Hi Mason, The Soil Contact Model (the original one from DLR, as well as the one implemented in Chrono) rely on the semi-empirical Bekker formula which includes those 3 parameters that you mention and relates the pressure to the sinkage. Note that this formula is derived from experiments and is not physics-based. As such, the parameters K_phi, K_c, and n do not have immediate physical meaning (although they can be somewhat related to physical properties). The “units” for K_c and K_phi are: [K_c] = N/m^(n+1) [K_phi] = N/m^(n+2) where n is the 3rd Bekker parameter.
You can read about the Chrono SCM implementation in this paper<https://www.researchgate.net/publication/359619160_Real-time_simulation_of_ground_vehicles_on_deformable_terrain>. These 3 Bekker parameters are usually obtained from experiments using a so-called “bevameter” and then some curve fitting. You can find more information about this in various textbooks, for example Chapter 4 in Wong’s “Terramechanics Behaviour, Off-Road Vehicle Performance and Design” (ISBN 978-0-7506-8561-0) Bevameter data (and therefore these Bekker parameters) are not always easy to obtain. Wong’s book contains (Table 12.10) some sets of parameters (for sand, 2 types of clay, and loam). KRC (Keweenaw Research Center) in Michigan has a bevameter and some data. You would need to contact them directly to see if/how you could get access to such data. --Radu From: [email protected] <[email protected]> On Behalf Of Mason Mitchell Sent: Wednesday, August 14, 2024 9:46 PM To: ProjectChrono <[email protected]> Subject: [chrono] SCM Terrain Parameter Units Hi, I am using SCMTerrain for my simulation ground, and am attempting to inlay my own parameters. The key parameters are: Bekker k_phi Bekker k_c Bekker n exponent Mohr cohesive limit Mohr friction limit Janosi shear coefficient Elastic stiffness Damping Some of these have labeled units in comments inside the demo_VEH_SCMTerrain_RigidTire.cpp that I am referencing, which gives us: Bekker k_phi Bekker k_c Bekker n exponent Mohr cohesive limit (Pa) Mohr friction limit (degrees) Janosi shear coefficient (m) Elastic stiffness (Pa/m) Damping (Pa s/m) So mainly I am wondering about the units for Bekker K_phi and Bekker k_c. Additionally, there are defined values for a soil called LETE sand in that demo file which have the following values: Bekker k_phi = 5301e3 Bekker k_c = 102e3 Bekker n exponent = 0.793 Mohr cohesive limit (Pa) = 1.3e3 Mohr friction limit (degrees) = 31.1 Janosi shear coefficient (m) = 1.2e-2 Elastic stiffness (Pa/m) = 4e8 Damping (Pa s/m) = 3e4 Is there a resource pointing to where/how you acquired these values so that I could compare and validate all of the parameterization with my own soil? Specifically just to clarify my method for mapping the damping and elastic stiffness parameters, alongside, again, extracting the right units for the Bekker k_phi and k_c values. Thanks so much! -Mason -- 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]<mailto:[email protected]>. To view this discussion on the web visit https://groups.google.com/d/msgid/projectchrono/c48f1f26-caa4-41b8-b10d-b431df72ed65n%40googlegroups.com<https://urldefense.com/v3/__https:/groups.google.com/d/msgid/projectchrono/c48f1f26-caa4-41b8-b10d-b431df72ed65n*40googlegroups.com?utm_medium=email&utm_source=footer__;JQ!!Mak6IKo!N6qPMAvYJ2Z9ebdtry4xpq8Wy8PUTOEopzHE1OqoBu2oF0BVH9OIG6-vXFhPVR1y2Bk44__7MCN9YekCVTuyJTFi2g$>. -- 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/CH3PPF46CDC2185394304937ACF53F6C5F0A7822%40CH3PPF46CDC2185.namprd06.prod.outlook.com.
