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Center of pressure

  1. Mar 19, 2016 #1
    1. The problem statement, all variables and given/known data
    can someone explain about the Fr acting at a distance 2b/3 from free surface firectly beneath the centroid of the surface ?

    2. Relevant equations


    3. The attempt at a solution
    does the author mean the center if pressure ( point where the FR acts) of the completely submerged plate (90 degree) is at 2b/3 from the top of the surface ? p/s : the whole vertical length of the submerged surface is b
     

    Attached Files:

  2. jcsd
  3. Mar 20, 2016 #2

    CWatters

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    Yes. When the top edge of the plate is at the surface Fr acts at a depth of 2b/3. If the plate sinks further Fr moves towards the centre of the plate (eg towards b/2).

    See "2. COP Fully submerged plate"...

    http://people.exeter.ac.uk/TWDavies...tic Force on a submerged vertical surface.htm
     
  4. Mar 20, 2016 #3
    can you explain why in this case , the center of pressure not at 2/3 of the submerged plane ? if it's 2/3 , it should be 8= (1.2/3) = 8.8 m , right ? why the working only showed 8.61m?
     

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  5. Mar 21, 2016 #4

    CWatters

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    It's only at 2/3rds of the height of the plate when the top edge of the plate is at the surface. In the case of the car the top edge is 8m down.

    I get the same answer using the equation in your notes...

    yp = s + b/2 + b2/(12(s+b/2)
    = 8 + 1.2/2 + 1.22/(12(8+b/2)
    = 8 + 0.6 + 0.014
    = 8.61m

    and the equation at the link I posted..

    = 2/3 * (y23 - y13)/(y22 - y12)
    = 2/3 * (9.23 - 83)/(9.22 - 82)
    = 2/3 * (778.69 - 512)/ (84.64 - 64)
    = 2/3 * 266.69/20.64
    = 8.61m
     
  6. Mar 22, 2016 #5
    so, when the top edges of the submerged object is located exactly at the water surface(s=0) , then the center of pressure of submerged object will be at exactly 2/3 of the height of the submerged object ?
     
  7. Mar 22, 2016 #6

    CWatters

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    Yes. That's mentioned in your image dsc_0525-jpg.
     
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