Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Mechanical measurement system
Reexamination Certificate
2000-12-07
2002-12-31
Hilten, John S. (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Mechanical measurement system
C342S203000, C342S204000, C702S076000, C340S946000
Reexamination Certificate
active
06502043
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process and device for reducing the spectral line noise inside an aircraft, especially a rotating-wing aircraft, and in particular a helicopter.
More particularly, it applies to the reducing of the noise in the cockpit and/or in the passenger cabin of said aircraft.
It is known that, on a rotating-wing aircraft, the acoustic spectra defined in the domain lying between 20 Hz and 20 kHz pertain to the superposition of noises of different origins, which can be clustered into two different groups depending on their spectral characteristics, namely pure sounds or spectral line noises and broadband noises.
In a known manner, pure sounds or spectral line noises occur especially, as the case may be:
at characteristic frequencies of the kinematic chain of the aircraft;
at the frequencies of rotation of the blades of the rotors (main and rear) and at the harmonics of these frequencies;
at the frequencies of rotation of the blades of the compressors of the turbomotor sets; and/or
at the frequencies of rotation of the blades of the fans for cooling the main gearbox and/or of electrical equipment, as well as at the harmonics of these frequencies,
while broadband noises comprise especially as the case may be:
noise from a boundary layer developing on the fuselage;
noise generated by the rotors;
noise from the flow in the air inlets and nozzles;
engine noise; and/or
noise from the air conditioning or heating circuits of the cockpit or of the passenger cabin.
Although all these noises may pose problems, the acoustic annoyance experienced by the passengers and the crew is caused essentially by spectral line noises. Consequently, the main object of the present invention, which reckons to limit this acoustic annoyance, is to reduce said spectral line noises.
There are various known solutions for reducing such noises inside a rotating-wing aircraft, especially a helicopter.
A first known solution has the object of reducing the vibratory level of or the radiation from noise sources and/or the fuselage. For this purpose, various physical actions may be implemented, especially:
a reduction in the vibrations of the structure and/or mechanical members, by damping or modifying the stiffness or the mass;
an attenuation in the acoustic transmission, by damping or modifying the stiffness or mass;
a double-partition effect, by shrouding the relevant source;
acoustic absorption by fibrous or cellular materials; and
acoustic absorption by Helmhotz resonators.
The first four physical actions above make it possible to decrease the general level of noise in a wide domain of frequencies, but they entail a considerable and very disadvantageous increase in mass. Moreover, the noise decrease then obtained is not selective enough to dispose of the acoustic annoyance specific to pure sounds.
On the other hand, the fifth and last physical action above makes it possible effectively to reduce the spectral line noise, although only in a narrow band of frequencies, defined during the design.
This above first solution based on passive processing of the noise is therefore hardly effective, especially for spectral line noises generated by vibratory or acoustic excitations dependent in particular on the rotation regime, prone to variations as a function of time, of rotating machines.
A second known solution advocates active noise control.
The document WO-98/06089 discloses a system for actively controlling noise and vibrations in the cabin of an aircraft. This known system comprises:
sensors for measuring the values of vibratory and/or acoustic parameters representative of vibratory and/or acoustic effects of sources of noise of said aircraft;
reference sensors for measuring the values of reference parameters;
active and controllable vibration absorber means which are able to reduce the vibratory and/or acoustic effects of said sources of noise; and
a main computer determining, on the basis of the values measured by said sensors and said reference sensors, control commands for said vibration absorber means, with a view to reducing the noise and the vibrations inside said aircraft.
Another example of active control is described in the document FR-2 732 807 which discloses a personal process and a personal device for acoustic attenuation. This known document envisages an attenuator assembly which comprises sensors and loudspeakers arranged in proximity to the head of a passenger of an aircraft. These loudspeakers are intended to create counter-noises in order to attenuate the noises existing in proximity to the head of the passenger, by combining with these noises.
This attenuator assembly thus only allows individual and very localized attenuation of the noise in proximity to a passenger's seat.
This known device has numerous drawbacks. In particular:
it requires a number of loudspeakers and of microphones which is proportional to the number of seats for which one wishes to carry out acoustic attenuation, this proving to be expensive, bulky and penalizing in terms of mass, in particular for large cabins;
a loss of available volume in the cabin occurs; and
it is necessary to adapt the existing seats, this of course being expensive.
Consequently, this known solution, which is based on active processing which is both localized and individual, is hardly satisfactory for reducing the spectral line noise in a rotating-wing aircraft furnished with a large cabin which may contain a plurality of pilots and passengers.
The document FR-2 769 396 from the applicant describes a device making it possible to remedy these drawbacks. This known device is a device of reduced mass, cost and bulk making it possible effectively to decrease, in a substantially global and nonindividual manner, the noise, and more particularly the spectral line noise, inside a rotating-wing aircraft. For this purpose, this known device comprises:
sensors for measuring the values of at least one vibratory and/or acoustic parameter representative of a vibratory and/or acoustic effect of at least one source of noise of said aircraft;
controllable mechanical means able to create a loading capable of reducing the vibratory and/or acoustic effect of said source of noise; and
a control unit, for controlling said mechanical means, as a function of the values measured by said sensors.
In a particular embodiment, this known device comprises P sensors Cp arranged at points Mp and capable of measuring one and the same vibratory and/or acoustic parameter, and Q mechanical means Aq able respectively to create loadings capable of reducing one and the same vibratory and/or acoustic effect, and the control unit carries out, repetitively, the following successive operations:
it calculates, for each of said P sensors Cp, a value P
1
p
satisfying the relation:
P
1
p=P
2
p+&Sgr;q
(
Tq,p.P
3
q
),
q varying from 1 to Q,
in which:
P
2
p
corresponds to the value of said vibratory and/or acoustic parameter which exists at the point Mp in the absence of action of said device and which depends on the value measured by the sensor Cp;
P
3
q
is the value of said vibratory and/or acoustic parameter, due to the action of the mechanical means Aq and dependent on the control of said mechanical means Aq; and
Tq,p is a value for transferring between the value of said parameter existing at the level of the mechanical means Aq and the corresponding value existing at the point Mp;
it calculates the sum:
&Sgr;
p|P
1
p|
2
,
p varying from 1 to P; and
it minimizes the above sum so as to deduce therefrom the control commands for said Q mechanical means Aq, which are addressed to these latter.
Consequently, this known device which can be adapted to the flight conditions, by controlling for this purpose said mechanical means, carries out in particular global attenuation, that is to say at least over the set of P controlled sensors, and not individual attenuation like the device described in the document FR-2 732 807, and is therefore particularly effective.
SUMMARY OF THE INVENTION
The object of the pre
Bhat Aditya S
Eurocopter
Hilten John S.
Stevens Davis Miller & Mosher LLP
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