#### CONNECTOR_SPRING

###### Connectors
*CONNECTOR_SPRING
coid, N${}_1$, N${}_2$, $m$, $k$, $\xi$, $F_{fail}$, direc
##### Parameter definition
VariableDescription
coid Spring connector ID
N${}_1$ Node 1
N${}_2$ Node 2
$m$ Mass
$k$ Stiffness (force per unit distance of elongation) or a FUNCTION defining the elastic force versus elongation
$\xi$ Fraction of critical damping or a FUNCTION defining the damping force versus elongation rate
$F_{fail}$ Spring failure force
default: No failure
direc Spring force direction
options:
0 $\rightarrow$ tension and compression
1 $\rightarrow$ tension only
2 $\rightarrow$ compression only
##### Description

This command defines a linear spring between two nodes.

##### Example
###### Linear spring connector

A linear spring with ID 5 connecting node 41 with node 42.

*PARAMETER
m = 0.01
k = 1.0e2
xi = 0.1
*CONNECTOR_SPRING
5, 41, 42, [%m], [%k], [%xi]
###### Non-linear spring connector

A spring with ID 10 connecting node 43 with node 44. Functions are used to define the elastic force versus elongation (dnorm) and the damping force versus rate of elongation (vnorm). Note that dnorm and vnorm are built in variables.

*PARAMETER
m = 0.01
k0 = 1.0e2
k1 = 1.0e3
c0 = 20.0
c1 = 5.0
*CONNECTOR_SPRING
10, 43, 44, [%m], fcn(10), fcn(20)
#
# Elastic force versus elongation
*FUNCTION
10
%k0*dnorm + %k1*dnorm^2
#
# Damping force versus elongation rate
*FUNCTION
20
%c0*(exp(%c1*vnorm)-1)