[PSUBS-MAILIST] model testing

Tue Dec 30 13:35:49 EST 2014

Reynolds number matching allows you to model viscous drag, but form drag modelling (eg. Surface wave resistance) requires matching the Froude number.
Sean

----- Original Message -----
From: Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Tue, 30 Dec 2014 07:44:51 -0700 (MST)
Subject: Re: [PSUBS-MAILIST] model testing

Hank, just to bring closure to this thread.  Stress on the boat due to depth scales geometrically between motel and prototype.  Drag scales based on Reynolds number.
As an example for stress, go to Psubs.org flat acrylic viewport calculator that Jon coded based on PVHO http://www.psubs.org/design/viewports/1ATMFD/
Put in a 500 ft depth and a 10" viewable diameter Di and record all results for the acrylic viewport.  Repeat with same depth but 1/10" the viewable diameter, i.e., 1" and record results.  Note that all dimension scale geometrically.  This is based on the assumption that the material is isotropic. These
 results would not be true for anisotropic materials like a carbon fiber layup were material properties are  directional dependent.  Additionally for carbon fiber, you would not be able to scale the scale the size of the fibers.
So if you are using an isotropic material such as steel, and can fabricate a dimensionally corrected scaled model of a component like a pressure hull including details like weld filler size, then crush depth observed in the motel test cell would match the full scale prototype.  Like any experiment, you would need multiple test to average the results.
Cliff

Cliff Redus
Redus Engineering
USA mobile:  830-931-1280
cliffordredus at sbcglobal.com

From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
Sent: Monday, December 29, 2014 2:41 PM
Subject: Re: [PSUBS-MAILIST] model testing

I am not looking for drag comparisons, I am looking for failure due to pressure comparisons.  I though I read that the Nekton subs
 were built as a model first to establish crush depth.Hank --------------------------------------------On Mon, 12/29/14, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote: Subject: Re: [PSUBS-MAILIST] model testing To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org> Received: Monday, December 29, 2014, 3:06 PM Drag results between a model and full scale does not scale geometrically.  You have to scale model and full scale off the dimensionless  Reynolds
 number.   Reynolds number scaling enables you to scale results between model and full scale using either a water tunnel or air tunnel. Cliff          From: Alan James via Personal_Submersibles <personal_submersibles at psubs.org> To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>  Sent: Monday, December 29, 2014 1:55 PM  Subject: Re: [PSUBS-MAILIST] model testing     Hank,I just ran a test on my pressure program & you get the same crush depthon a sphere of A516-70 steel that is 1000mm diameter & 10mm thick as youdo on a sphere 100mm diameter & 1mm thick.What I am not sure of is if you can scale up the drag results on a model.If you have a scale model that is 1/50th & it takes X amount of force to push  it at 3 knots, can you multiply X by 50 to get the required thrust?Alan        From: Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>  Sent: Tuesday, December 30, 2014 8:43 AM  Subject: Re: [PSUBS-MAILIST] model testing     Hank,       I would say no.  It would have to be so exact that it would be virtually impossible to extrapolate from the small model, and  aside from that I think there are other engineering principles involved that would come into play , Sean would be the person to ask !   I know that it is done in wave tanks and wind tunnels, but in those you are looking at laminar flow and such things, not structural strength so much.  You might be able to get a rough idea of how it would start to collapse maybe.  The larger the model the better I would think. Brian --- personal_submersibles at psubs.org wrote: From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> To: personal_submersibles at psubs.org Subject: [PSUBS-MAILIST] model testing Date: Mon, 29 Dec 2014 10:52:46 -0800 Hi all If you make a scale model of a submarine in complete detail.  Scale the size and metal thickness, is it a reasonable representation of depth capabilities when pressure tested? Hank _______________________________________________ Personal_Submersibles mailing listPersonal_Submersibles at psubs.orghttp://www.psubs.org/mailman/listinfo.cgi/personal_submersibles _______________________________________________ Personal_Submersibles mailing listPersonal_Submersibles at psubs.orghttp://www.psubs.org/mailman/listinfo.cgi/personal_submersibles     _______________________________________________ Personal_Submersibles
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