JP4883450B2 - Construction method of long-period wave reduction countermeasure structure - Google Patents

Description

  The present invention is a long-period wave reduction measure for reducing long-period waves by installing it inside a marine structure such as a quay, a pier, a seawall and a breakwater in a harbor where ship handling operations etc. are mainly performed. The present invention relates to a structure construction method.

  Conventionally, wave height reducing structures installed on breakwaters, coasts, etc., are provided with wave-dissipating blocks stacked on the front (sea side) of the structure (see, for example, Patent Document 1) A so-called slit caisson (see, for example, Patent Document 2) is known.

  The wave-dissipation by the wave-dissipating work is a structure in which wave-dissipating blocks are stacked on the front part of the structure to form the wave-dissipating work, and energy is lost when the wave passes through the wave-dissipating work. . On the other hand, the wave height reducing structure composed of slit caisson includes a shielding wall 10 in which a plurality of longitudinal slit-shaped through holes 10a are formed as shown in FIG. 11, and when the wave passes through the through-hole 10 a, the wave energy loss is caused to quench the wave.

In this slit caisson, the attenuation of wave energy increases as the flow velocity at the time of passing through the through hole 10a of the shielding wall 10 increases. In this slit caisson, as shown in FIG. 9, the incident wave λ1 from the front surface side of the shielding wall 10 overlaps with the reflected wave λ2 reflected by the innermost reflecting surface 12 of the water reserving part 2, and the back of the water reserving room Overlapping waves that form an antinode are formed on the reflecting surface, and the horizontal speed of the node a portion of the overlapping waves is maximized. Therefore, the wave energy can be attenuated most by setting the depth B of the water retentive unit 2 so that the position of the through hole 10a becomes the node a position where the horizontal velocity is maximum, and the wave energy advances to the front of the slit caisson. By installing a shielding wall at a position (B / L = 0.25) that is ¼ of the wavelength L of the incoming wave, the horizontal velocity of the overlapping wave passing through the slit is maximized, and the highest quenching It is known that an effect can be obtained.

  On the other hand, a wave that strikes from the sea side includes a long-period wave along with a normal wave, and this long-period wave has a period of a few tens of seconds to a few minutes. When entering the harbor, this long-period wave is reflected multiple times depending on various conditions such as the shape of the harbor and the position of the quay, and the ship touching the quay may be greatly shaken, which may hinder cargo handling work. In addition, damage such as the mooring line that moored the ship is cut off has occurred.

  In particular, when a large ship (tens of thousands to hundreds of thousands DWT) is moored using a mooring line made of a synthetic fiber having a high breaking strength, the ship's natural period of sway is tens of seconds to several minutes. Since the natural period of the sway and the period band of the long-period wave coincide, they both resonate and greatly shake the hull.

  For this reason, there is a demand for countermeasures for quenching or reducing long-period waves. However, since long-period waves have a long wavelength of several hundred m to several km, the above-described conventional extinction using a quenching block or slit caisson is required. In order to obtain a sufficient wave-dissipating effect by countermeasures against waves, it is necessary to use a large-scale structure having a depth of 100 m or more for the water reclaiming section and the wave-dissipating work, and there is a problem that the feasibility is poor.

  As means for reducing this long-period wave, a long-period wave reduction countermeasure structure having the structure shown in FIGS. 10 and 11 has been developed (Patent Document 3).

  The structure shown in FIG. 10 includes a so-called double-sided slit caisson 3 in which a shielding wall 1 and 2 each having a slit-shaped water-permeable hole are provided on the sea side and the land side, and the back side of the slit caisson 3 is backed. It has a structure in which a stone layer 4 in which large stones are laminated as a material is provided.

  Further, the structure shown in FIG. 11 includes a water permeable portion 5 having a slit-like opening 5a on the sea side, a water reserving portion 7 disposed on the back side (land side) with a side partition wall 6 therebetween, and a water permeable portion. A water-absorbing material layer 8 made of crushed stone and the like stacked in the portion 5, and the water-permeable portion 5 and the water retentive portion through the water-permeable holes 6 a formed in the side partition wall 6 as the water level in the water-permeable portion 5 varies. 7, water enters and exits, and water level fluctuations at the sea side of the permeable portion 5 are suppressed.

  10 and 11 are effective for reducing the long-period wave of the offshore structure, but both require a depth of about 50 m in order to obtain a sufficient wave-reducing effect. There is a problem that it is difficult to make a smaller structure. In addition, it is conceivable that conventional structures with long-period wave reduction measures are constructed by a method such as using a precast concrete structure or the like, and sinking to a harbor or a revetment. For this reason, the process of manufacturing a structure and the process of installing this in the field are required, and there are problems such as a yard for manufacturing the structure, and time and cost for manufacturing.

  Therefore, the present inventors, as a long-period wave reduction countermeasure structure that can solve such problems, as shown in FIG. 1, on the inner surface of a marine structure 20 such as a ship berthing quay, a breakwater, and a seawall in a harbor. , A front wall 21 that recedes toward the back side, and a slit-shaped water passage 24 having an opening ratio of 1 to 3% is opened on the front wall, and the water reserving section communicated with the rear of the water passage 24 A long-period wave reduction countermeasure structure with 25 is developed.

Unlike the conventional slit caisson described above, the mechanism of long-period wave energy attenuation by this long-period wave reduction countermeasure structure is different from the conventional slit caisson described above, as shown in FIGS. 12 (a) to 12 (c). The energy is consumed by the vortex generated by the drop and the horizontal spread after the wave passes, and it has been confirmed by experiments that the effects of long-period waves can be sufficiently reduced even at a small scale. It was.
JP 2000-204528 A JP 2002-146746 A Japanese Patent Laid-Open No. 2005-42528

  However, when designing the long-period wave reduction countermeasure structure as shown in FIG. 1 described above, the method for determining the depth B of the water retentive part 2 in the conventional slit caisson shown in FIG. 8, that is, as shown in FIG. The technique of reflecting energy by the reflection surface 3 at the back of the room and reducing the energy by the slit at the position of the overlapping wave node having the largest horizontal flow velocity cannot be applied because the mechanism of wave energy consumption is different.

  In addition, long-period waves cause problems such as hull swaying at ports throughout the country, and the period of problematic long-period waves varies depending on the shape of the port and the mooring vessel. Furthermore, it has been confirmed in the past experiments that the long-wave wave has a long period (wavelength is long) and the wave-dissipating performance of the countermeasure structure is reduced. If the period is long (wavelength is long), It has been confirmed that the reflectivity decreases when the structure width (depth of the water reclaiming part) is increased.

  Thus, since the period of the long-period wave which becomes a problem changes with harbors, there existed a problem that the optimal structure width | variety of a long-period wave countermeasure structure could not be determined uniquely.

  Therefore, when determining the optimum depth (B) for each wave-dissipating performance of the long-period wave countermeasure structure, it is desirable to determine the size of the structure by conducting a hydraulic model experiment. However, facilities with long water tank lengths that can generate long-period waves are limited, and long-period waves have long wavelengths, and it is difficult to generate waves with high accuracy.

  For example, in the case of a wave with a depth of 10 m and a period of 60 s, even if the scale is 1/50, the wavelength of the laboratory scale is 12 m, and even if a 50 m long water tank is used, the effective wave number is about 3 to 4 waves. is there. There are limited facilities that can generate long-period waves with high accuracy and experiment with a length of about 50m, and the depth B of the structure by experiment for each target long-period wave reduction countermeasure area such as the target harbor or revetment. There was a problem that it was difficult to determine.

  In view of such conventional problems, the present invention does not conduct experiments for each target long-period wave reduction countermeasure area such as a target port or revetment, and the wavelength of a long-period wave peculiar to the target port or revetment The purpose was to provide a method for constructing a long-period wave reduction countermeasure structure that can construct a long-period wave reduction countermeasure structure having the optimum depth of the recreational part by determining the required wave-absorbing performance (reflectance). It is.

  In view of the conventional problems as described above, the present inventors have conducted extensive research, and have used the relationship between the reflectance Kr and the structure width B / wavelength L obtained in advance through experiments, and the structure suitable for the conditions of the target harbor and quay. The knowledge that determining the object width is an effective means was obtained, and when the relationship between the structure width B / wavelength L and the reflectance Kr was obtained by experiments, the highest wave extinction performance was obtained at B / L = 0.07. Based on this, the present invention has been completed.

Thus, in order to solve the above-mentioned conventional problems and achieve the intended purpose, the invention according to claim 1 is characterized in that a front wall facing the inside of a harbor and a space behind the front wall are provided. A rear wall disposed between the two walls as a water reserving part, a slit-shaped water passage opening in the vertical direction is opened in the front wall, and the water reserving part is communicated behind the water passage, When constructing a long-period wave reduction countermeasure structure configured to reduce a long-period wave having a period of 30 s or more generated in a harbor, the distance between the front wall and the rear wall of the long-period wave reduction countermeasure structure The depth (B) when the depth is (B), the wavelength of the long-period wave wavelength is (L), and the long-period wave reflectivity of the long-period wave reduction countermeasure structure is (Kr ) The relationship between the ratio (B / L) of the wavelength of the long-period wave (L) and the reflectance of the long-period wave and (Kr) Advance determined by fit experiments, select the long-period waves of wavelengths of harbor reduction measures target to be placed the long periodic wave reduction measures structures fact, the length to be obtained with respect to the long periodic wave The depth (B) of the water retentive part corresponding to the periodic wave reflectivity (Kr) is to be determined using the results of the experiment .

The feature of the invention described in claim 2 is that, in addition to the configuration of claim 1, the long-period wave reflectivity (Kr) with respect to the ratio (B / L) of the long-period wave wavelength (L) to the depth (B). The experiment for obtaining the relationship is performed by installing a model in a two-dimensional water tank and measuring the long-period wave reflectivity (Kr) for each experiment case in which the water depth, the wavelength of the long-period wave, and the depth of the water retentive part are changed. There is.

  The feature of the invention described in claim 3 is that, in addition to the configuration of claim 1 or 2, the front wall is formed with a recess that recedes toward the ridge side for each water passage. In addition, the water inlet is open at a position on the heel side.

The construction method of a long-period wave structure according to the present invention includes a front wall facing the inside of a harbor and a rear wall that is installed behind the front wall with a space therebetween, and the wall between the two walls serves as a basin. A longitudinal slit-shaped water passage opening is formed in the front wall, and the water recirculation part is communicated behind the water passage so as to reduce a long-period wave having a period of 30 s or more generated in the harbor. In constructing the periodic wave reduction countermeasure structure , the depth which is the distance between the front wall and the rear wall of the long periodic wave reduction countermeasure structure is (B), and the wavelength of the long periodic wave wavelength is (L). In addition, the ratio (B / L) of the depth (B) to the wavelength (L) of the long period wave and the long period wave reflection when the long period wave reflectivity of the long period wave reduction countermeasure structure is Kr. leave obtained in advance by experiments the relation between the rate (Kr), actually setting the long-period wave reduction measures structure Select the long-period wave of the wavelength to be targeted for reduction of the port to be reduced, and set the depth (B) of the water retentive part corresponding to the long-period wave reflectance (Kr) to be obtained for the long-period wave. By determining using the result of the experiment, the wavelength of the long-period wave peculiar to the port , and the necessary, without performing the experiment for each port where the long-period wave reduction countermeasure structure is actually installed by determining the wave dissipating performance (reflectance), long period wave reduction measures structure depth optimal retarding unit can be constructed.

  Further, the front wall facing the sea side is formed for each water inlet to form a recessed part that recedes toward the reed, and the water is pushed to the front wall by providing the water reflow opening at the position on the reed side. The energy loss of the waves that are led to the water inlet and flowed into the water reserving section increases, and an effective wave-dissipating effect is obtained for long-period waves.

  Next, an embodiment of a long-period wave reduction countermeasure structure according to the present invention will be described with reference to the drawings.

  An example of a long-period wave reduction countermeasure structure to be constructed according to the present invention will be described with reference to FIGS. The long-period wave reduction countermeasure structure 20 shown in FIG. 1 has a front wall 21 facing the sea side that receives long-period waves, side partition walls 22 and 22 on both sides, and a rear-side wall 23 on the land side. In addition, the front wall 21 has a vertically long and narrow slit-shaped water passage 24, and a back portion of the water flow port 24 is a water reserving portion 25 communicating with the water flow port 14.

  The water reserving part 25 is surrounded by a peripheral wall made up of side partition walls 22, 22 and a rear wall 23, and the front wall 21 serves as a side partition wall that separates the sea side from the water reclaiming part 25. A plurality of water retentive portions 25, 25... Are continuously formed laterally across the side partition wall 22.

  The front wall 21 is provided with a recess 26 that recedes toward the ridge side for each water passage 24, and the water passage 24 is opened at a position on the heel side. The water inlet 24 is formed in a length that extends from the sea bottom to a position higher than the highest peak height of a normal long-period wave, and when the long-period wave enters and exits the water-reserving part 25 from the water outlet 24, The air is opened so as to reach a height at which the air in 25 can sufficiently enter and exit.

  In the illustrated example, the water outlet 24 is provided at the center of the front wall 21, but the water outlet 24 may be provided close to the side partition wall 22.

  Moreover, the slit width of the water inlet 24 is such that the opening ratio with respect to the front wall 21 of the water reserving part 25 is about 1 to 3%, for example, when the horizontal length of the front wall 12 of one water reserving part 25 is 30 m. The width is 0.5 m to 1.0 m.

  Furthermore, the long-period wave reduction countermeasure structure to be constructed according to the present invention is provided with a large number of water-reserving sections partitioned by the side partition walls 22 as shown in FIG. 1, but as shown in FIG. It may be continuous without a side partition wall between the front wall 21 and the rear wall 22.

  The construction may be such that each of the walls 21, 22, and 23 is made of cast-in-place concrete, and the walls may be constructed by placing sheet piles and piles side-by-side, and not shown. What is formed in a caisson shape integrally with the bottom plate may be installed on the bottom of the water. Moreover, you may make the rear surface wall 22 have a seawall, a quay wall, and other structures in a harbor itself. Further, as shown in FIG. 4, the front wall 21 may be provided with a water passage 24 on a flat surface without providing the recess 26.

Next, since the long-period wave reduction countermeasure structure described above can achieve the most appropriate long-period wave reduction effect in accordance with the characteristics of the target long-period wave reduction countermeasure area such as the target port or seawall. The construction method of will be described. In this method, the form of the long-period wave reduction countermeasure structure described above is determined in advance, and the long-period wave wavelength (L) , the front wall, and the rear wall , which are the characteristics of the long-period wave reduction countermeasure structure, are determined in advance through experiments. The relationship between the long-period wave reflectance Kr and the ratio (B / L) to the depth B of the water reserving part, which is the interval between the long-period wave and the long-period wave reduction countermeasure structure, is obtained in advance through experiments. In the installation target port to be installed, the depth (B) of the water retentive unit corresponding to the wavelength of the long period wave to be reduced and the long period wave reflectivity Kr to be obtained is determined.

First, the ratio of the initially desired depth of retarding section is the spacing of the long periodic wave wavelength is a characteristic of the above-described long period wave reduction measures structure (L) and the front wall and the rear wall (B) (B / L) An experiment for obtaining in advance the relationship of the long-period wave reflectivity with respect to is described.

The long-period wave reduction effect by the long-period wave reduction countermeasure structure, that is, the reflectance is measured by changing the water depth h, the long-period wave period T, and the depth B of the water retentive part.

  For this measurement, as shown in FIG. 5, a two-dimensional water tank is used, and a model comprising a front wall 21 having a water passage 25 in the water tank and a rear wall 22 installed behind the water retentive unit 25 is installed. This is done by experiment.

  Next, the experimental example will be specifically described.

  The two-dimensional water tank used in the experiment has a length of 50 m, a width of 60 cm, and a depth of 1.2 m, and a wave making device is installed on the offshore side. The experimental scale was 1/50. All subsequent figures are on a local scale.

The long-period wave reduction countermeasure structure model was manufactured by installing the front wall 21 and the rear wall 22 (water guide plate) shown in FIG. The structure model dimensions are as shown in Table 1, and the depth B of the water retentive part is 2 cases of 25 m and 30 m.

上記２次元水槽において、表２に示す周期の規則波を造波させ、水深を８ｍ，１０ｍ，１５ｍと変化させた。表３に示す実験ケースについて実験し、これにより幅広い波長のデータを取得した。尚、遊水部の奥行き２５ｍの模型を使った実験に関しては、水深７ｍについての実験も行った。 table 1

In the two-dimensional water tank, a regular wave having a period shown in Table 2 was generated, and the water depth was changed to 8 m, 10 m, and 15 m. Experiments were conducted on the experimental cases shown in Table 3, and data for a wide range of wavelengths were acquired. In addition, regarding the experiment using the model with a depth of 25 m in the water reserving part , an experiment was also performed for a water depth of 7 m.

  The water level in front of the front wall 21 was recorded on a laboratory scale at a sampling frequency of 20 Hz and for 300 seconds from the start of wave generation. The reflectivity of the long-period wave countermeasure structure was calculated by the incident reflection separation estimation method by Goda et al.

表３

この実験による水深と反射率の関係は図６に示すごとくであった。遊水部の奥行き２５ｍと３０ｍの結果を比較すると，周期の長い６０ｓ，９０ｓでは幅３０ｍで反射率が小さく消波性能が高いことが確認できたが，周期３０ｓではその違いは確認されなかった。また，周期６０ｓ，９０ｓでは水深が大きくなると波長が大きくなるため反射率が大きくなる傾向が現れている。 Table 2

Table 3

The relationship between the water depth and the reflectivity in this experiment was as shown in FIG. Comparing the results of the depths of 25 m and 30 m of the water retentive part, it was confirmed that the 60s and 90s with a long period had a width of 30 m, a low reflectance and a high wave-absorbing performance, but the difference was not confirmed at a period of 30s. In addition, in the periods of 60 s and 90 s, as the water depth increases, the wavelength increases and the reflectance tends to increase.

From the result of the above experiment, the relationship between the long-period wave reflectivity and the ratio (B / L) between the long-period wave wavelength (L) and the depth B of the water retentive part, which is the distance between the front wall and the rear wall , is calculated. The graph shown in FIG. 7 was obtained. According to this, a curve in which the reflectance becomes the smallest when B / L is 0.07 to 0.08 is shown.

  Based on the above experimental results, an appropriate length of the depth B of the water reserving part corresponding to the actual target port or revetment is set. That is, an appropriate length of the required depth B of the long-period wave reduction countermeasure structure is selected based on the relationship between the B / L and the reflectance Kr.

  This reflectance is a reflectance required as a countermeasure against long-period waves in the target harbor or revetment. First, the reflectance Kr required in the target harbor or revetment is selected.

  Next, from the graph shown in FIG. 7 of the experimental result, the length (B / L) of the water retentive part depth / long-period wave corresponding to the reflectance Kr is obtained. Further, the long-period wave wavelength L is obtained by the following formula-1 from the water depth h in the target port or the port serving as a revetment and the period T of the long-period wave in question at the port. In the case of a long period wave, Formula-1 can be approximated by Formula-2.

  The depth B of the water reserving part corresponding to this value L is the most suitable value for the target port or the port of the revetment. That is, in FIG. 7, when the reflectance Kr required at the target harbor or revetment is 0.7, B / L is about 0.045, and the long-period wave that needs to be reduced at the harbor. If the wavelength L is 600 m, the appropriate depth B of the water retentive part is B = 0.045 × 600 = 27 m.

In this manner, the long-period wave reflectance Kr, which is a characteristic of the structure, the long-period wave wavelength (L), and the distance between the front wall and the rear wall are experimentally determined in advance for the desired long-period wave reduction countermeasure structure. By calculating the relationship with the ratio (B / L) of the depth B of the irrigation section, that is, the relationship between Kr and B / L, it is a long time to take reduction measures from the target port and revetment conditions. By selecting the wavelength of the periodic wave and the required reflectance (long-period wave reduction rate), the optimum depth of the water-reserving unit can be easily set for each target port and revetment.

It is a perspective view which shows an example of the long period wave reduction countermeasure structure which is going to be constructed | assembled by the method to this invention. It is a longitudinal cross-sectional view same as the above. It is a top view which shows the other example of the long period wave reduction countermeasure structure which is going to be constructed | assembled by the method to this invention. It is a top view which shows the further another example of the long period wave reduction countermeasure structure which is going to be constructed | assembled by the method to this invention. It is a top view of an example of the test water tank used in the present invention. It is a graph which shows the relationship between the water depth and the reflectance of the experiment example in this invention. It is a graph which similarly shows the relationship between a reflectance and a water retentive part depth / long period wave wavelength. It is a perspective view which cuts and shows the conventional slit caisson longitudinally. It is explanatory drawing which shows the energy consumption mechanism of the wave of the slit caisson. It is a longitudinal cross-sectional view which shows the conventional example of a long-period wave reduction countermeasure structure. It is a longitudinal cross-sectional view which shows the other conventional example of a long-period wave reduction countermeasure structure. It is explanatory drawing which shows the energy consumption mechanism of the wave of the long period wave reduction countermeasure structure shown in FIG. 1, (a) is a top view which shows the motion of a near wave, (b) is a top view which shows the motion of a pulling wave, (C) is a top view which shows the motion of a near wave and a pulling wave.

20 long periodic wave reduction measures structure 21 front wall 22 side partition walls 23 after the wall 24 copies Mizuguchi 25 retarding portion depth L long periodic wave wavelength T long period wave period Kr reflected slit width h depth B retarding part of a communication Mizuguchi rate

Claims (3)

It has a front wall facing the inside of the harbor and a rear wall that is installed behind the front wall with a space therebetween. The wall between the two walls serves as a water retentive part, and a longitudinal slit-shaped water inlet is opened in the front wall. Then, in the construction of the long-period wave reduction countermeasure structure that communicates the recreational unit behind the water inlet and reduces a long-period wave having a period of 30 s or more generated in the harbor,
In the long-period wave reduction countermeasure structure , the depth that is the distance between the front wall and the rear wall is (B), the wavelength of the long-period wave wavelength is (L), and the long-period wave reduction countermeasure structure is The relationship between the ratio (B / L) between the depth (B) and the wavelength (L) of the long-period wave and the long-period wave reflectivity (Kr) when the long-period wave reflectivity is (Kr) The long period wave to be obtained for the long period wave by selecting the long period wave having a wavelength to be a countermeasure for reduction of the harbor where the long period wave reduction countermeasure structure is to be actually installed. A construction method of a long-period wave reduction countermeasure structure characterized in that the depth (B) of the water retentive unit corresponding to the wave reflectance (Kr) is determined using the result of the experiment .
Experiments to determine the relationship between the ratio (B / L) for long period wave reflectivity (Kr) and the depth (B) the long period wave wavelength (L) has established a model in a two-dimensional water tank, water depth, the length The construction method of a long-period wave reduction countermeasure structure according to claim 1, wherein the long-period wave reflectivity (Kr) is measured for each experiment case in which the wavelength of the periodic wave and the depth of the water retentive part are changed. The said front wall is formed with the recessed part which recedes toward the eaves side for every water flow opening, The said water flow opening is the claim of any one of Claim 1 or 2 in the position of the eaves side The construction method of the long-period wave reduction countermeasure structure described .

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