CN113657048B - Debris flow rainfall converging water source replenishment measuring and calculating method, debris flow dynamic process numerical simulation method and application - Google Patents
Debris flow rainfall converging water source replenishment measuring and calculating method, debris flow dynamic process numerical simulation method and application Download PDFInfo
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Abstract
The invention discloses a debris flow rainfall converging water source replenishment measuring and calculating method, a debris flow dynamic process numerical simulation method and application. According to the method, an object source erosion process is analyzed from an object source starting angle, a slope converging process is calculated based on a distributed hydrological model, slope converging with space-time variability is reasonably distributed in a channel, the solid-liquid interaction is represented by buoyancy and drag force, the flowing fluid and eroded ditch bed object source are reasonably coupled with the slope converging, a debris flow multi-fluid dynamics model comprehensively considering the ditch bed erosion effect and the slope converging effect is established, and numerical simulation of the debris flow dynamic process can be realized. The method also comprises optimization of debris flow gully bed erosion material source replenishment measurement and calculation. The invention also provides application of the power process numerical simulation method in debris flow process visualization and debris flow monitoring and early warning. The method can accurately restore the debris flow dynamic process, and provides basis for river basin risk assessment, prevention and control engineering planning and design and the like.
Description
Technical Field
The invention relates to a debris flow rainfall converging water source replenishment measuring and calculating method, a debris flow ditch erosion material source replenishment measuring and calculating method and a debris flow power numerical simulation method, in particular to a numerical simulation method for a debris flow power process considering slope converging replenishment and material source erosion replenishment conditions, and belongs to the technical fields of electric digital data processing technology, motion multiphase fluid measurement technology and mountain disaster monitoring and prevention and control.
Background
The debris flow is a mountain geological disaster type with extremely destructive power, the destructive power is related to the dynamic change in the movement process, so that the research on the debris flow dynamic process is the basis and the focus of the research on the prevention and the treatment of the debris flow. For example, debris flow is a solid-liquid two-phase fluid formed on slopes or valleys and composed of sand, stones and water, and during movement, the debris flow can continuously erode the material source of the ditch bed, and meanwhile, the fluid movement state can be continuously changed due to the confluence and supplement of slopes on two sides of the ditch. If the dynamic process of the channel fluid under the extreme rainfall condition of the river basin can be determined according to the object source conditions of the river basin channel, a theoretical basis can be provided for carrying out debris flow disaster prediction and forecast and prevention engineering planning and design. Early researches on the debris flow dynamic process mainly pay attention to the discussion of factors influencing the debris flow dynamic process and the functions thereof by virtue of experimental means. Along with the expansion of the processing capacity of a computer, the description of the whole power process by establishing a debris flow dynamic model becomes an important research method.
The debris flow fluid dynamic model comprises a single fluid model and a multi-fluid model. The multi-fluid model starts from the basic knowledge that mud-rock flow is formed by the interaction development of solid-liquid two-phase substances on hillside fields or in channels, and is a two-component fluid dynamics equation set established after the solid-liquid two-phase momentum exchange condition is considered, wherein each component has respective mass, momentum and energy conservation equations. Compared with a single fluid model, the mud-rock flow is regarded as a group of single-component fluids, so that when the two-phase speed difference of the mud-rock flow is obvious and strong inter-phase interaction exists, the defect of great deviation between a research result and an experiment and observation result can occur, and the multi-fluid model is more reasonable and is gradually more valued by researchers. The key problem of the multi-fluid model is to process the interaction between each component and the environment and the interaction among multiple components, the actual condition to be processed in the modeling process is extremely complex, and a reliable mud-rock flow interphase acting force formula does not exist at present, so that the sealing and numerical calculation of the whole equation set are difficult.
The Chinese patent application of application publication No. CN 109657322A discloses a dynamic numerical simulation method for solid-liquid multiphase application to debris flow. The method assumes that different mediums in a multiphase medium equation are fully mixed and stress conditions of a solid phase and a liquid phase of the debris flow are independently defined; simultaneously, a model of various interaction forces is introduced, two-phase media are coupled together through hydrostatic buoyancy and various hydrodynamic forces (drag force, lifting force and virtual mass force), a relative speed effect occurs due to different stress conditions in a motion process of a solid phase and a liquid phase, different flow state evolution and dynamic characteristics under the time-space evolution of concentration ratio occur, a forming-motion-accumulation numerical simulation method based on a mud-rock flow dynamic process of solid-liquid multiphase is formed, and finally a mass equation of solid-phase particles and liquid-phase slurry and a mud-rock flow solid-liquid two-phase momentum conservation equation are established. The method has the defect that only interaction force among components is considered, but two effects of debris flow as multiphase component fluid in complex environment during movement are not considered: one is the ramp confluence effect. The mud-rock flow often occurs simultaneously with a large-scale rainfall process, and rainwater falling to the ground surface can be converged into mud-rock fluid from different channel sections in a slope converging mode according to terrain conditions to serve as a water source to be supplied, so that the component characteristics of the mud-rock flow are continuously changed, and the kinematic characteristics of the mud-rock flow are changed; secondly, the mud-rock flow contains solid components which can continuously rub with the ditch bed to generate erosion action to wrap the solid matters of the ditch bed into solid matters to be supplied and added into the mud-rock flow, and the component characteristics of the mud-rock flow and the kinematic characteristics of the mud-rock flow are continuously changed.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a numerical simulation method for a debris flow dynamic process based on a debris flow multi-fluid model and application thereof.
In order to achieve the purpose, the invention firstly provides a debris flow rainfall converging water source replenishment measuring and calculating method, which has the following technical scheme:
a method for measuring and calculating the water source supply of mud-rock flow rainfall converging water source is used for measuring and calculating the water source supply process of the mud-rock flow converging to the mud-rock flow from the slope around a mud-rock flow channel in one rainfall, and is characterized in that: the method is implemented according to the following steps:
step SA1, on-site investigation
Basic data of the debris flow channel is acquired, a slope confluence area of the channel is defined,
step SA2, establishing a slope-channel coupling relation
Dividing the slope converging region into a plurality of slope converging regions along the channel direction according to the slope of the slope converging region and converging slope characteristics, wherein each slope converging region corresponds to a channel segment;
step SA3, measuring and calculating the debris flow rainfall water source replenishing process of each slope converging zone
Obtaining rainfall basic data, dividing each whole rainfall into net rainfall periods, and calculating flood peak flow q of each net rainfall period according to the formulas 1-5 p Peak time t p Time t of water withdrawal r ，
Wherein q is p Peak flood flow in m for the period of net rain 3 /s，
A-slope confluence zone catchment area, unit km 2 The basic survey data determines, based on the data,
t p peak time of the net rain period, unit h,
the net rain amount in mm,
l-slope confluence zone confluence length, unit m, basic survey data determination,
the percentage of the gradient of the confluent zone of the y-slope surface,%, which is determined by basic investigation data,
i-total rainfall in the period of rain purification, unit mm, basic survey data determination,
the S-slope confluence subarea has the largest possible rainfall retention in the period of net rain, the unit mm,
the comprehensive parameters of the characteristics of the basin before the CN-rainfall are determined according to the prior art,
t r -a water withdrawal time in h of the net rain period;
peak flood flow rate q per period of net rain p Peak time t p Time t of water withdrawal r Performing linear interpolation to establish a debris flow water source replenishing process of a clean rainfall period, superposing water source replenishing processes of all the clean rainfall periods of a whole rainfall, and establishing a water source replenishing process of the whole rainfall of each slope converging partition to obtain a converging partition replenishing function q 'of debris flow channel segments corresponding to each slope converging partition along with time and space changes in the whole rainfall process' s ；
Step SA4, measuring and calculating a water source converging and supplementing function Q of a debris flow channel in rainfall s
Supplementing the function q 'according to the confluent partition' s Measuring and calculating a water source replenishing process of a debris flow channel in rainfall by a slope-channel coupling relation to obtain a channel converging replenishing quantity function Q s 。
The debris flow rainfall converging water source replenishment measuring and calculating method can solve the measuring and calculating problem of a water source replenishment process provided for debris flow by a debris flow channel due to the surrounding slope converging effect in one rainfall, and the technical principle is that the slope converging effect is regarded as a dynamic space-time process. The time course is embodied as the rainfall course and the change of different time periods in the whole rainfall course, the space course is embodied as the water flow of different converging slopes of the watershed enters the channel from different points along the converging direction to form water source supply, and the water source supply has different influences on the fluid composition and the movement course of the debris flow. In order to process the time course, the measuring and calculating method adopts the index of the period of the net rain to decompose the rainfall variation of the whole rainfall. In order to process the space process, the measuring and calculating method establishes slope-channel coupling relation indexes according to the terrain conditions, decomposes the slope converging region into slope converging regions, and each slope converging region corresponds to one channel converging section.
In the process of causing the debris flow by rainfall, the rainfall generates an erosion effect besides a confluence effect on the debris flow, so that the movable solid sources around the channel are eroded by the fluid and enter the debris flow to be supplied by the debris flow erosion sources. The invention further provides a debris flow gully bed erosion material source supply measuring and calculating method, which has the following technical scheme:
the utility model provides a debris flow ditch bed erosion material source supply measuring and calculating method for measuring and calculating the erosion rate i of debris flow ditch bed unstable material source eroded into debris flow's solid material source supply, its characterized in that: the method is implemented according to the following steps:
step S21, on-site investigation
Basic data of a debris flow channel are acquired,
s22, measuring and calculating erosion rate i of unstable material source of ditch bed according to 6-7
Where i-the average rate at which the source is eroded per unit of base area, per unit,
the average thickness of the cross section of the z-source unstable layer, unit m,
the average flow velocity of the u-mixed fluid section, in m/s, is determined according to the prior art,
ρ T average density of mixed fluid section in kg/m 3 According to the prior art, the method is determined,
alpha-erosion coefficient is determined or valued 1.5 multiplied by 10 according to the water tank experiment of the dynamic process of the indoor debris flow 7 ，
d50-median particle diameter of the solid particles in the source, unit m, basic survey data,
γ m mixed fluid section average bulk weight in N/m 3 The basic survey data determines, based on the data,
h-average flow depth on the mixed fluid section, unit m, basic survey data determination,
the average internal friction angle of the beta-substance source, unit degrees, and the basic investigation data confirm,
θ—channel slope angle, in degrees, as determined by basic survey data,
γ sat -average saturated volume weight of the source in N/m 3 The basic survey data determines, based on the data,
γ s -average bulk density of solid particles in the source, unit N/m 3 The basic survey data determines, based on the data,
γ w water volume weight in N/m 3 A constant,
n-source average porosity, no units, basic survey data determination,
c-average cohesion of the source, unit N, as determined by basic survey data.
The debris flow erosion material source supply measuring and calculating method has the technical principle that: on the one hand, the stable state of the material source is closely related to the external rainfall condition and the geological structure effect, and under the combined effect of underground seepage and surface runoff, when the power such as gravity, shearing force and the like applied to the material source is greater than resistance, a potential sliding surface exists between the solid material sources, and an unstable layer is formed above the sliding surface. At this time, the gravitational potential energy of the material source has directional kinetic energy andtrend of frictional energy conversion. The thickness z of the unstable layer under the combined action of saturated seepage and surface runoff is expressed as formula 7; on the other hand, the unstable layer cannot be instantaneously moved as a whole, and a certain delay time is required for the unstable layer to enter the debris flow through the erosion process. The lag time is closely related to the fluid and the source properties of the ditch bed, the influence of the fluid on the erosion rate is represented by the flow rate and the volume weight of the fluid, the source properties of the ditch bed are mainly determined by the material composition, the influence of the source properties on the erosion rate is represented by the characteristic particle size of the available source, and the lag time is expressed as (alpha d 50 )/(uρ T ) The erosion rate i can be expressed by equation 6.
The invention further provides a numerical simulation method of the debris flow dynamic process by considering the two effects, which is based on the solution of the problems of water source supply and object source supply measurement and calculation provided by the debris flow process by the confluence effect and the erosion effect of space-time environmental conditions around a channel in the debris flow process, and has the technical scheme that:
the numerical simulation method for the debris flow power process realized by the debris flow rainfall converging water source replenishment and calculation method and the debris flow erosion material source replenishment and calculation method is characterized by comprising the following steps of: the method is implemented according to the following steps:
step S1, on-site investigation
Basic investigation data including debris flow channel basic data and rainfall basic data are obtained,
s2, establishing a mud-rock flow multi-fluid dynamics model
The mass conservation of solid particles and liquid phase slurry in the mud-rock flow is expressed by the formula 8 and the formula 9 respectively,
wherein t is the time, the unit s,
x, y-cartesian coordinates, unit m,
h-has the meaning as defined above,
(u s ,v s ,w s ) The velocity components of the solid phase particles in the source in the x, y, z directions, units m/s,
i-the average rate of erosion of the source per unit of floor area, per unit, determined by the debris flow erosion source replenishment calculation method or by the prior art,
(u f ,v f ,w f ) The velocity components of the liquid phase slurry in the x, y, z directions, units m/s,
ρ f1 average density of liquid phase slurry in substance source, unit kg/m 3 The basic survey data determines, based on the data,
ρ f density of liquid phase slurry in mixed fluid, unit kg/m 3 The basic survey data determines, based on the data,
ρ w density of water in kg/m 3 A constant,
p-rainfall intensity, unit m/h, basic survey data determination,
q s confluence compensation quantity obtained per unit length of channel section, m 3 S, according to the method of measuring and calculating the rainfall converging water source replenishment of the debris flow,
w-calculating the average ditch bed width of the micro-element section, and determining basic investigation data in unit of m;
the conservation of momentum of the debris flow solid particles along the x and y directions is expressed by the formula 10 and the formula 11 respectively,
in the formula, g-gravity acceleration is expressed in units of m/s 2 A constant,
the meaning of alpha-is the same as before,
the meaning of theta-is the same as before,
ρ s average density of solid particles in the mixed fluid, unit kg/m 3 The basic survey data determines, based on the data,
the momentum conservation of the debris flow liquid phase slurry along the x and y directions is expressed by the formulas 12 and 13 respectively,
wherein k is b -coefficients related to the viscosity of the fluid, determined from basic investigation data;
step S3, calculating the numerical value of the dynamic model
And carrying out numerical solution on the mud-rock flow multi-fluid dynamic model, setting time initial conditions and position control points calculated by the model, and obtaining fluid motion parameter data of any time point and any geographic coordinate point of the mud-rock flow in the channel motion process.
The numerical simulation method for the debris flow dynamic process has the technical principle that:
regarding the mass conservation equation: the mud-rock flow is carried out in two waysPhase separation is considered to be divided into two phases of solid particles and liquid phase slurry. If the mass change caused by the chemical reaction and the phase change of the fluid is not considered, the mass conservation equations of the solid particles and the liquid phase slurry in the deformation process of the fluid substance can be expressed as formulas 14 and 15 respectively; v in s 、v f Velocity vectors of solid-liquid phases, M s 、M f The mass increase rate per unit volume of the solid particles and liquid phase slurry due to the source of the gully bed, the slope confluence and the entry of the overhead rain, respectively, can be expressed as equations 16, 17, respectively.
Regarding the conservation of momentum equation: according to the principle of conservation of momentum, in the process of fluid movement, the change amount of momentum of a moving element along with time is equal to the sum of external forces born by the element, and then the momentum conservation equations of solid particles and liquid phase slurry can be respectively expressed as formulas 18 and 19; t in s 、T f The tensor of stress exerted on the solid phase particles and the liquid phase slurry are further expressed as formulas 20 and 21, respectively, wherein I is unit tensor and sigma e 、p f Respectively represents normal stress, tau, of solid phase particles and liquid phase slurry s 、τ f Represents the tangential stress to which the solid and liquid phases are subjected, respectively, the pore fluid pressure p at depth z f Expressed as hydrostatic pressure, formula 22; in the formulas 18 and 19, f is the interaction force between the solid phase and the liquid phase, and is expressed as a formula 23,wherein the first right term is buoyancy, p f Is the pore pressure in the mixed fluid, the second term is drag, η is drag coefficient, and hydrodynamic viscosity η f Osmotic coefficient κ, solid particle volume concentration
In this regard, the expression 24 may be expressed.
T s ＝σ e I+τ s 20 (20)
T f ＝p f I+τ f 21, a combination of
p f ＝ρ f g (b+h-z) cos θ 22
Regarding dynamic boundary conditions: in the debris flow movement process, the solid particles and the liquid phase slurry are required to meet the dynamic boundary condition 25 at the boundary of the upper bottom surface and the lower bottom surface, wherein z t Is the elevation, z of the fluid surface b Is the elevation of the bed (u) s ,v s ,w s )、(u f ,v f ,w f ) The velocity components of the solid particles and the liquid phase slurry along different directions, E st 、E sb The solid phase particles are respectively arranged on the upper part and the lower part of the solid phase particles in unit volume caused by the inlet of the ditch bed material sourceRate of change of elevation of floor, E ft 、E fb The change rates of the heights of the upper bottom surface and the lower bottom surface of the liquid phase slurry in unit volume are respectively caused by slope confluence and the entering of overhead rain. For the fluid upper boundary, a stress free boundary condition, equation 26, where n is the unit normal vector of the upper boundary, should be satisfied. For the lower boundary of the fluid, the solid phase particles in the fluid should satisfy coulomb friction law, expressed as formula 27, where sgn (v s ) Representing the direction of the velocity of the vehicle,
the subscript τ represents the projected value of the stress on the boundary, which is the effective coulomb friction coefficient between the bed particles. The friction condition of the liquid phase slurry in the mixed fluid at the bed can be expressed by the Navier friction condition 28. />
(T f n) τ ＝-k b v f 28, respectively
With respect to the control equation matrix form under boundary conditions: assuming that the fluid material is uniformly distributed on a cross section perpendicular to the channel direction during the fluid movement, integrating the left side of the mass conservation equations 14 and 15 along the z direction, differentiating and integrating the integration expression by applying the Laibnez theorem, and substituting the dynamic boundary condition expression 25 into the mass conservation equations 8 and 9 for converting the solid particles and the liquid phase slurry. The right hand term of equation 8 represents the mass of coarse particles in the eroded source of the gully bed, the first term to the right hand of equation 9 represents the mass of liquid phase slurry in the eroded source of the gully bed, and the second term represents the mass change caused by the convergence of rainfall and the two-sided slope into the channel. Thus equations 8, 9 are mass conservation equations that take into account the effects of erosion of the gully bed and the effects of ramp convergence. And respectively deducing the momentum conservation equations of the two phases by adopting the same method to obtain the momentum conservation equations of the two phases along the x and y directions. The derivation also takes into account the effects of erosion of the gully bed and the effect of ramp confluence.
The numerical simulation method for the debris flow dynamic process can simulate the movement process from the start to the formation and the scale expansion of the debris flow, thereby realizing the monitoring and the danger early warning of the debris flow process. Thus, the present invention simultaneously provides the following solutions:
the numerical simulation method for the debris flow dynamic process is applied to the visualization of the debris flow process.
The numerical simulation method for the debris flow dynamic process is applied to debris flow monitoring and early warning.
Compared with the prior art, the invention has the beneficial effects that: (1) According to the technical scheme, the object source erosion process is analyzed from the object source starting point of view based on the object source conditions and hydrodynamic conditions which are necessary for the debris flow outbreak, the slope converging process is calculated based on the distributed hydrologic model, and the slope converging with space-time variability is reasonably distributed in the channel. Meanwhile, the interaction of solid-liquid two phases is represented by buoyancy and drag force, flowing fluid, eroded ditch bed material sources and slope converging are reasonably coupled, a mud-rock flow multi-fluid dynamics model which comprehensively considers ditch bed erosion effect and slope converging effect is established, and numerical simulation of a river basin mud-rock flow dynamic process can be realized by performing numerical discrete and solving on the model. The simulation result can accurately display the change characteristics of debris flow property indexes such as flow speed, flow depth, volume weight and the like along with time space in the debris flow process, can accurately display the flow change process of the debris flow in any section, can accurately restore the debris flow dynamic process, and provides basis for river basin risk assessment, prevention and treatment engineering planning design and the like. (2) The numerical simulation method of the debris flow dynamic process not only considers the influence of the erosion effect of the ditch bed and the confluence effect of the slope on the debris flow dynamic process, but also considers the speed difference between solid phase particles and liquid phase slurry, and the interaction between solid phase and liquid phase is characterized by buoyancy and drag force. Therefore, the invention can more truly reflect the inherent dynamic mechanism of the debris flow and more accurately describe the dynamic characteristics of the debris flow by calculating the dynamic process of the debris flow. (3) In order to solve the numerical simulation problem of the debris flow power process, the invention provides a debris flow rainfall converging water source replenishment measuring and calculating method, which solves the measuring and calculating problem of the water source replenishment process for providing debris flow to a debris flow channel due to the surrounding slope converging effect in one rainfall. According to the method, the slope confluence effect is regarded as a dynamic space-time process, and the influence of the water source supply process generated by the slope confluence effect of the surrounding environment of the channel on the movement of the debris flow is analyzed from the two aspects of the rainfall time process and the confluence space distribution. (4) The debris flow erosion material source replenishment measuring and calculating method solves the problem that the erosion effect of the ditch bed caused by debris flow affects the debris flow movement in the debris flow solid material source replenishment process.
Drawings
FIG. 1 is a flow chart of a numerical simulation method of a debris flow dynamic process.
FIG. 2 is a schematic diagram of the slope confluence region division result.
Fig. 3 is a partial minute rainfall map (debris flow outbreak process) in "7.26".
Fig. 4 is a change in the depth of the debris flow with time and space.
Fig. 5 is a change in the flow rate of the debris flow with time and space.
Fig. 6 is a change in the volume weight of the debris flow with time and space.
FIG. 7 is a simulated monitored section volume weight change.
Fig. 8 is a simulated monitored profile flow rate variation.
Detailed Description
Preferred embodiments of the present invention will be further described with reference to the accompanying drawings.
Example 1
As shown in figures 1 to 8 of the drawings, the method of the invention is used for carrying out numerical simulation on the 7.26 mud-rock flow in 2013 of the ring rock ditch of the deep stream village in the urban river weir of Sichuan province.
FIG. 1 is a flow chart of a numerical simulation method of a debris flow dynamic process.
1. Site survey
And (3) carrying out field investigation in a research area (a deep stream basin, a boiler ring and a rock ditch) to obtain basic data of a debris flow basin channel and basic rainfall data. The field investigation comprises the steps of determining basic investigation data aiming at various mapping, measurement, simulation experiment tests, rainfall data acquisition, historical disaster record acquisition, experience data acquisition with reference function and the like of a debris flow basin where the project is located and a trench field. The basic investigation data comprise topographic data, object source characteristic data, rainfall data and confluence data.
Table 1 is the basic physical and mechanical property parameters of the material source, table 2 is the confluence data of the research area (wherein the determination of the comprehensive parameter CN value of the river basin characteristics before rainfall is according to Xu Liukai and the like, the SCS model is applied to simulate the yield and confluence flow rate of the clear and high-water river basin, the university of eastern traffic report, 8 th month, 28 th volume, 4 th period of 2011), fig. 2 is the schematic diagram of the division result of the slope confluence area, and fig. 3 is the partial minute rainfall chart (debris flow outbreak process) in 7.26.
TABLE 1 values of parameters of essential physical and mechanical properties of the source
2. Establishing a slope-channel coupling relation
And defining a slope surface confluence region of the channel of the research region according to the basic survey data, and dividing the slope surface confluence region into a plurality of slope surface confluence regions along the channel direction according to the slope of the slope surface confluence region and the confluence slope surface characteristics. The dividing method specifically determines the gradient change condition of the river basin according to the density of the medium-altitude lines in the digital elevation model of the boiler ring rock ditches, and divides the slope confluence partition according to the gradient change condition. The total of 11 confluence partitions are divided according to law and marked as A 1 ～A 11 The method comprises the steps of carrying out a first treatment on the surface of the 11 channel segments, denoted as l 1 ～l 11 . Basic survey data was matched to each slope confluence partition (table 2).
Table 2 study area confluence data establishing a ramp-channel coupling relationship
3. Debris flow rainfall water source replenishing process of each slope converging partition is calculated
Dividing each whole rainfall into net rain time periods according to the rainfall basic data, matching the rainfall basic data to each net rain time period, and calculating flood peak flow q of each net rain time period according to formulas 1-5 p Peak time t p Time t of water withdrawal r 。
In the A th 1 For example, the slope surface is converged and partitioned, the whole rainfall comprises 10 net rain time periods, which are marked as T 1 ～T 10 . For the T th 1 Period of net rain: combining the characteristics of the river basin before rainfall with the parameters CN=91, the total rainfall I=15 mm in the period of pure rain, and the area A=0.0092 m in the catchment area of the slope confluence zone 2 Substituting the slope confluence zone confluence length l=82m and the slope confluence zone gradient percentage y=0.0092% into the formulas 1-5, and calculating the maximum possible rainfall retention S= 25.1209mm of the slope confluence zone in the net rain period, the net rainfall Q= 2.8355mm in the net rain period and the peak current time t of the net rain period p Peak flow q=0.0082 h, net rain period p ＝0.6557m 3 Water withdrawal time t of/s, period of water purification r = 0.0137h. Linearly interpolating the three values to establish a debris flow water source replenishment process function (29) of the slope confluence partition in the net rain period
Calculating flood peak flow q of the slope confluence subarea in all the net rain periods in the rainfall according to the process p Time t of water withdrawal r And debris flow water source replenishment process function during the period of rain purificationOverlapping the water source supplementing process of all the net rain periods of the whole rainfall along time, and establishing a water source supplementing process function q 'of the slope converging and zoning whole rainfall to the corresponding debris flow channel section' s 。
4. Water source confluence supplement quantity function Q of debris flow channel in one rainfall is measured and calculated s
Supplementing the function q 'according to the confluent partition' s And (3) measuring and calculating a water source supplying process of the debris flow channel in one rainfall according to the slope-channel coupling relation to obtain a channel converging supplying quantity function Qs (the channel converging supplying quantity function Qs is omitted because each time period comprises the sum of 10 piecewise functions and is complex).
5. Calculating the average rate i of erosion of a unit bottom area material source
Taking the 60s calculation time of the channel start point as an example, the average density ρ of solid particles in the mixed fluid is calculated s ＝2650kg/m 3 、u s = 7.577m/s, volume concentration of solid phase particles in source
Density ρ of liquid phase slurry in mixed fluid f ＝1000.68kg/m 3 、u f The mixed fluid average density ρ= 1005.54kg/m is calculated by substituting 7.563m/s into equations 8 and 9 3 Mixed fluid section average flow rate u= 7.564m/s. And then the average volume weight gamma of the mixed fluid section m ＝10055.4N/m 3 Average flow depth h=0.0354m, average internal friction angle of object source beta=33.2, channel slope angle theta=28, average saturation volume weight gamma of object source on the calculated section of mixed fluid sat ＝21555N/m 3 Median particle diameter d of solid particles in the source 50 =0.025 m, average volume weight γ of solid particles in source s ＝26500N/m 3 Volumetric weight of water gamma w ＝10000N/m 3 Source average porosity n=0.3, source average cohesion c=4.8n, mixed fluid section average flow velocity u= 7.564m/s (for measurement and calculation methods see: qiao Cheng, mud-rock flow two-phase kinetic model study considering erosion effects, 2018), mixed fluid section average density ρ T ＝1005.54kg/m 3 (methods of measurement see Qiao Cheng, taking into account erosion effects)Mud-rock flow two-phase dynamics model study, 2018), erosion coefficient α=1.5x10 7 Substituting the formula 6 and the formula 7, calculating the average thickness z=0.0625m of the active source unstable layer section and the average erosion rate i=0.0013% of the active source per unit bottom area.
The above process of the embodiment adopts the optimized and optimized method to calculate the average rate i of the erosion of the material source in unit bottom area. The rate can also be determined by calculation in the prior art, and specifically can be calculated by a method of using a high bridge, kuang Shangfu, and a method of using a mechanism of forming debris flow in a variable slope flow path (second national debris flow academy of sciences, science publishers, 1991).
6. Establishing a mud-rock flow multi-fluid dynamics model
And respectively establishing mass conservation equations of solid particles and liquid phase slurry in the debris flow according to the formulas 8 and 9, respectively establishing momentum conservation equations of the solid particles in the debris flow along the x and y directions according to the formulas 10 and 11, and respectively establishing momentum conservation equations of the liquid phase slurry in the debris flow along the x and y directions according to the formulas 12 and 13.
7. Kinetic model numerical computation
And carrying out numerical discrete on the mud-rock flow multi-fluid dynamic model by adopting a finite difference method. The space dispersion adopts a first-order windward differential format, and the time dispersion adopts an Euler formula. And after space-time dispersion, obtaining a channel fluid motion numerical dispersion model. And continuously solving the modeling model to obtain fluid motion parameters at each moment of each point of the channel.
The moment when the basin begins to rainfall is taken as the initial moment of model calculation. Before the initial moment, the river basin is free from rainfall, the converging slope surface and the debris flow channel are free from generating flow and converging, and no fluid flows in the channel. At this time, the fluid flow depth, the solid-liquid two-phase fluid flow velocity and the solid-phase particle volume concentration at each control point of the channel are all zero, and the initial condition can be expressed as formula 30:
where x represents the spatial coordinates (distance from the channel start) of each control point and varies with the control point taken.
The initial value of the fluid motion parameter at the channel starting point can be calculated according to the channel converging region and expressed as
Formula 31:
after the initial parameters of the model are obtained, the initial parameters are substituted into a two-phase dynamic numerical discrete model of the debris flow, a fluid motion numerical discrete model solving program is written to simulate and solve the debris flow dynamic process, and then the fluid motion parameters at all moments of the channel can be obtained.
Confluence compensation quantity q obtained by parameter unit length channel section in numerical simulation process (9) s (Unit m) 3 And/s) determining according to a debris flow rainfall converging water source replenishment measuring and calculating method. However, the result of the debris flow rainfall converging water source replenishment measuring and calculating method is a water source converging replenishment quantity function Q of a debris flow channel in one rainfall s There is a simple process of channel segments per unit length between the two. Specifically by the channel compensation quantity Q s Dividing the channel length to obtain the confluence compensation quantity q of the channel section in unit length s 。
Simulation calculation was performed sequentially downstream from the channel start (the upper limit of the fluid volume weight in the simulation was set to 2.2 t/m) 3 ) And obtaining the simulation result of the debris flow dynamic process of 7.26.
The debris flow depth changes (fig. 4 is the change of the debris flow depth with time and space), the debris flow velocity changes (fig. 5 is the change of the debris flow velocity with time and space), and the debris flow volume weight changes (fig. 6 is the change of the debris flow volume weight with time and space).
Because the mud level monitoring device is arranged at the section of the downstream drainage groove of the boiler ring rock ditch (which is 370m away from the starting point of the ditch), in order to compare the simulation result with the field actual monitoring result, the simulation result of the mud-rock flow volume weight and the flow process at the section of the mud level monitoring in the simulation power process is intercepted and analyzed. The volume weight and flow evolution process at the fracture surface are shown in fig. 7 (fig. 7 is a simulated monitored fracture surface volume weight change process) and fig. 8 (fig. 8 is a simulated monitored fracture surface flow change process).
Simulation result verification (taking fig. 8 as an example): the flow rate change curve of FIG. 8 is bimodal as a whole, and the corresponding time of the two flow rate peaks is 14:02 and 14:09 respectively. In fig. 2, the change trend of minute rainfall is also bimodal, and the corresponding time of two peak rains is 14:01 and 14:08 respectively, which are about 1 minute earlier than the time of two peak rains. The time difference is consistent with the actual situation of the river basin runoff production and slope confluence. The peak flow rate in the flow rate variation curve of FIG. 8 is 16.86m 3 And/s, the actual measurement value of the peak flow rate of the mud-rock flow of 7.26 is 20.24m 3 S (obtained from the mud level monitoring device at the monitoring section). The relative error between the simulated and measured values was 16.7%. The simulation precision is higher, meets mountain disaster monitoring requirements.
Claims (5)
1. The method for measuring and calculating the water source supply of the debris flow rainfall converging water source is used for measuring and calculating the water source supply process of the debris flow converging to the debris flow from the slope around the debris flow channel in one rainfall, and is characterized in that: the method is implemented according to the following steps:
step SA1, on-site investigation
Acquiring basic data of a debris flow channel, and defining a slope confluence area of the channel;
step SA2, establishing a slope-channel coupling relation
Dividing the slope converging region into a plurality of slope converging regions along the channel direction according to the slope of the slope converging region and converging slope characteristics, wherein each slope converging region corresponds to a channel segment;
step SA3, measuring and calculating the debris flow rainfall water source replenishing process of each slope converging zone
Obtaining rainfall basic data, dividing each whole rainfall into net rainfall periods, and calculating flood peak flow q of each net rainfall period according to the formulas 1-5 p Peak time t p Time t of water withdrawal r ，
Wherein q is p Peak flood flow in m of period of net rain 3 /s，
A-slope confluence zone catchment area, unit km 2 The basic survey data determines, based on the data,
t p peak time, unit h,
q-the net rain amount in mm in the net rain period,
l-slope confluence zone confluence length, unit m, basic survey data determination,
y-slope confluence partition gradient percentage,%, basic survey data,
i-total rainfall in the period of rain purification, unit mm, basic survey data determination,
the S-slope confluence subarea has the largest possible rainfall retention in the period of net rain, the unit is mm,
CN-the comprehensive parameters of the characteristics of the watershed before rainfall, which are determined according to the prior art,
t r -the time of water withdrawal in units h of the period of clean rain;
peak flood flow rate q per period of net rain p Peak time t p Time t of water withdrawal r Linear interpolation to establish a period of net rainThe water source replenishing process of the debris flow is overlapped with the water source replenishing process of all the clean rain periods of the whole rainfall, the water source replenishing process of the whole rainfall of each slope converging zone is established, and the converging zone replenishing function q 'of the debris flow channel section corresponding to each slope converging zone along with the time and space change in the whole rainfall process is obtained' s ；
Step SA4, measuring and calculating a water source converging and supplementing function Q of a debris flow channel in rainfall s
Supplementing the function q 'according to the confluent partition' s Measuring and calculating a water source replenishing process of a debris flow channel in rainfall by a slope-channel coupling relation to obtain a channel converging replenishing quantity function Q s 。
2. The numerical simulation method for the debris flow power process realized by the debris flow rainfall converging water source replenishment measurement and calculation method according to claim 1 is characterized in that: the method is implemented according to the following steps:
step S1, on-site investigation
Basic investigation data including debris flow channel basic data and rainfall basic data are obtained,
s2, establishing a mud-rock flow multi-fluid dynamics model
The mass conservation of solid particles and liquid phase slurry in the mud-rock flow is expressed by the formula 8 and the formula 9 respectively,
wherein t is the time, the unit s,
x, y-cartesian coordinates, unit m,
h-average flow depth on the mixed fluid section, unit m, basic survey data determination,
(u s ,v s ,w s ) The velocity components of the solid phase particles in the source in the x, y, z directions, units m/s,
i-the average rate of erosion per unit of substrate area, unit, determined according to the prior art,
(u f ,v f ,w f ) The velocity components of the liquid phase slurry in the x, y, z directions, units m/s,
ρ f1 average density of liquid phase slurry in substance source, unit kg/m 3 The basic survey data determines, based on the data,
ρ f density of liquid phase slurry in mixed fluid, unit kg/m 3 The basic survey data determines, based on the data,
ρ w density of water in kg/m 3 A constant,
p-rainfall intensity, unit m/h, basic survey data determination,
q s confluence compensation quantity obtained per unit length of channel section, m 3 S, determining a channel confluence supplementing quantity function Q according to a debris flow rainfall confluence water source supplementing measuring and calculating method s Then converted into the channel quantity of unit length,
w-calculating the average ditch bed width of the micro-element section, and determining basic investigation data in unit of m;
the conservation of momentum of the debris flow solid particles along the x and y directions is expressed by the formula 10 and the formula 11 respectively,
in the formula, g-gravity acceleration is expressed in units of m/s 2 A constant,
alpha-erosion coefficient is determined or valued 1.5 multiplied by 10 according to the water tank experiment of the flow force process of the indoor debris flow 7 ，
θ—channel angle, in degrees, as determined by basic survey data,
ρ s average density of solid particles in the mixed fluid, unit kg/m 3 The basic survey data determines, based on the data,
the momentum conservation of the debris flow liquid phase slurry along the x and y directions is expressed by the formulas 12 and 13 respectively,
wherein k is b -coefficients related to the viscosity of the fluid, determined from basic investigation data;
step S3, calculating the numerical value of the dynamic model
And carrying out numerical solution on the mud-rock flow multi-fluid dynamic model, setting time initial conditions and position control points calculated by the model, and obtaining fluid motion parameter data of any time point and any geographic coordinate point of the mud-rock flow in the channel motion process.
3. The debris flow dynamic process numerical simulation method according to claim 2, wherein: the average rate i of the erosion of the material source in the unit bottom area is determined by measuring and calculating according to the formulas 6-7:
where i-the average rate at which the source is eroded per unit of base area, per unit,
the average thickness of the cross section of the z-material source unstable layer, the unit m,
u-average flow velocity of the mixed fluid section, unit m/s, determined according to the prior art,
ρ T average density of cross-section of mixed fluid in kg/m 3 According to the prior art, the method is determined,
d 50 the median particle diameter of the solid particles in the source, unit m, as determined by basic investigation data,
γ m mixed fluid section average volume weight in N/m 3 The basic survey data determines, based on the data,
h-average flow depth on the mixed fluid section, unit m, basic survey data determination,
the average internal friction angle of the beta-substance source, unit degrees, and the basic investigation data confirm,
γ sat average saturated volume weight of the source in N/m 3 The basic survey data determines, based on the data,
γ s the average volume weight of the solid particles in the source of material, unit N/m 3 The basic survey data determines, based on the data,
γ w water volume weight in N/m 3 A constant,
n-average porosity of the source, no units, basic survey data,
c-average cohesion of the source, unit N, determined by basic survey data.
4. Use of a numerical simulation method for a debris flow dynamic process according to claim 2 or 3, characterized in that: is an application in the visualization of the debris flow process.
5. Use of a numerical simulation method for a debris flow dynamic process according to claim 2 or 3, characterized in that: the method is applied to debris flow monitoring and early warning.
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