Dear Collegue 

I am trying plot time history of  a point mass on top of spring(interaction)

 - 2D planer,

 - 2 part, each part is just a point

- type:                    discrete rigid 

- Base feature:         point

- Inertia is defined to points

- spring is defined between two points.

- bottom point is fully fixed

- top point is released only vertical movement.

- Loading; explicit dynamic vertical force on top point  

// Error in job PointMass: There is no element available in the model to control the stable time increment for Step 1. Please add a deformable element to control the stable time increment. Alternatively, you can use DIRECT TIME INCREMENTATION to perform the analysis at a user specified time increment. //

What does this error mean ?

Why element is applicable to point mass?

It this possible model ?  

I used to do this point model for training purpose using LUSAS. 

Thank you.