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Dimension Analysis and buckingham pi

  1. Nov 10, 2014 #1
    1. The problem statement, all variables and given/known data

    can someone explain why we are interested in forming dimensionless products
    and why only n-j of them should be formed from the problem's variables?

    2. Relevant equations
    Step 1: List the variables in the problem
    Step 2: Express each of the variables in terms of basic dimensions
    Step 3: Determine the number of Π parameters. Buckingham Pi Theorem says we have k=n-j terms
    Step 4: Select j repeating variables from the n variables
    Step 5: Use the three repeating non-repeating variables to form k=n-j Π terms
    Step 6: Express the final form: Π1 = f(Π2,Π3)

    3. The attempt at a solution
    the only thing i know so far is that physical laws are independent of the system of units used
     
  2. jcsd
  3. Nov 10, 2014 #2
    It has to do with carrying out experiments on a physical system and also on doing small scale experiments so that you can scale up to a full sized system.

    If you do experiments on a system, and there are many variables that you can control, you want to save money by doing as small a number of experiments as you can. You don't want to have to vary every individual parameter over a range of values. By working with dimensionless groups, you can characterize the system behavior with fewer experiments, and convey the results in a more concise form.

    If you are designing a full sized system, you don't want to spend a lot of money buying several versions of the full sized equipment. You would like to do your experiments with much smaller pieces of experimental equipment, but then have the results translate directly into the design of the full sized equipment (so that you only need to buy it once).

    Chet
     
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