 For those of you who don't know me, I'm Arvina O'Raim. I do the education and knowledge transfer. And I'm really psyched about our student award program. And our first student talk is by Anders Dunsgaard, who won the student holder award this year. And we'll roast him during the roast at the bank. I've been like giving him a little more of a citation. And we just for here to like explain about the science, which is on green scale in the medical modeling of granular mechanics and steel dynamics. Yeah, thanks, Arvina. Thanks for coming. I'm currently a postdoc at the Christian Institution for Schnauropathie, but I did my PhD back at August University in Denmark. And I'm going to present those also there. Also, this talk is not very technical. I wanted to make it more accessible. But if you're interested in the specific mathematics and numerical specifics, please come up and talk me afterward for our military doing this workshop. So, yeah. And a bit of a motivation slide. Running on materials that are only honest, just in the sediments, icebergs, asteroids, serials, things, all sorts of materials. Even human clouds, they might end up on the surface under some conditions. And they are important for many processes. And thus, absolutely, the case of non-geodynamical problems, such as tensile motion, and disability of earthquake, rupture zones, tibial tube flows, or debris flows, man-slides and so on, crossing processes, and as we will see a bit later on, circulation processes. So, the running on zones can be defined as a conglomeration of discrete solids and macroscopic particles that are characterized by inelastic interaction. So, when granular grains interact, they lose a bit of energy in that interaction and that's typically a proof of fiction. So, taking sand as an example, that's a granular germ that we all know of. And it's really complex because it can change phase. So, on the left, we have some sandpipes, then we have gravel pits, and even though there's a surface room, they're stable. They're not very due to the importance of the best label. Unless we exceed the angle of repose, then the sand is almost on the surface, and they have been reviewed. Then, the third mode of kinematic state is the gas phase. We will have sandstorm, which has a stable bottom at the bottom, where it's highly diluted, there's not a connected energy, and relatively few interactions because of the high porous activity. And stress is inside of it, and the air on the dunes are transferred very heterogeneously. And this animation that we visualized by using great elastic discs that are put in polarized light. And you can see this stress as these light bands. And some of these grains are, you can see a lot of the stress in what we call force, and our genes on other grains in that ball. So, that's difficult to level in continuous modes anyway. If you have a dentist, it's going on a drill like you on the bottom left, there's an American model, and the colors correspond to the stress. And there's no bias intermediate stress, that's how. But you define a bench granule on a drill that has been pre-consolidated, then you have a curious behavior because you have a very linear developments, then you have a peak shear stress, and then you reduce the shear strength initially at bits to what we call the critical state, where everything is constant, or subsequent shear strains. And stress also at development velocities of volume. So during this early behavior, you typically have a dilation, if it's compacted to begin with, then you have a constant volume in the steady state. If on your hands the material is very loose, to begin with, you can have consolidation in the beginning and then convert you towards the steady state. So, so far, people within the field have been unable to control very general mathematical formulations of granule mechanics, and that's a problem because granule mechanics are important to many processes, and you need something to describe the mechanical features during the deflation process. And the main problems are caused to changes which I just showed, and also these space changes, and you need to capture all in the general model. So you can model this numerically, and the approach which is adequate depends on your scale of interest. So for instance, if you're interested in the contacts between grains, you can use that simple like finite element modeling to really resolve the stresses in this contact. You can take a more average approach where you consider the average behavior of the grain, and then interact between grains, and you can scale them all the way to material and structure scale. That's the continuing models that are on the material and structure scale are no better than the simplified assumptions that put into the mathematical models that work in and around materials in these cases. So for my research, I've been really interested in going from the path school to material scale to know how to better constrain the nations for the larger scale. So I chose to write my own codes instead of using other people's code because my experience of doing it like a black box using other people's code hands, I knew from the very sides that I would download like to play and we're pushing different processes into the bottom line and out again and doing everything from the bottom line to be allowed to have that disability as and quickly substitute in different cases. So it's three dimensional, it's called the numerical method that is going to discrete a limit which is quite computationally expensive because it relies on explicit time integration. So the runtime is can easily be weeks a month's possible duration. And then I've included an actual fluid coupling. So I've got everything saturated and then the fluid flow is solved through post-inclusions for many strokes or the ocean flow. All of the unsaturated case you can have a simplified model you've got to have an impregnation. It's left with 30,000 lines of code all of the heavy lifting in the computations done on GPUs using a really cooler CPU language. But it's really a pain to write in this language and the exception of the Z-button is horrendous because you have another layer of hardware abstraction that you need to do it. So the user has to occupy herself with just a way more easy to use Python into baseball and simulation setup and post-processing and things like that. It's being written first and built in general solution tools. And I'd like to just go on why I chose to write it in open source. And I'm sure some of these that I'm talking will actually add to review. So first of all, and the cells you produce with open source are reproducible because people can take out the space exactly on a software and run it by themselves. That's something within the macro modeling is quite unique, I think, because if you have some extensive lab equipment that you want to reproduce well, so with that it's just economically not possible in a lot of cases. So that's something that we really need, I think. I also think definitely that research products with publications, but also software should be available to the general public if we're able to. And I think it's also good to give others the opportunity to learn, build on, and preview your tools. Also I've loaded a lot of looking at other making software, so I think it's only reasonable to give it a bit back. Just in the model, the concepts between the grains are mapped through a spatial contact search on the domain. And once all of the grain pairs have been identified, you put a contact model into place where you resolve interactive forces. And once you have the sum of forces, you can translate that into the progressive behaviors, such as accelerations towards decent positions. And there's all the optional coupling to this fluid, hot fluid, which is a rather high form of pressure over here, no proper shell there. And the grains will feel a drag force, or a form of a degrading force, rather than towards the low pressures and away from the high pressures. And I've only used the digestion through the models for my problems, which for more outputs. So for the concept mechanics, I rely on something called the software, the contact model. And it's just a series of things, sliders, and sometimes people also use viscous dash putts to get rid of kinetic energy. But I chose to use this simple approach because it's very hard to get a good look at the viscosity of the dash putt between grains would be. So we have a linear spring between the grains, pushing them away from each other in the bottom of direction and it's a denture force, which is limited to the same fraction of the normal force by a cooling friction. So that's slider. And as a result, the grains are integrated through the explicit integration, which gives the time steps quite small. It's all often around 10 to the 7 seconds. So we need to do a lot of timestamps just to make a few seconds. And for the grid base, I use a liquid seed, which makes us explicitly inclusive solutions. So just some examples. Here we have a grain inside of the fluid grid and the grain is falling downwards due to gravity. This is the Stokes-Sethic experiment. The grain, when it's falling downwards, is feeling an upwards drag on the fluid due to its interaction forces. And the fluid means the grain because it starts to displace it as we start and we start building a high pressure in front of it and by flowing around along the grain. On the cathodine cohesion, we can create some really interesting structures that can turn off gravity and just let the cathodine cohesion come together into these real-time shapes. And this is my take on the classic Sandbox-Shorting experiment, which has been used as an energy or actually as a constant cohesion. So the method itself is really flexible. It's just a grain from boundaries and you can do with it whatever you want as long as you keep the short time steps in mind. But I would like to draw on a specific usage example, which involves Iselo. This animation shows the surface velocity is observed on remote sensing and articulations and the colors to represent the velocity magnitude where purple and pink colors are very high, like on the kilometer-green scale and these orange and green colors are more like on the meter-green scale. So you can immediately see how the flow is confined to fairly thin regions of very rapid flow and because up to very high global velocities and these features transport more than 90% of the ice tax for the immense areas of accumulation. It's not accumulation, it's the coastal areas of accumulation. And it very quickly becomes apparent that if you want to understand the behavior of the ice sheet as well, you need a very good understanding of these features. They're called ice streams and they're very important for the dynamics. So people have been very interested in them for a long time and have performed significant measurements where they're filled with ice and observed the deformation profile. And it turned out the ice on the surface, they're typically kilometer-thick or something like that. And the flame on the surface, which are water saturated and deforming. The ice itself is flowing as blood flow through those little to no internal ice deformation, but it's primarily used by sliding over the sediment or by deforming the sediment. And the sediment does reach because of higher circulation of a lot of pressures. And this is just an example showing how tightly coupled the circulation mechanics are with the pressure flow. So the dots here denote surface velocities across an ice stream and here in the background we have subracial geology interpreted from seismic studies. So you'll have a sedimentary basin and you can see that the location of the sedimentary basin is in good agreement with the observed surface velocities. So in a system like that, the mechanical behavior of the subracial system is really important, while the ice will fill both the presence area but also there are some changes in the system like increased melting, increased smoke ball or whatever it's going on. And people have been fighting for a very long time for what the appropriate solution mechanics would look like. And there is one incident of which very close to being a material through the separation regulatory which no one depends to stress it can provide. While other measurements are other subjects, there's no one small like a plastic material where it was placed into completely independent forces. And a viscous behavior will tend to down from any variations in life, however a plastic biology could really create instability. So I'm going to demonstrate this in this cartoon. So a viscous tool and we change the driving stresses, then subracial friction will move correspondingly and the velocity will not change very much. On the other hand, if we have a plastic biology, then the subracial friction is constant and we can really create wide changes in ice field velocity. So I'm just going to skip that for the interest of time but we have some surface measurements that you can see stations have been put with terminals of these ice streams and ties are particularly in this inflation water pressure. So it's a natural sensitivity experiment of the ice field mechanics on the chain of conditions. And the last, this is the dispersion record looks like this, so it goes that. So we have slow creep and fast slip, slow creep, fast slip. And so that points to some sort of non-linearity in the mechanical behavior. So we designed some local experiments to really understand what granular physics are like when you disturb the stress of spring and it's due to changing the water pressure. So we have a constant shear stress and a very normal stress in the observable of the movement velocity is right. So if the sediment biology was viscous, it would fill at all times but with different velocities as it was. But the plastic, it would not grow beneath the new stress before uncomplimenting costs and above the new stress. And so on the left, we have the grains colored to the initial positions. On the right, we have the fluid pressures. And in the middle, we have the stresses between grains. And as you can see here, now the fluid pressures are going due to artificial tights and once the pressures are rising, the intergranular stresses are beginning to be modified and then you exceed the yield stress and it starts to accelerate. So pulling up the data from an experiment like this, the blue curve is the variation in pore water pressure that we put into time. The black curve is an antifreeze that's the rate the sediment moves from the glacier bar into the bottom part. We have that slight velocity that the glacier base would feel. And you can see that it's neither viscous or perfect plastic because it's creeping at slow velocities and slipping like a plastic and high-dive integrations, sorry. So we have all of these days available in the morning that we can begin to and see that there's a lot of internal genetic and activity during the green spaces and it has a nonlinear viscous relationship relative to the boundary stresses. But during slimmer, I remember the stresses on the glacier slides, other than the upper boundary slides on the constraint. That's because we modify the contact network, the stress network in the sediment as a function of the boundary stresses that we exert onto the material. So during sticky aces where it's creeping, we change the pore water pressure and that's modifies the orientation of maximum compressive stress. And when we modify the orientation and magnitude of the maximum compressive stress, the granular contact network has to respond to this change. And when it does that and the portions change our orientation and some micro-declamations. And the micro-declamations sum up to a bulk-declamations can creep. So by the nature of it, this would mean that if we use this, it would go back in oil and the pressure pressure would vary due to this non-linearity of the viscosity. But as soon as we exceed the radius, the motion of the stress, the simulation can slide without being constrained by the friction by the bed. No, sorry. So just as a matter, the discrete element method of heavenly capture is going on with dynamics and velocity changes and phase changes and all of that, there's no commutation expense. Going on to this scenario, a true perfect passivity, on a small spot again, in those properties in each of these. And I think some of these creating classes could be rather than not only population mechanics, but also a general boundary to the health of the region and things like that. So thank you very much. I think we're going to see it. Yeah, the ice is neglected. Ice is the upper boundary. That's all of this. Thank you very much.