Dynamic analysis of an Air Handling Unit (AHU)

Abstract

The purpose of this study is to exercise the vibration methods for approaching a real case study which is, in this case, an air-handling unit (AHU) assembly that experiences a vibration-related problem. The methods that were utilised are the Finite Element Analysis (FEA), the Experimental Modal Analysis (EMA) and the Operating Deflection Shapes (ODS). Mathematical and analytical modelling were also done before the experimental methods where they are used as reference for estimation of the results. Initial vibration testing was done to verify the validity of the AHU was experiencing a vibration-related problem. Results between the analytical, FEA and experimental methodologies which are the EMA and ODS were compared for analysis. Dunkerley's and Rayleigh's technique were found to be good estimators for the fundamental natural frequency of the significant frame structure that supports the AHU. The corresponding mode shapes were used as reference for finding the relevant experimental mode shapes of the AHU. Then, FEA simulation were fine-tuned to best simulate the real case study AHU for future structural modification purposes. The ODS results show the belt pulley system that connects the motor and the fan of the AHU experienced a strong axial vibration as supported by the initial vibration testing. It was hypothesised that the AHU might be suffering from belt misalignment problem that introduces vibration to the whole AHU structure resulting in high vibration displacements. Limitations and the difficulties faced during the implementation of procedures for the theoretical and experimental methodologies were discussed. Further works can be done to simulate the rotational force of the belting system in the FEA model and tuning it to the ODS results to obtain a better simulation behaviour of the AHU under different conditions.