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Re: Questions about de_min in octave


From: Doug Stewart
Subject: Re: Questions about de_min in octave
Date: Thu, 28 Sep 2017 10:55:20 -0400



On Thu, Sep 28, 2017 at 10:18 AM, denizyazgac <address@hidden> wrote:
EDIT
Please forget previous one

Sorry;
I try to make a back calculation with using Johnson Champoux Allard
mathematical model, which defines acoustic impedance behaviour of acoustic
foams.
f,RRR,III vectors are measured data(frequency,real and imaginer parts) from
impedance tube (they are surface impedance), I try to obtain some critical
parameters like tortousity,char. viscous and thermal length from this data
with de_min function.

<http://octave.1599824.n4.nabble.com/file/t372543/back_calc_2.m>


#back_calclation for porous samples
clc
clear all
pkg load optim
gamma=1.401 # specific heat ratio
P0=99700 #pressure
eta= 1.56E-5; #dynamic viscosity
B=0.707 # Prandtl number
fi=0.95 # porosity
L=34.35/1000 #thickness
rho0=1.2 #air density
sigma=8197# air resistivity
c=340;# sound speed

f=[202.53
300.94
399.35
502.52
599.34
704.10
800.92
897.74
1002.50
1100.91
1204.09
1305.67
1404.09
1500.92
1604.09];

RRR=[0.731942065
0.701451715
0.641506283
0.596238299
0.580492187
0.535207505
0.504733852
0.48898774
0.473158139
0.457395329
0.471037507
0.469968842
0.468933572
0.497370082
0.496284719];

III=[-6.057454106
-4.070271408
-3.040378842
-2.422907504
-2.011571639
-1.688601017
-1.409863111
-1.219406958
-1.014356847
-0.868083316
-0.721893274
-0.590363981
-0.458884781
-0.312678041
-0.225364765];

w=2.*pi.*f(4); %f(4) can be change between f(1)....f(15) with length of f
vector.

#effective density
edn= @(x)  rho0.*x(1).*(1+ ( (fi.*sigma./(j.*w.*rho0.*x(1))).*sqrt(1+
(j.*(4.*w.*rho0.*eta.*(x(1).^2))./(sigma.^2.*fi.^2.*x(2).^2)))));
#effective bulk modulus
ebm= @(x) (gamma.*P0)./
(gamma-((gamma-1).*(1+(8.*eta./(j.*w.*B.*(x(3).^2).*rho0)).*sqrt(1+(j.*(w.*B.*rho0.*(x(3).^2))./(16.*eta)))).^(-1)));
#complex wave number
kwave= @(x) (w.*sqrt(edn(x)./ebm(x)));
#char impedance back_calc_2.m

ZC=@(x) sqrt(edn(x).*ebm(x));
#general function x(1) tortuosity,x(2) viscous characteristic length,x(3)
thermal characteristic length
ZS=@(x) ((-j.*ZC(x).*cot(kwave(x).*L))./(fi.*rho0.*c));
optim=@(x) abs(RRR(4)+i.*III(4)-ZC(x));

ctl.XVmin = [1 0 0];
ctl.XVmax = [4 1 1];
# note to forumers: as a result of theory x(3)>x(2) but I can not define in
ctl structure
[x, obj_value, nfeval, convergence] = de_min (optim, ctl)





--
Sent from: http://octave.1599824.n4.nabble.com/Octave-General-f1599825.html

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I had to modify line 70 to

ZC=@(x) sqrt(edn(x,w).*ebm(x,w));



and then I got this answer for x:
 -4.2643e-03  -1.1294e+00  -3.0383e-06 

and x(3) is more positive than x(2)  ie. x(3) >x(2)
I do not know what these numbers mean. Is this what you got?

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