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Chris Coker

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  1. mpv liked a post in a topic by Chris Coker in Flexible Body Assign Problems   
    Based on the limited information provided, we really can't offer much in terms of help.  The possible problems are to many to discuss here.
     
    Rather than start with a full vehicle model, you should be just the front and rear suspension separately.  Using this method, you can use the half-car events to fully debug your model before going to complex full vehicle simulation.
     
    When we assemble the full vehicle model, we first run simple events, like straight line acceleration and straight line braking.
    If the model looks good with these events, then we run events like constant radius, and swept steer.
    Only when the model is fully debugged, do we look at running events like lane change.
  2. LOKESH KATARI liked a post in a topic by Chris Coker in Gears   
    Two ways you can do this:
    1. Create a displacement output on each Gear body.  You will get displacements (and rotations) of the body, you could also request velocities, etc.
    2. Create a displacement output for the joint that attaches the gear body.
  3. francesca liked a post in a topic by Chris Coker in postprocess: motionview-motionsolve-PLOT   
    Yes, they are Torques.  They are resolved in the reference frame used when you created the Output to report that force.  It will default to Global if you didn't create a reference frame
     
  4. Chris Coker liked a post in a topic by ppraf in Impact/impulse force   
    Hi forestis - You could use the type "Expression" and have an expression something like this - `STEP(TIME, 1,0,1.1,100)+STEP(TIME,1.1,0,1.2,-100)`
    In this expression, the first STEP function increases the force to 100 from time 1 sec. until then it is 0. In the next STEP function,  the force is being dropped down back to 0.0. (otherwise the force will remain at 100 for the remaining time of the simulation)
     
    You may also use a Curve that has the impulse profile of your choice and use TIME as the independent variable while using the type Curve.
     
    regards
    praful
     
  5. Chris Coker liked a post in a topic by Hyperman in BALL JOINT   
    Hi,
     
    you can try to add torque based on BISTOP function to limit joint motion.  Please refer to the attached document (from Hyperworks for MBD 13).
    HyperWorks_for_MBD_v13.pdf
  6. Laura27 liked a post in a topic by Chris Coker in Detection interferences   
    "Collision Detection" is a feature that's only available in post-processing.  It allows you to visualize penetrations between different bodies in the mode, AFTER your simulation is completed.
     
    When you need to stop (or change) the model as a result of some condition in the model during run time, we use an entity called Sensors.  I would encourage you to read up on Sensors in our help, as they are quite powerful, but there are a few things to learn.
     
    A simple way to implement a sensor in your case would be for the sensor to monitor the displacement between two bodies (which you would define via an expression).  When the displacement reaches some threshold value, you tell the sensor to halt the simulation.
     
    Another possible way (I haven't personally tried this), would be to monitor the contact forces between two bodies, assuming you are using 3D contacts in the model.  When the contact force is generated, use that to trigger the sensor.
  7. Chris Coker liked a post in a topic by Felipe M Leila in how to fix components in multibody   
    Hi Laura,
    You can merge the bodies in MV keeping only the necessary components to represent your system.

     
    For instance, parts represented on the CAD like bolts, bearings, welds, etc do not need to be represented in your simulation. Therefore it is either recommended to group it in one single body or delete them.
     
    Best regards,
    Felipe.
  8. adriannunes liked a post in a topic by Chris Coker in Errors in events analysis   
    The static ride analysis contains user subroutines that rely on running a static analysis.  You should run the static ride analysis as a static solution, not transient.
     
    If you can switch off all of the outputs that rely on user subroutines, you and probably get the analysis to run, but this really isn't the purpose of the static ride analysis event.
  9. Chris Coker liked a post in a topic by ppraf in Steering ratio   
    Hello Tetoldini
     
    You should find a Coupler entity under the Rackpin Steering system where you can change the coupler ratio.
     
    regards
    Praful
     

  10. Chris Coker liked a post in a topic by Felipe M Leila in Global origin setting   
    Hi Tetoldini,
    One easy way to do it is using the System translation inside MotionView.

     
    You can select the master model system and all the other systems will follow it.
    Be careful with the Y axis since the assembly wizard models are parametrized in left and right side.
     
    Best regards,
    Felipe.
     
  11. Chris Coker liked a post in a topic by ppraf in Initial conditions on joints   
    Hello - To further add to Chris's description, the solver MotionSolve does not support applying displacement initial conditions on the joint. Hence it is not available for editing in MotionView.
     
    regards
    Praful
     
  12. Chris Coker liked a post in a topic by Felipe M Leila in Limit Switch   
    Hello,
    You have several ways to do this.
    1) You could use a template including a fix joint when certain distance is achieved (the computation of the system can be done using a sensor)
    https://altairhyperworks.com/hwhelp/Altair/2019/help/ms/topics/solvers/ms/understand_seq_sim_intro_t.htm
    2) You can add contact between the bodies as it happens in the real life I guess.
    https://altairhyperworks.com/hwhelp/Altair/2019/help/ms/topics/solvers/ms/3d_mesh_to_mesh_contact_sim_intro_r.htm
    https://altairhyperworks.com/hwhelp/Altair/2019/help/tutorials/mv-1012.pdf
    3) You could add a second force with a impact function to limit the movement (analog to use contacts)
    4) You could include a bistop function on the joint providing a range that the joint can translate.
    https://altairhyperworks.com/hwhelp/Altair/2019/help/ms/topics/solvers/ms/bistop.htm?zoom_highlightsub=bistop
     
    Best regards,
    Felipe.
     
  13. Hyperman liked a post in a topic by Chris Coker in stress analysis   
    Direct 3d contact onto flexbodies like you are attempting is currently not supported.
     
    There is a complicated workaround for this, but in general this is not recommended.  Essentially, you create many interface nodes over the surface of the flex body.  Then create tiny rigid bodies at each one of these location, at attach them with fixed joints.  Then, you would define contact for each one of the small rigid bodes that were created.
  14. Adit Agarwal liked a post in a topic by Chris Coker in Multi body dynamics   
    Hello Adit-
     
    Did you build your vehicle using the standard vehicle wizard library?  Use analysis -> Task wizard and you will see full choice of events.
     
    Note, if you did not build your model with a powertrain, some of the tasks will not show, since the required logic is not included if you do not include the right systems when you initially build the model using the wizard.
     
    Also, it would be helpful for you to provide information on what version of Motionview you are using.  The worfklow has been evolving a little over the past few versions.
  15. Hyperman liked a post in a topic by Chris Coker in Friction in MBD using motionsolve   
    Yuvaraj,
     
    Just to add some more detail to Felipe's great advice.
     
    It appears that maybe you are using joint friction, as well as friction on your contacts?  These are both very computationally complex, utilizing a LuGre friction model for joint friction, and in general it is common practice to leave these features turned off, unless we can answer two questions:
     
    1)  Is including this friction absolutely essential to capturing the required physics of my problem?  In most cases, the answer is "no", or can be achieved using computationally more efficient methods like damping.  Also, in the joint friction models, there are different levels of complexity that can be switched on and off.  Only use the friction features that are required.  For 3D contacts, static friction can add a lot of compute time to your runs.  Ensure you need these feature before activating them.
    2)  Do I have all of the correct input data to populate the friction model correctly?  The friction models required details about the size of the joint, friction properties, etc.  Do not assume that you can simply turn on the joint friction model, and use the default values.  Based on the size of your joints, and units of your model, the default values will usually not be a good starting point.
     
    If the answer to either of these questions is "no", but you need to damp your model's response to achieve a more physically accurate solution, a better choice is to add damping to the model.   This can be easily accomplished by adding a bushing on top of an existing joint, but don't assign it any stiffness properties.  Just give it some damping, in the desired directions of interest.  This is computationally much more efficient that the LuGre model, and can be used with great success.
     
    It's also curious that you are using the VSTIFF integrator, and not DSTIFF.  Also the integrator is taking a very, very small time step, with your max step size set to 1e-08.  If this is required to get your models to run, there is likely some other issue with your model configuration.
     
    Chris
  16. Chris Coker liked a post in a topic by asajd in Issue in creating "Contact" in MotionSolve   
    For simple spur gears it is often much simpler to just use a Coupler... it can run very efficiently because contact detection is not required.
    See attached ZIP file containing a model where coupler is used instead of contacts.
     
    Sincerely,
    Tony S.
    Spur_Gear_useCoupler.zip
  17. Chris Coker liked a post in a topic by Felipe M Leila in Friction in MBD using motionsolve   
    Hello Yuvaraj, 
    Does your model run fine if you deactivate the friction on the joints and contact?
    I would recommend you to run your model by steps to identify the error. First include only the joints, motion, springs, forces entities to represent the overall mechanism, does it work? If yes, then you include friction and tune your model to achieve the desired simulation.
     
    Please try to do that and let us know if you succeeded.
     
    Best regards, 
    Felipe. 
  18. Abdullah Bozkurt liked a post in a topic by Chris Coker in Flex Body Assign Problem   
    Hi Abdullabh-
     
    To answer your second question, the math behind flexbodies is based off of linear deflection, and linear material properties.  You will not get good results attempting to model a rubber component as a flexbody.  If you need to model something like a rubber component, you should investigate using the non-linear finite element feature in MotionSolve (NLFE). 
     
    For your first question:  MotionSolve does not currently support 3D contact with flexbodies today.   There is a workaround to this, where you attach many small rigid bodies to your flexible body with fixed joints.  These small rigid bodies can then be used with 3D contact.
  19. Hyperman liked a post in a topic by Chris Coker in Flex Body Assign Problem   
    Hi Abdullabh-
     
    To answer your second question, the math behind flexbodies is based off of linear deflection, and linear material properties.  You will not get good results attempting to model a rubber component as a flexbody.  If you need to model something like a rubber component, you should investigate using the non-linear finite element feature in MotionSolve (NLFE). 
     
    For your first question:  MotionSolve does not currently support 3D contact with flexbodies today.   There is a workaround to this, where you attach many small rigid bodies to your flexible body with fixed joints.  These small rigid bodies can then be used with 3D contact.
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