Simulation and optimization method for welding performance under ultrasonic pulsed current

Abstract

This invention provides a simulation optimization method for welding performance under ultrasonic pulsed current (UFPC), comprising the following steps: obtaining the transport coefficient of the arc plasma under UFPC; incorporating the transport coefficient into the governing equation to obtain simulation results under different UFPC conditions; wherein the transport coefficient includes diffusion coefficient, electrical conductivity, thermal conductivity, and viscosity coefficient. By establishing a method for determining simulation parameters adapted to UFPC conditions, the aim is to ensure accurate simulation and optimization of the welding process, thereby improving welding quality and providing reliable theoretical support for welding process control.

Description

Technical Field

[0001] This invention mainly relates to the technical field of welding data simulation, specifically a method for simulating and optimizing welding performance under the action of ultrasonic pulse current. Background Technology

[0002] Arc welding plays a crucial role in marine engineering, widely used in welding operations on ships, offshore platforms, and other marine structures. With increasingly stringent requirements for welding quality and efficiency, the thermophysical properties of the arc plasma have become key factors influencing weld quality. These thermophysical properties, including ordinary diffusion coefficient, thermal diffusivity, electrical conductivity, thermal conductivity, and viscosity coefficient, play a vital role in the welding process. They directly affect the stability of the arc, the temperature distribution and flow behavior of the molten pool, and consequently, the quality of the weld joint. Especially under the influence of high-frequency pulsed current, the thermophysical properties of the arc plasma undergo significant changes; therefore, accurate calculation of these properties is essential. Only through precise calculation of these properties can correct input data be provided for numerical simulation, ensuring the accuracy of the simulation results. Numerical simulation plays an irreplaceable role in optimizing the welding process, predicting heat input, temperature field, and molten pool flow behavior under different welding parameters, providing a theoretical basis for optimizing welding processes and improving production efficiency. However, the accuracy of numerical simulation results is closely related to the precision of the arc plasma properties.

[0003] Currently, most of the physical property parameters used in simulations rely on conventional thermophysical data, which are typically measured under standard environmental conditions, such as the characteristics of arc plasma at room temperature and pressure. However, these conventional physical property parameters do not fully consider the behavior of arc plasma under special welding methods (such as ultrasonic frequency pulse current (UFPC)) or extreme environments (such as high altitudes, deep water, and high pressure). Especially under the action of ultrasonic pulse current, the microscopic properties of the arc plasma, such as particle collision frequency, collision cross-section, and velocity distribution function, are significantly affected, and these effects are often not considered in existing physical property parameter models. Furthermore, in special environments such as deep water, changes in water pressure and temperature further affect the thermophysical behavior of the arc plasma, and existing models typically fail to effectively adjust physical property parameters under these conditions. Therefore, existing physical property parameter models cannot accurately describe the arc behavior under special welding methods and extreme environments. This lack of specificity and precision in physical property parameter calculations leads to a significant reduction in the accuracy of simulation results, thus failing to guarantee the optimization of the welding process and reliable quality control. Summary of the Invention

[0004] To address the shortcomings of current technologies, this invention, combining existing technologies and starting from practical applications, provides a simulation optimization method for welding performance under ultrasonic pulse current. By establishing a method for determining simulation parameters adapted to ultrasonic pulse current conditions, it aims to ensure accurate simulation and optimization of the welding process, thereby improving welding quality and providing reliable theoretical support for welding process control.

[0005] The technical solution of the present invention is as follows:

[0006] A simulation optimization method for welding performance under ultrasonic pulsed current includes the following steps:

[0007] The transport coefficient of arc plasma under the action of ultrasonic pulsed current UFPC is obtained, and the transport coefficient is introduced into the control equation to obtain simulation results under different UFPC conditions. The transport coefficient includes diffusion coefficient, electrical conductivity, thermal conductivity and viscosity coefficient.

[0008] Specifically, for the diffusion coefficient, the drift velocity of the particle relative to the plasma as a whole is used instead of the absolute velocity of a single particle. The change in particle diffusion coefficient is obtained based on the diffusion velocity terms caused by the temperature gradient and velocity gradient after applying UFPC, as well as the diffusion velocity terms caused by the particle diffusion driving force and velocity gradient. The arc plasma diffusion coefficient is obtained after correcting the change in diffusion coefficient.

[0009] For the conductivity, considering the electron diffusion caused by the electric field and ignoring the thermal diffusion term caused by the temperature gradient, the mass diffusion term of electrons is simplified, and the conductivity of the electric arc plasma is obtained based on Ohm's law.

[0010] For the thermal conductivity, the expression for the arc plasma heat flux is obtained by introducing a second-order approximation model of heat flux and combining it with the first-order approximation expression of arc plasma heat flux, and finally the thermal conductivity of arc plasma is obtained.

[0011] For the viscosity coefficient, the influence of electrons on the viscosity coefficient is ignored, and only the collision effect between heavy particles is considered. The viscosity coefficient of the arc plasma is obtained based on the pressure tensor.

[0012] Furthermore, the specific method for calculating the diffusion coefficient in the transport coefficient is as follows:

[0013] 1) Under the action of UFPC, the plasma drift velocity changes periodically, and the plasma drift velocity is expressed as follows:

[0014] (1)

[0015] In the formula, The plasma drift velocity, For particles average drift speed, For particles mass density, The total mass density of the arc plasma;

[0016] 2) Under the influence of UFPC, the increase in particle diffusion velocity is mainly related to the temperature gradient. and particle diffusion driving force The diffusion velocity increment caused by UFPC is expressed as follows:

[0017] (2)

[0018] In the formula, The total particle number density under UFPC action. It is the product of the total number of particles and their density under the action of UFPC. For particles number density, Let i be the mass density of particle i under UFPC. Let J be the mass density of particle j under UFPC. The total particle mass density under UFPC action. For particles quality For particles quality For pressure, For particles and The ordinary diffusion coefficient between them Let be the divergence of the particle's velocity. For particles thermal diffusivity, For temperature, For the i-th and the i-th The diffusion driving force vector caused by the difference in concentration distribution between components;

[0019] 3) Based on formula (2), the change in particle diffusion coefficient caused by UFPC is expressed as follows:

[0020] (3)

[0021] (4)

[0022] In the formula, This represents the change in the ordinary diffusion coefficient of particles caused by UFPC. The change in the thermal diffusivity of particle i caused by UFPC;

[0023] 4) Correct the change in particle diffusion coefficient to obtain the arc plasma diffusion coefficient, as shown in the following expression:

[0024] (5)

[0025] (6)

[0026] In the formula, The ordinary diffusion coefficient of arc plasma under UFPC is given. Let i be the thermal diffusivity of particle i under UFPC. These are the particle number density, velocity, and correction coefficients related to the UFPC parameters, respectively, induced by UFPC.

[0027] Furthermore, the specific method for calculating conductivity in the transport coefficient is as follows:

[0028] 1) The mass diffusion flux of electrons can be expressed using the generalized Fick's law as follows:

[0029] (7)

[0030] In the formula, For the mass diffusion flux of electrons, The total particle number density under UFPC action. For pressure, For electronic quality, The electron ordinary diffusion coefficient under UFPC is The external force acting on the electron. The electron thermal diffusion coefficient under UFPC is This represents the total number of particle types in the system. For temperature gradient;

[0031] 2) Considering electron diffusion caused by the electric field and ignoring thermal diffusion caused by the temperature gradient, equation (7) is simplified as follows:

[0032] (8)

[0033] In the formula, The electron number density under the action of UFPC The charge carried by one electron. The total electric field experienced by electrons;

[0034] 3) Based on the definition of current density, the contribution of electron migration to the current is expressed as follows:

[0035] (9)

[0036] In the formula, The contribution of electron migration to the electric current;

[0037] 4) Based on Ohm's law, the conductivity of the arc plasma under UFPC is obtained, and the expression is as follows:

[0038] (10)

[0039] In the formula, The conductivity of the arc plasma under UFPC action, The total particle mass density under UFPC action. Boltzmann's constant, For temperature.

[0040] Furthermore, the specific method for calculating thermal conductivity in the transport coefficient is as follows:

[0041] 1) In plasma, the expression for heat flux is as follows:

[0042] (11)

[0043] In the formula, The total heat flux density, Let be the random velocity vector of the i-th particle relative to the average flow velocity. Let be the velocity distribution function of the i-th particle. To integrate over all velocity spaces, For particles quality This represents the total number of particle types in the system.

[0044] 2) Introduce a second-order approximation model of heat flux to describe the effect of UFPC on the thermal conductivity of arc plasma. The second-order corrected heat flux is expressed as follows:

[0045] (12)

[0046] In the formula, This is the second-order corrected heat flux of the electric arc plasma. Let be the internal energy of particle i. Let i be the temperature of particle i. Let be the divergence of the particle's velocity. Let i be the mass density of particle i under UFPC. The total particle mass density under UFPC action. For pressure;

[0047] 3) Further quantify equation (12), as follows:

[0048] (13)

[0049] 4) The first-order approximate expression for the heat flux of the arc plasma under UFPC is as follows:

[0050] (14)

[0051] In the formula, The thermal conductivity of the arc plasma under normal conditions without the application of UFPC. Let be the diffusion direction vector of particle i. Boltzmann's constant, For particles number density, The total particle number density under UFPC action. For particles quality Let be the thermal diffusivity of particle i under the action of UFPC;

[0052] 5) Solving equations (13) and (14) simultaneously, we obtain the following expression for the heat flux of the arc plasma under the action of UFPC:

[0053] (15)

[0054] 6) Based on the heat flux expression, the thermal conductivity expression of the arc plasma under UFPC is obtained as follows:

[0055] (16)

[0056] In the formula, The thermal conductivity of the arc plasma under UFPC is The collision cross-section correction factor is related to the properties of particle i. Let i be the energy exchange coefficient between particles i and j. Let be the thermal diffusivity of particle j under UFPC. Let be the mass of particle j.

[0057] Furthermore, the specific method for calculating the viscosity coefficient in the transport coefficient is as follows:

[0058] 1) In plasma, the total pressure tensor can be expressed as follows:

[0059] (17)

[0060] In the formula, Let the total pressure tensor be... For unit tensors, Let be the kinetic viscosity coefficient of the i-th particle. The divergence of the particle's velocity;

[0061] 2) Based on the influence of UFPC, the pressure tensor is corrected as follows:

[0062] (18)

[0063] In the formula, This is the energy level correction factor. For the transition energy, This represents the macroscopic velocity vector of the matter. The viscosity coefficient of the arc plasma under UFPC is expressed as follows:

[0064] (19)

[0065] In the formula, The collision factor is a measure of the relationship between relative particle velocity, particle type, and distribution function. This is a correction function that takes into account the effects of UFPC peak current, base current, duty cycle, and pulse frequency.

[0066] The beneficial effects of this invention are:

[0067] The technical solution of this invention mainly relates to the calculation and acquisition of the transport coefficient of arc plasma under the action of ultrasonic frequency pulse current (UFPC), focusing on key physical properties such as conventional diffusion coefficient, thermal diffusion coefficient, electrical conductivity, thermal conductivity, and viscosity coefficient. Since the effect of UFPC significantly affects the microscopic behavior of arc plasma, especially particle collisions and particle velocity distribution, this solution establishes a calculation method adapted to ultrasonic frequency pulse current conditions. This aims to ensure accurate simulation and optimization of the welding process, thereby improving welding quality and providing reliable theoretical support for welding process control. Attached Figure Description

[0068] Figure 1 A comparison graph showing the variation of the ordinary diffusion coefficient of arc plasma at different UFPC frequencies.

[0069] Figure 2 A comparison graph showing the variation of the thermal diffusivity of the arc plasma at different UFPC frequencies.

[0070] Figure 3 A comparison graph showing the changes in the conductivity of arc plasma at different UFPC frequencies.

[0071] Figure 4 A comparison graph showing the changes in thermal conductivity of arc plasma at different UFPC frequencies.

[0072] Figure 5A comparison graph showing the variation of the viscosity coefficient of arc plasma at different UFPC frequencies.

[0073] Figure 6 The figure shows a schematic diagram of the simulated arc temperature distribution. In the figure, (a) represents the conventional welding conditions and (b) represents the UFPC-assisted welding conditions. Detailed Implementation

[0074] The present invention will be further described in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined in this application.

[0075] This embodiment provides a simulation optimization method for welding performance under ultrasonic pulsed current. This method can obtain more accurate transport coefficients under ultrasonic pulsed current. By incorporating these transport coefficients into the existing control equations of the simulation model, accurate simulation results can be obtained under different ultrasonic pulsed current (UFPC) conditions, improving the accuracy of predicted welding quality and providing strong theoretical support for optimizing the welding process. The transport coefficients mainly include diffusion coefficient, electrical conductivity, thermal conductivity, and viscosity coefficient. The specific methods for obtaining each coefficient are as follows.

[0076] The diffusion coefficient is calculated as follows:

[0077] In electric arc plasma, particles The diffusion rate of a particle is typically determined by its average drift velocity relative to the plasma. The drift velocity of a particle relative to the plasma can be represented by the difference between the particle velocity and the overall plasma velocity. To simplify the problem, the drift velocity of the particle relative to the overall plasma is used instead of the complex absolute velocity of individual particles. This method eliminates the drift effect between particles, making the calculation simpler. Under UFPC, the plasma drift velocity is affected by the ultrasonic pulse current, exhibiting a periodic variation. Specifically, the plasma drift velocity is expressed as:

[0078] (1)

[0079] In the formula, The plasma drift velocity, For particles average drift speed, For particles mass density, The total mass density of the arc plasma.

[0080] Under the influence of UFPC, the increase in particle diffusion velocity is mainly related to the temperature gradient ( ) and particle diffusion driving force ( Related to this. The expression for the diffusion rate increment caused by UFPC is:

[0081] (2)

[0082] For formula (2), the first term

[0083] The diffusion rate term is caused by the temperature and velocity gradients after applying UFPC; the second term...

[0084] It is the diffusion velocity term caused by the particle diffusion driving force and velocity gradient after the application of UFPC.

[0085] Therefore, the change in particle diffusion coefficient caused by UFPC can be expressed as follows:

[0086] (3)

[0087] (4)

[0088] In the formula, The total particle number density under UFPC action. It is the product of the total number of particles and their density under the action of UFPC. For particles number density, Let i be the mass density of particle i under UFPC. Let J be the mass density of particle j under UFPC. The total particle mass density under UFPC action. For particles quality For particles quality For pressure, For particles and The ordinary diffusion coefficient between them Let be the divergence of the particle's velocity. For particles thermal diffusivity, For temperature, For the i-th and the i-th The diffusion driving force vector caused by the difference in concentration distribution among components. This represents the change in the ordinary diffusion coefficient of particles caused by UFPC. This represents the change in the particle thermal diffusivity caused by UFPC.

[0089] Based on the foregoing analysis, the introduction of UFPC leads to significant changes in the particle number density and velocity in the arc plasma. Therefore, a correction is needed when calculating the particle diffusion coefficient, ultimately yielding the arc plasma diffusion coefficient under the influence of UFPC, expressed as:

[0090] (5)

[0091] (6)

[0092] In the formula, The ordinary diffusion coefficient of arc plasma under UFPC is given. Let i be the thermal diffusivity of particle i under UFPC. These are the particle number density, velocity, and correction coefficients related to the UFPC parameters, respectively, induced by UFPC.

[0093] The method for calculating electrical conductivity is as follows:

[0094] In plasma, because electrons are much smaller than heavy particles, they move more flexibly and respond faster. Electrons become the main charge carriers in arc plasma, responsible for transmitting most of the current. Therefore, the current contribution of heavy particles is negligible, and the main contribution to conductivity comes from electrons.

[0095] The mass diffusion flux of electrons can be expressed by the generalized Fick's law:

[0096] (7)

[0097] In the formula, the first term The second term represents particle diffusion caused by an external force field (usually an electric or magnetic field). This represents thermal diffusion caused by a temperature gradient.

[0098] The electron ordinary diffusion coefficient in formula (7) Total particle number density ,pressure and temperature gradient These variables collectively influence the dynamic behavior of electron migration processes in plasma.

[0099] In the calculation of electrical conductivity, electron diffusion caused by the electric field is mainly considered, while thermal diffusion caused by the temperature gradient is ignored. Therefore, the diffusion term is simplified to:

[0100] (8)

[0101] According to the definition of current density, the contribution of electron migration to the current can be expressed as:

[0102] (9)

[0103] According to Ohm's law, the conductivity of the arc plasma under UFPC can be expressed as:

[0104] (10)

[0105] In the above formula, For the mass diffusion flux of electrons, The total particle number density under UFPC action. For pressure, For electronic quality, The electron ordinary diffusion coefficient under UFPC is The external force acting on the electron. The electron thermal diffusion coefficient under UFPC is This represents the total number of particle types in the system. For temperature gradient, The electron number density under the action of UFPC The charge carried by one electron. The total electric field experienced by the electron. The contribution of electron migration to the electric current, The conductivity of the arc plasma under UFPC action, The total particle mass density under UFPC action. Boltzmann's constant, For temperature.

[0106] The method for calculating thermal conductivity is as follows:

[0107] Thermal conductivity is a physical quantity describing the ratio of the heat flux through a unit area per unit time to the temperature gradient in the presence of a temperature gradient in a plasma. It reflects the plasma's ability to transfer heat energy and plays a crucial role in heat transfer processes. Heat flux can be expressed by the following formula:

[0108] (11)

[0109] Considering the effect of UFPC, the thermal conductivity of the arc plasma needs to be corrected for the influence of high-frequency vibrations caused by UFPC on the nonlocal effects of the plasma. Specifically, by introducing a second-order approximation model of heat flux, the influence of UFPC on the thermal conductivity of the arc plasma can be effectively described. The expression for the second-order corrected heat flux is:

[0110] (12)

[0111] In the formula, the first term Item 2

[0112] and the fifth item Indicates the temperature gradient

[0113] The heat flux caused by the high frequency vibration of the UFPC and the third term; This represents the heat flux caused by the pressure gradient and particle vibration.

[0114] Fourth item It specifically represents the heat flux generated by particle vibration.

[0115] Because the high-frequency pulsed electromagnetic force generated by UFPC causes continuous oscillations of electrons and heavy particles, the density, pressure, and flow velocity in the arc medium are unevenly distributed at different locations. This unevenness affects the heat conduction process. To simplify the calculation, equation (12) only considers the terms caused by the temperature gradient, focusing on the change in the thermal conductivity coefficient. This process can be further quantified by the following formula:

[0116] (13)

[0117] The first-order approximate expression for the heat flux of arc plasma under UFPC is as follows:

[0118] (14)

[0119] By solving equations (13) and (14) simultaneously, the complete expression for the heat flux of the arc plasma under UFPC can be derived:

[0120] (15)

[0121] Based on this heat flux expression, the formula for calculating the thermal conductivity of arc plasma under UFPC can be derived:

[0122] (16)

[0123] In the above formula, The total heat flux density, Let be the random velocity vector of the i-th particle relative to the average flow velocity. Let be the velocity distribution function of the i-th particle. To integrate over all velocity spaces, For particles quality This represents the total number of particle types in the system. This is the second-order corrected heat flux of the electric arc plasma. Let be the internal energy of particle i. Let i be the temperature of particle i. Let be the divergence of the particle's velocity. Let i be the mass density of particle i under UFPC. The total particle mass density under UFPC action. For pressure, Thermal conductivity of arc plasma under normal conditions without the application of UFPC Let be the diffusion direction vector of particle i. Boltzmann's constant, For particles number density, The total particle number density under UFPC action. For particles quality Let i be the thermal diffusivity of particle i under UFPC. The thermal conductivity of the arc plasma under UFPC is The collision cross-section correction factor is related to the properties of particle i. Let i be the energy exchange coefficient between particles i and j. Let be the thermal diffusivity of particle j under UFPC. Let be the mass of particle j.

[0124] The viscosity coefficient is calculated as follows:

[0125] In plasma, the viscosity effect primarily stems from momentum exchange caused by collisions between particles. Since the mass of electrons is much smaller than that of heavy particles, their contribution to the viscosity coefficient is negligible. Therefore, collision effects between heavy particles are typically considered only. The total pressure tensor can be expressed as:

[0126] (17)

[0127] The first term in the formula Represents isotropic pressure, the second term Represents the non-equilibrium viscosity term. Let the total pressure tensor be... For unit tensors, Let be the kinetic viscosity coefficient of the i-th particle.

[0128] Taking into account the effects of UFPC, the pressure tensor is corrected as follows:

[0129] (18)

[0130] In the formula, This is the energy level correction factor. With transition energy, This represents the macroscopic velocity vector of the matter. The viscosity coefficient of the arc plasma under UFPC can be expressed as:

[0131] (19)

[0132] In the formula, The collision factor, which reflects the relationship between relative particle velocity, particle type, and distribution function, can be obtained by utilizing the orthogonality of the sonine polynomials. This is a correction function that takes into account the effects of UFPC peak current, base current, duty cycle, and pulse frequency.

[0133] Based on the derived formulas above, the transport coefficients of the arc plasma under UFPC were calculated, including the diffusion coefficient, thermal conductivity, electrical conductivity, and viscosity coefficient. The calculation results are as follows: Figures 1-5 As shown in the figure, the introduction of UFPC has a significant impact on the transport coefficient of the arc plasma. Compared with the 0 kHz condition, the ordinary diffusion coefficient of the arc plasma decreases with increasing UFPC frequency. This is because the high-frequency pulsed electromagnetic field enhances the confinement of charged particles, restricting their degrees of freedom of disordered motion and thus weakening their free diffusion ability. Conversely, the thermal diffusivity, electrical conductivity, thermal conductivity, and viscosity all gradually increase with increasing UFPC frequency. This is mainly attributed to the high-frequency pulsed current enhancing the electromagnetic interaction and energy input of the plasma, increasing the average energy and collision frequency of particles, thereby strengthening the heat and momentum transfer capabilities. This change in the arc plasma transport coefficient caused by UFPC is of great significance in numerical simulations because these transport parameters directly determine the heat and mass transfer processes in the arc plasma. Only by ensuring the accuracy of these parameters can the credibility and predictive ability of the numerical simulation results be effectively improved. Therefore, accurately calculating the transport coefficient of arc plasma under UFPC is of great significance for revealing its internal multi-physics coupling mechanism and guiding the optimization of welding processes.

[0134] Subsequently, these calculation results were substituted into the governing equations to obtain the arc temperature distribution under different UFPC conditions. The governing equations adopted were existing equations from the simulation model, which primarily describe the mass, momentum, and energy transfer processes of the arc plasma under external fields and influences. The final simulation results are as follows: Figure 6 As shown. (Through) Figure 6It can be seen that under the action of UFPC, the arc center temperature increases significantly, and with the increase of pulse frequency, the arc contraction effect intensifies, and the high-temperature region gradually concentrates at the arc axis. This indicates that UFPC effectively enhances the electromagnetic contraction effect and energy density distribution of the arc plasma, thereby changing the temperature field structure of the arc. Compared with the arc morphology under 0 kHz conditions, the arc temperature distribution under UFPC conditions is more concentrated and the heat input is more uniform. Therefore, Figure 6 This not only verified the rationality of the calculated transport coefficient in the governing equation, but also proved the effectiveness and reliability of the method in revealing the thermo-mechanical behavior of the arc under the action of UFPC from the perspective of temperature field distribution.

[0135] This process allows for a more precise description and optimization of the welding process, thereby improving welding quality.

Claims

1. A method for simulating and optimizing welding performance under ultrasonic pulsed current, characterized in that, Includes the following steps: The transport coefficient of arc plasma under the action of ultrasonic pulsed current UFPC is obtained, and the transport coefficient is introduced into the control equation to obtain simulation results under different UFPC conditions. The transport coefficient includes diffusion coefficient, electrical conductivity, thermal conductivity and viscosity coefficient. Specifically, for the diffusion coefficient, the drift velocity of the particle relative to the plasma as a whole is used instead of the absolute velocity of a single particle. The change in particle diffusion coefficient is obtained based on the diffusion velocity terms caused by the temperature gradient and velocity gradient after applying UFPC, as well as the diffusion velocity terms caused by the particle diffusion driving force and velocity gradient. The arc plasma diffusion coefficient is obtained after correcting the change in diffusion coefficient. For the conductivity, considering the electron diffusion caused by the electric field and ignoring the thermal diffusion term caused by the temperature gradient, the mass diffusion term of electrons is simplified, and the conductivity of the electric arc plasma is obtained based on Ohm's law. For the thermal conductivity, the expression for the arc plasma heat flux is obtained by introducing a second-order approximation model of heat flux and combining it with the first-order approximation expression of arc plasma heat flux, and finally the thermal conductivity of arc plasma is obtained. For the viscosity coefficient, the influence of electrons on the viscosity coefficient is ignored, and only the collision effect between heavy particles is considered. The viscosity coefficient of the electric arc plasma is obtained based on the pressure tensor. The specific method for calculating conductivity in the transport coefficient is as follows: 1) The mass diffusion flux of electrons can be expressed using the generalized Fick's law as follows: （7） In the formula, For the mass diffusion flux of electrons, The total particle number density under UFPC action. For pressure, For electronic quality, The electron ordinary diffusion coefficient under UFPC is The external force acting on the electron. The electron thermal diffusion coefficient under UFPC is This represents the total number of particle types in the system. For temperature gradient; 2) Considering electron diffusion caused by the electric field and ignoring the thermal diffusion term caused by the temperature gradient, equation (7) is simplified as follows: （8） In the formula, The electron number density under the action of UFPC The charge carried by one electron. The total electric field experienced by electrons; 3) Based on the definition of current density, the contribution of electron migration to the current is expressed as follows: （9） In the formula, The contribution of electron migration to the electric current; 4) Based on Ohm's law, the conductivity of the arc plasma under UFPC is obtained, and the expression is as follows: （10） In the formula, The conductivity of the arc plasma under UFPC action, The total particle mass density under UFPC action. Boltzmann's constant, For temperature; the specific method for calculating the viscosity coefficient in the transport coefficient is as follows: 1) In plasma, the total pressure tensor can be expressed as follows: （17） In the formula, Let the total pressure tensor be... For unit tensors, Let be the kinetic viscosity coefficient of the i-th particle. Let be the divergence of the particle's velocity. Boltzmann's constant, Let i be the temperature of particle i. For particles number density; 2) Based on the influence of UFPC, the pressure tensor is corrected as follows: （18） In the formula, This is the energy level correction factor. For the transition energy, This represents the macroscopic velocity vector of the matter. The viscosity coefficient of the arc plasma under UFPC is expressed as follows: （19） In the formula, The collision factor is a measure of the relationship between relative particle velocity, particle type, and distribution function. This is a correction function that takes into account the effects of UFPC peak current, base current, duty cycle, and pulse frequency.

2. The simulation and optimization method for welding performance under ultrasonic pulse current as described in claim 1, characterized in that, The specific method for calculating the diffusion coefficient in the transport coefficient is as follows: 1) Under the action of UFPC, the plasma drift velocity changes periodically, and the plasma drift velocity is expressed as follows: （1） In the formula, The plasma drift velocity, For particles average drift speed, For particles mass density, The total mass density of the arc plasma; 2) Under the influence of UFPC, the increase in particle diffusion velocity is mainly related to the temperature gradient. and particle diffusion driving force The diffusion velocity increment caused by UFPC is expressed as follows: （2） In the formula, The total particle number density under UFPC action. It is the product of the total number of particles and their density under the action of UFPC. For particles number density, Let i be the mass density of particle i under UFPC. Let J be the mass density of particle j under UFPC. The total particle mass density under UFPC action. For particles quality For particles quality For pressure, For particles and The ordinary diffusion coefficient between them Let be the divergence of the particle's velocity. For particles thermal diffusivity, For temperature, For the i-th and the i-th The diffusion driving force vector caused by the difference in concentration distribution between components; 3) Based on formula (2), the change in particle diffusion coefficient caused by UFPC is expressed as follows: （3） （4） In the formula, This represents the change in the ordinary diffusion coefficient of particles caused by UFPC. The change in the thermal diffusivity of particle i caused by UFPC; 4) Correct the change in particle diffusion coefficient to obtain the arc plasma diffusion coefficient, as shown in the following expression: （5） （6） In the formula, The ordinary diffusion coefficient of arc plasma under UFPC is given. Let i be the thermal diffusivity of particle i under UFPC. These are the particle number density, velocity, and correction coefficients related to the UFPC parameters, respectively, induced by UFPC.

3. The simulation and optimization method for welding performance under ultrasonic pulse current as described in claim 1, characterized in that, The specific method for calculating thermal conductivity in the transport coefficient is as follows: 1) In plasma, the expression for heat flux is as follows: （11） In the formula, The total heat flux density, Let be the random velocity vector of the i-th particle relative to the average flow velocity. Let be the velocity distribution function of the i-th particle. To integrate over all velocity spaces, For particles quality This represents the total number of particle types in the system. 2) Introduce a second-order approximation model of heat flux to describe the effect of UFPC on the thermal conductivity of arc plasma. The second-order corrected heat flux is expressed as follows: （12） In the formula, This is the second-order corrected heat flux of the electric arc plasma. Let be the internal energy of particle i. Let i be the temperature of particle i. Let be the divergence of the particle's velocity. Let i be the mass density of particle i under UFPC. The total particle mass density under UFPC action. For pressure; 3) Further quantify equation (12), as follows: （13） 4) The first-order approximate expression for the heat flux of the arc plasma under UFPC is as follows: （14） In the formula, The thermal conductivity of the arc plasma under normal conditions without the application of UFPC. Let be the diffusion direction vector of particle i. Boltzmann's constant, For particles number density, The total particle number density under UFPC action. For particles quality Let be the thermal diffusivity of particle i under the action of UFPC; 5) Solving equations (13) and (14) simultaneously, we obtain the following expression for the heat flux of the arc plasma under the action of UFPC: （15） 6) Based on the heat flux expression, the thermal conductivity expression of the arc plasma under UFPC is obtained as follows: （16） In the formula, The thermal conductivity of the arc plasma under UFPC is The collision cross-section correction factor is related to the properties of particle i. Let i be the energy exchange coefficient between particles i and j. Let be the thermal diffusivity of particle j under UFPC. Let be the mass of particle j.

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