Research method for generating compression waves according with engineering practice by simulating different train tunnel entering working conditions

Abstract

The invention discloses a research method for generating compression waves according with engineering practice by simulating different train tunnel-entering working conditions, and the method comprises the steps: building a tunnel compression wave simulation generation device which comprises an air compressor, a high-pressure cavity, a digital display pressure gauge, a polyurethane pipe, an electromagnetic valve, a flange end cover, a simulation tunnel, a pressure sensor, a data acquisition instrument and a computer; during an experiment, the electromagnetic valve group is kept closed, and the high-pressure cavity is filled with preset initial pressure through the air compressor according to a test target; setting the turn-on voltage, the number and the sequence of each electromagnetic valve according to a test target; opening an electromagnetic valve to control release of high-pressure gas in a high-pressure cavity; and the pressure change of the initial compression wave of the tunnel is measured and acquired through the pressure sensor and the data acquisition instrument. According to the invention, the process of the train entering the tunnel is simplified through the method of instantly releasing the high-pressure air in the high-pressure cavity, and a new experimental thought can be provided for researching initial compression wave evolution in the future, developing a novel buffer structure for reducing micro-pressure wave harm and providing a new experimental thought in engineering verification means.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel compression waves, and in particular to a research method for simulating different train entry conditions into tunnels to generate compression waves that meet engineering actual conditions. Background Art

[0002] In recent years, with the rapid development of high-speed railway technology in my country, the mountainous topography of my country has led to an increase in the number of tunnels dug along with the amount of line laying. When a train enters these tunnels at high speed, it is similar to a piston moving rapidly in a pipe, forming an initial compression wave, such as Figure 1 As shown. The initial compression wave will continue to propagate and reflect in the tunnel, causing drastic changes in the pressure inside the tunnel. These alternating loads will have potential impacts on the car body, tunnel and other auxiliary structures, such as large driving resistance, wall fatigue damage, wall fragments falling, etc., and affect the internal environment of the train so that passengers feel uncomfortable. On the other hand, the initial compression wave will radiate outward from the tunnel exit, inducing the generation of micro-pressure waves. Micro-pressure waves mainly appear in the form of infrasound waves, and are close to the vibration frequency of human organs and buildings, which can easily bring potential hazards. In extreme cases, unpleasant sonic booms will occur at the tunnel exit. As the speed of trains in countries around the world continues to advance, the problems caused by vehicle-tunnel coupling are becoming more and more serious. How to alleviate the initial compression wave and micro-pressure wave is a continuous research hotspot in aerodynamics.

[0003] The methods for studying train / tunnel coupled aerodynamics mainly include theoretical calculations, numerical simulations, real vehicle tests and model experiments based on different principles.

[0004] Theoretical analysis can provide some understanding and general conclusions of the problem, but it usually requires corresponding simplifications and assumptions. The method of characteristics (MOC) based on one-dimensional flow theory is still used to solve pressure waves. This method is particularly suitable for long tunnel conditions because it consumes less computational resources. However, for three-dimensional effects that cannot be ignored, such as when studying tunnel ventilation shafts and branch shafts, compensation correction terms need to be introduced.

[0005] In recent years, with the substantial improvement of computer performance, three-dimensional computational fluid dynamics (CFD) methods have been widely used. It is very convenient in studying buffer structures, vehicle speeds, and vehicle head shapes. It is mainly based on sliding grid and overlapping grid technology to simulate the mutual movement of trains and tunnels. However, the numerical calculation results are usually highly sensitive to the quality of grid division and the selection of flow models.

[0006] With direct measurements that are more in line with engineering practice, the results of real vehicle tests are often more convincing. However, the application of this method is often limited by harsh test environments and high costs, and usually in order to avoid damage to the vehicle body, it is not appropriate to arrange a large number of test points, resulting in relatively little on-site measurement data. Therefore, it is usually used to verify the accuracy of a class of methods.

[0007] Therefore, using the principles of motion similarity and flow similarity, scaled model devices have been widely studied and applied to simulate the pressure fluctuation law of high-speed trains passing through tunnels. A key to train / tunnel coupling is the pressure change caused by the generation, propagation and radiation of compression waves. Different from the traditional dynamic model device, the compression wave generating device studied in the present invention simplifies the process of the train entering the tunnel. It is based on the principle that the wavefront propagation speed is much greater than the vehicle speed, and uses the pressure difference relationship to generate an initial compression wave with the same characteristics as the air squeezed by the front of the train, and its propagation and radiation can be studied without any restrictions. In addition, by adjusting the various variables of the device, the generated waveform can be mapped with the waveform generated under various conditions of actual vehicles entering the tunnel. Compared with the traditional dynamic model device, the compression wave generating device focuses more on the research subject, ensuring that the subsequent initial compression wave propagates in the tunnel and the research on the micro-pressure wave at the tunnel exit continues. The research results of the present invention will provide new ideas for reducing micro-pressure waves in the future, especially in experimental verification. Summary of the invention

[0008] In order to solve the problems of poor accuracy, high cost and complex operation of current tunnel aerodynamic research methods, the present invention simplifies the vehicle entry process and adopts a compression wave generating device that can generate compression waves that meet engineering practice. Through the four parameters of the device: initial pressure of the high-pressure chamber, solenoid valve opening voltage, opening number and opening sequence, the train entry speed, train streamline length, vehicle-tunnel blocking ratio and typical tunnel entrance buffer structure can be mapped respectively, which can be used to simulate different train entry conditions.

[0009] The present invention is achieved by adopting the following technical solutions:

[0010] A research method for simulating different train entry conditions to generate compression waves that meet engineering actual conditions is established. A simulation generating device for tunnel compression waves is established, including an air compressor, a high-pressure chamber, a digital pressure gauge, a polyurethane tube, a solenoid valve, a flange end cover, a simulated tunnel, a pressure sensor, a data acquisition instrument and a computer; the air compressor is connected to one end of the high-pressure chamber, a digital pressure gauge is installed on the high-pressure chamber, a flange end cover is installed at one end of the simulated tunnel, a pressure sensor is installed in the front of the simulated tunnel, one end of a plurality of polyurethane tubes is connected to the high-pressure chamber, and the other end is connected to the flange end cover, each polyurethane tube is installed with a solenoid valve, all the solenoid valves are used as a solenoid valve group, and the solenoid valve group has a PLC control function, allowing the solenoid valve group to have different voltages, quantities and sequences when opened.

[0011] Before the experiment begins, a static air tightness test is carried out in the simulated tunnel to ensure good air tightness in the simulated tunnel. During the experiment, the solenoid valve group remains closed, and the high-pressure chamber is filled with a preset initial pressure through an air compressor according to the test objectives, that is, the pressure before entering the simulated tunnel. Secondly, the opening voltage, number and sequence of each solenoid valve are set according to the test objectives. After that, the solenoid valve is opened to control the release of high-pressure gas in the high-pressure chamber. Finally, the pressure sensor and data acquisition instrument are used to measure and collect the pressure changes of the initial compression wave of the simulated tunnel.

[0012] Through the four parameters of the tunnel compression wave simulation device: the initial pressure of the high-pressure chamber, the solenoid valve opening voltage, the number of openings and the opening sequence, the trains entering the tunnel at different speeds, the trains entering the tunnel with different streamline lengths, the trains entering the tunnel with different cross-sectional areas, and the trains entering the tunnel with a typical entrance buffer structure are mapped respectively to simulate different train entry conditions, as follows:

[0013] Ⅰ. Mapping of initial pressure in high-pressure chamber The experimental steps for simulating a train entering a tunnel at different speeds are as follows:

[0014] 1.1. Keep the solenoid valve group between the high-pressure chamber and the simulated tunnel closed, start the air compressor, and fill the high-pressure chamber with air. The digital pressure gauge on the top of the high-pressure chamber will display the pressure status in the chamber in real time. When the pressure in the high-pressure chamber reaches the stable preset value, that is, the initial pressure P0, cut off the air supply from the air compressor;

[0015] 1.2. The process of releasing air from the high-pressure chamber is as follows: the solenoid valve is powered by a DC power supply, and the opening strategy of the solenoid valve is kept unchanged, that is, the opening voltage U0, the opening number N0, and the opening sequence are kept consistent. After the solenoid valve is subjected to electromagnetic force, the valve core is opened, and high-pressure air enters the simulated tunnel through the polyurethane tube;

[0016] 1.3. High-pressure air pushes the static air in the simulated tunnel forward. The air in the simulated tunnel is squeezed, and its pressure rises instantly, forming an initial compression wave in the tunnel. The initial compression wave propagates forward at the speed of sound, and the pressure rises rapidly where it passes. The shape of the initial compression wave, that is, the change of pressure over time, is obtained by arranging pressure sensors on the wall of the simulated tunnel.

[0017] 1.4. By filtering and denoising the pressure signal measured by the pressure sensor, an initial compression wave curve is generated under different initial pressures P0, that is, the initial compression wave shape in the tunnel is simulated;

[0018] 1.5. To find out the initial pressure P0 of the high pressure chamber and the train speed V t The relationship between the initial pressure P0 of the high-pressure chamber is used to indirectly verify the engineering value of the initial pressure P0 of the high-pressure chamber;

[0019] The pressure amplitude P of the initial compression wave generated under different initial pressures of the high-pressure chamber is max Substitute into formula (1), formula (2), and formula (3) to obtain the corresponding train speed V t ;

[0020]

[0021] Where: γ is the gas specific heat ratio; P * is the ambient reference pressure; M and β are the Mach number and the blockage ratio, respectively, which are obtained by equations (2) and (3);

[0022]

[0023] Where c is the speed of sound, A t and A T are the cross-sectional areas of the train and the tunnel, respectively;

[0024] 1.6. Pressure amplitude P at different initial pressures P0 of high pressure chamber max Obtained V t , and further obtain the initial pressure P0 of the high-pressure chamber and the train speed V t The relationship between the pressure amplitude of the compression wave generated under different initial pressures of the high-pressure cavity is calculated, and the corresponding theoretical train speed obtained by the above calculation indicates that the initial pressure of the high-pressure cavity can be mapped to the train speed;

[0025] 1.7. Maximum pressure gradient G through the rising phase of the initial compression wave max Analyze the maximum pressure gradient from the perspective of

[0026]

[0027] Among them, L n is the streamlined length of the train, P max is the pressure amplitude of the initial compression wave generated under different initial pressures of the high-pressure chamber, G max is the maximum pressure gradient of the rising phase of the initial compression wave generated under different initial pressures of the high-pressure chamber, V t is the theoretical vehicle speed obtained by calculating the initial compression wave generated under different initial pressures of the high-pressure chamber; given an L n The constant value means that the compression wave pressure amplitude P obtained under different initial pressures of the high-pressure chamber is max and theoretical vehicle speed V t The theoretical maximum pressure gradient G of the compression wave obtained under different initial pressures of the high-pressure chamber is calculated by formula (4): max, while the experimental value is the maximum gradient value obtained by directly taking the first-order derivative of the initial compression wave curve; the comparison between the theoretical value and the experimental value shows the feasibility or accuracy of the above transformation mapping.

[0028] II. Solenoid valve opening strategy - Solenoid valve opening voltage mapping The experimental steps for simulating trains of different streamline lengths entering the tunnel are as follows:

[0029] 2.1. Keep the solenoid valve group between the high-pressure chamber and the tunnel model closed, start the air compressor, and fill the high-pressure chamber with air. The digital pressure gauge on the top of the high-pressure chamber will display the pressure status in the chamber in real time. When the pressure in the high-pressure chamber reaches a stable preset value, that is, the initial pressure P0, cut off the air supply from the air compressor;

[0030] 2.2. The process of releasing air from the high-pressure chamber is as follows: power is supplied to the solenoid valves through a DC power supply, the number of solenoid valves opened is kept unchanged and opened synchronously, the solenoid valve opening voltage U0 is increased, and the valve core of the solenoid valve is opened after being subjected to electromagnetic force, and high-pressure air enters the simulated tunnel through the polyurethane tube;

[0031] 2.3. High-pressure air pushes the static air in the simulated tunnel forward. The air in the simulated tunnel is squeezed, and its pressure rises instantly, forming an initial compression wave in the tunnel. The initial compression wave propagates forward at the speed of sound, and the pressure rises rapidly where it passes. The shape of the initial compression wave, that is, the change of pressure over time, is obtained by arranging pressure sensors on the wall of the simulated tunnel.

[0032] 2.4. By filtering and denoising the pressure signal measured by the pressure sensor, the initial compression wave curves generated under different solenoid valve opening voltages U0 are given, that is, the initial compression wave shapes in the tunnel; after the solenoid valve is opened, the initial compression wave has a constant pressure amplitude, and the maximum pressure gradient gradually increases, which can be compared to the situation when a train with a shorter head enters a tunnel;

[0033] 2.5. To illustrate the solenoid valve opening voltage U0 and the theoretical head streamline length L n The relationship between the solenoid valve opening voltage U0 is used to indirectly verify the engineering value of the solenoid valve opening voltage U0;

[0034] The maximum pressure gradient value G of the initial compression wave generated under different solenoid valve opening voltages U0 max Substitute into formula (4) to obtain the corresponding theoretical front streamline length L n ;

[0035]

[0036] Among them, P max and V tis the pressure amplitude of the initial compression wave generated under the initial pressure P0 of the high-pressure chamber and the theoretical speed of conversion; different front streamline lengths L are calculated by calculating the maximum pressure gradient of the initial compression wave obtained under different solenoid valve opening voltages n ;

[0037] 2.6. Maximum pressure gradient G at different solenoid valve opening voltage U0 max The obtained L n , and further obtain the solenoid valve opening voltage U0 and the front streamline length L n By comparing the relationship between the solenoid valve opening voltage U0 and the front streamline length L n Curve fitting shows that the solenoid valve opening voltage can be mapped to the streamlined length of the front of the vehicle.

[0038] III. Solenoid valve opening strategy - mapping the number of solenoid valves opened The experimental steps for simulating trains entering tunnels with different cross-sectional areas are as follows:

[0039] 3.1. Keep the solenoid valve group between the high-pressure chamber and the tunnel model closed, start the air compressor, and fill the high-pressure chamber with air. The digital pressure gauge on the upper part of the high-pressure chamber will display the pressure status in the chamber in real time. When the pressure in the high-pressure chamber reaches a stable preset value, that is, the initial pressure P0, cut off the air supply from the air compressor;

[0040] 3.2. The process of releasing air from the high-pressure chamber is as follows: power the solenoid valve through a DC power supply, keep the opening voltage U0 of the solenoid valve unchanged and open synchronously, increase the number of solenoid valve openings in sequence, and the valve core of the solenoid valve opens after being subjected to electromagnetic force, and high-pressure air enters the simulated tunnel through the polyurethane tube;

[0041] 3.3. High-pressure air pushes the static air in the simulated tunnel forward. The air in the simulated tunnel is squeezed, and its pressure rises instantly, forming an initial compression wave in the tunnel. The initial compression wave propagates forward at the speed of sound, and the pressure rises rapidly where it passes. The shape of the initial compression wave, that is, the change of pressure over time, is obtained by arranging pressure sensors on the wall of the simulated tunnel.

[0042] 3.4. The pressure signal measured by the pressure sensor is filtered and denoised, and the initial compression wave curves generated under different numbers of solenoid valves N0 are given respectively; when the number of solenoid valves opened is increased, after the solenoid valves are opened, the initial compression wave has a larger pressure amplitude and a larger pressure gradient value while the compression wave length remains unchanged, which can be compared with the wave surface shape caused by the train entering the tunnel with different cross-sectional areas;

[0043] 3.5. To further illustrate the relationship between the number of solenoid valve openings N0 and the theoretical vehicle-tunnel blocking ratio β, the engineering value of the number of solenoid valve openings N0 is indirectly verified;

[0044] The pressure amplitude P of the initial compression wave generated under different solenoid valve opening numbers N0 max Substitute into formula (1) to obtain the corresponding theoretical front streamline length L n ;

[0045]

[0046] Where: γ is the gas specific heat ratio; P * is the ambient reference pressure; M and β are Mach number and blockage ratio, respectively; P max and V t is the pressure amplitude of the initial compression wave generated under the initial pressure P0 of the high-pressure chamber and the theoretical speed of conversion; different vehicle-tunnel blocking ratios β are calculated by the pressure amplitude of the initial compression wave obtained under different solenoid valve opening numbers;

[0047] 3.6. Pressure amplitude P of compression wave generated when different solenoid valve opening numbers N0 are used max The obtained β is further used to obtain the relationship between the solenoid valve opening number N0 and the vehicle-tunnel blocking ratio β. Curve fitting is performed on the solenoid valve opening number N0 and the vehicle-tunnel blocking ratio β, which shows that the solenoid valve opening number can be mapped to the vehicle-tunnel blocking ratio.

[0048] IV. Solenoid Valve Opening Strategy - Solenoid Valve Opening Sequence Mapping The experimental steps for simulating a train entering a tunnel with a typical entrance buffer structure are as follows:

[0049] 4.1. Keep the solenoid valve group closed, start the air compressor, and fill the high-pressure chamber with air. The digital pressure gauge on the upper part of the high-pressure chamber will display the pressure status in the chamber in real time. When the pressure in the high-pressure chamber reaches a stable preset value, that is, the initial pressure P0, cut off the air supply from the air compressor;

[0050] 4.2. The process of releasing air from the high-pressure chamber is as follows: the solenoid valve is powered by a DC power supply to maintain the initial pressure of the high-pressure chamber. The solenoid valve opening voltage U0 and the number N0 remain unchanged. The sequence of the solenoid valves is controlled, and a part of the solenoid valves are opened first, and then the other part of the solenoid valves are opened. The sequence control guides the solenoid valves to open and change in sequence. The opening sequence is realized according to the delay relay and the PLC control system. After the solenoid valve is subjected to the electromagnetic force, the valve core opens, and the high-pressure air enters the simulated tunnel through the polyurethane tube;

[0051] 4.3. High-pressure air pushes the static air in the simulated tunnel forward. The air in the simulated tunnel is squeezed, and its pressure rises instantly, forming an initial compression wave in the tunnel. The initial compression wave propagates forward at the speed of sound, and the pressure rises rapidly where it passes. The shape of the initial compression wave, that is, the change of pressure over time, is obtained by arranging pressure sensors on the wall of the simulated tunnel.

[0052] 4.4. Since the solenoid valves are opened in batches, the shape of the initial compression wave rises first, then remains unchanged, and finally rises again to the final pressure amplitude. This can be compared to the waveform change law of the compression wave generated by a train entering a tunnel with a typical entrance buffer structure, indicating that the opening sequence of the solenoid valves can be mapped to the typical entrance buffer structure of the tunnel.

[0053] The present invention has a reasonable design. The proposed compression wave generating device simplifies the process of train entering a tunnel by instantly releasing high-pressure air in a high-pressure chamber. The device has a low cost and high data productivity. It can be used for future research on the evolution of initial compression waves and the development of new buffer structures that reduce the hazards of micro-pressure waves. It provides new experimental ideas in engineering verification methods and has good practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0055] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0056] Figure 1 Schematic diagram of actual train-tunnel coupling.

[0057] Figure 2 Schematic diagram of the simulated compression wave generation system.

[0058] Figure 3 The graph shows the initial compression wave (ICW) waveform generated under different initial pressures of the high-pressure chamber (U0=28V, N0=10pcs).

[0059] Figure 4 The mapping relationship between the initial pressure of the high-pressure chamber and the theoretical train speed (V t =42.9×P0 0.29 ).

[0060] Figure 5 The figure shows the comparison between the experimental maximum pressure gradient obtained according to formula (6) and the theoretical maximum pressure gradient.

[0061] Figure 6 Waveform diagram showing the initial compression wave generated under different valve opening voltages (P0=300kPa, N0=10pcs).

[0062] Figure 7A diagram showing the pressure amplitude of the initial compression wave generated under different valve opening voltages (P0=300kPa, N0=10pcs).

[0063] Figure 8 Pressure gradient diagram showing the initial compression wave generated under different valve opening voltages (P0=300kPa, N0=10pcs).

[0064] Fig. 9 The mapping relationship between the valve opening voltage and the theoretical streamline length of the train (Ln = 0.5 × U0 -1.03 ).

[0065] Fig.10 Waveform diagram showing the initial compression wave generated under different valve opening numbers (P0=300kPa, U0=28V).

[0066] Fig.11 A diagram showing the length of the initial compression wave generated under different valve opening numbers (P0=300kPa, U0=28V).

[0067] Fig.12 A diagram showing the mapping relationship between the number of valve openings and the theoretical blockage rate (β=-3.9+96.92×N0).

[0068] In the figure: 1-train, 2-tunnel, 3-air compressor, 4-high-pressure chamber, 5-digital pressure gauge, 6-polyurethane tube, 7-solenoid valve, 8-flange end cover, 9-simulated tunnel, 10-pressure sensor; A-initial compression wave, B-micro air pressure wave. DETAILED DESCRIPTION

[0069] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0070] In the description, it should be noted that the terms "first" and "second" are only used for descriptive purposes and should not be understood as indicating or implying relative importance. It should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be internal communication between two elements. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0071] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0072] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0073] A research method for simulating different train tunneling conditions to generate compression waves that meet engineering actual conditions is as follows:

[0074] First, a simulation device for generating tunnel compression waves is established, including an air compressor 3, a high-pressure chamber 4, a digital pressure gauge 5, a polyurethane tube 6, a solenoid valve 7, a flange end cover 8, a simulated tunnel 9, a pressure sensor 10, a data acquisition instrument and a computer, etc. The initial compression wave is generated by instantaneously releasing high-pressure air, so the device is different from the traditional mobile model device in terms of power source. Figure 2 As shown, the air compressor 3 is connected to one end of the high-pressure chamber 4 through an oil-water separator, a digital pressure gauge 5 is installed on the high-pressure chamber 4, flanges are provided at both ends of the simulation tunnel 9, a flange end cover 8 is installed at one end of the simulation tunnel 9, a pressure sensor 10 is installed in the front part of the simulation tunnel 9, 10 polyurethane tubes 6 are sealedly connected to the high-pressure chamber 4 at one end and sealedly connected to the flange end cover 8 at the other end, and a solenoid valve 7 is installed on each polyurethane tube 6.

[0075] In actual operation, the volume of the high-pressure chamber 4 needs to be large enough, and the air compressor 3 is used to provide different stable preset pressures for the high-pressure chamber 4, so as to support the full rise of the initial compression wave as much as possible in terms of pressure and maintain the upstream of the wave surface. The high-pressure chamber 4 and the simulation tunnel 9 are connected by 10 polyurethane tubes 6 with an inner diameter of 8 mm, and each tube is equipped with a solenoid valve 7 to control the release of high-pressure air. The ten solenoid valves are used as a solenoid valve group, which has a PLC control function, allowing the solenoid valve group to have different voltages, quantities and sequences when it is opened.

[0076] Considering the experimental cost and field conditions, the ratio of the diameter and length of the simulated tunnel 9 to the actual tunnel (hydraulic diameter 10 meters, length 1200 meters) is 1:100, and the shape of the tunnel cross section is simplified to a circle. This is because when the length is much larger than the diameter, obvious one-dimensional characteristics will be highlighted. The test system is mainly used to measure the pressure changes of the tunnel wall. It consists of three parts: pressure sensor, power supply and data acquisition instrument. The pressure sensor monitors the characteristics of the compression wave in real time and records the time series of pressure changes. The data acquisition instrument transmits the collected signals to the computer through a cable for analysis.

[0077] Before the experiment begins, a static air tightness test is conducted in the simulated tunnel to ensure good air tightness in the tunnel. During the experiment, the solenoid valve group remains closed, and the high-pressure chamber is filled with a preset initial pressure (the pressure before entering the simulated tunnel) through an air compressor according to the test objectives. Secondly, the opening voltage, number and sequence of each solenoid valve are set according to the test objectives. After that, the solenoid valve is opened to control the release of high-pressure gas in the high-pressure chamber. Finally, the pressure sensor and data acquisition instrument are used to measure and collect the pressure changes of the initial compression wave in the simulated tunnel.

[0078] The method of the present invention can respectively map the train entry speed, train streamline length, vehicle-tunnel blocking ratio and typical tunnel entrance buffer structure through the four parameters of the above-mentioned device: the initial pressure of the high-pressure chamber, the solenoid valve opening voltage, the opening number and the opening sequence, and can be used to simulate different train entry conditions.

[0079] The key indicators of the results generated by the simulation device of the tunnel compression wave mentioned above are used. The original intention of the design of this low-cost and simple device is to develop other buffer structures based on the evolution of the compression wave to provide guidance for practical applications. Therefore, if the generated initial compression wave is more similar to the real vehicle tunnel situation, especially if it can simulate the initial compression wave under complex and variable working conditions, it will further enhance its value.

[0080] Ⅰ. Mapping of initial pressure in high-pressure chamber The experimental steps for simulating a train entering a tunnel at different speeds are as follows:

[0081] 1.1. Keep the solenoid valve group between the high-pressure chamber and the simulation tunnel closed, start the air compressor, and inflate the high-pressure chamber. The digital pressure gauge on the top of the high-pressure chamber can display the pressure status in the chamber in real time. When the pressure in the high-pressure chamber reaches the stable preset value (P0=100kPa / 200kPa / 300kPa / 400kPa / 500kPa), cut off the air supply from the air compressor.

[0082] 1.2. The high-pressure chamber and the simulated tunnel are connected by 10 polyurethane tubes with an inner diameter of 8 mm. Each tube is equipped with a solenoid valve to control the release of high-pressure air in the high-pressure chamber. The high-pressure chamber air release process is as follows: the solenoid valve is powered by a DC power supply, and the solenoid valve opening strategy is kept unchanged (opening voltage U0 = 28V, opening number N0 = 10pcs, opening in sequence at the same time, keeping consistent). After the solenoid valve is subjected to electromagnetic force, the valve core opens, and the high-pressure air enters the simulated tunnel through the polyurethane tube.

[0083] 1.3. Similar to the piston propulsion process, high-pressure air will push the static air in the simulated tunnel forward. The air in the tunnel will be squeezed, and its pressure will rise instantly, forming the initial compression wave of the tunnel. This wave will propagate forward at the speed of sound, and the pressure will rise rapidly wherever it passes. The shape of the initial compression wave (pressure change over time) can be obtained by arranging pressure sensors on the tunnel wall.

[0084] 1.4. By filtering and denoising the pressure signal measured by the pressure sensor, the initial compression wave shape in the tunnel is as follows: Figure 3 As shown. The initial compression wave curves generated under P0=100kPa / 200kPa / 300kPa / 400kPa / 500kPa are given respectively, and P0 represents different initial pressures of the high-pressure chamber (corresponding to step 1.1). It can be seen that by increasing the initial pressure of the high-pressure chamber, the pressure amplitude and gradient of the generated initial compression wave increase, which means that the shape of the initial compression wave is steeper (the first pressure rise section). This is due to the increase in the intensity of the high-pressure air at the entrance of the tunnel and the more intense process of high-pressure air propulsion. It is worth noting that this is very similar to the waveform changes caused by the increase in speed when the train enters the tunnel.

[0085] 1.5. To further explore the initial pressure P0 of the high-pressure chamber and the train speed V t The relationship between the initial pressure of the high-pressure chamber P0 is used to indirectly verify the engineering value of the initial pressure of the high-pressure chamber. The verification process is as follows: the pressure amplitude of the initial compression wave generated under different initial pressures of the high-pressure chamber P max Substitute into formulas (1), (2), and (3) to obtain the corresponding train speed V t .

[0086]

[0087] Where: γ is the gas specific heat ratio; P * is the ambient reference pressure; M and β are the Mach number and blockage ratio, respectively, which can be obtained by equations (2) and (3).

[0088]

[0089] Where c is the speed of sound, A t and A T are the cross-sectional areas of the train and the tunnel, respectively. It is worth noting that there is no train model in the experiment, but in order to ensure the continuation of the calculation, a possible common blocking ratio β = 0.16 is introduced. In fact, due to the different tunnel clearance standards in many countries, any blocking ratio is possible.

[0090] 1.6. Pressure amplitude P at different initial pressures P0 of high pressure chamber max Obtained V t, we can further get the initial pressure P0 of the high-pressure chamber and the train speed V t relationship, Figure 4 The pressure amplitude of the compression wave generated under different initial pressures of the high-pressure chamber and the theoretical train speed calculated above are given. t By curve fitting, we can get V t =42.9×P0 0.29 At this point, it means that the initial pressure of the high-pressure chamber can be mapped to the train speed, which means that the initial pressure of the high-pressure chamber is converted to the train speed with more practical application value through this formula conversion (method).

[0091] 1.7. To further illustrate the feasibility of this mapping transformation method, the maximum pressure gradient G max The maximum pressure gradient is compared with formula (4) to verify the applicability of the conversion method here.

[0092]

[0093] Among them, L n is the streamlined length of the train, P max is the pressure amplitude of the initial compression wave generated under different initial pressures of the high-pressure chamber, G max is the maximum pressure gradient of the rising phase of the initial compression wave generated under different initial pressures of the high-pressure chamber, V t is the theoretical vehicle speed calculated by the initial compression wave generated under different initial pressures of the high-pressure chamber. Here, a L n (constant value), which means the compression wave pressure amplitude P obtained under different initial pressures of the high-pressure chamber max and theoretical vehicle speed V t The theoretical maximum pressure gradient G of the compression wave obtained under different initial pressures of the high-pressure chamber can be calculated by formula (4): max , while the experimental value is the maximum value (true) of the gradient obtained by directly taking the first-order derivative of the initial compression wave curve. In this way, the theoretical value can be compared with the experimental value, such as Figure 5 As shown, it can be found that the error between the theoretical value and the true value is relatively small, which indirectly reflects the feasibility or accuracy of the above-mentioned transformation mapping method.

[0094] II. Solenoid valve opening strategy - Solenoid valve opening voltage mapping The experimental steps for simulating trains of different streamline lengths entering the tunnel are as follows:

[0095] 2.1. Keep the solenoid valve group between the high-pressure chamber and the tunnel model closed, start the air compressor, and inflate the high-pressure chamber. The digital pressure gauge on the top of the high-pressure chamber can display the pressure status in the chamber in real time. When the pressure in the high-pressure chamber reaches a stable preset value (for example, P0 = 300 kPa), cut off the air supply from the air compressor.

[0096] 2.2. The high-pressure chamber and the simulation tunnel are connected by 10 polyurethane tubes with an inner diameter of 8 mm. Each tube is equipped with a solenoid valve to control the release of high-pressure air in the high-pressure chamber. The air release process of the high-pressure chamber is as follows: the solenoid valve is powered by a DC power supply, the number of solenoid valves opened remains unchanged (N0=10pcs) and is opened synchronously, the solenoid valve opening voltage is increased, and the valve core of the solenoid valve is opened after being subjected to electromagnetic force, and high-pressure air enters the simulation tunnel through the polyurethane tube. Specific scheme for increasing the opening voltage of the solenoid valve: In the PLC system, a PLC output point is set for each solenoid valve for control, and a voltage regulation module is added. The module can output the required voltage range (such as 20-30V), and its output is connected to each solenoid valve. In the PLC program, a target voltage value is set for each solenoid valve, and a voltage array can be defined to store the target voltage. The design of the PLC program includes an input interface, which allows the required solenoid valve opening voltage to be input through the interface.

[0097] 2.3. Similar to the piston propulsion process, high-pressure air will push the static air in the tunnel model forward. The air in the tunnel will be squeezed, and its pressure will rise instantly, forming the initial compression wave of the tunnel. This wave will propagate forward at the speed of sound, and the pressure will rise rapidly wherever it passes. The shape of the initial compression wave (pressure change over time) can be obtained by arranging pressure sensors on the tunnel wall.

[0098] 2.4. By filtering and denoising the pressure signal measured by the pressure sensor, the initial compression wave shape in the tunnel is as follows: Figure 6 As shown in FIG. The initial compression wave curves generated under U0 = 22V / 24V / 26V / 28V / 30V are respectively given, and U0 represents different solenoid valve opening voltages (corresponding to step 2.1). Figure 7 and Figure 8They are the pressure amplitude and pressure gradient change curves of the initial compression wave generated under different U0. It can be seen that after the solenoid valve is opened, the initial compression wave keeps the pressure amplitude unchanged, and the maximum pressure gradient gradually increases. This is because increasing the solenoid valve opening voltage will increase the electromagnetic force obtained by the valve core, making the opening response speed faster, and thus the time required for pressure rise shorter, but the total stroke of the valve core remains unchanged. Therefore, after the solenoid valve is opened, the initial compression wave keeps the pressure amplitude unchanged, and the maximum pressure gradient gradually increases. This is similar to the situation when a train with a shorter head enters a tunnel, which can also be found from formulas (1) and (4).

[0099] 2.5. To further determine the solenoid valve opening voltage U0 and the theoretical head streamline length L n The relationship between the electromagnetic valve opening voltage U0 and the engineering value of the electromagnetic valve opening voltage U0 is indirectly verified. The verification process is as follows: the maximum pressure gradient value G of the initial compression wave generated under different electromagnetic valve opening voltages U0 is max Substitute into formula (4) to obtain the corresponding theoretical front streamline length L n .

[0100]

[0101] Among them, P max and V t is the pressure amplitude of the initial compression wave generated under the initial pressure of 300 kPa in the high-pressure chamber and the theoretical speed of conversion (the control variable method is used in the study of the electromagnetic valve opening voltage or the whole process). From the experimental steps of the high-pressure chamber initial pressure mapping simulation of the train entering the tunnel at different speeds, it can be seen that as long as the initial pressure of the high-pressure chamber is fixed, the pressure amplitude of the initial compression wave generated and the theoretical speed of conversion are constant. Here, different front streamline lengths L can be calculated only by the maximum pressure gradient of the initial compression wave obtained under different electromagnetic valve opening voltages. n .

[0102] 2.6. Maximum pressure gradient G at different solenoid valve opening voltage U0 max The obtained L n , we can further get the solenoid valve opening voltage U0 and the front streamline length L n relationship, such as Fig. 9 The maximum pressure gradient G of the compression wave generated under different solenoid valve opening voltages is shown in the figure max , and the theoretical front streamline length L calculated above n By comparing the solenoid valve opening voltage U0 with the front streamline length L n By curve fitting, we can get L n =0.5×U0 -1.03At this point, it means that the solenoid valve opening voltage can be mapped to the front streamline length, which means that the solenoid valve opening voltage is converted to the front streamline length with more practical application value through the formula conversion (method).

[0103] III. Solenoid valve opening strategy - mapping the number of solenoid valves opened The experimental steps for simulating trains entering tunnels with different cross-sectional areas are as follows:

[0104] 3.1. Keep the solenoid valve group between the high-pressure chamber and the tunnel model closed, start the air compressor, and inflate the high-pressure chamber. The digital pressure gauge on the top of the high-pressure chamber can display the pressure status in the chamber in real time. When the pressure in the high-pressure chamber reaches a stable preset value (for example, P0 = 300 kPa), cut off the air supply from the air compressor.

[0105] 3.2. The high-pressure chamber and the tunnel model are connected by 10 polyurethane tubes with an inner diameter of 8 mm. Each tube is equipped with a solenoid valve to control the release of high-pressure air in the high-pressure chamber. The air release process of the high-pressure chamber is as follows: the solenoid valve is powered by a DC power supply, the opening voltage of the solenoid valve is kept constant (U0 = 28V) and opened synchronously, and the number of solenoid valve openings is increased from 2 to 10. After the solenoid valve is subjected to electromagnetic force, the valve core opens, and high-pressure air enters the tunnel model through the polyurethane tube. Specific scheme for increasing the number of solenoid valve openings: In the PLC system, a PLC output point is set for each solenoid valve for control. According to the requirements of the number of solenoid valve openings, a variable is set to define the number of solenoid valve openings each time. The design of the PLC program includes an input interface, which allows the required number of solenoid valve openings to be input through the interface. In the PLC program, a variable is first defined to store the input target opening number. Then, a counter is used to track the number of solenoid valves currently opened. The program will activate the opening signal of the solenoid valve in turn in the loop structure according to the input number of solenoid valve openings. By using parallel output, the system will send an opening signal to all the solenoid valves that need to be opened at the same time to ensure that they can work synchronously. In order to achieve synchronous opening, a timer can be used in the PLC program to control the opening sequence of the solenoid valves to ensure that all solenoid valves receive the signal at the same time point (the following uses the PLC delay setting to control the opening of two batches of valves in sequence).

[0106] 3.3. Similar to the piston propulsion process, high-pressure air will push the static air in the tunnel model forward. The air in the tunnel will be squeezed, and its pressure will rise instantly, forming the initial compression wave of the tunnel. This wave will propagate forward at the speed of sound, and the pressure will rise rapidly where it passes. The shape of the initial compression wave (pressure change over time) can be obtained by arranging pressure sensors on the tunnel wall.

[0107] 3.4. By filtering and denoising the pressure signal measured by the pressure sensor, the initial compression wave shape in the tunnel is as follows: Fig.10 As shown, the initial compression wave curves generated when N0=2 / 4 / 6 / 8 / 10pcs are respectively given, and N0 represents the number of different solenoid valves opened (corresponding to step 3.1). Fig.11 The wavefront length of the initial compression wave generated under different N0 (defined as the product of the time required for the pressure to rise from 0 to the amplitude and the wave speed). It can be seen that when the number of solenoid valves opened increases, the pressure amplitude and pressure gradient values ​​of the initial compression wave increase while the wavefront length remains unchanged after the solenoid valve is opened. This is because the greater the number of valves opened, the greater the intensity of the high-pressure air at the entrance of the tunnel, and the more intense the high-pressure air propulsion process. At this time, the valve opening voltage remains unchanged (the valve core opening speed remains unchanged), so the wavelength (the time for the first section to rise from 0 to the pressure amplitude) remains unchanged. Therefore, after the solenoid valve is opened, the initial compression wave gradually increases while the compression wave length remains unchanged, and the pressure amplitude and maximum pressure gradient gradually increase. This is similar to the wavefront shape caused when a train enters a tunnel with different cross-sectional areas.

[0108] 3.5. To further illustrate the relationship between the number of solenoid valve openings N0 and the theoretical train-tunnel blocking ratio β (ratio of the cross-sectional area of ​​the train to the cross-sectional area of ​​the tunnel), the engineering value of the number of solenoid valve openings N0 is indirectly verified. The verification process is as follows: the pressure amplitude P of the initial compression wave generated under different numbers of solenoid valve openings N0 is calculated. max Substitute into formula (1) to obtain the corresponding theoretical front streamline length L n .

[0109]

[0110] Where: γ is the gas specific heat ratio; P * is the ambient reference pressure; M and β are Mach number and blockage ratio, respectively; P max and V t is the pressure amplitude of the initial compression wave generated at the initial pressure of 300 kPa in the high-pressure chamber and the theoretical speed of conversion (speed V t Given, then the Mach number M is given). In studying the number of solenoid valve openings or the entire process, the control variable method is used. From the above experimental steps of studying the initial pressure mapping of the high-pressure chamber to simulate the train entering the tunnel at different speeds, it can be seen that as long as the initial pressure of the high-pressure chamber is fixed, the pressure amplitude of the initial compression wave and the corresponding Mach number M are fixed. Here, different vehicle-tunnel blocking ratios β can be calculated only by the pressure amplitude of the initial compression wave obtained under different numbers of solenoid valve openings.

[0111] 3.6. Therefore, according to the pressure amplitude P of the compression wave generated when the number of solenoid valves opened N0 is different maxThe obtained β can further be used to obtain the relationship between the number of solenoid valve openings N0 and the vehicle-tunnel blocking ratio β, as shown in Fig.12 The figure shows the pressure amplitude P of the compression wave generated when the number of solenoid valves is opened max , and the theoretical tunnel-vehicle blocking ratio β obtained by the above calculation. By curve fitting the number of solenoid valve openings N0 and the tunnel-vehicle blocking ratio β, we can get β = -3.9 + 96.92 × N0. In other words, even if the tunnel does not change in the experiment (replacing a tunnel with a different cross-sectional area), the tunnel clearance can be indirectly reduced by increasing N0. At this point, it means that the number of solenoid valve openings can be mapped to the tunnel-vehicle blocking ratio, which means that the solenoid valve opening number is converted to a tunnel-vehicle blocking ratio with more practical application value through this formula conversion (method).

[0112] IV. Solenoid valve opening strategy - Solenoid valve opening sequence mapping The experimental steps for a train entering a tunnel with a typical entrance buffer structure are as follows:

[0113] 4.1. Keep the solenoid valve group between the high-pressure chamber and the tunnel model closed, start the air compressor, and inflate the high-pressure chamber. The digital pressure gauge on the top of the high-pressure chamber can display the pressure status in the chamber in real time. When the pressure in the high-pressure chamber reaches a stable preset value (for example, P0 = 300 kPa), cut off the air supply from the air compressor.

[0114] 4.2. The high-pressure chamber and the simulated tunnel are connected by 10 polyurethane tubes with an inner diameter of 8 mm. Each tube is equipped with a solenoid valve to control the release of high-pressure air in the high-pressure chamber. The high-pressure chamber air release process is as follows: the solenoid valve is powered by a DC power supply to maintain the initial pressure of the high-pressure chamber. The solenoid valve opening voltage (U0=28V) and the number (N0=10pcs) remain unchanged. The sequence of the solenoid valves is controlled, and some solenoid valves are opened first, and then the other solenoid valves are opened. The sequence control guides the solenoid valves to open and change in sequence. The opening sequence can be realized according to the delay relay and PLC control system. The valve core of the solenoid valve is opened after the electromagnetic force is applied, and the high-pressure air enters the tunnel model through the polyurethane tube. Specific scheme for changing the opening sequence of the solenoid valves: The PLC program will first define two variables, which are used to store the opening number of the first and second batches of solenoid valves respectively. Then, a counter is used to track the number of solenoid valves that have been opened. At the beginning of the program, the PLC will first send a signal to the first batch of solenoid valves to start their opening process. Through parallel output, it is ensured that these batches of solenoid valves receive the opening signal at the same time. After the first batch of solenoid valves are opened, the PLC will start a timer and set a delay to ensure that the first batch of solenoid valves are fully opened and stable before sending a signal to the second batch of solenoid valves. The delay time can be set according to actual needs to ensure that the changes in the pressure compression wave in the two stages meet expectations. When the opening signal of the first batch of solenoid valves is completed, the PLC will activate the second batch of solenoid valves according to the status of the timer, so that they can be opened synchronously after the first batch of solenoid valves.

[0115] 4.3. Similar to the piston propulsion process, high-pressure air will push the static air in the tunnel model forward. The air in the tunnel will be squeezed, and its pressure will rise instantly, forming the initial compression wave of the tunnel. This wave will propagate forward at the speed of sound, and the pressure will rise rapidly where it passes. The shape of the initial compression wave (pressure change over time) can be obtained by arranging pressure sensors on the tunnel wall.

[0116] 4.4. Since the solenoid valves are opened in batches, the shape of the initial compression wave no longer rises gradually as before, but first rises a part (caused by the first part of the solenoid valves that are opened), then remains unchanged (the holding time is determined by the interval time of the solenoid valves that are opened one after another), and finally rises to the final pressure amplitude again (caused by the other part of the solenoid valves that are opened later). This is very similar to the waveform change law of the compression wave generated by the train entering the tunnel with a typical entrance buffer structure. This means that the opening sequence of the solenoid valves can be mapped to the typical entrance buffer structure of the tunnel, making the opening sequence of the solenoid valves more valuable for practical applications.

[0117] The present invention adopts a compression wave generating device, and simplifies the process of trains entering tunnels by instantly releasing high-pressure air in a high-pressure chamber, and the device cost is low and the data productivity is high. This can provide new experimental ideas for future research on the evolution of initial compression waves, the development of new buffer structures that hinder the formation of micro-pressure waves, and engineering verification methods. Secondly, according to the initial pressure of the high-pressure chamber, the opening voltage of the solenoid valve, the number of openings, and the opening sequence, it can simulate trains entering tunnels at different speeds, trains with different streamlined lengths entering tunnels, trains entering tunnels with different cross-sectional areas, and trains entering tunnels with typical entrance buffer structures. This can generate more waveforms that fit actual working conditions, and therefore has good application prospects.

[0118] The above is only a specific implementation of the present invention, which enables those skilled in the art to understand or implement the present invention. Although detailed descriptions are given with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments, and they should all be covered by the protection scope of the claims.

Claims

1. A research method for simulating different train tunnel entry conditions to generate compression waves that meet engineering practice, characterized by: A tunnel compression wave simulation generating device is established, comprising an air compressor (3), a high-pressure chamber (4), a digital pressure gauge (5), a polyurethane tube (6), an electromagnetic valve (7), a flange end cover (8), a simulated tunnel (9), a pressure sensor (10), a data acquisition instrument and a computer; the air compressor (3) is connected to one end of the high-pressure chamber (4), the digital pressure gauge (5) is installed on the high-pressure chamber (4), the flange end cover (8) is installed at one end of the simulated tunnel (9), the pressure sensor (10) is installed in the front of the simulated tunnel (9), one end of a plurality of polyurethane tubes (6) is connected to the high-pressure chamber (4), and the other end is connected to the flange end cover (8), each polyurethane tube (6) is installed with an electromagnetic valve (7), all the electromagnetic valves (7) are used as an electromagnetic valve group, and the electromagnetic valve group has a PLC control function, allowing the electromagnetic valve group to have different voltages, quantities and sequences when opened; During the experiment, the solenoid valve group remains closed, and the preset initial pressure is filled into the high-pressure chamber through the air compressor according to the test objectives, that is, the pressure before entering the simulated tunnel; secondly, the opening voltage, number and sequence of each solenoid valve are set according to the test objectives; then, the solenoid valve is opened to control the release of high-pressure gas in the high-pressure chamber; finally, the pressure sensor and data acquisition instrument are used to measure and collect the pressure changes of the initial compression wave in the simulated tunnel.

2. The research method for simulating different train tunnel entry conditions to generate compression waves that meet engineering practice according to claim 1, characterized in that: Through the four parameters of the tunnel compression wave simulation device: the initial pressure of the high-pressure chamber, the solenoid valve opening voltage, the number of openings and the opening sequence, the trains entering the tunnel at different speeds, the trains entering the tunnel with different streamline lengths, the trains entering the tunnel with different cross-sectional areas, and the trains entering the tunnel with a typical entrance buffer structure are mapped respectively to simulate different train entry conditions, as follows: Ⅰ. Mapping of initial pressure in high-pressure chamber The experimental steps for simulating a train entering a tunnel at different speeds are as follows: 1.

1. Keep the solenoid valve group closed, start the air compressor, and fill the high-pressure chamber with air. The digital pressure gauge on the upper part of the high-pressure chamber will display the pressure status in the chamber in real time. When the pressure in the high-pressure chamber reaches the stable preset value, that is, the initial pressure P0, cut off the air supply from the air compressor; 1.

2. The process of releasing air from the high-pressure chamber is as follows: the solenoid valve is powered by a DC power supply, and the opening strategy of the solenoid valve is kept unchanged, that is, the opening voltage U0, the opening number N0, and the opening sequence are kept consistent. After the solenoid valve is subjected to electromagnetic force, the valve core is opened, and high-pressure air enters the simulated tunnel through the polyurethane tube; 1.

3. High-pressure air pushes the static air in the simulated tunnel forward. The air in the simulated tunnel is squeezed, and its pressure rises instantly, forming an initial compression wave in the tunnel. The initial compression wave propagates forward at the speed of sound, and the pressure rises rapidly where it passes. The shape of the initial compression wave, that is, the change of pressure over time, is obtained by arranging pressure sensors on the wall of the simulated tunnel. 1.

4. By filtering and denoising the pressure signal measured by the pressure sensor, an initial compression wave curve is generated under different initial pressures P0, that is, the initial compression wave shape in the tunnel is simulated; 1.

5. To illustrate the initial pressure P0 of the high-pressure chamber and the train speed V t The relationship between the initial pressure P0 of the high-pressure chamber is used to indirectly verify the engineering value of the initial pressure P0 of the high-pressure chamber; The pressure amplitude P of the initial compression wave generated under different initial pressures of the high-pressure chamber is max Substitute into formula (1), formula (2), and formula (3) to obtain the corresponding train speed V t ; Where: γ is the gas specific heat ratio; P * is the ambient reference pressure; M and β are the Mach number and the blockage ratio, respectively, which are obtained by equations (2) and (3); Where c is the speed of sound, A t and A T are the cross-sectional areas of the train and the tunnel, respectively; 1.

6. Pressure amplitude P at different initial pressures P0 of high pressure chamber max Obtained V t , and further obtain the initial pressure P0 of the high-pressure chamber and the train speed V t The relationship between the pressure amplitude of the compression wave generated under different initial pressures of the high-pressure cavity is calculated, and the corresponding theoretical train speed obtained by the above calculation indicates that the initial pressure of the high-pressure cavity can be mapped to the train speed; II. Solenoid valve opening strategy - Solenoid valve opening voltage mapping The experimental steps for simulating trains of different streamline lengths entering the tunnel are as follows: 2.

1. Keep the solenoid valve group closed, start the air compressor, and fill the high-pressure chamber with air. The digital pressure gauge on the upper part of the high-pressure chamber will display the pressure status in the chamber in real time. When the pressure in the high-pressure chamber reaches a stable preset value, that is, the initial pressure P0, cut off the air supply from the air compressor; 2.

2. The process of releasing air from the high-pressure chamber is as follows: power is supplied to the solenoid valves through a DC power supply, the number of solenoid valves opened is kept unchanged and opened synchronously, the solenoid valve opening voltage U0 is increased, and the valve core of the solenoid valve is opened after being subjected to electromagnetic force, and high-pressure air enters the simulated tunnel through the polyurethane tube; 2.

3. High-pressure air pushes the static air in the simulated tunnel forward. The air in the simulated tunnel is squeezed, and its pressure rises instantly, forming an initial compression wave in the tunnel. The initial compression wave propagates forward at the speed of sound, and the pressure rises rapidly where it passes. The shape of the initial compression wave, that is, the change of pressure over time, is obtained by arranging pressure sensors on the wall of the simulated tunnel. 2.

4. By filtering and denoising the pressure signal measured by the pressure sensor, the initial compression wave curves generated under different solenoid valve opening voltages U0 are given, that is, the initial compression wave shapes in the tunnel; after the solenoid valve is opened, the initial compression wave has a constant pressure amplitude, and the maximum pressure gradient gradually increases, which can be compared to the situation when a train with a shorter head enters a tunnel; 2.

5. To illustrate the solenoid valve opening voltage U0 and the theoretical head streamline length L n The relationship between the solenoid valve opening voltage U0 is used to indirectly verify the engineering value of the solenoid valve opening voltage U0; The maximum pressure gradient value G of the initial compression wave generated under different solenoid valve opening voltages U0 max Substitute into formula (4) to obtain the corresponding theoretical front streamline length L n ; Among them, P max and V t is the pressure amplitude of the initial compression wave generated under the initial pressure P0 of the high-pressure chamber and the theoretical speed of conversion; different front streamline lengths L are calculated by calculating the maximum pressure gradient of the initial compression wave obtained under different solenoid valve opening voltages n ; 2.

6. Maximum pressure gradient G at different solenoid valve opening voltage U0 max The obtained L n , and further obtain the solenoid valve opening voltage U0 and the front streamline length L n By comparing the relationship between the solenoid valve opening voltage U0 and the front streamline length L n Curve fitting was performed, which showed that the solenoid valve opening voltage could be mapped to the streamlined length of the front of the vehicle; III. Solenoid valve opening strategy - mapping the number of solenoid valves opened The experimental steps for simulating trains entering tunnels with different cross-sectional areas are as follows: 3.

1. Keep the solenoid valve group closed, start the air compressor, and fill the high-pressure chamber with air. The digital pressure gauge on the upper part of the high-pressure chamber will display the pressure status in the chamber in real time. When the pressure in the high-pressure chamber reaches a stable preset value, that is, the initial pressure P0, cut off the air supply from the air compressor; 3.

2. The process of releasing air from the high-pressure chamber is as follows: power the solenoid valve through a DC power supply, keep the opening voltage U0 of the solenoid valve unchanged and open synchronously, increase the number of solenoid valve openings in sequence, and the valve core of the solenoid valve opens after being subjected to electromagnetic force, and high-pressure air enters the simulated tunnel through the polyurethane tube; 3.

3. High-pressure air pushes the static air in the simulated tunnel forward. The air in the simulated tunnel is squeezed, and its pressure rises instantly, forming an initial compression wave in the tunnel. The initial compression wave propagates forward at the speed of sound, and the pressure rises rapidly where it passes. The shape of the initial compression wave, that is, the change of pressure over time, is obtained by arranging pressure sensors on the wall of the simulated tunnel. 3.

4. The pressure signal measured by the pressure sensor is filtered and denoised, and the initial compression wave curves generated under different numbers of solenoid valves N0 are given respectively; when the number of solenoid valves opened is increased, after the solenoid valves are opened, the initial compression wave has a larger pressure amplitude and a larger pressure gradient value while the compression wave length remains unchanged, which can be compared with the wave surface shape caused by the train entering the tunnel with different cross-sectional areas; 3.

5. To further illustrate the relationship between the number of solenoid valve openings N0 and the theoretical vehicle-tunnel blocking ratio β, the engineering value of the number of solenoid valve openings N0 is indirectly verified; The pressure amplitude P of the initial compression wave generated under different solenoid valve opening numbers N0 max Substitute into formula (1) to obtain the corresponding theoretical front streamline length L n ; Where: γ is the gas specific heat ratio; P * is the ambient reference pressure; M and β are Mach number and blockage ratio, respectively; P max and V t is the pressure amplitude of the initial compression wave generated under the initial pressure P0 of the high-pressure chamber and the theoretical speed of conversion; different vehicle-tunnel blocking ratios β are calculated by the pressure amplitude of the initial compression wave obtained under different solenoid valve opening numbers; 3.

6. Pressure amplitude P of compression wave generated when different solenoid valve opening numbers N0 are used max The obtained β is used to further obtain the relationship between the number of solenoid valve openings N0 and the vehicle-tunnel blocking ratio β. The curve fitting of the number of solenoid valve openings N0 and the vehicle-tunnel blocking ratio β shows that the number of solenoid valve openings can be mapped to the vehicle-tunnel blocking ratio; IV. Solenoid Valve Opening Strategy - Solenoid Valve Opening Sequence Mapping The experimental steps for simulating a train entering a tunnel with a typical entrance buffer structure are as follows: 4.

1. Keep the solenoid valve group closed, start the air compressor, and fill the high-pressure chamber with air. The digital pressure gauge on the upper part of the high-pressure chamber will display the pressure status in the chamber in real time. When the pressure in the high-pressure chamber reaches a stable preset value, that is, the initial pressure P0, cut off the air supply from the air compressor; 4.

2. The process of releasing air from the high-pressure chamber is as follows: the solenoid valve is powered by a DC power supply to maintain the initial pressure of the high-pressure chamber. The solenoid valve opening voltage U0 and the number N0 remain unchanged. The sequence of the solenoid valves is controlled, and a part of the solenoid valves are opened first, and then the other part of the solenoid valves are opened. The sequence control guides the solenoid valves to open and change in sequence. The opening sequence is realized according to the delay relay and the PLC control system. After the solenoid valve is subjected to the electromagnetic force, the valve core opens, and the high-pressure air enters the simulated tunnel through the polyurethane tube; 4.

3. High-pressure air pushes the static air in the simulated tunnel forward. The air in the simulated tunnel is squeezed, and its pressure rises instantly, forming an initial compression wave in the tunnel. The initial compression wave propagates forward at the speed of sound, and the pressure rises rapidly where it passes. The shape of the initial compression wave, that is, the change of pressure over time, is obtained by arranging pressure sensors on the wall of the simulated tunnel. 4.

4. Since the solenoid valves are opened in batches, the shape of the initial compression wave rises first, then remains unchanged, and finally rises again to the final pressure amplitude. This can be compared to the waveform change law of the compression wave generated by a train entering a tunnel with a typical entrance buffer structure, indicating that the opening sequence of the solenoid valves can be mapped to the typical entrance buffer structure of the tunnel.

3. A research method for simulating different train entry conditions to generate compression waves that conform to engineering practice according to claim 2, characterized in that: in formula (1), the blocking ratio β=0.

16.

4. According to claim 3, a research method for simulating different train entry conditions to generate compression waves that meet engineering actual conditions is characterized by: Step 2.2, a specific plan for increasing the solenoid valve opening voltage: in the PLC system, a PLC output point is set for each solenoid valve for control, and a voltage regulation module is added. The voltage regulation module can output the required voltage range and connect its output to each solenoid valve; in the PLC program, a target voltage value is set for each solenoid valve, and a voltage array is defined to store the target voltage. The design of the PLC program includes an input interface, allowing the required solenoid valve opening voltage to be input through the interface.

5. The research method for simulating different train tunnel entry conditions to generate compression waves that conform to engineering practice according to claim 3 is characterized by: Step 3.2, specific plan to increase the number of solenoid valve openings: In the PLC system, set a PLC output point for each solenoid valve for control. According to the required number of solenoid valve openings, set a variable to define the number of solenoid valves opened each time. The design of the PLC program includes an input interface, which allows the required number of solenoid valve openings to be input through the interface. In the PLC program, first define a variable to store the input target opening number, and then use a counter to track the number of solenoid valves currently opened. The program will activate the solenoid valve opening signals in sequence in the loop structure according to the input number of solenoid valve openings. By utilizing parallel outputs, the system will simultaneously send opening signals to all solenoid valves that need to be opened to ensure that they can work synchronously. In order to achieve synchronous opening, a timer is used in the PLC program to control the opening timing of the solenoid valves to ensure that all solenoid valves receive signals at the same time.

6. The research method for simulating different train tunnel entry conditions to generate compression waves that meet engineering practice according to claim 3, characterized in that: Step 4.2, specific plan for changing the opening sequence of solenoid valves: the PLC program will first define two variables, which are used to store the number of solenoid valves opened in the first and second batches respectively; then, a counter is used to track the number of solenoid valves that have been opened; at the beginning of the program, the PLC will first send a signal to the first batch of solenoid valves to start their opening process, and ensure that these solenoid valves receive the opening signal at the same time through parallel output; after the first batch of solenoid valves are opened, the PLC will start a timer and set a delay to ensure that the first batch of solenoid valves are fully opened and stable before sending a signal to the second batch of solenoid valves; the length of the delay is set according to actual needs to ensure that the changes in the pressure compression wave in the two stages meet expectations; when the opening signal of the first batch of solenoid valves is completed, the PLC will activate the second batch of solenoid valves according to the status of the timer, so that they will open synchronously after the first batch of solenoid valves.

7. The research method for simulating different train tunnel entry conditions to generate compression waves that conform to engineering practice according to claim 2, characterized in that: The experimental steps of mapping the initial pressure of the high-pressure chamber to simulate the train entering the tunnel at different speeds also include: 1.

7. Maximum pressure gradient G through the rising phase of the initial compression wave max Analyze the maximum pressure gradient from the perspective of Among them, L n is the streamlined length of the train, P max is the pressure amplitude of the initial compression wave generated under different initial pressures of the high-pressure chamber, G max is the maximum pressure gradient of the rising phase of the initial compression wave generated under different initial pressures of the high-pressure chamber, V t is the theoretical vehicle speed obtained by calculating the initial compression wave generated under different initial pressures of the high-pressure chamber; given an L n The constant value means that the compression wave pressure amplitude P obtained under different initial pressures of the high-pressure chamber is max and theoretical vehicle speed V t The theoretical maximum pressure gradient G of the compression wave obtained under different initial pressures of the high-pressure chamber is calculated by formula (4): max , while the experimental value is the maximum gradient value obtained by directly taking the first-order derivative of the initial compression wave curve; the comparison between the theoretical value and the experimental value shows the feasibility or accuracy of the above transformation mapping.

8. The research method for simulating different train tunnel entry conditions to generate compression waves that conform to engineering practice according to claim 1 is characterized by: The ratio of the diameter and length of the simulated tunnel (9) to that of an actual tunnel is 1:100, and the cross-sectional shape of the simulated tunnel (9) is simplified to a circle.

9. The research method for simulating different train tunnel entry conditions to generate compression waves that meet engineering practice according to claim 1, characterized in that: The pressure sensor monitors the characteristics of the compression wave in real time and records the time series of pressure changes. The data acquisition instrument transmits the collected signals to the computer via cables for analysis.

10. The research method for simulating different train tunnel entry conditions to generate compression waves that meet engineering practice according to claim 1, characterized in that: Before the experiment begins, a static air tightness test is carried out in the tunnel to ensure that the simulated tunnel has good air tightness.

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