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[Xansys] FLuid Damping FLUID136 Elements
 
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ayo.brimmo
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Joined: 01 Jul 2013
Posts: 38
Location: Masdar City, Abu Dhabi

PostPosted: Sat Jan 10, 2015 4:19 am  Reply with quote

Dear All,

I am trying to use the FLUID136 elements to model the squeeze film damping of a cantilever beam. Below is the snippet I used to do this:

" et, 10, 136 ! Fluid 136 element
keyopt, 10, 3,2 !implicit treatment
Keyopt, 10, 4, 1 ! setting compressible linearized Reynolds equation
mp,dens,10,1.4 !density
mp,visc,10,1.8e-5 !effective viscosity

r, 10, 100e-6,,,100e3 ! 100e-6 fluid gap, 101e3 ambient pressure
rmore, 101e3, 65e-9 ! 101e3 reference pressure, 65e-9 Mean free fluid path at reference pressure

SETTOL, 1e-7 ! tolerance
Nsel,s,loc,z,8e-6
Esln,s
Type, 10
Mat, 10
Real, 10
Esurf

Nsel,s,loc,y, -369.5e-6 !x1 location of bottom surface
Nsel,a,loc y, 369.5e-6 !x2 location of bottom surface
Nsel,a,loc,x, 338e-6 !y1 location of bottom surface
Nsel,a,loc,x, 1338e-6 !y2 location of bottom surface

Nsel, r, loc, z, -1e-7, 1e-7
d,all,pres
allsel
"

When I introduce the FLUID136 elements at the bottom of the cantilever (with respect to the Z axis), everything goes well. However, if I try to do the same with the damping elements located at the top of the cantilever, then I start getting unreasonable deformation responses until the model diverges. I am pretty sure that this has something to do with the location of the squeeze film elements as flipping the cantilever-so the top surface now becomes the bottom surface with respect to the Z axis-would resolves the issue. But the problem is that I want to put the squeeze film elements on both surfaces as in reality, the cantilever is in a cavity where it experiences squeeze film at both surfaces.

Has anyone experienced this before? Any possible causes or suggestions on how to squeeze film on both surfaces would be greatly appreciated.

Best,
Ayo Brimmo
Research Engineer
Mechanical Engineering Program

[Description: InstDual]
Mobile: +971 50 90 42782; +971 52 6241862 |P.O. Box: 54224, Abu Dhabi, UAE
E-mail: abrimmo@masdar.ac.ae<mailto:abrimmo@masdar.ac.ae> |Web: www.masdar.ac.ae<http://www.masdar.ac.ae/>

P Please consider the environment before printing this email
This transmission is confidential and intended solely for the person or organization to whom it is addressed. It may contain privileged and confidential information. If you are not the intended recipient, you should not copy, distribute or take any action in reliance on it. If you have received this transmission in error, please notify us immediately by e-mail at info@masdar.ae<https://webmail.masdar.ac.ae/owa/redir.aspx?C=dabfad9ca57e476fa92ddb02fe861b6b&URL=mailto%3ainfo%40masdar.ae>

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Masdar Institute of Science and Technology
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Martin Liddle
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Joined: 15 Aug 2008
Posts: 1274
Location: Chesterfield, UK

PostPosted: Sat Jan 10, 2015 5:32 am  Reply with quote

On 10/01/2015 11:00, Ayoola Brimmo wrote:
Quote:
When I introduce the FLUID136 elements at the bottom of the cantilever (with respect to the Z axis), everything goes well. However, if I try to do the same with the damping elements located at the top of the cantilever, then I start getting unreasonable deformation responses until the model diverges.
How is the cantilever beam meshed (bricks, tets, shells)?

--
Martin Liddle, Tynemouth Computer Services,
Chesterfield, Derbyshire, UK.
www.tynecomp.co.uk

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| Send administrative requests to xansys-mod@tynecomp.co.uk |
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ayo.brimmo
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Joined: 01 Jul 2013
Posts: 38
Location: Masdar City, Abu Dhabi

PostPosted: Mon Jan 12, 2015 5:17 am  Reply with quote

Sorry for the omission.

It's all in bricks (hex meshes). Used solid187 elements

Ayo Brimmo
Research Engineer
Masdar, UAE

Quote:
On 10 Jan 2015, at 16:32, Martin Liddle <xansys05@tynecomp.co.uk> wrote:

Quote:
On 10/01/2015 11:00, Ayoola Brimmo wrote:
When I introduce the FLUID136 elements at the bottom of the cantilever (with respect to the Z axis), everything goes well. However, if I try to do the same with the damping elements located at the top of the cantilever, then I start getting unreasonable deformation responses until the model diverges.
How is the cantilever beam meshed (bricks, tets, shells)?

--
Martin Liddle, Tynemouth Computer Services,
Chesterfield, Derbyshire, UK.
www.tynecomp.co.uk

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| The Online Community for users of ANSYS, Inc. Software |
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| Send administrative requests to xansys-mod@tynecomp.co.uk |
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| Send administrative requests to xansys-mod@tynecomp.co.uk |
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Ayo Brimmo
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Masdar Institute of Science and Technology
UAE.
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ayo.brimmo
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Joined: 01 Jul 2013
Posts: 38
Location: Masdar City, Abu Dhabi

PostPosted: Sat Jan 24, 2015 2:21 pm  Reply with quote

To answer my own question:

First: For some reason, the squeeze film element must be oriented in the Z axis and attached to a surface at the origin of the axis. Hence, if a cantilever is to be damped using this element, the bottom of the cantilever must be at origin of the Z axis. However, I have not tried otherwise in ANSYS classic as I am using workbench with command snippets to introduce the Fluid136 elements.

Second: The squeeze film elements work like a spring attached to surface of the cantilever hence, there is no need to include it at the top of the cantilever aswell. As the beam oscillates, from the bottom to the top, the squeeze film elements damps the motion as a spring in compression and extension respectively. Hence, even if in reality you have fluid damping the cantilever at the top and bottom, while modeling this phenomena, you only need to include the elements at the bottom of the beam.

Hope someone finds this useful someday.

Best,
Ayo Brimmo
Research Engineer
Masdar UAE


-----Original Message-----
From: Xansys [mailto:xansys-bounces@xansys.org] On Behalf Of Ayoola Brimmo
Sent: Saturday, January 10, 2015 3:00 PM
To: ANSYS User Discussion List (xansys@xansys.org)
Subject: [Xansys] FLuid Damping FLUID136 Elements

Dear All,

I am trying to use the FLUID136 elements to model the squeeze film damping of a cantilever beam. Below is the snippet I used to do this:

" et, 10, 136 ! Fluid 136 element
keyopt, 10, 3,2 !implicit treatment
Keyopt, 10, 4, 1 ! setting compressible linearized Reynolds equation
mp,dens,10,1.4 !density
mp,visc,10,1.8e-5 !effective viscosity

r, 10, 100e-6,,,100e3 ! 100e-6 fluid gap, 101e3 ambient pressure
rmore, 101e3, 65e-9 ! 101e3 reference pressure, 65e-9 Mean free fluid path at reference pressure

SETTOL, 1e-7 ! tolerance
Nsel,s,loc,z,8e-6
Esln,s
Type, 10
Mat, 10
Real, 10
Esurf

Nsel,s,loc,y, -369.5e-6 !x1 location of bottom surface
Nsel,a,loc y, 369.5e-6 !x2 location of bottom surface
Nsel,a,loc,x, 338e-6 !y1 location of bottom surface
Nsel,a,loc,x, 1338e-6 !y2 location of bottom surface

Nsel, r, loc, z, -1e-7, 1e-7
d,all,pres
allsel
"

When I introduce the FLUID136 elements at the bottom of the cantilever (with respect to the Z axis), everything goes well. However, if I try to do the same with the damping elements located at the top of the cantilever, then I start getting unreasonable deformation responses until the model diverges. I am pretty sure that this has something to do with the location of the squeeze film elements as flipping the cantilever-so the top surface now becomes the bottom surface with respect to the Z axis-would resolves the issue. But the problem is that I want to put the squeeze film elements on both surfaces as in reality, the cantilever is in a cavity where it experiences squeeze film at both surfaces.

Has anyone experienced this before? Any possible causes or suggestions on how to squeeze film on both surfaces would be greatly appreciated.

Best,
Ayo Brimmo
Research Engineer
Mechanical Engineering Program

[Description: InstDual]
Mobile: +971 50 90 42782; +971 52 6241862 |P.O. Box: 54224, Abu Dhabi, UAE
E-mail: abrimmo@masdar.ac.ae<mailto:abrimmo@masdar.ac.ae> |Web: www.masdar.ac.ae<http://www.masdar.ac.ae/>

P Please consider the environment before printing this email This transmission is confidential and intended solely for the person or organization to whom it is addressed. It may contain privileged and confidential information. If you are not the intended recipient, you should not copy, distribute or take any action in reliance on it. If you have received this transmission in error, please notify us immediately by e-mail at info@masdar.ae<https://webmail.masdar.ac.ae/owa/redir.aspx?C=dabfad9ca57e476fa92ddb02fe861b6b&URL=mailto%3ainfo%40masdar.ae>

+-------------------------------------------------------------+
| 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 |
+-------------------------------------------------------------+

Post generated using Mail2Forum (http://www.mail2forum.com)
_________________
Ayo Brimmo
Research Engineer
Masdar Institute of Science and Technology
UAE.
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