Chain ring fatigue damage calculation method and system considering wear conditions

Abstract

The invention provides a chain ring fatigue damage calculation method and system considering wear conditions, under the conditions of multiple working conditions and multiple wear losses, fatigue load calculation and accumulated damage analysis are carried out on a suspension chain ring, and through time domain simulation, finite element calculation, rain flow counting and S-N curve combination, the fatigue damage of the chain ring is calculated. And a working condition-abrasion loss-fatigue damage database is established. According to the method and the system, accurate evaluation and early warning can be provided for safe service management of the anchor chain or the suspension chain in ship and ocean engineering, and the reliability and the economical efficiency of system operation are greatly improved. All the parts of the device can be independently implemented and can also be modularly combined.

Description

Technical Field

[0001] The present invention relates to the field of marine engineering mechanics and fatigue analysis technology, and mainly provides a chain link fatigue damage calculation method and system considering wear conditions, which can be used for chain link fatigue life assessment and safety monitoring under multiple working conditions of ships and offshore platforms. Background Art

[0002] Under the influence of complex marine environments such as wind, waves, and currents, ships often use anchor chains or suspension chains for mooring or launching unit suspension. Due to the changeable sea conditions and random load fluctuations, the anchor chain will produce repeated stretching and subsequent fatigue damage, which is one of the important factors leading to the destruction of the anchor chain links. As the service time increases, the chain links are often accompanied by adhesive wear, micro-motion wear and other phenomena. Current research on chain link fatigue analysis is mostly based on simplified load assumptions, and it is difficult to fully consider the impact of nonlinear coupling effects and actual wear on fatigue life. Therefore, how to effectively analyze chain link fatigue damage under multiple working conditions (sea conditions, speed, cable length, etc.) and multi-level wear conditions has become a technical problem that needs to be solved urgently. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiency in the prior art that it is impossible to systematically evaluate the suspension chain links under the coupled conditions of wear and fatigue, and to propose a chain link fatigue damage calculation method and system that takes wear conditions into consideration. The method can effectively evaluate the chain link fatigue damage under different wear amounts under multiple working load conditions, and form a corresponding fatigue damage database, thereby providing accurate safety prediction and service life management for ships or marine engineering systems.

[0004] The object of the present invention is achieved by the following technical solution. This chain link fatigue damage calculation method considering wear conditions comprises the following steps:

[0005] 1) Select the target chain link key position and multi-level wear range;

[0006] 2) Perform time-domain coupled dynamic simulation for specified sea conditions, ship speed, and cable length to extract the chain link tension time history;

[0007] 3) Establish a local finite element model of double or multiple chain links, calculate the ratio of hot spot stress to nominal stress under different wear amounts, and obtain the stress concentration factor SCF;

[0008] 4) Multiply the nominal stress history of the chain link by the stress concentration factor SCF to obtain the hot spot stress history, use the rain flow counting method to calculate the stress range and cycle number, and correct the average stress;

[0009] 5) Based on the SN curve and the linear cumulative damage criterion, calculate the fatigue damage of the chain link under various working conditions and wear amounts per unit time;

[0010] 6) The fatigue damage results are recorded in the database, and the cumulative fatigue damage of the chain link is queried or interpolated according to the real-time wear amount and working condition combination in actual service.

[0011] The specific steps are as follows:

[0012] (1) Load analysis

[0013] a) Based on project requirements, multiple combined operating conditions (combining sea state level, ship speed and cable length) and multiple levels of wear are selected to conduct fatigue analysis on the chain links at key locations;

[0014] b) Perform time-domain coupled dynamic analysis on the chain link tension under various working conditions to obtain the time-history load of the suspension chain and extract the average value and amplitude of the tension fluctuation.

[0015] (2) Finite element analysis and stress concentration factor

[0016] a) Establish a local finite element model of double or multiple chain links, using the bilinear kinematic hardening (BKIN) material constitutive model and considering contact nonlinearity and geometric nonlinearity;

[0017] b) Through tensile load simulation, mesh convergence and contact analysis are performed on chain links with different wear amounts, and the first principal stress at the hotspot location is calculated.

[0018] c) Define the nominal stress and calculate how the stress concentration factor changes with wear.

[0019] (3) Fatigue load history and rain flow counting method

[0020] a) Convert the suspension chain tension time history into the corresponding nominal stress time history in the time domain;

[0021] b) According to the SCF corresponding to different wear amounts, the nominal stress spectrum is modified to obtain the hot spot stress history;

[0022] c) The rain flow counting method is used to perform cyclic decomposition of the hot spot stress history to obtain the stress range and cycle number distribution.

[0023] (4) Fatigue correction considering mean stress

[0024] a) Use Goodman's straight line or other mean stress correction methods to correct the stress amplitude and obtain the equivalent stress amplitude;

[0025] b) Fatigue life calculation is performed in combination with the SN curve model in DNV or CCS specifications.

[0026] (5) Cumulative fatigue damage assessment

[0027] a) Based on the PM linear cumulative damage theory, the number of cycles of each stress amplitude obtained by rain flow counting is accumulated;

[0028] b) When the cumulative damage is less than 1.0, the chain link is considered to have not reached the fatigue limit.

[0029] (6) Fatigue damage database generation

[0030] a) Collect statistics on the fatigue damage of the chain links under various working conditions and wear amounts to obtain the fatigue damage per unit time (e.g., 1 hour);

[0031] b) Establish a database of "working conditions - wear amount - cumulative fatigue damage" and dynamically query the remaining life of the chain link by combining real-time wear amount and service time.

[0032] Furthermore, the multi-level wear amount includes at least 5 levels; when the real-time wear amount is in a certain interval, the stress concentration factor SCF of the corresponding interval is selected to perform interpolation calculation on the chain link hot spot stress time history.

[0033] Furthermore, the rain flow counting method includes performing peak and valley detection on the tension or stress time history, eliminating invalid amplitudes to obtain discrete load cycles, and performing mean stress correction in conjunction with the Goodman formula.

[0034] Furthermore, the SN curve is selected according to the marine engineering specification (DNVGL-OS-E301 or CCS), and a curve form with set parameters is adopted for the gear chain link.

[0035] Furthermore, the linear cumulative damage criterion adopts the PM linear method. When D<1, the chain link has not reached the fatigue limit. Otherwise, the system alarms or prompts maintenance.

[0036] At the same time, the present invention provides a chain link fatigue damage analysis system considering wear conditions, comprising:

[0037] Data acquisition module: used to input or collect real-time information about sea state level, ship speed, cable length, current wear and tear, and suspension chain tension;

[0038] Finite element modeling module: establishes a double chain link 1 / 4 model or transition mesh model based on chain link diameter, wear amount and material parameters, defines contact nonlinearity and material nonlinearity, and calculates the stress concentration factor (SCF);

[0039] Time domain load analysis module: Based on coupled dynamics software, chain link tension time history is derived and peak-valley detection is performed to obtain a true random load sequence;

[0040] Stress spectrum and rainflow counting module: Multiply the nominal stress by the stress concentration factor (SCF) to obtain the hotspot stress history, use the rainflow counting method to extract the stress amplitude and cycle number, and perform mean stress correction;

[0041] Fatigue life assessment module: Calculate the SN curve cumulative damage of the equivalent stress amplitude after mean stress correction, output the fatigue damage in each period and compare it with the safety factor to determine whether it meets the fatigue use requirements;

[0042] Database management module: stores fatigue damage results under various combined working conditions and different wear conditions in the database to facilitate subsequent query, interpolation and automatic warning;

[0043] Safety monitoring module: obtains the current wear and service load of the chain link in real time, queries the database and determines whether the accumulated fatigue damage has reached the preset threshold, and issues an early warning if it exceeds the limit.

[0044] In addition, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a computer or a processor, implements the steps of the chain link fatigue damage calculation method considering wear conditions.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] Strong systematization: From multi-condition load extraction to finite element calculation, and then to rainflow counting and SN curve analysis, the entire process covers the impact of wear on fatigue damage;

[0047] High accuracy: considering the cross-section loss and stress concentration effect after chain link wear, the average stress correction is adopted to be closer to the service condition of the chain link under real sea conditions;

[0048] Scalability: The establishment of a fatigue damage database enables quick subsequent query of the remaining life of any period and any amount of wear, and can be linked with real-time monitoring data;

[0049] Safety warning: Based on the PM linear cumulative damage theory, each key link can be monitored in real time or periodically. If the damage exceeds the threshold, an automatic alarm will be issued to ensure the safety and reliability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art or ordinary technicians, other drawings can be obtained based on these drawings without paying any creative work.

[0051] Figure 1 : Schematic diagram of the fatigue analysis process according to an embodiment of the present invention;

[0052] Figure 2 : The finite element equivalent stress cloud diagram according to the embodiment of the present invention;

[0053] Figure 3 : The finite element stress cloud diagram in the pulling direction according to the embodiment of the present invention;

[0054] Figure 4 : Hot spot stress diagram of the rain flow counting method according to an embodiment of the present invention; DETAILED DESCRIPTION

[0055] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0056] The present invention uses a time domain calculation method to evaluate the fatigue damage of the chain link according to engineering requirements. The main process is as follows: Figure 1 shown.

[0057] Step 1: Load Analysis. Key weak points are selected for consideration of varying wear levels. Fatigue analysis is performed on the links at these key locations, targeting various combined operating conditions (different sea conditions, ship speeds, and cable lengths) and multiple levels of wear. Fatigue damage per unit time (e.g., 1 hour) is calculated.

[0058] b) Perform time-domain coupled dynamic analysis on the chain link tension under various working conditions to obtain the time-history load of the suspension chain and extract the average value and amplitude of the tension fluctuation.

[0059] Step 2: Extract time-domain loads. Using coupled dynamics software such as Orcaflex, perform time-domain simulations to extract the time history curves of the chain link tension under various working conditions.

[0060] Step 3: Finite element analysis. Establish a local finite element model of double or multiple chain links, use bilinear kinematic hardening (BKIN) material constitutive model, consider contact nonlinearity and geometric nonlinearity, simulate the tensile load, perform mesh convergence and contact analysis on chain links with different wear amounts, and calculate the first principal stress at the hot spot, such as Figure 2 、 Figure 3 shown.

[0061] Under different wear levels, cross-sectional thinning may occur on the crown or inner edge of the chain link. By geometrically modeling multi-level wear or setting thinning treatment in local areas, re-meshing and performing contact nonlinear analysis.

[0062] Step 4: Determine the stress concentration factor. Perform progressive loading to obtain the hotspot stress under the working load. Calculate the hotspot stress by combining the nominal stress with the stress concentration factor (SCF) calculated by finite element analysis. Calculate how the stress concentration factor changes with wear.

[0063] The stress concentration factor is key to calculating fatigue damage. The purpose of finite element analysis is to determine the stress concentration factor under different wear levels and calculate hot spot stresses. Using the tensile force on the chain link under operating conditions as the tensile load, the chain link under different wear levels is analyzed to calculate its stress concentration factor (SCF). Stress concentration is a weak link in the fatigue strength of a structure and exists in almost any structure or component. The definition of the stress concentration factor is as follows:

[0064]

[0065] Where σ is the hot spot stress, σ n is the nominal stress.

[0066] Nominal stress refers to the stress calculated on the effective cross section of the structure without considering geometric discontinuities. For a chain link structure, it is:

[0067]

[0068] Where F is the chain link tension and A is the cross-sectional area of ​​the chain link.

[0069]

[0070] Where d is the chain link diameter.

[0071] Step 5: Extract fatigue load stress spectrum. According to the actual measurement or simulation results of the project, select typical sea conditions and speeds, obtain the suspension chain tension time history curves at various cable lengths, use the rain flow counting method to count the cycles of the hot spot stress time history, detect the peak and valley values ​​or waveforms, eliminate invalid small amplitude cycles, and obtain the stress amplitude and cycle number distribution, such as Figure 4 shown.

[0072] Step 6: Mean stress correction: Use the Goodman formula and other methods to correct the effect of mean stress on fatigue.

[0073] In the specification, the SN curve is the basic SN curve, which is obtained when the stress ratio R=-1. Therefore, the influence of the average stress needs to be considered in practical applications. When the life is given, the average stress S m The larger the stress amplitude, the greater the corresponding stress amplitude, but the final average stress will not be greater than the ultimate strength S of the material. u , under the condition of equal life S m -S uThe relationship can be expressed by the Goodman straight line as:

[0074]

[0075] Among them, S a is the stress amplitude, S -1 is the stress amplitude when R=-1, S m is the mean stress, S u For ultimate strength.

[0076] Step 7: Determine the SN curve and cumulative damage. Combined with the SN curve given by DNV and other standards, use the linear cumulative damage model to calculate the fatigue damage per unit time.

[0077] The present invention selects the SN curve of the stud anchor chain according to the DNVGL-OS-E301 and other standards.

[0078] n c (s) = 1.2 × 10 11 s -3

[0079] Step 8: Cumulative Damage Assessment. Using the stress spectrum and the SN curves given in DNV and other standards, a linear cumulative damage model is used to calculate fatigue damage per unit time. Cumulative damage is then assessed. When the cumulative damage is less than 1.0, the link is considered to have not reached the fatigue limit. When the cumulative damage is greater than or equal to 1.0, an alarm is issued or maintenance measures are required.

[0080] According to the PM linear cumulative damage model, the damage of the i-th working condition is:

[0081]

[0082] The criteria for judging whether a chain link has reached the fatigue limit state are:

[0083] 1-D c γ F ≥0

[0084] Step 9: Construct a fatigue damage database. Collect statistics on the fatigue damage of the chain links under various operating conditions and wear levels, and store the results to form a "operating condition-wear level-fatigue damage" mapping. Through interpolation or extrapolation, the fatigue damage at any intermediate wear level or operating condition can be quickly obtained for subsequent safety verification and life prediction.

[0085] Step 10: Chain Link Fatigue Damage Analysis System

[0086] Based on the above analysis method, a chain link fatigue damage analysis system was established. In actual engineering, based on real-time wear measurement and working condition detection, the corresponding fatigue damage rate can be queried from the database, and the current service time can be accumulated to evaluate the remaining life of the chain link. If the real-time calculation shows that the damage has reached the safety factor limit, the system will alarm and prompt maintenance or replacement of the chain link. The system mainly includes the following modules:

[0087] (1) Data acquisition module: used to input or collect real-time information such as sea condition level, ship speed, cable length, current wear and tear, and suspension chain tension.

[0088] (2) Finite element modeling module: A double chain link 1 / 4 model or transition mesh model is established based on the chain link diameter, wear amount and material parameters, and contact nonlinearity and material nonlinearity are defined.

[0089] (3) Time domain load analysis module: Based on the coupled dynamics software, the chain link tension time history is derived and peak and valley detection is performed to obtain a true random load sequence.

[0090] (4) Stress spectrum and rainflow counting module: The nominal stress is multiplied by the SCF to obtain the hotspot stress history, and the stress amplitude and cycle number are extracted using the rainflow counting method;

[0091] (5) Fatigue life assessment module: Calculate the SN curve cumulative damage of the equivalent stress amplitude after the mean stress correction, output the fatigue damage in each period and compare it with the safety factor to determine whether the fatigue use requirements are met;

[0092] (6) Database management module: The fatigue damage results under various combined working conditions and different wear conditions are stored in the database to facilitate subsequent query, interpolation and automatic warning.

[0093] (7) Safety monitoring module: obtains the current wear and service load of the chain link in real time, queries the database and determines whether the accumulated fatigue damage reaches the preset threshold, and issues an early warning if it exceeds the limit.

[0094] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the scope of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A chain link fatigue damage calculation method considering wear conditions, characterized by: The method comprises the following steps: 1) Select the target chain link key position and multi-level wear range; 2) Perform time-domain coupled dynamic simulation for specified sea conditions, ship speed, and cable length to extract the chain link tension time history; 3) Establish a local finite element model of double or multiple chain links, calculate the ratio of hot spot stress to nominal stress under different wear amounts, and obtain the stress concentration factor SCF; 4) Multiply the nominal stress history of the chain link by the stress concentration factor SCF to obtain the hot spot stress history, use the rain flow counting method to calculate the stress range and cycle number, and correct the average stress; 5) Based on the SN curve and the linear cumulative damage criterion, calculate the fatigue damage of the chain link under various working conditions and wear amounts per unit time; 6) The fatigue damage results are recorded in the database, and the cumulative fatigue damage of the chain link is queried or interpolated according to the real-time wear amount and working condition combination in actual service.

2. The chain link fatigue damage calculation method considering wear conditions according to claim 1, characterized in that: The multi-level wear amount includes at least 5 levels; when the real-time wear amount is in a certain interval, the stress concentration factor SCF of the corresponding interval is selected to perform interpolation calculation on the chain link hot spot stress time history.

3. The chain link fatigue damage calculation method considering wear conditions according to claim 1, characterized in that: The rain flow counting method includes performing peak and valley detection on the tension or stress time history, eliminating invalid amplitudes to obtain discrete load cycles, and performing mean stress correction in conjunction with the Goodman formula.

4. The chain link fatigue damage calculation method considering wear conditions according to claim 1, characterized in that: The SN curve is selected according to the marine engineering specification, and a curve with set parameters is adopted for the gear chain link.

5. The chain link fatigue damage calculation method considering wear conditions according to any one of claims 1 to 4, characterized in that: The linear cumulative damage criterion adopts the PM linear method. When D < 1, the chain link has not reached the fatigue limit. Otherwise, the system alarms or prompts maintenance.

6. A chain link fatigue damage analysis system considering wear conditions, using the chain link fatigue damage calculation method considering wear conditions according to any one of claims 1 to 5, characterized in that: include: Data acquisition module: used to input or collect real-time information about sea state level, ship speed, cable length, current wear and tear, and suspension chain tension; Finite element modeling module: establishes a double chain link 1 / 4 model or transition mesh model based on chain link diameter, wear amount and material parameters, defines contact nonlinearity and material nonlinearity, and calculates the stress concentration factor (SCF); Time domain load analysis module: Based on coupled dynamics software, chain link tension time history is derived and peak-valley detection is performed to obtain a true random load sequence; Stress spectrum and rainflow counting module: Multiply the nominal stress by the stress concentration factor (SCF) to obtain the hotspot stress history, use the rainflow counting method to extract the stress amplitude and cycle number, and perform mean stress correction; Fatigue life assessment module: Calculate the SN curve cumulative damage of the equivalent stress amplitude after mean stress correction, output the fatigue damage in each period and compare it with the safety factor to determine whether it meets the fatigue use requirements; Database management module: stores fatigue damage results under various combined working conditions and different wear conditions in the database to facilitate subsequent query, interpolation and automatic warning; Safety monitoring module: obtains the current wear and service load of the chain link in real time, queries the database and determines whether the accumulated fatigue damage has reached the preset threshold, and issues an early warning if it exceeds the limit.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a computer or a processor, the steps of the method according to any one of claims 1 to 5 are implemented.

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