Steady state analysis step dyna

SOFiSTiK Teddy
1

Hello,
I carry a dynamic analysis on a bridge. I want a steady state analysis by a dynamic load like pedestrians. I read that in dyna manual it is possible to make it with N<0. But what is exactly N in this command, what it represent. In Transient analysis N is the number of time steps. But like in steady state analysis we are’nt really in a temporaly analysis what does it means. And in a same way, what does DT represents. And last question what is the difference between inser N=0 or N<0.
Thanks for your respond.
Have a good day.

3

Steady-state (harmonic) analysis evaluates the response of a structure to periodic or stochastic excitations directly in the frequency domain, assuming the system has reached an equilibrium vibration state where responses are sinusoidal with fixed amplitude and phase.

  • Unlike transient time-domain simulations, no time-stepping is required when the analysis is done in the frequency domain.
  • The system’s response is calculated by solving the complex algebraic equation involving the stiffness, mass, and damping matrices for a given excitation frequency ω\omegaω, resulting in a complex displacement vector UUU. This vector encodes both amplitude and phase of the steady vibration at each degree of freedom.
  • The time-dependent displacement u(t)u(t)u(t) can be recovered from UUU by u(t)=∣U∣sin⁡(ωt+ϕ)u(t) = |U| \sin(\omega t + \phi)u(t)=∣U∣sin(ωt+ϕ), where ∣U∣|U|∣U∣ is amplitude and ϕ\phiϕ is phase.

According to the software handbook:

  • When no STEP command is defined or STEP ≤ 0, and the input is made to the EIGE module, periodic or stochastic loads are analyzed in the frequency domain. Only periodic loads or spectra are permitted.
  • Phase shifts of mode shapes within individual load cases are accounted for, and the extreme responses from different load cases are combined according to the STEU STYP setting.
  • If N < 0 is specified, a time window of the periodic response is analyzed, considering phase shifts. Here, N is the number of time points, and DT is the time window size preset to the excitation period. In this mode, all load cases are superimposed with phase shifts taken into account, effectively producing a time-domain segment of the periodic steady-state response.
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4

understood, thank you!
just a question according this topic, when i run a analysis with step n >0, i run a transient analysis but what is the difference between including a EIGE parameters or no in this code.

thank you very much

5

With EIGE you can perform a modal analysis, which requires less calculation performance. For a time step analysis you dont need EIGE.

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