CN117422006A - Road collapse disaster deduction simulation method based on CFD-DEM and FEM combined algorithm - Google Patents
Road collapse disaster deduction simulation method based on CFD-DEM and FEM combined algorithm Download PDFInfo
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Abstract
The embodiment of the invention provides a road collapse disaster deduction simulation method based on a CFD-DEM and FEM combined algorithm, and relates to the technical field of urban road collapse analysis and prediction treatment. The method is convenient for realizing deduction and simulation of urban road collapse disasters, and provides basis for realizing collapse prediction and treatment of urban roads with similar or same geological environment and soil body mechanical parameters. Comprising the following steps: obtaining geological environment and soil parameters according to the road collapse case, and calculating microscopic parameters; establishing a three-dimensional pipeline model and a flow field model in the CFD module; establishing a three-dimensional discrete element particle model in a DEM module; realizing the bidirectional fluid-solid coupling of the CFD module and the DEM module, and establishing a bidirectional fluid-solid coupling model; simulating the sinking process of soil around the damaged pipeline by using a bidirectional fluid-solid coupling model; and applying loads to different soil models at the FEM module, simulating external actions, and calculating the moulding damage of the soil. The method is suitable for road subsidence analysis, prediction and prevention engineering.
Description
Technical Field
The invention relates to the technical field of urban road collapse analysis and predictive treatment, in particular to a road collapse disaster deduction simulation method based on a CFD-DEM and FEM combined algorithm.
Background
In recent years, urban collapse disasters frequently happen, and urban safety and development are seriously affected. Pavement collapse is an important manifestation of urban collapse, which occurs on a smaller scale, but is often more severely lost and impacted by the presence in densely populated urban areas. Therefore, the deduction and simulation of urban road collapse disasters are researched, and the method has important significance for effectively preventing and controlling the collapse disasters.
Disclosure of Invention
In view of the above, the embodiment of the invention provides a road collapse disaster deduction simulation method based on CFD-DEM and FEM combined calculation. The analysis model is constructed, so that deduction and simulation of urban road collapse disasters are facilitated, and basis can be provided for the implementation of collapse prediction and treatment of urban roads with similar or identical geological environments and soil mechanical parameters.
In order to achieve the above purpose, the invention adopts the following technical scheme:
in a first aspect, an embodiment of the present invention provides a road collapse disaster deduction simulation method based on a CFD-DEM and FEM combined algorithm, where the method includes:
according to the obtained road collapse case, obtaining geological environment and soil mechanical parameters of the position of the collapse road through geological analysis, and calculating microscopic parameters of the three-dimensional discrete element particle model;
according to the geological environment, a three-dimensional pipeline model and a flow field model are established in the CFD module;
according to the microcosmic parameters, a three-dimensional discrete element particle model is established in a DEM module;
and carrying out bidirectional fluid-solid coupling on the three-dimensional pipeline, the flow field model and the three-dimensional discrete element particle model to obtain a bidirectional fluid-solid coupling model so as to simulate the sinking process and degree of soil around the damaged pipeline.
Simulating the sinking process and degree of soil around a damaged pipeline by using the bidirectional fluid-solid coupling model, and establishing a finite element model of the soil in an FEM module;
based on the soil mechanical parameters, loading finite element models of different soil bodies in an FEM module to simulate external action, and calculating and determining the moulding damage of the soil bodies; the loads applied by the FEM module to different soil models comprise the lateral soil pressure of surrounding soil, upper vehicle load and surrounding building construction disturbance.
Optionally, the simulating the sinking process and degree of the soil around the damaged pipeline by using the bidirectional fluid-solid coupling model includes:
A. setting a geometric model of a soil body and a pipeline in the DEM model;
B. setting a corresponding physical model and boundary conditions in the CFD model, and carrying out flow field calculation;
C. the flow field data obtained by the CFD model calculation is imported into a DEM model;
D. the DEM model calculates the movement and interaction of soil particles according to the imported flow field data;
E. and C to D, repeating the steps to obtain the bidirectional fluid-solid coupling model, and simulating the evolution process of the collapse road disease.
Optionally, the three-dimensional pipeline model has a plurality of different forms of failure including: upper orifice failure, left and right orifice failure, lower orifice failure, annular failure, and radial failure.
Optionally, the method further comprises: in the process of establishing the flow field model in the CFD module, according to the climate and the soil of the position where the collapse case is located, establishing seepage flow fields with different water volumes so as to simulate soil seepage scenes with different water volumes.
Optionally, the microscopic parameters include soil particle radius, density, modulus, poisson's ratio, and coefficient of friction.
Optionally, the simulating the sinking process and degree of the soil around the damaged pipeline by using the bidirectional fluid-solid coupling model includes: and simulating and calculating a collapse simulation model of three factors of water, soil and pipelines at the collapse position by using the bidirectional fluid-solid coupling model, and simulating 5 disease evolution processes of slight loosening, medium loosening, serious loosening, void and cavity of the soil body.
Optionally, after calculating and determining the plastic deformation of the soil body, the method further comprises: predicting the plastic region range and settlement of a road similar to or the same as geological environment and soil mechanics in a subsidence road case under different load actions;
and combining a result obtained by simulating the bidirectional fluid-solid coupling by the bidirectional fluid-solid coupling model, and analyzing the damage evolution trend of the road in a certain time.
Optionally, after calculating and determining the plastic deformation of the soil body, the method further comprises: determining the treatment and reinforcement measures of the corresponding road according to the calculation result and the analysis result;
reinforcement is based on roads that are similar or identical to the governance and reinforcement measures.
Optionally, the DEM model divides the calculation area into subareas of 130mm multiplied by 20mm multiplied by 100mm in the process of establishing the three-dimensional discrete element particle model;
in the process of establishing a three-dimensional pipeline model in the CFD module, the collapse case comprises a pipeline with the diameter of 30mm, the burial depth of 75mm and the size of a damaged port of 5.5mm multiplied by 5.5mm.
Optionally, establishing a flow field model in the CFD model includes:
fluid calculation is carried out by adopting FLUENT software; the boundary conditions to be considered in the calculation process comprise a speed inlet, a pressure outlet and symmetrical boundary conditions;
the flow field process calculated by the CFD model comprises the following steps:
dividing grids for calculation according to the collapse area to be analyzed, and dividing the grids into a plurality of sub-grids;
and selecting a solver and a physical model corresponding to the sub-grid;
and defining fluid properties and boundary conditions for the physical model, and configuring a corresponding solving algorithm to obtain the flow field model.
Optionally, after calculating and determining the plastic deformation of the soil body, the method further comprises: according to the calculation result and the analysis result, evaluating the safe bearing performance of the cement concrete pavement of the corresponding road:
number of axle load actions N of each level of road i Can be converted into the number of times N of the designed axle load according to the following formula s ：
Wherein P is i : the i-th level axle load (kN), the coupling is calculated according to each axle load separately;
P s : designing a shaft load (kN);
n: various shaft-type shaft-carrying level bits;
N i : i the number of times of action of the level shaft load;
N s : the number of times of the axle load is designed;
the limit state of the cement concrete pavement of the road adopts the following formula:
γ r (σ c.pr +σ c.tr )≤f c.r ；
γ r (σ c.p.max +σ c.t.max )≤f c.r ；
γ r ＝1+Ψ 1 +Ψ 2 ；
in the above, sigma c.pr Driving load fatigue stress (MPa) generated at critical load position of cement concrete pavement;
σ c.tr temperature gradient fatigue stress (MPa) generated at critical load position of cement concrete pavement;
σ c.p.max maximum load stress (MPa) generated by the heaviest axle load at the critical load position;
σ c.t.max maximum temperature warping stress (MPa) generated by the maximum temperature gradient of the region at the critical charge position;
f c.r standard value (MPa) of flexural tensile strength of cement concrete pavement;
γ r reliability coefficient;
beta is a target reliable index;
Ψ 1 constructing a variation level coefficient;
Ψ 2 determining a horizontal coefficient of the material parameter, wherein the first level is 0, the second level is 5%, and the third level is 10%;
design axle load P s Number of permitted applications N to the cement concrete pavement of the road s1 The method comprises the following steps:
the cement concrete pavement safety bearing conditions of the road are as follows: n (N) s ≤N s1 ；
Wherein m is 1 Is the constant sigma of the cement concrete pavement material s1 To design the axle load P s And stress is generated on the cement concrete pavement of the road.
Optionally, the evaluating the safe bearing performance of the corresponding road according to the calculation result and the analysis result further includes evaluating the foundation safe bearing performance of the corresponding road:
ultimate bearing capacity q of road foundation f The method comprises the following steps:
in the above formula, c is the cohesive force of soil; gamma is the soil weight; D. b is the burial depth and width of the foundation respectively; sigma (sigma) 0 Is the normal stress on the equivalent free surface; beta 0 Is the inclination angle of the equivalent free surface and the horizontal plane; k (k) 0 Is the static soil pressure coefficient; delta 0 Is the friction angle between the soil and the foundation side; n (N) c 、N q 、N γ Is the internal friction angle with the soilAnd beta 0 Angle dependent load bearing coefficients;
design axle load P s Number of permitted functions N on road foundation s2 The method comprises the following steps:
the foundation safety bearing conditions of the road are as follows: n (N) s ≤N s2 ；
Wherein m is 2 Is the constant of foundation material, sigma s2 To design the axle load P s And stress is generated on the road foundation.
According to the road collapse disaster deduction simulation method based on the CFD-DEM and FEM combined algorithm, which is provided by the embodiment of the invention, the model constructed based on the discrete unit method (CFD) and the computational fluid dynamics method (DEM) is subjected to fluid-solid coupling to obtain a bidirectional fluid-solid coupling model, so that the erosion degree of soil around the pipeline in factors such as soil, water, pipelines and loads can be simulated, and the soil damage process is simulated based on the finite unit method (FEM). The method can simulate and analyze the motion state of soil particles through a discrete element particle model and simulate the water flow state in the soil through a flow field model to obtain a bidirectional fluid-solid coupling model, realize the coupling simulation of the interaction of water flow and the soil, achieve the purposes of deduction and prediction of road collapse disasters, and calculate the plastic damage degree of local soil through finite element simulation. Therefore, the invention is convenient for realizing deduction and simulation of urban road collapse disasters, thereby providing basis for realizing collapse prediction and treatment of urban roads with similar or same geological environment and soil body mechanical parameters. .
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings required in the description of the embodiments or the prior art will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the invention and that other drawings may be obtained from these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic flow chart of a road collapse disaster deduction simulation method based on CFD-DEM and FEM combined calculation according to an embodiment of the invention;
FIG. 2 is a schematic diagram of a three-dimensional pipeline model according to an embodiment of the present invention;
FIG. 3 is a diagram illustrating a meshing result according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a flow field distribution with a break up opening in accordance with an embodiment of the present invention;
FIG. 5 is a diagram illustrating distribution of a left flow field with a break in one embodiment of the present invention;
FIG. 6 is a schematic diagram showing a downward flow field distribution of a break in an embodiment of the present invention;
FIG. 7 is a graph showing the relative displacement of particles with the mouth facing upward according to an embodiment of the present invention;
FIG. 8 is a graph showing the relative displacement of a broken orifice toward the left particle according to an embodiment of the present invention;
fig. 9 is a graph showing the relative displacement of particles with the broken mouth facing downward according to an embodiment of the present invention.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
It should be understood that the embodiments described below are only some embodiments of the present invention, but not all embodiments, and that numerous technical details are described in the following specific embodiments in order to more clearly illustrate the present invention, and it should be understood by one skilled in the art that the present invention may be practiced without some of these details. In addition, some methods, means, components and applications thereof, etc. which are well known to those skilled in the art, are not described in detail in order to highlight the gist of the present invention, but do not affect the implementation of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
FIG. 1 is a schematic diagram of a road collapse disaster deduction simulation method based on a CFD-DEM and FEM combined algorithm according to an embodiment of the invention; referring to fig. 1, the road collapse disaster deduction simulation method based on the CFD-DEM and FEM combined algorithm provided by the embodiment of the invention comprises the following steps of:
s10, according to the acquired road collapse case, obtaining geological environment and soil mechanical parameters of the position of the collapse road through geological analysis, and calculating to obtain microscopic parameters of the three-dimensional discrete element particle model;
in some embodiments, the microscopic parameters include soil particle radius, density, modulus, poisson's ratio, and coefficient of friction.
S20, establishing a three-dimensional pipeline model and a flow field model in the CFD module according to the geological environment;
and establishing a three-dimensional discrete element particle model in the DEM module according to the microscopic parameters;
s30, carrying out bidirectional fluid-solid coupling on the three-dimensional pipeline, the flow field model and the three-dimensional discrete element particle model to obtain a bidirectional fluid-solid coupling model so as to simulate the sinking process and degree of soil around the damaged pipeline.
S40, simulating the sinking process and degree of the soil around the damaged pipeline by using the bidirectional fluid-solid coupling model, and establishing a finite element model of the soil in the FEM module;
in some embodiments, simulating the sinking process and degree of the soil around the damaged pipe by using the bidirectional fluid-solid coupling model comprises: and simulating and calculating a collapse simulation model of three factors of water, soil and pipelines at the collapse position by using the bidirectional fluid-solid coupling model, and simulating 5 disease evolution processes of slight loosening, medium loosening, serious loosening, void and cavity of the soil body.
In this embodiment, the three factors of water, soil and pipeline collapse simulation model is calculated through the bidirectional fluid-solid coupling model (obtained through CFD-DEM coupling), so that the disease evolution process of 5 degrees of slight loosening, moderate loosening, severe loosening, void removal and cavity of the soil body can be simulated, and the simulation deduction of the specific geological environment is facilitated.
S50, applying loads to finite element models of different soil bodies in the FEM module based on the soil body mechanical parameters so as to simulate external actions, and calculating and determining the moulding damage of the soil bodies; the loads applied by the FEM module to different soil models comprise the lateral soil pressure of surrounding soil, upper vehicle load and surrounding building construction disturbance.
In this embodiment, the fluid-solid coupling is performed through a model constructed based on a discrete unit method (CFD) and a computational fluid Dynamics (DEM) to obtain a bidirectional fluid-solid coupling model, so that the erosion degree of the soil around the pipeline in the factors of soil, water, pipeline, load and the like can be simulated, and the soil destruction process can be simulated based on a Finite Element Method (FEM). The method can simulate and analyze the motion state of soil particles through a discrete element particle model and simulate the water flow state in the soil through a flow field model to obtain a bidirectional fluid-solid coupling model, realize the coupling simulation of the interaction of water flow and the soil, achieve the purposes of deduction and prediction of road collapse disasters, and calculate the plastic damage degree of local soil through finite element simulation. Therefore, the invention is convenient for realizing deduction and simulation of urban road collapse disasters, thereby providing basis for realizing collapse prediction and treatment of urban roads with similar or same geological environment and soil body mechanical parameters.
In some embodiments, a three-dimensional discrete element particle model is established, a groundwater flow field model is calculated, and a fluid-solid coupling model is formed based on the CFD module and the DEM module.
The discrete element model 100 is used for simulating stratum in a research area, the calculation groundwater flow field 200 is used for solving the flowing state of groundwater, and the fluid-solid coupling model 300 is used for realizing interaction calculation of water flow and soil body.
In the discrete meta model, the forces to which the soil particles are subjected are mainly divided into two types: contact force between particles and gravity. The contact force is due to the forces between adjacent particles, which are typically calculated using a linear spring damping model. Gravity is due to particle mass and gravitational acceleration and can be directly calculated.
Specifically, in discrete element simulation, each soil particle is given some physical properties and states such as mass, position, velocity, acceleration, angular velocity, etc., while a spring damping model is built up with adjacent particles. During each time step, each particle in the system is subjected to gravity and contact forces, thereby changing its state and position.
The contact force is obtained by calculating the relative displacement and velocity between the particles. When the distance between two particles is smaller than the length of the spring between them, an interaction force is generated between them, the magnitude and direction of which depend on the distance and speed between them. The contact force can be divided into a forward force and a shear force. The positive force is a force that compresses the particles toward the adjacent particles, and the shear force is a force that slides the particles relative to the adjacent particles.
In the discrete meta-model, a commonly used inter-particle contact force formula is the Hertz-Mindlin model. The model assumes that the contact between the particles is inelastic, i.e. plastic deformation occurs upon contact. This model assumes contact between two spherical particles, the contact force of which can be expressed as:
wherein F is n Is normal contact force perpendicular to the contact surface, E * Is equivalent elastic modulus, R * Is the equivalent radius of curvature, delta is the amount of overlap between two particles, v s Is the poisson's ratio of the material.
In addition, because of the non-linearity and non-elasticity of the contact force, it is often necessary to obtain an accurate contact force value by iterative calculation. Among discrete element methods, there are commonly used iterative methods such as methods based on Newton-Raphson iteration and methods based on semi-implicit methods.
The Newton-Raphson iterative method is a numerical solution method for solving the root of a nonlinear equation. Based on the concept of Taylor series, the nonlinear equation is converted into a problem of a linear equation set, and the linear equation set is solved through iteration to obtain a numerical solution of the nonlinear equation.
For the negative pressure of a pipeline with fluid inside at a pipe wall gap, in practical engineering, the calculation of the negative pressure at the gap usually requires the help of a Computational Fluid Dynamics (CFD) method. By establishing a numerical model, setting boundary conditions and solving corresponding flow equations, the negative pressure distribution at the notch can be obtained.
The fundamental principle of CFD numerical modeling is based on the conservation of mass, conservation of momentum, and conservation of energy equations of fluids, i.e., the Navier-Stokes equation. These equations describe the motion and interaction of the fluids and can be solved by numerical discretization.
The Navier-Stokes equation set contains a continuity equation, a momentum equation, and an energy equation. Wherein the continuity equation describes the conservation of mass of the fluid, the momentum equation describes the motion and stress conditions of the fluid, and the energy equation describes the temperature and heat transfer of the fluid.
The specific formula of the Navier-Stokes equation set is as follows:
continuity equation:
momentum equation:
where ρ is the density of the fluid, u is the velocity of the fluid, p is the pressure of the fluid, μ is the dynamic viscosity of the fluid, and f is the volumetric force to which the fluid is subjected. The momentum equation can be further developed into three component equations that describe the change in velocity in the x, y, and z directions, respectively
Energy equation:
where E is the total energy of the fluid, H is the enthalpy of the fluid, T is the temperature of the fluid, lambda is the heat transfer coefficient of the fluid, and q is the heat source and heat sink to which the fluid is subjected per unit volume per unit time. The energy equation may be further developed as a coupled equation of temperature and velocity describing the interaction between the temperature and kinetic energy of the fluid.
In some embodiments, the simulating the sinking process and degree of the soil around the damaged pipeline by using the bidirectional fluid-solid coupling model comprises:
A. setting a geometric model of a soil body and a pipeline in the DEM model;
B. setting a corresponding physical model and boundary conditions in the CFD model, and carrying out flow field calculation;
C. the flow field data obtained by the CFD model calculation is imported into a DEM model;
D. the DEM model calculates the movement and interaction of soil particles according to the imported flow field data;
E. and C to D, repeating the steps to obtain the bidirectional fluid-solid coupling model, and simulating the evolution process of the collapse road disease.
Specifically, the discrete element particle model is established by EDEM software, and the model size is 130mm multiplied by 20mm multiplied by 100mm in consideration of the computer performance limit.
In particular, the three-dimensional pipeline model has a plurality of different forms of failure including: upper orifice failure, left and right orifice failure, lower orifice failure, annular failure, and radial failure.
The three-dimensional pipeline model in the CFD module determines a plurality of pipeline damage types by analyzing actual collapse field cases: the upper orifice breaks, the left and right orifice breaks, the lower orifice breaks, the ring breaks, and the radial breaks.
In some embodiments, the method further comprises: in the process of establishing the flow field model in the CFD module, according to the climate and the soil of the position where the collapse case is located, establishing seepage flow fields with different water volumes so as to simulate soil seepage scenes with different water volumes.
In this embodiment, the flow field model in the CFD module may be used to create a seepage flow field for simulating different water volumes according to the climate type and soil characteristics of the case area.
In some embodiments, after the calculating determines the plastic failure of the soil body, the method further comprises: predicting the plastic region range and settlement of a road similar to or the same as geological environment and soil mechanics in a subsidence road case under different load actions;
and combining a result obtained by simulating the bidirectional fluid-solid coupling by the bidirectional fluid-solid coupling model, and analyzing the damage evolution trend of the road in a certain time.
It will be appreciated that over time, voids form around the drain pipe, which collapse once the ultimate load capacity is exceeded, causing significant loss of lives and properties to people. Based on the result obtained by the embodiment of the invention, a certain basis can be provided for the analysis of the coupling effect of various environmental factors in the later stage, and the method has important significance for promoting the application of the discrete element method in engineering dimensions and further revealing the large deformation and seepage damage mechanism of the underground engineering rock-soil body.
Further, after calculating and determining the plastic damage of the soil body, the method further comprises the following steps: determining the treatment and reinforcement measures of the corresponding road according to the calculation result and the analysis result; reinforcement is based on roads that are similar or identical to the governance and reinforcement measures.
In the embodiment, the coupling state of the underground water flow and the soil body of the similar or same road can be predicted according to the calculation result and the analysis result, so that the treatment and reinforcement measures of the corresponding road can be determined in a targeted manner, the prevention and treatment of the road collapse are realized, and the road safety is ensured.
For example, when structural analysis is performed according to fatigue fracture design criteria, 100kN single-axle-double-wheel set load can be taken as the design axle load forThe cement concrete pavement with the extremely heavy traffic load grade can select the axle load of the dominant extremely heavy truck type in the truck as the design axle load. Number of times of axle load action N at each stage i Can be converted into the number of times N of the designed axle load according to the following formula s ：
Wherein P is i : the i-th level axle load (kN), the coupling is calculated according to each axle load separately;
P s : designing a shaft load (kN);
n: various shaft-type shaft-carrying level bits;
N i : i the number of times of action of the level shaft load;
N s : the number of times of the axle load is designed.
The structural design of the cement concrete pavement takes the design standard that the pavement plate does not generate fatigue fracture under the comprehensive action of the running load and the temperature gradient in the design service life; and under the combined action of the heaviest axle load and the maximum temperature gradient, no limit fracture is generated as an inspection standard. The limit state design expression can respectively adopt the following formulas:
γ r (σ c.pr +σ c.tr )≤f c.r ；
γ r (σ c.p.max +σ c.t.max )≤f c.r ；
γ r ＝1+Ψ 1 +Ψ 2 ；
in sigma c.pr Driving load fatigue stress (MPa) generated at critical load position of cement concrete pavement;
σ c.tr temperature gradient fatigue stress (MPa) generated at critical load position of cement concrete pavement;
σ c.p.max maximum load stress generated by the heaviest axle load at critical load position(MPa)；
σ c.t.max Maximum temperature warping stress (MPa) generated by the maximum temperature gradient of the region at the critical charge position;
f c.r standard value (MPa) of flexural tensile strength of cement concrete pavement;
γ r reliability coefficient;
beta is a target reliable index;
Ψ 1 constructing a variation level coefficient;
Ψ 2 the material parameters determine the horizontal coefficient, the first level is 0, the second level is 5%, and the third level is 10%.
For cement concrete pavement, the design axle carries P s The stress generated on the cement concrete pavement of the road is sigma s1 If the stress has the same damage effect on the cement concrete pavement of the road each time, the stress is formed byThe following calculation formula is established:
wherein m is 1 、C 1 Is the constant of the cement concrete pavement material, N i To be under stress sigma i Number of times of cyclic action under the condition, N s1 To be under stress sigma s1 The number of cycles below.
Therefore, when the coupling state of underground water flow and soil mass is calculated for the cement concrete pavement, the conditions meeting the road safety are as follows:
N s ≤N s1 the method comprises the following steps:
when calculating the bearing capacity of soil under a road surface, an empirical formula can be used as an estimation, and when the problem of road collapse is solved, more factors such as complicated groundwater level, uneven soil quality, load distribution, foundation structure and the like need to be considered, and a certain formula cannot be used for accurate calculation.
The Meyerhof theory is an empirical formula for calculating soil bearing capacity, proposed by the student Karl Terzaghi of the canadian engineer Karl Terzaghi in 1951. The method is an empirical method widely applied to the fields of soil mechanics and foundation engineering and is used for estimating the bearing capacity of the soil body. The Meyerhof theory is an empirical formula suitable for a range of soil and stress conditions.
In the example, proper bearing capacity theory is selected according to specific conditions, and engineering design and evaluation are carried out by combining actual geological investigation, rock-soil test and field monitoring data, so that foundation ultimate bearing capacity q f The method comprises the following steps:
wherein c is the cohesive force of the soil; gamma is the soil weight; D. b is the burial depth and width of the foundation respectively; sigma (sigma) 0 Is the normal stress on the equivalent free surface; beta 0 Is the inclination angle of the equivalent free surface and the horizontal plane; k (k) 0 Is the static soil pressure coefficient; beta 0 Is the friction angle between the soil and the foundation side; n (N) c 、N q 、N γ Is the internal friction angle with the soilAnd beta 0 Angle dependent load bearing coefficient.
Likewise, for the ultimate bearing capacity q of the foundation f By the design axle load P s The stress generated on the road foundation is sigma s2 If the stress has the same damage to the road foundation each time, the stress is reduced byThe following calculation formula is established:
wherein m is 2 、C 2 Is the constant of foundation material, N i To be under stress sigma i Number of times of cyclic action under the condition, N s2 To be under stress sigma s2 The number of cycles below.
Therefore, for the foundation, when the underground water flow and soil body coupling state calculation is applied, the conditions meeting the road safety are as follows:
N s ≤N s2 the method comprises the following steps:
in order to further ensure the road safety, the calculation result and the analysis result of the road collapse disaster deduction simulation method are N according to the CFD-DEM and FEM combined algorithm s Not greater than N s1 、N s2 Is a smaller value of (a):
N s ≤min(N s1 ，N s2 ). Through the method, the safety bearing performance of the road under the condition of collapse disasters can be evaluated, and the method is better used for rescue and relief work.
In one embodiment, the DEM model divides the calculated area into 130mm x 20mm x 100mm sub-areas during the process of building the three-dimensional discrete meta-particle model;
referring to fig. 2, in the process of establishing a three-dimensional pipeline model in a CFD module, the collapse case includes a pipeline diameter of 30mm, a buried depth of 75mm, and a breakage size of 5.5mm×5.5mm.
Specifically, the establishing a flow field model in the CFD model includes: fluid calculation is carried out by adopting FLUENT software; the boundary conditions to be considered in the calculation process comprise a speed inlet, a pressure outlet and symmetrical boundary conditions;
dividing grids for calculation according to a collapse area to be analyzed, and dividing the grids into a plurality of sub-grids; and selecting a solver and a physical model corresponding to the sub-grid;
and defining fluid properties and boundary conditions for the physical model, and configuring a corresponding solving algorithm to obtain the flow field model.
Specifically, in this embodiment, the calculation of the groundwater flow field model is performed by using FLUENT software, grid division is performed on the calculation area according to the model size, a proper solver and a physical model are selected, fluid properties and boundary conditions are defined, and a SIMPLE algorithm is selected to solve, so as to obtain a groundwater flow field grid file and fluid data. And (3) importing the flow field grid file and the fluid data obtained by the FLUENT software into EDEM software, and coupling with the discrete element model to realize interaction (namely fluid-solid coupling) calculation of water flow and soil mass.
In this embodiment, performing meshing includes: dividing a calculation region of a specific geometric shape in a space into required sub-regions according to a topological structure, and determining nodes of each region; a specific grid arrangement is shown in fig. 3. Reasonable grid design and higher quality are preconditions for FLUENT computation. Rich boundary conditions in FLUENT can be selected, and the optimal import-export boundary conditions are as follows: the inlet is set as the speed inlet, and the outlet is set as the pressure outlet boundary in order to more accurately reflect the leakage condition of the pipeline. In addition, symmetric boundary conditions are used to calculate physical profiles and where the desired flow has mirror symmetry, and do not require any boundary physical properties to be defined. The model in this study was symmetric front-to-back and left-to-right, so the left-to-right and front-to-back boundaries were set as symmetric boundaries.
Further, through the fluid-solid coupling calculation, the movement deformation process of the soil body around the damaged pipeline under the action of water flow is simulated, the soil body loss with different degrees is obtained, the plastic region range and settlement of the soil body are analyzed, and the damage evolution trend is predicted.
Wherein, because the size of the discrete meta-model 100 considers the limitation of computer performance, the calculation of grid division dense of the groundwater flow field determines the subareas and nodes through the model size, and the fluid-solid coupling model introduces the flow field grid file and the fluid data to calculate, so that the simulation of the interaction between the accurate water flow and the soil body can be realized.
In order to help understand the technical scheme and the technical effect of the embodiment of the invention, deduction and simulation applied to a certain road collapse are taken as examples for explanation as follows:
according to the provided urban road collapse accident cases, analyzing and researching the road collapse formation reasons, deducing the interaction of soil, water, pipelines and loads at the position of the collapsed road, and gradually expanding and researching a simulation model for simulating the collapse value of 5 types of diseases.
Nine different conditions of water, soil and pipelines are provided, corresponding models are respectively built based on the scheme provided by the embodiment, the following table is provided, and the evolution process of erosion and subsidence of soil around the pipeline is obtained through analysis based on the model calculation.
In the analysis, the migration process of the soil body in the road collapse forming process under the action of water flow is mainly taken as a research object, the Calculation Fluid Dynamics (CFD) and Discrete Element (DEM) theory is based, and the CFD-DEM combined calculation numerical simulation scheme is based, namely, the particle flow program software EDEM is used for modeling the stratum to obtain three dimensions, the FLUENT module in ANSYS is used for calculating the groundwater flow field, and the groundwater flow field is led into the particle flow program software for combined calculation.
In the analysis, the road water and soil subsidence simulation method based on the CFD-DEM-FEM comprises the following steps:
step 1, determining physical and mechanical parameters of a water-soil body through field test and data analysis; and calculating to obtain microscopic parameters of the DEM model, wherein the method comprises the following steps:
the radius of the particles is comprehensively determined according to the content of the soil body fine particles;
poisson ratio is calculated according to the porosity and the water content of the soil body;
calculating the density according to the field test result;
friction coefficient is calculated according to cohesion force determined by triaxial test;
stiffness is calculated from the modulus of elasticity determined by triaxial test.
And 2, establishing a three-dimensional pipeline model in the CFD module, and determining 1-2 damage types and ranges according to cases by considering 5 forms of upper, left and right side, lower crack and annular damage.
And 3, establishing a three-dimensional flow field model in the CFD module, and determining the flow fields of different water volumes by considering 3 conditions of small seepage, large seepage and flood according to the climate type and soil characteristics.
And 4, establishing a three-dimensional discrete element soil body model in the DEM module, and constructing according to the microscopic parameters of the DEM model obtained by calculation in the step 1.
And 5, bidirectionally coupling the CFD module and the DEM module, and simulating soil migration around the damaged pipeline to different degrees to obtain soil disease evolution of 5 degrees of slight loosening, medium loosening, serious loosening, void and cavity.
And 6-8, establishing a soil finite element model matched with the CFD-DEM coupling model, applying different types of loads, calculating a shaping damage area and a deformation rule, and predicting the road collapse range and trend in a certain time in the future according to a calculation result.
The DEM module unit adopts a soft-sphere model, and elastic contact and viscous damping are arranged between the units to simulate the interaction among soil particles; when the DEM module unit moves to a certain unit of the CFD module, the flow field parameters of the CFD unit are obtained to be used as loading of the DEM module unit.
The analysis of the calculation results in the present stage can obtain that when water is accumulated on the surface of the upper part of the pipeline, external seepage exists in soil around the pipeline, the soil is sandy soil, and the damage types are three conditions when the orifice is damaged: when the damaged port is right above the pipeline, the soil body at the upper part of the pipeline starts to erode after simulating to about 2 ten thousand steps, the erosion speed is accelerated along with the increase of time, and an erosion pit starts to appear at about 10 ten thousand steps, and finally a funnel-shaped erosion pit appears, wherein the gradient of the erosion pit is about 30 degrees; when the damaged port is on the left side of the pipeline, the erosion degree is similar to that of the upper part, a funnel-shaped erosion pit starts to be formed gradually after 10 ten thousand steps, but the erosion position is shifted to the left, and the slope of the pit above the pipeline is similar to that of the pipeline; when the damaged port is right below the pipeline, two corrosion points which are bilaterally symmetrical appear, and finally two funnel-shaped corrosion pits with the shape of W are displayed.
When a large amount of infiltration ponding is caused by a large amount of precipitation on the surface above the pipeline, the groundwater level can be caused to rise in a short time, so that the infiltration flow field leading to the groundwater below can appear in the soil around the pipeline, under the condition of the infiltration flow field, the soil is still sandy soil, the damage type is that the hole is damaged, the soil particle loss degree is further deepened, the soil particles below the pipeline begin to appear erosion after simulating to 10 ten thousand steps, and finally erosion holes appear on the left side and the right side below the pipeline.
Wherein, the step corresponds to a preset time length, so that the time from the occurrence of symptoms to the occurrence of disasters can be predicted through conversion.
When the ground surface is free of precipitation and water logging on the ground, soil around the pipeline is dry and free of external seepage, under the condition, only fluid in the pipeline takes away a limited small part of particles around the orifice through the damaged orifice, after simulation to 10 ten thousand steps, the soil particles around the orifice of the pipeline are eroded to a lighter degree, and finally, only a very small eroded area is formed, so that the bearing capacity of the soil on the upper part of the pipeline is hardly influenced.
The following is a simulation calculation result of three pipeline damage orientations when the earth is sandy earth, and the earth is characterized by a certain precipitation, and the soil around the pipeline has external seepage. The flow velocity of the fluid in the pipeline in the model is kept at 5m/s, and the surface precipitation forms seepage flow fields which are converged in the soil body and are at the damaged mouth of the pipeline due to the pressure difference between the pipeline and the outside, as shown in figures 4, 5 and 6. After 15-25 ten thousand steps of simulation calculation, erosion pits with different degrees appear in all three models as shown in figures 7, 8 and 9.
In fig. 4, the seepage flow field corresponding to the damage port above the pipeline can be seen in fig. 7: in 5 ten thousand steps (leftmost diagram), soil particles above the pipeline gradually enter the pipeline along with the seepage flow field through the upper damaged port; running to 10 ten thousand steps (middle diagram), and initially forming funnel-shaped collapse above the pipeline; the upper part is trapped to a funnel-shaped etching pit of about 30 ° after 15 ten thousand steps (rightmost drawing).
As can be seen from fig. 8, when the pipeline breakage port is at the left side, soil particles gradually enter the pipeline after 5 ten thousands of steps (first diagram at the leftmost side) are operated; 10 ten thousand steps are to form a funnel-shaped etching pit preliminarily, and the etching pit is shifted leftwards; the erosion pit slope above the pipeline is approximately tangent to the pipeline after 15 ten thousand steps of operation.
As shown in fig. 9, the damaged port is positioned below the pipeline, and after 5 ten thousand steps of operation (the first image at the leftmost side of the upper row), soil particles begin to run off; about 10 ten thousand steps are operated, and left and right concave points appear; after 20 ten thousand steps of operation, obvious W-shaped etching pits appear.
According to the analysis, the distribution diagram of the flow field around the pipeline in fig. 4, 5 and 6 can be obtained, and due to the pressure difference between the interior of the pipeline and the outside, the seepage flow field formed around the pipeline is collected at the damaged mouth of the pipeline, so that part of soil particles in the soil body are brought into the pipeline to flow into the pipeline, thereby causing the soil body to run off. Fig. 7, 8 and 9 show the water and soil loss process at different calculation time points. In the early stage of leakage, the soil disturbance zone is positioned near the leakage. With the lapse of time (the increase of calculation time length), the disturbance zone is continuously expanded, the collapse cavity is larger and larger, and a settling soil tank is formed. And it can be seen that the soil particle loss speed is gradually increased along with the decrease of the compaction degree of the soil body above the pipeline in the erosion process.
According to the description of the embodiments, the technical scheme provided by the embodiment of the invention is that the discrete unit method and the computational fluid dynamics method (CFD-DEM) are used for carrying out fluid-solid coupling, the erosion degree of soil around the pipeline in the factors of soil, water, pipelines, loads and the like is simulated, and the Finite Element Method (FEM) is used for simulating soil damage. The method can analyze the movement state of soil particles through discrete element simulation, calculate the plastic damage degree of local soil through finite element simulation, and has important significance in disaster deduction and prediction of road collapse caused by pipeline leakage. It is noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "mounted," "connected," "coupled," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be directly connected or indirectly connected through an intermediate medium. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element. As will be appreciated by those of ordinary skill in the art, this may be the case.
The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and any changes or substitutions easily contemplated by those skilled in the art within the scope of the present invention should be included in the present invention. Therefore, the protection scope of the invention is subject to the protection scope of the claims.
Claims (10)
1. The road collapse disaster deduction simulation method based on the CFD-DEM and FEM combined algorithm is characterized by comprising the following steps of:
according to the obtained road collapse case, obtaining geological environment and soil mechanical parameters of the position of the collapse road through geological analysis, and calculating microscopic parameters of the three-dimensional discrete element particle model;
according to the geological environment, a three-dimensional pipeline model and a flow field model are established in the CFD module;
according to the microcosmic parameters, a three-dimensional discrete element particle model is established in a DEM module;
performing bidirectional fluid-solid coupling on the three-dimensional pipeline, the flow field model and the three-dimensional discrete element particle model to obtain a bidirectional fluid-solid coupling model so as to simulate the sinking process and degree of soil around the damaged pipeline;
simulating the sinking process and degree of soil around a damaged pipeline by using the bidirectional fluid-solid coupling model, and establishing a finite element model of the soil in an FEM module;
based on the soil mechanical parameters, loading finite element models of different soil bodies in an FEM module to simulate external action, and calculating and determining the moulding damage of the soil bodies; the loads applied by the FEM module to different soil models comprise the lateral soil pressure of surrounding soil, upper vehicle load and surrounding building construction disturbance.
2. The method of claim 1, wherein simulating the sinking process and degree of the soil around the damaged pipe using the bi-directional fluid-solid coupling model comprises:
A. setting a geometric model of a soil body and a pipeline in the DEM model;
B. setting a corresponding physical model and boundary conditions in the CFD model, and carrying out flow field calculation;
C. the flow field data obtained by the CFD model calculation is imported into a DEM model;
D. the DEM model calculates the movement and interaction of soil particles according to the imported flow field data;
E. and C to D, repeating the steps to obtain the bidirectional fluid-solid coupling model, and simulating the evolution process of the collapse road disease.
3. The method of claim 1 or 2, wherein the three-dimensional pipeline model has a plurality of different forms of failure including: upper orifice failure, left and right orifice failure, lower orifice failure, annular failure, and radial failure.
4. The method of claim 1, wherein the method further comprises: in the process of establishing the flow field model in the CFD module, according to the climate and the soil of the position where the collapse case is located, establishing seepage flow fields with different water volumes so as to simulate soil seepage scenes with different water volumes.
5. The method of claim 1, wherein the microscopic parameters include soil particle radius, density, modulus, poisson's ratio, and coefficient of friction.
6. The method of claim 1, wherein simulating the sinking process and extent of the soil surrounding the damaged pipe using the bi-directional fluid-solid coupling model comprises: and simulating and calculating a collapse simulation model of three factors of water, soil and pipelines at the collapse position by using the bidirectional fluid-solid coupling model, and simulating 5 disease evolution processes of slight loosening, medium loosening, serious loosening, void and cavity of the soil body.
7. The method of claim 1, wherein after computationally determining the plastic failure of the soil mass, the method further comprises: predicting the plastic region range and settlement of a road similar to or the same as geological environment and soil mechanics in a subsidence road case under different load actions;
and combining a result obtained by simulating the bidirectional fluid-solid coupling by the bidirectional fluid-solid coupling model, and analyzing the damage evolution trend of the road in a certain time.
8. The method of claim 1, wherein after computationally determining the plastic failure of the soil mass, the method further comprises: determining the treatment and reinforcement measures of the corresponding road according to the calculation result and the analysis result;
reinforcement is based on roads that are similar or identical to the governance and reinforcement measures.
9. A method according to claim 1, wherein the DEM model, in the process of building a three-dimensional discrete meta-particle model, partitions the calculation region into sub-regions of 130mm x 20mm x 100 mm;
in the process of establishing a three-dimensional pipeline model in the CFD module, the collapse case comprises a pipeline with the diameter of 30mm, the burial depth of 75mm and the size of a damaged port of 5.5mm multiplied by 5.5mm.
10. The method of claim 9, wherein establishing a flow field model in the CFD model comprises:
fluid calculation is carried out by adopting FLUENT software; the boundary conditions to be considered in the calculation process comprise a speed inlet, a pressure outlet and symmetrical boundary conditions;
the flow field process calculated by the CFD model comprises the following steps:
dividing grids for calculation according to the collapse area to be analyzed, and dividing the grids into a plurality of sub-grids;
and selecting a solver and a physical model corresponding to the sub-grid;
and defining fluid properties and boundary conditions for the physical model, and configuring a corresponding solving algorithm to obtain the flow field model.
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