JPH0685425U - Weir noise prevention device - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a weir noise prevention device that completely prevents generation of low frequency noise without significantly changing the original structure and performance of the gate. [Structure] In an overflow type full width gate having a moguri weir, the overflow water attached to the upper end of the moguri weir is divided into an upper water film 3 and a lower water film 3a, and each of the water films 3 and 3a is dropped. It was equipped with two-stage water film forming means 2, 4, 4a, 7 for dropping onto the downstream water surface without merging.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a weir noise prevention device that prevents low-frequency noise generated at an overflow gate provided in a general river, a waterway for agriculture, or the like.

[0002]

[Prior art]

 Overflow type gates installed in general rivers, waterways for agriculture, etc. are known to have a gate 1 and a spoiler 8 for laterally dividing the overflow water film, as shown in the perspective view of FIG. There is. In such an overflow gate, the water flow beyond the gate 1 overflows from the gate outflow end 4 to form a water film 3, and at this time, a plurality of water flows are provided in the gate width (perpendicular to the flow) direction. Since the water film is divided by the spoiler 8, the low-frequency sound is less likely to be generated. In addition, as shown in FIG. 4, the water film formed by the water flow beyond the gate 1 is disturbed by the spoiler 9 and becomes uneven, so that low-frequency noise is less likely to occur Is also known. As shown in Fig. 5, the cause of this low-frequency sounding in an overflow gate is considered to be the interaction between the closed cavity 6 composed of the gate 1 and the water film 3 and the water film itself. ing. That is, when a pressure fluctuation occurs in the cavity at the acoustic natural frequency in the cavity, the water film falls to the downstream water surface 5 while fluctuating in the direction perpendicular to the water film surface. At that time, the volume of the cavity fluctuates with the fluctuation of the water film, and this volume fluctuation causes pressure fluctuation in the cavity. At that time, as shown in FIG. 6, when the pressure is positive, the water film at the outflow end exerts an outward force as shown by the solid arrow, and when it is negative, as shown by the dashed arrow. , Inward force works. As a result, the outflow direction of the water film changes depending on whether the pressure inside the cavity is positive or negative, which is a major factor in fluctuations in the water film and the generation of crying. It is considered that the vibration of the is promoted and a sound is generated.

[0003]

[Problems to be solved by the device]

 By the way, the conventional spoiler for preventing noise is not designed according to the above-mentioned factors, but is adopted empirically, so it is necessary to meet all conditions such as various gates and various overflow conditions. Could not be effective against. For example, the conventional spoiler shown in FIGS. 3 to 4 has the following problems. (1) The one in Fig. 3 tries to change the natural frequency in the cavity by dividing the water film. For this purpose, the division width needs to be increased. In this case, the effective width of the gate is And the flow characteristics of the gate deteriorate. There are also problems such as the accumulation of debris flowing in the river. (2) The one shown in Fig. 4 prevents uneven volumetric fluctuations in the cavity by making the water film surface uneven, but in this case, it is not effective for all overflows. However, a sound is still generated at a specific flow rate.

The present invention has been proposed in view of such circumstances, and a weir noise prevention device that completely prevents generation of low-frequency noise without significantly changing the original structure and performance of the gate is provided. The purpose is to provide.

[0005]

[Means for Solving the Problems]

 Therefore, in the present invention, in an overflow type full width gate having a moguri weir, it is attached to the upper end of the moguri weir, and the overflow water is divided into an upper water film and a lower water film. It is characterized by comprising a two-stage water film forming means that drops on the downstream water surface without doing so.

[0006]

[Action]

 With such a configuration, as shown in FIG. 1, the outflow direction of the lower water film changes according to the fluctuation of the pressure in the cavity, but an air layer is formed between the upper water film and the lower water film. Due to the buffering effect of the air layer, the pressure fluctuation in the cavity does not affect or reduces the influence on the upper water film. For this reason, the main cause of ringing is eliminated, and ringing can be prevented.

[0007]

【Example】

 An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a vertical sectional view showing an overflow weir having the embodiment of the present invention, and FIG. 2 is a perspective view showing a II portion of FIG.

In the above drawings, the same reference numerals as those in FIGS. 3 to 6 respectively indicate the same members, and in FIGS. 1 and 2, 1 is a gate made of iron or the like, and 2 is an overflow surface. is there. A plurality of slits 7 are provided at appropriate intervals on the upstream overflow surface of the overflow end 4, and part of the overflow water that has dropped through the slits 7 flows on the lower overflow surface 2a and flows out from the lower outflow end 4a.

According to such a structure, the overflow water flows out from two places of the upper outflow end 4 and the lower outflow end 4a, and as shown in FIGS. 1 and 2, the upper water film 3 and the lower water film 3a. The two upper and lower water films and the air layer 6a are formed. The shape and size of the slit 7 are determined in consideration of the following points. (1) No spills such as dust should be retained. (2) The upper water film 3 and the lower water film 3a have almost the same thickness.

[0010]

[Effect of device]

 According to such a whirling noise prevention device, the upper and lower water films are formed, and the lower water film is directly affected by the pressure fluctuation in the cavity, so that the change in the outflow direction and the volume in the cavity. Although it causes a change, the pressure fluctuation in the cavity does not affect the upper water film due to the buffering action of the air layer existing between the upper water film and the lower water film. Or the impact will be less. For this reason, the main cause of the sound generation is eliminated, and the sound generation can be prevented.

In short, according to the present invention, in an overflow type full width gate having a moor weir, the overflow water is attached to the upper end of the moor weir, and the overflow water is divided into an upper water film and a lower water film. By including the two-stage water film forming means that drop onto the downstream water surface without merging in the middle, the generation of low-frequency noise is completely prevented without significantly changing the original structure and performance of the gate. The present invention is extremely useful in industry because it provides a damming noise prevention device.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing an overflow gate having a damming noise prevention device according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a portion II of FIG. 1, that is, a damming noise prevention device.

FIG. 3 is a perspective view showing a conventional weir noise prevention device for an overflow weir.

FIG. 4 is a perspective view showing a conventional weir noise prevention device for an overflow weir different from that shown in FIG. 3;

FIG. 5 is an explanatory diagram showing a mechanism of sound generation of an overflow weir.

6 is a diagram showing the relationship between the positive and negative pressures inside and outside the water film in FIG. 5 and the outflow direction of the water film.

[Explanation of symbols]

 1 Gate 2 Overflow Surface 2a Lower Overflow Surface 3 Water Film 3a Lower Water Film 4 Upper Outflow End 4a Lower Outflow End 5 Downstream Water Surface 6 Cavity 6a Air Layer 7 Slit

Claims (1)

[Scope of utility model registration request] 1. An overflow type full-width gate having a moguri weir, which is attached to the upper end of the moguri weir and divides overflow water into an upper water film and a lower water film, and joins the water films on the way. A damming noise prevention device characterized by including two-stage water film forming means that respectively drop on the downstream water surface.