A temperature field simulation analysis method and system for an oil-immersed cooled underwater inverter

Abstract

The present application belongs to the field of underwater cooling and thermal management technology, and specifically relates to a method and system for simulating the temperature field of an underwater frequency converter with oil-immersion cooling, the method comprising: establishing a geometric model of the underwater frequency converter and a model of its internal fluid domain; meshing the solid grid and fluid domain of the underwater frequency converter model, and setting material properties; setting the contact type and friction conditions between objects inside the underwater frequency converter; setting the ambient temperature of the underwater frequency converter, the convection coefficient between the shell and seawater, the natural convection and heat transfer coefficient of the internal oil, and the heat load of each heating module, and verifying and optimizing the overall heat dissipation performance through simulation. The present application solves the technical problems in the prior art of long heat conduction paths and low heat dissipation efficiency caused by the large thickness of the pressure cabin shell, as well as local overheating caused by the inability to adapt to water temperature changes and the complex distribution of heating devices. By simulating the natural convection of the internal oil and the distribution of heat loads, the accuracy of heat dissipation simulation is improved and the overall heat dissipation performance is optimized.

Description

Technical Field

[0001] The present invention belongs to the technical field of underwater cooling and thermal management, and in particular relates to a temperature field simulation analysis method and system for an underwater frequency converter with oil immersion cooling. Background Art

[0002] In modern underwater equipment, frequency converters (VFDs), as core components, are primarily responsible for regulating electrical energy to drive the proper operation of underwater motors. However, the unique characteristics of the underwater environment place higher demands on the VFD's heat dissipation. Existing VFD enclosures typically utilize a pressure-resistant chamber design to withstand the high pressures of the deep sea. While this pressure-resistant chamber design effectively protects the device's internal components from external high pressure, the thicker the enclosure, the longer the heat conduction path through the casing, resulting in inefficient heat dissipation.

[0003] Existing heat dissipation methods primarily rely on attaching internal heat-generating components directly to the pressure chamber's outer shell, dissipating heat through direct contact between the shell and the surrounding water. This cooling efficiency relies on the thermal conductivity of the shell material. However, due to the thickness of the shell, heat must travel a long conduction path to reach the water, resulting in low heat transfer efficiency. Furthermore, when the inverter has numerous heat-generating components and their distribution is uneven, heat easily accumulates within the device, leading to localized overheating and further increasing the device's thermal load.

[0004] Furthermore, underwater water temperature fluctuates significantly depending on factors such as depth, season, and geographic location. Traditional heat dissipation methods struggle to maintain stable performance under varying water temperatures. Especially during extended periods of operation in deep sea conditions, fluctuations in external water temperature can significantly impact heat dissipation efficiency. In such prolonged high-temperature environments, the electronic components of underwater inverters may experience performance degradation, shortened lifespan, and even equipment failure due to the sustained high temperatures.

[0005] In summary, the main problems with existing technologies include: the thick pressure chamber shell results in a long heat conduction path and low heat dissipation efficiency; the significant fluctuations in water temperature make traditional heat dissipation methods difficult to adapt to complex operating conditions; and the complex distribution of heat-generating components results in a suboptimal heat dissipation path, which can easily lead to localized overheating. To address these issues, further exploration and optimization of heat dissipation solutions are needed to improve the overall heat dissipation performance and reliability of underwater inverters. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, the present invention proposes a temperature field simulation and analysis method and system for an underwater inverter with oil-immersed cooling. The analysis is based on the heat dissipation insulating oil filled inside the underwater inverter. The internal heat flow of the underwater inverter is simulated through optimized modeling and simulation technology, thereby improving the accuracy of the heat dissipation performance simulation and the overall heat dissipation effect.

[0007] In one aspect, the present invention provides a method for simulating and analyzing the temperature field of an oil-immersed cooled underwater frequency converter, the method comprising:

[0008] Step 1: Establish the geometric model of the underwater inverter and its internal fluid domain model;

[0009] Step 2: Mesh the solid mesh and fluid domain of the underwater inverter model and set the material properties;

[0010] Step 3: Set the contact type and friction conditions between objects inside the underwater inverter;

[0011] Step 4: Set the ambient temperature of the underwater inverter, the convection coefficient between the casing and seawater, the natural convection and heat transfer coefficient of the internal oil, and the heat load of each heating module. Verify and optimize the overall heat dissipation performance through simulation.

[0012] Furthermore, step 1 includes:

[0013] Step 1.1: Construct the geometric model of the underwater inverter according to the principle of simplification;

[0014] Step 1.2: Based on the structure of the inverter's internal non-pressure-bearing casing and shielded casing, determine the fluid domain boundary of the inverter's internal insulating oil, set the contact surface between the fluid domain and the simplified key components, and establish an internal fluid domain model.

[0015] Furthermore, in step 1.1, the simplification principles include: ignoring non-critical components, maintaining the structural features of critical components, and adjusting the size and shape of components.

[0016] Furthermore, step 2 includes:

[0017] Step 2.1: Use hexahedron meshing for the submersible inverter housing and tetrahedron meshing for the submersible inverter's internal key modules.

[0018] Step 2.2: Use tetrahedral mesh pairs to divide the fluid domain filled with insulating oil inside the shell;

[0019] Step 2.3: Define the overall structural materials of the subsea drive based on the pressure and temperature loads it will withstand in the deep sea environment.

[0020] Furthermore, step 3 includes:

[0021] Step 3.1: Based on the geometric structure of each heat-generating module inside the inverter, identify potential contact surfaces and label the contact type for each contact surface;

[0022] Step 3.2: Set the contact stiffness parameters for each contact surface and the friction coefficient for contact surfaces with sliding potential;

[0023] Step 3.3: Set the thermal contact impedance and heat dissipation coefficient for the contact surface between each heating module and the heat dissipation insulating oil.

[0024] Furthermore, step 4 includes:

[0025] Step 4.1: Set the external ambient temperature of the housing and the thermal convection parameters between the housing and the seawater according to the seawater temperature at the operating depth of the submersible inverter.

[0026] Step 4.2: Based on the power loss of each heat-generating module, calculate the heat power of each module and apply it as a heat load to the simulation model;

[0027] Step 4.3: Set the heat convection conditions between the underwater inverter housing and the seawater;

[0028] Step 4.4: Set the natural convection coefficient of the oil inside the underwater inverter and the heat transfer coefficient between the oil and each heating module;

[0029] Step 4.5: Apply all calculated thermal loads and boundary conditions to the simulation model. Observe the heat flow path and overall temperature distribution through preliminary simulation to check for local overheating or uneven cooling. If so, adjust the thermal load or convection parameters to optimize the model.

[0030] Furthermore, in step 1.1, the simplified underwater frequency converter includes a housing and a main heat-generating module inside the housing, wherein the main heat-generating module includes an inverter unit module, a reactor module, a control box module and a phase-shifting transformer.

[0031] Furthermore, in step 1, the internal fluid domain model of the underwater frequency converter is a three-dimensional structure in which heat-dissipating insulating oil is filled in the housing of the underwater frequency converter.

[0032] Furthermore, the simulation model of the underwater frequency converter in step 4.5 is determined by the following formula:

[0033]

[0034] Where: ρ represents the material density (kg / m3); C p represents specific heat capacity (J / kg·℃); T represents temperature field (℃); k represents thermal conductivity (W / m·℃); P loss,i represents the power loss of the i-th heating module (W); V i represents the volume of the i-th heating module (m3); h sea represents the convective heat transfer coefficient between the shell and seawater (W / m2·℃); T shell Indicates the shell temperature (℃); T sea Indicates seawater temperature (℃); R th,jrepresents the thermal contact impedance between the jth heating module and the oil (°C / W); T module represents the temperature of the jth heating module (°C); T oil Indicates oil temperature (°C).

[0035] On the other hand, the present invention also provides a temperature field simulation and analysis system for an underwater frequency converter with oil immersion cooling, comprising:

[0036] The geometric modeling module is used to establish the geometric model of the underwater frequency converter and its internal fluid domain model;

[0037] The meshing and material property setting module is used to mesh the solid and fluid domains of the underwater inverter and set the corresponding material properties;

[0038] The contact definition module is used to set the contact type and friction conditions between objects inside the underwater inverter;

[0039] The boundary condition setting and simulation module is used to set the ambient temperature of the underwater inverter, the convection coefficient between the shell and seawater, the natural convection and heat transfer coefficient of the internal oil, and the heat load of each heating module, and verify and optimize the overall heat dissipation performance through simulation.

[0040] The beneficial effects of the present invention are:

[0041] First, the method of the present invention establishes a geometric model and a fluid domain model of the underwater frequency converter, performs precise mesh division and material property setting, and combines the optimization of contact type and friction conditions to achieve accurate simulation of the internal oil natural convection and the thermal load of each heating module, thereby effectively improving the accuracy of the heat dissipation performance simulation, optimizing the overall heat dissipation effect, and ensuring the stable operation of the underwater frequency converter.

[0042] Second, in a preferred implementation, the present method utilizes the principle of simplification to effectively remove non-critical components during geometric modeling while retaining the structural characteristics of critical components, thereby simplifying model complexity, reducing computing resource consumption and simulation time. Furthermore, the method rationally adjusts component size and shape, and optimizes fluid domain boundary settings, ensuring simulation results with high accuracy and engineering feasibility, improving modeling efficiency and consistency in simulation results.

[0043] Third, in a preferred implementation, the present method utilizes a combination of hexahedral and tetrahedral meshes for the outer shell and key internal modules, improving the adaptability and computational stability of the model mesh and ensuring accuracy and efficiency during the simulation. Furthermore, the rational meshing of the fluid domain and the precise definition of material properties under deep-sea environmental conditions help to more realistically reflect the thermodynamic behavior of the underwater inverter under actual operating conditions, optimizing the reliability and accuracy of the simulation results.

[0044] Fourth, in a preferred implementation, the present method improves the accuracy of the heat conduction path by precisely identifying the contact surfaces of the heating modules and labeling the contact types. Furthermore, by setting appropriate contact stiffness and friction coefficients for each contact surface, the mechanical stability between modules is optimized. Furthermore, by setting the thermal contact impedance and heat dissipation coefficient of the oil-liquid contact surface, the overall thermal management effect is further enhanced, ensuring efficient heat transfer and heat dissipation performance, and improving the inverter's stable operation in deep-sea environments.

[0045] Fifth, in a preferred implementation, the present method accurately simulates the heat conduction and heat dissipation behavior of the inverter under deep-sea conditions by comprehensively adjusting the seawater ambient temperature and the heat load of each heating module. By carefully adjusting the thermal convection conditions between the housing and the seawater, as well as the natural convection and heat transfer coefficient of the oil, a more optimized temperature distribution and uniform heat flow path are achieved, reducing the risk of local overheating.

[0046] Sixth, in a preferred implementation, the present method uses the three-dimensional structure of heat-dissipating insulating oil filling the interior of an underwater inverter housing as an analytical foundation to simulate and evaluate the inverter's internal heat dissipation performance. By filling the housing with heat-dissipating insulating oil, the fluid forms a stable circulation within the housing, effectively dissipating heat generated within the inverter, reducing device temperature and extending its service life. Furthermore, the insulating oil provides excellent electrical insulation, preventing electrical short circuits and arcing, and ensuring safe operation of the equipment.

[0047] Seventh, the system of this invention integrates geometric modeling, meshing, contact definition, and boundary condition setting, providing an integrated temperature field simulation and analysis solution. Through its modular design, users can efficiently complete the entire process from modeling to simulation optimization, significantly improving simulation accuracy and efficiency. Furthermore, the system helps quickly identify and resolve heat dissipation issues, improving the heat dissipation performance and operational reliability of underwater inverters, and meeting practical engineering requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a flow chart of the temperature field simulation analysis method of the oil-immersed cooling underwater frequency converter of the present invention;

[0049] Figure 2 1. The initial appearance structure and simplified appearance structure diagram of the underwater frequency converter housing of an embodiment of the present invention;

[0050] Figure 3 1. The complete internal component structure and simplified internal component structure diagram of the underwater frequency converter according to the embodiment of the present invention;

[0051] Figure 4 Schematic diagram of the geometric model of an underwater frequency converter not filled with insulating oil and filled with insulating oil according to an embodiment of the present invention;

[0052] Figure 5 1. It is a diagram showing the division structure of the hexahedral mesh of the shell and the tetrahedral mesh of the internal module according to an embodiment of the present invention;

[0053] Figure 6 is a tetrahedral mesh division structure diagram of a fluid domain according to an embodiment of the present invention;

[0054] Figure 7 Schematic diagram of the material assignment of the housing and internal structure and heat-dissipating insulating oil of an embodiment of the present invention;

[0055] Figure 8 1. It is a schematic diagram of the contact binding definition between the inverter unit module and the housing according to an embodiment of the present invention;

[0056] Figure 9 is a schematic diagram of contact definition between a reactor module and a fluid domain according to an embodiment of the present invention;

[0057] Figure 10 Schematic diagram of contact definition between the phase-shifting transformer and the bottom of the oil tank according to an embodiment of the present invention;

[0058] Figure 11 1. The four main heat-generating modules of the underwater frequency converter according to the embodiment of the present invention and their corresponding power loss diagrams;

[0059] Figure 12 is a schematic diagram of seawater convection boundary loading according to an embodiment of the present invention;

[0060] Figure 13 is a schematic diagram of oil convection boundary loading according to an embodiment of the present invention;

[0061] Figure 14 Schematic diagram of heat load application to internal modules of an underwater frequency converter according to an embodiment of the present invention;

[0062] Figure 15 Schematic diagram of the temperature field distribution inside the underwater frequency converter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0063] In order to enable those skilled in the art to better understand the technical solution of the present application, the present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0064] In the description of this application, the terms "first", "second", and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance; the term "plurality" refers to two or more, unless otherwise expressly defined. Terms such as "installed", "connected", "connected", and "fixed" should be understood in a broad sense. For example, "connected" can mean a fixed connection, a detachable connection, or an integral connection; "connected" can mean a direct connection or an indirect connection through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0065] In the description of this application, it should be understood that the terms "up", "down", "left", "right", "front", "back", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or unit referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limitations on this application.

[0066] Throughout this specification, terms such as "one embodiment / method," "some embodiments / methods," and "specific embodiments / methods" mean that the specific features, structures, materials, or characteristics described in conjunction with that embodiment / method or example are included in at least one embodiment / method or example of the present application. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment / method or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments / methods or examples.

[0067] As the instruction manual Figure 1 The purpose of the present invention is to provide a temperature field simulation analysis method for an oil-immersed cooling underwater frequency converter, the method comprising:

[0068] Step 1: Establish the geometric model of the underwater inverter and its internal fluid domain model.

[0069] The purpose of step 1 is to accurately reflect the structural characteristics and internal heat exchange environment of the underwater frequency converter during the simulation process of temperature field analysis, so as to improve the accuracy of simulation analysis. Due to the complex internal structure and numerous components of the underwater frequency converter, directly using a complete geometric model for simulation will greatly increase the computational burden and may affect the stability of the results. Therefore, the present invention retains the geometric and thermal characteristics of key components by reasonably simplifying the geometric model. The interior of the underwater frequency converter is filled with heat-dissipating insulating oil, which is used to cool the main heat-generating components. Based on this, a fluid domain model is constructed to simulate the natural convection and heat conduction of the heat-dissipating insulating oil, thereby providing a reliable basis for subsequent temperature field analysis.

[0070] The geometric model of the subsea inverter can be designed using SolidWorks, AutoCAD, or CATIA software, and the internal fluid domain model can be modeled using fluid simulation software (such as Fluent or Star-CCM+).

[0071] Step 1 specifically includes:

[0072] Step 1.1: Construct the geometric model of the underwater inverter according to the principle of simplification.

[0073] The simplification principle includes: ignoring non-critical components, maintaining the structural characteristics of critical components, and adjusting the size and shape of components. Based on the simplification principle, the geometric model construction process of the underwater inverter is as follows:

[0074] First, the main structural components of the underwater inverter were determined. The underwater inverter includes a non-pressurized housing, a shielded housing, a pressure compensation device, an inverter unit module, a reactor module, a phase-shifting transformer, a control box module, and a frame circuit breaker. The non-pressurized housing provides protection and support. The shielded housing separates the high and low voltage circuits and prevents electromagnetic interference. The pressure compensation device regulates internal pressure to maintain equilibrium between the internal system and the external pressure of the deep sea. The inverter unit module converts DC power into AC power to drive the underwater motor and is the primary source of heat generated by power conversion. The reactor module limits current surges, reduces electromagnetic interference and grid harmonics, and maintains system electrical stability. The phase-shifting transformer reduces harmonics through phase-shifting control, optimizes power transmission efficiency, and reduces power loss. The control box module integrates various control circuits and signal processing units to ensure precise control and monitoring of the system. The frame circuit breaker provides overload and short-circuit protection to ensure safe operation of the underwater inverter. The inverter unit module and reactor module are the primary heat sources, requiring high heat dissipation, which directly affects the temperature distribution of the entire system. Phase-shifting transformers significantly impact power quality by shifting phases. The heat generated by these transformers stems from conversion losses, necessitating effective heat dissipation under high loads. Control box modules generate relatively low heat, but due to their high integration density, localized overheating can easily impact system stability, necessitating appropriate heat dissipation design. Frame circuit breakers primarily provide circuit protection, generating heat primarily through frequent opening and closing operations. Therefore, ensuring this heat does not affect surrounding modules is crucial.

[0075] Therefore, components that have little impact on temperature field analysis, such as small connectors, fixed brackets, and external pipes, are ignored to reduce the complexity of the geometric model. These components have little impact on heat conduction, so their omission will not affect the simulation accuracy. During the model simplification process, the main heat-generating modules include the inverter unit module, reactor module, phase-shifting transformer, and control box module, and their key geometric features are retained to ensure the reliability of the simulation data. Appropriate size reduction or shape simplification is performed on the geometric features of the core heat-generating modules. While keeping the thermal properties consistent with the actual situation, the details of the components are simplified to achieve higher computational efficiency in the simulation. For example, components with complex structures such as the reactor module and control box module are simplified into solid models suitable for temperature field analysis while maintaining the representativeness of their volume and position.

[0076] As the instruction manual Figure 2-3 , Figure 2 (a) shows the initial appearance structure of the underwater inverter housing 1. External components such as pipes, brackets, and valve bodies are clearly visible. These components have little impact in the temperature field simulation and can be ignored when simplifying the model. Figure 2 (b) shows the simplified appearance structure of the shell 1, retaining the main structure of the shell 1 to provide necessary physical protection and support for the internal heat-generating components. Figure 3 (a) in the figure shows the complete internal component structure of the underwater inverter, including all core heat-generating modules and auxiliary components. Figure 3 (b) shows the simplified internal component structure of the underwater inverter, retaining the main heat-generating modules, including the inverter unit module 2, the reactor module 3, the control box module 4 and the phase-shifting transformer 5, and removing the minor components that do not affect the temperature field analysis.

[0077] Step 1.2: Based on the structure of the inverter's internal non-pressure-bearing casing and shielded casing, determine the fluid domain boundary of the inverter's internal insulating oil, set the contact surface between the fluid domain and the simplified key components, and establish an internal fluid domain model.

[0078] As the instruction manual Figure 4 , Figure 4 (a) is a schematic diagram of the underwater inverter geometric model without insulating oil filling. Figure 4 (b) is a schematic diagram of the underwater inverter geometric model filled with insulating oil. Figure 4 As can be seen from (b), the fluid domain boundary surrounds the key heat-generating modules such as the inverter unit module, reactor module, control box module and phase-shifting transformer. Through the contact surface between the fluid domain boundary and the key heat-generating modules, the insulating oil can absorb and conduct the heat generated by the modules, forming an internal natural convection heat dissipation effect. This design ensures the path for heat to be transferred from each heat-generating module to the casing.

[0079] Step 2: Mesh the solid mesh and fluid domain of the underwater inverter model and set the material properties.

[0080] Step 2 aims to achieve higher computational accuracy and efficiency during finite element analysis by properly meshing the solid and fluid domains of the underwater inverter. Furthermore, to ensure realistic simulation results, the structure's primary materials are defined to reflect their true physical properties under varying loads and temperatures. These meshing and material property definitions provide a scientifically sound foundation for subsequent temperature field and mechanical analysis.

[0081] In this step, mainstream finite element simulation software (such as ANSYS and Abaqus) is used to perform meshing and material property settings.

[0082] Step 2 specifically includes:

[0083] Step 2.1: Use hexahedral meshing for the submersible inverter housing and tetrahedral meshing for the submersible inverter's internal key modules.

[0084] It should be noted that the use of hexahedral meshes to divide the underwater inverter's housing allows it to better adapt to large-area planar structures and improve the computational efficiency of the underwater inverter's housing. The mesh size of the underwater inverter's housing is defined based on its actual dimensions of length, width, and height. The use of tetrahedral meshes to divide the key internal modules of the underwater inverter is because the inverter unit, reactor module, phase-shifting transformer, and control box have complex geometric shapes and most of them bear loads. To ensure that the mesh density of the main internal heat-generating components is high enough, the heat generation and conduction details of each module can be more accurately captured during the simulation process. Selecting a smaller mesh size helps improve the simulation accuracy of the local temperature field and ensures that the local heat flux density distribution can be accurately simulated.

[0085] As the instruction manual Figure 5 , Figure 5 The hexahedral mesh of the submersible inverter's housing and the tetrahedral mesh of its internal modules are shown. The housing's mesh size is defined as 60 mm based on its actual length, width, and height, while the refined mesh size of the internal modules is 40 mm.

[0086] Step 2.2: Use tetrahedral mesh pairs to divide the fluid domain filled with insulating oil inside the shell.

[0087] As the instruction manual Figure 6 , Figure 6 The tetrahedral meshing of the fluid domain is shown, with an overall mesh size of 80 mm to balance computational complexity and simulation accuracy. The meshing scheme for the fluid domain takes into account the flow characteristics of the insulating oil and its impact on heat transfer efficiency.

[0088] Step 2.3: Define the overall structural materials of the subsea drive based on the pressure and temperature loads it will withstand in the deep sea environment.

[0089] In this application, the overall structural materials of the underwater inverter are 316L stainless steel, 980 steel (10CrNi5MoV) and TC4 titanium alloy. The material selection is allocated according to the environmental requirements and component functions as follows: 316L stainless steel is used for the shell of the underwater inverter. It can provide excellent corrosion resistance and mechanical strength, is suitable for long-term operation in deep-sea high-pressure environments, and has excellent heat dissipation performance. 980 steel (10CrNi5MoV) is used for internal pressure-bearing components and main structural supports. It has high strength and toughness and is suitable for maintaining stability under extreme pressure and impact loads. TC4 titanium alloy is used for key connecting components and some high-strength, lightweight modules. Combined with high corrosion resistance and strength characteristics, it is suitable for deep-sea applications that require lightweight design.

[0090] According to the requirements of the simulation analysis, the physical and mechanical properties of each material are provided as shown in Table 1, including density, thermal conductivity, Young's modulus, Poisson's ratio, yield strength, ultimate strength, thermal expansion coefficient, nonlinear tangent modulus, and specific heat capacity.

[0091] In Table 1, thermal conductivity reflects the material's ability to conduct heat in deep-sea environments, particularly 316L stainless steel and 980 steel, which are used in areas with high thermal conductivity requirements. Yield and ultimate strengths assess the material's structural stability in high-pressure environments, protecting equipment from damage due to external impacts. The thermal expansion coefficient defines the material's volume change under temperature fluctuations, with particular attention paid to the impact of thermal expansion of heat-dissipating insulating oil on internal pressure and heat dissipation performance. These materials will be used in the simulation model to realistically replicate their behavior under deep-sea conditions:

[0092] Table 1

[0093]

[0094]

[0095] As the instruction manual Figure 7 , Figure 7 A schematic diagram shows the material assignments for the underwater inverter's housing, internal structure, and heat-dissipating insulating oil. The green portion represents the housing and internal structure, primarily providing mechanical strength and corrosion resistance to withstand the high pressure and corrosive seawater environment of deep seawater. These areas protect internal components and stabilize the entire device. The blue portion represents the heat-dissipating insulating oil filling the housing, which cools the internal heat-generating components.

[0096] Step 3: Set the contact type and friction conditions between objects inside the underwater inverter.

[0097] In underwater inverter simulation analysis, the contact and friction conditions between objects directly impact the accuracy of overall thermal conductivity and mechanical behavior. Considering the close connections and interactions between components within the device, setting appropriate contact and friction conditions allows for realistic simulation of each component's thermal conductivity, stress distribution, and mechanical stability under high-pressure deep-sea conditions. The goal of Step 3 is to optimize simulation accuracy by setting the contact type and friction parameters between objects, ensuring model accuracy under varying load conditions.

[0098] Step 3 specifically includes:

[0099] Step 3.1: Based on the geometric structure of each heat-generating module inside the inverter, identify potential contact surfaces and label the contact type for each contact surface.

[0100] It's important to note that this step labels the contact type of each contact surface in simulation software (such as ANSYS Workbench). For example, in ANSYS Workbench, users can use the "Contact Definition" tool to specify different contact types, such as "Rigid Contact," "Friction Contact," or "Frictionless Contact." ANSYS provides automatic contact detection to quickly identify contact surfaces in the model and allows users to manually adjust contact properties to suit specific engineering needs.

[0101] Specifically, the contact parts of each heating module in the underwater frequency converter of the present invention include: the contact surface between the inverter unit module and the fixed bracket, the contact surface between the reactor module and the casing, the contact interface between the phase-shifting transformer and the heat dissipation insulating oil, etc. The contact surface between the inverter unit module and the fixed bracket mainly affects the structural stability and heat conduction path of the module. The contact surface between the reactor module and the casing affects the force distribution and heat dissipation efficiency of the casing. The contact interface between the phase-shifting transformer and the heat dissipation insulating oil needs to pay attention to heat conduction and heat exchange of the cooling medium. When marking the contact type, for tightly connected components, it is marked as "rigid contact"; for components that may slide relative to each other, it is marked as "sliding contact".

[0102] Step 3.2: Set the contact stiffness parameters for each contact surface and the friction coefficient for contact surfaces with sliding potential.

[0103] Setting contact stiffness ensures that closely spaced components do not experience unreasonable deformation or displacement under mechanical loads. Contact stiffness values are typically determined based on the material's elastic modulus and geometric properties. For example, high stiffness values should be set in areas where loads are transferred to critical structures to maintain system stability.

[0104] The friction coefficient for metal-to-metal contact is generally set between 0.2 and 0.3. The specific value can be adjusted based on actual operating conditions, especially for areas bearing critical loads or high-frequency vibration. If the contacting surfaces are coated with lubricants or anti-corrosion coatings, the friction coefficient should be fine-tuned based on the material manual or experimental data.

[0105] Step 3.3: Set the thermal contact impedance and heat dissipation coefficient for the contact surface between each heating module and the heat dissipation insulating oil.

[0106] It should be noted that low thermal contact impedance is used for efficient heat conduction, while high thermal contact impedance simulates the thermal resistance effect of air gaps or non-close contact areas. This parameter needs to be determined based on the actual assembly accuracy and surface finish to simulate the thermal resistance effect. The heat dissipation coefficient should comprehensively consider the thermal conductivity, viscosity and fluid dynamics of the cooling medium to ensure that the simulation results are consistent with the actual performance. The embodiment of this application uses 20W / (m2·℃) to simulate the actual heat dissipation effect.

[0107] As the instruction manual Figure 8 , Figure 8 A schematic diagram showing the definition of the bonding contact between the inverter unit module and the casing. Figure 8 The red areas in the figure represent the contact surfaces between the inverter module's geometrical surfaces and the housing. These contact surfaces are typically configured for tight contact to ensure a stable connection under mechanical loads and temperature fluctuations, and to achieve effective force and heat transfer. The blue areas represent the contact surfaces within the housing, representing the other end of the contact configuration. This target surface is the area receiving mechanical loads and heat transfer from the inverter module. The inverter module's binding contact type is set to "rigid contact" or "no-slip contact." This setting ensures no relative displacement between the inverter module and the housing, resulting in a rigid connection with respect to force and heat dissipation. The mechanical conditions for the inverter module's binding contact with the housing are set to high contact stiffness to prevent loosening or displacement in the high-pressure deep-sea environment. The thermal conditions for the inverter module's binding contact with the housing are set to low thermal contact impedance to ensure rapid transfer of heat generated by the inverter module to the housing.

[0108] As the instruction manual Figure 9 , Figure 9 Schematic diagram showing the contact definition between the reactor module and the fluid domain. Figure 9The red area in the figure represents the contact surface between the reactor module and the fluid domain (heat dissipation insulating oil). This contact surface is a key area for heat conduction. The heat generated by the reactor module during operation will be transferred to the fluid domain through this surface. The blue area represents the fluid domain, which is the area where the heat dissipation insulating oil is located. Through natural convection and thermal conductivity, the fluid domain further transfers the heat absorbed from the reactor module to other cooling paths, such as the casing, and finally dissipates it to the external environment. The bonding contact type between the reactor module and the fluid domain is set to "frictionless contact", which can simulate the fluidity of the heat dissipation insulating oil around the reactor module while ensuring realistic physical performance under force or environmental changes. The thermal condition in the bonding contact condition between the reactor module and the fluid domain is set to a low thermal contact impedance value to maximize the heat conduction effect.

[0109] As the instruction manual Figure 10 , Figure 10 Schematic diagram showing the contact definition between the phase-shifting transformer and the tank bottom. Figure 10 The red area in the figure represents the contact surface between the phase-shifting transformer and the oil tank bottom. This contact surface is the primary support area for the phase-shifting transformer and must effectively transfer mechanical loads and participate in heat conduction. The blue area represents the structure on which the phase-shifting transformer rests. This supports the transformer's weight and thermal conduction loads, further transferring heat to the heat-dissipating insulating oil in the oil tank, which then dissipates it to the external environment. The bonding contact type between the phase-shifting transformer and the oil tank bottom is set to "rigid contact" or "fixed contact" because the phase-shifting transformer is subject to significant external pressure and vibration in deep-sea environments. This setting ensures that the phase-shifting transformer remains stable during operation, preventing displacement or slippage. The phase-shifting transformer generates heat during operation, which is transferred through the contact surface with the oil tank bottom. Therefore, the thermal contact impedance in the bonding contact conditions between the phase-shifting transformer and the oil tank bottom is set based on the material properties. A low thermal resistance value ensures efficient heat transfer to the oil tank bottom, where it is dispersed and cooled by the oil.

[0110] Step 4: Set the ambient temperature of the underwater inverter, the convection coefficient between the casing and seawater, the natural convection and heat transfer coefficient of the internal oil, and the heat load of each heating module. Verify and optimize the overall heat dissipation performance through simulation.

[0111] The goal of step 4 is to establish accurate heat conduction and convection models to ensure that the cooling effect of the underwater inverter in the actual operating environment can be accurately simulated and optimized. By properly setting external environmental conditions and internal heat load parameters, the device's temperature distribution can be predicted, potential overheating areas can be identified, and effective design adjustments can be made to improve cooling performance.

[0112] Step 4 specifically includes:

[0113] Step 4.1: Set the external ambient temperature of the housing and the heat convection parameters between the housing and the seawater according to the seawater temperature at the operating depth of the submersible inverter.

[0114] The ambient temperature outside the enclosure is set based on the actual seawater temperature of the deep-sea environment in which the submersible drive is located. This temperature affects the convection between the enclosure and the surrounding seawater, thus affecting heat dissipation efficiency. The convection heat transfer coefficient between the enclosure and the seawater is set based on the actual seawater temperature in the simulation environment. This parameter simulates the heat exchange process between the seawater and the enclosure, ensuring that heat is efficiently dissipated from the enclosure to the surrounding seawater. The convection heat transfer coefficient can be adjusted based on the simulated water depth and flow rate to reflect the actual seawater's cooling capacity for the device.

[0115] Step 4.2: Based on the power loss of each heat-generating module, calculate the thermal power of each module and apply it as a thermal load to the simulation model.

[0116] The thermal power of each module is determined by the following formula:

[0117]

[0118] Where: Q represents the thermal power input per unit volume; P represents the total power loss of the module; V represents the volume of the module.

[0119] It should be noted that the power loss of each heating module is a known parameter, usually provided by the module manufacturer. Formula (1) is used to convert the thermal power of each module into a heat load. This heat load is then distributed to each heating module (such as the inverter unit, reactor, etc.) to ensure that the heat distribution conforms to actual usage and accurately reflects the heat input of the heat source.

[0120] As the instruction manual Figure 11 , Figure 11 The four main heat-generating modules within the subsea inverter and their corresponding power losses are shown: the inverter module and phase-shifting transformer have a power loss of 4.286kW, the reactor module has a power loss of 3kW, and the control box module has a power loss of 150W.

[0121] Step 4.3: Set the heat convection condition between the submersible inverter housing and the seawater.

[0122] For example, based on a seawater temperature of 10°C, the convection coefficient is set to 500W / (m²·°C) to realistically simulate the cooling effect of seawater on the shell. The convection coefficient can be adjusted to varying water depths and flow velocities, ensuring that the simulation model accurately reproduces the heat exchange behavior between the shell and seawater.

[0123] As the instruction manual Figure 12 , Figure 12This is a schematic diagram of the seawater convection boundary loading. The seawater ambient temperature marked in the figure is 10°C, which is the baseline temperature when the device exchanges heat with the surrounding seawater in a deep-sea environment. The marked seawater convection parameter is 500W / (m2·℃), which indicates the intensity of thermal convection between the casing and the surrounding seawater. The yellow area represents the heat dissipation effect of the device casing in contact with seawater. The convection coefficient of 500W / (m2·℃) shows that the inverter design has taken into account the demand for efficient heat dissipation under deep-sea conditions. The uniform distribution of colors shown in the figure represents that the casing has a consistent temperature gradient at the set time point, which means that the inverter can effectively manage internal heat and maintain a stable temperature field through thermal convection between the casing and seawater under deep-sea conditions.

[0124] Step 4.4: Set the natural convection coefficient of the oil inside the underwater inverter and the heat transfer coefficient between the oil and each heating module.

[0125] In this application, since the inverter lacks active convection equipment, natural convection of the oil is caused by differences in oil density. For example, the convection coefficient is set to 20W / (m²·°C) to reflect the natural flow and heat exchange behavior of the oil under temperature gradients. By defining the heat transfer coefficient between the oil and each heat-generating module, we ensure that the heat-dissipating insulating oil can effectively absorb and disperse heat. The thermal conductivity of the heat-dissipating insulating oil is used in calculations to maintain the accuracy of the heat transfer process.

[0126] As the instruction manual Figure 13 , Figure 13 Schematic diagram of oil convection boundary loading. Figure 13 The heat input of internal modules (such as inverter units, reactors, phase-shifting transformers, control boxes, etc.) is shown in the figure. The marked yellow areas represent the heat load of each module, and the heat input parameters given in the legend are 32°C and 0.025W / (m2·°C). This setting shows the heat generated continuously by each heat-generating module during operation and is used to simulate the overall temperature field distribution. The color scale at the bottom (from 7500 to 30000kW / m3) represents the temperature gradient in different areas, reflecting the distribution of heat throughout the system. Darker colors represent areas with higher heat generation, which usually correspond to major heat-generating components.

[0127] Step 4.5: Apply all calculated thermal loads and boundary conditions to the simulation model. Observe the heat flow path and overall temperature distribution through preliminary simulation to check for local overheating or uneven cooling. If so, adjust the thermal load or convection parameters to optimize the model.

[0128] The simulation model of heat transfer of underwater inverter is expressed by the following formula:

[0129]

[0130] Where: ρ represents the material density (kg / m3); C p represents specific heat capacity (J / kg·℃); T represents temperature field (℃); k represents thermal conductivity (W / m·℃); P loss,i represents the power loss of the i-th heating module (W); V i represents the volume of the i-th heating module (m3); h sea represents the convective heat transfer coefficient between the shell and seawater (W / m2·℃); T shell Indicates the shell temperature (℃); T sea Indicates seawater temperature (℃); R th,j represents the thermal contact impedance between the jth heating module and the oil (°C / W); T module represents the temperature of the jth heating module (°C); T oil Indicates oil temperature (°C).

[0131] Specifically, The temperature change rate is described, which shows the transient thermal behavior of the underwater inverter.

[0132] represents heat transfer by conduction, using the thermal conductivity k to describe the diffusion of temperature gradients. The heat conduction term is determined by the following formula:

[0133]

[0134] In the heat conduction In the temperature gradient These gradients represent the rate of change of temperature in the x, y, and z directions, respectively. These gradients are used to calculate how heat is transferred and diffused in space.

[0135] It represents the sum of the power loss of all n heating modules (such as inverter units, reactors, control modules, etc.) converted into volume heat source generation rate, reflecting that the power loss of the heating modules is converted into heat and applied to the system. sea (T shell -T sea ) represents the convective heat transfer between the shell and the seawater, reflecting the heat exchange between the shell and the surrounding seawater. Represents the heat transfer between each heating module and the oil, through the thermal contact impedance R th,j To calculate heat flow, temperature difference (T module -T oil ) drives the heat flow from the heating module to the oil, reflecting the contact interface characteristics between the module and the oil.

[0136] In step 4.5, the process of optimizing the model includes:

[0137] S1: Identify local overheating areas: Analyze the temperature field based on the simulation results and locate areas with excessively high temperatures. Check whether these areas are located around heat-generating modules or at bottlenecks in the heat flow path.

[0138] S2: Adjust heat load distribution: If a heating module's temperature is too high, its heat load needs to be redistributed to optimize the heat source distribution for more even heat dissipation. Based on the specific heat load analysis, the location of the heating module or the heat dissipation design can be adjusted.

[0139] S3: Optimize the convection heat transfer coefficient: For the convection heat transfer between the shell and the seawater, the convection coefficient h can be optimized by adjusting the seawater flow rate or depth conditions. sea , increasing the seawater flow rate or using high-efficiency heat dissipation coatings can improve the heat exchange efficiency.

[0140] S4: Adjust material properties: Consider replacing the original material with a material with better thermal conductivity, especially in key areas of the housing and heat-generating module to enhance the overall heat dissipation effect.

[0141] S5: Optimize geometry: Check the geometry, especially the internal flow channel design, to ensure that there are no obvious obstructions or dead zones in the oil flow path. The flow channel can be redesigned to enhance the natural convection capacity of the oil and ensure that heat is quickly transferred to the heat dissipation housing.

[0142] S6: Use multiple simulation iterations: gradually adjust each parameter and perform multiple simulation iterations to verify the effect of each adjustment. After each simulation, analyze the new temperature field and heat flow path until a uniform temperature distribution and optimal heat dissipation performance are achieved.

[0143] Instructions attached Figure 14 , Figure 14Schematic diagram of the thermal load application to each internal component. The heat input to each module is represented by a different symbol and thermal power density, as follows: A: Inverter module 36640 W / m3, B: Inverter module 37000 W / m3, C: Inverter module 58250 W / m3, D: Reactor module 14290 W / m3, E: Control box module 7070 W / m3, F: Phase-shifting transformer 12869 W / m3. These values represent the heat generated by each module during operation. The inverter modules (A, B, and C) have high thermal power densities and are distributed in the upper and middle areas of the equipment. This means that these modules are the main heat sources, placing high demands on the cooling system. In particular, the thermal power density of 58250 W / m3 requires special attention to cooling efficiency and rapid heat dissipation. The reactor module (D) is located in the middle area and has a thermal power density of 14,290 W / m3. Although it generates less heat, it still needs to be effectively dissipated through natural convection and an oil cooling system. The control box module (E): has a thermal power density of 7,070 W / m3 and generates less heat. It is distributed in the lower area of the equipment. The thermal management requirements for this module are relatively low, but the temperature must still be kept stable to ensure the normal operation of the circuit. The phase-shifting transformer (F): Located in the lower area, it has a thermal power density of 12,869 W / m3 and requires temperature control through an oil cooling system to prevent temperature rise from affecting the performance of the transformer.

[0144] Instructions attached Figure 15 , Figure 15 The temperature field distribution inside the underwater inverter is shown, using different colors to represent the temperature gradient in each area. The color gradually transitions from blue (low temperature area) to red (high temperature area), intuitively reflecting the heat distribution within the device. The inverter unit module and upper structure at the top clearly show higher temperatures, with colors close to red. This indicates that these components are the main heat sources, heat is concentrated, and special attention needs to be paid to the cooling design to avoid local overheating of the equipment. The lower area of the figure, especially the reactor and phase-shifting transformer, has a more uniform temperature distribution of blue or green, indicating that these components have good heat dissipation and the heat has been effectively dispersed by the cooling system.

[0145] Another object of the present invention is to provide a temperature field simulation and analysis system for an oil-immersed cooled underwater frequency converter, the system comprising:

[0146] The geometric modeling module is used to establish the geometric model of the underwater frequency converter and its internal fluid domain model.

[0147] The meshing and material property setting module is used to mesh the solid and fluid domains of the underwater converter and set the corresponding material properties.

[0148] The contact definition module is used to set the contact type and friction conditions between objects inside the underwater inverter.

[0149] The boundary condition setting and simulation module is used to set the ambient temperature of the underwater inverter, the convection coefficient between the shell and seawater, the natural convection and heat transfer coefficient of the internal oil, and the heat load of each heating module, and verify and optimize the overall heat dissipation performance through simulation.

[0150] Through precise modeling and optimized simulation, this invention realistically reproduces the natural convection behavior of the heat-dissipating insulating oil filling the inverter, improving heat transfer efficiency. By employing appropriate thermal contact impedance and heat dissipation coefficient settings, the oil is efficiently transferred between the heat-generating modules, optimizing overall temperature distribution and effectively reducing the risk of local overheating, ensuring stable heat dissipation performance of the underwater inverter in deep-sea environments.

[0151] The above is only an embodiment of the present invention, and common sense such as the specific structure and characteristics of the scheme are not described in detail here. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes that fall within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claim involved.

Claims

1. A method for simulating and analyzing the temperature field of an oil-immersed cooling underwater frequency converter, characterized in that: Methods include: Step 1: Establish the geometric model of the underwater inverter and its internal fluid domain model; Step 2: Mesh the solid mesh and fluid domain of the underwater inverter model and set the material properties; Step 3: Set the contact type and friction conditions between objects inside the underwater inverter; Step 4: Set the ambient temperature of the underwater inverter, the convection coefficient between the housing and seawater, the natural convection and heat transfer coefficient of the internal oil, and the heat load of each heating module. Verify and optimize the overall heat dissipation performance through simulation. Step 1 includes: Step 1.1: Construct the geometric model of the underwater inverter according to the principle of simplification; Step 1.2: Based on the structure of the inverter's internal non-pressure-bearing housing and shielded housing, determine the fluid domain boundary of the inverter's internal insulating oil, set the contact surface between the fluid domain and the simplified key components, and establish an internal fluid domain model. Step 2 includes: Step 2.1: Use hexahedron meshing for the submersible inverter housing and tetrahedron meshing for the submersible inverter's internal key modules. Step 2.2: Use tetrahedral meshing to divide the fluid domain filled with insulating oil inside the shell; Step 2.3: Define the overall structural materials of the subsea drive based on the pressure and temperature loads it will withstand in the deep sea environment.

2. The temperature field simulation analysis method of an oil-immersed cooling underwater inverter according to claim 1 is characterized in that: In step 1.1, the simplification principles include: ignoring non-critical components, maintaining the structural characteristics of critical components, and adjusting the size and shape of components.

3. The temperature field simulation analysis method of an oil-immersed cooling underwater inverter according to claim 1 is characterized in that: Step 3 includes: Step 3.1: Based on the geometric structure of each heat-generating module inside the inverter, identify potential contact surfaces and label the contact type for each contact surface; Step 3.2: Set the contact stiffness parameters for each contact surface and the friction coefficient for contact surfaces with sliding potential; Step 3.3: Set the thermal contact impedance and heat dissipation coefficient for the contact surface between each heating module and the heat dissipation insulating oil.

4. The temperature field simulation analysis method for an oil-immersed cooled underwater frequency converter according to claim 1, characterized in that: Step 4 includes: Step 4.1: Set the external ambient temperature of the housing and the thermal convection parameters between the housing and the seawater according to the seawater temperature at the operating depth of the submersible inverter. Step 4.2: Based on the power loss of each heat-generating module, calculate the heat power of each module and apply it as a heat load to the simulation model; Step 4.3: Set the heat convection conditions between the underwater inverter housing and the seawater; Step 4.4: Set the natural convection coefficient of the oil inside the underwater inverter and the heat transfer coefficient between the oil and each heating module; Step 4.5: Apply all calculated thermal loads and boundary conditions to the simulation model. Observe the heat flow path and overall temperature distribution through preliminary simulation to check for local overheating or uneven cooling. If so, adjust the thermal load or convection parameters to optimize the model.

5. The temperature field simulation analysis method for an oil-immersed cooled underwater frequency converter according to claim 2, characterized in that: In step 1.1, the simplified underwater inverter includes a housing and main heat-generating modules inside the housing. The main heat-generating modules include an inverter unit module, a reactor module, a control box module, and a phase-shifting transformer.

6. The temperature field simulation analysis method for an oil-immersed cooled underwater frequency converter according to claim 1, characterized in that: In step 1, the internal fluid domain model of the underwater inverter is a three-dimensional structure in which heat-dissipating insulating oil is filled inside the housing of the underwater inverter.

7. The temperature field simulation analysis method for an oil-immersed cooled underwater frequency converter according to claim 1, characterized in that: The simulation model of the underwater inverter in step 4.5 is determined by the following formula: ； Where: Indicates the material density (kg / m³); represents specific heat capacity (J / kg·°C); represents the temperature field (°C); k represents the thermal conductivity (W / m·°C); represents the power loss of the i-th heating module (W); represents the volume of the i-th heating module (m³); represents the convective heat transfer coefficient between the shell and seawater (W / m²·°C); Indicates the shell temperature (°C); represents the seawater temperature (°C); represents the thermal contact impedance between the jth heating module and the oil (°C / W); represents the temperature of the jth heating module (°C); Indicates the oil temperature (°C).

8. A temperature field simulation and analysis system for an oil-immersed cooling underwater frequency converter, characterized in that: include: The geometric modeling module is used to establish the geometric model of the underwater inverter according to the principle of simplification. It also determines the fluid domain boundary of the internal insulating oil based on the structure of its internal non-pressure-bearing shell and shielding shell, sets the contact surface between the fluid domain and key components, and establishes the internal fluid domain model. The meshing and material property setting module is used to mesh the solid structure of the underwater inverter model and the fluid domain filled with insulating oil. Hexahedral meshing is used for the inverter housing, while tetrahedral meshing is used for the internal key modules and fluid domain of the underwater inverter. The material properties of each component are set according to the pressure and temperature loads that the underwater inverter will withstand in the deep sea environment. The contact definition module is used to set the contact type and friction conditions between objects inside the underwater inverter; The boundary condition setting and simulation module is used to set the ambient temperature of the underwater inverter, the convection coefficient between the shell and seawater, the natural convection and heat transfer coefficient of the internal oil, and the heat load of each heating module, and verify and optimize the overall heat dissipation performance through simulation.

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