Method for damping common mode vibrations of a branch pipe and polishing device for a modular system

Abstract

The present application relates to the technical field of modular construction of pressurized water reactor nuclear power plant, and particularly relates to a method for alleviating co-frequency vibration of a normal-closing branch pipe of a modular system and a polishing device. The method comprises the following steps: obtaining the length of the normal-closing branch pipe and the propagation speed of sound in the fluid medium, obtaining the fluid acoustic standing wave frequency according to the length of the normal-closing branch pipe and the propagation speed, making the fluid pressure fluctuation frequency equal to the fluid acoustic standing wave frequency, obtaining the fluid velocity in the main pipe and the inner diameter of the normal-closing branch pipe, obtaining the resonance round corner radius according to the fluid pressure fluctuation frequency, the fluid velocity and the inner diameter of the normal-closing branch pipe, polishing the inlet round corner at the stagnation point of the normal-closing branch pipe, and the radius of the inlet round corner is greater than the resonance round corner radius. The present application makes the fluid pressure fluctuation frequency far away from the fluid acoustic standing wave frequency, thereby alleviating or eliminating the co-frequency vibration.

Description

Technical Field

[0001] This invention relates to the field of modular construction technology for pressurized water reactor nuclear power plants, and in particular to a method and grinding device for mitigating the co-frequency vibration of normally closed branch pipes in modular systems. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] In pressurized water reactor nuclear power plants, piping vibration has always been a complex issue. Piping systems inevitably contain normally closed branch connections, including welded joint normally closed branch pipes or threaded connection normally closed branch pipes, such as those for various normally closed valves. Figure 1 As shown.

[0004] Generally, nuclear power plants have a wide distribution of small-diameter pipes and numerous normally closed branch connections. If resonance occurs between the fluid pressure fluctuation frequency and the fluid acoustic standing frequency, the long-term steady-state resonant vibration of the small-diameter pipes will cause periodic stress cyclic loading, leading to fatigue cracking. Figure 2 The image shows fatigue crack penetration detection results for a normally closed branch pipe. This type of resonant vibration in small-diameter pipes can be easily resolved by improving the pipe system support structure and adding or optimizing the constraint and fixing methods of the pipe system supports.

[0005] However, for the large-diameter piping systems of nuclear power plants, although their distribution is small and normally closed branch connections are relatively few, normally closed branch connections also exist in some nuclear-grade pressure-bearing dedicated safety piping systems. If the fluid pressure fluctuation frequency and the fluid acoustic standing frequency resonate, there will be large amplitude and large vibration force, which will damage the existing piping system support system and endanger related equipment connected to the piping system, posing the greatest danger.

[0006] Under modular construction technology, a large-scale modular piping system can be prefabricated in a workshop and then installed in the nuclear island room via overall hoisting. In certain special cases, it is impossible to change the fluid parameters, nor the support system of the normally closed branch pipes in the large modular piping system. Such resonant vibrations in large-diameter pipes are difficult to address due to the complexity of the piping system structure, the large constraint forces required, and the significant challenges in adding or optimizing the constraint and fixing methods of the piping system supports. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for mitigating the co-frequency vibration of normally closed branch pipes in modular systems, thereby reducing or eliminating co-frequency vibration by keeping the fluid pressure fluctuation frequency away from the fluid acoustic standing frequency.

[0008] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0009] A method for mitigating resonant vibration in a normally closed branch pipe in a modular system includes: obtaining the length of the normally closed branch pipe and the speed of sound propagation in a fluid medium; obtaining the fluid acoustic standing wave frequency based on the length of the normally closed branch pipe and the propagation speed; setting the fluid pressure fluctuation frequency equal to the fluid acoustic standing wave frequency; obtaining the fluid velocity in the main pipe and the inner diameter of the normally closed branch pipe; obtaining the resonant fillet radius based on the fluid pressure fluctuation frequency, the fluid velocity, and the inner diameter of the normally closed branch pipe; and grinding the inlet fillet at the flow-facing blunt standing point of the normally closed branch pipe, wherein the inlet fillet radius is larger than the resonant fillet radius.

[0010] Preferably, the range of the flow-facing blunt stagnation point is the flow-facing surface portion where the normally closed branch pipe connects to the main pipe.

[0011] Preferably, the formula for calculating the frequency of the fluid acoustic standing wave is:

[0012] f1 = c / (4L)

[0013] Where f1 is the frequency of the fluid acoustic standing wave, c is the speed of sound propagation in the fluid medium, and L is the length of the normally closed branch pipe;

[0014] The formula for calculating the resonant fillet radius is:

[0015] r=(S×U) / f1-d

[0016] Where r is the resonance fillet radius, S is the correction coefficient, U is the fluid velocity in the main pipe, and d is the inner diameter of the normally closed branch pipe.

[0017] Preferably, the calculation is performed based on the selected inlet fillet and the allowable alternating stress limit for durability single amplitude peak, vibration velocity, and minimum wall thickness.

[0018] Preferably, measurement grid points are drawn at the upstream blunt stagnation point to measure the amount of grinding.

[0019] Preferably, before, during, and after grinding, ultrasonic thickness measurement and three-dimensional measurement scanning methods are used to measure and control the grinding amount at each measurement grid point.

[0020] This invention also provides a grinding device for performing the method described above for mitigating the common-frequency vibration of a normally closed branch pipe in a modular system, comprising a centering fixing plate, a central rotating shaft, a fixing frame, and a grinding machine; the centering fixing plate is used to be installed inside the normally closed branch pipe, the central rotating shaft is rotatably connected to the centering fixing plate, the fixing frame is installed on the central rotating shaft, and the grinding machine is slidably connected to the fixing frame and can grind the incoming blunt stagnation point into the inlet rounded corner.

[0021] Preferably, the fixing frame includes a first fixing plate, a reinforcing sleeve, a second fixing plate, and a grinding guide rail; the first fixing plate, the reinforcing sleeve, and the second fixing plate are sequentially sleeved on the central rotating shaft; one end of the grinding guide rail is connected to the first fixing plate, and the other end is connected to the second fixing plate; the grinding guide rail is provided with a guide groove, which is an arc-shaped through groove; the radius of the arc-shaped through groove is calculated based on the grinding machine and the inlet fillet radius; the grinding machine is installed on the guide groove.

[0022] Preferably, the first fixed plate is provided with a first sliding groove, and the second fixed plate is provided with a second sliding groove. Both the first and second sliding grooves are perpendicular to the central rotating shaft. One end of the grinding guide rail is slidably connected to the first sliding groove, and the other end is slidably connected to the second sliding groove.

[0023] Preferably, the centering fixing plate is provided with an adjusting screw, the adjusting screw is arranged radially along the centering fixing plate, the inner end of the adjusting screw points to the center of the centering fixing plate, and the outer end can penetrate the outer wall of the centering fixing plate and abut against the inner wall of the normally closed branch pipe.

[0024] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0025] This invention assumes that the fluid pressure fluctuation frequency is equal to the fluid acoustic standing wave frequency, and then obtains the resonant fillet radius. The incoming blunt standing point is then ground into an inlet fillet that differs significantly from the resonant fillet radius, thereby making the fluid pressure fluctuation frequency far away from the fluid acoustic standing wave frequency, thus alleviating or eliminating resonant vibration.

[0026] Advantages of additional aspects of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0028] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0029] Figure 1 This is a schematic diagram of the resonant vibration of fluid pressure wave and acoustic standing wave in a normally closed valve branch pipe;

[0030] Figure 2 This is a schematic diagram showing the fatigue crack penetration test of a certain normally closed branch pipe;

[0031] Figure 3 This is a flowchart of a method for mitigating common-frequency vibration of normally closed branch pipes in a modular system according to an embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram of the fluid pressure fluctuation frequency and fluid acoustic standing frequency in a normally closed branch pipe.

[0033] Figure 5 This is a schematic diagram of the radius R of the inlet of the normally closed branch pipe facing the flow obtuse stagnation point;

[0034] Figure 6 This is a schematic diagram of the polishing device according to an embodiment of the present invention;

[0035] Figure 7 This is a top view of the centering and fixing plate according to an embodiment of the present invention;

[0036] Figure 8 This is a schematic diagram of the grinding area of ​​a nuclear-grade pressure-bearing normally closed branch pipe according to an embodiment of the present invention;

[0037] Figure 9 This is a schematic diagram of the actual situation after grinding the normally closed branch pipe according to an embodiment of the present invention;

[0038] In the diagram: 1. Central pivot; 2. Centering fixing plate; 3. Fixing pin; 4. First fixing plate; 5. Grinding guide rail; 6. Grinding machine; 7. Second fixing plate; 8. Reinforcing sleeve; 9. 3D measuring scanner; 10. Adjusting screw;

[0039] The distances or dimensions between parts have been exaggerated to show their positions; the diagram is for illustrative purposes only. Detailed Implementation

[0040] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0041] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless otherwise expressly indicated by the invention, the singular form is intended to include the plural form as well. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0042] Terminology Explanation: The terms "installation," "connection," "linking," and "fixing" in this invention should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, a direct connection, or an indirect connection through an intermediate medium; they can refer to an internal connection between two components, or the interaction between two components. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature.

[0043] Example 1

[0044] In large-diameter solid water pipelines of nuclear-grade pressure without entrained gas in modular systems, if there are normally closed stagnant branch pipes in the pipeline system, without changing the fluid parameters or the support structure of the pipeline system, vortex street formation will occur at the flow-facing blunt stagnation point of the branch pipe, causing pressure fluctuations and acoustic stagnation fluctuations in the normally closed branch pipe. If the frequency of fluid pressure fluctuations and the frequency of fluid acoustic stagnation fluctuations are close, steady-state resonant vibration will occur. Long-term vibration will cause periodic stress cyclic loading, leading to potential fatigue cracking.

[0045] To address the aforementioned technical problems, one embodiment of the present invention proposes a method for mitigating the resonant vibration of a normally closed branch pipe in a modular system. The method includes: obtaining the length of the normally closed branch pipe and the speed of sound propagation in a fluid medium; obtaining the fluid acoustic stagnation frequency based on the length of the normally closed branch pipe and the propagation speed; setting the fluid pressure fluctuation frequency equal to the fluid acoustic stagnation frequency; obtaining the fluid velocity in the main pipe and the inner diameter of the normally closed branch pipe; obtaining the resonant fillet radius based on the fluid pressure fluctuation frequency, fluid velocity, and the inner diameter of the normally closed branch pipe; and grinding the inlet fillet at the flow-facing blunt stagnation point of the normally closed branch pipe, wherein the inlet fillet radius is larger than the resonant fillet radius. The flow-facing blunt stagnation point is defined as the flow-facing surface portion where the normally closed branch pipe connects to the main pipe.

[0046] By assuming that the fluid pressure fluctuation frequency is equal to the fluid acoustic stagnation frequency, the resonant fillet radius is obtained. The inlet fillet of the obtuse stagnation point is then ground into a radius that is significantly different from the resonant fillet radius, thereby making the fluid pressure fluctuation frequency far away from the fluid acoustic stagnation frequency, thus alleviating or eliminating the resonant vibration.

[0047] Specifically, a method for grinding the inlet fillet of a normally closed branch pipe in a modular nuclear-grade pressurized water pipeline to change the pressure fluctuation frequency, such as... Figure 3 As shown:

[0048] S1. Determine the acoustic standing wave frequency: The fluid acoustic standing wave frequency can be calculated using the simplified formula f1 = c / (4L). Where f1 is the fluid acoustic standing wave frequency, c is the speed of sound in the fluid medium, and L is the length of the normally closed branch pipe. For relevant parameters, see [link to relevant parameters]. Figure 4 As shown.

[0049] S2. Calculate the fillet radius based on the pressure fluctuation frequency: The fluid pressure fluctuation frequency can be calculated using the simplified formula f2 = (S × U) / (d + r). Where f2 is the fluid pressure fluctuation frequency, S is a correction factor, U is the fluid velocity in the main pipe, d is the inner diameter of the normally closed branch pipe, and r is the inlet fillet radius at the flow-facing blunt stagnation point of the normally closed branch pipe. For relevant parameters, see [link to relevant parameters]. Figure 4 As shown.

[0050] Based on the condition of resonant vibration, f1 = f2, we first calculate f1, and then obtain r = (S × U) / f2 - d = (S × U) / f1 - d.

[0051] S3. Determine the fillet radius R value: To prevent resonance characteristics, the inlet fillet radius R value at the flow-facing blunt stagnation point should be far from the calculated value. Based on the calculated r value, determine the fillet radius R value to be ground. For operability, ensure that the R value is greater than the r value, such as... Figure 5 As shown.

[0052] S4. Verification Calculation: Verification calculations are performed based on the allowable alternating stress limit for single-amplitude peak values, vibration velocity, and minimum wall thickness. Specifically, this includes:

[0053] S41. Perform alternating stress verification calculations based on the selected R fillet value. Nuclear safety grade pipelines, including pipelines with dedicated safety facilities, are all made of austenitic stainless steel. Based on the power plant's 60-year service life conditions (L0×L... 11 The maximum alternating stress limit (number of fatigue cycles) is 93.7 Ma, which is used as the allowable alternating stress limit for single amplitude peak in durability calculations and as the benchmark value for verification calculations.

[0054] S42. Based on the selected radius (R) value, perform a verification calculation for the pipeline vibration velocity. For nuclear safety grade pipelines, the vibration velocity should be less than 22 mm / s, which should be used as the benchmark value for the verification calculation.

[0055] S43. Based on the selected radius (R) value, perform a minimum wall thickness check calculation. The minimum wall thickness of the pipe is used as the benchmark value for the check calculation, determining whether it meets the design requirements.

[0056] S5. Install the grinding measurement equipment (i.e., the grinding device in Example 2).

[0057] S6. Gridded Original Size Measurement: Before and during grinding, draw a 10mm × 10mm measurement grid at the grinding location for measurement. Figure 8 As shown, the grid points facilitate point-to-point measurement of the grinding area.

[0058] S7. Grinding (with gridded dimensional measurement and monitoring during the process), specifically including:

[0059] Before grinding, the thickness of the pipe wall at the grinding location is measured using ultrasonic thickness measurement.

[0060] Before polishing, the original surface at the polishing location is measured using a 3D measurement scanner. The polishing amount at each measurement location is verified by comparing the results of ultrasonic thickness measurement, 3D measurement scanning, and the calculated polishing amount.

[0061] During the polishing process, the polished areas are transitioned smoothly.

[0062] During the grinding process, the grinding speed and depth must be controlled each time to prevent grinding temperatures exceeding 200°C on the metal surface. This is to prevent severe sensitization of austenitic stainless steel due to cold working, which could lead to intergranular stress corrosion cracking after commissioning.

[0063] During the polishing process, a 3D measurement scanner is used to measure the amount of polishing at the polishing location and monitor the amount of polishing.

[0064] During the polishing process, low-melting-point elements and harmful elements that contaminate austenitic stainless steel should be strictly controlled, and thorough cleaning should be carried out.

[0065] After sanding, use fine-grit sandpaper to sand the sanded area to eliminate the cold working effect.

[0066] S8. Complete grinding (structural dimension measurement and acceptance), specifically including:

[0067] After grinding, the pipe wall thickness at this location is measured ultrasonically. Based on the three-dimensional measurement scan results, the minimum wall thickness verification calculation benchmark for this location is determined.

[0068] After polishing, the polished area was visually inspected to ensure that all polished areas had a smooth transition and that the roughness was up to standard. Non-destructive testing of the polished area was performed using liquid penetration, and the test results were satisfactory.

[0069] Example 2

[0070] Based on the method of Embodiment 1, this embodiment proposes an inlet rounding grinding device for mitigating the co-frequency vibration of normally closed branch pipes in modular systems. Grinding the inlet rounding can effectively solve the problem of co-frequency vibration caused by changing the pressure fluctuation frequency of normally closed branch pipes in nuclear-grade pressurized water solid pipelines.

[0071] like Figure 6 , Figure 7 As shown, the grinding device includes a centering fixing plate 2, a central rotating shaft 1, a fixing frame, and a grinding machine 6. The centering fixing plate 2 is used to install inside the normally closed branch pipe. The central rotating shaft 1 is rotatably connected to the centering fixing plate 2. The fixing frame is installed on the central rotating shaft 1. The grinding machine 6 is slidably connected to the fixing frame and can grind the inlet blunt stagnation point into the inlet rounded corner. The entire grinding device is installed inside the normally closed branch pipe through the fixing plate. The central rotating shaft 1 can rotate around its axis, and the grinding machine 6 is used to grind the inlet blunt stagnation point.

[0072] The fixing frame includes a first fixing plate 4, a reinforcing sleeve 8, a second fixing plate 7, and a grinding guide rail 5. The first fixing plate 4, the reinforcing sleeve 8, and the second fixing plate 7 are sequentially sleeved on the central rotating shaft 1. One end of the grinding guide rail 5 is connected to the first fixing plate 4, and the other end is connected to the second fixing plate 7. The grinding guide rail 5 is provided with a guide groove, which is an arc-shaped through groove. The radius of the arc-shaped through groove is calculated based on the diameter of the grinding wheel of the grinding machine 6 and the radius of the inlet fillet. The guide groove of the grinding guide rail 5 is determined according to the grinding radius R value of the inlet fillet and the diameter of the grinding wheel, so that the grinding machine 6 is installed on the guide groove. During grinding, the grinding machine 6 slides along the guide groove and grinds the inlet fillet R at the obtuse point facing the flow.

[0073] like Figure 6 The first fixed plate 4 is the upper end grinding guide rail 5 fixed plate, and the second fixed plate 7 is the lower end grinding guide rail 5 fixed plate. A three-dimensional measuring scanner 9 is installed on the lower end grinding guide rail 5 fixed plate. The surface at the grinding position is measured by rotating the central shaft 1 using the three-dimensional measuring scanner 9.

[0074] Furthermore, the first fixed plate 4 is provided with a first sliding groove, and the second fixed plate 7 is provided with a second sliding groove. Both the first and second sliding grooves are perpendicular to the central rotating shaft 1. One end of the grinding guide rail 5 is slidably connected to the first sliding groove, and the other end is slidably connected to the second sliding groove. After grinding for a period of time, the position of the grinding guide rail 5 is adjusted, specifically according to... Figure 6 Move the grinding guide 5 to the right as shown, and fix it with the fixing pin 3.

[0075] By sliding between the chute and the grinding guide rail 5, the passive stagnation point facing the flow is ground layer by layer to prevent severe sensitization effect on the metal surface, which could lead to intergranular stress corrosion cracking after commissioning, while ensuring the dimensional accuracy and surface finish of the grinding.

[0076] like Figure 7 As shown, the centering fixing plate 2 is provided with adjusting screws 10. The adjusting screws 10 are arranged radially along the centering fixing plate 2. The inner end of the adjusting screw 10 points to the center of the centering fixing plate 2, and the outer end can penetrate the outer wall of the centering fixing plate 2 and abut against the inner wall of the normally closed branch pipe. In this embodiment, four adjusting screws 10 are arranged in a circumferential array, and four connecting ribs are also provided. The outer diameter of the centering fixing plate 2 is smaller than the inner diameter of the normally closed branch pipe. In use, the centering fixing plate 2 is inserted into the normally closed branch pipe, and the adjusting screws 10 are adjusted so that the adjusting screws 10 protrude from the outer wall of the centering fixing plate 2 and abut against the inner wall of the normally closed branch pipe. By adjusting the adjusting screws 10, the centering fixing plate 2 (i.e., the central rotating shaft 1) is adjusted to the centerline position of the normally closed branch pipe.

[0077] This invention disperses the energy of vortex shedding to a greater extent and changes the pressure fluctuation frequency by changing the inlet radius of the obtuse stagnation point, thereby mitigating resonant vibration.

[0078] Example 3

[0079] A certain nuclear-grade pressurized water pipeline is a dedicated safety facility pipeline for the primary coolant system of a pressurized water reactor nuclear power plant, constructed using modular technology. According to nuclear safety requirements, a normally closed branch pipe is installed on this pipeline during normal plant operation; fluid can only flow in this branch pipe under emergency and accident conditions. This main pipe has an inner diameter of 790 mm, a flow velocity of 20 m / s, and a fluid temperature of 300℃; the normally closed branch pipe has an inner diameter of 450 mm and a length of 12000 mm; both are made of austenitic stainless steel. During normal operation of the nuclear power plant, the normally closed branch pipe connected to this main pipeline experienced significant vibration at a frequency of 24 Hz (resonance frequency).

[0080] Calculate f1 of the normally closed branch pipe according to f1=c / (4L), where f1 is the frequency of the fluid acoustic standing wave, c is the speed of sound in the fluid medium, and L is the length of the normally closed branch pipe.

[0081] The value of r is calculated using the formula r = (S × U) / f2 - d = (S × U) / f1 - d. Here, f2 is the fluid pressure fluctuation frequency, S is the correction coefficient, U is the fluid velocity in the main pipe, d is the inner diameter of the normally closed branch pipe, and r is the inlet radius of the blunt stagnation point of the normally closed branch pipe.

[0082] Determine the fillet radius R after grinding the obtuse point facing the flow, ensuring that R is greater than r. The area to be ground is as follows: Figure 8 As shown.

[0083] For the fillet radius R value after grinding, the calculation is performed based on the allowable alternating stress limit of single amplitude peak for durability, vibration velocity, and minimum wall thickness.

[0084] The guide groove of the grinding guide rail is manufactured according to the R value of the entry fillet.

[0085] Manufacture the first fixed plate, the reinforcing sleeve, and the second fixed plate according to the R-value of the inlet fillet grinding and the size of the grinding machine.

[0086] Install the grinding device.

[0087] By adjusting the centering plate, the center shaft is adjusted to the centerline position of the branch pipe.

[0088] A 10mm × 10mm measurement grid was drawn at the grinding location, and the grinding area was measured using a 3D measurement scanner. The thickness of the grid points was then measured using an ultrasonic thickness gauge.

[0089] By comparing the results of three-dimensional measurement scanning, ultrasonic thickness measurement, and the calculated grinding amount, the grinding amount at each measurement location is verified.

[0090] During the polishing process, the polishing speed and depth must be controlled each time to prevent polishing temperatures exceeding 200°C on the metal surface. The polishing areas should transition smoothly within the polishing zone.

[0091] During the polishing process, a 3D measurement scanner is used to measure and monitor the amount of polishing.

[0092] After polishing, the polished area was measured using a 3D scanner based on the previously established 10mm x 10mm measurement grid. An ultrasonic thickness gauge was then used to measure the thickness at each grid point. The actual amount of polishing was then calculated.

[0093] After sanding, use 100# fine-grit sandpaper to sand the sanded area to eliminate the cold working effect.

[0094] After polishing, the polished area was visually inspected to ensure a smooth transition across all polished areas, with a surface roughness of less than 3.0 μm. Non-destructive testing of the polished area was then performed using liquid penetrant testing, and the results were satisfactory.

[0095] After sanding, wipe the sanded surface clean with deionized water. Figure 9 As shown.

[0096] By grinding the inlet fillet at the blunt stagnation point of the normally closed branch pipe, the fluid pressure fluctuation frequency is made to be far away from the fluid acoustic stagnation fluctuation frequency, thereby alleviating or eliminating the resonant vibration.

[0097] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

[0098] Finally, it should be noted that, unless otherwise specified, the embodiments of the present invention and the various features thereof can be combined with each other, all of which are within the protection scope of the present invention. Furthermore, although the steps are listed in the order 1, 2, 3…, in some cases, the steps shown or described may be performed in a different order than that presented here.

Claims

1. A method for mitigating common-frequency vibration of normally closed branch pipes in modular systems, characterized in that, include: The length of the normally closed branch pipe and the speed of sound propagation in the fluid medium are obtained, and the frequency of fluid acoustic standing wave is obtained based on the length of the normally closed branch pipe and the propagation speed. Set the fluid pressure fluctuation frequency to be equal to the fluid acoustic standing wave frequency; Obtain the fluid velocity in the main pipeline and the inner diameter of the normally closed branch pipe. Based on the fluid pressure fluctuation frequency, fluid velocity, and inner diameter of the normally closed branch pipe, obtain the resonant fillet radius. The inlet fillet of the normally closed branch pipe is ground at the obtuse stagnation point facing the flow, and the radius of the inlet fillet is larger than the radius of the resonant fillet. The range of the incoming flow blunt stagnation point is the incoming flow surface portion where the normally closed branch pipe connects to the main pipe; The formula for calculating the frequency of the fluid acoustic standing wave is: f1 = c / (4L) Where f1 is the frequency of the fluid acoustic standing wave, c is the speed of sound propagation in the fluid medium, and L is the length of the normally closed branch pipe; The formula for calculating the resonant fillet radius is: r = (S × U) / f1 - d Where r is the resonance fillet radius, S is the correction coefficient, U is the fluid velocity in the main pipe, and d is the inner diameter of the normally closed branch pipe; The grinding device for implementing the method for mitigating the common-frequency vibration of normally closed branch pipes in a modular system includes a centering plate, a central rotating shaft, a fixing frame, and a grinding machine. The centering plate is installed inside the normally closed branch pipe. The central rotating shaft is rotatably connected to the centering plate. The fixing frame is installed on the central rotating shaft. The grinding machine is slidably connected to the fixing frame and can grind the inlet blunt stagnation point into the inlet rounded corner. The fixing frame includes a first fixing plate, a reinforcing sleeve, a second fixing plate, and a grinding guide rail; the first fixing plate, the reinforcing sleeve, and the second fixing plate are sequentially sleeved on the central rotating shaft; one end of the grinding guide rail is connected to the first fixing plate, and the other end is connected to the second fixing plate; a guide groove is provided on the grinding guide rail; the guide groove is an arc-shaped through groove; the radius of the arc-shaped through groove is calculated based on the grinding machine and the inlet fillet radius; the grinding machine is installed on the guide groove. The first fixed plate is provided with a first sliding groove, and the second fixed plate is provided with a second sliding groove. Both the first and second sliding grooves are perpendicular to the central rotating shaft. One end of the grinding guide rail is slidably connected to the first sliding groove, and the other end is slidably connected to the second sliding groove.

2. The method for mitigating common-frequency vibration of normally closed branch pipes in a modular system as described in claim 1, characterized in that, The calculation is performed based on the selected inlet fillet and the allowable alternating stress limit for single amplitude peak, vibration velocity, and minimum wall thickness.

3. The method for mitigating common-frequency vibration of normally closed branch pipes in a modular system as described in claim 1, characterized in that, A measurement grid is drawn at the upstream blunt stagnation point to measure the amount of grinding.

4. The method for mitigating common-frequency vibration of normally closed branch pipes in a modular system as described in claim 3, characterized in that, Before, during, and after grinding, ultrasonic thickness measurement and three-dimensional measurement scanning methods are used to measure and control the grinding amount at each measurement grid point.

5. The method for mitigating common-frequency vibration of normally closed branch pipes in a modular system as described in claim 1, characterized in that, An adjusting screw is provided on the centering fixing plate. The adjusting screw is arranged radially along the centering fixing plate. The inner end of the adjusting screw points to the center of the centering fixing plate, and the outer end can penetrate the outer wall of the centering fixing plate and abut against the inner wall of the normally closed branch pipe.

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