Error in for loop (issue with variable calling)

I am trying to find natural frquency for two sets of data. For that we have to follow this method

I am facing issue with calculation of Wd and Wn where i have to call values of Time from specific range.

for i = 1:1
    z1 = importdata("XXsv0000"+i+".txt");
                          
    Time{i} = z1.data(:,1);            % select the first column of data from rows defined in ind as time data  
    Veloc{i} = z1.data(:,2);           % select the second column of data from rows defined in ind as velocity data
    ind = 1:550;                 % redefine the range of indices to select data from Veloc
    % find local maxima in Veloc data within the range of indices defined in ind
    % returns peak amplitude (Ypk), peak index (Xpk), peak width (Wpk), and peak prominence (Ppk)
    [Ypk,Xpk,Wpk1,Ppk] = findpeaks(Veloc{i}(ind));
    Ypk_plot{i} = Ypk(11:35);
    Xpk_plot{i} = Xpk(11:35);
    Y{i} = Ypk;  X{i} = Xpk; W{i} = Wpk1; P{i} = Ppk;
    figure(i)
    plot(Time{i},Veloc{i},Time{i}(Xpk_plot{i}),Ypk_plot{i},'dr'); % plot data against time data and mark the locations of the peaks found
    grid on
    legend(["data","Pick points"])
    sgtitle("File " + string(i))
    n_peaks = numel(X{i});
    Log_Dec = zeros(1, n_peaks-1);
    t_new = Time{i}; % contains 1024 values (which is wrong) it shoud be 81x1
    y_new = Y{i};  
    for nn = 1:n_peaks-1 %
        Log_Dec(nn) = log(y_new(nn)/y_new(nn+1));  % computed with n = 1 periods apart
    end  
    %Calculate Average Logarithmic Decrement  
    Mean_dec = mean(Log_Dec); 
    %Assesses Damping Constant
    damp_ratio(1,i) = 1/sqrt(1+((2*pi/(Mean_dec))^2));
end 

Error using importdata
Unable to open file.

Answer 1

[Voss]

Time{i} is all the times from the file. To get the times of the peaks found by findpeaks, index Time{i} with the peak locations X{i}. Also, the name of the file was misspelled.

for i = 1:1
%     z1 = importdata("XXsv0000"+i+".txt");
    z1 = importdata("Xxsv0000"+i+".txt");
                          
    Time{i} = z1.data(:,1);            % select the first column of data from rows defined in ind as time data  
    Veloc{i} = z1.data(:,2);           % select the second column of data from rows defined in ind as velocity data
    ind = 1:550;                 % redefine the range of indices to select data from Veloc
    % find local maxima in Veloc data within the range of indices defined in ind
    % returns peak amplitude (Ypk), peak index (Xpk), peak width (Wpk), and peak prominence (Ppk)
    [Ypk,Xpk,Wpk1,Ppk] = findpeaks(Veloc{i}(ind));
    Ypk_plot{i} = Ypk(11:35);
    Xpk_plot{i} = Xpk(11:35);
    Y{i} = Ypk;  X{i} = Xpk; W{i} = Wpk1; P{i} = Ppk;
    figure(i)
    plot(Time{i},Veloc{i},Time{i}(Xpk_plot{i}),Ypk_plot{i},'dr'); % plot data against time data and mark the locations of the peaks found
    grid on
    legend(["data","Pick points"])
    sgtitle("File " + string(i))
    n_peaks = numel(X{i});
    Log_Dec = zeros(1, n_peaks-1);
    
%     t_new = Time{i}; % contains 1024 values (which is wrong) it shoud be 81x1
    t_new = Time{i}(X{i})
    
    y_new = Y{i};  
    for nn = 1:n_peaks-1 %
        Log_Dec(nn) = log(y_new(nn)/y_new(nn+1));  % computed with n = 1 periods apart
    end  
    %Calculate Average Logarithmic Decrement  
    Mean_dec = mean(Log_Dec); 
    %Assesses Damping Constant
    damp_ratio(1,i) = 1/sqrt(1+((2*pi/(Mean_dec))^2));
end 

t_new = 81×1

0.0684 0.1367 0.2051 0.2637 0.3320 0.4004 0.4688 0.5371 0.5957 0.6641

[AL]

Dear @Voss Thank you so much for your effort. I really appricate it. Have a wonderful week.

[Voss]

You're welcome! Have a good one.

Answer 2

[David Hill]

for i = 1:1
    z1 = importdata("Xxsv0000"+num2str(i)+".txt");
                          
    Time{i} = z1.data(:,1);            % select the first column of data from rows defined in ind as time data  
    Veloc{i} = z1.data(:,2);           % select the second column of data from rows defined in ind as velocity data
    ind = 1:550;                 % redefine the range of indices to select data from Veloc
    % find local maxima in Veloc data within the range of indices defined in ind
    % returns peak amplitude (Ypk), peak index (Xpk), peak width (Wpk), and peak prominence (Ppk)
    [Ypk,Xpk,Wpk1,Ppk] = findpeaks(Veloc{i}(ind));
    Ypk_plot{i} = Ypk(11:35);
    Xpk_plot{i} = Xpk(11:35);
    Y{i} = Ypk;  X{i} = Xpk; W{i} = Wpk1; P{i} = Ppk;
    figure(i)
    plot(Time{i},Veloc{i},Time{i}(Xpk_plot{i}),Ypk_plot{i},'dr'); % plot data against time data and mark the locations of the peaks found
    grid on
    legend(["data","Pick points"])
    sgtitle("File " + string(i))
    n_peaks = numel(X{i});
    Log_Dec = zeros(1, n_peaks-1);
    t_new = Time{i}; % contains 1024 values (which is wrong) it shoud be 81x1
    y_new = Y{i};  
    for nn = 1:n_peaks-1 %
        Log_Dec(nn) = log(y_new(nn)/y_new(nn+1));  % computed with n = 1 periods apart
    end  
    %Calculate Average Logarithmic Decrement  
    Mean_dec = mean(Log_Dec); 
    %Assesses Damping Constant
    damp_ratio(1,i) = 1/sqrt(1+((2*pi/(Mean_dec))^2));
end 

[AL]

Can please explain me, what have you changed?

[David Hill]

This line:

z1 = importdata("Xxsv0000"+num2str(i)+".txt");

[AL]

my code is working property and importing the data. I am facing error in line

t_new = Time{i}; % contains 1024 values (which is wrong) it shoud be 81x1

[David Hill]

Your text file has 1024 rows of data. The above code is working properly. You need to explain why it should only be 81x1.

[Star Strider]

@David Hill —

The ‘t_new’ cell array should be indexed by the index vector ‘Xpk’ —

t_new = Time{i}(Xpk)

That will produce the (81x1) vector.

.

[AL]

@Star Strider

Motor_plate = 17.010;   
First_Story = 2.162;    
Sec_Story = 2.162;      
Top_strory = 1.790;     
L_leg = 0.278;          
S_Leg = 0.042;
bracket =19.75/1000;
boltnut =12.45/1000 ;
%Unbalance_mass = 0.044;
m1 = Motor_plate + 4*L_leg + 4*S_Leg + First_Story+40*bracket+64*boltnut;
m2 = 4*S_Leg+ First_Story+16*bracket+16*bracket;
m_for_k = [m1 m2];
M1 = Motor_plate + 2*S_Leg +2*L_leg ; %In kgs
M2 = First_Story+ 4*S_Leg;
M3 = Sec_Story + 4 * S_Leg;
M4 = Top_strory+2*S_Leg;
V = [M1 M2 M3 M4];
M = diag(V); % in Kgs
clear M1 M2 M3 M4 m1 m2 Motor_plate First_Story Sec_Story S_Leg;
clear Top_strory V L_leg bracket boltnut
for i = 1:2
    z1 = importdata("Xxsv0000"+num2str(i)+".txt");
                          
    Time{i} = z1.data(:,1);            % select the first column of data from rows defined in ind as time data  
    Veloc{i} = z1.data(:,2);           % select the second column of data from rows defined in ind as velocity data
    ind = 1:550;                 % redefine the range of indices to select data from Veloc
    % find local maxima in Veloc data within the range of indices defined in ind
    % returns peak amplitude (Ypk), peak index (Xpk), peak width (Wpk), and peak prominence (Ppk)
    [Ypk,Xpk,Wpk1,Ppk] = findpeaks(Veloc{i}(ind));
    Ypk_plot{i} = Ypk(11:35);
    Xpk_plot{i} = Xpk(11:35);
    Y{i} = Ypk;  X{i} = Xpk; W{i} = Wpk1; P{i} = Ppk;
    figure(i)
    plot(Time{i},Veloc{i},Time{i}(Xpk_plot{i}),Ypk_plot{i},'dr'); % plot data against time data and mark the locations of the peaks found
    grid on
    legend(["data","Pick points"])
    sgtitle("File " + string(i))
    n_peaks = numel(X{i});
    Log_Dec = zeros(1, n_peaks-1);
    t_new = Time{i}; % contains 1024 values (which is wrong) it shoud be 81x1
    y_new = Y{i};  
    Log_Dec = abs(log(y_new(1:end-1) ./ y_new(2:end)));
    Mean_dec = mean(Log_Dec);
    Damp_period = (t_new(end) - t_new(1)) / length(t_new);
    wd(i) = 2*pi / Damp_period;
    damp_ratio(i) = Mean_dec / sqrt(1 + Mean_dec^2);
    wn(i) = wd(i) * sqrt(1 - damp_ratio(i)^2);

    % calculate spring constant

    K_ex(i) = m_for_k * wn(i)^2;
end 

I am facing issue with K_ex(i)

I am unable to find the mistake. error is due to size difference in K_ex(i). Hoping piror steps all are correct.

Can you please help me with this?

regards,

AL

[Star Strider]

@AL — I just now saw this.

I see the problem, and the solution is therefore straightforward. However you already accepted another Answer, so I will not post my solution.