What is Power spectral Density analysis and Steady state analysis?

What is Power spectral Density analysis and Steady state analysis?

Power-spectral-density (PSD) analysis is a type of frequency-domain analysis in which a structure is subjected to a probabilistic spectrum of harmonic loading to obtain probabilistic distributions for dynamic response measures. A root-mean-square (RMS) formulation translates the PSD curve for each response quantity into a single, most likely value. Because PSD curves represent the continuous probability density function of each response measure, most of the integrated area will occur near the resonant frequencies of the structure. For accuracy, it is important to capture response at frequency steps near the natural modes of the structure.

Harmonic loading, characterized by sine and cosine functions, may have various components at different phase angles. Either hysteretic or viscous damping may be specified, though hysteretic (displacement-based) is most common for frequency-domain applications. The frequency-dependent behaviors assigned to links and supports are applied during PSD analysis.

Steady-state analysis is another type of frequency-domain analysis in which a structure is subjected to a given set of one or more harmonic load patterns. The response is then calculated in a deterministic manner for each frequency of vibration.

Additional notes on PSD include:

  1. Fatigue analysis is one application for which PSD analysis is useful. 
  2. Use a constant function to ensure that the magnitude of the probable load is the same at all frequencies.
  3. The shape of the power-spectral-density input function is dependent upon the probability of loading for each frequency, and the variation in likely load magnitude as a function of its frequency.

    • Related Articles

    • What is the Construction Sequence analysis?

      Implicit in most analysis programs is the assumption that the structure is not subjected to any load until it is completely built. This is probably a reasonable assumption for live, wind and seismic loads and other superimposed loads. However, in ...
    • What is the difference between Time History and Response Spectrum?

      Time History  This method calculates the response of a structure subjected to earthquake excitation at every instant of time (hence the name Time History). Various seismic data are necessary to carry out the seismic analysis i.e. acceleration, ...
    • What are Difference between the thin shell, thick shell, membrane element and Layered. Uses and applications. Why?

      Thin Shell Element  Inplane & Out of plane stiffness shall be calculated by the program by performing analysis.  Finite element meshing is compulsory for modeling such type of element Applications Normal RC Beam and slab structures. Irregular slabs, ...
    • Discuss about Eigen Vector and Ritz Vector?

      Eigenvector analysis determines the undamped free-vibration mode shapes and frequencies of the system. These natural modes provide an excellent insight into the behaviour of the structure. Ritz-vector the analysis seeks to find modes that are excited ...
    • What are the types and uses of the Diaphragm?

      Diaphragm are the mathematical operator which transfers the lateral forces to the vertical elements. Diaphragm are of two types. Rigid Diaphragm and Semi-Rigid Diaphragm. Rigid Diaphragm Software will consider the infinite stiffness in its own plane. ...