Forced vibration response Ode45

I am suck on a question for an assignment. I can not get matlab to work the following function I keep getting error messages.

function f=t

F=940*sin(10*pi*t);

k=50000;

damping=0.05;

r=3.224;

x(1+t)=(F/k)/sqrt((1-R^2)^2+4*(damping^2)*r^2);

t=1/(10*pi);

[x,t]=ode45('f',[T,T*50],0);

plot(x)

[A Jenkins]

Yes, you need some more practice at MATLAB. Type

doc ode45

to see some example problems to work though that will help you learn how it works.

(Some hints for this code...

• MATLAB cares what order you write things, and how you declare functions.
• It is also case sensitive, so that 'r' and 'R' are not the same thing.
• A function handle should be written @f.)

[Ryan]

Thanks for the reply. I have read the helper page however it doesn't help me figure out where the error is as I have defined things as it states it should be done.

[A Jenkins]

Perhaps you should start with an example that works and slowly make modifications to it until you get to your final result?

Then you will know exactly what change you made and therefore only one line will be incorrect at a time.

(We try not to do people's homework for them, so we only answer specific questions here.)

[Ryan]

I didn't ask for you to do it for me as you don't have the assignment question. I asked for help with the code I wrote. I have figured out how to do the problem any way.

function [du]=QuestionE(t,u);

du=zeros(2,1);

Damping=0.05;

wn=9.74;

du(1)=-2*Damping*wn*u(1)-u(2)*(wn^2)+(940/530)*sin(10*pi*t);

du(2)=u(1);

end

Damping=0.05;

wn=9.75;

omega=10*pi;

k=50000

m=527.1;

g=9.81;

r=omega/wn;

F=940

wd=wn.*sqrt(1-Damping.^2);

timespan=(50*2*pi)/omega

xst=-(m*g)/k;

v0=0;

A=xst;

B=(v0+Damping*wn*xst)/wd;

[t,u]=ode45(@QuestionE1,[0 timespan],[v0,xst]);

u=exp(-Damping.*wn.*t).*(A.*cos(wd.*t)+B.*sin(wd.*t));

y=(2*Damping*r)/(1-r^2);

fi=atan(y);

X=((F/k)/(sqrt((1-(r^2))^2+4*(Damping^2)*(r^2))))

u1=X.*cos(omega.*t-fi)+u;

plot(t,u,'k')

hold on

plot(t,u1,'b')

title('Forced Vibration Responce')

xlabel('Time')

ylabel('x(t)')

Answer 1

[Mohammed Siraj]

 Write the program for the task given: The motion of the forced vibratory system with spring-
mass system is modeled by the following equation, solve the differential equation and find the 
displacement, velocity with respect to time (from 0 to 120 seconds).Analyze the system by 
MATLAB Programming and validate the solution by using SIMULINK. Assume m=1 kg, k=2 
N/m, F=120N and ω=1 rad/sec.