Just one more thing. I cannot access the paper that has the physical meanings of the parameters that you mentioned since it's on the university website. I cannot even see its name. Would you mind sharing the name of the paper so I can search for it online.
Thank you so much in advance, On Wednesday, August 23, 2023 at 9:28:26 PM UTC-7 Mohammad Wasfi wrote: > This is great. Thank you so much Luning. I appreciate your help! > > On Wednesday, August 23, 2023 at 4:11:51 PM UTC-7 [email protected] wrote: > >> Hello Mohammad, >> >> Please take a look at my reply in blue. >> >> 1- the bed looked too rigid. I have tried to figure out what to change to >> get a similar bed to what is in my DEM simulation but I could not. My bed >> in the DEM sim is generated using a PD sampler and then is allowed to >> settle. I have noticed that there is no settling phase in the FSI >> simulation. Is this normal for FSI simulations? What is controlling the >> rigidity of the bed in this simulation? >> >> As you have mentioned, DEM and CRM are different approaches for modeling >> granular material. For DEM, you need a settling phase, so the particles are >> packed. For CRM approach, the entire soil bed is modeled as a continuum, >> you don't need settling phase, in fact, whatever soil depth you got after >> settling in DEM, you can use that thickness to model the soil bed in SPH. >> The rigidity of the soil can be tuned using Young's Modulus, I will cover >> more later. >> That being said, when I looked at the CMakeCache you posted, I noticed >> you set the flag "USE_FSI_DOUBLE" to be "ON". For the release/8.0 branch >> (which is what I believe you are using now), there is a bug when using >> double precision, which results in your terrain look rigid. The bug was >> fixed in main, see here >> <https://github.com/projectchrono/chrono/commit/46bea8f535074bcdf49ed08822e3abf098ed790d> >> >> . You can either make the change in your own code, or switch to single >> precision (set USE_FSI_DOUBLE to be OFF in your cmake). >> >> 2- Bed properties? I have noticed that you get some of the >> parameters from a JSON file and some of them are defined in the simulation. >> However, it seems that FSI simulations use some different properties for >> the bed than what is used in DEM. Is it possible to define the bed using >> ONLY the material properties that I used in my DEM simulation (mentioned >> above)? Also, I could not find where the particle radius is defined in the >> simulation and was wondering if the kernelLength parameter is the same as >> the particle radius. Finally, I would like to set all my simulation >> parameters in my .cpp file instead of using a JSON file and was wondering >> about the appropriate way to set such parameters (such as Young's modulus, >> Can I have a code example?). >> >> Every parameters you see in JSON file can be set using APIs. For >> parameters related to granular soil, take a look at the code here >> <https://github.com/projectchrono/chrono/blob/release/8.0/src/chrono_fsi/ChSystemFsi.cpp#L626>. >> >> There's some book keeping you need to sort out, in terms of what parameters >> are included in the struct ElasticMaterialProperties, such as particle >> diameter, friction coefficient, Youngs modulus, etc. For more details on >> the physical meaning of those parameters, you can read this paper >> <https://doi-org.ezproxy.library.wisc.edu/10.1016/j.cma.2021.114022>(sec >> 2.1.1 on the rheology, and some applications). You can use the API >> SetElasticSPH() to modify your terrain parameters, rather than JSON. See an >> example in demo_VEH_SPHTerrain_Obstacles.cpp >> <https://github.com/projectchrono/chrono/blob/main/src/demos/vehicle/terrain/demo_VEH_SPHTerrain_Obstacles.cpp>. >> >> Note that kernelLength defines how large a neighborhood of particles is >> going to have influence on the particle of interest, which is not the same >> as particle radius. >> >> 3- I was wondering about the best way to restrict motion in some of the >> directions. Also, what is the best way to apply forces to the mesh? >> >> This is on the multibody dynamics setup. Note that in the single wheel >> test demo, global x is the longitudinal direction of the wheel, and global >> y is the lateral direction, global z is the gravity. There is a prismatic >> joint between chassis and the axle allowing motion in z direction, >> prismatic joint between ground and chassis with a prescribed velocity in x >> direction, and prescribed rotation on the wheel in y direction. In this >> example, the wheel has restricted motion in y dir. You can modify your >> screw problem accordingly. For more examples on multibody setup, you can >> look at the demos in demos/mbs folder. To apply force to your screw object, >> you can modify the mass of the axle body. >> >> [image: single_wheel_sketch.png] >> >> Thank you, >> Luning >> >> On Tuesday, August 22, 2023 at 11:26:13 AM UTC-5 [email protected] >> wrote: >> >>> Hi, >>> >>> I had some questions that I was hoping you could help me with. I have >>> been studying the FSI demos to try to better understand the FSI module. I >>> have mostly been using the DEM engine, so I have noticed some >>> significant differences between the DEM module and the FSI module. I am >>> trying to duplicate a simulation that I have done in the DEM ( >>> https://drive.google.com/file/d/1L9Br1Vf9hsFkjXqbhAZGNpgVep3p5YK_/view?usp=drive_link). >>> >>> In this simulation, I first initialize a bed with specific materials' >>> properties (Young's modulus, possession ratio, static friction, rolling >>> friction, coefficient of restitution, and cohesion energy density (the >>> cohesion module is implemented by me)). Then I settle the bed. After the >>> bed is settled, I drop the screw in a drop phase. After the screw is >>> settled on the bed, I start rotating the screw at 1 rad/s while >>> restricting its movement in the x direction and applying a down force on >>> it. >>> >>> To duplicate this simulation, I started with the >>> DEMO_FSI_SingleWheelTest where I started switching the wheel geometry to my >>> geometry and changing the bed size to what is in the DEM simulation( >>> https://drive.google.com/file/d/18KhOFfXNEIlgcoLTvxTi27XL5soYB4yz/view?usp=drive_link >>> >>> - FSI_ScrewTest.cpp). The simulation looks okay but I got stuck on many >>> things after. I was wondering if you could help me with this stuff: >>> >>> 1- the bed looked too rigid. I have tried to figure out what to change >>> to get a similar bed to what is in my DEM simulation but I could not. My >>> bed in the DEM sim is generated using a PD sampler and then is allowed to >>> settle. I have noticed that there is no settling phase in the FSI >>> simulation. Is this normal for FSI simulations? What is controlling the >>> rigidity of the bed in this simulation? >>> >>> 2- Bed properties? I have noticed that you get some of the >>> parameters from a JSON file and some of them are defined in the simulation. >>> However, it seems that FSI simulations use some different properties for >>> the bed than what is used in DEM. Is it possible to define the bed using >>> ONLY the material properties that I used in my DEM simulation (mentioned >>> above)? Also, I could not find where the particle radius is defined in the >>> simulation and was wondering if the kernelLength parameter is the same as >>> the particle radius. Finally, I would like to set all my simulation >>> parameters in my .cpp file instead of using a JSON file and was wondering >>> about the appropriate way to set such parameters (such as Young's modulus, >>> Can I have a code example?). >>> >>> 3- I was wondering about the best way to restrict motion in some of the >>> directions. Also, what is the best way to apply forces to the mesh? >>> >>> Thank you so much for your help in advance, >>> >>> -- You received this message because you are subscribed to the Google Groups "ProjectChrono" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/projectchrono/47303b22-2a12-4455-bdb4-f29cf49dd110n%40googlegroups.com.
