Sliding bearing impact rigidity dynamic model building method

Abstract

The invention discloses a sliding bearing impact stiffness dynamical model building method, which comprises the following steps of building a lubricating medium flow field finite element model, and obtaining a relationship between the pressure and thickness change of a lubricating medium based on the lubricating medium flow field finite element model; converting the relationship between the pressure and the thickness change of the lubricating medium into the relationship between stress and strain, and fitting by adopting a nonlinear constitutive relationship; processing the bearing bush into a sample, and measuring an impact stress-strain curve of the bearing bush sample under different strain rates; fitting the impact stress-strain curve to obtain a nonlinear constitutive relation of the bearing bush material; and establishing a propulsion shafting simulation model, and endowing a nonlinear constitutive relation of a bearing bush material in material parameters of the propulsion shafting simulation model. According to the sliding bearing impact rigidity dynamic model establishment method, the confidence coefficient of the sliding bearing impact dynamic simulation model is improved, and the impact resistance simulation calculation precision of a propulsion shafting is improved.

Description

Technical Field

[0001] The invention relates to the field of ship impact resistance design tools, and in particular to a method for establishing an impact stiffness dynamic model of a sliding bearing. Background Art

[0002] The propulsion shaft system is an important component of the ship's power system and one of the most critical systems to ensure the ship's maneuverability, safety and reliability. Under impact loads, the dynamic stress generated by the shaft section and bearing is directly related to whether the power system can operate normally. The results of many ships withstanding underwater explosions show that the propulsion shaft system is one of the weakest links in its impact resistance.

[0003] The propulsion shaft system can be tens of meters long, and it is difficult to evaluate its performance through impact tests. Simulation calculations are required to conduct impact analysis. At present, when establishing a shaft system simulation model, the bearing is usually equivalent to a linear spring, and then the stiffness of the lubricating medium such as the oil film / water film is determined according to theoretical formulas or empirical judgment as the spring stiffness. This simplified method has the following shortcomings: 1) Theoretical formulas often idealize boundary conditions, and the reference range of empirical judgment is too large, resulting in large errors in the selected oil film / water film stiffness values; 2) Under high-speed impact, the stiffness of the oil film / water film may show nonlinear characteristics, and due to the strain rate effect, the stiffness will also change at different impact speeds. A single stiffness value cannot reflect the above characteristics; 3) When the propulsion shaft system is displaced under the action of impact, it is very likely to cause the oil film / water film to collapse. At this time, the shaft section is in direct contact with the bearing shell, and the bearing stiffness should be determined by the impact dynamic characteristics of the bearing shell.

[0004] Therefore, it is necessary to propose a new sliding bearing impact dynamics simulation model to improve the model confidence and thus improve the calculation accuracy of the propulsion shafting anti-impact simulation. Summary of the invention

[0005] The main purpose of the present invention is to provide a method for establishing a dynamic model of the impact stiffness of a sliding bearing, aiming to improve the confidence of the model and thereby enhance the accuracy of the simulation calculation of the impact resistance of the propulsion shaft system.

[0006] To achieve the above object, the present invention provides a method for establishing a sliding bearing impact stiffness dynamic model, comprising the following steps: Establishing a finite element model of the lubricating medium flow field, and obtaining the relationship between the lubricating medium pressure and thickness change based on the finite element model of the lubricating medium flow field; The relationship between lubricating medium pressure and thickness change is transformed into the relationship between stress and strain, and a nonlinear constitutive relationship is used for fitting; The bearings were processed into samples, and the impact stress-strain curves of the bearing samples at different strain rates were measured using a split Hopkinson pressure bar. The impact stress-strain curve is fitted to obtain the nonlinear constitutive relationship of the bearing material; A propulsion shaft system simulation model is established, and the nonlinear constitutive relationship of the bearing material is assigned to the material parameters of the propulsion shaft system simulation model.

[0007] Preferably, when establishing a finite element model of the lubricating medium flow field, the inner wall surface where the lubricating medium contacts the shaft segment is set as a moving wall surface, and the outer wall surface in contact with the bearing is set as a stationary wall surface. Different impact velocity boundary conditions are applied to the inner wall surface to obtain the relationship between the lubricating medium pressure and thickness change.

[0008] Preferably, when converting the relationship between the lubricating medium pressure and the thickness change into the relationship between stress and strain, the lubricating medium is regarded as a homogeneous material.

[0009] Preferably, the nonlinear constitutive relation is a Johnson-Cook nonlinear constitutive relation.

[0010] Preferably, when the bearing is propulsion shaft system simulation model is carried out, the body unit is used to simulate the oil film and the bearing shell, and the fitted nonlinear constitutive relationship is assigned to each of them.

[0011] Preferably, when the bearing shell is processed into a sample, the diameter of the sample is less than 100 mm and the height is less than 10 mm.

[0012] Preferably, when measuring the impact stress-strain curve of the bearing bush sample at different strain rates, at least three impact stress-strain curves at three stress rates are measured.

[0013] Preferably, when obtaining the relationship between the lubricating medium pressure and the thickness change, at least three impact velocity boundary conditions are applied to the inner wall surface to extract the curve of the relationship between the oil film pressure and the thickness change.

[0014] Preferably, when establishing the finite element model of the lubricating medium flow field, density and viscosity parameters are assigned according to the type of the lubricating medium.

[0015] The method for establishing the sliding bearing impact stiffness dynamics model proposed by the present invention improves the confidence of the sliding bearing impact dynamics simulation model, thereby improving the accuracy of the propulsion shaft system anti-impact simulation calculation. At the same time, the method is simple and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic flow chart of a method for establishing a sliding bearing impact stiffness dynamics model according to the present invention; Figure 2 The relationship between the oil film pressure and thickness change of the sliding bearing impact stiffness dynamic model establishment method of the present invention; Figure 3 The impact stress-strain relationship curve diagram of the bearing material at different strain rates in the first embodiment of the method for establishing the impact stiffness dynamic model of the sliding bearing of the present invention; Figure 4 This is a schematic cross-sectional structure diagram of the fitting constitutive relationship curve of the bearing material in an embodiment of the method for establishing the impact stiffness dynamic model of a sliding bearing of the present invention.

[0017] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0018] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0019] The invention provides a method for establishing a sliding bearing impact stiffness dynamics model.

[0020] Reference Figure 1 The present invention proposes a method for establishing a sliding bearing impact stiffness dynamic model, comprising the following steps: Step S1, establishing a finite element model of a lubricating medium flow field, and obtaining a relationship between a lubricating medium pressure and a thickness change based on the finite element model of the lubricating medium flow field; Step S2, fitting the nonlinear constitutive relationship according to the impact stress-strain curve to verify the correctness of the fitting parameters in the nonlinear constitutive relationship; Step S3, fitting the impact stress-strain curve to obtain the nonlinear constitutive relationship of the bearing material; Step S4, fitting the parameters in the nonlinear constitutive relationship according to the impact stress-strain curve to verify the correctness of the fitted nonlinear constitutive relationship; Step S5, establishing a propulsion shaft system simulation model, and assigning a nonlinear constitutive relationship of the bearing material to the material parameters of the propulsion shaft system simulation model.

[0021] In step S1, when establishing the finite element model of the lubricating medium flow field, the inner wall surface where the lubricating medium contacts the shaft segment is set as a moving wall surface, and the outer wall surface in contact with the bearing is set as a stationary wall surface. Different impact velocity boundary conditions are applied to the inner wall surface to obtain the relationship between the lubricating medium pressure and thickness change.

[0022] When the relationship between the lubricating medium pressure and thickness change is converted into the relationship between stress and strain, the lubricating medium is regarded as a homogeneous material. The nonlinear constitutive relation is the Johnson-Cook nonlinear constitutive relation.

[0023] Specifically, the Johnson-Cook nonlinear constitutive relation adopts the following expression: , in, is stress, is the strain rate, is the reference strain rate, and the parameters A, B, C, and n are obtained by fitting.

[0024] When measuring the impact stress-strain curve of the bearing specimen at different strain rates, at least three impact stress-strain curves at three stress rates shall be measured.

[0025] In step S5, when the bearing is propulsed into the shaft system simulation model, the body element is used to simulate the oil film and the bearing shell, and the fitted nonlinear constitutive relationship is assigned to each of them.

[0026] In step S3, when the bearing shell is processed into a sample, the diameter of the sample is less than 100 mm and the height is less than 10 mm.

[0027] In step S1, when obtaining the relationship between the lubricating medium pressure and the thickness change, at least three impact velocity boundary conditions are applied to the inner wall surface to extract the relationship curve between the oil film pressure and the thickness change.

[0028] In addition, when establishing the finite element model of the lubricating medium flow field, density and viscosity parameters are assigned according to the type of lubricating medium.

[0029] The following is a specific example to illustrate the method for establishing the impact stiffness dynamic model of the sliding bearing.

[0030] 1. Establish a finite element model of the oil film flow field with a thickness of 0.5 mm and a density of 859 kg / m 3 , the viscosity is 0.017Pa·s. The oil film flow field is set to laminar flow, the inner wall surface in contact with the shaft segment is set to the moving wall surface, and the outer wall surface in contact with the bearing is set to the stationary wall surface. Three impact velocity boundary conditions of 0.2m / s, 1m / s, and 3m / s are applied to the inner wall surface, and the relationship curve between the oil film pressure and thickness is extracted, as shown in Figure 2 When the oil film thickness is less than 0.002mm, it is considered to have collapsed and the pressure drops to 0.

[0031] 2. The oil film is regarded as a homogeneous material, and the pressure and thickness changes are converted into stress and strain. Formula (1) is used to fit the stress-strain relationship under different impact velocities. The fitting parameters are A=27MPa, B=22MPa, C=0.31, and n=1.

[0032] 3. The bearing material (tin-based babbitt alloy) was processed into a small cylindrical specimen with a diameter of ~10mm and a height of ~4mm, and impacted using a split Hopkinson pressure bar (SHPB) for 2200s. -1 , 3200s -1 , 4600s -1The stress-strain curves under three strain rates are as follows: Figure 3 shown.

[0033] 4. Formula (1) is used to fit the stress-strain relationship of the bearing material at different strain rates. The fitting parameters are A=27MPa, B=22MPa, C=0.31, n=1. The fitting effect of the constitutive relationship is as follows: Figure 4 shown.

[0034] 5. When modeling the impact dynamics of the bearing, the body element is used to simulate the oil film and the bearing shell, and the fitted constitutive relationship of formula (1) is assigned to each of them, thus completing the dynamic equivalence of the impact stiffness of the sliding bearing.

[0035] The method for establishing the sliding bearing impact stiffness dynamics model proposed by the present invention improves the confidence of the sliding bearing impact dynamics simulation model, thereby improving the accuracy of the propulsion shaft system anti-impact simulation calculation. At the same time, the method is simple and easy to operate.

[0036] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for establishing a dynamic model of impact stiffness of a sliding bearing, characterized in that: The following steps are involved: Establishing a finite element model of the lubricating medium flow field, and obtaining the relationship between the lubricating medium pressure and thickness change based on the finite element model of the lubricating medium flow field; The relationship between lubricating medium pressure and thickness change is transformed into the relationship between stress and strain, and a nonlinear constitutive relationship is used for fitting; The bearings were processed into samples, and the impact stress-strain curves of the bearing samples at different strain rates were measured using a split Hopkinson pressure bar. The impact stress-strain curve is fitted to obtain the nonlinear constitutive relationship of the bearing material; A propulsion shaft system simulation model is established, and the nonlinear constitutive relationship of the bearing material is assigned to the material parameters of the propulsion shaft system simulation model.

2. The method for establishing a sliding bearing impact stiffness dynamic model according to claim 1, characterized in that: When establishing the finite element model of the lubricating medium flow field, the inner wall surface where the lubricating medium contacts the shaft segment is set as the moving wall surface, and the outer wall surface in contact with the bearing is set as the stationary wall surface. Different impact velocity boundary conditions are applied to the inner wall surface to obtain the relationship between the lubricating medium pressure and thickness change.

3. The method for establishing a sliding bearing impact stiffness dynamic model according to claim 1, characterized in that: When converting the relationship between lubricating medium pressure and thickness change into the relationship between stress and strain, the lubricating medium is regarded as a homogeneous material.

4. The method for establishing a sliding bearing impact stiffness dynamic model according to claim 1, characterized in that: The nonlinear constitutive relation is the Johnson-Cook nonlinear constitutive relation.

5. The method for establishing a sliding bearing impact stiffness dynamic model according to claim 1, characterized in that: When the bearing is propulsion shaft system simulation model is carried out, the body element is used to simulate the oil film and the bearing shell, and the fitted nonlinear constitutive relationship is assigned respectively.

6. The method for establishing a sliding bearing impact stiffness dynamic model according to claim 1, characterized in that: When the bearing bush is processed into a sample, the diameter of the sample is less than 100 mm and the height is less than 10 mm.

7. The method for establishing a sliding bearing impact stiffness dynamic model according to claim 1, characterized in that: When measuring the impact stress-strain curve of the bearing specimen at different strain rates, at least three impact stress-strain curves at three stress rates shall be measured.

8. The method for establishing a sliding bearing impact stiffness dynamic model according to claim 1, characterized in that: When obtaining the relationship between the lubricating medium pressure and thickness change, at least three impact velocity boundary conditions are applied to the inner wall surface to extract the relationship curve between the oil film pressure and thickness change.

9. The method for establishing a sliding bearing impact stiffness dynamic model according to any one of claims 1 to 8, characterized in that: When establishing the finite element model of the lubricating medium flow field, density and viscosity parameters are assigned according to the type of lubricating medium.

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