CN111210502B - Calculation method for predicting vertical impact acting force of landslide suffered by submarine pipeline - Google Patents
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Abstract
The invention discloses a computer method for simulating that a submarine pipeline is subjected to landslide vertical impact acting force, which is technically characterized by comprising the following steps: establishing a three-dimensional model of the submarine pipeline subjected to landslide vertical impact acting force; step 2: dividing the three-dimensional model into grids, enabling a control volume which is not repeated to exist around each grid point, and solving a result by using a calculation equation; step 3: determining model parameters according to submarine sediment sampling and testing of a submarine landslide pre-judging area; step 4: the obtained parameters are input into the model established in the step 2, and the invention provides technical reference for prediction of landslide disaster acting force of the submarine pipeline and disaster prevention design.
Description
Technical Field
The invention relates to a calculation method for predicting the vertical impact acting force of a landslide on a submarine pipeline.
Background
In recent years, with the rapid development of ocean engineering, the number of laid submarine pipeline facilities such as submarine pipelines and cables directly related to ocean energy development is increasing, and whether the pipelines are stable in the service period directly influences the safety of ocean oil and gas exploitation, personnel lives and properties and ocean ecological environments. However, at the same time, the submarine pipeline is also faced with more complex and variable marine disaster geological environment, wherein the submarine landslide is a marine soil disaster which frequently occurs, has wide influence area and extremely high threat, gradually changes into a submarine flow sliding body under the complex action of water environment after triggered sliding, has the characteristics of large volume, high speed, long sliding distance and the like, has the highest sliding speed of 30m/s, can generate strong impact force, and seriously threatens the stability and safety of submarine pipeline engineering facilities in the easy-occurrence area of the submarine landslide and the adjacent area thereof. Therefore, it is important to explore the impact of a subsea landslide on a pipeline for the design work of subsea pipeline engineering facilities.
At present, in the research of impact action of a submarine landslide on a pipeline, an evaluation method of normal impact acting force (the normal acting force direction is consistent with the landslide moving direction) generated by the submarine landslide is relatively perfect, but the research of vertical impact acting force (the vertical acting force direction is perpendicular to the landslide moving direction) of the submarine landslide is very limited, and the vertical acting force of the submarine landslide can cause vertical deformation or periodic vibration of the pipeline, so that the method has great disaster action on the pipeline and has great engineering research value; furthermore, the impact of the real situation of varying subsea pipeline to seabed on impact forces is often not considered.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a calculation method for predicting the vertical impact acting force of a landslide on a submarine pipeline, which can accurately and effectively simulate the distance change between the submarine pipeline and the seabed and accurately analyze the impact acting force under the influence of the distance change.
In order to achieve the above purpose, the present invention provides the following technical solutions: a calculation method for predicting the vertical impact acting force of a landslide on a submarine pipeline comprises the following steps: step 1: establishing a three-dimensional model of the submarine pipeline subjected to landslide vertical impact acting force; step 2: dividing the three-dimensional model into grids, enabling a control volume which is not repeated to exist around each grid point, and solving a result by using a calculation equation; step 3: determining model parameters according to submarine sediment sampling and testing of a submarine landslide pre-judging area; step 4: and inputting the obtained parameters into the model established in the step 2.
Further, step 1 includes: the three-dimensional model comprises a geometric configuration stage, a grid division stage, a fluid calculation domain setting stage, a material property setting stage and a boundary condition setting stage;
further, step 1 includes: geometric configuration arrangement: the submarine pipeline is a flat pipeline, the diameter (D) is 25mm, and the fluid calculation domain size is 16D (x-axis direction) x 9D (y-axis direction) x 1D (z-axis direction); different distances can be arranged between the pipeline and the seabed; and (3) grid division setting: dividing grids by adopting an ICEM-CFD module in an ANSYS-Workbench, dividing the whole calculation domain into unstructured grids into tetrahedral units, and arranging 5 layers of high-density boundary layer grids on the surface of the interaction of a sliding body and a pipeline, wherein the thickness of the grids is 2mm; fluid computing domain settings: setting the submarine fluid slider as a continuous free-surface flow taking buoyancy into account, and simulating by using an incompressible two-phase flow; material property setting: in the setting part of the material rheological model, the remolding yield strength, the yield viscosity and the rheological index are respectively 7.3Pa, 94 Pa.s and 0.35, so as to meet the constitution relation of classical sea-phase soil bodies (10 percent clay, 35 percent water and 55 percent sand), and the material density is 1681kg/m 3 The method comprises the steps of carrying out a first treatment on the surface of the Boundary condition setting: the landslide inlet is set as an inlet boundary with stable inflow and certain speed (the movement speed of the sliding body is set to be 0.48-15.82 m/s), the outlet is set as an opening boundary, the top of the calculation domain is set as a free sliding boundary, the bottom and the pipeline surface are both rough and non-sliding boundaries, and the equivalent roughness ks of the pipeline surface is set to be 0.5mm and 0.0015mm respectively.
Further, step 2 includes: step 3-1: according to the submarine sediment sampling and testing of the submarine landslide pre-judging area, basic physical and mechanical parameters such as sediment non-drainage shear strength, density and the like which can form a submarine landslide body are determined; step 3-2: determining the size parameter of the submarine pipeline to be laid according to the working requirement of the submarine pipeline, wherein the size parameter is the diameter and the cross-sectional area of the submarine pipeline; step 3-3: according to the risk bearing grade, the sliding speed of the submarine landslide is estimated, and the movement Reynolds number of the submarine landslide body is calculated according to the following formula:
Re non-Newtonian ＝ρ·V 2 /s u (1)
wherein: re (Re) non-Newtonian Reynolds number for the seabed landslide body movement; v is the sliding speed of the submarine landslide, m/s; ρ and s u The density and the non-drainage shear strength of the seabed landslide body are respectively in kg/m 3 And kPa; step 3-4: considering the influence of the submarine pipeline and the seabed space, estimating the size of the submarine pipeline-seabed space in the submarine landslide impact pipeline effect, and fully combining the conditions of the submarine pipeline such as relief of paving topography, erosion of seabed sediments by a landslide body and the like; step 3-5: based on a theoretical frame of the mechanics of the mixed soil and the hydrodynamics, a calculation formula of the vertical impact acting force of the landslide suffered by the submarine pipeline is constructed, wherein the formula is as follows
Wherein: f (F) V The vertical impact acting force of the submarine landslide is N; the first term on the right side of the equation is the geomechanical term, where A is the cross-sectional area of the pipeline subjected to landslide impact; n (N) V Is the coefficient of the bearing capacity of the soil body, and the value of the coefficient can be determined byCalculating; wherein: h is the distance between the submarine pipeline and the seabed; d is the diameter of the subsea pipeline; the second term on the right side of the equation is the hydrodynamic term, C V Is a fluid lift coefficient, the value of which can be represented by +.>Calculating, wherein: h C Is the spacing between the critical submarine pipeline and the seabed; reynolds number Re of seabed landslide body motion non-Newtonian Determining the formula asWherein: r is R a A bypass acceleration zone formed for the subsea landslide impact line; delta seabed Forming a boundary layer thickness for seabed landslide movement, l x The characteristic distance of the submarine landslide movement depends on the distance between the submarine pipeline and the submarine landslide trigger area; step 3-6: the soil body bearing capacity coefficient and the fluid lift coefficient are calculated, and the soil body bearing capacity coefficient and the fluid lift coefficient and other related parameters are brought into a mixed soil mechanics-fluid mechanics theoretical frame, so that accurate prediction of the vertical acting force of landslide suffered by the submarine pipeline can be realized.
The invention has the beneficial effects that:
1. establishing a three-dimensional model to clearly and intuitively simulate complex fluid movement;
2. the calculation method is based on a mixed soil mechanics-fluid mechanics theoretical framework, and can accurately reflect the influence of the sea bottom landslide body material attribute on the vertical impact acting force formed by the sea bottom landslide body material attribute; the influence of the real situation of the change of the distance between the submarine pipeline and the seabed is comprehensively considered, so that the prediction result of the vertical acting force of the submarine landslide impact pipeline is more accurate; the method has good application effect after a large number of numerical simulation and physical model tests are used for inspection, and reasonable basis is provided for prediction of landslide disaster acting force of the submarine pipeline and disaster prevention design;
3. by arranging 5 layers of high-density boundary layer grids (the total thickness of the grids is 2 mm) at the interface of the submarine landslide and pipeline interaction, the simulation precision of interaction force can be greatly improved.
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FIG. 1 is a schematic flow chart of establishing a virtual model;
fig. 2 is a schematic flow chart of extracting data.
Detailed Description
The invention will now be described in further detail with reference to the drawings and examples. Wherein like parts are designated by like reference numerals. It should be noted that the words "front", "back", "left", "right", "upper" and "lower" used in the following description refer to directions in the drawings, and the words "bottom" and "top", "inner" and "outer" refer to directions toward or away from, respectively, the geometric center of a particular component.
Referring to fig. 1 to 2, a calculation method for predicting a vertical impact force of a landslide for a subsea pipeline according to the present embodiment includes the steps of:
step 1: establishing a three-dimensional model of the submarine pipeline subjected to landslide vertical impact acting force;
step 2: dividing the three-dimensional model into grids, enabling a control volume which is not repeated to exist around each grid point, and solving a result by using a calculation equation;
step 3: determining model parameters according to submarine sediment sampling and testing of a submarine landslide pre-judging area;
step 4: and inputting the obtained parameters into the model established in the step 2.
On the basis of the above embodiment, step 1 includes: the three-dimensional model comprises a geometric configuration stage, a grid division stage, a fluid calculation domain setting, a material property setting and a boundary condition setting;
the improvement is specifically as follows: the three-dimensional model building software in this embodiment may use commercial CFD software CFX to perform simulation analysis, where each sub-module involved in the modeling process includes: the method comprises the steps of a Geometry geometric module (corresponding to a geometric configuration stage), an ICEM-CFD grid module (corresponding to a grid division stage), a CFX-Pre preprocessing module (corresponding to a fluid calculation domain setting, a material attribute setting, a boundary condition setting and other stages), a CFX-slot solving module (corresponding to a numerical value solving stage) and a CFX-Post processing module (corresponding to a result analysis stage), wherein the CFX-slot solving module adopts a finite volume method, also called a control volume method, the basic idea is that a calculation domain is divided into grids, a control volume which is not repeated with each other is arranged around each grid point, a differential equation (control equation) to be solved is integrated for each control volume, so that a set of discrete equations are obtained by the finite volume method, the balance of the control volume flux is physically represented, and each approximation in the equations contains a definite physical meaning; and the method is suitable for any type of cell grid, and is convenient to apply to simulate complex fluid movement.
On the basis of the above embodiment, step 1 includes:
(1) Geometric configuration arrangement: the submarine pipeline is a flat pipeline, the diameter (D) is 25mm, and the fluid calculation domain size is 16D (x-axis direction) x 9D (y-axis direction) x 1D (z-axis direction); different distances can be arranged between the pipeline and the seabed; and (3) grid division setting: dividing grids by adopting an ICEM-CFD module in an ANSYS-Workbench, dividing the whole calculation domain into unstructured grids into tetrahedral units, and arranging 5 layers of high-density boundary layer grids on the surface of the interaction of a sliding body and a pipeline, wherein the thickness of the grids is 2mm; fluid computing domain settings: setting the submarine fluid slider as a continuous free-surface flow taking buoyancy into account, and simulating by using an incompressible two-phase flow; material property setting: in the setting part of the material rheological model, the remolding yield strength, the yield viscosity and the rheological index are respectively 7.3Pa, 94 Pa.s and 0.35, so as to meet the constitution relation of classical sea-phase soil bodies (10 percent clay, 35 percent water and 55 percent sand), and the material density is 1681kg/m 3 The method comprises the steps of carrying out a first treatment on the surface of the Boundary condition setting: the landslide inlet is set as an inlet boundary with stable inflow and certain speed (the movement speed of the sliding body is set to be 0.48-15.82 m/s), the outlet is set as an opening boundary, the top of the calculation domain is set as a free sliding boundary, the bottom and the pipeline surface are both rough and non-sliding boundaries, and the equivalent roughness ks of the pipeline surface is set to be 0.5mm and 0.0015mm respectively. .
The improvement is specifically as follows: (1) Geometric configuration setting, the object studied in this example is that the submarine pipeline is a tiled pipeline, the diameter (D) is set to 25mm, and the fluid calculation domain size is 16D (x-axis) x 9D (y-axis) x 1D (z-axis); the distance between the pipeline and the seabed is set to 1D, which is considered by zakri et al as a suspended pipeline, although the present study will discuss the effect of different pipeline-seabed clearances on landslide impact pipelines in later sections, here the same set as zakri et al is used for comparison with the results of the study; further, the slip thickness is set to 7D;
(2) The mesh division is set, in this embodiment, the ICEM-CFD module in ANSYS-Workbench is adopted to divide meshes, the whole calculation domain is divided into unstructured meshes which are tetrahedral units, the number of the units is 25 ten thousand, the maximum mesh size is 12mm, mesh encryption (minimum size 2 mm) is carried out around a pipeline, and 5 layers of high-density boundary layer meshes (total thickness 2 mm) are arranged on the surface of the interaction of the sliding body and the pipeline, so that simulation precision can be greatly improved;
(3) Setting a fluid calculation domain, namely setting a submarine flow sliding body as a continuous free surface flow taking buoyancy into consideration, simulating by using an incompressible two-phase flow, and adopting an expanded standard k-epsilon turbulence model for the movement of the high-speed launching and the flow sliding body, wherein k is turbulence kinetic energy (J); epsilon is the dissipation ratio (%) of turbulent kinetic energy;
(4) Setting material properties, namely assuming that the sea bottom flow sliding body is sufficiently remolded, taking 7.3Pa, 94 Pa.s and 0.35 for remolded yield strength, yield viscosity and rheological index respectively in a material rheological model setting part in CFX so as to meet the rheological relation of (10% clay+35% water+55% sand) constitution in Zaker and other experiments, and setting material density to 1681kg/m 3 ；
(5) Boundary condition setting. The landslide inlet is set as an entrance boundary with stable inflow and constant speed (the movement speed of the sliding body is set as (0.48-15.82 m/s), the outlet is set as an opening boundary, the top of the calculation domain is set as a free sliding boundary, the bottom and the pipeline surface are both rough and non-sliding boundaries, and for comparison with previous researches, the equivalent roughness ks of the pipeline surface is set as 0.5mm and 0.0015mm respectively.
On the basis of the above embodiment, step 2 includes:
step 3-1: according to the submarine sediment sampling and testing of the submarine landslide pre-judging area, basic physical and mechanical parameters such as sediment non-drainage shear strength, density and the like which can form a submarine landslide body are determined;
step 3-2: determining the size parameter of the submarine pipeline to be laid according to the working requirement of the submarine pipeline, wherein the size parameter is the diameter and the cross-sectional area of the submarine pipeline;
step 3-3: according to the risk bearing grade, the sliding speed of the submarine landslide is estimated, and the movement Reynolds number of the submarine landslide body is calculated according to the following formula:
Re non-Newtonian ＝ρ·V 2 /s u (1)
wherein: re (Re) non-Newtonian Reynolds number for the seabed landslide body movement; v is the sliding speed of the submarine landslide, m/s; ρ and s u The density and the non-drainage shear strength of the seabed landslide body are respectively in kg/m 3 And kPa;
step 3-4: considering the influence of the submarine pipeline and the seabed space, estimating the size of the submarine pipeline-seabed space in the submarine landslide impact pipeline effect, and fully combining the conditions of the submarine pipeline such as relief of paving topography, erosion of seabed sediments by a landslide body and the like;
step 3-5: based on a theoretical frame of the mechanics of the mixed soil and the hydrodynamics, a calculation formula of the vertical impact acting force of the landslide suffered by the submarine pipeline is constructed, wherein the formula is as follows
Wherein: f (F) V The vertical impact acting force of the submarine landslide is N; the first term on the right side of the equation is the geomechanical term, where A is the cross-sectional area of the pipeline subjected to landslide impact; NV is the soil body bearing capacity coefficient, and the value of NV can be determined byCalculating; wherein: h is the distance between the submarine pipeline and the seabed; d is the diameter of the subsea pipeline; the second term on the right side of the equation is the hydrodynamic term, C V Is a fluid lift coefficient, the value of which can be represented by +.>Calculating, wherein: h C Is the spacing between the critical submarine pipeline and the seabed; reynolds number Re of seabed landslide body motion non-Newtonian Determining the formula asWherein: r is R a A bypass acceleration zone formed for the subsea landslide impact line; delta seabed Forming a boundary layer thickness for seabed landslide movement, l x The characteristic distance of the submarine landslide movement depends on the distance between the submarine pipeline and the submarine landslide trigger area;
step 3-6: the soil body bearing capacity coefficient and the fluid lift coefficient are calculated, and the soil body bearing capacity coefficient and the fluid lift coefficient and other related parameters are brought into a mixed soil mechanics-fluid mechanics theoretical frame, so that accurate prediction of the vertical acting force of landslide suffered by the submarine pipeline can be realized.
The improvement is specifically as follows: the proposed calculation method is based on a mixed soil mechanics-fluid mechanics theoretical framework, and can accurately reflect the influence of the sea bottom landslide body material attribute on the vertical impact acting force formed by the sea bottom landslide body material attribute; the influence of the real situation of the change of the distance between the submarine pipeline and the seabed is comprehensively considered, so that the prediction result of the vertical acting force of the submarine landslide impact pipeline is more accurate; and the method is verified by a large number of numerical simulation and physical model tests, has good application effect, and provides reasonable basis for prediction of landslide disaster acting force of the submarine pipeline and disaster prevention design.
The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above examples, and all technical solutions belonging to the concept of the present invention belong to the protection scope of the present invention. It should be noted that modifications and adaptations to the present invention may occur to one skilled in the art without departing from the principles of the present invention and are intended to be within the scope of the present invention.
Claims (2)
1. A calculation method for predicting vertical impact acting force of a landslide on a submarine pipeline is characterized by comprising the following steps of: the calculation method is based on a mixed soil mechanics-fluid mechanics theory and comprises the following steps:
step 1: establishing a three-dimensional model of the submarine pipeline subjected to landslide vertical impact acting force;
step 2: dividing the three-dimensional model into grids, enabling a control volume which is not repeated to exist around each grid point, and solving a result by using a calculation equation;
step 3: determining model parameters according to submarine sediment sampling and testing of a submarine landslide pre-judging area;
step 4: inputting the obtained parameters into the model established in the step 2;
the step 1 comprises the following steps:
the three-dimensional model comprises a geometric configuration stage, a grid division stage, a fluid calculation domain setting, a material property setting and a boundary condition setting;
the step 1 comprises the following steps:
geometric configuration arrangement: the submarine pipeline is a tiled pipeline, the diameter D is 25mm, the fluid calculation domain size is 16D multiplied by 9D multiplied by 1D, and the fluid calculation domain sizes are respectively in the x-axis direction multiplied by the y-axis direction multiplied by the z-axis direction; the distance between the pipeline and the seabed is 1D;
and (3) grid division setting: dividing grids by adopting an ICEM-CFD module in an ANSYS-Workbench, dividing the whole calculation domain into unstructured grids into tetrahedral units, and arranging 5 layers of high-density boundary layer grids on the surface of the interaction of a sliding body and a pipeline, wherein the thickness of the grids is 2mm;
fluid computing domain settings: setting the submarine fluid slider as a continuous free-surface flow taking buoyancy into account, and simulating by using an incompressible two-phase flow;
material property setting: in the setting part of the material rheological model, the remolding yield strength, the yield viscosity and the rheological index are respectively 7.3Pa, 94 Pa.s and 0.35, so as to meet the constitution relation of classical sea-phase soil bodies, namely 10 percent of clay, 35 percent of water and 55 percent of sand, and the material density is 1681kg/m 3 ；
Boundary condition setting: the landslide inlet is set as an inlet boundary with stable inflow and certain speed, the movement speed of the flow sliding body is set to be 0.48-15.82 m/s, the outlet is set as an opening boundary, the top of the calculation domain is set as a free sliding boundary, the bottom and the pipeline surface are both rough and non-sliding boundaries, and the equivalent roughness ks of the pipeline surface is set to be 0.5mm and 0.0015mm respectively.
2. A computing method for predicting the vertical impact force of a landslide in a subsea pipeline according to claim 1, wherein: the step 2 comprises the following steps:
step 3-1: according to the submarine sediment sampling and testing of the submarine landslide pre-judging area, determining sediment non-drainage shear strength and density which are likely to form a submarine landslide body;
step 3-2: determining the size parameter of the submarine pipeline to be laid according to the working requirement of the submarine pipeline, wherein the size parameter is the diameter and the cross-sectional area of the submarine pipeline;
step 3-3: according to the risk bearing grade, the sliding speed of the submarine landslide is estimated, and the movement Reynolds number of the submarine landslide body is calculated according to the following formula:
Re non-Newtonian ＝ρ·V 2 /s u (1)
wherein: re (Re) non-Newtonian Reynolds number for the seabed landslide body movement; v is the sliding speed of the submarine landslide, m/s; ρ and s u The density and the non-drainage shear strength of the seabed landslide body are respectively in kg/m 3 And kPa;
step 3-4: considering the influence of the submarine pipeline and the seabed space, estimating the size of the submarine pipeline-seabed space in the submarine landslide impact pipeline effect, and fully combining the situation that the submarine pipeline is laid with relief and seabed sediment is corroded by a landslide body;
step 3-5: based on a theoretical frame of the mechanics of the mixed soil and the hydrodynamics, a calculation formula of the vertical impact acting force of the landslide suffered by the submarine pipeline is constructed, wherein the formula is as follows
Wherein: f (F) V The vertical impact acting force of the submarine landslide is N; the first term on the right side of the equation is the geomechanical term, where A is the cross-sectional area of the pipeline subjected to landslide impact; n (N) V Is the coefficient of the bearing capacity of the soil body, and the value of the coefficient can be determined byCalculating; wherein: h is the distance between the submarine pipeline and the seabed; d is the diameter of the subsea pipeline; the second term on the right side of the equation is the hydrodynamic term, C V Is a fluid lift coefficient, the value of which canBy->Calculating, wherein: h C Is the spacing between the critical submarine pipeline and the seabed; reynolds number Re of seabed landslide body motion non-Newtonian Determining the formula asWherein: r is R a A bypass acceleration zone formed for the subsea landslide impact line; delta seabed Forming a boundary layer thickness for seabed landslide movement, l x The characteristic distance of the submarine landslide movement depends on the distance between the submarine pipeline and the submarine landslide trigger area;
step 3-6: the soil body bearing capacity coefficient and the fluid lift coefficient are calculated, and the soil body bearing capacity coefficient and the fluid lift coefficient and other related parameters are brought into a mixed soil mechanics-fluid mechanics theoretical frame, so that accurate prediction of the vertical acting force of landslide suffered by the submarine pipeline can be realized.
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