Method for determining influence effect of submerging depth on semi-submersible structure under action of solitary wave

Abstract

The invention belongs to the field of wave modeling, and provides a method for determining the influence effect of submerging depth on a semi-submersible structure under the action of a solitary wave, and the method comprises the steps: building a viscous fluid model, expressing the viscous fluid model through a control equation which comprises a continuity equation and a momentum equation, and carrying out the boundary setting of the fluid model; establishing a solitary wave model; establishing a semi-submersible structure model; and according to the viscous fluid model, the solitary wave model and the semi-submersible structure model, simulating the influence of the submerging depth on the wave surface elevation, the transmission coefficient, the reflection coefficient, the flow velocity, the vorticity and the wave load around the semi-submersible structure.

Description

Technical Field

[0001] The invention belongs to the field of wave modeling, and in particular relates to a method for determining the effect of submergence depth on a semi-submerged structure under the action of a solitary wave. Background Art

[0002] Semi-submersible platforms are widely used in the development of deep-sea marine resources because they can adapt to a wide range of water depths and have strong resistance to harsh environments. The deep-sea marine environment is complex and harsh, and extreme waves occur frequently, which poses a serious threat to the operation and maintenance safety of semi-submersible structures. The submergence depth is of great significance in the design parameters of semi-submersible structures and directly affects the safety of the structure. When the semi-submersible structure is submerged to a large extent, deck waves and wave impacts are very likely to occur, resulting in damage to the platform structure, equipment damage, and even platform capsizing, threatening the safety of mechanical equipment and operators on the platform. Although reducing the submergence depth of the semi-submersible platform and increasing the deck height can reduce the deck waves and wave impact loads, the deep-sea marine environment is more severe. Simply increasing the deck height and reducing the submergence degree cannot guarantee that overtopping is completely avoided on the one hand, and on the other hand, the submergence degree cannot be too low due to the stability and economic requirements of the platform. Therefore, studying the influence of submergence depth on the hydrodynamic characteristics and wave loads of semi-submersible platforms under extreme waves and determining the reasonable submergence depth of semi-submersible platforms is of great significance to the design and operation and maintenance safety of semi-submersible platforms.

[0003] At present, researchers have conducted extensive research on the interaction between waves and structures, among which research on extreme waves and their interaction with semi-submersible structures has also been carried out to a certain extent. Hu et al. introduced new wave boundary conditions in OpenFOAM and conducted numerical simulations on the interaction between solitary waves and fixed and floating truncated cylinders and simplified floating oil platforms. Geng et al. used the parallel three-dimensional boundary element method to simulate the interaction between solitary waves and three-dimensional submerged horizontal plates under the potential flow assumption, and analyzed the wave height, horizontal force and vertical force of the plate, and pitching moment. Pan et al. used the SPH model to simulate the interaction between solitary waves and floating marine structures, and analyzed the drift motion of the tension leg platform under the impact of solitary waves. Wang et al. used a multi-lens stereo reconstruction system and underwater pressure measuring elements to conduct physical model experiments, studied the interaction between solitary waves and horizontal plates submerged at 1 / 4 water depth, and discussed the characteristics of horizontal force, vertical force and pitching moment of the horizontal plate. In the above-mentioned study on the interaction between extreme waves and semi-submerged structures, solitary waves are used to replace extreme waves because they can show strong nonlinearity of extreme wave conditions when the wave height is large. This substitution is also widely used in other studies on the interaction between waves and structures.

[0004] Although researchers have conducted some research on the extreme wave hydrodynamic characteristics of semi-submersible structures, the research is not sufficient, and the impact of submergence depth on the hydrodynamic characteristics and wave loads of semi-submersible structures needs further analysis and research. Summary of the invention

[0005] In order to solve the problems in the prior art, the present invention provides a method for determining the effect of submergence depth on a semi-submerged structure under the action of a solitary wave, the method comprising the following steps:

[0006] Establishing a viscous fluid model, wherein the viscous fluid model is expressed by a control equation, wherein the control equation includes a continuity equation and a momentum equation, and setting boundaries for the fluid model;

[0007] Establish solitary wave model;

[0008] Establish a semi-submersible structure model;

[0009] The influence of the submerged depth on the wave surface elevation, transmission coefficient, reflection coefficient, flow velocity, vorticity and wave load around the semi-submerged structure is simulated based on the viscous fluid model, solitary wave model and semi-submerged structure model.

[0010] The present invention can produce the following beneficial effects through the above technical solution:

[0011] The present invention adopts a viscous fluid model and a dynamic boundary method to accurately simulate the wave surface elevation, transmission coefficient, reflection coefficient, flow velocity, vorticity and wave load when a solitary wave interacts with a semi-submerged structure, thereby solving the problem of insufficient calculation accuracy of the model in the prior art.

[0012] The present invention is applicable to various submergence depth conditions and can obtain empirical formulas for transmission coefficient, reflection coefficient and wave load through polynomial fitting, which provides an important basis for the design and operation of semi-submersible structures, especially in severe sea conditions in deep sea and has great application potential.

[0013] Through the simulation method of the present invention, the effects of different submergence depths on the semi-submersible structure can be analyzed, thereby optimizing the design parameters of the semi-submersible platform, especially determining the reasonable submergence depth of the platform to improve its wave impact resistance and ensure the safe operation of the platform.

[0014] Compared with the traditional explicit boundary processing method, the dynamic boundary method can effectively reduce the computational complexity, and is especially suitable for fluid simulation involving complex boundaries. At the same time, the processing method of boundary particles can naturally simulate the fluid-structure interaction process, simplifying the implementation of the numerical model.

[0015] By replacing extreme waves with solitary waves, the present invention solves the strong nonlinear problem in actual extreme wave simulation, provides an effective tool for studying the hydrodynamic characteristics of semi-submersible structures under extreme waves, and helps to improve the impact resistance of structures in marine engineering.

[0016] In summary, the present invention not only improves the numerical simulation accuracy of the interaction between solitary waves and semi-submersible structures, but also provides theoretical support and practical reference for the design of offshore platforms, and has important engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 It is the comparison between the wave height duration calculated by the wave model and the theoretical value;

[0019] Figure 2 It is a submerged horizontal plate model arrangement;

[0020] Figure 3 is the comparison between the simulated and experimental values ​​of wave forces;

[0021] Figure 4 It is the semi-submersible structure model layout structure;

[0022] Figure 5 The wave height and load conditions of semi-submerged and above-water examples at different submerged depths;

[0023] Figure 6 is the wave height duration at the downstream measuring point where the solitary wave interacts with structures at different submergence depths;

[0024] Figure 7 is the comparison between the fitting curve and the numerical calculation results;

[0025] Figure 8 It is the semi-submerged and overwater wave load;

[0026] Fig. 9 is the vertical wave load;

[0027] Fig.10 It is the wave load on the structure in horizontal and vertical directions;

[0028] Fig.11 It is the velocity field of the solitary wave interacting with structures at different submerged depths;

[0029] Fig.12It is the vorticity field of the interaction between solitary waves and structures at different submerged depths. DETAILED DESCRIPTION

[0030] Below, the invention is preferably described in conjunction with the accompanying drawings and specific implementation methods.

[0031] Establishing a viscous fluid control equation, wherein the control equation includes a continuity equation and a momentum equation;

[0032] The continuity equation is

[0033]

[0034] Where: i is the fluid density; t is the time; N is the number of particles; i, j are the particle numbers; m j is the particle mass; u ij is the velocity vector; W ij is the kernel function; is the average speed of sound; δ = 0.1 is the empirical coefficient; h s is the smooth length; r ab is the distance vector.

[0035] The momentum equation is

[0036]

[0037] Among them, u i is the velocity vector; t is the time; m j is the particle mass; P i , P j is pressure; W ij is the kernel function; g is the gravitational acceleration; Γ ij Is a sticky item.

[0038] Furthermore, the kernel function in the model adopts a quintic kernel function, which can provide high-order interpolation characteristics while maintaining a low amount of calculation.

[0039] The boundary is processed by the dynamic boundary method. The core idea of ​​the dynamic boundary method is to treat the boundary particles as a special "fluid particle", that is, they have the same state variables as the fluid particles (such as density, pressure, etc.), but the velocity change of the boundary particles is not considered in the momentum equation. This means that these boundary particles will not participate in the actual motion simulation, but their density and pressure will be dynamically adjusted according to the surrounding fluid particles. The specific setting steps are as follows:

[0040] In the computational domain of the numerical simulation, the surface of the boundary objects (such as walls, solid structures, etc.) is discretized into a series of boundary particles. These particles are defined as the same units as the fluid particles, but have special properties: their velocities are not updated through the momentum equation, so their positions in space remain unchanged.

[0041] Dynamic boundary particles, like fluid particles, satisfy the continuity equation and state equation. For example, their density ρ and pressure P can be calculated by the interaction with the surrounding particles. In particular, the update of density is usually determined by the change of relative distance between fluid particles, while the pressure is determined by the state equation (such as Tait state equation).

[0042] When a fluid particle approaches a boundary particle, a repulsive mechanism is generated between the fluid particle and the boundary particle, since the boundary particle also participates in the evolution of density and pressure. This mechanism prevents the fluid particle from "penetrating" the solid boundary. Usually, this repulsive force is applied by the pressure difference between the boundary particle and the fluid particle. When the fluid particle approaches the boundary, the pressure of the boundary particle increases, thereby exerting a repulsive force on the fluid particle, preventing it from entering the solid region.

[0043] Although the state variables of the boundary particles change over time, their positions remain constant. This is achieved by ignoring the momentum equations of the boundary particles, ensuring that the boundary always remains fixed. This makes the dynamic boundary method particularly suitable for dealing with fixed geometric boundaries such as walls, obstacles, etc.

[0044] In each time step, the dynamic boundary method treats boundary particles the same as fluid particles, and the density and pressure of boundary particles are continuously updated when solving the control equations. When fluid particles approach the boundary, the boundary particles will exert a gradually increasing repulsive force on the fluid particles to prevent them from penetrating the boundary. This treatment method closely combines the application of boundary conditions with the solution of control equations, avoiding the complex process of setting boundary conditions separately in the explicit boundary treatment method.

[0045] Solitary waves and semi-submerged structure model.

[0046] A solitary wave is an isolated, single, non-periodic wave that occurs in shallow water. It has the characteristics of maintaining waveform, concentrating energy, and not dispersing. A solitary wave is a nonlinear wave that can maintain its shape and speed during propagation. Solitary waves were first discovered by Russell in the 19th century, who observed that such waves can propagate over long distances in shallow water without attenuation.

[0047] In order to verify the accuracy of solitary wave propagation and wave load calculation of the model, solitary wave propagation and submerged horizontal plate examples were selected. The numerical model was used to simulate the two examples, and the wave surface and wave load calculated by the model were compared with the theoretical values ​​or experimental data. Among them, the theoretical value of the wave surface of the solitary wave propagation example is obtained by the following formula

[0048]

[0049] in

[0050] x is the coordinate, t is the time, and η(x,t) represents the generated solitary wave;

[0051] H is the wave height;

[0052] c is the velocity of the solitary wave;

[0053] T f is the solitary wave generation time;

[0054] d is the water depth;

[0055] k is the wave number;

[0056] sech(x) is the hyperbolic secant function, defined as

[0057] In order to verify the simulation calculation accuracy of solitary wave generation and propagation in the model, a solitary wave propagation example with an initial water depth of d0 = 1.0m and a relative wave height of H0 / d0 = 0.3 was selected, and the calculated wave heights at four measuring points of the model were compared with the theoretical values. The numerical flume length is L0 / d0 = 65, and the wave-making plate is on the left side of the flume. The solitary wave is generated by the wave-making plate and propagates to the right. The particle spacing is set to 0.03m, the output time interval is 0.15s, and the total calculation time is 20s.

[0058] The comparison results of wave height duration calculated by the four measuring point models x / H0=2, 10, 20, 50 and theoretical values ​​are as follows: Figure 1 As shown. The wave height calculated by the model at the first three measuring points is in good agreement with the theoretical value, and the phase and amplitude are basically consistent with the theoretical value; the phase at the x / H0=50 measuring point is consistent with the theoretical value, but the amplitude is slightly lower than the theoretical value. The reason for this result is that due to the influence of viscosity, as the wave propagates forward, the peak value of the isolated wave decreases slightly along the way, causing the calculation error to gradually increase; the maximum absolute error of the peak value at the x / H0=50 measuring point is 0.025m, and the relative error is 8.4%.

[0059] In order to quantitatively analyze the calculation accuracy of the solitary wave propagation simulation of the model, the L2 error of the solitary wave height calculated by the model at different measuring points is given in Table 1. The L2 error is the smallest at the measuring point x / H0=2, with a minimum value of 0.107. As the solitary wave propagates forward, the model calculation error gradually increases, and the L2 error reaches a maximum value of 0.137 at the measuring point x / H0=50.

[0060]

[0061] In the formula and represents the numerical solution and theoretical value at time t; N represents the total number of samples (the samples select data within the wavelength range of the solitary wave).

[0062] Table 1. L2 error of wave height calculated by the model

[0063]

[0064] In summary, except that the peak value of isolated waves calculated by the model decreases slightly with increasing distance, the model calculation results are in good agreement with the theoretical values. The maximum absolute error of the peak value is 0.025m, the relative error is 8.4%, and the maximum L2 error of the wave height at the measuring point is 0.137.

[0065] In order to verify the calculation accuracy of wave loads of solitary waves interacting with semi-submerged structures, the solitary waves interacting with submerged horizontal plates with an initial water depth of d0 = 0.144 m, relative wave height H0 / d0 = 0.301, and z / d0 = 0 ( Figure 2 ) to perform numerical simulation and compare the numerical calculation results of the structure load with the experimental data. In order to reduce the calculation time, the length of the water tank in the model is reduced to 11m. The height of the water tank is 0.3m. The length of the horizontal plate is 0.305m and the thickness is 0.0127m. The particle spacing is Δx / H0=0.04m, and the physical process is simulated for a total of 15s, with an output time interval of 0.15s.

[0066] Figure 3Comparison of model-calculated wave forces for submerged horizontal plates in the x and z directions with experimental data. It should be noted that t = 0 does not indicate the time when the calculation starts. Due to the different geometric dimensions of the numerical and experimental flumes, the time when the solitary waves reach the structure is also different. In order to compare the model calculation results with the experimental data, the figure uses the peak moment of the force in the x direction as the reference for the translation correction of the numerical calculation results. In the horizontal direction, the force results calculated by the model are in good agreement with the experiment; while in the vertical direction, the accuracy of the model calculation is slightly worse, and the numerical results overestimate the force on the horizontal plate in the vertical direction. In the horizontal direction, the peak values ​​of the wave forces calculated by the model and the experiment are 1.06N and 0.69N, respectively, with an absolute error of 0.37N and a relative error of 54%; the trough values ​​are -0.41N and -0.51N, respectively, with an absolute error of 0.1N and a relative error of 20%. In the vertical direction, the peak values ​​of wave forces calculated numerically and experimentally are 9.11N and 7.59N, respectively, with an absolute error of 1.52N and a relative error of 20%. The trough values ​​are -3.44N and -2.07N, respectively, with an absolute error of 1.37N and a relative error of 40%.

[0067] In order to analyze the influence of submergence depth on wave surface elevation, flow velocity, vorticity and wave load around the semi-submerged structure, a numerical model was used to simulate the interaction between solitary waves and semi-submerged structures with different submergence depths. The length and height of the numerical tank are 100m×2m, and the water depth is d0=1.0m. The size of the semi-submerged structure is 5.0m×0.6m, fixed near the still water surface, and the distance between the bottom of the structure and the bottom of the tank is d r , the initial flooding depth is d s =d0-d r , model layout see Figure 4 The wave height H0 is set to 0.5m, d r Take 0m, 0.2m, 0.4m...1.6m, a total of 9 working conditions (Table 2). Model1-Model5 are submerged cases where the structure is in a semi-submerged or submerged state, while Model6-Model10 are overwater cases where the structure is above the water surface. The relative particle spacing H0 / Δx is set to 40. A total of 40s of physical process are simulated, and the output time interval is 0.25s.

[0068] Table 2 (unit: m)

[0069]

[0070] Figure 5 It is the wave height duration of the upstream measuring point (x=35m) where the solitary wave interacts with structures at different submerged depths. Figure 5(a) Submerged cases with submerged depths ds = 0.9, 0.7, ..., 0.1 m (for the convenience of comparing the wave height and load conditions of the semi-submerged and surface cases, Figure 5 , 6 , 8, and 9(a) all plot the variable duration curve for the condition ds = 0.0). Figure 5 (b) Overwater cases with submerged depths ds = 0.0, -0.1, ..., -0.6. In all cases, the solitary wave reaches the measuring point at about t = 11s, and the wave height at the measuring point reaches the maximum value; then the solitary wave continues to propagate downstream, interacts with the structure after reaching the structure and forms a reflected wave to form a left-moving reflected wave; around t = 20s, the left-moving reflected wave reaches the measuring point, causing the wave height to rise twice, accompanied by a trough, forming a series of complete waves with gradually weakening wave heights. For Submerged cases, the reflected wave height gradually increases with the decrease of submerged depth; on the contrary, for Overwater cases, the reflected wave height gradually decreases with the decrease of submerged depth; Model 6 reaches the maximum reflected wave height, with a maximum value of 0.20m.

[0071] Figure 6 The wave height duration of the downstream measuring point (x = 60m) where the solitary wave interacts with the structure at different submerged depths. In Model1–Model3, the structure is basically in a completely submerged state, and the interaction between the water flow and the structure is relatively strong, which causes the solitary wave to arrive at the measuring point slightly later, and the solitary wave arrives at the measuring point at about t = 18s; the structure of Model4–Model5 is in a semi-submerged state, and the interaction between the water flow and the wave crest and the structure is weaker than that of Model1–Model3, so the solitary wave passes through the structure and arrives at the measuring point slightly earlier, and the solitary wave arrives at the measuring point at about t = 17s; the structure of Model6–Model10 is above the water surface, and the solitary wave crest interacts strongly with the structure, and the time when the wave crest arrives at the measuring point gradually shifts to the right. The solitary wave crest of Model6 arrives at the measuring point at t = 17s, and the solitary wave crest of Model10 arrives at the measuring point at t = 17.5s. The peak value of the downstream measuring point of Model1–Model4 gradually decreases, while the peak value of Model4–Model10 gradually increases; the peak value of the downstream measuring point of Model4 reaches the minimum value of 0.19m.

[0072] Transmission and Reflection

[0073] The transmission coefficient and reflection coefficient of the structure are Figure 7 The transmission coefficient and reflection coefficient in the figure are calculated as follows:

[0074]

[0075]

[0076] In the formula, H i is the incident wave height, K t is the transmission coefficient, H t is the transmission wave height, K rf is the reflection coefficient, H rf is the reflected wave height.

[0077] The transmission coefficient of the structure generally decreases first and then increases with the increase of the submergence depth; d s =0.3, the transmission coefficient reaches the minimum, the minimum value is 0.36; after the submergence depth ≥0.7m, the transmission coefficient basically reaches stability, the stable value is 0.71. The reflection coefficient of the structure increases first and then decreases with the increase of submergence depth; d s = 0.0, the reflection coefficient reaches the maximum, and the maximum value is 0.39. By fitting the calculation results of the transmission coefficient and the reflection coefficient with polynomials, we can get the empirical calculation formula of the transmission coefficient and the reflection coefficient with the submergence depth, as follows:

[0078]

[0079] The fitting results are as follows Figure 7 As shown, Figure 7 The comparison between the fitting curve and the numerical calculation results is given in the figure. The determination coefficients of the transmission coefficient and reflection coefficient fitting formula are R 2 =0.975 and 0.966, both above 0.95, and the fitting results are good.

[0080] Wave load

[0081] Figure 8 and Fig. 9 are the wave load coefficients C in the horizontal and vertical directions of the structure respectively x and C z The duration curve of C x and C z The calculation formula is:

[0082]

[0083] Where: F x 、F z F are the resultant forces in the horizontal and vertical directions of the structure respectively; A = 0.6m × 5m is the area of ​​the rectangular structure. x 、F z The value of is obtained by first calculating the force on a single particle that constitutes the structure, and then summing up all the particles that constitute the structure. The calculation formula is:

[0084]

[0085]

[0086] Where: F a is the force on any particle a constituting the structure; F(F x 、F z ) is the resultant force acting on the structure.

[0087] Figure 8 In the figure, since the solid wall boundary is treated by the dynamic boundary method, there is a small fluctuation at the initial moment, which basically reaches stability after t=4s. The arrival time of the peak value of the horizontal wave load is basically the same, which is about t=15s. With the increase of the submergence depth, the peak value of the horizontal wave load of the structure basically increases gradually; the trough value also increases with the increase of the submergence depth. There is overtopping at the top of the Model2–Model5 structure, which causes the wave surface to oscillate, resulting in certain fluctuations in the horizontal wave load.

[0088] Fig. 9 In the above figure, due to the use of the dynamic boundary method to simulate the solid wall boundary, there is a certain fluctuation in the initial moment of the vertical wave load, which basically reaches stability after t = 12s; among them, Model1-Model3 has a large submergence depth of the structure, the structure is basically in the water body, and the fluid particles and the structure particles are in contact more, resulting in greater instability; while Model4-Model10, due to the small submergence depth, the fluid particles and the structure particles are in contact less, and it quickly reaches stability. Therefore, for the dynamic boundary method, the greater the submergence of the structure, the longer the initial stabilization time. It is basically consistent with the horizontal wave load, and the peak arrival time of the vertical wave load is basically consistent, all around t = 15s. Fig. 9 In (a), for Submerged cases, the peak value of vertical wave load decreases with the increase of submergence depth, but the change of peak value is small; while for Overwater cases ( Fig. 9 (b) The peak value of the vertical wave load first increases rapidly and then decreases rapidly with the increase of the submergence depth, and the peak value changes greatly. Model2–Model6 has overtopping waves on the top of the structure, which collide and break with the downstream water body, causing the wave surface to oscillate, causing the wave load to fluctuate greatly, and the oscillation amplitude first increases and then decreases.

[0089] In order to analyze the quantitative relationship between submergence depth and wave load on structures, Fig.10 The maximum wave loads (C xmax , C zmax ) and minimum (C xmin , C zmin) value changes with the flooding depth. The point data in the figure are numerical calculation results, and the curve data are fitting results. As the flooding depth increases, C xmax Basically gradually increase, d s =0.7 reaches a maximum of 0.13, and then decreases slightly; C xmin Basically decreases with increasing submergence depth, d s =0.7 reaches the minimum value -0.05. zmax It increases rapidly with the increase of submergence depth, and then decreases gradually. s = -0.1 reaches a maximum value of 0.78; C zmin As the submergence depth increases, d s =0.9 reaches the minimum value of -0.39. The calculation results are fitted with polynomials, and the empirical calculation formulas for the maximum and minimum values ​​of wave loads in the horizontal (Equation 8) and vertical (Equation 9) directions as the submerged depth change are obtained as follows:

[0090]

[0091] The fitting results are as follows Fig.10 As shown, Fig.10 The comparison between the fitting curve and the numerical calculation results is given in Figure C zmax The fitting result is in d s <0.0m, the error is slightly larger. zmax The fitting results have a determination coefficient of 0.788, C xmax , C xmin , C zmin R of the fitted curve 2 All of them are above 0.9, and the fitting results are good.

[0092] Flow velocity and vorticity results

[0093] Fig.11 The velocity field of solitary waves interacting with structures at different submerged depths is given. As the submerged depth decreases, the flow field gradually stabilizes. In Model1–Model6, there are overtopping and wave breaking on the top of the structure. The solitary wave propagates downstream from the top and bottom of the structure. The overtopping water falls into the water downstream of the structure to produce water collision, resulting in a more complex flow field with a large flow velocity in the flow field, and the maximum flow velocity is above 3.5 m / s. In Model7–Model9, the overtopping basically disappears, and the solitary wave propagates downstream from the bottom of the structure. There is a certain wave breaking phenomenon when the wave passes over the structure. In Model10, the solitary wave passes completely from the bottom of the structure, and there is no interaction between the solitary wave and the structure, and the flow field is relatively stable.

[0094] Fig.12The vorticity field of the interaction between solitary waves and structures with different submerged depths. As the submerged depth decreases, the vorticity field gradually becomes stable. The overtopping waves on the top of the Model1–Model6 structures collide with the downstream water body, resulting in drastic changes in vorticity; the breaking of waves causes the water flow to be aerated, forming a complex vortex field, with clockwise and counterclockwise vortices appearing simultaneously, and the maximum and minimum vorticity ±10s -1 The above. Model7–Model9 overtopping basically disappears, and the vorticity field is small in scale, mainly concentrated at the bottom of the structure. Model1 is close to the bottom of the tank, the vorticity field is not developed, and the vorticity is small. Model2–Model9 has a developed vorticity field at the lower left foot of the structure, with a large counterclockwise vortex and a small clockwise vortex. Model10 has basically no vorticity.

[0095] The prior art mentioned in the aforementioned background technology part and specific embodiment part of the present invention may be regarded as a part of the present invention, and is used to understand the meaning of some technical features or parameters.

Claims

1. A method for determining the effect of submergence depth on a semi-submerged structure under the action of a solitary wave, characterized in that: The method comprises the following steps: Establishing a viscous fluid model, wherein the viscous fluid model is expressed by a control equation, wherein the control equation includes a continuity equation and a momentum equation, and setting boundaries for the fluid model; Establish solitary wave model; Establish a semi-submersible structure model; The influence of the submerged depth on the wave surface elevation, transmission coefficient, reflection coefficient, flow velocity, vorticity and wave load around the semi-submerged structure is simulated based on the viscous fluid model, solitary wave model and semi-submerged structure model.

2. The method for determining the effect of submergence depth on a semi-submerged structure under the action of a solitary wave according to claim 1, characterized in that: The continuity equation is: Where: i is the fluid density; t is the time; N is the number of particles; i, j are the particle numbers; m j is the particle mass; u ij is the velocity vector; W ij is the kernel function; is the average speed of sound; δ = 0.1 is the empirical coefficient; h s is the smooth length; r ab is the distance vector.

3. The method for determining the effect of submergence depth on a semi-submerged structure under the action of a solitary wave according to claim 1, characterized in that: The momentum equation is: Among them, u i is the velocity vector; t is the time; m j is the particle mass; P i , P j is pressure; W ij is the kernel function; g is the gravitational acceleration; Γ ij Is a sticky item.

4. The method for determining the effect of submergence depth on a semi-submerged structure under the action of a solitary wave according to claim 1, characterized in that: The boundary setting includes: Discretize the surface of the boundary object into a series of boundary particles; The dynamic boundary particles, like the fluid, satisfy the control equations of the viscous fluid; When solving the governing equations, the density and pressure of the boundary particles are continuously updated. When fluid particles approach the boundary, the boundary particles will exert a gradually increasing repulsive force on the fluid particles to prevent them from penetrating the boundary.

5. The method for determining the effect of submergence depth on a semi-submerged structure under the action of a solitary wave according to claim 1, characterized in that: The solitary wave model is Where x is the coordinate, t is the time, η(x,t) represents the generated solitary wave; H is the wave height; c is the wave velocity of the solitary wave; T f is the solitary wave generation time; d is the water depth; k is the wave number; sech(x) is the hyperbolic secant function, defined as 6. The method for determining the effect of submergence depth on a semi-submerged structure under the action of a solitary wave according to claim 1, characterized in that: The semi-submerged structure model is: The length of the water tank is 100m, the height is 2m, the water depth is d0=1.0m, the size of the semi-submerged structure is 5.0m×0.6m, it is fixed near the still water surface, and the distance between the bottom of the structure and the bottom of the water tank is d r , the initial flooding depth is d s =d0-d r , the wave height H0 is set to 0.5m, d r Take 0m, 0.2m, 0.4m...1.6m, a total of 9 working conditions.

7. The method for determining the effect of submergence depth on a semi-submerged structure under the action of a solitary wave according to claim 1, characterized in that: The transmission coefficient and the reflection coefficient are calculated as follows: In the formula, H i is the incident wave height, K t is the transmission coefficient, H t is the transmission wave height, K rf is the reflection coefficient, H rf is the reflected wave height.

8. The method for determining the effect of submergence depth on a semi-submerged structure under the action of a solitary wave according to claim 7, characterized in that: The calculation results of the transmission coefficient and the reflection coefficient were fitted with polynomials, and the empirical calculation formulas of the transmission coefficient and the reflection coefficient varying with the submergence depth were obtained as follows: Where Y1 is the transmission coefficient or reflection coefficient, A0, A1, A2, A3, A4 are fitting parameters, d s is the submergence depth.

9. The method for determining the effect of submergence depth on a semi-submerged structure under the action of a solitary wave according to claim 1, characterized in that: The wave load coefficient C of the structure in horizontal and vertical directions x and C z The calculation formula is: Among them, F x 、F z are the resultant forces acting on the structure in the horizontal and vertical directions respectively; A is the area of ​​the rectangular structure; ρ0 is the density of the liquid, and g is the acceleration due to gravity.

10. The method for determining the effect of submergence depth on a semi-submerged structure under the action of a solitary wave according to claim 1, characterized in that: The calculation results of the horizontal and vertical wave load coefficients were fitted with polynomials to obtain the empirical calculation formulas for the maximum and minimum values ​​of the horizontal and vertical wave loads as a function of the submerged depth: Among them, Y2 is the maximum wave load in the horizontal or vertical direction; Y3 is the minimum wave load in the horizontal or vertical direction; B0, B1, B2 are fitting coefficients, C0, C1, C2, C3 are fitting coefficients, d s is the submergence depth.

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