Nonlinear Dynamics of Marine Rotor System Coupled with Air Bag-Floating Raft Subjected to the Basement Excitations in Lateral Directions

Abstract

This paper presents an investigation into the nonlinear dynamic behaviors of the mechanical isolation system coupled with air-bag and floating-raft subject to basement excitation in lateral directions. First, the coupling effects between the excitation source and isolation system are considered. Also, the mechanical isolation model under basic excitation and its motion equation are deduced, and then the dynamic responses are mainly investigated by using the techniques of displacement response, frequency spectrum, rotor orbit, Poincaré maps, and the bifurcation diagram. Last, the bifurcations of the mechanical isolation system with different parameters are analyzed through numerical methods, especially the effect of excitation frequency and amplitude. The result predicts that period-5 is mainly performed, with the increase of rotor speed, and the system moves into quasi-bifurcation. However, the system stays in chaos state at high rotor speed, and the vibration amplitude rises rapidly until against bearing bush. Furthermore, the effects of basement excitation on the mechanical isolation system are mainly concentrated on the stage of lower rotor speed, but with the increasing speed, the effects become weak and at the same time the vibration amplitude reduces significantly. The points projected on the Poincaré section are five, three, or two solitary attractors, in which the system stays in periodic motion. Above all, the dynamic characteristics can provide the theoretic supporting for the dynamic, vibration control and its parametric optimization of the marine mechanical isolation system coupled with air-bag and floating-raft.

Dynamics of on-board rotors on finite-length journal bearings subject to multi-axial and multi-frequency excitations: numerical and experimental investigations

“…The shaft is discretized into 27 beam finite elements, as shown in Figure 3. The shaft radius is 6.35 mm for the FEs 4 to 24 and 6 mm for the FEs (1,2,3,25,26,27). In order to model the shaft local stiffening due to the tightening of the disks on the shaft, angular stiffness coefficients of 100 N.m/rad are added to the coefficients related to the DOFs ψ and θ of Nodes 9 and 21 in the structural stiffness matrix K of equation (1).…”

“…Sousa et al [22] and Stanica et al [23] carried out several numerical investigations such as the analysis of the influence of a constant support rotation on the variation of critical speeds. Other simplified models have been developed recently to assess the impact of the wave motions on the engine rotors of maritime vessels [24,25].…”

“…Nevertheless, most of the works remain numerical, with assumptions that are often far from those occurring in real industrial systems. This is the case for instance with the papers devoted to journal bearings [5,[10][11][12][13]24,25] which exploited the short bearing hypothesis so as to use analytical solutions of the Reynolds equation and thus facilitate the numerical investigations. Furthermore, the base excitations were still too restricted to mono-axial and mono-frequency cases as well as limited to the shaft bending dynamics without accounting for the axial and torsional effects [5,[7][8][9][10][11]14].…”