Fatigue analysis method for controllable-pitch propeller hub mechanism under multi-load phase difference

Abstract

The invention relates to a fatigue analysis method for a controllable-pitch propeller hub mechanism under multi-load phase difference, which comprises the following steps of: determining a basic model simplification method according to actual engineering conditions on the basis of a full-size geometric model of the controllable-pitch propeller hub mechanism; a sine fatigue load spectrum is compiled through finite element analysis and fatigue simulation analysis software by adopting a linear damage accumulation theory and a nominal stress method in consideration of multiple loads of thrust, thrust torque, shearing force, shearing force torque and rotating blade torque and 72-degree phase difference existing on five blades, and fatigue analysis of typical parts of the controllable-pitch propeller hub mechanism is achieved. According to the method, the full-size model of the controllable-pitch propeller hub mechanism is adopted to establish the high-precision finite element model, so that the relationship among parts in the propeller hub mechanism model can be better reflected; thrust, thrust torque, shearing force, shearing force torque and blade rotating torque with the phase difference of 72 degrees are sequentially applied to the five blades, and the working environment with the complex structure is reflected more truly.

Description

Technical Field

[0001] The invention relates to a fatigue analysis method for a hub mechanism of a controllable pitch propeller, and in particular to a fatigue analysis method for a hub mechanism of a controllable pitch propeller under multi-load phase differences. Background Art

[0002] The controllable pitch propeller (CPP) consists of blades, hub, oil distributor, oil pipe in the shaft, hydraulic system and electronic control system. The blades are connected to the hub by high-strength bolts and can rotate around an axis perpendicular to the propeller shaft. The pitch adjustment mechanism in the hub drives the blades to rotate, changing the propeller pitch, thereby changing the size and direction of the thrust on the blades to meet the requirements of the ship's forward, backward, braking and speed change.

[0003] Since the first controllable pitch propeller (CPP) was introduced in Canada more than 80 years ago, it has been attracting people's attention with its unique and excellent performance. Compared with ordinary fixed pitch propellers, the advantage of controllable pitch propellers is that the pitch can be adjusted at any time according to the ship's sailing conditions, thereby reducing fuel consumption and extending the life of the main engine. Therefore, it is very important to analyze the characteristics of adjustable pitch propellers.

[0004] The external loads of the controllable pitch propeller device mainly come from the thrust and shear force generated by water on the blades during the navigation of the ship, the hydrodynamic blade torque generated during the pitch adjustment of the blades, and the centrifugal force of the blades caused by the rotation of the shaft system. These external loads act on the hub mechanism. Due to the repeated action of the alternating external loads, fatigue cracks will be generated and expanded at local locations and finally suddenly broken when the alternating stress borne by the hub mechanism has not reached the allowable stress of the strength design. This phenomenon is called fatigue failure of the hub mechanism. From a macroscopic point of view, when the cyclic stress level is low, elastic strain plays a leading role, and the fatigue life is longer at this time, which is called stress fatigue or high-cycle fatigue; when the cyclic force level is high, plastic strain plays a leading role, and the fatigue life is shorter at this time, which is called strain fatigue or low-cycle fatigue. Since fatigue failure is accumulated, fatigue failure is very dangerous and must be given great attention during design. The purpose of fatigue analysis of the hub mechanism of the controllable pitch propeller device is to understand the parts where fatigue failure is predicted before the strength failure is reached, so as to carry out local safety design and improve the safety performance of the entire component.

[0005] In the process of static strength analysis and fatigue analysis of the hub mechanism of the traditional adjustable pitch propeller, it is usually limited by the rotational symmetry boundary conditions of the one-fifth model, and the structural stiffness and elastic deformation cannot be accurately reflected. 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 hub mechanism of the adjustable pitch propeller 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 phase difference of 72° on the five blades in turn, which more truly reflects the complex working environment of the structure. In order to solve the above problems, the present invention adopts the linear damage accumulation theory and the nominal stress method, and compiles the full-scale fatigue load spectrum of the hub mechanism of the adjustable pitch propeller 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 prior art and provide a fatigue analysis method for a pitch-controlled propeller hub mechanism under multi-load phase difference. Compared with the fatigue analysis method of a one-fifth rotationally symmetrical model under traditional amplitude load, this method can more realistically calculate the fatigue life of the pitch-controlled propeller hub mechanism.

[0007] To achieve the above-mentioned purpose, the technical solution adopted by 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 various 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 a 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: Based on the full-size geometric shape of the controllable pitch propeller hub mechanism and the boundary conditions of the working environment, a high-precision finite element model is established;

[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, according to the load curve and rotation speed in one rotation cycle, conduct static strength simulation analysis of the controllable pitch propeller hub mechanism at 180 load points in two cycles;

[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. The boundary conditions are determined according to the assembly relationship between the controllable pitch propeller hub mechanism and the overall ship.

[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 easy to apply 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 is performed on typical components using fatigue analysis software.

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

[0018] The advantages of the present invention compared with the prior art are: the present invention adopts a full-size model of a 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 moment, shear force, shear moment and blade rotation moment with a phase difference of 72° on five blades in sequence, which more truly reflects the working environment with a complex structure; the present invention analyzes the fatigue life of various typical components more accurately by compiling a full-size sinusoidal fatigue load spectrum of the controllable pitch propeller hub mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

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

[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 It is a 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, a fatigue analysis method for a pitch controllable propeller hub mechanism under multiple load phase differences provided by an embodiment of the present invention specifically includes the following steps:

[0028] Step 1: Based on the full-scale geometric shape of the controllable pitch propeller hub mechanism, determine the basic simplification method of the full model of the controllable pitch propeller hub mechanism according to the actual engineering situation, and simplify the tiny holes or bosses that are not on the main force transmission path in the static strength and fatigue simulation analysis into features suitable for finite element analysis. According to the assembly relationship and working environment of the controllable pitch propeller hub mechanism and the ship, determine the boundary conditions and establish a high-precision finite element model;

[0029] Step 2: According to the load data, select the load application point on the symmetry line of the five blades and the axis of the hub mechanism. According to the relationship between force and torque, convert the load data into load data that is easy to apply in the finite element analysis software, and apply thrust, thrust torque, shear force, shear torque and blade rotation torque with a phase difference of 72° on the five blades in turn;

[0030] Step 3: 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 under the working environment, the static strength simulation of the hub mechanism of the controllable pitch propeller is performed at 180 load points in two cycles according to the load curve and rotation speed in one rotation cycle, and the static strength analysis and fatigue life analysis are performed using the simulation data of the second cycle;

[0031] Step 4: Using the linear damage accumulation theory and the nominal stress method, according to the simulation data of the second cycle in step 3, compile the full-scale sinusoidal 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.

[0032] Specific application examples:

[0033] like Figure 2 As shown in the figure, a full-size structure of a pitch-controlled propeller hub mechanism is considered, which includes: hub body, blade root bolts, blade root pins, bearing rings, crank plates, piston rods, sliders, cylinders, cylinder bolts, shaft flanges, shaft flange bolts, and shaft flange pins. All materials are set bilinearly. All friction coefficients are set to 0.1. In engineering, 0.5 times the allowable tensile stress is usually used as the allowable shear stress value, so the allowable shear stress of all materials here is 0.5 times the corresponding yield limit. The main mechanical properties of the materials used in the calculation are shown in Table 1.

[0034] Table 1 Mechanical properties of materials used in calculation

[0035]

[0036] Construction of finite element simulation model of hub mechanism: After the three-dimensional model of hub mechanism is imported into finite element software, in order to ensure the accuracy of the numerical value of the fitting clearance between each part, the node translation function is used to slightly translate the two groups of node groups corresponding to the clearance while ensuring the quality of the mesh, so as to ensure that the influence of the clearance in the simulation analysis can be accurately considered. The loads of the hub mechanism under different working conditions mainly include the bolt preload and the equivalent concentrated force acting on the blades; the constraints mainly consider limiting the degrees of freedom of all nodes of the shaft end face connected to the hub and the piston rod end face. In actual operation, the piston rod of the adjustable pitch propeller mechanism is mainly coupled to the axial rotation and translation degrees of freedom through the middle anti-rotation strip and oil pressure. Therefore, two node groups and corresponding two small mass points are established at the end of the piston rod to capture the mpc. The corresponding axial translation and rotation degrees of freedom are coupled through the cerig command flow. A node group and a small mass point are established on the shaft end face connected to the hub, and all degrees of freedom of the mass point and the node group are constrained by cerig. The boundary conditions are as follows: Figure 3 shown.

[0037] Application of bolt preload in the finite element model of the hub mechanism: First, create a preload element PRETS 179 in the middle axial part 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 establish an mpc flexible constraint, and distribute the thrust, shear force, thrust moment, shear moment, and blade rotation 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 rotation 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 show 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 Figure 5 The SN curves of various materials of the adjustable pitch propeller mechanism are shown in Figure 6 shown.

[0039] The simulation analysis of this embodiment considers the fatigue strength of the hub mechanism of the controllable pitch propeller under the total hydrodynamic force, and takes the change of 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 the minimum value (T = 1.0667), the hub stress is 325.276MPa, and the hub stress is also at the minimum value; when the thrust condition is at the maximum value (T = 1.1444), the hub stress is 344.407MPa, and the hub stress is also at the 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 level of the structure is related to the local stress state of the structure. When analyzing the fatigue strength of components, on the one hand, it is necessary to focus on the parts with the highest stress level under fatigue conditions, and on the other hand, it is necessary to focus on the parts with obvious changes in stress levels.

[0041] Table 2 Fatigue life of main parts of the 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 life span position Blade root bolt 7 Blade root bolt nut position Shaft flange bolts 7 Shaft flange bolt nut location Cylinder bolts 7 Cylinder bolt 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 Crank disc inner cylindrical surface slider 7 Surface near the inner hole of the slider propeller hub body 7 Hub bridge interior

[0047] It can be seen from the analysis results that, except for the bolts, crank disc and hub body, the fatigue life of each part tends to infinite life, and the most serious fatigue parts are basically distributed in the area with greater stress. At the same time, the contact parts are most seriously fatigued, because these parts are prone to stress concentration, and these parts need to be strengthened during the design process to increase safety and reliability. In the traditional fatigue analysis method, whether it is 100% or 60% hydrodynamic conditions, the fatigue life of each component tends to infinite life. It can be seen that the analysis results of the method proposed in the present invention are more accurate than those of the traditional fatigue analysis method.

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

[0049] The present invention does not elaborate on some of the well-known technologies that belong to those skilled in the art.

Claims

1. A fatigue analysis method for a controllable pitch propeller hub mechanism under multiple load phase differences, characterized by: Based on the full-size geometric model of the controllable pitch propeller hub mechanism, the basic model simplification method was determined according to the actual engineering situation. Considering the various loads of thrust, thrust moment, shear force, shear moment and blade rotation moment as well as the 72° phase difference on the five blades, the finite element analysis and fatigue simulation analysis software were used, and the linear damage accumulation theory and nominal stress method were used to compile the sinusoidal fatigue load spectrum to realize the fatigue analysis of typical components of the controllable pitch propeller hub mechanism.

2. The fatigue analysis method of the controllable pitch propeller hub mechanism under multiple load phase differences according to claim 1 is characterized in that: The specific implementation steps of this method are as follows: Step 1: Based on the full-scale geometric shape of the controllable pitch propeller hub mechanism, a high-precision finite element model is established according to 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. 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 according to 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.

3. The fatigue analysis method of the controllable pitch propeller hub mechanism under multiple load phase differences according to claim 2 is characterized in that: In step one, 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. The boundary conditions are determined according to the assembly relationship between the controllable pitch propeller hub mechanism and the overall ship.

4. The fatigue analysis method of the controllable pitch propeller hub mechanism under multiple load phase differences according to claim 2 is characterized in that: In step two, 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 torque, the load data is converted into load data that is easy to apply in the finite element analysis software, and thrust, thrust moment, shear force, shear moment and blade rotation moment with a phase difference of 72° are applied to the five blades in turn.

5. The fatigue analysis method of the controllable pitch propeller hub mechanism under multiple load phase differences according to claim 2 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 simulation data of the second cycle is used for static strength analysis and fatigue life analysis.

6. The fatigue analysis method of the controllable pitch propeller hub mechanism under multiple load phase differences according to claim 5 is characterized in that: 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 is performed on typical components using fatigue analysis software.

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