Equivalent model design method of shafting shock resistance protection structure

Abstract

The invention discloses an equivalent model design method for a shafting shock-resistant protection structure, which comprises the following steps: simplifying a high-elasticity coupling into four parts, namely a driven end flange, a diaphragm assembly, a rubber material assembly and a driving end flange, and constructing an equivalent model of which the total mass, the gravity center position and the rigidity are consistent with those of a solid model; establishing models of a propulsion shaft system and a motor, and assembling the equivalent model of the high-elasticity coupling at the joint of the propulsion shaft and the motor; a propeller is simplified into a concentrated mass point, the supporting effect of each bearing is assumed as a point support, the effect of the bearings is simulated by adopting mutually vertical spring units, and proper boundary conditions are applied to a model to simulate the effect of a ship bottom plate; and designing an impact spectrum, solving an impact displacement response and a stress response of the shafting model, completing the design if a standard and a compensation requirement are met, otherwise, modifying the Young modulus and recalculating. According to the equivalent model designed by the invention, the calculation time is greatly shortened while the calculation precision is ensured.

Description

Technical Field

[0001] The invention relates to the technical field of ship shaft protection structures, and in particular to an equivalent model design method for a shaft anti-impact protection structure. Background Art

[0002] The normal operation of a ship's propulsion shaft system requires the cooperation of multiple shaft systems and multiple auxiliary components to complete normal power transmission. Therefore, the impact of shaft system accessories must be considered in the impact resistance calculation, among which the high-elastic coupling is an important device. As a component connecting the motor or diesel engine to the propulsion shaft system, the high-elastic coupling is mainly used to transmit torque. From the perspective of the impact resistance of the ship's propulsion shaft system, another important role of the high-elastic coupling is displacement compensation, that is, after the propulsion shaft system is subjected to an impact load, the high-elastic coupling relies on its own displacement compensation ability to perform longitudinal and radial displacement compensation, thereby protecting the equipment before the high-elastic coupling.

[0003] Since the structure of the solid high elastic coupling is relatively complex, it contains many factors that increase the difficulty of finite element calculation of the solid model, especially the existence of the diaphragm component, which increases the difficulty of meshing. In addition, a lot of time and computer storage space are required in the process of calculating the impact response. Summary of the invention

[0004] The main purpose of the present invention is to propose an equivalent model design method for a shaft system anti-impact protection structure. The designed equivalent model can greatly reduce the calculation time while ensuring the calculation accuracy, and can more quickly assist in the design of the propulsion shaft system to ensure the safe operation of the shaft system.

[0005] The technical solution adopted by the present invention is:

[0006] An equivalent model design method for a shaft system anti-impact protection structure comprises the following steps:

[0007] S1. Establishing an equivalent model of a highly elastic coupling

[0008] According to the structural characteristics of the high elastic coupling, it is simplified into four parts: the driven end flange, the diaphragm assembly, the rubber material assembly and the active end flange. Equivalent parts with the same dimensions as the outline dimensions of each part of the solid high elastic coupling are established respectively, and combined to form an equivalent model of the high elastic coupling; combined with the solid model, the density of each part of the equivalent model and the Young's modulus of the equivalent model of the high elastic coupling are calculated, and an equivalent model with total mass, center of gravity position and stiffness consistent with the solid model is constructed;

[0009] S2. Establish the axis system model

[0010] The propulsion shaft system and motor model are established, and the equivalent model of the high elastic coupling established by S1 is assembled at the connection between the propulsion shaft and the motor; the propeller is simplified as a concentrated mass point, which acts on the center of gravity of the propeller; the support function of each bearing is assumed to be point support, and mutually perpendicular spring units are used to simulate the function of the bearing. The spring units are arranged vertically and radially and in the same section of the shaft system, and the support stiffness of the spring units is given according to the bearing stiffness; and appropriate boundary conditions are applied to the model to simulate the function of the bottom plate;

[0011] S3. Shock response calculation

[0012] Design the impact spectrum, and solve the impact displacement response and stress response of the shaft system model; after the calculation is completed, extract the displacement and stress response of each shaft section, as well as the maximum impact displacement of the high elastic coupling and the displacement of the active and driven ends, and calculate whether the standards and compensation requirements are met according to the standards; if so, complete the design; if not, modify the Young's modulus and recalculate until the standards and compensation requirements are met.

[0013] In the above scheme, in step S1, the specific method for simplifying the structure of the high elastic coupling is: simplify the oblique flange and the straight flange of the high elastic coupling according to the position, that is, the side close to the motor is the active end and the other side is the driven end, into the active end flange and the driven end flange, that is, two circular solid plates, the diameter should be the same as the original flange, and the thickness is 0.95-1.05 times the thickness of the thickest part of the original flange; simplify the diaphragm into a diaphragm assembly, that is, a circular solid plate, the diameter and thickness should be the same as the original diaphragm; simplify the rubber into a rubber assembly, that is, a cylindrical entity, the diameter and thickness should be the same as the original rubber; combine the simplified active end flange, driven end flange, diaphragm assembly, and rubber assembly using binding contact to form an equivalent model of the high elastic coupling, and the four components are tightly fitted to reduce the difficulty of meshing and calculation.

[0014] In the above scheme, in step S1, the calculation method for calculating the density of each component of the equivalent model is:

[0015]

[0016]

[0017] In the formula, ρ 1-2 , ρ3, ρ4 are the density of the active end flange and the driven end flange, the density of the diaphragm assembly, and the density of the rubber assembly in the equivalent model respectively; M 1-2 M3, M4 are the total mass of the oblique flange and the straight flange, the mass of the diaphragm, and the mass of the rubber in the solid model respectively; V 1-2 , V3, and V4 are the total contour volumes of the oblique flange and the straight flange, the contour volume of the diaphragm, and the contour volume of the rubber in the solid model, respectively.

[0018] In the above scheme, in step S1, the calculation method of the Young's modulus of the equivalent model of the high elastic coupling is as follows:

[0019] (1) Using the finite element method, a static analysis is performed on the established high-elastic coupling model. External force or torque is applied to the equivalent model of the high-elastic coupling. By adjusting the Young's modulus of the material property, the high-elastic coupling is deformed accordingly to meet the radial stiffness and torsional stiffness provided by the physical high-elastic coupling model.

[0020] (2) According to the stiffness parameters of the physical high elastic coupling and combined with the analysis of the simulation values, the longitudinal stiffness and torsional stiffness are calculated respectively during the stiffness simulation of the high elastic coupling;

[0021] (3) In the calculation of torsional stiffness, a fixed constraint is applied to one end of the highly elastic coupling, and a certain torque is applied to the other end according to the given initial torsional stiffness. When the displacement and rotation angle of the solid model and the equivalent model are consistent, the Young's modulus of the equivalent model can be determined.

[0022] In the above scheme, in step S2, the propeller is simplified to a concentrated mass point, and the mass is 0.85-0.90 times of its mass in the air.

[0023] In the above scheme, in step S2, for the shaft system model, the shaft section from the stern tube seal to the propeller is treated with water to simulate the effect of buoyancy on the shaft system, and the buoyancy coefficient is 1025kg / m 3 .

[0024] In the above scheme, in step S2, a bottom plate is established at an appropriate position at the lower end of the propulsion shaft system to simulate the bottom plate of the ship; the vertical spring unit used to simulate the action of the propulsion shaft system bearing and the bottom plate simulating the bottom plate of the ship adopt a Body-Body connection method, that is, the moving end of the spring unit acts on the center of the cross section of the propulsion shaft system bearing support position, and the reference end is connected to the bottom plate, and the two end points of the spring are controlled to be on a vertical line by adjusting the coordinates of the moving end and the reference end of the spring unit; the radial spring unit adopts a Body-Ground connection method, that is, the moving end of the spring unit acts on the center of the cross section of the propulsion shaft system bearing support position, and the reference end is fixed at the coordinate position, and its reference end is controlled by the coordinate to make its position in the horizontal direction.

[0025] In the above scheme, in step S3, the method for designing the shock spectrum is: calculating the design shock acceleration value and the design shock velocity value of the shaft system model according to the standard GJB1060.1-91, drawing the shock response spectrum according to the shock acceleration and shock velocity, and calculating the shock frequency.

[0026] In the above scheme, in step S3, according to the calculation method provided in GJB1060.1-91, the response spectrum is used to calculate the anti-impact characteristics of the propulsion shafting, so as to obtain the impact displacement response and stress response of the shafting model.

[0027] The beneficial effects produced by the present invention are:

[0028] The equivalent model design method of the shafting anti-impact protection structure proposed in the present invention simplifies the complex high-elastic coupling into a simple equivalent model by simplifying the structure, mass and center of gravity, and stiffness characteristics; simplifies the shafting model by simplifying the propeller into a concentrated mass point, using mutually perpendicular spring units to simulate the effect of the bearing, and applying appropriate boundary conditions to the model to simulate the effect of the bottom plate. The equivalent model of the shafting anti-impact protection structure designed by this method can greatly reduce the calculation time while ensuring that the high-elastic coupling has the same displacement compensation capability, and can more quickly assist in the design of the propulsion shafting to ensure the safe operation of the shafting system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 It is a flow chart of an equivalent model design method of a shaft system anti-impact protection structure of the present invention;

[0031] Figure 2 This is a solid model diagram of a diaphragm rubber type high elastic coupling;

[0032] Figure 3 It is an equivalent model diagram of diaphragm rubber type high elastic coupling;

[0033] Figure 4 It is a schematic diagram of the spring unit arranged at a certain bearing cross section;

[0034] Figure 5 It is a schematic diagram of the established shaft system model;

[0035] Figure 6 is a comparison diagram of compensation capabilities between an equivalent model and a physical model in an embodiment of the present invention;

[0036] Figure 7 It is the impact deformation cloud diagram of the equivalent model and the solid model in the embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. 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.

[0038] It should be noted that the illustrations provided in the embodiments of the present invention are only used to illustrate the basic concept of the present invention in a schematic manner. Therefore, the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout type may also be more complicated.

[0039] In the present invention, it is also necessary to explain that, if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, if the terms "first" and "second" appear, they are only used for description and distinction purposes, and cannot be understood as indicating or implying relative importance.

[0040] like Figure 1 As shown, the present invention proposes an equivalent model design method for a shaft system anti-impact protection structure, comprising the following steps:

[0041] S1. Establishing an equivalent model of a highly elastic coupling

[0042] The established equivalent model must not only have the performance of a high-elastic coupling, but also make the calculation more convenient and efficient. For the diaphragm rubber type high-elastic coupling commonly used in propulsion shaft systems, according to its structural characteristics, it is simplified into four components: the driven end flange, the diaphragm assembly, the rubber material assembly, and the active end flange. Equivalent components with the same dimensions as the outline dimensions of each component of the solid high-elastic coupling are established respectively, and combined to form an equivalent model of the high-elastic coupling; combined with the solid model, the density of each component of the equivalent model and the Young's modulus of the equivalent model of the high-elastic coupling are calculated to construct an equivalent model with a total mass, center of gravity position and stiffness consistent with the solid model. Specifically, the following steps are included:

[0043] S11. Simplified structure

[0044] In the design of propulsion shafting, once the main engine power and shafting size are determined, the size of the coupling can be determined according to the shafting size. The diaphragm rubber type high elastic coupling commonly used in propulsion shafting is shown in Figure 2, mainly including steel straight flange, rubber, steel bevel flange, and diaphragm. According to the radius and thickness of the structure, the steel bevel flange and steel straight flange can be simplified into the driven end flange and the driving end flange according to their positions, that is, the side close to the motor is the active end, and the other side is the driven end, that is, two circular solid plates, the diameter should be the same as the original flange, and the thickness is 0.95-1.05 times the thickness of the thickest part of the original flange; the diaphragm is simplified to a diaphragm assembly, that is, a circular solid plate, the diameter and thickness should be the same as the original diaphragm, which greatly reduces the extremely small surface inside the diaphragm and reduces the difficulty of meshing; the rubber is simplified to a rubber assembly, that is, a cylindrical entity, the diameter and thickness should be the same as the original rubber; when the rubber is a chiral structure, it is also simplified to a cylindrical entity. The simplified active end flange, driven end flange, diaphragm assembly, and rubber assembly are combined using binding contact to form an equivalent model of a high elastic coupling, such as Figure 3 As shown, these four components should fit closely together to reduce the difficulty of meshing and calculation.

[0045] S12, Simplification of mass and center of gravity

[0046] Combined with the solid model, the density of each component of the equivalent model is calculated according to the mass and contour volume of each part of the solid model, and an equivalent model with a total mass consistent with the solid model is constructed.

[0047] The calculation method of the density of each component of the equivalent model is:

[0048]

[0049] In the formula, ρ 1-2 , ρ3, ρ4 are the density of the active end flange and the driven end flange, the density of the diaphragm assembly, and the density of the rubber assembly in the equivalent model respectively; M 1-2 M3, M4 are the total mass of the oblique flange and the straight flange, the mass of the diaphragm, and the mass of the rubber in the solid model, respectively. 1-2 , V3, and V4 are the total contour volumes of the oblique flange and the straight flange, the contour volume of the diaphragm, and the contour volume of the rubber in the solid model, respectively.

[0050] By assigning density to each component of the equivalent model, an equivalent model with a total mass and center of gravity position consistent with the solid model can be constructed.

[0051] S13, Stiffness Feature Simplification

[0052] When the equivalent model required is a highly elastic coupling with a solid rubber matrix, it is necessary to calculate the equivalent model of the highly elastic coupling based on the stiffness definition, that is, to apply external force or torque and examine its displacement change. The calculation process is the process of converting the stiffness characteristics into an equivalent model.

[0053] (1) The established high elastic coupling model is statically analyzed using the finite element method. External force or torque is applied to the coupling equivalent model, and the Young's modulus of the material property is adjusted to make the coupling produce corresponding deformation to meet the radial stiffness and torsional stiffness provided by the solid high elastic coupling model.

[0054] (2) According to the stiffness parameters of the physical high elastic coupling and combined with the analysis of simulation values, the longitudinal stiffness and torsional stiffness are calculated separately during the stiffness simulation of the high elastic coupling.

[0055] (3) In the calculation of torsional stiffness, a fixed constraint is applied to one end of the highly elastic coupling, and a certain torque is applied to the other end according to the given initial torsional stiffness. When the displacement and rotation angle of the solid model and the equivalent model are consistent, the Young's modulus of the equivalent model can be determined.

[0056] S14. Assign material properties

[0057] The equivalent model is established by assigning the calculated density and Young's modulus to the equivalent model.

[0058] S2. Establish the shaft system model, including:

[0059] S21, establishing a model of the propulsion shaft and the motor, and assembling the high elastic coupling equivalent model established in S1 at the connection between the propulsion shaft and the motor;

[0060] S22, simplifying the propeller into a concentrated mass point, which acts on the center of gravity of the propeller, and the mass is 0.85-0.90 times (0.87 times in this embodiment) of its mass in the air;

[0061] S23. The shaft section from the stern tube seal to the propeller is covered with water to simulate the effect of buoyancy on the shaft system. The buoyancy coefficient is 1025kg / m 3 ;

[0062] S24. In the finite element model, the bearing support is assumed to be point support, and mutually perpendicular spring units are used to simulate the bearing function. The spring units are arranged vertically and radially and in the same section of the shaft system, such as Figure 4 As shown, the support stiffness of the spring unit is given according to the bearing stiffness;

[0063] S25. Build a bottom plate at an appropriate position below the propulsion shaft system to simulate the bottom plate of the ship;

[0064] S26. The vertical spring unit used to simulate the action of the propulsion shaft system bearing and the bottom plate simulating the bottom plate of the ship adopt a Body-Body connection method, that is, the moving end of the spring unit acts on the center of the cross-section of the propulsion shaft system bearing support position, and the reference end is connected to the bottom plate. The two end points of the spring are controlled to be on a vertical line by adjusting the coordinates of the moving end and the reference end of the spring unit; the radial spring unit adopts a Body-Ground connection method, that is, the moving end of the spring unit acts on the center of the cross-section of the propulsion shaft system bearing support position, and the reference end is fixed at the coordinate position, and its reference end is controlled by the coordinate to keep its position in the horizontal direction.

[0065] The shaft system model established in this embodiment is as follows Figure 5 shown.

[0066] S3. Impact response calculation, including:

[0067] S31, Design shock spectrum

[0068] The shock design value is the shock input value for dynamic analysis. It uses the shock spectrum to simulate the underwater shock environment of marine equipment. The shock environment of the propulsion shaft system is mainly manifested as the shock load on the foundation, including displacement, velocity and acceleration. The propulsion shaft system installation area is the hull installation. my country's standard GJB1060.1-91 stipulates that the design shock acceleration value and design shock velocity value of marine equipment in the hull installation area of ​​surface ships are shown in Table 1.

[0069] Table 1 Design impact acceleration value A of the hull installation area a and impact velocity value V a

[0070]

[0071] The calculation formulas for A0 and V0 in the table are:

[0072]

[0073]

[0074] Where A0 is the reference acceleration; V0 is the reference speed; A a is the design acceleration; V a is the design speed; ω a is the modal circular frequency; m a is the modal mass.

[0075] V determined from Table 1 and the above formula a and A a , take V a ω a With A aThe smaller value is taken as the impact acceleration in that direction.

[0076] According to standard GJB1060.1-91 and the calculated impact acceleration and impact velocity, the impact response spectrum is plotted and the impact frequency is calculated.

[0077] S32. Solve the impact displacement response and stress response of the shafting model

[0078] According to the calculation method provided in GJB1060.1-91, the response spectrum is used to calculate the anti-shock characteristics of the propulsion shafting.

[0079] After the calculation is completed, the displacement and stress response of each shaft section, as well as the maximum impact displacement of the high elastic coupling and the displacement of the active end and the driven end are extracted, and the standard calculation is used to determine whether the standard and compensation requirements are met; if so, the design is completed; if not, the Young's modulus is modified. Specifically, when the impact displacement of the high elastic coupling is large, the Young's modulus should be increased, otherwise it should be decreased, and then the impact response calculation is performed again until the standard and compensation requirements are met.

[0080] In order to verify the effectiveness of the equivalent model of the shafting anti-impact protection structure designed by the method of the present invention, the unique compensation capability and calculation timeliness of the equivalent model and the solid model are compared as follows.

[0081] Considering that the loads on the propulsion shaft system are mostly vertical impacts, the radial stiffness of the high elastic coupling is most significantly affected. The equivalent model and the solid model were established respectively, and the finite element method was used to apply certain radial loads to them, and the radial deformation of the coupling under multiple groups of loads was extracted, such as Figure 6 As shown in the figure, it can be seen that the displacement compensation capabilities of the two models are comparable, and the two curves are mainly reflected in the difference in nonlinearity, with the maximum error being 14%, which is within the allowable error range.

[0082] In order to compare the calculation efficiency, the active end of the high elastic coupling is fixed, the same vertical impact acceleration is applied, and the time step and load step of the transient analysis are set to be the same, so that the comparison of the solution time has greater credibility. Figure 7 The figure shows the transient calculation results of the maximum displacement of the two models (the solid model on the left and the equivalent model on the right) after being excited. The calculation of the solid model takes about 1.5 hours, while the calculation of the equivalent model takes only 11 minutes, which greatly reduces the calculation time.

[0083] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, and two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0084] The order of execution of each step in the above embodiment does not mean the order of execution. The order of execution of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present application.

[0085] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. An equivalent model design method for a shafting anti-impact protection structure, characterized in that: The following steps are involved: S1. Establishing an equivalent model of a highly elastic coupling According to the structural characteristics of the high elastic coupling, it is simplified into four parts: the driven end flange, the diaphragm assembly, the rubber material assembly and the active end flange. Equivalent parts with the same dimensions as the outline dimensions of each part of the solid high elastic coupling are established respectively, and combined to form an equivalent model of the high elastic coupling; combined with the solid model, the density of each part of the equivalent model and the Young's modulus of the equivalent model of the high elastic coupling are calculated, and an equivalent model with total mass, center of gravity position and stiffness consistent with the solid model is constructed; S2. Establish the axis system model The propulsion shaft system and motor model are established, and the equivalent model of the high elastic coupling established by S1 is assembled at the connection between the propulsion shaft and the motor; the propeller is simplified as a concentrated mass point, which acts on the center of gravity of the propeller; the support function of each bearing is assumed to be point support, and mutually perpendicular spring units are used to simulate the function of the bearing. The spring units are arranged vertically and radially and in the same section of the shaft system, and the support stiffness of the spring units is given according to the bearing stiffness; and appropriate boundary conditions are applied to the model to simulate the function of the bottom plate; S3. Shock response calculation Design the shock spectrum and solve the shock displacement response and stress response of the shafting model; After the calculation is completed, the displacement and stress response of each shaft segment, as well as the maximum impact displacement of the high elastic coupling and the displacement of the active and driven ends are extracted, and the standard calculation is used to determine whether the standard and compensation requirements are met; if so, the design is completed; if not, the Young's modulus is modified and recalculated until the standard and compensation requirements are met.

2. The equivalent model design method of the shafting anti-impact protection structure according to claim 1 is characterized in that: In step S1, the specific method for simplifying the structure of the high elastic coupling is: The oblique flange and straight flange of the high elastic coupling are simplified into the active end flange and the driven end flange according to their positions, that is, the side close to the motor is the active end and the other side is the driven end, that is, two circular solid plates, the diameter of which should be the same as the original flange, and the thickness should be 0.95-1.05 times the thickness of the thickest part of the original flange; the diaphragm is simplified into a diaphragm assembly, that is, a circular solid plate, the diameter and thickness of which should be the same as the original diaphragm; the rubber is simplified into a rubber assembly, that is, a cylindrical entity, the diameter and thickness of which should be the same as the original rubber; the simplified active end flange, driven end flange, diaphragm assembly, and rubber assembly are combined using binding contact to form an equivalent model of the high elastic coupling, and the four components are tightly fitted to reduce the difficulty of meshing and calculation.

3. The equivalent model design method of the shafting anti-impact protection structure according to claim 1 is characterized in that: In step S1, the density of each component of the equivalent model is calculated as follows: In the formula, ρ 1-2 , ρ3, ρ4 are the density of the active end flange and the driven end flange, the density of the diaphragm assembly, and the density of the rubber assembly in the equivalent model respectively; M 1-2 M3, M4 are the total mass of the oblique flange and the straight flange, the mass of the diaphragm, and the mass of the rubber in the solid model respectively; V 1-2 , V3, and V4 are the total contour volumes of the oblique flange and the straight flange, the contour volume of the diaphragm, and the contour volume of the rubber in the solid model, respectively.

4. The equivalent model design method of the shafting anti-impact protection structure according to claim 1 is characterized in that: In step S1, the Young's modulus of the equivalent model of the high elastic coupling is calculated as follows: (1) Using the finite element method, a static analysis is performed on the established high-elastic coupling model. External force or torque is applied to the equivalent model of the high-elastic coupling. By adjusting the Young's modulus of the material property, the high-elastic coupling is deformed accordingly to meet the radial stiffness and torsional stiffness provided by the physical high-elastic coupling model. (2) According to the stiffness parameters of the physical high elastic coupling and combined with the analysis of the simulation values, the longitudinal stiffness and torsional stiffness are calculated respectively during the stiffness simulation of the high elastic coupling; (3) In the calculation of torsional stiffness, a fixed constraint is applied to one end of the highly elastic coupling, and a certain torque is applied to the other end according to the given initial torsional stiffness. When the displacement and rotation angle of the solid model and the equivalent model are consistent, the Young's modulus of the equivalent model can be determined.

5. The equivalent model design method of the shafting anti-impact protection structure according to claim 1 is characterized in that: In step S2, the propeller is simplified to a concentrated mass point, and the mass is 0.85-0.90 times of its mass in the air.

6. The equivalent model design method of the shafting anti-impact protection structure according to claim 1 is characterized in that: In step S2, for the shaft system model, the shaft section from the stern tube seal to the propeller is covered with water to simulate the effect of buoyancy on the shaft system, and the buoyancy coefficient is 1025 kg / m 3 .

7. The equivalent model design method of the shafting anti-impact protection structure according to claim 1 is characterized in that: In step S2, a bottom plate is established at an appropriate position at the lower end of the propulsion shaft system to simulate the bottom plate of the ship; the vertical spring unit used to simulate the action of the propulsion shaft system bearing and the bottom plate simulating the bottom plate of the ship adopt a Body-Body connection method, that is, the moving end of the spring unit acts on the center of the cross section of the propulsion shaft system bearing support position, and the reference end is connected to the bottom plate, and the two end points of the spring are controlled to be on a vertical line by adjusting the coordinates of the moving end and the reference end of the spring unit; the radial spring unit adopts a Body-Ground connection method, that is, the moving end of the spring unit acts on the center of the cross section of the propulsion shaft system bearing support position, and the reference end is fixed at the coordinate position, and its reference end is controlled by the coordinate to be in a horizontal position.

8. The equivalent model design method for the shafting anti-impact protection structure according to claim 1 is characterized in that: In step S3, the method for designing the shock spectrum is: calculating the design shock acceleration value and the design shock velocity value of the shaft system model according to the standard GJB1060.1-91, drawing the shock response spectrum according to the shock acceleration and the shock velocity, and calculating the shock frequency.

9. The equivalent model design method of the shafting anti-impact protection structure according to claim 8 is characterized in that: In step S3, according to the calculation method provided in GJB1060.1-91, the response spectrum is used to calculate the anti-impact characteristics of the propulsion shafting, thereby obtaining the impact displacement response and stress response of the shafting model.

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