INTRODUCTION

All the rotating machinery systems experiences torsional oscillations during their operations. Excessive torsional vibrations leads to gear wear, gear tooth failure, key failure &, in severe cases, breakage of shafts. So a torsional response characteristics should be evaluated for rotating & reciprocating structures in order to ensure the system’s reliability. TVA consists of different stages as torsional natural frequencies & modes extraction, Campbell diagram creation & stress evaluations. Torsional natural frequencies should be away from external excitation frequency by enough margins. API Standard (610 & 684) have mentioned in, this margin should be ± 10% of any external possible excitation frequency.

Renowned Pump Manufacturer from India approached ANALYZER to seek assistance in evaluating the design of their newly developed pump assembly for its powertrain.

FEA WORKFLOW

• Creation of powertrain model in ANSYS Solver with the help of preprocessing tool.
• The FEA model of powertrain is solved for torsional natural frequencies in ANSYS Solver.
• Campbell diagram creation for powertrain. It is an interference diagram showing possible external excitation frequencies along with the torsional natural frequencies. The intersection point of this two indicates resonance condition.
• Performing Stress analysis (if necessary) in some cases.
• Report the results for client’s reference.

CHALLENGES

• Element type for different parts of powertrain,
• Proper DOF Connection between horizontal driver & vertical driven member.
• Stress evaluation for short circuit conditions in case of motor driven powertrain

THE SOLUTION

The structure was analyzed using Finite Element Method for Torsional Vibration Analysis. Different modes of natural frequencies are extracted along with corresponding mode shapes. Campbell diagram for the given powertrain is prepared.

The results showed that the natural frequency of powertrain is away from all the possible external excitation frequencies by sufficient margin. Consequently, stress analysis was not performed for this case. Thus the powertrain’s design was predicted to be safe against torsional excitation failures during its service life.

BENEFITS

• Campbell diagram gives exact idea about resonance point.
• Stress analysis helps to evaluate the powertrain more precisely against any torsional resonance failure.