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Infinite Elements for wave propagation
 
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ahmed.el-ghandour
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Joined: 23 Sep 2014
Posts: 13

PostPosted: Thu Oct 30, 2014 1:39 pm  Reply with quote

Hello All,

I have a model where I am using solid elements ( Solid185 ) to model the soil, and I want to apply infinite elements around the boundaries to absorb any wave reflection. I was reading the help but it was not clear for me which element if the : INFIN elements I should use?? I am planning on applying transient analysis .

Also, how can I pick the length of the infinite element to make sure it does not reflect or at least minimize it?

Any suggestions??

Thanks
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Ahmed El-Ghandour

PhD Student at University of Illinois at Chicago (UIC)
Civil Engineering Department
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jose.galan
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Joined: 21 Oct 2008
Posts: 140

PostPosted: Thu Oct 30, 2014 2:01 pm  Reply with quote

Dear Mr. El-Ghandour,

if you look at the help (help/ans_elem/Hlp_E_CH3_2.html), you will see
that INFIN elements are only valid for magnetic, thermal, electrostatic
or electric current conduction problems. You just have to check the
nodal degrees of freedom (DOF).

For acoustics, you could use the Perfectly Matched Layers.

For solids, I think that Ansys does not provide any alternative.

Best regards,

Jose M. Galan

Constr. Eng. Dept.

Univ. Sevilla

Spain

El 30/10/2014 21:39, ahmed.el-ghandour escribió:

Quote:
Hello All,

I have a model where I am using solid elements ( Solid185 ) to model the soil, and I want to apply infinite elements around the boundaries to absorb any wave reflection. I was reading the help but it was not clear for me which element if the : INFIN elements I should use?? I am planning on applying transient analysis .

Also, how can I pick the length of the infinite element to make sure it does not reflect or at least minimize it?

Any suggestions??

Thanks

------------------------
Ahmed El-Ghandour

PhD Student at University of Illinois at Chicago (UIC)
Civil Engineering Department


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ahmed.el-ghandour
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PostPosted: Thu Oct 30, 2014 2:07 pm  Reply with quote

Dear Mr. Galan

Thanks for your fast reply.

I agree with you about INFIN , I was just reading about it and it is exactly as you said.

Do you think there is a way to apply the PML in my work? or the number of DOF will be a limitation??

Thanks again.
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Civil Engineering Department
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mark.belloni3
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Joined: 15 Oct 2014
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Location: White Plains Office, New York

PostPosted: Thu Oct 30, 2014 2:11 pm  Reply with quote

Just a thought -

You could try putting quiet boundaries in the regions of interest using damping elements.

It used to work for modeling wave propagation problems, using ADINA, for studies related to The Nevada Test Site survivability program.

Mark Belloni; P.Eng.
New York Power Authority
White Plains Office, New York
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ahmed.el-ghandour
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Joined: 23 Sep 2014
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PostPosted: Thu Oct 30, 2014 2:20 pm  Reply with quote

Thanks Mark,

I thought about, but the problem will how can i define the length of the elements and the damping value?? trial and error ? or there is a way to calculate it assuming I know the wave speed??

Thanks
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Ahmed El-Ghandour

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Civil Engineering Department
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ernst.hustedt
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Joined: 22 Oct 2010
Posts: 127

PostPosted: Thu Oct 30, 2014 2:30 pm  Reply with quote

Have a look at the spring/damper COMBIN elements. You can have more than
one attached to a node to get a combined effect. Also, may be SURF154
could work as damper/absorber for you - never used it myself, though.


Ernst Hustedt
AMES Ltd.
Christchurch, NZ


On 31/10/2014 09:39, ahmed.el-ghandour wrote:
Quote:
Hello All,

I have a model where I am using solid elements ( Solid185 ) to model the soil, and I want to apply infinite elements around the boundaries to absorb any wave reflection. I was reading the help but it was not clear for me which element if the : INFIN elements I should use?? I am planning on applying transient analysis .

Also, how can I pick the length of the infinite element to make sure it does not reflect or at least minimize it?

Any suggestions??

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| Send administrative requests to xansys-mod@tynecomp.co.uk |
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jose.galan
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Joined: 21 Oct 2008
Posts: 140

PostPosted: Thu Oct 30, 2014 2:31 pm  Reply with quote

You could try adding spring and dashpots at the boundaries (Lysmer and
Kuhlemeyer boundary conditions) to absorb the compressional and shear
waves. At each node, you have to add one spring and one dashpot in the
direction normal to the boundary to absorb longitudinal waves, and you
will need two springs and two dashpots in the tangential directions, to
absorb shear waves.

You will find plenty of references on the subject. I will just point out
a couple of them:

Modeling Methods for Silent Boundaries in Infinite Media, Mike Ross , 26
February 2004, ASEN 5519-006: Fluid-Structure Interaction, Aerospace
Engineering Sciences- University of Colorado at Boulder

http://www.colorado.edu/engineering/CAS/courses.d/FSI.d/FSI.projects.d/FSI.projects.Ross.silent.pdf


A unified viscous-spring artificial boundary for
3-D static and dynamic applications
LIU Jingbo & LI Bin

Science in China Ser. E Engineering & Materials Science 2005 Vol.48 No.5
570--584

http://tech.scichina.com:8082/sciEe/fileup/PDF/05ye0570.pdf

I think that there are some threads on xansys about this topic. Check
this one:

http://www.xansys.org/forum/viewtopic.php?t=16142&start=0&postdays=0&postorder=asc&highlight=infinite+elements


Best regards,

Jose M. Galan

Constr. Eng. Dept.

Univ. Sevilla

Spain


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ahmed.el-ghandour
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Joined: 23 Sep 2014
Posts: 13

PostPosted: Thu Oct 30, 2014 2:55 pm  Reply with quote

Thanks a lot Jose,

these are great help I will look at these papers. I guess from the above discussions that the idea of the spring/damper elements is the most convenient. but I will look at the thread you sent to see if there is any thing I can use.

Thanks a lot.

All the best
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Ahmed El-Ghandour

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Civil Engineering Department
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frank.exius
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Joined: 21 Oct 2008
Posts: 50

PostPosted: Fri Oct 31, 2014 3:19 am  Reply with quote

Ahmed El-Ghandour,

check this http://ansys.net/?mycat=search&mytype=Tips&mycategory=Acoustics

has info on different options to model infinite acoustic boundaries.
Please report back wether you succeed, thanks.

Mit freundlichen Gruessen,
Frank Exius

IFE Deutschland
Am Hellenberg 31
53489 Sinzig bei BONN
www.ife-ansys.de

Tel. +49-(0)2642-980409
Geschaeftszeiten Mo-Fr 9:00-18:00 Uhr
Alljaehrliche Betriebsferien im August
-----Original Message-----
From: Xansys [mailto:xansys-bounces@xansys.org] On Behalf Of
ahmed.el-ghandour
Sent: Thursday, October 30, 2014 9:39 PM
To: xansys@xansys.org
Subject: [Xansys] Infinite Elements for wave propagation

Hello All,

I have a model where I am using solid elements ( Solid185 ) to model the
soil, and I want to apply infinite elements around the boundaries to absorb
any wave reflection. I was reading the help but it was not clear for me
which element if the : INFIN elements I should use?? I am planning on
applying transient analysis .

Also, how can I pick the length of the infinite element to make sure it does
not reflect or at least minimize it?

Any suggestions??

Thanks

------------------------
Ahmed El-Ghandour

PhD Student at University of Illinois at Chicago (UIC) Civil Engineering
Department






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| 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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| 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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mark.belloni3
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Joined: 15 Oct 2014
Posts: 20
Location: White Plains Office, New York

PostPosted: Fri Oct 31, 2014 4:15 am  Reply with quote

Ahmed El-Ghandour: As per Jose's recent post, that should get you going.

I recall installing those damper elements - circa 1989 - using the same equations that are in the publication that Jose cited.

Enjoy.

Mark Belloni
New York Power Authority
White Plains Office, New York
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ahmed.el-ghandour
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Joined: 23 Sep 2014
Posts: 13

PostPosted: Fri Oct 31, 2014 8:14 am  Reply with quote

Thanks Frank ,

I will look at it, although my work is not about acoustic, but I will see may be it can give me a clue.

Thanks
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Ahmed El-Ghandour

PhD Student at University of Illinois at Chicago (UIC)
Civil Engineering Department
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ahmed.el-ghandour
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Joined: 23 Sep 2014
Posts: 13

PostPosted: Fri Oct 31, 2014 8:15 am  Reply with quote

Thanks Mark,

I will read it and try to implement it in my work and see how it will go from there.

Thanks a lot everyone for the great suggestions and help
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Ahmed El-Ghandour

PhD Student at University of Illinois at Chicago (UIC)
Civil Engineering Department
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