A method for fatigue analysis of a variable-pitch propeller hub mechanism under multiple load phases

Abstract

The present application relates to a kind of fatigue analysis methods of pitch propeller hub mechanism under multiple load phase difference, based on the full-size geometric model of pitch propeller hub mechanism, according to the basic model simplification method of actual engineering situation, consider the multiple load of thrust, thrust torque, shear force, shear force torque and rotating blade torque and the 72 ° phase difference existing on five pieces of propeller, through finite element analysis and fatigue simulation analysis software, using linear damage accumulation theory and nominal stress method, compile sinusoidal fatigue load spectrum, realize the fatigue analysis of typical components of pitch propeller hub mechanism.The present application uses the full-size model of pitch propeller hub mechanism to establish high-precision finite element model, can better reflect the relationship between each part in hub mechanism model;Thrust, thrust torque, shear force, shear force torque and rotating blade torque with 72 ° phase difference are sequentially applied on five pieces of propeller, more truly reflect the complex working environment of structure.

Description

TECHNICAL FIELD

[0001] The application relates to a method for analyzing fatigue of a propeller hub mechanism of a controllable pitch propeller, in particular to a method for analyzing fatigue of a propeller hub mechanism of a controllable pitch propeller under a plurality of load phase differences. BACKGROUND

[0002] A controllable pitch propeller (CPP) is composed of a blade, a hub, an oil distributor, an in-shaft oil pipe, a hydraulic system and an electric control system. The blade is connected to the hub by high-strength bolts and can rotate around an axis perpendicular to the propeller shaft. The blade is driven to rotate by a pitch control mechanism in the hub to change the pitch of the propeller, so as to change the magnitude and direction of the thrust on the blade to meet the requirements of ship forward movement, backward movement, braking and speed change.

[0003] Since the first controllable pitch propeller (CPP) was invented in Canada more than 80 years ago, it has attracted people's attention with its unique excellent performance. Compared with a common fixed pitch propeller, the CPP can adjust the pitch at any time according to the working condition of the ship, so as to reduce fuel consumption and prolong the service life of the main engine. Therefore, it is very important to analyze the characteristics of the controllable pitch propeller.

[0004] The external load of the CPP device mainly comes from the thrust and shear force of water on the blade during the ship sailing, the water power turning moment generated in the pitch adjustment process of the blade, and the centrifugal force of the blade caused by the rotation of the shaft system. These external loads all act on the hub mechanism. Due to the repeated action of the alternating external load, fatigue cracks will be generated in the local position of the hub mechanism before the alternating stress borne by the hub mechanism reaches the allowable stress of the strength design, and then the fatigue cracks will expand and finally suddenly break. This phenomenon is called fatigue failure of the hub mechanism. From a macroscopic point of view, when the cyclic stress level is low, the elastic strain plays a leading role, and at this time, the fatigue life is long, which is called stress fatigue or high-cycle fatigue; when the cyclic stress level is high, the plastic strain plays a leading role, and at this time, the fatigue life is short, which is called strain fatigue or low-cycle fatigue. Since the fatigue failure is cumulative, the fatigue failure has great danger, and therefore, great attention must be paid in the design. The fatigue analysis of the hub mechanism of the CPP device aims to understand the position where the fatigue failure will occur before the strength failure, so as to carry out local safety design and improve the safety performance of the whole component.

[0005] In the process of static strength analysis and fatigue analysis of the traditional controllable pitch propeller hub mechanism, it is usually restricted by the rotational symmetry boundary conditions of the one-fifth model, and cannot accurately reflect the structural stiffness and elastic deformation. In terms of load application, the traditional analysis method only uses the load amplitude point and the center point to compile a five-point fatigue load spectrum, and the fatigue life simulation results are often too conservative. In order to avoid the above problems, the present invention uses a full-scale model of the controllable pitch propeller hub mechanism to establish a high-precision finite element model, which can better reflect the relationship between the various components in the model. At the same time, the present invention applies thrust, thrust torque, shear force, shear torque and blade rotation torque with a 72° phase difference on the five blades in sequence, which more realistically reflects the complex working environment of the structure. In order to solve the above problems, the present invention uses the linear damage accumulation theory and the nominal stress method to compile a full-scale fatigue load spectrum of the controllable pitch propeller hub mechanism according to the load curve, and analyzes the fatigue life of each typical component through fatigue analysis software. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a fatigue analysis method for the hub mechanism of a controllable pitch propeller under multiple load phase differences. Compared with the fatigue analysis method of the one-fifth rotationally symmetric model under the traditional amplitude load, this method can more realistically calculate the fatigue life of the hub mechanism of the controllable pitch propeller.

[0007] To achieve the above-mentioned purpose, the technical solution adopted in the present invention is: a fatigue analysis method for a controllable pitch propeller hub mechanism under multiple load phase differences, which is based on the full-size geometric model of the controllable pitch propeller hub mechanism, determines the basic model simplification method according to the actual engineering situation, considers multiple loads such as thrust, thrust moment, shear force, shear moment and blade rotation moment, and the 72° phase difference on the five blades, and uses finite element analysis and fatigue simulation analysis software, adopts linear damage accumulation theory and nominal stress method, compiles sinusoidal fatigue load spectrum, and realizes fatigue analysis of typical components of the controllable pitch propeller hub mechanism.

[0008] Furthermore, the implementation steps of this method are as follows:

[0009] Step 1: Build a high-precision finite element model of the full-scale geometric shape of the controllable pitch propeller hub mechanism based on the boundary conditions of the working environment;

[0010] Step 2: Apply a hydrodynamic load with a phase difference of 72° to the five blades of the controllable pitch propeller. By selecting the load points, load the thrust, thrust moment, shear force, shear moment and blade rotation moment in sequence.

[0011] Step 3: Using finite element analysis software, perform static strength simulation analysis of the controllable pitch propeller hub mechanism at 180 load points within two cycles based on the load curve and rotation speed within one rotation cycle;

[0012] Step 4: Use the linear damage accumulation theory and nominal stress method to compile the full-scale fatigue load spectrum of the controllable pitch propeller hub mechanism. Use fatigue analysis software to calculate the fatigue life of the main parts for analysis.

[0013] Furthermore, in step 1, the basic simplification method of the full model of the controllable pitch propeller hub mechanism is determined according to the actual engineering situation, and the tiny holes or bosses that are not on the main force transmission path in the static strength and fatigue simulation analysis are simplified into features suitable for finite element analysis. According to the assembly relationship between the controllable pitch propeller hub mechanism and the overall ship, the boundary conditions are determined.

[0014] Furthermore, in step two, load application points are selected on the symmetry lines of the five blades and the axis of the hub mechanism. According to the relationship between force and torque, the load data is converted into load data that is convenient for application in the finite element analysis software, and thrust, thrust torque, shear force, shear torque and blade rotation torque with a phase difference of 72° are applied to the five blades in turn.

[0015] Furthermore, in step three, due to the residual stress that cannot be eliminated by the finite element software and the fact that the hub mechanism is not in a stable rotation state in the first cycle, the load data in two cycles are calculated, and the simulation data of the second cycle is used to perform static strength analysis and fatigue life analysis.

[0016] Furthermore, in step 4, a sinusoidal fatigue load spectrum is compiled based on the simulation data of the second cycle in step 3, and fatigue life analysis of typical components is performed using fatigue analysis software.

[0017] The beneficial effects of the present invention are:

[0018] The advantages of the present invention over the prior art are: the present invention uses a full-scale model of the controllable pitch propeller hub mechanism to establish a high-precision finite element model, which can better reflect the relationship between the various parts in the hub mechanism model; the present invention applies thrust, thrust torque, shear force, shear torque and blade rotation torque with a 72° phase difference on the five blades in sequence, which more realistically reflects the working environment with a complex structure; the present invention more accurately analyzes the fatigue life of each typical component by compiling a full-scale sinusoidal fatigue load spectrum of the controllable pitch propeller hub mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 1. It is a schematic flow chart of a fatigue analysis method for a controllable pitch propeller hub mechanism under multiple load phase differences according to the present invention;

[0020] Figure 2 is a schematic diagram of an embodiment of the present invention;

[0021] Figure 3 1. It is a schematic diagram of the constraints of the full model for fatigue analysis of the controllable pitch propeller hub mechanism according to an embodiment of the present invention;

[0022] Figure 4 This is a schematic diagram of blade numbering according to an embodiment of the present invention;

[0023] Figure 5 : These are the hydrodynamic load curves of each blade after a 72° phase difference shift in an embodiment of the present invention, wherein (a) is the thrust curve of a single blade after a 72° phase difference shift; (b) is the thrust torque curve of a single blade after a 72° phase difference shift; (c) is the blade rotation torque curve of a single blade after a 72° phase difference shift; (d) is the shear force curve of a single blade after a 72° phase difference shift; and (e) is the shear force torque curve of a single blade after a 72° phase difference shift.

[0024] Figure 6 SN curve diagram of the material of the embodiment of the present invention, wherein (a) is the SN curve of the crank plate; (b) is the SN curve of the slider; (c) is the SN curve of the blade root pin; (d) is the SN curve of the shaft flange pin; (e) is the SN curve of the blade root bolt, shaft flange bolt, and cylinder bolt; (f) is the SN curve of the hub body;

[0025] Figure 7 This is the sinusoidal fatigue load spectrum of the controllable pitch propeller hub mechanism according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0027] like Figure 1 As shown, an embodiment of the present invention provides a fatigue analysis method for a controllable pitch propeller hub mechanism under multiple load phase differences, which specifically includes the following steps:

[0028] Step 1: Based on the full-scale geometry of the CPP hub mechanism, a basic simplification method for the full CPP hub mechanism model was determined based on actual engineering conditions. Small holes or bosses not located in the main force transmission path during static strength and fatigue simulation analysis were simplified into features suitable for finite element analysis. Based on the assembly relationship between the CPP hub mechanism and the vessel, as well as the operating environment, boundary conditions were determined, and a high-precision finite element model was established.

[0029] Step 2: Based on the load data, select load application points on the symmetry line of the five blades and the axis of the hub mechanism. Based on the relationship between force and torque, convert the load data into load data that is convenient for application in the finite element analysis software. Then, apply thrust, thrust torque, shear force, shear torque, and blade rotation torque with a 72° phase difference on the five blades in sequence.

[0030] Step three: Because of the finite element software can not eliminate the residual stress and the working environment in the first cycle, the propeller hub mechanism has not yet in a stable rotating state, according to a rotating cycle load curve and rotating speed, 180 load points in two cycles of pitch propeller hub mechanism static strength simulation, using the second cycle of simulation data for static strength analysis and fatigue life analysis;

[0031] Step four: using linear damage accumulation theory and nominal stress method, according to step three in the second cycle of simulation data, the pitch propeller hub mechanism full size sinusoidal fatigue load spectrum, through the fatigue analysis software, the fatigue life of the main parts are analyzed.

[0032] Specific application examples:

[0033] As shown in Figure 2 , considering a pitch propeller hub mechanism full size structure, including: hub, blade root bolt, blade root pin, bearing ring, crank disc, piston rod, slider, oil cylinder, oil cylinder bolt, shaft flange, shaft flange bolt, shaft flange pin. All materials are set to bilinear. All the friction coefficient is set to 0.1. Usually used in engineering, the allowable tensile stress is 0.5 times the allowable shear stress value, so here all the materials of the corresponding yield limit of the shear stress is 0.5 times. The main mechanical properties of the materials used in the calculation are shown in table 1.

[0034] Table 1 mechanical properties of the materials used in the calculation

[0035]

[0036] Propeller hub mechanism finite element simulation model construction: after the three-dimensional model of the propeller hub mechanism is imported into the finite element software, in order to ensure the accuracy of the gap value between the parts, the node translation function is used to retranslate the two groups of nodes corresponding to the gap under the premise of ensuring the mesh quality, so as to ensure that the influence of the gap can be accurately considered in the simulation analysis. The load of the propeller hub mechanism under different working conditions mainly includes the bolt pretightening force and the equivalent concentrated force acting on the blade; the constraint condition mainly considers limiting the freedom degrees of all nodes on the shaft end surface and its piston rod end surface connected with the propeller hub. In actual operation, the piston rod of the pitch propeller mechanism mainly couples the axial rotation and translation freedom degrees through the intermediate anti rotation bar and oil pressure. Therefore, two node groups and corresponding two small mass points are established at the end of the piston rod. The corresponding axial translation and rotation freedom degrees are coupled through the cerig command stream. A node group and a small mass point are established on the shaft end surface connected with the propeller hub, and all the freedom degrees of the mass point and the node group are constrained by cerig. The boundary conditions are shown in Figure 3 .

[0037] Application of bolt preload in the finite element model of the hub mechanism: First, create a preload element PRETS 179 in the axial middle of the bolt, use PSMESH to cut the bolt into two parts, and use the preload element to generate a preload section. Then use the SLOAD command to apply the preload load on the preload section.

[0038] Application of external loads to blades in the finite element model of the hub mechanism: Create a node group on each blade, and take a point on the central axis to grab the mpc. Use the rbe3 command to create an mpc flexible constraint, and distribute the thrust, shear force, thrust moment, shear moment, and blade moment to the node group of the blade through this point to simulate the hydrodynamic force during the operation of the blade. According to the table of external load spectra such as thrust, shear force, thrust moment, shear moment and blade moment of the corresponding blade, create a cyclic command flow with one time step per cycle. Read in and load a set of loads on the mpc point, and then solve to get the final result; use OMEGA to set the angular velocity along the axial direction to simulate the centrifugal force during operation. Under actual working conditions, the hydrodynamic loads on the five blades are not completely equivalent, but present a phase difference of 72°. The blade numbers are as follows: Figure 4 According to the single blade simulation data, after a 72° phase difference shift, the load curves of blade thrust, thrust moment, blade rotation moment, shear force and shear moment are obtained as shown in the figure below. Figure 5 The SN curves of various materials of the controllable pitch propeller mechanism are shown in Figure 6 shown.

[0039] The simulation analysis of this embodiment considers the fatigue strength of the controllable pitch propeller hub mechanism under the total hydrodynamic force, and takes the change in the structural force amplitude caused by the total thrust working condition as the main load drive, such as Figure 7 When the thrust condition is at its minimum value (T=1.0667), the hub stress is 325.276MPa, and the hub stress is also at its minimum value. When the thrust condition is at its maximum value (T=1.1444), the hub stress is 344.407MPa, and the hub stress is also at its maximum value.

[0040] The fatigue strength under 100% hydrodynamic conditions and 60% hydrodynamic conditions were analyzed respectively. Under 100% hydrodynamic conditions, the minimum fatigue life of the blade root bolt is 10 6.492 times, the minimum fatigue life of the shaft flange bolts is 10 6.88925 times, the minimum fatigue life of the crank disc is 10 6.3001 The minimum fatigue life of the hub is only 10 6.0009The fatigue life of a structure is related to its local stress state. When analyzing the fatigue strength of a component, it is important to focus on the areas with the highest stress levels under fatigue conditions and the areas with significant stress changes.

[0041] Table 2 Fatigue life of main parts of the controllable pitch propeller hub mechanism under 100% hydrodynamic conditions

[0042]

[0043]

[0044] Compared with the 100% hydrodynamic load condition, the fatigue life of the main parts of the hub mechanism under the 60% hydrodynamic load condition tends to infinite life.

[0045] Table 3 Fatigue life of main parts of hub mechanism

[0046] part Minimum fatigue life / 10^times Minimum lifespan position Blade root bolt 7 Blade root bolt nut position Shaft flange bolts 7 Shaft flange bolt and nut location Cylinder bolts 7 Cylinder bolt and nut position Leaf root pin 7 At the cylindrical edge of the blade root pin Shaft flange pin 7 On the cylindrical edge of the shaft flange pin crank plate 7 Cylinder surface inside the crank disk slider 7 Surface near the inner hole of the slider propeller hub body 7 Inside the hub bridge

[0047] The analysis results show that, with the exception of the bolts, crank plate, and propeller hub, the fatigue life of all components approaches infinity, with the most severe fatigue occurring primarily in areas of high stress. Fatigue is also most severe in contact areas, as these areas are prone to stress concentration and require enhanced design to improve safety and reliability. Traditional fatigue analysis methods, however, show that the fatigue life of all components approaches infinity under both 100% and 60% hydrodynamic conditions. This demonstrates that the proposed method provides more accurate analysis results than traditional fatigue analysis methods.

[0048] The above are only specific steps of the present invention and do not constitute any limitation to the scope of protection of the present invention; it can be extended to the field of static structural uncertainty analysis based on convex polyhedron models. Any technical solution formed by equivalent transformation or equivalent replacement falls within the scope of protection of the present invention.

[0049] Some parts of the present invention are well known to those skilled in the art and are not described in detail.

Claims

1. A fatigue analysis method for a controllable pitch propeller hub mechanism under multiple load phase differences, characterized by: Based on the full-scale geometric model of the controllable pitch propeller hub mechanism, a basic model simplification method was determined according to actual engineering conditions. Considering multiple loads including thrust, thrust moment, shear force, shear moment, and blade rotation moment, as well as the 72° phase difference on the five blades, a sinusoidal fatigue load spectrum was compiled using finite element analysis and fatigue simulation software, using the linear damage accumulation theory and nominal stress method to perform fatigue analysis on typical components of the controllable pitch propeller hub mechanism. The specific implementation steps of this method are as follows: Step 1: Build a high-precision finite element model of the full-scale geometric shape of the controllable pitch propeller hub mechanism based on the boundary conditions of the working environment; Step 2: Apply a hydrodynamic load with a phase difference of 72° to the five blades of the controllable pitch propeller. By selecting the load points, load the thrust, thrust moment, shear force, shear moment and blade rotation moment in sequence. The load application points are selected on the symmetry line of the five blades and the axis of the hub mechanism. According to the relationship between force and moment, the load data is converted into load data that is easy to apply in the finite element analysis software. Then, thrust, thrust moment, shear force, shear moment and blade rotation moment with a phase difference of 72° are applied to the five blades in sequence. Step 3: Using finite element analysis software, perform static strength simulation analysis of the controllable pitch propeller hub mechanism at 180 load points within two cycles based on the load curve and rotation speed within one rotation cycle; Step 4: Using the linear damage accumulation theory and the nominal stress method, compile the full-scale fatigue load spectrum of the controllable pitch propeller hub mechanism according to the load curve, and calculate the fatigue life of the main parts through fatigue analysis software for analysis.

2. The fatigue analysis method for a controllable pitch propeller hub mechanism under multiple load phase differences according to claim 1 is characterized by: In step one, the basic simplification method for the full model of the controllable pitch propeller hub mechanism is determined based on the actual engineering situation. The tiny holes or bosses that are not on the main force transmission path in the static strength and fatigue simulation analysis are simplified into features suitable for finite element analysis. The boundary conditions are determined based on the assembly relationship between the controllable pitch propeller hub mechanism and the overall ship.

3. The fatigue analysis method for a controllable pitch propeller hub mechanism under multiple load phase differences according to claim 1 is characterized in that: In step three, due to the residual stress that cannot be eliminated by the finite element software and the fact that the hub mechanism is not in a stable rotation state in the first cycle, the load data in two cycles are calculated, and the static strength analysis and fatigue life analysis are performed using the simulation data of the second cycle.

4. The fatigue analysis method for a controllable pitch propeller hub mechanism under multiple load phase differences according to claim 3 is characterized by: In step 4, a sinusoidal fatigue load spectrum is compiled based on the simulation data of the second cycle in step 3, and fatigue life analysis of typical components is performed using fatigue analysis software.

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