CN114740220B - Method for measuring linear flow velocity based on ultrasonic Doppler - Google Patents
Method for measuring linear flow velocity based on ultrasonic Doppler Download PDFInfo
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- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
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- G01P5/241—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the direct influence of the streaming fluid on the properties of a detecting acoustical wave by using reflection of acoustical waves, i.e. Doppler-effect
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Abstract
The invention provides a method for measuring linear flow velocity based on ultrasonic Doppler, which comprises the steps of mixing an echo signal with another path of reference signal with the same frequency and the same phase, filtering out an emission fundamental frequency, outputting a difference frequency signal, wherein the difference frequency signal comprises different water layer flow velocity data, dividing an AD value corresponding map of the difference frequency signal into blocks with the same number as the water layers, and providing data support for subsequent invalid flow velocity identification and layering flow velocity calculation, wherein each block corresponds to one water layer data; different water layer signal frequencies overlapped in the echo signals can be unfolded through wavelet 6-order transformation, the method has higher resolution, all frequency signals in the echo signals can be identified, time domain positions corresponding to all characteristic frequencies in signal data of each water layer are positioned, and therefore real water flow frequency signals and invalid interference frequency signals of each water layer are obtained, the problem that layering flow velocity cannot be calculated by the existing single ultrasonic Doppler flow velocity equipment is solved, and the real flow velocity value obtained through the method is closer to the real situation.
Description
Technical Field
The invention relates to the field of liquid phase flow velocity measurement, in particular to a method for measuring linear flow velocity based on ultrasonic Doppler.
Background
At present, a conventional ultrasonic Doppler flow rate meter applies the principle of acoustic Doppler effect, uses an ultrasonic transducer and detects the flow rate by ultrasonic waves. The instantaneous flow rate and the average flow rate can be measured, and the flow rate meters belong to point flow rates, namely the flow rate values at the positions of the ultrasonic sensors can be measured, and the average flow rate of the period of time is calculated by recording the instantaneous flow rate values of the period of time. However, the flow rate in both the pipe and the channel is never a point, the flow rate between the different water layers is different, the surface flow rate is the largest, the bottom flow rate is the smallest, and the flow rate between the different water layers is different, and if the flow rate is measured only by the position of the water layer where the flow meter is installed, the error is large. On the other hand, the self-rotation of the float in the water and the penetration after entering the measurement zone have a large error on the instantaneous flow rate. Therefore, in order to solve the above problems, the present invention provides a method for measuring a linear flow velocity based on ultrasonic doppler, which solves the technical problem that a single ultrasonic doppler flow velocity device cannot calculate a stratified flow velocity, and identifies and filters ineffective flow velocity in the process of calculating the stratified flow velocity, so as to obtain a flow velocity closer to a real water flow velocity.
Disclosure of Invention
In view of the above, the invention provides a method for measuring linear flow velocity based on ultrasonic Doppler, which solves the technical problem that a single ultrasonic Doppler flow velocity device cannot calculate the layered flow velocity, and identifies and filters ineffective flow velocity in the process of calculating the layered flow velocity so as to obtain the flow velocity of water flow which is more similar to the real flow velocity.
The technical scheme of the invention is realized as follows: the invention provides a method for measuring linear flow velocity based on ultrasonic Doppler, which comprises the following steps:
s1, an ultrasonic probe periodically transmits a frequency signal and receives an echo signal, the echo signal is mixed with another path of same-frequency and same-phase signal to obtain difference frequency signals formed by different water layers, and a plurality of difference frequency signals are subjected to AD conversion to form a plurality of maps;
s2, identifying invalid flow velocity characteristic signals and real flow velocity signals of each water layer based on discrete wavelet transformation, carrying out time-sharing Fourier transformation on the real flow velocity signals of each water layer to obtain frequency values of the real flow velocity signals of each water layer, and calculating the flow velocity values of each water layer based on a Doppler frequency shift formula.
On the basis of the above technical solution, preferably, S2 specifically includes the following steps:
s101, equally dividing the cache data of each map into blocks with the same number as that of water layers, wherein each block corresponds to one water layer signal data;
s102, positioning time domain positions corresponding to all characteristic frequencies in water layer signal data of each layer by using Daubechies wavelet 6-order transformation;
s103, if flow velocity signals with different frequency characteristics appear in the same water layer at different moments, the flow velocity signals are the interference signals of the protruding objects;
if flow velocity signals with different frequency characteristics appear in different water layers at the same moment, the flow velocity signals are self-rotation interference signals;
if flow velocity signals conforming to flow velocity layering appear in different water layers at different moments, the flow velocity signals are real flow velocity signals;
s104, carrying out time-sharing Fourier transform on the water layer signal data of each layer to obtain frequency values of real flow velocity signals in different water layers, and substituting the frequency values of the real flow velocity signals of the different water layers into a Doppler frequency shift formula to calculate the real flow velocity of the different water layers.
On the basis of the technical scheme, preferably, the buffer data of each map in S101 occupies 16384 int data, each map is equally divided into four blocks, and the four blocks correspond to four layers of water layer signal data; the data length of [0,4095] is the first water layer signal data, the data length of [4096,8191] is the second water layer signal data, the data length of [8192,12287] is the third water layer signal data, and the data length of [12287,16383] is the fourth water layer signal data.
On the basis of the above technical solution, preferably, S102 specifically includes the following steps:
s201, carrying out 6-order wavelet transformation on each layer of water layer signal data to obtain a window with the minimum resolution of [0,160] hz and 64int data lengths;
s202, grabbing maximum amplitude signals after wavelet transformation in different windows;
s203, normalizing amplitude signals with maximum amplitude values captured by different windows;
s204, constructing a multidimensional matrix based on different water layers and frequency signals at different moments.
Based on the above technical scheme, preferably, in S204, the multidimensional matrix is f.max [ n ] [ m ] (x), n represents the nth map, m represents the mth water layer, and x represents the xth int data.
On the basis of the above technical solution, preferably, S103 specifically includes the following steps:
s301, setting a first window length threshold, selecting water layer signal data of the same water layer at different moments, defining frequency signals with the two data lengths being larger than the first window length threshold as first characteristic points, defining flow velocity signals with different frequency characteristics at different moments of the same water layer if the two first characteristic points are not equal, and judging the flow velocity signals as the protrusion interference signals;
s301, setting a second window length threshold value, wherein the second window length threshold value is larger than the first window length threshold value, selecting water layer signal data of different water layers and at the same moment, defining frequency signals with the two data lengths being larger than or equal to the second window length threshold value as second characteristic points, defining flow velocity signals with different frequency characteristics at different water layers and at the same moment if the two second characteristic points are not equal, and judging the flow velocity signals as self-rotation interference signals;
s303, setting a third window length threshold value, wherein the third window length threshold value is larger than or equal to the first window length threshold value and smaller than the second window length threshold value, selecting water layer signal data of different water layers and at different moments, defining frequency signals with the two data lengths equal to the third window length threshold value as third characteristic points, defining flow rate signals conforming to flow rate layering at different time points as different water layers if the two third characteristic points are equal, and judging the flow rate signals as real flow rate signals.
On the basis of the above technical solution, preferably, S104 specifically includes the following steps:
s401, carrying out Fourier transform on the signal data of each layer of water layer to obtain energy values and modulus values of different frequency components in each block;
s402, taking a frequency point corresponding to the maximum modulus value in the water layer signal data of each layer as a maximum signal frequency point, and calculating the frequency of the maximum signal frequency point based on a frequency calculation formula, wherein the frequency of the maximum signal frequency point is the frequency of a real flow velocity signal;
s403, substituting the frequency of the real flow velocity signal of each water layer into a Doppler frequency shift formula to calculate the flow velocity of different water layers.
On the basis of the above technical solution, preferably, the energy values of the different frequency components in S401 and their modulus values are respectively:
wherein the factors are: e, e jw ＝cos(y)+j*sin(y)；
Wherein X (k) and +.>
K is the k-th difference frequency signal frequency point which is the frequency component after Fourier transformation; y is the time domain AD signal; w represents an angle; q is the sequence; n represents the window size of the fourier transform, n=4096;
the modulus of the kth frequency point is:
on the basis of the above technical solution, preferably, the frequency calculation formula in S402 is:
wherein m represents an m-th aqueous layer; f (m) represents the frequency of the true flow rate signal in the m-th water layer; k (m) represents the maximum difference frequency signal frequency point of the m-th water layer; f (F) S Representing the sampling frequency; n denotes the window size of the fourier transform, n=4096.
Based on the above technical solution, preferably, the doppler shift frequency formula in S403 is:
wherein f represents the transmitting frequency of the ultrasonic probe; f (f) d Representing the received frequency, f d =f-F (m); c represents the ultrasonic velocity; v (m) represents the flow rate of the mth layer; θ represents the angle between the water flow and the ultrasonic wave.
Compared with the prior art, the method for measuring the linear flow velocity based on ultrasonic Doppler has the following beneficial effects:
(1) The method comprises the steps that a mixing circuit is arranged to mix an echo signal with another same-frequency and same-phase reference signal, then the transmitted fundamental frequency is filtered, and a difference frequency signal is output, wherein the difference frequency signal comprises different water layer flow velocity data, the data length of the difference frequency signal is divided into blocks with the same number as the water layers based on the time of the echo signal returned by ultrasonic waves in water, each block corresponds to one water layer data, and data support is provided for subsequent invalid flow velocity identification and layered flow velocity calculation;
(2) Different water layer signals superimposed in the echo signals can be frequency-unfolded by adopting wavelet 6-order transformation, so that the method has higher resolution, all frequency signals in the echo signals can be identified, and the time domain positions corresponding to all characteristic frequencies in the water layer signal data of each layer are positioned, so that the real water flow frequency signals and the invalid interference frequency signals of each layer of water layer are obtained;
(3) The problems that the existing ultrasonic Doppler flow velocity equipment cannot identify and filter invalid flow velocity are solved by comparing the same water layer, different moments, or different water layers, the same moments, or frequency characteristics of different water layers and different moments;
(4) The frequency value of the real flow velocity signal of each layer of water layer is calculated by adopting time-sharing Fourier transform, and the flow velocity of different water layers can be calculated based on Doppler frequency shift formula, so that the problem that the layering flow velocity cannot be calculated by the existing single ultrasonic Doppler flow velocity equipment is solved, and the real flow velocity value obtained by the method is closer to the real condition.
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In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of the use of the ultrasonic Doppler measurement line flow rate device of the present invention;
FIG. 2 is a block diagram of an ultrasonic Doppler line flow rate measurement device of the present invention;
FIG. 3 is a circuit diagram of a signal transmitting circuit in the ultrasonic Doppler measurement line flow rate device of the present invention;
FIG. 4 is a circuit diagram of an echo receiving circuit in an ultrasonic Doppler measurement line flow rate device of the present invention;
FIG. 5 is a circuit diagram of a mixer circuit in an ultrasonic Doppler measurement line flow rate device of the present invention;
FIG. 6 is a circuit diagram of a signal amplifying circuit in the ultrasonic Doppler measurement line flow rate device of the present invention;
FIG. 7 is a flow chart of a method for measuring linear velocity based on ultrasonic Doppler according to the present invention;
FIG. 8 is a graph of echo signals received based on the ultrasonic Doppler line flow method of the present invention;
FIG. 9 is a signal spectrum after wavelet transformation of a spectrum corresponding to a difference frequency signal in a linear velocity measurement method based on ultrasonic Doppler according to the present invention;
FIG. 10 is an exploded view of real-time data of a first aqueous layer in a first image based on an ultrasonic Doppler measurement line flow rate method according to the present invention.
Detailed Description
The following description of the embodiments of the present invention will clearly and fully describe the technical aspects of the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, are intended to fall within the scope of the present invention.
Example 1
Conventional ultrasonic Doppler flowmeters are point flowrates, i.e. flow rate values at the location of an ultrasonic sensor can be measured, and the average flow rate over a period of time is calculated by recording instantaneous flow rate values over that period of time. However, the flow rate in both the pipe and the channel is never a point, the flow rate between the different water layers is different, the surface flow rate is the largest, the bottom flow rate is the smallest, and the flow rate between the different water layers is different, and if the flow rate is measured only by the position of the water layer where the flow meter is installed, the error is large. Therefore, in order to solve the above-mentioned problem, this embodiment provides a device for measuring a linear flow velocity based on ultrasonic doppler, which is provided with a mixing circuit, mixes an echo signal with another reference signal with the same frequency and the same phase through the mixing circuit, filters out a transmitting fundamental frequency and outputs a difference frequency signal, wherein the difference frequency signal includes different water layer flow velocity data, and based on the time of the echo signal returned by the ultrasonic wave in water, the data length of an AD value corresponding map of the difference frequency signal is divided into blocks with the same number as the water layers, each block corresponds to one water layer data, and data support is provided for subsequent ineffective flow velocity identification and layered flow velocity calculation.
Specifically, as shown in fig. 2, the device for measuring the linear flow velocity by ultrasonic doppler includes an ultrasonic transmitting probe, an ultrasonic receiving probe, a signal transmitting circuit, an echo receiving circuit, a mixing circuit, a signal amplifying circuit, and a signal processing circuit. The input end of the signal transmitting circuit is electrically connected with the signal processing circuit, the output end of the signal transmitting circuit is connected with the ultrasonic transmitting probe, the ultrasonic receiving probe is electrically connected with the input end of the echo receiving circuit, the output end of the echo receiving circuit is electrically connected with the input end of the mixing circuit, and the output end of the mixing circuit is electrically connected with the analog input end of the signal processing circuit through the signal amplifying circuit.
Preferably, the ultrasonic emission probe is arranged in the water layer at the bottommost layer, and the ultrasonic emission probe forms a preset included angle with the water layer. The higher the transmission frequency of the ultrasonic wave is, the larger the viscosity coefficient of the medium to the acoustic wave is, the larger the loss is, the shorter the response distance is, the lower the transmission frequency is, the smaller the loss is, and the longer the response distance is; however, the higher the transmission frequency, the higher the resolution of the frequency response, the higher the accuracy of the flow rate that can be measured, and the lower the opposite frequency, the lower the accuracy of the flow rate that can be measured. As shown in FIG. 1, in this embodiment, the water depth of 5M is taken as an example, and the difference of layering definition is considered in the comprehensive consideration of the recognition accuracy of the flow velocity and the linear flow velocity calculation, wherein the transmission frequency of the ultrasonic transmission probe is 450KHZ, the distance range of the recognized water layer is 0-5M, the flow velocity range is 0-5M/s, the flow velocity accuracy is 0.01M/s, and the water layer is divided into 4 layers. The ultrasonic probe transmits a frequency signal of 4ms each time, the transmission speed of sound waves in water is about 1450M/s, the inclination angle is 30 degrees, the ultrasonic waves are transmitted to a distance of 5 meters from the ultrasonic waves to return, the ultrasonic receiving probe receives echo signals, and the maximum time is: 5/cos (30 °)/1450=0.00398 s 2= 0.00796s≡8ms. The transmission time of the trigger here is 10ms sufficient for a signal reception over a distance of 5 meters.
Preferably, the signal transmitting circuit transmits ultrasonic signals of 4ms at intervals of 96ms, and stores 10 sets of data and forms 10 maps, wherein each set of data comprises 16384 int data. Further preferably, the signal transmitting circuit adopts a structure as shown in fig. 3, wherein YS is a 450Khz square wave signal, IRF7301 is a double MOS tube structure, the signal is input from a U2_2 pin, the MOS tube is controlled by switch shaping, a U3_7 pin outputs the signal, T1 is a magnetic ring and U3 together shape the square wave signal into a sine wave signal, the input signal is a 0-3.3V signal, and the peak-to-peak value of the output signal is 33V, so as to drive the ultrasonic probe. C5 adjusts the integral delay capacitance of the input signal, R14 and R4 are current resistors and R5 together regulate the driving current of the input end of T1.
Preferably, the echo receiving circuit adopts a structure as shown in fig. 4, wherein the SIGNAL is an echo input SIGNAL, because the echo SIGNAL is a mA-stage current SIGNAL, the echo SIGNAL is transmitted into a base stage of a triode Q1 after being subjected to voltage division through R16, R26 and R30, and is output from an emitter after being amplified, and the SIGNAL U6 is an inverting amplifier to amplify the speed R12/R17, and output the SIGNAL of 0-5V.
Preferably, since different flow rate frequencies are superimposed on the transmission frequency in the echo signal, the transmission fundamental frequency in the echo signal is filtered after hardware mixing, so that difference frequency signals formed by different water layers are obtained. Further preferably, the mixer circuit adopts a structure as shown in fig. 5, RF is a signal input end of the mixer, Y3 is another path of 450KHZ signals with the same frequency and the same phase input by the control unit, and the mixer performs vector subtraction on the RF and the Y3 signals and outputs a difference frequency signal IF.
Preferably, the signal amplifying circuit adopts a structure as shown in fig. 6, wherein C44 is an isolated ac capacitor, R44 and R45 are together adjusted to have a bias voltage of 1.5V, and a difference frequency ac signal is superimposed on the same phase end of the operational amplifier, the IF receives the output signal of the mixer, filters the dc component, and then sends the output signal to the same phase end of the operational amplifier, the gain of the output signal is ag=r40/r42=5.1, and the output signal TP2 is sent to the ADC of the signal processing circuit.
The working principle of the embodiment is as follows: the signal transmitting circuit drives the ultrasonic receiving probe to transmit ultrasonic waves, the ultrasonic waves pass through different water layers from the water layer at the bottommost layer and form reflection on the water surface, echo signals of the ultrasonic waves are received by the ultrasonic receiving probe and are amplified by the echo receiving circuit and then input to the mixing circuit, the mixing circuit carries out vector subtraction on the echo signals and 450KHZ signals with the same frequency and the same phase with the other channel and then outputs difference frequency signals, the difference frequency signals are amplified by the signal amplifying circuit and then output to the signal processing circuit, and the signal processing circuit filters errors brought by self-rotation and the abrupt objects by different signal processing methods, so that the true different water layer flow rates are calculated.
The beneficial effects of this embodiment are: the method comprises the steps of mixing an echo signal with another same-frequency and same-phase reference signal by a mixing circuit, filtering out an emission fundamental frequency and outputting a difference frequency signal, wherein the difference frequency signal comprises different water layer flow velocity data, and dividing an AD value map of the difference frequency signal into blocks with the same number as water layers according to the data length based on the time of the echo signal returned by ultrasonic waves in water, wherein each block corresponds to one water layer data, so that data support is provided for subsequent invalid flow velocity identification and layered flow velocity calculation.
Example 2
Because the self-rotation of the floating object in the water and the influence of the penetrating object on the instantaneous flow velocity after entering the measurement interval have larger errors, the embodiment provides a method for measuring the linear flow velocity based on ultrasonic Doppler on the basis of the embodiment 1, and the errors brought by the self-rotation and the penetrating object are identified and filtered through a signal processing method, so that the true flow velocity of different water layers is calculated. As shown in fig. 7, the method specifically comprises the following steps:
s1, an ultrasonic probe periodically transmits a frequency signal and receives an echo signal, the echo signal is mixed with another path of same-frequency and same-phase signal to obtain difference frequency signals formed by different water layers, and a plurality of difference frequency signals are subjected to AD conversion to form a plurality of maps;
preferably, the present embodiment transmits an ultrasonic signal of 4ms at intervals of 96ms, and stores 10 sets of data and forms 10 maps, wherein each set of data includes 16384 int data.
S2, identifying invalid flow velocity characteristic signals and real flow velocity signals of each layer of water layer based on discrete wavelet transformation, carrying out time-sharing Fourier transformation on the real flow velocity signals of each layer of water layer to obtain frequency values of the real flow velocity signals of each layer of water layer, and calculating the flow velocity values of each layer of water layer based on a Doppler frequency shift formula.
Wherein, S2 specifically includes the following steps:
s101, equally dividing the cache data of each map into blocks with the same number as that of water layers, wherein each block corresponds to one water layer signal data;
preferably, this step is to acquire data for each water layer. In this example, taking water depths of 5 and 4 water layers as an example, 10 sets of data were collected in total. The buffer data of each map occupies 16384 int data, therefore, in this embodiment, [0,4095] data length is the first water layer signal data, [4096,8191] data length is the second water layer signal data, [8192,12287] data length is the third water layer signal data, and [12287,16383] data length is the fourth water layer signal data.
S102, positioning time domain positions corresponding to all characteristic frequencies in water layer signal data of each layer by using Daubechies wavelet 6-order transformation;
preferably, the discrete wavelet transform may decompose the original signal at different resolution levels to obtain two sub-signals, a smoothed signal and a detail signal, respectively, wherein the smoothed signal is decomposed at a lower level, reflecting the profile and trend of the signal sequence, and the detail signal is decomposed at a higher level, reflecting the detail change of the signal sequence. By such decomposition, signals of different time periods in the original signal are decomposed. The method comprises the steps of performing time domain expansion on each layer of water layer signal data, and specifically comprises the following steps:
s201, carrying out 6-order wavelet transformation on each layer of water layer signal data to obtain a window with the minimum resolution of 0-160 hz and 64int data lengths;
preferably, since different water layer flow velocity signals are superimposed in one layer of water layer signal data in the echo signal, each decomposition layer obtained by wavelet decomposition measures the original signal by using different scales. Therefore, there are several scales with several decomposition levels, and the analysis frequency determines the decomposition level, i.e. how fine the scales are needed to measure the signals, and if the scales are not properly selected, the frequency signals contained in the signal data of each water layer cannot be distinguished. Experiments show that when the number of the decomposition layers of wavelet decomposition is 6, the method has higher resolution, and can identify all frequency signals in echo signals, so that the real water flow frequency signals and the invalid interference frequency signals of each layer of water layer are obtained.
Preferably, the sampling frequency of this embodiment is 20480Hz, and therefore, the pre-decomposition frequency of each spectrum is 20480Hz. Because the principle of the discrete wavelet transform method of the signal data of each layer of water layer is the same, only the discrete wavelet transform decomposition process of the signal data of the first layer of water layer in the first group of maps is described herein. Specifically, the corresponding frequency before the first water layer signal data is decomposed is 20480Hz, and the first water layer signal data is decomposed in order 6 to finally form a real-time data decomposition diagram of the first water layer. As shown in fig. 10, after the first-order decomposition frequency, two sub-signals are obtained, and the two sub-signals are respectively represented by D1 and A1, wherein the first-order decomposition frequency of D1 is: d1[0,5120] hz; the first-order decomposition frequency of A1 is as follows: a1[5120,10240] hz; the secondary D1 fraction has a frequency of D11[0,2560] hz, D12[2560,5120] hz, and the secondary A1 fraction has a frequency of A11[5120hz,7680] hz and A12[7680,10240] hz; the third-level decomposition frequency of D1 is D111[0,1280] hz, D112[1280,2560] hz, D121[2560,3840] hz, D122[3840,5120] hz; the frequency of the A1 three-stage decomposition is A111[5120hz,6400] hz, A112[6400,7680] hz, A121[7680,8960] hz and A122[8960,10240] hz; the method is further divided into a 4 th level, a 5 th level and a 6 th level, so that the minimum resolution of the 6 th level is 0,160 hz, and the data length is 64int.
FIG. 8 is a received echo signal, the echo signal of FIG. 8 superimposed with different flow rate signals of 100hz, 4Khz, 500hz and 7Khz, denoted by f1-f4, respectively; fig. 9 is a wavelet transform diagram, in which a part of signals are disassembled, because the original signals include four different frequency signals f1, f2, f3 and f4, according to the principle of the above data decomposition:
1) The D1 window is [0,5120] hz, the A1 window is [5120,10240] hz signal, and the signal identification of f1 and f3 in the D1 window is maximum; f4 the signal identification is the largest in the A1 window; f2 can be identified in both the D1 window and the A1 window, so the first level decomposition cannot filter the f2 signal;
2) The D11 window is [0,2560] hz, and the D12 window is [2560,5120] hz, so that the signal recognition of f1 and f3 is maximum in the D11 window, and the signal recognition of f2 is maximum in the D12 window;
3) The D111 window is [0,1280] hz, and the D112 window is [1280,2560] hz, so that the signal identification of f1 and f3 in the D111 window is maximum, and the signal of f3 in the D112 window is smaller than that of the D111 window;
4) The D1111 window is [0,640] hz, the D1112 window is [640,1280] hz, so that the signal identification of f1 and f3 is maximum in the D1111 window, and the signal of f3 in the D1112 window is smaller than the D1111 window;
5) The D11111 window is [0,320] hz, the D11112 window is [320,640] hz, the signal identification of f1 is maximum in the D11111 window, and the signal identification of f3 is maximum in the D11112 window;
6) The D111111 window is [0,160] hz, the D111112 window is [160,320] hz, and the signal recognition of f1 is largest in the D111111 window.
The above list is that the original signal contains 4 signal combinations with different frequencies, and the 6 th order wavelet transform can display all the signals with different frequencies separately through windowing, and only the signals with all the frequencies are identified, the identification process can be started.
In this embodiment, as shown in fig. 10, D0-D9 are used to represent real-time data decomposition signals of the first layer of water layer signal data after 6-order decomposition in 10 maps, specifically:
D[0]＝D1[0]+A1[0]＝D11[0]+D12[0]+A11[0]+A12[0]＝....＝D111111[0]+D11111 2[0]+D111121[0]+D111122[0]+....+A122221[0]+A122222[0]；
D[1]＝D1[1]+A1[1]＝D11[1]+D12[1]+A11[1]+A12[1]＝....＝D111111[1]+D11111 2[1]+D111121[1]+D111122[1]+....+A122221[1]+A122222[1]；
......
D[9]＝D1[9]+A1[9]＝D11[9]+D12[9]+A11[9]+A12[9]＝....＝D111111[9]+D11111 2[9]+D111121[9]+D111122[9]+...+A 122221[9]+A 122222[9]。
wherein, D1[0] -D1[9] respectively represent D1 first-order decomposition frequency of the first layer water layer signal in 10 maps; a1[0] -A1[9] respectively represent the A1 first-order decomposition frequency of the first layer water layer signal in 10 maps; d11[0] -D11[9] and D12[0] -D12[9] respectively represent the two secondary fraction frequencies of D1 of the first layer water layer signal in 10 maps; a11[0] -A11[9] and A12[0] -A12[9] respectively represent the two secondary fraction frequencies of A1 of the first layer water layer signal in 10 maps; and so on until the last level of decomposition frequency. The mathematical expression after 6-level decomposition is:
fd (n) =fd 111111 (n) +fd111112 (n) +fd111121 (n) +fd111122 (n) +fa122221 (n) +fa12222 (n), where n represents the nth Zhang Tupu.
S202, grabbing maximum amplitude signals after wavelet transformation in different windows;
preferably, the specific mode is as follows: taking x-i, x and x+i, x-i epsilon [1:64], x epsilon [1:64], x+i epsilon [1:64], if Fd111111 (x+i) is less than or equal to Fd111111 (x) and Fd111111 (x-i) is less than or equal to Fd111111 (x), then Fd111111max (x) =fd 111111 (x), and Fd111112max (x),. The same method can obtain Fd 122222max (x). Where x represents the xth int data and i represents the i int data.
S203, normalizing amplitude signals with maximum amplitude values captured by different windows;
specific: all fd.max (x), fa.max (x) are normalized to f.max (x), x e [1,2,., 64];
s204, constructing a multidimensional matrix based on different water layers and frequency signals at different moments.
Specific: there is F.max [ n ] [ m ] (x) for m and n for different maps for different aqueous layers, with the nth map, m representing the aqueous layer, x representing the xth int data, in this example, n.epsilon.1, 2,..10 ], m.epsilon.1, 2,3,4, x.epsilon.1, 2,..64.
S103, if flow velocity signals with different frequency characteristics appear in the same water layer at different moments, the flow velocity signals are the interference signals of the protruding objects;
if flow velocity signals with different frequency characteristics appear in different water layers at the same moment, the flow velocity signals are self-rotation interference signals;
if flow velocity signals conforming to flow velocity layering appear in different water layers at different moments, the flow velocity signals are real flow velocity signals;
this step is used to identify and extract the true flow rate signal for each water layer. Through the step S1, 10 sets of data are obtained, each set of data is divided into blocks with the same number as the water layer in step S101, the frequency of the signal data of each water layer is subjected to time domain expansion in step S102, at this time, the protrusion interference signal is judged based on the frequency variation characteristic of the protrusion after entering the water layer, the self-rotation interference signal is judged based on the self-rotation to water layer frequency variation characteristic, and the real flow velocity signal is judged based on whether each layer of flow velocity signal accords with the flow velocity layering rule. Preferably, S103 specifically includes the following steps:
s301, setting a first window length threshold, selecting water layer signal data of the same water layer at different moments, defining frequency signals with the two data lengths being larger than the first window length threshold as first characteristic points, defining flow velocity signals with different frequency characteristics at different moments of the same water layer if the two first characteristic points are not equal, and judging the flow velocity signals as the protrusion interference signals;
in general, the protrusion is generated by different conditions such as falling leaves or throwing sundries, and in the process of transmitting ultrasonic signals and receiving echo signals for many times by the Doppler velocimeter, if mh frequency is not recognized for the first N1 times in the same water layer, mh is recognized for the middle N1-N2 times, and the front and rear frequencies are greatly different, then the signals with mh frequency are necessarily the protrusions.
Preferably, the first window length threshold is denoted by Δε, and since the smallest window occupies 64int, Δε=64 in this embodiment.
S302, setting a second window length threshold, wherein the second window length threshold is larger than the first window length threshold, selecting water layer signal data of different water layers and at the same moment, defining frequency signals with the two data lengths being larger than or equal to the second window length threshold as second characteristic points, defining flow velocity signals with different frequency characteristics at different water layers and at the same moment if the two second characteristic points are not equal, and judging the flow velocity signals as self-rotation interference signals;
in general, the self-rotating water flow may be generated due to a vortex generated in fluid mechanics or due to self-rotation caused by entanglement, and the spin rotation generates a flow rate, but this flow rate is not a true water flow rate, and if the self-rotating flow rate is introduced, a true flow rate value must be increased, which is actually wrong. Because the device is installed at the water bottom at an angle of 30 degrees, the self-rotation interference can interfere with a certain layer of water flow signal, and the self-rotation interference is identified by comparing whether the difference of echo flow velocity signals received at the same time between different water layers is large or not.
Preferably, the second window length threshold is denoted as Δε ', Δε' = 3Δε.
S303, setting a third window length threshold value, wherein the third window length threshold value is larger than or equal to the first window length threshold value and smaller than the second window length threshold value, selecting water layer signal data of different water layers and at different moments, defining frequency signals with the two data lengths equal to the third window length threshold value as third characteristic points, defining flow rate signals conforming to flow rate layering at different time points as different water layers if the two third characteristic points are equal, and judging the flow rate signals as real flow rate signals.
In general, after the protrusion interference signal and the self-rotation interference signal are identified, a real flow velocity signal is also required to be identified, and in the real different water layer flow velocity signals, the distribution rule is that v1 is not less than v2 is not less than v3 is not less than v4, wherein v1 represents the bottom layer flow velocity, v2 represents the middle lower layer flow velocity, v3 represents the middle upper layer flow velocity, v4 represents the surface flow velocity, and the frequency difference between v4 and v1 does not exceed the flow velocity layering rule.
Preferably, the third window length threshold is denoted by Δε ", Δε+.Δε" < Δε'.
S104, extracting real flow velocity signals of each water layer, carrying out time-sharing Fourier transform on the signal data of each water layer to obtain frequency values of the real flow velocity signals in different water layers, and substituting the frequency values of the different water layers into Doppler frequency shift formulas to calculate the flow velocity of the different water layers.
The real flow velocity signals in the water layer signal data of each layer can be obtained after the steps, but the real flow velocity signals obtained by the steps can only judge the window where the real flow velocity signals are located and the corresponding time domain, and the frequency values of the real flow velocity signals of different water layers cannot be obtained, so that the flow velocity of different water layers can be calculated by substituting the frequency values into Doppler frequency shift formulas respectively through Fourier transformation. Preferably, S104 specifically includes the following steps:
s401, carrying out Fourier transform on the signal data of each layer of water layer to obtain energy values and modulus values of different frequency components in each block;
preferably, the energy values of the different frequency components in S401 and their modulus values are respectively:
wherein the factors are: e, e jw ＝cos(y)+j*sin(y)；
Wherein X (k) and +.>
K is the k-th difference frequency signal frequency point which is the frequency component after Fourier transformation; y is the time domain AD signal; w represents an angle; q is the sequence; n denotes the window size of the fourier transform, n=4096.
The modulus of the kth frequency point is:
the first frequency point DC component has a modulus value of +.>
Starting from the second point as a different frequency component.
S402, taking a frequency point corresponding to the maximum modulus value in the water layer signal data of each layer as a maximum signal frequency point, and calculating the frequency of the maximum signal frequency point based on a frequency calculation formula, wherein the frequency of the maximum signal frequency point is the frequency of a real flow velocity signal;
preferably, the frequency calculation formula is:
wherein m represents an m-th aqueous layer; f (m) represents the frequency of the true flow rate signal in the m-th water layer; k (m) represents the maximum difference frequency signal frequency point of the m-th water layer; f (F) S Representing the sampling frequency; n denotes the window size of the fourier transform, n=4096.
S403, substituting the frequency of the real flow velocity signal of each water layer into a Doppler frequency shift formula to calculate the flow velocity of different water layers.
Preferably, the doppler shift formula is:
wherein f represents the transmitting frequency of the ultrasonic probe; f (f) d Representing the received frequency, f d =f-F (m); c represents the ultrasonic velocity; v (m) represents the flow rate of the mth layer; θ represents water flowIncluded angle of ultrasonic wave incident wave.
The beneficial effects of this embodiment are: different water layer signals superimposed in the echo signals can be frequency-unfolded by adopting wavelet 6-order transformation, so that the method has higher resolution, all frequency signals in the echo signals can be identified, and the time domain positions corresponding to all characteristic frequencies in the water layer signal data of each layer are positioned, so that the real water flow frequency signals and the invalid interference frequency signals of each layer of water layer are obtained;
the problems that the existing ultrasonic Doppler flow velocity equipment cannot identify and filter invalid flow velocity are solved by comparing the same water layer, different moments, or different water layers, the same moments, or frequency characteristics of different water layers and different moments;
the frequency value of the real flow velocity signal of each layer of water layer is calculated by adopting time-sharing Fourier transform, and the flow velocity of different water layers can be calculated based on Doppler frequency shift formula, so that the problem that the layering flow velocity cannot be calculated by the existing single ultrasonic Doppler flow velocity equipment is solved, and the real flow velocity value obtained by the method of the embodiment is closer to the real condition.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.
Claims (8)
1. A method for measuring linear flow velocity based on ultrasonic doppler, characterized by: the method comprises the following steps:
s1, an ultrasonic probe periodically transmits a frequency signal and receives an echo signal, the echo signal is mixed with another path of same-frequency and same-phase signal to obtain difference frequency signals formed by different water layers, and a plurality of difference frequency signals are subjected to AD conversion to form a plurality of maps;
s2, identifying invalid flow velocity characteristic signals and real flow velocity signals of each water layer based on discrete wavelet transformation, carrying out time-sharing Fourier transformation on the real flow velocity signals of each water layer to obtain frequency values of the real flow velocity signals of each water layer, and calculating the flow velocity values of each water layer based on a Doppler frequency shift formula;
the step S2 specifically comprises the following steps:
s101, equally dividing the cache data of each map into blocks with the same number as that of water layers, wherein each block corresponds to one water layer signal data;
s102, positioning time domain positions corresponding to all characteristic frequencies in water layer signal data of each layer by using Daubechies wavelet 6-order transformation;
s103, if flow velocity signals with different frequency characteristics appear in the same water layer at different moments, the flow velocity signals are the interference signals of the protruding objects;
if flow velocity signals with different frequency characteristics appear in different water layers at the same moment, the flow velocity signals are self-rotation interference signals;
if flow velocity signals conforming to flow velocity layering appear in different water layers at different moments, the flow velocity signals are real flow velocity signals;
s104, carrying out time-sharing Fourier transform on the water layer signal data of each layer to obtain frequency values of real flow velocity signals in different water layers, and substituting the frequency values of the real flow velocity signals of the different water layers into a Doppler frequency shift formula to calculate the real flow velocity of the different water layers.
2. A method of measuring linear flow velocity based on ultrasonic doppler as claimed in claim 1, wherein: the step S102 specifically includes the following steps:
s201, carrying out 6-order wavelet transformation on each layer of water layer signal data to obtain a window with the minimum resolution of [0,160] hz and 64int data lengths;
s202, grabbing maximum amplitude signals after wavelet transformation in different windows;
s203, normalizing amplitude signals with maximum amplitude values captured by different windows;
s204, constructing a multidimensional matrix based on different water layers and frequency signals at different moments.
3. A method of measuring linear flow velocity based on ultrasonic doppler as claimed in claim 2, wherein: the multidimensional matrix in S204 is F.max [ n ] [ m ] (x), n represents the nth graph, m represents the mth water layer, and x represents the xth int data.
4. A method of measuring linear flow velocity based on ultrasonic doppler as claimed in claim 1, wherein: the step S103 specifically includes the following steps:
s301, setting a first window length threshold, selecting water layer signal data of the same water layer at different moments, defining frequency signals with the two data lengths being larger than the first window length threshold as first characteristic points, defining flow velocity signals with different frequency characteristics at different moments of the same water layer if the two first characteristic points are not equal, and judging the flow velocity signals as the protrusion interference signals;
s301, setting a second window length threshold value, wherein the second window length threshold value is larger than the first window length threshold value, selecting water layer signal data of different water layers and at the same moment, defining frequency signals with the two data lengths being larger than or equal to the second window length threshold value as second characteristic points, defining flow velocity signals with different frequency characteristics at different water layers and at the same moment if the two second characteristic points are not equal, and judging the flow velocity signals as self-rotation interference signals;
s303, setting a third window length threshold value, wherein the third window length threshold value is larger than or equal to the first window length threshold value and smaller than the second window length threshold value, selecting water layer signal data of different water layers and at different moments, defining frequency signals with the two data lengths equal to the third window length threshold value as third characteristic points, defining flow rate signals conforming to flow rate layering at different time points as different water layers if the two third characteristic points are equal, and judging the flow rate signals as real flow rate signals.
5. A method of measuring linear flow velocity based on ultrasonic doppler as claimed in claim 1, wherein: the step S104 specifically includes the following steps:
s401, carrying out Fourier transform on the signal data of each layer of water layer to obtain energy values and modulus values of different frequency components in each block;
s402, taking a frequency point corresponding to the maximum modulus value in the water layer signal data of each layer as a maximum signal frequency point, and calculating the frequency of the maximum signal frequency point based on a frequency calculation formula, wherein the frequency of the maximum signal frequency point is the frequency of a real flow velocity signal;
s403, substituting the frequency of the real flow velocity signal of each water layer into a Doppler frequency shift formula to calculate the flow velocity of different water layers.
6. A method of measuring linear flow velocity based on ultrasonic doppler as claimed in claim 5, wherein: the energy values and the modulus values of the different frequency components in S401 are respectively:
wherein the factors are: e, e jw ＝cos(y)+j*sin(y)；
Wherein X (k) and +.>
K is the k-th difference frequency signal frequency point which is the frequency component after Fourier transformation; y is the time domain AD signal; w represents an angle; q is the sequence; n represents the window size of the fourier transform, n=4096;
the modulus of the kth frequency point is:
7. a method of measuring linear flow velocity based on ultrasonic doppler as claimed in claim 5, wherein: the frequency calculation formula in S402 is:
wherein m represents an m-th aqueous layer; f (m) represents the frequency of the true flow rate signal in the m-th water layer; k (m) represents the maximum difference frequency signal frequency point of the m-th water layer; f (F) S Representing the sampling frequency; n denotes the window size of the fourier transform, n=4096.
8. A method of measuring linear flow velocity based on ultrasonic doppler as claimed in claim 5, wherein: the doppler shift formula in S403 is:
wherein f represents the transmitting frequency of the ultrasonic probe; f (f) d Representing the received frequency, f d =f-F (m); c represents the ultrasonic velocity; v (m) represents the flow rate of the mth layer; θ represents the angle between the water flow and the ultrasonic wave.
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