Compress & External Pressure Charts/Tables 1

[BigTank]

I am having trouble correlating a value for 'A' given by Compress and one looked up (and even interpolated) manually when calculating a shell and ellipsoidal head for external pressure.

I was wondering if anyone knows how Compress finds this value? I would assume that the method used for finding a value from Figure or Table G would be the same method for finding value B from the appropriate chart.

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[doct9960]

BigTank,

I believe Compress uses double logarithmic interpolation of Table G.

I have developed a spreadsheet for doing logarithmic interpolation. Tell me the values of L/Do and Do/t, and I will give you the value for 'A'. See if it matches the one calculated by Compress.

 

[BigTank]

Thanks, doct!

L/Do = 1.7037
Do/t = 247.8448

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[doct9960]

I get A = 0.000195

 

[BigTank]

That is very close to what Compress gives in the calcs.

Interesting...UG-28(c)(1) Step 3 states: '...interpolation may be made for intermediate values of Do/t...'

I used linear interpolation using the tables...probably not the best method. Looks like I'll be developing your spreadsheet for myself, doc.

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[doct9960]

BigTank,

Your double logarithmic interpolation should like this...
y = 10^[log(y1) + (log(x) - log(x1)) * (log(y2) - log(y1)) / (log(x2) - log(x1))]

I've attached my "rough" spreadsheet for your reference.

 

[BigTank]

Thanks again, doc!

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Fitter, happier, more productive