Harmonic Response Analysis of Structure

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INTRODUCTION

Most of the process equipment is subjected to cyclic (Harmonic) loading during their operation. Due to such loading, the structure is subjected to completely reversed stresses. If the external harmonic frequency matches with the natural frequency of the structure, then resonance occurs & structure vibrates with maximum amplitude. This condition of resonance should be avoided as maximum vibration may lead to excessive stresses or in extreme cases failure of the structure.

Process equipment manufacturer from India & Abroad approached ANALYZER to seek assistance in evaluating the design of their newly developed equipment against harmonic loading & provide the solution in case of any observed failure.

FEA WORKFLOW

  • Determining the material properties for different MoCs of equipment, design parameters to be considered in FEA.
  • Preparing FEA Model for Harmonic Response Analysis. Based on the scope of different components the meshing approach is decided for this analysis also the element types for different mesh types are of utmost importance.
  • Solving the FEA model for described loading in ANSYS APDL Solver. The loading may be constant over frequency range or varying as per frequency.
  • From the results of FEA, the structure is either evaluated for the resonance condition (max. induced stresses) or completely reversed fatigue stresses. It depends upon design requirements.
  • Report the results for the client’s reference.

CHALLENGES

  • Meshing approach & element type for Harmonic Response Analysis,
  • Performing Completely reversed stress fatigue calculations.

THE SOLUTION

The structure was analyzed using the Finite Element Method for Harmonic Response Analysis. The loading is applied as per design requirements. The structure is solved for Harmonic analysis & evaluated as per requirements either for resonance or completely reversed fatigue.

The results showed that the structure is able to sustain the harmonic load for its service life for resonance as well as fatigue loading. Hence, the structure’s design was predicted to safe against cyclic (harmonic) loading.

BENEFITS

  • A design can be evaluated for possible harmful effects of harmonic loadings.
  • Structural failure can be investigated for its cause of failure.
  • Design modifications based on observed failure can be made possible.