Abstract: An aerofoil assembly, for example a bladed rotor assembly (40B) comprises a rotor (42) carrying a plurality of rotor blades (44), at least one of the rotor blades (44) having a coating (46) on the surface of the rotor blade (44). At least one of the rotor blades (44) has a coating (46) having a different thickness, a different area of contact with the surface of the rotor blade (44), a different position of contact on the surface of the rotor blade (44), a different shape of contact on the surface of the rotor blade (44) and/or a different composition compared to at least one of the other rotor blades (44). The coating (46) is applied in a non-uniform manner to reduce the vibration level of the rotor blade (44), or rotor blades (44), with the highest vibration response for a given excitation by changing the bladed rotor assembly (40B) mode shapes and the relative vibration of the rotor blades (44).

Abstract: A method of resolving vibration behaviour of a rotor assembly having a plurality of rotor blades. The method including generating a computational model of the rotor by discretization of the rotor geometry and assigning parameter values representative of a plurality of physical characteristics of the rotor. An artificial parameter feature is applied to each rotor blade such that the parameter values for the artificial parameter feature substantially depart from the physical characteristics of the rotor. A vibration response is calculated for the rotor or blade thereof for the applied artificial parameter features and compared to a predetermined vibration response so as to determine a value of the artificial parameter feature which results in a calculated vibration response that substantially matches the predetermined vibration response.

Abstract: A method which permits the transformation of non-stationary response measurements into stationary data for analysis is provided. Many standard analysis techniques, particularly for oscillatory responses, are based on stationary data, and the method allows these techniques to be performed on originally non-stationary data. The method may be a method of processing oscillatory response data from a resonant system including: obtaining data measuring an oscillatory response of the system; estimating the variation in natural frequency of a mode of said response; filtering the data around a selected frequency to obtain a filtered response; determining a carrier signal whose frequency variation with respect to time is equal in magnitude to said estimated variation in natural frequency; and modulating the amplitude of said carrier signal using said filtered response to obtain a modulated carrier signal. A corresponding system for processing oscillatory response data is also provided.

Abstract: A method which permits the transformation of non-stationary response measurements into stationary data for analysis is provided. Many standard analysis techniques, particularly for oscillatory responses, are based on stationary data, and the method allows these techniques to be performed on originally non-stationary data. The method may be a method of processing oscillatory response data from a resonant system comprising: obtaining data measuring an oscillatory response of the system; estimating the variation in natural frequency of a mode of said response; filtering the data around a selected frequency to obtain a filtered response; determining a carrier signal whose frequency variation with respect to time is equal in magnitude to said estimated variation in natural frequency; and modulating the amplitude of said carrier signal using said filtered response to obtain a modulated carrier signal. A corresponding system for processing oscillatory response data is also provided.

Abstract: A method of processing oscillatory response data from a resonant system includes: obtaining data measuring an oscillatory response of the system at a plurality of evenly spaced time intervals; obtaining a plurality of reference frequencies from the data at a plurality of times in the data, each reference frequency preferably being the natural frequency of a mode of the response at the respective time or an estimate of the natural frequency; and transforming the data to an uneven data set having unevenly spaced time intervals by adjusting the evenly spaced time intervals according to the values of the measured reference frequencies. The method can transform non-stationary response data to make it effectively stationary, and thus in a more useful form for further analysis. A method of analysing a resonant system and an apparatus for processing oscillatory response data are also provided.

Abstract: An aerofoil assembly, for example a bladed rotor assembly (40B) comprises a rotor (42) carrying a plurality of rotor blades (44), at least one of the rotor blades (44) having a coating (46) on the surface of the rotor blade (44). At least one of the rotor blades (44) has a coating (46) having a different thickness, a different area of contact with the surface of the rotor blade (44), a different position of contact on the surface of the rotor blade (44), a different shape of contact on the surface of the rotor blade (44) and/or a different composition compared to at least one of the other rotor blades (44). The coating (46) is applied in a non-uniform manner to reduce the vibration level of the rotor blade (44), or rotor blades (44), with the highest vibration response for a given excitation by changing the bladed rotor assembly (40B) mode shapes and the relative vibration of the rotor blades (44).

Abstract: An adaptive control method is provided with particular relevance in methods which use a varying input frequency for analysis of an oscillatory response of a system, such as sine sweep testing. In one aspect the method includes the steps of applying a drive force having at least one sinusoidal component to said system, the frequency of the sinusoidal component being changed with time; and measuring an oscillatory response of said system; the method further including the step of providing a control signal based on at least a comparison between the frequencies of the sinusoidal component and the oscillatory response, wherein the rate at which the frequency of the sinusoidal component is changed is adjusted according to the control signal, so as to adapt the rate of frequency change to the region of the response spectrum being analyzed. A test apparatus capable of carrying out the methods of the invention is also provided.

Abstract: A method of processing oscillatory response data from a resonant system is provided, the method comprising: obtaining data measuring an oscillatory response of the system at a plurality of evenly spaced time intervals; obtaining a plurality of reference frequencies from said data at a plurality of times in said data, each reference frequency preferably being the natural frequency of a mode of the response at the respective time or an estimate of said natural frequency; and transforming said data to an uneven data set having unevenly spaced time intervals by adjusting said evenly spaced time intervals according to the values of said measured reference frequencies. The method can transform non-stationary response data to make it effectively stationary, and thus in a more useful form for further analysis. A method of analysing a resonant system and an apparatus for processing oscillatory response data are also provided.

Abstract: A method of monitoring engine order forcing frequency comprises the steps of: selecting at least one engine order for an engine, the engine order being related in a known manner to one or more engine vibration responses generated by the forcing of the engine order; receiving measurement data which provide a measure of the change in the frequency of the or each vibration response as the engine speed varies, and calculating therefrom the change in the engine order forcing frequency; and determining, on the basis of the calculated change in the engine order forcing frequency, a corresponding change in at least one second engine order forcing frequency for the engine as the engine speed varies.

Abstract: An adaptive control method is provided with particular relevance in methods which use a varying input frequency for analysis of an oscillatory response of a system, such as sine sweep testing. In one aspect the method includes the steps of applying a drive force having at least one sinusoidal component to said system, the frequency of the sinusoidal component being changed with time; and measuring an oscillatory response of said system; the method further including the step of providing a control signal based on at least a comparison between the frequencies of the sinusoidal component and the oscillatory response, wherein the rate at which the frequency of the sinusoidal component is changed is adjusted according to the control signal, so as to adapt the rate of frequency change to the region of the response spectrum being analysed. A test apparatus capable of carrying out the methods of the invention is also provided.

Abstract: Method for Monitoring Engine Order Forcing Frequency A method of monitoring engine order forcing frequency comprises the steps of: