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[apdl] how to reassign uniform temp to all nodes
 
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debabrata.podder
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Joined: 21 Feb 2013
Posts: 51
Location: NIT Meghalaya, India

PostPosted: Sat Jun 21, 2014 4:01 am  Reply with quote

Dear experts,

I applied preheat by assigning, TUNIF,200 to my thermal model. After preheating I applied my heat flux to the concerned area. A little later the temperature of the whole model is turned down to room temp (30 deg C). Now I want to preheat it again and thereafter I want to apply the heat flux again. But in the second stage when I was going to preheat the model by 'TUNIF' or by 'BF,ALL,TEMP' command, the uniform heating was not applied at all !!!
Why ? How can I heat up the whole model uniformly in between the analysis again ?

Regards-
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Debabrata Podder(PhD)
Assistant Professor
NIT Meghalaya
India
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danbohlen
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Joined: 18 Aug 2008
Posts: 951
Location: Evendale OH

PostPosted: Sat Jun 21, 2014 5:42 am  Reply with quote

I would avoid the whole TUNIF command. Try only applying BF commands.

Think of it this way TUNIF only acts if there are no BF commands applied. You start with TUNIF=300, apply some BF's. If you want to do another TUNIF, you have to delete all the applied BFs first.


Dan becarefullnotbebe"BF"edbythere commands Bohlen
Senior/ SSt Engineer, Military HPT Analysis
STAR review chairman, Fan and Booster
GE Aircraft Engines
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-----Original Message-----
From: Xansys [mailto:xansys-bounces@xansys.org] On Behalf Of debabrata.podder
Sent: Saturday, June 21, 2014 7:02 AM
To: xansys@xansys.org
Subject: [Xansys] [apdl] how to reassign uniform temp to all nodes

Dear experts,

I applied preheat by assigning, TUNIF,200 to my thermal model. After preheating I applied my heat flux to the concerned area. A little later the temperature of the whole model is turned down to room temp (30 deg C). Now I want to preheat it again and thereafter I want to apply the heat flux again. But in the second stage when I was going to preheat the model by 'TUNIF' or by 'BF,ALL,TEMP' command, the uniform heating was not applied at all !!!
Why ? How can I heat up the whole model uniformly in between the analysis again ?

Regards-

------------------------
Debabrata Podder
Research Scholar
IIT Kharagpur
PIN NO.: 721302
India






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Dan Bohlen
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summer.shen
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Joined: 14 May 2014
Posts: 53
Location: Shanghai, China

PostPosted: Sat Jun 21, 2014 6:59 am  Reply with quote

Not sure if you are running a thermal analysis or a structural analysis.
For a thermal analysis, I am afraid you cannot assign temperature with BF command. In a thermal analysis, temperature is the DOF of nodes, different from a load in structural analysis.

As you have already tried, TUNIF(or another similar but more general command, IC) can only be used before the first solution step. As it is documented in the manual, 'for the transient, the initial value is specified at the beginning of the first load step,that is, at time = 0.0'.

I guess I am facing similar problem like yours. Check this thread:
http://www.xansys.org/forum/viewtopic.php?t=25770

Basically,if I got this right, we are both trying to change the DOF value (i.e. nodal temperature in a thermal analysis), hope we can get some insight from ANSYS experts.


debabrata.podder wrote:
Dear experts,

I applied preheat by assigning, TUNIF,200 to my thermal model. After preheating I applied my heat flux to the concerned area. A little later the temperature of the whole model is turned down to room temp (30 deg C). Now I want to preheat it again and thereafter I want to apply the heat flux again. But in the second stage when I was going to preheat the model by 'TUNIF' or by 'BF,ALL,TEMP' command, the uniform heating was not applied at all !!!
Why ? How can I heat up the whole model uniformly in between the analysis again ?

Regards-

_________________
Summer Shen
--
MSc,Shanghai Jiao Tong University
Dongchuan Rd. 800, Shanghai, China. 200240
Laser cladding
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francis.ku
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Joined: 31 Jul 2009
Posts: 23

PostPosted: Sat Jun 21, 2014 10:40 am  Reply with quote

For your situation, the D,ALL,TEMP,200 command would work. Assign a dummy step and solve for the preheat, then DDELE the temperatures on the nodes that you do not want in the next step.


Francis H. Ku
Senior Consultant

Structural Integrity Associates, Inc.
5215 Hellyer Ave Ste 210
San Jose CA 95138
USA



-----Original Message-----
From: Xansys [mailto:xansys-bounces@xansys.org] On Behalf Of debabrata.podder
Sent: Saturday, June 21, 2014 4:02 AM
To: xansys@xansys.org
Subject: [Xansys] [apdl] how to reassign uniform temp to all nodes

Dear experts,

I applied preheat by assigning, TUNIF,200 to my thermal model. After preheating I applied my heat flux to the concerned area. A little later the temperature of the whole model is turned down to room temp (30 deg C). Now I want to preheat it again and thereafter I want to apply the heat flux again. But in the second stage when I was going to preheat the model by 'TUNIF' or by 'BF,ALL,TEMP' command, the uniform heating was not applied at all !!!
Why ? How can I heat up the whole model uniformly in between the analysis again ?

Regards-

------------------------
Debabrata Podder
Research Scholar
IIT Kharagpur
PIN NO.: 721302
India






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debabrata.podder
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Joined: 21 Feb 2013
Posts: 51
Location: NIT Meghalaya, India

PostPosted: Sat Jun 21, 2014 12:45 pm  Reply with quote

Hi all, thanks for your time. I have applied the thermal load as suggested by Mr. Francis like below:

!For preheat application
ALLSEL,ALL

CSYS,0
ESEL,S,LIVE
NSLE,S
D,all,temp,200

ALLSEL,ALL

But still I am unable to apply preheat in between the analysis !!!
What's the problem !!!
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christopher.wright
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Joined: 17 Jun 2009
Posts: 927

PostPosted: Sat Jun 21, 2014 2:11 pm  Reply with quote

On Jun 21, 2014, at 2:45 PM, debabrata.podder wrote:

Quote:
What's the problem !!!
Sounds like physics. You can impose temperatures or heat flows--not
both.

Christopher Wright P.E. |"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/



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francis.ku
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Joined: 31 Jul 2009
Posts: 23

PostPosted: Sat Jun 21, 2014 6:17 pm  Reply with quote

You will need to add a SOLVE after ALLSEL,ALL to keep the preheat temperatures. Then, in the next load step, use DDELE to remove the temperatures on the nodes you don't want, and apply the heat flux.


Francis H. Ku
Senior Consultant

Structural Integrity Associates, Inc.
5215 Hellyer Ave Ste 210
San Jose CA 95138
USA
www.structint.com



-----Original Message-----
From: Xansys [mailto:xansys-bounces@xansys.org] On Behalf Of debabrata.podder
Sent: Saturday, June 21, 2014 12:46 PM
To: xansys@xansys.org
Subject: Re: [Xansys] [apdl] how to reassign uniform temp to all nodes

Hi all, thanks for your time. I have applied the thermal load as suggested by Mr. Francis like below:

!For preheat application
ALLSEL,ALL

CSYS,0
ESEL,S,LIVE
NSLE,S
D,all,temp,200

ALLSEL,ALL

But still I am unable to apply preheat in between the analysis !!!
What's the problem !!!

------------------------
Debabrata Podder
Research Scholar
IIT Kharagpur
PIN NO.: 721302
India






+-------------------------------------------------------------+
| XANSYS web - www.xansys.org/forum |
| The Online Community for users of ANSYS, Inc. Software |
| Hosted by PADT - www.padtinc.com |
| Send administrative requests to xansys-mod@tynecomp.co.uk |
+-------------------------------------------------------------+
+-------------------------------------------------------------+
| XANSYS web - www.xansys.org/forum |
| The Online Community for users of ANSYS, Inc. Software |
| Hosted by PADT - www.padtinc.com |
| Send administrative requests to xansys-mod@tynecomp.co.uk |
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debabrata.podder
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Joined: 21 Feb 2013
Posts: 51
Location: NIT Meghalaya, India

PostPosted: Sun Jun 22, 2014 4:20 am  Reply with quote

Thanks Mr. Francis. The problem is solved now. Now I have added an extra SOLVE after applying the preheating again.

Regards-
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