Device and method for measuring sound velocity in middle-high pressure hydraulic pipeline

Abstract

The invention discloses a device and a method for measuring sound velocity in a middle-high pressure hydraulic pipeline, and relates to the technical field of measuring devices, the device comprises a driving shaft, a rotary valve, a transition end cover, a hydraulic pipeline, a first fiber grating sensor and a second fiber grating sensor; an axial output port of the rotary valve is connected with a transition end cover, and the transition end cover is connected with a hydraulic pipeline; the front end of the hydraulic pipeline is connected with a first fiber grating sensor, and the tail end is connected with a second fiber grating sensor; the rotary valve comprises a valve cover, a valve body, and a rotary valve core and a bearing which are arranged in the valve body; the driving shaft is connected with the rotary valve element, and an explosion flushing cavity and a low-pressure cavity which are isolated from each other are formed in the rotary valve element; the blasting cavity is provided with a first conical nozzle, and the low-pressure cavity is provided with a second conical nozzle; an axial output port of the rotary valve is provided with a third conical nozzle; the transition end cover is provided with a fourth conical nozzle; measurement of the propagation sound velocity of oil in a hydraulic pipeline under a certain pressure is realized.

Description

Technical Field

[0001] This application belongs to the technical field of measuring devices, and particularly relates to a measuring device and a measuring method for the sound velocity in a medium and high-pressure hydraulic pipeline. Background Art

[0002] In the research on the AC pulsation theory in AC hydraulic technology and how to improve the accuracy and stability of pulses, as well as the discrete flow research on the discrete transmission of hydraulic fluid similar to AC hydraulic technology, an in-depth understanding and measurement of the accuracy and stability of fluid pulses or pulsations in hydraulic pipelines are indispensable. Among them, the measurement of the pulse formation and propagation speed in hydraulic pipelines has always been difficult. If the sound velocity in the oil can be accurately obtained, the oil noise characteristics of hydraulic components and systems can be measured with appropriate accuracy.

[0003] In the design scheme of the Zhejiang University - Pressure Pulsation Test Bench, since it is difficult to directly and accurately measure the pressure pulsation of the pump source in the hydraulic system, this test equipment adopts a "dual-pressure dual-system" test scheme, and indirectly obtains the pressure pulsation by measuring the source flow pulsation and source impedance of the motor pump or hydraulic pump to be tested. This pressure pulsation test bench is mainly used to test the pump source pressure pulsation of a certain type of motor pump with noise control requirements, providing an experimental basis for the continuous optimization of noise reduction in the servo system.

[0004] "Determination of the Noise Characteristics of Hydraulic Transmission Oil - Part 2: Measurement of the Sound Velocity of Oil in Pipelines" describes a method for measuring the sound velocity in a fluid enclosed in a pipeline by installing a pressure sensor in the pipeline. This method is based on the application of the plane wave transmission line theory in the analysis of oil pressure fluctuations in a rigid pipeline to determine the sound velocity in the pipeline oil. In order to obtain the wave source for transmission, a hydraulic noise generator is required to cause pressure fluctuations in the loop by generating flow fluctuations, or directly generating pressure fluctuations in the loop to induce flow fluctuations; such fluctuations all have clutter or harmonics, and the calculation of their wave velocities also requires setting simplified conditions and performing relatively complex auxiliary calculations to indirectly obtain.

[0005] That is to say, there is currently no effective measurement method for the propagation speed of pulses in oil. The calculation formula for the sound velocity in metal c = √K e / ρ cannot be used for oil because although the density ρ of oil can be approximately stable, it is generally considered that the pressure of oil is different, and the elastic modulus K of oil e varies greatly, especially the influence of the free air content is the largest. Therefore, the propagation speed of pulses at different pressures is different.

[0006] In the discrete transmission of hydraulic fluid in discrete flow research, in order to effectively utilize the high-speed propagation of pulses, a method and device for calculating the sound velocity in a medium and high-pressure hydraulic pipeline are required. The sound velocity c = √K in metal eThe calculated value of 1 / ρ is relatively high. Currently, for the measurement of high-speed motion, such as the measurement of the speed of light, the Fizeau gear method or the rotating mirror method is generally used. Both the Fizeau gear method and the rotating mirror method assume that the speed of light traveling and the reflected light are the same. By measuring the distance L traveled and the time t of reflection, the speed of light c can be obtained through a simple division calculation c = L / t. For a finite distance L and a high speed c, the measurement time t will be very short. Therefore, a measurement device with a very fast scanning speed is required to ensure the possibility of implementation.

[0007] Since the scanning period of a spectrometer usually refers to the time required for the spectrometer to complete one scan. The specific time depends on factors such as the scanning speed and wavelength range of the spectrometer. For example, the scanning time of some spectrometers may be only 100 milliseconds. With the development of technology, currently, the scanning time of foreign spectrometers can reach 9 μs, and the scanning time of domestic spectrometers can reach the millisecond level, which provides a support for the basic equipment for measuring the propagation speed of pressure pulsations in hydraulic pipelines.

[0008] Therefore, there is an urgent need to invent a measurement device and method for the speed of sound in medium and high-pressure hydraulic pipelines. Summary of the Invention

[0009] This application provides a measurement device and method for the speed of sound in medium and high-pressure hydraulic pipelines to solve the problem of measuring the speed of sound of pulsating flow required for the high-speed transmission of discrete hydraulic fluids in the above technical problems. Therefore, a measurement device and method for the speed of sound in medium and high-pressure hydraulic pipelines are needed.

[0010] The technical solution adopted in this application is as follows:

[0011] A measurement device for the speed of sound in medium and high-pressure hydraulic pipelines includes a drive shaft, a rotary valve, a transition end cover, a hydraulic pipeline, a first fiber Bragg grating sensor, and a second fiber Bragg grating sensor; the axial output port of the rotary valve is connected to the transition end cover, and the transition end cover is connected to the hydraulic pipeline; the front end of the hydraulic pipeline is connected to the first fiber Bragg grating sensor, and the tail end is connected to the second fiber Bragg grating sensor; the rotary valve includes a valve cover, a valve body, a rotating valve core and a bearing arranged in the valve body; the drive shaft is connected to the rotating valve core, and the rotating valve core has a separated explosion chamber and a low-pressure chamber; the explosion chamber has a first conical nozzle, and the low-pressure chamber has a second conical nozzle; the axial output port of the rotary valve has a third conical nozzle; the transition end cover has a fourth conical nozzle;

[0012] The rotary valve is configured to: control the rotation of the rotary spool through the rotation of the drive shaft, so that a Laval tube is formed by the first conical nozzle and the third conical nozzle, a pulse-making cavity in a spindle shape is formed by the third conical nozzle and the fourth conical nozzle, the fourth conical nozzle is connected to the hydraulic pipeline, and the hydraulic oil in the hydraulic pipeline remains in the pulse-making cavity. When the hydraulic oil in the explosion chamber is sprayed into the pulse-making cavity, it pushes the hydraulic oil in the pulse-making cavity to be pressed into the hydraulic pipeline through the fourth conical nozzle to form an impact pulsating flow, presenting a state where the rotary valve injects the pulsating flow into the hydraulic pipeline; or, the second conical nozzle and the third conical nozzle form a Laval tube to recover the pulsating flow of the hydraulic pipeline into the low-pressure cavity after forming a spindle-shaped pulse-eliminating cavity through the fourth conical nozzle and the third conical nozzle; or, a closed state where the third conical nozzle between the two states is closed;

[0013] The hydraulic oil pressure, hydraulic pulse amplitude and number of times of the hydraulic pipeline are scanned, measured and recorded through the first fiber Bragg grating sensor and the second fiber Bragg grating sensor, so as to measure the propagation sound speed of the oil in the hydraulic pipeline under a certain pressure.

[0014] A measuring device for the sound speed in a medium-high pressure hydraulic pipeline of the present application further has the following additional technical features:

[0015] A first fluid channel communicating with the explosion chamber and a second fluid channel communicating with the low-pressure chamber are further opened in the rotary spool;

[0016] A first flow channel communicating with the first fluid channel is circumferentially opened in the valve body, so that the hydraulic oil source with a pressure greater than the constant pressure oil source pressure enters the explosion chamber through the first flow channel and the first fluid channel; a second flow channel communicating with the second fluid channel is also circumferentially opened in the valve body, so that the hydraulic oil in the low-pressure chamber flows back to the fuel tank through the second fluid channel and the second flow channel.

[0017] A check valve is arranged in the first fluid channel, so that when the hydraulic oil in the explosion chamber is impacted, the hydraulic oil in the explosion chamber does not flow back to the hydraulic oil source, and during the rotation of the rotary valve, the explosion chamber always receives the replenishment or supply of high-pressure oil from the hydraulic oil source through the check valve;

[0018] A back pressure valve connecting the low-pressure chamber and the second flow channel is arranged in the second flow channel to ensure that the oil flowing back to the fuel tank through the back pressure valve has a certain back pressure in the low-pressure chamber.

[0019] A diaphragm that divides the explosion chamber into two parts, an air chamber and a liquid chamber, is connected in the explosion chamber, and an inflation port communicating with the air chamber is opened in the rotary spool.

[0020] A blind hole is provided at the end of the hydraulic pipeline, and a second fiber Bragg grating sensor is arranged in the blind hole. The external constant-pressure oil source supplies hydraulic oil to the hydraulic pipeline through a bypass check valve at the blind hole end of the hydraulic pipeline. When the air to be discharged from the hydraulic pipeline is rotated to the recovery state by the rotary valve, it passes through the pulse generation cavity, the low-pressure cavity, the second fluid passage, the back pressure valve, and the second flow passage, and then is discharged from the open-type oil tank.

[0021] At least two groups of centering bearings are connected to the outer periphery of the rotary spool along the axial direction to support the rotation of the rotary spool. At least two groups of thrust bearings are respectively arranged at both ends of the rotary spool. The thrust bearing at the valve cover end pushes the rotary spool through the valve cover to ensure that the dynamic and static sealing rings between the rotary spool and the inner end face of the valve body are in close contact. The thrust bearing connected to the inner end face of the valve body is used to ensure that there is enough clearance between the rotary spool and the inner end face of the valve body to reduce friction.

[0022] Anti-friction grooves are formed on the circumferential side of the rotary spool. The anti-friction grooves are communicated with the low-pressure cavity through a third fluid passage, so that the pressure oil with a certain pressure is in the anti-friction grooves, and the rotary spool can be assisted by the pressure oil to be suspended in the circumferential hole of the valve body, and leaks to the centering bearings and thrust bearings that support the rotation of the rotary spool to provide lubrication for the bearings.

[0023] At least two groups of dynamic sealing structures are spaced along the radial direction between the coaxial circular ring surfaces of the rotary spool and the valve body. The rotary ring surface where the third conical nozzle is located is arranged between the two groups of dynamic sealing structures to ensure that the oil in the third conical nozzle is not interfered by the external oil.

[0024] Dynamic sealing structures are spaced along the axial direction between the circumferential surfaces of the rotary spool and the valve body. There are at least two pairs of dynamic sealing structures on both sides of the first flow passage. There are at least two pairs of dynamic sealing structures on both sides of the second flow passage.

[0025] This application also relates to a method for measuring the sound velocity in a medium-high pressure hydraulic pipeline. Based on the above-mentioned device for measuring the sound velocity in a medium-high pressure hydraulic pipeline, the specific steps include:

[0026] S1: Set the pulse quantity:

[0027] First, close the hydraulic oil source supply. Control the rotary spool to rotate or swing multiple times so that the oil pressure in the burst chamber is the same as the pressure of the constant pressure oil source. Then, after switching the rotary spool from the closed state to the injection state, set the safety valve opening pressure to 1.1 times the stable pressure in the hydraulic pipeline. Then, charge high-pressure gas into the air chamber in the burst chamber. Stop charging after detecting that the safety valve at the front end of the hydraulic pipeline opens. After that, adjust the safety valve opening pressure to 1.3 times the stable pressure in the hydraulic pipeline. After switching the rotary spool from the injection state to the closed state, ensure that the hydraulic oil source supply pressure is greater than 1.3 times the stable pressure in the hydraulic pipeline, then open the hydraulic oil source supply. Then, switch the rotary spool from the closed state to the injection state, and measure and record the duration t' from when the rotary spool is switched from the closed state to the injection state and remains in the injection state until the safety valve at the front end of the hydraulic pipeline opens.

[0028] S2: Set the pulsating flow test time period t:

[0029] Control the rotary spool to switch from the recovery state to the closed state so that the hydraulic oil in the hydraulic pipeline reaches the set pressure. Then, after switching the rotary spool from the closed state to the injection state for 1 / 3t' duration, and then switching the rotary spool from the injection state to the closed state for 1 / 3t' duration to ensure that the safety valve at the front end of the hydraulic pipeline does not open.

[0030] During the above process, measure the pressure pulse amplitude A of the hydraulic oil in the hydraulic pipeline through the first fiber Bragg grating sensor and record it in the time sequence of the spectrometer scanning period T 1i value until A 1Ni ≤0.707A 11 value. Let the A 11 value be the maximum value among the A 1i values (i = 1, 2, 3,...), where the pulse amplitude values are all the amplitudes within the effective width of the spectrometer filtering the collected signals; find and record the number of scans N of the scanning period T measured by the first fiber Bragg grating sensor from A 11 to A 1Ni in the record of the spectral recorder i ; At the same time, measure the pressure pulse amplitude A of the hydraulic oil in the hydraulic pipeline through the second fiber Bragg grating sensor and record it in the time sequence of the spectrometer scanning period T 2j value until A 2Nj value ≤ 0.707A 21 value. Let the A 21 value be the maximum value among the A 2j values (j = 1, 2, 3,...); find and record the number of scans N of the scanning period T measured by the second fiber Bragg grating sensor from A 21 to A 2Ni in the record of the spectral recorder j; Denote \(N = \min\{N i , N j \}\);

[0031] Calculate and record the pulsating flow decay duration \(t1 = N\times T\), where \(T\) is the spectrometer scanning period shared by the first fiber Bragg grating sensor and the second fiber Bragg grating sensor; Set the pulsating flow test time period \(t < t1\);

[0032] S3: Test procedure for single - pulse emission:

[0033] Set the duration \(t3\) for the rotary spool to maintain the recovery state such that \(t3\geq t1\times3\), ensuring that the high - pressure hydraulic oil in the hydraulic pipeline flows back to the oil tank through the low - pressure chamber within more than 3 times the pulsating flow decay duration \(t1\), thereby reducing the pressure value of the hydraulic oil in the hydraulic pipeline and fully eliminating the pressure pulsating flow; Then transfer from the recovery state to the closed state, and maintain the closed state for a duration \(t5\geq t1\times5\) to ensure that the front end of the hydraulic pipeline remains closed for a certain period of time, so that the pressure of the hydraulic oil in the hydraulic pipeline rises to a constant value under the replenishment of the external constant - pressure oil source to keep the elastic modulus of the oil fluid constant and then enter the test cycle: During the rotation of the spool, set the total rotation angle of the Laval nozzle channel from the zero - opening state to fully open and then continue to rotate back to the zero - opening state of the Laval nozzle channel as a pulsating flow process, and set the total duration \(t2\) of a pulsating flow process; Transfer the rotary spool from the injection state to the closed state, and maintain the closed state for a duration \(t4=t / 3 = 2N\times T / 9\), then transfer to the duration \(t3\) for the rotary spool to maintain the recovery state such that \(t3\geq t1\times3\) to enter the test cycle of the next emission pulse;

[0034] S4: Test procedure for multi - pulse modulated emission:

[0035] Set the duration t3 for the rotary spool to maintain the recovery state such that t3≥t1*3, ensuring that the high-pressure hydraulic oil in the hydraulic pipeline flows back to the fuel tank through the low-pressure chamber within more than three times the pulsating flow attenuation duration t1, thereby reducing the pressure value of the hydraulic oil in the hydraulic pipeline and fully eliminating the pressure pulsating flow; then transfer from the recovery state to the closed state, and maintain the closed state for a duration t5 = t1*5 to ensure that the front end of the hydraulic pipeline remains closed for a certain period of time, enabling the pressure of the hydraulic oil in the hydraulic pipeline to rise to a constant value under the replenishment of the external constant-pressure oil source to maintain the constant elastic modulus of the oil fluid and then enter the test cycle; set the rotation speed of the rotary spool to a uniform speed ω. During the rotation of the spool, set the total rotation angle of the Laval nozzle channel from the zero-opening state to the fully open state and then continue to rotate to the zero-opening state of the Laval nozzle channel as a pulsating flow process, and set the radius of the rotation center where the Laval nozzle is located as R and the diameter of the Laval nozzle as d. The total duration t6 of a pulsating flow process is approximately t6≈(d / R) / ω; the spool continues to rotate at the speed ω. After rotating about half a week in the closed state, set the total rotation angle of the Laval nozzle channel from the zero-opening state to the fully open state and then continue to rotate to the zero-opening state of the Laval nozzle channel as a pulse-eliminating flow process. The radius of the rotation center where the Laval nozzle is located is still R, and the diameter of the Laval nozzle is still d. The total duration t7 of a pulse-eliminating flow process is approximately t7≈(d / R) / ω; the spool continues to rotate at the speed ω. After rotating about half a week in the closed state, it enters the next pulsating flow process,... The spool rotates continuously at the speed ω, and a cycle of constant-period pulsating flow process - pulse-eliminating flow process - pulsating flow process is obtained;

[0036] S5: Selection of the spectrometer scanning period T:

[0037] Estimate the sound speed propagation velocity c in the oil fluid. The magnitude of the sound speed c can be calculated through the formula:

[0038] c = √K e / ρ;

[0039] In the formula, K e is the elastic modulus of the oil fluid under a certain pressure in the hydraulic pipeline, with the unit Pa; ρ is the density of the oil fluid, with the unit kg / m 3 ; c is the sound speed propagation velocity in the oil fluid, with the unit m / s;

[0040]

[0041] In the formula, p is the pressure of the oil fluid in the closed pipeline, with the unit MPa; K e is the fitted elastic modulus, with the unit of 10 2 MPa; e is the natural constant 2.718;

[0042] It can be obtained that when the length of the hydraulic pipeline is L, the duration between adjacent pulses measured by the first fiber Bragg grating sensor and the second fiber Bragg grating sensor is not greater than Δt = L / c;

[0043] If the selected detection accuracy is 10%, then set the spectrometer scanning period T1 ≤ Δt / 10;

[0044] By comparing the maximum pulse amplitude A max ={A 11} of the first fiber Bragg grating sensor within a test period, the pulse scan count N 11max , with the maximum pulse amplitude A max ={A 21} of the second fiber Bragg grating sensor, the pulse scan count N 21max ;

[0045] If N min = min{N 11max , N 21max} ≥ 10, then select the spectrometer scanning period T = T1;

[0046] S6: Measurement data processing for single - pulse emission:

[0047] Within the test period, by comparing the maximum pulse amplitude A 11 measured by the first fiber Bragg grating sensor to the maximum pulse amplitude A 21 measured by the second fiber Bragg grating sensor, the scan pulse period count N 20 ; Then, the running time Δt of the pulse from the first fiber Bragg grating sensor to the second fiber Bragg grating sensor can be obtained as Δt = T * N 20

[0048] The sound speed in the hydraulic oil at this pressure in the hydraulic pipeline can be obtained as:

[0049] c1 = L / [N 20 * T]

[0050] In the formula, c1 is the sound speed of the pulse in the hydraulic oil under a constant pressure, with the unit m / s; N 20 is the scan pulse period count for comparing the maximum pulse amplitude A 11 measured by the first fiber Bragg grating sensor to the maximum pulse amplitude A 21 measured by the second fiber Bragg grating sensor; L is the length between the first fiber Bragg grating sensor and the second fiber Bragg grating sensor of the hydraulic pipeline for pulse testing, with the unit m; T is the scanning period of the spectrometer, with the unit s;

[0051] S7: Measurement method for multi - pulse modulation emission:

[0052] In the test procedure of multi-pulse modulation emission, similar to the Fizeau gear method for measuring the speed of light, adjust the rotational speed ω so that when the pulse generated in the pulse-making cavity during the pulsating flow process is reflected back to the pulse-making cavity, the pulse-making cavity enters the pulse-eliminating flow process, thereby eliminating pulsation and ensuring a constant pressure in the hydraulic pipeline. Since the second fiber Bragg grating sensor is at the blind end of the pipeline, near the constant pressure source for oil supply, the influence of the pulse-eliminating flow process on its pressure can be ignored, and it can only measure the pulse generated in the pulse-making cavity and the pulse superposition. Adjust the rotational speed ω so that the amplitude of the pulse generated in the pulse-making cavity measured by the second fiber Bragg grating sensor at the blind end of the pipeline is greater than the constant pressure in the hydraulic pipeline and not greater than the initial value A of the pulse amplitude measured by the first fiber Bragg grating sensor 1max , and there is no subsequent superposition and increase, while the maximum value of the pulse amplitude measured by the first fiber Bragg grating sensor is equal to the initial value A 1max , the minimum value A of the pulse amplitude 1min is lower than the constant pressure in the hydraulic pipeline, and there is no subsequent superposition and change either - it can be considered that in the test of multi-pulse modulation emission, when the pulse generated in the pulse-making cavity during the pulsating flow process returns to the pulse-making cavity after being reflected by the blind end of the pipeline, the pulse-making cavity just enters the pulse-eliminating flow process; record the scanning pulse cycle count N 1max of A measured by the first fiber Bragg grating sensor 1max and the scanning pulse cycle count N 1min of A measured 1min ; take M = ceiling(abs(N 1min - N 1max ));

[0053] The speed of sound in the hydraulic oil under this pressure in the hydraulic pipeline can be obtained as follows:

[0054] c2 = 2L / [M * T]

[0055] Alternatively, in a cycle of pulsating flow process and pulse-eliminating flow process, the modulation period T1 = π / ω is equal to the total distance 2L traveled by the pulse generated in the pulse-making cavity and reflected back to the pulse-making cavity divided by the speed of sound c. The third speed of sound in the hydraulic oil under this pressure in the hydraulic pipeline can be obtained as follows:

[0056] c3 = 2L / [π / ω]

[0057] In the formula, c2 or c3 is the speed of sound of the pulse in the hydraulic oil under constant pressure, with the unit m / s; M is the scanning pulse cycle count N 1min of A measured by the first fiber Bragg grating sensor 1min and the scanning pulse cycle count N 1max of A measured 1maxThe maximum positive integer value other than zero of the difference; T is the scanning period of the spectrometer, in s; ω is the rotational speed of the rotary spool when the pulse generated in the pulse-making cavity in the pulsating flow process returns to the pulse-making cavity after reflection during the multi-pulse modulation emission test and the pulse-making cavity enters the pulse-eliminating flow process, in rad / s; L is the length between the first fiber Bragg grating sensor and the second fiber Bragg grating sensor of the hydraulic pipeline for pulse testing, in m;

[0058] Compare abs(c3 - c2) / c3 or abs(c3 - c2) / c2. When the percentage is not greater than 1%, select c2 or c3 as the measured value of the sound speed of the pulse in the hydraulic oil without bubbles under constant pressure.

[0059] The driving mechanism drives the drive shaft to rotate according to the set program. When the explosion chamber of the rotary spool rotates to communicate with the nozzle of the valve body, the air in the air chamber of the explosion chamber expands. Through the action of the diaphragm, the high-pressure oil is sprayed into the pulse-making cavity through the Laval nozzle. The high-pressure oil that cannot return due to inertia and the limitation of the third conical nozzle continues to rush forward in the pulse-making cavity and enters the hydraulic pipeline after being compressed by the fourth conical nozzle. Blocked by the high-pressure oil at the front end of the hydraulic pipeline, a sudden change occurs on the wave front of the oil at the front end of the hydraulic pipeline, forming a compression wave and propagating along the hydraulic pipeline at the sound speed c, which is recorded as the high-pressure pulse shock wave; when the throat of the explosion chamber of the rotary spool rotates out of the Laval nozzle of the valve body, it enters the closed state between the injection state and the recovery state of the rotary valve, that is, the third conical nozzle is closed and the Laval nozzle of the Laval pipe is cut off and closed, so that the high-pressure pulse shock wave propagating along the hydraulic pipeline at the sound speed c is reflected at the end of the hydraulic pipeline, and after attenuation through the hydraulic pipeline and the pulse-making cavity, it is completely reflected by the third conical nozzle and the rotary spool in the pulse-making cavity. The formed reflected shock wave rushes forward again in the pulse-making cavity, enters the hydraulic pipeline after being compressed by the fourth conical nozzle, and propagates along the pipeline at the sound speed c, forming a secondary high-pressure pulse shock wave after attenuation; this high-pressure pulse shock wave reflects back and forth and attenuates in the hydraulically pipeline with closed ends, thereby forming a single oscillating pulse wave that oscillates back and forth and attenuates without superposition in the closed hydraulic pipeline.

[0060] Before setting the sufficient pulse quantity, it also includes: in the initial stage of the test method, by switching the rotary spool to the recovery state, the oil in the hydraulic pipeline to be tested is subjected to flow replacement, so that the air in the hydraulic pipeline can enter from the closed blind end and flow back to the fuel tank from the low-pressure chamber, achieving the purpose of flushing and removing bubbles; the rotary spool is switched to the closed state and left standing for a set time under the set pressure to ensure that the residual free bubbles in the hydraulic pipeline dissolve and disappear under pressure, so that the oil has a relatively constant bulk modulus of elasticity at a certain temperature and pressure.

[0061] Due to the adoption of the above technical solutions, the beneficial effects obtained by this application are:

[0062] 1. A measuring device for the sound velocity in a medium and high pressure hydraulic pipeline of the present application includes a drive shaft, a rotary valve, a transition end cover, a hydraulic pipeline, a first fiber Bragg grating sensor and a second fiber Bragg grating sensor; there are isolated explosion chambers and low pressure chambers in the rotary valve's rotary spool; there is compressed gas that can explode in the explosion chamber, similar to the expanding gas after the gunpowder explosion in the bullet of a revolver, to utilize the jet of oil; the explosion chamber is connected to the external pipeline, so that a single pulse can be emitted in the explosion chamber; by rotating the spool, the explosion chamber and the low pressure chamber are alternately connected to the external pipeline, which can realize the modulation of the emission pulse period, so that the pressure of the hydraulic pipeline is "artificially" controllably inserted with a pressure mark for calculating the round-trip time, which brings convenience to the measurement of time or period; the second conical nozzle and the third conical nozzle form a Laval tube to accelerate the pulsating flow of the hydraulic pipeline; the third conical nozzle and the fourth conical nozzle can form a pulse-forming chamber, and the liquid in the pulse-forming chamber is similar to the bullet of the bullet in a revolver; the fourth conical nozzle and the third conical nozzle can also form a pulse-eliminating chamber, similar to the silencer formed by the sudden change of the space in the barrel for the bullet gas.

[0063] 2. As a preferred implementation mode of the present application, a first fluid passage communicating with the explosion chamber and a second fluid passage communicating with the low pressure chamber are also opened in the rotary spool; a first flow passage communicating with the first fluid passage is opened in the valve body along the circumferential direction, so that the hydraulic oil source with a pressure greater than that of the constant pressure oil source enters the explosion chamber through the first flow passage and the first fluid passage; a second flow passage communicating with the second fluid passage is also opened in the valve body along the circumferential direction, so that the hydraulic oil flows back to the fuel tank through the second fluid passage and the second flow passage, which can eliminate the free air bubbles in the hydraulic oil of the hydraulic pipeline, and quickly attenuate the pulsation of the hydraulic oil in the hydraulic pipeline or eliminate the influence of the "ammunition" in the explosion chamber on the pressure increase of the hydraulic oil in the hydraulic pipeline by the oil flowing back to the fuel tank, so as to achieve the stability or constancy of the pressure in the pipeline.

[0064] The rotating spool valve is provided with a first fluid passage for forming an input passage with the first fluid passage, which can continuously input the hydraulic oil from the constant-pressure oil source into the explosion chamber, ensuring the timeliness of "ammunition" filling and the stability of pressure energy in the explosion chamber, and providing a new way for preparing single or continuous pulse impacts; 3. As a preferred embodiment of the present application, a check valve is arranged in the first fluid passage, so that when the hydraulic oil in the explosion chamber is impacted, the hydraulic oil in the explosion chamber does not flow back to the oil source, and during the rotation of the rotary valve, the explosion chamber always receives the replenishment or supply of high-pressure oil from the oil source through the check valve, ensuring the pressure stability of the oil source and the energy concentration of the energy group transmitted from the explosion chamber to the hydraulic pipeline without bypass overflow;; A back-pressure valve connected to the low-pressure chamber is arranged in the second flow passage to ensure that the oil flowing back to the oil tank through the back-pressure valve has a certain back pressure in the low-pressure chamber: on the one hand, this back pressure prevents the oil flowing back to the oil tank through the low-pressure chamber of the hydraulic pipeline from flowing too fast and generating bubbles, and on the other hand, it ensures that the oil in the low-pressure chamber can lubricate the bearing.

[0065] 4. As a preferred embodiment of the present application, a diaphragm that divides the explosion chamber into two parts, an air chamber and a liquid chamber, is connected in the explosion chamber. The liquid chamber is filled with hydraulic oil, and the air chamber is filled with gas. The characteristic that the compression ratio of gas is greater than that of oil can be effectively utilized to ensure that the explosion chamber has enough volume to transmit the energy group to the hydraulic pipeline; the rotating spool valve has an air inlet connected to the air chamber, so that the pressure or volume of the gas in the air chamber can be conveniently regulated through the air inlet.

[0066] 5. As a preferred embodiment of the present application, a blind hole is arranged at the end of the hydraulic pipeline, and a bypass check valve is arranged at the blind hole end. Through the bypass check valve, the external constant-pressure oil source can supply hydraulic oil to the hydraulic pipeline, so that the air in the hydraulic pipeline can enter from the closed blind end and flow back to the oil tank from the low-pressure chamber, achieving the purpose of removing bubbles and flushing; on the other hand, when the front end of the hydraulic pipeline is closed, the bypass check valve can also provide stable and constant pressure for the hydraulic oil in the hydraulic pipeline, and ensure that the hydraulic oil in the hydraulic pipeline will not flow back to the constant-pressure oil source and cause pollution through the bypass check valve. Description of the Drawings

[0067] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The schematic embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings:

[0068] Figure 1 It is a schematic structural diagram of a device for measuring the sound speed in a medium-high pressure hydraulic pipeline of the present application;

[0069] Figure 2 It is a schematic curve diagram of the formation process of a pulse volume v and pressure p;

[0070] Figure 3 Schematic diagram of the first fiber Bragg grating sensor for scanning measurement of a single oscillating decaying pulsation;

[0071] Figure 4 Schematic diagram of the second fiber Bragg grating sensor for scanning measurement of a single oscillating decaying pulsation;

[0072] Figure 5 Schematic diagram of the first fiber Bragg grating sensor for scanning measurement of a modulated pulsation;

[0073] In the figure,

[0074] 1. drive shaft; 2. rotary valve; 21. valve cover; 22. valve body; 23. rotating spool; 3. transition valve cover; 4. hydraulic pipeline; 5. first fiber Bragg grating sensor; 6. second fiber Bragg grating sensor; 7. blast chamber; 71. gas chamber; 72. liquid chamber; 8. low-pressure chamber; 9. first conical nozzle; 10. second conical nozzle; 11. third conical nozzle; 12. fourth conical nozzle; 13. Laval tube; 14. first fluid passage; 15. second fluid passage; 16. first flow passage; 17. second flow passage; 18. fuel tank; 19. constant pressure oil source; 20. hydraulic oil source; 24. back pressure valve; 25. bypass check valve; 26. safety valve; 27. gas filling port; 28. pulse generation chamber; 29. centering bearing; 30. thrust bearing; 31. antifriction groove; 32. dynamic seal structure; 33. Laval throat; 34. third fluid passage; 35. diaphragm. Detailed implementation manners

[0075] In order to more clearly explain the overall concept of this application, the following will be described in detail by way of examples in conjunction with the accompanying drawings of the specification.

[0076] In the following description, many specific details are set forth in order to fully understand this application. However, this application can also be implemented in other ways different from those described herein. Therefore, the scope of protection of this application is not limited by the specific embodiments disclosed below.

[0077] In addition, in the description of this application, it should be understood that the orientation or positional relationships indicated by terms such as "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0078] In this application, unless otherwise clearly specified or defined, terms such as "installed", "connected", "joined", "fixed", etc. shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection, an electrical connection, or a communication connection; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0079] In this application, unless otherwise clearly specified or defined, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. In the description of this specification, the description with reference to terms such as "embodiment", "example", "an embodiment", "example" or "specific example", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of this application. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0080] Embodiment 1

[0081] As Figure 1 shown, this application relates to a device for measuring the sound speed in a medium-high pressure hydraulic pipeline, including a drive shaft, a rotary valve 2, a transition end cover, a hydraulic pipeline, a first fiber Bragg grating sensor 5 and a second fiber Bragg grating sensor 6; the axial output port of the rotary valve 2 is connected to the transition end cover, and the transition end cover is connected to the hydraulic pipeline; the front end of the hydraulic pipeline is connected to the first fiber Bragg grating sensor 5, and the tail end is connected to the second fiber Bragg grating sensor 6; the rotary valve 2 includes a valve cover 21, a valve body 22, a rotary valve core 23 and a bearing arranged in the valve body 22; the drive shaft is connected to the rotary valve core 23, and the rotary valve core 23 has a separated explosion chamber and a low-pressure chamber 8; the explosion chamber has a first conical nozzle 9, and the low-pressure chamber 8 has a second conical nozzle 10; the axial output port of the rotary valve 2 has a third conical nozzle 11; the transition end cover has a fourth conical nozzle 12;

[0082] The rotary valve 2 is configured to: control the rotation of the rotary spool 23 by rotating the drive shaft, so that the first conical nozzle 9 and the third conical nozzle 11 form a Laval tube 13, the third conical nozzle 11 and the fourth conical nozzle 12 form a spindle-shaped pulse generation cavity 28, the fourth conical nozzle 12 is connected to the hydraulic pipeline, and the hydraulic oil in the hydraulic pipeline is retained in the pulse generation cavity 28. When the hydraulic oil in the explosion chamber is sprayed into the pulse generation cavity 28, the hydraulic oil in the pulse generation cavity 28 is pushed into the hydraulic pipeline through the fourth conical nozzle 12 to form an impact pulsating flow, presenting a state where the rotary valve 2 injects the pulsating flow into the hydraulic pipeline; or, the second conical nozzle 10 and the third conical nozzle 11 form a Laval tube 13 to recover the pulsating flow of the hydraulic pipeline into the low-pressure cavity 8 through the fourth conical nozzle 12 and the Laval tube 13; or, a closed state where the third conical nozzle 11 is closed between the two states;

[0083] The hydraulic oil pressure, hydraulic pulse amplitude and number of times in the hydraulic pipeline are scanned, measured and recorded by the first fiber Bragg grating sensor 5 and the second fiber Bragg grating sensor 6, so as to measure the propagation sound velocity of the oil in the hydraulic pipeline under a certain pressure.

[0084] The above-mentioned closed state specifically means that between the injection state and the recovery state of the rotary valve 2, the rotary spool 23 closes the third conical nozzle 11 at the front end of the hydraulic pipeline, completing the completely closed state at the front end of the hydraulic pipeline, so as to complete the complete reflection of the impact pulsating flow oscillating back and forth in the pipeline at the front end.

[0085] By setting the explosion chamber 7 and the low-pressure cavity 8, the communication switching between the explosion chamber 7 and the low-pressure cavity 8 and the hydraulic pipeline 4 can be realized, so as to realize the three working states of the rotary valve 2. The three working states are respectively: when the hydraulic oil in the explosion chamber 7 is sprayed into the pulse generation cavity, it presents a state where the rotary valve 2 injects the pulsating flow into the hydraulic pipeline 4; and, the second conical nozzle 10 is connected to the third conical nozzle 11 to recover the pulsating flow of the hydraulic pipeline 4 into the low-pressure cavity 8; or, a closed state where the third conical nozzle 11 is closed between the two states; through the programmed control conversion of the three working states, a relatively single pulsating impact is prepared in the closed pipeline to form an oscillating decay wave that reflects back and forth; furthermore, the hydraulic oil pressure, hydraulic pulse amplitude and number of times in the hydraulic pipeline 4 are scanned, measured and recorded by the first fiber Bragg grating sensor 5 and the second fiber Bragg grating sensor 6 at both ends of the closed pipeline, so as to further measure the propagation sound velocity of the oil in the hydraulic pipeline 4 under a certain pressure. On the other hand, by alternately connecting the explosion chamber 7 and the low-pressure cavity 8 to the hydraulic pipeline 4, the pressure of the hydraulic pipeline 4 is "artificially" controllably inserted with a pressure mark for calculating the round-trip time, which brings convenience to the measurement of time or period.

[0086] Specifically, a transition valve cover 23 is also connected to the outside of the valve body.

[0087] Specifically, the fiber Bragg grating sensor may include a Bragg grating or a chirped grating, preferably a chirped grating.

[0088] As a preferred embodiment, a first fluid passage 14 communicating with the blast chamber and a second fluid passage 15 communicating with the low-pressure chamber 8 are further provided in the rotary valve core 23; a first flow passage 16 communicating with the first fluid passage 14 is circumferentially provided in the valve body 22, so that the hydraulic oil source 20 with a pressure greater than that of the constant-pressure oil source 19 enters the blast chamber through the first flow passage 16 and the first fluid passage 14; a second flow passage 17 communicating with the second fluid passage 15 is also circumferentially provided in the valve body 22, so that the hydraulic oil in the low-pressure chamber flows back to the oil tank 18 through the second fluid passage 15 and the second flow passage 17.

[0089] Specifically, the pressure value of the hydraulic oil source 20 is much greater than that of the constant-pressure oil source 19, preferably 30 MPa, and the pressure value of the constant-pressure oil source 19 is greater than 10 MPa to ensure the relatively constant characteristic of the oil fluid elastic modulus, preferably set to 20 MPa. For the constant pressure of the constant-pressure oil source, a weight-type accumulator is preferably used for pressure maintaining; the oil tank 18 is an open-type oil tank, which is communicated with the atmosphere and can be provided with an air filter.

[0090] Through the above implementation scheme, the rotary valve core 23 is provided with a first fluid passage 14 and a second fluid passage 15, and the valve body 22 is provided with a first flow passage 16 and a second flow passage 17. The first flow passage 16 is used to form an input passage with the first fluid passage 14, and can continuously input the hydraulic oil of the external constant-pressure oil source 19 into the blast chamber, ensuring the timeliness of "ammunition" filling and the stability of pressure energy in the blast chamber 7, and providing a new way for preparing single or continuous pulse impacts;

[0091] The second flow passage 17 is used to form an output passage with the second fluid passage 15, and can output the hydraulic oil after the low-pressure chamber 8 is communicated with the hydraulic pipeline 4 back to the oil tank 18 through the output passage, which can eliminate the free air bubbles in the hydraulic oil of the hydraulic pipeline 4 and quickly attenuate the hydraulic oil pulsation of the hydraulic pipeline 4 or ensure the influence of the "ammunition" in the blast chamber 7 on the pressure increase of the hydraulic oil in the hydraulic pipeline 4 through the oil fluid flowing back to the oil tank 18, so as to achieve the stability or constancy of the pressure in the hydraulic pipeline.

[0092] As a preferred embodiment, a check valve 25 is provided in the first fluid passage 14 so that when the hydraulic oil in the blast chamber is impacted, the hydraulic oil in the blast chamber does not flow back to the hydraulic oil source 20. During the rotation of the rotary valve, the blast chamber always receives the replenishment or supply of high-pressure oil from the hydraulic oil source 20 through the check valve 25, ensuring the pressure stability of the hydraulic oil source 20 and the energy concentration of delivering the energy mass into the hydraulic pipeline 4 through the blast chamber 7 without bypass overflow. By providing a back pressure valve 24, the oil in the low-pressure chamber 8 has a certain back pressure. On the one hand, this back pressure prevents the oil flowing back to the fuel tank 18 through the low-pressure chamber 8 from flowing too fast through the hydraulic pipeline 4 and generating bubbles. On the other hand, it ensures that the oil in the low-pressure chamber 8 can lubricate the bearing.

[0093] As a preferred embodiment, the interior of the blast chamber 7 is divided into a gas chamber 71 and a liquid chamber 72 by a diaphragm 35. The gas chamber 71 is filled with high-pressure gas, and the hydraulic oil in the liquid chamber 72 is supplied through the first flow passage 14 and the first fluid passage 14. The rotary spool 23 has an inflation port 27 communicating with the gas chamber 72, so that the pressure or volume of the gas in the gas chamber 71 can be conveniently regulated through the inflation port 27. Filling the gas chamber 71 with gas can effectively utilize the characteristic that the compression ratio of the gas is greater than that of the oil, ensuring that the blast chamber has enough volume to deliver the energy mass into the hydraulic pipeline 4.

[0094] As a preferred embodiment, a blind hole is provided at the end of the hydraulic pipeline 4, and a second fiber Bragg grating sensor 6 is provided in the blind hole. A bypass check valve 25 is provided at the blind hole end. Through the bypass check valve 25, the external constant-pressure oil source 19 can supply hydraulic oil to the hydraulic pipeline, enabling the air in the hydraulic pipeline 4 to be discharged from the open fuel tank 18 through the pulse control chamber 28, the low-pressure chamber 8, the back pressure valve 24, etc. when the rotary valve rotates to the recovery state, achieving the purpose of removing bubbles and flushing, so as to ensure that the hydraulic oil in the hydraulic pipeline 4 has no air bubbles and maintains a relatively constant pressure, which is greater than the opening pressure of the back pressure valve 24. On the other hand, when the front end of the hydraulic pipeline 4 is closed, the bypass check valve 25 can also provide a stable and constant pressure for the hydraulic oil in the hydraulic pipeline 4 and ensure that the hydraulic oil in the hydraulic pipeline 4 does not flow back to and contaminate the constant-pressure oil source through the bypass check valve 25.

[0095] When the hydraulic oil in the hydraulic pipeline 4 is impacted, the bypass check valve 25 can prevent the oil from flowing back to the constant-pressure oil source 19. When the rotary valve is in the closed state, it ensures that the front end of the hydraulic pipeline 4 is closed, so that the oil in the hydraulic pipeline 4 maintains a constant pressure and does not flow. In this way, it can not only dissolve and eliminate the residual air bubbles in the hydraulic oil in the hydraulic pipeline 4, but also keep the oil pressure and elastic modulus in the hydraulic pipeline 4 constant through long-term static placement.

[0096] As a preferred embodiment, at least two sets of centering bearings 29 are connected to the outer periphery of the rotary valve core 23 in the axial direction to support the rotation of the rotary valve core 23; at least two sets of thrust bearings 30 are respectively arranged at both ends of the rotary valve core 23, and the thrust bearing 30 at the valve cover end pushes the rotary valve core 23 through the valve cover 21 to ensure that the dynamic and static sealing rings between the rotary valve core 23 and the inner end face of the valve body 22 are in close contact; the thrust bearing 30 connected to the inner end face of the valve body 22 is used to ensure that there is enough clearance between the rotary valve core 23 and the inner end face of the valve body 22 to reduce friction; a friction reduction groove 31 is formed on the circumferential side of the rotary valve core 23, and the friction reduction groove 31 is communicated with the low-pressure chamber 8 through a third fluid passage 34, so that there is pressure oil with a certain pressure in the friction reduction groove 31, so that the rotary valve core 23 can be assisted by the pressure oil to be suspended in the circumferential hole of the valve body 22, and leaks to the centering bearing 29 and the thrust bearing 30 that support the rotation of the rotary valve core 23 to provide lubrication for the bearings.

[0097] Specifically, a pair of dynamic seal structures 32 between the first flow passage 16 and the second flow passage 17 can be combined into one, so at least 3 sets of dynamic and static ring seal structures are required. These seal structures prevent the oil between the first flow passage 16 and the second flow passage 17 of the rotary valve core 23 from interfering with each other, and prevent high-pressure oil from filling into low-pressure and low-pressure oil from sucking into high-pressure; in order to ensure the high-speed rotation of the rotary valve core 23, the friction reduction groove 31 is communicated with the oil with a certain back pressure in the low-pressure chamber 8 through a throttle hole, ensuring that the rotary valve core 23 is assisted by the pressure oil to be suspended in the circumferential hole of the valve body 22, assisting the axial centering bearing 29 for auxiliary support, and further leaking to the centering bearing 29 and the thrust bearing 30 that support the rotation of the rotary valve core 23 to provide lubrication for the bearings; the thrust bearings 30 at both ends of the rotary valve core 23 can push the rotary valve core 23 against the injection outlet through the valve cover 21.

[0098] As a preferred embodiment, at least two sets of dynamic seal structures 32 are spaced along the radial direction between the coaxial circular ring surfaces of the rotary valve core 23 and the valve body 22, and the rotating ring surface where the third conical nozzle 11 is located is arranged between the two sets of dynamic seal structures 32 to ensure that the oil in the third conical nozzle 11 is not interfered by external oil; dynamic seal structures 32 are spaced along the axial direction between the circumferential surfaces of the rotary valve core 23 and the valve body 22, and there are at least two pairs of dynamic seal structures 32 on both sides of the first flow passage 16; there are at least two pairs of dynamic seal structures 32 on both sides of the second flow passage 17.

[0099] Specifically, a plurality of dynamic seal structures 32 are provided between the rotary valve core 23 and the valve body 22; the dynamic seal structure 32 includes a dynamic ring and a static ring, the dynamic ring is arranged on the rotary valve core 23, and the static ring is arranged on the valve body 22; the rotary ring surface where the third conical nozzle 11 is located is arranged between two groups of dynamic seal structures 32. Particularly, when the rotary valve core 23 connects the third conical nozzle 11 with the low-pressure chamber 8, it is ensured that the third conical nozzle 11 is not interfered by external high-pressure hydraulic oil.

[0100] The dynamic seal structure 32 achieves axial end face sealing through the two end faces of the static ring and the dynamic ring under the action of fluid pressure and the spring pressure of the compensation mechanism, thereby preventing fluid leakage. The mechanical seal mainly consists of elements such as a stationary ring (static ring), a rotating ring (dynamic ring), an elastic element, a spring seat, a set screw, a rotating ring auxiliary sealing ring, and a stationary ring auxiliary sealing ring. The end faces of the dynamic ring and the static ring are perpendicular to the rotation axis, and the dynamic ring is tightly pressed against the static ring by the spring force to form a seal. The end face materials of the dynamic ring and the static ring usually have good wear resistance and thermal conductivity to reduce friction and conduct heat in a timely manner, and have the advantages of reliable sealing performance, small leakage, long service life, low power loss, and wide application range. They are particularly suitable for working conditions with high rotational speed, high pressure difference, and strongly corrosive process media.

[0101] Embodiment 2

[0102] This application relates to a method for measuring the sound speed in a medium-high pressure hydraulic pipeline. Based on the above-mentioned device for measuring the sound speed in a medium-high pressure hydraulic pipeline, the specific steps include:

[0103] S1: Set the pulse quantity:

[0104] First, close the oil supply of the hydraulic oil source 20, control the rotary valve core 23 to rotate multiple times so that the oil pressure in the burst chamber is the same as the pressure of the constant pressure oil source 19; then, after the rotary valve core 23 is transferred from the closed state to the injection state, set the opening pressure of the safety valve 26 to 1.1 times the stable pressure in the hydraulic pipeline 4, and then fill the gas chamber 71 in the burst chamber with high-pressure gas. After detecting that the safety valve 26 at the front end of the hydraulic pipeline 4 opens, stop inflating, and then adjust the opening pressure of the safety valve 26 to 1.3 times the stable pressure in the hydraulic pipeline 4; after the rotary valve core 23 is transferred from the injection state to the closed state, ensure that the oil supply pressure of the hydraulic oil source 20 is greater than 1.3 times the stable pressure in the hydraulic pipeline 4, then open the oil supply of the hydraulic oil source 20, and then transfer the rotary valve core 23 from the closed state to the injection state, and measure and record the duration t' from when the rotary valve core 23 is transferred from the closed state to the injection state and remains in the injection state until the safety valve 26 at the front end of the hydraulic pipeline 4 opens.

[0105] S2: Set the pulsating flow test time period t:

[0106] Control the rotary spool 23 to switch from the recovery state to the closed state, so that the hydraulic oil in the hydraulic pipeline 4 reaches the set pressure; then switch the rotary spool 23 from the closed state to the injection state for 1 / 3t' duration, and then switch the rotary spool 23 from the injection state to the closed state for 1 / 3t' duration to ensure that the safety valve at the front end of the hydraulic pipeline does not open;

[0107] In the above process, measure the pressure pulse amplitude A of the hydraulic oil in the hydraulic pipeline 4 through the first fiber Bragg grating sensor 5 and record it in the time sequence of the spectrometer scanning period T 1i value until A 1Ni ≤0.707A 11 value. Let the A 11 value be the maximum value among A 1i values (i = 1, 2, 3,...), where the pulse amplitude values are all the amplitudes within the effective width of the spectrometer filtering the collected signal; find and record the number of scans N 11 from A 1Ni to A i measured by the first fiber Bragg grating sensor 5 during the scanning period T of the spectrometer in the spectral recorder; meanwhile, measure the pressure pulse amplitude A of the hydraulic oil in the hydraulic pipeline 4 through the second fiber Bragg grating sensor 6 and record it in the time sequence of the spectrometer scanning period T 2j value until A 2Nj value ≤ 0.707A 21 value. Let the A 21 value be the maximum value among A 2j values (j = 1, 2, 3,...), where the pulse amplitude values are all the amplitudes within the effective width of the spectrometer filtering the collected signal; find and record the number of scans N 21 from A 2Ni to A j measured by the second fiber Bragg grating sensor 6 during the scanning period T of the spectrometer in the record of the spectral recorder; record N = min{N i , N j};

[0108] Calculate and record the pulsating flow attenuation duration t1 = N*T, where T is the spectrometer scanning period shared by the first fiber Bragg grating sensor 5 and the second fiber Bragg grating sensor 6; set the pulsating flow test time period t < t1, preferably t = 2t1 / 3;

[0109] S3: Test procedure for single pulse emission:

[0110] Set the duration t3 for the rotary spool 23 to maintain the recovery state such that t3 ≥ t1 * 3, ensuring that the high-pressure hydraulic oil in the hydraulic pipeline 4 flows back into the oil tank 18 through the low-pressure chamber 8 within a time longer than three times the pulsating flow attenuation duration t1, thereby reducing the pressure value of the hydraulic oil in the hydraulic pipeline 4 and fully eliminating the pressure pulsating flow. Then, transfer from the recovery state to the closed state, and maintain the closed state for a duration t5 ≥ t1 * 5 to ensure that the front end of the hydraulic pipeline 4 in the closed state by the rotary spool 23 remains closed for a certain period, ensuring that a certain amount of hydraulic oil is replenished to the hydraulic pipeline 4 by the external constant-pressure oil source 19 through the bypass check valve 25 at the blind hole end of the hydraulic pipeline 4, so that the pressure of the hydraulic oil in the hydraulic pipeline 4 rises to a constant value and is maintained at a constant value under the replenishment of the external constant-pressure oil source, to maintain the constant elastic modulus of the oil and then enter the test cycle: During the rotation of the spool, set the total rotation angle of the Laval nozzle channel from the zero opening state to the fully open state and then continue to rotate back to the zero opening state of the Laval nozzle channel as one pulsating flow process, and set the total duration t2 of one pulsating flow process such that t2 ≤ t / 2, preferably t2 = t / 2 = N * T / 3; After transferring the rotary spool from the injection state to the closed state and maintaining the closed state for a duration t4 = t / 3 = 2N * T / 9, transfer to the duration t3 for the rotary spool to maintain the recovery state such that t3 ≥ t1 * 3 to enter the test cycle of the next emission pulse;

[0111] S4: Test procedure for multi-pulse modulation emission:

[0112] Set the duration \(t_3\) for the rotary spool 23 to maintain the recovery state such that \(t_3\geq t_1\times3\), ensuring that the high-pressure hydraulic oil in the hydraulic pipeline 4 within more than 3 times the pulsating flow attenuation duration \(t_1\) flows back to the oil tank through the low-pressure chamber, thereby reducing the pressure value of the hydraulic oil in the hydraulic pipeline and fully eliminating the pressure pulsating flow; then transition from the recovery state to the closed state, and maintain the closed state for a duration \(t_5\geq t_1\times5\) to ensure that the front end of the hydraulic pipeline in the closed state of the rotary spool remains closed for a certain period of time, enabling the pressure of the hydraulic oil in the hydraulic pipeline to rise to a constant value under the replenishment of the external constant-pressure oil source to maintain the constant elastic modulus of the oil fluid and then enter the test cycle; set the rotation speed of the rotary spool to a uniform speed \(\omega\). During the rotation of the spool, set the total rotation angle of the Laval nozzle channel of the Laval tube 13 from the zero-opening state to the fully open state and then continue to rotate back to the zero-opening state of the Laval nozzle channel as one pulsating flow process. Set the radius of the rotation center where the Laval nozzle 33 is located as \(R\), the diameter of the Laval nozzle as \(d\), and the total duration \(t_6\) of one pulsating flow process is approximately \(t_6\approx(d / R) / \omega\); the spool continues to rotate at the speed \(\omega\). After rotating about half a week in the closed state, set the total rotation angle of the Laval nozzle channel of the Laval tube 13 from the zero-opening state to the fully open state and then continue to rotate back to the zero-opening state of the Laval nozzle channel as one pulse-eliminating flow process. The radius of the rotation center where the Laval nozzle is located is still \(R\), the diameter of the Laval nozzle is still \(d\), and the total duration \(t_7\) of one pulse-eliminating flow process is approximately \(t_7\approx(d / R) / \omega\); the rotary spool 23 continues to rotate at the speed \(\omega\). After rotating about half a week in the closed state, it enters the next pulsating flow process,... The rotary spool 23 rotates continuously at the speed \(\omega\) to obtain a cycle of constant pulsating flow process - pulse-eliminating flow process - pulsating flow process;

[0113] S5: Selection of the scanning period \(T\) of the spectrometer:

[0114] Estimate the sound speed propagation velocity \(c\) in the oil fluid. The magnitude of the sound speed \(c\) can be calculated through the formula:

[0115] \(c = \sqrt{K}\) e / \(\rho\);

[0116] In the formula, \(K\) e is the elastic modulus of the oil fluid under a certain pressure in the hydraulic pipeline 4, with the unit Pa; \(\rho\) is the oil fluid density, with the unit kg / m 3 ; \(c\) is the sound speed propagation velocity in the oil fluid, with the unit m / s;

[0117]

[0118] In the formula, \(p\) is the pressure of the oil fluid in the closed pipeline, with the unit MPa; \(K\) e is the fitted elastic modulus, with the unit of \(10\) 2 MPa; \(e\) is the natural constant 2.718;

[0119] When the length of the hydraulic pipeline 4 is L, the time duration between adjacent pulses measured by the first fiber Bragg grating sensor 5 and the second fiber Bragg grating sensor 6 is not greater than Δt = L / c;

[0120] Select the detection accuracy to be 10%, then set the spectrometer scanning period T1 ≤ Δt / 10;

[0121] By comparing the maximum pulse amplitude A max = {A 11} of the pulses scanned by the first fiber Bragg grating sensor 5 within a test period 11max , with the number of pulse scans N max = {A 21} of the pulses scanned by the second fiber Bragg grating sensor 6 22max ;

[0122] If N min = min{N 11max , N 22max} ≥ 10, then select the spectrometer scanning period T = T1;

[0123] S6: Measurement data processing for single - pulse emission:

[0124] Within the test period, by comparing the maximum pulse amplitude A 11 measured by the first fiber Bragg grating sensor 5 to the maximum pulse amplitude A 21 measured by the second fiber Bragg grating sensor 6 for the scanning pulse period count N 20 ; Then, the running time duration Δt between the first fiber Bragg grating sensor 5 and the second fiber Bragg grating sensor 6 can be obtained as Δt = T * N 20

[0125] The sound speed in the hydraulic oil under this pressure in the hydraulic pipeline can be obtained as:

[0126] c1 = L / [N 20 * T]

[0127] In the formula, c1 is the sound speed of the pulse in the hydraulic oil under constant pressure, with the unit of m / s; N 20 is the scanning pulse period count for comparing the maximum pulse amplitude A 11 measured by the first fiber Bragg grating sensor 5 to the maximum pulse amplitude A 21 measured by the second fiber Bragg grating sensor 6; L is the length between the first fiber Bragg grating sensor 5 and the second fiber Bragg grating sensor 6 of the hydraulic pipeline for pulse testing, with the unit of m; T is the scanning period of the spectrometer, with the unit of s;

[0128] S7: Measurement method for multi - pulse modulation emission:

[0129] In the test procedure of multi-pulse modulation emission, similar to the Fizeau gear method for measuring the speed of light, adjust the rotational speed ω so that when the pulses generated in the pulse-making cavity during the pulsating flow process are reflected back to the pulse-making cavity, the pulse-making cavity enters the pulse-eliminating flow process, thereby eliminating pulsation and ensuring a constant pressure in the hydraulic pipeline 4. Since the second fiber Bragg grating sensor 6 is at the blind end of the pipeline, close to the constant pressure oil source 19 for oil supply, the influence of the pressure on it can be ignored, and it can only measure the pulses generated in the pulse-making cavity and pulse superposition. Adjust the rotational speed ω so that the amplitude of the pulses generated in the pulse-making cavity measured by the second fiber Bragg grating sensor at the blind end of the pipeline is greater than the constant pressure in the hydraulic pipeline and not greater than the initial value A of the pulse amplitude measured by the first fiber Bragg grating sensor 1max , and there is no subsequent superposition and increase, while the maximum value of the pulse amplitude measured by the first fiber Bragg grating sensor is equal to the initial value A 1max , the minimum value A of the pulse amplitude 1min is lower than the constant pressure in the hydraulic pipeline, and there is no subsequent superposition and change - it can be considered that in the test of multi-pulse modulation emission, when the pulses generated in the pulse-making cavity during the pulsating flow process are reflected back to the pulse-making cavity through the blind end of the pipeline, the pulse-making cavity just enters the pulse-eliminating flow process; record the scanning pulse period count N of the A measured by the first fiber Bragg grating sensor 5 1max and the scanning pulse period count N of the measured A 1max ; take M = ceiling(abs(N 1min -N 1min )); 1min 1max ))

[0130] The speed of sound in the hydraulic oil at this pressure in the hydraulic pipeline can be obtained as follows:

[0131] c2 = 2L / [M*T]

[0132] Or, in a cycle of pulsating flow process and pulse-eliminating flow process, the modulation period T1 = π / ω is equal to the total distance 2L traveled by the pulses generated in the pulse-making cavity when reflected back to the pulse-making cavity divided by the speed of sound c. The third speed of sound in the hydraulic oil at this pressure in the hydraulic pipeline can be obtained as follows:

[0133] c3 = 2L / [π / ω]

[0134] In the formula, c2 or c3 is the speed of sound in the hydraulic oil without bubbles under constant pressure, with the unit m / s; M is the scanning pulse period count N of the A measured by the first fiber Bragg grating sensor 5 1min and the scanning pulse period count N of the measured A 1min ; 1max and the scanning pulse period count N of the measured A 1max ​The maximum positive integer value that is not zero for the difference; T is the scanning period of the spectrometer, in s; ω is the rotational speed of the rotary valve core when the pulse generated in the pulse-making cavity in the pulsating flow process returns to the pulse-making cavity after reflection and the pulse-making cavity enters the pulse-eliminating flow process during the test of multi-pulse modulation emission, in rad / s; L is the length between the first fiber Bragg grating sensor 5 and the second fiber Bragg grating sensor 6 of the hydraulic pipeline for pulse testing, in m;

[0135] Compare abs(c3 - c2) / c3 or abs(c3 - c2) / c2. When the percentage is not greater than 1%, select c2 or c3 as the measured value of the sound speed of the hydraulic oil without bubbles under constant pressure.

[0136] Preferably, the oil pressure in the burst chamber is basically the same as the set pressure of the pressure supply of the hydraulic oil source 20 (with a difference of the opening pressure of a one-way valve 25). The pressure value of the hydraulic oil source 20 should be much greater than the pressure value of the constant-pressure oil source 19, preferably 30 MPa. The pressure value of the constant-pressure oil source 19 should be greater than 10 MPa to ensure the relatively constant characteristic of the oil elastic modulus. The set pressure of the hydraulic pipeline 4 is the same as the pressure of the constant-pressure oil source 19, preferably 20 Mpa.

[0137] Specifically, measure the pressure pulse amplitude A of the hydraulic oil in the hydraulic pipeline 4 through the first fiber Bragg grating sensor 5 and record it in the time sequence of the spectrometer scanning period T 1i values (the count i of the scanning period T = 1, 2, 3,..., Ni) until the measured A 1Ni ≤0.707A 11 value. Let the A 11 value be the maximum value among the A 1i values (i = 1, 2, 3,...); find and record the number Ni of the scanning periods T measured by the first fiber Bragg grating sensor 5 from A 11 to A 1Ni from the spectral recorder; at the same time, measure the pressure pulse amplitude A of the hydraulic oil in the hydraulic pipeline 4 through the second fiber Bragg grating sensor 6 and record it in the time sequence of the spectrometer scanning period T 2j values (the count j of the scanning period T = 1, 2, 3,..., N j ).

[0138] It should be noted that within the total duration t2 of a pulsating flow process, if too many pulses are input from the burst chamber to the hydraulic pipeline 4, it is easy to cause the pressure at the front end of the hydraulic pipeline 4 to rise, resulting in the opening of the safety valve 26 and the occurrence of oil drainage.

[0139] It should be noted that the driving mechanism drives the drive shaft to adjust the rotation angle and speed ω (in units of rad / s or rad / ms) according to the program, so that the rotation speed of the rotary valve core 23 relative to the valve body 22 is ω.

[0140] It should be noted that the length of the hydraulic pipeline 4 is set as L, and L >> the length of the third conical nozzle 11 of the valve body 22. In this way, the length of the sensor can be ignored. The propagation speed of the pulse oscillating in the closed hydraulic pipeline 4 is c, and the propagation duration of the pulse from the front end to the tail end of the hydraulic pipeline 4 each time is Δt. Then, Δt = L / c.

[0141] Set the scanning period of the first fiber Bragg grating sensor 5 and the second fiber Bragg grating sensor 6 as T, then T should be much smaller than 10 times the Δt = L / c; when the explosion chamber of the rotary spool 23 rotates to communicate with the third conical nozzle 11 of the valve body 22, the pressure pulse amplitude A of the hydraulic oil in the hydraulic pipeline 4 is denoted as A max ; when the low-pressure chamber 8 of the rotary spool 23 rotates to communicate with the third conical nozzle 11 of the valve body 22, the pressure pulse amplitude A of the hydraulic oil in the hydraulic pipeline 4 is denoted as A min ; when the same scanning period T of the first fiber Bragg grating sensor 5 and the second fiber Bragg grating sensor 6 << Δt, a pulse width of the same amplitude can be recorded by [Δt / T] = m small rectangular pulses; when the same scanning period T of the first fiber Bragg grating sensor 5 and the second fiber Bragg grating sensor 6 ≤ Δt, the pulse will have a width distortion phenomenon (such as the magenta rectangular pulse widths of different widths in the figure), affecting the recording of the number of pulses; when the scanning period T > Δt, the pulse will have a serious width distortion phenomenon, resulting in a test failure.

[0142] Taking No. 46 hydraulic oil as an example for further explanation:

[0143] The density of No. 46 hydraulic oil is 0.85 g / cm 3 ×1000 = 850 kg / m 3 ; the elastic modulus at 20 Mpa pressure is 1.58 GPa, then the estimated sound speed c = √K e / ρ = 1363 m / s. Through the following formula:

[0144]

[0145] In the formula, K e is the fitted elastic modulus of the oil in the hydraulic pipeline 4 under a certain pressure, with the unit of 10 2 MPa; ρ is the density of the oil, with the unit of kg / m 3 ; the pressure p is the pressure of the oil in the hydraulic pipeline 4, with the unit of MPa; e is the natural constant 2.718. Substituting into the above formula for calculation, we can get:

[0146] K e=-13.37*POWER(2.718,-20 / 2.73)-8.59*POWER(2.718,-20 / 48.31)+21.4 = 15

[0147] .713(0.1GPa)≈1.57GPa.

[0148] The fitting error is approximately (1.58GPa - 1.57GPa) / 1.58GPa = 0.6%. Therefore, the fitting formula can be adopted, and take K e20 = 1.57GPa.

[0149] Suppose the pressure in the experimental hydraulic pipeline 4 is 20MPa. After the safety valve 26 is adjusted to 1.3 times, the opening pressure of the safety valve 26 needs to reach 20MPa * 1.3 = 26MPa; the fitting formula can be adopted to calculate the bulk modulus of elasticity of the oil at 26MPa:

[0150] K e26 =-13.37*POWER(2.718,-26 / 2.73)-8.59*POWER(2.718,-26 / 48.31)+21.4 =

[0151] 16.383(0.1GPa)≈1.64GPa.

[0152] Although the pressure change amount Δp = 26MPa - 20MPa = 6MPa, but K e26 and K e20 The fitting error is approximately (1.64GPa - 1.57GPa) / 1.57GPa = 4.4%. The bulk modulus of elasticity of the oil basically does not change. Select the bulk modulus of elasticity of the oil K e = K e20 = 1.57GPa.

[0153] Suppose the length L of the experimental hydraulic pipeline 4 is 5m and the inner diameter is Φ10mm. The volume of the oil contained in it is:

[0154] V = π / 4 * 0.01 * 0.01 * 5m3 = 393ml

[0155] From the reciprocal of the bulk modulus of elasticity formula of the oil , when the safety valve 26 opens, the pressure change amount Δp = 26MPa - 20MPa = 6MPa, and the change amount of the oil volume (negative for compression), then we can get:

[0156] -Δv = V * Δp / K e = 393ml * 6MPa / 1.57GPa = 1.5ml

[0157] That is to say, when the gas in the explosion chamber expands into the sealed hydraulic pipeline 4 with a pressure of 20 MPa by Δv = 1.5 ml of oil at 30 MPa, the safety valve 26 with an opening pressure set at 26 MPa will overflow. Obviously, this can be achieved by various methods. For example: after setting the inflation pressure to 1.1 times the set value and stopping inflation, then adjusting the opening pressure of the safety valve 26 to 1.3 times the stable pressure in the hydraulic pipeline 4; after transferring the rotary spool 23 from the injection state to the closed state, ensuring that the oil supply pressure of the hydraulic oil source 20 is greater than 1.3 times the stable pressure in the hydraulic pipeline 4, then opening the oil supply of the hydraulic oil source 20, and then transferring the rotary spool 23 from the closed state to the injection state, and measuring and recording the duration t' from the moment when the rotary spool 23 is transferred from the closed state to the injection state and remains in the injection state until the safety valve 26 at the front end of the hydraulic pipeline 4 opens; controlling the rotary spool 23 to transfer from the recovery state to the closed state so that the hydraulic oil in the hydraulic pipeline 4 reaches the set pressure; then transferring the rotary spool 23 from the closed state to the injection state for 1 / 3t' duration, and then transferring the rotary spool 23 from the injection state to the closed state for 1 / 3t' duration.

[0158] Therefore, assuming that the 1.5 ml of oil is completely and evenly ejected within the duration t', then, the maximum volume Δv' ejected within the duration of 1 / 3t' + 1 / 3t' = 2 / 3t' is 2 / 3 * 1.5 ml = 1 ml. The actual inflation volume in the air chamber 71 is at least Δv' * 5 / 4 = 1.25 ml, which is a very small gas volume. Therefore, the diaphragm air chamber can also be replaced by a small balloon.

[0159] For V = π / 4 * 0.01 * 0.01 * 5 m 3 = 393 ml, the total impact volume Δv' = 1 ml is less than 0.25% of V = 393 ml, and it will soon annihilate or disappear in the pipeline, but the oscillating pulse will not disappear.

[0160] Furthermore, the driving mechanism drives the driving shaft 1 to rotate according to the set program. When the explosion chamber of the rotary spool 23 rotates to communicate with the nozzle of the valve body 22, the air in the air chamber of the explosion chamber expands. Under the action of the diaphragm 35, the high-pressure oil is sprayed into the pulse generation chamber 28 through the Laval throat 33 of the Laval tube 13. The high-pressure oil that cannot return due to inertia and the limitation of the third conical nozzle continues to rush forward in the pulse generation chamber 28 and is compressed into the hydraulic pipeline 4 through the fourth conical nozzle 12. Blocked by the high-pressure oil at the front end of the hydraulic pipeline 4, a sudden change occurs on the wave front of the oil at the front end of the hydraulic pipeline 4 to form a compression wave in the hydraulic pipeline 4 and propagate along the hydraulic pipeline 4 at the speed of sound c, which is recorded as the high-pressure pulse shock wave;

[0161] When the throat of the blast chamber of the rotating spool valve 23 rotates out of the Laval throat 33 of the Laval tube 13 of the valve body 22, it enters the closed state where the third conical nozzle 11 between the injection state and the recovery state of the rotary valve is closed, that is, the third conical nozzle 11 is closed, and the Laval throat of the Laval tube is cut off and closed, so that the high-pressure pulse shock wave propagating at the speed of sound c along the hydraulic pipeline 4 is reflected at the end of the hydraulic pipeline, and after passing through the hydraulic pipeline and the pulse suppression chamber for attenuation, it is completely reflected by the third conical nozzle 11 and the rotating spool valve 23 in the pulse suppression chamber. The formed reflected shock wave rushes forward again in the pulse suppression chamber, enters the hydraulic pipeline 4 after being compressed by the fourth conical nozzle, and propagates along the pipeline at the speed of sound c, forming a secondary high-pressure pulse shock wave after attenuation; this high-pressure pulse shock wave is reflected back and forth and attenuated in the hydraulically pipeline closed at both ends, thus forming a single oscillating pulse wave that oscillates back and forth and attenuates without superposition in the closed hydraulic pipeline 4.

[0162] It should be noted that a compression wave in which stress (or pressure), density, and temperature undergo sudden changes on the wave front in gas, liquid, and solid media is also called a shock wave. Shock waves appear in processes such as supersonic flow and explosion. The shock wave formed during an explosion is also called an explosion wave. The wave formed by suddenly closing a valve in a water pipe is also a kind of shock wave.

[0163] When the oil volume V of the above-mentioned 5m hydraulic pipeline is impacted instantaneously by the pressure (p + Δp) at a certain pipe end, V is almost unchanged, and the elastic modulus K of No. 46 hydraulic oil e is basically stable between 1.57 GPa and 1.64 GPa, and the elastic modulus hardly fluctuates. For a 10mm hydraulic pipeline, the cross-sectional area of the hydraulic pipeline is 78.5 (mm 2 ), that is, the length L of the 10mm diameter hydraulic pipeline occupied by the oil volume compression caused by the pipe end pressure impact ΔP = 6 MPa is L = Δv’ / 78.5 = 1000mm 3 / 78.5mm 2 ≈ 12.7mm, that is, when the rotating spool valve is transferred from the closed state to the injection state, the longest distance occupied by the injected oil in the entire 5m pipe length is 12.7mm, and the linear average is 12.7mm / 5m = 0.254%. According to the law of conservation of matter and mass conservation, that is, a compression wave, also called a shock wave, in which the density at the front end of the hydraulic pipeline undergoes a sudden change, during subsequent shock operation, the density attenuation per meter in the running direction is about 0.254% (assuming that the density of the shock wave is not changed due to the limitation of the steel pipe in the radial direction of the pipeline).

[0164] In fact, during the process of transitioning the rotary spool from the closed state to the injection state and then from the injection state back to the closed state, it is not a sudden change. That is to say, when the rotary spool is just transitioned from the closed state to the injection state, some hydraulic fluid (assumed to be 1%v' = 0.01ml) will be injected into the hydraulic pipeline with a volume of Δv' = 1ml of compressible liquid that can be injected, thus forming a shock wave. Assuming the propagation speed of sound in the hydraulic fluid is c = √Ke / ρ = √1.57*1000000000 / 850 = 1359m / s (taking K e20 = 1.57GPa and the density of No. 46 hydraulic oil is 850kg / m 3 ), it will quickly return to the end in a 5m long straight hydraulic pipeline and then coincide with the new pulse at the subsequent emission end, resulting in the superposition of the mass and energy at the emission end, thereby forming a Fibonacci sequence F(0) = 0, F(1) = 1, F(n) = F(n - 1) + F(n - 2) (n≥2, n∈N*) (Fibonacci sequence, also known as the golden ratio sequence, referring to such a sequence: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34,... In mathematics, the Fibonacci sequence is defined recursively as follows: F(0) = 0, F(1) = 1, F(n) = F(n - 1) + F(n - 2) (n≥2, n∈N*)) of pulse superposition in the hydraulic pipeline. This quickly causes the pressure at the pipe end to continuously rise until the process of transitioning the rotary spool from the injection state to the closed state ends. After Δv' = 1ml is completely injected into the hydraulic pipeline and no new high-pressure hydraulic fluid enters the hydraulic pipeline, a single pulse preparation process is completed, as Figure 2 shown, which is a schematic curve diagram of the formation process of a single pulse volume v and pressure p during the process of preparing a single pulse by opening and closing the explosion chamber.

[0165] The moving speed of the hydraulic fluid is much lower than c = √K e / ρ = 1359m / s. In this way, through the accumulation of the pulses of the Fibonacci sequence on the pressure impact of the Δv' = 1ml hydraulic fluid entering the pipeline at the pipe end, the front-end pressure gradually rises, forming a pulse with an average pressure 1.3 times that of a constant-pressure oil source (20MPa) (26MPa) for a volume of 1ml. The moving speed of the pulse hydraulic fluid is much lower than the propagation speed of the density wave, that is, the speed of sound c = √K e / ρ = 1359m / s. Therefore, this 1ml volume of liquid becomes one of the carriers for the negligible-volume density wave oscillation transmission at the front end of the closed hydraulic pipeline.

[0166] The density wave is also a kind of existence, a conductive material structure, similar to the existence of a field, which can be detected in a closed pipeline through the pressure change caused by the density change. A first fiber Bragg grating sensor is arranged at the front end of the hydraulic pipeline; a blind hole is arranged at the tail end of the hydraulic pipeline, and a second fiber Bragg grating sensor is arranged in the blind hole; as Figure 3 , Figure 4 and Figure 5 shown, the hydraulic oil pressure, the amplitude and the number of hydraulic pulses of the hydraulic pipeline are scanned, measured and recorded by the first fiber Bragg grating sensor and the second fiber Bragg grating sensor, so as to measure the propagation sound speed of the oil in the hydraulic pipeline under a certain pressure.

[0167] Because the estimated sound speed c = √K e / ρ = 1359m / s is very fast, therefore, lengthening the distance L of the hydraulic pipeline is more conducive to having sufficient time length to capture the pulsation and measure the sound speed. Suppose the pipeline length L = 800m, then Δt = L / c = 800 / 1359 = 0.58s; then set the same scanning period T of the first fiber Bragg grating sensor 5 and the second fiber Bragg grating sensor 6 << Δt = 0.58s, and select T = Δt / 10 = 0.058s. At present, the scanning time of spectrometers abroad can reach 9μs, and the scanning time of spectrometers in China can reach the ms level, and T can be achieved.

[0168] According to the setting, the length of the hydraulic pipeline 4 is L long enough, and the straightness is ensured to be not more than 1mm / 1000mm. Moreover, at least one fixed pipe clamp is required to fix the pipeline every 2m. (The length of the hydraulic pipeline 4 is much longer than the length l of the third conical nozzle 11 of the valve body 22, so the length of sensors and the like can be ignored.) Assemble the long and straight hydraulic pipeline 4: the connecting end of the hydraulic pipeline 4 and the fourth conical nozzle 12 is inserted into the measuring joint of the first fiber Bragg grating sensor 5; the measuring joint of the second fiber Bragg grating sensor 6 is arranged at the far end of the pressure pipeline away from the third conical nozzle 11, and the measuring joint of the second fiber Bragg grating sensor 6 has a blind hole, and the second fiber Bragg grating sensor 6 is arranged at the bottom of the blind hole for receiving the impact and reflection of the pulse; and the hydraulic pipeline 4 is a long and straight pipeline with a preset length and is reliably fixed to ensure the stiffness of the hydraulic pipeline 4 itself, so that its natural frequency avoids more than 1.5 times of the pulse excitation frequency of the experiment.

[0169] Furthermore, the driving mechanism includes a driving motor, or a driving motor and a gear assembly. The driving motor can ensure the quantitative control of a programmable high operating speed, such as a servo motor, etc.; the gear assembly can be a speed increasing box or a gearbox, which can ensure a constant transmission ratio, and is connected between the driving motor and the driving shaft 1 through the gear assembly, so that the driving shaft 1 rotates quantitatively according to a preset speed or angle.

[0170] Further, before setting a sufficient amount of pulses, it also includes: at the initial stage of the test method, by rotating the valve core 23 to the recovery state, the oil in the hydraulic pipeline 4 to be tested is subjected to flow replacement, so that the air in the hydraulic pipeline 4 can enter from the closed blind end and flow back to the oil tank from the low-pressure chamber, achieving the purpose of flushing and removing bubbles; rotating the valve core 23 to the closed state and standing for a set time under a set pressure to ensure that the residual free bubbles in the hydraulic pipeline 4 dissolve and disappear under pressure, so that the oil has a relatively constant bulk modulus of elasticity at a certain temperature and pressure.

[0171] What is not described in this application can be achieved by adopting or referring to the existing technology.

[0172] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments.

[0173] The above are only the embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the scope of the claims of the present application.

Claims

1. A measuring device for the sound velocity in a medium and high pressure hydraulic pipeline, characterized in that, It includes a drive shaft, a rotary valve, a transition end cover, a hydraulic pipeline, a first fiber Bragg grating sensor and a second fiber Bragg grating sensor; the axial output port of the rotary valve is connected to the transition end cover, and the transition end cover is connected to the hydraulic pipeline; the front end of the hydraulic pipeline is connected to the first fiber Bragg grating sensor, and the tail end is connected to the second fiber Bragg grating sensor; the rotary valve includes a valve cover, a valve body, a rotary spool and a bearing arranged in the valve body; the drive shaft is connected to the rotary spool, and there are an isolated blast chamber and a low-pressure chamber in the rotary spool; the blast chamber has a first conical nozzle, and the low-pressure chamber has a second conical nozzle; the axial output port of the rotary valve has a third conical nozzle; the transition end cover has a fourth conical nozzle; The rotary valve is configured to: control the rotation of the rotary spool by rotating the drive shaft, so that the first conical nozzle and the third conical nozzle form a Laval tube, the third conical nozzle and the fourth conical nozzle form a spindle-shaped pulse generation cavity, the fourth conical nozzle is connected to the hydraulic pipeline, the hydraulic oil in the hydraulic pipeline remains in the pulse generation cavity, and when the hydraulic oil in the blast chamber is sprayed into the pulse generation cavity, it pushes the hydraulic oil in the pulse generation cavity to be pressed into the hydraulic pipeline through the fourth conical nozzle to form an impact pulsating flow, presenting the injection state of the rotary valve outputting pulsating flow to the hydraulic pipeline; or, the second conical nozzle and the third conical nozzle form a Laval tube to recycle the pulsating flow of the hydraulic pipeline through the fourth conical nozzle and the third conical nozzle to form a spindle-shaped pulse elimination cavity and then enter the low-pressure chamber; or, the closed state in which the third conical nozzle is closed between the two states; The first fiber Bragg grating sensor and the second fiber Bragg grating sensor are used to scan, measure and record the hydraulic oil pressure, hydraulic pulse amplitude and number of times of the hydraulic pipeline, so as to measure the propagation sound speed of the oil in the hydraulic pipeline under a certain pressure.

2. The measuring device for the sound velocity in a medium and high pressure hydraulic pipeline according to claim 1, wherein A first fluid passage communicating with the blast chamber and a second fluid passage communicating with the low-pressure chamber are further opened in the rotary spool; A first flow passage communicating with the first fluid passage is circumferentially opened in the valve body, so that the hydraulic oil source with a pressure greater than the constant pressure oil source pressure enters the blast chamber through the first flow passage and the first fluid passage; a second flow passage communicating with the second fluid passage is also circumferentially opened in the valve body, so that the hydraulic oil in the low-pressure chamber flows back to the oil tank through the second fluid passage and the second flow passage.

3. The measuring device for the sound velocity in a medium-high pressure hydraulic pipeline according to claim 2, wherein A check valve is arranged in the first fluid passage, so that when the hydraulic oil in the blast chamber is impacted, the hydraulic oil in the blast chamber does not flow back to the hydraulic oil source, and during the rotation of the rotary valve, the blast chamber always receives the supplement or supply of high-pressure oil from the hydraulic oil source through the check valve; A back pressure valve connecting the low-pressure chamber and the second flow passage is arranged in the second flow passage to ensure that the oil flowing back to the oil tank through the back pressure valve has a certain back pressure in the low-pressure chamber.

4. The measuring device for the sound velocity in a medium and high pressure hydraulic pipeline according to claim 3, wherein, A diaphragm that divides the blast chamber into a gas chamber and a liquid chamber is connected in the blast chamber, and the rotary spool is provided with an inflation port communicating with the gas chamber.

5. The measuring device for the sound velocity in a medium and high pressure hydraulic pipeline according to claim 3, characterized in that, A blind hole is provided at the end of the hydraulic pipeline, and a second fiber Bragg grating sensor is arranged in the blind hole; an external constant-pressure oil source supplies hydraulic oil to the hydraulic pipeline through a bypass check valve at the blind hole end of the hydraulic pipeline, and the air to be discharged from the hydraulic pipeline passes through the pulse-making cavity, the low-pressure cavity, the second fluid passage, the back-pressure valve, and the second flow passage when the rotary valve rotates to the recovery state, and then is discharged from the open-type oil tank.

6. The measuring device for the sound velocity in a medium and high pressure hydraulic pipeline according to claim 1, wherein At least two groups of centering bearings are connected along the axial direction on the outer periphery of the rotary valve core to support the rotation of the rotary valve core; at least two groups of thrust bearings are respectively arranged at both ends of the rotary valve core, and the thrust bearing at the valve cover end pushes the rotary valve core through the valve cover to ensure that the dynamic and static sealing rings between the rotary valve core and the inner end face of the valve body are in close contact; the thrust bearing connected to the inner end face of the valve body is used to ensure that there is enough clearance between the rotary valve core and the inner end face of the valve body to reduce friction. Anti-friction grooves are provided on the circumferential side of the rotary valve core, and the anti-friction grooves are communicated with the low-pressure cavity through a third fluid passage, so that the pressure oil with a certain pressure is in the anti-friction grooves, so that the rotary valve core can be assisted by the pressure oil to be suspended in the circumferential hole of the valve body, and leaks to the centering bearing and thrust bearing that support the rotation of the rotary valve core to provide lubrication for the bearing.

7. The measuring device for the sound velocity in a medium-high pressure hydraulic pipeline according to claim 6, characterized in that, At least two groups of dynamic sealing structures are spaced along the radial direction between the coaxial circular ring surfaces of the rotary valve core and the valve body, and the rotating ring surface where the third conical nozzle is located is arranged between the two groups of dynamic sealing structures to ensure that the oil in the third conical nozzle is not disturbed by the external oil. Dynamic sealing structures are spaced along the axial direction between the circumferential surfaces of the rotary valve core and the valve body, and there are at least two pairs of dynamic sealing structures on both sides of the first flow passage; there are at least two pairs of dynamic sealing structures on both sides of the second flow passage.

8. A method for measuring the sound velocity in a medium- and high-pressure hydraulic pipeline, based on the measuring device for the sound velocity in a medium- and high-pressure hydraulic pipeline according to any one of the above-mentioned claims 1-7, characterized in that, The specific steps include: S1: Set the pulse quantity: First, close the oil supply of the hydraulic oil source, control the rotary valve core to rotate or swing multiple times, so that the oil pressure in the explosion chamber is the same as the pressure of the constant-pressure oil source; then, after the rotary valve core is transferred from the closed state to the injection state, set the opening pressure of the safety valve to 1.1 times the stable pressure in the hydraulic pipeline, and then fill the air chamber in the explosion chamber with high-pressure gas. After the safety valve at the front end of the hydraulic pipeline is detected to open, stop inflating, and then adjust the opening pressure of the safety valve to 1.3 times the stable pressure in the hydraulic pipeline; after the rotary valve core is transferred from the injection state to the closed state, ensure that the oil supply pressure of the hydraulic oil source is greater than 1.3 times the stable pressure in the hydraulic pipeline, then open the oil supply of the hydraulic oil source, and then transfer the rotary valve core from the closed state to the injection state, and measure and record the duration t' from the closed state to the injection state of the rotary valve core and maintaining the injection state until the safety valve at the front end of the hydraulic pipeline opens. S2: Set the pulsating flow test time period t: Control the rotary valve core to be transferred from the recovery state to the closed state, so that the hydraulic oil in the hydraulic pipeline reaches the set pressure; then transfer the rotary valve core from the closed state to the injection state according to the duration of 1 / 3t', and then transfer the rotary valve core from the injection state to the closed state according to the duration of 1 / 3t' to ensure that the safety valve at the front end of the hydraulic pipeline does not open. In the above process, the pressure pulse amplitude A of the hydraulic oil in the hydraulic pipeline is measured by the first fiber Bragg grating sensor and recorded in the time sequence of the spectrometer scanning period T 1i value until A 1Ni ≤0.707A 11 value is measured. Let the A 11 value be the maximum value among A 1i values (i = 1, 2, 3,...), where the pulse amplitude values are all the amplitudes within the effective width of the spectrometer-filtered acquisition signal; find and record the number of scans N 11 of the scanning period T measured by the first fiber Bragg grating sensor from A 1Ni to A i from the record of the spectral recorder; at the same time, the pressure pulse amplitude A of the hydraulic oil in the hydraulic pipeline is measured by the second fiber Bragg grating sensor and recorded in the time sequence of the spectrometer scanning period T 2j value until A 2Nj value ≤ 0.707A 21 value is measured. Let the A 21 value be the maximum value among A 2j values (j = 1, 2, 3,...); find and record the number of scans N 21 of the scanning period T measured by the second fiber Bragg grating sensor from A 2Ni to A j from the record in the spectral recorder; record N = min{N i , N j}; Calculate and record the pulsating flow decay duration \(t1 = N*T\), where \(T\) is the spectrometer scanning period shared by the first fiber Bragg grating sensor and the second fiber Bragg grating sensor; set the pulsating flow test time period \(t \lt t1\). S3: Test procedure for single pulse emission: Set the duration \(t3\) for the rotary spool to maintain the recovery state such that \(t3\geq t1*3\), ensuring that the high-pressure hydraulic oil in the hydraulic pipeline flows back to the oil tank through the low-pressure chamber within more than 3 times the pulsating flow decay duration \(t1\), thereby reducing the pressure value of the hydraulic oil in the hydraulic pipeline and fully eliminating the pressure pulsating flow; then transfer from the recovery state to the closed state, and maintain the closed state for a duration \(t5\geq t1*5\) to ensure that the front end of the hydraulic pipeline remains closed for a certain period of time, so that the pressure of the hydraulic oil in the hydraulic pipeline rises to a constant value under the replenishment of the external constant-pressure oil source to keep the elastic modulus of the oil constant and then enter the test cycle: During the rotation of the spool, set the total rotation angle of the Laval nozzle channel from the zero opening state to the fully open state and then continue to rotate back to the zero opening state of the Laval nozzle channel as one pulsating flow process, and set the total duration \(t2\) of one pulsating flow process; transfer the rotary spool from the injection state to the closed state, and maintain the closed state for a duration \(t4 = t / 3 = 2N*T / 9\), then transfer to the duration \(t3\) for the rotary spool to maintain the recovery state such that \(t3\geq t1*3\) to enter the test cycle of the next emission pulse; S4: Test procedure for multi-pulse modulated emission: Set the duration \(t3\) for the rotary spool to maintain the recovery state such that \(t3\geq t1*3\), ensuring that the high-pressure hydraulic oil in the hydraulic pipeline flows back to the oil tank through the low-pressure chamber within more than 3 times the pulsating flow decay duration \(t1\), thereby reducing the pressure value of the hydraulic oil in the hydraulic pipeline and fully eliminating the pressure pulsating flow; then transfer from the recovery state to the closed state, and maintain the closed state for a duration \(t5 = t1*5\) to ensure that the front end of the hydraulic pipeline remains closed for a certain period of time, so that the pressure of the hydraulic oil in the hydraulic pipeline rises to a constant value under the replenishment of the external constant-pressure oil source to keep the elastic modulus of the oil constant and then enter the test cycle; set the rotation speed of the rotary spool to a constant \(\omega\). During the rotation of the spool, set the total rotation angle of the Laval nozzle channel from the zero opening state to the fully open state and then continue to rotate back to the zero opening state of the Laval nozzle channel as one pulsating flow process, and set the radius of the rotation center of the Laval nozzle as \(R\) and the diameter of the Laval nozzle as \(d\), and the total duration \(t6\) of one pulsating flow process is approximately \((d / R) / \omega\); the spool continues to rotate at the speed \(\omega\). After rotating about half a week in the closed state, set the total rotation angle of the Laval nozzle channel from the zero opening state to the fully open state and then continue to rotate back to the zero opening state of the Laval nozzle channel as one pulse-eliminating flow process, the radius of the rotation center of the Laval nozzle is still \(R\), the diameter of the Laval nozzle is still \(d\), and the total duration \(t7\) of one pulse-eliminating flow process is approximately \((d / R) / \omega\); the spool continues to rotate at the speed \(\omega\). After rotating about half a week in the closed state, enter the next pulsating flow process,... The spool rotates continuously at the speed \(\omega\) to obtain a cycle of pulsating flow process - pulse-eliminating flow process - pulsating flow process with a constant period; S5: Selection of the spectrometer scanning period \(T\): Estimate the sound velocity c of the oil in the hydraulic fluid. The magnitude of the sound velocity c can be calculated by the formula: c = √K e / ρ; Where, K e is the elastic modulus of the oil under a certain pressure in the hydraulic pipeline, with the unit of Pa; ρ is the oil density, with the unit of kg / m 3 ; c is the sound propagation speed in the oil, with the unit of m / s; where p is the pressure of the oil in the closed pipeline, with the unit of MPa; K e is the fitted elastic modulus, with the unit of 10 2 MPa; e is the natural constant 2.718; When the length of the hydraulic pipeline is L, the time interval between adjacent pulses measured by the first fiber Bragg grating sensor and the second fiber Bragg grating sensor is not greater than Δt = L / c; Select a detection accuracy of 10%, then set the spectrometer scanning period T1 ≤ Δt / 10; By comparing the pulse scan count N of the first fiber Bragg grating sensor for the maximum pulse amplitude A within a test period max ={A 11}, with the pulse scan count N of the second fiber Bragg grating sensor for the maximum pulse amplitude A 11max ={A max}; 21} 21max ; If N min = min{N 11max , N 21max} ≥ 10, then the spectrometer scanning period T = T1 is selected; S6: Measurement data processing for single-pulse emission: During the test period, by comparing the maximum pulse amplitude A measured by the first fiber Bragg grating sensor 11 with the maximum pulse amplitude A measured by the second fiber Bragg grating sensor 21 to obtain the scanning pulse period count N 20 ; Then, the running time Δt of the pulse from the first fiber Bragg grating sensor to the second fiber Bragg grating sensor can be obtained as Δt = T * N 20 The sound velocity of the hydraulic oil at this pressure in the hydraulic pipeline can be obtained as: c1 = L / [N 20 *T] where c1 is the sound speed of the pulse in hydraulic oil under constant pressure, with the unit of m / s; N 20 is the count of the scanning pulse period for comparing the maximum pulse amplitude A 11 measured by the first fiber Bragg grating sensor to the maximum pulse amplitude A 21 measured by the second fiber Bragg grating sensor; L is the length between the first fiber Bragg grating sensor and the second fiber Bragg grating sensor of the hydraulic pipeline for pulse testing, with the unit of m; T is the scanning period of the spectrometer, with the unit of s; S7: Measurement method for multi-pulse modulation emission: In the test procedure of multi-pulse modulation transmission, similar to the Fizeau gear method for measuring the speed of light, adjust the rotational speed ω so that when the pulse generated in the pulse generation cavity during the pulsating flow process is reflected back to the pulse generation cavity, the pulse generation cavity enters the pulse elimination flow process, thereby eliminating pulsation and ensuring a constant pressure in the hydraulic pipeline. Since the second fiber Bragg grating sensor is at the blind end of the pipeline, close to the constant pressure source for oil supply, the influence of the pulse elimination flow process on its pressure can be ignored, and it can only measure the pulse generated in the pulse generation cavity and the pulse superposition. Adjust the rotational speed ω so that the amplitude of the pulse generated in the pulse generation cavity measured by the second fiber Bragg grating sensor at the blind end of the pipeline is greater than the constant pressure in the hydraulic pipeline and not greater than the initial value A of the pulse amplitude measured by the first fiber Bragg grating sensor 1max , and there is no subsequent superposition and increase, while the maximum value of the pulse amplitude measured by the first fiber Bragg grating sensor is equal to the initial value A 1max , the minimum value A of the pulse amplitude 1min is lower than the constant pressure in the hydraulic pipeline, and there is no subsequent superposition and change either. It can be considered that in the test of multi-pulse modulation transmission, when the pulse generated in the pulse generation cavity during the pulsating flow process is reflected back to the pulse generation cavity after passing through the blind end of the pipeline, the pulse generation cavity just enters the pulse elimination flow process; record the scanning pulse period count N 1max measured by the first fiber Bragg grating sensor 1max and the scanning pulse period count N 1min measured by the first fiber Bragg grating sensor 1min ; take M = ceiling(abs(N 1min -N 1max )); The sound velocity of the hydraulic oil at this pressure in the hydraulic pipeline can be obtained as: c2 = 2L / [M*T] Alternatively, in a cycle of a pulsating flow process and a pulse-attenuating flow process, the modulation period T1 = π / ω is equal to the total distance 2L traveled by the pulse generated by the pulse-forming cavity and reflected back to the pulse-forming cavity divided by the sound velocity c. The third sound velocity of the hydraulic oil at this pressure in the hydraulic pipeline can be obtained as: c3 = 2L / [π / ω] wherein, c2 or c3 is the sound velocity of the pulse in the hydraulic oil under a constant pressure, with the unit of m / s; M is the scanning pulse period count N of A measured by the first fiber Bragg grating sensor 1min and the maximum positive integer value other than zero of the difference between the scanning pulse period count N of the measured A 1min and the scanning pulse period count N of the measured A 1max ; T is the scanning period of the spectrometer, with the unit of s; ω is the rotational speed of the rotary valve core when the pulse generated in the pulse-making cavity in the pulsating flow process returns to the pulse-making cavity after reflection and the pulse-making cavity enters the pulse-eliminating flow process during the test of multi-pulse modulation emission, with the unit of rad / s; L is the length between the first fiber Bragg grating sensor and the second fiber Bragg grating sensor of the hydraulic pipeline for pulse test, with the unit of m; 1max ​ Compare abs(c3 - c2) / c3 or abs(c3 - c2) / c2. When the percentage is not greater than 1%, select c2 or c3 as the measured value of the sound velocity of the pulse in the hydraulic oil without bubbles under a constant pressure.

9. The method for measuring the sound velocity in a medium and high pressure hydraulic pipeline according to claim 8, characterized in that, Drive the drive shaft to rotate according to the set program through the drive mechanism. When the blast chamber of the rotary spool rotates to be connected to the nozzle of the valve body, the air in the air chamber of the blast chamber expands, and through the action of the diaphragm, the high-pressure oil is sprayed into the pulse-forming cavity through the Laval nozzle. The high-pressure oil that cannot retreat due to inertia and the limitation of the third conical nozzle continues to rush forward in the pulse-forming cavity and is compressed into the hydraulic pipeline through the fourth conical nozzle. Blocked by the high-pressure oil at the front end of the hydraulic pipeline, a sudden change occurs on the wave front of the oil at the front end of the hydraulic pipeline to form a compression wave and propagate along the hydraulic pipeline at the sound velocity c, which is recorded as a high-pressure pulse shock wave; When the throat of the blast chamber of the rotary spool rotates out of the Laval nozzle of the valve body, it enters the closed state between the injection state and the recovery state of the rotary valve, that is, the third conical nozzle is closed, and the Laval nozzle of the Laval tube is cut off and closed, so that the high-pressure pulse shock wave propagating along the hydraulic pipeline at the sound velocity c is reflected at the end of the hydraulic pipeline, and after attenuation through the hydraulic pipeline and the pulse-forming cavity, it is completely reflected by the third conical nozzle and the rotary spool in the pulse-forming cavity. The formed reflected shock wave rushes forward again in the pulse-forming cavity, is compressed into the hydraulic pipeline through the fourth conical nozzle, and propagates along the pipeline at the sound velocity c to form a secondary high-pressure pulse shock wave after attenuation; This kind of high-pressure pulse shock wave reflects back and forth and attenuates in the hydraulic pipeline with both ends closed, thus forming a single oscillating pulse wave that oscillates back and forth and attenuates without superposition in the closed hydraulic pipeline.

10. A method for measuring the sound speed in a medium and high pressure hydraulic pipeline according to claim 8, characterized in that, Before setting the sufficient number of pulses, it also includes: In the initial stage of the test method, by switching the rotary spool to the recovery state, the oil in the hydraulic pipeline to be tested is flow-replaced, so that the air in the hydraulic pipeline can enter from the closed blind end and flow back to the fuel tank from the low-pressure chamber, achieving the purpose of flushing and removing bubbles; switch the rotary spool to the closed state and stand for a set time under the set pressure to ensure that the residual free bubbles in the hydraulic pipeline dissolve and disappear under pressure, so that the oil has a relatively constant bulk modulus of elasticity at a certain temperature and pressure.

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