Influence of 3D modification on dynamic characteristics of herringbone gearbox system and vibration reduction design

The vibration and noise of marine power systems mainly comes from gearbox in addition to engine, while gearbox vibration is mainly caused by internal excitation of gear transmission system (GTS) and transmitted to ship hull through the box. This paper proposes a vibration reduction method of 3D modification controlling the strength of vibration source and constrained damping structure restraining vibration transmission energy. For herringbone gear,The 3D modification form of tooth surface combining with two parabolas and one straight line is proposed and the modified tooth surface equation is derived based on the principle of forming grinding.Combined with tooth contact analysis (TCA) technology and loaded tooth contact analysis (LTCA) technology, three internal excitations of GTS after 3D modification are determined. Through force balance and node connection relationship between each element, the coupling dynamic model of gear-shaft-bearing with three internal excitations i.e., time-varying meshing stiffness, transmission error and meshing impact is established to calculate dynamic load of journal bearing.The load is loaded into the finite element model of the gearbox to obtain its vibration value and six symmetrical pressing plates are applied force to fix the foundation with adding the same constrained damping structure in the middle.The purpose of reducing gearbox vibration is realized by combining 3D modification technology with constrained damping structure.The results of numerical examples show 3D modification can effectively reduce the radial and axial vibration of the gearbox, while the constrained damping structure can availably cut down transverse vibration. Compared with modification, constrained damping structure is more obvious effect. This study will contribute to the in-depth study of vibration reduction measures of marine gearbox system under variable excitations, and analyze its vibration characteristics under different vibration reduction measures, so as to meet the requirements of its vibration reduction and realize safety and stability of ship hull.