Hello, I'm working on replacing physical damping with global damping for a mass-spring-damper system in steady state.

The system is expected to have a natural frequency of 0.634 rad/s and a damping ratio of approximately 0.0786. For the Rayleigh damping parameters, I set α (alpha) to 0 and computed β (beta) near resonance to be 0.247.

Based on these parameters, I've created the following input file. However, I'm encountering three errors that look like this:

***ERROR: in keyword *DAMPING, file "MSD_R.inp", line 24: Misplaced keyword.

My questions are: should Rayleigh damping for this case be defined under material properties—since I don't have material properties available not able to use and I considered it under step but got error outside of step as well? does it only work with continuum models? Would it also work for discrete models like a mass-spring-damper system? I would appreciate any help in correcting the input file if it should work with a mass-spring-damper system. Thanks.

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*Heading
Steady-State Response of 1-DOF Mass-Spring-Damper (Rayleigh Damping)
*Node, Nset=FILE
1, 10.0
2, 15.0
*Element, type=SPRING2, elset=S
2, 1, 2
*Spring, elset=S
1,1
0.8087
*Element, type=MASS, elset=M
3, 2
*Mass, elset=M
2.0
*Nset, NSET=Nout
2
*Boundary
1, 2, 3
2, 2, 3
*AMPLITUDE, TIME=TOTAL TIME, VALUE=RELATIVE, INPUT=QUAKE.AMP, NAME=EQ
*Step, Name=Steady_State_Response
*Steady State Dynamics, Direct, Frequency Scale=Linear
0.001, 3.0, 1000
*DAMPING, ALPHA=0.0, BETA=0.247
*BOUNDARY, TYPE=DISPLACEMENT, AMPLITUDE=EQ
1, 1, 1, 1.0
*Output, Field, Frequency=1
*Node Output, NSET=Nout
U, V, A
*Element Output, ELSET=S
S, E
*End Step