Method for selecting time window of large ship stern bearing press-fitting operation in open environment

Abstract

This invention discloses a method for selecting the time window for press-fitting operations of stern bearings on large ships in open-air environments. The method includes constructing a full-size finite element model and setting press-fitting parameters; analyzing the effective interference fit variation of the stern bearing and stern tube mating surfaces under different temperature differences through steady-state temperature field simulation, thereby determining the critical temperature difference value leading to press-fitting failure and providing quantitative criteria for subsequent transient testing; performing transient thermo-structural coupling calculations in a real-world scenario to determine candidate press-fitting times; performing press-fitting simulation calculations for each candidate press-fitting time and plotting the stern bearing press-fitting curve based on the simulation results; evaluating the press-fitting quality based on the press-fitting curve and determining the ideal time window. This invention quantifies the critical temperature difference value for stern bearing press-fitting failure through steady-state simulation and, combined with transient thermal analysis, achieves scientific optimization of press-fitting timing in open-air environments, effectively avoiding the risk of interference failure caused by temperature differences and significantly improving the first-time success rate of stern bearing press-fitting.

Description

Technical Field

[0001] This invention relates to the field of shipbuilding technology, and in particular to a method for predicting and optimizing the time window for press-fitting stern bearings of large ships in an open-air environment. Background Technology

[0002] The press-fitting of stern bearings is a core and critical process in shafting installation, and the quality of its interference fit directly determines the long-term operational stability and reliability of the shafting system. Currently, the press-fitting of stern bearings on large ships is usually carried out in open slipways or dry docks. Due to the significant diurnal periodic fluctuations in air temperature in open environments, the stern bearing-stern shaft tube assembly is placed in a non-uniform, transiently changing temperature field, posing a severe challenge to traditional press-fitting processes based on the assumption of constant temperature. In recent years, scholars (Shi et al., 2025) have revealed the influence mechanism of transient temperature fields on the form and position tolerances of stern shaft tubes and the press-fitting curve in open environments by establishing a full-scale finite element model, providing a theoretical basis for understanding the relationship between temperature field and press-fitting quality. Although this study revealed the influence mechanism of transient temperature fields, its core conclusion remains at the level of "the ambient temperature affects the press-fitting quality," failing to further refine the essential physical quantity of press-fitting failure—the real-time temperature difference between the stern bearing and the stern shaft tube. Current technology has not yet clearly defined the critical temperature difference value for stern bearing press-fitting failure. Based on this research, the present invention adds a method for calculating the critical temperature, and scientifically optimizes the pressing time window solution accordingly to improve the success rate of pressing and ensure the quality of ship construction. Summary of the Invention

[0003] The main objective of this invention is to propose a method for selecting the time window for press-fitting operations of stern bearings of large ships in open-air environments. By establishing a full-size finite element model and combining it with the simulation of multiphysics coupling, the actual ambient temperature curve is introduced as a boundary condition to perform transient thermo-structural coupling numerical simulation. This allows for the prediction of the impact of ambient temperature on the thermal deformation of the structure at different times, as well as the calculation of the press-fitting curve, ultimately determining the optimal press-fitting operation period.

[0004] The technical solution adopted in this invention is: A method for selecting the time window for press-fitting operations of stern bearings on large ships in an open-air environment includes the following steps: S1. Construct a full-size finite element model and set the press-fitting parameters; S2. Through steady-state temperature field simulation, the effective interference variation law of the mating surface of the stern bearing and stern tube under different temperature difference conditions is analyzed, so as to determine the critical temperature difference value that leads to press-fit failure and provide quantitative criteria for subsequent transient testing. S3. Perform transient thermal-structural coupling calculations in real-world scenarios to determine candidate press-fitting times; S4. Perform press-fit simulation calculations for each candidate press-fitting moment, and plot the stern bearing press-fitting curve based on the simulation results; S5. Evaluate the pressing quality based on the pressing curve and determine the ideal time window.

[0005] In the above scheme, step S1 specifically includes: S1.1 Based on the design drawings of the target vessel, establish a full-size three-dimensional geometric model including the stern bearing, stern tube and fairing assembly, and determine the effective interference according to the design requirements of the target vessel; S1.2, Assign material properties and generate a mesh; S1.3, Calibrate the contact friction coefficient; S1.4 Set the pressing process time and pressing amount.

[0006] In the above scheme, the specific method of S1.3 is as follows: in the finite element model, the same displacement load conditions are set, and the friction coefficient between the stern bearing and the stern tube contact surface is set according to "CB / Z 233-87 Stern tube bearing press fitting calculation and quality requirements"; the specific method of S1.4 is as follows: in the simulation calculation, the total time of the simulation calculation is set as the total press fitting time, and the length of the stern bearing is set as the displacement to be press-fitted.

[0007] In the above scheme, step S2 specifically includes: S2.1 Design a steady-state uniform temperature field difference test table, set different temperatures for the stern bearing and stern tube, so as to form a uniform temperature difference between the two; S2.2. Based on the simulation results of the steady-state uniform temperature field difference, plot the pressing curves under different critical temperature differences. By comparing the pressing curves under different temperature differences with the maximum and minimum pressing curves, determine the critical temperature difference value of pressing.

[0008] In the above scheme, in S2.1, since the fairing and the stern tube are welded as an integrated structure, the temperature of the stern tube and the fairing is set to be the same in the design of the steady-state uniform temperature field difference experiment table.

[0009] In the above scheme, step S3 specifically includes: S3.1 Obtain the ambient temperature curve for the day of the experiment: Obtain the curve of the ambient temperature changing over time from the weather station where the shipyard is located. S3.2 Setting thermal simulation boundary conditions: In the transient thermal-structural coupling analysis module, set the initial temperature field of the structure, and use the ambient temperature curve obtained in S3.1 as the temperature load, which is applied to all outer surfaces of the model by natural convection heat transfer. S3.3 Perform transient thermal-structural coupling calculations to obtain the surface temperature of the structure at different times, and select multiple characteristic times as potential press-fitting starting points; S3.4. Based on the calculated surface temperature of the structure, analyze the temperature difference between the stern bearing and the stern tube, and select the pressing operation time that meets the critical temperature difference range as the candidate pressing time.

[0010] In the above scheme, in S3.2, the initial temperature field of the structure is taken as the structure temperature at 00:00 AM.

[0011] In the above scheme, S3.3, the potential pressing start points include at least: the reference time in the early morning, multiple times during the morning heating period, the high temperature time at noon, and multiple times during the evening cooling period.

[0012] In the above scheme, the specific method for drawing the press-fit curve in step S4 is as follows: divide the frictional force in the displacement direction obtained from the press-fit simulation calculation by the actual working area of ​​the hydraulic jack piston during the press-fit operation, convert it into pressure, and draw the pressure-displacement curve at time Ti, where Ti represents the candidate press-fit time.

[0013] In the above scheme, the characteristics of the ideal time window in step S5 include: uniform temperature field; effective interference is positive along the entire path and is evenly distributed; the pressing curve is smooth and without abrupt changes, and the whole is located within the theoretical allowable pressure zone determined according to the material strength and press capacity.

[0014] The beneficial effects of this invention are: To ensure a correct understanding of the transient deformation of the stern tube in engineering and to rationally select the window period for press-fitting operations, this invention proposes a method for selecting the time window for press-fitting operations of stern bearings in large ships under open-air environments. Addressing the problem that existing simplified models cannot accurately predict the actual press-fitting process, a full-scale stern bearing press-fitting model is established. Based on the processing of the steady-state temperature field, the critical temperature difference for stern bearing press-fitting failure is derived. Through transient thermo-structural coupling simulation calculations, the press-fitting curve distribution of the structure under natural convection heat transfer is analyzed based on the ambient temperature curve of a certain day. The optimal press-fitting time period is predicted based on the press-fitting curve. This method can significantly improve the first-time success rate of stern bearing press-fitting, reduce the risk of press-fitting failure, and provide key theoretical basis and engineering guidance for formulating scientific press-fitting windows, avoiding press-fitting risks, and improving the first-time success rate. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1This is a flowchart of the method for selecting the time window for press-fitting operations of stern bearings of large ships in an open-air environment, according to the present invention. Figure 2 This is a schematic diagram of a full-size three-dimensional geometric model established in the embodiment of the method of the present invention; Figure 3 This is a schematic diagram of the mesh generation profile of the full-size finite element model in the embodiment of the method of the present invention; Figure 4 This is a steady-state temperature difference pressing curve diagram in an embodiment of the method of the present invention; Figure 5 This is a graph showing the actual ambient temperature on the day of the experiment in the method embodiment of the present invention; Figure 6 This is a pressing curve diagram in an embodiment of the method of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] It should be noted that the illustrations provided in the embodiments of the present invention are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0019] In this invention, it should also be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first" and "second" are used only for descriptive and distinguishing purposes and should not be construed as indicating or implying relative importance.

[0020] Furthermore, it should be noted that the features of the various embodiments of the present invention can be combined or integrated in whole or in part, and as those skilled in the art will understand, they can interact and operate in different ways. Each embodiment can be implemented independently of each other or in association with one another.

[0021] like Figure 1As shown, this invention proposes a method for selecting the time window for press-fitting large ship stern bearings in an open-air environment. This method can significantly improve the first-time success rate of stern bearing press-fitting and reduce the risk of press-fitting failure. The following description uses an example of a 63,600t bulk carrier as an example. The effective interference fit is set to 0.04mm according to "CB / Z 233-87 Calculation and Quality Requirements for Press-fitting of Stern Tube Bearings". The specific steps include: S1. Construct a high-precision full-size finite element model and set the press-fit parameters. This step aims to establish a full-size digital simulation model of the stern bearing press-fit of the target ship, which is the foundation for all subsequent analyses. Specifically, it includes: S1.1 Based on the design drawings of the target vessel, establish a full-size three-dimensional geometric model including the stern bearing, stern tube, and fairing assembly, such as... Figure 2 As shown, the effective interference is determined according to the design requirements of the target ship (the effective interference in this embodiment is 0.04 mm).

[0022] S1.2 Assigning Material Properties and Meshing. Based on the material parameters, accurate mechanical and thermophysical properties are assigned to each component in the finite element software, as shown in Table 1. The simulation structural model is then meshed using a tetrahedral mesh type. Mesh sensitivity analysis is used to determine the optimal mesh size to ensure a balance between computational accuracy and efficiency. The meshing is as follows: Figure 2 As shown.

[0023] Table 1: Material Performance Parameters

[0024] S1.3, Calibrate the contact friction coefficient. In the finite element model, the same displacement load conditions are set, and the friction coefficient between the stern bearing and the stern tube contact surface is set according to "CB / Z233-87 Stern Tube Bearing Press-fit Calculation and Quality Requirements". In this embodiment, the contact friction coefficient is 0.2.

[0025] S2. Through steady-state temperature field simulation, the system analyzes the variation law of the effective interference fit between the stern bearing and the stern tube under different temperature differences, thereby determining the critical temperature difference value that leads to press-fit failure and providing quantitative criteria for subsequent transient testing. Specifically, this includes: S2.1 A steady-state uniform temperature field difference experimental table is designed, setting different temperatures for the stern bearing and stern tube to create a uniform temperature difference between them. The temperature field difference table designed in this embodiment is shown in Table 2. According to research by Shi et al. (2025), the main reason for stern bearing press-fit failure is the temperature difference between the stern bearing and the stern tube, while the temperature field of the fairing has a relatively small impact on the press-fit quality. Therefore, in designing the temperature difference experimental table, this patent sets the temperature of the stern tube and the fairing to the same value, thereby determining the range of the critical temperature difference value.

[0026] Table 2: Steady-State Critical Temperature Design Table

[0027] S2.2. Based on the simulation results of the steady-state uniform temperature field difference, press-fit curves under different critical temperature differences are plotted. By comparing the press-fit curves under different temperature differences with the maximum and minimum press-fit curves, the critical temperature difference value for press-fitting is determined. 14 sets of press-fit curves are shown below. Figure 4 As shown, based on the steady-state uniform temperature field setting, the critical temperature value of the press-fit curve is ±4℃. That is, when there is a 4-degree deviation between the stern bearing and the stern tube, the failure risk of the press-fit curve will be greatly increased.

[0028] S3. Simulate the real-world pressing process to determine candidate pressing times. This includes: S3.1 Obtain the ambient temperature curve for the day of the experiment: Obtain the curve of the ambient temperature changing over time from the weather station where the shipyard is located, such as... Figure 5 As shown.

[0029] S3.2 Setting thermal simulation boundary conditions: In the transient thermal-structure coupling analysis module, set the initial temperature field of the structure (generally take the structure temperature at 00:00 am as the initial temperature), and use the ambient temperature curve obtained in S3.1 as the temperature load, which is applied to all outer surfaces of the model in the form of natural convection heat transfer.

[0030] S3.3 Perform transient thermal-structural coupling calculations to obtain the structural surface temperature at different times, and select multiple characteristic times as potential press-fitting starting points. These should include at least: the baseline time at dawn, multiple times during the morning heating period, the high-temperature time at noon, and multiple times during the evening cooling period. The time point selection design scheme in this embodiment is shown in Table 3.

[0031] Table 3: Experimental Design for Pressing at Different Time Periods

[0032] S3.4. Based on the calculated surface temperature of the structure, analyze the temperature difference between the stern bearing and the stern tube, and select the pressing operation time that meets the critical temperature difference range as the candidate pressing time.

[0033] Based on transient thermal simulation results, several representative nodes were selected in key areas on the outer surface of the stern bearing and the inner surface of the stern tube. The time history data of temperature change of each node in the all-weather temperature field were extracted, and the average temperature values ​​of the stern bearing and the stern tube were calculated to obtain the structural temperature difference between the two at different times. , Indicates the stern bearing temperature. This represents the stern tube temperature. The structural temperature difference at each moment is compared with the critical temperature difference value determined in step S2: when the structural temperature difference at a certain moment is within the critical temperature difference range (i.e., ... When the temperature difference exceeds the critical temperature range, the pressure fitting condition is met, and the time is considered a candidate for pressure fitting. If the temperature difference exceeds the critical temperature range, the pressure fitting risk is high, and the time is determined not to meet the pressure fitting condition. In this embodiment, according to... Figure 5 Transient thermal simulation was performed on the ambient temperature curve shown. The average temperature difference between the stern bearing and the stern tube at each time point was extracted as shown in Table 4. Based on the criterion of critical temperature difference ±4℃, it was determined that the temperature difference at times C, D, and G exceeded the critical temperature difference range, and the press fitting risk was high. Meanwhile, times B, E, and F were within the critical temperature difference range and were selected as candidate press fitting times.

[0034] Table 4: Average Temperature Difference During Pressing Experiments at Different Time Periods

[0035] S4. Perform press-fitting simulation calculations for the three candidate press-fitting times B, E, and F. Solve for the frictional force in the press-fitting displacement direction at each candidate time, then divide by the actual working area of ​​the hydraulic jack piston during the press-fitting operation to convert it into pressure. Plot the pressure-displacement curve at time Ti, where Ti represents the candidate press-fitting time. Figure 6 As shown. Figure 6 The horizontal axis represents the pressing displacement (mm), and the vertical axis represents the pressure (bar). It includes pressing curves for three candidate times, as well as a baseline curve (temperature difference 0℃) for comparison. Figure 6 It is evident that the pressing curves at different candidate times show significant differences: the curve at time B is generally higher, the curve at time E is closer to the baseline curve, and the curve at time F is generally lower.

[0036] S5. Evaluate the pressing quality based on the pressing curve and determine the ideal time window. The characteristics of the ideal time window include: the effective interference is positive throughout the path, the pressing curve is smooth and without abrupt changes, and the entire curve lies within the theoretical allowable pressure zone determined based on material strength and press capacity. Based on the above criteria, time segments that simultaneously meet the characteristics of the ideal time window are marked as "recommended pressing windows," while time segments exhibiting high-risk window characteristics (such as large temperature gradients, negative effective interference, drastic fluctuations in the pressing curve, or exceeding the allowable pressure zone) are marked as "prohibited pressing windows." Intermediate states are assessed as "operational windows under permissible conditions," with corresponding risk warnings and compensation recommendations (such as "temporary sunshades need to be installed in the stern tube area").

[0037] In this embodiment, the pressing curves at each candidate time point are as follows: Figure 6As shown. At time B, the temperature difference is +4℃, which is near the upper limit of the critical temperature difference (+4℃). The overall pressing curve is too high and close to the upper limit of the allowable pressure band, posing a risk of pressing jamming due to excessive interference. This is determined to be a "pressing window with a high risk of failure". At time E, the temperature difference is +1℃, which is within the critical temperature difference range. The pressing curve is close to the ideal control curve, with a smooth overall shape and located in the middle of the allowable pressure band. The pressing condition is good and meets the characteristics of the ideal window, so it is determined to be a "recommended pressing window". At time F, the temperature difference is -3℃, which is close to the lower limit of the critical temperature difference (-4℃). This results in a lower final pressing curve, posing a risk of loosening due to insufficient interference. This is determined to be a "pressing window with a high risk of failure". In summary, through a comprehensive evaluation of the pressing curves at each time point, the optimal pressing window in this embodiment is determined to be time E.

[0038] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0039] The order of the steps in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0040] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for selecting the time window for press-fitting operations of stern bearings on large ships in an open-air environment, characterized in that, Includes the following steps: S1. Construct a full-size finite element model and set the press-fitting parameters; S2. Through steady-state temperature field simulation, the effective interference variation law of the mating surface of the stern bearing and stern tube under different temperature difference conditions is analyzed, so as to determine the critical temperature difference value that leads to press-fit failure and provide quantitative criteria for subsequent transient testing. S3. Perform transient thermal-structural coupling calculations in real-world scenarios to determine candidate press-fitting times; S4. Perform press-fit simulation calculations for each candidate press-fitting moment, and plot the stern bearing press-fitting curve based on the simulation results; S5. Evaluate the pressing quality based on the pressing curve and determine the ideal time window.

2. The method for selecting the time window for press-fitting operations of stern bearings of large ships in an open-air environment, as described in claim 1, is characterized in that... Step S1 specifically includes: S1.1 Based on the design drawings of the target vessel, establish a full-size three-dimensional geometric model including the stern bearing, stern tube and fairing assembly, and determine the effective interference according to the design requirements of the target vessel; S1.2, Assign material properties and generate a mesh; S1.3, Calibrate the contact friction coefficient; S1.4 Set the pressing process time and pressing amount.

3. The method for selecting the time window for press-fitting operations of stern bearings of large ships in an open-air environment, as described in claim 2, is characterized in that... The specific method for S1.3 is as follows: In the finite element model, the same displacement load conditions are set, and the friction coefficient between the stern bearing and the stern tube contact surface is set according to "CB / Z233-87 Stern tube bearing press fitting calculation and quality requirements"; The specific method for S1.4 is as follows: In the simulation calculation, the total time of the simulation calculation is set as the total press fitting time, and the length of the stern bearing is set as the displacement to be press-fitted.

4. The method for selecting the time window for press-fitting operations of stern bearings of large ships in an open-air environment, as described in claim 1, is characterized in that... Step S2 specifically includes: S2.1 Design a steady-state uniform temperature field difference test table, set different temperatures for the stern bearing and stern tube, so as to form a uniform temperature difference between the two; S2.

2. Based on the simulation results of the steady-state uniform temperature field difference, plot the pressing curves under different critical temperature differences. By comparing the pressing curves under different temperature differences with the maximum and minimum pressing curves, determine the critical temperature difference value of pressing.

5. The method for selecting the time window for press-fitting operations of stern bearings of large ships in an open-air environment, as described in claim 4, is characterized in that... In S2.1, since the fairing and stern tube are welded as an integrated structure, the temperature of the stern tube and the fairing is set to be the same in the experimental table for designing the steady-state uniform temperature field difference.

6. The method for selecting the time window for press-fitting operations of stern bearings of large ships in an open-air environment, as described in claim 1, is characterized in that... Step S3 specifically includes: S3.1 Obtain the ambient temperature curve for the day of the experiment: Obtain the curve of the ambient temperature changing over time from the weather station where the shipyard is located. S3.2 Setting thermal simulation boundary conditions: In the transient thermal-structural coupling analysis module, set the initial temperature field of the structure, and use the ambient temperature curve obtained in S3.1 as the temperature load, which is applied to all outer surfaces of the model by natural convection heat transfer. S3.3 Perform transient thermal-structural coupling calculations to obtain the surface temperature of the structure at different times, and select multiple characteristic times as potential press-fitting starting points; S3.

4. Based on the calculated surface temperature of the structure, analyze the temperature difference between the stern bearing and the stern tube, and select the pressing operation time that meets the critical temperature difference range as the candidate pressing time.

7. The method for selecting the time window for press-fitting operations of stern bearings of large ships in an open-air environment, as described in claim 6, is characterized in that... In S3.2, the initial temperature field of the structure is taken as the structure temperature at 00:00 AM.

8. The method for selecting the time window for press-fitting operations of stern bearings of large ships in an open-air environment, as described in claim 6, is characterized in that... In S3.3, potential press-fit starting points include at least: the baseline time in the early morning, multiple times during the morning heating period, the high temperature time at noon, and multiple times during the evening cooling period.

9. The method for selecting the time window for press-fitting operations of stern bearings of large ships in an open-air environment, as described in claim 1, is characterized in that... The specific method for plotting the press-fit curve in step S4 is as follows: divide the frictional force in the displacement direction obtained from the press-fit simulation calculation by the actual working area of ​​the hydraulic jack piston during the press-fit operation, convert it into pressure, and plot the pressure-displacement curve at time Ti, where Ti represents the candidate press-fit time.

10. The method for selecting the time window for press-fitting operations of stern bearings of large ships in an open-air environment according to claim 1, characterized in that, In step S5, the characteristics of the ideal time window include: a uniform temperature field; a positive effective interference along the entire path and a uniform distribution; a smooth pressing curve without abrupt changes, and the entire curve being within the theoretical allowable pressure zone determined based on the material strength and press capacity.

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