He’s trying to get you guys to do his homework. Durr.
Negative. No textbook would give you a problem that vague and open ended. It’s all good though, I enjoy this BS…
Ouch…my head!
Hah - I actually started a reply asking about why is ‘a’ equal to 0, implying a disc, as opposed to a ring, but my head hurt, another beer sounded good, and sleep eventually ensued.
I think “I am solving for sigma” has been posted 6 times now.
Edit: Although I’m not sure why I said Sigma, since I clearly meant Omega. Omega is the only variable I did not provide, what else WOULD I be solving for??
I take no responsibility for things I post after midnight, or on Tuesday or Thursday nights.
Uhhhh don’t you mean Omega?
I studied the derivations of the Navier-Stokes equations today, trying to get a handle on the use of the modulus of elasticity for stress in these equations instead of the Ultimate stress which I would have expected.
I was originally using the ultimate stress for my initial calculations, but I quickly realized my answer was off by an order a magnitude, so therefore one of my variables had to be off my 2 orders of magnitude.
I then noticed the the modulus of elasticity also has units of pressure, and it was 2 orders of magnitude larger than the ultimate stress.
The equation now provides plausible angular velocity limits.
I’m still not sure the use of the modulus of elasticity was the right way to go, but it gives reasonable values.
I have been studying the Navier-Stokes based derivations on the principles of elasticity. Unfortunatly these are expressed as Jacobian matricies of differental equations, with each component of all 3 tensors having its own unique partial derivitive. It’s a nightmare. I’m working on it.
I do however see E directly in their use of this formula. So now I know my assumption is correct, my solutions are correct, so im good there.
I would however like to have a complete understanding of the Calc 3 based matricies, and the use of E where Poissons ratio is present in the equation. Its something I learned several years ago, and I just don’t remember.
I do know that E is the derivitve of the stress strain function, I just dont recall how to complete the E, Nu, x? triangle.
I guess thats what I’m working on now.
John - Get a blog. It’s free.
Yes I do. Mind you I posted at 2 am.
Tomato, tamato…
And I just got home from 8 hours of class today, calc 2 until 9 tonight.
I’m totally spent.
And who on earth is OsoiNA6?
I’m interested to know. Because you are on your game!
I can’t believe there are people who even responded intelligently to this thread.
It is quite refreshing.
What do you do OsoiNA6?
Lyndon you are blowing my mind. We totally need to talk more. I had a blast at the SCCA Divisional championships.
For a guy who works with computers, your a natural mechanical engineer!
Your assumption is correct. The formula I was given is called exactly the thread title: “Tangential Stresses in rotating ring”. I was assured by the Dynamics professor they were totally applicable for discs when Ri is 0.
You will note several terms fall right out of the equations for this unique condition. I left all terms in my excel formulas, only eliminating terms that divided by zero.
Its a shame I don’t drink. 
Archie keeps it real son
I’m an engineer but lately been working more on the sales end trying to peddle small time goods (power plant upgrades) to utility companies / independent power producers.
Stop posting lifes little secrets. Man, thats like scoring a goal for the other team! !!!
My bad.
I retract my previous post…
Young bucks: Always be sure to run your mouth as much as possible how good you really could be, complain about your boss and how he does nothing, establish a sense of entitlement, and also try to be as lackadaisical as possible when you do land that job. You’ll be VP in no time.
There it is!
QUESTION:
What is the right unit for density in the imperial system?
it is NOT lb/ft^3
I have mass/g/12/12?
I’m terribly confused.
Slugs/ft^3???
:banghead
density should be in lbm/ft^3 or slugs/ft^3
or just complete the problem in metric and convert back once you have your answer since the english unit system is retarded and the US is the only fuckin country that doesn’t use metric.
Bah, what a bunch of losers… :banghead
Agreed, the imperial system is stupid.
After much investigation of this formula, the appropriate unit of p (density) is Slugs per square inch?
I had originally been using a value of .275lb / in^3 which is the published value for 440c. However, I had noticed in an example problem that the value of p was very small, around .0007. I had no idea how they arrived at this number until i took my density and divided by “G” 32.2 ft/sec/sec.
I then get .00854 but not .000x
I then divided by 12, apparently changing feet “ft/sec/sec” to “inches/sec/sec” ??
p=.0007116 for 440C steel?
This seems logical, since all the radii in the formula are in inches, not feet. I now get seemingly valid results when comparing the output of this formula to real life experience. I am however not entirely sure I have done everything correctly.
For my 6.75" diameter disk, I calculate, using all my radii in inches, and a p of .0007116, that at a speed of 40,000 RPM (4188 Rad/Sec) both the tangential and radial stresses are equal to 58.6 Ksi at R=0, the maximum.
Evaluating the two formulas i supplied in the last email, the tangential and radial forces at the center of a rotating disk with NO central hole are equal.
OK so that’s the stress…
Now the influence of Kt…
I had originally assumed the stress tangential would be at maximum at Ro but this is not true according to the formula. Based on my initial assumptions I assumed that the stress concentrations of radially drilled and tapped holes on the OD would be significant.
However having now studied the formula, the radial stress is zero at the OD, therefore stress concentrations of holes with respect to radial stress would be concentrating a stress of zero. The holes would need to be very deep before they would have a significant effect on the radial stress.
Tangential or hoop stress decreases as radius increases, but does not go to zero.
Therefore, the radial holes should have a stress concentration effect on the tangential stress in the ranges of radius where the holes are present. The holes are approximately 1" deep. They are tapped what I believe is 10-32 thread, 0.5" deep.
I suppose the stress concentration of a radial hole in a tangential plane is similar to that of a hole in a rectangular section in bending.
Do you think this is a reasonable assumption?
I am satisfied with the validity of my stress calculations.
Ignoring the combined stress effects of bending, radial, and tangential stresses, the burst speed is 86,468 RPM