Power component service life evaluation method and system and storage medium

Abstract

The invention relates to a power component service life evaluation method and system and a storage medium. The power part especially refers to a nuclear turbine long blade. The method comprises the following steps: S1, monitoring the vibration displacement of a predetermined blade flutter area, and carrying out finite element calculation by taking the vibration displacement as a boundary condition to obtain the theoretical vibration stress distribution of the whole blade; and S2, correcting the theoretical vibration stress distribution according to a predetermined correction relation to obtain the actual vibration stress distribution of the whole blade. And S3, based on the actual vibration stress distribution, the fatigue strength coefficient of the blade material, the fatigue strength index of the blade material and the time when the blade enters the flutter area, obtaining an accumulated damage value of the blade. And S4, calculating the residual fatigue life of the blade according to the accumulated damage value. According to the method, the blade life evaluation range is more accurate, the collected data is more accurate, and a reliable basis is provided for safe operation and maintenance of a nuclear turbine.

Description

Technical Field

[0001] This invention relates to the field of nuclear power turbine life assessment technology, and in particular to a method, system and storage medium for assessing the service life of power components. Background Technology

[0002] As a key component of nuclear power plants, nuclear power turbines exhibit complex three-dimensional flow characteristics in their long blades. The low natural frequency of the blades makes them more sensitive to flutter. In recent years, there have been reports of root cracking in the last-stage moving blades of commercial units due to flutter. Furthermore, with changes in the energy landscape, turbines in thermal power systems require more variable operating conditions. Studies have revealed that the low-pressure last stage exhibits rotational instability similar to that in compressors under low-load conditions, leading to asynchronous vibration. When the fluid-structure interaction frequencies are close to or even identical, the dynamic stress on the last-stage moving blades increases exponentially. While this may not destroy the blades in a very short time like classic flutter, there is still a risk of high-cycle fatigue failure.

[0003] Therefore, life assessment of long blades in nuclear power turbines is directly related to the safety and reliability of the turbines. Currently, traditional methods for assessing the life of long blades in nuclear power turbines are mostly based on empirical formulas and limited experimental data, failing to fully consider the dynamic changes of various complex factors during actual operation. This results in low accuracy and reliability of the assessment results, making it difficult to meet the high safety and reliability requirements of nuclear power equipment. Therefore, there is an urgent need to develop a more scientific and accurate method for assessing the life of long blades in nuclear power turbines. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method, system and storage medium for assessing the service life of power components, in order to address the above-mentioned deficiencies.

[0005] The technical solution adopted by this invention to solve its technical problem is: a method for assessing the service life of power components, specifically referring to long blades of nuclear power turbines, comprising the following steps: S1. Monitor the vibration displacement of the predetermined blade flutter region, and perform finite element calculations using the vibration displacement as the boundary condition to obtain the theoretical vibration stress distribution of the entire blade. S2. Correct the theoretical vibration stress distribution according to the predetermined correction relationship to obtain the actual vibration stress distribution of the entire blade; S3. Based on the actual vibration stress distribution, the fatigue strength coefficient and fatigue strength index of the blade material, and the time it takes for the blade to enter the flutter region, the cumulative damage value of the blade is obtained. S4. Based on the cumulative damage value, the remaining fatigue life of the blade is calculated.

[0006] Furthermore, in the life assessment method described in this invention, the method further includes a correction relationship determination step: The relationship between blade tip vibration displacement and blade dynamic stress was determined by long blade dynamic frequency test and finite element calculation, respectively, and a corrected relationship between finite element and test was obtained accordingly.

[0007] Furthermore, in the life assessment method of the present invention, the step of determining the correction relationship includes: The experimental ratio between the blade tip vibration displacement and the blade dynamic stress was determined through dynamic frequency tests on long blades, as follows: The theoretical ratio between the blade tip vibration displacement and the blade dynamic stress was determined through finite element analysis, as follows: Therefore, the correction factor between the finite element method and the experiment is obtained as follows: Where i represents the i-th mode of the blade; The blade tip vibration displacement is measured during a dynamic frequency test of a long blade under the i-th mode of the blade. The vibration stress is measured during dynamic frequency testing of a long blade under the i-th mode of the blade. The blade tip vibration displacement is obtained from the finite element analysis under the i-th mode of the blade. The vibration stress is obtained from the finite element analysis of the i-th mode of the blade.

[0008] Furthermore, in the life assessment method described in this invention, the method further includes a step of determining the blade flutter region: During the load increase and decrease process of the low-pressure cylinder of the nuclear power unit, the low-pressure cylinder flow range G1-G2 and the corresponding back pressure range Pb1-Pb2 when the blade vibration exceeds the limit are monitored. A quadrilateral area is formed by point A with coordinates (Pb1, G1) and point B with coordinates (Pb2, G2) as the diagonal vertices, and this area is regarded as the flutter area of ​​the low-pressure last stage moving blade.

[0009] Furthermore, in the life assessment method described in this invention, step S3 includes: S3-1: The fatigue life of the blade corresponding to each vibration stress state is calculated based on the actual blade vibration stress distribution, the fatigue strength coefficient of the blade material, and the fatigue strength index of the blade material. S3-2: Statistically determine the number of fatigue cycles under each vibration stress state based on the time it takes for the blade to enter the flutter region each time. S3-3: The cumulative damage value is calculated based on the blade fatigue life corresponding to each vibration stress state and the number of fatigue cycles under each vibration stress state.

[0010] Furthermore, in the life assessment method described in this invention, in step S3-1, the calculation formula obtained using the Basquin equation is as follows: In the formula, The blade vibration stress amplitude is obtained based on the actual blade vibration stress distribution. The fatigue strength coefficient of the blade material, in MPa; The fatigue strength index of the blade material; This represents the blade fatigue life corresponding to each vibration stress state.

[0011] Furthermore, in the life assessment method described in this invention, in step S3-3, the formula for calculating the cumulative damage value of the blade is as follows: In the formula, This represents the number of fatigue cycles under each vibration stress state.

[0012] Furthermore, in the life assessment method described in this invention, the method further includes: When it is determined that the remaining fatigue life of the blade is approaching zero, a reminder signal is sent to the terminal of the unit operator to inform him to check or replace the blade.

[0013] In addition, the present invention also provides a service life assessment system for power components, specifically referring to long blades of nuclear power turbines, including: The theoretical vibration stress distribution determination module monitors the vibration displacement of a pre-determined blade flutter region and performs finite element calculations using the vibration displacement as boundary conditions to obtain the theoretical vibration stress distribution of the entire blade. The correction module is used to correct the theoretical vibration stress distribution according to a predetermined correction relationship to obtain the actual vibration stress distribution of the entire blade. The cumulative damage value calculation module is used to obtain the cumulative damage value of the blade based on the actual blade vibration stress distribution, the fatigue strength coefficient and fatigue strength index of the blade material, and the time when the blade enters the flutter region. The life assessment module is used to calculate the remaining fatigue life of the blade based on the cumulative damage value.

[0014] In addition, the present invention provides a computer-readable storage medium storing a computer program adapted for loading by a processor to perform the life assessment steps as described above.

[0015] The method, system, and storage medium for assessing the service life of power components, specifically referring to long blades of nuclear power turbines, implemented in this invention have the following beneficial effects: This invention establishes a correction relationship between finite element analysis and experimental data for long blades of nuclear power turbines. Based on the actual measured blade vibration displacement, the theoretical vibration stress distribution of the entire blade is obtained through finite element calculation. By determining the flutter region of the long blade during operation, the remaining service life of the long blade is accurately assessed, thereby ensuring the accuracy of blade fatigue life calculation. This makes the blade service life assessment range more precise and the data collection more accurate, providing a reliable basis for the safe operation and maintenance of nuclear power turbines and helping to ensure the safe and stable operation of long blades in nuclear power turbines. Attached Figure Description

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is a flowchart illustrating the power component service life assessment method provided in an embodiment of the present invention; Figure 2 This is a flowchart illustrating a method for assessing the service life of power components according to some embodiments of the present invention; Figure 3 This is a schematic diagram of the power component service life assessment system provided in an embodiment of the present invention. Detailed Implementation

[0017] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific embodiments are now described in detail with reference to the accompanying drawings. In the following description, it should be understood that the orientations or positional relationships indicated by terms such as "front," "rear," "upper," "lower," "left," "right," "longitudinal," "horizontal," "vertical," "horizontal," "top," "bottom," "inner," "outer," "head," and "tail" are based on the orientations or positional relationships shown in the accompanying drawings, and are constructed and operated in a specific orientation. They are only for the convenience of describing this technical solution and do not indicate that the device or element referred to must have a specific orientation; therefore, they should not be construed as limitations on this invention.

[0018] It should also be noted that, unless otherwise explicitly specified and limited, terms such as "installation," "connection," "joining," "fixing," and "setting" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. When a component is referred to as being "on" or "below" another component, that component can be located "directly" or "indirectly" on the other component, or there may be one or more intermediary components.

[0019] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0020] refer to Figure 1 In a preferred embodiment, this method is mainly applied to the service life assessment of power components, specifically referring to the long blades of a nuclear power turbine. The service life assessment method for power components in this embodiment includes the following steps: S1. Monitor the vibration displacement of the pre-determined blade flutter region, and perform finite element calculations using the vibration displacement as the boundary condition to obtain the theoretical vibration stress distribution of the entire blade.

[0021] S2. Correct the theoretical vibration stress distribution according to the predetermined correction relationship to obtain the actual vibration stress distribution of the entire blade.

[0022] In some embodiments, the service life assessment method for power components further includes a correction relationship determination step: determining the relationship between the blade tip vibration displacement and the blade dynamic stress through long blade dynamic frequency tests and finite element calculations, respectively, and obtaining a correction relationship between the finite element method and the test based on this. It is understood that the finite element calculation is performed after the long blade dynamic frequency tests are completed.

[0023] Specifically, the steps for determining the modified relationship can be as follows: The experimental ratio between the blade tip vibration displacement and the blade dynamic stress was determined through dynamic frequency tests on long blades, as follows: The theoretical ratio between the blade tip vibration displacement and the blade dynamic stress was determined through finite element analysis, as follows: Therefore, the correction factor between the finite element method and the experiment is obtained as follows: Where i represents the i-th mode of the blade. The vibration displacement at the blade tip is measured during a dynamic frequency test of a long blade under the i-th mode of the blade. This represents the vibration stress measured during a dynamic frequency test of a long blade under the i-th mode of the blade. The displacement at the blade tip is obtained from the finite element method calculation under the i-th mode of the blade. The vibration stress is obtained from the finite element analysis of the i-th mode of the blade.

[0024] In other words, this step first establishes the relationship between blade tip vibration displacement and blade vibration stress through long-blade dynamic frequency testing. Strain gauges are attached to locations of high stress on the long blade; preferably, the location of maximum stress can be determined by software calculation before attaching the strain gauges. Blade vibration stress is measured using wireless telemetry, and simultaneously, blade tip-timing (BTT) technology is used to monitor the blade tip vibration displacement, thereby establishing the experimental ratio between the two. After completing the long-blade dynamic frequency testing, a theoretical ratio between the two is established through finite element analysis (FEM). Based on the theoretical and experimental ratios, correction coefficients are obtained between the FEM and experimental results, ensuring that the blade tip displacement and vibration stress locations obtained from the FEM calculations and experiments remain consistent.

[0025] In some embodiments, the method for assessing the service life of power components further includes a step of determining the blade flutter region: During the load increase and decrease process of the low-pressure cylinder of the nuclear power unit, the low-pressure cylinder flow range G1-G2 and the corresponding back pressure range Pb1-Pb2 when the blade vibration exceeds the limit are monitored. A quadrilateral area is formed by point A with coordinates (Pb1, G1) and point B with coordinates (Pb2, G2) as the diagonal vertices, and this area is regarded as the flutter area of ​​the low-pressure last stage moving blade.

[0026] It is understandable that in this step, a non-contact blade health monitoring system for measuring blade vibration is installed on the low-pressure cylinder of the nuclear power unit. This system can monitor the vibration state of the long low-pressure blades in real time, acquiring the blade's vibration displacement, vibration frequency, and tip clearance. During the load increase and decrease process of the low-pressure cylinder, the low-pressure cylinder flow range G1-G2 and the corresponding back pressure range Pb1-Pb2 when the blade vibration exceeds the limit are monitored. The quadrilateral region formed by points (Pb1, G1) and (Pb2, G2) as diagonal vertices is the flutter region M of the last-stage moving blade of the low-pressure cylinder.

[0027] S3. Based on the actual vibration stress distribution, the fatigue strength coefficient and fatigue strength index of the blade material, and the time it takes for the blade to enter the flutter region, the cumulative damage value of the blade is obtained.

[0028] In some embodiments, reference is made to Figure 2 Step S3 includes: S3-1: The fatigue life of the blade corresponding to each vibration stress state is calculated based on the actual blade vibration stress distribution, the fatigue strength coefficient of the blade material, and the fatigue strength index of the blade material.

[0029] S3-2: Calculate the number of fatigue cycles under each vibration stress state by counting the time the blade enters the flutter zone each time. This can be understood as the blade health monitoring system counting the time the blade enters the flutter zone M each time, and then deriving the number of fatigue cycles under each vibration stress state from the flutter time.

[0030] S3-3: The cumulative damage value is calculated based on the blade fatigue life corresponding to each vibration stress state and the number of fatigue cycles under each vibration stress state.

[0031] Specifically, in step S3-1, the calculation formula is obtained using the Basquin equation: In the formula, The amplitude of blade vibration stress is obtained based on the actual blade vibration stress distribution. The fatigue strength coefficient of the blade material is expressed in MPa. This represents the fatigue strength index of the blade material. This represents the blade fatigue life corresponding to each vibration stress state.

[0032] In other words, within the flutter region M, the blade vibration displacement is obtained by the blade health monitoring system. This displacement is then used as the boundary condition for the finite element method (FEM) to calculate the blade vibration stress. A correction factor is then applied to the FEM calculation to obtain the true dynamic stress distribution of the blade under vibration, thus yielding the blade vibration stress amplitude. Due to the existence of mean stress, the Goodman formula is used to obtain the corrected vibration stress value. Finally, the Basquin equation is used to calculate the fatigue life of the blade under various vibration stress states in practice.

[0033] Specifically, in step S3-3, the formula for calculating the cumulative damage value of the blade is: In the formula, This represents the number of fatigue cycles under each vibration stress state.

[0034] S4. Based on the cumulative damage value, the remaining fatigue life of the blade is calculated. It should be noted that the specific calculation formula for calculating the remaining fatigue life based on the cumulative damage value in this invention can be found in existing technology and will not be repeated here.

[0035] In some embodiments, the method further includes sending a reminder signal to the unit operator's terminal when the remaining fatigue life of the blade is determined to be zero or approaching zero, to inform the operator to inspect or replace the blade. It is understood that this method can monitor the remaining fatigue life of the blade in real time, and when the remaining fatigue life of the blade approaches zero, it notifies the unit operator to inspect or replace the blade. Of course, the reminder signal can be in the form of voice, text, email notification, etc.

[0036] This embodiment establishes a correction relationship between finite element analysis and experimental data for long blades of nuclear power plant turbines. By using the measured blade vibration displacement and finite element calculations, a more realistic vibration stress is obtained. By determining the flutter region of the long blades during operation, the remaining lifespan of the long blades can be accurately assessed, ensuring the accuracy of blade fatigue life calculations. This makes the blade life assessment range more precise and the data collection more accurate, providing a reliable basis for the safe operation and maintenance of nuclear power turbines and helping to ensure the safe and stable operation of long blades in nuclear power turbines.

[0037] In another preferred embodiment, reference Figure 3 The life assessment system of this embodiment includes: The theoretical vibration stress distribution determination module monitors the vibration displacement of a pre-determined blade flutter region and performs finite element calculations using the vibration displacement as a boundary condition to obtain the theoretical vibration stress distribution of the entire blade.

[0038] The correction module is used to correct the theoretical vibration stress distribution according to a predetermined correction relationship to obtain the actual vibration stress distribution of the entire blade.

[0039] The cumulative damage value calculation module is used to obtain the cumulative damage value of the blade based on the actual blade vibration stress distribution, the fatigue strength coefficient and fatigue strength index of the blade material, and the time when the blade enters the flutter region.

[0040] The life assessment module is used to calculate the remaining fatigue life of the blade based on the cumulative damage value.

[0041] This embodiment first establishes a correction relationship between experimental and finite element calculations. Then, using a data acquisition system—a blade health monitoring system—it identifies the blade flutter region and obtains the actual vibration displacement of the blade within this region. Further, it obtains the vibration stress, fatigue life, and fatigue cycle count under various vibration states. Finally, it uses the cumulative loss formula to calculate the remaining blade life. This embodiment ensures the accuracy of blade fatigue life calculations, making the blade life assessment range more precise and the collected data more accurate. This provides a reliable basis for the safe operation and maintenance of nuclear power turbines, helping to ensure the safe and stable operation of long blades in nuclear power turbines.

[0042] In another preferred embodiment, the computer-readable storage medium of this embodiment stores a computer program adapted for loading by a processor to perform the life assessment steps as described in the above embodiment. This embodiment establishes a correction relationship between finite element analysis and experimental data for the long blades of a nuclear power plant turbine. Based on the actually measured blade vibration displacement, finite element calculations are used to obtain a more realistic vibration stress of the blade. By determining the flutter region of the long blade during operation, the remaining life of the long blade is accurately assessed, thereby ensuring the accuracy of blade fatigue life calculation. This makes the blade life assessment range more precise and the data collection more accurate, providing a reliable basis for the safe operation and maintenance of nuclear power turbines and helping to ensure the safe and stable operation of long blades in nuclear power turbines.

[0043] The computer-readable storage medium of the present invention can be any computer-readable storage medium capable of storing program code, such as a USB flash drive, a portable hard drive, a read-only memory (ROM), a magnetic disk, or an optical disk.

[0044] The processor of this invention provides computing and control capabilities to support the operation of the entire device. It should be understood that, in the embodiments of this application, the processor may be a Central Processing Unit (CPU), or it may be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor.

[0045] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0046] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly by hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0047] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A method for assessing the service life of power components, specifically referring to long blades of nuclear power turbines, characterized in that... Includes the following steps: S1. Monitor the vibration displacement of the predetermined blade flutter region, and perform finite element calculations using the vibration displacement as the boundary condition to obtain the theoretical vibration stress distribution of the entire blade. S2. Correct the theoretical vibration stress distribution according to the predetermined correction relationship to obtain the actual vibration stress distribution of the entire blade; S3. Based on the actual vibration stress distribution, the fatigue strength coefficient and fatigue strength index of the blade material, and the time it takes for the blade to enter the flutter region, the cumulative damage value of the blade is obtained. S4. Based on the cumulative damage value, the remaining fatigue life of the blade is calculated.

2. The life assessment method according to claim 1, characterized in that, The method also includes a step for determining the modified relationship: The relationship between blade tip vibration displacement and blade dynamic stress was determined by long blade dynamic frequency test and finite element calculation, respectively, and a corrected relationship between finite element and test was obtained accordingly.

3. The life assessment method according to claim 2, characterized in that, The step of determining the correction relationship includes: The experimental ratio between the blade tip vibration displacement and the blade dynamic stress was determined through dynamic frequency tests on long blades, as follows: The theoretical ratio between the blade tip vibration displacement and the blade dynamic stress was determined through finite element analysis, as follows: Therefore, the correction factor between the finite element method and the experiment is obtained as follows: Where i represents the i-th mode of the blade; The blade tip vibration displacement is measured during a dynamic frequency test of a long blade under the i-th mode of the blade. The vibration stress is measured during dynamic frequency testing of a long blade under the i-th mode of the blade. The blade tip vibration displacement is obtained from the finite element analysis under the i-th mode of the blade. The vibration stress is obtained from the finite element analysis of the i-th mode of the blade.

4. The life assessment method according to claim 1, characterized in that, The method also includes a step for determining the blade flutter region: During the load increase and decrease process of the low-pressure cylinder of the nuclear power unit, the low-pressure cylinder flow range G1-G2 and the corresponding back pressure range Pb1-Pb2 when the blade vibration exceeds the limit are monitored. A quadrilateral area is formed by point A with coordinates (Pb1, G1) and point B with coordinates (Pb2, G2) as the diagonal vertices, and this area is regarded as the flutter area of ​​the low-pressure last stage moving blade.

5. The life assessment method according to claim 1, characterized in that, Step S3 includes: S3-1: The fatigue life of the blade corresponding to each vibration stress state is calculated based on the actual blade vibration stress distribution, the fatigue strength coefficient of the blade material, and the fatigue strength index of the blade material. S3-2: Statistically determine the number of fatigue cycles under each vibration stress state based on the time it takes for the blade to enter the flutter region each time. S3-3: The cumulative damage value is calculated based on the blade fatigue life corresponding to each vibration stress state and the number of fatigue cycles under each vibration stress state.

6. The life assessment method according to claim 5, characterized in that, In step S3-1, the calculation formula is obtained using the Basquin equation: In the formula, The blade vibration stress amplitude is obtained based on the actual blade vibration stress distribution. The fatigue strength coefficient of the blade material, in MPa; The fatigue strength index of the blade material; This represents the blade fatigue life corresponding to each vibration stress state.

7. The life assessment method according to claim 6, characterized in that, In step S3-3, the formula for calculating the cumulative damage value of the blade is: In the formula, This represents the number of fatigue cycles under each vibration stress state.

8. The life assessment method according to claim 1, characterized in that, The method also includes: When it is determined that the remaining fatigue life of the blade is approaching zero, a reminder signal is sent to the terminal of the unit operator to inform him to check or replace the blade.

9. A service life assessment system for power components, specifically referring to long blades of nuclear power turbines, characterized in that, include: The theoretical vibration stress distribution determination module monitors the vibration displacement of a pre-determined blade flutter region and performs finite element calculations using the vibration displacement as boundary conditions to obtain the theoretical vibration stress distribution of the entire blade. The correction module is used to correct the theoretical vibration stress distribution according to a predetermined correction relationship to obtain the actual vibration stress distribution of the entire blade. The cumulative damage value calculation module is used to obtain the cumulative damage value of the blade based on the actual blade vibration stress distribution, the fatigue strength coefficient and fatigue strength index of the blade material, and the time when the blade enters the flutter region. The life assessment module is used to calculate the remaining fatigue life of the blade based on the cumulative damage value.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program adapted for loading by a processor to perform the life assessment steps as described in any one of claims 1 to 8.

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