I found that modal frequency results between Opensees Navigator and hand calculation is different.
I assumed a simple truss model : cross section 0.04 m^2, mass density 5000 kg/m^3, elastic modulus 200 GPa, 3 nodes, 2 elements.
This truss model has 2 mode and 2 modal frequency. My hand calculation modal frequencies are 711.7625 hertz and 711.7625 hertz, respectively.
However, Modal frequencies from Opensees Navigator are 142.3525 hertz and 142.3525 hertz, respectively.
I wonder why two results have different. Does Opensees Navigator have postprocessing?
I'll post my Opensees Navigator files. Please describe the reason why two results have different.
I can confirm your natural frequencies f_1 = f_2 = 7.11763E+02 Hz if I use a lumped mass matrix.
Nils Wagner I also used lumped mass matrix and got 711.7625 Hz. I want to know the reason why result from Opensees is 142.3525 Hz.
Dear Jae Min Lee
I checked your Opensees model files. You have defined two truss members with a value of 5000 for the density. For the truss member in Opensees, you must enter the density per unit length. The density per unit length for your model is equal to: 5000*0.04=200kg/m. Just define the value of 200. I did this correction for your model and got a frequency of 711.7625 Hz for the first two modes.
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