Shock Response Spectrum (SRS) in Matlab

[tomirvine]

Here is an SRS code in Matlab. I have more of these types of programs for shock and vibration, so please let me know if there is an interest.

Tom Irvine

******************************************

disp(' ')
disp(' srs.m ver 1.4 January 31, 2005')
disp(' by Tom Irvine Email: tomirvine@aol.com')
disp(' ')
disp(' This program calculates the shock response spectrum')
disp(' of an acceleration time history, which is pre-loaded into Matlab.')
disp(' The time history must have two columns: time(sec) & acceleration')
disp(' ')
%
clear t;
clear y;
clear yy;
clear n;
clear fn;
clear a1;
clear a2
clear b1;
clear b2;
clear jnum;
clear THM;
clear resp;
clear x_pos;
clear x_neg;
%
iunit=input(' Enter acceleration unit: 1= G 2= m/sec^2 ');
%
disp(' ')
disp(' Select file input method ');
disp(' 1=external ASCII file ');
disp(' 2=file preloaded into Matlab ');
file_choice = input('');
%
if(file_choice==1)
disp(' Enter the input filename ');
filename = input(' ','s');
fid = fopen(filename,'r');
THM = fscanf(fid,'%g %g',[2 inf]);
THM=THM';
else
THM = input(' Enter the matrix name: ');
end
%
t=THM,1);
y=THM,2);
%
tmx=max(t);
tmi=min(t);
n = length;
%
out1 = sprintf('\n %d samples \n',n);
disp(out1)
%
dt=(tmx-tmi)/(n-1);
sr=1./dt;
%
out1 = sprintf(' SR = %g samples/sec dt = %g sec \n',sr,dt);
disp(out1)
%
fn(1)=input(' Enter the starting frequency (Hz) ');
if fn(1)>sr/30.
fn(1)=sr/30.;
end
%
idamp=input(' Enter damping format: 1= damping ratio 2= Q ');
%
disp(' ')
if(idamp==1)
damp=input(' Enter damping ratio (typically 0.05) ');
else
Q=input(' Enter the amplification factor (typically Q=10) ');
damp=1./(2.*Q);
end
%
tmax=(tmx-tmi) + 1./fn(1);
limit = round( tmax/dt );
n=limit;
yy=zeros(1,limit);
for i=1:length
yy(i)=y(i);
end
%
disp(' ')
disp(' Calculating response..... ')
%
% SRS engine
%
for j=1:1000
%
omega=2.*pi*fn(j);
omegad=omega*sqrt(1.-(damp^2));
cosd=cos(omegad*dt);
sind=sin(omegad*dt);
domegadt=damp*omega*dt;
a1(j)=2.*exp(-domegadt)*cosd;
a2(j)=-exp(-2.*domegadt);
b1(j)=2.*domegadt;
b2(j)=omega*dt*exp(-domegadt);
b2(j)=b2(j)*( (omega/omegad)*(1.-2.*(damp^2))*sind -2.*damp*cosd );
%
forward=[ b1(j), b2(j), 0 ];
back =[ 1, -a1(j), -a2(j) ];
%
resp=filter(forward,back,yy);
%
x_pos(j)= max(resp);
x_neg(j)= min(resp);
%
jnum=j;
if fn(j) > sr/8.
break
end
fn(j+1)=fn(1)*(2. ^ (j*(1./12.)));
end
%
% Output options
%
disp(' ')
disp(' Select output option ');
choice=input(' 1=plot only 2=plot & output text file ' );
disp(' ')
%
if choice == 2
disp(' Enter output filename ');
SRS_filename = input(' ','s');
%
fid = fopen(SRS_filename,'w');
for j=1:jnum
fprintf(fid,'%7.2f %10.3f %10.3f \n',fn(j),x_pos(j),abs(x_neg(j)));
end
fclose(fid);
end
%
% Plot SRS
%
disp(' ')
disp(' Plotting output..... ')
%
% Find limits for plot
%
srs_max = max(x_pos);
if max( abs(x_neg) ) > srs_max
srs_max = max( abs(x_neg ));
end
srs_min = min(x_pos);
if min( abs(x_neg) ) < srs_min
srs_min = min( abs(x_neg ));
end
%
figure(1);
plot(fn,x_pos,fn,abs(x_neg),'-.');
%
if iunit==1
ylabel('Peak Accel (G)');
else
ylabel('Peak Accel (m/sec^2)');
end
xlabel('Natural Frequency (Hz)');
Q=1./(2.*damp);
out5 = sprintf(' Acceleration Shock Response Spectrum Q=%g ',Q);
title(out5);
grid;
set(gca,'MinorGridLineStyle','none','GridLineStyle',':','XScale','log','YScale','log');
legend ('positive','negative',2);
%
ymax= 10^(round(log10(srs_max)+0.8));
ymin= 10^(round(log10(srs_min)-0.6));
%
fmax=max(fn);
fmin=fmax/10.;
%
fmax= 10^(round(log10(fmax)+0.5));
%
if fn(1) >= 0.1
fmin=0.1;
end
if fn(1) >= 1
fmin=1;
end
if fn(1) >= 10
fmin=10;
end
if fn(1) >= 100
fmin=100;
end
axis([fmin,fmax,ymin,ymax]);
%
disp(' ')
disp(' Plot pseudo velocity? ');
vchoice=input(' 1=yes 2=no ' );
if(vchoice==1)
figure(2);
%
% Convert to pseudo velocity
%
for j=1:jnum
if iunit==1
x_pos(j)=386.*x_pos(j)/(2.*pi*fn(j));
x_neg(j)=386.*x_neg(j)/(2.*pi*fn(j));
else
x_pos(j)=x_pos(j)/(2.*pi*fn(j));
x_neg(j)=x_neg(j)/(2.*pi*fn(j));
end
end
%
srs_max = max(x_pos);
if max( abs(x_neg) ) > srs_max
srs_max = max( abs(x_neg ));
end
srs_min = min(x_pos);
if min( abs(x_neg) ) < srs_min
srs_min = min( abs(x_neg ));
end
%
plot(fn,x_pos,fn,abs(x_neg),'-.');
%
if iunit==1
ylabel('Velocity (in/sec)');
else
ylabel('Velocity (m/sec)');
end
xlabel('Natural Frequency (Hz)');
Q=1./(2.*damp);
out5 = sprintf(' Pseudo Velocity Shock Response Spectrum Q=%g ',Q);
title(out5);
grid;
set(gca,'MinorGridLineStyle','none','GridLineStyle',':','XScale','log','YScale','log');
legend ('positive','negative',2);
%
ymax= 10^(round(log10(srs_max)+0.8));
ymin= 10^(round(log10(srs_min)-0.6));
%
axis([fmin,fmax,ymin,ymax]);
end

 

[MikeyP]

I don't understand. What is your question?

M

--
Dr Michael F Platten

 

[IRstuff]

Tom didn't have question, he was essentially posting the answer to a FAQ, which is probably where it should go.

TTFN