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• A comprehensive stiffness model of intermediate bearing is presented. • A reduced model of dual rotor-bearing-casing coupling system is developed. • The effects of typical parameters on the vibration of the system are discussed. • The mechanism of the comprehensive stiffness and system vibration is revealed. This paper focuses on the vibrational properties of a dual rotor-casing coupled system with nonlinear clearance in the intermediate bearing, considering both the oil film stiffness and Hertzian contact stiffness between rolling elements and raceways. A comprehensive stiffness model for the intermediate bearing has been developed based on elastohydrodynamic lubrication (EHL) and Hertz contact theory. Subsequently, a dynamical model of the dual rotor-bearing-casing system is established using the finite element method, thereby verifying the feasibility of simulating the casing with beam elements. The dimensionality of the system equation is reduced using the fixed-interface component mode synthesis (CMS) method, and the resulting reduced-dimensionality equation is solved using the improved Newmark- β method. The effects of casing support, rotational speed, and radial clearance on the vibration characteristics of the system are investigated. Then, the comprehensive stiffness and coupled vibration characteristics of the system are analyzed to elucidate its intrinsic mechanism. Finally, the contact characteristics within the intermediate bearing under dynamic load are also studied. The results indicate that the support stiffness of the casing has a more significant impact on the second resonance caused by both the inner and outer rotors. The system is prone to experiencing varying compliance (VC) resonance at low rotational speeds. The excessive bearing clearance leads to complex vibrational characteristics of the system, making it challenging to predict its motion. The impact of minor changes in stiffness on system vibration is small when the comprehensive stiffness is large. At this time, the limited effect of oil film stiffness allows it to be disregarded in terms of comprehensive stiffness. Furthermore, the speed significantly influences the contact characteristics within the intermediate bearing under the unbalanced force of the rotor and gravity. [ABSTRACT FROM AUTHOR]

In this paper, the coupling effect between the crankshaft torsional vibration and the low speed diesel engine block vibration is investigated. Using finite element method (FEM), a model of low speed diesel engine is established to study the vibration response. The mode results of FEM agree very well with the test. The additional torques acting on the low-speed diesel engine caused by torsional vibration are discussed in detail. The vibration response of the low-speed diesel engine considering the effect of torsional vibration is studied using FEM simulation. By analyzing the effect of torsional vibration, the results demonstrate that the crankshaft torsional vibrations have important effects on the engine block vibration. The results from this study can provide useful theoretical guidance to predict vibration of low-speed diesel engine. [ABSTRACT FROM AUTHOR]

In this paper, free vibration and transmission properties of single and composite thin annular plate (TAP) structures are presented by wave approach. The propagation matrix, continuity matrix and reflection matrix are introduced to carry out the analysis. Using the wave approach, natural frequencies of single and composite TAP are calculated theoretically. The results obtained by this method agree well with those calculated by the classical Bessel and Hankel methods. Additionally, transfer matrix is introduced and combined with the boundary conditions to obtain the transmission behaviors of composite multilayer TAP. To thoroughly understand the composite TAP, the influences of thickness, density ratio and radius ratio on natural frequencies are investigated. This study provides very useful information for transverse vibration suppression of TAP structure. [ABSTRACT FROM AUTHOR]

Planetary gears are one part of the whole transmission chain, and the dynamics and vibration characteristics of them are strongly coupled with external rotors. In this paper, to demonstrate the interaction between multistage planetary gears and external rotors as well as investigate the lateral-torsional coupling characteristics of them, a coupling model of a two-stage planetary gear rotor system is proposed. In such a model, the two-stage planetary gear subsystem is established as a lumped-parameter model and the external rotor subsystem is established as a finite element model. The vibration mode distribution properties and lateral-torsional coupling characteristics are both analyzed by modal strain energy. Three different conditions are considered: uncoupled, partially coupled, and fully coupled. The results indicate that the coupling among multiple subsystems and the lateral-torsional coupling mainly exist in the low-mode region. Natural frequencies dominated by the two-stage planetary gear subsystem are sensitive to coupled conditions, whereas natural frequencies dominated by the input rotor subsystem are remarkably insensitive to coupled conditions. Furthermore, the natural frequency of the first torsional mode can be obtained only in the fully coupled condition. Experiments are implemented to obtain natural frequencies, and the experiment results validate the numerical results. [ABSTRACT FROM AUTHOR]

Radial vibration of the circular plate is presented using wave propagation approach and classical method containing Bessel solution and Hankel solution for calculating the natural frequency theoretically. In cylindrical coordinate system, in order to obtain natural frequency, propagation and reflection matrices are deduced at the boundaries of free-free, fixed-fixed, and fixed-free using wave propagation approach. Furthermore, radial phononic crystal is constructed by connecting two materials periodically for the analysis of band phenomenon. Also, Finite Element Simulation (FEM) is adopted to verify the theoretical results. Finally, the radial and piezoelectric effects on the band are also discussed. [ABSTRACT FROM AUTHOR]

A class of radial phononic crystals (RPC) is generated by periodically placing the piezoelectric material (PZT-4) on the base plate along the radial direction. Torsional vibration transmissibility inwards through an RPC's plate is studied. Afterwards, the homogeneous material plate case is also computed for comparison. The obtained results are verified by finite element simulation. Both numerical results and finite element simulation results show that a single band is obtained in the piezoelectric RPC, but in the uniform base RESIN plate, the result shows that it forms a wide band which almost covers the whole frequency range. The effect of an external shunting circuit on the vibration band is studied as well. The results show that, in the low frequency range, the shunting resistance plays an important role in weakening this local resonant band. Investigating the influence of inner radius and span ratio of PRC's plate on the wave band shows that varying the inner radius or the span ratio of PRC's plate will affect the Bragg and local resonant band greatly. By setting structural parameters properly and controlling external circuit parameters effectively, the band becomes wider and attenuates faster. Hence, such band can be controlled reasonably. It is important in the torsional vibration control for composite structures consisting of shaft and gear. [ABSTRACT FROM AUTHOR]

• A fracture failure of a marine diesel engine timing gear is investigated in detail. • Both experimental and numerical investigations are performed. • Influence of associated structures is considered while analyzing the fracture. • Two models, one is with inclusion and the other is non-inclusion, are constructed. • Results indicate the fracture is a fatigue fracture and is caused by the inclusion. In this paper, a fracture failure of a marine diesel engine timing gear in a chemical tanker was investigated in detail using both experimental analysis and numerical analysis. The experimental analysis includes macroscopical inspection, Scanning Electron Microscope analysis, Energy Dispersive Spectroscopy analysis, metallographic investigation and mechanical property investigation. The numerical analysis includes torsional vibration analysis and finite element method (FEM) simulations. In the torsional vibration analysis, the coupling influence of the associated structures on the timing gear system was taken into account, not only analyzing the fault gear itself. In the FEM simulations, two models, one is with inclusion and the other is non-inclusion, were constructed. Both investigations indicate that the fracture is a fatigue fracture and the initial cracks are caused by the inclusion. Further investigation should pay attention to finding a way to overcome the problem of fatigue fracture. [ABSTRACT FROM AUTHOR]