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2464 views
09:11 Dec-14-2007
lamb waves
how to Exciting lamb waves ?

hi

i am trying to simulate Lamb waves on Ansys or ABAQUS.

but i am confused by Excitation of Lamb waves(A0 / S0 mode).

someone says that applying a harmonic normal force to small regions of the top and bottom surfaces of your model could be a simple way.

i also get another way from one article ,which apply a shear force on the surface of model.

as we know, if i wana Excitate lamb waves , shouldn't i put the incident wave and the plane surface with a particular angle, rather than vertical or horizontal orientation ?

somebody helps me please.




 
04:17 Dec-14-2007

Michael Moles †2014 *1948

,
Joined

Re: how to Exciting lamb waves ? ----------- Start Original Message -----------
: hi
: i am trying to simulate Lamb waves on Ansys or ABAQUS.
: but i am confused by Excitation of Lamb waves(A0 / S0 mode).
: someone says that applying a harmonic normal force to small regions of the top and bottom surfaces of your model could be a simple way.
: i also get another way from one article ,which apply a shear force on the surface of model.
: as we know, if i wana Excitate lamb waves , shouldn't i put the incident wave and the plane surface with a particular angle, rather than vertical or horizontal orientation ?
: somebody helps me please.
------------ End Original Message ------------

May I suggest contacting Prof. Joseph Rose at Penn State or Peter Cawley at Imperial College, London.

Michael


 
09:02 Dec-14-2007

Thomas Vogt

R & D, - -
Guided Ultrasonics Ltd,
United Kingdom,
Joined Apr 2007
22
Re: how to Exciting lamb waves ? Basically both ways are valid to excite a certain guided wave mode, it just requires different ways of thinking about it.

For modelling, what you do is to match the excitation to the mode shape (stress and displacement fields). Experimentally, to excite a certain mode you can do the same (for example to excite A0 in a plate you could place two shear PZT-elements on either side of the plate and drive them out of phase, to excite S0 you would do the same but drive them in phase).

The other way is to send in a plane wave at a certain angle - this way you make sure that the excited guided wave has a certain wavelength. Together with the frequency this fixes one point in the dispersion plot - if the dispersion curve of your desired mode runs through this point it will be excited.

Hope this helps,
Tom

----------- Start Original Message -----------
: hi
: i am trying to simulate Lamb waves on Ansys or ABAQUS.
: but i am confused by Excitation of Lamb waves(A0 / S0 mode).
: someone saysthat applying a harmonic normal force to small regions of the top and bottom surfaces of your model could be a simple way.
: i also get another way from one article ,which apply a shear force on the surface of model.
: as we know, if i wana Excitate lamb waves , shouldn't i put the incident wave and the plane surface with a particular angle, rather than vertical or horizontal orientation ?
: somebody helps me please.
------------ End Original Message ------------




 
06:19 Dec-16-2007
lamb waves
Re: how to Exciting lamb waves ? Thanks tom!
that helps me a lot!

but i'm still curious about driving pzt-elements out of phase or in phase.

if i wanna use direct force or displacement instead of pzt-elements, how to apply my loads?

for A0, apply the same harmonic normal forces ,which start towards the same directions, to small regions of the top and bottom surfaces.

for S0, apply the same harmonic normal forces ,which start towards the opposite directions, to small regions of the top and bottom surfaces.

for A0+S0, apply the same harmonic normal forces only to the top surfaces.

am i right?

sorry for my poor english.

waiting for your reply.

Charles

----------- Start Original Message -----------
: Basically both ways are valid to excite a certain guided wave mode, it just requires different ways of thinking about it.
: For modelling, what you do is to match the excitation to the mode shape (stress and displacement fields). Experimentally, to excite a certain mode you can do the same (for example to excite A0 in a plate you could place two shear PZT-elements on either side of the plate and drive them out of phase, to excite S0 you would do the same but drive them in phase).
: The other way is to send in a plane wave at a certain angle - this way you make sure that the excited guided wave has a certain wavelength. Together with the frequency this fixes one point in the dispersion plot - if the dispersion curve of your desired mode runs through this point it will be excited.
: Hope this helps,
: Tom
: : hi
: : i am trying to simulate Lamb waves on Ansys or ABAQUS.
: : but i am confused by Excitation of Lamb waves(A0 / S0 mode).
: : someone says that applying a harmonic normal force to small regions of the top and bottom surfaces of your model could be a simple way.
: : i also get another way from one article ,which apply a shear force on the surface of model.
: : as we know, if i wana Excitate lamb waves , shouldn't i put the incident wave and the plane surface with a particular angle, rather than vertical or horizontal orientation ?
: : somebody helps me please.
------------ End Original Message ------------




 
00:11 Dec-18-2007

Sang Kim

Consultant, NDT Trainer
Guided Wave Analysis LLC,
USA,
Joined Feb 2008
44
Re: how to Exciting lamb waves ? Another way to generate guided waves in plate directly excites the particle displacement in the material. Magnetostrictive sensor (MsS) technology is used to generate symmetric Lamb(S0), asymmetric Lamb(A0), and shear-horizontal (SH0). The S0- and AO-mode waves have out-of-plane and in-plane (parallel to wave propagation direction) particle motion. The SH0-wave has in-plane (perpendicular to the wave propagation direction) particle motion. In order to check how strongly these guided waves are generated with MsS probe, please refer to http://www.gwanalysis.com/plate_structure.html for shear-horizontal wave and to http://www.gwanalysis.com/matrix_breaking.html for S0 Lamb wave.

I hope it help you.

Sang

----------- Start Original Message -----------
: Thanks tom!
: that helps me a lot!
: but i'm still curious about driving pzt-elements out of phase or in phase.
: if i wanna use direct force or displacement instead of pzt-elements, how to apply my loads?
: for A0, apply the same harmonic normal forces ,which start towards the same directions, to small regions of the top and bottom surfaces.
: for S0, apply the same harmonic normal forces ,which start towards the opposite directions, to small regions of the top and bottom surfaces.
: for A0+S0, apply the same harmonic normal forces only to the top surfaces.
: am i right?
: sorry for my poor english.
: waiting for your reply.
: Charles
: : Basically both ways are valid to excite a certain guided wave mode, it just requires different ways of thinking about it.
: : For modelling, what you do is to match the excitation to the mode shape (stress and displacement fields). Experimentally, to excite a certain mode you can do the same (for example to excite A0 in a plate you could place two shear PZT-elements on either side of the plate and drive them out of phase, to excite S0 you would do the same but drive them in phase).
: : The other way is to send in a plane wave at a certain angle - this way you make sure thatthe excited guided wave has a certain wavelength. Together with the frequency this fixes one point in the dispersion plot - if the dispersion curve of your desired mode runs through this point it will be excited.
: : Hope this helps,
: : Tom
: : : hi
: : : i am trying to simulate Lamb waves on Ansys or ABAQUS.
: : : but i am confused by Excitation of Lamb waves(A0 / S0 mode).
: : : someone says that applying a harmonic normal force to small regions of the top and bottom surfaces of your model could be a simple way.
: : : i also get another way from one article ,which apply a shear force on the surface of model.
: : : as we know, if i wana Excitate lamb waves , shouldn't i put the incident wave and the plane surface with a particular angle, rather than vertical or horizontal orientation ?
: : : somebody helps me please.
------------ End Original Message ------------




 


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