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REDUCTION OF

HELICOPTER GEAR

MESHING NOISEReduction of 2192 Hz gear meshing frequency

noise in the helicopter

Noise in Helicopter cabin comes from transmission of

sound from the wall of cabin and is also radiated by dipoles

in the walls .

E64221

11/24/2014

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Valutazione del trasferimento delle potenze acustiche indotte dalla

trasmissione principale verso la cabina dell elicottero

Comprensione del modello di trasferimento di tali potenza ( analisi da

bibliografica ) ed implementazione di un algoritmo di calcolo mediante

supporto di attivit sperimentale dedicata

Preparazione della specifica di testing delle Trasmissioni mirata alla

determinazione dei parametri a supporto del metodo .

1. Studio della bibliografia esistente

2. Mesa a punto di una metodologia di trasmissione acustica delle potenze

3. Implementazione dellalgoritmo di calcolo

4. Preparazione di una modalit sperimentale di acquisizione dei parametri

fondamentali a supporto dellalgoritmo di predizione

5. Report di consuntiva dellalgoritmo e report della specifica di prova del

banco trasmissione

Evaluation of the transfer of acoustic powers introduced from the

transmission system to the main cabin of helicopter

Understanding the pattern of transferof such power (bibliographic analysis)

and implementation of an algorithm using support experimental work

dedicated

Preparation of specific testing of transmissions targeted to the determination

of the parameters in support of the method.

1. Study of the existing bibliography.

2. Development of a methodology for acoustic transmission powers

3. Implementation of the algorithm

4. Preparation of an experimental mode of acquisition of the basic parameters

in support of the prediction algorithm

5. Reports consecutive algorithm and report on the specific test benchtransmission

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AW139 :

Source Descriptor Model : The audio frequency vibration of gearbox are generated by

internal excitation forces from gear meshing and bearing forces and these vibration energy

is being transmitted via connection of transmission system gearbox to the airframe

structure . The exact analytical description of vibration of gearbox is complex due to

unknown distribution of internal excitation forces . A convenient model of vibration of

gearbox and transmission of vibratory power to airframe structure is SOURCE DESCRIPTION

MODEL , a simple multimodal system composed of a finite length source beam as depicted

in figure and connected to a receiving infinite length beam via two springs .

Flexure Wave :

consider a element at location x,y of dimension dx and dy

transverse displacement in y direction

= Transverse velocity of the element= Rotation of plane about z azis of the element= Rotational velocity about z axis

Moment about z axis Radius of curvature =

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The Kinetic energy associated with this bending motion is neglected in comparison with translationmotion as long as bending wavelength is large compared to cross section dimension .

S = square cross section of area :

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The solution for infinite beam , exited at x = : ( )

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No rotation at x =

Taking on wave propagating towards positive x , x = 0 to

*| | | |+

*|

| |

|+

* +

* + * +

* +

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* + * +

* +

* +

[

] [

] * + * + * +

* + * +

Rotational rigid body mode : Translational rigid body mode : ................. for r 1

The

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Approximation for r > 7 is krl = ( 2 r + 1 ) / 2 is correct with in 10 digits

The wave number k is related to by

A is the cross section of beam

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