081 - The origins of FDS with Kevin McGrattan

Transcript

WEBVTT 00:00:00.300 --> 00:00:05.551 <v Wojciech Wegrzynski>Hello, everybody and welcome to what seems to be a holiday special episode of the Fire Science Show. 00:00:05.915 --> 00:00:11.914 <v Wojciech Wegrzynski>And the episodes is definitely special because it seems to be one of the most requested interviews to be done on the podcast. 00:00:11.914 --> 00:00:13.141 <v Wojciech Wegrzynski>So I'm super happy. 00:00:13.141 --> 00:00:14.521 <v Wojciech Wegrzynski>I finally arranged that. 00:00:15.031 --> 00:00:16.800 <v Wojciech Wegrzynski>Today I have the pleasure to interview Dr. 00:00:16.830 --> 00:00:23.487 <v Wojciech Wegrzynski>Kevin McGrattan from NIST who's, better known as the creator of FDS fire dynamic simulator, a tool that. 00:00:23.710 --> 00:00:30.245 <v Wojciech Wegrzynski>I guess every fire engineering their career has used at least once That's my belief, maybe not true, but. 00:00:30.355 --> 00:00:32.375 <v Wojciech Wegrzynski>I think everyone, Of us has is. 00:00:32.405 --> 00:00:34.325 <v Wojciech Wegrzynski>And I, I guess I could just stop the. 00:00:34.354 --> 00:00:41.688 <v Wojciech Wegrzynski>The introduction at this point and just jump into the interview, but, uh, I still have some stuff to tell you before we do that. 00:00:42.228 --> 00:00:48.000 <v Wojciech Wegrzynski>So, I'm super excited, not only because of the fantastic guest I'm having today, but also. 00:00:48.000 --> 00:00:52.390 <v Wojciech Wegrzynski>Because the podcast has just breached another milestone that is 50,000. 00:00:52.420 --> 00:00:54.040 <v Wojciech Wegrzynski>Individual podcast listens. 00:00:54.161 --> 00:00:56.140 <v Wojciech Wegrzynski>Uh, thank you so much for, for being here. 00:00:56.170 --> 00:00:57.761 <v Wojciech Wegrzynski>Thank you so much for listening to the show. 00:00:58.180 --> 00:01:01.621 <v Wojciech Wegrzynski>I'm super happy to be a part of your professional life. 00:01:01.987 --> 00:01:07.207 <v Wojciech Wegrzynski>And I'm super grateful that you choose to spend your time with the Fire Science Show and. 00:01:07.420 --> 00:01:10.305 <v Wojciech Wegrzynski>It has been a challenging journey to reach this point. 00:01:10.335 --> 00:01:13.150 <v Wojciech Wegrzynski>But, today the podcast is better than ever before. 00:01:13.150 --> 00:01:13.905 <v Wojciech Wegrzynski>I have. 00:01:13.995 --> 00:01:15.974 <v Wojciech Wegrzynski>All the things set up in place. 00:01:15.974 --> 00:01:17.775 <v Wojciech Wegrzynski>All the automations set up in place. 00:01:18.007 --> 00:01:19.477 <v Wojciech Wegrzynski>All the routine going. 00:01:19.658 --> 00:01:22.658 <v Wojciech Wegrzynski>It's a pure pleasure to create a podcast nowadays. 00:01:23.257 --> 00:01:25.358 <v Wojciech Wegrzynski>I get to interview magnificent people. 00:01:25.358 --> 00:01:26.647 <v Wojciech Wegrzynski>I get to share with you. 00:01:26.647 --> 00:01:28.477 <v Wojciech Wegrzynski>I get to interact with my audience. 00:01:28.647 --> 00:01:31.257 <v Wojciech Wegrzynski>I'm talking to you through my newsletter. 00:01:31.257 --> 00:01:32.608 <v Wojciech Wegrzynski>If you haven't signed up for that. 00:01:33.087 --> 00:01:41.721 <v Wojciech Wegrzynski>You can through the websites and, I try to use more and more ways to listen to you more and produce the show that you want. 00:01:42.171 --> 00:01:45.891 <v Wojciech Wegrzynski>Uh, so I hope there's some good times ahead for the podcast. 00:01:45.921 --> 00:01:47.480 <v Wojciech Wegrzynski>I'm very sure about that. 00:01:47.990 --> 00:01:48.984 <v Wojciech Wegrzynski>And, yeah, Eleni. 00:01:49.045 --> 00:01:54.144 <v Wojciech Wegrzynski>Early next year, some more interesting and big updates coming your way. 00:01:54.564 --> 00:01:56.665 <v Wojciech Wegrzynski>Well for now, let's, let's focus on. 00:01:56.935 --> 00:01:58.045 <v Wojciech Wegrzynski>What's here now. 00:01:58.105 --> 00:02:02.843 <v Wojciech Wegrzynski>And, uh, what's here now is it's a great episode of the show where you will learn. 00:02:03.021 --> 00:02:09.264 <v Wojciech Wegrzynski>A lot of stuff where FDS came from, what was the rational behind building this. 00:02:09.294 --> 00:02:10.405 <v Wojciech Wegrzynski>A set of tools. 00:02:10.914 --> 00:02:14.365 <v Wojciech Wegrzynski>How did the landscape look when Kevin did build it up? 00:02:14.395 --> 00:02:16.375 <v Wojciech Wegrzynski>How did the team look up in the early days? 00:02:16.735 --> 00:02:18.655 <v Wojciech Wegrzynski>How did the solver look up in the early days? 00:02:18.715 --> 00:02:18.955 <v Wojciech Wegrzynski>Oh man. 00:02:19.014 --> 00:02:20.125 <v Wojciech Wegrzynski>It's so fantastic. 00:02:20.407 --> 00:02:21.937 <v Wojciech Wegrzynski>to discover the. 00:02:22.055 --> 00:02:24.514 <v Wojciech Wegrzynski>Fairly recent but very important. 00:02:24.604 --> 00:02:25.955 <v Wojciech Wegrzynski>Part of the history of. 00:02:26.185 --> 00:02:27.264 <v Wojciech Wegrzynski>Of the fire science. 00:02:27.294 --> 00:02:29.485 <v Wojciech Wegrzynski>And I would also like to encourage you. 00:02:30.085 --> 00:02:37.104 <v Wojciech Wegrzynski>If you have some great memories from the early days of FDS development, I don't know if you use version 1, 2, 3, 4, 5. 00:02:37.465 --> 00:02:41.064 <v Wojciech Wegrzynski>Or started with version six doesn't matter, share it with others. 00:02:41.365 --> 00:02:42.715 <v Wojciech Wegrzynski>Let's see how the. 00:02:42.902 --> 00:02:46.258 <v Wojciech Wegrzynski>path to using the more or less of this today look like. 00:02:46.288 --> 00:02:49.841 <v Wojciech Wegrzynski>And, uh, maybe we'll, have some fun sharing. 00:02:49.961 --> 00:02:53.155 <v Wojciech Wegrzynski>And collecting experiences the fire science, your audience. 00:02:53.724 --> 00:02:59.064 <v Wojciech Wegrzynski>And yeah, I won't take more of your time because you're waiting to, to hear Kevin and, you're right. 00:02:59.100 --> 00:03:03.661 <v Wojciech Wegrzynski>you should thank you for being here with me and now enjoy your episodes. 00:03:27.151 --> 00:03:27.872 <v Wojciech Wegrzynski>Hello everybody. 00:03:28.021 --> 00:03:31.771 <v Wojciech Wegrzynski>I'm here today with an episode everyone was asking for. 00:03:32.084 --> 00:03:33.913 <v Wojciech Wegrzynski>I have invited Dr. 00:03:33.919 --> 00:03:35.743 <v Wojciech Wegrzynski>Kevin McGrattan from NIST hey, Kevin. 00:03:35.770 --> 00:03:36.591 <v Kevin McGrattan>Hey, how are you? 00:03:37.183 --> 00:03:38.324 <v Wojciech Wegrzynski>I'm super good. 00:03:38.324 --> 00:03:39.204 <v Wojciech Wegrzynski>Thank you very much. 00:03:39.204 --> 00:03:42.790 <v Wojciech Wegrzynski>And we are gonna talk fire dynamic simulator development. 00:03:42.790 --> 00:03:45.191 <v Wojciech Wegrzynski>Man, that's a, that's a topic that's a. 00:03:45.626 --> 00:03:52.092 <v Wojciech Wegrzynski>many times I, I've said fds is among, maybe three best, uh, or most impactful things that, happen to fire science. 00:03:52.461 --> 00:04:04.419 <v Wojciech Wegrzynski>I, I would put it on par with SFPE handbook and, and Oxygen calorimetry I'm not sure , if that's where you would place it as well, but, there's not many things that would have such an impact over the, the whole discipline. 00:04:04.419 --> 00:04:11.349 <v Wojciech Wegrzynski>So first of all, Kevin, Thank you so much for building and managing that you and this team. 00:04:11.349 --> 00:04:12.969 <v Wojciech Wegrzynski>That is amazing effort. 00:04:13.192 --> 00:04:13.521 <v Kevin McGrattan>Yep. 00:04:14.062 --> 00:04:19.440 <v Kevin McGrattan>Well, it's interesting and fun to work every day and enjoy what you're doing. 00:04:19.507 --> 00:04:20.257 <v Kevin McGrattan>that's a plus. 00:04:20.502 --> 00:04:21.312 <v Wojciech Wegrzynski>Yeah, for sure. 00:04:21.475 --> 00:04:30.348 <v Wojciech Wegrzynski>That makes sense when you say that because I, don't know how you manage all of this looking through the issue tracker and stuff like that. 00:04:30.348 --> 00:04:32.389 <v Wojciech Wegrzynski>Uh, I, I don't know how much I would handle, 00:04:32.641 --> 00:04:37.803 <v Kevin McGrattan>Well, you know, one of the, fun parts about the job is that every day there's something new. 00:04:38.187 --> 00:04:46.057 <v Kevin McGrattan>and sometimes it's some, some issue having to do with, you know, computer science, some, some fire that occurred somewhere that's of interest. 00:04:46.363 --> 00:04:50.564 <v Kevin McGrattan>Some little bit of science that I know very little about, and I learn something about. 00:04:50.564 --> 00:04:58.697 <v Kevin McGrattan>I mean, every day there's something new and you just come in in the morning and you look at that issue tracker in the discussion group and, I didn't know that's 00:05:01.769 --> 00:05:02.608 <v Wojciech Wegrzynski>That's so cool. 00:05:02.809 --> 00:05:05.755 <v Wojciech Wegrzynski>So, uh, Kevin, as far as I know, you are a mathematician. 00:05:05.898 --> 00:05:06.098 <v Kevin McGrattan>am. 00:05:06.471 --> 00:05:10.331 <v Wojciech Wegrzynski>How, how does a mathematician end up working in a fire laboratory 00:05:10.466 --> 00:05:14.952 <v Kevin McGrattan>Uh, so I studied mathematics in graduate school at New York University. 00:05:15.163 --> 00:05:16.610 <v Kevin McGrattan>it was called the Courant Institute. 00:05:16.860 --> 00:05:31.000 <v Kevin McGrattan>And after I graduated, I found a post-doc position, a post-doctoral fellowship down here at NIST and my advisor was named, uh, Ron Rehm and he was in the applied math lab. 00:05:31.387 --> 00:05:39.536 <v Kevin McGrattan>So I came down and I found out that Ron Rehm was, uh, working with a fellow named Howard Baum and Howard Baum was doing, uh, model calculations. 00:05:39.930 --> 00:05:43.550 <v Kevin McGrattan>And so I started doing fire model calculations after all that was a postdoc. 00:05:44.247 --> 00:05:45.747 <v Kevin McGrattan>And I found it pretty interesting. 00:05:45.937 --> 00:05:51.906 <v Kevin McGrattan>when I was in graduate school, I worked on high speed flow, you know, flow at supersonic speeds, and then I came down here. 00:05:52.242 --> 00:05:55.975 <v Kevin McGrattan>Completely turned the tables and started looking at low speed flow. 00:05:55.975 --> 00:06:02.454 <v Kevin McGrattan>Believe it or not, fire, fire in the realm of speeds is, is relatively low speed, low mock number. 00:06:02.685 --> 00:06:03.175 <v Wojciech Wegrzynski>Nice. 00:06:03.334 --> 00:06:10.649 <v Kevin McGrattan>in fact, that's, what Ron and Howard really pioneered where this was this idea of the low mach number approximation of the narrative stokes equations. 00:06:10.819 --> 00:06:14.425 <v Kevin McGrattan>So, that was a refreshing change for me because up to that point in. 00:06:15.319 --> 00:06:21.069 <v Kevin McGrattan>My education, I've been looking at shockwaves and high speed flow and now something completely different. 00:06:21.560 --> 00:06:24.709 <v Kevin McGrattan>So, um, you know, that's how I, that's how I got into it. 00:06:24.759 --> 00:06:29.959 <v Kevin McGrattan>My other, connection to fire though is that my uncle's name is Bernie McCaffrey. 00:06:30.329 --> 00:06:35.663 <v Kevin McGrattan>So of you who are familiar with, fire science would, would recognize the name McCaffrey. 00:06:35.663 --> 00:06:39.029 <v Kevin McGrattan>Um, he did a lot of work, experimental work plume correlations. 00:06:39.029 --> 00:06:39.589 <v Kevin McGrattan>He develop. 00:06:39.740 --> 00:06:43.300 <v Kevin McGrattan>the bidirectional probe or one type of bidirectional probe. 00:06:43.713 --> 00:06:52.966 <v Kevin McGrattan>And just by coincidence, you know, he is my mother's brother, and I always, I always wondered, know, what was fire science? 00:06:52.966 --> 00:07:04.401 <v Kevin McGrattan>I would go to my grandmother's house when I was growing up and she would have a, there was a picture of him from one of these meetings and he won the, you know, Fire Scientist of the year award or something like that. 00:07:05.031 --> 00:07:06.562 <v Kevin McGrattan>. What is fire science? 00:07:07.312 --> 00:07:12.742 <v Kevin McGrattan>Well, I got a good education when I came down, uh, here to NIST after graduating from graduate school. 00:07:12.752 --> 00:07:13.901 <v Kevin McGrattan>So that's how I got started. 00:07:13.901 --> 00:07:19.291 <v Kevin McGrattan>There was no, no other reason other than that's just happened to be what my advisor was doing. 00:07:19.422 --> 00:07:19.771 <v Kevin McGrattan>So 00:07:20.007 --> 00:07:20.427 <v Wojciech Wegrzynski>Wow. 00:07:20.682 --> 00:07:21.851 <v Kevin McGrattan>I started doing it too. 00:07:22.016 --> 00:07:24.987 <v Wojciech Wegrzynski>I gu I, I guess we should be grateful then. 00:07:25.286 --> 00:07:28.346 <v Wojciech Wegrzynski>And institute, like the Courant number. 00:07:28.346 --> 00:07:28.747 <v Wojciech Wegrzynski>Huh? 00:07:28.966 --> 00:07:29.387 <v Kevin McGrattan>Yes. 00:07:29.543 --> 00:07:30.545 <v Kevin McGrattan>exactly, exactly. 00:07:33.204 --> 00:07:34.264 <v Wojciech Wegrzynski>interesting. 00:07:34.264 --> 00:07:44.540 <v Kevin McGrattan>Richard a German mathematician who fled the Nazis in the 1930s and he started up the program at New York University and, know, he and his other, cohorts. 00:07:44.540 --> 00:07:46.564 <v Kevin McGrattan>Yeah, we're famous for that car number. 00:07:46.564 --> 00:07:51.843 <v Kevin McGrattan>So that's, that's something that was, uh, tattooed onto my brain when I was in school. 00:07:51.843 --> 00:07:52.843 <v Kevin McGrattan>The importance of the. 00:07:53.603 --> 00:07:54.403 <v Wojciech Wegrzynski>Fantastic. 00:07:54.783 --> 00:08:03.757 <v Wojciech Wegrzynski>And now, now, when I was going through some files, I saw, uh, in one of them that the, the FDS was in development since 1978. 00:08:03.826 --> 00:08:10.240 <v Wojciech Wegrzynski>Well, I guess this would, uh, trace back all the way to these, uh, Low mach number Howards approximation times 00:08:10.774 --> 00:08:11.555 <v Kevin McGrattan>Yes, exactly. 00:08:12.437 --> 00:08:26.877 <v Wojciech Wegrzynski>became like reality that are going to build a three-dimensional model that's, uh, supposed to, to simulate fire environment because I should actually ask like, how, how did the playing field look at that point? 00:08:27.067 --> 00:08:29.521 <v Wojciech Wegrzynski>That's the, time of CFAST and stuff like that. 00:08:29.521 --> 00:08:29.800 <v Wojciech Wegrzynski>Right? 00:08:30.000 --> 00:08:30.461 <v Kevin McGrattan>Yeah. 00:08:30.461 --> 00:08:42.355 <v Kevin McGrattan>So what, what Ron and Howard were doing was, uh, was somewhat, ahead of its time and whole concept of the low MAch number and their, and their approximation that they made to the equation. 00:08:42.655 --> 00:08:54.745 <v Kevin McGrattan>That was absolutely necessary because if you wanna run these CFD calculations for long periods of time, I mean like when we do fire simulations, sometimes we're simulating hours worth of time. 00:08:54.900 --> 00:08:55.061 <v Wojciech Wegrzynski>Hmm. 00:08:55.282 --> 00:09:04.182 <v Kevin McGrattan>you've gotta make some approximations and not having to track these pressure waves they bounce around your domain is a huge advantage. 00:09:04.182 --> 00:09:05.341 <v Kevin McGrattan>That's what allows us. 00:09:06.162 --> 00:09:08.032 <v Kevin McGrattan>To run FDS relatively fast. 00:09:08.032 --> 00:09:18.755 <v Kevin McGrattan>Now, a lot of people do complain that it takes forever to run your FDS calculation, but if you actually look at other, CFD packages or other CFD techniques, it, it's actually relatively fast. 00:09:18.755 --> 00:09:23.316 <v Kevin McGrattan>What we're doing and, and a lot of it is, is due to the low MAch number approximation. 00:09:24.089 --> 00:09:28.326 <v Kevin McGrattan>Ron and Howard actually had a background in meteorology. 00:09:28.577 --> 00:09:41.989 <v Kevin McGrattan>. Um, Ron went to m mit, uh, the Massachusetts Institute of Technology, and Howard went to Harvard and they were working with, uh, some of the pioneers of, you know, meteorology and, um, meteorological CFD. 00:09:42.499 --> 00:09:47.745 <v Kevin McGrattan>So a lot of the techniques that went into, their model was borrowed. 00:09:48.466 --> 00:09:53.785 <v Kevin McGrattan>You know, the weather people, not the, not the people who were designing missiles and rockets. 00:09:53.785 --> 00:10:02.422 <v Kevin McGrattan>A lot of CFD at that time was all about, shooting intercontinental ballistic missiles, and landing men on the moon and high speed flow and all of that. 00:10:02.422 --> 00:10:07.269 <v Kevin McGrattan>But, you, and you need certain approximations in the equation to handle those kinds of flows. 00:10:07.269 --> 00:10:12.509 <v Kevin McGrattan>But, uh, Ron and Howard looked to the meteorologist and they said, you know, what do we have here? 00:10:12.509 --> 00:10:13.948 <v Kevin McGrattan>We have buoyant thermal. 00:10:14.807 --> 00:10:20.573 <v Kevin McGrattan>So not, we're not talking about, you know, rockets reentering the earth's atmosphere you know, Mach 10. 00:10:20.783 --> 00:10:26.134 <v Kevin McGrattan>Uh, we're talking about, weekly buoyant, know, thermal plumes, and that's, that's how the equation is developed. 00:10:26.458 --> 00:10:31.763 <v Wojciech Wegrzynski>And the most, uh, fundamental tool you would use at for modeling at that time would be the zone model, I guess. 00:10:31.971 --> 00:10:32.390 <v Kevin McGrattan>Yep. 00:10:32.850 --> 00:10:33.270 <v Kevin McGrattan>Yep. 00:10:33.331 --> 00:10:42.000 <v Wojciech Wegrzynski>so can you tell me about the moment where you started to think that, okay, uh, zone model is great, but it would be greater to, to go 3D dimensional and use 00:10:42.000 --> 00:10:42.421 <v Kevin McGrattan>Yes. 00:10:42.640 --> 00:10:43.081 <v Wojciech Wegrzynski>tools 00:10:43.500 --> 00:10:44.061 <v Kevin McGrattan>Right. 00:10:44.061 --> 00:10:54.063 <v Kevin McGrattan>So when I first started working with Ron and Howard in the early nineties, we developed a couple of different of software to handle different problems. 00:10:54.063 --> 00:11:02.566 <v Kevin McGrattan>So I worked with one group and they were looking at Big oil, plume fire, big oil fires that created, big plumes, in the outdoors. 00:11:02.566 --> 00:11:06.292 <v Kevin McGrattan>And we're talking about, tens of kilometers into the atmosphere. 00:11:06.412 --> 00:11:06.542 <v Wojciech Wegrzynski>Hmm. 00:11:06.629 --> 00:11:15.229 <v Kevin McGrattan>And then I was working with another group and we were doing these little tiny spread calculations of flames and outer space. 00:11:15.318 --> 00:11:21.749 <v Kevin McGrattan>So we had some money from NASA to look at the spread of fire on the space shuttle or the space station. 00:11:22.119 --> 00:11:25.749 <v Kevin McGrattan>So we were doing these tiny fundamental little flame spread calculations. 00:11:25.933 --> 00:11:31.048 <v Kevin McGrattan>then I was just doing some simple, calculations within simple compartments. 00:11:31.375 --> 00:11:34.966 <v Kevin McGrattan>So I had a whole series of different codes that I was working. 00:11:35.591 --> 00:11:41.543 <v Kevin McGrattan>And I was kind of slamming these different algorithms together for each one, for each different application. 00:11:41.543 --> 00:11:43.024 <v Kevin McGrattan>And it's, that's not unusual. 00:11:43.024 --> 00:11:50.520 <v Kevin McGrattan>And CFD oftentimes you find that someone takes, a bunch kind bits and pieces, core solvers, if you will, and. 00:11:51.225 --> 00:11:53.755 <v Kevin McGrattan>Puts them together for, for each application. 00:11:53.785 --> 00:12:04.682 <v Kevin McGrattan>Well, I found after a couple of years of this that I was getting stretched way too thin, so I had too many codes to keep care, take care of, and I needed to consolidate. 00:12:05.011 --> 00:12:11.761 <v Kevin McGrattan>So the idea was that, you know, I should be able to combine all these different bits and pieces into one. 00:12:12.090 --> 00:12:15.214 <v Kevin McGrattan>that can handle this range of different applications. 00:12:15.214 --> 00:12:24.254 <v Kevin McGrattan>And it's, that's a bit of a stretch going from these tiny little, know, flames and outer space to, you know, gigantic oil fires. 00:12:24.663 --> 00:12:29.836 <v Kevin McGrattan>But if you look at just the core solver, the Naver Stokes equation, it's common to all of these things. 00:12:30.116 --> 00:12:35.201 <v Kevin McGrattan>In fact, I mean, all CFD codes at the end of the day have some kind basic transport equations. 00:12:35.201 --> 00:12:37.441 <v Kevin McGrattan>And so I combine that all into. 00:12:37.871 --> 00:12:44.708 <v Kevin McGrattan>Code and then we started applying it to some applications that, were on our plate at the time. 00:12:44.889 --> 00:12:56.966 <v Kevin McGrattan>The, one of the first applications was we got involved with the, N F P A Research Foundation, and they were looking at this issue that involved sprinklers, vents, and draft curtains in, uh, warehouses. 00:12:57.456 --> 00:13:00.645 <v Kevin McGrattan>So that was, that was a bit of a controversy at that time. 00:13:00.861 --> 00:13:08.221 <v Kevin McGrattan>. in the nineties, at least here in the United States, we started to see all of these, what we call big box stores. 00:13:08.221 --> 00:13:13.101 <v Kevin McGrattan>I don't know what you call 'em in Europe, but uh, think like the IKEA warehouse, right? 00:13:13.101 --> 00:13:13.501 <v Kevin McGrattan>Okay. 00:13:13.501 --> 00:13:14.221 <v Kevin McGrattan>You know what that is? 00:13:14.336 --> 00:13:14.537 <v Wojciech Wegrzynski>Yeah. 00:13:14.936 --> 00:13:22.321 <v Kevin McGrattan>So that was somewhat new in the nineties, and the new concept there was that we were combining, what would you wanna call it? 00:13:22.321 --> 00:13:29.140 <v Kevin McGrattan>Like, industrial fire protection with, the type of life safety, fire protection you would find in a small store. 00:13:29.171 --> 00:13:40.701 <v Kevin McGrattan>Okay, so now you basically have people in a large industrial facility, and so there was on controversy as to, you know, how do we protect both property and life safety at the. 00:13:40.937 --> 00:13:46.496 <v Kevin McGrattan>Okay, so that's where this, this problem of, uh, sprinklers, vents, and draft curtains came up. 00:13:46.496 --> 00:13:49.341 <v Kevin McGrattan>Cause, in these stores, you would've sprinklers. 00:13:49.341 --> 00:13:54.943 <v Kevin McGrattan>But then they also wanted to keep the vents and the draft curtains, which was a sort of an earlier technology. 00:13:55.484 --> 00:14:01.823 <v Kevin McGrattan>And make a long story short, some people complain that these three, fire did not work well. 00:14:01.958 --> 00:14:06.225 <v Wojciech Wegrzynski>They, they still do, Kevin, they that that discussion has not ended. 00:14:06.791 --> 00:14:08.270 <v Kevin McGrattan>Right, right, right. 00:14:08.505 --> 00:14:11.818 <v Wojciech Wegrzynski>interesting that you say, um, it was multiple codes, applied together. 00:14:11.849 --> 00:14:16.176 <v Wojciech Wegrzynski>I, heard different versions of this story said by different people. 00:14:16.176 --> 00:14:18.975 <v Wojciech Wegrzynski>Like some people were saying, oh, there was this industrial. 00:14:19.895 --> 00:14:22.546 <v Wojciech Wegrzynski>Fire model, uh, that, that originated. 00:14:22.546 --> 00:14:27.025 <v Wojciech Wegrzynski>Someone was saying No, no, there was like ALOFT for, uh, external plumes. 00:14:27.025 --> 00:14:27.946 <v Wojciech Wegrzynski>They, they used ALOFT 00:14:27.971 --> 00:14:28.390 <v Kevin McGrattan>Yep. 00:14:28.846 --> 00:14:38.259 <v Wojciech Wegrzynski>And I, I, I see all of them have, bits of truth and, the truth, truth is that, uh, you are done with this with writing, model for every application, 00:14:38.744 --> 00:14:38.864 <v Kevin McGrattan>right. 00:14:38.864 --> 00:14:39.583 <v Kevin McGrattan>That's right. 00:14:39.583 --> 00:14:45.356 <v Kevin McGrattan>We had, there was something called Aloft, which we used for these big oil plume fires. 00:14:45.417 --> 00:14:50.037 <v Kevin McGrattan>And um, then there was something called the industrial fire simulator or ifs. 00:14:50.245 --> 00:14:58.532 <v Kevin McGrattan>and that's just typical of the way things were, where you would put together a special code for each special application. 00:14:58.532 --> 00:15:00.796 <v Kevin McGrattan>But it's a nightmare in terms of maintenance. 00:15:00.826 --> 00:15:02.606 <v Kevin McGrattan>I mean, it's just, it's impossible. 00:15:02.655 --> 00:15:08.686 <v Kevin McGrattan>So I just combined everything into, into fds and it's been that way ever since. 00:15:08.686 --> 00:15:12.605 <v Kevin McGrattan>And it makes my life a lot easier to just try to keep track of one code 00:15:12.841 --> 00:15:13.331 <v Wojciech Wegrzynski>It's, 00:15:13.405 --> 00:15:14.046 <v Kevin McGrattan>not three, or. 00:15:14.350 --> 00:15:17.140 <v Wojciech Wegrzynski>it, it sounds like the best investment in your life, I guess 00:15:17.620 --> 00:15:18.041 <v Kevin McGrattan>Yes. 00:15:18.157 --> 00:15:18.636 <v Kevin McGrattan>right. 00:15:18.657 --> 00:15:30.620 <v Kevin McGrattan>But there's also something, there's a bit of like, sort of academic politics involved, and that is oftentimes people rename or rebrand research that they're doing, because then it sounds like it's something new. 00:15:30.880 --> 00:15:37.900 <v Kevin McGrattan>And, and even today, sometimes, you know, when I talk to my managers, they say, you know, this FDS thing, it's been great, but what's next? 00:15:37.900 --> 00:15:39.100 <v Kevin McGrattan>What are we doing next? 00:15:39.807 --> 00:15:41.417 <v Kevin McGrattan>I know we're just trying to make it better. 00:15:41.937 --> 00:15:44.017 <v Kevin McGrattan>We're not necessarily gonna rebrand it. 00:15:44.547 --> 00:15:45.027 <v Wojciech Wegrzynski>like iPhone. 00:15:45.027 --> 00:15:48.187 <v Wojciech Wegrzynski>You can make FDS 6S now or, or something. 00:15:49.366 --> 00:15:54.780 <v Wojciech Wegrzynski>now I need to ask you like, When you were merging these models, you must have done some choices. 00:15:55.721 --> 00:16:02.073 <v Wojciech Wegrzynski>And, now, 20 something years later, are all, uh, doomed with, uh, with your choices. 00:16:02.124 --> 00:16:07.374 <v Wojciech Wegrzynski>So I, would love to, I would love to understand, especially the, the first and most, impactful one, I guess. 00:16:07.384 --> 00:16:09.269 <v Wojciech Wegrzynski>Uh, LES model. 00:16:09.438 --> 00:16:21.899 <v Wojciech Wegrzynski>So, uh, for the listeners, f d s, uh, works turbulence model, the way, how you model the turbulent, part of the flow of, of the air called Large Eddy Simulation, uh, Smagorinsky version of it. 00:16:23.285 --> 00:16:35.042 <v Wojciech Wegrzynski>would say, um, even today, If I, if I was making a proposal to write a new code and said, and I would like to make it LES code may, maybe today it would not be very odd, but 00:16:35.167 --> 00:16:35.586 <v Kevin McGrattan>Yes. 00:16:35.586 --> 00:16:35.947 <v Kevin McGrattan>Right. 00:16:36.201 --> 00:16:39.121 <v Wojciech Wegrzynski>some years ago, I guess that was, that was a bold decision. 00:16:39.121 --> 00:16:39.522 <v Wojciech Wegrzynski>Like, 00:16:40.807 --> 00:16:49.533 <v Kevin McGrattan>Right, Well, well remember I said that we had our start in meteorology and Smagorinsky was a meteorologist, I believe. 00:16:49.822 --> 00:16:52.551 <v Kevin McGrattan>I think Google search on it, but I believe. 00:16:53.275 --> 00:16:56.946 <v Kevin McGrattan>Gregsky was, was developing algorithms from meteorological models. 00:16:57.316 --> 00:16:58.905 <v Kevin McGrattan>So it was natural for us. 00:16:59.525 --> 00:17:04.991 <v Kevin McGrattan>And the other thing too was that we, we did some, have some experience with, RANS codes. 00:17:05.041 --> 00:17:12.306 <v Kevin McGrattan>Uh, Reynolds averaged Navor Stokes, but I found Rand's codes to be so uninteresting. 00:17:12.756 --> 00:17:33.021 <v Kevin McGrattan>So for example, , When, when we do a fire simulation and you see the, the buoyant plume and you see the smoke behaving the way smoke really behaves, and if you've had experience working in a lab as I have had, it gives me great satisfaction to see on the computer screen exactly what I see in the laboratory, or at least something fairly close to it. 00:17:33.561 --> 00:17:37.541 <v Kevin McGrattan>But when you run a a rans model, I mean, you may get a reason. 00:17:37.830 --> 00:17:39.121 <v Kevin McGrattan>Result or answer. 00:17:39.121 --> 00:17:47.780 <v Kevin McGrattan>But I just find it to be so unsatisfying to see that, you know, time average portrayal of the of the smoke movement. 00:17:48.401 --> 00:17:51.446 <v Kevin McGrattan>And so for me it was more of academic interest. 00:17:51.457 --> 00:17:56.086 <v Kevin McGrattan>We weren't, at that time when we chose LES, we were thinking that this was just gonna be an academic exercise. 00:17:56.086 --> 00:18:00.797 <v Kevin McGrattan>We didn't realize that people were gonna actually use it to shopping mall. 00:18:01.696 --> 00:18:06.136 <v Kevin McGrattan>thought we were just gonna, run calculations, go to meetings, you know, live the academic life. 00:18:06.473 --> 00:18:17.696 <v Kevin McGrattan>Um, and it wasn't until, you know, around the year 2000 or approaching the year 2000, I started to give the code out just to some, you know, friends in the area who wanted to play around with it. 00:18:18.156 --> 00:18:24.497 <v Kevin McGrattan>And I was startled when they came back with these, you know, fairly sophisticated. 00:18:24.692 --> 00:18:26.332 <v Kevin McGrattan>, renditions of buildings. 00:18:26.332 --> 00:18:32.251 <v Kevin McGrattan>Some of these buildings were in the Washington DC area and I thought, wow, I mean, this is fantastic. 00:18:32.251 --> 00:18:37.051 <v Kevin McGrattan>And I found that the engineers who were doing these calculations, they really enjoyed it. 00:18:37.205 --> 00:18:39.655 <v Kevin McGrattan>I mean, almost like a little kid playing with Lego Box. 00:18:39.766 --> 00:18:41.135 <v Kevin McGrattan>I mean, we all enjoyed that. 00:18:41.135 --> 00:18:47.336 <v Kevin McGrattan>We still do building up, you know, complicated geometries and then looking at the smoke move. 00:18:47.959 --> 00:18:52.776 <v Kevin McGrattan>I just found it was interesting and I think that the engineers who were doing the work also found it interesting. 00:18:53.066 --> 00:19:02.528 <v Kevin McGrattan>so don't discount that, you know, work should be fun, . And I know, and I know it's, it's, it's somewhat difficult to say that, you know, fire is not always fun. 00:19:02.528 --> 00:19:04.209 <v Kevin McGrattan>Sometimes fire is not very fun. 00:19:04.923 --> 00:19:14.983 <v Kevin McGrattan>You know, setting up these calculations, it's challenging, it's fun, it's rewarding, and I think that, you know, I was having a good time and I think that the engineers who were using the model were having a good time. 00:19:14.983 --> 00:19:21.584 <v Kevin McGrattan>I thought, you know, if they're interested in it and they put that extra bit of effort into doing these calculations, why not? 00:19:21.808 --> 00:19:22.229 <v Wojciech Wegrzynski>Now, 00:19:22.384 --> 00:19:23.846 <v Kevin McGrattan>mean, that's gonna advance the field. 00:19:23.986 --> 00:19:29.311 <v Wojciech Wegrzynski>I've read in one of your papers or maybe in an interview with you that, you chose LES because it was interesting. 00:19:29.311 --> 00:19:33.231 <v Wojciech Wegrzynski>So again, this one is, this one is, is confirmed. 00:19:33.342 --> 00:19:33.832 <v Wojciech Wegrzynski>It's 00:19:34.047 --> 00:19:34.606 <v Kevin McGrattan>Right, 00:19:34.791 --> 00:19:35.951 <v Wojciech Wegrzynski>is like MythBusters in here. 00:19:36.406 --> 00:19:37.287 <v Kevin McGrattan>right, right. 00:19:37.317 --> 00:19:48.007 <v Kevin McGrattan>Well, I mean, could, I could spend an hour arguing as to why l e s is technically superior and we can go into turbulence models and closure methods and all of that. 00:19:48.386 --> 00:19:55.523 <v Kevin McGrattan>But, you know, for me, at the end of the day, I just was much more satisfied running these, you know, realistic looking. 00:19:55.724 --> 00:20:05.372 <v Kevin McGrattan>fire simulations, and then when we, you know, when we discovered that we could actually do these calculations on desktop, personal computers, I mean, that was a win-win. 00:20:05.372 --> 00:20:11.036 <v Kevin McGrattan>We said, all right, you know, if we can do l a s on a manageable platform, why not do l a s. 00:20:11.645 --> 00:20:23.112 <v Wojciech Wegrzynski>I find it also fascinating that you've built this as a, a tool for science, not imagining the, um, impact it would have over the engineering discipline that you were discovering that as the tool was, was given. 00:20:23.112 --> 00:20:26.432 <v Wojciech Wegrzynski>That that must have been very rewarding to see how. 00:20:26.696 --> 00:20:33.596 <v Wojciech Wegrzynski>Creatively people use it maybe sometimes even too creatively but, reach that point for sure. 00:20:33.676 --> 00:20:34.076 <v Kevin McGrattan>right. 00:20:34.076 --> 00:20:41.756 <v Kevin McGrattan>But, again, that's part of the fund because you develop a technology and then you see that technology grow in ways you never imagined. 00:20:41.784 --> 00:20:49.183 <v Kevin McGrattan>I mean, that could be said of so many things that have happened in the past 30 years with, the boom and computing and information technology. 00:20:49.213 --> 00:20:53.263 <v Kevin McGrattan>I mean, a lot of the things that we take for granted were develop. 00:20:53.421 --> 00:20:59.300 <v Kevin McGrattan>know, just out of the blue and the developers themselves never had a clue that it would take off the way it. 00:20:59.540 --> 00:21:05.590 <v Wojciech Wegrzynski>so if, if, we think fds version one, what was it like compared to the modern fds? 00:21:05.941 --> 00:21:12.453 <v Wojciech Wegrzynski>Like, what are the things that we would take for granted that, they were not even, uh, in, in inception at that point? 00:21:12.453 --> 00:21:13.894 <v Wojciech Wegrzynski>Like, how, how, how, how did it look? 00:21:14.193 --> 00:21:16.814 <v Wojciech Wegrzynski>Did it, had he transferred to the surfaces? 00:21:16.864 --> 00:21:17.213 <v Wojciech Wegrzynski>Uh, 00:21:17.709 --> 00:21:18.635 <v Kevin McGrattan>it, it really didn't. 00:21:18.635 --> 00:21:22.115 <v Kevin McGrattan>So it, one of the things that FDS one lack was radiation. 00:21:22.596 --> 00:21:33.338 <v Kevin McGrattan>we had a very, very crude rendition of radiation and where we, we literally assumed that the fire were, were just a bunch of burning, like little particles, little burning ping pong balls. 00:21:33.759 --> 00:21:38.298 <v Kevin McGrattan>And each ping pong ball would radiate a certain amount of energy in all directions. 00:21:38.298 --> 00:21:46.638 <v Kevin McGrattan>And we just used a, like a simple, , Montecarlo type algorithm that just randomly shot the energy out in different directions. 00:21:47.179 --> 00:21:54.971 <v Kevin McGrattan>And at about that time when we were developing fds one, Simo Hostikka from Finland came to visit us for a year. 00:21:55.343 --> 00:22:01.568 <v Kevin McGrattan>And remember when I, when I first met him and he said, you gotta put in a new radiation solver. 00:22:01.568 --> 00:22:02.689 <v Kevin McGrattan>This one you have is terrible. 00:22:03.876 --> 00:22:10.455 <v Kevin McGrattan>So I said, okay, cmo, if you think it's so terrible, then you put a new one in it, come at it. 00:22:10.643 --> 00:22:15.662 <v Kevin McGrattan>and I'll tell you, within a month he had essentially what is still in the code today. 00:22:15.662 --> 00:22:21.409 <v Kevin McGrattan>I mean, he, he developed something within a month, um, that is still a workhorse. 00:22:21.645 --> 00:22:24.846 <v Kevin McGrattan>and quite frankly, we've never really improved on it. 00:22:24.846 --> 00:22:25.566 <v Kevin McGrattan>It's, it's that, 00:22:25.625 --> 00:22:26.115 <v Wojciech Wegrzynski>Yeah. 00:22:26.276 --> 00:22:29.612 <v Kevin McGrattan>and that's where FDS one went, to FDS two and so forth. 00:22:29.872 --> 00:22:31.592 <v Wojciech Wegrzynski>Uh, next combustion model. 00:22:31.781 --> 00:22:32.271 <v Wojciech Wegrzynski>Like 00:22:32.521 --> 00:22:33.011 <v Kevin McGrattan>Yeah, 00:22:33.311 --> 00:22:35.592 <v Wojciech Wegrzynski>at the beginning or also you used some clever approximations. 00:22:35.711 --> 00:22:37.301 <v Kevin McGrattan>no, it didn't really have combustion. 00:22:37.301 --> 00:22:50.038 <v Kevin McGrattan>All it, all it had were, again, these ping pong balls each ping pong ball you could think of as representing a certain amount of fuel and the energy would be deposited Onto the grid, in a certain amount of time. 00:22:50.808 --> 00:23:01.818 <v Kevin McGrattan>So in some sense the, the most basic type of, you know, aian model where we just, we had a, a, a burnout time for these particles that was just fixed. 00:23:01.818 --> 00:23:04.338 <v Kevin McGrattan>So it wasn't tied to any turbulence or anything else. 00:23:04.338 --> 00:23:06.538 <v Kevin McGrattan>It just wants the ping pong ball. 00:23:06.538 --> 00:23:11.346 <v Kevin McGrattan>And in half a second, say, um, its energy is deposited onto the. 00:23:11.467 --> 00:23:11.916 <v Wojciech Wegrzynski>Okay. 00:23:11.979 --> 00:23:16.459 <v Kevin McGrattan>and we adjusted that burning time based on the flame heights. 00:23:16.459 --> 00:23:20.798 <v Kevin McGrattan>So if, if the fire was too short, then we just extended time 00:23:20.848 --> 00:23:21.338 <v Wojciech Wegrzynski>Okay, 00:23:21.548 --> 00:23:22.238 <v Kevin McGrattan>a little taller. 00:23:22.251 --> 00:23:24.642 <v Kevin McGrattan>So there really was no combustion in it at all. 00:23:24.642 --> 00:23:29.909 <v Kevin McGrattan>It was just really a way to, to deposit a fixed amount of energy onto the grid. 00:23:29.919 --> 00:23:30.338 <v Wojciech Wegrzynski>but. 00:23:30.548 --> 00:23:35.471 <v Kevin McGrattan>mean, it's, it's almost like what you, what you do now, sometimes you have these volumetric. 00:23:35.471 --> 00:23:43.273 <v Kevin McGrattan>Heat sources where the fire is really just like a cone and you deposit the energy in a, like a shape on your grid. 00:23:43.273 --> 00:23:45.926 <v Kevin McGrattan>It was about that level of complexity. 00:23:46.384 --> 00:23:49.844 <v Wojciech Wegrzynski>so at that point, it was mostly the, the flow solver. 00:23:50.013 --> 00:23:52.884 <v Wojciech Wegrzynski>So you, you had the flow, you had the turbulent flow with l e s, 00:23:53.124 --> 00:23:53.733 <v Kevin McGrattan>Mm-hmm. 00:23:54.023 --> 00:24:02.243 <v Wojciech Wegrzynski>you, you have created this ping pong, ping pong balls to basically release the energy to capture the, the buoy flows and, and 00:24:02.409 --> 00:24:02.808 <v Kevin McGrattan>Mm-hmm. 00:24:03.263 --> 00:24:06.003 <v Wojciech Wegrzynski>you just used the, the mixture fraction model. 00:24:06.147 --> 00:24:10.832 <v Kevin McGrattan>that didn't, that, that came later fds one, there was no mixture fraction. 00:24:11.192 --> 00:24:18.301 <v Kevin McGrattan>we just used these ping pong balls to visualize the smoke, and so also that's when smoke view was born. 00:24:18.612 --> 00:24:19.102 <v Wojciech Wegrzynski>Okay. 00:24:19.432 --> 00:24:26.165 <v Kevin McGrattan>Smoke View was originally just a simple visualization tool that allowed us to visualize the particles. 00:24:26.445 --> 00:24:26.935 <v Wojciech Wegrzynski>Okay. 00:24:27.296 --> 00:24:32.526 <v Kevin McGrattan>So the particles were colored orange when they were burning and they were colored black when they weren't. 00:24:32.665 --> 00:24:37.903 <v Kevin McGrattan>And so , so you have the fire and then you have the smoke, that was the original smoke view. 00:24:38.125 --> 00:24:40.672 <v Kevin McGrattan>And then, Glenn Forney who, who develop. 00:24:41.442 --> 00:24:47.672 <v Kevin McGrattan>Um, you know, as time went on, he, he started studying all sorts of other techniques to visualize the smoke. 00:24:47.862 --> 00:24:52.031 <v Kevin McGrattan>I mean, a lot of his inspiration comes from the movies. 00:24:52.241 --> 00:24:59.006 <v Kevin McGrattan>So he reads, he reads a lot of books about how, computer graphics are used in, in the film industry. 00:24:59.306 --> 00:25:07.471 <v Kevin McGrattan>And so some of what you see in smokeview now are simple renditions of what, the Pixar people are doing. 00:25:07.589 --> 00:25:16.506 <v Wojciech Wegrzynski>you, you have, I must say fairly advanced camera operations within smoeview that is misaligned with, uh, with the needs. 00:25:16.506 --> 00:25:22.705 <v Wojciech Wegrzynski>Uh, I guess, uh, that explains why, if, if someone with, uh, would love to film in this stream made it, that it makes actually. 00:25:23.963 --> 00:25:25.703 <v Wojciech Wegrzynski>and also not no heat transfer. 00:25:25.703 --> 00:25:25.983 <v Wojciech Wegrzynski>Okay. 00:25:25.983 --> 00:25:27.784 <v Wojciech Wegrzynski>You didn't have heat transfer to solids. 00:25:28.250 --> 00:25:30.440 <v Wojciech Wegrzynski>um, okay, so, so you had the solver. 00:25:30.440 --> 00:25:33.960 <v Wojciech Wegrzynski>How did you choose, like, okay, now, now let's add the heat transfer. 00:25:33.960 --> 00:25:35.640 <v Wojciech Wegrzynski>Now let's add the combustion. 00:25:35.779 --> 00:25:42.400 <v Wojciech Wegrzynski>Was it because of certain cases or was there, um, like a grant plan for the next, uh, 10 years? 00:25:42.775 --> 00:25:43.805 <v Kevin McGrattan>Uh, no, there's not. 00:25:44.384 --> 00:25:48.565 <v Kevin McGrattan>I'd like, I'd love to think that there was a grand plan, but it usually came case by case. 00:25:49.301 --> 00:25:55.382 <v Kevin McGrattan>and so the heat transfer came about because, you know, again, our original problem with these. 00:25:55.452 --> 00:25:57.074 <v Kevin McGrattan>Storage fires, right? 00:25:57.074 --> 00:26:13.114 <v Kevin McGrattan>So you've got boxes piled up in a warehouse, and we would start the fire at the base of the boxes, and obviously we needed to heat up the surfaces of those boxes until we got to some, you know, quote unquote ignition temperature, and then the boxes would start burning. 00:26:13.163 --> 00:26:22.594 <v Kevin McGrattan>So in order to do this sort of simple fire spread, we had to have, you know, a relatively simple, you know, heat transfer algorithm into the box. 00:26:22.939 --> 00:26:26.333 <v Wojciech Wegrzynski>and combustion, like, when did you figure out, okay, I, I want to see the flames 00:26:26.333 --> 00:26:26.805 <v Kevin McGrattan>Yeah. 00:26:26.805 --> 00:26:30.444 <v Kevin McGrattan>Yeah, so, so combustion came about like an FDS two. 00:26:30.555 --> 00:26:32.525 <v Kevin McGrattan>I started working with Jason Floyd. 00:26:32.525 --> 00:26:37.729 <v Kevin McGrattan>So Jason Floyd was my postdoc, and he had graduated from the University of Maryland. 00:26:38.528 --> 00:26:50.261 <v Kevin McGrattan>You know, with a PhD in, I think it's nuclear engineering, but, he's a clever guy and he, he figured out how fire works and he was doing work as a postdoc, looking at unventilated fires. 00:26:50.922 --> 00:27:00.949 <v Kevin McGrattan>And so we knew that in order to do unventilated fires, we couldn't just continue, you know, with this burning ping pong ball, idea that wasn't gonna do it. 00:27:01.648 --> 00:27:15.648 <v Kevin McGrattan>So, so Jason and I developed the, you know, the mixture fraction approach and a, as sort of a first way to look at combustion more realistically, and also to look at combustion in an unventilated environment. 00:27:15.648 --> 00:27:22.261 <v Kevin McGrattan>Now we, have to then, you know, evolve beyond the mixture fraction approach, to what we do today. 00:27:22.632 --> 00:27:29.311 <v Kevin McGrattan>Which is where we have these so-called lump species, you know, fuel plus air goes to products. 00:27:29.769 --> 00:27:33.509 <v Kevin McGrattan>but FDS two sort of introduced the concept of the mixture fraction. 00:27:33.509 --> 00:27:36.028 <v Kevin McGrattan>And then, you know, Jason's been working with us ever since. 00:27:36.028 --> 00:27:40.959 <v Kevin McGrattan>And you know, over time he has evolved, the combustion model to what it is today. 00:27:41.114 --> 00:27:42.423 <v Wojciech Wegrzynski>Uh, j Jason's a star. 00:27:42.423 --> 00:27:43.663 <v Wojciech Wegrzynski>He, he was also at the podcast 00:27:43.777 --> 00:27:44.267 <v Kevin McGrattan>Yeah. 00:27:44.267 --> 00:27:44.586 <v Kevin McGrattan>Yeah. 00:27:44.586 --> 00:27:45.565 <v Kevin McGrattan>I listen to podcast 00:27:45.906 --> 00:27:46.586 <v Wojciech Wegrzynski>the best to Jason. 00:27:47.589 --> 00:27:52.910 <v Wojciech Wegrzynski>so, okay, now you have mixture, fraction approach and, capability to do under ventilated fires. 00:27:52.910 --> 00:27:58.344 <v Wojciech Wegrzynski>I think now this point, F Ds gains, that highly. 00:27:59.029 --> 00:28:09.888 <v Wojciech Wegrzynski>Go above what we could do as, uh, as a fire modelers like, balances of heat, uh, small compartment fires, stuff like that you could do with CFAs. 00:28:10.308 --> 00:28:15.311 <v Wojciech Wegrzynski>But once you solve, oxygen and you know how much oxygen is in your room, you 00:28:15.531 --> 00:28:16.092 <v Kevin McGrattan>Right, 00:28:16.392 --> 00:28:24.625 <v Wojciech Wegrzynski>next to your doors and how much is in the back of the room, you create very like environment in your compartment. 00:28:25.241 --> 00:28:25.662 <v Kevin McGrattan>Yes. 00:28:25.814 --> 00:28:31.413 <v Wojciech Wegrzynski>and this is when you start to see inside the fire, like no one ever, uh, done. 00:28:31.784 --> 00:28:36.576 <v Wojciech Wegrzynski>So, so, when did you start like doing, I dunno, back drafts or, or smoke explosions with it? 00:28:36.576 --> 00:28:40.656 <v Wojciech Wegrzynski>I guess, I guess you, you probably immediately went for that when you gained these capabilities. 00:28:41.914 --> 00:28:42.375 <v Kevin McGrattan>Yeah. 00:28:42.429 --> 00:28:47.755 <v Kevin McGrattan>well, I think we were, again, Jason was doing his, post-doc, uh, research. 00:28:48.182 --> 00:28:54.404 <v Kevin McGrattan>down at Virginia Tech and he was working with another fellow named Chris Wieczorek who's now at Factory Mutual. 00:28:54.691 --> 00:29:05.964 <v Kevin McGrattan>And they were, you know, they had a, a reduced scale enclosure and they were, putting big fires in the reduced scale enclosure and measuring, uh, soot and co and, and other gases within the box. 00:29:06.505 --> 00:29:08.285 <v Kevin McGrattan>And so we were trying to model that. 00:29:08.285 --> 00:29:11.575 <v Kevin McGrattan>And our, you know, our big goal was to try to predict the co. 00:29:12.026 --> 00:29:15.606 <v Kevin McGrattan>, that would build up in the upper layer of this, flashed over compartment. 00:29:16.021 --> 00:29:18.602 <v Kevin McGrattan>you know, that kept pushing the combustion modeling. 00:29:18.602 --> 00:29:30.551 <v Kevin McGrattan>Because if you wanna actually predict co as opposed to just specifying it, you know, then you've gotta now have something a little bit more sophisticated than fuel plus oxygen goes to products. 00:29:30.551 --> 00:29:35.672 <v Kevin McGrattan>Now we have to have something like fuel plus oxygen goes to you. 00:29:36.041 --> 00:29:44.516 <v Kevin McGrattan>Some initial set of products and then those initial set of products have to then, know, combine with oxygen and, and to form the final set of products. 00:29:44.516 --> 00:29:48.316 <v Kevin McGrattan>That is the CO has to oxidize and form co2. 00:29:48.935 --> 00:29:59.715 <v Kevin McGrattan>And that's where the lump species approach, um, came into play because we needed some way to account for all of these major and minor species without breaking the. 00:30:00.640 --> 00:30:15.267 <v Kevin McGrattan>because in fds, if you track all of these different species, fuel, oxygen, nitrogen, soot, co, co2, water vapor, blah, blah, blah, blah, blah, you know, each of these is his own transport equation and the cost of the calculations would get higher and higher and higher. 00:30:15.717 --> 00:30:25.003 <v Kevin McGrattan>So Jason was really the, the one who, worked out, you know, the simplification of, of the kinetics to the point where you would. 00:30:25.769 --> 00:30:29.269 <v Kevin McGrattan>The minimum number of species that you would need to track. 00:30:29.568 --> 00:30:38.548 <v Kevin McGrattan>But once you get into under ventilated combustion and you form CO and that sort of thing, you know, basically now you have four species to track rather than three, right? 00:30:38.548 --> 00:30:40.788 <v Kevin McGrattan>You've got these two sets of, of products. 00:30:41.036 --> 00:30:47.336 <v Kevin McGrattan>the initial set, you know, has the CO in it, and then the, uh, the secondary set has the, the CO2. 00:30:47.820 --> 00:30:56.290 <v Wojciech Wegrzynski>by like developing, you mean like literally solving the equations on, on the blackboard then figuring out how to transfer that into a code. 00:30:56.290 --> 00:30:57.931 <v Wojciech Wegrzynski>Like how did you even write it? 00:30:58.295 --> 00:31:01.019 <v Kevin McGrattan>well, well, Jason's very good with algebra, so 00:31:01.039 --> 00:31:02.259 <v Wojciech Wegrzynski>and you're a mathematician? 00:31:03.646 --> 00:31:08.044 <v Kevin McGrattan>I'm supposed to be the mathematician, but Jason actually is, is really clever. 00:31:08.044 --> 00:31:12.215 <v Kevin McGrattan>And, and what this involves is, you, you, you write down your basic. 00:31:12.517 --> 00:31:18.537 <v Kevin McGrattan>equations where you have, okay, the fuel molecule plus oxygen plus nitrogen goes to, know, X, Y, and Z. 00:31:18.807 --> 00:31:23.676 <v Kevin McGrattan>Well, now you have to lump these things together and there's just a lot of, a lot of algebra. 00:31:23.817 --> 00:31:29.757 <v Kevin McGrattan>And then when you start to code it up, you know, you have to make sure that you know all the, all the atoms balance. 00:31:30.446 --> 00:31:35.997 <v Kevin McGrattan>Um, and, and you've probably heard from people who try to run FDS in sort of primitive species mode. 00:31:36.592 --> 00:31:37.281 <v Kevin McGrattan>It's tricky. 00:31:37.311 --> 00:31:45.208 <v Kevin McGrattan>Just figure out, okay, you know, what are my tric coefficients for this, you know, complicated set of set of equations. 00:31:45.491 --> 00:31:51.422 <v Wojciech Wegrzynski>I, I find it fascinating, you know, because I, I really like to put it in the, um, timeline. 00:31:51.422 --> 00:31:55.521 <v Wojciech Wegrzynski>You know, was time when people listened to Britney Spears and NSync. 00:31:55.541 --> 00:32:05.739 <v Wojciech Wegrzynski>I guess this is, this is times where you, you surely could not go stuck overflow and just, okay, give me like nice this particular problem. 00:32:05.739 --> 00:32:07.019 <v Wojciech Wegrzynski>You have to figure it out. 00:32:07.769 --> 00:32:08.259 <v Kevin McGrattan>Yeah. 00:32:08.259 --> 00:32:09.739 <v Kevin McGrattan>Well, yeah, for us, 00:32:10.314 --> 00:32:11.394 <v Wojciech Wegrzynski>because there was no YouTube. 00:32:11.605 --> 00:32:17.375 <v Kevin McGrattan>I think the problem was is that a lot of, I mean, there's certainly a lot of people doing CFD related to combustion. 00:32:18.279 --> 00:32:24.740 <v Kevin McGrattan>But a lot of them are doing these fundamental calculations where they don't have these lump species. 00:32:24.740 --> 00:32:30.539 <v Kevin McGrattan>They just literally, you know, track all of the major and minor species directly. 00:32:30.799 --> 00:32:35.819 <v Kevin McGrattan>And it's computationally expensive, but it's a little bit easier in terms of the formulation. 00:32:36.299 --> 00:32:45.467 <v Kevin McGrattan>for us, often the difficulty in programming FDS is we have to make these approximations to get things to work in a reasonable amount of. 00:32:45.682 --> 00:32:54.249 <v Kevin McGrattan>Whereas sometimes someone, if we just talk to combustion people, they'll say, well, why don't you just solve for everything explicitly and don't worry about, the lump species. 00:32:54.249 --> 00:33:00.009 <v Kevin McGrattan>And we say, well, you know, we have to get our calculations done in a day or two, not a week or two, or a month or two. 00:33:00.409 --> 00:33:04.769 <v Kevin McGrattan>Sometimes in, in the academic world, if it, if your calculation takes a month 00:33:04.848 --> 00:33:05.338 <v Wojciech Wegrzynski>It's, 00:33:05.689 --> 00:33:06.565 <v Kevin McGrattan>Well, so what 00:33:06.628 --> 00:33:08.148 <v Wojciech Wegrzynski>and what, what came next? 00:33:08.469 --> 00:33:09.669 <v Wojciech Wegrzynski>Pyrolysis suppression. 00:33:10.467 --> 00:33:11.140 <v Kevin McGrattan>Let's see. 00:33:11.303 --> 00:33:22.472 <v Kevin McGrattan>so Pyrolysis came about, I'd say next because again, Simo Hostikka um, who had returned to Finland at that point was starting to get interested in pyrolysis. 00:33:22.472 --> 00:33:22.873 <v Kevin McGrattan>And wood. 00:33:22.873 --> 00:33:23.913 <v Kevin McGrattan>Wood in particular. 00:33:23.942 --> 00:33:27.593 <v Kevin McGrattan>I think in Finland, they, they're very interested in wood. 00:33:27.742 --> 00:33:29.553 <v Kevin McGrattan>It's an important part of their economy. 00:33:29.960 --> 00:33:34.083 <v Kevin McGrattan>and so he started to know, put the basic pyrosis equation. 00:33:34.637 --> 00:33:38.887 <v Kevin McGrattan>Into fds and I also became quite interested in it. 00:33:38.887 --> 00:33:46.961 <v Kevin McGrattan>So he and I both started to, to work out, the detailed kinetics models that one can choose to use in FDS today. 00:33:47.340 --> 00:33:50.480 <v Kevin McGrattan>But it was, it was Simo who really, who really pioneered that. 00:33:50.480 --> 00:33:56.280 <v Kevin McGrattan>And he was again, just interested in doing, um, simulations involving wood. 00:33:56.280 --> 00:33:57.320 <v Kevin McGrattan>He, and he got a number. 00:33:57.861 --> 00:33:58.971 <v Kevin McGrattan>Of coworkers. 00:33:59.101 --> 00:34:01.505 <v Kevin McGrattan>Anna Matala, was one who I remember. 00:34:01.894 --> 00:34:04.115 <v Kevin McGrattan>and she was also very interested in this. 00:34:04.125 --> 00:34:09.505 <v Kevin McGrattan>So, I decided as long as Simo was interested in coding it up, I was more than happy to work with him. 00:34:09.550 --> 00:34:10.349 <v Wojciech Wegrzynski>Fantastic. 00:34:10.994 --> 00:34:11.485 <v Kevin McGrattan>Yeah. 00:34:11.789 --> 00:34:12.070 <v Wojciech Wegrzynski>suppression. 00:34:12.070 --> 00:34:16.869 <v Wojciech Wegrzynski>How, how did you end up putting lagrangian aggression particles, water, and uh, and all the suppression 00:34:17.119 --> 00:34:25.503 <v Kevin McGrattan>Well, well, the, all the suppression stuff was around from the very beginning, even before we released fds we were doing these warehouse fires. 00:34:25.503 --> 00:34:29.012 <v Kevin McGrattan>So we had, we had the sprinkler model in place. 00:34:29.505 --> 00:34:36.150 <v Kevin McGrattan>But one of the things that we really wanted to do, after we released FDS officially, is. 00:34:36.875 --> 00:34:43.010 <v Kevin McGrattan>We wanted to do more with droplet sizes and distributions and, and that sort of thing. 00:34:43.630 --> 00:34:54.378 <v Kevin McGrattan>And there's a fellow named Dave Shepherd who, for his graduate work, know, developed a, a fairly sophisticated treatment of water droplets that we built into fds. 00:34:54.697 --> 00:35:02.860 <v Kevin McGrattan>The problem there though, is, For any given sprinkler, it's very difficult to get the data that we would need for this sophisticated model. 00:35:03.391 --> 00:35:11.581 <v Kevin McGrattan>So, I mean, if you go into any building and look up and look at the sprinkler, there are, you know, an infinite number of different types of sprinklers. 00:35:11.851 --> 00:35:17.447 <v Kevin McGrattan>Each one has its own sort of characteristic, spray pattern and, and droplet distribution. 00:35:18.422 --> 00:35:30.230 <v Kevin McGrattan>. And so we got to a point where we had to kind of keep in place the relatively simple model that we still use today, simply because we don't have, the details of any given sprinkler. 00:35:30.230 --> 00:35:31.309 <v Kevin McGrattan>I know it can be measured. 00:35:31.309 --> 00:35:36.456 <v Kevin McGrattan>I mean, one can go to a testing lab measure these things, but that's a very expensive thing to do. 00:35:36.456 --> 00:35:42.663 <v Kevin McGrattan>And I've, I've found by talking to a lot of the fire protection engineers who use fds, they're quite happy to. 00:35:42.766 --> 00:35:49.952 <v Kevin McGrattan>Have fds predict when the sprinklers are gonna activate and they wanna have a, a reasonable idea of where the water is gonna go. 00:35:50.275 --> 00:36:00.715 <v Kevin McGrattan>But in terms of suppression, in terms of actually predicting, if you know a pile of commodity that's burning is gonna go out, that's still something that I don't think we can, we can. 00:36:01.090 --> 00:36:01.581 <v Wojciech Wegrzynski>Yeah. 00:36:02.010 --> 00:36:10.891 <v Kevin McGrattan>mean, we have rough empirical models in FDS to make some approximation as to how much the heat release rate will decrease when you throw water on something. 00:36:10.891 --> 00:36:16.474 <v Kevin McGrattan>But that's never really been something that we're gonna be able to do, like reliably. 00:36:16.474 --> 00:36:26.045 <v Kevin McGrattan>Like we'll never be able to replace a full scale test in terms of predicting whether or not, you know, that burning pile of boxes is gonna. 00:36:26.340 --> 00:36:29.177 <v Kevin McGrattan>Put out by, sprinkler X, Y, or Z. 00:36:29.422 --> 00:36:34.081 <v , Wojciech Wegrzynski>now, I, I'm, I'm switching to the difficult question spot the list. 00:36:35.166 --> 00:36:39.336 <v , Wojciech Wegrzynski>I remember there a thing around FDS four. 00:36:40.047 --> 00:36:42.186 <v , Wojciech Wegrzynski>It was the, material database. 00:36:42.847 --> 00:36:52.927 <v , Wojciech Wegrzynski>then when, when you move to FDS five, the material database has disappeared, uh, causing, uh, causing almost a collapse to a whole industry of fire safety engineering. 00:36:53.376 --> 00:37:05.889 <v , Wojciech Wegrzynski>So I would love to ask you like, uh, first, uh, about the development and the destruction of the material database and the world of default values in, in modeling, because the, these, these two things connect. 00:37:06.599 --> 00:37:07.159 <v Kevin McGrattan>Right. 00:37:07.297 --> 00:37:16.757 <v Kevin McGrattan>the original idea behind that database was just to put in, you know, some K - rho - C for some basic materials, brick gypsum board. 00:37:16.916 --> 00:37:25.833 <v Kevin McGrattan>But over time it started to creep and we, we started to develop much more sophisticated, property data that we put into that data. 00:37:26.494 --> 00:37:39.925 <v Kevin McGrattan>and then we just started adding numbers that, you know, came out of this paper or that paper or this handbook or, or wherever it, the, the database started getting filled up with a lot of numbers that we really couldn't validate or verify, 00:37:40.369 --> 00:37:40.530 <v Wojciech Wegrzynski>Hmm. 00:37:40.824 --> 00:37:47.925 <v Kevin McGrattan>and at this time we were doing more and more work with regulatory authorities, like in this country, the Nuclear Regulatory Commission. 00:37:48.139 --> 00:37:51.838 <v Kevin McGrattan>And they were all very interested in validating these models. 00:37:52.411 --> 00:37:59.262 <v Kevin McGrattan>I mean, they're essentially the authorities having jurisdiction and they wanna have some idea as to how accurate these models are. 00:37:59.771 --> 00:38:07.858 <v Kevin McGrattan>And know, the question arose when we were starting to do the validation work is, okay, well what do we do about these material properties? 00:38:07.918 --> 00:38:10.298 <v Kevin McGrattan>How do we quote unquote validate them? 00:38:10.469 --> 00:38:16.489 <v Kevin McGrattan>And I looked through the database and I found that, you know, I really couldn't rigorously justify. 00:38:16.585 --> 00:38:22.355 <v Kevin McGrattan>Some of these numbers, I mean, some of 'em were just, you know, ballpark order of magnitude guesses. 00:38:22.675 --> 00:38:26.085 <v Kevin McGrattan>some of, and we, we started to notice that they were being used inappropriately. 00:38:27.510 --> 00:38:28.909 <v Wojciech Wegrzynski>They, they, were cited like to 00:38:29.074 --> 00:38:35.965 <v Kevin McGrattan>were being cited sort of standard reference materials, and that's a problem here at N I S T. 00:38:36.577 --> 00:38:44.487 <v Kevin McGrattan>We do have, as an agency, we have what are known as standard reference materials and standard reference data. 00:38:45.094 --> 00:38:47.684 <v Kevin McGrattan>and our materials database was not that 00:38:47.719 --> 00:38:48.208 <v Wojciech Wegrzynski>Okay. 00:38:49.074 --> 00:38:55.284 <v Kevin McGrattan>It's a big deal when you, when you stamp, you know, standard reference data onto something. 00:38:55.653 --> 00:38:58.583 <v Kevin McGrattan>I mean, the funniest thing that we, we, we sell peanut butter here. 00:38:58.583 --> 00:39:00.983 <v Kevin McGrattan>Did you ever hear that story about peanut butter? 00:39:02.835 --> 00:39:16.728 <v Kevin McGrattan>so nist, you can buy for about $500 a jar, peanut butter from nist, and it's a standard reference material and it's used by, food producers for measuring caloric content. 00:39:17.179 --> 00:39:23.969 <v Kevin McGrattan>So if you have an apparatus for measuring the caloric content of food, you can use the NIST peanut butter. 00:39:24.653 --> 00:39:31.539 <v Kevin McGrattan>As a standard to make sure that your apparatus for measuring the calorie content of the food is okay. 00:39:32.050 --> 00:39:42.806 <v Kevin McGrattan>so the long, so the long story short is we were not going through all of the necessary, hoops to call our database standard reference. 00:39:43.297 --> 00:39:45.847 <v Kevin McGrattan>So when we went to FDS five, we just decided. 00:39:46.099 --> 00:39:48.646 <v Kevin McGrattan>This was too much of a burden for us to take on. 00:39:48.797 --> 00:39:50.766 <v Kevin McGrattan>It's hard enough to maintain the code. 00:39:50.777 --> 00:40:01.827 <v Kevin McGrattan>We really weren't comfortable maintaining this database of material properties, especially when we were just pulling these, these numbers from just a whole variety of different sources. 00:40:02.257 --> 00:40:10.867 <v Kevin McGrattan>It's almost like, you know, going onto the web these days and just Google searching on something and putting the number, I mean, that's really all our database. 00:40:11.692 --> 00:40:16.112 <v Kevin McGrattan>And so I'd rather have the end user pick a number off the web rather than us 00:40:16.202 --> 00:40:17.369 <v Wojciech Wegrzynski>and justify ma'am. 00:40:17.492 --> 00:40:18.282 <v Kevin McGrattan>justify it. 00:40:18.422 --> 00:40:20.762 <v Kevin McGrattan>And that's, and that's what the authorities said to us. 00:40:20.762 --> 00:40:28.762 <v Kevin McGrattan>They said, look, when someone runs an FDS calculation and we review it, we will ask them where they came up with all these properties. 00:40:28.762 --> 00:40:32.161 <v Kevin McGrattan>And we don't want to hear from them that it's just comes from this database. 00:40:32.608 --> 00:40:33.179 <v Kevin McGrattan>I agree. 00:40:33.179 --> 00:40:34.320 <v Kevin McGrattan>I don't wanna hear that either. 00:40:35.184 --> 00:40:35.304 <v Wojciech Wegrzynski>question. 00:40:36.231 --> 00:40:36.871 <v Wojciech Wegrzynski>it taste good? 00:40:36.871 --> 00:40:39.231 <v Wojciech Wegrzynski>Like, is, is it better taste? 00:40:39.391 --> 00:40:40.081 <v Kevin McGrattan>Terrible 00:40:40.541 --> 00:40:41.032 <v Wojciech Wegrzynski>Well, 00:40:42.461 --> 00:40:43.391 <v Kevin McGrattan>have the sugar. 00:40:43.442 --> 00:40:46.005 <v Kevin McGrattan>It doesn't have, it's just like peanut and. 00:40:46.900 --> 00:40:47.389 <v Wojciech Wegrzynski>okay. 00:40:47.530 --> 00:40:48.019 <v Wojciech Wegrzynski>Okay. 00:40:48.570 --> 00:41:01.467 <v Wojciech Wegrzynski>as, as we discussed this, this material database, I had this discussion with Wolfram Jahn a long, long time ago in the podcast um, users using default values without giving, without giving it a serious thought. 00:41:02.211 --> 00:41:08.052 <v Wojciech Wegrzynski>and you, you had to use some defaults in, in FDS there's, there's many defaults. 00:41:08.052 --> 00:41:12.172 <v Wojciech Wegrzynski>There's, uh, smoke extinction, specific smoke extinction, coefficient default. 00:41:12.172 --> 00:41:13.675 <v Wojciech Wegrzynski>There's, suit default. 00:41:13.675 --> 00:41:18.715 <v Wojciech Wegrzynski>I think there, no, now you have to specify your reaction because you, you, you have taken away that from 00:41:18.980 --> 00:41:22.309 <v Kevin McGrattan>Yeah, we even, we even took that away cause that was problematic too. 00:41:22.309 --> 00:41:23.349 <v Kevin McGrattan>We didn't, we dunno. 00:41:23.349 --> 00:41:25.150 <v Kevin McGrattan>The smoke yield of your burning couch. 00:41:25.179 --> 00:41:26.710 <v Kevin McGrattan>I mean, that's something I want you to 00:41:26.715 --> 00:41:33.434 <v Wojciech Wegrzynski>Actually, actually, actually that's a great example because half of the world was burning pole urethane because that was their default reaction. 00:41:33.929 --> 00:41:36.860 <v Kevin McGrattan>I forget what the default re I think the default reaction was. 00:41:36.864 --> 00:41:37.514 <v Wojciech Wegrzynski>yeah, yeah. 00:41:37.514 --> 00:41:37.755 <v Wojciech Wegrzynski>Sorry. 00:41:37.755 --> 00:41:37.994 <v Wojciech Wegrzynski>Yeah. 00:41:37.994 --> 00:41:38.355 <v Wojciech Wegrzynski>Prop point. 00:41:38.355 --> 00:41:39.074 <v Wojciech Wegrzynski>But that was like 00:41:39.244 --> 00:41:47.715 <v Kevin McGrattan>But there was, but there was polyurethane in this database that we had just pieced together from some experiments that were done here at nist. 00:41:48.135 --> 00:41:54.802 <v Kevin McGrattan>And I can't even tell you, you know, in detail what that polyurethane consisted of, what kind of fabric was in it. 00:41:54.802 --> 00:42:01.885 <v Kevin McGrattan>It was just like a one off from one test and we just, were not comfortable, declaring that to be, standard reference data. 00:42:02.005 --> 00:42:08.661 <v Wojciech Wegrzynski>now, okay, now, there are still some defaults, I guess they are like, you probably put a lot more attention into, into having them. 00:42:08.802 --> 00:42:13.461 <v Wojciech Wegrzynski>But what, what, how do you feel about this, uh, user responsibility? 00:42:13.461 --> 00:42:15.641 <v Wojciech Wegrzynski>Like from from a developer perspective, 00:42:16.226 --> 00:42:16.836 <v Kevin McGrattan>Mm-hmm. 00:42:16.842 --> 00:42:17.842 <v Wojciech Wegrzynski>from your point of view? 00:42:17.842 --> 00:42:25.278 <v Wojciech Wegrzynski>Like the, the user is fully, uh, Responsible for, for choosing the numbers, whether they, they leave default or, or pick one. 00:42:25.824 --> 00:42:26.384 <v Kevin McGrattan>right. 00:42:26.398 --> 00:42:27.958 <v Wojciech Wegrzynski>you have the impression that they actually do that? 00:42:28.074 --> 00:42:40.168 <v Kevin McGrattan>well, we, they have to cause we force them , for example, I was talking to someone the other day who was doing an analysis of a fire in, in some building, and he kept talking about the, the visibility. 00:42:40.402 --> 00:42:43.942 <v Kevin McGrattan>And I asked him, I said, well, what have you specified for the so yield? 00:42:44.342 --> 00:42:44.692 <v Wojciech Wegrzynski>Hm. 00:42:45.181 --> 00:42:46.251 <v Kevin McGrattan>And he didn. 00:42:47.126 --> 00:42:57.456 <v Kevin McGrattan>No, what he was specifying for the soot yield, and I'm guessing if he didn't specify anything, then there's no soot at all, which means that the visibility is always going to be, you know, at it's maximum. 00:42:57.880 --> 00:43:07.289 <v Kevin McGrattan>And so, so we decided that it was much better to sort of force the user to think about these things rather than to specify it. 00:43:07.289 --> 00:43:13.289 <v Kevin McGrattan>Because, I mean, let's face it, when I run a computer program, and I'm not talking about fds, but some other, you know, program. 00:43:13.751 --> 00:43:15.481 <v Kevin McGrattan>, I generally go with the default. 00:43:15.731 --> 00:43:22.762 <v Kevin McGrattan>If I don't go any better, I'm just gonna go with the default unless the program forces me to make a decision. 00:43:23.262 --> 00:43:33.349 <v Kevin McGrattan>And so we, We often argue amongst ourselves, to what extent do we wanna force the users to make these decisions, or do we wanna provide them with a default? 00:43:33.974 --> 00:43:36.664 <v Kevin McGrattan>Over the years, we've kind of come to this compromise. 00:43:36.934 --> 00:43:40.844 <v Kevin McGrattan>Like for example, 35% is our default, radi theft fraction. 00:43:41.259 --> 00:43:48.302 <v Kevin McGrattan>but that's, I mean, I'm trying to think of what other, what other defaults do we have in there that the user doesn't have to really specify? 00:43:48.452 --> 00:43:49.382 <v Kevin McGrattan>I mean, that, 00:43:49.427 --> 00:43:50.347 <v Wojciech Wegrzynski>my Extinction Co. 00:43:50.436 --> 00:43:51.027 <v Wojciech Wegrzynski>Is, is 00:43:51.442 --> 00:43:52.492 <v Kevin McGrattan>that's another one. 00:43:52.492 --> 00:43:52.931 <v Kevin McGrattan>Okay. 00:43:52.947 --> 00:43:53.186 <v Wojciech Wegrzynski>that's 00:43:53.612 --> 00:43:54.032 <v Kevin McGrattan>Yes. 00:43:54.467 --> 00:43:56.027 <v Wojciech Wegrzynski>Mulholland's Research that, that 00:43:56.367 --> 00:44:01.056 <v Kevin McGrattan>Right, And that's a number that, I mean, we haven't seen anything better than that. 00:44:01.146 --> 00:44:05.489 <v Kevin McGrattan>So we heard, let's at least provide the best data that's out there. 00:44:06.269 --> 00:44:14.914 <v Kevin McGrattan>And, but then for, for other things the soot yield, co yield, know, those are things that we really think the user has to think, especially if they're doing a life safety. 00:44:15.889 --> 00:44:23.923 <v Wojciech Wegrzynski>So, we, we've covered, I, I hope, quite torr the, the first 10 years of fds FDS five came, what, 2008, nine. 00:44:24.264 --> 00:44:25.425 <v Kevin McGrattan>Something like that. 00:44:25.485 --> 00:44:25.905 <v Kevin McGrattan>Yep. 00:44:25.905 --> 00:44:26.425 <v Kevin McGrattan>Mm-hmm. 00:44:26.690 --> 00:44:31.250 <v Wojciech Wegrzynski>six came 2013, 14, around that time, 00:44:31.824 --> 00:44:32.244 <v Kevin McGrattan>Yes. 00:44:32.519 --> 00:44:39.250 <v Wojciech Wegrzynski>I, I guess some people were lucky to get into better version for, and, and I, that that was quite a long one as well. 00:44:39.514 --> 00:44:40.074 <v Kevin McGrattan>Right. 00:44:40.074 --> 00:44:40.434 <v Kevin McGrattan>Great. 00:44:40.489 --> 00:44:43.289 <v Wojciech Wegrzynski>how did the development of the modern versions look like? 00:44:43.289 --> 00:44:49.530 <v Wojciech Wegrzynski>Because you had now combustion model, you had a radiation model, you had model, you had the pressure model. 00:44:50.394 --> 00:44:50.815 <v Kevin McGrattan>Yep. 00:44:50.974 --> 00:44:55.121 <v Wojciech Wegrzynski>point, was it like improving the models, a changes 00:44:55.501 --> 00:45:00.612 <v Kevin McGrattan>so as we went from FDS five to FDS six, we were joined by Randy McDermott. 00:45:01.094 --> 00:45:01.869 <v Kevin McGrattan>and he. 00:45:02.117 --> 00:45:04.757 <v Kevin McGrattan>, you know, he actually has a formal CFD background. 00:45:04.954 --> 00:45:10.153 <v Kevin McGrattan>you know, Jason, CMO and I who kind learned it as we went along. 00:45:10.349 --> 00:45:22.693 <v Kevin McGrattan>Randy actually had, a very, extensive background in cfd and you know, one of the things we asked him to do when he first came on board was just to look at everything in the code and. 00:45:22.907 --> 00:45:34.010 <v Kevin McGrattan>Start running, you know, verification tests, and we started running more validation tests and we started to get a little bit, more strict with the way we handled a lot of things. 00:45:34.010 --> 00:45:37.849 <v Kevin McGrattan>I mean, it's hard to go, I mean, there'd be a laundry list of different things, 00:45:38.150 --> 00:45:38.309 <v Wojciech Wegrzynski>Hmm. 00:45:38.510 --> 00:45:44.086 <v Kevin McGrattan>but, but Randy started to really apply a lot more rigor, to what we were doing. 00:45:44.961 --> 00:45:45.722 <v Kevin McGrattan>up to that point. 00:45:45.722 --> 00:45:53.635 <v Kevin McGrattan>Up to that point, you know, sometimes we were, we were being a little bit fast and loose with some of the, know, the turbulence models, boundary layer correlations. 00:45:54.335 --> 00:46:00.994 <v Kevin McGrattan>And, and Randy brought some discipline to that and introduced the, the whole concept of running verification cases. 00:46:01.050 --> 00:46:01.523 <v Wojciech Wegrzynski>Okay. 00:46:01.523 --> 00:46:04.592 <v Kevin McGrattan>And so that's, a lot of that went into fds. 00:46:05.027 --> 00:46:21.360 <v Kevin McGrattan>you know, one of the major problems that we had with FDS five is that the, the algorithm at the time that we were using, which was the simplest form of, of the transport algorithm, would allow temperatures to drop down to extremely low values right around the fire. 00:46:22.059 --> 00:46:32.592 <v Kevin McGrattan>And, you know, to make a long story short, you have a situation where you go from like a really high temperature in the fire, and then in just one or two grid cells you're down to ambient temperature. 00:46:33.161 --> 00:46:37.112 <v Kevin McGrattan>So the temperature kind of goes through this dip, and it's purely numerical. 00:46:37.112 --> 00:46:38.911 <v Kevin McGrattan>There's nothing physical about this at all. 00:46:38.911 --> 00:46:40.911 <v Kevin McGrattan>It's just a, it's a numerical artifact. 00:46:41.302 --> 00:46:44.831 <v Kevin McGrattan>It's just part of that particular algorithm that we were using. 00:46:45.411 --> 00:46:49.072 <v Kevin McGrattan>But it really, you know, got a lot of people bent outta shape. 00:46:49.072 --> 00:46:50.112 <v Kevin McGrattan>A lot of our users. 00:46:50.324 --> 00:46:56.844 <v Kevin McGrattan>Did not like to see, you know, minus 10 degrees Celsius right next to a big fire. 00:46:57.159 --> 00:47:02.030 <v Kevin McGrattan>And we tried to explain that this was, you know, purely a numerical artifact. 00:47:02.280 --> 00:47:08.150 <v Kevin McGrattan>It doesn't affect the overall accuracy of the calculation, but still, you know, it was a, it was a thorn in our side. 00:47:08.449 --> 00:47:11.949 <v Kevin McGrattan>And so we said to Randy, I said, Randy, what can we do about this? 00:47:11.949 --> 00:47:15.670 <v Kevin McGrattan>And he knew of more sophisticated transport algorithms. 00:47:16.235 --> 00:47:20.005 <v Kevin McGrattan>Would eliminate this spurious, flow temperature. 00:47:20.005 --> 00:47:23.844 <v Kevin McGrattan>So those are the, those are the kinds of things that, that Randy brought to the table. 00:47:24.235 --> 00:47:30.445 <v Kevin McGrattan>A lot of it is under the hood, know, you don't notice a lot of this stuff, but it was absolutely necessary in order for us to continue. 00:47:30.445 --> 00:47:42.414 <v Kevin McGrattan>Because as we start using, you know, near flame temperatures for extinction and suppression and those sorts of things, you know, if you have these fictitious values, You can't do anything. 00:47:42.585 --> 00:47:49.141 <v Kevin McGrattan>So we really needed to tighten up the basic algorithm before we could move onto to other things. 00:47:49.152 --> 00:47:52.822 <v Kevin McGrattan>So, so we needed someone, we needed like a, a real cfd. 00:47:52.931 --> 00:47:53.731 <v Wojciech Wegrzynski>you, you needed Randy. 00:47:53.922 --> 00:47:55.132 <v Wojciech Wegrzynski>It's great you got him. 00:47:56.612 --> 00:47:57.411 <v Wojciech Wegrzynski>Fantastic. 00:47:57.722 --> 00:48:04.512 <v Wojciech Wegrzynski>I remember from those times, a lot of, discussion on Jet fans and, how the core is solved. 00:48:04.512 --> 00:48:08.681 <v Wojciech Wegrzynski>you, I think you went to like two or three durations of the l e s model at the. 00:48:08.931 --> 00:48:09.351 <v Kevin McGrattan>Yes. 00:48:09.782 --> 00:48:10.271 <v Kevin McGrattan>Yeah. 00:48:10.586 --> 00:48:16.043 <v Wojciech Wegrzynski>case of, having to put a pressure inlet every mesh to, to keep the background pressure. 00:48:16.313 --> 00:48:18.545 <v Wojciech Wegrzynski>I, I mean, of course, a of things, but, 00:48:18.889 --> 00:48:23.568 <v Kevin McGrattan>another thing that Randy did is that he coded up into fds all of. 00:48:23.925 --> 00:48:25.925 <v Kevin McGrattan>Like most popular turbulence models. 00:48:26.335 --> 00:48:35.911 <v Kevin McGrattan>So when we say l e s, there are about half a dozen different ways of representing the viscosity of the gas. 00:48:36.222 --> 00:48:36.711 <v Kevin McGrattan>Okay. 00:48:36.711 --> 00:48:42.351 <v Kevin McGrattan>And you, you've heard like s gorinsky, that's one type and then there's a, there a variety of others. 00:48:42.532 --> 00:48:44.711 <v Kevin McGrattan>And Randy coded up every single one. 00:48:44.851 --> 00:48:49.192 <v Kevin McGrattan>And then we ran all of our test cases with all of these different turbulence. 00:48:49.730 --> 00:48:59.500 <v Kevin McGrattan>And the one that we came to, which is known as the Deardorff model, is the one we're using now simply because over the wide range of our applications, this one performed the best. 00:49:00.190 --> 00:49:05.487 <v Wojciech Wegrzynski>And, and now having this, massive, uh, library of, of reference cases, 00:49:06.327 --> 00:49:06.746 <v Kevin McGrattan>Yes, 00:49:06.989 --> 00:49:09.909 <v Wojciech Wegrzynski>in such a better position to understand and it changed to the code. 00:49:09.909 --> 00:49:10.230 <v Wojciech Wegrzynski>You do 00:49:10.469 --> 00:49:11.650 <v Kevin McGrattan>yes, yes. 00:49:11.710 --> 00:49:15.150 <v Wojciech Wegrzynski>understood, every night you run the simulations again and again and again 00:49:15.650 --> 00:49:16.210 <v Kevin McGrattan>Right, 00:49:16.469 --> 00:49:17.429 <v Wojciech Wegrzynski>for errors, right. 00:49:17.690 --> 00:49:18.570 <v Kevin McGrattan>right, right. 00:49:18.570 --> 00:49:20.730 <v Kevin McGrattan>And we also, we run these validation cases. 00:49:20.780 --> 00:49:32.536 <v Kevin McGrattan>So if, if we introduce some new, variant of a, of our extinction model, we can run half a dozen different test series and see, okay, are, is, are we improving or are we getting worse? 00:49:32.722 --> 00:49:33.331 <v Wojciech Wegrzynski>That's, 00:49:33.777 --> 00:49:38.177 <v Kevin McGrattan>and we can do that literally within a few days, whereas before. 00:49:38.677 --> 00:49:43.916 <v Kevin McGrattan>Something like this would be, you know, something a graduate student would spend two years doing. 00:49:44.217 --> 00:49:49.099 <v Kevin McGrattan>Now we can do it in a couple of days just because we have all of this stuff at the push of a button. 00:49:49.389 --> 00:49:53.219 <v Kevin McGrattan>So we, we just simply make the change in a test version of the code. 00:49:53.219 --> 00:49:59.739 <v Kevin McGrattan>We push the button a couple days later, we look at the results and we can tell whether or not, you know, things are getting better or things are getting worse. 00:50:00.105 --> 00:50:01.304 <v Wojciech Wegrzynski>how big is the team nowadays? 00:50:01.568 --> 00:50:12.650 <v Kevin McGrattan>So, the core people, it's, it's basically myself, Jason Floyd, Randy McDermott, a fellow named Marcus Vanella who's, who's working on the, non rectangular geometry, 00:50:12.905 --> 00:50:13.065 <v Wojciech Wegrzynski>Hmm. 00:50:13.396 --> 00:50:16.708 <v Kevin McGrattan>Simo And, and his students, uh, help out. 00:50:16.918 --> 00:50:21.987 <v Kevin McGrattan>Um, Glen Forney is doing smoke view plus a lot of the, um, the IT support. 00:50:22.413 --> 00:50:31.880 <v Kevin McGrattan>and then we have, we have various other people, um, Susan Killian from Germany, for example, you know, sometimes works on the pressure solving features. 00:50:32.269 --> 00:50:42.483 <v Kevin McGrattan>but the day-to-day, maintenance is myself, Jason, Floyd, Randy and Marcos we're the ones when you, when you send in an issue tracker, it's gonna be one us who takes it. 00:50:43.880 --> 00:50:46.684 <v Wojciech Wegrzynski>such a big, How to even say it. 00:50:46.684 --> 00:50:49.804 <v Wojciech Wegrzynski>I mean, uh, is, this is not important for fire science. 00:50:49.804 --> 00:50:51.684 <v Wojciech Wegrzynski>This is fundamental for fire science. 00:50:51.684 --> 00:50:58.867 <v Wojciech Wegrzynski>You know, this, I, tomorrow F ds disappeared, would be like a stock market crash in the world of fire science and engineering. 00:50:58.918 --> 00:50:59.268 <v Wojciech Wegrzynski>So, 00:50:59.300 --> 00:51:05.494 <v Kevin McGrattan>Well, we, one of the reasons why we've put together this kind of elaborate, set of online tools like, you know, the Gith. 00:51:05.748 --> 00:51:08.577 <v Kevin McGrattan>is that if we were all hit by a bus tomorrow, 00:51:08.657 --> 00:51:08.818 <v Wojciech Wegrzynski>Hmm. 00:51:08.856 --> 00:51:11.161 <v Kevin McGrattan>someone could step in and, and take over. 00:51:11.161 --> 00:51:13.681 <v Kevin McGrattan>I mean, that's the beauty of open source software. 00:51:13.731 --> 00:51:13.851 <v Wojciech Wegrzynski>Hmm. 00:51:13.951 --> 00:51:19.920 <v Kevin McGrattan>I mean, we do the day-to-day maintenance, but there are others who are kind of following us in a way 00:51:19.940 --> 00:51:20.291 <v Wojciech Wegrzynski>Hm. 00:51:20.581 --> 00:51:24.394 <v Kevin McGrattan>who if we went away, they could step in and, and take it over. 00:51:24.394 --> 00:51:27.675 <v Kevin McGrattan>So we wanna make sure that this thing lasts longer than just. 00:51:27.809 --> 00:51:32.735 <v Wojciech Wegrzynski>I I think the, and I think the impact, uh, of the tool is tremendous. 00:51:32.786 --> 00:51:33.275 <v Wojciech Wegrzynski>Okay. 00:51:33.275 --> 00:51:37.675 <v Wojciech Wegrzynski>Kevin, that, that was fascinating to go, uh, through the development of fds. 00:51:37.905 --> 00:51:43.876 <v Wojciech Wegrzynski>I I think you've cleared a lot about, the origins and, and the solver and how it was built. 00:51:43.876 --> 00:51:45.556 <v Wojciech Wegrzynski>It's, it's a fantastic so story. 00:51:45.746 --> 00:51:48.596 <v Wojciech Wegrzynski>I was told It's a good story and, and it truly is. 00:51:49.606 --> 00:51:50.795 <v Wojciech Wegrzynski>um, yeah. 00:51:50.795 --> 00:51:52.476 <v Wojciech Wegrzynski>Thank you very much for coming to the 00:51:52.681 --> 00:51:53.451 <v Kevin McGrattan>You're welcome. 00:51:53.675 --> 00:51:56.795 <v Wojciech Wegrzynski>Thank you very much for, uh, building this for us. 00:51:56.797 --> 00:51:57.275 <v Kevin McGrattan>Okay. 00:51:57.275 --> 00:51:58.065 <v Kevin McGrattan>I enjoyed it. 00:51:58.177 --> 00:51:58.927 <v Wojciech Wegrzynski>And that's it. 00:51:59.106 --> 00:51:59.496 <v Wojciech Wegrzynski>Oh man. 00:51:59.521 --> 00:52:00.061 <v Wojciech Wegrzynski>so good. 00:52:00.090 --> 00:52:01.710 <v Wojciech Wegrzynski>It was on the podcast bucket list. 00:52:01.951 --> 00:52:04.471 <v Wojciech Wegrzynski>We have Kevin talk about FDS on, on the air. 00:52:04.891 --> 00:52:08.670 <v Wojciech Wegrzynski>And it finally happened and I'm super happy to have conducted this interview. 00:52:09.121 --> 00:52:12.360 <v Wojciech Wegrzynski>So many golden nuggets from the early days of FDS development. 00:52:12.360 --> 00:52:13.771 <v Wojciech Wegrzynski>So many interesting insights. 00:52:14.190 --> 00:52:15.751 <v Wojciech Wegrzynski>How the model grew. 00:52:15.780 --> 00:52:19.603 <v Wojciech Wegrzynski>What's Power to this growth and, how it changed over the years? 00:52:19.960 --> 00:52:24.460 <v Wojciech Wegrzynski>the most astonishing part I think is, uh, how it was built as an academic tool. 00:52:24.574 --> 00:52:28.264 <v Wojciech Wegrzynski>And then it quickly was rediscovered as a commercial powerhouse. 00:52:28.324 --> 00:52:28.623 <v Wojciech Wegrzynski>Now. 00:52:29.164 --> 00:52:32.014 <v Wojciech Wegrzynski>It's fueling so many companies around the world. 00:52:32.014 --> 00:52:35.884 <v Wojciech Wegrzynski>So many people are basically FDS engineers nowadays. 00:52:35.914 --> 00:52:36.753 <v Wojciech Wegrzynski>And that's great. 00:52:36.784 --> 00:52:37.893 <v Wojciech Wegrzynski>That's great that the tool. 00:52:37.983 --> 00:52:39.963 <v Wojciech Wegrzynski>Uh, developed by scientists. 00:52:40.384 --> 00:52:43.023 <v Wojciech Wegrzynski>Powered by fire science has found away. 00:52:43.034 --> 00:52:47.443 <v Wojciech Wegrzynski>To fire engineering, what's the better testament or for fire science and the need of. 00:52:48.043 --> 00:52:51.494 <v Wojciech Wegrzynski>Development of fundamental stuff in this field. 00:52:51.702 --> 00:52:56.646 <v Wojciech Wegrzynski>What's a better example of how great investment fundamental fire science can be. 00:52:57.326 --> 00:53:00.385 <v Wojciech Wegrzynski>If you really enjoyed this episode and you would love to. 00:53:00.755 --> 00:53:02.485 <v Wojciech Wegrzynski>hear Kevin, once again. 00:53:02.606 --> 00:53:03.865 <v Wojciech Wegrzynski>Uh, I have. 00:53:04.135 --> 00:53:04.916 <v Wojciech Wegrzynski>Nice for you. 00:53:05.246 --> 00:53:12.338 <v Wojciech Wegrzynski>So there's no, the only Christmas special episode, but there's also, let's say new year's special episode coming your way next Wednesday. 00:53:12.338 --> 00:53:18.889 <v Wojciech Wegrzynski>And that's Kevin McGrattan and again, And we're going to talk about experiment that has certainly changed the fire science. 00:53:18.889 --> 00:53:32.675 <v Wojciech Wegrzynski>And this experiment was the investigation after the World Trade Center collapse, which is also heavily tied into the developing the fDS and, uh, How the software had to be changed to. 00:53:32.858 --> 00:53:33.909 <v Wojciech Wegrzynski>Um, make. 00:53:34.141 --> 00:53:35.612 <v Wojciech Wegrzynski>This investigation, the possibility. 00:53:35.942 --> 00:53:40.021 <v Wojciech Wegrzynski>So I hope you will enjoy it as much as this episode. 00:53:40.472 --> 00:53:41.282 <v Wojciech Wegrzynski>And for now. 00:53:41.322 --> 00:53:43.121 <v Wojciech Wegrzynski>thank you very much for being here with me. 00:53:43.300 --> 00:53:49.806 <v Wojciech Wegrzynski>Thank you for sharing your listener experience with me, I've received so much feedback through the listener experience survey. 00:53:49.867 --> 00:53:52.146 <v Wojciech Wegrzynski>Uh, I'm very, very happy with that. 00:53:52.146 --> 00:53:53.827 <v Wojciech Wegrzynski>And very glad you did. 00:53:53.954 --> 00:54:02.376 <v Wojciech Wegrzynski>Share that with me, I'm going to dedicate a half of the Q and a episode in early January answering some of the stuff. 00:54:02.476 --> 00:54:06.036 <v Wojciech Wegrzynski>I cannot just reply you with an email because it was kind of anonymous. 00:54:06.606 --> 00:54:11.226 <v Wojciech Wegrzynski>But, uh, I'm going to reflect on what feedback I've received in the QA. 00:54:11.586 --> 00:54:13.867 <v Wojciech Wegrzynski>And I'm going to tell you what I'm going to do with it. 00:54:13.956 --> 00:54:18.757 <v Wojciech Wegrzynski>What's the outcome of the survey and what I have processed out of that. 00:54:19.266 --> 00:54:22.476 <v Wojciech Wegrzynski>Um, one of the Fitbit was to make this outros shorter. 00:54:22.936 --> 00:54:25.907 <v Wojciech Wegrzynski>I seem to just fail, incorporating that one, but I'll improve. 00:54:26.356 --> 00:54:29.177 <v Wojciech Wegrzynski>I'll make this thing more concise in the future. 00:54:29.496 --> 00:54:32.501 <v Wojciech Wegrzynski>Anyway, thank you very much for being here with me. 00:54:32.753 --> 00:54:33.864 <v Wojciech Wegrzynski>Christmas coming soon. 00:54:33.864 --> 00:54:38.963 <v Wojciech Wegrzynski>So if you celebrate Christmas or Christmas to you and your family, I hope you have a lovely time. 00:54:39.023 --> 00:54:42.173 <v Wojciech Wegrzynski>If you don't celebrate Christmas, just have a great time around there. 00:54:42.713 --> 00:54:48.951 <v Wojciech Wegrzynski>And, uh, I hope you will find some joy in the calmness and, escape from the mad world that surrounds us. 00:54:49.400 --> 00:54:51.110 <v Wojciech Wegrzynski>In this special time. 00:54:51.365 --> 00:54:53.510 <v Wojciech Wegrzynski>this year not taking any Christmas break. 00:54:53.811 --> 00:54:57.320 <v Wojciech Wegrzynski>I have a podcasts prepared all the way into the new year. 00:54:57.681 --> 00:55:01.161 <v Wojciech Wegrzynski>So next Wednesday, I see you here again. 00:55:01.311 --> 00:55:01.791 <v Wojciech Wegrzynski>Thank you. 00:55:01.820 --> 00:55:02.210 <v Wojciech Wegrzynski>Bye.

081 - The origins of FDS with Kevin McGrattan

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