7 Replies Latest reply on Sep 13, 2012 9:50 AM by Chris Michalski

    Checking for overturn?

    Legt Chevrollier

      Is it possible to check an object for overturn (overturning momentum) in Solidworks?

       

      I used to do an analysis for for overturning effect by hand until now, for objects in 2d plane (extruded in third dimension). This is an example of bench:

       

      wall2a.jpg

      ("A" point represents the reference point for overturning)

      Overturn condition:

      F1 * a ≤ 1.5 * F2 *b

       

       

      But what should I do when the objects are not planar (planar but extruded in third dimension like this bench)?

      Here is an example of a 3d irregular shaped object:

       

      wall5.jpg

      It is not possible to check for overturn this kind of irregular shaped object by hand. Because forces no longer lie in the same plane:

       

      wall6.jpg

       

      Some other combinations:

      wall7.jpg

       

      here is .3ds file of this object:
      http://www.mediafire.com/?qxx7gqp1ndt9s6x

      Can Solidworks help when it comes to this check for overlturn?

       

      Thank you.

        • Re: Checking for overturn?
          Karan Lingerkar

          May be you can just determine the COM (center of mass) of the part to analyze the tipping effect.

          The link below might throw some insight.

           

          http://ruina.tam.cornell.edu/Book/COMRuinaPratap.pdf

            • Re: Checking for overturn?
              Phil Perlich

              I have no idea if SW can do that. But you should still be able to do this by hand. If it is going to tip the axis of rotation will be the line from point A to the vertex on the front right corner of the middle 'leg'.  Sum moments about that axis (including weight applied at the CoM).

                • Re: Checking for overturn?
                  Legt Chevrollier

                  Thank you for the replies.

                   

                  @Phil Perlich:
                  Ok, I will do it by hand. Still solid works can give me the center of the mass (resultant force and it's position for self weight load of the object).

                  But how did you determine that rotation axis?

                  Is there some universal rule which can be applied to any object checked for tipping(overturn)?

                   

                   

                  @Karan Lingerkar:

                  My problem is not to determine the point where the resultant of the self weight load should be applied. It's the principle in which it has to be calculated.

                    • Re: Checking for overturn?
                      Phil Perlich

                      In a 2-D problem the object tips about a point, which actually an axis perpendicular to the 2-D plane.

                       

                      In a 3-D problem objects still tip about an axis, but the axis may not be perpendicular to a standard plane.

                       

                      I looked at the "footprint" of the table. The footprint is a quadrilateral. If the object tips it will have to be about one of the four sides its footprint. To be entirely thorough you should check for overturning about each of these axes. Since it appears that the loads are primarily concentrated on the center-right portion of the table it makes sense that it would tip about that axis.

                      • Re: Checking for overturn?
                        Chris Michalski

                        you should be able to constrain the corner of the 3 "legs" to the top plane (along with restrains to prevent lateral displacement and rotation) and apply the forces.  If one of those legs is in tension it means that it actually wants to lift off the ground and the object would roll.  You will however have to test several sets of points in order to verify all possible directions of roll.

                        You might also try adding constraints to all of the supporting corner points that are no-penetration to a dummy ground body.  It will likely take some experimentation with soft springs and large displacement but this may eliminate the iterations required above.

                          • Re: Checking for overturn?
                            Phil Perlich

                            Its good to know that it can be done in simulation. However, I think for this problem Simulation would take far more time and work than doing hand calcs, and would be more prone to user induced errors.

                              • Re: Checking for overturn?
                                Chris Michalski

                                I still use Simulation Express for most things like this for a fast answer.  I would extrude a small square base at each corner of the supports, make them fixed, apply the surface distributed or point loads - similar to using bolted connections in full simulation but much cruder and faster.

                                 

                                It would be nice if SW would make it easier to define a point at the center of pressure or center of mass (I'm still using 2007 mostly so it may be easier in newer versions but I have to manually update such a sketch).  Then a simple 3D sketch would give you your resultant force vector to determine if it's inside your base or if it's unstable.  It gets more time consuming when you have other forces to consider (i.e. gravity at CofG plus distributed load at CofP then you need to pick the axes to sum the moments).

                                 

                                (I defaulted to a simulation based answer because he posted it in this category)