics?

You should do a video on Warren Weaver's essay 'Science and Complexity' in which he (somewhat accurately) predicted our ability to model such systems as our computational power increased far beyond what they could imagine in the mid-20th century.

I really enjoyed this little slice of expertise from a field I am unlikely to ever be involved in. But even if I'm never directly involved in modeling airflow through a building, it could very well prove useful to understand how such complex dynamics are simplified into models that can be simulated, and therefore provide utility.

What would be immensely useful would be a system, from Dassault Systems, which allows people to roughly model their own building's (layout, people positions, and windows) with primitive shapes and locally run a simulation (on a gaming pc GPU) of how covid could spread and how it could be limited.

The artist formally known as particle 😂

I love your videos, Steve. Your way of explaining things makes things so incredibly easy to understand to me. Thank you so much for doing this!

I worked using heat introduction into structures for pest control for years and became quite good at determining beforehand what windows to open, which to close, which rooms or areas should have fans placed and in which direction, how to get the fastest and most even proliferation and distribution of the heat really. It was important to reach temperature in a relatively simultaneous time to avoid giving the insect time to leave the areas or hunker down beneath something that provided them higher insulation. It was not an intuitive process and I found it was remarkably difficult to teach. It's one thing to react to the temperature readouts throughout the structure and then, through trial and error, make adjustments to see what works, and another to do so beforehand. This video was an excellent explanation as to why and also what to look (or feel) for. Thank you!

Except, most hospitals that I have ever been to have a very slight negative pressure in all of the rooms, only the hallways and entries provide the air for the hospital....which is bio filtered.

01:00

Those animations of a person just SPEWING diseased air at another person is unintentionally hilarious.

I did particle simulation in the 1970s for electron plasma flow for CTR. It used 1.5D 2D and 3D modeling.

« Coronavirus » & « fake virus » in the same video. Finally someone is intelligent there...

When you are early you Don't know what to write...; )

My partner pointed out another corona virus airflow issue that she came across when converting a theatre in an area for covid patients (needed because they are running out of space in the normal places). Operating theatres run a positive-pressure air-conditioning system (air con pushes in clean air, dirty air goes out the door) which is the exact opposite of what you want in an infection control area as all it'll mean it's that,as soon as anyone opens a door, there's a risk that covid particles get pushed out the door - so they had to get all the air-conditioning turned off

Steve kept his word with Emmanuel. Those comments at the end, were indeed, the last words in the video. ;) As usual, both fascinating and informative... and applying science and models to real life.

5:41 Fenton!!!!

The hospitals have positive pressure systems to control air flow.

Thanks for this one, Steve! Lord it reminds me of statistical mechanics lectures when I was a chemistry under grad in Manchester in the 70s. We used to keep a score of how many blakcboards this guy filled in a lecture. the record was, I think, 11, closely packed with partial differential equations. And that was just ideal gases in closed containers. All to derive the gas equations. We did a bit on diffusion, which is toward the topic of this talk, which gave a feel for the subject and hinted at the complexity of making more simple models that adequately reflect reality. PS it might have been Dr Bullock (He pronounced it Boo 'lock)

What an incredible thumbnail. I have never been more intrigued by a video thumbnail

The Liam Neeson impression was epic🤣

Fenton!

On November 8, 2020 I suffered a STEMI heart attack (the worst kind) and survived (obviously) and was admitted to ICU during a peek in the Corona crisis. I have no idea what other patinas were on my ward, but I was alone in my room. The following day I was transferred to IMCU and the day after I was sent home. If memory serves, when my grandmother suffered a heart attack in 1978 I think she spent a week in ICU and 2 weeks after that in the hospital (when we kids could visit, we were not allowed to visit her in ICU). I do remember quite clearly thinking in the ambulance, "Oh no, they are taking me to where all the sickest Covid people are!" Luckily, it's a very good hospital, and I was not infected, but they were sure anxious to get me out of there. I do wonder if I would have spent more time if it were not for Covid.

Quite amazing. I hope things like this will get fully integrated into our future way of thinking about crowded spaces.

Thank you Tony the Taiwanese Turtle!

5:40 Matt Parker Loves Tau I see what you did there 😂

So underrated channel :o still after so many years and wonderful, informative, interesting and funny videos!

Reminds me of John Carmack talking about how a lot of simulation can boil down to the right amount of substep mixed with very basic rules.

"Matt Parker loves Tau" that very brave of you to say

There's so many variables, though... How do they know that the models correctly predict reality when there's so much abstraction? Do they track air flow experimentally to validate the results?

Nice video, Steve. There is certainly a whole world of information that was not covered in this video. There was no mention of boundary conditions in the simulation. As it looked like the hospital simulation didn't account for external building flow, it would be nice to know the boundary conditions used at all of the doors and windows. External building flow would have a significant impact on the low pressure areas around the building, and therefore which windows and doors pull/push air. Another significant aspect to this kind of science/engineer is validation, which I heard no mention of. Was there any validation work performed at the hospital? Without this, there's really no good way to know if the model is accurate. Garbage in = garbage out.

5:40 10 is hilarious! Love the Tom Scott reference!

"Buoyancy", what a beautiful word !

"matt parker loves tau"

Military Industrial Complex-sponsored videos ARE THE BEST!

I'm skeptical on the accuracy of a lot of these particle simulations. This video goes into a lot of specifics, but it really just scratches the surface. For example it doesn't appear that this simulation considers that people are breathing in. It seems like it's assuming that these sick patients are introducing more air (more fluid) into the system. However they are not, they are taking in just as much fluid as they are (forcefully) expelling. It's also not considering how doctors and nurses and patients are "stirring" this fluid as they walk around the hospital. It's not considering curtains or the central air system either. That said, I really like the closing of the video though where it explains wearing a mask keeps your particles close to you which limits their spread. (Kind of reflecting my skepticism of the macro model.) Something else I wonder about mask usage is even though much of the air your breath out is ejected through the sides of the mask, the path of the particles out the sides is quite turbulent and chaotic. Much of these particles will come in contact with the surface of the mask as well as your face (and beard if you have one). While there's a lot of experiments on the effectiveness of forcefully coughing through mask material, there doesn't seem to be much information on the more practical every day activity of casually breathing into a mask and the turbulent flow of particles around it. Considering how effective masks are in the aggregate I have to assume this is more effective than what most people assume it is; even with materials that are rated poorly when forcefully coughed through.