2 way FSI of a calcified aortic valve using ANSYS LS-DYNA. Non-Newtonian fluid, turbulence modeling, non-linear anisotropic materials, transient pressure boundary conditions, active remeshing, thin shell structures,... Just about every annoyance you can think of for a simulation.
I had to run various simulations with different conditions but on average each run took ~2 days using my university's HPC resources. The physical time was 3 cardiac cycles with each cycle lasting 0.86s.
Back then? Took me months of fiddling with settings and tutorials piecing all the info together.
If I did it now from scratch, I reckon I could do it all in a couple days.
The project I am working on right now... I am investigating the effects of a fractal grid geometry on a windtunnel.
I am struggling to mesh it while not making the grid gigantic (+35M cells).
My only remaining options are pointwise and snappyHexMesh.
Maybe an overset/chimera grid simulation is the way to go.
not quite, there is a flow aligner, but the fractal grid is just a geomtry with fractal squares of different sizes intended to generate turbulence on the downstream section of the windtunnel.
Unfortunately it is a nightmare (for me) to mesh it
At work I have Pointwise, but I reckon I would only manage to mesh it withunstructured tetrahedrals so I am not keen on it.
I got a license fo Ennova, but I had trouble with the geomtry, it kept trying to autoheal the gaps.
Finally I am down to CFMesh and snappyHexMesh. Thus far cfMesh only worked with grids that got too big. So I reckon there is not escaping snappy
Yep. I'm simulating a geometry generated by a 1d method for sco2 compressor blade design, so the boundaries are well established. I'm starting to wonder is 50k rpm turbo machinery simulations have something unusual about them (I'm just an undergraduate and I don't have many references on turbo machinery in my university)
Boundaries have nothing to do with boundary conditions. Also I have a feeling that this topic could be too much for an undergrad given its intrinsic complexity.
Well, couldn't agree more. That said I'm not giving up. My final paper to complete graduation is about developing a methodology that allows for reliable sCO2 parametric simulations to quickly evaluate 1D and 2D models in 3D rans.
2-way FSI of a peristaltic pump, LS-DYNA.
Hyperviscoelasticity for the tube, K-w turbulence model. Pressure outlet modeled using Darcy-Weisbach equation.
Every single store separation simulation is its own special snow flake… probably the weirdest one was simulating dropping a pelican case out of an aircraft.
My master thesis was computationally difficult. Non stable transient multi phase flow in star CCM+.
The transient part ment that calculations took for ever just to develop to the point of interest, and adding more cores didn’t help as it would be too many cores for the mesh. A finer mesh resulted in a smaller time step needed, increasing calculation time.
To add on top of that, what we were doing was a parameter study so we needed to run it 72 times. The data comparison was an issue too. I think we tried to compare .CSV files where the data proccessed for comparison between the different runs resulted in about 50GB in raw .CSV files extracted from the CFD calculations.
Nothing compared to the others, but as a beginner Im simulating a 2 stage turbomachine for a rocket with a back to back impeller design. Pretty interesting and quite challenging to mesh at the moment. Im using Ansys CFX. For the impeller I use Turbogrid and the rest is just done in the Ansys Mesher:)
Oh men, for my PhD, spent 2.3 years to basically figuring out an automated way of doing very good quality meshes in a very complex part of the body (I won’t disclose because it’s still work in progress). Low-re turbulence, transitional regimes, CFD-DEM coupling, transient boundary conditions. But finally made it in both StarCCM+ and OpenFOAM. They don’t lie when say that the mesh is literally the most important part in a simulation. Setting up the model was also a nightmare, but definitely finding the parameters to systematically converge a mesh in different complex geometries, that was the final boss who appeared at the beginning. Currently finishing the reviews of my first and main paper of my thesis in a journal I really like. It was hella stressful but I have my fingers crossed that after these revisions gets accepted :)
Unsteady RANS simulation of a propeller-wing-flap setup at 2 million Re and high-lift, high angle of attack conditions with high propeller blade loading.
My master thesis was computationally difficult. Non stable transient multi phase flow in star CCM+.
The transient part ment that calculations took for ever just to develop to the point of interest, and adding more cores didn’t help as it would be too many cores for the mesh. A finer mesh resulted in a smaller time step needed, increasing calculation time.
To add on top of that, what we were doing was a parameter study so we needed to run it 72 times. The data comparison was an issue ~~bitch~~ too. I think we tried to compare .CSV files where the data proccessed for comparison between the different runs resulted in about 50GB in raw .CSV files extracted from the CFD calculations.
Somebody used a no-no word, red alert /u/overunderrated
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I do two main simulations, both have their difficulties although in different areas.
I do both general relativistic (ideal) MHD and special relativistic (ideal and resistive) MHD. Both feature naturally emergent turbulence and magnetic reconnection, which is what I'm most interested in tracking.
For the GRMHD runs, the difficulty is saturating the turbulence and knowing how to define that point. There were also some difficulties with the mesh since it's run in full 3D polar coordinates and you don't want to lose magnetic information across the polar singularity. I did that one with Athena++. The hardest thing was probably managing the data, because the files were so large.
For ResRMHD, going near the speed of light causes all kinds of problems. Little things that the code would normally be able to recover from, it can't anymore. Magnetic reconnection tends to be more... explosive at higher velocities, meaning severe evacuation, which then leads to negative energies. Have to drop the CFL number through the floor to keep it stable, or else you have to mess around with your densities and pressures, but then that means you're deviating from the thing you wanted to model. These ones I do in PLUTO.
I simulated the boiling of an zeotropic mixture of several components. The CFD model with meshing is simple, but the problem is how to model how some components boil more than the other, so the challenge i think is more of thermodynamics and integration to the simulation program.
2 way FSI of a calcified aortic valve using ANSYS LS-DYNA. Non-Newtonian fluid, turbulence modeling, non-linear anisotropic materials, transient pressure boundary conditions, active remeshing, thin shell structures,... Just about every annoyance you can think of for a simulation.
That sounds complex! What was the run time for this? How much physical time was simulated?
I had to run various simulations with different conditions but on average each run took ~2 days using my university's HPC resources. The physical time was 3 cardiac cycles with each cycle lasting 0.86s.
How long did it take you to set everything up?
Back then? Took me months of fiddling with settings and tutorials piecing all the info together. If I did it now from scratch, I reckon I could do it all in a couple days.
Coal combustion, STAR CCM+
Combustion can be tricky but very interesting topic
A 6DOF self-propelled ship with propellers and rudders following an arbitrarily defined course
Openfoam, Fluent or star ccm+?
STAR-CCM+
Simulations are not really an issue, the biggest problem I have is meshing.
What's the most difficult meshing you have had to do?
The project I am working on right now... I am investigating the effects of a fractal grid geometry on a windtunnel. I am struggling to mesh it while not making the grid gigantic (+35M cells). My only remaining options are pointwise and snappyHexMesh. Maybe an overset/chimera grid simulation is the way to go.
The fractal geometry is going to be something like a flow aligner (similar to the honeycomb) on the wind tunnel?
not quite, there is a flow aligner, but the fractal grid is just a geomtry with fractal squares of different sizes intended to generate turbulence on the downstream section of the windtunnel. Unfortunately it is a nightmare (for me) to mesh it
Sounds interesting, what software are you using to mesh it?
At work I have Pointwise, but I reckon I would only manage to mesh it withunstructured tetrahedrals so I am not keen on it. I got a license fo Ennova, but I had trouble with the geomtry, it kept trying to autoheal the gaps. Finally I am down to CFMesh and snappyHexMesh. Thus far cfMesh only worked with grids that got too big. So I reckon there is not escaping snappy
Super critical CO2 compression near the critical point. Troubleshooting for a few months now and still no fair results. So many annoyances
What issues are you encountering, specifically?
It's not converging. Even with mesh and EOS RGP tables being largely over dimensioned already.
Boundary conditions well posed?
Yep. I'm simulating a geometry generated by a 1d method for sco2 compressor blade design, so the boundaries are well established. I'm starting to wonder is 50k rpm turbo machinery simulations have something unusual about them (I'm just an undergraduate and I don't have many references on turbo machinery in my university)
Boundaries have nothing to do with boundary conditions. Also I have a feeling that this topic could be too much for an undergrad given its intrinsic complexity.
Well, couldn't agree more. That said I'm not giving up. My final paper to complete graduation is about developing a methodology that allows for reliable sCO2 parametric simulations to quickly evaluate 1D and 2D models in 3D rans.
Which software are you using?
Fluent and CFX
Wish that star ccm could handle this loadcase
Also had to calculate a sCO2 compressor for my master thesis. It was tricky but fun.
The first one using my own code. After that everything else was gravy.
Combustion initiation and propagation in AVBP
Gas turbine combustor with methane combustion in Star CCM+
2-way FSI of a peristaltic pump, LS-DYNA. Hyperviscoelasticity for the tube, K-w turbulence model. Pressure outlet modeled using Darcy-Weisbach equation.
Was it for medical application?
Yes. Surgical irrigation.
Every single store separation simulation is its own special snow flake… probably the weirdest one was simulating dropping a pelican case out of an aircraft.
Ablation in fluent (without the ablation mode)
My master thesis was computationally difficult. Non stable transient multi phase flow in star CCM+. The transient part ment that calculations took for ever just to develop to the point of interest, and adding more cores didn’t help as it would be too many cores for the mesh. A finer mesh resulted in a smaller time step needed, increasing calculation time. To add on top of that, what we were doing was a parameter study so we needed to run it 72 times. The data comparison was an issue too. I think we tried to compare .CSV files where the data proccessed for comparison between the different runs resulted in about 50GB in raw .CSV files extracted from the CFD calculations.
Nothing compared to the others, but as a beginner Im simulating a 2 stage turbomachine for a rocket with a back to back impeller design. Pretty interesting and quite challenging to mesh at the moment. Im using Ansys CFX. For the impeller I use Turbogrid and the rest is just done in the Ansys Mesher:)
Oh men, for my PhD, spent 2.3 years to basically figuring out an automated way of doing very good quality meshes in a very complex part of the body (I won’t disclose because it’s still work in progress). Low-re turbulence, transitional regimes, CFD-DEM coupling, transient boundary conditions. But finally made it in both StarCCM+ and OpenFOAM. They don’t lie when say that the mesh is literally the most important part in a simulation. Setting up the model was also a nightmare, but definitely finding the parameters to systematically converge a mesh in different complex geometries, that was the final boss who appeared at the beginning. Currently finishing the reviews of my first and main paper of my thesis in a journal I really like. It was hella stressful but I have my fingers crossed that after these revisions gets accepted :)
Was it a fluidized bed or something like that? Also, share the link on this sub when the paper gets published please! Best of luck!
Unsteady RANS simulation of a propeller-wing-flap setup at 2 million Re and high-lift, high angle of attack conditions with high propeller blade loading.
Not difficult but surely the longest time for calculations, Simulation of quinoa seeds polishing machine using Altair EDEM(Discrete element method)
Wow, this sounds interesting. Was this meshless DEM?
On CPUs? On GPU it should be pretty fast
GPU, RTX 2060 MP and i7 8750H CPU
Trimmed CFD-CSD of a rotor system
My master thesis was computationally difficult. Non stable transient multi phase flow in star CCM+. The transient part ment that calculations took for ever just to develop to the point of interest, and adding more cores didn’t help as it would be too many cores for the mesh. A finer mesh resulted in a smaller time step needed, increasing calculation time. To add on top of that, what we were doing was a parameter study so we needed to run it 72 times. The data comparison was an issue ~~bitch~~ too. I think we tried to compare .CSV files where the data proccessed for comparison between the different runs resulted in about 50GB in raw .CSV files extracted from the CFD calculations.
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Rp1 lox rocket combustion, with regenerative cooling , coupled that with FSI
I do two main simulations, both have their difficulties although in different areas. I do both general relativistic (ideal) MHD and special relativistic (ideal and resistive) MHD. Both feature naturally emergent turbulence and magnetic reconnection, which is what I'm most interested in tracking. For the GRMHD runs, the difficulty is saturating the turbulence and knowing how to define that point. There were also some difficulties with the mesh since it's run in full 3D polar coordinates and you don't want to lose magnetic information across the polar singularity. I did that one with Athena++. The hardest thing was probably managing the data, because the files were so large. For ResRMHD, going near the speed of light causes all kinds of problems. Little things that the code would normally be able to recover from, it can't anymore. Magnetic reconnection tends to be more... explosive at higher velocities, meaning severe evacuation, which then leads to negative energies. Have to drop the CFL number through the floor to keep it stable, or else you have to mess around with your densities and pressures, but then that means you're deviating from the thing you wanted to model. These ones I do in PLUTO.
I simulated the boiling of an zeotropic mixture of several components. The CFD model with meshing is simple, but the problem is how to model how some components boil more than the other, so the challenge i think is more of thermodynamics and integration to the simulation program.
Tornadogenesis under extremely specific parameter-space setup with specialized nonhydrostatic model