Method for estimating stress of mechanical structure and method for monitoring mechanical structure

Abstract

The present invention provides a method for estimating the stress of a mechanical structure and a method for monitoring the mechanical structure, which can grasp the state of the evaluation object position of the mechanical structure during the operation of the mechanical structure without stopping the operation of the mechanical structure. The stress estimation method of the mechanical structure according to the embodiment includes a calculation process for calculating the relationship between the stress generated at the evaluation object position during the excitation of the mechanical structure and the physical quantity including sound pressure or vibration generated at a detection position different from the evaluation object position. In addition, the stress estimation method of the mechanical structure includes a detection process for detecting the physical quantity generated at the detection position during the operation of the mechanical structure. In addition, the stress estimation method of the mechanical structure includes an estimation process for estimating the stress generated at the evaluation object position during the operation of the mechanical structure based on the relationship calculated in the calculation process and the physical quantity detected in the detection process.

Description

Technical Field

[0001] Embodiments of the present invention relate to a method for estimating stress in a mechanical structure and a method for monitoring a mechanical structure. Background Art

[0002] Generally, the stress generated at the evaluation target position of a mechanical structure can be grasped by measuring with a stress sensor such as a strain gauge attached to the evaluation target position. However, when the mechanical structure is in operation, it is sometimes difficult to attach a stress sensor to the evaluation target position. In addition, in order to attach a stress sensor to the mechanical structure, it may be necessary to stop the operation of the mechanical structure, and there may be an opportunity loss due to the operation stop.

[0003] For example, when the mechanical structure is a hydraulic structure such as a Francis turbine, in order to grasp the state of the runner blades of the runner during the operation of the hydraulic structure, it is considered to measure the stress generated in the runner blades during the operation of the hydraulic structure. In this case, since the runner is a part that rotates at high speed under pressure from running water during the operation of the hydraulic structure, it is difficult to attach a stress sensor to the runner blades. In addition, even if it is assumed that a stress sensor is attached, in order to attach the stress sensor to the runner blades, it is necessary to stop the operation of the hydraulic structure. More specifically, to stop the operation of the hydraulic structure, the water is pumped out from the hydraulic structure, and then the upper cover is removed and the runner is lifted out together with the main shaft. In order to perform the stress sensor attachment operation, the operator has to enter the hydraulic structure through the maintenance holes provided in the casing and the draft tube. Therefore, the operation stop period of the hydraulic structure becomes longer, and the maintenance and inspection work of the hydraulic structure also increases, and there may be an opportunity loss due to the operation stop of the hydraulic structure.

[0004] As such a configuration, there is Japanese Patent Publication Gazette, Japanese Unexamined Patent Application Publication No. 2013-41448 (hereinafter referred to as Patent Document 1). Summary of the Invention

[0005] The present invention has been made in view of such circumstances, and an object thereof is to provide a method for estimating stress in a mechanical structure and a method for monitoring a mechanical structure, which can grasp the state of the evaluation target position of the mechanical structure during the operation of the mechanical structure without stopping the operation of the mechanical structure.

[0006] The stress estimation method of the mechanical structure according to the embodiment is a method for estimating the stress generated at the evaluation target position of the mechanical structure during the operation of the mechanical structure. The stress estimation method of the mechanical structure includes a calculation process for calculating the relationship between the stress generated at the evaluation target position during the excitation of the mechanical structure and the physical quantity including sound pressure or vibration generated at a detection position different from the evaluation target position. In addition, the stress estimation method of the mechanical structure includes a detection process for detecting the physical quantity generated at the detection position during the operation of the mechanical structure. In addition, the stress estimation method of the mechanical structure includes an estimation process for estimating the stress generated at the evaluation target position of the mechanical structure during the operation of the mechanical structure based on the relationship calculated in the calculation process and the physical quantity detected in the detection process.

[0007] In addition, the monitoring method of the mechanical structure according to the embodiment is a method for monitoring the state of the evaluation target position of the mechanical structure during the operation of the mechanical structure. The monitoring method of the mechanical structure includes a calculation process for calculating the relationship between the stress generated at the evaluation target position during the excitation of the mechanical structure and the physical quantity including sound pressure or vibration generated at a detection position different from the evaluation target position. In addition, the monitoring method of the mechanical structure includes a determination process for determining the notification threshold of the physical quantity during the operation of the mechanical structure based on the relationship calculated in the calculation process and the allowable stress of the set evaluation target position. In addition, the monitoring method of the mechanical structure includes: a detection process for detecting the physical quantity generated at the detection position during the operation of the mechanical structure; and a notification process for notifying that the physical quantity detected in the detection process exceeds the notification threshold.

[0008] Advantages of the Invention

[0009] According to the present invention, it is possible to grasp the state of the evaluation target position of the mechanical structure during the operation of the mechanical structure without stopping the operation of the mechanical structure. Description of the Drawings

[0010] Figure 1 is a meridional sectional view of a Francis turbine according to the embodiment.

[0011] Figure 2 is Figure 1 a partially enlarged sectional view of

[0012] Figure 3 is Figure 2 a modified example of

[0013] Figure 4 is Figure 2 a modified example of

[0014] Description of Reference Numerals

[0015] 1: Francis turbine; 5: impeller; P2: position of the object to be evaluated; P3: detection position. Detailed implementation mode

[0016] Hereinafter, with reference to the drawings, a method for estimating the stress of a mechanical structure and a method for monitoring a mechanical structure according to an embodiment of the present invention will be described.

[0017] (First Embodiment)

[0018] First, use Figure 1 and Figure 2 to describe a water turbine structure, especially a Francis turbine, as an example of the mechanical structure of this embodiment. Hereinafter, the description will be made according to the flow of water during the operation of the water turbine.

[0019] As Figure 1 shown, the Francis turbine 1 includes a casing 2, a plurality of stay vanes 3, a plurality of guide vanes 4, an impeller 5, a generator 6, and a draft tube 7.

[0020] The casing 2 is formed in a spiral shape and is configured such that water flows into the water turbine from an upper pond through a penstock (both not shown) during the operation of the water turbine, and the water flows inside. As Figure 2 shown, a maintenance hole 10 is provided in the casing 2. The maintenance hole 10 is covered by a maintenance hole cover 10a. During the maintenance of the Francis turbine 1, the maintenance hole cover 10a is removed, and an operator can enter the inside of the casing 2 from the maintenance hole 10.

[0021] The stay vanes 3 are provided on the downstream side of the casing 2. The stay vanes 3 are configured to guide the water flowing into the casing 2 to the guide vanes 4. The stay vanes 3 are arranged at a predetermined interval in the circumferential direction. A flow path for water flow is formed between the stay vanes 3.

[0022] The guide vanes 4 are provided on the downstream side of the stay vanes 3. The guide vanes 4 are configured to guide the water flowing in from the stay vanes 3 to the impeller 5. The guide vanes 4 are arranged at a predetermined interval in the circumferential direction. A flow path for water flow is formed between the guide vanes 4. Each guide vane 4 is configured to be rotatable, and by rotating each guide vane 4, the opening degree can be changed, and the flow rate of the water guided to the impeller 5 can be adjusted. In this way, the power generation amount of the generator 6 described later can be adjusted.

[0023] The impeller 5 is disposed on the downstream side of the guide vane 4. The impeller 5 is configured to be rotatable about the rotation axis X with respect to the housing 2, and is rotationally driven by the water flowing in from the guide vane 4. The impeller 5 has a crown 12 connected to the main shaft 11 (rotation shaft), a hub 13 provided on the outer peripheral side of the crown 12, and a plurality of impeller blades 14 provided between the crown 12 and the hub 13. The impeller blades 14 are arranged at a prescribed interval in the circumferential direction. Each impeller blade 14 is joined to the crown 12 and the hub 13 respectively. Flow paths for water flow are formed between the impeller blades 14. The water from the guide vane 4 flows in the flow paths, and each impeller blade 14 is pressured by the water to rotationally drive the impeller 5. Thus, the pressure energy of the water flowing into the impeller 5 is converted into rotational energy.

[0024] As Figure 2 shown, an upper cover 15 is provided above the impeller 5. That is, the upper part of the impeller 5 is covered by the upper cover 15. The upper cover 15 extends from above the guide vane 4 to above the crown 12.

[0025] In addition, as Figure 2 shown, a lower cover 16 is provided below the impeller 5. That is, the lower part of the impeller 5 is covered by the lower cover 16. The lower cover 16 extends from below the guide vane 4 to below the hub 13.

[0026] The generator 6 is connected to the impeller 5 via the main shaft 11. The generator 6 is configured such that during the operation of the water turbine, the rotational energy of the impeller 5 is transmitted to generate electricity. Additionally, the generator 6 may also be configured to have the function of a motor, and rotationally drive the impeller 5 by being supplied with electricity. In this case, the water in the lower pond can be pumped up and discharged into the upper pond via the draft tube 7 described later, and the Francis turbine 1 can be operated as a pump turbine (pumping operation). At this time, the opening degree of the guide vane 4 is changed to an appropriate pumping volume according to the pump head.

[0027] The draft tube 7 is provided on the downstream side of the impeller 5. The draft tube 7 is connected to a lower pond or a water discharge passage (not shown), and the water after rotationally driving the impeller 5 restores pressure and is discharged into the lower pond or the water discharge passage.

[0028] As Figure 1 and Figure 2 shown, a maintenance hole 20 is provided on the wall surface of the draft tube 7. As Figure 2 shown, the maintenance hole 20 is provided near the outlet end 14a of the impeller blade of the impeller 5 and below the lower cover 16. The maintenance hole 20 is connected to a maintenance passage 22 from the inside of the draft tube 7. The maintenance hole 20 is covered by a maintenance hole cover 21. During the maintenance of the Francis turbine 1, the maintenance hole cover 21 is removed, and an operator can enter the inside of the draft tube 7 through the maintenance passage 22.

[0029] In the case of operating the Francis turbine 1 configured as described above, when the turbine is in operation, water flows from the upper reservoir through the penstock, the casing 2, and the stay vanes 3 into the guide vanes 4, and then from the guide vanes 4 into the impeller 5. The water flowing into the impeller 5 drives the impeller 5 to rotate. The rotationally driven impeller 5 transmits rotational energy to the generator 6 via the connected main shaft 11 to generate electricity in the generator 6. The water flowing into the impeller 5 flows out into the draft tube 7 after passing through the impeller 5 and is discharged into the lower reservoir through the draft tube 7.

[0030] Here, when water flows out from the impeller 5, Karman's vortices may be generated on the downstream side of the impeller blade outlet end 14a of the impeller blade 14. These Karman's vortices may cause pressure pulsations in the draft tube 7, resulting in significant vibrations and noise, and generating stress concentrated at the impeller blade root 14b. Due to this stress, the impeller blade 14 may break at the impeller blade root 14b. To avoid such breakage of the impeller blade 14, it is important to determine the stress Sb generated at the impeller blade root 14b during the operation of the Francis turbine 1.

[0031] Next, a method for estimating the stress of the mechanical structure according to the first embodiment of the present invention will be described. The method for estimating the stress of the mechanical structure in this embodiment is a method for estimating the stress generated at the evaluation target position of the mechanical structure during the operation of the mechanical structure. Hereinafter, a method for estimating the stress generated at the impeller blade root 14b during the operation of the Francis turbine 1 using the method for estimating the stress of the mechanical structure in this embodiment will be described.

[0032] The method for estimating the stress of the mechanical structure in this embodiment includes a determination step of determining the evaluation target frequency fr, a calculation step of calculating the relationship between the stress Sa and the sound pressure La during excitation, a detection step of detecting the sound pressure Lb during operation, and an estimation step of estimating the stress Sb during operation. Hereinafter, each step will be described.

[0033] First, a determination process is performed. In this determination process, the evaluation object frequency fr is determined. The determination process includes a process of selecting the vibration phenomenon to be evaluated and a process of determining the evaluation object frequency fr. In the process of selecting the vibration phenomenon to be evaluated, for example, the vibration phenomenon caused by the von Kármán vortex generated downstream of the outlet end 14a of the impeller blade can be selected as the evaluation object. In the process of determining the evaluation object frequency fr, the main frequency vibration of the vibration phenomenon selected as the evaluation object is determined as the evaluation object frequency fr. For example, when the vibration phenomenon caused by the above-mentioned von Kármán vortex is selected as the evaluation object, the main frequency vibration of the von Kármán vortex can be calculated according to the operating conditions such as the flow rate of the water turbine. Here, the evaluation object frequency fr can be a specific single frequency, but it can also be a frequency band with a certain range width.

[0034] Next, a calculation process is performed. In this calculation process, the relationship between the stress Sa generated at the evaluation object position P2 and the sound pressure La generated at the detection position P3 during excitation at the excitation position P1 of the mechanical structure is calculated. More specifically, the ratio of the sound pressure La generated at the detection position P3 to the stress Sa generated at the evaluation object position P2 when the excitation position P1 is excited at the above-mentioned evaluation object frequency fr is calculated. That is, the stress-sound pressure transfer function H between the evaluation object position P2 and the detection position P3 at the evaluation object frequency fr is calculated. This transfer function H can be expressed by the following formula (1).

[0035]

Equation 1

[0036]

[0037] The excitation position P1, the evaluation object position P2, and the detection position P3 can be set at arbitrary positions respectively. The evaluation object position P2 can be set at a position different from the excitation position P1, or can be set at the same position as the excitation position P1. The detection position P3 is set at a position different from the excitation position P1 and the evaluation object position P2. For example, when the vibration phenomenon caused by the above-mentioned von Kármán vortex is used as the evaluation object, von Kármán vortices are generated near the outlet end 14a of the impeller blade (downstream of the outlet end 14a of the impeller blade). Therefore, as Figure 2 shown, the excitation position P1 can be set at the outlet end 14a of the impeller blade. In Figure 2 the example shown, the excitation position P1 is set at the central part of the outlet end 14a of the impeller blade. In addition, as Figure 2 shown, the evaluation object position P2 can be set at the impeller blade root 14b where the stress caused by the von Kármán vortex is concentrated. In Figure 2 the example shown, the evaluation object position P2 is set at the impeller blade root 14b on the side of the bush 13. In addition, asFigure 2 As shown, the detection position P3 can be set within the maintenance passage 22 so as to be able to detect the sound pressure La generated by the pressure pulsation generated in the suction pipe 7 due to the Karman vortex. In this way, it is possible to calculate the relationship between the stress Sa generated at the evaluation object position P2 provided at the root 14b of the impeller blade and the sound pressure La generated at the detection position P3 provided within the maintenance passage 22 when exciting the excitation position P1 provided at the outlet end 14a of the impeller blade by simulating the vibration phenomenon caused by the Karman vortex.

[0038] The relationship (transfer function H) between the stress Sa and the sound pressure La can also be calculated by computer simulation. That is, it is possible to calculate the stress Sa generated at the evaluation object position P2 when exciting the excitation position P1 at the evaluation object frequency fr by performing a frequency response analysis using a calculation model having the same structure as the above-mentioned Francis turbine 1. In addition, it is also possible to calculate the sound pressure La generated at the detection position P3 by combining acoustic analysis. Here, in the frequency response analysis, it is also possible to simulate the operation of the Francis turbine 1 and use a calculation model filled with water inside. And it is also possible to calculate the relationship (transfer function H) between the stress Sa and the sound pressure La by substituting the stress Sa and the sound pressure La calculated in this way into the above formula (1).

[0039] Next, a detection process is performed. In this detection process, the sound pressure Lb generated at the detection position P3 during the operation of the mechanical structure is detected. The sound pressure Lb can also be detected by a sound pressure sensor 30 such as a microphone. That is, as Figure 2 shown, the sound pressure sensor 30 can also be provided at the detection position P3 provided within the maintenance passage 22, and the sound pressure Lb during the operation of the Francis turbine 1 can be detected by the sound pressure sensor 30. As described above, in the case where the Karman vortex is generated, pressure pulsation is generated in the suction pipe 7, and relatively large noise may be generated. The sound pressure sensor 30 can detect the sound pressure Lb of this noise. More specifically, the sound pressure Lb at the above-mentioned evaluation object frequency fr is detected. For example, it is also possible to perform FFT (Fast Fourier Transform) analysis on the measurement data after measuring the noise with the sound pressure sensor 30 in a wide frequency band (for example, 0 to 20 kHz), and extract the sound pressure Lb at the determined frequency fr from the spectrum obtained thereby, so as to obtain the sound pressure Lb. The sound pressure sensor 30 can also be a sensor suitable for detecting the sound pressure at the evaluation object frequency fr. That is, it is also possible to use the sound pressure sensor 30 having a higher sensitivity at the evaluation object frequency fr.

[0040] After that, a presumption process is performed. In this presumption process, based on the relationship between the stress Sa calculated in the calculation process and the sound pressure La, and the sound pressure Lb detected in the detection process, the stress Sb generated at the evaluation target position P2 during the operation of the mechanical structure is presumed. More specifically, the stress Sb at the above-mentioned evaluation target frequency fr is presumed. As described above, the relationship (transfer function H) between the stress Sa generated at the evaluation target position P2 when the excitation position P1 of the mechanical structure is excited and the sound pressure La generated at the detection position P3 can be expressed by the above formula (1). On the other hand, the same relationship also holds between the stress Sb generated at the evaluation target position P2 and the sound pressure Lb generated at the detection position P3 when vibration is generated at the excitation position P1 of the mechanical structure. Therefore, the stress Sb generated at the evaluation target position P2 can be expressed by the following formula (2).

[0041]

Equation 2

[0042]

[0043] By substituting the transfer function H calculated by the above formula (1) in the above formula (2) and the sound pressure Lb detected in the detection process, the stress Sb generated at the evaluation target position P2 can be calculated.

[0044] In this way, by using the stress presumption method of the mechanical structure of the present embodiment, the stress Sb generated at the root 14b of the impeller blade during the operation of the Francis turbine 1 due to the vibration phenomenon caused by the Karman vortex can be presumed.

[0045] In this way, according to the present embodiment, based on the relationship between the stress Sa generated at the evaluation target position P2 when the mechanical structure is excited and the sound pressure La generated at the detection position P3, and the sound pressure Lb generated at the detection position P3 during the operation of the mechanical structure, the stress Sb generated at the evaluation target position P2 during the operation of the mechanical structure can be presumed. In this way, by pre-calculating the relationship between the stress Sa generated at the evaluation target position P2 when the mechanical structure is excited and the sound pressure La generated at the detection position P3, the stress Sb generated at the evaluation target position P2 during the operation of the mechanical structure can be presumed according to the sound pressure Lb generated at the detection position P3 during the operation of the mechanical structure. Therefore, without stopping the operation of the mechanical structure, the state of the evaluation target position P2 of the mechanical structure during the operation of the mechanical structure can be grasped.

[0046] In addition, according to the present embodiment, the relationship between the stress Sa generated at the evaluation target position P2 during the excitation of the mechanical structure and the sound pressure La generated at the detection position P3 is calculated by computer simulation. In this way, by using computer simulation, it is possible to easily calculate the relationship between the stress Sa and the sound pressure La without conducting experiments. In addition, in computer simulation, a calculation model in which the interior is filled with water, such as a water turbine structure, can be used to calculate the relationship between the stress Sa and the sound pressure La. Therefore, the relationship between the stress Sa and the sound pressure La can be calculated in a state close to the operating state, and the estimation accuracy of the stress Sb can be improved.

[0047] In addition, according to the present embodiment, the mechanical structure includes an impeller 5 that rotates under pressure from a fluid, and the evaluation target position P2 is provided on the impeller 5. In this way, when the evaluation target position P2 is provided on a rotating device that rotates under pressure from a fluid during operation, it is difficult to attach a stress sensor such as a strain gauge at the evaluation target position P2. In addition, even if it is assumed that a stress sensor is attached, in order to attach the stress sensor, the operation of the mechanical structure has to be stopped, and there may be an opportunity loss due to the operation stop. In contrast, according to the present embodiment, even when the evaluation target position P2 is provided on such a rotating device, the stress Sb generated at the evaluation target position P2 during the operation of the mechanical structure can be estimated. Therefore, it is not necessary to stop the operation of the mechanical structure, and the state of the evaluation target position P2 of the mechanical structure during the operation of the mechanical structure can be grasped.

[0048] In addition, according to the present embodiment, the mechanical structure is a water turbine structure. In this way, when the mechanical structure is a water turbine structure, it is difficult to attach a stress sensor inside the water turbine structure during the operation of the water turbine structure. In addition, even if it is assumed that a stress sensor is attached, in order to attach the stress sensor inside the water turbine structure, the operation of the water turbine structure has to be stopped. In this case, sometimes the stress sensor attachment operation is performed after pumping out the water from inside the water turbine structure, the operation stop period of the water turbine structure becomes longer, and the maintenance and inspection work of the water turbine structure also increases, and there may be an opportunity loss due to the operation stop of the water turbine structure. In contrast, according to the present embodiment, the stress Sb generated at any evaluation target position P2 of the water turbine structure during the operation of the water turbine structure can be estimated. Therefore, it is not necessary to stop the operation of the mechanical structure, and the state of the evaluation target position P2 of the mechanical structure during the operation of the mechanical structure can be grasped.

[0049] (First Modification of the First Embodiment)

[0050] In the above-described embodiment, an example was described in which, based on the relationship between the stress Sa generated at the evaluation object position P2 during the excitation of the mechanical structure and the sound pressure La generated at the detection position P3, and the sound pressure Lb generated at the detection position P3 during the operation of the mechanical structure, the stress Sb generated at the evaluation object position P2 during the operation of the mechanical structure was estimated. However, it is not limited thereto, and the stress Sb generated at the evaluation object position P2 during the operation of the mechanical structure may also be estimated based on the relationship between the stress Sa generated at the evaluation object position P2 during the excitation of the mechanical structure and the vibration Va generated at the detection position P3, and the vibration Vb generated at the detection position P3 during the operation of the mechanical structure.

[0051] In this case, in the calculation process, the relationship between the stress Sa generated at the evaluation object position P2 during the excitation at the excitation position P1 of the mechanical structure and the vibration Va generated at the detection position P3 is calculated. More specifically, the ratio of the vibration Va generated at the detection position P3 to the stress Sa generated at the evaluation object position P2 when the excitation position P1 is excited at the above-described evaluation object frequency fr is calculated. That is, the stress-vibration transfer function H between the evaluation object position P2 and the detection position P3 at the evaluation object frequency fr is calculated. This transfer function H can be represented by the following formula (3).

[0052]

Equation 3

[0053]

[0054] Here, the detection position P3 can be set at any position of the mechanical structure as long as it can detect the vibration generated during the operation of the mechanical structure. For example, as Figure 3 shown, the detection position P3 can also be set on the maintenance hole cover 21.

[0055] The relationship (transfer function H) between the stress Sa and the vibration Va can also be calculated by computer simulation. That is, the stress Sa generated at the evaluation object position P2 and the vibration Va generated at the detection position P3 when the excitation position P1 is excited at the evaluation object frequency fr can be calculated by performing a frequency response analysis using a calculation model having the same structure as the above-described Francis turbine 1. Here, in the frequency response analysis, the operation of the Francis turbine 1 can be simulated, and a calculation model filled with water inside can be used. And the relationship (transfer function H) between the stress Sa and the vibration Va can also be calculated by substituting the stress Sa and the vibration Va calculated in this way into the above formula (3).

[0056] In addition, in the detection process, vibration Vb generated at the detection position P3 during the operation of the mechanical structure is detected. Vibration Vb can also be detected by a vibration sensor 32 such as an acceleration sensor. That is, as Figure 3 shown, it can also be configured such that the vibration sensor 32 is provided at the detection position P3 provided on the maintenance hole cover 21, and the vibration Vb during the operation of the Francis turbine 1 is detected by the vibration sensor 32. As described above, in the case where Karman vortices are generated, pressure pulsations are generated in the draft tube 7, and relatively large vibrations may be generated. The vibration sensor 32 can detect this vibration Vb. More specifically, vibration Vb at the above-mentioned evaluation target frequency fr is detected. For example, after vibration measurement is performed by the vibration sensor 32 in a wide frequency band (e.g., 0 to 20 kHz), the measurement data can be subjected to FFT analysis, and vibration Vb at the determined frequency fr can be extracted from the resulting frequency spectrum, thereby obtaining vibration Vb. The vibration sensor 32 can also be a sensor suitable for detecting vibration at the evaluation target frequency fr. That is, a vibration sensor 32 having a relatively high sensitivity at the evaluation target frequency fr can also be used.

[0057] In addition, in the estimation process, based on the relationship between the stress Sa calculated in the calculation process and the vibration Va, and the vibration Vb detected in the detection process, the stress Sb generated at the evaluation target position P2 during the operation of the mechanical structure is estimated. More specifically, the stress Sb at the above-mentioned evaluation target frequency fr is estimated. As described above, the relationship (transfer function H) between the stress Sa generated at the evaluation target position P2 when the excitation position P1 of the mechanical structure is excited and the vibration Va generated at the detection position P3 can be represented by the above formula (3). On the other hand, the same relationship also holds between the stress Sb generated at the evaluation target position P2 when vibration is generated at the excitation position P1 of the mechanical structure and the vibration Vb generated at the detection position P3. Therefore, the stress Sb generated at the evaluation target position P2 can be represented by the following formula (4).

[0058]

Equation 4

[0059]

[0060] By substituting the transfer function H calculated by the above formula (3) in the calculation process and the vibration Vb detected in the detection process into the above formula (4), the stress Sb generated at the evaluation target position P2 can be calculated.

[0061] In this way, using the stress estimation method for the mechanical structure of this modified example, the stress Sb generated at the root 14b of the impeller blade during the operation of the Francis turbine 1 due to the vibration phenomenon caused by Karman vortices can be estimated.

[0062] Thus, according to this modified example, it is possible to estimate the stress Sb generated at the evaluation object position P2 during the operation of the mechanical structure based on the relationship between the stress Sa generated at the evaluation object position P2 during the excitation of the mechanical structure and the vibration Va generated at the detection position P3, and the vibration Vb generated at the detection position P3 during the operation of the mechanical structure. Thus, it is possible to estimate the stress Sb generated at the evaluation object position P2 during the operation of the mechanical structure based on the relationship between the stress Sa generated at the evaluation object position P2 during the excitation of the mechanical structure and the physical quantity including the sound pressure La or the vibration Va generated at the detection position P3, and the physical quantity generated at the detection position P3 during the operation of the mechanical structure.

[0063] In addition, according to this modified example, it is possible to eliminate the calculation error caused by the acoustic analysis of the part where the sound pressure propagates in the air, and improve the estimation accuracy of the stress Sb.

[0064] (Second Modified Example of the First Embodiment)

[0065] In the above embodiment, an example in which the relationship between the stress Sa and the sound pressure La is calculated by computer simulation is described. However, it is not limited thereto, and the relationship between the stress Sa and the sound pressure La can also be calculated by an excitation experiment.

[0066] In this case, in the calculation process, for example, when the Francis turbine 1 stops, an operator can enter the inside of the Francis turbine 1 from the maintenance hole 10 provided in the casing 2 or the maintenance hole 20 provided in the draft tube 7, paste a stress sensor such as a strain gauge at the evaluation object position P2 provided at the root 14b of the impeller blade, and excite the excitation position P1 provided at the outlet end 14a of the impeller blade by a hammer or a shaker to obtain the stress Sa generated at the evaluation object position P2 and the sound pressure La generated at the detection position P3. Then, by substituting the stress Sa and the sound pressure La obtained in this way into the above formula (1), the relationship (transfer function H) between the stress Sa and the sound pressure La is calculated.

[0067] Instead of computer simulation, the relationship between the stress Sa and the sound pressure La can also be calculated by such an excitation experiment.

[0068] According to this modified example, it is possible to calculate the relationship between the stress Sa and the sound pressure La without performing computer simulation. In addition, it is possible to eliminate the calculation error caused by computer simulation and improve the estimation accuracy of the stress Sb.

[0069] (Third Modified Example of the First Embodiment)

[0070] In addition, in the above-described embodiment, the relationship between the stress Sa and the sound pressure La can also be calculated by a combination of computer simulation and excitation experiments.

[0071] In this case, in the calculation process, for example, as Figure 4 shown, the stress Sa generated at the evaluation object position P2 provided at the root 14b of the impeller blade when exciting the excitation position P1 provided at the outlet end 14a of the impeller blade and the stress Sm generated at the relay position P4 provided at the maintenance hole cover 21 are calculated by computer simulation. Thus, the transfer function H1 between the evaluation object position P2 and the relay position P4 can be obtained. In addition, the sound pressure Lm generated at the detection position P3 provided in the maintenance passage 22 when exciting the relay position P4 is obtained through an excitation experiment. Thus, the transfer function H2 between the relay position P4 and the detection position P3 can be obtained. By multiplying these transfer functions H1 obtained by computer simulation and the transfer function H2 obtained by the excitation experiment, the transfer function H between the evaluation object position P2 and the detection position P3 can be obtained.

[0072] In this way, by combining computer simulation and excitation experiments, the relationship between the stress Sa and the sound pressure La can be calculated.

[0073] According to this modified example, by performing computer simulation on the part filled with water inside the hydraulic turbine structure, the calculation accuracy can be improved, and by performing excitation experiments on the part where the sound pressure propagates in the air, calculation errors can be eliminated. Therefore, the estimation accuracy of the stress Sb can be further improved.

[0074] (Other modified examples of the first embodiment)

[0075] In the above-described embodiment, an example in which the evaluation object position P2 is provided on the impeller 5 has been described. However, it is not limited thereto, and the evaluation object position P2 can also be provided at any position. For example, the evaluation object position P2 can also be provided on the stay vane 3 and the guide vane 4. In this case, the stress generated on the stay vane 3 and the guide vane 4 during the operation of the Francis turbine 1 can be calculated. In addition, the excitation position P1 can also be provided at a position other than the impeller 5. In this case, vibration phenomena other than the vibration phenomenon caused by the Karman vortex can be used as the evaluation object. In addition, the detection position P3 can be provided at any other position as long as it can detect the sound pressure and vibration caused by this vibration phenomenon.

[0076] In addition, in the above-described embodiment, an example where the mechanical structure is a water turbine structure has been described. However, it is not limited thereto, and the mechanical structure may also be a turbine structure such as a steam turbine or a gas turbine. In this case, the excitation position P1 and the evaluation target position P2 can also be set on the rotating device of the turbine structure. Furthermore, the mechanical structure is not limited to a water turbine structure or a turbine structure, and may be any other mechanical structure.

[0077] (Second Embodiment)

[0078] Next, a method for monitoring a mechanical structure according to a second embodiment of the present invention will be described.

[0079] In the second embodiment, the method for monitoring a mechanical structure is mainly different from that of the first embodiment Figures 1 to 4 shown in that it includes a determination step of determining a notification threshold of the sound pressure during operation of the mechanical structure based on the relationship calculated in the calculation step and the allowable stress at the set evaluation target position, and a notification step of notifying that the sound pressure detected in the detection step exceeds the notification threshold, and the other configurations are substantially the same. In addition, in the second embodiment, the same parts as those in the first embodiment Figures 1 to 4 shown are denoted by the same reference numerals and detailed descriptions thereof are omitted.

[0080] The method for monitoring a mechanical structure in the present embodiment is a method for monitoring the state of an evaluation target position of a mechanical structure during operation of the mechanical structure. Hereinafter, a method for monitoring the state of the root portion 14b of the impeller blade during operation of the Francis turbine 1 using the method for monitoring a mechanical structure in the present embodiment will be described.

[0081] The method for monitoring a mechanical structure in the present embodiment includes a determination step of determining an evaluation target frequency fr, a calculation step of calculating the relationship between the stress Sa and the sound pressure La during excitation, a determination step of determining a notification threshold Lt of the sound pressure during operation, a detection step of detecting the sound pressure Lb during operation, and a notification step of notifying that the sound pressure Lb during operation exceeds the notification threshold Lt. Hereinafter, each step will be described.

[0082] First, the determination step is performed. In this determination step, the evaluation target frequency fr is determined. Here, the same as in the above-described first embodiment, the main frequency vibration of the vibration phenomenon caused by the Karman vortex generated on the downstream side of the outlet end portion 14a of the impeller blade can be determined as the evaluation target frequency fr.

[0083] Next, a calculation process is performed. In this calculation process, the relationship between the stress Sa generated at the evaluation object position P2 during the excitation at the excitation position P1 of the mechanical structure and the sound pressure La generated at the detection position P3 is calculated. Here, similar to the first embodiment described above, through the above formula (1), the transfer function H of the stress-sound pressure between the evaluation object position P2 and the detection position P3 at the evaluation object frequency fr can be calculated. In addition, similar to the first embodiment described above, the excitation position P1 can be set at the outlet end 14a of the impeller blade, the evaluation object position P2 can be set at the root 14b of the impeller blade, and the detection position P3 can be set within the maintenance passage 22 (refer to Figure 2 ). In addition, similar to the first embodiment described above, the relationship (transfer function H) between the stress Sa and the sound pressure La can be calculated by computer simulation.

[0084] Next, a determination process is performed. In this determination process, based on the relationship calculated in the calculation process and the allowable stress Sc of the set evaluation object position P2, the notification threshold Lt of the sound pressure during the operation of the mechanical structure is determined. More specifically, the allowable stress Sc of the evaluation object position P2 at the above evaluation object frequency fr is set, and the notification threshold Lt of the sound pressure at the evaluation object frequency fr is determined. Here, the allowable stress Sc refers to the maximum allowable stress allowed to be generated at the evaluation object position P2 of the mechanical structure. When the evaluation object position P2 is set at the root 14b of the impeller blade, the allowable stress Sc is the maximum allowable stress allowed to be generated at the root 14b of the impeller blade, and is a design value determined according to the type and material of the impeller blade 14. In the Francis turbine 1, in order to avoid damage to the impeller blade 14, it is required to operate in such a way that the stress generated at the root 14b of the impeller blade does not exceed the allowable stress Sc. The notification threshold Lt of the sound pressure can be expressed by the following formula (5).

[0085]

Equation 5

[0086] L t =HS c ....(5)

[0087] By substituting the transfer function H calculated by the above formula (1) in the calculation process and the allowable stress Sc of the evaluation object position P2 into the above formula (5), the notification threshold Lt of the sound pressure can be calculated. This notification threshold Lt corresponds to the sound pressure generated at the detection position P3 when a stress equal to the allowable stress Sc is generated at the evaluation object position P2, and means that when a sound pressure exceeding this notification threshold Lt is detected at the detection position P3, a stress exceeding the allowable stress Sc is generated at the evaluation object position P2.

[0088] After that, an inspection process is performed. In this inspection process, the sound pressure Lb generated at the inspection position P3 during the operation of the mechanical structure is inspected. Here, similar to the first embodiment described above, a sound pressure sensor 30 is provided at the inspection position P3 provided in the maintenance passage 22, and the sound pressure Lb during the operation of the Francis turbine 1 can be detected by the sound pressure sensor 30 (refer to Figure 2 ). More specifically, the sound pressure Lb at the above-mentioned evaluation target frequency fr is detected.

[0089] Then, a notification process is performed. In this notification process, it is notified that the sound pressure Lb detected in the inspection process exceeds the notification threshold Lt. The notification process may be performed simultaneously with the inspection process. More specifically, during the period when the sound pressure Lb is detected in the inspection process, when the detected sound pressure Lb exceeds the notification threshold Lt, the notification process may be performed. Here, the sound pressure Lb and the notification threshold Lt are compared at the above-mentioned evaluation target frequency fr, and when the sound pressure Lb exceeds the notification threshold Lt, this situation is notified. The notification can be performed in various ways. For example, the notification can be performed by methods such as displaying a warning on a display device and sounding an alarm. Through this notification, during the operation of the mechanical structure, it can be presumed that a stress Sb exceeding the allowable stress Sc is generated at the evaluation target position P2. Therefore, the operator can take countermeasures such as stopping the operation of the mechanical structure and changing the operating conditions.

[0090] In this way, according to the present embodiment, based on the relationship between the stress Sa generated at the evaluation target position P2 during the excitation of the mechanical structure and the sound pressure La generated at the inspection position P3, and the allowable stress Sc of the set evaluation target position P2, the notification threshold Lt of the sound pressure during the operation of the mechanical structure can be determined. Thereby, it can be notified that the sound pressure La generated at the inspection position P3 during the operation of the mechanical structure exceeds the notification threshold Lt, and it is presumed that a stress exceeding the allowable stress Sc is generated at the evaluation target position P2 during the operation of the mechanical structure. Therefore, without stopping the operation of the mechanical structure, the state of the evaluation target position P2 of the mechanical structure during the operation of the mechanical structure can be grasped. As a result, the operator can take countermeasures such as stopping the operation of the mechanical structure and changing the operating conditions, and the breakage at the evaluation target position of the mechanical structure can be avoided.

[0091] In addition, according to the present embodiment, the relationship between the stress Sa generated at the evaluation target position P2 and the sound pressure La generated at the detection position P3 during the excitation of the mechanical structure is calculated by computer simulation. Thus, by using computer simulation, the relationship between the stress Sa and the sound pressure La can be easily calculated without conducting experiments. Further, in computer simulation, a calculation model in which the interior is filled with water, such as a hydraulic turbine structure, can be used to calculate the relationship between the stress Sa and the sound pressure La. Therefore, the relationship between the stress Sa and the sound pressure La can be calculated in a state close to the operating state, and the estimation accuracy of the stress Sb can be improved.

[0092] In addition, according to the present embodiment, the mechanical structure includes an impeller 5 that rotates under pressure from a fluid, and the evaluation target position P2 is provided on the impeller 5. Thus, when the evaluation target position P2 is provided on a rotating device that rotates under pressure from a fluid during operation, it is difficult to attach a stress sensor such as a strain gauge at the evaluation target position P2. Further, even if it is assumed that a stress sensor is attached, in order to attach the stress sensor, the operation of the mechanical structure has to be stopped, and an opportunity loss may occur due to the operation stop. In contrast, according to the present embodiment, even when the evaluation target position P2 is provided on such a rotating device, it is possible to determine when a stress exceeding the allowable stress Sc is generated at the evaluation target position P2 during the operation of the mechanical structure. Therefore, it is possible to determine the state of the evaluation target position P2 of the mechanical structure during the operation of the mechanical structure without stopping the operation of the mechanical structure.

[0093] In addition, according to the present embodiment, the mechanical structure is a hydraulic turbine structure. Thus, when the mechanical structure is a hydraulic turbine structure, it is difficult to attach a stress sensor inside the hydraulic turbine structure during its operation. Further, even if it is assumed that a stress sensor is attached, in order to attach the stress sensor inside the hydraulic turbine structure, the operation of the hydraulic turbine structure has to be stopped. In this case, sometimes the stress sensor attachment operation is performed after pumping out the water from inside the hydraulic turbine structure, the operation stop period of the hydraulic turbine structure becomes long, and the maintenance and inspection work of the hydraulic turbine structure also increases, and an opportunity loss may occur due to the operation stop of the hydraulic turbine structure. In contrast, according to the present embodiment, it is possible to determine when a stress exceeding the allowable stress Sc is generated at the evaluation target position P2 during the operation of the hydraulic turbine structure. Therefore, it is possible to determine the state of the evaluation target position P2 of the mechanical structure during the operation of the mechanical structure without stopping the operation of the mechanical structure.

[0094] (First Modification of the Second Embodiment)

[0095] In the above-described embodiment, an example was described in which the notification threshold Lt of the sound pressure during the operation of the mechanical structure was determined based on the relationship between the stress Sa generated at the evaluation target position P2 and the sound pressure La generated at the detection position P3 during the excitation of the mechanical structure, and the allowable stress Sc of the set evaluation target position P2. However, the present invention is not limited thereto, and the notification threshold Vt of the vibration during the operation of the mechanical structure may be determined based on the relationship between the stress Sa generated at the evaluation target position P2 and the vibration Va generated at the detection position P3 during the excitation of the mechanical structure, and the allowable stress Sc of the set evaluation target position P2.

[0096] In this case, in the calculation process, the relationship between the stress Sa generated at the evaluation target position P2 and the vibration Va generated at the detection position P3 during the excitation at the excitation position P1 of the mechanical structure is calculated. Here, similar to the first modification of the first embodiment described above, the stress-vibration transfer function H between the evaluation target position P2 and the detection position P3 at the evaluation target frequency fr can be calculated by the above formula (3). In addition, similar to the first modification of the first embodiment described above, the detection position P3 can be set on the maintenance hole cover 21 (refer to Figure 3 ). In addition, similar to the first modification of the first embodiment described above, the relationship (transfer function H) between the stress Sa and the vibration Va can be calculated by computer simulation.

[0097] In addition, in the determination process, based on the relationship calculated in the calculation process and the allowable stress Sc of the set evaluation target position P2, the notification threshold Vt of the vibration during the operation of the mechanical structure is determined. More specifically, the allowable stress Sc of the evaluation target position P2 at the evaluation target frequency fr is set, and the notification threshold Vt of the vibration at the evaluation target frequency fr is determined. The notification threshold Vt of the vibration can be expressed by the following formula (6).

[0098]

Equation 6

[0099] V t =HS c (6)

[0100] By substituting the transfer function H calculated by the above formula (3) and the allowable stress Sc of the evaluation target position P2 into the above formula (6), the notification threshold Vt of the vibration can be calculated. This notification threshold Vt corresponds to the vibration generated at the detection position P3 when a stress equal to the allowable stress Sc is generated at the evaluation target position P2, and means that when a vibration exceeding this notification threshold Lt is detected at the detection position P3, a stress exceeding the allowable stress Sc is generated at the evaluation target position P2.

[0101] In addition, in the detection process, the vibration Vb generated at the detection position P3 during the operation of the mechanical structure is detected. Here, similar to the first modification of the first embodiment described above, a vibration sensor 32 is provided at the detection position P3 provided on the maintenance hole cover 21, and the vibration Vb during the operation of the Francis turbine 1 can be detected by the vibration sensor 32 (see Figure 3 ). More specifically, the vibration Vb at the above-described evaluation target frequency fr is detected.

[0102] In addition, in the notification process, it is notified that the vibration Vb detected in the detection process exceeds the notification threshold value Vt. The notification process may be performed simultaneously with the detection process. More specifically, during the period when the vibration Vb is detected in the detection process, when the detected vibration Vb exceeds the notification threshold value Vt, the notification process may be performed. Here, the vibration Vb and the notification threshold value Vt are compared at the above-described evaluation target frequency fr, and when the vibration Vb exceeds the notification threshold value Vt, this situation is notified. Through this notification, it can be presumed that a stress Sb exceeding the allowable stress Sc is generated at the evaluation target position P2 during the operation of the mechanical structure.

[0103] In this way, according to this modification, based on the relationship between the stress Sa generated at the evaluation target position P2 during the excitation of the mechanical structure and the vibration Va generated at the detection position P3, and the allowable stress Sc set for the evaluation target position P2, the notification threshold value Vt of the vibration during the operation of the mechanical structure can be determined. As a result, it can be notified that the vibration Vb generated at the detection position P3 during the operation of the mechanical structure exceeds the notification threshold value Vt, and it can be presumed that a stress exceeding the allowable stress Sc is generated at the evaluation target position P2 during the operation of the mechanical structure. Therefore, without stopping the operation of the mechanical structure, the state of the evaluation target position P2 of the mechanical structure can be grasped during the operation of the mechanical structure. In this way, based on the relationship between the physical quantities including the sound pressure La or the vibration Va generated at the evaluation target position P2 during the excitation of the mechanical structure and the allowable stress Sc set for the evaluation target position P2, the notification threshold values Lt and Vt of the physical quantity during the operation of the mechanical structure can be determined.

[0104] In addition, according to this modification, calculation errors caused by acoustic analysis of the part where the sound pressure propagates in the air can be eliminated, and the estimation accuracy of the stress Sb can be improved.

[0105] (Second modification of the second embodiment)

[0106] In the above-described embodiment, an example of calculating the relationship between the stress Sa and the sound pressure La through computer simulation has been described. However, it is not limited thereto, and similar to the second modification example of the first embodiment, the relationship between the stress Sa and the sound pressure La can also be calculated through an excitation experiment.

[0107] According to this modification example, it is possible to calculate the relationship between the stress Sa and the sound pressure La without performing computer simulation. In addition, it is possible to eliminate the calculation errors caused by computer simulation, and the estimation accuracy of the stress Sb can be improved.

[0108] (The third modification example of the second embodiment)

[0109] In addition, in the above-described embodiment, similar to the third modification example of the first embodiment, the relationship between the stress Sa and the sound pressure La can also be calculated through a combination of computer simulation and excitation experiment.

[0110] According to this modification example, by performing computer simulation on the part of the hydraulic turbine structure filled with water inside, the calculation accuracy can be improved, and by performing excitation experiment on the part where the sound pressure propagates in the air, the calculation errors can be eliminated. Therefore, the estimation accuracy of the stress Sb can be further improved.

[0111] (Other modification examples of the second embodiment)

[0112] In the above-described embodiment, an example in which the evaluation object position P2 is provided on the impeller 5 has been described. However, it is not limited thereto, and the evaluation object position P2 can also be provided at any position. For example, the evaluation object position P2 can also be provided on the stay vane 3 and the guide vane 4. In this case, it is possible to monitor the states of the stay vane 3 and the guide vane 4 during the operation of the Francis turbine 1. In addition, the excitation position P1 can also be provided at a position other than the impeller 5. In this case, it is possible to take as the evaluation object the vibration phenomena other than the vibration phenomena caused by the Karman vortex. In addition, as long as the detection position P3 can detect the sound pressure and vibration caused by the vibration phenomena, it can also be provided at any other position.

[0113] In addition, in the above-described embodiment, an example in which the mechanical structure is a hydraulic turbine structure has been described. However, it is not limited thereto, and the mechanical structure can also be a turbine structure such as a steam turbine or a gas turbine. In this case, the excitation position P1 and the evaluation object position P2 can also be provided on the rotating equipment of the turbine structure. Furthermore, the mechanical structure is not limited to the hydraulic turbine structure and the turbine structure, and can also be any other mechanical structure.

[0114] According to the embodiments described above, without stopping the operation of the mechanical structure, it is possible to grasp the state of the evaluation object position of the mechanical structure during the operation of the mechanical structure.

[0115] As described above, several embodiments of the present invention have been described, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the scope equivalent thereto.

Claims

1. A method for estimating stress of a mechanical structure, which estimates the stress generated at an evaluation target position of the rotating device provided in the mechanical structure during the operation of the mechanical structure having a rotating device that rotates under pressure from a fluid, comprising: A calculation step of calculating the relationship between the stress generated at the evaluation target position during the excitation of the mechanical structure and the physical quantity including sound pressure or vibration generated at a detection position separated from the rotating device; A detection step of detecting the physical quantity generated at the detection position during the operation of the mechanical structure; And An estimation step of estimating the stress generated at the evaluation target position during the operation of the mechanical structure based on the relationship calculated in the calculation step and the physical quantity detected in the detection step.

2. The method for estimating stress of a mechanical structure according to claim 1, wherein The relationship in the calculation step is calculated by computer simulation.

3. The method for estimating stress of a mechanical structure according to claim 1, wherein The relationship in the calculation step is calculated by an excitation experiment.

4. The method for estimating stress of a mechanical structure according to claim 1, wherein The relationship in the calculation step is calculated by a combination of computer simulation and an excitation experiment.

5. The method for estimating stress of a mechanical structure according to any one of claims 1 to 4, wherein The mechanical structure is a hydraulic turbine structure.

6. A method for monitoring a mechanical structure, which monitors the state of an evaluation target position of the rotating device provided in the mechanical structure during the operation of the mechanical structure having a rotating device that rotates under pressure from a fluid, comprising: A calculation step of calculating the relationship between the stress generated at the evaluation target position during the excitation of the mechanical structure and the physical quantity including sound pressure or vibration generated at a detection position separated from the rotating device; A determination step of determining a notification threshold of the physical quantity during the operation of the mechanical structure based on the relationship calculated in the calculation step and the allowable stress of the evaluation target position set; A detection step of detecting the physical quantity generated at the detection position during the operation of the mechanical structure; And A notification step of notifying that the physical quantity detected in the detection step exceeds the notification threshold.

7. The method for monitoring a mechanical structure according to claim 6, wherein The relationship in the calculation step is calculated by computer simulation.

8. The method for monitoring a mechanical structure according to claim 6, wherein The relationship in the calculation step is calculated by an excitation experiment.

9. The method for monitoring a mechanical structure according to claim 6, wherein The relationship in the calculation step is calculated by a combination of computer simulation and an excitation experiment.

10. The method for monitoring a mechanical structure according to any one of claims 6 to 9, wherein The mechanical structure is a hydraulic turbine structure.

Images