LNG dynamic metering compensation method based on multi-reference target distributional decoupling

Abstract

The application provides an LNG dynamic metering compensation method based on multi-reference target distributed decoupling, N reference reflection targets are arranged in the axial direction of a waveguide tube, and the whole rod is divided into N-1 microelement sections; reflection echo signals of each reference target and a target interface are collected, and original echo arrival times are extracted; the original echo arrival time difference of adjacent reference targets is operated, and the time difference in each microelement section is obtained; an observation equation set containing an actual sound speed and a unit length thermal strain is constructed; an iterative identification algorithm is used to solve the equation set, and the actual sound speed and the actual strain of each microelement section after decoupling are output; based on the decoupling result, the target echo is compensated in a segmented path, and is calculated to an equivalent time under a standard state; and the liquid level height or the instantaneous flow value after compensation is calculated and output. The application realizes complete decoupling of sound speed change and thermal expansion and contraction of the waveguide rod, eliminates the cross-coupling error in the transmission metering method, and improves the precision of LNG dynamic metering.

Description

Technical Field

[0001] This invention relates to the field of metrology and testing technology, specifically to a dynamic metering compensation method for LNG based on distributed decoupling of multiple reference targets. Background Technology

[0002] Currently, LNG (liquefied natural gas) transfer pumping stations on ships widely employ guided wave radar (GWR) or ultrasonic guided wave sensors for level and flow measurement. The core measurement logic of these sensors is as follows: a pulse is emitted to a waveguide rod (detector) immersed in LNG. The pulse generates an echo upon encountering the liquid surface or a flowing target. By accurately measuring the total time of flight (TOF) between pulse emission and echo reception, combined with a preset waveguide rod length and the speed of sound in the medium, the liquid level or flow rate is calculated.

[0003] To ensure measurement accuracy, existing technologies mainly employ the following two maintenance strategies: First, a platinum resistance temperature sensor (such as Pt100) is installed at the root of the waveguide rod or the flange end to measure the LNG medium temperature in real time. The current medium sound velocity is corrected in real time using a "temperature-sound velocity" empirical reference table pre-stored in the control unit to eliminate the influence of temperature changes on sound velocity. Second, a fixed reference reflection target is set at a known mechanical position of the waveguide rod (such as at 1 / 2 of the total length or the end). The system periodically detects the echo time of the reference target. If the time drifts, it is assumed to be caused by a change in the medium sound velocity, and the wave velocity parameters are automatically adjusted to correct the subsequent target echo measurement value.

[0004] However, the aforementioned existing technologies have significant systemic drawbacks and shortcomings when applied to the rapid refueling of large-volume LNG on ships. Firstly, existing technologies neglect the geometric errors caused by the thermal expansion and contraction of the waveguide itself. In particular, the single-reference-target method suffers from a physical-logical coupling error: when the system detects a time drift in the reference target echo, it attributes all the drift to changes in the medium's sound velocity. However, in the initial stage of LNG refueling, the waveguide is instantly immersed from a room temperature environment (approximately 20°C) into cryogenic LNG (approximately -162°C), a temperature difference of up to 180°C. This inevitably causes severe thermal contraction of the metal waveguide, resulting in a shortening of the actual physical distance between the probe and the liquid surface. Existing algorithms misinterpret this "distance shortening" as a "sound velocity change," leading to cross-coupling errors in the corrected measurement results. This error is particularly significant under non-uniform temperature fields. Secondly, during LNG refueling, a significant temperature difference exists between the gas phase space (approximately -40°C) and the liquid phase space (-162°C) within the LNG tank. This results in a severe non-uniform temperature gradient field along the waveguide rod axis. Existing single-point temperature correction methods can only obtain the temperature at a single point on the rod end, failing to reflect the temperature distribution along the entire length of the waveguide rod. This leads to non-negligible high-order residual errors during dynamic refueling. Furthermore, the total echo time of the waveguide is physically dependent on… It is determined that temperature T simultaneously affects length L and sound speed v, and the two influence in the same direction (as temperature decreases, length shortens and sound speed decreases). Existing technology lacks independent observation variables for L and v, making it impossible to decouple them through a single or two traditional observation equations. Summary of the Invention

[0005] The purpose of this invention is to provide a dynamic metering and compensation method for LNG based on distributed decoupling of multiple reference targets, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A dynamic metering compensation method for LNG based on distributed decoupling of multiple reference targets includes:

[0008] Step S1: Arrange N reference reflection targets along the waveguide axis, divide the entire rod into N-1 continuous and non-overlapping micro-segments, and obtain the design length of each micro-segment, where N≥3;

[0009] Step S2: Send a probe pulse to the waveguide rod, collect the reflected echo signals of each reference target and target interface, and extract the original echo arrival time of each reference target and target interface;

[0010] Step S3: Perform differential calculation on the arrival time of the original echoes from adjacent reference targets to obtain the pure propagation time difference within each micro-segment;

[0011] Step S4: For each infinitesimal segment, construct a set of simultaneous observation equations that include the actual sound velocity and thermal strain per unit length within that infinitesimal segment;

[0012] Step S5: Using the observation values ​​of N reference targets, the simultaneous observation equations are solved by an iterative identification algorithm, and the actual sound velocity and actual strain of each micro-segment after decoupling are output.

[0013] Step S6: Based on the actual sound velocity and actual strain of each micro-segment obtained by decoupling, perform segmented path compensation on the original echo arrival time of the target interface to reduce it to the equivalent time under standard conditions.

[0014] Step S7: Based on the equivalent time under standard conditions, combined with the design length and standard sound velocity, calculate the compensated liquid level height or instantaneous flow rate value, and output it to the host computer or flow computer system.

[0015] Preferably, in step S1, the reference reflecting targets are arranged along the axial direction of the waveguide from the signal transmitting end to the end, and the designed coordinate positions of each reference target from the wave source are as follows: ,in As the starting end face, The end face is the design length of each micro-element segment.

[0016] ;

[0017] Where i = 1, 2, ..., N-1.

[0018] Preferably, in step S1, a distributed temperature sensing sub-unit composed of thin-film platinum resistance is embedded at a position adjacent to each reference target or along the inner wall of the waveguide rod to provide initial temperature field data.

[0019] Preferably, in step S2, the original echo arrival time of the i-th reference target is extracted. Where i = 1, 2, ..., N; and the original echo arrival time of the target interface is extracted. .

[0020] Preferably, in step S3, the difference operation is performed according to the following formula:

[0021]

[0022] Where i = 1, 2, ..., N-1; the difference value Only related to the current medium velocity within the i-th infinitesimal segment and current actual length Related.

[0023] Preferably, the simultaneous observation equations in step S4 include:

[0024] Length-strain equation: ,in This represents the average linear strain within the infinitesimal segment;

[0025] The sound time-velocity equation: ;

[0026] Sound velocity-temperature property constraint equation: Based on the initial temperature value collected by the distributed temperature sensing unit, and combined with the LNG standard property database, a nonlinear function of sound velocity with respect to temperature is established for parameter initialization in the iterative process.

[0027] Preferably, the iterative identification algorithm in step S5 is a joint solution using a fixed-point iterative method, specifically including the following steps:

[0028] Step S5.1: Set the initial thermal strain vector The initial sound velocity vector is obtained by looking up a table using the initial temperature field. ;

[0029] Step S5.2: Based on the current strain estimate Update the current actual length of each micro-element segment:

[0030] ;

[0031] Step S5.3: Utilize the measured differential time By working backwards, we can estimate the current speed of sound:

[0032] ;

[0033] Step S5.4: Introduce sound velocity-temperature property gradient constraints to correct strain estimates:

[0034] ;

[0035] in, For relaxation factor ( ), The temperature coefficient of sound velocity for LNG is given. This is to assist the temperature sensor in measuring the temperature change of the micro-segment;

[0036] Step S5.5: Repeat steps S5.2 to S5.4 until the convergence threshold is met. ,in Pick Once the threshold is met, the iteration stops, and the actual sound velocity of each segment is output. and actual strain in each segment .

[0037] Preferably, in step S6, the standard state is the designed length of the waveguide rod. and LNG standard reference speed of sound ,in The segmented path compensation, derived from the LNG standard property database, specifically includes the following steps:

[0038] Step S6.1: Determine the set Ω of all infinitesimal segments traversed by the target echo path;

[0039] Step S6.2: Calculate the standard state equivalent time segment by segment:

[0040] ,

[0041] in For the target echo after the first The actual time spent by the infinitesimal segment The sound speed deviation factor. This is the length deviation factor;

[0042] Step S6.3: Accumulate the equivalent time of all infinitesimal segments to obtain the total path equivalent time:

[0043] .

[0044] Preferably, in step S7, the standard state is the reference state corresponding to the waveguide design length and the standard reference sound velocity of LNG, wherein the standard reference sound velocity... Standard reference speed of sound The formula for calculating the compensated liquid level height, taken from the LNG standard physical property database, is as follows:

[0045] ;

[0046] The instantaneous flow rate can be converted from the compensated liquid level height to the flow meter coefficient.

[0047] Preferably, the method further includes step S8: In the continuous LNG refueling operation, steps S2 to S7 are repeated, and the strain of each micro-segment obtained by convergence in the previous measurement cycle is used as the prior estimate of the current cycle, so as to reduce the number of iterations and realize online real-time dynamic compensation.

[0048] Compared with the prior art, the beneficial effects of the present invention are:

[0049] This invention, through the synergistic effect of "multi-reference target distributed layout" and "joint online identification of sound velocity and strain dual parameters," introduces a dual-parameter decoupling mechanism for the first time in the field of metrology. It establishes a set of two independent observation equations and completely severs the coupling influence chain of temperature on length and sound velocity by independently solving the real-time length of the waveguide rod and the real-time sound velocity of the medium. From the physical mechanism level, it eliminates the systematic theoretical residual of traditional algorithms that misjudge the geometric deformation of the waveguide rod as a change in sound velocity. Compared with the existing technology, it realizes the real-time reconstruction of the metrological benchmark and fundamentally eliminates the coupling residual.

[0050] This invention discretizes a continuous nonlinear physical field into N-1 micro-segments and independently identifies the sound velocity and strain in each segment. Under the transient temperature change environment (temperature change rate 5°C / min-15°C / min) of simulated rapid marine refueling, the linearity error of liquid level measurement is reduced from ±1.2%FS of the traditional single-point temperature compensation method to within ±0.08%FS. At the same time, since the algorithm only relies on the relative time difference of the reference target echo rather than the absolute accuracy of the temperature sensor, the repeatability error over the entire life cycle is reduced from 0.3% to 0.05%, which significantly improves the measurement accuracy compared with the prior art.

[0051] This invention allows the waveguide rod to directly contact the LNG medium without the need for stringent external temperature control measures. Even when the upper part of the waveguide rod is in the ambient gas phase (-40°C) and the lower part is immersed in the liquid phase (-162°C), resulting in an axial extreme non-uniform temperature gradient of over 120°C, the sound velocity and strain distribution of each segment can still be accurately reconstructed through segmented micro-element processing. This ensures metering consistency across the entire length of the rod. Compared to existing technologies, this invention significantly relaxes the insulation process requirements of the pump station system, realizing a shift from "passive insulation" to "active interference resistance".

[0052] This invention employs real-time differential calculation based on time of flight, which does not rely on the sensor thermal equilibrium time constant. It can complete the joint refresh of the sound velocity field and strain field of the entire rod within a single refueling cycle (<1 second), and uses the convergence result of the previous cycle as the prior estimate of the current cycle to reduce the number of iterations. When encountering sudden changes in flow, it automatically decays the prior weight by monitoring the echo time change rate to avoid divergence. Compared with the existing technology, it significantly improves the dynamic response capability and meets the requirements of accurate capture of millisecond-level flow changes in marine trade settlement. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of an existing technical solution;

[0054] Figure 2 A rough schematic diagram illustrating the relationship between existing technology calculation errors and time, temperature difference, and flow rate;

[0055] Figure 3 This is a schematic diagram of the overall technical solution of the present invention;

[0056] Figure 4 This is a diagram showing the overall layout structure of the hardware distributed reference target of the present invention.

[0057] Figure 5 This is a flowchart of the fixed-point iterative two-parameter joint identification algorithm of the present invention. Detailed Implementation

[0058] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0059] Example:

[0060] like Figure 1 and Figure 2 As shown, in existing technical solutions, the level and flow rate measurement of marine LNG (liquefied natural gas) transfer pumping stations widely adopts sensors based on guided wave radar or ultrasonic guided wave principles. The core measurement logic is as follows: a pulse is emitted to a waveguide rod immersed in LNG; the pulse generates an echo upon encountering the liquid surface or a flowing target; the total time of flight (TOF) between pulse emission and echo reception is accurately measured, and the level or flow rate is calculated by combining this with a preset waveguide rod length and the sound velocity of the medium.

[0061] Existing technologies have the following systemic drawbacks and shortcomings when applied to rapid LNG refueling operations on ships:

[0062] (1) Existing technology ignores the geometric errors caused by the thermal expansion and contraction of the waveguide rod itself. During the initial LNG refueling phase, the waveguide rod is instantly immersed from a normal temperature environment (approximately 20°C) into cryogenic LNG (approximately -162°C), a temperature difference of up to 180°C. This inevitably causes severe thermal contraction of the metal waveguide rod, resulting in a shortening of the actual physical distance between the probe and the liquid surface. Existing algorithms misjudge this "distance shortening" as a "change in sound velocity," leading to cross-coupling errors in the corrected measurement results, such as... Figure 2 As shown, this error increases with increasing temperature difference.

[0063] (2) During LNG refueling, there is a huge temperature difference between the gas phase space (approximately -40°C) and the liquid phase space (-162°C) inside the tank, resulting in a severe non-uniform temperature gradient field along the waveguide rod axis. Existing single-point temperature correction methods can only obtain the temperature at a certain point on the rod end, and cannot reflect the temperature distribution along the entire length of the waveguide rod, which will generate non-negligible high-order residual errors during dynamic refueling.

[0064] (3) The total echo time t of the waveguide is determined by physical relationships It is determined that temperature T affects both length L and speed of sound v. Current technology lacks independent observation variables for L and v, making it impossible to decouple them through a single or two traditional observation equations.

[0065] To address the problems of the existing technology, this invention provides a dynamic LNG metering compensation method based on distributed decoupling of multiple reference targets. The core of this method lies in: dividing the entire rod into several micro-segments by axially deploying multiple reference targets and a distributed temperature sensing array along the waveguide; constructing a redundant set of observation equations regarding the actual sound velocity and thermal expansion strain of the micro-segments using the difference in echo times between adjacent reference targets; independently solving the two coupled physical quantities using an iterative identification algorithm to achieve complete decoupling between sound velocity changes and the thermal expansion and contraction of the rod; and finally, performing segmented path compensation on the target liquid surface echo, reducing it to the equivalent time under standard conditions, and outputting high-precision liquid level and instantaneous flow rate results.

[0066] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and specific steps.

[0067] Please see Figures 3 to 5 As shown, the method of the present invention includes the following main steps:

[0068] Step S1: Arrange N reference reflection targets along the waveguide axis, divide the entire rod into N-1 continuous and non-overlapping micro-segments, and obtain the design length of each micro-segment, where N≥3.

[0069] Step S2: Send a probe pulse to the waveguide rod, collect the reflected echo signals of each reference target and target interface, and extract the original echo arrival time of each reference target and target interface.

[0070] Step S3: Perform differential calculation on the arrival time of the original echoes of adjacent reference targets to obtain the pure propagation time difference within each micro-segment.

[0071] Step S4: For each infinitesimal segment, construct a set of simultaneous observation equations that include the actual sound velocity and thermal strain per unit length within that infinitesimal segment.

[0072] Step S5: Using the observation values ​​of N reference targets, the simultaneous observation equations are solved by an iterative identification algorithm, and the actual sound velocity and actual strain of each micro-segment after decoupling are output.

[0073] Step S6: Based on the actual sound velocity and actual strain of each micro-segment obtained by decoupling, perform segmented path compensation on the original echo arrival time of the target interface to reduce it to the equivalent time under standard conditions.

[0074] Step S7: Based on the equivalent time under standard conditions, combined with the design length and standard sound velocity, calculate the compensated liquid level height or instantaneous flow rate value, and output it to the host computer or flow computer system.

[0075] In this invention, through the synergistic effect of steps S1 to S7, independent solution and decoupled compensation of the thermal expansion strain of the waveguide rod and the sound velocity of the medium are realized in the field of metrology.

[0076] In this embodiment, the reference reflecting targets described in step S1 are arranged along the axial direction of the waveguide from the signal transmitting end to the end. Starting from the wave source, the designed coordinate positions of each reference target are as follows: ,in As the starting end face, The end face is the end feature; the design length of each micro-element segment is:

[0077] ,

[0078] Where i = 1, 2, ..., N-1.

[0079] By setting the coordinates as described above, the total length of the rod will be... The system is precisely divided into N-1 (and no less than 3) continuous and non-overlapping micro-segments. The design length of each micro-segment is known under standard conditions (calibration at room temperature 20°C). The difference (not the absolute value) between the echo times of adjacent reference targets is used to provide basic data for subsequent difference operations and solving the system of simultaneous equations.

[0080] In this embodiment, in step S1, a distributed temperature sensing sub-unit is embedded at a position adjacent to each reference target or along the inner wall of the waveguide rod to provide initial temperature field data.

[0081] Specifically, the distributed temperature sensing subunit is composed of a high-precision thin-film platinum resistance thermometer.

[0082] During the algorithm initialization phase, the initial temperature values ​​of each micro-segment are obtained through this sub-unit, and a nonlinear function of sound velocity with respect to temperature is established based on the LNG standard physical property database to provide an initial sound velocity vector for the iterative identification algorithm.

[0083] In another embodiment, the distributed temperature sensing subunit can also use a fiber optic temperature sensing array instead of a thin-film platinum resistance thermometer, which can also achieve the function of distributed temperature acquisition along the waveguide rod axis.

[0084] It should be noted that the core of this invention lies in achieving independent decoupling of sound velocity and strain through spatial redundancy observations from multiple reference targets. The distributed temperature sensing subunit is only used for initial value setting during the algorithm initialization phase and is not used as a direct basis for final compensation. Even in the event of partial failure or decreased accuracy of the temperature sensing subunit, the system can still maintain high metrological accuracy because the algorithm mainly relies on the relative difference value of the echo time of the reference targets for calculation. This significantly improves the robustness of the system in harsh marine environments.

[0085] In this embodiment, step S2 involves transmitting a probe pulse to the waveguide rod via a pulse generator and high-speed acquisition unit, and simultaneously acquiring the reflected echo signals from each reference target and the target interface. The original echo arrival time of the i-th reference target is then extracted. Where i = 1, 2, ..., N; and the original echo arrival time of the target interface (liquid surface or flow target). .

[0086] The aforementioned raw echo arrival time includes the system's fixed circuit delay. This delay will be eliminated in subsequent difference operations.

[0087] The difference operation described in step S3 is performed according to the following formula:

[0088] ;

[0089] Where i = 1, 2, ..., N-1.

[0090] The above differential operation eliminates the system's fixed circuit delay. The uncertainty of the start time of the transmitted pulse. The difference value Only related to the current medium velocity within the i-th infinitesimal segment and current actual length It is related to the circuit's fixed delay.

[0091] Specifically, this difference value This is the only pure input for subsequent two-parameter identification. By discretizing the continuous nonlinear physical field into N-1 micro-segments, assuming uniform sound velocity and strain within each micro-segment, each segment is identified independently, and the total compensation value for the entire rod length is obtained by summing the segments. This strategy of "approximating distributed parameters with segmented lumped parameters" enables the present invention to accurately reconstruct the sound velocity and strain distribution of each segment even under conditions of extreme non-uniform temperature gradients (gas phase -40°C, liquid phase -162°C) during LNG refueling.

[0092] It should be noted that traditional existing technologies typically use the absolute value of the reference target echo time for calibration, while this invention creatively uses the difference between adjacent reference target echo times. This difference completely eliminates the inherent circuit delay of the system, significantly reduces the dependence on the hardware accuracy of the high-speed acquisition unit, and also gives the algorithm a natural anti-interference capability against long-term sensor drift.

[0093] The simultaneous observation equations described in step S4 include three equations:

[0094] Length-strain equation: ,in The average linear strain within this micro-segment (determined by temperature and stress, including thermal expansion and contraction and installation prestress).

[0095] The sound time-velocity equation: ;

[0096] Sound velocity-temperature property constraint equation: Based on the initial temperature value collected by the distributed temperature sensing unit, and combined with the LNG standard property database, a nonlinear function of sound velocity with respect to temperature is established.

[0097] The three equations described above constitute a complete observation model for each infinitesimal segment. Specifically, the length-strain equation provides geometric constraints (material mechanical thermal expansion characteristics), the sound time-velocity equation provides physical constraints (basic kinematic relationships), and the sound velocity-temperature property constraint equation provides property constraints (used for setting initial values ​​for iteration). The synergistic effect of these three equations enables the decoupling of sound velocity from traditional single observation equations. With strain It can be solved independently.

[0098] It should be noted that the sound velocity-temperature property constraint equation is only used for setting initial values ​​for iteration and is not used as the final compensation basis. The key to the high-precision compensation achieved by this invention lies in the redundant observation equation set composed of the length-strain equation and the sound time-sound velocity equation, combined with the spatial redundancy information of multiple reference targets, which allows sound velocity and strain to be independently identified. Regardless of the initialization method used, the final convergence result is dominated by the measured flight time, thus ensuring that the compensation accuracy does not depend on the absolute accuracy of the temperature sensor.

[0099] The iterative identification algorithm described in step S5 employs a joint solution using a fixed-point iteration method. Please refer to [link / reference]. Figure 5 The algorithm specifically includes the following steps:

[0100] Step S5.1 (Parameter Initialization): Set the initial thermal strain vector The initial sound velocity vector is obtained by looking up a table using the initial temperature field. ;

[0101] Step S5.2 (Length Update): Based on the current strain estimate Update the current actual length of each micro-element segment:

[0102] ;

[0103] Step S5.3 (Sound Velocity Update): Utilize measured differential time By working backwards, we can estimate the current speed of sound:

[0104] ;

[0105] Step S5.4 (Strain Update): Introduce the sound velocity-temperature property gradient constraint to correct the strain estimate:

[0106] ;

[0107] in, For relaxation factor ( ), The temperature coefficient of sound velocity for LNG is given. This is to assist the temperature sensor in measuring the temperature change of the micro-segment;

[0108] Step S5.5: Repeat steps S5.2 to S5.4 until the convergence threshold is met. ,in Pick Once the threshold is met, the iteration stops, and the actual sound velocity of each segment is output. and actual strain in each segment .

[0109] The core of the above iterative process lies in: by continuously updating the "length-strain" and "sound speed-time" relationships alternately, forcing ε and v to converge simultaneously to the optimal solution that satisfies all observation equations. Relaxation factor The introduction of this control measures the update step size for each iteration, ensuring the stability of the algorithm when the initial value deviation is large.

[0110] In another embodiment, the iterative identification algorithm can use recursive least squares (RLS) instead of fixed-point iterative method for joint identification. Specifically, the two-factor decoupling problem is regarded as a linear regression problem, and an observation matrix Y=H·X is constructed, where Y is the measured flight time vector of each reference target, H is a coefficient matrix containing the design length and temperature coefficient, and X is the state vector of "strain" and "sound speed deviation" to be identified. The state estimates are updated online using recursive least squares with a forgetting factor.

[0111] In another embodiment, the iterative identification algorithm can use extended Kalman filtering (EKF) instead of fixed-point iteration for joint identification. Specifically, the waveguide rod's "temperature change rate" and "stress relaxation" are incorporated into the state equation, the echo time is used as the observation equation, and extended Kalman filtering is used to fuse multi-sensor (echo time + temperature sensor) data, while simultaneously outputting the optimal estimated sound velocity and strain values.

[0112] It should be noted that the core of this invention lies in constructing redundant observation equations using spatially distributed reference targets, and jointly solving for the thermal expansion strain of the waveguide as an unknown independent of the sound velocity. Regardless of whether the fixed-point iteration method, recursive least squares method, or extended Kalman filter method is used, any scheme that utilizes the spatial redundancy information of multiple reference targets to simultaneously identify the two parameters of "medium sound velocity" and "rod thermal strain" falls within the protection scope of this invention.

[0113] In this embodiment, the standard state refers to the designed length of the waveguide rod. and LNG standard reference speed of sound ,in Taken from the LNG standard physical property database (usually the velocity of sound at -162°C and saturated liquid density).

[0114] The segmented path compensation specifically includes the following steps:

[0115] Step S6.1: Determine the set Ω of all infinitesimal segments traversed by the target echo path;

[0116] Step S6.2: Calculate the standard state equivalent time segment by segment:

[0117] ,

[0118] in For the target echo after the first The actual time spent by the infinitesimal segment The sound speed deviation factor. This is the length deviation factor;

[0119] Step S6.3: Accumulate the equivalent time of all infinitesimal segments to obtain the total path equivalent time:

[0120]

[0121] The physical meaning of the above compensation logic is that: since the speed of sound of the i-th infinitesimal segment in the actual state is The actual length is The speed of sound under standard conditions is , length is Therefore, the actual measurement time It needs to be divided by the sound speed deviation factor at the same time. and length deviation factor Only then can it be recalculated to the equivalent time under standard conditions.

[0122] In another embodiment, the above-mentioned segmented path compensation can be replaced by a compensation method based on global integral reconstruction: the discrete sound velocity points measured by N discrete reference targets are... A continuous sound velocity distribution curve was fitted using cubic spline interpolation. and strain distribution curve Path integral correction is performed on the target echo time:

[0123] ,

[0124] Instead of summing the segments.

[0125] It should be noted that regardless of whether segmented accumulation or global integral reconstruction is used, the essence is the same: "using the sound velocity and strain information of each micro-segment obtained from the distributed reference target to perform point-by-point / segment-by-segment compensation on the target echo path." Any method that acquires multi-point sound velocity and strain distribution information along the waveguide axis and performs path length weighted compensation on the target echo utilizes the core concept of this invention. Segmented accumulation and integral reconstruction are merely differences in mathematical implementation; they are equivalent in their compensation principle.

[0126] The standard state mentioned in step S7 is the reference state corresponding to the waveguide design length and the standard reference sound velocity of LNG, where the standard reference sound velocity... Retrieved from the LNG standard property database. The formula for calculating the compensated liquid level height is:

[0127] ;

[0128] Based on the compensated liquid level height and the preset flow meter coefficient, the instantaneous flow rate value can be converted and output to the host computer or flow computer system.

[0129] The above formula is formally consistent with the basic time-domain reflectometry formula in the prior art, but its input quantity... The complete compensation process, from steps S1 to S6, eliminates the dual errors caused by the thermal expansion and contraction of the waveguide rod and changes in the sound velocity of the medium. Therefore, the final output liquid level height and instantaneous flow rate values ​​have a much higher accuracy than those of existing technologies.

[0130] In this embodiment, step S8 is also included: during the continuous LNG refueling operation, steps S2 to S7 are repeated, and the strain of each micro-segment obtained by convergence in the previous measurement cycle is used as the prior estimate of the current cycle, so as to reduce the number of iterations and realize online real-time dynamic compensation.

[0131] Specifically, during continuous LNG refueling, as the refueling flow rate changes, the system repeats steps S2 to S7 in each measurement cycle. Unlike the initial startup, in subsequent cycles, the algorithm directly calculates the strain of each micro-element obtained from the convergence of the previous cycle. Instead of setting the initial thermal strain vector to zero, the system uses a relaxation factor as a priori estimate for the current cycle. Control the update step size, and when encountering sudden flow changes (such as emergency shut-off valve operation), monitor the rate of change of echo time. Automatic decay of prior weights prevents algorithm divergence.

[0132] Through the above mechanism, the system can usually converge with only a few iterations under steady-state conditions, with a typical convergence time of less than 1 second, which meets the requirements of marine trade settlement for accurate capture of millisecond-level flow changes.

[0133] In summary, this invention, through the synergistic effect of "multi-reference target distributed layout" and "joint online identification of sound velocity and strain dual parameters," fundamentally changes the inherent mode of traditional guided wave metering systems that "rely solely on a single flight time or a single temperature measuring resistor" for simple table lookup correction. It transforms the physical deformation of the waveguide rod due to thermal expansion and contraction, originally considered "interference noise," into an effective physical parameter that can be independently extracted and monitored. This enables real-time reconstruction of the metering benchmark, improving the accuracy, environmental adaptability, and dynamic response capability of LNG dynamic metering.

[0134] All other parts of this invention not described herein are the same as existing technologies, or are known technologies, or can be implemented using existing technologies, and will not be described in detail here.

[0135] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A dynamic metering compensation method for LNG based on distributed decoupling with multiple reference targets, characterized in that, Includes the following steps: Step S1: Arrange N reference reflection targets along the waveguide axis, divide the entire rod into N-1 continuous and non-overlapping micro-segments, and obtain the design length of each micro-segment, where N≥3; Step S2: Send a probe pulse to the waveguide rod, collect the reflected echo signals of each reference target and target interface, and extract the original echo arrival time of each reference target and target interface; Step S3: Perform differential calculation on the arrival time of the original echoes from adjacent reference targets to obtain the pure propagation time difference within each micro-segment; Step S4: For each infinitesimal segment, construct a set of simultaneous observation equations that include the actual sound velocity and thermal strain per unit length within that infinitesimal segment; Step S5: Using the observation values ​​of N reference targets, the simultaneous observation equations are solved by an iterative identification algorithm, and the actual sound velocity and actual strain of each micro-segment after decoupling are output. Step S6: Based on the actual sound velocity and actual strain of each micro-segment obtained by decoupling, perform segmented path compensation on the original echo arrival time of the target interface to reduce it to the equivalent time under standard conditions. Step S7: Based on the equivalent time under standard conditions, combined with the design length and standard sound velocity, calculate the compensated liquid level height or instantaneous flow rate value, and output it to the host computer or flow computer system.

2. The LNG dynamic metering compensation method based on multi-reference target distributed decoupling according to claim 1, characterized in that, In step S1, the reference reflecting targets are arranged along the axial direction of the waveguide from the signal transmitting end to the end. The designed coordinate positions of each reference target from the wave source are as follows: ,in As the starting end face, For the end face; The design length of each micro-element segment is ； Where i = 1, 2, ..., N-1.

3. The LNG dynamic metering compensation method based on multi-reference target distributed decoupling according to claim 1, characterized in that... In step S1, a distributed temperature sensing sub-unit is embedded at a position adjacent to each reference target or along the inner wall of the waveguide rod to provide initial temperature field data.

4. The LNG dynamic metering compensation method based on multi-reference target distributed decoupling according to claim 1, characterized in that... In step S2, the original echo arrival time of the i-th reference target is extracted. Where i = 1, 2, ..., N; and the original echo arrival time of the target interface is extracted. .

5. The LNG dynamic metering compensation method based on multi-reference target distributed decoupling according to claim 1, characterized in that... In step S3, the difference operation is performed according to the following formula: Where i = 1, 2, ..., N-1; the difference value Only related to the current medium velocity within the i-th infinitesimal segment and current actual length Related.

6. The LNG dynamic metering compensation method based on multi-reference target distributed decoupling according to claim 1, characterized in that, The simultaneous observation equations described in step S4 include: Length-strain equation: ,in This represents the average linear strain within the infinitesimal segment; The sound time-velocity equation: ; Sound velocity-temperature property constraint equation: Based on the initial temperature value collected by the distributed temperature sensing unit, and combined with the LNG standard property database, a nonlinear function of sound velocity with respect to temperature is established.

7. The LNG dynamic metering compensation method based on multi-reference target distributed decoupling according to claim 1, characterized in that... The iterative identification algorithm described in step S5 is a joint solution using a fixed-point iterative method, specifically including the following steps: Step S5.1: Set the initial thermal strain vector The initial sound velocity vector is obtained by looking up a table using the initial temperature field. ; Step S5.2: Based on the current strain estimate Update the current actual length of each micro-element segment: ； Step S5.3: Utilize the measured differential time By working backwards, we can estimate the current speed of sound: ； Step S5.4: Introduce sound velocity-temperature property gradient constraints to correct strain estimates: ； in, For relaxation factor ( ), The temperature coefficient of sound velocity for LNG is given. This is to assist the temperature sensor in measuring the temperature change of the micro-segment; Step S5.5: Repeat steps S5.2 to S5.4 until the convergence threshold is met. ,in Pick Once the threshold is met, the iteration stops, and the actual sound velocity of each segment is output. and actual strain in each segment .

8. The LNG dynamic metering compensation method based on multi-reference target distributed decoupling according to claim 1, characterized in that, In step S6, the standard state is the designed length of the waveguide rod. and LNG standard reference speed of sound ,in The segmented path compensation, derived from the LNG standard property database, specifically includes the following steps: Step S6.1: Determine the set Ω of all infinitesimal segments traversed by the target echo path; Step S6.2: Calculate the standard state equivalent time segment by segment: ， in For the target echo after the first The actual time spent by the infinitesimal segment The sound speed deviation factor. This is the length deviation factor; Step S6.3: Accumulate the equivalent time of all infinitesimal segments to obtain the total path equivalent time: 。 9. The LNG dynamic metering compensation method based on multi-reference target distributed decoupling according to claim 1, characterized in that, In step S7, the standard state is the reference state corresponding to the waveguide design length and the standard reference sound velocity of LNG, wherein the standard reference sound velocity... Standard reference speed of sound The formula for calculating the compensated liquid level height, taken from the LNG standard physical property database, is as follows: ； The instantaneous flow rate can be converted from the compensated liquid level height to the flow meter coefficient.

10. The LNG dynamic metering compensation method based on multi-reference target distributed decoupling according to claim 9, characterized in that, It also includes step S8: In the continuous LNG refueling operation, steps S2 to S7 are repeated, and the strain of each micro-segment obtained by convergence in the previous measurement cycle is used as the prior estimate of the current cycle, so as to reduce the number of iterations and realize online real-time dynamic compensation.

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