Query regarding creating tire file in Chrono

[Ekansh Chaturvedi]

Hi,

Hope this email finds you well.

We are using Chrono to conduct an on-rig analysis of different tires and we are pretty new to using Chrono. We are stuck while trying to create a custom tire file that takes tire inflation pressure in units of pressure, along with the other structural dimensions, as an input . It's been a month and we are still trying to figure that out. We have realized that we cannot waste time anymore  on trying ourselves as the deadlines are coming close, and we need help. 

We would really appreciate it if you could help us out with this through a zoom meeting. Please share your availability and feel free to let us know if you have any questions or concerns.

Thanks and regards,

Sincerely,

Ekansh Chaturvedi

Graduate Student,

Terramechanics, Multibody and Vehicle Systems Laboratory (TMVS),

Computational Sciences Laboratory (CSL),

Department of Mechanical Engineering

Virginia Tech

[Dan Negrut]

Hi Ekansh,

Can you spell out, step by step, how you went about implementing your solution?

How do you envision the flow of the work process, its steps? Not the gory details, but high level approach.

 

Also, what type of tires do you plan to model?

On-road or off-road?

Of the tire models available in Chrono, what model[s] do you plan to use?

 

Thank you,

Dan

---------------------------------------------

Bernard A. and Frances M. Weideman Professor

NVIDIA CUDA Fellow

Department of Mechanical Engineering

Department of Computer Science

University of Wisconsin - Madison

4150ME, 1513 University Avenue

Madison, WI 53706-1572

608 772 0914

http://sbel.wisc.edu/

http://projectchrono.org/

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[Dan Negrut]

Ekansh - one can't use Pacejka or TMEasy with SCM or CRM or DEM (deformable terrains, that is). The only way to do that would be to use an FEA tire model. That would be though painstaking and would run very slowly.

Is it a possibility to consider the terrain rigid? Then you are good to go with TMEasy.

Dan

[Ekansh Chaturvedi]

Hello Dr. Negrut,

Thank you for the reply. We are trying to simulate a terramechanics rig using the "CHTiretestrig" class functions. In the experiment, the output I'm looking for is the tire forces (which as far as I understand from ReportTireForces()is, the force at the spindle and not the contact patch forces?) and for input, I want to vary the inflation pressure and other tire parameters. This will help us to obtain the drawbar pull for different inputs in addition to inflation pressure, such as wheel speed, slip ratios etc. Specifically, studying tire behaviors on deformable terrain is a priority in this project.

For this purpose, I used the TMeasytire model as it had a functionality of giving tire inflation pressure as input. Could you please give your thoughts on formulating this problem using the available libraries in chrono? We basically need a test rig mechanism, tire and deformable terrain. Please let us know your thoughts.

Thank you,

Sincerely,

Jyotirmoy Mukherjee

[Radu Serban]

Jyotirmoy and Ekansh,

 

Just a couple more clarifications and details beyond what Dan already told you.

 

• None of the tire models from the family of “force element”-type models (i.e., derived from ChForceElementTire, including Pacejka, Fiala, TMeasy) carry any collision geometry and as such cannot be used on deformable terrain.  This is without also considering that the range of applicability of these models is relatively limited to rigid, relatively flat surfaces.
• These tire models can currently be used only in conjunction with a RigidTerrain (or with a custom terrain system which implements the necessary which implements the necessary functions for querying terrain height and normal at a given (x,y) location).
• If you are interested in deformable terrain, the two options for appropriate tire models currently available in Chrono are rigid tire and an FEA tire.  Beside the drawbacks of using an FEA tire that Dan already mentioned, keep in mind that appropriate data for such a tire model is not easy to obtain.
• As a side note: the Chrono FEA tire models properly consider internal tire pressure (which is interpreted as a distributed load on the inward faces of the shell elements used to model them.  TMeasy has an option (which I assume you use) of specifying internal tire pressure as a mechanism for estimating the actual TMeasy model parameters (in other words, the internal pressure is not an actual parameter of the TMeasy model).  There are variants of the Pacejka model that account for internal tire pressure, but those are not in the Chrono implementations.
• Finally, although that is probably irrelevant for your immediate needs, I hope we will have a model of deformable tire that can interact with deformable terrain at a computational cost much less than that of current FEA tires in the not-too-distant future. But that’s WIP.

 

Regarding your question about reporting tire forces, note that there are two versions of the function ReportTireForce. See ChForceElementTire (lines 36 & 42). One reports the resultant force and moment (expressed in the global reference frame) at the spindle COM; the other returns the tire force and moment expressed in the tire frame (which is also returned by this function).  This is a change I made about a month ago.  Update to the latest code if you have not done so already.

 

--Radu

 

From: projec...@googlegroups.com <projec...@googlegroups.com> On Behalf Of Ekansh Chaturvedi
Sent: Wednesday, March 29, 2023 5:51 PM
To: ProjectChrono <projec...@googlegroups.com>

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[Radu Serban]

Ekansh,

 

Both Dan and I already answered these questions. See the other thread with my reply to Jyotirmoy’s post. 

 

--Radu

 

 

From: projec...@googlegroups.com <projec...@googlegroups.com> On Behalf Of Ekansh Chaturvedi
Sent: Wednesday, March 29, 2023 1:57 PM
To: ProjectChrono <projec...@googlegroups.com>

Subject: Re: [chrono] Query regarding creating tire file in Chrono

 

Thanks for your email Dr. Negrut. I really appreciate it.

 

I am trying to set up a passenger car tire and test it on the sandy loam terrain. I am using ChTeameasy class to make a tire file where we can input inflation pressure. There it asks for two values namely Inflation Pressure design and Inflation pressure use. To make the tire file, I copied an existing passenger car tire file (sedan), erased all the data except the mass, inertia and tire's dimensional data, and included "Inflation Pressure design [Pa]" and "Inflation Pressure use [Pa]" , as per the online  documentation. 

 

When I simulated the same on the rigid terrain, with different values of inflation pressures, I got descent results in terms of Fx, Fy and Fz (using ReportTireForces). However, when I am trying to simulate on the sandy loam terrain (using SetTerrainSCM), I am getting exactly same values that I got with rigid terrain, which doesn't make sense. Further, changing inflation pressures with soil terrain does not change the output results and I see no deformation in soil terrain mesh (which is clearly visible when I run the demo file). Since I copied the exact line of code for setting soil terrain from a demo file, I am not sure if the problem in the tire file or I am missing something while setting the terrain. I am unable to figure out where the problem lies. Please share your thoughts on the same.

 

My apologies for a lengthy email. I really appreciate your help.

 

Have a great day!

 

Sincerely

Ekansh

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[Radu Serban]

Jyotirmoy,

 

The reported “tire force” is the force/moment that are applied to the wheel spindle as result of the tire/terrain interaction. It is neither the motion resistance (look at the direction of the Fx component) nor the drawbar pull.  You should be able to work out the motion resistance from this. As for drawbar pull, that could be obtained as the reaction force in the linear actuator that imposes the specified rig longitudinal speed (assuming you set a given longitudinal speed and given wheel angular speed, hence a given longitudinal slip value, that would give you one point on the slip-DBP curve).  I believe there is no accessor method to return that reaction force. I’ll add it.

 

--Radu

 

From: projec...@googlegroups.com <projec...@googlegroups.com> On Behalf Of Jyotirmoy Mukherjee
Sent: Friday, April 7, 2023 2:59 PM
To: ProjectChrono <projec...@googlegroups.com>
Subject: Re: [chrono] Query regarding creating tire file in Chrono

 

Hello Dr. Negrut and Dr. Serban,

 

Thank you for the reply. I would like to clarify somethning about the tire forces. I'm using the function ReportTireForces() in the ChTireTestRig class,

 

auto Force_out = rig.ReportTireForces(), the Force_out.force.x() is the Fx force. Could you please let me know if this force is the motion resistance or drawbar pull? I wanted to make sure that I am printing out the right Force. Also, is there any specific variable that gives the motion resistance/drawbar pull separately?

 

Thank you in advance.

 

Sincerely,

Jyotirmoy

To view this discussion on the web visit https://groups.google.com/d/msgid/projectchrono/b0544e3c-dffa-4aa3-8ab6-72d71388d953n%40googlegroups.com.