Learning Forum

[akilles.aj]

Hi everyone,

I’m modeling a transient impulse load on a cantilever beam in ANSYS Mechanical (LS-DYNA). The goal is to apply a 20,000 N load on the free end of the beam for 0.005 seconds, and then release it so that the beam vibrates freely.

When I perform the same simulation in Explicit Dynamics, the motion looks physically correct, the beam deflects under the short pulse and then oscillates freely around zero displacement.

However, in LS-DYNA, the deformation and stress results differ.
The amplitude of the oscillation is not consistent with the expected physical response,
and the displacement does not start at zero even though the loading is transient and begins at time = 0.

Current LS-DYNA Keyword setup:

*DEFINE_CURVE_TITLE

LoadPulse

1001,1,1.0,1.0

$ time(s), pressure(N/mm^2)

0.000, 2.0

0.001, 2.0

0.002, 2.0

0.003, 2.0

0.004, 2.0

0.005, 2.0

0.006, 0.0

0.050, 0.0

 

*SET_SEGMENT_TITLE

hej

*LOAD_SEGMENT_SET

1,1001,1.0

 

Notes to understand code:

The loaded surface area is 10,000 mm², so 2.0 N/mm² corresponds to a total load of 20,000 N.
Named Selection = hej.

What is going wrong , is my keyword setup incorrect, or am I using *LOAD_SEGMENT_SET in the wrong way? 

Specifically:

• Is this the correct approach to apply a transient surface pressure in LS-DYNA Mechanical?
• Do I need to include any additional control cards or database options to get a proper transient response?
• Is there a better way to define a force (N) rather than pressure (N/mm²) on a surface?

I will attach:

• Plots of the expected response (from Explicit Dynamics)
• Plots of the current LS-DYNA results
• Pictures of named selection and fixed support

Any advice on what might be missing or incorrect in this keyword definition would be greatly appreciated.

// Ahmad Jaber, Industrial Engineering, Student Research Assistant, Örebro University