Introduction

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

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 scope of different components the meshing approach is decided for these analyses also the element types for different mesh types is 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 results of FEA, 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 client’s reference.

CHALLENGES

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

SOLUTION

The structure was analysed using 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 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 evaluated for possible harmful effects of harmonic loadings.
• Structural failure can be investigated for its cause to failure.
• Design modifications based on observed failure can be made possible.