Step input applied for different seconds

Question

Mustafa Furkan 2022-12-21

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1882362-step-input-applied-for-different-seconds

评论： Star Strider 2022-12-25

I want to apply step input to the system as in the graphs above, where the second values are seen in the row and column. Entries will start at 1 second and end at 5 and 40 seconds respectively. I want to plot the vibration graph x(t), and the amplitude graph of these vibrations, but I couldn't find where to start.

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Answer 1

Star Strider 2022-12-21

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1882362-step-input-applied-for-different-seconds#answer_1133262

在 MATLAB Online 中打开

Experiment with this approach —

N = 1500; % Desired Length Of Simulation

t = linspace(0, 50, N);

u = @(tlen,lz) [zeros(1,lz) 10*ones(1,size(t(t<=tlen),2)-lz) zeros(1,size(t(t>tlen),2))]; % 'tlen'=Length Of '10' Region, 'lz'=Length Of Leading Zero Vector

u5 = u(5,2);

u40 = u(40,2);

figure

subplot(2,1,1)

plot(t, u5, 'g', 'LineWidth',1.5)

grid

title('u(5,2)')

axis('padded')

ylim([0 15])

subplot(2,1,2)

plot(t, u40, 'b', 'LineWidth',1.5)

grid

title('u(40,2)')

axis('padded')

ylim([0 15])

Use ‘t’ and ‘u(tlen,lz)’ as inputs to lsim to get the system response. Change ‘u(tlen,lz)’ to get the result you want.

.

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Star Strider 2022-12-25

在 MATLAB Online 中打开

The step function itself cannot do what you want. The best you can do is to cobble together (i.e. concatenate) outputs from different step calls and plot them together —

systf = @(id) tf(3,[1 2 3], 'InputDelay',id); % From The 'lsim' Documentation, Adding 'InputDelay' As A Variable Argument To The Anonymous Function Implementation

N = 1500; % Desired Length Of Simulation

t = linspace(0, 50, N);

t0 = t(t<=5);

t5 = t(t>5);

opts = stepDataOptions;

opts.InputOffset = 0;

opts.StepAmplitude = 10;

[y{1},tout{1},x{1}] = step(systf(0),t0,opts);

opts.InputOffset = y{1}(end);

opts.StepAmplitude = -y{1}(end);

[y{2},tout{2},x{2}] = step(systf(5),t5,opts);

figure

plot(tout{1}, y{1})

hold on

plot(tout{2}, y{2})

hold off

grid

figure

subplot(2,1,1)

plot(tout{1}, y{1})

grid

axis([0 50 -2 12])

subplot(2,1,2)

plot(tout{2}, y{2})

grid

axis([0 50 -2 12])

t0 = t(t<=40);

t40 = t(t>40);

opts = stepDataOptions;

opts.InputOffset = 0;

opts.StepAmplitude = 10;

[y{1},tout{1},x{1}] = step(systf(0),t0,opts);

opts.InputOffset = y{1}(end);

opts.StepAmplitude = -y{1}(end);

[y{2},tout{2},x{2}] = step(systf(40),t40,opts);

figure

plot(tout{1}, y{1})

hold on

plot(tout{2}, y{2})

hold off

grid

figure

subplot(2,1,1)

plot(tout{1}, y{1})

grid

axis([0 50 -2 12])

subplot(2,1,2)

plot(tout{2}, y{2})

grid

axis([0 50 -2 12])

Combining 'InputDelay' with the system object ‘systf’ (making that an anonymous function for convenience) and the step options structure stepDataOptions together makes this work. (I learned something about both functions in the process.)

It would be possible to use a for loop for this, and with more such simulations that would be an option, however with only two iterations, it didn’t seem worth the effort.

.

Mustafa Furkan 2022-12-25

It worked now thank you. Unfortunately, as you said, I don't get a different result than before. I guess I'll have to include values like mass stiffness to get a result as expected.

Star Strider 2022-12-25

As always, my pleasure!

I have no idea what results are expected. It would appear that you would be using a state space realisation. There are likely documentation examples that could help code your system.

If necessary, you can use stepinfo with the arguments of all the step calls to get that information from each of them.

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