 Okay great well so thanks everybody my name is Nicole Key I'm here on behalf of Eckerd Grohl who couldn't make it today so it's my honor to introduce Ivan Kristoff one of our outstanding associate professors in mechanical engineering. Ivan is established himself as an incredible scholar in fluid mechanics and especially in the areas of suspension dynamics, interface dynamics and flow induced deformation. His applications for his research are very broad and they include areas such as biomedical devices, hydraulic fracture, microfluidics, and soft robotics. So he's the guy that everybody wants to work with and in me when they have special applications that could use his expertise. One of the things I think I really wanted to point out maybe because I'm a grad chair and in me is that he received the outstanding a mentor award voted upon by our graduate students so he is takes his job seriously in all aspects. He's an amazing instructor for our fluid mechanics area as well so with that I'll turn it over to Ivan and take it away. All right thank you Nicole for the introduction and thank you everybody for joining us here today. It's a pleasure to be up here. Maybe I'll start off with a little joke. I don't know how many of you are old enough. I think some of you are to remember the the cult classic film Clerics from the 1990s. It's one of the original Kevin Smith movies. The protagonist Dante here that you see he keeps repeating this quote throughout the entire movie. I'm not even supposed to be here today and what is that relevant? Technically I'm on sabbatical but the organizers were very insistent that I'm here and so I am here for you right now so I thought okay I'll join and I'll be happy to talk about what I'm doing but I just wanted to make some of you jealous maybe that next week I'm back on all my sabbatical travels and this will be my view for the first couple of days at least. I'll actually be in the Republic of Cyprus so it's this tiny island here off the coast of Syria and Turkey in the far eastern Mediterranean. I'm there courtesy of the Department of State's Fulbright program and I'm doing some research at the University of Nicosia. It's a very interesting place. There's two stats I want to mention to you about it. In fact their first major research university was founded in or opened in 1992 and didn't graduate students until 94 or 96 I guess maybe four years. I don't know when they started yet if you read the statistics this is considered to be the most educated country in Europe judging by the number of higher degrees per capita and you might say well how can you have like a single research university well they have some small universities and a lot of people go to Greece Cyprus at least Republic of Cyprus is Greek speaking so they go to Greece to get their degrees but it's kind of an interesting place right it's very educated but they're sort of major research universities of which there is basically one and a half let's say only about 30 years old and so it's kind of very interesting to be there and to kind of collaborate on some new research initiatives with the faculty there so for those of you who you know from the colleagues here who got tenure or are about to get tenure and we'll have a sabbatical the Fulbright program is a great way to go do something new and interesting okay so that's my plug about my view next week but let me tell you a little bit about my research group so I wouldn't be here without the the the significant efforts of the very talented students and researchers that I work with so here's the evolution of the group from 2017 that was my second year at Purdue to 2021 I guess we didn't take a picture last year and 2020 is missing as well we didn't we didn't take our customary zoom photo but but what do we do so the name for the group is transport modeling numerics and theory it's a bit of a mouthful but what we're interested in is transport so how do things flow where do they go why did they flow how do they flow we have to come up with basic equations for that mathematical theories that's the modeling part we have to solve them somehow you're using mathematics or simulations or something else and then we like to have fun as well so you might notice that the the acronym for the lab TMNT also also spells something that's from the 90s might remember the the teenage ninja mutant turtles so that's an Easter egg if anybody caught it but here it is so so what do we work on work on many things as Nicole mentioned here's a little collage of some of them it's not it's not exhaustive but the things that we're very active in is flow and just deformation so you see here is actually a collaboration with a vitally raised in biomedical engineering this is flow in an aneurysm so this is a model created from an actual MRI image of an aneurysm in a patient and we've running simulations here where you see the flow in there that's what the stream lines are showing you as well as the deformation of it on a more basic level we're just interested also in the deformation of things like just channels or rectangular channel a very basic kind of fluid mechanical problem we're also working suspensions that's what the picture on the right is so it's a kind of particularly interesting micro mixer element in which there's a suspension flow and you see the particles which are quantified by the volume fraction and in color they kind of seem to go to the corners up here and we can explain that and have some detailed simulations of that as well somewhere in my past I worked on granular materials these are powders so here's some interesting patterns that's from my PhD work of how red particles and black particles separate and and form really interesting patterns in when they're agitated in certain ways so that's sort of a little overview of what we do but I'd like to tell you sort of how we think about research I think that's maybe helpful for those of which are not in the field maybe even the students first of all our mission statement it's kind of a mouthful right we're interested in things that are flowing fluid solid gases we like to explain experiments that people have made on this kind of things and like to make progress on fundamental problems basic stuff and that's really my goal in my research has been for a long time is to we want to generate new knowledge when I see something something that somebody has observed measured an experiment and we'd like to explain it and if we can then maybe generate some new knowledge right some new fundamental insights and so in the limited time that I have I'll tell you about just one of the the major research directions and a little bit of our success there to do so make oh sorry I forgot before before I tell you about that that particular example let me tell you how we go about research right we're interested in generating new scientific knowledge and and you know before I was at Purdue actually spent two years as the Richard P. Feynman postdoctoral fellow at Los Halls National Lab and so I read some of Richard Feynman's writings he has a lot of them maybe many of you have read them as well popular books and stories and so forth but I'm sort of interested in you know how he thought about research and because that time as a postdoc I was trying to figure out what am I going to do how am I going to think about research if I want to be a faculty member and one very nice quote is the very top where he says this is a letter he wrote to one of his students who had some questions to him so he says it though the worth all problems are the ones you can really solve or help solve all right so if you can make a contribution you should nothing that's that's the way I read it right no problem is too small to trivial if you can really make a new contribution generate some new knowledge solve the problem and another quote that I really like from him it's a little bit different this is a very famous address he gave to Caltech to Caltech's undergraduates in 1974 the commencement address it's called cargo code science there's a lot of interesting things in there but one thing he talks one thing he talks about is the importance of integrity in scientific research and he could read that he could read a number of different ways but but the sort of quote always stuck out stood out to me the bending over backwards to show you're maybe wrong right so you have to be your in science sometimes you have to be your own biggest critic you have to make sure whatever you're saying really is true you can back it up you can you can you really have discovered something you know just making big bold claims to get some press right so I think that's that's sort of one thing that also struck me about how he thought that you should sort of take on no problem is too small but even then you should just make sure that whatever you're doing is important and correct then and and you've really made sure of that okay so I will show you one technical slide and this is actually a slide from my course and me 308 is the undergraduate fluid mechanics course in a mechanical engineering and it's about flowing a pipe so this is we call fully developed laminar flow flowing a pipe down here this is something that every mechanical engineer every civil engineer anyone has to do anything to do with flows learns about how does a fluid flow in a pipe and what one very fundamental thing we know about that great days back to the 1800s is the so-called Hagen Poise law so it tells you that you have a pipe here it is just a piece of pipe and you have some flow coming in some amount of fluid then the amount of that you can push through the flow rate the amount of fluid per unit time is directly proportional to the pressure drops of the pressure difference the amount of force you're applying to push the fluid through and in one small miracle this this this proportionality can be derived from the basic equations of fluid mechanics as this equation here in the middle right so the fluids viscosity the length of the pipe the radius of the pipe and some numbers like 8 and pi show up right so it's a very basic fundamental law everybody who's ever studied any kind of pipe flows hydraulics has to learn about it this back to Hagen Poise one of the things that I'm most proud of from what we've done in our research group in the last six years is we've kind of come up with generalizations of this law that we call sort of soft hydraulics so I say okay well this is for a rigid pipe going back to the 1800s where the pipe can deform due to the flow as the pipe changes shape that changes the flow the flow that forms a pipe back and forth it's it's coupled in this kind of infinite loop and so we've developed sort of a very general theory we call soft hydraulics of how this flows go through to soft confinement so here's what one equation that we've come up with but but I'm pretty particularly proud of that is because this is sort of a mathematical result right just like how the Hagen Poise law here's the viscosity the length this were a channel the height the width and then there's some other stuff here that we actually have calculated exactly starting from the basic equations of fluid mechanics and solid mechanics right this thing can deform so you need to know some fluid mechanics and some solid mechanics anyway so along the way we got some press so for example we had a nice sort of nice little story that came out rewriting the book on on the fluid mechanics of blood vessels because it turns out once we solve this there's equations got this kind of basic laws from scratch it turns out some of the equations you will find from for example blood vessels which are deforming pipes in some of the biomechanics textbook we're not quite accurate and we got some attention for that here this was an editor choice article in this journal which has a very very long name but some of you in fluid mechanics might recognize there's this the journal where Prento published his boundary layer theory in the 1900s it's kind of a well-known mechanics journal even though it's kind of hard to hard to pronounce if you're not German anyway so I think I have only about a minute or two left so I want to say one particular place where I see a lot of applications of our results and that's why I'm very excited about them is in this idea of microfluidic hydraulic circuits so maybe some of you have seen this very nice analogy between electrical circuits and hydraulic circuits right a battery can generate a voltage difference which can drive electric current and resistors can slow down will provide resistance in the fluid analogy a pump can provide a pressure difference which can drive a flow and then deformations contractions of the pipe can lead to resistance and that's very classic based on sort of rigid pipes now the pipes are soft as I showed you before then this resistance to the flow can depend also not just in the pipe and the pipe and the fluid properties but in the pressure itself there's some kind of self-regulating kind of resistor and people are thinking about that in particular I was very excited there's a group in Denmark that I just saw in November who are trying to use our theory to explain certain certain features of self-regulating biological valves certain valves in the circulatory system of animals and mammals that can have some sort of self-regulating properties and that can be maybe explained by the fact that they're not rigid pipes they're soft pipes and the resistance can depend on the pressure so that's one little interesting thing that I want to point out so anyways I just say something about what's next I think my time is running out there's a lot of interesting things that I don't like to work on we've figured out hydraulic resistance but what about capacitance impedance these are also concepts from hydro from electrical circuits that can be generalized to hydraulic circuits and I think we don't know anything about them so so I'd like to do that and maybe if you can take just 10 more seconds I was really curious to see this this story APS is the American Physical Society that's the major society in my field and Sidney Nagel from the University of Chicago actually works in my area I've read a lot of his papers he won the APS medal which is the highest medal for research and given by the society and this was just last month and he was asked you know so now that you you've reached the top of the field you won the biggest research medal from your society what what are you going to do next there's one problem you could work on what would it be if there's one thing you can solve and become famous for what would it be and he says you know now I'm not interested in that I'll just try to have fun it's very much the process that's fun and I kind of like that right it's about discovering things it's about no problem is too small it's about sort of solving something and and the pleasure is in that not necessarily in in getting a lot of fame so anyways I think my time is up and I'll stop there thank you thanks Ivan are there any questions for him I saw that you work on the soft hydraulic circuits and the applications that you mentioned were more towards you know biology like blood vessels and things are there like any engineering applications too yeah so I think the the applications of the hydraulic things to to blood vessels things like that are the easiest ones to I think kind of understand to visualize but actually microfluidics people are interested in this as well because you would like to miniaturize things like assays and testing and things like that to sort of small devices tiny channels etched on a little soft PDMS chip and in that case you have to understand the hydraulic circuit as well you have to know how much pressure you have to put in to drive the the flow through it maybe have a reagent that has to mix with something if you're doing a assay or test and I think people were interested in that in that area as well in fact actually my my interest in this arose from that from microfluidics people are trying to design labs on a chip and and we saw some problems there had not been understood or solved anyone else yeah hi firstly thanks a lot for your talk it was really interesting and informative so I had a question on basically how you approach research because you already spoke about it right so I've noticed that you've done a lot of theoretical work as you showed from that beautiful equation so and you told that you want to work on problems that you can solve so how is it that you find like what's the process behind that you know finding problems that are easy enough to solve and are also I mean they are also important yeah that's a great question I think every PhD student has to eventually face that question what is the problem you can solve and is actually worth solving you know it's not very easy to answer sometimes we attempt to solve a problem we don't or we put aside it takes a long time come back to them figured out it's kind of hard so I think it takes a lot of sort of guessing and iterations I would say and I think working with sort of telling the students and postdocs I think helps a lot so it sit down I mean we brainstorm the ideas okay so you know somebody measured this they didn't explain it can we explain it and then we start working on it and see see how far we can go and if we can't maybe we sort of put aside and go back but but maybe just to make one particular point is that yeah we a lot of theory but we're driven by by sort of questions in the field right so maybe read a paper somebody has measured something and they say we don't know why this depends on that but they measured it right X depends on why it was a measurement why and so that's that's kind of how we usually start on finding problems that we think are interesting to solve somebody's measure something they can explain it maybe we can and then and then whether we can or not depends a lot right so I think there's been always some dead ends in every in every research program every PhD but you kind of try to try to iterate until you find the one you can solve anybody else we have time for one more well Ivan I guess I can ask a quick question so since you won that mentoring award do you have any advice for some and maybe the junior faculty sitting in here who you could kind of share some of the the keys that you think led to that award that your students really appreciate about your mentoring style sure so I guess you know everyone has their own mentoring style everyone has their different research groups some are small some are big I think what works for me because the kind of research that we do is to maintain sort of a smaller research group maybe four to five graduate students that any given time and kind of work closely with them especially if we have to kind of come up with some some some theories of some difficult equations I think it helps a lot to do to work hand-in-hand so it's kind of very collaborative style so that's my style of mentoring them and I think some students have appreciated that I think the other thing that I think someone appreciated and maybe you're all about in that nomination was that you know kind of helping them figure out what what they want to do as well right so I want student I wanted to pick up a master's in statistics to help her also with her mechanical engineering PhD get into something more more some more some more different kind of feels like machine learning and data science things that apply to engineering and so I think being supportive and trying to figure out a way to help them do that while also getting our research done I think they appreciated it so kind of trying to help them realize their own goals as well as kind of working hands on with them thank you oh we got another question way back in the corner Ivan so this is a question very specifically for you know fluid mechanics professor right what's your favorite non-dimensional number and if there were to be a Kristoff number right based on all these you know flexible hydrodynamics what would it capture what's not been captured by by those numbers two-part question what's my favorite one well I think I think our Reynolds number will be two will be two to simple as everybody knows about that one is their favorite but but in fact we did we did actually in all of this there is a non-dimensional number here it's hiding somewhere in this expression it involves a pressure a young's modulus and some geometric factors and so that that number we were we were boring we called it the fluid structure interaction parameter a big mouthful but it is a dimensions number that quantifies how much can the walls the channel bend the bending on the pressure within the channel so if it's very low it cannot bend very much very little deformation no matter how much pressure you put in if it's very high you get a lot of deformation for the pressure maybe a compliance parameter might be a better thing but there's one very particular one that comes out of here that involves like a width a height a young's modulus and a pressure drop so maybe that's my favorite one right now or there's many versions of it depending on the geometry but yeah okay all right thank you so much