Polar region ship crack propagation monitoring method
By screening crack initiation hotspots on a polar ship and deploying ring-shaped fiber optic sensors to monitor strain data at key nodes, the inefficiency and inaccuracy of existing crack propagation monitoring technologies have been solved, achieving efficient and accurate crack propagation monitoring and ensuring structural safety.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CNNC MARINE NUCLEAR POWER DEV CO LTD
- Filing Date
- 2024-11-07
- Publication Date
- 2026-05-08
AI Technical Summary
Existing technologies struggle to achieve efficient and accurate monitoring of crack propagation on polar ships, especially in complex structural health monitoring environments where the reliability of a single sensor is low.
By screening hotspots for crack initiation in the hull structure, selecting key nodes, and deploying ring-shaped fiber optic sensors at these nodes to monitor strain data, the data is analyzed in conjunction with a crack propagation monitoring system to classify safety levels and provide warning information.
This improved the scope, accuracy, and efficiency of crack propagation monitoring, ensuring the safety and reliability of the structure.
Smart Images
Figure CN121994155A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of crack propagation monitoring technology, and in particular to a method for monitoring crack propagation in polar ships. Background Technology
[0002] Icebreakers are subjected to random waves and ice impacts, resulting in alternating stresses on their hull structures. This leads to localized stress concentrations that facilitate the initiation and propagation of fatigue cracks. In recent years, research on fatigue crack propagation has been a hot topic in structural health monitoring. Structural health monitoring methods can be categorized into active and passive monitoring based on the signal source. Active monitoring applies excitation signals to the structure and analyzes the structural response signals received by sensors to achieve structural health monitoring. Active Lamb wave technology uses relatively simple equipment and can achieve long-distance, large-area detection of plate structures. While active monitoring methods have many applications in crack propagation monitoring, continuous monitoring is difficult. Passive methods involve continuously monitoring certain parameters of the structure as the crack grows, including acoustic emission signals, strain, and thermal energy. Strain, which is affected by crack propagation, is relatively easy to monitor and can be continuously monitored. However, due to the complexity of structural crack propagation, using a single sensor for condition monitoring and fault diagnosis is difficult to accurately capture fault characteristics, resulting in low reliability. Summary of the Invention
[0003] The technical problem to be solved by this invention is to provide a method for monitoring crack propagation on polar ships, which improves the monitoring range, accuracy and efficiency.
[0004] This invention provides a method for monitoring crack propagation in polar ships, comprising the following steps:
[0005] Step S1: Screening hotspots for the initiation of cracks in the hull structure;
[0006] Step S2: Filter key nodes;
[0007] Step S3: Monitor strain data at key nodes by deploying ring-shaped fiber optic sensors at the key nodes;
[0008] Step S4: Analyze the monitoring data using the crack propagation monitoring system, classify the safety levels according to different intervals, and provide warning information.
[0009] Step S1 specifically involves:
[0010] Based on the stress calculation results of the entire ship and the hot spot location selection recommendations of the classification society, fatigue hot spot areas of the hull structure were screened out. In accordance with the requirements of the specifications, the mesh of the fatigue hot spot areas was refined. The mesh size of the refined area should be smaller than the plate thickness. The fine mesh area extends outward from the hot spot location by more than 10 times the plate thickness. The transition of mesh density in the refined mesh area between the fine mesh and the coarse mesh is smooth. Finally, the hot spot area for crack initiation in the hull structure was determined.
[0011] Step S2 specifically involves:
[0012] Based on the rainflow counting method, the stress response time domain results of nodes with large stress in hot spots are analyzed, the amplitude and mean of node stress are statistically obtained, and the average stress is corrected by the Goodman correction method. Based on the sea state information of the icebreaker, an appropriate wave spectral density function is selected to calculate the nodal stress power spectral density.
[0013] For each short-term sea state, according to the theory of stochastic processes, when considering a narrow-band stationary stochastic process of nodal alternating stress with zero mean, the stress range follows a Rayleigh distribution, and the probability density is calculated.
[0014] Based on the wave statistics of the navigation area provided by the wave scattering diagram, the stress distribution of nodes under various short-term sea states can be further obtained. The wave scattering diagram is selected according to the actual operating route of the ship. Then, the fatigue cumulative damage value of the node can be obtained through the SN curve.
[0015] The cumulative node damage of the ship in the i-th sea state and j-th course is calculated based on the spectral analysis method.
[0016] Considering bandwidth correction and fatigue damage correction in low stress range, the total damage within the node's design life T is obtained using Miner's linear cumulative damage theory.
[0017] Based on the fatigue life and fatigue damage results of each stress-high node in the hot spot area obtained by spectral analysis and screening, the key nodes are identified and designated as crack propagation monitoring points.
[0018] The method for calculating the nodal stress power spectral density is as follows:
[0019] S σ (ωH s ,T z ,θ)=|H σ (ωθ) 2 S ζ (ωH s ,T Z )
[0020] Where: H σ(ωθ) is the nodal stress transfer function, where ω and θ are the frequency and wave angle, respectively. σ H is the nodal stress power spectral density function. S Significant wave height for short-term sea states; T Z The average zero-crossing period for short-term sea states.
[0021] The probability density is calculated as follows:
[0022]
[0023] In the formula: S is the range of nodal stress; σ σ This represents the standard deviation of the alternating stress process.
[0024] The cumulative damage to the vessel in sea state i and course j is shown in the formula:
[0025]
[0026] In the formula: T ij The sailing time for the i-th sea state and the j-th course; f 0ij Let f be the zero-crossing frequency of the stress alternation process in the i-th sea state and j-th course; K is the SN curve parameter; m is the reciprocal of the slope of SN; f Sij (S) is the probability density function of the stress alternation process in the i-th sea state and j-th heading.
[0027] The total damage during the designed lifespan T of the node is:
[0028]
[0029] In the formula: λ ij μ is the bandwidth correction factor. ij n is the fatigue damage correction factor for the low stress range; s n represents the number of sea states. H p is the number of course divisions; i p represents the probability of occurrence for each sea state. j This represents the probability of occurrence in each heading.
[0030] In step S3, the ring fiber optic sensor is arranged around the crack propagation path. With the initial crack as the center, ring fiber optic sensors with radii of 5mm, 10mm, 20mm, 50mm and 100mm are arranged respectively. The safety level interval is set by the radius difference between two adjacent ring fiber optic sensors.
[0031] In step S4, the criteria for security registration classification are as follows:
[0032] Microcracks of 0–5 mm are within a safe range and require routine monitoring; they usually do not require immediate intervention.
[0033] Small cracks of 5-50mm are within the warning range; an immediate assessment should be conducted, and consideration should be given to discontinuing use and repairing the affected area.
[0034] Medium and larger cracks (greater than 50 mm) are considered dangerous and should be discontinued immediately.
[0035] Different warning and alert messages will be used for different security levels:
[0036] Microcracks of 0–5 mm are indicated by routine monitoring and usually do not require immediate treatment;
[0037] Small cracks of 5-50mm indicate the need for immediate evaluation, and consideration should be given to discontinuing use and repairing the affected area.
[0038] Medium or larger cracks (greater than 50mm) indicate that the product should be discontinued immediately.
[0039] Compared with existing technologies, the polar ship crack propagation monitoring method of this invention obtains the hotspot areas for crack initiation in the hull structure based on fatigue life calculations under various operating conditions. Then, it analyzes points with high local stress in these areas to identify key nodes for crack initiation. By deploying fiber optic sensors at these nodes, the monitoring data is input into the system. The system displays a comparison between the predicted crack propagation value and the threshold value in a bar chart, and simultaneously records early warning and alarm information for each measuring point within a certain time period in a list format, facilitating user access to alarm times and information. This invention improves the monitoring range, accuracy, and efficiency. Attached Figure Description
[0040] Figure 1 This is a flowchart illustrating the method of the present invention.
[0041] Figure 2 This diagram illustrates the calculation of fatigue damage.
[0042] Figure 3 This diagram illustrates the arrangement of a ring-shaped distributed optical fiber sensor. Detailed Implementation
[0043] To further understand the present invention, embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the present invention.
[0044] An embodiment of the present invention discloses a method for monitoring crack propagation in polar ships, such as... Figure 1 As shown, it includes the following steps:
[0045] Step S1: Screening hotspots for the initiation of cracks in the hull structure;
[0046] Specifically:
[0047] Based on the fatigue strength assessment and overall ship stress calculation results, and combined with the classification society's recommendations for selecting hot spot locations, fatigue hot spot areas of the hull structure were screened out. In accordance with the requirements of the specifications, the mesh of the fatigue hot spot areas was refined. The mesh size of the refined areas should be smaller than the plate thickness. The fine mesh areas should extend outward from the hot spot location by more than 10 times the plate thickness. The transition of mesh density in the refined mesh areas between the fine and coarse meshes should be smooth. Finally, the hot spot areas for the initiation of cracks in the hull structure were determined.
[0048] Step S2: Filter key nodes;
[0049] Specifically:
[0050] Based on the rainflow counting method, the stress response time domain results of nodes with large stress in hot spots are analyzed, the amplitude and mean of node stress are statistically obtained, and the average stress is corrected by the Goodman correction method. Based on the sea state information of the icebreaker, an appropriate wave spectral density function is selected to calculate the nodal stress power spectral density.
[0051] The method for calculating the nodal stress power spectral density is as follows:
[0052] S σ (ωH s ,T z ,θ)=|H σ (ωθ) 2 S ζ (ωH s ,T Z )
[0053] Where: H σ (ωθ) is the nodal stress transfer function, where ω and θ are the frequency and wave angle, respectively. σ H is the nodal stress power spectral density function. S Significant wave height for short-term sea states; T Z The average zero-crossing period for short-term sea states.
[0054] For each short-term sea state, according to the theory of stochastic processes, when considering a narrow-band stationary stochastic process of nodal alternating stress with zero mean, the stress range follows a Rayleigh distribution, and the probability density is calculated.
[0055] The probability density function is shown in the following equation:
[0056]
[0057] In the formula: S is the range of nodal stress; σ σ This represents the standard deviation of the alternating stress process.
[0058] Based on the wave statistics of the navigation area provided by the wave scattering diagram, the stress distribution of nodes under various short-term sea states can be further obtained. The wave scattering diagram is selected according to the actual operating route of the ship. Then, the fatigue cumulative damage value of the node can be obtained through the SN curve.
[0059] The cumulative node damage of the ship in the i-th sea state and j-th course is calculated based on the spectral analysis method.
[0060] The cumulative damage is shown in the formula:
[0061]
[0062] In the formula: T ij The sailing time for the i-th sea state and the j-th course; f 0ij Let f be the zero-crossing frequency of the stress alternation process in the i-th sea state and j-th course; K is the SN curve parameter; m is the reciprocal of the slope of SN; f Sij (S) is the probability density function of the stress alternation process in the i-th sea state and j-th heading.
[0063] Considering bandwidth correction and fatigue damage correction in low stress range, the total damage within the node's design life T is obtained using Miner's linear cumulative damage theory.
[0064] The total damage during the designed lifespan T of the node is:
[0065]
[0066] In the formula: λ ij μ is the bandwidth correction factor. ij n is the fatigue damage correction factor for the low stress range; s n represents the number of sea states. H p is the number of course divisions; i p represents the probability of occurrence for each sea state. j This represents the probability of occurrence in each heading.
[0067] Based on the fatigue life and fatigue damage results of each stress-high node in the hot spot area obtained by spectral analysis and screening, the key nodes are identified and designated as crack propagation monitoring points.
[0068] Step S3: By deploying ring-shaped fiber optic sensors at key nodes, such as... Figure 3 As shown, strain data at key monitoring nodes;
[0069] The ring fiber optic sensors are arranged around the crack propagation path. With the initial crack as the center, ring fiber optic sensors with radii of 5mm, 10mm, 20mm, 50mm and 100mm are arranged respectively. The safety level interval is set by the radius difference between two adjacent ring fiber optic sensors.
[0070] Step S4: Analyze the monitoring data using the crack propagation monitoring system, classify the safety levels according to different intervals, and provide warning information.
[0071] Crack length classification is a crucial part of material and structural safety assessments. Based on the specific crack length range, appropriate monitoring and maintenance measures can be implemented to ensure the safety and reliability of the structure. In practical applications, a comprehensive judgment is usually necessary, taking into account factors such as material properties, operating environment, and load conditions. Safety registration and warning information are shown in Table 1.
[0072] Table 1
[0073]
[0074] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.
[0075] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A method for monitoring crack propagation in polar ships, characterized in that, Includes the following steps: Step S1: Screening hotspots for the initiation of cracks in the hull structure; Step S2: Filter key nodes; Step S3: Monitor strain data at key nodes by deploying ring-shaped fiber optic sensors at the key nodes; Step S4: Analyze the monitoring data using the crack propagation monitoring system, classify the safety levels according to different intervals, and provide warning information.
2. The method for monitoring crack propagation in polar ships according to claim 1, characterized in that, Step S1 specifically involves: Based on the stress calculation results of the entire ship and the hot spot location selection recommendations of the classification society, fatigue hot spot areas of the hull structure were screened out. In accordance with the requirements of the specifications, the mesh of the fatigue hot spot areas was refined. The mesh size of the refined area should be smaller than the plate thickness. The fine mesh area extends outward from the hot spot location by more than 10 times the plate thickness. The transition of mesh density in the refined mesh area between the fine mesh and the coarse mesh is smooth. Finally, the hot spot area for crack initiation in the hull structure was determined.
3. The method for monitoring crack propagation in polar ships according to claim 1, characterized in that, Step S2 specifically involves: Based on the rainflow counting method, the stress response time domain results of nodes with large stress in hot spots are analyzed, the amplitude and mean of node stress are statistically obtained, and the average stress is corrected by the Goodman correction method. Based on the sea state information of the icebreaker, an appropriate wave spectral density function is selected to calculate the nodal stress power spectral density. For each short-term sea state, according to the theory of stochastic processes, when considering a narrow-band stationary stochastic process of nodal alternating stress with zero mean, the stress range follows a Rayleigh distribution, and the probability density is calculated. Based on the wave statistics of the navigation area provided by the wave scattering diagram, the stress distribution of nodes under various short-term sea states can be further obtained. The wave scattering diagram is selected according to the actual operating route of the ship. Then, the fatigue cumulative damage value of the node can be obtained through the SN curve. The cumulative node damage of the ship in the i-th sea state and j-th course is calculated based on the spectral analysis method. Considering bandwidth correction and fatigue damage correction in low stress range, the total damage within the node's design life T is obtained using Miner's linear cumulative damage theory. Based on the fatigue life and fatigue damage results of each stress-high node in the hot spot area obtained by spectral analysis and screening, the key nodes are identified and designated as crack propagation monitoring points.
4. The method for monitoring crack propagation in polar ships according to claim 3, characterized in that, The method for calculating the nodal stress power spectral density is as follows: Sσ(ωH s ,T z ,θ)=|Hσ(ωθ) 2 Sζ(ωH s ,T Z ) In the formula: H σ (ωθ) is the nodal stress transfer function. ω θ and θ represent the frequency and wave angle, respectively, S σ H is the nodal stress power spectral density function. S Significant wave height for short-term sea states; T Z The average zero-crossing period for short-term sea states.
5. The method for monitoring crack propagation in polar ships according to claim 3, characterized in that, The probability density is calculated as follows: In the formula: S is the range of nodal stress; σ σ This represents the standard deviation of the alternating stress process.
6. The method for monitoring crack propagation in polar ships according to claim 3, characterized in that, The cumulative damage to the vessel in sea state i and course j is shown in the formula: In the formula: T ij The sailing time is for the i-th sea state and the j-th course; f 0ij Let f be the zero-crossing frequency of the stress alternation process in the i-th sea state and j-th course; K is the SN curve parameter; m is the reciprocal of the slope of SN; f Sij (S) is the probability density function of the stress alternation process in the i-th sea state and j-th heading.
7. The method for monitoring crack propagation in polar ships according to claim 3, characterized in that, The total damage during the designed lifespan T of the node is: In the formula: λ ij μ is the bandwidth correction factor. ij n is the fatigue damage correction factor for the low stress range; s n represents the number of sea states. H p is the number of course divisions; i p represents the probability of occurrence for each sea state. j This represents the probability of occurrence in each heading.
8. The method for monitoring crack propagation in polar ships according to claim 1, characterized in that, In step S3, the ring fiber optic sensor is arranged around the crack propagation path. With the initial crack as the center, ring fiber optic sensors with radii of 5mm, 10mm, 20mm, 50mm and 100mm are arranged respectively. The safety level interval is set by the radius difference between two adjacent ring fiber optic sensors.
9. The method for monitoring crack propagation in polar ships according to claim 1, characterized in that, In step S4, the criteria for security registration classification are as follows: Microcracks of 0–5 mm are within a safe range and require routine monitoring; they usually do not require immediate intervention. Small cracks of 5-50mm are within the warning range; an immediate assessment should be conducted, and consideration should be given to discontinuing use and repairing the affected area. Medium and larger cracks (greater than 50 mm) are considered dangerous and should be discontinued immediately.
10. The method for monitoring crack propagation in polar ships according to claim 9, characterized in that, Different warning and alert messages will be used for different security levels: Microcracks of 0–5 mm are indicated by routine monitoring and usually do not require immediate treatment; Small cracks of 5-50mm indicate the need for immediate evaluation, and consideration should be given to discontinuing use and repairing the affected area. Medium or larger cracks (greater than 50mm) indicate that the product should be discontinued immediately.