Patent ID: 8548780
Filing Date: 2013-10-01
Classification: F01D,F16C,G01H

Abstract:
1. A method for predicting dynamic behavior of an aircraft structure, the aircraft including at least one dimensioning rotating device, whose effect on at least one part of the aircraft structure is to be evaluated, each dimensioning rotating device including one or more rotors, of which at least one rotor is guided in rotation by at least one fixed-bracket bearing, which is provided with a fixed bearing bracket, a conjugate bearing cage inserted inside the bearing bracket and a fluid damping film, confined between the bearing cage and the bearing bracket, the method comprising: using a numerical global model of the aircraft structure, which comprises, for each dimensioning rotating device, a numerical basic model of the dimensioning rotating device furnishing at least vibration frequency of one rotor of the dimensioning rotating device according to a speed of rotation of the rotor and of perturbations undergone by the rotor; creating for each fixed-bracket bearing a non-linear numerical model of the damping film of the bearing; integrating, for each dimensioning rotating device, the model of the damping film of each fixed-bracket bearing of the dimensioning rotating device in the basic model of the dimensioning rotating device to form a numerical model with film, of the dimensioning rotating device in the global model; applying, in the global model, perturbations to at least one rotor of at least one dimensioning rotating device; and calculating, by the global model, the vibration frequency of at least one rotor of each dimensioning rotating device and the corresponding frequency of the vibrations induced in a part of the aircraft, wherein, to form the model with film of each dimensioning rotating device: a model with damping of the dimensioning rotating device, capable of furnishing the vibration frequency of at least one analyzed rotor, of the dimensioning rotating device and the eccentricity of each fixed-bracket bearing of this rotor according to the speed of rotation of the analyzed rotor is used, the model with damping being formulated from the basic model of the dimensioning rotating device so as to simulate linear damping at least at each of the fixed-bracket bearings of the analyzed rotor, a value with cavitation of the vibration frequency of the analyzed rotor is calculated for each speed of rotation of the rotor, in the following manner: for each fixed-bracket bearing of the analyzed rotor, the matrix of damping coefficients and the matrix of stiffnesses of the damping film of the bearing furnished by the model with cavitation of the damping film are calculated for the value of the eccentricity of the bearing established at the end of the physical verification loop, a loop of convergence of the eccentricities of the fixed-bracket bearings of the analyzed rotor is constructed on the model with damping of the dimensioning rotating device, similarly, a value without cavitation of the vibration frequency of the analyzed rotor is calculated for each speed of rotation of the rotor; to calculate the value of the vibration frequency of the analyzed rotor for each speed of rotation of the rotor, a percentage of the value with cavitation of the previously calculated vibration frequency and a complementary percentage of the value without cavitation of the previously calculated vibration frequency are added.