Flat disk with pressure. Results are too low.
Flat disk with pressure. Results are too low.
(OP)
I have a diaphragm disk, .0625" thick, 4.944" diameter, 17-4 PH H-900. I fixed the very edge around the diameter, the .0625" thick OD edge, and put 50 psi on one face. I end up with .004" max deflection in the very center. That seemed low so I had a friend run the same test on Pro-E and he came up with .042" which seems correct. Hmmm, off by a factor of 10???
I check units, pressure, etc. and everything seems OK.
Could someone run this piece and see what they get?
Thanks!
I check units, pressure, etc. and everything seems OK.
Could someone run this piece and see what they get?
Thanks!





RE: Flat disk with pressure. Results are too low.
RE: Flat disk with pressure. Results are too low.
Roark's, 6th edition, Table 24, Case 10b with r0 = 0:
y = -q*a^4/(64D) = -0.04438"
Looks pretty good to me.
Garland E. Borowski, PE
Engineering Manager
Star Aviation
RE: Flat disk with pressure. Results are too low.
I could definately see a descrepency between fixing only translation versus with rotation too... Don't know about the factor of 10, but possibly.
-- MechEng2005
RE: Flat disk with pressure. Results are too low.
RE: Flat disk with pressure. Results are too low.
By "Quarter Symmetry Model", I have set boundary conditions along the x-axis and y-axis that simulate the entire disk. Think about it for a minute: Any deflection that would pull the nodes on the x-axis in the positive y-direction has an equal force trying to pull it in the negative y-direction. Because of this, you can set "x-symmetry" meaning that the line of nodes on the x-axis can only displace along the x- or z-axes...not the y. Using that same logic, you can constrain the y-axis nodes to move only along the y- or z-axes. That means that the middle node can only move straight down.
As for your model, I'm guessing you are using brick elements, which are completely inappropriate for a thin disk. They are stiff in bending (reduces displacement).
Are you able to set element types in Design Check? If so, you should use plates in your case. This should result in a mid-plane mesh of your solid disk. As an alternative, see if you can use the surface modeling capabilities and just model a 2-D surface of the disk. Apply your boundary conditions and loads and try to run design check. If it recognizes the 2-D geometry, it should use plate theory to calculate displacements and your answer should be closer to correct.
Hopefully this will get you started.
RE: Flat disk with pressure. Results are too low.
Deflection will be very inaccurate. You need 3 brick elements through the thickness. This is probably not practicable with Design Check. You could try quarter symmetry as suggested by GBOR and reduce element size which will get you closer.
Design Check will only do symmetry on orthoganal axes. It will not do any other smaller angle or axisysmmetic.
RE: Flat disk with pressure. Results are too low.
Thanks for running this and making me realize the limitations of Design Check.
I apparently have a lot to learn.
RE: Flat disk with pressure. Results are too low.
Design Check sounds exactly like Cosmos Express, which I usually refer to as "dangerous". The package is too limited and you have too little control. If you don't know what you are looking at, it will get you in trouble. If you do know what you are looking at, you probably have a more capable package.
At least now you know a little bit of what you didn't know before. Keep searching...you will find something useful.
If cost is the issue, a low-cost, but very good package is Roshaz (www.Roshaz.com). Right now, they are running a special for $595 for the package and 1 month of maintenance. Additional maintenance is $600/year. Couple this with the free, open-source code Calculix (www.bconverged.com) and you have a VERY capable package for a VERY reasonable pricetag. The Calculix pre-processor used to be horrible, but Roshaz helps ease the pain.
RE: Flat disk with pressure. Results are too low.
Oh well, I have friends with complete packages so we'll just trade work.