CN118549989B - A frequency domain electromagnetic device and numerical simulation method for hole surrounding rock detection - Google Patents

Abstract

The present invention relates to the technical field of exploration electromagnetic methods, and discloses a frequency domain electromagnetic device and numerical simulation method for hole surrounding rock detection. The frequency domain electromagnetic device includes an eccentric transmitting component and a receiving coil component; the eccentric transmitting component includes two semicircular transmitting coils; the receiving coil component includes multiple receiving coils. An eccentric transmitting component is used to transmit frequency domain electromagnetic waves, and multiple different planar coils are used to receive magnetic field responses, so as to enhance the difference of signals in different directions of the receiving coil and have the ability to identify directions; the frequency domain electromagnetic device uses multiple rotation angles, multiple coils to transmit, multiple coils to receive, and multiple frequencies to measure to improve data collection efficiency and reliability. The present invention proposes to carry out numerical simulation in a cylindrical coordinate system, and use the residual conductivity and residual permeability of the electrical anomaly to calculate the imaginary and real parts of the secondary magnetic field respectively, which has a fast response and helps to improve the accuracy of hole surrounding rock detection to the actual engineering needs.

Description

A frequency domain electromagnetic device and numerical simulation method for hole surrounding rock detection

Technical Field

The invention relates to the technical field of exploration electromagnetic methods, and in particular to a frequency domain electromagnetic device and a numerical simulation method for hole surrounding rock detection.

Background Art

Hidden underground water bodies are potential sources of geological disasters in tunnel construction and mineral mining. Accurately exploring the location and scale of underground water-rich areas can effectively avoid the risks of underground engineering operations.

It is an advanced geophysical method to use electromagnetic devices to arrange existing boreholes to conduct advance detection of low-resistance water bodies around them. However, due to the limited detection construction space in the borehole and the fact that the detection signal at any position in the hole comes from the three-dimensional space, the current electromagnetic device detection signal in the hole does not have the ability to distinguish the direction of the water-rich body. The existing numerical simulation method does not take into account the existence of residual conductivity and magnetic permeability of electrical anomalies, and the traditional three-dimensional numerical simulation of differential equations requires a lot of time to solve large equations, or stays at the one-dimensional analytical solution of layered media. For the existing technology, please refer to Article 1 (An Iterative Inversion Method using Transient Electromagnetic Data to Predict Water-filled Caves during the Excavation of a Tunnel[J]. Geophysics, 84(2): E83-E103) and Article 2 (Yang Haiyan, Xiao Zhanshan, Liu Zhixin, Yue Jianhua, Hu Haitao, Su Benyu, Li Zhe. 2023. Analytical analysis of tensor transient electromagnetic response in horizontal layered medium holes[J]. Chinese Journal of Geophysics, 66(5): 2167-2180).

In summary, there is an urgent need for a device and method with direction recognition capability and fast response to solve the problems existing in the prior art.

Summary of the invention

The purpose of the present invention is to provide a frequency domain electromagnetic device for hole surrounding rock detection. In order to solve the problem of poor lateral resolution of circular or rectangular transmitting coil signals, the frequency domain electromagnetic device uses an eccentric transmitting assembly including two semicircular transmitting coils to transmit frequency domain electromagnetic waves, and uses multiple different planar coils at a certain distance from the transmitting coil to receive the magnetic field response, thereby enhancing the difference of signals in different directions of the receiving coil and having a strong direction identification ability. In view of the limited space of the hole, the frequency domain electromagnetic device uses multiple rotation angles, multiple coils for transmission, multiple coils for reception, and multiple frequency measurements to improve data collection efficiency and reliability. The specific technical scheme is as follows:

A frequency domain electromagnetic device for detecting surrounding rocks of a hole, comprising a device body having a straight axis;

The device body includes an eccentric transmitting assembly and a receiving coil assembly; the eccentric transmitting assembly includes two semicircular transmitting coils, the centers of the two semicircular transmitting coils are both located on the straight axis, and the centers of the two semicircular transmitting coils are staggered with the straight axis; the receiving coil assembly is located between the two semicircular transmitting coils, and the receiving coil assembly includes a plurality of receiving coils arranged in parallel along the straight axis, and the centers of the plurality of receiving coils are all located on the straight axis;

The straight axis is perpendicular to the planes where the two semicircular transmitting coils are located respectively, and there is no overlapping area when the two semicircular transmitting coils are projected on the same plane perpendicular to the straight axis.

Preferably, the semicircular transmitting coil and the receiving coil are spaced apart, as well as between two adjacent receiving coils.

Preferably, there is a rectangular receiving coil in the receiving coil, the center point of the rectangular receiving coil coincides with the midpoint of the line connecting the centers of the two semicircular transmitting coils, and the diameters of the two semicircular transmitting coils are perpendicular to the plane where the rectangular receiving coil is located.

Preferably, the radius and number of turns of the two semicircular transmitting coils are equal; under the condition of uniform background in the whole space, the initial magnetic fields generated by the two semicircular transmitting coils in the rectangular receiving coil are equal, and the secondary magnetic fields generated by the anomalies in different orientations are not equal.

The present invention also discloses a numerical simulation method. In view of the characteristics of electromagnetic waves attenuating with propagation distance, it is proposed to carry out efficient numerical simulation in a cylindrical coordinate system, and use the residual conductivity and residual permeability of the electrical anomaly to calculate the imaginary and real parts of the secondary magnetic field of the frequency domain electromagnetic device, respectively. The method has a fast response and helps to improve the detection accuracy of the surrounding rock of the hole to the actual engineering needs. The specific scheme is as follows:

A numerical simulation method, using the above-mentioned frequency domain electromagnetic device for hole surrounding rock detection to perform numerical simulation, comprises the following steps:

Step S1, define the cylindrical coordinate z-axis, the straight axis of the device body in the frequency domain electromagnetic device and the center axis of the hole to coincide with each other, and discretize the surrounding rock of the hole in the cylindrical coordinate system;

Step S2, using the magnetic dipole in the whole space, uniform background conductivity and magnetic permeability conditions, the electric field and magnetic field Green's function expressions are used to calculate the initial electric field caused by the semicircular transmitting coil in the discrete unit of the hole surrounding rock and the initial magnetic field of the receiving coil;

Step S3, using the electric dipole formed by the initial electric field obtained in step S2 to form the magnetic field Green's function expression under the conditions of uniform background conductivity and magnetic permeability in the whole space, multiply it by the residual conductivity and residual magnetic permeability of the electrical anomaly body, and obtain the imaginary part and real part of the secondary magnetic field measured in the hole.

Preferably, the step S1 specifically includes:

Set the background conductivity value of the hole surrounding rock, the uniform value of the magnetic permeability, the residual conductivity value of the electrical anomaly body, and the residual magnetic permeability value of the electrical anomaly body to be c0, u0, ca, and ua respectively; define the cylindrical coordinate z axis as the center axis of the hole, and the plane polar coordinate is located at the hole depth of 0;

Take the columnar surrounding rock within the hole depth range with the z axis as the center, and use the cylindrical coordinate system to discretize the surrounding rock into I×J×K units, where: I is the number of discrete parts in the z direction, J is the angle in the cylindrical coordinate system Discrete number, K is the radius in the cylindrical coordinate system Discrete number of copies.

Preferably, in step S2:

The initial magnetic field of the receiving coil includes a primary magnetic field With the secondary magnetic field ;

Primary magnetic field The Green function expression of the magnetic field generated by a unit strength magnetic dipole in a uniform full space background The calculation is as follows:

;

Where: t is the transmitting coil number, r is the receiving coil number, rt is the magnetic dipole source position formed by the transmitting coil, rh is the magnetic field receiving point position of the receiving coil, c0 is the uniform full-space conductivity, f is the transmitting frequency, and P is the magnetic dipole moment strength of the transmitting coil;

Initial electric field caused by semicircular transmitting coil in discrete units of surrounding rock of hole The Green's function expression of the electric field generated by a magnetic dipole in a uniform full-space background The calculation is as follows:

;

Among them: m is an element in the depth record point number array M, which takes a natural number from 1 to M; n is an element in the rotation number array N of a single record point, which takes a natural number from 1 to N; i is the discrete unit number of the surrounding rock in the z direction in the cylindrical coordinate system, which takes a natural number from 1 to I; j is the angle of the surrounding rock in the cylindrical coordinate system Discrete unit number, a natural number from 1 to J; k is the radius in the cylindrical coordinate system. Discrete unit number, a natural number from 1 to K; re is The location of the electric field receiving point of the discrete unit;

Calculate the secondary magnetic field of the receiving coil caused by the initial electric field of the discrete unit , receiving coil secondary magnetic field Imaginary part With real part , the calculation formula is as follows:

;

;

in: is the expression of the magnetic field generated by a unit-strength electric dipole in a uniform full-space background; when and and When , we have: , ; When i, j, k are the discrete unit numbers of the uniform surrounding rock background, then: , .

Preferably, in step S3, the real part IP and the imaginary part OP of the secondary magnetic field measured in the hole are calculated using the following formula:

;

;

in: An absolute value operator for arrays.

Preferably, before the numerical simulation is performed using the frequency domain electromagnetic device for hole surrounding rock detection, the frequency domain electromagnetic device is also calibrated, specifically including:

Step 1: Place the frequency domain electromagnetic device into the hole, keep the center line of the semicircular transmitting coil on the central axis of the hole, and perform N different angle measurements on M recording points at different depths in the hole; wherein: the center of the semicircular transmitting coil T1 is recorded as TO1, and the center of the semicircular transmitting coil T2 is recorded as TO2; the receiving coil assembly includes a rectangular receiving coil R0, a circular receiving coil R1 and a circular receiving coil R2;

Step 2: During the measurement of each depth recording point, keep the recording point coincident with the midpoint TO of the line connecting the center TO1 and the center TO2, rotate the frequency domain electromagnetic device along the line connecting the center TO1 and the center TO2 until the rectangular receiving coil R0 rotates more than 180 degrees, and obtain N rotation angle measurement data for each recording point;

Step 3. During each depth and rotation angle measurement process, two semicircular transmitting coils T1 and T2 are used to transmit electromagnetic wave signals of F frequencies, and each receiving coil records the real and imaginary parts of the generated secondary magnetic field, and the real part of the secondary magnetic field IP (T, M, N, R, F) and the imaginary part of the secondary magnetic field OP (T, M, N, R, F) measured in the hole are obtained. They are both 2×M×N×R×F dimensional vectors, where: T is the transmitting coil number array, and the element t corresponds to the semicircular transmitting coil T1 when the value is 1, and the element t corresponds to the semicircular transmitting coil T2 when the value is 2; M is the depth recording point number array, and its element m takes the value of a natural number from 1 to M; N is the rotation number array of a single recording point, and its element n takes the value of a natural number from 1 to N; R is the receiving coil number array, and its element r takes the value of a natural number from 1 to R, when r=1 represents the rectangular receiving coil R0; F is the transmitting frequency number array, and its element f takes the value of a natural number from 1 to F;

Step 4: Extract the measurement data of the rectangular receiving coil, and compare the measurement data IP (1, M, n, 1, f), OP (1, M, n, 1, f) of different depths of the semicircular transmitting coil T1 under the conditions of n angle and f frequency with the measurement data IP (2, M, n, 1, f), OP (2, M, n, 1, f) of different depths of the semicircular transmitting coil T2;

Step 5: Use the two parameters of the relative deviation of the real part of the secondary magnetic field evIP and the relative deviation of the imaginary part of the secondary magnetic field evOP to evaluate the data quality. The calculation formula is as follows:

;

.

Preferably, the data quality is evaluated in step 5 as follows: when evIP<5% and evOP<5%, the data quality is considered qualified.

In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

FIG1 is a schematic structural diagram of a frequency domain electromagnetic device for detecting surrounding rocks of a hole in an embodiment;

FIG2 is a schematic diagram of the frequency domain electromagnetic device in FIG1 when measuring at two different depth recording points;

FIG3 is a schematic diagram of the frequency domain electromagnetic device in FIG1 when measuring at different rotation angles at a single depth recording point;

Figure 4 (a) is a schematic diagram of the section of the hole surrounding rock and the abnormal body along the vertical axis of the hole in the cylindrical coordinate system;

Figure 4 (b) is a schematic diagram of the section of the hole surrounding rock and the abnormal body perpendicular to the hole axis in the cylindrical coordinate system;

FIG5 is a schematic diagram of the geometric positions of a layered model and a frequency domain electromagnetic device under a layered medium model;

FIG. 6 is a normalized secondary magnetic field curve diagram of the semicircular transmitting coil T1 transmitting and the circular receiving coil R1 receiving.

DETAILED DESCRIPTION

The embodiments of the present invention are described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered.

Example

A frequency domain electromagnetic device for detecting surrounding rocks of holes, see FIG1 , includes a device body having a straight axis L; the device body includes an eccentric transmitting assembly and a receiving coil assembly, details of which are as follows:

The eccentric transmitting assembly includes two semicircular transmitting coils, the centers of the two semicircular transmitting coils are both located on the straight axis L, and the centers of the two semicircular transmitting coils are staggered with the straight axis; the receiving coil assembly is located between the two semicircular transmitting coils, and the receiving coil assembly includes a plurality of receiving coils arranged along the straight axis, the centers of the plurality of receiving coils are all located on the straight axis, and there is a rectangular receiving coil in the receiving coil. In this embodiment: the eccentric transmitting assembly includes a semicircular transmitting coil T1 and a semicircular transmitting coil T2, the center of the semicircular transmitting coil T1 is marked as TO1, and the center of the semicircular transmitting coil T2 is marked as TO2; the receiving coil assembly includes a rectangular receiving coil R0, a circular receiving coil R1 and a circular receiving coil R2. As shown in FIG1 , R0, R1 and R2 are located between T1 and T2, and the center of T1, the center of T2, the center of R0, the center of R1 and the center of R2 are all on the straight axis L. The semicircular transmitting coil and the receiving coil and the two adjacent receiving coils are spaced apart. The straight axis is perpendicular to the planes where the two semicircular transmitting coils are located, and there is no overlapping area when the two semicircular transmitting coils are projected on the same plane perpendicular to the straight axis. The center point TO of the rectangular receiving coil R0 coincides with the midpoint of the line connecting the centers of the two semicircular transmitting coils (TO1 and TO2), and the diameters of the two semicircular transmitting coils are perpendicular to the plane where the rectangular receiving coil is located. The radius and number of turns of the two semicircular transmitting coils are equal; under the condition of uniform background in the whole space, the initial magnetic fields generated by the two semicircular transmitting coils in the rectangular receiving coil are equal, and the secondary magnetic fields generated by the anomalies in different orientations are not equal.

Before using the frequency domain electromagnetic device of this embodiment to perform numerical simulation, the frequency domain electromagnetic device is first calibrated, which specifically includes the following process:

Data collection was carried out at different recording points at different depths and rotation angles along the hole, as shown in Figures 2 and 3. The details are as follows:

As shown in FIG2 , M recording points at different depths are located on the central axis of the hole, and the recording point number increases with increasing depth (two records, m and m+1, are illustrated in FIG2 ).

The frequency domain electromagnetic device is placed in the hole. During the data collection process of a single recording point, the straight axis L of the frequency domain electromagnetic device is kept coincident with the central axis of the hole. The recording points at M different depths in the hole are measured at N different rotation angles (two rotation angles are shown in FIG3 ); the recording point is located at the midpoint of T1 and T2;

During the measurement of each depth recording point, the recording point is kept coincident with the midpoint TO of the line connecting the center TO1 and the center TO2, and the frequency domain electromagnetic device is rotated at a certain angle along the line connecting the center TO1 and the center TO2 until the rectangular receiving coil R0 rotates more than 180 degrees, and N rotation angle measurement data of each recording point are obtained;

In each depth and rotation angle measurement process, two semicircular transmitting coils T1 and T2 are used to transmit electromagnetic wave signals of F frequencies, and each receiving coil records the real part and imaginary part of the secondary magnetic field generated, and the real part of the secondary magnetic field IP (T, M, N, R, F) and the imaginary part of the secondary magnetic field OP (T, M, N, R, F) measured in the hole are obtained. They are both 2×M×N×R×F dimensional vectors, where: T is the transmitting coil number array, and the element t corresponds to the semicircular transmitting coil T1 when the value is 1, and the element t corresponds to the semicircular transmitting coil T2 when the value is 2; M is the depth recording point number array, and its element m takes the value of a natural number from 1 to M; N is the rotation number array of a single recording point, and its element n takes the value of a natural number from 1 to N; R is the receiving coil number array, and its element r takes the value of a natural number from 1 to R, when r=1 represents the rectangular receiving coil R0; F is the transmitting frequency number array, and its element f takes the value of a natural number from 1 to F;

Extract the measurement data of the rectangular receiving coil and compare the n angle, f frequency, the measurement data IP (1, M, n, 1, f), OP (1, M, n, 1, f) of the semicircular transmitting coil T1 at different depths with the measurement data IP (2, M, n, 1, f), OP (2, M, n, 1, f) of the semicircular transmitting coil T2 at different depths;

The data quality is evaluated by using the relative deviation of the real part of the secondary magnetic field evIP and the relative deviation of the imaginary part of the secondary magnetic field evOP. The calculation formula is as follows:

and ;

When evIP<5% and evOP<5%, the data quality is considered qualified; otherwise, adjust the transmitting coil and receiving coil in the frequency domain electromagnetic device, and recalibrate the device under uniform background conditions in the entire space so that the initial magnetic fields generated by the two transmitting coils in the rectangular receiving coil are equal, and remeasure.

The numerical simulation using the frequency domain electromagnetic device of this embodiment includes the following steps:

Step S1, define the cylindrical coordinate z-axis, the straight axis of the device body in the frequency domain electromagnetic device and the center axis of the hole to coincide with each other, and discretize the surrounding rock of the hole in the cylindrical coordinate system;

Step S2, using the electric field and magnetic field Green's function expressions of the magnetic dipole in the whole space and under the conditions of uniform background conductivity and magnetic permeability, respectively calculate the initial electric field caused by the semicircular transmitting coil in the discrete unit of the surrounding rock of the hole and the initial magnetic field of the receiving coil;

Step S3, using the magnetic field Green's function expression of the electric dipole formed by the initial electric field of the discrete unit in step S2 under the conditions of uniform background conductivity and magnetic permeability in the whole space, multiplying it by the residual conductivity and residual magnetic permeability of the electrical anomaly body, respectively, to obtain the imaginary part and the real part of the secondary magnetic field, respectively.

In this embodiment, preferably, step S1 specifically includes:

Set the background conductivity of the hole surrounding rock, the uniform value of the magnetic permeability, the residual conductivity of the electrical anomaly, and the residual magnetic permeability of the electrical anomaly as c0, u0, ca, and ua respectively; define the cylindrical coordinate z axis as the center axis of the hole, and the plane polar coordinate is located at the hole depth of 0, that is, define the cylindrical coordinate system z axis as the center line of the hole, and the horizontal plane where the top of the hole (depth 0) is located as the cylindrical coordinate polar coordinate; in the cylindrical coordinate system, the numbering of the discrete units of the anomaly in the z axis, angle, and radius is Ia~Ib, Ja~Jb, Ka~Kb respectively. See Figure 4 (a) and Figure 4 (b) for details.

Take the columnar surrounding rock within the hole depth range with the z axis as the center, and use the cylindrical coordinate system to discretize the surrounding rock into I×J×K units. Among them, I is the number of discrete parts in the z direction, and J is the angle in the cylindrical coordinate system. Discrete number, K is the radius in the cylindrical coordinate system Discrete number of copies.

In this embodiment, preferably, in step S2:

The initial electric field caused by the semicircular transmitting coil in the discrete unit of the surrounding rock of the hole and the initial magnetic field of the receiving coil include the primary magnetic field With the secondary magnetic field ;

Primary magnetic field The Green function expression of the magnetic field generated by a unit strength magnetic dipole in a uniform full space background The calculation is as follows:

;

Wherein, t is the transmitting coil number, r is the receiving coil number, rt is the magnetic dipole source position formed by the transmitting coil, rh is the magnetic field receiving point position of the receiving coil, c0 is the uniform full-space conductivity, f is the transmitting frequency, and P is the magnetic dipole moment strength of the transmitting coil;

Initial electric field caused by semicircular transmitting coil in discrete units of surrounding rock of hole , using the Green function expression of the electric field generated by a magnetic dipole in a uniform full-space background The calculation is as follows:

;

Where: i is the discrete unit number of the surrounding rock in the z direction in the cylindrical coordinate system, which is a natural number from 1 to I; j is the angle of the surrounding rock in the cylindrical coordinate system Discrete unit number, a natural number from 1 to J; k is the radius in the cylindrical coordinate system. The discrete unit number is a natural number ranging from 1 to K; m is an element in the depth recording point number array M, which is a natural number ranging from 1 to M; n is an element in the rotation number array N of a single recording point, which is a natural number ranging from 1 to N; rt is The position of the magnetic dipole emission source formed by the transmitting coil in the middle; re is The location of the electric field receiving point of the discrete unit.

Calculate the secondary magnetic field of the receiving coil caused by the initial electric field of the discrete unit , receiving coil secondary magnetic field Imaginary part With real part , the calculation formula is as follows:

;

;

in: is the expression of the magnetic field generated by a unit-strength electric dipole in a uniform full-space background; when and and When , we have: , ; When i, j, k are the discrete unit numbers of the uniform surrounding rock background, then: , .

In this embodiment, the real part IP and the imaginary part OP of the secondary magnetic field measured in the hole in step S3 are preferably calculated using the following formula:

;

;

in: An absolute value operator for arrays.

Further preferably, in this embodiment, the distance between each coil along the straight axis of the device is d(T1, R1) = d(R1, R0) = d(R0, R2) = d(R2, T2) = 1m, and the diameter or side length of each coil is 0.2m; the parameters of the layered surrounding rock model are: the thickness of the first layer is infinite, the conductivity is c0 = 0.01S/m, and the magnetic permeability is u0 = 4π×107H/m; the second layer is an electrical abnormal layer with a thickness of 2 meters, the residual conductivity is ca = 0.09S/m, and the residual magnetic permeability is ua = 4π×106H/m; the thickness of the third layer is infinite, the conductivity is 0.01S/m, and the magnetic permeability is u0 = 4π×107H/m. Specific measurement parameters are used: M = 100, each recording point is equally spaced 2 meters, N = 4, each measuring point rotates a total of 180 degrees, and the coil transmission frequency is 10000Hz. See Figures 1-5.

Numerical simulation is carried out based on the above parameters, and the results are shown in Figure 6.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (10)

1. A frequency domain electromagnetic device for detecting surrounding rocks of holes, characterized in that it comprises a device body having a straight axis; The device body includes an eccentric transmitting assembly and a receiving coil assembly; the eccentric transmitting assembly includes two semicircular transmitting coils, the centers of the two semicircular transmitting coils are both located on the straight axis, and the centers of the two semicircular transmitting coils are staggered with the straight axis; the receiving coil assembly is located between the two semicircular transmitting coils, and the receiving coil assembly includes a plurality of receiving coils arranged in parallel along the straight axis, and the centers of the plurality of receiving coils are all located on the straight axis; The straight axis is perpendicular to the planes where the two semicircular transmitting coils are located, and there is no overlapping area when the two semicircular transmitting coils are projected on the same plane perpendicular to the straight axis; There is a rectangular receiving coil in the receiving coil, the center point of the rectangular receiving coil coincides with the midpoint of the line connecting the centers of the two semicircular transmitting coils, and the diameters of the two semicircular transmitting coils are perpendicular to the plane where the rectangular receiving coil is located. 2. The frequency domain electromagnetic device for detecting surrounding rocks of holes according to claim 1 is characterized in that the semicircular transmitting coil and the receiving coil and the two adjacent receiving coils are arranged at intervals. 3. The frequency domain electromagnetic device for hole surrounding rock detection according to claim 2 is characterized in that the radius and number of turns of the two semicircular transmitting coils are equal. 4. The frequency domain electromagnetic device for detecting surrounding rocks of holes according to claim 2 is characterized in that under the condition of uniform background in the entire space, the initial magnetic fields generated by the two semicircular transmitting coils in the rectangular receiving coil are equal, and the secondary magnetic fields generated by abnormal bodies in different orientations are not equal. 5. A numerical simulation method, characterized in that the numerical simulation is performed using the frequency domain electromagnetic device for hole surrounding rock detection as claimed in claim 4, comprising the following steps: Step S1, define the cylindrical coordinate z-axis, the straight axis of the device body in the frequency domain electromagnetic device and the center axis of the hole to coincide with each other, and discretize the surrounding rock of the hole in the cylindrical coordinate system; Step S2, using the magnetic dipole in the whole space, uniform background conductivity and magnetic permeability conditions, the electric field and magnetic field Green's function expressions are used to calculate the initial electric field caused by the semicircular transmitting coil in the discrete unit of the hole surrounding rock and the initial magnetic field of the receiving coil; Step S3, using the electric dipole formed by the initial electric field obtained in step S2, the magnetic field Green's function expression under the conditions of uniform background conductivity and magnetic permeability in the whole space is multiplied by the residual conductivity and residual magnetic permeability of the electrical anomaly body to obtain the imaginary and real parts of the secondary magnetic field measured in the hole. 6. The numerical simulation method according to claim 5, characterized in that the step S1 specifically comprises: Set the background conductivity value of the hole surrounding rock, the uniform value of the magnetic permeability, the residual conductivity value of the electrical anomaly body, and the residual magnetic permeability value of the electrical anomaly body to be c0, u0, ca, and ua respectively; define the cylindrical coordinate z axis as the center axis of the hole, and the plane polar coordinate is located at the hole depth of 0; Take the columnar surrounding rock within the hole depth range with the z-axis as the center, and use the cylindrical coordinate system to discretize the surrounding rock into I×J×K units, where: I is the number of discrete portions in the z direction, J is the number of discrete portions according to the angle ψ in the cylindrical coordinate system, and K is the number of discrete portions according to the radius ρ in the cylindrical coordinate system. 7. The numerical simulation method according to claim 6, characterized in that in step S2: The initial magnetic field of the receiving coil includes the primary magnetic field H ^p and the secondary magnetic field ^HS ; The primary magnetic field H ^p is calculated using the Green's function expression G _H ^H for the magnetic field generated by a unit strength magnetic dipole in a uniform full-space background, as follows: H ^p (t, r, f) = G _H ^H (rt, rh, c0, f) × P (t); Where: t is the transmitting coil number, r is the receiving coil number, rt is the magnetic dipole source position formed by the transmitting coil, rh is the magnetic field receiving point position of the receiving coil, c0 is the uniform full-space conductivity, f is the transmitting frequency, and P is the magnetic dipole moment strength of the transmitting coil; The initial electric field E ^p caused by the semicircular transmitting coil in the discrete unit of the surrounding rock of the hole is calculated using the Green function expression G _H ^E of the electric field generated by the magnetic dipole in the uniform full space background, as follows: E ^p (t, m, n, i, j, k, f) = G _H ^E (rt, re, c0, f) × P (t); Wherein: m is an element in the depth recording point number array M, which takes a natural number from 1 to M; n is an element in the rotation number array N of a single recording point, which takes a natural number from 1 to N; i is the discrete unit number of the surrounding rock in the z direction in the cylindrical coordinate system, which takes a natural number from 1 to I; j is the discrete unit number of the surrounding rock according to the angle ψ in the cylindrical coordinate system, which takes a natural number from 1 to ^J ; k is the discrete unit number according to the radius ρ in the cylindrical coordinate system, which takes a natural number from 1 to K; re is the position of the electric field receiving point of the discrete unit in _GHE ; Calculate the secondary magnetic field ^HS of the receiving coil caused by the initial electric field of the discrete unit. The secondary magnetic field ^HS of the receiving coil is divided into the imaginary part and the real part H _I ^s , the calculation formula is as follows: in: is the magnetic field expression generated by a unit strength electric dipole in a uniform full-space background; when Ia≤i≤Ib and Ja≤j≤Jb and Ka≤k≤Kb, then: When i, j, k are the discrete unit numbers of the uniform surrounding rock background, then: 8. The numerical simulation method according to claim 7, characterized in that the real part IP and the imaginary part OP of the secondary magnetic field measured in the hole in step S3 are calculated using the following formula: Among them: ABS[] is the absolute value operator for an array. 9. The numerical simulation method according to claim 5 is characterized in that before the numerical simulation is performed using the frequency domain electromagnetic device for hole surrounding rock detection according to claim 4, the method further comprises calibrating the frequency domain electromagnetic device, specifically comprising: Step 1: Place the frequency domain electromagnetic device into the hole, keep the center line of the semicircular transmitting coil on the central axis of the hole, and perform N different angle measurements on M recording points at different depths in the hole; wherein: the center of the semicircular transmitting coil T1 is recorded as TO1, and the center of the semicircular transmitting coil T2 is recorded as TO2; the receiving coil assembly includes a rectangular receiving coil R0, a circular receiving coil R1 and a circular receiving coil R2; Step 2: During the measurement of each depth recording point, keep the recording point coincident with the midpoint TO of the line connecting the center TO1 and the center TO2, rotate the frequency domain electromagnetic device along the line connecting the center TO1 and the center TO2 until the rectangular receiving coil R0 rotates more than 180 degrees, and obtain N rotation angle measurement data for each recording point; Step 3. During each depth and rotation angle measurement process, two semicircular transmitting coils T1 and T2 are used to transmit electromagnetic wave signals of F frequencies, and each receiving coil records the real and imaginary parts of the generated secondary magnetic field, and the real part of the secondary magnetic field IP (T, M, N, R, F) and the imaginary part of the secondary magnetic field OP (T, M, N, R, F) measured in the hole are obtained. They are both 2×M×N×R×F dimensional vectors, where: T is the transmitting coil number array, and the element t corresponds to the semicircular transmitting coil T1 when the value is 1, and the element t corresponds to the semicircular transmitting coil T2 when the value is 2; M is the depth recording point number array, and its element m takes the value of a natural number from 1 to M; N is the rotation number array of a single recording point, and its element n takes the value of a natural number from 1 to N; R is the receiving coil number array, and its element r takes the value of a natural number from 1 to R, and when r=1 represents the rectangular receiving coil R0; F is the transmitting frequency number array, and its element f takes the value of a natural number from 1 to F; Step 4: Extract the measurement data of the rectangular receiving coil, and compare the measurement data IP(1,M,n,1,f) and OP(1,M,n,1,f) of different depths of the semicircular transmitting coil T1 under the conditions of angle n and frequency f with the measurement data IP(2,M,n,1,f) and OP(2,M,n,1,f) of different depths of the semicircular transmitting coil T2; Step 5: Use the two parameters of the relative deviation of the real part of the secondary magnetic field evIP and the relative deviation of the imaginary part of the secondary magnetic field evOP to evaluate the data quality. The calculation formula is as follows: evIP＝ABS[(IP(1,M,n,1,f)-IP(2,M,n,1,f))/(IP(1,M,n,1,f)+IP(2,M,n,1,f))]; evOP＝ABS[(OP(1,M,n,1,f)-(OP(2,M,n,1,f))/(OP(1,M,n,1,f)+OP(2,M,n,1,f))]; where: ABS[] is the absolute value operator for an array. 10. The numerical simulation method according to claim 9 is characterized in that the data quality is evaluated in step 5 specifically: when evIP<5% and evOP<5%, the data quality is considered to be qualified.