Calculation method, piston-type wave-making device, and calculation program

Abstract

To bring the waveform of a wave made in a piston-type wave-making device closer to a target waveform even when a slope simulating a submarine topography is provided on the bottom face of a water tank.SOLUTION: A calculation method (M10) includes: a water level waveform calculation step (S11) of calculating a water-level waveform η0 at a wave-forming plate position, from a target tsunami water-level waveform η at a target position being the depth of water h, the depth of water h, and the depth of water h0 within a movable range of the wave-making plate; and a wave-making displacement calculation step (S13) of calculating wave-making displacement by time-integrating horizontal water particle speed at the wave-making plate position.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a piston-type wave-making device. [Background technology]

[0002] Non-Patent Document 1 describes a piston-type wave-making device (called a self-propelled wave-making flume in Non-Patent Document 1) that includes a tank filled with water to a predetermined depth and having a rectangular shape in a plan view, and a wave-making plate that creates waves with any waveform by moving back and forth within the tank along the long side of the tank. Compared to gate-type wave-making devices (see Patent Document 1, for example), which create waves by moving a gate up and down, piston-type wave-making devices are easier to create waves with any desired waveform. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-009587 [Non-patent literature]

[0004] [Non-Patent Document 1] Akihiro Usui, Shinichi Aoki, Koji Kawasaki, Numerical Study on Arbitrary Wave Generation by a Self-Propelled Wave Maker, Journal of the Japan Society of Civil Engineers, Vol. 73, No. 2, I_234-I-239, 2017. Summary of the Invention [Problem to be solved by the invention]

[0005] One of the motivations for using such a wave-making device to create tsunami-like waves is to create a slope on the bottom of the tank that mimics the actual seabed topography, thereby visualizing the wave motion at different positions of water depth.

[0006] However, Non-Patent Document 1 uses a model in which the water depth is constant throughout the entire water-filled section (see Figure 2 in Non-Patent Document 1). Therefore, if a slope is created on the bottom of the tank to mimic the actual seabed topography, the waveform obtained at a predetermined position (hereinafter referred to as the target position) with a predetermined water depth is unlikely to match the waveform that was previously assumed (hereinafter referred to as the target waveform). Note that Figure 1 in Non-Patent Document 1 shows an image of a piston-type wave-making device in which a slope is formed on the bottom and the water depth is not constant depending on the position. However, Figure 1 is merely an image, and Non-Patent Document 1 does not take into account cases in which a slope is formed on the bottom and the water depth is not constant.

[0007] One aspect of the present invention has been developed in consideration of the above-mentioned problems, and its purpose is to make the waveform of the generated waves in a piston-type wave-making device closer to the target waveform, even when a slope that mimics the seabed topography is provided on the bottom of the water tank. [Means for solving the problem]

[0008] In order to solve the above problems, a calculation method according to one embodiment of the present invention is a calculation method for calculating the wave-generating displacement due to the displacement of a wave-generating plate in a piston-type wave-making device, and includes a water level waveform calculation step of calculating the water level waveform η0 at the wave-generating plate position from the target tsunami water level waveform η at the target position where the water depth is h, the water depth h, and the water depth h0 within the movable range in which the wave-generating plate moves translationally, and a wave-generating displacement calculation step of calculating the horizontal water particle velocity at the wave-generating plate position from the water level waveform η0 and calculating the wave-generating displacement by integrating the horizontal water particle velocity over time.

[0009] In order to solve the above problems, another aspect of the present invention provides a piston-type wave-making device comprising: a water tank filled with water to a predetermined depth and having a rectangular shape in a plan view; a wave-making unit that creates waves with an arbitrary waveform by translating a wave-making board along the long sides of the water tank; and a control unit that calculates the wave-making displacement due to the displacement of the wave-making board position where the wave-making board is located.The control unit comprises a water level waveform calculation unit that calculates the water level waveform η0 at the wave-making board position from the target tsunami water level waveform η at the target position, which is water depth h, the water depth h, and the water depth h0 within the movable range in which the wave-making board moves translationally; and a wave displacement calculation unit that calculates the horizontal water particle velocity at the wave-making board position from the water level waveform η0 and calculates the wave-making displacement from the horizontal water particle velocity.

[0010] The control unit of the piston-type wave-making device according to each aspect of the present invention may be realized by a computer. In this case, a calculation program that causes the computer to operate as each unit (software element) of the control unit to realize the control unit on a computer is also within the scope of the present invention. Also, a computer-readable recording medium on which the calculation program is recorded is also within the scope of the present invention. [Effects of the Invention]

[0011] According to one aspect of the present invention, in a piston-type wave-making device, when the water depth h0 at the wave-making plate position is different from the water depth h at the target position, the waveform of the generated waves can be made closer to the target waveform. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of a cross section along the longitudinal axis of a piston-type wave-making device according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a front view of a wave-making plate provided in the piston-type wave-making device shown in FIG. 1. [Figure 3] FIG. 2 is a block diagram of a control unit provided in the piston-type wave-making device shown in FIG. 1. [Figure 4] Graphs showing water level waveforms at each part of the control unit shown in Figure 3. (a) shows the target tsunami water level waveform given before the start of calculation in the calculation method, (b) is a graph showing the water level waveform at the wave-making board position calculated by the water level waveform calculation unit, and (c) to (e) are graphs showing the water level waveform at the wave-making board position corrected by the wave-making displacement correction unit. [Figure 5] 3(a) and 3(b) are enlarged front views of a first modified example and a second modified example of the wave-making board shown in FIG. 2, respectively. [Figure 6] 10 is a flowchart of a calculation method according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Embodiment 1] <Piston-type wave maker> A piston-type wave-making device 10 according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 5. FIG. 1 is a schematic cross-sectional view of the piston-type wave-making device 10 taken along its longitudinal axis. Therefore, FIG. 1 illustrates only the interior space of the water tank 11 in the piston-type wave-making device 10. FIG. 2 is a front view of the wave-making board 153 included in the piston-type wave-making device 10. FIG. 3 is a block diagram of the control unit 16 included in the piston-type wave-making device 10. FIG. 4 is a graph showing water level waveforms at each step of a calculation method M10 performed by the control unit 16. (a) of FIG. 4 shows the target tsunami water level waveform η given before the start of calculations in the calculation method M10, and (b) of FIG. 4 is a graph showing the water level waveform η0 at the wave-making board position calculated by the water level waveform calculation unit 161. (c) to (e) of FIG. 4 are graphs showing the water level waveform η0 at the wave-making board position corrected by the wave-making displacement correction unit 162. 5(a) and 5(b) are enlarged front views of a first modified example and a second modified example of the wave-making board 153, respectively.

[0014] As shown in FIG. 1, the piston-type wave-making device 10 includes a water tank 11, a seabed model 12, a buffer material 13, water 14, a wave-making unit 15, and a control unit 16.

[0015] (aquarium) The water tank 11 is a rectangular parallelepiped container having a bottom surface 111, a front wall, a rear wall, and a pair of side walls, and is a container filled with water as shown in FIG. 1. The bottom surface 111 is rectangular when viewed from the zenith direction in a plan view. That is, the water tank 11 is rectangular when viewed from the zenith direction in a plan view. The size of the bottom surface 111 (in other words, the planar size of the piston-type wave-making device 10) is not limited, but for example, the length of the long side of the bottom surface 111 is 50,000 mm, and the length of the short side of the bottom surface 111 is 600 mm. FIG. 1 is a schematic diagram of a cross section perpendicular to the bottom surface 111 and parallel to the long side of the bottom surface 111.

[0016] The bottom surface 111 is surrounded on all four sides by a front wall and a rear wall corresponding to a pair of short sides, and a pair of side walls corresponding to a pair of long sides. In the aquarium 11, the height of these walls (in other words, the depth of the interior space) is, for example, 1200 mm. As will be described later, a wave-making board 153 is disposed in the interior space of the aquarium 11. Hereinafter, of the front and rear walls, the wall farthest from the position where the wave-making board 153 is disposed will be referred to as the front wall, and the wall closer to the position where the wave-making board 153 is disposed will be referred to as the rear wall. In FIG. 1, the front wall is located on the left side of the page, and the rear wall is located on the right side of the page. As can be seen from FIG. 1, the front wall is located on the shore side, and the rear wall is located offshore.

[0017] In FIG. 1, the direction parallel to the long side of the bottom surface 111 is defined as the x-axis direction, the direction parallel to the short side of the bottom surface 111 is defined as the y-axis direction, and the direction perpendicular to the bottom surface 111 is defined as the z-axis direction. The direction from offshore to shore in the x-axis direction is defined as the positive x-axis direction, and the direction toward the zenith in the z-axis direction is defined as the positive z-axis direction. The positive y-axis direction is defined so that the positive x-axis direction and the positive z-axis direction form a right-handed Cartesian coordinate system. This method of defining the Cartesian coordinate system is common to FIGS. 1, 4, and 5. Note that in FIG. 1, the structure is enlarged in the z-axis direction to make the shape of the seabed easier to understand. Therefore, the aspect ratio of the structure shown in FIG. 1 does not reflect the actual aspect ratio.

[0018] As shown in Figure 1, the internal space of the water tank 11 is divided into two areas, area 112 and area 113, by a wave-making board 153. Area 112 is an area located on the shore side, and area 113 is an area located offshore.

[0019] (Undersea model) The seabed model 12 is a model created to imitate the shape of the seabed topography. The seabed topography imitated by the seabed model 12 may be either an actual seabed or an imagined seabed. In this embodiment, as shown in FIG. 1, a cross-sectional shape is adopted in which the height is highest at the part in contact with the front wall located on the shore side and decreases toward the offshore side (negative x-axis direction). However, the cross-sectional shape of the seabed model 12 is not limited to this and can be set freely. Note that the cross-sectional shape of the seabed model 12 may include a seabed topography such as an uneven shape in which the height decreases toward the offshore side (negative x-axis direction) and then increases again.

[0020] By fabricating the seabed model 12 configured in this manner in the internal space of the water tank 11, it is possible to reproduce a slope that mimics the seabed topography on the bottom surface 111 of the water tank 11.

[0021] When conducting a wave-making experiment using piston-type wave-making device 10, water 14 is poured into the internal space of water tank 11 to a predetermined height, as shown in Figure 1. Hereinafter, the part of seabed model 12 that is covered by water 14 will be referred to as seabed surface 121, and the part exposed above water 14 will be referred to as land 122.

[0022] (buffer material) The buffer material 13 is a sponge block placed in the area 113. The buffer material 13 is fixed so as to contact the rear wall. When waves are generated using the wave-making board 153 described below, waves propagating in the positive direction of the x-axis are eventually reflected by the surface of the seabed model 12 or the front wall. The buffer material 13 is placed to attenuate the reflected waves propagating in the negative direction of the x-axis.

[0023] The material, shape, size, etc. of the cushioning material 13 are not limited and can be designed as appropriate.

[0024] (Wave making department) 1, wave-making unit 15 includes rails 151, a drive unit 152, and a wave-making board 153. Wave-making unit 15 translates wave-making board 153 in a direction along the long side of bottom surface 111 of water tank 11 (x-axis direction) to make waves having any waveform.

[0025] Rail 151 is a steel columnar member installed above water tank 11. Rail 151 is installed so that its axial direction is parallel to the x-axis direction. Because drive unit 152, which will be described later, moves parallel to the axial direction of rail 151, rail 151 serves as a track for translating wave-making board 153 parallel to the x-axis direction. In this embodiment, as shown in FIG. 2, two rails 151 are used. However, the number of rails 151 is not limited.

[0026] Although not shown in Figures 1 and 2, the driving unit 152 has wheels that rotate by the power of a motor. The wheels are fitted with the rails 151, and when they rotate, they cause the driving unit 152 to translate parallel to the axial direction of the rails 151. In addition, the upper end of a wave-making board 153, which will be described later, is fixed to the driving unit 152 (see Figure 2). In other words, the wave-making board 153 is fixed below the driving unit 152 in a hanging state.

[0027] The motor of the drive unit 152 is driven by a control signal Sc supplied from the control unit 16, which will be described later. Therefore, the position x of the wave-making board 153 fixed to the drive unit 152 is controlled by the control signal Sc. In this embodiment, the position x of the wave-making board 153 is defined by the position of the front main surface (x-axis positive side) of the pair of main surfaces of the wave-making board 153, and is called the wave-making board position.

[0028] The wave-making board 153 is a plate-like member made of steel. The main surface of the wave-making board 153 is rectangular as shown in FIG. 2, with the length of its short side being shorter than the length of the short side of the bottom surface 111 (600 mm in this embodiment) and the length of its long side being longer than the depth of the internal space of the water tank 11 (1200 mm in this embodiment). In this embodiment, the length of the short side of the main surface of the wave-making board 153 is 500 mm. Therefore, a gap b (b = 50 mm in this embodiment) is generated between the long side of the wave-making board 153 and the side wall of the water tank 11 (see FIG. 2). The length of the long side of the main surface is 1300 mm.

[0029] The wave-making board 153 configured in this manner is inserted into the internal space of the water tank 11 so that its main surface is parallel to the yz plane, and is fixed to the driving unit 152. In this embodiment, the wave-making board 153 is fixed to the driving unit 152 so that the gap a between the short side constituting the lower end of the wave-making board 153 and the bottom surface 111 of the water tank 11 is 100 mm.

[0030] Furthermore, the wave-making unit 15 configured in this manner can translate the wave-making board 153 in a direction parallel to the x-axis direction (the direction of arrow A in FIG. 1). As shown in FIG. 1, the wave-making board 153 has a movable range R with a lower limit at position x0 and an upper limit at position x1. That is, the movable range R is an area where the position x satisfies x0≦x≦x1.

[0031] In the following, x = x0 is defined as the starting position of the wave-making board 153. By translating the wave-making board position from the starting position in the positive x-axis direction (toward the shore), the piston-type wave maker 10 creates waves that mimic tsunamis mainly in the area 112 of the water tank 11.

[0032] (Control unit) The control unit 16 calculates the wave-making displacement due to the displacement of the wave-making board position, and controls the translational movement of the actual wave-making board position based on the calculated wave-making displacement. The control unit 16 calculates the wave-making displacement at the wave-making board position so that the water level waveform obtained as a result of wave generation at the target position xt approaches a predetermined target tsunami water level waveform η. The configuration of the control unit 16 is described below.

[0033] As shown in FIG. 3, the control unit 16 includes a water level waveform calculation unit 161, a wave-making displacement correction unit 162, and a wave-making displacement calculation unit 163.

[0034] Tsunami wave heights develop near coasts, in bays, and in topographically confined areas. Therefore, by applying analysis of wave refraction and shoaling, the water level waveform calculation unit 161 calculates the water level waveform η0 (see FIG. 4(b)) at the wave-making board position from the target tsunami water level waveform η at the target position xt (see FIG. 4(a)), the water depth h at the target position xt, and the water depth h0 within the range of translational movement R of the wave-making board. As described above, in one aspect of the present invention, the seabed model 12 may include seabed topography such as unevenness. Therefore, there may be one or more positions (e.g., position x') where the water depth h is equal to the target position xt. Even in this case where there are multiple positions with a given water depth h, one aspect of the present invention can calculate the water level waveform η0 from the target tsunami water level waveform η, the water depth h, and the water depth h0. In such a case, the water level waveform η0 obtained according to one aspect of the present invention is the same at both the target position xt and the position x'.

[0035] According to Green's law, if the width of the water tank 11, i.e., the channel width of the incident wave, is constant, there is no need to consider changes in the channel width. Therefore, the relationship between water depth h, target tsunami water level waveform η, water depth h0, and water level waveform η0 is (η / η0) = (h0 / h). 1 / 4 Or (η / η0)=(h / h0) -1 / 4 Therefore, when an arbitrary target tsunami water level waveform η is given, the water level waveform η0 is given as η0=η / (h0 / h) 1 / 4 Or (η / η0)=(h / h0) -1 / 4 is.

[0036] The wave-making displacement correction unit 162 corrects the amplitude deviation of the water level waveform η0 due to a decrease in wave-making efficiency caused by the outflow of water from the region 112 to the region 113 that occurs near the wave-making plate 153, which is caused by the translational movement of the wave-making plate 153, and generates a corrected water level waveform η01 (see (c) of Figure 4). As described above, gaps a and b exist between the wave-making plate 153 and the bottom surface 111 of the water tank 11. These gaps a and b serve as water flow paths connecting the region 112 and the region 113. Therefore, when the wave-making plate 153 is translated in the positive direction of the x-axis, a difference in water level occurs between the front and rear surfaces of the wave-making plate 153, causing water to outflow from the region 112 to the region 113. This outflow of water acts to reduce the amplitude of the water level waveform of the generated wave (incident wave). Therefore, in order to correct the deviation of the water level waveform η0 caused by the outflow of water, the wave-making displacement corrector 162 corrects the amplitude of the water level waveform η0 in the direction of increasing it.

[0037] In addition to correcting the amplitude deviation due to water outflow, the wave-making displacement correction unit 162 also corrects for shoaling water deformation and the wave-making plate displacement, generating a corrected water level waveform η02 after correcting for shoaling water deformation and a corrected water level waveform η03 after correcting for the wave-making plate displacement. These corrections for shoaling water deformation and wave-making plate displacement can be performed using equations (3) and (11) in Non-Patent Document 1, respectively, with reference to "(3) Summary of Wave-Making Plate Position Calculation Method." Therefore, a description of these corrections will be omitted here. Figures 4(d) and (e) respectively show the corrected water level waveform η02 after correcting for shoaling water deformation and the corrected water level waveform η03 after correcting for the wave-making plate displacement.

[0038] The above-mentioned corrected water level waveforms η01 to η03 are examples of the corrected water level waveform η0fix. The corrected water level waveform η0fix is ​​a general name for the corrected water level waveforms η01 to η03.

[0039] The wave-making displacement calculation unit 163 calculates the horizontal water particle velocity at the wave-making plate position from one of the corrected water level waveforms η0fix (i.e., one of the corrected water level waveforms η01 to η03) generated by the wave-making displacement correction unit 162, and calculates the wave-making displacement from the horizontal water particle velocity.

[0040] More specifically, the wave-making displacement calculation unit 163 calculates the horizontal water particle velocity (i.e., the corrected horizontal water particle velocity ufix) at the wave-making plate position from one of the corrected water level waveforms η0fix (i.e., one of the corrected water level waveforms η01 to η03) generated by the wave-making displacement correction unit 162, and obtains the corrected wave-making displacement in which the deviation has been corrected by integrating the corrected horizontal water particle velocity ufix over time.

[0041] The calculation method for calculating horizontal water particle velocity from the water level waveform, whether corrected or not, and obtaining wave-generating displacement by time-integrating the obtained horizontal water particle velocity is described in "(3) Summary of calculation methods for wave-generating plate position" in Non-Patent Document 1. Therefore, a description of these calculation methods will be omitted here.

[0042] The control unit 16 calculates the wave-making displacement using either the corrected water level waveform η0fix, so it is possible to obtain a corrected wave-making displacement in which at least the deviation in the amplitude of the water level waveform η0 caused by water outflow is corrected. However, it is preferable to use the corrected water level waveform η02 rather than the corrected water level waveform η01, and it is preferable to use the corrected water level waveform η03 rather than the corrected water level waveform η02. By using the corrected water level waveform η03, the waveform of the generated waves can be made closer to the target waveform than when the corrected water level waveforms η01 and η02 are used.

[0043] Here, the corrected horizontal water particle velocity ufix is ​​expressed by equation (1), where a is the gap between the bottom surface 111 and the wave-making board 153 in the section where the wave-making board 153 moves translationally (i.e., the movable range R), g is the gravitational acceleration, and Cc is a predetermined coefficient. Furthermore, equation (1) shows the case where the corrected water level waveform η03 is used as the corrected water level waveform η0fix.

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[0044] Tsunamis have a very long wavelength L because they occur over a wide area of ​​the ocean. Tsunamis occur under the boundary condition that the water depth h is very shallow relative to the wavelength L. Therefore, since tsunamis satisfy the relative water depth h / L < 1 / 20, they can be treated as so-called long waves. It is known that in long waves, the velocity at the wave-making plate location, which is parallel to the translational direction (horizontal water particle velocity), and the wave-making plate velocity are equal. This relationship holds regardless of whether or not the deviation due to water outflow is compensated for, so the corrected horizontal water particle velocity and the corrected wave-making plate velocity are equal. As described in Non-Patent Document 1, the wave-making plate velocity is obtained by time-differentiating the wave-making displacement per unit time at the wave-making plate location. Therefore, the wave-making displacement corrected for the deviation due to water outflow can be obtained by time-integrating the corrected wave-making plate velocity (i.e., the corrected horizontal water particle velocity).

[0045] (Software implementation example) The functions of the piston-type wave-making device 10 (hereinafter referred to as the "device") can be realized by a program that causes a computer to function as the device, and a program that causes a computer to function as each control block of the device (particularly the water level waveform calculation unit 161, the wave-making displacement correction unit 162, and the wave-making displacement calculation unit 163 included in the control unit 16).

[0046] In this case, the device includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., a memory) as hardware for executing the program. The control device and storage device execute the program, thereby realizing the functions described in each of the above embodiments.

[0047] The program may be non-transitory and may be recorded on one or more computer-readable recording media. The recording media may or may not be included in the device. In the latter case, the program may be supplied to the device via any wired or wireless transmission medium.

[0048] Furthermore, some or all of the functions of the control blocks can be realized by logic circuits. For example, an integrated circuit in which a logic circuit that functions as each of the control blocks is formed is also included in the scope of the present invention. In addition, the functions of the control blocks can also be realized by, for example, a quantum computer.

[0049] (Modified wave-making board) As shown in Figure 2, gaps a and b are formed between wave-making board 153 and bottom surface 111 and side wall of water tank 11, respectively. This reduces the possibility that wave-making board 153 will come into contact with or get caught on bottom surface 111 and side wall of water tank 11 when making waves. On the other hand, gaps a and b serve as water flow paths connecting area 112 and area 113. As mentioned above, these flow paths are likely to cause deviations in the amplitude of the water level waveform η0 due to water outflow.

[0050] Therefore, when a gap is provided between the short side, which is the lower end of the wave-making board 153, and the bottom surface 111 (see FIG. 5(a)), it is preferable to provide a sealing member 154 at the lower end of the wave-making board 153. The sealing member 154 is configured to fill the gap a. Therefore, as shown in FIG. 5(a), the gap a can be made zero.

[0051] Even when the sealing member 154 is added to the wave-making board 153 in this way, the gap b remains between the long side of the wave-making board 153 and the side wall of the water tank 11. Even in such a case, the control unit 16 can optimize the value of the coefficient Cc to make the waveform of the waves generated at the position of the wave-making board even closer to the target waveform at the target position xt.

[0052] Furthermore, when it is desired to close gap b in addition to gap a, it is preferable to provide sealing members 154A on both the short side, which is the lower end of wave-making board 153, and on the long side of wave-making board 153 so as to fill both gaps, as shown in Figure 5(b). With this configuration, it is possible to further suppress the outflow of water from region 112 to region 113.

[0053] The material constituting the sealing member 154 and the sealing member 154A is preferably a material that has a smaller coefficient of friction with the bottom surface 111 than the material (steel in this embodiment) constituting the lower end of the wave-making plate 153. An example of such a material is fluororesin (polytetrafluoroethylene, PTFE).

[0054] An intermediate layer made of an elastic material may be provided between the wave-making board 153 and the sealing members 154, 154A. This configuration reduces the possibility that the wave-making board 153 and the sealing members 154, 154A will get caught on the inner wall of the water tank 11, while making it easy to reduce at least one of the gaps a and b to nearly zero (zero in this embodiment).

[0055] [Embodiment 2] A calculation method M10 according to the second embodiment of the present invention will be described with reference to Fig. 6. Fig. 6 is a flowchart of the calculation method M10.

[0056] Calculation method M10 expresses the configuration of the control unit 16 of the piston wave maker 10 as a calculation method. That is, calculation method M10 is implemented prior to conducting a wave-making experiment using the piston wave maker 10 in order to generate waves at the target position xt that have a waveform with a small deviation from the desired water level waveform (target tsunami water level waveform η). In this embodiment, a description of each component of the piston wave maker 10 will be omitted, and the correspondence between each step of calculation method M10 and each part (each functional block) of the control unit 16 will be explained, followed by a brief description of each step.

[0057] 6, the calculation method M10 includes a water level waveform calculation step S11, a wave-making displacement correction step S12, and a wave-making displacement calculation step S13. The water level waveform calculation step S11, the wave-making displacement correction step S12, and the wave-making displacement calculation step S13 are steps processed by a water level waveform calculation unit 161, a wave-making displacement correction unit 162, and a wave-making displacement calculation unit 163, respectively, which are provided in the control unit 16.

[0058] That is, calculation method M10 is a calculation method for calculating the wave-making displacement due to the displacement of the wave-making plate 153 in the piston-type wave maker 10, in which the water level waveform calculation process S11 calculates the water level waveform η0 at the wave-making plate position from the target tsunami water level waveform η at the target position xt, which is water depth h, the water depth h, and the water depth h0 in the movable range R within which the wave-making plate 153 moves translationally, the wave-making displacement correction process S12 generates a corrected water level waveform η0fix by correcting the deviation in amplitude of the water level waveform η0 caused by the outflow of water that occurs with the translational movement of the wave-making plate 153, and the wave-making displacement calculation process S13 calculates the horizontal water particle velocity (corrected horizontal water particle velocity ufix in embodiments 1 and 2) at the wave-making plate position from the water level waveform η0 corrected in the wave-making displacement correction process S12 (corrected water level waveform η0fix in embodiments 1 and 2), and calculates the wave-making displacement by integrating the horizontal water particle velocity over time.

[0059] In addition, it is preferable that the wave-making displacement calculation step S13 calculates the corrected horizontal water particle velocity ufix from the corrected water level waveform η0fix and time-integrates the corrected horizontal water particle velocity ufix to obtain the corrected wave-making displacement in which the deviation has been corrected. In this embodiment, as in embodiment 1, the corrected water level waveform η03 is used as the corrected water level waveform η0fix.

[0060] Here, the corrected horizontal water particle velocity ufix is ​​expressed by equation (2), where a is the gap between the bottom surface 111 and the wave-making board 153 within the movable range R of the wave-making board 153, g is the gravitational acceleration, and Cc is a predetermined coefficient.

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[0061] [Additional Notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0062] 〔summary〕 In order to solve the above problems, the calculation method according to the first aspect of the present invention is a calculation method for calculating the wave-generating displacement due to the displacement of a wave-generating plate in a piston-type wave-making device, and includes a water level waveform calculation step for calculating the water level waveform η0 at the wave-generating plate position from the target tsunami water level waveform η at the target position where the water depth is h, the water depth h, and the water depth h0 in the movable range within which the wave-generating plate moves translationally, and a wave-generating displacement calculation step for calculating the horizontal water particle velocity at the wave-generating plate position from the water level waveform η0 and calculating the wave-generating displacement by integrating the horizontal water particle velocity over time.

[0063] With the above configuration, the water level waveform η0 at the wave-making plate position is obtained from the target tsunami water level waveform η at the target position, taking into account the target tsunami water level waveform η, water depth h, and water depth h0. The wave-making displacement is then calculated to create waves with the water level waveform η0 at the wave-making plate position. Therefore, this piston-type wave-making device can make the waveform of the generated waves approach the target waveform, even if the bottom of the water tank has a slope that mimics the seabed topography.

[0064] In the calculation method according to the second aspect of the present invention, in addition to the configuration of the calculation method according to the first aspect described above, a wave-making displacement correction process is further included which is carried out after the water level waveform calculation process, and the wave-making displacement correction process is configured to generate a corrected water level waveform η0fix by correcting the deviation of the water level waveform η0 caused by the outflow of water that occurs with the translational movement of the wave-making board.

[0065] In piston-type wave-making devices, there is often a gap, although the size may vary, between the wall of the water tank and the wave-making board. When the water tank is filled with water, this gap functions as a flow path connecting two areas separated by the wave-making board (the area located on the shore side and the area located offshore, based on the position of the wave-making board). Therefore, when waves are generated by translating the wave-making board toward the shore, water flows from the area located on the shore side near the wave-making board 153 to the area located offshore, reducing wave-making efficiency and causing the waveform of the generated waves to deviate from the target waveform. With the above configuration, the difference between water depth h and water depth h0 and the deviation caused by the water outflow are taken into account, allowing the waveform of the generated waves to be closer to the target waveform.

[0066] In the calculation method according to the third aspect of the present invention, in addition to the configuration of the calculation method according to the second aspect described above, the wave-making displacement calculation step calculates a corrected horizontal water particle velocity ufix from the corrected water level waveform η0fix in which the deviation has been corrected in the wave-making displacement correction step, and obtains a corrected wave-making displacement in which the deviation has been corrected by integrating the corrected horizontal water particle velocity ufix over time.

[0067] Here, the corrected horizontal water particle velocity ufix is ​​expressed by equation (3), where a is the gap between the bottom surface and the wave-making plate in the movable range, g is the gravitational acceleration, and Cc is a predetermined coefficient. Note that equation (1) described in embodiment 1 and equation (2) described in embodiment 2 show the case where the corrected water level waveform η03 is used as the corrected water level waveform η0fix. On the other hand, equation (3) does not limit which of the corrected water level waveforms η01 to η03 is used as the corrected water level waveform η0fix.

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[0068] Tsunamis can be treated as so-called long waves because their water depth is very shallow compared to their wavelength. It is known that in long waves, the velocity at the wave-making plate position, which is parallel to the translational direction (horizontal water particle velocity), and the wave-making plate velocity are equal. This relationship holds regardless of whether or not the deviation due to water outflow is compensated for, so the corrected horizontal water particle velocity and the corrected wave-making plate velocity are equal. As described in Non-Patent Document 1, the wave-making plate velocity is obtained by time-differentiating the wave-making displacement per unit time at the wave-making plate position. Therefore, by time-integrating the corrected wave-making plate velocity (i.e., the corrected horizontal water particle velocity), the wave-making displacement corrected for the deviation due to water outflow can be obtained.

[0069] Even when waves are generated based on the corrected wave-making displacement obtained using this calculation method, there is a possibility that the amplitude of the generated waves may deviate from the target waveform. In this case, it is preferable to conduct wave-making experiments using multiple coefficients Cc to identify the deviation for each coefficient Cc and then use the coefficient Cc that produces the smallest deviation. It is also possible to obtain the correlation between the coefficient Cc and the amplitude deviation by conducting the above-mentioned experiments and then use the coefficient Cc that is predicted to produce the smallest deviation.

[0070] The inventors of the present application discovered that even when the same corrected wave-making displacement is used, the deviation varies from one piston-type wave-making device to another due to differences in the configuration of the piston-type wave-making device that actually generates waves. Furthermore, this calculation method assumes that waves are generated after creating a slope on the bottom of the tank that mimics the actual seabed topography. The shape of the slope that mimics the seabed topography often affects the way the deviation occurs. For example, even if the water depth h at the target position is the same, the deviation may vary depending on the slope in the surrounding area including the target position. This calculation method can also use the coefficient Cc as a correction coefficient to minimize such deviation, thereby enabling the waveform of the generated waves to more closely match the target waveform.

[0071] In order to solve the above problems, the piston-type wave-making device 10 according to a fourth aspect of the present invention is a piston-type wave-making device 10 comprising: a water tank filled with water to a predetermined depth and having a rectangular shape in a plan view; a wave-making unit 15 that creates waves having an arbitrary waveform by translating a wave-making board 153 along the long side of the water tank; and a control unit 16 that calculates the wave-making displacement due to the displacement of the wave-making board position where the wave-making board 153 is located.The control unit 16 comprises a water level waveform calculation unit that calculates the water level waveform η0 at the wave-making board position from the target tsunami water level waveform η at the target position xt, which is water depth h, the water depth h, and the water depth h0 within the movable range in which the wave-making board 153 translates; and a wave displacement calculation unit 163 that calculates the horizontal water particle velocity at the wave-making board position from the water level waveform η0 and calculates the wave-making displacement from the horizontal water particle velocity.

[0072] In the piston-type wave-making device of the fifth aspect of the present invention, in addition to the configuration of the piston-type wave-making device 10 of the fourth aspect described above, the control unit 16 further includes a wave-making displacement correction unit 162 that generates a corrected water level waveform η0fix by correcting the deviation of the water level waveform η0 caused by the outflow of water that occurs with the translational movement of the wave-making plate 153.

[0073] In the piston-type wave-making device 10 according to the sixth aspect of the present invention, in addition to the configuration of the piston-type wave-making device according to the fifth aspect described above, the wave-making displacement calculation unit 163 calculates the corrected horizontal water particle velocity ufix from the corrected water level waveform η0fix in which the deviation has been corrected in the wave-making displacement correction unit 162, and obtains the corrected wave-making displacement in which the deviation has been corrected by integrating the corrected horizontal water particle velocity ufix over time.

[0074] Here, the corrected horizontal water particle velocity ufix is ​​expressed by equation (4), where a is the gap between the bottom surface and the wave-making plate 153 within the movable range, g is the gravitational acceleration, and Cc is a predetermined coefficient. Note that, similar to equation (3), equation (4) does not limit which of the corrected water level waveforms η01 to η03 is used as the corrected water level waveform η0fix.

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[0075] The piston type wave-making devices 10 according to the fourth to sixth aspects each have the same effects as the calculation methods according to the first to third aspects described above, respectively.

[0076] In the piston-type wave-making device 10 according to the seventh aspect of the present invention, in addition to the configuration of the piston-type wave-making device 10 according to any one of the fourth to sixth aspects described above, a gap is provided between the lower end of the wave-making board 153 and the bottom surface of the tank, and a sealing member is provided at the lower end to fill the gap, and the material constituting the sealing member is made of a material that has a smaller coefficient of friction with the bottom surface than the material constituting the lower end.

[0077] With the above configuration, the cross-sectional area of ​​the flow path can be reduced, which reduces the outflow of water that can occur when waves are generated, from an area located on the shore side of the wave-making board 153 to an area located offshore from the wave-making board 153. This increases the conversion efficiency when converting the translational movement of the wave-making board 153 into waves. In other words, the energy efficiency of the piston-type wave-making device can be increased, and a target tsunami water level waveform η at the target position xt can be generated.

[0078] Furthermore, depending on how the sealing member is provided, the outflow of water described above can be reduced to a negligible level. If the outflow of water described above is negligible, the configuration of the control unit can be simplified.

[0079] The control unit 16 of the piston wave maker according to each aspect of the present invention may be realized by a computer. In this case, the calculation program for the piston wave maker 10 is a calculation program that causes the computer to operate as each unit (software element) of the control unit 16, thereby realizing the control unit. The calculation program is also within the scope of the present invention. A computer-readable recording medium on which the calculation program is recorded is also within the scope of the present invention. [Explanation of symbols]

[0080] 10 Piston-type wave maker 11 Aquarium 111 bottom 12 Undersea model 121 Seabed (slope) 122 Land 13 Cushioning material 14 water 15 Wave making section 151 Rail 152 Drive unit 153 Wave board 154,154A Sealing material 16 Control Unit 161 Water level waveform calculation section 162 Wave-making displacement correction section 163 Wave displacement calculation section

Claims

1. A calculation method for calculating wave displacement due to the displacement of a wave-making plate in a piston-type wave-making device, comprising: a water level waveform calculation step of calculating a water level waveform η0 at the position of the wave-making board from a target tsunami water level waveform η at a target position where the water depth is h, the water depth h, and the water depth h0 within the movable range in which the wave-making board translates; and a wave displacement calculation step of calculating the horizontal water particle velocity at the wave-making plate position from the water level waveform η0 and calculating the wave displacement by integrating the horizontal water particle velocity over time.

2. The method further includes a wave-making displacement correction step performed after the water level waveform calculation step, The wave-making displacement correction step generates a corrected water level waveform η0fix by correcting a deviation of the water level waveform η0 caused by the outflow of water that occurs with the translational movement of the wave-making board. The calculation method of claim 1 .

3. The wave-making displacement calculation step calculates a corrected horizontal water particle velocity ufix from the corrected water level waveform η0fix, and obtains a corrected wave-making displacement in which the deviation has been corrected by time-integrating the corrected horizontal water particle velocity ufix. The calculation method according to claim 2. Here, the corrected horizontal water particle velocity ufix is ​​expressed by equation (1), where a is the gap between the bottom surface and the wave-making board in the movable range, g is the gravitational acceleration, and Cc is a predetermined coefficient. [Equation 1]

4. A piston-type wave-making device comprising: a water tank filled with water to a predetermined depth and having a rectangular shape in a plan view; a wave-making unit that creates waves having an arbitrary waveform by translating a wave-making board along the long side of the water tank; and a control unit that calculates wave-making displacement due to displacement of the wave-making board position where the wave-making board is located, The control unit a water level waveform calculation unit that calculates the water level waveform η0 at the wave-making board position from the target tsunami water level waveform η at the target position where the water depth is h, the water depth h, and the water depth h0 within the movable range in which the wave-making board translates; A piston-type wave-making device comprising: a wave-making displacement calculation unit that calculates the horizontal water particle velocity at the position of the wave-making plate from the water level waveform η0 and calculates the wave-making displacement from the horizontal water particle velocity.

5. The control unit further includes a wave-making displacement correction unit that generates a corrected water level waveform η0fix by correcting a deviation of the water level waveform η0 caused by water outflow that occurs with the translational movement of the wave-making board.

5. The piston type wave making device according to claim 4.

6. The wave-making displacement calculation unit calculates a corrected horizontal water particle velocity ufix from the corrected water level waveform η0fix, and obtains a corrected wave-making displacement in which the deviation has been corrected by time-integrating the corrected horizontal water particle velocity ufix.

6. The piston-type wave-making device according to claim 5. Here, the corrected horizontal water particle velocity ufix is ​​expressed by equation (2), where a is the gap between the bottom surface of the wave-making board and the wave-making board when the board is in the movable range, g is the gravitational acceleration, and Cc is a predetermined coefficient. [Equation 2]

7. A gap is provided between the lower end of the wave-making board and the bottom surface of the water tank, a sealing member provided at the lower end and filling the gap; The piston-type wave-making device according to any one of claims 4 to 6, wherein the material constituting the sealing member is made of a material having a smaller coefficient of friction with the bottom surface than the material constituting the lower end portion.

8. A calculation program for causing a computer to function as the control unit of the piston-type wave-making device according to claim 4, the calculation program causing a computer to function as the water level waveform calculation unit and the wave-making displacement calculation unit.

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