CN-122021018-A - Laser irradiation rock phase change and pore forming process prediction method

CN122021018ACN 122021018 ACN122021018 ACN 122021018ACN-122021018-A

Abstract

A method for predicting the phase change and pore-forming process of laser irradiated rock includes such steps as choosing and simplifying geometric model, defining laser irradiation parameters and laser heat source model, defining thermophysical parameters for rock model, treating solid-liquid phase change of rock by equivalent hot-melting method, defining heat transfer boundary condition, setting moving grid condition, dynamically evolving pore-forming morphology interface, dividing the rock model, calculating by preset solver, comparing simulation with experimental pore-forming depth, and judging if the error meets the requirement. The prediction method of rock phase change and pore forming process under laser irradiation can be accurately described, nonlinear phase change heat transfer and pore forming rules of the inside of rock under the action of laser are deeply disclosed, and reliable theoretical basis is provided for optimizing the laser rock breaking process and field application.

Inventors

WANG YIJIANG
YU DONGXU
LI SHUCHEN
Fang Hexuan
WANG JIANZHOU
LI RUILIN

Assignees

中国矿业大学

Dates

Publication Date: 20260512
Application Date: 20260130

Claims (8)

1. A method for predicting the phase change and pore-forming process of laser irradiated rock is characterized by comprising the following steps: S1, selecting and simplifying a geometric model; S2, defining laser irradiation parameters and a laser heat source model; s3, defining thermophysical parameters for the rock model, and treating a solid-liquid phase change process of the rock by adopting an equivalent hot melting method; S4, defining heat transfer boundary conditions including heat conduction, heat convection and heat radiation boundary conditions; s5, setting a mobile grid condition, namely constructing a functional relation describing the evolution of the pore-forming depth along with time, and loading the functional relation into a mobile grid control equation as a constraint condition of pore-forming boundary position evolution to realize dynamic evolution of a pore-forming morphology interface under laser irradiation; s6, carrying out grid division on the rock model, and calculating by adopting a preset solver; S7, comparing simulation with experimental hole forming depth, and judging whether the error meets the requirement; s8, obtaining the model temperature, the phase change and the pore forming rule.
2. The method for predicting the phase change and pore forming process of the laser irradiated rock according to claim 1, wherein the specific process of S1 is as follows: selecting a two-dimensional axisymmetric model, simplifying an actual three-dimensional cylinder sample into a geometric domain with length and width of R and H respectively, and expressing the geometric domain as: ; where r and z are the radial and axial coordinates of the cylinder, respectively.
3. The method for predicting the phase change and pore forming process of the rock irradiated by the laser according to claim 2, wherein the laser irradiation parameters in S2 include laser power, irradiation time, spot diameter and energy distribution pattern; The laser heat source model is loaded on the surface of the rock sample in the form of heat flux density, and the following formula is shown: ; wherein T is the temperature of the rock sample, K, P is the laser power, W, eta is the absorptivity of the rock sample to the laser, zeta is the concentration coefficient, and d b is the diameter of the laser beam, mm.
4. The method for predicting the phase transition and pore-forming process of a rock irradiated with laser according to claim 1 or 2, wherein the thermophysical parameters in S3 include thermal conductivities of solid and liquid phases, densities and specific heat capacities; The equivalent heat capacity method comprises the steps of constructing an equivalent heat conductivity k eff , an equivalent density rho eff and an equivalent specific heat capacity c peff , and correcting the heat capacity by introducing phase change latent heat between the solidus temperature and the liquidus temperature of the rock, wherein the correction formula meets the following conditions: ; ; ; ; ; Wherein k s and k l are the solid and liquid phase thermal conductivities of the rock sample, respectively, ρ s and ρ l are the solid and liquid phase densities of the rock sample, respectively, c ps and c pl are the solid and liquid phase specific heats of the sample, respectively, B is a smooth Heaviside function representing the solid-liquid phase transition, where f is the continuous second derivative of the smooth Heaviside function, D m is a gaussian function normalized around the melting point temperature T m , T is the rock temperature, δ T is the solidification interval, L m is the latent heat of liquefaction; the rock heat conduction control equation is: ; r and z are the radial and axial coordinates of the cylinder, T is the rock sample temperature, k eff is the equivalent thermal conductivity, ρ eff is the equivalent density, c peff is the equivalent specific heat capacity, and Q v is the laser heat source.
5. The method according to claim 1, wherein the step S4 is simplified to an equivalent convective heat transfer process applied to the gasification interface after the rock reaches the gasification temperature under the irradiation of the laser, and when the rock surface unit temperature exceeds the gasification temperature of the rock, the equivalent convective heat transfer coefficient is applied to the boundary to simulate the energy carried away by the gasification of the material, and the relationship between the energy carried away by the gasification and the equivalent convective heat transfer coefficient is as follows: ; wherein q vap is heat quantity taken away in unit area and unit time when the material is gasified, J; Indicating gasification rate, wherein kg/(m 2 ·s);L v ) is vaporization latent heat, J/kg, h vap is equivalent convection heat exchange coefficient, and W/(m 2 ·K);T surface ) and T amb are temperature of rock sample evaporation surface and ambient temperature, K respectively; setting the temperature of the evaporation surface of the rock sample to be equal to the gasification temperature of the rock sample, and determining the equivalent convective heat transfer coefficient value according to the laser power density.
6. The method for predicting the phase transition and pore forming process of the laser irradiated rock according to claim 1, wherein the functional relation describing the evolution of pore forming depth with time constructed in S5 is: ; Wherein y (t) represents the hole forming depth at the moment t, m and n are coefficients related to drilling state, and the function reflects the physical rule that the hole forming depth increases with the increase of time, but the increasing rate gradually decays with the increase of depth; in a moving grid physical field of a finite element model, a fitting function is applied to grid nodes of a laser spot action area as a normal deformation speed boundary condition, so that the grid nodes move downwards along with time to update pore-forming geometric forms, and the following relation is satisfied: ; Where X is the displacement of the boundary node, v m is the deformation speed, n is the unit normal vector, q l is the heat taken away by evaporation, L m is the latent heat of fusion, and L v is the latent heat of evaporation.
7. The prediction method for the laser irradiation rock phase transition and pore forming process according to claim 1, wherein when grid division is performed on a rock model in the step S6, local encryption of grids is achieved by controlling boundary node distribution, the specific method is that a, b, c, d boundary nodes are respectively arranged on the upper boundary, the lower boundary, the left boundary and the right boundary of a rectangular domain per centimeter of boundary length, 2b < a and 2d < c are met, and the preset solver is a MUMPS solver.
8. The method for predicting the phase change and pore forming process of the laser irradiated rock according to claim 1, wherein the error judging method in S7 is to compare the hole depth results obtained by simulation and experiment, and if the simulation and experiment errors are smaller than a preset error threshold, the model is considered to be reliable, otherwise, the condition parameters set in the model need to be corrected and recalculated.

Description

Laser irradiation rock phase change and pore forming process prediction method Technical Field The invention relates to a laser irradiation rock phase change and pore-forming process prediction method, and belongs to the technical field of rock breaking. Background Along with the development and utilization of underground space and the continuous expansion of deep underground resource exploitation scale, the traditional drilling and blasting method construction has the defects of large potential safety hazard, difficult control of super-undermining and the like. The development of a mechanical rock breaking method (such as TBM of a full-face tunnel boring machine) overcomes the problems to a certain extent, but when facing hard rock and extremely hard rock geological conditions, the conventional mechanical rock breaking method generally has the problems of low rock breaking efficiency, severe cutter abrasion, high construction cost and the like, and is difficult to meet the requirements of modern rock engineering on efficient and low-consumption construction. The laser rock breaking technology is used as a novel non-contact thermal rock breaking method, and is widely focused and studied in the field of hard rock breaking due to the advantages of high energy density, strong controllability and the like. The core mechanism of the technology is that the surface of the rock is irradiated by high-energy laser beams, extremely high temperature and temperature gradient are induced in the rock, and wide thermal damage is generated, and the rock is removed and broken by thermal stress cracking or high-temperature melting and gasification, so that the technology is considered to be one of the most potential technical approaches for solving the hard rock tunneling problem in the future. At present, researches on the laser rock breaking technology are focused on technological parameter experiments or fracture effect observation, but a set of efficient prediction method is not available for complex multiphase transformation inside the rock and a pore-forming process under the influence of a melt, and reliable theoretical basis cannot be provided for optimizing the laser rock breaking technology and field application. Disclosure of Invention The invention aims to provide a prediction method for a rock phase change and pore forming process by laser irradiation, which can accurately describe the prediction method for the rock phase change and pore forming process under the laser irradiation, and further reveals nonlinear phase change heat transfer and gas pore forming rules in the rock under the laser action, thereby providing a reliable theoretical basis for optimizing the laser rock breaking process and field application. In order to achieve the above purpose, the invention provides a laser irradiation rock phase transformation and pore-forming process prediction method, which comprises the following steps: S1, selecting and simplifying a geometric model; S2, defining laser irradiation parameters and a laser heat source model; s3, defining thermophysical parameters for the rock model, and treating a solid-liquid phase change process of the rock by adopting an equivalent hot melting method; S4, defining heat transfer boundary conditions including heat conduction, heat convection and heat radiation boundary conditions; s5, setting a mobile grid condition, namely constructing a functional relation describing the evolution of the pore-forming depth along with time, and loading the functional relation into a mobile grid control equation as a constraint condition of pore-forming boundary position evolution to realize dynamic evolution of a pore-forming morphology interface under laser irradiation; s6, carrying out grid division on the rock model, and calculating by adopting a preset solver; S7, comparing simulation with experimental hole forming depth, and judging whether the error meets the requirement; s8, obtaining the model temperature, the phase change and the pore forming rule. Further, the specific process of S1 is as follows: considering the rock size and the axisymmetric characteristics of the heat source, and to reduce the calculation cost and the calculation amount, a two-dimensional axisymmetric model is selected, and the actual three-dimensional cylinder sample is simplified into a geometric domain with the length and the width of R and H respectively, which is expressed as: ; where r and z are the radial and axial coordinates of the cylinder, respectively. Further, the laser irradiation parameters in the S2 include laser power, irradiation time, spot diameter and energy distribution pattern; The laser heat source model is loaded on the surface of the rock sample in the form of heat flux density, and the following formula is shown: ; wherein T is the temperature of the rock sample, K, P is the laser power, W, eta is the absorptivity of the rock sample to the laser, zeta is the concentration coefficient, and d b is