The following file, spring.ssc, implements
a component called spring.
The declaration section of the component contains:
Two rotational nodes, r and c (for
rod and case, respectively)
Parameter k, with a default value
of 10 N*m/rad, specifying the spring rate
Through and Across variables, torque t and
angular velocity w, to be connected to the rotational
domain Through and Across variables later in the file
Internal variable theta, with a
default value of 0 rad, specifying relative angle,
that is, deformation of the spring
The branches section establishes the relationship
between the component Through variable and the component nodes (and
therefore the domain Through variable). The t : r.t ->
c.t statement indicates that the torque through the spring
acts from node r to node c.
The equation section starts with an assert construct, which checks that
the spring rate is greater than zero. If the block parameter is set incorrectly, the
assert triggers a run-time error.
The first equation, w == r.w - c.w, establishes the relationship
between the component Across variable and the component nodes (and therefore the domain Across
variable). It defines the angular velocity across the spring as the difference between the
node angular velocities.
The following two equations define the spring action:
t = k * theta, that is, torque
equals spring deformation times spring rate
w = theta.der, that is, angular
velocity equals time derivative of spring deformation
component spring
nodes
r = foundation.mechanical.rotational.rotational;
c = foundation.mechanical.rotational.rotational;
end
parameters
k = { 10, 'N*m/rad' };
end
variables
theta = { 0, 'rad' };
t = { 0, 'N*m' }; % torque through
w = { 0, 'rad/s' }; % velocity across
end
branches
t : r.t -> c.t; % torque through from node r to node c
end
equations
assert(k>0) % spring rate must be greater than zero
w == r.w - c.w; % velocity across between node r and node c
t == k * theta;
w == theta.der;
end
end