The effect of shaft-coupling penetration ratio on torsional vibration analysis

Irannejadparizi, Mostafa; Asgharifard Sharabiani, Pouya; Navabi, Hamed; Naderpour, Akbar; Hekmatgolmakani, Saeed

doi:10.22064/tava.2025.2065737.1269

The effect of shaft-coupling penetration ratio on torsional vibration analysis

Document Type : Invited by Abdolreza Ohadi

Authors

Mostafa Irannejadparizi ¹^{, 2}

Pouya Asgharifard Sharabiani ²

Hamed Navabi ²

Akbar Naderpour ²

saeed hekmatgolmakani ²

¹ Assistant Professor, College of Engineering, University of Tehran, Tehran, Iran.

² Rotor-dynamics Researcher, Oil Turbo-Compressor Equipment (OTCE), Tehran, Iran.

10.22064/tava.2025.2065737.1269

Abstract

When designing typical rotating equipment, torsional natural frequencies (TNFs) must be studied to identify possible resonances. Accurate computation of TNFs and torsional modes requires precise modeling of the shaft-coupling connection. The shaft penetration factor (SPF), representing the shaft's penetration into the coupling hub, significantly affects torsional stiffness calculations. This paper develops a comprehensive torsional vibration software (TVS) for the analysis of a centrifugal compressor train. The torsional analysis of an electrocompressor train, based on API 617 criteria, examines the SPF's effect on torsional output. Five modeling approaches for shaft penetration are considered: SPF values of 0, ⅓, ½, 1, and an end-to-end shaft-coupling connection. These approaches' effects on the torsional behavior of a real centrifugal compressor train designed by OTCE are investigated. Results show that different modeling approaches change the 2nd and 4th flexible TNFs by about 21% and 13%, respectively, plus noticeable differences in mode shapes. The Campbell diagram reveals that intersections of the 2X excitation line with the 2nd and 4th TNFs fall near or within the API separation margin, shifting closer or farther from the critical speed range depending on the modeling approach. Therefore, precise modeling of flexible coupling stiffness is crucial for correctly addressing compressor train torsional natural frequencies, as minor uncertainties in the shaft-coupling connection may cause significant differences in torsional behavior.

Highlights

Torsional finite element modeling of the motor/gear/compressor train is performed.
Shaft penetration factor (SPF), representing the shaft-coupling connection, is studied.
Different modeling approaches, such as SPF = 0, ⅓, ½, 1, are investigated.
Torsional Natural Frequencies and mode shapes of the compressor train are studied.
Shaft-coupling connection uncertainties significantly affect torsional modeling.

Keywords

Torsional vibratio

Flexible coupling

Torsional Natural Frequencies (TNFs)

Shaft Penetration Factor

Finite Element Modeling (FEM)

Centrifugal compressor train

Subjects