Is my flexible multi-body dynamic (MBD) simulation (more particularly my FlexPrep) properly implemented ? How to properly add a physical payload to my assembly ?

Theo Saclier
Theo Saclier Altair Community Member
edited August 2022 in Community Q&A

Hello everyone,

I am actually working on implementing a flexible MBD using MotionView and MotionSolve as a part of my master's thesis. The point is that I have started using Altair's product (i.e. student license) few month ago but the main focus of my work is Topology Optimization (i.e. using HyperMesh and OptiStruct) such that I am not particularly familiar with MotionView/Solve. However, I would like to use flexible MBD during the design analysis phase. That is why I am looking for help from someone more experienced.

The assembly of interest is a robot arm that consists in one rigid body and two flexible ones. Both flexible body has been generating by first defining the finite element model (i.e. .fem file) using HyperMesh before preparing them using the FlexPrep tool from MotionView. The final flexible MBD set-up has been achieved by activating the flexibility of the concerned bodies into a pre-prepared rigid MBD (i.e. whose kinematics have already been verified as being correct). The flexible MBD has already been performed and the result has been post-processed using HyperView.  It seems that there is no big mistake in the implementation (i.e. motion is fine & stress and strain time evolution can be extracted).

I am quite confident about the workflow/implementation process since I have read a lot of tutorials but not totally I'm not entirely sure that the qualitative results obtained make physically sense (there is maybe a unit system consitency error between my .fem file and my FlexPrep one). 

Is there anyone who could quickly check if my flexible MBD is well implemented?

All files of interest (i.e. files relating to the flexible bodies themselves and files relating to the flexible MBD) are available at the following WeTransfer link: https://we.tl/t-4Rq75U7LNN . Feel free to ask me to provide a WT link again or to add other file if necessary.

I also have a second small question concerning the flexible MBD. In the next step of complexity, I would like to add a payload (i.e. a rigid body with given mass and inertia properties) at the end-effector of the robot arm assembly in order to extract the time evolution of the stress in both flexible bodies when the robot arm is manipulating this payload. So that I have the following question :

What are the different ways that exist in HyperWork to attach a rigid mass object to a flexible moving component of an MBD?

Thank you a lot in advance for your answers, they will be really helpful for me. I hope I have been clear enough to be understood.

Kind regards,

Theo Saclier

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Answers

  • AnanthK
    AnanthK
    Altair Employee
    edited August 2022

    Hi Theo, 

     

    Since no one else has responded, let me take a stab at a quick answer. The process you described is exactly how we'd like our customers to progress an MBD model (i.e. start with a rigid body model, verify the kinematic constraints and overall physical behavior is correct, then incorporate a flexbody).  So that is a good sign you've diligently setup this model! 

    As far as unit consistency, I would like you to check very quickly in Flexprep that you've selected the right units for mass (in SI, it is typically Megagrams, NOT kilograms). That could potentially be one source of error. 

    To add a rigid mass to a flexbody at any location, you have to re-create the flexbody and specify an interface node at that particular location. Then proceed in MV to attach with the appropriate constraint, typically a fixed joint for a payload. There are other ways to do distributed forces like aero forces on a wing for example, see the Tutorial here: https://2022.help.altair.com/2022/hwdesktop/mv/topics/tutorials/mv/tut_mv_2040_t.htm

     

    Thanks,

    Ananth

     

     

     

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