Dynamic Characteristics Analysis Of A Rotor System Subject To Base Excititations

Rotating machinery is subjected by unavoidable environment exciting due tocomplex working condition and external environment. Thus most of them areconsidered as on-board rotors. The aero-engine installed in a maneuvering airplane, thegas turbine installed in a ship under non-contact underwater explosions, the vehicleturbocharger installed on the ground under seismic excitation are belong to on-boardrotors. The on-board rotor systems are subject to mass unbalance exciting and frequentexternal movements of their base. This article set up two rotor models aim at studyingthe dynamic behavior of the on-board rotors and designing the method to reducevibration and shock isolation.A complex gas turbine dynamic model is proposed by finite element modelingmethod and relative coordinate, considering base movement and rotor shear effect, tostudying the dynamic characters when base is rotating at a constant speed or harmonicvibration in horizontal direction. We study the influence on critical speed, frequencyresponse and the rotor orbits in the different cases of base motions. The result showsthat the rotor keeps a non-symmetric dynamic behavior in the case of the rotor rotationaround the axial direction but has a symmetric dynamic behavior in the case of the rotorrotation around lateral direction. The base transverse simple harmonic motion has noinfluence on the basic character but has a influence on the rotor response.In order to study squeeze film damper reduces vibration and the influence of shockisolation, a rigid rotor model with nonlinear elastic bearing and squeeze film damper isproposed to studying nonlinear dynamic response, The main work and results for thismodel are as follows:Firstly, the differential equations of motion of the5degrees of freedom rotorsystem are proposed which takes into the motion in axial direction. Elastic support withcubic nonlinearity is considering, and oil film force of the squeeze film damper isobtained by using dynamic oil film force model. We analyze how the linear andnonlinear stiffness and squeeze film damper affect the rotor response.Secondly, by the orbit, the time course response, the spectrum and the poincarémap of the system response, squeeze film damper has obviously vibration dampingeffect, reduces the influence of nonlinear elastic support and the vibration amplitude,makes the orbit close to the circle, weakens the non-primary frequency, thus thevibration is close to simple harmonic motion. The base harmonic rotation induces thevibration in axis direction and the axis vibration frequency is twice as the frequency ofrotation.Finally, the base lateral shock motion has a greater impact on the right bearing, the squeeze film damper reduces the vibration amplitude. The transient impulse responsedisappears in one or two cycles and the movement restores to its original state. From thefigure of dynamic film force, the transient impulse response is different due to thedifferent shock applied timing.