Turbine component online monitoring method based on crack three-dimensional propagation analysis

Abstract

The invention discloses a turbine component online monitoring method based on crack three-dimensional propagation analysis, which belongs to the technical field of mechanical monitoring, and mainly comprises the following steps: establishing a finite element model of a crack-free turbine component and obtaining the inherent frequency of the finite element model; establishing a finite element model with cracks, mapping the stress distribution matrix for driving the cracks to expand into the finite element model with the cracks to obtain the finite element models under the condition of the cracks with different sizes, and obtaining the inherent frequency and the cumulative cycle number of the turbine component under each finite element model; the corresponding relation between the frequency variation and the residual fatigue life of the component under the condition of cracks of different sizes relative to the condition without cracks is established, the residual fatigue life of the turbine component is determined by monitoring the frequency change of the turbine component on line, and the running safety of a gas turbine is guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of mechanical monitoring technology, specifically relating to an online monitoring method for turbine components based on three-dimensional crack propagation analysis. Background Technology

[0002] Fatigue fracture is the most common form of mechanical and structural failure in engineering practice. Turbine components are subjected to multi-source unsteady excitation under extreme high-temperature operating conditions, and fatigue fracture is a prominent problem that is a major factor affecting the service life of gas turbines.

[0003] To ensure the safe operation of turbine components, various testing methods are currently used for monitoring them. For example, high-temperature strain gauges and accelerometers can be installed on various turbine components to monitor their vibration frequency and surface stress. For turbine rotor blades, non-contact measurement using techniques such as tip-time (BTT) can be achieved to obtain vibration frequency and tip amplitude. By continuously monitoring the resonant frequency of turbine components during resonant speed processes using these testing methods, abnormal frequency changes can be used to identify the initiation of structural cracks, which can then be confirmed and located through borehole inspection while the turbine is shut down.

[0004] However, under actual operating conditions, some cracks, such as those in the turbine rotor blade area, pose significant safety hazards to gas turbine operation, and the blades should be replaced as soon as possible if discovered. Cracks in other parts of the turbine rotor blades and other turbine components are difficult to avoid and propagate slowly. Long-term monitoring should be conducted based on the remaining fatigue life to improve the economic efficiency of turbine components. Current borehole probing techniques under non-cylinder operation conditions are insufficient to quantitatively characterize the specific details of crack propagation, making it difficult to predict the remaining fatigue life of turbine components based on frequency changes, and thus unable to confirm whether the gas turbine can continue to operate safely. Summary of the Invention

[0005] In response to one or more of the above-mentioned defects or improvement needs of the prior art, the present invention provides an online monitoring method for turbine components based on three-dimensional crack propagation analysis, which can identify the remaining life of turbine components while monitoring frequency changes, thereby ensuring the safe operation of the gas turbine.

[0006] To achieve the above objectives, the present invention provides an online monitoring method for turbine components based on three-dimensional crack propagation analysis, which includes the following steps: (1) Establish a finite element model M0 of a crack-free turbine component, assign it material data, and apply loads and boundary conditions to it; analyze the finite element model M0 to obtain the stress distribution matrix and natural frequency f0; (2) Set an initial crack on the finite element model M0 to obtain the finite element model M containing the crack. i ; (3) applying the load and boundary conditions consistent with step (1) to the finite element model M i containing initial cracks and performing vibration analysis to obtain the natural frequency f i of the turbine component under the finite element model M i ; (4) mapping the stress distribution matrix driving crack propagation to the finite element model M i containing cracks; (5) performing fracture mechanics analysis on the finite element model M i to obtain the cycle number N i and the maximum stress intensity factor K1 at the crack tip under the corresponding load step, and obtaining the finite element model M i+1 containing new cracks; (6) applying the load and boundary conditions consistent with step (1) to the finite element model M i+1 and performing vibration analysis to obtain the natural frequency f i+1 of the turbine component under the finite element model M i+1 ; (7) repeating steps (4) to (6) until the maximum stress intensity factor K i at the crack tip is greater than the fracture toughness K IC of the turbine component; (8) calculating the total fracture life and determining the corresponding relationship between the change amount of the current frequency relative to the initial frequency and the current cumulative propagation cycle number; determining the remaining life of the component according to the change amount of the current frequency relative to the initial frequency of the turbine component, and realizing online monitoring of the turbine component.

[0007] As a further improvement of the application, in step (1), the stress distribution matrix includes a stress distribution matrix A under stable operation conditions after long-term creep, and the stress distribution matrix A is obtained by performing creep analysis on the finite element model M0 of the turbine component; and / or, In step (1), the stress distribution matrix includes a residual stress distribution matrix B after shutdown, and the residual stress distribution matrix B is obtained by performing statics analysis on the finite element model M0 of the turbine component; and / or, In step (1), the stress distribution matrix includes a modal stress distribution matrix C under a dangerous vibration mode, and the modal stress distribution matrix C is obtained by performing vibration analysis on the finite element model M0 of the turbine component.

[0008] As a further improvement of the application, the load applied to the finite element model M0 in step (1) includes temperature load and mechanical load, and the mechanical load at least includes centrifugal force and aerodynamic force.

[0009] As a further improvement of the present application, in step (2), the initial crack is arranged at the position of the minimum dynamic stress reserve of the finite element model M0, or arranged at the position of the maximum static stress of the finite element model M0, or arranged at the position of the maximum residual stress of the finite element model M0.

[0010] As a further improvement of the present application, in step (4), the stress distribution matrix mapped to the finite element model M i is a modal stress distribution matrix C', which is obtained by scaling the modal stress distribution matrix C under the no-crack condition with the stress σ at the key position of the component obtained through dynamic measurement under the resonance condition, and taking the measured stress σ as the reference.

[0011] As a further improvement of the present application, in step (4), the stress distribution matrix mapped to the finite element model M i is a stress distribution matrix A under the stable operation condition after long-term creep.

[0012] As a further improvement of the present application, in step (4), the stress distribution matrix mapped to the finite element model M i is a residual stress distribution matrix B under the shutdown condition after long-term creep.

[0013] As a further improvement of the present application, based on the stress values of the known element nodes in the stress distribution matrix corresponding to the finite element model M0, it is determined which known element the new node in the finite element model M i belongs to, the stress value of the new node is calculated, and the stress distribution matrix driving crack propagation is mapped to the finite element model M i .

[0014] As a further improvement of the present application, the mapping of the stress distribution matrix of the finite element model M i is completed by the space interpolation method of octree algorithm, which specifically includes the following steps: (4.1) determining the region boundary of the finite element model M0 and the minimum bounding box of the component; (4.2) equally dividing in X, Y and Z directions to form (x×y×z) small cubes of equal size; (4.3) determining whether the node density inside each small cube meets the difference requirement, and further dividing the small cube that does not meet the requirement until the node density inside each small cube meets the interpolation requirement; (4.4) finding the unit of the no-crack model M i to which the node of the crack model M belongs according to the overall coordinates of the node of the crack model M (4.5) constructing the element shape function of the model M0, and obtaining the M iThe node stress value of the model should be completed to require the stress field mapping.

[0015] The above technical features can be combined with each other as long as they do not conflict with each other.

[0016] Overall, compared with the prior art, the above technical solutions conceived by the present application have the beneficial effects including: The turbine component online monitoring method based on crack three-dimensional expansion analysis provided by the present application realizes determination of the remaining fatigue life of the turbine component through online monitoring of the frequency change of the turbine component, and guarantees the safety of the operation of the gas turbine. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0018] Fig. 1 is the overall flowchart of the turbine component online monitoring method based on crack three-dimensional expansion analysis in the embodiments of the present application; Fig. 2 is the specific steps of mapping the stress distribution matrix by using the space interpolation method of the octree algorithm in the embodiments of the present application; Fig. 3 is the change amount of the frequency in the embodiments of the present application f and the relationship curve of the cumulative expansion cycle times ΣN. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0020] Embodiment: Please refer to Figs. 1-3 The turbine component online monitoring method based on crack three-dimensional expansion analysis in the preferred embodiments of the present application includes the following steps: (1) Establish a finite element model M0 of the turbine component without cracks, give it material data, and apply loads and boundary conditions to it; analyze the finite element model M0 to obtain a stress distribution matrix and an inherent frequency f0.

[0021] Preferably, the loads applied to the finite element model M0 include at least mechanical loads and temperature loads, such as centrifugal force, aerodynamic force, temperature field, etc.

[0022] Preferably, the analysis of the finite element model M0 under the condition of no cracks includes statics analysis, creep analysis, and vibration analysis; wherein the stress distribution matrix A under the stable operating condition after long-term creep is obtained through the creep analysis, the residual stress distribution matrix B after shutdown is obtained through the statics analysis, and the modal stress distribution matrix C under the dangerous vibration mode and the inherent frequency f0 of the component are obtained through the vibration analysis.

[0023] (2) Set an initial crack at a dangerous position through a crack propagation analysis software to obtain a finite element model M i .

[0024] The initial crack can be set through the Franc3D crack propagation analysis software, and other crack propagation analysis software can also be used.

[0025] When the finite element model M i containing the initial crack is set, the addition position of the initial crack needs to be selected according to the actual situation; if it is found in the design or test that the turbine component needs to stay in the resonance zone for a long time, the initial crack should be set at the position with the lowest dynamic stress reserve in combination with the vibration and static strength analysis results, to simulate the high-cycle fatigue problem, and the measured vibration stress is used as the cyclic load driving the crack propagation.

[0026] Preferably, the stress σ at the key position of the component is obtained through the dynamic measurement results under the resonance condition, the modal stress distribution matrix C under the condition of no cracks is scaled based on σ to obtain the real stress distribution matrix C' of the current turbine component, and the real stress distribution matrix C' is used as the cyclic load driving the crack propagation.

[0027] Correspondingly, if more attention needs to be paid to the low-cycle fatigue problem, the change of the start-stop state should be used as the cyclic load driving the crack propagation, and for the positive thermal mechanical fatigue, the initial crack should be set at the position with the maximum static stress, and for the reverse thermal mechanical fatigue, the initial crack should be set at the position with the maximum residual stress.

[0028] (3) Apply the same loads and boundary conditions as in step (1) to the finite element model M i containing the initial crack and perform vibration analysis to obtain the inherent frequency f of the turbine component under the finite element model M i containing the initial crack.i , obtaining f i = f i -f0.

[0029] (4) mapping the stress distribution matrix driving crack propagation into the finite element model M i ; In actual operation, according to the situation to be concerned, the stress distribution matrix required by the corresponding situation is mapped into the finite element model M i ; for example, if high-cycle fatigue is concerned, the modal stress distribution matrix C' is mapped into the finite element model M i as the stress field driving crack propagation; if forward thermomechanical fatigue is concerned, the stress distribution matrix A under the stable operating condition after long-term creep is mapped into the finite element model M i as the stress field driving crack propagation, and preferably the influence of creep relaxation is considered, and the stress distribution matrix A is corrected accordingly; if reverse thermomechanical fatigue is concerned, the residual stress distribution matrix B under the shutdown state after long-term creep is mapped into the finite element model M i as the stress field driving crack propagation.

[0030] Preferably, based on the stress values of the known element nodes in the stress distribution matrix corresponding to the finite element model M0, it is determined which known element the new node in the finite element model M i belongs to, the stress value of the new node is calculated and stored, and the stress distribution matrix driving crack propagation is mapped into the finite element model M i .

[0031] Preferably, the stress field mapping of the finite element model M i is completed by the spatial interpolation method of octree algorithm, as shown in Fig. 2 , which specifically includes the following steps: (4.1) determining the region boundary of the finite element model M0, and constructing the minimum bounding box of the component; (4.2) equally dividing in X, Y and Z directions to form (x×y×z) small cubes of equal size; (4.3) determining whether the node density inside each small cube meets the difference requirement, and further dividing the small cube that does not meet the requirement until the node density inside each small cube meets the interpolation requirement; (4.4) finding the unit of the crack-free model M0 to which the node of the crack-containing model M i belongs according to the overall coordinates of the node; (4.5) constructing the shape function of the unit of the model M0, obtaining the node stress value of the model M i inside the unit by equal parameter change interpolation, and completing the required stress field mapping.

[0032] (5) In the crack propagation analysis software, the finite element model M i Fracture mechanics analysis was performed to obtain the number of cycles N under the corresponding load step. i The maximum stress intensity factor K at the crack tip was obtained. i And obtain the finite element model M containing the new crack. i+1 .

[0033] (6) Using finite element analysis software, in the finite element model M containing cracks i+1 Apply the same loads and boundary conditions as in step (1), and perform vibration analysis to obtain the finite element model M. i+1 The natural frequency f of the lower turbine component i+1 ,but f i+1 =f i+1 -f i .

[0034] (7) Repeat steps (4) to (6) until the maximum stress intensity factor K at the crack tip is reached. i Greater than the fracture toughness K of the turbine component IC .

[0035] (8) Calculate the total fracture life N of the turbine component. 总 and total frequency change f 总 Determine the change in current frequency relative to the initial frequency. The correspondence between f and the current cumulative extended cycle number ∑N; the remaining life of the turbine component is determined based on the change in the current frequency of the turbine component relative to the initial frequency, thereby realizing online monitoring of the turbine component.

[0036] It is understandable that the total fracture life N of a turbine component 总 K is the maximum stress intensity factor at the crack tip. i Greater than the fracture toughness K of the turbine component IC The cumulative number of extended loops during the time period.

[0037] like Fig. 3 As shown, you can first plot the change in the current frequency relative to the initial frequency. The relationship curve between f and the current cumulative extended cycle number ∑N is used to fit the functional relationship between the two: ∑N=F( f) can be used to obtain the current cumulative extended cycle number through frequency changes. The difference between the total fracture life and the current cumulative cycle number can then be used to obtain the remaining life of the component, i.e., N. 余 =N 总 -F( f).

[0038] The turbine component on-line monitoring method based on crack three-dimensional propagation analysis of the present application realizes determination of the remaining fatigue life of the turbine component through on-line monitoring of the frequency change of the turbine component, and guarantees the safety of the operation of the gas turbine.

[0039] Those skilled in the art can understand that the above description is only the preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for online monitoring of turbine components based on three-dimensional crack propagation analysis, characterized in that, Includes the following steps: (1) Establish a finite element model M0 of a crack-free turbine component, assign it material data, and apply loads and boundary conditions to it; analyze the finite element model M0 to obtain the stress distribution matrix and natural frequency f0; (2) Set an initial crack on the finite element model M0 to obtain the finite element model M containing the crack. i ; (3) In the finite element model M i Apply the same loads and boundary conditions as in step (1) and perform vibration analysis to obtain the finite element model M containing the initial crack. i The natural frequency f of the lower turbine component i ; (4) Map the stress distribution matrix that drives crack propagation to the finite element model M containing the crack. i middle; (5) For the finite element model M i Fracture mechanics analysis yields the number of cycles N under the corresponding load step. i And the maximum stress intensity factor K1 at the crack tip, to obtain the finite element model M containing the new crack. i+1 ; (6) In the finite element model M i+1 Apply the same loads and boundary conditions as in step (1), and perform vibration analysis to obtain the finite element model M. i+1 The natural frequency f of the lower turbine component i+1 ; (7) Repeat steps (4) to (6) until the maximum stress intensity factor K at the crack tip is reached. i Greater than the fracture toughness K of the turbine component IC ; (8) Calculate the total fracture life and determine the correspondence between the change of the current frequency relative to the initial frequency and the current cumulative extended cycles; determine the remaining life of the component based on the change of the current frequency of the turbine component relative to the initial frequency, and realize online monitoring of the turbine component.

2. The online monitoring method for turbine components based on three-dimensional crack propagation analysis according to claim 1, characterized in that, In step (1), the stress distribution matrix includes the stress distribution matrix A under stable operating conditions after long-term creep, and the stress distribution matrix A is obtained by creep analysis of the finite element model M0 of the turbine component; And / or, In step (1), the stress distribution matrix includes the residual stress distribution matrix B after shutdown, which is obtained by static analysis of the finite element model M0 of the turbine component; And / or, In step (1), the stress distribution matrix includes the modal stress distribution matrix C under the dangerous vibration mode, which is obtained by vibration analysis of the finite element model M0 of the turbine component.

3. The online monitoring method for turbine components based on three-dimensional crack propagation analysis according to claim 1, characterized in that, The loads applied to the finite element model M0 in step (1) include temperature loads and mechanical loads, and the mechanical loads include at least centrifugal force and aerodynamic force.

4. The online monitoring method for turbine components based on three-dimensional crack propagation analysis according to any one of claims 1 to 3, characterized in that, In step (2), the initial crack is set at the position where the dynamic stress reserve of the finite element model M0 is the lowest, or at the position where the static stress of the finite element model M0 is the highest, or at the position where the residual stress of the finite element model M0 is the highest.

5. The online monitoring method for turbine components based on three-dimensional crack propagation analysis according to claim 1, characterized in that, In step (4), the mapping is performed to the finite element model M. i The stress distribution matrix in the figure is the modal stress distribution matrix C'. This modal stress distribution matrix C' is obtained by scaling the modal stress distribution matrix C under crack-free conditions based on the measured stress σ at the key position of the component obtained by dynamic measurement under resonance conditions.

6. The online monitoring method for turbine components based on three-dimensional crack propagation analysis according to claim 1, characterized in that, In step (4), the mapping is performed to the finite element model M. i The stress distribution matrix in the figure is the stress distribution matrix A under stable operating conditions after long-term creep.

7. The online monitoring method for turbine components based on three-dimensional crack propagation analysis according to claim 1, characterized in that, In step (4), the mapping is performed to the finite element model M. i The stress distribution matrix in the figure is the residual stress distribution matrix B under the shutdown state after long-term creep.

8. The online monitoring method for turbine components based on three-dimensional crack propagation analysis according to any one of claims 5 to 7, characterized in that, Based on the known stress values ​​of the element nodes in the stress distribution matrix corresponding to the finite element model M0, determine the finite element model M i Determine which known element the new node belongs to, calculate the stress value of the new node, and map the stress distribution matrix onto the finite element model M. i middle.

9. The online monitoring method for turbine components based on three-dimensional crack propagation analysis according to claim 8, characterized in that, The finite element model M was completed using the spatial interpolation method of the octree algorithm. i The mapping of the stress distribution matrix specifically includes the following steps: (4.1) Determine the boundary of the M0 region of the finite element model and the minimum bounding box of the components; (4.2) Divide the cubes at equal intervals in the X, Y, and Z directions to form (x×y×z) small cubes of equal size; (4.3) Determine whether the node density inside each small cube meets the interpolation requirement. For small cubes that do not meet the requirement, further divide them until the node density inside each small cube meets the interpolation requirement. (4.4) Based on the cracked model M i The overall coordinates of the nodes are used to find the M0 element of the crack-free model to which the node belongs; (4.5) The element shape function of the component M0 model is obtained by interpolation through isoparametric transformation to obtain the M within the element. i The nodal stress values ​​of the model are used to complete the required stress field mapping.

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