JPH0546883B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method and apparatus for diagnosing abnormal vibrations in pipe groups, etc., and in particular, in cases where fluid is piped into a structure, such as a cooling water system in a nuclear power plant. The present invention relates to a method and apparatus for diagnosing abnormal vibrations that occur in a group of pipes or structures when the fluid flows outside and is in a so-called two-phase fluid state in which gas and liquid are mixed.

[Background of the Invention] A group of heat transfer tubes in a heat exchanger is a structure inside a nuclear reactor.
In many parts, the fluid flowing outside is in a two-phase flow atmosphere.

There are many studies and documents related to two-phase flow inside pipes. However, in the case of flow outside the pipe, even the classification of flow modes such as bubble flow, slug flow, froth flow, annular flow, etc. has not been accurately determined, and the determination thereof is still in a qualitative state.

The present invention mainly relates to two-phase flow flowing outside a pipe, but since the current state of the research is as described above, for the time being, the flow pattern of two-phase flow in a vertical upward flow inside a pipe is shown in Figure 2 as a reference. show. In these two-phase flow states, a steady excitation force is generated due to flow turbulence, and the pipes and structures are excited and vibrate. When the frequency of the cumulative force generated by the turbulence of the two-phase fluid matches the natural frequency of the tube group or structure, the vibration of the tube group or structure increases, causing abnormal vibrations. Abnormal vibrations may result in pipe-to-pipe collisions or damage to the pipes or structural supports.

FIG. 3 shows the power spectrum density of the excitation force for the flow modes of a bubble flow and b slug flow. In bubble flow, peaks below 10Hz and 60Hz
There are nearby peaks. In the slug flow, a peak of 5 Hz or less exists. Generally, in a two-phase flow in a device, the flow modes of each two-phase flow shown in FIG. 2 do not exist independently, but rather often exist in a mixture. Therefore, the frequency of the excitation force of the two-phase fluid also has a spectrum corresponding to the above-mentioned mixed flow modes. On the other hand, the natural frequency of a tube group or structure changes depending on the void ratio, which indicates the mixing ratio of gas and liquid.

Therefore, by comparing the vibration frequency analysis of pipe groups and structures generated by the excitation force of two-phase fluid with the analysis results of natural frequencies that take void ratio into consideration, it is possible to determine the cause of abnormal vibrations occurring in pipe groups and structures. It is thought that it will be possible to distinguish between excessive excitation force and resonance phenomenon.

An example of the above-mentioned literature is Shiraki et al., "Vibration of heat exchanger tube group subjected to two-phase flow," Mitsubishi Heavy Industries Technical Report, Vol. 19, No. 5.

[Purpose of the invention]

An object of the present invention is to provide an abnormal vibration diagnosing method and apparatus for identifying the cause of abnormal vibration in a group of pipes or structures in a two-phase fluid state.

[Summary of the invention]

In order to achieve the above object, the present invention measures vibrations in a two-phase fluid of a pipe group or a structure and analyzes its frequency, while also measuring the void ratio of the two-phase fluid and pipes corresponding to this void ratio. It is characterized by diagnosing the cause of abnormal vibration by calculating the natural frequency of a group or structure and comparing the vibration frequency and the natural frequency.

[Embodiments of the invention]

An embodiment of the present invention applied to a two-phase fluid flowing outside a tube will be described in detail with reference to FIG. FIG. 1 is a block diagram of an abnormal vibration diagnosis apparatus according to the present invention. In the figure, 1 is a pipe or structure, 2 is a gas-liquid two-phase fluid containing a mixture of gas and liquid, 3 is a void sensor, 4 is a vibration sensor, 5 is a vibration meter, 6 is a vibration analyzer, 7 is a void meter, 8 is a computing unit, and 9 is a display.

A vibration signal of the pipe or structure 1 generated by the turbulence of the two-phase fluid 2 is detected by a vibration sensor 4, amplified by a vibration meter 5, and subjected to frequency analysis in a vibration analyzer 6. On the other hand, a void signal of the two-phase fluid 2 is detected by a void sensor 3, and a void ratio is calculated by a void meter 7. Arithmetic unit 8
calculates the natural frequency of the pipe or structure using this void fraction. The method for determining the natural frequency will be described later. The obtained natural frequency and the previous vibration analysis results are displayed on the calculator 9 at the same time.

FIG. 4 shows an example of the display. In the display example of FIG. 4, when the analysis result and the natural frequency obtained from the void fraction of the two-phase fluid match, it can be diagnosed that the pipe is in a resonant state. On the other hand, when the vibration peak in the analysis results does not match the natural frequency, it can be diagnosed that the excitation force acting on the pipe is an abnormal excitation force specific to two-phase flow.

Next, a simple calculation method for determining the natural frequency of a pipe or structure using the calculator 8 will be described.

First, let's define the symbols: m: mass of the pipe m _TP , m _a , m _w : additional mass k: spring constant of the pipe ρ: liquid density γ: void ratio ω, ω _a , ω _w , ω _TP : natural frequency of the pipe a: in air w: water TP: in two-phase fluid Now, if the pipe or structure is replaced by a mechanical model of a spring-mass system, the natural frequency ω of the pipe is ω ² =k/m...(1) is given by. Further, the natural frequency ω _w of the pipe in water is obtained as follows, where m _w is the added mass of water: ω _w ² =k/(m+m _w ) (2). Introducing void fraction to the additional mass m _TP in the two-phase fluid and the additional mass in air and water, m _TP = γm _a + (1-γ)m _w ...(3). As a result, the natural frequency ω _TP of the pipe in the two-phase fluid is determined by ω _TP ² =k/(m+m _TP =k/m+γm _a +(1−γ)m _w ……(4). Equation (4) ) can be rewritten as the following formula.

ω _TP ² =k/m{1+γm _a /m+(1-γ)m _w /m}
...(5) The additional mass m _a in the air is small, and as a result
m _a m≪1≒0. From this, equation (5) becomes ω _TP ² =k/m{1+(1-γ)m _w /m} = ω ² /1+(1-γ) m _w /m (6). From equation (2), m _w /m=(ω/ω _w ) ² −1 ...(7) is obtained. Substituting equation (7) into equation (6), ω _TP ² = ω ² /1+(1-γ) {(ω/ω _w ) ² −1}...
(8) is obtained. Also, the natural frequency of the tube in the air is m _a /m
From the relationship <<1, it is approximately the same as the value obtained by equation (1). As a result, if the natural frequencies of the tube 1 in air and water are determined in advance, the natural frequency of the tube at the void ratio γ can be easily calculated.

In formula (8), calculation programs such as experimental or structural analysis may be used to calculate the natural frequencies of the pipes in air and water. Also, if the additional mass in the air (gas) cannot be ignored,
Equation (8) can be replaced by the following equation.

ω _TP ² = ω ² /1+γ{(ω/ω _a ) ² −1}+
(1−γ) {(ω/ω _w ) ² −1}……(9) According to equation (9), the natural frequency when the added mass effect in gas cannot be ignored in a two-phase fluid is found. It will be done.

〔Effect of the invention〕

In the abnormal vibration diagnosis method and apparatus of the present invention, the vibration of a group of tubes in a two-phase fluid is measured and the vibration frequency is analyzed, while the void fraction of the two-phase fluid is calculated to determine the natural frequency of the tube. Since these vibration frequencies are compared with the natural frequency, it is possible to accurately determine whether the abnormal vibration of the pipe caused by the two-phase fluid is due to resonance with the natural frequency of the pipe or the abnormal excitation force of the two-phase fluid. can be diagnosed.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing an embodiment of the abnormal vibration diagnosis device according to the present invention, Figure 2 is a diagram showing the flow pattern of two-phase flow in vertical upward flow in a pipe, and Figure 3 is a diagram showing the flow of bubble flow and slag flow. FIG. 4 is a diagram showing the power spectrum density of the excitation force with respect to the mode, and FIG. 4 is a diagram showing an example in which the vibration analysis result and the natural frequency are displayed on the display at the same time. 1... Tube group, 2... Two-phase fluid, 3... Void sensor, 4... Vibration sensor, 5... Vibration meter, 6...
Vibration analyzer, 7... Void meter, 8... Arithmetic unit, 9
……display.

Claims (1)

[Scope of Claims] 1. Vibration of a group of tubes, etc. in a two-phase fluid is measured and its frequency is analyzed, while the void ratio of the two-phase fluid is measured and the natural frequency of the group of tubes, etc. corresponding to this void ratio is determined. The frequency analysis result is compared with this natural frequency to determine whether the cause of vibration of the tube group, etc. in the two-phase fluid is resonance of the tube group, etc. or abnormal excitation force of the two-phase fluid. Characteristic method for diagnosing abnormal vibrations in tube groups, etc. 2 In claim 1, the natural frequencies of a group of tubes, etc. in air and the natural frequencies of a group of tubes, etc. in water are determined in advance, and their inclusion ratio is determined according to the void ratio of the two-phase fluid. A method for diagnosing abnormal vibrations in a group of tubes, etc., characterized in that the natural frequency of the group of tubes, etc. in a two-phase fluid is calculated by changing the . 3 A vibration sensor that detects vibrations of a group of tubes placed in a two-phase fluid, a vibration meter that amplifies the detected vibration signal, a vibration analyzer that analyzes the frequency of the amplified signal, and a void in the two-phase fluid. a void sensor that detects the void ratio, a void meter that obtains the void ratio from the signal of the void sensor, a calculator that calculates the natural frequency of a group of tubes, etc. in a two-phase fluid based on the void ratio, and the vibration analyzer. It consists of a display device that superimposes and displays the output of the computer and the computer, and the cause of vibration in a group of tubes in a two-phase fluid can be determined based on whether the peak value generated in the frequency analysis result matches the natural frequency. An apparatus for diagnosing abnormal vibrations of pipe groups, etc.