JPH03684A - Sloshing control construction for liquid storage tank - Google Patents

Abstract

PURPOSE:To easily, satisfactorily control the sloshing of stored liquid by a method wherein low density substances having lower specific gravity than that of stored liquid are put in floating state in a liquid storage tank. CONSTITUTION:A plenty of granular low density substances 2 having lower specific gravity than that of stored liquid are put all over the liquid surface of the stored liquid with every substance independently kept free to float on the liquid, so that a granular substance layer 3 is formed on the surface of the stored liquid. The low density substances 2 are of formed products of synthetic resin, wood, or ice pieces, and the depth ratio of the granular substance layer 3 to the stored liquid layer 4 is about 1:4-2:3. The surface of the stored liquid is pressed down by the weight of the low density substances 2, and the low density substances 2 collide each other, so that the sloshing energy of the stored liquid is wasted and the sloshing is prevented.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is applicable to liquid storage tanks in various industrial fields, such as architectural equipment water tanks such as elevated water tanks and heat storage tanks, oil storage tanks, and LNG storage tanks. This invention relates to a structure for controlling sloshing of stored liquid caused by shaking due to external forces such as earthquakes.

[Conventional technology]

For the purpose of suppressing sloshing, the sloshing system 'qTJ structure of the liquid storage tank includes one in which a partition wall (IA) is provided to partition the inside of the liquid storage tank (1) into a plurality of parts, as shown in FIG. As shown in Fig. 20, a partition wall CIA') is provided on the side wall of the liquid storage tank (1) as shown in Fig. 21. It is generally known that a tank is provided with a series of suppression plates (IB) that suppress the liquid level downward.

[Problem to be solved by the invention]

However, in the case of the conventional structure, the wave energy of the stored liquid is attenuated only by waves colliding with the bulkheads and shear restraint plates, so the bulkheads and shear restraint plates are constructed to withstand the impact force upon collision with waves. Therefore, the structure of the liquid storage tank becomes large and the cost becomes high. Moreover,
Since the structure of the liquid storage tank is a large fixed structure and it is difficult to change the specifications after manufacture, it is necessary to fully understand the sloshing conditions at the design stage, and the design and construction itself is very difficult. It's difficult. In other words, since it has to be designed and manufactured to specifications suitable for each sloshing condition, it lacks flexibility to respond to sloshing conditions, that is, it lacks versatility. This leads to increased costs.

An object of the present invention is to provide a sloshing control structure for a liquid storage tank that is highly flexible regarding sloshing conditions and can be realized at low cost.

(Means for Solving the Problems) A characteristic configuration of the sloshing control structure for a liquid storage tank according to the present invention is that a low specific gravity object having a specific gravity smaller than that of the stored liquid is placed in the liquid storage tank so as to float on the stored liquid. At a certain point.

The low specific gravity object is preferably in the form of granules or slurry.

[For production]

Sloshing is suppressed by the low specific gravity objects floating on the liquid that press the liquid storage surface downward.

Since the low specific gravity object is simply floating in the liquid storage, the low specific gravity object for suppressing sloshing is not required to function as a structure. As a result, it is easy to adjust the amount of small specific gravity objects, and the amount of small specific gravity objects! - By adjusting the amount, the force pressing down on the liquid storage surface can be freely changed to easily achieve the desired sloshing control state, that is, the sloshing attenuation rate.

Particularly when using granular objects as low specific gravity objects, not only can the amount of small specific gravity objects be adjusted extremely easily, but also frictional resistance occurs between the granular and low specific gravity objects, causing waves in the stored liquid. Because it consumes energy, the attenuation rate of sloshing can be made thicker.

When damping vibrations of a building using a pendulum supported swingably by the building, it is necessary to damp the vibrations of the pendulum in accordance with various conditions such as the natural frequency of the building. In such a case, if a liquid storage tank is provided as a weight for the damping pendulum and the amount of the small specific gravity object is adjusted to appropriately control the sloshing of the stored liquid, the pendulum can be moved to an appropriate level as shown in the data below. can be attenuated to

〔Effect of the invention〕

In summary, according to the present invention, it is possible to economically and easily control the sloshing of a stored liquid as desired, and the sloshing is particularly suitable for controlling the sloshing of a liquid storage tank used as a weight for a vibration damping pendulum in a building. Control structures can now be provided.

〔Example〕

Next, examples of the present invention will be shown.

[Example 1] As shown in Fig. 1, in order to control the sloshing of the stored liquid due to the rocking movement of the liquid storage tank (1), a large number of granular small specific gravity objects (2) whose specific gravity is lower than that of the stored liquid are used. are arranged so that they are floating independently and freely in the liquid storage, and are arranged so as to cover the entire liquid storage surface. That is, the upper layer of the liquid storage layer is formed as a granular object layer (3).

Examples of the low specific gravity object (2) include molded articles of synthetic resin, wooden products, ice chips, and the like.

The amount of the small specific gravity object (2) is such that the ratio of the thicknesses of the granular object layer (3) and the liquid layer (4) is about 1:4 to 2:3.

The liquid storage tank (1) may include a building equipment water tank such as an elevated water tank or a heat storage tank, a stockpiling/storage tank for petroleum or LNG,
Examples include mobile tanks for tankers and tank trucks, water tanks for live fish transport vehicles, etc., which are specified in various fields and installed in various forms.

Therefore, according to this embodiment 1, the liquid storage surface is a small specific gravity object (2
) is pressed down by the weight of the objects (2), and the collision of the small specific gravity objects (2) consumes the energy of sloshing and suppresses sloshing.

[Example 2] As shown in Fig. 2, a vibration damping pendulum (7) is suspended and supported in a swingable manner from a frame (6) installed on the upper floor of a building (5). As the weight (7A) of the pendulum (7),
A liquid storage tank (1) is provided to generate sloshing of the stored liquid to attenuate the vibration of the vibration damping pendulum (7), and the vibration damping pendulum (7) In a building allocating device that suppresses the shaking of the building (1) by damped and controlled shaking, a small specific gravity object (2) similar to that of Example 1 is placed in the liquid storage tank (1). This is what I did.

In the case of this embodiment 2, the damping pendulum (7) is effectively damped by suppressing the sloshing of the stored liquid with the small specific gravity object (2), and the damping pendulum (7) is oscillated. motion (vibration)
It is possible not only to reduce the size of oil dampers and the like for damping, but also to eliminate the need for them.

Next, an experiment conducted by the present inventor to confirm the damping effect in Example 2 will be described.

First, to explain the pendulum model (8) used in the experiment, as shown in Figs.
1) is suspended and supported on a support frame (10) using four length-adjustable rods (9) with the long side direction being the vibration direction, and the water depth (D) is 30 cm in the water tank (1). Water was added so that Note that the rod (9) is supported on the support frame (10) and the rod (9) of the water tank (1) is
) are both bearing bearings.

Then, using two parameters: the length of the rod (9), that is, the length of the pendulum, and the amount of ice pieces put into the water 1 (1) as the small specific gravity object (2), the pendulum-sloshing fast generation system were set as shown in Table 1.

The amount of ice chips is expressed as the ratio of the amount of ice chips to the total amount of water and ice chips (in other words, the contents), and the length of the pendulum is determined from the liquid size because the resonance with sloshing is the subject of the experiment. The expected sloshing frequency is 1.0 of 0.77Hz.
The frequency of the pendulum was set to be twice, 1/1.1 times, and 1/1.2 times. Incidentally, the state of the contents in the aquarium (1) is in a liquid phase when the water ratio is 0%, and when the water ratio is 20% and 40%.
In each case, it is a state of fluid sleet with a solid-liquid mixed phase,
When the water ratio is 60%, the ice pieces are all compacted into sleet.

Next, the water tank (1) is forcibly displaced about 5 cm from the amplitude center and then released to vibrate the pendulum to make it vibrate freely, and the two accelerations acting on the pendulum, in the vibration direction and the direction of the support axis, and the water tank (1) Measure the dynamic water pressure at two locations separated by a set interval above and below, and achieve each of the results set in the above parameters for the case of a single pendulum without water or ice chips in the water tank (1), and for each achievement set in the above parameters. The free vibration waveform of the pendulum in the case of the system was obtained, and the natural frequency and damping constant were calculated based on it. The damping constant is calculated from the logarithmic damping rate after separating the mold vibration waveform into first-order and second-order components through Fourier transformation. Figure 5 shows the free vibration waveform and acceleration power spectrum for a single pendulum with a pendulum length of 426 mm.
In () and (0), the free vibration waveform and acceleration power spectrum for each rate system are shown in (a) of Figures 6 to 14.
, (shown in [1) respectively. In addition, the natural frequency and damping number in each case are shown in Table 2, the relationship between the water ratio and the natural frequency is shown in Figure 15, and the relationship between the water ratio and the damping constant is shown in Figure 1.
They are shown in Figure 6.

As a result of the above, the following facts were revealed.

[1] In a system with an ice ratio of 0 to 40%, the frequency is approximately 80% lower than that of a pendulum alone, but when the water ratio is approximately 60%, the frequency is almost the same as that of a pendulum alone. Match. This is considered to be because when the water ratio is about 60%, it becomes a solid phase and no sloshing occurs.

[2] The damping constants in a coupled system with an ice ratio of 0% are low at around 1% for both primary and secondary orders, but in a fast-forming system with a water ratio of 20 to 40%, the damping constants for both primary and secondary orders reach around 10%. Rise. Further, at a water ratio of about 60%, the water becomes a solid phase, so the influence of sloshing is small, and the water ratio decreases to about 1%.

[3] In a fast-forming system in which the contents flow, changes in vibration frequency due to differences in the state of the contents are extremely small.

Furthermore, the present inventors calculated the eigenvalues of the coupled system using a conventional sloshing model based on the above three facts. As shown in FIG. 17, the sloshing model used was one in which the liquid stored in the liquid storage tank (1) was replaced with an equivalent system of mass points.

In the sloshing model, length 2p, mass mp
The eigenvalue of a two-degree-of-freedom system of pendulum (11) with circular frequency -3, mass lll5 of free water (12), and mass mt of fixed water (13) with sloshing replaced with an equivalent mass point is ωZ=
μ/2((ω!□10g/i p)± (ω”a+g
/j2p)" 4μω2.g/l... (1) Here, g = gravitational acceleration, u = (m
9+ m t＞/ (mp+ m w) 1 m w=
m*+m t+m5m, ωt, = (πg/L) tanh(πIt/L)
...” (2) ms = tanh (πH/L
) mw / ((π/2)3(ll/L) )...
...(3) Find it. L and H are water tank (1) as shown in Figure 18.
The length in the vibration direction and the water depth are shown respectively.

m9=60kg, ms=48kg, mt=21kg
Table 3 shows the trial calculation results for each pendulum length.

As is clear from Table 3, the trial calculation results are in good agreement with the experimental results. As a result, the content is a small specific gravity object of ice chips (
It has been found that even if 2) is included, the frequency of the fast-forming system can be evaluated using the conventional sloshing model using equivalent award substitution.

Table 1 Soshimecho table table Numbers in parentheses do not indicate analysis/experiment. [Another example] Another embodiment of the present invention will be shown below.

[1] In the above example, a large number of granular objects were shown as the small specific gravity object (2), but the small specific gravity object (2) was
It may be a slurry-like material, a viscous substance, or a plate-like material that covers the entire or almost the entire liquid storage surface all at once or in portions.

[2] In the above example, the granular small specific gravity object (2) was made independent, but the granular small specific gravity object (2) is
It may be tied together with string or net.

[3] Although reference numerals are written in the claims section for convenient comparison with the drawings, the present invention is not limited to the structure shown in the accompanying drawings.

[Brief explanation of drawings]

1 and 2 show an embodiment of the present invention, with FIG. 1 being a schematic sectional view and FIG. 2 being a front view. Figures 3 and 4 are front and side views of the pendulum model used in the experiments conducted by the present invention, and figures (a) and (b) in Figures 5 to 14 respectively show vibration waveforms showing the experimental results. Graph and spectrum graph, Figure 15 is a graph showing the relationship between the water ratio and natural frequency obtained by experiment, Figure 16 is a graph showing the relationship between water ratio and damping constant obtained by experiment, Figure 17 , FIG. 18 is a schematic diagram showing a model used for considering the experimental results. FIGS. 19 to 21 are schematic cross-sectional views showing conventional examples. (1)...Liquid storage tank, (2)...Low specific gravity object, (7)...Vibration damping pendulum, (78)...
... Weight.

Claims (1)

[Scope of Claims] 1. A sloshing control structure for a liquid storage tank, in which a small specific gravity object (2) whose specific gravity is lower than that of the stored liquid is placed in the liquid storage tank (1) so as to float on the stored liquid. 2. A sloshing control structure for a liquid storage tank according to claim 1, wherein the liquid storage tank (1) is a weight (7A) of a control pendulum (7) swingably supported by a building. 3. Claim 1, wherein the low specific gravity object (2) is granular.
Or the sloshing control structure of a liquid storage tank according to 2.