RU2282160C2 - Method of measuring input complex acoustic impedance - Google Patents

Abstract

FIELD: mechanical engineering acoustics.

SUBSTANCE: method comprises exciting sound wave by means of the vibration source and measuring sound pressure and phase difference between the sound pressures in the first and second cross sections of the pipeline which are at a distance one from the other. To obtain the dependence of the impedance on frequency, the analyzing frequency or frequency of the vibration source are varied.

EFFECT: enhanced precision.

2 cl, 1 dwg

Description

The invention relates to engineering acoustics and can be used to determine acoustic characteristics, in particular impedance, various hydraulic devices, such as pumps and piping systems.

A known method of measuring the input complex acoustic impedance by the method of standing waves in the so-called Kundt pipe [Skuchik E. Fundamentals of acoustics, M., 1958, v. 1, p. 150], based on the search for a node and antinode of a standing wave. When the frequency of the sound signal changes, the node search procedure and the antinodes of the standing wave are repeated. However, this method requires placement in the pipe of a movable receiver of sound pressure, which is not feasible for pipes filled with liquid.

A known method of measuring the input complex acoustic impedance of a vane pump using a system of two piston emitters [A.S. USSR No. 1560800. IPC 5 F 04 B 51/00 1977]. When the phase relationship of the radiation is changed, an antinode and a node of the standing wave are achieved at the installation site of the sound pressure sensor. After that, acoustic impedance is determined by the calculation formulas. With a very controversial methodology for obtaining the initial data for calculating the impedance, the known method requires a cumbersome mechanical device for adjusting the phase difference of the working emitters. Moreover, the measurement process takes a very long time, since the measurement at each frequency requires careful tuning of the emitters: first at the antinode of the standing wave, and then at its node.

The objective of the present invention is to obtain the values of the real and imaginary parts of the acoustic impedance to predict the resonant frequencies of the column of the pumped medium in the complex "pump-system" or "fan (compressor) -system". For reliable forecasting of resonant frequencies, it is necessary to separate, for example, in a test bench, to measure the complex acoustic impedance of a working pump and measure the complex acoustic impedance of a real system.

The drawing shows a diagram of a device for implementing the method of determining the input impedance of a vane pump or system. The hydraulic line 1 is connected to the input of the test object 2 (pump or pipeline system). The sound emitter 3 is installed in the line 1 and is connected to the vibrating stand 4. Two sound pressure sensors 5, 6 are located between the sound emitter 3 and the test object 2.

The method is as follows. Set the required operating mode of the pump, turn on the emitter of sound vibrations 3 (in the monochromatic or noise mode of radiation) and measure the sound pressures with sensors 5, 6 and the phase difference between the indicated sound pressures. After that, either the radiation frequency (with a monochromatic radiation mode) is changed, or the frequency of the analysis of sound vibrations (with a noise radiation mode). According to the measurement results, the real and imaginary parts of the acoustic impedance are determined. In this case, the distance from the auxiliary oscillation source to the sensor at point 1 must be at least two calibers, the distance from the obstacle under investigation to the sensor at point 2 must also be at least two calibers, the frequency range for determining the acoustic impedance is determined by the following conditions:

Where:

f _min , f _max (Hz) - the lower and upper boundaries of the frequency range;

b (m) - distance between sound pressure sensors:

s (m / s) is the speed of sound in the medium filling the pipeline;

D (m) - diameter (caliber) of the pipe,

and acoustic impedance is determined from the following relationships:

Where:

- действительная и мнимая часть акустического импеданса соответственно;

- the real and imaginary part of the acoustic impedance, respectively;

ρ (kg / m ³ ) is the density of the medium filling the pipeline;

s (m / s) is the speed of sound in the medium filling the pipeline;

P ₁ , P ₂ (Pa) - sound pressure measured at points with coordinates x ₁ , x _2, respectively;

Δφ is the phase difference between sound pressures;

- волновое число;

- wave number;

f (Hz) is the frequency.

The proposed method also provides for the possibility of using the emitter 3 to excite sound waves both in the form of monochromatic and in the form of noise signals.

Application of the proposed method will allow using a simple device and for a minimum test time to obtain the values of the real and imaginary parts of the acoustic impedance necessary for:

- prediction of resonant frequencies of the column of the pumped medium in the complex "pump-system" or "fan (compressor) -system";

- studies of processes occurring in the flowing parts of the pump (fan).

Claims (3)

1. The method of measuring the input complex acoustic impedance, which consists in the fact that in the pipeline connected to the measured object, sound waves are excited using a vibration source, sound pressure is measured using sensors in the first and second sections spaced along the length of the pipe, and the real and imaginary parts of the impedance, characterized in that for determining the real and imaginary parts of the impedance when exciting sound waves and measuring sound pressures in these sections, the first of s located at a distance of at least two calibers from the source of oscillations, and the second at the same distance from the measured object, the phase difference between the sound pressures in the first and second sections is additionally measured, either the analysis frequency or the radiation frequency is changed and the measurement procedure is repeated, after why, using the measured values of sound pressures, phase differences, sound velocity and distance between the sensors, the following expressions are used:

Where

- the real and imaginary part of the acoustic impedance, respectively; ρ - (kg / m ³ ) the density of the medium filling the pipeline; s (m / s) is the speed of sound in the medium filling the pipeline; P ₁ , P ₂ (Pa) - sound pressure measured at points with coordinates x ₁ , x _2, respectively; Δφ is the phase difference between sound pressures;

- wave number; f (Hz) - frequency, moreover, the frequency range for determining the impedance is set by the following conditions:

Where f _min , f _max (Hz) - the lower and upper boundaries of the frequency range; b (m) - distance between sound pressure sensors: D (m) - diameter (caliber) of the pipe. 2. The method of measuring the input complex acoustic impedance according to claim 1, characterized in that the sound waves excite in the form of monochromatic signals. 3. The method of measuring the input complex acoustic impedance according to claim 1, characterized in that the sound waves excite in the form of a noise signal.