CN111368429A - Method for confirming influence of terrain change on narrow slit resonance - Google Patents
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Abstract
The invention belongs to the field of ocean engineering, and particularly relates to a method for confirming influence of terrain change on narrow slit resonance.
Description
Technical Field
The invention belongs to the field of ocean engineering, and particularly relates to a method for confirming influence of terrain change on narrow slit resonance.
Background
In recent years, with the continuous promotion of ocean engineering, the application of ocean floating structures is increasingly widespread. When these floating structures are arranged side by side/adjacent to each other, the gaps between the floating structures may be small narrow slits with respect to the structures themselves in terms of dimension. Under certain wave frequency conditions, severe fluid oscillation occurs in narrow micro-gaps between structures, and narrow gap resonance (gap resonance) is generated. The oscillation not only has great influence on the local stress of the structure, but also has great influence on the overall performance of the structure; the loading and unloading efficiency of the structure is seriously influenced, and even the safety of engineering operation is threatened. Therefore, the study of narrow slit resonance has attracted an increasing attention.
The existing narrow slit resonance research is mainly carried out based on the classical linear potential flow theory. However, such studies tend to significantly overestimate the height of the resonant wave within the narrow gap, and thus the wave loading of the structure. In order to solve this problem, researchers have adopted some special numerical processing methods, but the existing processing methods always have unknown dissipation coefficients (discrete coefficients), and the existing processing methods must be calibrated by experimental data.
In addition, the conventional studies on the narrow gap resonance have mainly focused on the fluid resonance between a plurality of fixed/floating structures, and the narrow gap resonance between a large ship and a dock has been rarely studied. In the study of the resonance of a narrow gap between a ship and a dock, the seabed is also set to be a flat structure. In fact, the landform of the port is often uneven, and the water depth in front of the port also changes obviously according to the difference of the landform, and the factors can influence the narrow slit resonance. However, the existing research methods fail to take the above factors into consideration.
In conclusion, the research method comprehensively considering the influence of the terrain change on the narrow slit resonance has important practical significance.
Disclosure of Invention
The invention aims to provide a research method for confirming the influence of terrain change on wave load.
In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows: a research method for confirming influence of terrain change on wave load comprises the following steps:
(1) establishing a numerical value wave water tank, wherein a square box is arranged in the numerical value wave water tank to simulate a ship, and 1 numerical value wave water tank is used as a structural unit; forming an incident wave at a boundary of the numerical wave water trough;
(2) establishing a mass conservation and momentum conservation control equation of water and air;
(3) using a scalar field α to represent the volume fraction of water in the calculation unit, wherein the volume fraction is water when the volume fraction is 1, the volume fraction is air when the volume fraction is 0, and the intermediate value between 1 and 0 is the mixture of air and water;
(4) discretizing the time derivative;
(5) and obtaining the wave load on the square box through the pressure and the shear stress of each time step on the surface of the square box.
Preferably, in the step (1), the velocity at the boundary of the entrance of the incident wave is designated as the velocity of the regular wave, and the pressure gradient at the boundary is set to 0.
Preferably, a relaxation zone is provided adjacent to the inlet boundary.
Preferably, the boundary condition of the upper part of the numerical wave water tank is set as 'air'; and adopting a 'no-slip' boundary condition on the right side and the bottom edge of the numerical wave water tank and the wall surface of the tank body.
Preferably, the mass conservation and momentum conservation control equation in step (2) is as follows:
wherein the content of the first and second substances,
represents a gradient operator; u ═ u, v, w, and representsA fluid motion velocity vector; x ═ x, y, z, representing a cartesian coordinate vector; t represents time; ρ represents the fluid density; p represents the hydrodynamic pressure; g represents the gravitational acceleration; μ represents hydrodynamic viscosity; sigmatDenotes the surface tension coefficient, kαRepresenting the surface curvature.
Preferably, the formula for calculating α distribution in step (3) is:
wherein u isr＝uwater-uairRefers to the relative velocity between air and water.
Preferably, the discretization method of the time derivative in the step (4) is as follows:
the gradient condition is estimated by Gaussian integration in a control volume VPConsider the integral transformation of phi:
wherein, VPRepresenting the volume of the cell;
the gaussian integration method is based on linear interpolation from the center of the building block to the surface of the building block, and the divergence term is calculated from the specific format of gaussian convection.
Preferably, the method for obtaining the wave load on the square box in the step (5) comprises the following steps:
1) placing the square box in front of a vertical wall, and arranging an inclined slope below the square box;
2) generating regular waves with different frequencies and incident wave heights at the inlet boundary of the incident wave;
3) by using Open
A built-in grid generation tool which discretizes the numerical wave water tank of the figure 1;
4) and adjusting the height of the incident wave, and calculating to obtain the wave load on the square box.
Preferably, the discretization method of the numerical wave water tank of fig. 1 in the step 3) includes the following steps:
generating a hexahedron structured grid as a background grid; from the water bottom to the static water surface, the size of the structural unit in the vertical direction is gradually reduced; the number of units in the horizontal direction is increased around the square box;
and removing the grids at the positions occupied by the terrain from the generated background grids to form the boundaries of the square boxes and the terrain.
Preferably, the maximum number of grooms for each of the grids is set to 0.25, and the number of grooms is defined as follows:
wherein δ t is a time step, | U | is a velocity modulus in a grid, δ x is a grid length in a velocity direction; if the number of the coulombs of some structural units exceeds 0.25, the corresponding time step is automatically decreased to satisfy that the number of the coulombs is less than 0.25.
The invention has the following beneficial effects: the invention provides a research method for comprehensively considering the influence of terrain change on narrow slit resonance by utilizing a two-dimensional numerical wave water tank; the influence of port topography, water depth in front of a wharf and the like on the narrow slit resonance can be researched, and a basis is provided for further researching the narrow slit resonance rule; provide the basis for the marine floating structure of pertinence design according to harbour topography.
Drawings
FIG. 1 is a schematic diagram of a three-dimensional structure of a numerical wave water tank;
FIG. 2 is a schematic diagram of a two-dimensional structure of a numerical wave water tank;
FIG. 3 is a schematic diagram of a simulation grid on an inclined slope;
FIG. 4 is a schematic diagram of a simulation grid around a square box;
FIG. 5 is H0When the wave force is 0.005m, S is 0 and kh is 1.350, the relationship between the maximum horizontal wave force and the corresponding vertical wave force, wave moment and grid resolution is shown schematically;
FIG. 6 is H0When the wave length is 0.005m, S is 0.113 and kh is 0.840, the relationship between the maximum horizontal wave force and the corresponding vertical wave force and moment is shown schematically;
FIG. 7 is a schematic diagram of a wave meter configuration in a physical simulation model according to the prior art;
FIG. 8 is a schematic diagram of a force sensor arrangement in a prior art physical simulation model;
FIG. 9 is a schematic diagram of a pressure probe placement in a prior art physical simulation model;
FIG. 10 is a schematic diagram of free surface height data measured by each of the wave meters at different time histories for two different incident waves in a prior art physical simulation model;
FIG. 11 is a schematic diagram of wave force data measured by each of the pressure probes at different time histories under an incident wave 2 in a physical simulation model according to the prior art;
FIG. 12 is a graph of wave force data of a ship side under two different incident waves and different time histories in a physical simulation model according to the prior art;
FIG. 13 shows the incident wave height H using the method of the present invention0The relation between the horizontal wave force and the terrain is shown as 0.005 m;
FIG. 14 shows the incident wave height H using the method of the present invention0The relation between the horizontal wave force and the terrain is shown as 0.024 m;
FIG. 15 shows the incident wave height H using the method of the present invention0The relation between the horizontal wave force and the terrain is shown as 0.050 m;
FIG. 16 shows the incident wave height H using the method of the present invention0The relation between horizontal wave force and terrain is shown as 0.075 m;
FIG. 17 shows the incident wave height H using the method of the present invention0The relation between the horizontal wave force and the terrain is shown as 0.100 m;
FIG. 18 is a graph of incident light using the method of the present inventionWave height H0The relation between the horizontal wave force and the terrain is shown in a graph of 0.005m, 0.024m, 0.050m, 0.075m and 0.100 m;
FIG. 19 shows the incident wave height H using the method of the present invention0The relationship between the maximum horizontal wave force and the gradient is shown in a schematic diagram when the maximum horizontal wave force is 0.005m, 0.024m, 0.050m, 0.075m and 0.100 m;
FIG. 20 shows the incident wave height H using the method of the present invention0The relation between the vertical wave force and the terrain is shown as 0.005 m;
FIG. 21 shows the incident wave height H using the method of the present invention0The relation between the vertical wave force and the terrain is shown as 0.024 m;
FIG. 22 shows the incident wave height H using the method of the present invention0The relation between the vertical wave force and the terrain is shown as 0.050 m;
FIG. 23 shows the incident wave height H using the method of the present invention0The relation between the vertical wave force and the terrain is shown as 0.075 m;
FIG. 24 shows the incident wave height H using the method of the present invention0The relation between the vertical wave force and the terrain is shown as 0.100 m;
FIG. 25 shows the incident wave height H using the method of the present invention0The relationship between the vertical wave force and the terrain is shown schematically when the vertical wave force is 0.005m, 0.024m, 0.050m, 0.075m and 0.100 m.
FIG. 26 is a schematic illustration of the relationship between maximum vertical wave force and slope using the method of the present invention;
FIG. 27 shows the incident wave height H using the method of the present invention0The relation between the moment and the terrain is shown as 0.005 m;
FIG. 28 shows the incident wave height H using the method of the present invention0The relation between the moment and the terrain is shown as 0.024 m;
FIG. 29 shows the incident wave height H using the method of the present invention0The relation between the moment and the terrain is shown as 0.050 m;
FIG. 30 shows the incident wave height H using the method of the present invention0Between moment and terrain when 0.075mA schematic diagram of the relationship of (1);
FIG. 31 shows the incident wave height H using the method of the present invention0The relation between the moment and the terrain is shown when the distance is 0.100 m.
Detailed Description
The invention provides a research method capable of confirming influence of terrain change on wave load in narrow slit resonance. The method specifically comprises the following steps:
1. and establishing a control equation. By using Open
A built-in two-phase flow solver 'interFoam' performs numerical simulation. Wherein, the control formula of mass conservation and momentum conservation of the incompressible two-phase flow of water and air is as follows:
wherein the content of the first and second substances,
represents a gradient operator; u ═ u, v, w, and represents the fluid motion velocity vector; x ═ x, y, z, representing a cartesian coordinate vector; t represents time; ρ represents the fluid density; p represents the hydrodynamic pressure; g represents the gravitational acceleration; μ represents hydrodynamic viscosity; sigmatDenotes the surface tension coefficient, kαRepresenting the surface curvature.
The two equations above are solved simultaneously (water and air) by using scalar field α to represent the volume fraction of water in the cell, water at 1 and air at 0, with the intermediate value between 1 and 0 being the mixture of air and water.
Using the VOF method (Volume of Fluid method), the distribution of α was calculated by the following formula:
wherein u isr＝uwater-uairRefers to the relative velocity between air and water.
Based on the volume fraction α (i.e., the value calculated by equation (3)), the spatial variation in fluid density and dynamic viscosity can be calculated by the following equations:
ρ＝(1-α)ρair+αρwater(4)；
μ＝(1-α)μair+αμwater(5)。
wherein the subscript "air" and the subscript "water" represent the fluid properties of air and water, respectively.
2. A boundary condition is set.
As shown in fig. 1 and 2, a numerical wave water tank is established. A square box is arranged in the numerical wave water tank to simulate a ship. The invention simplifies the cross section of the ship into a square shape. Figure 2 shows a numerical wave flume from a two-dimensional perspective. In the present invention, the length of the numerical wave water tank is set to 14m, the height is set to 0.8m, and the width W on the y-axis is set to 0.1m as an example. The 1 wave water tanks with the set values are used as a calculation unit (structural unit).
And incident waves are formed at the boundary of the numerical wave water tank, so that the re-reflection of waves in the numerical wave water tank is avoided. The velocity at the boundary of the incident wave entrance is designated as the velocity of the regular wave, and the pressure gradient at the boundary is set to 0. While a relaxation zone is provided near the entrance boundary. The specific setting method of the relaxation area comprises the following steps: a rectangular area is arranged from the wave inlet to the 1.5 times wavelength; in particular, from the coordinates of two diagonal points of the rectangle and the direction of one side (and the direction of relaxation). The relaxation zone technique is based on weighting between the calculated solution of the velocity field and the target solution with the aim of dissipating the reflected waves generated by the tank wall system. The boundary condition at the upper part of the numerical wave water tank was set to "air" (atmosphere). And adopting a 'non-slip' (non-slip) boundary condition on the right side and the bottom edge of the numerical wave water tank and the wall surface of the tank body. If the numerical wave water tank setting is considered to be two-dimensional, then both its front and back boundary conditions are set to "none" (empty).
With the above arrangement, the above equations (1) to (3) are solved by a finite volume method. The time derivative is discretized using a first order Euler implicit format. The specific procedure is carried out With reference to the literature "Jasak, H. error Analysis and estimation for the finished Volume Method With Applications to fluid flows.1996, PhD thesis, Imperial College, London", With reference to the following formula.
Wherein φ represents a face value represented by a cell value at a time step; superscripts n and o denote the new time step and the previous time step, respectively; p is the neighbor cell center node, representing this cell; Δ t represents the new-old time difference.
The gradient condition is estimated by Gaussian integration in a control volume VPConsider the integral transformation of phi:
wherein, VPRepresenting the volume of the cell; p is the central node of the adjacent unit and represents the unit; x is a base point of the surface value phi Taylor series expansion; Δ is the gradient operator.
The gaussian integration method is based on linear interpolation from the center of the building block to the surface of the building block, and the divergence term is calculated from the specific format of gaussian convection. The speed and pressure are calculated by PISO (pressure Implicit with separating of operators) algorithm and by using the idea of projection. The method comprises the following specific steps: firstly, the speed is predicted based on the momentum equation, then the pressure is solved based on the pressure equation, and then the speed is corrected through the momentum equation according to the obtained pressure. For a specific calculation method, reference is made to the literature "Issa, R.I. solution of the iterative flow equations by operator-splitting. journal of computational Physics.1986, (62 (1): 40-65".
To ensure accurate and stable numerical results, the maximum number of coulombs per grid in all simulations was set to 0.25. The number of kurang is defined as follows:
where δ t is the time step, | U | is the velocity modulus within the grid, and δ x is the length of the grid in the velocity direction. If the number of the coulombs of some structural units exceeds 0.25, the corresponding time step will be automatically decreased to satisfy the number of the coulombs less than 0.25.
3. After equations (1) to (3) are solved by the above method, the wave load on the square box can be obtained by the pressure and shear stress of each time step on the surface of the square box. The moment acting on the square box corresponds to the mass center of the square box. The specific method comprises the following steps:
the square box is arranged in front of a vertical wall, and an inclined slope is arranged below the square box. Examples of the inventive arrangements are: narrow gap width B between square box and wallgIs 0.05 m. And setting the fixed water depth h to be 0.5m within the range of 0-12.0 m. 6 water depths h are set in front of the wallsRespectively is as follows: 0.5m, 0.45m, 0.40m, 0.35m, 0.30m, 0.27 m. The slopes S of the terrain below the square box are set to 0, 0.025, 0.050, 0.075, 0.100, 0.113, respectively. Air height h in the whole wave water tankaIs a constant number ha＝0.3m。
Subsequently, regular waves of different frequencies and wave heights are generated at the entrance boundary of the incident wave. Wherein, the range of the frequency omega of the regular wave is from 2.514rad/s to 5.586 rad/s. Correspondingly, the dimensionless wave number kh is in the range of 0.6 to 1.7; wherein k represents wave number, k is 2 pi/L; l represents the incident wavelength.
Five different incident wave heights H are set00.005m, 0.024m, 0.050m, 0.075m and 0.100m, respectively. The width W of the slack near the wave entry boundarysAnd 8.0 m.
By using Open
The built-in grid generation tool discretizes the numerical wave water tank of fig. 1. The specific method comprises the following steps:
(1) a hexahedral structured grid (background grid) is generated by the "blockMesh" tool. Meanwhile, the size of the vertical direction of the structural unit is gradually reduced from the bottom (water bottom) to the stationary water surface to accurately track the free water surface. In addition, the length of the grid units in the horizontal direction is reduced, namely the number of the units in the horizontal direction is increased, around the square box, particularly in a narrow gap between the square box and the wall surface, so that a wave field is accurately simulated.
(2) Removing part of the grid from the background grid generated in step (1) and forming the boundary of the square box and the terrain (inclined slope surface) by using a 'snappyHexMesh' tool. Fig. 3, 4 are typical grid displays in a simulation. Fig. 3 shows a mesh on the inclined slope, and fig. 4 shows a mesh around the square box (for example, S is 0.113).
In general, for hydrodynamic problems, the results of CFD (Computational Fluid Dynamics) based simulations are more influenced by the grid. Therefore, the invention uses three different grids of thick, medium and thin to study the influence of grid density on the wave load acting on the square box. When S is equal to 0, the number of grid computing units of the three specifications is respectively: 117280, 203890, and 281660. Since the structural units under the slope are removed, the number of grid computing units of the three specifications of the other five terrains (S ═ 0.025, 0.050, 0.075, 0.100, 0.113) is slightly lower than that of S ═ 0.
According to the arrangement of the steps, only the height (H) of the incident wave is required to be adjusted0) The relationship between the terrain variation and the wave load can be easily determined. The present invention will be further explained with reference to specific examples.
Example one
When H is present0When the maximum horizontal wave force, the corresponding vertical wave force, the wave moment, and the grid resolution are 0.005m, 0S, and 1.350 kh, the relationships between the maximum horizontal wave force and the corresponding vertical wave force are shown in fig. 5. Wherein A is0＝H0/2 represents the vibration of the incident waveAnd (6) web. When incident wave height H0At 0.005m, for terrain with a slope S of 0 and S of 0.113, the maximum of the horizontal wave force in the slot occurs at kh of 1.350 and 0.840, respectively.
In order to further check the mesh convergence of the result of the waveform number for S ≠ 0, the present invention also presents H, as shown in FIG. 60Maximum horizontal wave force and corresponding vertical wave force and moment when the wave length is 0.005m, S is 0.113 and kh is 0.840. As can be seen from fig. 5 and 6, in both cases, the time histories (including horizontal wave forces, vertical wave forces, and moments) of all wave loads are nearly identical for the three-gauge grid. This shows that three kinds of grids can all obtain more accurate wave load. The grids described above all use medium density grids in view of computational cost and computational accuracy. The total time calculated above was 40 s. As can be seen from fig. 5 and 6, at 20s, all wave loads reached steady state; therefore, the results in the following are all obtained on the basis of the steady-state wave load of 20-40 s.
As shown in fig. 7 to 9, a physical model experiment is performed to detect the relationship between the terrain and the wave load together with the method provided by the present invention, so as to verify the accuracy of the method provided by the present invention. The physical simulation model includes a wave water tank. The wave water tank is 46m in length, 0.7m in width and 1.0m in height. A wave generator is arranged at one end of the wave water tank to generate incident waves. The ship model has a length B of 0.6m, a width E of 0.4m and a height of 0.45 m. The ship model is arranged 27.4m away from the wave maker and is fixed by a support rod. A vertical quay wall is arranged 0.06m away from the ship model. A box body with the width of 0.147m is respectively arranged on two sides of the ship model, and a narrow slit with the width of 0.003m is arranged between the box body and the ship model so as to avoid the mutual friction between the box body and the ship model. And simultaneously, arranging a plurality of data sensors on the ship model. As shown in fig. 7, 1 wave measuring instrument is respectively arranged on the middle shaft in the wave water tank at a position 7m away from the wave generator and at a position 25.2m away from the wave generator and on two sides of the ship model to measure the height of the free water surface; wherein, the wave measuring apparatu of boats and ships model both sides is symmetrical to be set up, and two wave measuring apparatu interval 0.83 m. As shown in fig. 8 and 9, force sensors are provided on the transverse section of the ship model to test the transverse and longitudinal wave forces, respectively. Meanwhile, 20 pressure probes are arranged on the ship model according to the mode shown in the table 1 and are respectively arranged at the bottom and two sides of the ship body; wherein, pressure probes 8, 13 are respectively placed on the left and right sides of the hull section, and pressure probes 9-12 are arranged at the bottom of the ship. To measure the wave load experienced by the hull section.
TABLE 1 arrangement of pressure probes on a model ship
In the above physical model experiment, 2 sine waves, i.e., incident waves 1 and 2, were generated by a wave generator. The parameters of the incident waves 1, 2 are shown in table 2.
Table 2 incident wave parameters of comparative examples
In order to obtain the accuracy of the data, in this embodiment, the data of the numerical wave water tank of the present invention is set to be the same as that of fig. 7, and no relaxation region is set at the boundary of the incident wave inlet. The numerical simulation is terminated when the reflected wave reaches the boundary of the entrance of the incident wave from the ship's wall system. Using the above-described mesh configuration of medium mesh density, the number of computational cells in the mesh is 413200.
Data simulations were performed using the physical model and the inventive setup described above, respectively, and the results are shown in fig. 10, 11, and 12. FIG. 10 is free surface height data from each of the wave meters at different time histories for two different incident waves. Fig. 11 shows the wave force data measured by each of the pressure probes at different time histories under the incident wave 2. Fig. 12 shows wave force data of the ship side under two different incident waves and different time histories.
As can be seen from the above figure, the difference between the data obtained by the method of the invention and the data (wave height and force) obtained by the physical model test is very small, and the data predicted by the numerical model of the invention is well matched with the experimental data obtained by the physical model. The method is proved to be capable of accurately predicting the free surface height of the narrow slit resonance problem formed by the box body system and accurately predicting the wave load on the unit structure.
Example two
1. The method provided by the invention is used for researching the relation between horizontal wave force and terrain change.
FIGS. 13-17 show horizontal wave force versus terrain (slope S), incident wave height (H)0) The relationship between (H in FIGS. 13 to 17)00.005m, 0.024m, 0.050m, 0.075m, and 0.100 m). The left and right broken lines in fig. 13 to 17 represent the fluid resonance frequency (kh) when S is 0.113, respectivelyHgAnd frequency of occurrence of maximum horizontal wave force (kh)Fx. As can be seen in FIGS. 13-17: (kh)FxDecreases with increasing slope S. Fig. 18 further illustrates this variation. This change is similar to the fluid resonance frequency versus slope S, indicating that the wavelength within the narrow slit dominates the horizontal wave force on the tank. As can also be seen from FIGS. 13-17: frequency of occurrence of maximum horizontal wave force (kh) regardless of incident wave height when S is 0.113FxResonant frequency with fluid (kh)HgThere are significant deviations from each other. Fig. 18 further illustrates this phenomenon. As can be seen from FIG. 18, in most cases, (kh)FxAre all greater than (kh)HgThere are only two counter-examples. (kh)FxAnd (kh)HgThe possible reasons for data inconsistency are: the height of the horizontal wave force on the box body depends on the horizontal plane difference of the two sides of the box body. The horizontal wave force on the tank can be qualitatively expressed by the following formula:
wherein C represents a proportionality constant of ηgIndicating the free surface height in the slot, ηLIndicating the free surface height to the left of the slot. As can be seen from equation (10), although the horizontal wave force is mainly affected by the wavelength in the narrow slit, it is also affected to some extent by the wavelength on the left side of the tank. As can also be seen in FIG. 18, H0When equal to 0.005m, (kh)FxAnd (k)h)HgThe difference between them is significantly smaller.
Fig. 19 shows the relationship between the maximum horizontal wave force and the slope S. As can be seen from fig. 19, the maximum horizontal wave force fluctuates with the slope.
2. The method provided by the invention is used for measuring the relationship between vertical wave force and terrain variation.
FIGS. 20-24 show vertical wave force versus terrain (slope S), incident wave height (H)0) The relationship between (H in each of FIGS. 20 to 24)00.005m, 0.024m, 0.050m, 0.075m, and 0.100 m). The left and right broken lines in fig. 20 to 24 represent the fluid resonance frequency (kh) when S is 0.113HgAnd the frequency of occurrence of the maximum vertical wave force (kh)Fz. As can be seen from the figure, the maximum vertical wave force (kh)FzDecreases with increasing slope S. Fig. 25 further illustrates this phenomenon. This indicates that the wavelength within the narrow slit also dominates the vertical wave force on the square box.
In addition, it can be seen from the figure that when S is 0.113, the frequency (kh) at which the maximum vertical wave force appearsFzResonant frequency with fluid (kh)HgThere are also significant deviations between. It can also be seen that when the incident wave height is large and the terrain slope is small, the vertical wave force is insensitive to the wave frequency when the wave frequency is less than a certain critical value. In this case, (kh)FzThe critical wave frequency. However, with (kh)FxIn most cases greater than (kh)HgDifferent, (kh)FzThe value of (a) is relatively lower. FIG. 26 further shows (kh)FzAnd (kh)HgThe relationship (2) of (c). As can be seen from FIG. 26, (kh)FzValue of less than (kh)HgThe value of (c).
It can also be seen from FIGS. 20-24 that the terrain slope is substantially positively correlated to the vertical wave force. When S is less than or equal to 0.100, the maximum vertical wave force is obviously increased along with the increase of the gradient S. When S increases to 0.113, the maximum vertical wave force is only slightly less than when S is 0.100.
3. The method provided by the invention is used for determining the relationship between the torque on the box body and the terrain change.
FIGS. 27-31 show the torque sumTopography (slope S), incident wave height (H)0) The relationship between (H in FIGS. 27 to 31)00.005m, 0.024m, 0.050m, 0.075m, and 0.100 m). The left and right broken lines in fig. 27 to 31 represent the fluid resonance frequency (kh) when S is 0.113, respectivelyHgAnd the frequency of occurrence of the maximum moment (kh)My。
As can be seen from FIGS. 27 to 31, overall, the frequency of occurrence of the maximum moment (kh)MyDecreases with increasing slope S. The wavelength within the narrow slit also dominates the moment variations on the square box.
Claims (10)
1. A research method for confirming influence of terrain change on wave load is characterized by comprising the following steps: the method comprises the following steps:
(1) establishing a numerical value wave water tank, wherein a square box is arranged in the numerical value wave water tank to simulate a ship, and 1 numerical value wave water tank is used as a structural unit; forming an incident wave at a boundary of the numerical wave water trough;
(2) establishing a mass conservation and momentum conservation control equation of water and air;
(3) using a scalar field α to represent the volume fraction of water in the structural unit, wherein the volume fraction is water when the volume fraction is 1, the volume fraction is air when the volume fraction is 0, and the intermediate value between 1 and 0 is a mixture of air and water;
(4) discretizing the time derivative;
(5) and obtaining the wave load on the square box through the pressure and the shear stress of each time step on the surface of the square box.
2. The method for determining the influence of terrain variations on wave loading according to claim 1, wherein: in step (1), the velocity at the boundary of the entrance of the incident wave is designated as the velocity of the regular wave, and the pressure gradient at the boundary is set to 0.
3. The method for determining the influence of terrain variations on wave loading according to claim 2, wherein: a relaxation zone is provided adjacent the entrance boundary.
4. A method of investigating the effect of topographical variations on wave loading as claimed in claim 3, wherein: the boundary condition of the upper part of the numerical wave water tank is set as 'air'; and adopting a 'no-slip' boundary condition on the right side and the bottom edge of the numerical wave water tank and the wall surface of the tank body.
5. The method for determining the influence of terrain variations on wave loading according to claim 1, wherein: the mass conservation and momentum conservation control equation in the step (2) is as follows:
wherein the content of the first and second substances,
represents a gradient operator; u ═ u, v, w, and represents the fluid motion velocity vector; x ═ x, y, z, representing a cartesian coordinate vector; t represents time; ρ represents the fluid density; p represents the hydrodynamic pressure; g represents the gravitational acceleration; μ represents hydrodynamic viscosity; sigmatDenotes the surface tension coefficient, kαRepresenting the surface curvature.
6. The system for determining the influence of terrain variations on wave loading according to claim 5, wherein the formula for calculating α the distribution in step (3) is:
wherein u isr＝uwater-uairRefers to the relative velocity between air and water.
7. The method for determining the influence of terrain variations on wave loading according to claim 1, wherein: the discretization method of the time derivative in the step (4) is as follows:
the gradient condition is estimated by Gaussian integration in a control volume VPConsider the integral transformation of phi:
wherein, VPRepresenting the volume of the cell;
the gaussian integration method is based on linear interpolation from the center of the building block to the surface of the building block, and the divergence term is calculated from the specific format of gaussian convection.
8. The method for studying the effect of the terrain variation on the wave loading according to claim 7, wherein: the method for obtaining the wave load on the square box in the step (5) comprises the following steps:
1) placing the square box in front of a vertical wall, and arranging an inclined slope below the square box;
2) generating regular waves with different frequencies and incident wave heights at the inlet boundary of the incident wave;
3) by using
A built-in grid generation tool discretizes the numerical wave water tank;
4) and adjusting the wave height of the incident wave, and calculating to obtain the wave load on the square box.
9. The method for determining the influence of terrain variations on wave loading according to claim 8, wherein: the method for discretizing the numerical wave water tank in the step 3) comprises the following steps:
generating a hexahedron structured grid as a background grid; from the water bottom to the static water surface, the size of the structural unit in the vertical direction is gradually reduced; the number of units in the horizontal direction is increased around the square box;
and removing the grids at the positions occupied by the terrain from the generated background grids to form the boundaries of the square boxes and the terrain.
10. The method for studying the effect of the terrain variation on the wave loading according to claim 9, wherein: setting the maximum number of grooms for each of the grids to 0.25, the number of grooms being defined as follows:
wherein δ t is a time step, | U | is a velocity modulus in a grid, δ x is a grid length in a velocity direction; if the number of the structure units exceeds 0.25, the corresponding time step is automatically reduced to satisfy the number of the structure units less than 0.25.
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