CN107506543A - High-voltage direct-current submarine cable simulation method and system - Google Patents

Abstract

The invention relates to a high-voltage direct current submarine cable simulation method and system. By establishing the electric field module control equation, the flow field module control equation, the solid heat transfer module control equation, the fluid heat transfer module control equation and the electrothermal coupling module control equation, the high-voltage direct current Submarine cables provide an electric-thermal-flow multiphysics coupling simulation method, which directly couples the physical process of electric-thermal-flow multiphysics, and provides a temperature, electric field and flow velocity simulation method for high-voltage direct current submarine cables. The quick determination method is simple and universal, easy to popularize and apply, and is of great significance to ensure the safe and reliable operation of the power grid and prolong the service life of submarine cables.

Description

High voltage direct current submarine cable simulation method and system

technical field

The invention relates to the technical field of electric power simulation, in particular to a high-voltage direct current submarine cable simulation method and system.

Background technique

The radial temperature distribution and electric field distribution of high-voltage DC cables are important operating parameters that reflect the performance of the cable and determine the long-term safe and stable operation of the cable. The difference between high-voltage DC cables and AC cables is mainly in the distribution of the electric field of the insulating layer and its influencing factors. Under DC conditions, the loss caused by conductor loss and insulation leakage current (the latter is negligible during normal operation) is the reason for the temperature gradient distribution of the cable, and changes in temperature and electric field strength will cause significant changes in the conductivity of the insulating material. The electric field distribution of the insulating layer depends on the conductivity distribution, so the electric field distribution and temperature distribution of the high-voltage DC cable are mutually coupled. Secondly, in addition to the conductor temperature, the high-voltage DC cable needs to consider the limitation of the current carrying capacity on the temperature distribution of the insulating layer and its coupling with the electric field distribution.

The submarine cable is in the ocean environment, and the operation process of the submarine cable is closely related to the sea water. The heat generated by the loss of the submarine cable conductor conducts solid heat transfer in the submarine cable body and soil, and conducts fluid heat transfer in water. The flow of seawater continuously takes away the heat generated by the submarine cable, and the heat generated by the submarine cable also continuously heats the seawater. Changes in seawater flow rate and temperature will change the flow of seawater, and the temperature distribution of the submarine cable will change accordingly, thereby changing the electrical conductivity of the insulating material to change the electric field distribution of the insulating layer, and the change in the electric field distribution will in turn affect the conductivity and then affect the temperature. distribution, so it is of great significance to study the law of submarine cable electrothermal coupling considering the flow field.

Various working conditions and experimental schemes can be simulated through numerical simulation, and the results can be obtained more accurately. It has become a research hotspot in recent years, but most of the research is only aimed at the aspects of electrothermal, electromagnetic-thermal and heat-flux (air flow) coupling, etc., and concentrated For the research on terrestrial cables, the electric-thermal-fluid (water flow) coupling simulation of submarine cables is seldom involved, and some are only simulated by imposing corresponding environmental parameters and boundary conditions, and the simulation accuracy is low.

Contents of the invention

Based on this, it is necessary to provide a high-voltage direct current submarine cable simulation method and system for the problem of low simulation accuracy.

A high voltage direct current submarine cable simulation method, comprising the following steps:

Establish a three-dimensional model of the submarine cable body and its laying environment;

According to the three-dimensional model, the control equations of electric-heat-flow coupling simulation are established; wherein, the control equations include electric field module control equations, flow field module control equations, solid heat transfer module control equations, fluid heat transfer module control equations and electrothermal Coupling module governing equations;

According to the control equation of the electric field module, the control equation of the flow field module, the control equation of the solid heat transfer module, the control equation of the fluid heat transfer module and the control equation of the electrothermal coupling module, the high voltage direct current submarine cable simulation is performed.

A high-voltage direct current submarine cable simulation system, including:

The model building module is used to build a three-dimensional model of the submarine cable body and its laying environment;

An equation establishment module, used to establish control equations for electric-heat-flow coupling simulation according to the three-dimensional model; wherein, the control equations include electric field module control equations, flow field module control equations, solid heat transfer module control equations, fluid transfer Thermal module control equations and electrothermal coupling module control equations;

The simulation module is used to simulate the high-voltage DC submarine cable according to the electric field module control equation, the flow field module control equation, the solid heat transfer module control equation, the fluid heat transfer module control equation and the electrothermal coupling module control equation.

The above-mentioned high-voltage direct current submarine cable simulation method and system provide a high-voltage direct current submarine cable with An electric-heat-flow multi-physics coupling simulation method, which directly couples the physical process of the electric-heat-flow multi-physics field, provides a fast method for determining temperature, electric field and flow velocity for high-voltage DC submarine cables, It is simple and universal, easy to popularize and apply, and is of great significance to ensure the safe and reliable operation of the power grid and prolong the service life of submarine cables.

Description of drawings

Fig. 1 is a flow chart of a high-voltage direct current submarine cable simulation method of an embodiment;

Fig. 2 is a geometric model diagram of a submarine cable and its laying environment of an embodiment;

Fig. 3 (a) is the overall temperature distribution nephogram in the simulation result of an embodiment;

Fig. 3 (b) is the temperature distribution nephogram of the submarine cable in the simulation result of an embodiment;

Fig. 4 is the electric field distribution cloud diagram in the simulation result of an embodiment;

Fig. 5 is the velocity distribution nephogram in the simulation result of an embodiment;

Fig. 6 is a schematic structural diagram of a high-voltage direct current submarine cable simulation system of an embodiment.

detailed description

The technical solution of the present invention will be described below in conjunction with the accompanying drawings.

As shown in Fig. 1, the present invention provides a kind of high-voltage DC submarine cable simulation method, may comprise the following steps:

S1, establish a three-dimensional model of the submarine cable body and its laying environment;

Establish the three-dimensional model diagram of the submarine cable body and its laying environment as shown in Figure 2, including the seawater area, the soil area and the submarine cable body; wherein, the seawater area is located in the upper layer of the soil area, and the submarine cable body passes through through the seawater area. By establishing a three-dimensional model of the submarine cable body and its laying environment including the seawater area, the soil area and the submarine cable body, the submarine cable body and its laying environment can be simulated to the greatest extent, which is more similar to the actual scene and improves the simulation. Result accuracy. According to Figure 2, the laying environment in this step is equivalent to two cuboids during simulation, that is, the upper layer of the laying environment is the "sea water area" (including an inlet and an outlet), and the lower layer is the "soil area".

S2, according to the three-dimensional model to establish the control equation of electric-heat-flow coupling simulation; wherein, the control equation includes electric field module control equation, flow field module control equation, solid heat transfer module control equation, fluid heat transfer module control equation and the governing equations of the electrothermal coupling module;

In this step, in the three-dimensional electrothermal flow coupling model of the submarine cable body and its laying environment, the process of loading current in the conductor, water flow, heat transfer in fluid, heat transfer in solid, and electrothermal coupling can be described by the following governing equations :

In one embodiment, the following electric field module governing equations can be established:

J＝σE+J _e

In the formula, is the vector differential operator; J is the current density vector, the unit is A/m ³ ; Q _j is the current source, the unit is A/m ³ ; σ is the conductivity, the unit is S/m; E is the electric field vector, the unit is V/m; V is the potential in V; J _e is the external injection current density. In this system of equations, the basic parameter to be solved is V, and other parameters are calculated based on V.

In one embodiment, the following flow field module governing equations can be established:

In the formula, ρ1 is the density _of the fluid material, the unit is kg/ ^m3 ; u is the velocity vector, the unit is m/s; p is the pressure, the unit is Pa; μ is the dynamic viscosity, the unit is Pa·s; identity matrix.

In one embodiment, the governing equations for the fluid heat transfer module can be established as follows:

In the formula, C ₁ is the specific heat capacity of the fluid material under normal pressure, in J/(kg K); T ₁ is the temperature of the fluid material, in K; t is time; q is the conduction heat flux, in W /m ² ; τ is the viscous stress tensor, in Pa; is the strain rate tensor, the unit is 1/s; Q ₁ is the heat source in the fluid material (excluding viscous heating), the unit is W/m ³ .

In one embodiment, the governing equations for the Heat Transfer in Solids module can be established as follows:

In the formula, _ρ2 is the density of the solid material; _C2 is the specific heat capacity of the solid material under normal pressure; λ is the thermal conductivity of the solid material, the unit is W/(m K) _; T2 is the temperature of the solid material, the unit is K; Q ₂ is the heat source in the solid material, the unit is W/m ³ .

In one embodiment, the following electrothermal coupling module control equation can be established:

In the _formula , _ρ2 is the density of the solid material; T2 is the temperature of the solid material, the unit is K; λ is the thermal conductivity of the solid material, the unit is W/(m K); u is the velocity vector; Is the vector differential operator; J is the current density vector; E is the electric field vector.

By establishing the above five equations, the equations that need to be established for each physical place involved in the simulation content are clarified, so that the high-voltage DC submarine cable simulation can be carried out comprehensively and accurately, and the simulation process is more intuitive. By establishing the electrothermal coupling equation, the electric field and the thermal field can be coupled. Because the change of thermal field (temperature distribution) will affect the distribution of electrical conductivity and the distribution of electric field will change; and the change of electric field distribution will in turn affect the distribution of electrical conductivity and then affect the temperature distribution of the submarine cable. Therefore, the electric field distribution and temperature distribution of HVDC cables are coupled with each other.

S3, performing a high-voltage direct current submarine cable simulation according to the control equations of the electric field module, the flow field module, the solid heat transfer module, the fluid heat transfer module and the electrothermal coupling module.

This step can be achieved by:

Step S3.1, adding materials for each layer of the submarine cable body and its laying environment, and accurately defining the thermal conductivity, heat capacity at normal pressure, density and electrical conductivity of the material;

Step S3.2, adding an electric field, a flow field, a solid heat transfer field, and a fluid heat transfer field, and respectively setting electric field boundary conditions, flow field boundary conditions, solid heat transfer field boundary conditions, and fluid heat transfer field boundary conditions;

Step S3.3, load a high voltage on the submarine cable conductor, load the current in the form of normal current density, set the outer surface of the XLPE (cross-linked polyethylene insulated cable, cross-linked polyethylene insulated cable) insulation to ground, and Simulating the electric field of the high-voltage direct current submarine cable according to the electric field module equation and the electric field boundary condition;

In step S3.4, a water flow inlet and a water flow outlet are respectively provided at both ends of the seawater area, and the flow velocity is given at the water flow inlet, and the flow field of the HVDC submarine cable is calculated according to the flow field module equation and the flow field boundary conditions simulation;

Step S3.5, set the seawater area as fluid heat transfer, set the water temperature at the water inlet, set the upper boundary of the water temperature as the convective heat flux, simulate heat dissipation, and according to the fluid heat transfer module equation and the solid heat transfer field Boundary conditions simulate the solid heat transfer field of HVDC submarine cables;

Step S3.6, set the submarine cable and the soil area as solid heat transfer, set the lower boundary of the soil area as a constant temperature, representing the deep soil, and calculate the high-voltage DC seabed according to the solid heat transfer equation and the fluid heat transfer field boundary conditions The fluid heat transfer field of the cable is simulated;

Step S3.7, using the free tetrahedron for grid division, performing fine grid division for the submarine cable body, and performing coarse grid division for the laying environment.

The role of grid division is to divide a complex model into several simple models, and these simple individuals are interconnected and constrained to form the whole structure. By solving these simple structures, the overall change trend can be obtained. The finer and more tidy the grid, the more accurate the result, and the rougher the grid, the greater the error in the result. The above four modules are for setting boundary conditions and adding physical fields, after which grid division is carried out. After the simulation, the temperature distribution, electric field distribution and flow velocity distribution of the submarine cable can be calculated using the full coupling of the steady-state solver. The temperature distribution cloud map, electric field distribution cloud map and flow velocity distribution cloud map of the submarine cable can be obtained by solving the solution, as shown in Figures 3 to 5. Among them, Figure 3(a) is the overall temperature distribution, and Figure 3(b) is the temperature distribution of the submarine cable.

The present invention simultaneously considers such a complex physical process as the direct coupling of electric-heat-flow multi-physics fields, and provides a high-voltage direct current submarine cable with a temperature, electric field and flow velocity under the condition of accurately setting material properties and boundary conditions. The quick determination method is simple and universal, easy to popularize and apply, and is of great significance to ensure the safe and reliable operation of the power grid and prolong the service life of submarine cables.

As shown in Figure 6, the present invention also provides a high-voltage direct current submarine cable simulation system, which may include:

The model building module 10 is used to set up a three-dimensional model of the submarine cable body and its laying environment;

Establish the three-dimensional model diagram of the submarine cable body and its laying environment as shown in Figure 2, including the seawater area, the soil area and the submarine cable body; wherein, the seawater area is located in the upper layer of the soil area, and the submarine cable body passes through through the seawater area. By establishing a three-dimensional model of the submarine cable body and its laying environment including the seawater area, the soil area and the submarine cable body, the submarine cable body and its laying environment can be simulated to the greatest extent, which is more similar to the actual scene and improves the simulation. Result accuracy. According to Figure 2, the laying environment in this step is equivalent to two cuboids during simulation, that is, the upper layer of the laying environment is the "sea water area" (including an inlet and an outlet), and the lower layer is the "soil area".

Equation establishment module 20, for establishing the control equation of electric-heat-flow coupling simulation according to described three-dimensional model; Wherein, described control equation comprises electric field module control equation, flow field module control equation, solid heat transfer module control equation, fluid Control equations of heat transfer module and electrothermal coupling module;

In this module, in the three-dimensional electrothermal flow coupling model of the submarine cable body and its laying environment, the process of loading current in the conductor, water flow, heat transfer in fluid, heat transfer in solid, and electrothermal coupling can be described by the following governing equations :

In one embodiment, the following electric field module governing equations can be established:

J＝σE+J _e

In the formula, is the vector differential operator; J is the current density vector, the unit is A/m ³ ; Q _j is the current source, the unit is A/m ³ ; σ is the conductivity, the unit is S/m; E is the electric field vector, the unit is V/m; V is the potential in V; J _e is the external injection current density. In this system of equations, the basic parameter to be solved is V, and other parameters are calculated based on V.

In one embodiment, the following flow field module governing equations can be established:

In the formula, ρ1 is the density _of the fluid material, the unit is kg/ ^m3 ; u is the velocity vector, the unit is m/s; p is the pressure, the unit is Pa; μ is the dynamic viscosity, the unit is Pa·s; identity matrix.

In one embodiment, the governing equations for the fluid heat transfer module can be established as follows:

In the formula, C ₁ is the specific heat capacity of the fluid material under normal pressure, in J/(kg K); T ₁ is the temperature of the fluid material, in K; t is time; q is the conduction heat flux, in W /m ² ; τ is the viscous stress tensor, in Pa; is the strain rate tensor, the unit is 1/s; Q ₁ is the heat source in the fluid material (excluding viscous heating), the unit is W/m ³ .

In one embodiment, the governing equations for the Heat Transfer in Solids module can be established as follows:

In the formula, _ρ2 is the density of the solid material; _C2 is the specific heat capacity of the solid material under normal pressure; λ is the thermal conductivity of the solid material, the unit is W/(m K) _; T2 is the temperature of the solid material, the unit is K; Q ₂ is the heat source in the solid material, the unit is W/m ³ .

In one embodiment, the following electrothermal coupling module control equation can be established:

In the _formula , _ρ2 is the density of the solid material; T2 is the temperature of the solid material, the unit is K; λ is the thermal conductivity of the solid material, the unit is W/(m K); u is the velocity vector; Is the vector differential operator; J is the current density vector; E is the electric field vector.

By establishing the above five equations, the equations that need to be established for each physical place involved in the simulation content are clarified, so that the high-voltage DC submarine cable simulation can be carried out comprehensively and accurately, and the simulation process is more intuitive. By establishing the electrothermal coupling equation, the electric field and the thermal field can be coupled. Because the change of thermal field (temperature distribution) will affect the distribution of electrical conductivity and the distribution of electric field will change; and the change of electric field distribution will in turn affect the distribution of electrical conductivity and then affect the temperature distribution of the submarine cable. Therefore, the electric field distribution and temperature distribution of HVDC cables are coupled with each other.

The simulation module 30 is used to perform HVDC submarine cable simulation according to the electric field module control equation, flow field module control equation, solid heat transfer module control equation, fluid heat transfer module control equation and electrothermal coupling module control equation.

The functions of this module can be realized in the following ways:

Step S3.1, adding materials for each layer of the submarine cable body and its laying environment, and accurately defining the thermal conductivity, heat capacity at normal pressure, density and electrical conductivity of the material;

Step S3.2, adding an electric field, a flow field, a solid heat transfer field, and a fluid heat transfer field, and respectively setting electric field boundary conditions, flow field boundary conditions, solid heat transfer field boundary conditions, and fluid heat transfer field boundary conditions;

Step S3.3, load high voltage on the conductor of the submarine cable, load the current in the form of normal current density, set the outer surface of the XLPE insulation as grounded, and calculate the high voltage direct current submarine cable according to the electric field module equation and the electric field boundary conditions Electric field simulation;

In step S3.4, a water flow inlet and a water flow outlet are respectively provided at both ends of the seawater area, and the flow velocity is given at the water flow inlet, and the flow field of the HVDC submarine cable is calculated according to the flow field module equation and the flow field boundary conditions simulation;

Step S3.5, set the seawater area as fluid heat transfer, set the water temperature at the water inlet, set the upper boundary of the water temperature as the convective heat flux, simulate heat dissipation, and according to the fluid heat transfer module equation and the solid heat transfer field Boundary conditions simulate the solid heat transfer field of HVDC submarine cables;

Step S3.6, set the submarine cable and the soil area as solid heat transfer, set the lower boundary of the soil area as a constant temperature, representing the deep soil, and calculate the high-voltage DC seabed according to the solid heat transfer equation and the fluid heat transfer field boundary conditions The fluid heat transfer field of the cable is simulated;

Step S3.7, using the free tetrahedron for grid division, performing fine grid division for the submarine cable body, and performing coarse grid division for the laying environment.

The role of grid division is to divide a complex model into several simple models, and these simple individuals are interconnected and constrained to form the whole structure. By solving these simple structures, the overall change trend can be obtained. The finer and more tidy the grid, the more accurate the result, and the rougher the grid, the greater the error in the result. The above four modules are for setting boundary conditions and adding physical fields, after which grid division is carried out. After the simulation, calculations can be performed using the full coupling of the steady-state solver. The temperature distribution cloud map, electric field distribution cloud map and flow velocity distribution cloud map of the submarine cable can be obtained by solving the solution, as shown in Figures 3 to 5. Among them, Figure 3(a) is the overall temperature distribution, and Figure 3(b) is the temperature distribution of the submarine cable.

The present invention simultaneously considers such a complex physical process as the direct coupling of electric-heat-flow multi-physics fields, and provides a high-voltage direct current submarine cable with a temperature, electric field and flow velocity under the condition of accurately setting material properties and boundary conditions. The quick determination method is simple and universal, easy to popularize and apply, and is of great significance to ensure the safe and reliable operation of the power grid and prolong the service life of submarine cables.

The high-voltage direct current submarine cable simulation system of the present invention corresponds to the high-voltage direct current submarine cable simulation method of the present invention, and the technical features and beneficial effects described in the above-mentioned high-voltage direct current submarine cable simulation method are applicable to high-voltage direct current submarine cable simulation Embodiments of the system are hereby declared.

The logic and/or steps represented in the flowcharts or otherwise described herein, for example, can be considered as a sequenced listing of executable instructions for implementing logical functions, can be embodied in any computer-readable medium, For use with instruction execution systems, devices, or devices (such as computer-based systems, systems including processors, or other systems that can fetch instructions from instruction execution systems, devices, or devices and execute instructions), or in conjunction with these instruction execution systems, devices or equipment used. For the purposes of this specification, a "computer-readable medium" may be any device that can contain, store, communicate, propagate or transmit a program for use in or in conjunction with an instruction execution system, device or device.

More specific examples (non-exhaustive list) of computer-readable media include the following: electrical connection with one or more wires (electronic device), portable computer disk case (magnetic device), random access memory (RAM), Read Only Memory (ROM), Erasable and Editable Read Only Memory (EPROM or Flash Memory), Fiber Optic Devices, and Portable Compact Disc Read Only Memory (CDROM). In addition, the computer-readable medium may even be paper or other suitable medium on which the program can be printed, since the program can be read, for example, by optically scanning the paper or other medium, followed by editing, interpretation or other suitable processing if necessary. The program is processed electronically and stored in computer memory.

It should be understood that various parts of the present invention can be realized by hardware, software, firmware or their combination. In the embodiments described above, various steps or methods may be implemented by software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented by any one or combination of the following techniques known in the art: Discrete logic circuits, ASICs with suitable combinational logic gates, programmable gate arrays (PGAs), field programmable gate arrays (FPGAs), etc.

In the description of this specification, descriptions with reference to the terms "one embodiment", "some embodiments", "example", "specific examples", or "some examples" mean that specific features described in connection with the embodiment or example , structure, material or characteristic is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The technical features of the above-mentioned embodiments can be combined arbitrarily. To make the description concise, all possible combinations of the technical features in the above-mentioned embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, should be considered as within the scope of this specification.

The above-mentioned embodiments only express several implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but should not be construed as limiting the patent scope of the invention. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (9)

1. A high-voltage direct current submarine cable simulation method is characterized in that, comprising the following steps: Establish a three-dimensional model of the submarine cable body and its laying environment; According to the three-dimensional model, the control equations of electric-heat-flow coupling simulation are established; wherein, the control equations include electric field module control equations, flow field module control equations, solid heat transfer module control equations, fluid heat transfer module control equations and electrothermal Coupling module governing equations; According to the control equation of the electric field module, the control equation of the flow field module, the control equation of the solid heat transfer module, the control equation of the fluid heat transfer module and the control equation of the electrothermal coupling module, the high voltage direct current submarine cable simulation is performed. 2. The high-voltage direct current submarine cable simulation method according to claim 1, wherein the three-dimensional model includes a seawater region, a soil region and a submarine cable body; Wherein, the seawater area is located on the upper layer of the soil area, and the submarine cable body passes through the seawater area. 3. The high-voltage direct current submarine cable simulation method according to claim 1, wherein, the step of establishing the control equation of electric-thermal-flow coupling simulation according to the three-dimensional model comprises: Establish the governing equation of the electric field module as follows: ▽ J＝Q _j J＝σE+J _e E＝-▽V In the formula, ▽ is the vector differential operator; J is the current density vector, Q _j is the current source, σ is the conductivity, E is the electric field vector, V is the electric potential, J _e is the external injection current density. 4. The high-voltage direct current submarine cable simulation method according to claim 1, wherein the step of establishing the governing equation of electric-thermal-flow coupling simulation according to the three-dimensional model also includes: The governing equations of the flow field module are established as follows: ▽·(ρ ₁ u)=0 <mrow><msub><mi>&amp;rho;</mi><mn>1</mn></msub><mrow><mo>(</mo><mi>u</mi><mo>&amp;CenterDot;</mo><mo>&amp;dtri;</mo><mo>)</mo></mrow><mi>u</mi><mo>=</mo><mo>-</mo><mo>&amp;dtri;</mo><mi>p</mi><mo>+</mo><mo>&amp;dtri;</mo><mo>&amp;CenterDot;</mo><mo>{</mo><mi>&amp;mu;</mi><mo>&amp;lsqb;</mo><mo>&amp;dtri;</mo><mi>u</mi><mo>+</mo><msup><mrow><mo>(</mo><mo>&amp;dtri;</mo><mi>u</mi><mo>)</mo></mrow><mi>T</mi></msup><mo>&amp;rsqb;</mo><mo>-</mo><mfrac><mn>2</mn><mn>3</mn></mfrac><mi>&amp;mu;</mi><mrow><mo>(</mo><mo>&amp;dtri;</mo><mo>&amp;CenterDot;</mo><mi>u</mi><mo>)</mo></mrow><mi>I</mi><mo>}</mo></mrow> In the formula, ρ1 is the density _of the fluid material, u is the velocity vector, p is the pressure, μ is the dynamic viscosity, and I is the identity matrix. 5. The high-voltage direct current submarine cable simulation method according to claim 1, wherein, the step of establishing the control equation of electric-thermal-flow coupling simulation according to the three-dimensional model also includes: Establish the following governing equations for the fluid heat transfer module: <mfenced open = "" close = ""><mtable><mtr><mtd><mrow><msub><mi>&amp;rho;</mi><mn>1</mn></msub><msub><mi>C</mi><mn>1</mn></msub><mo>&amp;lsqb;</mo><mfrac><mrow><mo>&amp;part;</mo><msub><mi>T</mi><mn>1</mn></msub></mrow><mrow><mo>&amp;part;</mo><mi>t</mi></mrow></mfrac><mo>+</mo><mrow><mo>(</mo><mi>u</mi><mo>&amp;CenterDot;</mo><mo>&amp;dtri;</mo><mo>)</mo></mrow><msub><mi>T</mi><mn>1</mn></msub><mo>&amp;rsqb;</mo><mo>=</mo><mo>-</mo><mrow><mo>(</mo><mo>&amp;dtri;</mo><mo>&amp;CenterDot;</mo><mi>q</mi><mo>)</mo></mrow><mo>+</mo><mi>&amp;tau;</mi><mo>:</mo><mi>S</mi><mo>-</mo></mrow></mtd></mtr><mtr><mtd><mrow><mfrac><msub><mi>T</mi><mn>1</mn></msub><msub><mi>&amp;rho;</mi><mn>1</mn></msub></mfrac><mfrac><mrow><mo>&amp;part;</mo><msub><mi>&amp;rho;</mi><mn>1</mn></msub></mrow><mrow><mo>&amp;part;</mo><msub><mi>T</mi><mn>1</mn></msub></mrow></mfrac><msub><mo>|</mo><mi>p</mi></msub><mo>&amp;lsqb;</mo><mfrac><mrow><mo>&amp;part;</mo><msub><mi>&amp;rho;</mi><mn>1</mn></msub></mrow><mrow><mo>&amp;part;</mo><mi>t</mi></mrow></mfrac><mo>+</mo><mrow><mo>(</mo><mi>u</mi><mo>&amp;CenterDot;</mo><mo>&amp;dtri;</mo><mo>)</mo></mrow><mi>p</mi><mo>&amp;rsqb;</mo><mo>+</mo><msub><mi>Q</mi><mn>1</mn></msub></mrow></mtd></mtr></mtable></mfenced> where C ₁ is the specific heat capacity of the fluid material under normal pressure, T ₁ is the temperature of the fluid material, q is the conduction heat flux, τ is the viscous stress tensor, S=0.5[▽u+(▽u) ^T ] is _The strain rate tensor, Q1, is the heat source in the fluid material. 6. The high-voltage direct current submarine cable simulation method according to claim 1, wherein, the step of establishing the control equation of electric-thermal-flow coupling simulation according to the three-dimensional model also includes: Establish the governing equations for the Heat Transfer in Solids module as follows: ρ ₂ C ₂ ·▽T＝▽·(λ▽T)+Q ₂ In the formula, _ρ2 is the density of the solid material, _C2 is the specific heat capacity of the solid material under normal pressure, λ is the thermal conductivity of the solid material, and _Q2 is the heat source in the solid material. 7. The high-voltage direct current submarine cable simulation method according to claim 1, wherein, the step of establishing the control equation of electric-thermal-flow coupling simulation according to the three-dimensional model also includes: Establish the governing equation of the electrothermal coupling module as follows: <mfenced open = "" close = ""><mtable><mtr><mtd><mrow><msub><mi>&amp;rho;</mi><mn>2</mn></msub><mi>C</mi><mfrac><mrow><mo>&amp;part;</mo><msub><mi>T</mi><mn>2</mn></msub></mrow><mrow><mo>&amp;part;</mo><mi>t</mi></mrow></mfrac><mo>+</mo><msub><mi>&amp;rho;</mi><mn>2</mn></msub><mi>C</mi><mi>u</mi><mo>&amp;CenterDot;</mo><mo>&amp;dtri;</mo><msub><mi>T</mi><mn>2</mn></msub><mo>=</mo><mo>&amp;dtri;</mo><mo>&amp;CenterDot;</mo><mrow><mo>(</mo><mi>&amp;lambda;</mi><mo>&amp;dtri;</mo><msub><mi>T</mi><mn>2</mn></msub><mo>)</mo></mrow><mo>+</mo><mi>Q</mi><mo>=</mo></mrow></mtd></mtr><mtr><mtd><mrow><mo>&amp;dtri;</mo><mo>&amp;CenterDot;</mo><mrow><mo>(</mo><mi>&amp;lambda;</mi><mo>&amp;dtri;</mo><msub><mi>T</mi><mn>2</mn></msub><mo>)</mo></mrow><mo>+</mo><mi>J</mi><mo>&amp;CenterDot;</mo><mi>E</mi></mrow></mtd></mtr></mtable></mfenced> In the _formula , _ρ2 is the density of the solid material; T2 is the temperature of the solid material in K; λ is the thermal conductivity of the solid material in W/(m K); u is the velocity vector; ▽ is the vector differential Operator; J is the current density vector; E is the electric field vector. 8. The high-voltage direct current submarine cable simulation method according to claim 1, characterized in that, according to the electric field module control equation, the flow field module control equation, the solid heat transfer module control equation, the fluid heat transfer module control equation and the electrothermal coupling The steps to simulate the HVDC submarine cable using the module control equation include: Add electric field, flow field, solid heat transfer field, and fluid heat transfer field, and set electric field boundary conditions, flow field boundary conditions, solid heat transfer field boundary conditions, and fluid heat transfer field boundary conditions; Load high voltage on the conductor of the submarine cable, load the current in the form of normal current density, set the outer surface of the XLPE insulation to ground, and simulate the electric field of the high voltage direct current submarine cable according to the electric field module equation and the electric field boundary conditions; A water flow inlet and a water flow outlet are respectively provided at both ends of the seawater area, and the flow velocity is given at the water flow inlet, and the flow field of the high-voltage DC submarine cable is simulated according to the flow field module equation and the flow field boundary conditions; Set the seawater area as fluid heat transfer, set the water temperature at the water inlet, set the upper boundary of the water temperature as the heat flux, simulate heat dissipation, and conduct high-voltage DC The solid heat transfer field of the submarine cable is simulated; Set the submarine cable and the soil area as solid heat transfer, set the lower boundary of the soil area as a constant temperature, which represents the deep soil, and conduct the fluid heat transfer of the HVDC submarine cable according to the solid heat transfer equation and the fluid heat transfer field boundary conditions field simulation; Coupling the electric field with the solid heat transfer field and the fluid heat transfer field respectively through the control equation of the electrothermal coupling module; Use the free tetrahedron for grid division, fine grid division for the submarine cable body, and coarse grid division for the laying environment. 9. A high voltage direct current submarine cable simulation system, characterized in that it comprises: The model building module is used to build a three-dimensional model of the submarine cable body and its laying environment; An equation establishment module, used to establish control equations for electric-heat-flow coupling simulation according to the three-dimensional model; wherein, the control equations include electric field module control equations, flow field module control equations, solid heat transfer module control equations, fluid transfer Thermal module control equations and electrothermal coupling module control equations; The simulation module is used to simulate the high-voltage DC submarine cable according to the electric field module control equation, the flow field module control equation, the solid heat transfer module control equation, the fluid heat transfer module control equation and the electrothermal coupling module control equation.