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2 Questions I cannot Answer

  1. Apr 21, 2010 #1
    To all mechanical engineers,

    I have two questions I cannot answer in my structural 4th year project. They are not structurally related, but more mechanical. Can anyone please help. Thanks. I don't know why the give structural engineers these questions at university?

    1)A dredger has to pump sand to a height of 70m (cliff) above sea level firstly and
    from there another 5 km horizontally to an inland reclamation area. The inboard
    pumps of the dredger can provide just sufficient pressure to bring the material to
    the top of the cliff with the minimum required speed. What to do? Also think of
    the dynamics of the process. What details would you keep an eye on?After having
    pumped 50% of the required quantity, material starts to become coarser. What are
    the consequences? How to resolve?

    2) You need to deliver a certain capacity (m3/s water). You have designed a pump
    and pipeline and you have submitted a plan. However, when the actual delivery
    has to start, the pipeline diameter is measured and it is found that it is 95% of
    what you had designed. How much additional pump pressure is required to
    deliver still the same capacity. How can you achieve that?
  2. jcsd
  3. Apr 22, 2010 #2


    User Avatar

    1) A problem of viscosity and lot of stuff. I hope the dredger is land based as if not it would not be able to pump the 5 km inland. If so use steps, pump up to 50m first, move the dreger there and from then on to the end. Coarser might be easier to move if I remember it right, but without knowing any material data that is a mystery. Pipe friction for the 5km inland pipe might be harder then the 70m ascent.

    2) Smaller pipes have more friction so more pressure needed for the same capacity, look into Reynold's formula for this kind of stuff. About how you can achieve your goal, considering that most land based stuff is engineered with a safety factor of at least 2 the pump might do just fine with a little more engine power.
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