RU2238595C2 - Method of spatial rejection of noise of revolving propeller in preset direction - Google Patents

Abstract

FIELD: physical and technical acoustics; directed sources of sound.

SUBSTANCE: for creation of zero in noise directivity characteristic of revolving propeller in direction φ ₀ , propeller thrust P _pr.0 is created at number of revolutions n ₀ per second and torque M _t.0 according to ratio indicated in Service Log.

EFFECT: enhanced efficiency.

2 cl, 4 dwg

Description

The invention relates to the field of physical and technical acoustics, and more particularly to directional sound sources.

In technical acoustics, in many cases, the problem arises of controlling the directivity of the sound emitter in such a way that there is no sound radiation in a selected direction. It seems necessary to solve such a problem for the sound created by a rotating screw, in particular, for fan installations.

Basically, methods of forming zero in the directivity characteristic in a given direction are known for the reception and emission modes. All these methods are based on a specific effect on individual elements of the receiving and emitting devices. However, they are not suitable for controlling the directional characteristic of a rotary screw, since Direct impact on screw elements is not possible.

A known method of forming the so-called "difference" directional characteristics (A.M. Tyurin. A.P. Stashkevich, E.S. Taranov, Fundamentals of hydroacoustics. L .: Shipbuilding, 1966. - 186). This method comprises dividing the hydroacoustic antenna into two equal parts and subtracting the signals between these "halves" of the antenna. In this case, a zero is formed in the directivity characteristic.

This method - an analogue is not suitable for creating zero in the sound created by the screw. In addition, zero in the difference directivity characteristic is formed in only one direction, perpendicular to the aperture of the hydroacoustic antenna.

The known method of "Creating zero in the radiation pattern to attenuate unwanted interfering signals" (US patent No. 4214244). This analogue method comprises receiving signals by an antenna array and generating an amplitude-phase distribution in the received signals before summing them up for spatial rejection in a selected direction.

This analogue method is not suitable for creating zero in the noise of the propeller.

A known method implemented in the "System for generating a radiation pattern of an antenna array with zero gain in a given direction" (US patent No. 3503069). This analogue method includes receiving signals by an antenna array, amplifying signals from each receiver, generating an amplitude-phase distribution prior to summing to form zero in a given direction.

The disadvantage of the analogue method is the inability to use it to form zeros in the screw noise in a given direction.

The known method implemented in the "Device for forming zero in the region of the side lobes of a mirror antenna" (Germany patent No. 203183). The method consists in moving the receiver in the focal plane of the antenna and subtracting the signal from another fixed receiver.

The disadvantage of the latter method is the impossibility of this way to form zero in the noise characteristic of the propeller.

The objective of the proposed method is to perform operations to generate zero in the directional characteristic of the noise of the propeller in a given direction.

The proposed method of creating zero in the noise of a rotating screw in a given direction φ ₀ contains the selection of the propulsive force of the screw P _in , the number of revolutions n _{0 of the} screw per second and the torque M _{cr, about} according to the ratio

where C ₀ is the speed of sound in the medium in which the screw rotates,

R _e - equivalent radius of the screw, approximately equal to 0.7 R,

where R is the radius of the screw,

z is the number of propeller blades.

In an aqueous medium, the method comprises, for forming zero in a given direction φ _0, selecting the total power T ₀ supplied to the screw and selecting the screw speed n ₀ per second according to the relation

where η is the propeller efficiency.

, поскольку скорость движения судна пропорциональна кубу числа оборотов винта.From this formula it is clear that you want to choose the speed of the vessel according to

since the speed of the vessel is proportional to the cube of the number of revolutions of the screw.

The technical result of the proposed method is the possibility of deformation of the noise directivity characteristics of the rotary screw in such a way that the noise of the rotary screw is spatially cut in the desired direction.

To justify the cause-effect relationships between the essential features and the desired result, we give the necessary evidence.

As shown in the book of V.M. Bomova, D.D. Plakhova, V.E. Yakovleva. "Acoustic noise and interference on ships." - L .: Shipbuilding, 1984. -s, 48, rotation noise arises due to the static and dynamic imbalance of the propeller in the water and due to the influence of heterogeneities of the water flow within the propeller disk. The propeller sections are differently surrounded by water during the movement of the vessel, and each blade periodically during one turn of the screw is in the area with increased and reduced speeds of water relative to the vessel. These reasons lead to the fact that m harmonic frequencies that are proportional to the product of the number of blades z and the angular frequency of rotation n, the number of revolutions per second, are clearly distinguished in the noise spectrum of the propeller

According to the work of L.Ya. Gubina "On the sound field of a rotating screw" - ZhTF, t.6. issue 2-3, 1942, the sound pressure created by a rotating screw has the form

where are indicated:

P _in - propeller traction force,

With ₀ - the speed of sound in the aquatic environment,

r is the distance between the center of rotation of the screw and the observer,

φ is the angle between the axis of rotation of the screw and the direction of

observer

M _cr - torque

_Imz is a Bessel function of the first kind.

Obviously, in the direction of φ _{о, the} acoustic pressure is zero, Р _m (φ _o ) = 0, and for all harmonics, if

Then, the last expression for n _o ; P _{b, o} ; M _{cr, about} can be rewritten in the form, substituting the value of P _{b, about} from the expression (3):

For the main first harmonics m that prevail in the noise of the rotor

Therefore, one can use the expansion of the Bessel function in a series

and confine ourselves to the first term of decomposition

Then expression (4) can be written as

, тоIf normalized to

then

Then the directivity characteristic of the screw noise at selected P _{b, o} ; n is ₀ ; M _{cr, o} for spatial rejection of noise in the direction φ _o , can be written as

It can be seen that the directivity characteristic is deformed in such a way that for φ _о there is a zero value for all harmonics m, B (φ, φ _o ) = 0, i.e. spatial noise rejection in the direction of φ _about .

Thus, the desired result is achieved. A particular characteristic for a propeller in an aqueous medium can be justified as follows. The dependence of the traction force Р _В on the power T supplied to the screw is determined by the relation [L.Ya. Gubin. On the sound field of a rotating screw, - ZhTF, t.6, issue 2-3, 1942]

where ρ is the density of the marine environment.

Motor torque

where is the angular speed of rotation of the motor

Substituting (II), (12), (13) and the values of the speed of sound and water density in the formula (3), we find

Thus, for a particular feature, causal relationships with the desired result are justified.

In addition to the noise of rotation of the screw, there is the so-called volumetric noise, but it is much smaller than the noise of rotation and is neglected.

The invention is illustrated by examples in Fig 1-4.

Figure 1 shows the characteristic directivity of the noise of the propeller for the first mode (m = 1) when zero is formed in the direction φ _о = 85 °.

Figure 2 shows the characteristic directivity of the noise of the propeller for the third mode (m = 3) when forming zero in the direction φ _o = 85 °.

Figure 3 shows the characteristic directivity of the noise of the propeller for the second mode (m = 2) when forming zero in the direction φ _about = 40 °.

Figure A shows the characteristic of the directivity of the noise of the propeller for the fourth mode (m = 4) when zero is formed in the direction φ _о = 45 °.

It can be seen from the above examples that the spatial noise rejection of the propeller is carried out for all modes, but the directional characteristics of the modes are deformed in different ways.

The implementation of the method is achieved by selecting the input power and the number of revolutions of the propeller according to the proposed method. Ultimately, this leads to a change in the speed of the vessel.

Thus, the proposed method is technically feasible.

Claims (2)

1. The method of spatial rejection in a given direction of the noise of a rotary screw, characterized in that to create a zero in the directional characteristic of the noise of the rotary screw in the direction φ _о create a thrust force of the screw P _{in, about} , the number of revolutions of the screw n _o per second and the torque M _{cr .o} according to the relation

where C _about - the speed of sound in the medium in which the screw rotates; R _e is the equivalent radius of the screw, approximately equal to 0.7R, where R is the radius of the screw; Z is the number of propeller blades. 2. The method of spatial rejection in a given direction in the noise of a rotating screw according to claim 1, characterized in that to create zero in the noise of a rotating screw in an aqueous medium in the direction φ _о , the total power T _о and the number of revolutions of the screw per second n _o according to the ratio

where η is the propeller efficiency.

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