JPH109999A - Circular flow water tank equipped with straight permeation type multilayered sound absorbing chamber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the adverse effect of fluid noise exerted on the evaluation of acoustic measurement in a measuring part to the utmost by absorbing the fluid noise generated when water is forcibly circulated to the utmost by the sound absorbing chamber provided to the corner part of a circular flow water tank without reflecting the same. SOLUTION: In a circular flow water tank forcibly circulating water in a water tank to generate water streams in a definite direction within a measuring part and measuring the sound generated by the matter placed in the water streams of the measuring part, a sound absorbing chamber 2 is provided to the corner part 1e of the circular flow water tank to be filled with the same fluid as the fluid in the circular flow water tank 1 and the bondary surface of the sound absorbing chamber 2 and the corner part 1e of the circular flow water tank 1 is formed of a sound transmitting material 2a and the interior of the sound absorbing chamber 2 is partitioned by a sound absorbing material 2b and the inner surface of the sound absorbing chamber 2 is covered with a sound absorbing wedge material 2c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention forcibly circulates water in a water tank to generate a water flow in a fixed direction in a measuring unit, and measures a sound caused by an object placed in the water flow of the measuring unit. For the circulating water tank used for, in particular, to absorb as much as possible in the sound absorbing chamber provided in the corner of the circulating water tank, the fluid noise generated when forced circulation of water,
The present invention relates to a circulating water tank provided with a straight-through transmission type multi-layer sound absorbing chamber for minimizing adverse effects of fluid noise on sound measured by a measuring unit.

[0002]

2. Description of the Related Art Conventionally, water in a water tank is forcibly circulated using, for example, an impeller or the like to generate a water flow in a fixed direction in a measurement unit, and a sound caused by an object placed in the water flow of the measurement unit is measured. A circulating water tank used to perform the water circulation is known.

The circulating water tank has a structure in which water in the water tank is forcibly circulated to generate a water flow in a fixed direction in the measuring section. That is, the circulation water tank is provided with a communication pipe for circulation, for example, below the bottom of the measurement unit, and both ends of the communication pipe are bent upward and connected to both side surfaces of the measurement unit, and the communication pipe is connected to the communication pipe. For example, an impeller for forcibly circulating water is provided inside the pipe.

In the circulating water tank, the impeller is driven to force water to flow into the measuring section from one side of the measuring section, and to flow out of water from the other side of the measuring section. The water is circulated and flown again into the measuring section to generate a water flow in a fixed direction in the measuring section.

[0005]

By the way, in an experiment in which a sound caused by an object placed in the water flow of the measuring unit is measured using a circulating water tank, noise is generated. There are the following causes. (1) Noise generated by axial flow pumps (impeller and stator) for generating water flow (2) Fluid noise generated by guide vanes (guide vanes) (3) Turbulent noise generated in water tank (including boundary layer noise) (4) Noise generated by mechanical vibrations of guide vanes, tank outer plates, etc. (5) Noise generated by drive motor and drive shaft system Among these, (1), (2) and (3) are fluid noise, and (4),
(5) is mechanical noise. The largest noise level in the fluid noise is the fluid noise generated by the impeller in (1).

The sound wave of the noise generated by the impeller (also in the case of the stator) reaches the measuring section while mainly reflecting each corner of the circulating water tank, and adversely affects the evaluation of acoustic measurement in the measuring section. there were.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made in order to solve the problems. It is an object of the present invention to reduce the fluid noise generated when water is forcibly circulated in a circulating water tank. A straight transmissive multi-layer sound-absorbing chamber that absorbs as much as possible without being reflected by the sound-absorbing chamber provided at the corner and minimizes the adverse effect of fluid noise on the evaluation of acoustic measurement in the measuring section. It is an object of the present invention to provide a circulating water tank provided with a circulating water tank.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention forcibly circulates water in a water tank to generate a water flow in a fixed direction in a measuring section, and to immerse the water in the measuring section. In the circulating water tank that measures the sound caused by the object, a sound absorbing room is provided at the corner of the circulating water tank,
The inside of the sound absorbing chamber is filled with the same fluid as the fluid in the circulating water tank, the boundary between the sound absorbing chamber and the corner of the circulating water tank is formed of a sound transmitting material, and the inside of the sound absorbing chamber is partitioned back and forth by the sound absorbing material, The inner surface of the sound absorbing chamber is covered with a sound absorbing wedge material.

Here, as a preferred mode, the inside of the sound absorbing chamber is preferably partitioned into multiple layers with a plurality of sound absorbing materials arranged at regular intervals.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically based on embodiments of the invention shown in the drawings. Here, FIG. 1 is a schematic overall sectional side view of the circulating water tank, FIG. 2 is a sectional side view of the sound absorbing chamber, FIG. 3 is a perspective view of the sound absorbing wedge material, and FIG. 4 is a relationship between the taper length of the sound absorbing wedge material and the cutoff frequency. FIG. 5 and FIG. 5 are diagrams showing the influence of the length of the tapered portion on the characteristics of the sound absorbing wedge member.

In the figure, a circulating water tank provided with a straight-through transmission type multi-layer sound absorbing chamber is a device for forcibly circulating the water in the water tank to generate a water flow in a certain direction in the water tank. A circulating water tank 1 for circulating water through the water tank to generate a water flow in a certain direction in the water tank, and a sound absorbing chamber 2 provided at a corner 1e of the circulating water tank 1 for absorbing fluid noise.

The circulating water tank 1 is, for example, a vertical type, that is, a circulating water tank that circulates up and down. On the upper side of the circulating water tank, an acoustic object caused by an object placed in a water flow with a test object floating or submerged. Is provided.

An inlet for water circulating into the measuring section 1a is opened on one side in the longitudinal direction of the measuring section 1a.
Further, a discharge port for discharging water flowing through the inside of the measuring section 1a is opened on a side opposite to the inflow port. The inflow pipe 1 is located outside both ends of the measuring section 1a where the inlet and outlet are formed.
b and a discharge line 1c are provided respectively.

The inflow conduit 1b and the discharge conduit 1c are formed with corner portions 1e, 1e, each of which has a distal end curved downward by about 90 degrees, and are curved downward. Are formed at the corners 1e, 1e, which are curved by about 90 degrees toward the inward horizontal direction, and are connected to the end of a communication pipe 1d provided below the measuring section 1a.

The circulating water tank 1 forms a circulation path of water for causing a flow in the measuring section 1a by the inflow pipe 1b, the discharge pipe 1c, the communication pipe 1d, and each corner 1e. Is done.

The sound absorbing chamber 2 is a chamber that absorbs fluid noise generated by rotation of the impeller 3 and the like without reflecting it at the corner 1e and minimizes the noise, and is located downstream of the communication pipe 1d in which the impeller 3 is installed. The front side of the corner 1e on the end side,
That is, they are provided in the direction in which the sound waves travel straight.

The inside of the sound absorbing chamber 2 is sealed, and the inside of the sealed sound absorbing chamber 2 is filled with the same fluid as that in the circulating water tank 1, for example, water. By making the fluid inside the sound absorbing chamber 2 and the inside of the circulation water tank 1 the same,
The sound is prevented from being reflected at the boundary surface between the sound absorbing chamber 2 and the circulating water tank 1 so as not to be transmitted.

A sound transmitting material 2a is attached to a boundary surface between the sound absorbing chamber 2 and the corner 1e. The sound transmitting material 2 a has a function of causing sound waves of the noise of the impeller 3 to enter the sound absorbing chamber 2 without disturbing the flow in the circulation water tank 1. The boundary surface is the sound transmitting material 2a
It is formed in a curved shape so that circulating water can be smoothly reflected. For the sound transmitting material 2a, for example, polymethyl methacrylate (organic glass) or the like, which is substantially equal to the specific acoustic impedance of water used in the circulation water tank 1, is used.

The inside of the closed sound absorbing chamber 2 is divided into a plurality of layers by arranging a plurality of sound absorbing members 2b in front of and behind at regular intervals. Each sound absorbing material 2b is mounted inside the sound absorbing chamber 2 so as to block at right angles to the direction of the sound wave. Each sound absorbing material 2b absorbs sound, and a traveling sound wave is absorbed while passing through the multilayer sound absorbing material 2b.

The thicker the sound absorbing material 2b, the more the sound wave from a low frequency band can be blocked. Normally, the thickness of the sound absorbing material 2b needs to be at least １ of the wavelength λ of the sound wave to be cut off.

A sound absorbing wedge member 2c is attached to the inner surface of the sound absorbing chamber 2, that is, the left and right side surfaces, the rear end surface, the ceiling surface, and the bottom surface except for the boundary surface with the corner portion 1e of the circulating water tank 1.
The inner surface of the sound absorbing chamber 2 is covered with the sound absorbing wedge member 2c.

The sound-absorbing wedge member 2c has a conical or wedge-shaped shape. When the length of the tapered portion is increased, a lower cutoff frequency (the lowest frequency at which the sound pressure reflectance becomes 0.10 is called a cutoff frequency). Can be absorbed up to.

The length of the tapered portion of the roughly sound absorbing wedge member 2c has to be one or more of the length of the sixth of the wavelength lambda _c of the cut-off frequency f _c. The expression is as follows. λ _c = c / f _c ≧ 6L where λ _c : wavelength of sound wave at cut-off frequency c: propagation speed of sound wave f _c : cut-off frequency L: length of tapered portion of sound absorbing wedge member 2c

An impeller 3 for generating a water flow is mounted inside the communication pipe 1d. The rotation shaft of the impeller 3 extends outside the communication line 1d, and is interlocked with a motor 3a installed below the outside of the discharge line 1c. The impeller 3 is one of the major causes of fluid noise.

A guide vane 4 is provided at each corner 1e of the circulating water tank 1. The guide vane 4 functions to smoothly change the flow direction of water at the corner 1e. The guide vanes 4 have been subjected to a sound absorbing process so that sound waves are not reflected.

Next, the operation based on the configuration of the embodiment of the present invention will be described below. Measuring part 1a of circulating water tank 1
The motor 3a is driven in order to generate a water flow. When the motor 3a is driven, the impeller 3 in the communication pipe 1d rotates to pump water in the communication pipe 1d toward the inflow pipe 1b via the corner 1e. The water pressure-fed from the communication pipe 1d to the inflow pipe 1b via the corner 1e flows through the inflow pipe 1b, and flows into the measuring section 1a from the downstream inlet of the inflow pipe 1b.

The water that has flowed into the measuring section 1a flows at a constant flow rate toward the discharge port on the opposite side. Therefore, the measuring unit 1
A water flow in a certain direction is generated in a. In the measurement unit 1a, acoustic measurement caused by an object placed in a water flow is performed in a state where the object for experiment is floating or submerged.

The water that has caused a constant water flow in the measuring section 1a is discharged from the discharge port into the discharge line 1c, and is discharged from the discharge line 1c.
c into the communication conduit 1d, where the impeller 3
Thus, it is circulated and pumped to the inflow pipe 1b via the corner 1e.

By the way, the sound wave of the noise generated during rotation of the impeller 3 for forcibly circulating the water in the circulating water tank 1 travels straight inside the communication pipe 1d and reaches the front corner 1e. A sound transmitting material 2a is attached to an outer curved surface of 1e, and a guide vane 4 subjected to a sound absorbing process is attached to a corner 1e.

For this reason, the sound wave of the noise generated by the impeller 3 which has traveled straight to the corner 1e continues straight without being reflected at the corner 1e.
And enters the sound absorbing chamber 2 through the sound transmitting material 2a having an outer curved surface.

A part of the sound wave that has entered the sound absorbing chamber 2 continues to travel straight, and another part of the sound wave is reflected on the ceiling, bottom, left and right side surfaces of the sound absorbing chamber 2. A plurality of sound absorbing members 2b are attached to the sound absorbing chamber 2 at predetermined intervals so as to intercept the sound waves at right angles to the straight traveling direction of the sound waves, and the sound waves traveling straight are absorbed by each sound absorbing material 2b and weakened. Go.

Some sound waves reflected on the inner surface of the sound absorbing chamber 2, that is, on the ceiling side, both left and right sides, the bottom side, the back end side, etc.
When reflected, the sound is absorbed and weakened by the sound absorbing wedge member 2c attached to the inner surface, and the sound wave is absorbed and weakened each time the reflection is repeated.

It should be noted that the present invention is not limited to the above embodiments of the present invention, and it is needless to say that various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the case where the circulating water tank 1 is composed of a vertical type, that is, a circulating water tank that circulates vertically is described. However, the present invention is not limited to this, and the circulating water tank 1 circulates horizontally. A circulating water tank may be used. Further, in the above-described embodiment, the case where the sound absorbing chamber 2 is provided at the corner 1e on the downstream end side of the communication pipe 1d where the impeller 3 is installed has been described. However, the sound absorbing chamber 2 may be provided at another corner 1e other than this. Of course, it is possible. Furthermore, the case where a plurality of sound absorbing materials 2b are arranged inside the sound absorbing chamber 2 has been described, but one or more sound absorbing materials 2b may be used.
It is sufficient that b is arranged and partitioned.

[0034]

As is apparent from the above description, according to the circulating water tank provided with the straight-through transmission type multi-layer sound absorbing chamber according to the present invention, the water in the water tank is forcibly circulated, and the water is circulated in the measuring section in a certain direction. In the circulating water tank that generates the water flow and measures the sound caused by the object placed in the water flow of the measuring unit, a sound absorbing chamber is provided at the corner of the circulating water tank, and the same as the fluid in the circulating water tank inside the sound absorbing chamber Filling the fluid, forming the boundary surface between the sound absorbing chamber and the corner of the circulating water tank with sound transmitting material,
The interior of the sound absorbing chamber is partitioned back and forth with a sound absorbing material, and the inner surface of the sound absorbing chamber is covered with a sound absorbing wedge material. The sound absorbing material and the inner sound absorbing wedge material on the inner surface absorb as much as possible, and the adverse effect of the fluid noise on the evaluation of the acoustic measurement by the measuring unit can be minimized.

Further, when the inside of the sound absorbing chamber is divided into a plurality of layers with a plurality of sound absorbing materials arranged at regular intervals, the fluid noise is further absorbed by the plurality of sound absorbing materials. It has a very novel and beneficial effect.

[Brief description of the drawings]

FIG. 1 is a schematic overall sectional side view of a circulating water tank showing an embodiment of the present invention.

FIG. 2 is a side sectional view of the sound absorbing chamber showing the embodiment of the present invention.

FIG. 3 is a perspective view of a sound absorbing wedge member showing the embodiment of the present invention.

FIG. 4 is a diagram showing the relationship between the length of the tapered portion of the sound absorbing wedge member and the cutoff frequency, showing the embodiment of the present invention.

FIG. 5 is a diagram illustrating the influence of the length of the tapered portion on the characteristics of the sound absorbing wedge member according to the embodiment of the present invention.

[Explanation of symbols]

 1 time water tank 1a measuring unit 1b inflow line 1c discharge line 1d communication line 1e corner 2 sound absorbing room 2a sound transmitting material 2b sound absorbing material 2c sound absorbing wedge material 3 impeller 3a motor 4 guide vane

Claims (2)

[Claims] 1. A circulating water tank for forcibly circulating water in a water tank to generate a water flow in a fixed direction in a measuring unit and to measure a sound caused by an object placed in the water flow of the measuring unit. A sound absorbing chamber is provided at the corner of the tank, and the inside of the sound absorbing chamber is filled with the same fluid as the fluid in the circulating water tank,
The boundary surface between the sound absorbing chamber and the corner of the circulating water tank is formed of a sound transmitting material, the inside of the sound absorbing chamber is divided back and forth by the sound absorbing material, and the inner surface of the sound absorbing chamber is formed by covering with a sound absorbing wedge material. A circulating water tank equipped with a transmission type multi-layer sound absorbing room. 2. A circulating water tank provided with a straight transmission type multi-layer sound absorbing chamber according to claim 1, wherein a plurality of sound absorbing materials are arranged at regular intervals and partitioned into multiple layers inside the sound absorbing chamber.