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  • I have question about Impulse with pendulum. Please help me ............

    Discussion in 'Calculations' started by ursvijayv, Jun 11, 2012.

    1. ursvijayv

      ursvijayv New Member

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      I have question about Impulse with pendulum.
      Alpha (α)= ø ( Angular Velocity )
      Angular Acceleration α ̊= - (B/ml[SUP]2[/SUP])* α – (g/l) sin (θ)= f(t, θ, α)
      B – damping co- efficient
      g- Acceleration due to gravity
      L – length of rod.
      Since the angle more than 20 Degree its calculated by Runge- Kutta Method
      Finally finding the Angular velocity from the above method in term of negative value.
      Impulse F∆T = ml ø[SUB]2[/SUB] - ml ø[SUB]1 [/SUB]
      Initial Angular velocity is zero when max angle.
      So, F∆T = ml ø[SUB]2[/SUB]
      angular velocity is calculated from the damping co-efficient value.
      I have result of Impulse for the Damping co-efficient ( B) from 5000 ft-lbf-s – 65000 ft-lbf-s
      Mass ( m) – 5000 Lb and length of rod is 15 ft
      Answer Impulse Damping Co-efficient (ft-lbf-s)
      1 -3372.45 5000
      2 -3931.99 15000
      3 -3417.23 25000
      4 -2673.93 35000
      5 -1882.30 45000
      6 -1233.07 55000
      7 -687.47 65000
      My question is When damping co-efficient is like friction so, when it increase the impulse (input also should increase right, But I don’t know how this value is arrived, this study is done by industry. if anyone know the reason. Let me know I would be glad to you. Thanks in Advance.
       
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    3. RSS

      RSS Member

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      Are you sure that you have your signs right? I would have thought that damping would decrease the impulse.
       
    4. ursvijayv

      ursvijayv New Member

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      Hi RSS,

      Thanks for your reply,your the one who respond my question and once again thank for your time

      Let me know how you saying that Damping will decrease the Impulse. If possible guide me with some online content of it to read about the Impulse and I would glad to you. Also I have attached the online link to see the document.

      https://docs.google.com/viewer?a=v&...nZlZXJhaXlhbnxneDo1YmU2YTVmNjEzMWE5N2Yz&pli=1

      I am sure the sign is correct even you check in the above link appendix

      Here is the problem, I have problem with relating pendulum motion and impulse to pendulum system.
      The pendulum has damping co-efficient because of that it comes to rest position after certain period, But, in order to make the pendulum to oscillate in continuous motion we plan to apply impulse to the pendulum. we have pendulum study document done by company called Mantere, show that when we increase the damping co-efficient the applying impulse power getting reducing. In my knowledge and perception I feel when we increase the friction we should apply more energy to the system but the study shows in opposite, weather I might be wrong in understanding the concept behind it. So, I am little confusing with study of report and which parameter makes the applying impulse getting reduced when we increase the damping co-efficient. I would be glad to you if you could help me to figure out about my issue
       
    5. RSS

      RSS Member

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      I cannot see from this study that the required impulse reduces with increased damping coefficient. The impulse must increase with the initial velocity at the return angle after one cycle but this return angle will be smaller by an increasing margin than the starting angle, as the damping coefficient increases. This would increase the pendulum velocity, at this return angle as the position is passed initially. I repeat, this article does not suggest that impulse reduces with increasing damping coefficient, rather the opposite.
       

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