Following Cadence Design Systems’ acquisition of the Design & Engineering (D&E) business, the D&E Community Forum on the Nexus Community Center has been migrated in the Cadence Physical System Simulation Community. For more details and if you have any questions, please refer to the FAQ.

Stats

  • State Not Answered
  • Replies 11
  • Subscribers 3
  • Views 6
  • Members are here 0
More Content

How to define BUSHING element in Adams correctly?

viktor.kulagin
Hello, colleagues.
 
I have a question about proper bushing definition in Adams (especially in Car). Probably this issue have already solved many times, but it is still essential for modelling.
 
The question is: what is the right way to define active and reactive bodies in bushing? Some say that one should use the mechanism (say, vehicle suspension) topology and follow through it from part that give an excitation (a wheel, for example) to parts which react on this excitation. Also, there is an idea to consider I/J parts for bushing as inner/outer rings.
 
There is an issue when it comes to bushings with different radial stiffness. When you model such a bushing with different I/J parts order, you receive different results of bushing reaction. This difference may lead to different behaviour of related elements. I suppose it's related with bushing formulation described in the KB8013987 tech article.
 
For instance, there is a toelink, which has a bushing with different radial stiffnesses and a spherical joint. In this case different I/J parts order lead to different rotation of toelink around its axis and to different values of spherical joint working angle.
 
Thanks a lot for the explanation in advance
  • 0
    I always go form in to out. So start with the chassis then subframe to control arms then to knuckle. If we assume that they all where connected with bushings, I would have:
    Chassis (j) to subframe (i)
    Subframe (j) to control arms (i)
    Control arms (j) to knuckle (i)
     
    But it does not really matter. You just find a convention that you like. But remember that in general Adams terms, you should think about the i-marker (action) moving relative to the j-marker (reaction). That is how forces and measure functions typically work.
     
  • 0
    I also follow JSlat's method "in to out". In case of suspension-body related bushes, I assume the bush inner ring as J-Part (Attached to the Body) and  the bush outer ring is as I-Part (Attached to Suspension component) 
    I also pay attention to the rig and fixture assembly on which the bush stiffness (Force - Deflection) curves are measured.
    For example, it is possible that in a Bush-A, the inner ring is fixed and the outer ring is deflected for measuring the force​. Where as in Bush-B, the opposite is done. In case of Bush-B, the measured stiffness curve needs to be inversed (multiplied by -1) before using it in bush formulation.
     
    On that note,  in the toe-link bushing example, have you inversed the stiffness curve when you change I/J parts? Does it still lead to different results after inversion? 
  • 0
    JSlat, ilapakurti,
    Thank you for your answers. But I can't agree with the point that it does not really matter.
    Here is an example: a rear suspension toelink is connected with a subframe by a rubber bushing and with a knuckle by a spherical joint. Radial stiffnesses X and Y of the bushing are equal and symmetric. There are options of toelink/subframe bushing definition: in I/J order or in J/I order. Assume that general rules of bushing definition are unknown, so we can consider both options. Bushing property file stays the same for both options. Spherical joint doesn't get changed as well.
    So, we perform parallel wheel travel simulation and get the following result (see the picture attached):
    The upper 6 graphs show bushing deformation. Some of them show same results (symmetric relative to H graph axis), some of them differ. This difference leads to different spherical joint reaction (the lower 3 graphs), as it shows different rotation angles
    In this very case this difference is crutial, as the maximum working (inclination) angle is both in the limit of working angle range (with one I/J order) and beyond the limit (with another I/J order).
     
    You can check this with your models. I need to make it clear that this affects primary on bushing reaction (loads, deformation) and on link behaviour (rotation about axis following through joints); K&C properties can change in minor values.
    Attached Files (1)
  • 0
    Viktor,
     
    Are the bush stiffness curves you are using linear? Can you post a picture of your bush properties (translation and rotation)? 
     
    Another point to remember is in post processor from output files, the bush results are on "I-part" defined in the model by default.  ​
  • 0
    Ilapakurti,
     
    The attached file contains the bushing properties. As you can see, this bushing works primarily in linear ranges
    Attached Files (1)
Cadence Guidelines

Community Guidelines

The Cadence Design Communities support Cadence users and technologists interacting to exchange ideas, news, technical information, and best practices to solve problems and get the most from Cadence technology. The community is open to everyone, and to provide the most value, we require participants to follow our Community Guidelines that facilitate a quality exchange of ideas and information. By accessing, contributing, using or downloading any materials from the site, you agree to be bound by the full Community Guidelines.