how to calculate the contribution of different parts in the total deformation of a modal structure

- October 18, 2019 at 2:09 pm
  
  Arjunvy
  Subscriber
  
  Hi,
  I am doing a structural analysis of a door. The door is connected to the hinge and the hinge is connected to the front panel.
  I am applying a force of 100 lbf on the top of the door in the vertical direction.
  I am getting a displacement of 9mm on the washer door.
  Now I want to find out the exact contribution of the washer door, hinge and the front panel. How can I do that?
  I tried inserting a very large amount for the young's modulus for the hinge and the front panel to find the contribution for the door,
  a very large amount for the youngs modulus for the door and the hinge to find the contribution for front panel. And same procedure for the hinge.
  But i feel something is wrong as the contribution for door + hinge + front panel is not equal to 9mm.
  Can some one help me with this
- October 18, 2019 at 2:47 pm
  
  peteroznewman
  Subscriber
  
  You have three springs in series.
  
  You used a very high Young's Modulus on the second and third components to obtain k1 for the first component by computing F/x. You repeated that two more times, switching the high Young's Modulus to the first and third components to obtain k2, etc. Recall that the spring rate of a system of two springs in series is to combine the individual spring rates using this formula:
  
  Expand that formula to three spring rates. Does that come closer to matching the system displacement of 9 mm for 100 lbs? It might not because of the nonlinear nature of the deformation, which involves a lot of rotation. The formula works perfectly for three linear springs being pulled in a straight line.
- October 18, 2019 at 2:55 pm
  
  Arjunvy
  Subscriber
  
  But is there any way to identify the exact contribution of each part in the final displacement?
- October 18, 2019 at 3:22 pm
  
  Arjunvy
  Subscriber
  
  Will it work if i define the other two parts rigid in the stiffness behavior option.
- October 18, 2019 at 3:31 pm
  
  peteroznewman
  Subscriber
  
  Yes, you can just set the other two parts rigid, but you might have to replace a Fixed Support with a Fixed Joint.
- October 18, 2019 at 4:33 pm
  
  Arjunvy
  Subscriber
  
  So now I have added
  
  a contact between the door and the hinge
  
  a fixed joint between the hinge and the front panel
  
  and a fixed joint between the front panel and the ground.
  
  the front panel and the hinge will not mesh since they act like a point mass because they are rigid right?
  
  but at least there should be a mesh on the surface of the hinge which is in contact with the door. ansys is failing to mesh on the surface of the hinge.
  
  I have added a pinball radius between the hinge and the door to suffice the gap.
  
  Is there something which I am missing?
  
  also I have another doubt. Now since I am allowed to apply a force of 100 lbf on the door because it is flexible right now. But will I guess I'll not be able to apply the same amount of force on the door when it is rigid. So what should i do at that time?
- October 18, 2019 at 5:54 pm
  
  Arjunvy
  Subscriber
  
  Do you have any link or any example where someone has performed a rigid-flexible body structural analysis. I am new to this and I am getting a lot of errors
- October 18, 2019 at 7:01 pm
  
  peteroznewman
  Subscriber
  
  Return to your original model and stick with the Young's Modulus method. Are you adding 000 to Young's Modulus to increase it by 1000 times? You are only looking for guidance for the contribution of total deformation among three contributors, and it will not be exact anyway because of nonlinearities. That will be good enough.
- October 18, 2019 at 7:20 pm
  
  Arjunvy
  Subscriber
  
  yes I am looking for an approximation. I just want to know what is the contribution of door, hinge and front panel in the total deformation. I am multiplying the young's modulus by 1000 just to make it act rigid.
  
  And by non linearity you mean the geometric, material and BC non linearity right?
  
  I have more question, just imagine door and hinge is rigid (defined as rigid in the behavior) and front panel is a flexible body. Then since door and hinge are rigid body I cannot directly apply a force on that, then can I apply a moment (F*r) on the front panel? since rigid body do transfer the same load right and we need to maintain the force equilibrium as well.
- October 18, 2019 at 9:11 pm
  
  peteroznewman
  Subscriber
  
  Replace the Force with a Remote Force to use on a body that you converted from Flexible to Rigid.
  
  Mostly it is geometric nonlinearity due to large rotations.
- October 18, 2019 at 11:56 pm
  
  Arjunvy
  Subscriber
  
  Okay thanks, a last doubt I had. I am getting this warning message.
  
  One or more MPC contact regions or remote boundary conditions may have conflicts with other applied boundary conditions or other contact or symmetry regions. This may reduce solution accuracy. Tip: You may graphically display FE Connections from the Solution Information Object for non-cyclic analysis. Refer to Troubleshooting in the Help System for more details.
  
  what is the meaning of this warning.
- October 19, 2019 at 1:01 am
  
  peteroznewman
  Subscriber
  
  This is a common warning and can almost always be ignored.
  
  It is usually issued because one face might have contact defined, while an adjacent face has a remote force applied. There is a common edge. The nodes along that edge are required to both participate in the contact definition and apply a force. There is no conflict there. That is why the warning says it may have conflicts. It can't tell, so it issues a needless warning.
  
  Please post a table of the results of the three components and how they predict the total.
- October 21, 2019 at 5:07 pm
  
  Arjunvy
  Subscriber
  
  total displacement when all the parts are flexible is 5.2 mm
  
  total displacement when door and hinge is rigid and front panel is flexible is 0.015 mm
  
  total displacement when door and front panel is rigid and hinge is flexible is 0.035 mm
  
  total displacement when front panel and hinge is rigid and door is flexible is 3 mm
  
  thus contribution of front panel + contribution of hinge + contribution of door = 3.05 mm
  
  Does geometric non linearity affect so much?
- October 21, 2019 at 5:42 pm
  
  peteroznewman
  Subscriber
  
  Are you measuring displacement of the same corner of the door for each of the three models?
- October 21, 2019 at 5:47 pm
  
  Arjunvy
  Subscriber
  
  yes I am measuring the displacement at the same corner.
- October 21, 2019 at 6:31 pm
  
  peteroznewman
  Subscriber
  
  Yes, that is how much nonlinearity there is in the system.
- October 22, 2019 at 2:09 pm
  
  Arjunvy
  Subscriber
  
  okay thank you so much for your help.
- October 22, 2019 at 2:38 pm
  
  Arjunvy
  Subscriber
  
  Also can please redirect me to any thread where I can learn more about residual forces. How are they calculated. What criteria can lead to increasedecrease of the residual forces. Are residual forces linked with non linearity and if yes how.
- November 7, 2019 at 6:05 pm
  
  Arjunvy
  Subscriber
- November 7, 2019 at 6:10 pm
  
  Arjunvy
  Subscriber
  
  So now as you said I solved the system of 3 springs.
  
  As you can see that in the above image, I have attached the equations.
  
  we got K = 1.75 * K equivalent.
  
  thus, deformation * 1.75 = deformation equivalent.
  
  but I am getting deformation for the assembly (K) = 5.24
  
  and equivalent deformation (K equivalent) = 3.
  
  where equivalent deformation is the addition of 3 different deformations when young's modulus is multiplied by 1000 for different parts.
  
  so the equation does not hold.
  
  Can you tell what is wrong? And I don't think so this is because of the geometric non linearity.
  
  We have also had Large deformations ON, shouldn't it take care of geometric non linearity?