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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)
  • 0
    Viktor,
     
    Your observation seems to be correct!
     
    My first thought was, since reference frame for request calculation is changed by changing I,J parts; the deviation must be occurring. Bush force calculation in request file is given in this article. KB8015473​
     
    Even after changing the reference frame and definitions in bush request, the said deviation is present.
     
    Having said that, the variation is too small to be measured using testing. May need to study and change based on the specific load case.
     
    If you find a suitable answer, do update here.
     
     
  • 0
    Of course it matters to you. But as long as you know which direction is which and can adjust property files accordingly, you can do it anyway you want. There is no universal rule for how you should build your model.
     
  • 0
    Hello,
    I can not find tech articles KB8015473​ and KB8013987, could you please help?
    Thanks in advance!
  • 0
    Hello, Marek.
     
    Here are the links:
     
    You can also enter tech articles number in the Ask a Question table in the main SimCompanion page, these articles will be opened after the search
  • 0
    Hello ,everyone
    Could I follow this question to ask my another related question.
    How about it in the damper/spring/ bump?
    1. damper: we normally choose rod as i part and tube as j part,just like what has done in the acar-template. But the action part (i Part) should be tube in the real and reaction part should be rod. They are contradiction.
    2. spring: for instance with four arm, action part should be arm and reaction should be chassis ?
    3. bump: i pat should be tube and j part should be chassis or rod according to the function and construction of bump?
    all in all ,my rule about i and j part is force flow. But this rule has sometimes contradiction with acar-intern-template for spring/damper/bump.
    could anyone please help, which one is right.
    thanks in avdanced.
     
     
     
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