how to plot frf from given mode shapes and natural frequency?

Question

zainab malik 2018-10-22

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/425462-how-to-plot-frf-from-given-mode-shapes-and-natural-frequency

编辑： Image Analyst 2023-10-30

This script calculate transfer functions for a dynamic system based on the modes shapes, natural frequencies, and damping ratios.

Can someone help me please in the below code that whats the meaning of these few lines in the below code that what they are asking about? what is starting figure and how may I enter "enter response dof"

if true
  % code
end
fig_num=input(' Enter starting figure number ');
end
%
ikv=1;
while(1)
%
if(ipim==1)
    disp(' ');
    if(iam<=3)
        i=input(' Enter response   dof ');
        k=input(' Enter excitation dof ');
    else
        i=input(' Enter response   dof ');
        k=input(' Enter base       dof ');

This is full code below.

if true
  % code
end
disp(' ');
disp(' This program calculates a transfer function for each   ');
disp(' degree-of-freedom in a system based on the mode shapes, ');
disp(' natural frequencies, and damping ratios. ');
%
clear freq;
clear fnv;
clear dampv;
clear QE;
clear H;
clear HM;
clear HP;
clear H_response_force;
clear H_base_force;
clear max;
clear PHA;
clear PPP;
%
close all;
%
tpi=2*pi;
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
disp(' ');
disp(' Select input method ');
disp('  1=mass & stiffness matrices ');
disp('  2=natural frequencies and mass-normalized eigenvectors ');
%
imethod=input(' ');
%
disp(' ');
disp(' Select output metric ');
disp('  1=displacement/force ');
disp('  2=velocity/force ');
disp('  3=acceleration/force ');
disp('  4=acceleration/acceleration ');
disp('  5=force/displacement');
%
iam=input(' ');
%
disp(' ');
disp(' Enter units: ');
if(iam==1 || iam==5)
  disp(' 1= inches, lbf ');
  disp(' 2= meters, N ');
end
if(iam==2)
  disp(' 1= inches/sec, lbf ');
  disp(' 2= meters/sec, N ');
end
if(iam==3 || iam==4)
  disp(' 1= G, lbf ');
  disp(' 2= meters/sec^2, N ');
end
iu=input(' ');
%
if(imethod==1)
  disp(' ');
      mass = input(' Enter the mass matrix name:  ');
  %    mass
  disp(' ');
  disp(' Divide mass by 386? ');
  disp(' 1=yes 2=no ');
  idm=input(' ');
  if(idm==1)
      mass=mass/386;
 %     mass
  end
  m=mass;
  disp(' ');
  stiffness = input(' Enter the stiffness matrix name:  ');
%  stiffness
%
  num=max(size(mass));
%
  [fnv,omega,ModeShapes,MST]=Generalized_Eigen(stiffness,mass,1);
  QE=ModeShapes;
%
else
  disp(' ');
  disp(' Enter the name of the mass-normalized eigenvector matrix ');
  QE=input(' ');
  QE
  num=max(size(QE));
%
  disp(' ');
  disp(' Enter the natural frequency (Hz) vector or matrix ');
  clear fff;
  fff=input(' ');
  sz=size(fff);
  fnv=zeros(sz(1),1);
  if(sz(1)==sz(2))
      for i=1:sz(1)
          fnv(i)=fff(i,i);
      end
  else
      fnv=fff;
  end
  fnv
end
%
num_modes=max(size(fnv));
%
[dampv]=enter_modal_damping(num_modes);
dampv
%
disp(' ');
num_columns=input(' Enter the maximum mode number of interest ');
%
nrb=0;
%
if(fnv(1)<1.0)
  disp(' ');
  disp(' Does the system have any rigid-body modes which are to be suppressed? ');  
  disp(' 1=yes 2=no ');
  isr=input(' ');
  if(isr==1)
      disp(' ');
      nrb=input(' Enter the number of rigid-body modes ');
  end
end    
%
disp(' ');
disp(' Enter the frequency step ');
df=input(' ');
%
disp(' ');
disp(' Enter the minimum frequency for plots');
minf=input(' ');
%
disp(' ');
disp(' Enter the maximum frequency for plots');
maxf=input(' ');
%
if(maxf<=minf)
  maxf=100*minf;
end
%
nf=floor((maxf-minf)/df);
clear omega;
%
freq=zeros(nf,1);
omega=zeros(nf,1);
omega2=zeros(nf,1);
for i=1:nf
  freq(i)=(i-1)*df+minf;
  omega(i)=2*pi*freq(i);
  omega2(i)=(omega(i))^2;
end
%
clear omn;
omn=tpi*fnv;
omn2=omn.*omn;
%
sz=size(QE);
if(num_columns>sz(2))
  num_columns=sz(2);
end
%
disp(' ');
disp(' Select dof pair input method ');
disp('  1=manual  2=table ');
ipim=input(' ');
%
if(ipim==2)
  disp(' ');
  dof_pair_table=input(' Enter table name:  ');
  sz=size(dof_pair_table);
  mtable=1;
  if( (sz(1)+sz(2))>3)
      mtable=max(sz);
  end
end
%
disp(' ');
disp(' Display plots?  1=yes 2=no ');
impl=input(' ');
%
if(impl==1)
 disp(' ');
 fig_num=input(' Enter starting figure number ');
end
%
ikv=1;
while(1)
%
  if(ipim==1)
      disp(' ');
      if(iam<=3)
          i=input(' Enter response   dof ');
          k=input(' Enter excitation dof ');
      else
          i=input(' Enter response   dof ');
          k=input(' Enter base       dof ');            
      end
  else
      i=dof_pair_table(ikv,1);
      k=dof_pair_table(ikv,2);
  end
%
  [H_response_force]=...
  transfer_core(freq,fnv,dampv,QE,omn2,omega,omega2,iam,nf,num_columns,i,k,nrb);
%
  if(iam ~=4)
      H=H_response_force;
  else
      [H_base_force]=...
      transfer_core(freq,fnv,dampv,QE,omn2,omega,omega2,iam,nf,num_columns,k,k,nrb);
%
      for s=1:nf % frequency loop  
          H(s)=H_response_force(s)/H_base_force(s);
      end
%
  end
%
  HM=abs(H);
  HP=-atan2(imag(H),real(H))*180/pi;
%
%
  if(iam==3 && iu==1)
      HM=HM/386;
  end
%
  ijk=0;
%
  ijk=ijk+1;
  clear PPP;
  PPP=zeros(nf,1);
  PHA=zeros(nf,1);
%    
  for ia=1:nf
      PPP(ia)=HM(ia);
      PHA(ia)=HP(ia);
%
      while(PHA(ia)<0)
          PHA(ia)=PHA(ia)+360.;
      end
%
      ymax=max(PPP);
      ymin=min(PPP);
  end  
%
  freq=fix_size(freq);
  H=fix_size(H);
  HM=fix_size(HM);
  PPP=fix_size(PPP);       
  PHA=fix_size(PHA);
  AAA=angle(H);
%
  [varname1,varname2,varname3]=transfer_from_modes_H_files(iam,i,k,freq,H,HM);
% 
  disp(' ');
  disp(' Matlab array names ');
    disp(' ');
    eval([varname1 ' = [freq H];']);    % need to do in main script
    out1=sprintf('           Complex:  %s ',varname1);
    disp(out1);
%
    eval([varname2 ' = [freq PPP];']);
    out1=sprintf('         Magnitude:  %s ',varname2);
    disp(out1);
%
    eval([varname3 ' = [freq PPP AAA];']);
    out1=sprintf(' Magnitude & phase:  %s ',varname3);
    disp(out1);
%
    if(impl==1)
       [fig_num]=...
       transfer_from_modes_plots(iu,iam,i,k,fig_num,minf,maxf,ymin,ymax,freq,PPP,PHA);    
    end
%
    if(ipim==1)
        disp(' ');
        disp(' Perform calculation for another pair ? ');
        disp(' 1=yes  2=no ');
        inc=input(' ');
        if(inc==2)
            break;
        end
    else
        ikv=ikv+1;
        if(ikv>mtable)
            break;
        end
    end
end

2 个评论
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venkatesu u 2023-10-30

编辑：venkatesu u 2023-10-30

Also I have downloaded from the internet and have no clarification on

1. unrecognized function "fix_size"

2. How can i apply this code for 4 degrees of freedom system.

Can anyone give explaination to the above questions?

Image Analyst 2023-10-30

编辑：Image Analyst 2023-10-30

Probably not. This was posted 5 years ago and the original poster hasn't been here since then. He didn't even bother to answer me and I replied to him immediately.

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