Spring TYPE4 - 1 DOF Spring (/PROP/SPRING)

Spring TYPE4 is a simple physical spring, physical dashpot or parallel spring and dashpot.

Time step depends on spring mass, stiffness and damping.

Figure 1. Spring TYPE4 - Time Step

Critical spring time step ensures the stability of explicit time integration scheme, but it does not ensure a high accuracy on spring vibration behavior. Only two time steps are available during one vibration period of a free spring. To reproduce the true sinusoidal behavior, reduce the time step by a factor of at least 5. If the spring is used to connect two parts together, the spring vibration period increases and the default spring time step ensures stability and accuracy.

Spring TYPE4 has only one degree of freedom, it can only resist to axial traction and axial compression. The forces applied on the two nodes are always co-linear with local x direction.

Figure 2. Co-linear Forces in Spring TYPE4
If the spring works under compression, it can reach a zero length situation in which the orientation of internal forces can be arbitrary (Figure 3). That can result in stability problems and should be avoided.

Figure 3. Instability of a Zero Length Spring

For further information, refer to the Radioss Theory Manual.