Simulink model of Continuous Stirred-Tank Reactor in series

Here's a simple Simulink model I created today. This model simulates the concentration in three Continuous Stirred-Tank Reactor (CSTR) in a row and how these concentration values affected by the influent concentration. Sometimes the CSTR is also called well-mixed continuous flow through reactor.

The S-function of this CSTR model is shown below.


function [sys, x0 str, ts]=cstr_sfcn(t,x,u,flag,Cinit)
switch flag
    case 0 %initialize
        str=[];
        ts=[0 0];
        x0=Cinit;
        
        s=simsizes;
        s.NumContStates=1;
        s.NumDiscStates=0;
        s.NumOutputs=1;
        s.NumInputs=1;
        s.DirFeedthrough=0;
        s.NumSampleTimes=1;
        
        sys=simsizes(s);
        
    case 1 % derivatives


        sys=cstr(t,x,u);
    
    case 3 %output
        sys=x;
        
    case {2 4 9}
        sys=[];
    otherwise
        error(['unhandled flag=', num2str(flag)])
end


And below is the function of the reactor.


function dx=cstr(t, x, u)
Ca=x;
dCa=0.2*(u-Ca);
dx=dCa;

The Simulink model looks like this:

All of the three tanks has the same characteristics, except the initial concentrations were different.
C1(0)=5, C2(0)=3, and C3(0)=1. And the influent concentration was simulated by the pulse generator. The simulation results is shown below.

Set marker edge width in Matlab figures

A couple of days ago, I plotted about twenty figures and was trying to set the markers with thicker edge. This would be very easy if it was in Excel: just change the 'Marker Line Style' in the 'Format data series' tab. However, it was kind difficult to do in Matlab. At least I didn't get a good solution from the google results on that day.

Today I happened to find the solution when I was playing with Matalb just for fun. The fact is that the 'Marker Edge Width' is actually defined by the 'LineWidth', even when the plot does not use a line to connect the markers..

t=[1:5];
plot(t,sin(t), 's', 'Markersize', 20,'LineWidth', 5)  

Concatenate text and convert to numbers in Excel

I have a long Excel file which keep the date, month, year, hour, minute, and second in separate columns (figure 1). I want to use only one column to present the time, so it would be easier to plot the time as x-axis. Here is the function I used in cell G2:

=VALUE(CONCATENATE(A2,"/",B2,"/",C2," ",D2,":",E2,":", F2))

The Value function convert the text into numbers.
The Concatenate function connects all the text and convert them into one string.

remove any rows that contains a specific number in Matlab

In this post, I am trying to solve the problem given in the comments of one of the old post.

Here's the problem, if I understand it correctly:

a =

     1     2     3     4     5

     2     3     4   -99     6

     3     4     5     6     7

     4   -99     6     7     8

     5     6     7     8     9

How to remove all the rows that contains the number -99, in this case, the row #2 and #4?

And here's the code I wrote to do this job:

[rows col]=size(a); %count the number of rows and columns of matrix a

j=0; %initialize a counter;

for i=1: rows

    if sum(a(i,:)~=-99)==col; %This determines if the row has -99 or not, if not, do nothing

    else     %shift all of the rest of the rows up one row

        for m=i: rows-1; 

        a(m,:)=a(m+1,:);

        end

        j=j+1; %count how many rows has -99, which equals how many times the rows has been shifted up 

    end

end

b=a((1:rows-j),:); %get rid of the last j rows


The result is:



b =


     1     2     3     4     5
     3     4     5     6     7
     5     6     7     8     9

I hope this can work for you, Winifred. Thanks for your comments!

calculate average of every 5 cells in Excel

I have some data sampled at a rate of 1 sample per minutes. However, to use them as input for the following calculation, I have to convert them to the 5 minutes average. Simply put, I want to let B1=average(A1:A5), B2=average(A6:A10), B3=average(A11:A15), ... til B10=average(A46:A50).

I tried VBA code in Excel but didn't make it work. Then I tried Matlab-the code works but it's troublesome to copy/paste all the data between Excel and Matlab back and forth. Finally I figured out a simple way to do this in Excel, by using the OFFSET, ROW, and INDIRECT functions.

The formula to put in cell B1 is:

=AVERAGE(OFFSET(INDIRECT("A"&ROW(A1)*5-4),0,0,5,1))


The Row(A1) returns the row number of the cell, which is '1' in this case. So the INDIRECT("A"&ROW(A1)) *5-4, 0,0,5,1) returns the cell A1 to A5. When dragged to cell B2, the INDIRECT("A"&ROW(A2)) *5-4, 0,0,5,1) returns the cell A6 to A10. So I can drag this formula all the way down to B10 to finish this task.

The file looks like this:

How to concatenate two datasets in Matlab?

I wanted to vertically combine two datasets, so I can keep a long file of all the test results. The join function does not work here anymore. Of course this is even not a problem in Excel. However, to make it work in Matlab, it did took me a while to figure it out.

c=cat(1, a, b)

Excel slope function vs linest function

To get the slope of a pair of x and y, usually I first plot the curve and then add the trend line.

 

Actually there are two functions in Excel to help me do this. The first one is the 'SLOPE' function. However, it only gives what is shown by the red trend line (slope=0.25). The second one is 'LINEST' function, which is more flexible. By setting the third parameters in the function to 'False', it automatically set the intercept to zero (slope=0.36).

'LINEST=(y series, x series, False)'