Special-shaped non-closed large-plane sealing structure of nuclear power centrifugal pump and design method thereof

Abstract

The invention relates to the technical field of nuclear power centrifugal pumps, in particular to a nuclear power centrifugal pump special-shaped non-closed large plane sealing structure and a design method thereof.The design method of the nuclear power centrifugal pump special-shaped non-closed large plane sealing structure comprises the following steps that S1, a parameterized finite element model is established; s2, performing multi-physics field coupling simulation analysis; s3, identifying a deformation rule; s4, optimizing the target; s5, designing a non-closed part; s6, performing iterative optimization to determine a final scheme; the sealing surface deformation error can be actively compensated, the possibility of insufficient local sealing specific pressure is reduced, and then the possibility of sealing surface leakage is reduced.

Description

Technical Field

[0001] This invention relates to the field of nuclear power centrifugal pump technology, specifically to a non-enclosed large planar sealing structure for nuclear power centrifugal pumps and its design method. Background Technology

[0002] In the primary and secondary loop systems of nuclear power plants, a large number of large centrifugal pumps are used. Due to flow channel design, strength requirements, or installation space limitations, the pump casings and covers of these centrifugal pumps often have irregularly shaped large flat interfaces and the sealing surfaces are not closed. Since such interfaces are often pressure-bearing boundaries, their sealing reliability is particularly important.

[0003] Irregularly shaped large flat surfaces are prone to uneven deformation during processing, heat treatment, and pressure application. At the same time, under pressure conditions, the sealing surface is subjected to uneven stress, resulting in complex stress conditions such as sealing force. However, the existing sealing structure of centrifugal pumps cannot effectively compensate for these complex conditions, which can easily lead to insufficient local sealing pressure and leakage. Summary of the Invention

[0004] To address the aforementioned shortcomings in existing technologies, this invention provides a non-enclosed, large-planar sealing structure for nuclear power centrifugal pumps and its design method. This addresses the problem that existing centrifugal pump sealing structures cannot effectively compensate for uneven stress on the sealing surface, which can easily lead to insufficient local sealing pressure and leakage.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A design method for a non-enclosed, large-planar sealing structure of a nuclear power centrifugal pump includes the following steps: S1. Establish a parametric finite element model: Establish a parametric finite element model of the entire pressure-bearing boundary of the centrifugal pump, including the pump body, pump cover, fasteners and initial sealing structure. S2. Multiphysics Coupled Simulation Analysis: Thermal-structural coupling analysis, mechanical-structural coupling analysis, and sealing performance analysis are performed using the finite element model; S3. Identify Deformation Patterns: Based on simulation analysis results, identify the maximum deformation gap area and uneven contact pressure area of ​​the irregular sealing surface under thermo-mechanical coupling conditions. S4. Optimization Objective: Optimize the arrangement of the sealing groove to compensate for the deformation of the area with the largest deformation gap and the area with uneven contact pressure to the greatest extent, and ensure that a uniform and sufficient contact pressure is formed on the entire sealing contact surface. S5. Design of non-enclosed areas: The non-enclosed areas on the sealing contact surface are supplemented with a localized dendritic redundant sealing structure to enhance the sealing effect. S6. Iterative optimization to determine the final scheme: Using the position and structural parameters of the sealing groove as design input variables, and taking the minimum contact pressure under all working conditions as greater than the required specific pressure and the uniformity of contact pressure as optimization objectives, multiple rounds of simulation iterations are carried out to determine the optimal sealing groove layout scheme.

[0006] In this way, by iteratively determining the optimal sealing groove arrangement scheme, sealing grooves are opened on the sealing contact surface according to the scheme to reduce contact pressure, thereby compensating for deformation errors, reducing the possibility of insufficient local sealing specific pressure, and thus reducing the possibility of leakage on the sealing surface.

[0007] Furthermore, the specific steps of the thermal-structural coupling analysis in S2 are as follows: The temperature field distribution is calculated based on the thermoelastic theory and Fourier's law of heat conduction, with the governing equation being the transient heat conduction equation:

[0008] Where ρ is density, c_p is specific heat capacity, k is thermal conductivity, T is temperature, and Q is internal heat source; At the same time, thermal strain needs to be considered: the strain of the material caused by temperature changes;

[0009] Where α is the coefficient of thermal expansion of the material; The temperature field distribution T(x,y,z) of the entire structure under different operating conditions is obtained through thermal analysis. This temperature field is then applied as a load to the structural analysis. The resulting thermal strain is superimposed on the mechanical strain, causing thermal deformation of the structure and altering the contact state of the sealing surfaces. The governing equations in the structural analysis are extended as follows: .

[0010] In this way, by applying a pure heat load, the rapid temperature change caused by the transient change of the system can be simulated, and the deformation on the sealing surface can be seen directly. This allows for the identification of thermal deformation gaps on the sealing surface, which facilitates subsequent compensation for the deformation of the area with the largest deformation gap.

[0011] Furthermore, the mechanical-structural coupling analysis in S2 specifically involves: based on dynamics and plasticity, converting the initial compressive stress generated at the joint surface by the bolt preload into a nonlinear statics problem, which is then solved using dynamic equations. [M]{ü} + [C] + [K]{u} = {F(t)} Where [M] is the mass matrix, [C] is the damping matrix, [K] is the stiffness matrix, and {ü} is the acceleration vector. Let {u} be the velocity vector, {f(t)} be the displacement vector, and {F(t)} be the time-varying load vector.

[0012] In this way, by using nonlinear static analysis, the initial contact pressure field of the sealing surface after bolt pre-tightening is established. Then, this structural model with initial stress and initial contact state is used as the initial condition for dynamic analysis. This allows us to calculate the real-time change curve and distribution diagram of the sealing contact pressure under dynamic load, which is convenient for subsequent identification of whether there are periodic or instantaneous weak points in the sealing pressure distribution under dynamic load.

[0013] Furthermore, the sealing performance analysis in S2 specifically involves obtaining the deformation results of the flange mating surface based on thermal-structural coupling analysis and mechanical-structural coupling analysis. Hertzian contact theory is used to provide theoretical solutions for point contact or line contact, and the contact pressure distribution on the sealing contact surface is calculated. This allows for the identification of the region with the largest deformation gap, facilitating subsequent optimization of the sealing groove path.

[0014] Furthermore, in the mechanical-structural coupling analysis in S2, explicit or implicit time integration algorithms are used to analyze transient dynamics, and response spectrum analysis or time history analysis is used to analyze seismic loads and nozzle loads. This allows for the identification of the deformation of the sealing surface under transient dynamics or continuous loads, facilitating subsequent optimization of the sealing groove layout and reducing the possibility of the sealing pressure being lower than the medium pressure.

[0015] Furthermore, in the finite element analysis of the contact pressure distribution in S4, the penalty function method is used to enforce the contact constraints, thereby obtaining an accurate solution for the pressure distribution on the sealing surface based on Hertzian contact theory.

[0016] Furthermore, in S6, the optimization function for the minimum contact pressure being greater than the required specific pressure and the uniformity of the contact pressure under all working conditions is obtained by substituting all boundary conditions and the structural parameters of the sealing groove itself, and the formula is as follows;

[0017] At the same time, the following constraints must be met:

[0018] ,

[0019] in is a vector function of the spatial path of the centerline of the sealing groove, where s is the path length and p is the cross-sectional shape parameter vector of the sealing groove; It represents a specific working condition, which includes all loads and boundary conditions, and Ω is the set of all working conditions that need to be considered; In working conditions Lower edge sealing groove path Contact pressure at any point above, Specific pressure is required for sealing; For the penalty function, Let σ be the equivalent stress at a point inside the pump body structure, and [σ] be the allowable stress of the material.

[0020] In this way, by simulating the full working conditions through optimization functions, the layout of the sealing groove can be optimized, thereby obtaining the optimal solution for the sealing groove layout after iteration.

[0021] Furthermore, the local contact pressure in S6 is insufficient, i.e. When the penalty function exerts a positive penalty on the optimization function, the local contact pressure is sufficient, i.e. When the penalty function penalizes the optimization function, the penalty is 0, which enables accurate calculation of the contact pressure of the sealing path, improves the uniformity of the contact pressure, and reduces the possibility of insufficient contact pressure in the sealing groove.

[0022] The nuclear power centrifugal pump features a non-enclosed, large-plane sealing structure, including a pump body and a pump cover. The pump body and pump cover are fixedly connected by fasteners. A sealing groove is provided at the connection between the pump body and the pump cover, which can compensate for deformation errors, reduce the possibility of insufficient local sealing pressure, and thus reduce the possibility of leakage at the sealing surface.

[0023] Furthermore, a strip-shaped sealing gasket is provided inside the sealing groove, which facilitates the transportation of the sealing gasket and the filling of the sealing groove. Attached Figure Description

[0024] Figure 1 This is a three-dimensional structural schematic diagram of an embodiment of the irregularly shaped, non-enclosed, large planar sealing structure of the nuclear power centrifugal pump of the present invention. Figure 2 This is a cross-sectional schematic diagram of an embodiment of the irregularly shaped, non-enclosed, large-planar sealing structure of the nuclear power centrifugal pump of the present invention. Figure 3 This is a cross-sectional view of the sealing surface in an embodiment of the irregularly shaped, non-enclosed, large planar sealing structure of the nuclear power centrifugal pump of the present invention. Figure 4 This is a schematic diagram of the sealing groove arrangement (initial state) of an embodiment of the design method for the irregular non-enclosed large planar sealing structure of the nuclear power centrifugal pump of the present invention. Figure 5 This is a schematic diagram of the sealing groove arrangement (after one iteration) of the design method for the irregular non-enclosed large planar sealing structure of the nuclear power centrifugal pump of the present invention. Figure 6 This is a schematic diagram of the sealing groove arrangement (after two iterations) of the design method for the irregular non-enclosed large planar sealing structure of the nuclear power centrifugal pump of the present invention. Reference numerals in the accompanying drawings: 1. Pump body; 2. Pump cover; 3. Fasteners; 4. Sealing groove. Detailed Implementation

[0025] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0026] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual images. They should not be construed as limiting the scope of this patent. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0027] Example 1: like Figures 1-4 As shown, the design method for the irregularly shaped, non-enclosed, large-planar sealing structure of the nuclear power centrifugal pump of the present invention includes the following steps: S1. Establish a parametric finite element model: Establish a parametric finite element model of the entire pressure-bearing boundary of the centrifugal pump, including the pump body, pump cover, fasteners and initial sealing structure. S2. Multiphysics Coupled Simulation Analysis: Thermal-structural coupling analysis, mechanical-structural coupling analysis, and sealing performance analysis are performed using the finite element model; S3. Identify Deformation Patterns: Based on simulation analysis results, identify the maximum deformation gap area and uneven contact pressure area of ​​the irregular sealing surface under thermo-mechanical coupling conditions. S4. Optimization Objective: Optimize the arrangement of the sealing groove to compensate for the deformation of the area with the largest deformation gap and the area with uneven contact pressure to the greatest extent, and ensure that a uniform and sufficient contact pressure is formed on the entire sealing contact surface. S5. Design of non-enclosed areas: The non-enclosed areas on the sealing contact surface are supplemented with a localized dendritic redundant sealing structure to enhance the sealing effect. S6. Iterative optimization to determine the final scheme: Using the position and structural parameters of the sealing groove as design input variables, and taking the minimum contact pressure under all working conditions as greater than the required specific pressure and the uniformity of contact pressure as optimization objectives, multiple rounds of simulation iterations are carried out to determine the optimal sealing groove layout scheme.

[0028] The specific steps of the thermal-structural coupling analysis in S2 are as follows: The temperature field distribution is calculated based on the thermoelastic theory and Fourier's law of heat conduction; the governing equation is the transient heat conduction equation.

[0029] Where ρ is density, c_p is specific heat capacity, k is thermal conductivity, T is temperature, and Q is internal heat source; At the same time, thermal strain needs to be considered: the strain of the material caused by temperature changes;

[0030] Where α is the coefficient of thermal expansion of the material; The temperature field distribution T(x,y,z) of the entire structure under different operating conditions is obtained through thermal analysis. This temperature field is then applied as a load to the structural analysis. The resulting thermal strain is superimposed on the mechanical strain, causing thermal deformation of the structure and altering the contact state of the sealing surfaces. The governing equations in the structural analysis are extended as follows: .

[0031] The mechanical-structural coupling analysis in S2 specifically involves: based on dynamics and plasticity, converting the initial compressive stress generated at the joint surface by the bolt preload into a nonlinear statics problem, which is then solved using dynamic equations. [M]{ü} + [C] + [K]{u} = {F(t)} Where [M] is the mass matrix, [C] is the damping matrix, [K] is the stiffness matrix, and {ü} is the acceleration vector. Let {u} be the velocity vector, {f(t)} be the displacement vector, and {F(t)} be the time-varying load vector.

[0032] The sealing performance analysis in S2 specifically involves: obtaining the deformation results of the flange mating surface based on thermal-structural coupling analysis and mechanical-structural coupling analysis; using Hertzian contact theory to provide theoretical solutions for point contact or line contact; and calculating the contact pressure distribution on the sealing contact surface.

[0033] In the mechanical-structural coupling analysis in S2, explicit or implicit time integration algorithms are used to analyze transient dynamics, and response spectrum analysis or time history analysis is used to analyze seismic loads and nozzle loads.

[0034] The penalty function method is used to enforce contact constraints in the finite element analysis of the contact pressure distribution in S4.

[0035] The optimization function in S6, which optimizes the minimum contact pressure under all working conditions to be greater than the required specific pressure and the uniformity of the contact pressure, is obtained by substituting all boundary conditions and the structural parameters of the sealing groove itself. The formula is as follows:

[0036] At the same time, the following constraints must be met:

[0037] ,

[0038] in is a vector function of the spatial path of the centerline of the sealing groove, where s is the path length and p is the cross-sectional shape parameter vector of the sealing groove; It represents a specific working condition, such as cold preload + normal operating pressure + thermal expansion, which includes all loads and boundary conditions. Ω is the set of all working conditions that need to be considered, such as start-up, shutdown, thermal shock, earthquake, etc. In working conditions Lower edge sealing groove path The contact pressure at any point is a complex function of the path, groove parameters, and operating conditions. The required specific pressure for sealing is a function of material properties and medium pressure, and is the minimum contact pressure threshold to ensure the seal is effective. As a penalty function, when the local contact pressure is insufficient, i.e. When the penalty function exerts a positive penalty on the optimization function, the local contact pressure is sufficient, i.e. When the penalty function penalizes the optimization function, the penalty is 0 or very small. This integral represents the cumulative penalty applied to all areas with insufficient sealing pressure along the entire sealing path. The smaller the integral value, the more uniform and higher the sealing pressure is along the entire path than the required specific pressure. Maximizing the operation involves considering the worst-case scenario among all operating conditions, and the goal of the optimization function is to ensure that the sealing performance is reliable even under the most dangerous operating conditions. Let σ be the equivalent stress at a point inside the pump body structure, and [σ] be the allowable stress of the material.

[0039] The nuclear power centrifugal pump has an irregular, non-enclosed, large-plane sealing structure, including a pump body 1 and a pump cover 2. The pump body 1 and the pump cover 2 are fixedly connected by fasteners 3, and a sealing groove 4 is opened at the connection between the pump body 1 and the pump cover 2.

[0040] After the sealing groove 4 is set according to the optimized function layout, the stress on the sealing surface is shown in the table below:

[0041] Table 1: Stress Data for Sealing Surfaces Meanwhile, the ultimate fluid pressure measured under high pressure for the seal is 19.5 MPa.

[0042] Example 2: like Figures 1-4 As shown, the other features of this embodiment are the same as those of Embodiment 1, except that: The Lagrange multiplier method is used to enforce contact constraints in the finite element analysis of the contact pressure distribution in S4. Specifically, compared to the approximate solution obtained by the penalty function, the Lagrange multiplier method can obtain a more accurate solution, providing more reliable data for the subsequent dendritic redundant sealing structure of the non-closed area and improving the sealing performance of the sealing structure.

[0043] Example 3: like Figure 5 As shown, the other features of this embodiment are the same as those of Embodiment 2, except that: Based on Example 2, the layout of the sealing groove is optimized and iterated to obtain the sealing groove layout path of this example; Specifically, the stress on the sealing surface after the sealing groove 4 is re-optimized according to the optimization function is shown in the table below:

[0044] Table 2: Stress Data for Sealing Surfaces Meanwhile, the ultimate fluid pressure measured under high pressure for the seal is 14.5 MPa.

[0045] Example 4: like Figure 6 As shown, the other features of this embodiment are the same as those of Embodiment 3, except that: Based on Example 3, the layout of the sealing groove is optimized and iterated to obtain the sealing groove layout path of this example; Specifically, the stress on the sealing surface after the sealing groove 4 is re-optimized according to the optimization function is shown in the table below:

[0046] Table 3: Stress Data for Sealing Surfaces Meanwhile, the ultimate fluid pressure measured under high pressure for the seal is 9.5 MPa.

[0047] Example 5: like Figures 1-6 As shown, the other features of this embodiment are the same as those of embodiment 4, except that: The sealing groove 4 is also provided with a strip-shaped sealing gasket. Specifically, the layout of the sealing groove is iteratively optimized according to the optimization function, so that the strip-shaped sealing gasket can be directly filled in the sealing groove 4 without the need to make a special sealing gasket. Special sealing gaskets cannot be folded and have low material utilization during production, are inconvenient to transport, and have high production costs.

[0048] In summary, the present invention has the following advantages: 1. This invention can compensate for the deformation error of the sealing surface, reduce the possibility of insufficient local sealing pressure, and thus reduce the possibility of leakage of the sealing surface; 2. This invention improves the sealing performance of the sealing structure and greatly reduces the burden on the sealing structure; 3. This invention reduces the manufacturing cost of the sealing gasket and facilitates its transportation.

[0049] The above are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, and are capable of using conventional experimental methods prior to that date. They can improve and implement the present invention based on the guidance provided in this application and their own capabilities. Typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention. These modifications and improvements should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the invention or the practicality of the patent.

Claims

1. A design method for a non-enclosed, large-planar sealing structure of a nuclear power centrifugal pump, characterized in that, Includes the following steps: S1. Establish a parametric finite element model: Establish a parametric finite element model of the entire pressure-bearing boundary of the centrifugal pump, including the pump body, pump cover, fasteners and initial sealing structure. S2. Multiphysics Coupled Simulation Analysis: Thermal-structural coupling analysis, mechanical-structural coupling analysis, and sealing performance analysis are performed using the finite element model; S3. Identify Deformation Patterns: Based on simulation analysis results, identify the maximum deformation gap area and uneven contact pressure area of ​​the irregular sealing surface under thermo-mechanical coupling conditions. S4. Optimization Objective: Optimize the arrangement of the sealing groove to compensate for the deformation of the area with the largest deformation gap and the area with uneven contact pressure to the greatest extent, and ensure that a uniform and sufficient contact pressure is formed on the entire sealing contact surface. S5. Design of non-enclosed areas: The non-enclosed areas on the sealing contact surface are supplemented with a localized dendritic redundant sealing structure to enhance the sealing effect. S6. Iterative optimization to determine the final scheme: Using the position and structural parameters of the sealing groove as design input variables, and taking the minimum contact pressure under all working conditions as greater than the required specific pressure and the uniformity of contact pressure as optimization objectives, multiple rounds of simulation iterations are carried out to determine the optimal sealing groove layout scheme.

2. The design method for the irregularly shaped, non-enclosed, large-planar sealing structure of the nuclear power centrifugal pump as described in claim 1, characterized in that: The specific steps of the thermal-structural coupling analysis in S2 are as follows: The temperature field distribution is calculated based on the thermoelastic theory and Fourier's law of heat conduction. The governing equation is the transient heat conduction equation: Where ρ is density, c_p is specific heat capacity, k is thermal conductivity, T is temperature, and Q is internal heat source; At the same time, thermal strain needs to be considered: the strain of the material caused by temperature changes; Where α is the coefficient of thermal expansion of the material; The temperature field distribution T(x,y,z) of the entire structure under different operating conditions is obtained through thermal analysis. This temperature field is then applied as a load to the structural analysis. The resulting thermal strain is superimposed on the mechanical strain, causing thermal deformation of the structure and altering the contact state of the sealing surfaces. The governing equations in the structural analysis are extended as follows: 。 3. The design method for the irregularly shaped, non-enclosed, large-planar sealing structure of the nuclear power centrifugal pump as described in claim 1, characterized in that: The mechanical-structural coupling analysis in S2 specifically includes: Based on dynamics and plasticity, the initial compressive stress generated at the joint surface by the bolt preload is transformed into a nonlinear statics problem, which is then solved using dynamic equations: [M]{ü} + [C] + [K]{u} = {F(t)} Where [M] is the mass matrix, [C] is the damping matrix, [K] is the stiffness matrix, and {ü} is the acceleration vector. Let {u} be the velocity vector, {f(t)} be the displacement vector, and {F(t)} be the time-varying load vector.

4. The design method for the irregularly shaped, non-enclosed, large-planar sealing structure of a nuclear power centrifugal pump as described in claim 2 or 3, characterized in that: The sealing performance analysis in S2 is specifically as follows: The deformation results of the flange mating surface are obtained based on thermal-structural coupling analysis and mechanical-structural coupling analysis. Hertzian contact theory is used to provide theoretical solutions for point contact or line contact, and the contact pressure distribution on the sealing contact surface is calculated.

5. The design method for the irregularly shaped, non-enclosed, large-planar sealing structure of a nuclear power centrifugal pump as described in claim 3, characterized in that: In the mechanical-structural coupling analysis in S2, explicit or implicit time integration algorithms are used to analyze transient dynamics, and response spectrum analysis or time history analysis is used to analyze seismic loads and nozzle loads.

6. The design method for the irregularly shaped, non-enclosed, large-planar sealing structure of a nuclear power centrifugal pump as described in claim 4, characterized in that: The penalty function method is used to enforce contact constraints in the finite element analysis of the contact pressure distribution in S4.

7. The irregularly shaped, non-enclosed, large-planar sealing structure of the nuclear power centrifugal pump and its design method as described in claim 1, characterized in that: The optimization function in S6, which optimizes the minimum contact pressure under all working conditions to be greater than the required specific pressure and the uniformity of the contact pressure, is obtained by substituting all boundary conditions and the structural parameters of the sealing groove itself. The formula is as follows: At the same time, the following constraints must be met: ， in is a vector function of the spatial path of the centerline of the sealing groove, where s is the path length and p is the cross-sectional shape parameter vector of the sealing groove; It represents a specific working condition, which includes all loads and boundary conditions, and Ω is the set of all working conditions that need to be considered; In working conditions Lower edge sealing groove path Contact pressure at any point above, Specific pressure is required for sealing; For the penalty function, Let σ be the equivalent stress at a point inside the pump body structure, and [σ] be the allowable stress of the material.

8. The irregularly shaped, non-enclosed, large-planar sealing structure of the nuclear power centrifugal pump and its design method as described in claim 7, characterized in that: The local contact pressure in S6 is insufficient, that is... When the penalty function exerts a positive penalty on the optimization function, the local contact pressure is sufficient, i.e. When the penalty function penalizes the optimization function, the penalty is 0.

9. A non-enclosed, large-planar sealing structure for a nuclear power centrifugal pump based on the design method of any one of claims 1 to 8, characterized in that, It includes a pump body (1) and a pump cover (2), which are fixedly connected by fasteners (3), and a sealing groove (4) is opened at the connection between the pump body (1) and the pump cover (2).

10. The irregularly shaped, non-enclosed, large-planar sealing structure of the nuclear power centrifugal pump as described in claim 9, characterized in that: A strip-shaped sealing gasket is provided inside the sealing groove (4).

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