JP2000009516A - Sloshing liquid level measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sloshing wave height measuring instrument for precisely measuring a rise in the liquid level in a storage tank due to the sloshing phenomenon in an earthquake after the earthquake. SOLUTION: This is a sloshing wave height measuring instrument which measures variation in the liquid level in the liquid storage tank in case of an earthquake and equipped with a liquid level measuring instrument 2 which measures liquid levels at >=2 positions in the tank and outputs their liquid level values, an earthquake detector 3 which detects the occurrence of an earthquake and outputs an earthquake detection signal, a recorder 4 which records and stores the liquid level values in synchronism with the output timing of the earthquake detection signal, and an analyzer 5 which estimates the liquid level variation at the time of the earthquake from the recorded and stored liquid level values.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for estimating a liquid level displacement caused by a sloshing phenomenon that occurs during an earthquake in a tank for storing liquids such as liquefied natural gas, crude oil, and water. The present invention relates to a sloshing wave height measuring device that mathematically estimates a liquid level displacement based on data recorded by a simple liquid level measuring device and estimates a rise in the liquid level due to a sloshing phenomenon generated in a tank.

[0002]

2. Description of the Related Art Liquids such as liquefied natural gas, crude oil and water are usually stored in storage tanks. These storage tanks are designed to be seismic resistant with a focus on safety during an earthquake. When the storage tank is shaken at regular intervals due to an earthquake, the liquid in the storage tank undulates. This phenomenon is well known as a sloshing phenomenon. When this sloshing phenomenon occurs, the level of the stored liquid reaches a level that cannot be expected under normal storage conditions, and in some cases, may exceed the junction between the side wall and the roof of the storage tank. A higher dynamic water pressure is applied to the tank inner wall where the liquid level has risen than usual. Therefore, the size of the storage tank is assumed at the time of the earthquake at the time of construction, and consideration is made so that the tank will not be damaged even if a sloshing phenomenon occurs due to the earthquake of the scale.

[0003]

However, the fixed roof type storage tank has a problem that the degree of rise in the liquid level due to the sloshing phenomenon cannot be estimated unless the storage liquid is discharged from a roof nozzle or the like. In addition, there is a problem that the estimation of the degree of rise of the liquid level tends to be inaccurate even when the liquid is ejected. On the other hand, in the existing liquid level gauge, a fast cycle such as a sloshing phenomenon (for example, 2 to 10 seconds)
There is a problem that the rise of the liquid level cannot be measured.
In addition, there is a problem that the liquid level height on the side plate, which is the most important, cannot be known. The inventor of the present invention, as described in, for example, "Technical Guidelines for Industrial Safety and Disaster Prevention-Earthquake Countermeasures in Chemical Factories" edited by the High Pressure Gas Safety Association, the liquid level displacement due to the sloshing phenomenon of the liquid in the storage tank due to the earthquake. By paying attention to the fact that it can be expressed by a unique mathematical formula, a device for estimating the liquid level displacement due to the sloshing phenomenon from the data of the liquid level displacement at several places was invented.

[0004] The present invention has been devised in view of the above-mentioned problems, and provides a sloshing wave height measuring device for accurately estimating a rise in the liquid level in a storage tank due to a sloshing phenomenon during an earthquake after an earthquake. try to. further,
Sloshing to accurately and quickly estimate the rise in the liquid level in the storage tank due to the sloshing phenomenon during an earthquake without major modification of existing level gauge equipment and without adding complicated level gauge equipment Attempts to provide a wave height measurement device. Still another object of the present invention is to provide a sloshing wave height measuring device for estimating a rise in liquid level at a side plate important for safety of a tank. Providing a sloshing wave height measuring device with these features, maintenance of storage tanks after an earthquake,
Make inspections accurate and accurate.

[0005]

In order to achieve the above object, a sloshing wave height measuring apparatus according to the present invention measures a liquid level at two or more positions in a tank and outputs the liquid level value. A surface measuring device (2), an earthquake detector (3) that detects the occurrence of an earthquake and outputs an earthquake detection signal, and a record that records and saves the liquid level value in synchronization with the output timing of the earthquake detection signal. And an analyzer (5) for estimating the liquid level displacement at the time of the earthquake from the liquid level value stored and stored.

According to the configuration of the present invention, the liquid level measuring device (2) measures the liquid level at at least two or more positions in the tank and outputs the liquid level value. The earthquake detector (3) detects that an earthquake has occurred, and outputs an earthquake signal. The recorder (4) records and saves the liquid level value in synchronization with the output timing of the earthquake signal, and records and saves the fluctuation of the liquid level due to the sloshing phenomenon due to the earthquake.
The analyzer (5) estimates the liquid level displacement at the time of the earthquake from the liquid level values at two or more positions recorded and stored.

Preferably, in order to achieve the above object, in the sloshing wave height measuring apparatus according to the present invention, the liquid level measuring device (2) includes a first liquid level meter (2a) for measuring the liquid level in the tank and the tank. Approximately 90 from the first measuring instrument when viewed from the center
It had a second liquid level meter (2b) for measuring the liquid level at a position shifted by a degree. According to the configuration of the present invention, the first liquid level gauge (2a) and the second liquid level gauge (2b) of the liquid level measuring device measure the liquid level at two mutually separated positions in the tank. , A liquid level value indicating the liquid level at two positions separated from each other in the tank is obtained. The analyzer (5) estimates the liquid level displacement at the time of the earthquake from the liquid level values representing the liquid level at the two positions.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. In each of the drawings, common portions are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 1 is a block diagram of a cylindrical tank facility provided with one sloshing wave height measuring device according to an embodiment of the present invention. The sloshing wave height measuring device of the present tank equipment includes a liquid level measuring device 2, an earthquake detector 3, a recorder 4, an analyzer 5, and an earthquake level display 6. Further, the liquid level measuring device of the present embodiment has a function of detecting the liquid level in the tank during operation in a normal state, and includes a normal liquid level indicator 7. The liquid level gauge 2 has two liquid level gauges (hereinafter, referred to as a first liquid level gauge 2a and a second liquid level gauge 2b) and a liquid level gauge control unit 2c. The first liquid level gauge 2 a is arranged at a position near the side plate in the storage tank 1. Second liquid level meter 2
b is approximately 90% from the first measuring instrument 2a when viewed from the center of the tank.
It is arranged at a position shifted by degrees. The first liquid level meter 2a and the second liquid level meter 2b detect the liquid level in the storage tank 1 and output a liquid level signal according to the liquid level. Liquid level measurement control unit 2
c converts the respective liquid level signals from the first liquid level meter 2a and the second liquid level meter 2b into respective liquid level values and outputs them. When an earthquake does not occur (hereinafter, referred to as normal time), the liquid level measurement control unit 2c converts the liquid level signal into a liquid level value at a slow cycle (hereinafter, referred to as normal time cycle) and outputs the value. When an earthquake detection signal is received from the earthquake detector 3, the liquid level signal is converted into a liquid level value at a predetermined earlier cycle (hereinafter referred to as an earthquake cycle) and output. The earthquake detector 3 includes a seismometer 3a and an earthquake detection control unit 3b.
And The seismometer 3a outputs a vibration signal according to the vibration of the ground. The earthquake detection control unit 3b compares the vibration signal with a preset numerical value, and determines that the time when the vibration signal is larger is the time of the earthquake. The earthquake detection control unit 3b outputs an earthquake detection signal during an earthquake. The recorder 4 records and stores each liquid level value output from the liquid level measuring device 2.
The analyzer 5 prepares a mathematical expression including an undetermined coefficient assuming a liquid level displacement when the sloshing phenomenon occurs in advance.

FIG. 2 is a diagram for explaining variables used in mathematical expressions. In the present embodiment, on an arbitrary straight line passing through the center, 面 represents the liquid level displacement on the inner surface of the side plate, a represents the distance from the center of the storage tank to the side plate, ω represents the frequency of sloshing caused by the earthquake, and t represents the time. Then, it is assumed that the liquid level displacement h at an arbitrary position whose distance from the center of the storage tank is x is expressed by the following equation (1).

[0011]

(Equation 1)

Further, assuming that the position where the liquid level displacement on the circumference of the inner surface of the side plate becomes maximum is point P, and the liquid surface displacement at point P is ζ0, the inner surface of the side plate rotated clockwise θ from point P is Is assumed to be expressed by Equation 2.

[0013]

(Equation 2)

The analyzer 5 calculates a coefficient value of the undetermined coefficient ζ0 from a group of liquid level values recorded and stored in the recorder 4. The analyzer 5 introduces the coefficient value into the undetermined coefficient of the equation, and assumes that the equation is the liquid level displacement in the tank. The analyzer 5 calculates a liquid level value at a predetermined position from the mathematical expression, and outputs the liquid level value to the liquid level indicator 6 at the time of the earthquake. The normal next liquid level display 7 displays the liquid level value output from the liquid level measuring device 2 at the normal time. The earthquake liquid level indicator 6 displays the liquid level value output from the analyzer 5 during an earthquake.

The operation of the sloshing wave height measuring apparatus for tank equipment according to the present invention will be described in accordance with signal processing. Normal time,
The liquid level in the storage tank is horizontal. Earthquake detector 3
Does not output an earthquake detection signal. The liquid level signal is output by the first liquid level meter 2a and the second liquid level meter 2b which measured the liquid level. The liquid level signal is converted into a liquid level value by the liquid level measurement control unit 2c in a normal time cycle. The liquid level value is supplied to the normal liquid level indicator 7 and displayed. When an earthquake occurs, the liquid in the storage tank undergoes sloshing, causing the liquid level to wave. An earthquake detection signal is supplied to the liquid level measurement device 2 by the earthquake detector 3 that has detected the earthquake. The liquid level signal is converted into a liquid level value by the liquid level measurement control unit 2c at the time of the earthquake. The liquid level value is supplied to the recorder 4 and recorded and held. When the earthquake subsides, the earthquake detection signal is interrupted, and the measurement cycle of the liquid level detector 2 returns to the normal time cycle after an appropriately set time. The liquid level value recorded in the recording unit 4 is sent to the analyzer. The liquid level displacement is analyzed by the analyzer 5 as follows. First level gauge 2a
From the difference between the liquid level value of a group of the liquid level values with time and the liquid level value L at normal time, the amplitude h1 of the sloshing is obtained.
Is calculated. Next, assuming that the liquid level amplitude of the first liquid level meter 2a is h1 and the distance from the center of the storage tank to the first liquid level meter 2a is x1, the individual level values of a group of liquid level levels of the liquid level type 2a are given. On the other hand, the liquid level amplitude ζ1 at the inner wall of the side plate is calculated by Expression 3.

[0016]

(Equation 3)

Further, a time-series group of liquid level values of the second liquid level meter 2b and a normal liquid level value L
From this difference, the sloshing amplitude h2 is calculated. Assuming that the liquid level amplitude h2 of the second liquid level meter 2b and the distance from the center of the storage tank to the second liquid level meter 2b are x2, the liquid level displacement ζ2 at the inner wall of the side plate is calculated by Expression 4.

[0018]

(Equation 4)

Assuming that the angle difference between the position of the first liquid level gauge 2a and the position of the second liquid level gauge 2b is α, the maximum liquid level displacement ζ0 on the circumference inside the side plate is calculated by Equation 5.

[0020]

(Equation 5)

The obtained maximum liquid level displacement ζ0 is the maximum liquid level displacement generated on the inner surface of the storage tank side plate due to the sloshing phenomenon during an earthquake. The maximum liquid level displacement ζ0 is output to the liquid level indicator during an earthquake. This maximum liquid level displacement ζ0 is compared with the magnitude of the sloshing phenomenon assumed at the time of design. By comparing the maximum liquid level displacement ζ0 and the liquid level displacement due to the sloshing phenomenon assumed at the time of design, it is possible to judge the necessity, contents and degree of inspection of the storage tank after the earthquake.

According to this embodiment, it is possible to estimate a change in the liquid level due to the sloshing phenomenon from data in which the liquid level in the storage tank is recorded and stored with time, and after the earthquake, the storage tank can be estimated. It is possible to accurately determine whether or not there is any possibility of damage. Therefore, it is possible to determine whether or not to perform a post-earthquake check. Also,
The change in the liquid level due to the sloshing phenomenon can be estimated only by measuring the liquid level at two positions, so that the existing liquid level gauge can be used and the design of the storage tank is changed. It is not necessary and can be easily applied to existing storage tanks. In addition, the displacement of the liquid level in the cylindrical storage tank that caused the sloshing phenomenon is expressed by a mathematical formula, and the liquid level displacement can be estimated analytically from the recorded and stored data, so automation is easy and after an earthquake, It is possible to easily and accurately determine whether or not the storage tank has been damaged. Therefore, it is possible to quickly determine whether or not to perform an inspection after an earthquake. Further, since Equation 1 is an approximate expression representing the free vibration of the liquid in the fixed container, the liquid level displacement due to the sloshing phenomenon can be accurately and accurately estimated. Therefore, it is possible to accurately determine whether or not to perform a post-earthquake inspection.

The present invention is not limited to the embodiments described above, and various changes can be made without departing from the gist of the invention. For example, the shape of the storage tank may be a fixed container, and is not particularly limited to a tank shape. Further, the installation position of the liquid level gauge is not limited to two places, and may be any number as long as it is larger than the number of undetermined coefficients of the assumed mathematical expression.

[0024]

As described above, with the configuration of the sloshing wave height measuring apparatus of the present invention, it is possible to estimate the change in the liquid level due to the sloshing phenomenon from the data in which the liquid level in the storage tank is recorded and stored. After the earthquake, it is possible to easily and accurately determine whether or not the storage tank may have been damaged. Therefore, it is easy to determine whether or not to perform an inspection after an earthquake. Also, it is only necessary to measure the liquid level at two positions, and the existing liquid level gauge can be diverted, so that there is no need to change the design of the storage tank, and it is easy to use the existing storage tank. Applicable to In addition, the displacement of the liquid level in the storage tank that caused the sloshing phenomenon is expressed by a mathematical formula, and the liquid level displacement can be estimated analytically from the recorded and stored data, so automation is easy and the storage tank can be quickly stored after the earthquake. It is possible to easily and accurately determine whether there is a possibility of damage. Therefore, it is possible to quickly determine whether or not to perform an inspection after an earthquake. Furthermore, since the liquid level displacement due to the sloshing phenomenon is represented by using an approximate expression representing the free vibration of the liquid in the fixed container, the liquid level displacement due to the sloshing phenomenon can be accurately and accurately estimated. Therefore, it is possible to accurately determine whether or not to perform a post-earthquake inspection.

[Brief description of the drawings]

FIG. 1 is a block diagram of a storage tank provided with a sloshing wave height measuring device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of variables in a mathematical expression representing a wavefront displacement according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Storage tank 2 Level gauge 2a First level gauge 2b Second level gauge 2c Level measurement controller 3 Earthquake detector 3a Seismometer 3b Earthquake detection controller 4 Recorder 5 Analyzer 6 Level display at the time of earthquake 7 Normal liquid level indicator

Claims (2)

[Claims] 1. A sloshing wave height measuring device for measuring a liquid level displacement in a liquid storage tank at the time of an earthquake, wherein the liquid level is measured at two or more positions in the tank and the liquid level value is measured. Liquid level measuring device (2) to output, and earthquake detector (3) to detect occurrence of earthquake and output earthquake detection signal
And a recorder (4) for recording and storing the liquid level value in synchronization with the output timing of the earthquake detection signal, and an analyzer (5) for estimating the liquid level displacement during an earthquake from the recorded and stored liquid level value. ), A sloshing wave height measuring device comprising: 2. A liquid level measuring device (2) comprising: a first liquid level meter (2a) for measuring a liquid level in a tank and a liquid surface at a position substantially 90 ° shifted from the first measuring device when viewed from the center of the tank. The sloshing wave height measuring device according to claim 1, further comprising a second level gauge (2 b) for measuring the wave height.