[Mechanical] User defined result temperature difference
In my a transient thermal model in Mechanical I want to plot a temperature difference vs. time for two nodes. I can make separate User Defined result for each node and give them an identifier, e.g. TopTemp and BottomTemp and each of these works correctly. When I create a 3rd user defined result of (= TopTemp - BottomTemp), the result is just zero. I'm obviously using the User Defined Results incorrectly, but I'm stuck.
Is there a way to do this in Mechanical without resorting to copy/paste into Excel?
Aaron C. Caba, Ph.D.
Sr. Principal R&D Engineer
BAE Systems, Inc.
4050 Peppers Ferry Road, Radford VA 24143-0100
www.baesystems.com
Aaron,
That should have worked. How about going even simpler? Avoid the equation at first. Try to see if you can use a UDR to grab the TopTemp (from the earlier identifier)? Does that work for you? If so, see if you can do the same for BottomTemp. Did that work? Would "units" be the issue with your equation - I bet you were careful with that. So, how about this, are you selecting a subset of nodes/elements, rather than all of them, in the initial requests? And then, do you request more than the subset of nodes/elements in the UDR's with the calculation. I can foresee problems with that.
Let us know.
Regards,
Irene Slater
Corning Incorporated
-----Original Message-----
From: Caba, Aaron (US) via Xansys xansys-temp@list.xansys.org
Sent: Wednesday, April 6, 2022 12:00 PM
To: XANSYS Mailing List Home xansys-temp@list.xansys.org
Cc: Caba, Aaron (US) Aaron.Caba@baesystems.com
Subject: [EXTERNAL]--[Xansys] [Mechanical] User defined result temperature difference
In my a transient thermal model in Mechanical I want to plot a temperature difference vs. time for two nodes. I can make separate User Defined result for each node and give them an identifier, e.g. TopTemp and BottomTemp and each of these works correctly. When I create a 3rd user defined result of (= TopTemp - BottomTemp), the result is just zero. I'm obviously using the User Defined Results incorrectly, but I'm stuck.
Is there a way to do this in Mechanical without resorting to copy/paste into Excel?
Aaron C. Caba, Ph.D.
Sr. Principal R&D Engineer
BAE Systems, Inc.
4050 Peppers Ferry Road, Radford VA 24143-0100 www.baesystems.com
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Aaron,
I would either
a. export the two user defined results to excel, and do the subtraction
there, or
b. write a command snippet to do the math in post26, and write the data to a
file.
Tom Caltabellotta
Senior Mechanical Engineer
CACI inc.
-----Original Message-----
From: Caba, Aaron (US) via Xansys xansys-temp@list.xansys.org
Sent: Wednesday, April 6, 2022 12:00 PM
To: XANSYS Mailing List Home xansys-temp@list.xansys.org
Cc: Caba, Aaron (US) Aaron.Caba@baesystems.com
Subject: [Xansys] [Mechanical] User defined result temperature difference
In my a transient thermal model in Mechanical I want to plot a temperature
difference vs. time for two nodes. I can make separate User Defined result
for each node and give them an identifier, e.g. TopTemp and BottomTemp and
each of these works correctly. When I create a 3rd user defined result of
(= TopTemp - BottomTemp), the result is just zero. I'm obviously using the
User Defined Results incorrectly, but I'm stuck.
Is there a way to do this in Mechanical without resorting to copy/paste into
Excel?
Aaron C. Caba, Ph.D.
Sr. Principal R&D Engineer
BAE Systems, Inc.
4050 Peppers Ferry Road, Radford VA 24143-0100 www.baesystems.com
Xansys mailing list -- xansys-temp@list.xansys.org To unsubscribe send an
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which will send a single email per day.
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Irene - The issue is that the a UDR take the geometric intersection of the input UDRs. If UDRTop selects node 1 and UDRBottom selects node 2, the intersection of UDRDiff=UDRTop-UDRBottom is the empty set. I just want the arithmetic difference of the list of values, irrespective of where they are on the geometry.
Tom - I may end up using the post26 command snip option since I don't see a better one in the GUI.
Aaron C. Caba, Ph.D.
Sr. Principal R&D Engineer II
BAE Systems, Inc. | Ordnance Systems, Inc.
E-mail: aaron.caba@baesystems.com | Mail: 4050 Peppers Ferry Road, Radford VA 24143-0100 www.baesystems.com
-----Original Message-----
From: Slater, Irene M SlaterIM@corning.com
Sent: Wednesday, April 6, 2022 12:09 PM
To: XANSYS Mailing List Home xansys-temp@list.xansys.org
Cc: Caba, Aaron (US) Aaron.Caba@baesystems.com
Subject: RE: [EXTERNAL]--[Xansys] [Mechanical] User defined result temperature difference
Aaron,
That should have worked. How about going even simpler? Avoid the equation at first. Try to see if you can use a UDR to grab the TopTemp (from the earlier identifier)? Does that work for you? If so, see if you can do the same for BottomTemp. Did that work? Would "units" be the issue with your equation - I bet you were careful with that. So, how about this, are you selecting a subset of nodes/elements, rather than all of them, in the initial requests? And then, do you request more than the subset of nodes/elements in the UDR's with the calculation. I can foresee problems with that.
Let us know.
Regards,
Irene Slater
Corning Incorporated
-----Original Message-----
From: Caba, Aaron (US) via Xansys xansys-temp@list.xansys.org
Sent: Wednesday, April 6, 2022 12:00 PM
To: XANSYS Mailing List Home xansys-temp@list.xansys.org
Cc: Caba, Aaron (US) Aaron.Caba@baesystems.com
Subject: [EXTERNAL]--[Xansys] [Mechanical] User defined result temperature difference
In my a transient thermal model in Mechanical I want to plot a temperature difference vs. time for two nodes. I can make separate User Defined result for each node and give them an identifier, e.g. TopTemp and BottomTemp and each of these works correctly. When I create a 3rd user defined result of (= TopTemp - BottomTemp), the result is just zero. I'm obviously using the User Defined Results incorrectly, but I'm stuck.
Is there a way to do this in Mechanical without resorting to copy/paste into Excel?
Aaron C. Caba, Ph.D.
Sr. Principal R&D Engineer
BAE Systems, Inc.
4050 Peppers Ferry Road, Radford VA 24143-0100 www.baesystems.com
Xansys mailing list -- xansys-temp@list.xansys.org To unsubscribe send an email to xansys-temp-leave@list.xansys.org If you are receiving too many emails from XANSYS please consider changing account settings to Digest mode which will send a single email per day.
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Dear XANSYS Members,
I am trying to obtain a methodology that uses an equivalent static
loading in modeling shock impact.
In this methodology, I wanted to use static analysis to generate the same
displacements of transient analysis at a certain instant of time. Using
simple single-degree-of-freedom theory, I found that the equivalent static
"input acceleration (Gst)" is equal to Gst = Xdyn*(wn)^2 where Xdyn is the
displacement from transient solution at a time point (t), and wn is the
natural frequency of the structure in rad/sec. This equation is also
available in Harris' shock and vibration handbook, sixth edition (Equation
20.30).
When I apply the equivalent static load using the ACEL command, the static
displacements are 12 times higher than those of the transient analysis.
Keeping in mind that I am using a simple plate model with fixed boundary
conditions at all edges.
Is there anything I am missing here? I would appreciate your invaluable
suggestions.
I hope that my problem description was clear and sound.
Best Regards,
Mohammad
---====
Mohammad A Gharaibeh, Ph.D.
Associate Professor
Department of Mechanical Engineering
The Hashemite University
P.O. Box 330127
Zarqa, 13133, Jordan
Tel: +962 - 5 - 390 3333 Ext. 4771
Fax: +962 - 5 - 382 6348
---====
On Apr 10, 2022, at 3:14 AM, Mohammad A Gharaibeh via Xansys xansys-temp@list.xansys.org wrote:
Is there anything I am missing here? I would appreciate your invaluable
suggestions.
Equivalent static load is a common artifice, if you believe that only the fundamental response matters, and if the dynamic response resembles the static response. Sometimes this happens; sometimes not, so you need to exercise some judgment here. if your loading is time-varying it probably isn't. But that's between you and your client.
Common practice is to apply the load statically, as it sounds like you're attempting, only you multiply the load by a so-called dynamic amplification factor (DAF). For example a force, F, applied instantaneously implies DAF = 2. So your load input is 2xF. The dynamic response is twice the static response. IIRC my undergraduate strength of materials class went through this all. The major assumption is that the under dynamic loading the structure has the same 'shape' as the static response multiple by the DAF. This approach is commonly used because a lot of engineers forget their dynamics classwork within minutes of finishing the final.
That sounds like what you're trying to do. Maybe with a different DAF. If your loading is highly dynamic, meaning that the frequency response of the structure matters, like in a piping system or a system where the mass is oddly distributed, or the loading is frequency dependent you need to obtain the modal solution and operate on that, typically by combining each modal response using one of several conventions.
Specifically addressing your question the 12x difference you're seeing is the difference between a steady state loading and the same loading applied and removed instantaneously, or at least over a small interval during which the structure can't respond completely. For example a 2g steady state load is much more severe than a 2g spike over an interval much less than the fundamental period of the response.
But maybe you already know that. I used to do such things for a living so if you have any specific issues I'd be happy to amplify any of this.
Christopher Wright P.E. (ret'd) |"They couldn't hit an elephant at
chrisw@skypoint.com | this distance" (last words of Gen.
| John Sedgwick, Spotsylvania (1864)
http://www.skypoint.com/members/chrisw/
Thanks Chris for the invaluable discussion. I was able to identify what
dynamic amplification factor I need.
Suppose a spring with stiffness (K) that is axially loaded by a force (F).
The deflection here is (d).
To compute the the required static load to simulate the dynamic case with
displacement (Xdyn), let d=Xdyn then the equivalent static load would be
Fst=K*Xdyn. The challenge now is to find the equivalent stiffness of the
structure under study. For a plate vibrating at the first mode, the
stiffness is the bending stiffness of this plate. To obtain that, I applied
acceleration of 1 m/s2 in FEA and computed the transverse deflection (Uz).
Divide 1 by Uz and I got the equivalent bending of the plate Keq.
Now, the equivalent static load is Fst = Keq*Xdyn and it gave me static
displacements that are exactly equal to the dynamic displacement! Yay!
In conclusion, my dynamic amplification factor is the bending stiffness of
the plate I study.
I would still appreciate your, and everyone’s, comments on this.
Best,
Mohammad
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--
---====
Mohammad A Gharaibeh, Ph.D.
Associate Professor
Department of Mechanical Engineering
The Hashemite University
P.O. Box 330127
Zarqa, 13133, Jordan
Tel: +962 - 5 - 390 3333 Ext. 4771
Fax: +962 - 5 - 382 6348
---====
On 12-Apr-22 8:40, Mohammad A Gharaibeh via Xansys wrote:
Thanks Chris for the invaluable discussion. I was able to identify what
dynamic amplification factor I need.
???????????????????????????
Is it just me ? - This discussion must have gone straight past me. I
had may be 3 emails in the past 3-4 days.
Ernst Hustedt
Semi-retired
Chch, NZ
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Lots of similar problems recently. Once Kenneth Brian Gomez resubscribed me and my own I/T folks stopped withholding my subsequent incoming xansys emails, I was back in business.
Robert Dillworth, PE
Principal Engineer
T.: +1 212 233 2737 x966
Robert.Dillworth@socotec.us
SOCOTEC Engineering, Inc
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, NY 10036
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-----Original Message-----
From: Ernst Hustedt ernst.hustedt@ames.co.nz
Sent: Monday, April 11, 2022 5:24 PM
To: xansys-temp@list.xansys.org
Subject: [Xansys] Re: Replacing shock load by an equivalent static load
On 12-Apr-22 8:40, Mohammad A Gharaibeh via Xansys wrote:
Thanks Chris for the invaluable discussion. I was able to identify
what dynamic amplification factor I need.
???????????????????????????
Is it just me ? - This discussion must have gone straight past me. I had may be 3 emails in the past 3-4 days.
Ernst Hustedt
Semi-retired
Chch, NZ
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Thanks Robert
Still rather odd. I got yours, obviously, but my own you are replying
to did not show up, which is what normally happens.
Well, let's see what happens after I have had another coffee.
Ernst Hustedt
Christchurch, NZ
On 12-Apr-22 10:08, Robert Dillworth wrote:
Lots of similar problems recently. Once Kenneth Brian Gomez resubscribed me and my own I/T folks stopped withholding my subsequent incoming xansys emails, I was back in business.
Robert Dillworth, PE
Principal Engineer
T.: +1 212 233 2737 x966
Robert.Dillworth@socotec.us
SOCOTEC Engineering, Inc
151 W 42nd Street, 24th Floor
New York
, NY 10036
www.socotec.us
We are now SOCOTEC. Click here to read the press release.
Consider the environment before printing this email
This e-mail may contain confidential, copyright or privileged information. If you are not the intended recipient or if you have received this e-mail in error, please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden.
SOCOTEC cannot guarantee the integrity of this communication. As the Internet is not a guaranteed secure environment, SOCOTEC cannot ensure that an e-mail is not interfered with during transmission, as such will not be held responsible for any damage from e-mail transmission.
-----Original Message-----
From: Ernst Hustedt ernst.hustedt@ames.co.nz
Sent: Monday, April 11, 2022 5:24 PM
To: xansys-temp@list.xansys.org
Subject: [Xansys] Re: Replacing shock load by an equivalent static load
On 12-Apr-22 8:40, Mohammad A Gharaibeh via Xansys wrote:
Thanks Chris for the invaluable discussion. I was able to identify
what dynamic amplification factor I need.
???????????????????????????
Is it just me ? - This discussion must have gone straight past me. I had may be 3 emails in the past 3-4 days.
Ernst Hustedt
Semi-retired
Chch, NZ
--
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