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Entering mathematical formula

  1. #1
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    Entering mathematical formula

    Firstly I'm not sure if this is the correct forum for this question, so apologies.

    I am doing a Motorsport Degree at Uni and as part of one of my assignments I've been asked to produce an Excel spreadsheet to show how changes in crank angle affect in-cylinder volume.

    The full question that I've been given is as follows:

    Based on the equation provided below, produce an excel spreadsheet showing how changes in the crank angle affect the in-cylinder volume. Start from an angle of θ= 180° up to an angle of θ=540° by moving 5° at a time. Produce a graph of the crank angle (θ) vs. volume of cylinder (V)

    V = Vcc + 1/4πBē [L+T-(Tcosθ+√(Lē-Tēsinēθ)]

    Where:
    V = Volume of the cylinder
    Vcc = Volume of the combustion chamber
    B = Bore
    L = Rod Length
    T = Throw of the Crankshaft

    Basically I'm pretty much clueless as how I will go about entering it into excel as a formula to work out the volume of the cylinder for every 5° the crank angle changes.

    If anyone could give me a few steps as to how I would go about it, would appreciate it very much!
    Last edited by ju boy; 10-21-2009 at 06:47 PM.

  2. #2
    Valued Forum Contributor jj72uk's Avatar
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    Re: Uni assignment help needed.

    Hi Ju Boy,

    Welcome to the forum.

    Please take a moment to read the forum rules and then re do you thread title so we can help

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    Re: Help with entering complex formulae into excel needed

    Sorry about that! Has been changed; hopefully it is ok now, please let me know if not.

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    Valued Forum Contributor jj72uk's Avatar
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    Re: Help with entering complex formulae into excel needed

    See if this helps.

    You'll need to enter the correct values for L, T etc etc And you'll need to copy the V formula all the way down.

    I've written out the above forumla in excel..

    On a side note you may want to make the title more specific
    Attached Files Attached Files

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    Re: Help with entering complex formulae into excel needed

    Ah, that's made things a lot clearer for me thank you.

    I'm not quite sure how i'd make it more specific, not too familiar with the correct terms to use!

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    Re: Help with entering complex formulae into excel needed

    Quote Originally Posted by jj72uk View Post
    See if this helps.

    You'll need to enter the correct values for L, T etc etc And you'll need to copy the V formula all the way down.

    I've written out the above forumla in excel..

    On a side note you may want to make the title more specific
    hi again, was just wondering, when i try and use the formula with the correct values in place i am still not getting the desired outcome? i no what the first result should be. but excel comes out different?
    if,
    Vcc=0.00045
    B=0.09
    L=0.15
    T=0.035
    θ=180

    V should equal 0.044577076
    but when i use the excel formula its different? if there is any chance you could show me how to modify the formula to get the desired result? or point out what i'm doing wrong i would be very grateful.

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    Re: Entering mathematical formula

    Check to make sure all your measurements are in the same units. Also check jj's excel formula carefully to make sure it matches what you are expecting. One error I found was that Excel computes trig functions in radians and you are using degrees. You'll need to convert your degrees to radians. That still doesn't give the answer you are expecting so there must be an error somewhere else.
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    Re: Entering mathematical formula

    I've looked into the formula, and I found 1 error. I intailly was dividing 0.25 into Pi, whereas it should be timeds.

    This still didnt give the answer you were expecting.

    I then broke it down into parts. So doing each part of the equation as a sperate sum and the result was still incorrect...

  9. #9
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    Re: Entering mathematical formula

    Take a look a the worksheet I've attached. The formular is not correct, but I think it will put you on the right road. I'm curious to know if you can make it work. Good Luck
    Attached Files Attached Files

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    Re: Entering mathematical formula

    1/4πBē [L+T-(Tcosθ+√(Lē-Tēsinēθ)]
    is that
    1/{4πBē [L+T-(Tcosθ+√(Lē-Tēsinēθ)]}
    or
    (1/(4πBē)* [L+T-(Tcosθ+√(Lē-Tēsinēθ)]
    or
    (1/4)*πBē*[L+T-(Tcosθ+√(Lē-Tēsinēθ)]
    Last edited by martindwilson; 11-08-2009 at 08:04 AM.
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    Valued Forum Contributor jj72uk's Avatar
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    Re: Entering mathematical formula

    Martin,

    The way I thought it was is:

    ((1/4)*Pi*Bē)*[L+T-(T*cosθ+√((Lē-Tē)*sinēθ)]

  12. #12
    Forum Expert martindwilson's Avatar
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    Re: Entering mathematical formula

    i tried all 3 and still didnt come up with op answer!
    ok
    i make this bit
    (Tcosθ+√(Lē-Tēsinēθ) = 0.115
    using
    =D2*COS(RADIANS(E2))+SQRT(C2^2-(D2^2*SIN(RADIANS(E2))^2))
    where
    C2=L
    D2=T
    E2=θ
    now do we agree on that or is my algebra wrong or even excel functions wrong??
    Last edited by martindwilson; 11-08-2009 at 08:03 AM.

  13. #13
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    Re: Entering mathematical formula

    Just for fun, i elaborated an example based on Martin's formula in post # 12.
    The example works with centimeters and cubic centimeters, because i'm more familiar with those. My conclusion: Martin's formula gives plausible results, the data posted by ju boy in post # 6 do not seem to correspond with his expected result, but again, i'm not too familiar with non-metric data.
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    Last edited by WHER; 11-08-2009 at 06:01 PM. Reason: including graph

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