In this coding when i am giving m2=0 value, why no graph is coming?

function dxdt = my_ode(i,x)

% Conversion to first order parameters

% z = x(1); %% displacement of damper

% zdot = x(2); %% velocity of damper

% zddot = x(2)dot; %% acceleration of damper

% y = x(3); %% displacement of structure

% ydot = x(4); %% velocity of structure

% yddot = x(4)dot; %% acceleration of structure

% x = [x(1) x(2) x(3) x(4)]; %% Output parameters

% tspan = i; %% Time span

%% Initial inputs

m1 = 10; %% mass of the structure(kg)

k1 = 15; %% stiffness of the structure(N/m)

c1 = 5; %% damping of the structure(Ns/m)

m2 = 10; %% mass of the damper(kg)

k2 = 15; %% stiffness of the damper(N/m)

c2 = 5; %% damping of the damper(Ns/m)

R = 1; %% Radius of the tank(m)

h = 0.05; %% Height of the water level in tank(m)

g = 9.81; %% Acceleration due to gravity(m/s^2)

A = 0.05; %% Amplitude of ground displacement(m)

w = 6.981; %% Input natural frequencycy(rad/s)

rho = 1000; %% Density of fluid(Kg/m^3)

xi = 1.841; %% First derivative of the Bessel function for first mode

%% define frequency

w2 = sqrt(xi*g*tanh(xi*h/R)/R); %% frequency of damper

w1 = sqrt(k1/m1); %% frequency of structure

%% define damping factor of damper

r2 = c2/(2*m2*w2);

%% define damping factor of structure

r1 = c1/(2*m1*w1);

%% define mass ratio

barm = (((R^3*pi*rho)/(2.2))*tanh(xi*h/R))/(m1);

%% define ground acceleration

ugdd = -A*w^2*sin(w*i);

%% Equation to solve

dxdt = [x(2);

(-ugdd-(2*r2*w2*x(2))-((w2)^2*x(1)));

x(4);

(-ugdd-(2*r1*w1*x(4))-((w1)^2*x(3))+(2*r2*barm*w2)+(barm*(w2)^2*x(1)))];

%% To run mass spring damper system

i = 0:0.01:20;

x = [0 0 0 0];

% Mass matrix function

% M = zeros(4,4);

% M(1,1) = 1;

% M(2,2) = 1;

% M(2,4) = 1;

% M(3,3) = 1;

% M(4,4) = 1;

% opts = odeset('Mass',@(t,x) mass(t,x));

%% Solve using ode45

[tsol,xsol] = ode45('my_ode', i, x,[1 0 0 0 ;0 1 0 1; 0 0 1 0;0 0 0 1]);

%% plotting

plot(tsol,xsol(:,3))

xlabel('time(sec)')

ylabel('displacement(m)')

grid on

title('Displacement response of structure')

figure

plot(tsol,xsol(:,4))

xlabel('time(sec)')

ylabel('velocity(m/s)')

grid on

title('Velocity response of structure')

Answer 1

[VBBV]

When m2 is zero, the ode45 returns NaN values. That's why you don't see the graph

[RAJKUMAR SAHA]

So what to do?