 can you hear me now online yes no yes yes I guess we were just looking at the results from assignment one and I just said about assignment two that I will give you additional time to work on it and if you have questions feel free to ask and I have been asked here to if we can plot velocity as arrows instead of colors the answer is yes and usually use a glyph is up there in para view you apply after a long time usually you see things oh that was ugly well you have to work on it I will find the solution to this keep doing exercise I guess you how I have because you have to decide which parameter so you have to decide which vector to use and we want to use you the velocity after a while give me a sec oh yeah now you can it's you have to select glyph and then you have to set that orientation arrays based on velocity and the scale arrays based on velocity now you have a lot of arrows you can reduce them now we have 5000 points I think you can do 1000 and you can remove these and only see the arrows then you can play around with the size of the arrows with the color of the arrows you can do many things but this is not really open form related this is part of you related just and typically in part of you you can find quite a bit of documentation online now to use part of you and it's the same if you're using probably for open form or for any other tool for those that are online I've been asked why there are two default fluxes the reason is that when you need to do sp3 instead of diffusion you need to provide initial and boundary condition for the flux and for the first moment of the flag for the second moment of the flux so in your case you're doing the fusion you can't forget about the second default flux is there anyone that has finished what's the K effective you obtain group is there anyone from group 1 what's the K effective group 2 anyone 1.4 4 raise your voice 1.4 4 6 this is a K effective don't be shy with number 1.406 give me another 2 6 another one let's get PCM at least and this is for a zero gradient or for a fixed value you should have a fixed value and a zero gradient boundary condition so zero gradient and do you also have results for the fixed value that's the same thing for everyone group 1 again fixed value how much is the same group 3 0.5 there's a problem 0.4 39 give me another number group 4 interesting gonna be interesting to figure out what changed because now the funny thing is that yesterday I obtained both and I don't know why but we'll try to figure out why in the morning yesterday obtained one and the afternoon the other I think it's a matter of which temperature we are solving it at but let's see let's try to do it together so I'll tell you what I would do hopefully I will remember to do all of it would be nice so let me get the folders if you get a wrong number don't be worried sometimes it can be that you forget to set a little parameter and no GenFoam is big sometimes you need time to go through all of it and make sure that everything is correct they said even myself yesterday did it and I obtained two different K effective and I think it was because at some point I forgot to set a temperature somewhere anyway so what I would do is what I already did while waiting I copy pasted the case into a starting case to just not to lose what I did before so this is what we had from exercise one and as I said we have a lot of inputs that are given in the input folder and I said that there are nuclear data and there is a mesh and you need both and you need both where well in the neutron in the neutral region so you're going to constant going to neutral region you have a poly mesh you want to change it into the new poly mesh can you leave it like this no you need to change the name it has to be called a poly mesh we call it poly mesh then we have all the nuclear data that we're in there that we don't like because they were kind of dummy files with no content or very little content and we want those that I gave you that includes real cross-section data put it in there I said the idea is let's take a look it's gonna be small but I will do it anyway because you can open it on your computer you look into it you will see things like energy group 6 precursor groups 8 so we are solving for 6 energy groups 8 precursor groups and we have different cross-sections for the heat exchanger intermediate circuit main etc and you will see that cross-sections are each one of them is into 6 groups yes it is there for a later exercise it's not no not at all no I mean in open-form you can throw in random files it's we'll simply not read them and I ask you to check parameterization and nuclear data axial expansion you look at it and there's nothing well of course because we don't have cross-sections for axial expansion this is for fast reactor for solid fuel fast reactor there's nothing in there so we don't parameterize for that what about t cool nothing because our coolant is the fuel what about fuel temperature there you have something if you look at it you will see that the cross-section are slightly different than those in nuclear data these are cross-sections that are valid for a different temperature this is how we parameterize the cross-section which give one cross-section set at a nominal temperature one cross-section step at a perturbed temperature and we do an interpolation so we are parametrizing our cross-section based on the temperature of our fuel coolant we call it fuel here because it's a molten salt reactor so what's in there that we may need to change so we have our nuclear data we have them parametrized we have control rod movement I haven't mentioned control rods so we don't touch it we have the mesh what about Neutronic properties and it's a smith small but it's already diffusion we are happy we keep it we wanted to have a diffusion but it says eigenvalue falls we want it true it was in the assignment we want an eigenvalue solution so we set eigenvalue Neutronics to true so now we look into this and we realize we have touched everything we wanted to touch so we forget about constant hopefully I did everything we don't touch fluid we don't touch thermomechanics because we are doing just Neutronics and then we look into system and of course we will have to touch the control dict we do it now it's small so let me do it because this is important I want to do it in a way that you see what we do so we go to our starting case 2 and we look at system control dict and you look at it as usual you have a start time okay we start from zero you have an end time and we don't care about the time as I said before these are all time steps we want to simply iterate and I said we would like to have approximately 100 iterations so if our start time is zero and now our end time is 10 what's the delta t to get to 100 iterations 0.1 right 0.1 time steps we do it 100 times we will get to 10 seconds this is the way we iterate 100 times in open form some things we don't really care about standard open form things what do we want to solve for I said we want to solve only for Neutronics so no fluid mechanics no energy all Neutronics true salt thermomechanics false liquid fuel stays as it was just true just time step do we need it no we are not doing thermo hydraulics we don't want to adjust we just want to run 100 iterations so we want our time step to stay 0.1 and get to 10 in 100 iterations this is how we set iterations we use a fake time stepping what happens if you leave adjust time step to false well it will try to adjust your time step based on current number and it is not calculating the current number so you may run into some problem the rest we don't care we have questions about this control dict does these times the fake time stepping make sense to you not really maybe a little bit we want to iterate 100 times we do 100 times type of 0.1 that will not enter anyway but just force open form to do 100 solutions we will be in a loop it will start to okay I solve one am I at the end no I need to solve once again once again once again for 100 times that's how we create iteration and since we are solving for eigenvalue the DDT the derivative over time has been taken off so we don't really care if our time step is 0.1 1 10 as far as we do it 100 times it's tricky this is a very open foamish way of doing things because open form was born for CFD and you always have time somehow so we do it this way what else am I missing I said that we need to set the power to 20 megawatts and I said that this thing is inside the reactor state how do I find reactor state you can locate you can grab you can think what it could be you can imagine that reactor state may change over time right so the most logical place for it to be is in the time folders so you get to not here you get into your time folder from zero could be in neutral region it's not and I'm sorry about that this is again a way we have in open form because in these folders we typically have fields a reactor state as a k effective and power it's not a field we keep those things in something called uniform and in there there is something called reactor state if you cannot find it you grab it you locate it or best thing when you are alone at home and you want to do this thing before doing anything you look everything that there is inside your folder you want to familiarize with every file that is in there and while doing that you will bump into something called reactor state that has a power and a k effective we said that our target power is 20 may or you look at the documentation if you have you know two three hours read the documentation these things are explained so we have our 20 megawatts is to the seven right we said we want to megawatts so well not of zeros for not much to the seven what's this is 20 megawatts what about k effective while k effective is what we want to find does it make sense to give a k effective in there at the beginning kind of this is the initial condition it is you know when you set a new field you set an initial condition you also should do it for k effective is the initial guess that you provide not change much but it's gonna make your computation faster so another thing that we need initial and boundary conditions many of you notice that there are default flux and the default flux to full flux to it is for sp3 simulations you don't need it default flux let me open it on the terminal now what you had here was clearly wrong we were giving a fixed value to everything and well it's not completely wrong there are at least two things that were wrong which is the boundary conditions for the wedges so we are doing 2d and you need your front and back to be treated as wedges I don't remember the name of the front and back front and back okay so what you need to do was to create two things that are called well I can actually do it right very front oh yeah sorry right double check why I think it's the first one it finds more relatively sure it's the opposite you sure okay we'll try here the question is you may wonder why we are discussing it's because this thing it says all fields equal to fixed value and we are wondering we don't remember if openform gets the first one that it finds or the last one so if it says okay I found something called front I use it or I found something called front and then I something something else that tells me all the fields equal to fixed value second case is wrong first case is right we'll try it if it gives us a mistake we'll change it when we have front back wedge wedge you understand why this wedge thing right we have our front and back that are kind of similar strange symmetry conditions and this strange symmetry in openform is treated using a specific boundary condition that has a name and the name of this boundary condition is wedge same as Monday and this is standard it's not gen form this openform right finger crossed this is correct am I missing something let's try we go up to the roots of our folder and we try to run gen form at the beginning you always see this mesh to mesh addressing that takes a while do you understand what openform which gen form is doing we have and now we have two different mesh even though fluid dynamics is not used we gave gen form a mesh for fluid and a mesh for neutronics and since it has to transfer field between the two at the beginning it does a mesh to mesh projection and creates an addressing to be able to project fields from one mesh to the other and traction field from one mesh to the other the complicated thing and it takes a while for openform to do it it worked so it was not wrong Alessandro if it worked okay that's interesting I'm curious now let's let's try so you said that if we change the control dict to liquid field falls which I don't find it if it fuel you run it I should get a 1.2 something right faster than thermal hydraulic so give me food for those while I give you the next exercise let's change it back to what it was and then I will think about what happened here I just wanted to show you some results so let's run it again I think I know what happened I will tell you so someone online asked me how to do to visualize with part of you in case part of form doesn't work I told some of you so what you do is you create a file that you can call whatever you want case dot form just an empty file then you do part of you WSL to do these things on time apparently then you open a case you search for your case dot form and it will open simple as that so we have our case we go to the last time steps that we hope it was enough to converge the solution and you look at things you can look at fluxes for different energy groups does this make sense to you as a flux I in the center it goes to zero this was the fixed value Dirichlet boundary condition it was fixed value zero have you tried to look at what happened if you gave zero gradient everywhere so if you give zero gradient everywhere your flux will be flat because there is no reason for the flux to diminish towards the boundary you will see a flat flux and why do you have a higher k effective cause you have no leakages higher no leakages your k effective will increase you remember the six factor factor formula last two factor in the six factor formula leakages and if you remove leakages with a zero gradient your k effective will increase right which will be actually equal to the k infinity exactly so when you do is actually when you have a geometry like this giving zero gradient everywhere is actually a good way to check that your k infinity is what you expect because often when you get cross-section data the tool that gives you the cross-section data will also give you the k infinity typically serpent does that I assume open MC does that no good it's it's a good check it's like in serpent they typically give you the k infinity then you give the cross-sections to gen from and you check that k infinity is the same that way you make sure that you your transfer of cross-sections from Monte Carlo to deterministic was correct well the other fluxes are very similar actually so it doesn't change much to flux five pretty much the same what happens if you look at precar source they look always the same they of course the scale is different but why well because we didn't move our fuel now we did just a single neotronic solution so there's no moving fluid our precursors are sitting there and you have higher for a car so where you have higher flutes in the city things will change in the next assignment next assignment we want to try to put together fluid dynamics neotronics and get our first multi physics simulation before we move forward we have questions about this exercise all right then I will answer a question that I got online sometimes ago I've been asked if you can do both porous medium and heterogeneous geometry in gen form the answer was no a month ago and now it's yes and no meaning we are working on that it's probably going to be ready in a couple of months we should be able to heterogeneous fuel and homogeneous fuel depending on what you prefer to do without even an option it will automatically recognize if you're doing homogeneous or heterogeneous so for the personal line was if you can be patient and couple of months we will be there for the moment when you do fuel we mainly do porous medium that's how gen form was born but we are modifying it to be a bit more flexible may missing something I can go to many things that's why I thought that we need I need to think what happened there liquid fuel impacts a lot of different things it impacts the fact that you move around the precursor or not it impacts the fact that you provide the power directly to the liquid instead of giving it to a structure and then to a liquid and there's at least another which I believe is the reason why you can get different results is that it decides whether we use the temperature of the coolant to parameterize nuclear data t fuel or field temperature because you remember we gave different cross-section set for nuclear data nuclear data field temperature it means we are trying to parameterize based on temperature of the fuel if you have a solid fuel reactor the temperature of the fuel it what comes from the power model fuel pin if you have a molten salt reactor the temperature of the fuel is actually the T of this free dynamic solver so you have to use that switch to decide how you are parameterizing and I believe what happened there is that gen form when you say false is go is try to go and read instead of the temperature of the coolant the temperature of a fuel that is not there and that is set automatically to zero so you are essentially parameterizing your cross-section based on a temperature that was never calculated that makes sense it's not easy but you can see how you know fuel has two different meanings for a fluid react fluid fuel reactor and a solid fuel reactor and that switch as implications and one of the implication is parameterization and I think for those of you who set liquid field to false gen form was trying to parameterize the cross-section based on a fuel temperature that has never been calculated and that is set to zero that would explain why you got a much higher K effective because the parameterization of cross-section makes it for a higher reactivity for lower temperature because we have a negative feedback so if all of a sudden open form gen form was reading or was using a temperature of zero because it was never calculated you would get much higher K effective or this is my call it educated guess about what's happening that I should double check that makes sense 30,000 PCM it's a lot and it may only come from a completely wrong parameterization of cross-section so always be careful if there is a flag that tells you liquid fuel and you have a liquid fuel set it to true all right I would suggest since we are very late as expected I would suggest that we move to the third exercise that is a bit more interesting this time we try to solve the two things together so we show it to you so the idea here is let's see if the velocity field doesn't impact on neutronics for that we need a couple solution we need fluid dynamics plus neutronics since we don't want to run a transit which can keep doing eigenvalue may seem strange but eigenvalue solver will not care if you change it's underlying precursors distribution the eigenvalue solver will adapt it will keep being an eigenvalue solver so what we want to do now is we start from what we had and from the previous two exercises and I would suggest to start from exercise 2 because it now includes both exercise 1 and 2 that's why I told you please copy paste exercise 1 to 2 the second so now you should have a case where you have both matches you have neutronics that has been set your fluid dynamics that has been set you have everything start from there and you try to run a case with coupled solution and fluid dynamics and I would like you to try to plot the results see how the precursor distribution change and see how the case effective changes this is gonna be interesting it's gonna change and I have as usual some tips on how to do the exercise think about what's changing physically for neutronics is there something that we need to solve for now that we were not solving for before maybe there's something that is starting to move around and if you want to solve for that something moving around you will need initial and boundary conditions you will need a new field that you will have to introduce in zero because otherwise it will simply tell you I cannot find it you can try it this is a tricky one so I have to give you a hint sometimes when you use this kind of solvers you will run into numerical troubles you will add this physics and all of a sudden it doesn't converge to well and that's the moment where you look at things like PV solution and Phoebe schemes and when you look at Phoebe schemes as Stefano mentioned to you on Monday most of the time the problem comes from the divergence it's the tricky part to solve and you can choose different schemes there is one that is always bounded meaning it doesn't give strange oscillatory behavior it's first order so it's not super accurate but it's stable it's the upwind scheme think about it you will need to use it and the last hint that I give you is you can start as we did before you start from zero your initial condition is gonna be zero velocity zero pressure is it a good starting point or can we start from something better since we already have solutions for velocity I'm already telling you yeah you should use the velocity solution how to do that you can think about it is the assignment and suggestions so are there sign assignment and suggestions clear enough you have questions otherwise I will let you have fun and as usual we are here if you have questions you call us if you have doubts that you think out of interest for the whole group you let us know and we're answer to the whole group okay I go back to the assignment and anyway you should have the PDF so you can keep also the suggestions with you check what I said this should be a bit shorter than the one we did before so hopefully we can do it before we have to go to the discussion session oh we have the coffee break now now now now okay so think about this for two minutes and then we go to the coffee break so for those that are online we are taking a break will be back in 10 15 minutes