Re: [PSUBS-MAILIST] Scale hull testing

Chip,

Sorry, I can't help you with your question but I have to ask you; why would you go through all the work of building a half scale model to test?

You have to do all the same steps in constructing a half scale model at about three quarters of the time and three quarters the expense of the real thing. After you test it and it passes, you have only a half size sub that you can't do a thing with and still have to build your full size sub.

Maybe build a fifth or tenth scale, or just build the real thing and test the hull before you install the hardware.

Dan H.

----- Original Message -----

From: Chuck Will

To: personal_submersibles@psubs.org

Sent: Monday, December 19, 2005 5:16 PM

Subject: [PSUBS-MAILIST] Scale hull testing

I need some help here. This is probably a rather simple physics question that I can't seem to find an answer for.

If I was to construct an exact 1/2 scale pressure hull using my design (everything would be 1/2 size, hull thickness, support rib thickness and size, rib spacing, hull diameter, everything...) and did an unmanned test in open ocean or lake, would it withstand the same depth as a full size hull or would it only withstand half the depth of the full size hull?

I ran the hull calculation formula for both and most of the numbers matched up but a few didn't.

Shell failure values matched exactly for Buckle, at frame, and at midbay but the general instability value was less than half on the scale vs. the full size.

Frame failure values matched up exactly for both hulls

Predicted failure listed the full size hull as 1915 ft with "shell yield" as the failure mode. The scale hull as came in at 1071 ft with "general instability" as the failure mode.

Can someone help me interpret these results. I was thinking it would cost me a lot less to test a half scale hull design before making the plunge financially on the full scale hull.

Chip