any FREE finite element analyses SW for anlayzing acoustics?

21 views
Skip to first unread message

RobertMacy

unread,
Dec 8, 2014, 9:17:15 AM12/8/14
to
There are a myriad of free PC Tools out there for circuit simulation,
magnetic field, RF/Microwave, etc. are there any free FEA for acoustics?

I have an unusal situation where the structure will model well as 2D, or
planar. Usually a 2D structure allows a simplifying assumption, which then
means simple software will handle it.

Also, any URLs that technically discuss boundary conditions in AIR? Like
differences between AIR that is of different temperature, or air that is
carrying huge high frequency [40kHz to 60kHz] audio signal. There are
several companies that take advantage of modulatin HF Audio, beaming it
out, and letting the air's nonlinearity demodulate the carrier into
providing 'beamed' messages. I know the Navy has such for beaming foreign
meassages from ship to pirates etc. Info, more importantly experience, in
this area would be greatly appreciated.

Prefer to have it run on Win98, but will accept running on WinXP. Possibly
time to migrate to Ubuntu.

Can't do searches, so need EXACT URLs.

Scott Dorsey

unread,
Dec 8, 2014, 10:07:41 AM12/8/14
to
RobertMacy <robert...@gmail.com> wrote:
>There are a myriad of free PC Tools out there for circuit simulation,
>magnetic field, RF/Microwave, etc. are there any free FEA for acoustics?
>
>I have an unusal situation where the structure will model well as 2D, or
>planar. Usually a 2D structure allows a simplifying assumption, which then
>means simple software will handle it.

If you can do it 2D, writing a raytracer should be an afternoon's work,
or you can just do it by hand with graph paper and a ruler. Or make a
wave tank on yout kitchen table.

It is so rare that 2D simulation would ever be useful for anything that I
do not know if any actual 2D software out there.

>Also, any URLs that technically discuss boundary conditions in AIR? Like
>differences between AIR that is of different temperature, or air that is
>carrying huge high frequency [40kHz to 60kHz] audio signal. There are
>several companies that take advantage of modulatin HF Audio, beaming it
>out, and letting the air's nonlinearity demodulate the carrier into
>providing 'beamed' messages. I know the Navy has such for beaming foreign
>meassages from ship to pirates etc. Info, more importantly experience, in
>this area would be greatly appreciated.

That's simple heterodyning, it's really got nothing to do with boundary
conditions per se. Harry Olson's book on acoustical engineering has some
discussion of nonlinearity due to compressability of air. This has been
extensively studied because there are a number of very high pressure
applications, such as compression drivers for horn speakers, where it
becomes a major source of nonlinearity.
--scott
>
>Prefer to have it run on Win98, but will accept running on WinXP. Possibly
>time to migrate to Ubuntu.
>
>Can't do searches, so need EXACT URLs.


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

RobertMacy

unread,
Dec 8, 2014, 12:52:24 PM12/8/14
to
On Mon, 08 Dec 2014 08:07:40 -0700, Scott Dorsey <klu...@panix.com> wrote:

>> ...snip...
> If you can do it 2D, writing a raytracer should be an afternoon's work,
> or you can just do it by hand with graph paper and a ruler. Or make a
> wave tank on yout kitchen table.
>
> It is so rare that 2D simulation would ever be useful for anything that I
> do not know if any actual 2D software out there.
>
>> ...snip...
> That's simple heterodyning, it's really got nothing to do with boundary
> conditions per se. Harry Olson's book on acoustical engineering has some
> discussion of nonlinearity due to compressability of air. This has been
> extensively studied because there are a number of very high pressure
> applications, such as compression drivers for horn speakers, where it
> becomes a major source of nonlinearity.
> --scott

Thank you for your excellent reply. The final analyses will require 3D for
certain. Being a EE, I have no allegory [is that the right word?] to even
begin. I have NO idea what the basic constants are for AIR, or even what
to do with them to model this phenomenon.

The test setup will be launching variable 60kHz up to 100kHz into AIR,
from an aperture that will be several wavelengths across [From
RF/Microwave antenna designs I know how aperture, wavelength, etc combine
to create beam spreading based on those two. Sadly, when I had the
opportunity to learn about acoustics [see below] I didn't. Right now, I
have NO idea what the coefficients of attenuation are with distance, nor
how much energy it takes to start getting into that non-linear saturation
condition. Especially important is how to model the medium as it tries to
carry both this high energy. I do know that sound is a slippery critter
and any modeling will quickly turn into 3 dimensional math.

Are you skilled in acoustics enough to give me some basic terminology and
equations representing the compressibility/elasticity etc of AIR? And tell
me how to use them? Or provide some URL that has all this background in
the form of tutorial? Need basics here. I don't mind rederiving up from
basics to get there from here.

The water tank idea did NOT occur to me. Possibly because while developing
Non-invasive Medical Diagnostic Instrumentation [ultrasonic
echocardiography] we used water tanks and lasers to 'view' the 2MHz to
5MHz transducers' beams and I didn't notice that water compressed like air
and therefore didn't think it would display the non-linearities I'm trying
to find the effects of. [Yes, English is my first language] Try again: It
is my understandng that air can be driven into non-linearity fairly
easily. I wish to explore that condition. And have NO idea how to go about
it. ...help




Glen Walpert

unread,
Dec 8, 2014, 4:04:38 PM12/8/14
to
This is not a simple matter with an answer that can be provided in a
reasonable sized message or with reasonable effort. You should read
"Physical Acoustics" by Blackstock for the clearest explanation of basic
theory available. Harry Olson's "Acoustical Engineering" book was once a
classic but has little on nonlinearity and is generally light on theory
and somewhat dated, not likely to be useful to you. Another good source
of information is "Nonlinear Acoustics" edited by Hamilton and Blackstock,

BTW even the lossless propagation of sound in an ideal gas is inherently
nonlinear. The range over which the linear approximation is useful
depends on how much error you can tolerate in the results. Olson and
most other acoustics book authors who acknowledge nonlinearity state
correctly that the nonlinearities are below the limits of measurement for
sound not louder than a symphony orchestra with frequency within human
hearing (or something similar), and then completely disregard
nonlinearity from there on. If on the other hand your concern is loud
and high frequency, see Blackstock. There is no other reasonable source
of info on nonlinear acoustics theory that I know of.

Regards,
Glen

RobertMacy

unread,
Dec 8, 2014, 6:44:33 PM12/8/14
to
On Mon, 08 Dec 2014 14:04:38 -0700, Glen Walpert <nos...@null.void> wrote:

>> ...snip....
> This is not a simple matter with an answer that can be provided in a
> reasonable sized message or with reasonable effort. You should read
> "Physical Acoustics" by Blackstock for the clearest explanation of basic
> theory available. Harry Olson's "Acoustical Engineering" book was once a
> classic but has little on nonlinearity and is generally light on theory
> and somewhat dated, not likely to be useful to you. Another good source
> of information is "Nonlinear Acoustics" edited by Hamilton and
> Blackstock,
>
> BTW even the lossless propagation of sound in an ideal gas is inherently
> nonlinear. The range over which the linear approximation is useful
> depends on how much error you can tolerate in the results. Olson and
> most other acoustics book authors who acknowledge nonlinearity state
> correctly that the nonlinearities are below the limits of measurement for
> sound not louder than a symphony orchestra with frequency within human
> hearing (or something similar), and then completely disregard
> nonlinearity from there on. If on the other hand your concern is loud
> and high frequency, see Blackstock. There is no other reasonable source
> of info on nonlinear acoustics theory that I know of.
>
> Regards,
> Glen
>

Thank you for the explanation of the lack of literature, and your
recommendation of Blackstock.

I had hoped there were some kind of 'tutorials' on line to view.

Glen Walpert

unread,
Dec 9, 2014, 1:06:44 PM12/9/14
to
On Mon, 08 Dec 2014 16:46:41 -0700, RobertMacy wrote:

>>
> Thank you for the explanation of the lack of literature, and your
> recommendation of Blackstock.
>
> I had hoped there were some kind of 'tutorials' on line to view.

I don't know of any, perhaps the closest is the on line Journal of the
Acoustical Society of America at:
http://acousticalsociety.org/
http://scitation.aip.org/content/asa/journal/jasa
which has a lot of articles on specific aspects of nonlinear acoustics
available for free download to members - membership is $115/year, perhaps
they sell papers to non-members, I haven't checked. You could search the
list of titles and abstracts to see if your specific problem is
addressed, a detailed solution to your problem already worked out could
be worth a few bucks. But for a general understanding of the subject the
previously mentioned books are your best bet, the JASA articles generally
presume a good understanding of the basics in the books.

Scott Dorsey

unread,
Dec 9, 2014, 4:02:44 PM12/9/14
to
Glen Walpert <nos...@null.void> wrote:
>> On Mon, 08 Dec 2014 08:07:40 -0700, Scott Dorsey <klu...@panix.com>
>> wrote:
>>
>> The water tank idea did NOT occur to me. Possibly because while
>> developing Non-invasive Medical Diagnostic Instrumentation [ultrasonic
>> echocardiography] we used water tanks and lasers to 'view' the 2MHz to
>> 5MHz transducers' beams and I didn't notice that water compressed like
>> air and therefore didn't think it would display the non-linearities I'm
>> trying to find the effects of. [Yes, English is my first language] Try
>> again: It is my understandng that air can be driven into non-linearity
>> fairly easily. I wish to explore that condition. And have NO idea how to
>> go about it. ...help

Back in the days before there were computers, folks would do architectural
modelling with cross-sections in wave tanks and with schlieren photographs
of impulses in air and scale models. It's still a valid method and not
hard to do. It can be very hard to interpret but so can computer models.

>This is not a simple matter with an answer that can be provided in a
>reasonable sized message or with reasonable effort. You should read
>"Physical Acoustics" by Blackstock for the clearest explanation of basic
>theory available. Harry Olson's "Acoustical Engineering" book was once a
>classic but has little on nonlinearity and is generally light on theory
>and somewhat dated, not likely to be useful to you. Another good source
>of information is "Nonlinear Acoustics" edited by Hamilton and Blackstock,

These are all good books. You are right that Olson only has a couple of
paragraphs on the subject, but by the same token he has all the background
needed to understand those couple of paragraphs.

Physical Acoustics is a really good reference though. Again, not much on
compressible flow, but an excellent buildup to it.

>BTW even the lossless propagation of sound in an ideal gas is inherently
>nonlinear. The range over which the linear approximation is useful
>depends on how much error you can tolerate in the results. Olson and
>most other acoustics book authors who acknowledge nonlinearity state
>correctly that the nonlinearities are below the limits of measurement for
>sound not louder than a symphony orchestra with frequency within human
>hearing (or something similar), and then completely disregard
>nonlinearity from there on. If on the other hand your concern is loud
>and high frequency, see Blackstock. There is no other reasonable source
>of info on nonlinear acoustics theory that I know of.

Olson does briefly touch on it in the subject of compression drivers, and
that's really the only application I have ever seen where people were carefully
looking at it.
--scott

Glen Walpert

unread,
Dec 9, 2014, 8:41:08 PM12/9/14
to
For theory of compressible flow it is hard to beat The Dynamics and
Thermodynamics of Compressible Fluid Flow Vol. 1, by Shapiro. Shapiro
also has a concise and correct basic explanation of sound. (Vol. 2 is an
interesting collection of design examples which were classified during
WWII, all of which would be solved using CFD today.)

>>BTW even the lossless propagation of sound in an ideal gas is inherently
>>nonlinear. The range over which the linear approximation is useful
>>depends on how much error you can tolerate in the results. Olson and
>>most other acoustics book authors who acknowledge nonlinearity state
>>correctly that the nonlinearities are below the limits of measurement
>>for sound not louder than a symphony orchestra with frequency within
>>human hearing (or something similar), and then completely disregard
>>nonlinearity from there on. If on the other hand your concern is loud
>>and high frequency, see Blackstock. There is no other reasonable source
>>of info on nonlinear acoustics theory that I know of.
>
> Olson does briefly touch on it in the subject of compression drivers,
> and that's really the only application I have ever seen where people
> were carefully looking at it.
> --scott

The nonlinear propagation of sound is also the reason shock waves exist,
is part of the reason for the production of harmonics in wind
instruments, and is a limiting factor in ultrasound and sonar.

Back to the original question I see that there are some free CFD programs
capable of unsteady flow, which might be usable for some acoustics
problems - first two hits:
http://flowsquare.com/
http://www.openfoam.com/
I haven't used either and it might or might not be easy to set up an
oscillating boundary condition.

Regards,
Glen

RobertMacy

unread,
Dec 10, 2014, 11:22:52 AM12/10/14
to
sounds like a good sources, alas, my budget for this project is zero.

RobertMacy

unread,
Dec 10, 2014, 11:26:13 AM12/10/14
to
On Tue, 09 Dec 2014 18:41:08 -0700, Glen Walpert <nos...@null.void> wrote:

>> ...snip...
>
> Back to the original question I see that there are some free CFD programs
> capable of unsteady flow, which might be usable for some acoustics
> problems - first two hits:
> http://flowsquare.com/
> http://www.openfoam.com/
> I haven't used either and it might or might not be easy to set up an
> oscillating boundary condition.
>
> Regards,
> Glen


THANKS!
Reply all
Reply to author
Forward
0 new messages