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.
Highlights
Ere are many researches on the basic excitation
The mechanical isolation model subjected to basic excitation and its motion equation are developed, and its dynamic responses are mainly investigated by using the techniques of displacement response, frequency spectrum, rotor orbit, Poincaremaps, and the bifurcation diagram
An investigation into the nonlinear dynamic behavior of the mechanical isolation system coupled with air-bag and floating-raft under lateral basement excitation is presented
Summary
Due to the low frequency vibration of ship hull and other power machinery equipment, mainly motor or diesel engine and other power equipment, the form of its vibrations is mainly harmonic vibrations [20]. It is well known that any form of excitation can be converted into harmonic excitation by the FFT technique; basement motions in this paper are considered as harmonic motion S(t) driven by the angular frequency Ω1 and Ω2 in the longitudinal and transverse directions, respectively, and by considering the coupling effects between the excitation source and isolation system, the mechanical model of rotating machinery under base excitation is established. Where Fx and Fy are the nonlinear oil film forces components of journal bearing in the x and y direction, respectively. E motion styles of system under the unbalanced excitation and basement excitation are complex, where η1 and η2 are the dimensionless vibration frequency in the vertical and horizontal direction and φa and φb are the dimensionless excitation amplitude, respectively. Equation (10) could be discussed on the state space, and the four second-order equations can be converted into eight first-order ones and the equation of motion governing the behavior of the mechanical isolation system can be written as equation (12)
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