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RE: [PSUBS-MAILIST] FEA Work on Acrylic CT for KLH-500
Jon,
That was a really good reply and while it is great to see Brent doing these
FEA's there are people who will think that the results are correct.
I have spent about $25,000 on recent FEA from 4 different professionals.
Only one of these guys was correct. We were also doing our own FEA so we
could get a steer on the design before we gave it to the pro's. Our results
with FEA were up to 50% out from the proper FEA. Most of the problem is in
the size and type of mesh that is done. The other area where huge errors
are made is in the placement and type of forces and restraints placed on the
model. It was explained to me that the 8 point mesh is far more accurate
than the normal triangular 4 point. It is an art form as much as a science.
By all means play with it for information but don't rely on it unless you
have it checked by a pro. Chs Hugh
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Jon Wallace
Sent: 04 September 2009 02:40
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] FEA Work on Acrylic CT for KLH-500
Brent,
Just trying to provide you with some constructive criticism here.
The FEA work you've been doing is interesting, and because you are the
only one sharing such data, it's also very valuable if it was done
correctly and your results are valid. However, that's the big
question. I suspect your sharing the results are not the problem, but
the presentation you use to share it. You tend to present ideas and
information as factually correct when a better method would be to
present them as "findings" and ask people to analyze and confirm your
results to make sure they are correct.
Your statement about the group knowing you are not a professional
analyst is a bad assumption. You only interact with about10% of the
total number of people signed-up to receive email from the group. In
reality, the vast majority of people who receive your mail know nothing
about you. This goes exactly to one of Jay's points in that the
drawings you are providing look very professional and without proper
context they could be interpreted as professional results by people who
do not know anything about you. You also need to keep in mind that we
average 10k visitors to the web site each month who can view your email
through the archives, and they almost certainly know nothing about any
of the contributors.
What you say matters because somebody at a later time could be making
assumptions about your assumptions. That doesn't mean you can't provide
interesting data like the FEA results, or suggest innovative solutions
to old problems. However, it does mean that having proper context will
result in a much more receptive audience by those who have expertise in
the subject you are discussing.
Jon
**
Brent Hartwig wrote:
> *Jay,*
> **
> *The input like you and others are giving, is why I post this material
> to the group. One doesn't need to be a professional FEA analyst to
> have good input. This group knows I'm not a professional FEA analyst.
> They also are well aware by now that they are responsible for there
> own submarine designs, and what data they choose to use to design
> there subs. I could choose to only send this material to a select few
> I know and/or suspect would have good input. But there are many in
> this group that I don't know at all, and others I do know that have a
> wide array of back ground experience in so many things, that I don't
> wish to miss out on there input. Besides it's been said before, why
> should the select few get all the fun of looking at different proposed
> designs?....*
> **
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