How to excite a beam through a spring?

[Gardenfence]

Hi,

I have modelled the transient response of a free-free (unconstrained) beam in ABAQUS, however, I now want to model the transient response when the force is placed on a spring. I have attached a rough sketch of the problem.

I have applied a two point spring to the beam model using a node on the beam and a reference point and placed a concentrated force on this reference point

The issue is that no matter the choice of spring stiffness the transient response is the same as it was without the spring! When i view the response it looks like the spring is moving as a rigid body with the beam, hence why potentially the transient response is not changing.

Any idea how else to model the spring so a force can be placed on it?

 

[FEA way]

It will fly away with the beam if it's unconstrained. If you want the bottom node of the spring to be fixed but still allow the spring to extend (as if the beam was raised by a vertical actuator mounted to the floor), it will be easiest to use the Axial connector instead - fix its bottom node and apply connector force to it (with proper amplitude). Of course, you can also define the stiffness via connector elastic behavior.

 

[Gardenfence]

Thankyou for responding!

I'm looking at the acceleration response of the free-free beam, the displacement response does just grow with time.

I dont want to fix anything in place, i want to model how the inclusion of a spring where the force is placed may change this acceleration response, if at all.

 

[FEA way]

So even the spring is not supposed to be fixed to the ground somewhere ? Then it will follow the beam in its rigid body motion, as you said and the results may not be satisfying. Is this model supposed to represent some real-life problem or is it just a theoretical study ? What kind of analysis step are you using ?