A simulation design method for an integrated mud pump piston based on multi-physical field coupling

Abstract

The application provides a kind of simulation design method of integral mud pump piston based on multi-physical field coupling, on the basis of completely retaining the original integral mud pump piston structure, coupling structure field, flow field and wear field for the first time, a complete simulation system including Ogden super-elastic constitutive model, sealing contact pressure model, Archard wear model and coupling control equation is established. Through finite element simulation, the minimum contact pressure, maximum wear depth, predicted service life and leakage rate and other key design indicators can be quantitatively output, and the rubber hardness, arc curvature radius and interference amount and other parameters can be iteratively optimized accordingly. This method can accurately simulate the sealing performance degradation and wear process of the piston under different working conditions in a virtual environment without repeated trial production of physical objects, significantly shortening the design cycle, improving the design quality and reliability of the piston, and having a clear mathematical model and reproducible calculation process, facilitating industry application.

Description

Technical Field

[0001] This invention relates to the field of simulation design and performance prediction technology for mud pump pistons, and in particular to an integral simulation design method for mud pump pistons based on multi-physics coupling. Background Technology

[0002] The mud pump piston is one of the core components of the mud pump's hydraulic end system and also one of the most easily damaged parts during drilling operations. The discharge pressure of the mud pump is generated by the reciprocating linear motion of the piston assembly within the cylinder. Its sealing performance and service life directly determine the overall working efficiency and maintenance costs of the mud pump. Currently, most mud pump pistons widely used in the market are of a modular structure, where a rubber sheet is installed onto a metal piston core using a nut, and then the piston core is spliced ​​onto the piston rod using clips or threads. While this modular piston design is convenient to manufacture and allows for individual replacement of parts, it has significant technical drawbacks in practical use.

[0003] First, the sealing performance of the combined piston is not perfect. Due to the multiple mechanical assembly interfaces between the rubber sheet and the piston core, and between the piston core and the piston rod, even with precision machining, micro-gaps are unavoidable. In high-pressure mud environments, materials containing solid particles can easily enter these gaps, exacerbating abrasive wear on the parts and making subsequent disassembly extremely difficult, even causing the piston core and piston rod to seize and become unusable. Second, existing mud pump pistons require frequent disassembly to replace the easily worn rubber sheet. Each disassembly and assembly causes new damage to the mating surfaces, leading to accelerated wear and tear and a significant reduction in overall service life. To improve sealing, some industry professionals have proposed an integral mud pump piston structure (such as authorized publication number CN212337607U), designing the rubber plug and rubber sheet as a single unit and fitting it onto the piston rod with a rubber sleeve, reducing the risk of material entering gaps to some extent. However, the design of this integral piston still relies on empirical formulas and repeated trial production, lacking scientific and systematic simulation design methods to predict its sealing performance and wear life under real-world operating conditions. The parameters such as fluid pressure, piston speed, and mud sand content vary greatly under different drilling conditions. It is difficult to guarantee that the piston can achieve the best sealing effect and the longest service life under various conditions based solely on experience design.

[0004] Therefore, there is an urgent need in this field to develop a method that can quantitatively predict and optimize the sealing performance and lifespan of pistons by using multiphysics coupling simulation while retaining the advantages of the integral piston structure. This would overcome the technical problems of existing designs that rely on experience-based prototyping, cannot predict performance, have long design cycles, and lack reliability. Summary of the Invention

[0005] The purpose of this invention is to provide a simulation design method for an integral mud pump piston based on multi-physics coupling, so as to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides the following solution: This invention provides a simulation design method for an integral mud pump piston based on multiphysics coupling, comprising the following steps: Step 1: Establish a parametric geometric model of the integral mud pump piston, which includes a piston rod, rubber plug, fixed sleeve, rubber sheet, fixed ring, rubber layer, push plate, rubber sleeve, push rod, connecting rod, circular groove, stop block, and fixing bolt; extract key geometric parameters, including piston rod diameter, rubber plug outer diameter, rubber plug axial length, rubber sleeve inner diameter, rubber sheet thickness, rubber sheet radius of curvature, and fixed sleeve length; Step 2: Construct a hyperelastic constitutive model of the rubber material, and use the Ogden model or Mooney-Rivlin model to describe the mechanical behavior of the rubber plug, rubber sheet, rubber sleeve and rubber layer; Step 3: Establish a sealing contact pressure model, calculate the contact pressure distribution between the piston and cylinder, and determine the sealing effectiveness based on the relationship between contact pressure and fluid pressure; Step 4: Establish a wear life prediction model based on the Archard wear model, calculate the wear depth between the rubber sheet and the cylinder, and predict the service life of the piston; Step 5: Establish a multiphysics coupled simulation model based on finite element software, set material properties, contact pairs, loads and boundary conditions, and perform coupled iterative calculations of structural field, flow field and wear field; Step 6: Output simulation results, including minimum contact pressure, maximum wear depth, predicted service life and leakage rate. If the output indicators do not meet the design requirements, adjust the geometric parameters or material parameters and repeat steps one to five for optimization design.

[0007] Preferably, the Ogden hyperelastic constitutive model in step two is expressed as: ; in, For strain energy density, and For material constants, The main elongation ratio; the Mooney-Rivlin model is expressed as: ; in, , For the Cauchy-Green invariant tensor, , This is the material coefficient.

[0008] Preferably, the sealing contact pressure model in step three uses the following formula to calculate the contact pressure at the axial position: ; in, This is the equivalent elastic modulus of rubber. For compression deformation, The thickness of the rubber sheet in a localized area. For speed correction factor, The piston's speed. For reference speed; the criterion for seal effectiveness is: ≥ + ,in For fluid pressure distribution, This is the minimum safe sealing pressure.

[0009] Preferably, the Archard wear model in step four is expressed as: ; in, For wear depth, The sliding distance, The wear coefficient is... To contact pressure, The sliding speed is: The cumulative wear depth is: ; The formula for predicting service life is: ; in, To allow the maximum wear depth, One work cycle This represents the number of working cycles.

[0010] Preferably, the multiphysics coupling simulation in step five includes the coupling of the structural field, the flow field, and the wear field, and its coupling control equation is: ; in, The pressure diffusion coefficient is... For contact pressure, the Laplace operator, The wear-pressure coupling coefficient is... The wear depth is the rate of change over time; the mesh is updated and the simulation is repeated each time the wear reaches a preset threshold.

[0011] Preferably, the boundary conditions in step five include: the inner wall of the cylinder is fixed, the piston rod moves axially, and the displacement is: ; in, For amplitude, The frequency is ; the fluid pressure load is . =5-20MPa gradual pressure.

[0012] Preferably, the contact pair arrangement in step five includes: frictional contact between the rubber sheet and the inner wall of the cylinder, with a friction coefficient μ=0.3; and binding contact between the rubber sleeve and the piston rod.

[0013] Preferably, the design specification output in step six is: minimum contact pressure. ≥ +0.5MPa, maximum wear depth ≤0.5mm, predicted service life ≥106 cycles, leakage rate ≤0.1mL / min; if any index is not met, adjust the rubber hardness, radius of curvature of the arc or the interference and resimulate.

[0014] Preferably, the parametric geometric model in step one is established using a two-dimensional axisymmetric model or a three-dimensional solid model.

[0015] Preferably, the finite element software in step five is Abaqus or ANSYS, the rubber material uses hybrid elements, and the metal parts use linear elements.

[0016] The present invention achieves the following beneficial technical effects compared to the prior art: This invention provides a simulation design method for an integral mud pump piston based on multiphysics coupling. While retaining the original integral mud pump piston structure, it for the first time couples the structural field, flow field, and wear field, establishing a complete simulation system including the Ogden hyperelastic constitutive model, sealing contact pressure model, Arcard wear model, and coupled control equations. Through finite element simulation, key design indicators such as minimum contact pressure, maximum wear depth, predicted service life, and leakage rate can be quantified and output. Based on this, parameters such as rubber hardness, radius of curvature, and interference fit can be iteratively optimized. This method eliminates the need for repeated physical prototyping, accurately simulating the piston's sealing performance degradation and wear process under different operating conditions in a virtual environment. This significantly shortens the design cycle, improves the piston's design quality and reliability, and features a clear mathematical model and reproducible calculation process, facilitating widespread application within the industry. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The flowchart of the integrated mud pump piston simulation design method based on multi-physics field coupling provided by the present invention is shown. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] The purpose of this invention is to provide a simulation design method for an integral mud pump piston based on multi-physics coupling, so as to solve the problems existing in the prior art.

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] Example 1: This invention provides a simulation design method for an integral mud pump piston based on multiphysics coupling. The method uses an integral mud pump piston (authorization number CN212337607U) as its basic structure. This piston includes a piston rod, rubber plug, fixed sleeve, rubber sheet, fixed ring, rubber layer, push plate, rubber sleeve, push rod, connecting rod, circular groove, stop block, and fixing bolts. In implementation, the first step is to establish a parametric geometric model of the integral mud pump piston. Specifically, designers can construct a two-dimensional axisymmetric model or a three-dimensional solid model of the piston in 3D modeling software (such as SolidWorks or CATIA) based on the engineering drawings of the actual piston. To facilitate subsequent finite element simulation, key geometric parameters need to be extracted and recorded, including but not limited to the piston rod diameter, rubber plug outer diameter, rubber plug axial length, rubber sleeve inner diameter, rubber sheet thickness, rubber sheet radius of curvature, and fixed sleeve length. These parameters will serve as design variables for subsequent simulation optimization. After modeling is completed, the geometric model is imported into finite element analysis software (such as Abaqus or ANSYS), and the model is cleaned and simplified as necessary, such as removing chamfers, small holes and other details that do not affect sealing performance and wear calculation.

[0023] Next, we proceed to step two: constructing a hyperelastic constitutive model for the rubber material. Since the rubber plug, rubber sheet, rubber sleeve, and rubber layer are all made of rubber, they exhibit large deformation and nonlinear elastic behavior during reciprocating compression; therefore, conventional linear elastic constitutive models cannot be used. This invention employs the Ogden hyperelastic constitutive model or a simplified Mooney-Rivlin model to describe the mechanical behavior of rubber. Specifically, the strain energy density expression of the Ogden model is: ; in, For strain energy density, and For material constants, The main elongation ratio. For commonly used rubber materials in engineering, N=2 is usually sufficient to obtain adequate accuracy. If the Mooney-Rivlin model is used, its expression is: ; in, , For the Cauchy-Green invariant tensor, , These are material constants, which can be determined through biaxial tensile or planar shear tests. In finite element software, users only need to input the corresponding material constants, and the program will automatically calculate the stress-strain relationship based on the constitutive model. For metal parts such as piston rods, fixed sleeves, and fixed rings, a linear elastic constitutive model is used, and the elastic modulus and Poisson's ratio are input.

[0024] Step three involves establishing a sealing contact pressure model. When the piston reciprocates within the cylinder, a sealing contact is formed between the rubber sheet and the inner wall of the cylinder. The magnitude of the contact pressure directly determines the sealing effect and the wear rate. This invention uses the following formula to calculate the contact pressure at the axial position: ; in, This is the equivalent elastic modulus of rubber. For compression deformation, The thickness of the rubber sheet in a localized area. For speed correction factor, The piston's speed. The reference speed is used; this formula considers the effects of rubber compression deformation and speed on contact pressure. The seal effectiveness criterion is... ≥ + ,in For fluid pressure distribution, This represents the minimum safe sealing pressure. If this inequality is not met at a certain axial position, it indicates a risk of leakage, requiring adjustment of the rubber interference fit or the rubber sheet thickness.

[0025] Step four involves establishing a wear life prediction model based on the Archard wear model. The rubber sheet gradually wears down during repeated friction with the cylinder wall, and fails when the wear depth exceeds the allowable value. This invention employs the classic Archard wear model, whose differential form is: ; in, For wear depth, The sliding distance, The wear coefficient is... To contact pressure, Let be the sliding velocity. Integrate along the entire sliding path to obtain the cumulative wear depth: ; The formula for predicting service life is: ; in, To allow the maximum wear depth, One work cycle This represents the number of working cycles. This prediction directly reflects the piston's wear resistance, allowing designers to adjust material or structural parameters in reverse order based on target life requirements.

[0026] Step five involves establishing a multiphysics coupled simulation model in the finite element software and performing coupled iterative calculations of the structural field, flow field, and wear field. First, the geometric model established in step one is imported into the finite element software, and the material properties determined in step two are assigned to each component. For rubber components, hybrid elements (such as CAX4H or C3D8H elements in Abaqus) are recommended to avoid volumetric self-locking; for metal components, linear reduced integral elements (such as C3D8R) are used. Then, contact pairs are set: the outer surface of the rubber sheet and the inner wall of the cylinder are defined as frictional contact, with a friction coefficient of μ=0.3; the inner surface of the rubber sleeve and the outer surface of the piston rod are defined as bonded contact, simulating the fixed connection state. Regarding boundary conditions, all degrees of freedom of the inner wall of the cylinder are constrained to be fixed, and axial displacement is applied to the piston rod. The amplitude Typical value is 50mm, frequency A typical value is 2Hz. Simultaneously, a fluid pressure load is applied, given along the cylinder axis according to the working pressure distribution, for example... =5-20MPa gradual pressure. To simulate the evolution of contact pressure during wear, this invention introduces a wear-pressure coupling control equation: ; in, The pressure diffusion coefficient is... For contact pressure, the Laplace operator, The wear-pressure coupling coefficient is... Let h be the rate of change of wear depth over time. After each small time increment, the wear depth hh is updated according to the Archard model. When the cumulative wear depth reaches a preset threshold (e.g., 0.01 mm), the finite element mesh is automatically re-meshed or the nodes are moved, and then the calculation continues for the next time step. This process is repeated until the entire work cycle is completed or the set total simulation time is reached.

[0027] Finally, proceed to step six: output the simulation results and evaluate the design. After the simulation is complete, extract the following key performance indicators from the post-processing module: minimum contact pressure. ≥ +0.5MPa, maximum wear depth ≤0.5mm, predicted service life ≥106 cycles, leakage rate ≤0.1mL / min. If all indicators meet the design requirements, the current piston design is a feasible solution; if any indicator fails to meet the requirements, the designer should return to step one, adjust the geometric parameters (such as the radius of curvature of the rubber sheet, interference fit) or material parameters (such as rubber hardness, wear coefficient), and repeat steps one through five until all indicators meet the requirements. Through this iterative optimization, the optimal piston design can be quickly obtained in a computer virtual environment, significantly reducing the number of physical prototypes and bench tests.

[0028] In practical engineering applications, designers can flexibly adjust simulation parameters according to specific drilling conditions (such as high pressure, high sand content, high frequency reciprocating motion, etc.), for example, increasing the fluid pressure to 25MPa or the motion frequency to 3Hz, thereby obtaining a dedicated piston design for specific conditions. Furthermore, this method can be combined with Design of Experiments (DOE) to systematically study the sensitivity of various design parameters to piston performance, providing a theoretical basis for subsequent product serialization.

[0029] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0030] It should be noted that the components mentioned in the above embodiments are all general standard parts or components known to those skilled in the art. Their structures and principles can be learned by those skilled in the art through technical manuals or conventional experimental methods.

[0031] This invention has illustrated its principles and implementation methods using specific examples. The descriptions of these embodiments are merely illustrative of the method and its core ideas; furthermore, those skilled in the art will recognize that modifications may be made to the specific implementation methods and application scope based on the principles of this invention. Therefore, the content of this specification should not be construed as limiting the invention.

Claims

1. A simulation design method for an integral mud pump piston based on multiphysics coupling, characterized in that, Includes the following steps: Step 1: Establish a parametric geometric model of the integral mud pump piston, which includes a piston rod, rubber plug, fixed sleeve, rubber sheet, fixed ring, rubber layer, push plate, rubber sleeve, push rod, connecting rod, circular groove, stop block, and fixing bolt; extract key geometric parameters, including piston rod diameter, rubber plug outer diameter, rubber plug axial length, rubber sleeve inner diameter, rubber sheet thickness, rubber sheet radius of curvature, and fixed sleeve length; Step 2: Construct a hyperelastic constitutive model of the rubber material, and use the Ogden model or Mooney-Rivlin model to describe the mechanical behavior of the rubber plug, rubber sheet, rubber sleeve and rubber layer; Step 3: Establish a sealing contact pressure model, calculate the contact pressure distribution between the piston and cylinder, and determine the sealing effectiveness based on the relationship between contact pressure and fluid pressure; Step 4: Establish a wear life prediction model based on the Archard wear model, calculate the wear depth between the rubber sheet and the cylinder, and predict the service life of the piston; Step 5: Establish a multiphysics coupled simulation model based on finite element software, set material properties, contact pairs, loads and boundary conditions, and perform coupled iterative calculations of structural field, flow field and wear field; Step 6: Output simulation results, including minimum contact pressure, maximum wear depth, predicted service life and leakage rate. If the output indicators do not meet the design requirements, adjust the geometric parameters or material parameters and repeat steps one to five for optimization design.

2. The simulation design method for an integral mud pump piston based on multiphysics coupling according to claim 1, characterized in that, The Ogden hyperelastic constitutive model in step two is expressed as follows: ； in, For strain energy density, and For material constants, The main elongation ratio; the Mooney-Rivlin model is expressed as: ； in, , For the Cauchy-Green invariant tensor, , This is the material coefficient.

3. The simulation design method for an integral mud pump piston based on multiphysics coupling according to claim 1, characterized in that, The sealing contact pressure model in step three uses the following formula to calculate the contact pressure at the axial position: ； in, This is the equivalent elastic modulus of rubber. For compression deformation, The thickness of the rubber sheet in a localized area. For speed correction factor, The piston's speed. For reference speed; the criterion for seal effectiveness is: ≥ + ,in For fluid pressure distribution, This is the minimum safe sealing pressure.

4. The simulation design method for an integral mud pump piston based on multiphysics coupling according to claim 1, characterized in that, The Archard wear model in step four is expressed as follows: ； in, For wear depth, The sliding distance, The wear coefficient is... To contact pressure, The sliding speed is: The cumulative wear depth is: ； The formula for predicting service life is: ； in, To allow the maximum wear depth, One work cycle This represents the number of working cycles.

5. The simulation design method for an integral mud pump piston based on multiphysics coupling according to claim 1, characterized in that, The multiphysics coupling simulation in step five includes the coupling of the structural field, flow field, and wear field, and its coupling control equation is as follows: ； in, The pressure diffusion coefficient is... For contact pressure, the Laplace operator, The wear-pressure coupling coefficient is... The wear depth is the rate of change over time; the mesh is updated and the simulation is repeated each time the wear reaches a preset threshold.

6. The simulation design method for an integral mud pump piston based on multiphysics coupling according to claim 1, characterized in that, The boundary conditions in step five include: the inner wall of the cylinder is fixed, the piston rod moves axially, and the displacement is: ； in, For amplitude, The frequency is ; the fluid pressure load is . =5-20MPa gradual pressure.

7. The simulation design method for an integral mud pump piston based on multiphysics coupling according to claim 1, characterized in that, The contact pair setup in step five includes: frictional contact between the rubber sheet and the inner wall of the cylinder, with a friction coefficient μ=0.3; and binding contact between the rubber sleeve and the piston rod.

8. The simulation design method for an integral mud pump piston based on multiphysics coupling according to claim 1, characterized in that, The specific design specification output in step six is: minimum contact pressure. ≥ +0.5MPa, maximum wear depth ≤0.5mm, predicted service life ≥106 cycles, leakage rate ≤0.1mL / min; if any index is not met, adjust the rubber hardness, radius of curvature of the arc or the interference and resimulate.

9. The simulation design method for an integral mud pump piston based on multiphysics coupling according to claim 1, characterized in that, The parametric geometric model in step one is established using a two-dimensional axisymmetric model or a three-dimensional solid model.

10. The simulation design method for an integral mud pump piston based on multiphysics coupling according to claim 1, characterized in that, The finite element software used in step five is Abaqus or ANSYS. Hybrid elements are used for rubber materials, and linear elements are used for metal parts.

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