CN109914339A - A circular cylindrical breakwater with an external cylindrical grid and its numerical calculation method - Google Patents

Abstract

A circular-cylindrical breakwater with an external cylindrical grid and a numerical calculation method thereof belong to the technical field of wave-proof structures. Including inner and outer steel mesh, porous stone filling layer, cylindrical grid, steel pipe beam. The porous stone filling layer is located inside the cylindrical grid, which is clamped and fixed by the inner and outer steel meshes. The inner and outer steel meshes and the cylindrical grid are concentric rings at any horizontal section. The bottom of the inner and outer steel meshes is fixedly connected with the seabed, and the external cylindrical grille and the inner and outer steel meshes are fixedly connected by a plurality of steel pipe beams. According to the proportional boundary finite element method, the force of the annular cylindrical breakwater is calculated, and the numerical results show that the annular cylindrical breakwater has better anti-wave performance. The breakwater provided by the invention combines the opening structure and the opening structure with porous filling interlayer. By adjusting the opening coefficient and the filling coefficient, the advantages of the two are integrated, and the wave prevention effect is remarkable; and the opening grid and the porous stone layer Independent of each other, the design is simple, and the construction is convenient.

Description

A circular cylindrical breakwater with an external cylindrical grid and its numerical calculation method

technical field

The invention belongs to the technical field of wave-proof structures, and relates to a circular-cylindrical breakwater with an external cylindrical grid, in particular to a kind of wave force that can absorb part of the seawater through a porous stone filling layer and a cylindrical grid, thereby A wave-proof structure that protects the structures within its surrounding area from excessive wave force.

Background technique

In recent years, with the development of industries such as offshore oil and gas, marine transportation, marine fishery, coastal tourism and marine new energy, more and more offshore buildings have emerged, such as offshore drilling platforms, artificial islands, large-scale sea-crossing bridges, etc. These offshore structures play a pivotal role in economic development and social progress, but due to the particularity of the environment, these structures are more vulnerable to damage than land-based structures, and various marine disasters, such as disastrous waves, storm surges Even tsunamis are a huge test for marine structures. If the preventive measures are unreasonable, once damaged, if it occurs in the field of marine mining, it may cause crude oil leakage, damage the marine ecosystem, and even cause an explosion to cause more serious life and property. Safety, if it occurs in the field of marine traffic, the seriousness of the consequences is even more inestimable, so it is necessary to understand and master the technology to reduce the wave force on marine structures.

One of the effective ways to reduce or prevent these marine natural disasters is to build supporting marine engineering facilities at sea or on the coast through relevant technical equipment. Among them, the open-pore structure has been gradually popularized and applied in port, coastal and offshore engineering due to its good characteristics of reducing wave reflection and the wave force on itself. This kind of expansion has not been studied and applied by scholars at home and abroad. Therefore, for the first time, the present invention proposes a circular-cylindrical breakwater with an external cylindrical grid. This breakwater combines an open-pore structure with an interlayer open-pore structure with porous filling. By adjusting the opening coefficient and the filling coefficient, the two The advantages of the two are integrated, and a new numerical simulation method, the proportional boundary finite element method, is used to prove that the wave-proof structure has good wave-proof performance.

SUMMARY OF THE INVENTION

In view of the problems existing in the prior art, the present invention provides a circular-cylindrical breakwater with a circumscribed cylindrical grid, specifically a circular-cylindrical breakwater capable of dissipating seawater waves by means of the circumscribed cylindrical grid energy, so as to achieve a wave-proof structure that protects the function of the structure.

A circular-cylindrical breakwater with circumscribed cylindrical grid is proposed for the first time. This kind of breakwater combines the opening structure and the opening structure with porous filling interlayer. By adjusting the opening coefficient and filling coefficient, it integrates the advantages of the two. The numerical results of proportional boundary finite element prove that it reduces the amount of structures within its protection range. The effectiveness of the wave force experienced.

In order to achieve the above object, the technical scheme of the present invention is:

The utility model relates to a circular-cylindrical breakwater with an external cylindrical grid, comprising an inner steel mesh 1 , a porous stone filling layer 2 , an outer steel mesh 3 , a cylindrical grill 4 , and a steel pipe beam 5 . The porous stone filling layer 2 is located inside the cylindrical grid 4, and is clamped and fixed by the inner reinforcement mesh 1 and the outer reinforcement mesh 3. The inner reinforcement mesh 1, the outer reinforcement mesh 3, and the cylindrical grid 4 are at any level. Sections are concentric rings. The porosity and linear resistance coefficient of the porous stone filling layer 2 are uniform, the opening coefficient of the cylindrical grid 4 is uniform, and the inner reinforcement mesh 1 and outer reinforcement mesh 3 only serve to protect the two. The clamping and fixing effect of the porous stone filling layer between them has a negligible effect on the porosity and linear resistance coefficient of the anti-wave structure. The inner reinforcement mesh 1, the outer reinforcement mesh 3 and the seabed 7 are fixedly connected, and the top elevation of the circular cylindrical wave-proof structure of the circumscribed cylindrical grid 4 is greater than the elevation of the sea level 6, and the circumscribed cylindrical grid 4. The inner reinforcement mesh 1 and the outer reinforcement mesh 3 are connected by welding through a plurality of steel pipe beams 5 .

The circular cylindrical breakwater circumscribed with the cylindrical grille absorbs part of the wave force of seawater through the porous stone filling layer and the cylindrical grille, thereby achieving a wave-proof structure that avoids the structure within the surrounding area from being subjected to excessive wave force. Let the radius of the cylindrical grid be b, the radius of the outer steel mesh be c, the radius of the inner steel mesh be a, the porosity of the porous stone filling layer is ε, the linear resistance coefficient is f; the opening coefficient of the cylindrical grid is G, The seawater depth is H, the anti-wave structure is upright and the bottom end is fixedly connected to the seabed. In the calculation process, the following parameters will also be used: liquid density ρ, gravitational acceleration g and inertia coefficient λ.

The calculation method of the wave force on the system includes the following steps:

In the first step, the entire watershed is divided into three calculation sub-domains, namely the area Ω _Ι surrounded by the inner steel mesh 1, the area Ω _ΙΙ surrounded by the inner steel mesh 1 and the outer steel mesh 3, the outer steel mesh 3 and the cylinder The annular cylindrical region Ω _ΙΙΙ between the grids 4, and the infinite domain Ω _ΙV outside the cylindrical grid 4.

In the second step, for an ideal fluid without rotation and viscosity, the velocity potential function Φ(x, y, z, t) of the fluid in each subdomain can be decomposed into:

In the above formula ω is the angular frequency, which satisfies the equation ω ² =gktanh(kH), k is the wave number, i is the imaginary unit, The three-dimensional Laplace equation is satisfied, and the two-dimensional Helmholtz equation is obtained after simplification:

Assume The normal derivative on the boundary is Representing the normal wave velocity, using the variational principle and introducing the proportional boundary finite element (SBFEM) coordinate system, the basic governing equation of SBFEM and the expressions of the inner and outer boundary conditions can be obtained:

In the formula, is expressed in terms of proportional boundary finite element coordinates with respect to , ζ=k ₀ bξ, s, ξ are the hoop and radial coordinates in the finite element coordinates of the proportional boundary, respectively, ξ ₀ is the radial coordinate at the similarity center, ξ ₁ is the radial coordinate on the boundary , N is Lagrangian interpolation shape function, E ₀ , E ₂ , F _s are coefficient matrices, respectively The second and first derivatives of ζ.

The third step is to introduce boundary conditions to solve the above proportional boundary finite element governing equations. Assume respectively represent the velocity potentials in the domains Ω _Ι , Ω _ΙΙ , Ω _ΙΙΙ and Ω _ΙV , the coupling boundary conditions should be satisfied between the sub-domains: at the interface of the inner steel mesh Outside reinforcement mesh interface Cylindrical grid interface In addition, Ω _ΙV also needs to satisfy the Sommerfeld boundary condition at infinity, namely:

in, and is the normal derivative of the velocity potential, and r is the distance between the node and the scale center.

The fourth step, wait and After obtaining, the total field velocity potential Φ can be obtained, and then the wave surface height η and dynamic pressure p can be obtained, p=-ρΦ _,t ; the total force on the domain is calculated as follows: The first to third items in parentheses are the inner steel mesh (filling the inner wall), the outer steel mesh (filling the outer wall), and the wave force on the structural unit length at the cylindrical grid (outer wall), and R represents the calculated interface distance. distance from the center axis.

Compared with the prior art, the present invention has the following advantages: 1) the anti-wave effect is remarkable; 2) the opening grid and the porous stone layer are independent of each other, the design is simple, and the construction is convenient; 3) the ring-shaped anti-wave structure layer adopts the stone material Filling, material source is wide and economical.

Description of drawings

Figure 1 is a schematic diagram of a circular cylindrical breakwater circumscribed by a cylindrical grid;

Figure 2 is a simplified diagram of the model.

Figure 3 is a graph showing the change of wave force at different parts of the structure with different porosity ε of the porous stone filling layer.

Figure 4 is a graph showing the variation of the total wave force on the structure with the dimensionless wave number kb under the condition of different porosity ε of the porous stone filling layer.

Figure 5 is a graph showing the change of the wave force at different parts of the structure with different linear resistance coefficients f of the porous stone filling layer.

Figure 6 is a graph showing the relationship between the wave force at different parts of the structure and the opening coefficient G of the cylindrical grid.

Figures 7 and 8 are schematic diagrams of wave amplitudes within a certain range of the region where the structure is located when the opening coefficients of the cylindrical grid are G=0.1 and G=1.0, respectively.

Figures 9 and 10 are schematic diagrams of the wave amplitude within a certain range of the area where the structure is located when the radius of the outer steel mesh is c=6 and c=8, respectively.

Figures 11 and 12 are schematic diagrams of wave amplitudes within a certain range of the area where the structure is located when different inner steel mesh radii a=2 and a=4, respectively.

In the figure: 1 is the inner reinforcement mesh; 2 is the porous stone filling layer; 3 is the outer reinforcement mesh; 4 is the cylindrical grid; 5 is the steel pipe beam, 6 is the sea level; 7 is the seabed.

Detailed ways

The application principle of the present invention will be further described below in conjunction with the accompanying drawings and simulation examples. It should be understood that the simulation examples described herein are only used to explain the present invention, and are not intended to limit the present invention.

Referring to Figures 1-12, the present invention discloses a circular-cylindrical anti-wave structure that circumscribes a cylindrical grid. It includes inner reinforcement mesh 1, porous stone filling layer 2, outer reinforcement mesh 3, cylindrical grid 4, and steel pipe beam 5. The porous stone filling layer 2 is located inside the cylindrical grid 4, and is clamped and fixed by the inner reinforcement mesh 1 and the outer reinforcement mesh 3. The inner reinforcement mesh 1, the outer reinforcement mesh 3, and the cylindrical grid 4 are at any level. Sections are concentric rings. The porosity and linear resistance coefficient of the porous stone filling layer 2 are uniform, the opening coefficient of the cylindrical grid 4 is uniform, and the inner reinforcement mesh 1 and outer reinforcement mesh 3 only serve to protect the two. The clamping and fixing effect of the porous stone filling layer between them has a negligible effect on the porosity and linear resistance coefficient of the anti-wave structure. The inner reinforcement mesh 1, the outer reinforcement mesh 3 and the seabed 7 are fixedly connected, and the top elevation of the circular cylindrical wave-proof structure of the circumscribed cylindrical grid 4 is greater than the elevation of the sea level 6, and the circumscribed cylindrical grid 4. The inner reinforcement mesh 1 and the outer reinforcement mesh 3 are connected by welding through a plurality of steel pipe beams 5 .

In the present invention, the correlation calculation follows the linear potential flow theory, and the numerical calculation method adopted is the proportional boundary finite element method.

The entire watershed is divided into three calculation sub-domains, namely the area Ω _Ι surrounded by the inner reinforcement mesh 1 and the wall of the internal structure 4, the area Ω _ΙΙ surrounded by the inner reinforcement mesh 1 and the outer reinforcement mesh 3, and the outer reinforcement mesh 3. The infinite field Ω _ΙΙΙ .

For an ideal fluid without rotation and viscosity, the velocity potential function Φ(x, y, z, t) of the fluid in each subdomain can be decomposed into:

In the above formula ω is the angular frequency, k is the wave number, i is the imaginary unit, Simplify the 3D Laplace equation to get the 2D Helmholtz equation:

Assume The normal derivative on the boundary is Representing the normal wave velocity, using the variational principle and introducing the proportional boundary finite element (SBFEM) coordinate system, the basic equation of SBFEM and the expressions of the inner and outer boundary conditions can be obtained:

Introduce boundary conditions to solve the above-mentioned solution proportional boundary finite element control equation, then we can find Then the total field velocity potential Φ can be obtained, and the liquid velocity, wave height and dynamic pressure are respectively determined by the following expressions: p=-ρΦ, _t ; the total x-axial force on the domain is calculated as follows: The first to third items in parentheses are the forces on the inner steel mesh, the outer steel mesh, and the cylindrical grid on the unit length of the structure.

In order to illustrate the hydrodynamic characteristics of the system, relevant examples will be given for related expressions; the internal structure is simplified as a cylindrical structure coaxial with the circular cylindrical breakwater circumscribed by the cylindrical grid, referred to as the inner column. In the examples involved, b=10m, H=15m. In the figure, k all represent the wave number, η is the liquid level height (based on z=0), and the absolute value of |F _x | wave force.

The porosity ε and the linear resistance coefficient f are related to the density of the porous stone filling layer. The denser the filling, the smaller the porosity ε, and the larger the linear resistance coefficient f. On the contrary, the larger the porosity ε, the smaller the linear resistance coefficient f.

Referring to Figure 3, it can be seen that the wave force on the cylindrical grid is hardly affected by the porosity ε of the porous stone filling layer. With the increase of porosity ε, the wave force on the interface of the inner steel mesh first increases greatly and then tends to balance. The wave force on the interface of the outer steel mesh and the total wave force of the system both decrease gradually with the increase of the porosity ε. And the total force of the system is slightly larger than the wave force on the outer steel mesh surface, which shows that with the decrease of the density of the porous stone filling layer, the wave energy absorbed by the anti-wave structure gradually decreases, and the elimination of the cylindrical grid is reduced. The energy characteristics are basically not affected by the filling coefficient of the stone filling layer. Therefore, the filling coefficient of the porous stone filling layer can be independently designed independently of the opening coefficient of the external cylindrical grid, and the denser the porous stone filling layer is, the more wave energy can be absorbed. However, the total wave force the system is subjected to is also greater, so in order to improve the anti-wave capacity of the anti-wave structure, the compactness of the filling layer should be appropriately increased, but the overall stability of the system should also be taken into account.

Referring to Fig. 4, it can be seen that with the increase of porosity ε, the first-order and second-order resonance wave numbers of the system gradually decrease, that is, the resonance frequency of the system gradually advances, and the peak wave force increases gradually, which once again confirms the reference The conclusion of Figure 3, however, when the relative wave number of the external excitation is small, the larger the void ratio ε, the smaller the total wave force of the system, so the design of the circular-cylindrical anti-wave structure should also consider the external excitation wave number that may occur in the environment. scope.

Referring to Figure 5, it can be seen that the wave force on the cylindrical grid decreases slightly with the increase of the linear damping coefficient f of the porous stone filling layer, but the influence is small. With the increase of the linear damping coefficient f, the total wave force on the system first decreases and then increases steadily, while the wave force on the inner and outer reinforcement mesh surfaces shows an increasing trend, and the outer and inner reinforcement mesh interfaces are subject to an increasing trend. The difference of wave force increases gradually, which shows that with the increase of the density of the porous stone filling layer (the increase of the linear damping coefficient f), more and more wave energy is consumed by the porous stone filling layer. The compactness of the filling layer can improve the anti-wave capability of the anti-wave structure, but it also increases the wave force that the structure itself bears, so the design of the anti-wave structure filling layer should take into account the stability of the structure itself.

Referring to Figure 6, it can be seen that with the increase of the opening coefficient G of the cylindrical grid, the total wave force of the system first decreases sharply and then tends to balance, while the wave force on the cylindrical grid gradually decreases until it approaches At zero, the wave force on the interface of the outer and inner steel meshes first increases sharply and then tends to remain unchanged, and the difference between the two also shows a similar law, which shows that with the increase of the opening coefficient G of the cylindrical grid Increase, the wave energy consumed by the porous stone filling layer increases and finally tends to a constant value, while the wave energy shared by the cylindrical grid gradually decreases until it approaches zero. Therefore, in the design of the circular-cylindrical wave-proof structure with an external cylindrical grid provided by the present invention, an appropriate grid aperture factor should be selected so as to reasonably distribute the wave energy consumed by each part of the structure.

With reference to Figures 7 and 8, it can be seen intuitively that when the opening coefficient of the cylindrical grid is small (G=0.1), the amplitude of the annular area surrounded by the cylindrical grid and the outer steel mesh changes sharply, while the outer steel bars change sharply. There is basically no change in the regional wave amplitude within the net, which shows that the smaller opening coefficient G can make the cylindrical grid consume most of the wave energy. When the opening coefficient of the cylindrical grid is slightly larger (G=1.0), the circular The amplitude of the annular area surrounded by the cylindrical grid and the inner steel mesh changes sharply, and the amplitude of the area within the inner steel mesh tends to be gentle, which shows that the appropriate opening coefficient G can make the cylindrical grid and the porous stone filling layer reasonable. Distribute the energy consumption of waves, so that the anti-wave structure can play a more stable role.

Referring to Figures 9-12, it can be seen that the radius and thickness (c-a) of the porous stone filling layer have a significant impact on the wave height inside the breakwater. When the thickness of the porous stone filling layer is larger, the wave amplitude at the center of the wave breaking structure is significantly lower than that of the filling layer. When it is thinner, at the same time, when the radius of the porous stone filling layer is larger, the amplitude of the wave at the center of the anti-wave structure is obviously lower than that when the radius of the filling layer is small. The thickness and radius of the porous stone filling layer should be considered in the design of the circular-cylindrical wave-proof structure.

Claims (2)

1. The circular cylindrical breakwater externally connected with the cylindrical grid is characterized by comprising an inner steel bar mesh (1), a porous stone filling layer (2), an outer steel bar mesh (3), the cylindrical grid (4) and a steel pipe cross beam (5); the porous stone filling layer (2) is positioned inside the cylindrical grid (4) and is clamped and fixed by the inner reinforcing mesh (1) and the outer reinforcing mesh (3), the inner reinforcing mesh (1), the outer reinforcing mesh (3) and the cylindrical grid (4) are of circular ring structures and are concentric in any horizontal section; the porosity and the linear resistance coefficient of the porous stone filling layer (2) are uniform, and the aperture coefficient of the cylindrical grating (4) is uniform; the bottom of the inner side reinforcing mesh (1) and the bottom of the outer side reinforcing mesh (3) are fixedly connected with the sea bottom (7); the external cylindrical grid (4), the inner side reinforcing mesh (1) and the outer side reinforcing mesh (3) are connected through a plurality of steel pipe cross beams (5) in a welding manner; the top elevation of the circular cylindrical wave-preventing structure externally connected with the cylindrical grating (4) is greater than the elevation of the sea level (6).

2. The method for calculating the stress of the circular cylindrical breakwater externally connected with the cylindrical grating according to claim 1, characterized by comprising the following steps:

setting the radius of a cylindrical grid as b, the radius of an outer reinforcing mesh as c, the radius of an inner reinforcing mesh as a, the porosity of a porous stone filling layer as epsilon and the linear resistance coefficient as f; the aperture coefficient of the cylindrical grating is G, the seawater depth is H, the wave-proof structure is upright, and the bottom end of the wave-proof structure is fixedly connected with the seabed; in the calculation process, the following parameters are also used: liquid density rho, gravity acceleration g and inertia coefficient lambda;

the method for calculating the wave force borne by the system comprises the following steps:

in a first step, the whole watershed is divided into three sub-calculation domains, namely a region omega surrounded by the inner reinforcing mesh (1)_ΙThe region omega enclosed by the inner steel bar mesh (1) and the outer steel bar mesh (3)_ΙΙThe circular cylindrical area omega between the outer steel bar net (3) and the cylindrical grid (4)_ΙΙΙAnd an infinite region omega outside the cylindrical grating (4)_ΙV；

In the second step, for the ideal fluid without rotation and viscosity, the velocity potential function phi (x, y, z, t) of the fluid in each sub-domain is decomposed into:

in the formulaOmega is angular frequency and satisfies the equation omega²Gk tanh (kH), k is the wave number, i is the imaginary unit,satisfying the three-dimensional Laplace equation, and obtaining a two-dimensional Helmholtz equation after simplification:

is provided withThe normal derivative at the boundary is Expressing normal wave velocity, adopting variation principle and introducing proportional boundary finite element SBFEM coordinate system to obtain SBFEM basic control equation and inner and outer boundary condition expression:

in the formula,for using proportional boundary finite element coordinate representationThe node value of (1), ζ ═ k₀b ξ, s, ξ are the circumferential and radial coordinates, respectively, in the proportional boundary finite element coordinatesCoordinates, ξ₀As radial coordinates at the center of similarity, ξ₁As radial coordinates on the boundary, N being a Lagrangian interpolation shape function, E₀、E₂、F_sIs a coefficient matrix;

thirdly, introducing boundary conditions to solve the proportional boundary finite element control equation; is provided with Respectively represent the domain omega_Ι，Ω_ΙΙ、Ω_ΙΙΙAnd Ω_ΙVThe coupling boundary condition should be satisfied between sub-fields: inside reinforcing bar net interfaceOuter steel bar mesh interfaceCylindrical grid interfaceIn addition, Ω_ΙVThe Sommerfeld boundary conditions at infinity need to be satisfied, namely:

wherein,andis the normal derivative of the velocity potential, r is the distance between the node and the proportional center;

the fourth step is toAndafter the calculation, the total field velocity potential phi can be calculated, and further the wave surface height η and the dynamic pressure p can be calculated,p＝-ρΦ_,t(ii) a The total force exerted by the domain is calculated as follows:wherein the first to third terms in the brackets are the wave force applied to the structure unit length at the inner side reinforcing mesh filling inner wall, the outer side reinforcing mesh filling outer wall and the cylindrical grid outer wall respectively, and R represents the distance from the calculation interface to the central axis.