The rainflow counting method is a reasonable cyclecounting procedure for fatigue life calculation and simulation testing of structures.It defines cycles as closed stress /strain hysteresis loops.Application of the rai...The rainflow counting method is a reasonable cyclecounting procedure for fatigue life calculation and simulation testing of structures.It defines cycles as closed stress /strain hysteresis loops.Application of the rainflow counting method requires a data processing of the loading spectrum,which consists of the elimination of non-peak value data points,load time histories adjustment and loop extraction.In the data processing of the loading spectrum,if a stress point is neither the peak nor the valley,it will be identified and eliminated from the loading spectrum.Generally,the loading process is idealized as a single peak-valley straight line.But in actually,there are polylines or nearly straight lines between peaks and valleys which can't be ignored.Therefore,in the process of eliminating such data points,it will produce error in method itself.To reduce the error produced by the traditional method itself,a new method which can well simplify the polylines in data processing of loading spectrum is proposed in this paper.Comparing with the original approximation method,the proposed method has higher precision.展开更多
For the randomness of crane working load leading to the decrease of load spectrum prediction accuracy with time,an adaptive TSSA-HKRVM model for crane load spectrum regression prediction is proposed.The heterogeneous ...For the randomness of crane working load leading to the decrease of load spectrum prediction accuracy with time,an adaptive TSSA-HKRVM model for crane load spectrum regression prediction is proposed.The heterogeneous kernel relevance vector machine model(HKRVM)with comprehensive expression ability is established using the complementary advantages of various kernel functions.The combination strategy consisting of refraction reverse learning,golden sine,and Cauchy mutation+logistic chaotic perturbation is introduced to form a multi-strategy improved sparrow algorithm(TSSA),thus optimizing the relevant parameters of HKRVM.The adaptive updatingmechanismof the heterogeneous kernel RVMmodel under themulti-strategy improved sparrow algorithm(TSSA-HKMRVM)is defined by the sliding window design theory.Based on the sample data of the measured load spectrum,the trained adaptive TSSA-HKRVMmodel is employed to complete the prediction of the crane equivalent load spectrum.Applying this method toQD20/10 t×43m×12mgeneral bridge crane,the results show that:compared with other prediction models,although the complexity of the adaptive TSSA-HKRVMmodel is relatively high,the prediction accuracy of the load spectrum under long periods has been effectively improved,and the completeness of the load information during thewhole life cycle is relatively higher,with better applicability.展开更多
Based on the basic theory of mechanics,kinematic and dynamic analysis for a slider-crank mechanism with a balance mechanism is performed.The theoretical formula of the load spectrum for the interaction between the cra...Based on the basic theory of mechanics,kinematic and dynamic analysis for a slider-crank mechanism with a balance mechanism is performed.The theoretical formula of the load spectrum for the interaction between the crank shaft and the bearing seat of the upper beam is achieved by approximately simplifying the mechanical model of the crank shaft.The simulation for the load spectrum data of combined frame under the operating conditions of blanking or piling is performed using Matlab and the law of the load spectrum curves under these two conditions is analyzed.The simulation results show that under a no-load condition,the load spectrum curves of the interaction between the crank shaft and the bearing seat of the upper beam present a form of periodic sine wave and under the piling condition,the load spectrum curves of the interaction between the crank shaft and the bearing seat of the upper beam present a form of periodic pulse wave.The simulation results can provide a theoretical foundation for the load determination during the process of analyzing the dynamic characteristics on the combined frame of a closed high-speed press through the finite element method.展开更多
A filtering method of aero-engine load spectrum based on the rain flow counting is proposed in this paper.Firstly,the original load spectrum is counted through the rain flow method to get the peak and valley values.Th...A filtering method of aero-engine load spectrum based on the rain flow counting is proposed in this paper.Firstly,the original load spectrum is counted through the rain flow method to get the peak and valley values.Then,some data points in the original load spectrum are added between the peak and valley values.Finally,the filtering spectrum is obtained.The proposed method can reflect the path information of the original load spectrum.In addition,it can also eliminate the noise in the signal and improve the efficiency of signal processing,which is of practical significance for the research of aero-engine.展开更多
The rain-flow counting method is widely used to compile the fatigue load spectrum, The second stage counting of the rain-flow method is a troublesome process. In order to overcome this drawback, the rain-flow and reve...The rain-flow counting method is widely used to compile the fatigue load spectrum, The second stage counting of the rain-flow method is a troublesome process. In order to overcome this drawback, the rain-flow and reverse rain-flow counting method is proposed in this paper. In this counting method, the rule for counting of the rain-flow method is modified, so that the sequence of load-time need not be adjusted. This is a valid and useful method to count cycles and compile the load spectrum and it can be widely used in ocean engineering.展开更多
A new, more actual approach for omitting small loads in a loading history was pres-ented according to crack closure, and load interactive effects which are large on damage of com-ponents were studied. Intrinsic period...A new, more actual approach for omitting small loads in a loading history was pres-ented according to crack closure, and load interactive effects which are large on damage of com-ponents were studied. Intrinsic periodic spectrum block representing a damage element of a loadhistory, a new concept, was put out. It has been proven by theoretic analysis and tests that themodes of constructing fatigue loading spectrum have little effect on damage of components,which will change the incomplete knowledges on constructing fatigue spectrum ago.展开更多
In order to study the fatigue fracture behavior of the rear axle of certain China-made car, the strain loading spectrum near the rear axle fracture location is collected, the modified Neuber rule and the cyclic stress...In order to study the fatigue fracture behavior of the rear axle of certain China-made car, the strain loading spectrum near the rear axle fracture location is collected, the modified Neuber rule and the cyclic stress-strain hysteresis loop curve equation are used to convert the nominal strain his- tory into the local stress-strain response. The impact of mean stress on fatigue damage is corrected according to the Manson-Coffin model, and programming calculation of the fatigue damage of the fracture crack is conducted in the INFIELD software, the electromagnetic vibrators are used to sweep the vibration modal frequencies of the rear axle and car body. The enhancement test and fre- quency sweep results show that the rear axle fatigue damage mainly concentrates on the washboard road, and when the forced vibration excitation frequency is 24. 07 Hz, the vibration modal frequency of the rear axle is close to the excitation frequency of the washboard road, leading to resonance and making the rear axle subjected to large strain and fatigue damage, and then vibration fatigue fracture due to high stress concentration.展开更多
Cavitation erosion is an especially destructive and complex phenomenon. To understand its basic mechanism, the fatigue process of materials during cavitation erosion was investigated by numerical simulation technology...Cavitation erosion is an especially destructive and complex phenomenon. To understand its basic mechanism, the fatigue process of materials during cavitation erosion was investigated by numerical simulation technology. The loading spectrum used was generated by a spark-discharged electrode. Initiation crack life and true stress amplitude was used to explain the cavitation failure period and damage mechanism. The computational results indicated that the components of different materials exhibited various fatigue lives under the same external conditions. When the groove depth was extended, the initiation crack life decreased rapidly, while the true stress amplitude was increased simultaneously. This gave an important explanation to the accelerating material loss rate during cavitation erosion. However, when the groove depth was fixed and the length varied, the fatigue life became complex, more fluctuant than that happened in depth. The results also indicate that the fatigue effect of cavitation plays an important role in contributing to the formation and propagation of characteristic pits.展开更多
Based on the platform of Matlab and the theory of digital signal processing, we propose a method in the cepstrum domain for dynamic load spectra identification of machinery. We demonstrate that the dynamic load spectr...Based on the platform of Matlab and the theory of digital signal processing, we propose a method in the cepstrum domain for dynamic load spectra identification of machinery. We demonstrate that the dynamic load spectra can be identified from the response signal of the system, based on cepstra. An ARMA model is built based on the harmonic retrieval by high-order spectra. The coefficients of a Green function are determined and the window width can be estimated. Finally the effectiveness of the method is validated by simulation results.展开更多
Drive system is the key device of armored chassis. Its working state and reliability influence the maneuver performance of armored chassis directly. In order to simulate the failure process and evaluate the service re...Drive system is the key device of armored chassis. Its working state and reliability influence the maneuver performance of armored chassis directly. In order to simulate the failure process and evaluate the service reliability of drive system in training or battle missions,a new kind of dynamic simulation model and driving simulation platform of the complete drive system were established based on virtual prototype and finite element technology in this paper. Using the platform, the kinematics and dynamic characteristics of drive system were studied and analyzed in detail,the dynamic load spectrum of key components was obtained,the service life was predicted, and the service reliability evaluation results were provided. A simulation example of transmission gear was shown to illustrate the simulation and evaluation process. The result proves that the simulation method not only can be used to compute and evaluate the service reliability of complex mechanical mechanism, but also has high precision and reasonable computational cost. Therefore,simulation and reliability analysis based on virtual prototype of the armored chassis drive system will provide scientific reference for the formulation of armored chassis reasonable repair cycle.展开更多
In order to predict the extreme load of the mechanical components during the entire life,an automatic method based on the bootstrapping technology(BT)is proposed to determine the most suitable threshold.Based on all t...In order to predict the extreme load of the mechanical components during the entire life,an automatic method based on the bootstrapping technology(BT)is proposed to determine the most suitable threshold.Based on all the turning points of the load history and a series of thresholds estimated in advance,the generalized Pareto distribution is established to fit the exceedances.The corresponding distribution parameters are estimated with the maximum likelihood method.Then,BT is employed to calculate the mean squared error(MSE)of each estimated threshold based on the exceedances and the specific distribution parameters.Finally,the threshold with the smallest MSE will be the optimal one.Compared to the kurtosis method and the mean excess function method,the average deviation of the probability density function of exceedances determined by BT reduces by 38.52%and 29.25%,respectively.Moreover,the quantile-quantile plot of the exceedances determined by BT is closer to a straight line.The results suggest the improvement of the modeling flexibility and the determined threshold precision.If the exceedances are insufficient,BT will enlarge their amount by resampling to solve the instability problem of the original distribution parameters.展开更多
The simplification of fatigue load spectrum,which can effectively reduce experimental cost,is of great importance for structural fatigue tests.By introducing random variables,the probabilistic tolerance method of remo...The simplification of fatigue load spectrum,which can effectively reduce experimental cost,is of great importance for structural fatigue tests.By introducing random variables,the probabilistic tolerance method of removing small amplitude cycles proposed in this paper takes into account the randomness of both load and fatigue limit.The probability of the damage occurrence caused by the removed small loads is calculated to ensure that it cannot exceed the given probabilistic tolerance.Accordingly,the omission level is obtained and the truncated spectrum is formed.The unnotched aluminum sheet specimens are used to perform the fatigue test on the original fatigue spectrum and truncated fatigue spectrum of a transporter.The test results show that there is no statistical difference between the test life of the truncated spectrum and that of the original spectrum,which demonstrates the validity of the small-load-omitting method that considers randomness.展开更多
The load spectrum of the main bearing of tunnel boring machine( TBM) is difficult to establish because of the complex factors affecting the driving load of tunneling. In this paper, a simulation model of dynamic load ...The load spectrum of the main bearing of tunnel boring machine( TBM) is difficult to establish because of the complex factors affecting the driving load of tunneling. In this paper, a simulation model of dynamic load of cutterhead is established,with a view to structural features and special conditions, based on a complex combination stratum, the cutter layout model and cutterhead control parameters,and it is a dynamic load boundary of the main drive bearing. Combined with the load distribution calculation of the main bearing and Hertz contact theory, the prediction model of dynamic load spectrum of the main drive bearing is completed during tunneling,and in accordance with the predicted results,the static and dynamics characteristics of load spectrum for the main drive bearing on the thrust and tilting moment are analyzed. The results of cutterhead load show that,in the certain complex stratum, the fluctuations of load for thrust rollers can reflect formation interface information of complex stratum in current tunneling. The main drive bearing bear the thrust and overturning moment of cutterhead under the composite,the external load has a greater influence on the load-spectrum of reverse thrust roller than that of main thrust roller,and the maximum contact stress of the two row roller is almost the same. The load spectrum,obtained by this method,can provide a meaningful reference for the design and checking of the main drive bearing,and also can be the basis of its fatigue reliability.展开更多
The dynamic load spectrum is one of the most important basis of design and dynamic characteristics analysis of machines. But it is difficult to measure it on many occasions, especially for mining machines, due to thei...The dynamic load spectrum is one of the most important basis of design and dynamic characteristics analysis of machines. But it is difficult to measure it on many occasions, especially for mining machines, due to their bad working circumstances and high cost of measurements. For such situation, the load spectrum has to be obtained by indirect determination methods. A new method to identify the load spectrum, cepstrum analysis method, was presented in this paper. This method can be used to eliminate the filtering influence of transfer function to the response signals so that the load spectrum can be determined indirectly. The experimental and engineering actual examples indicates that this method has the advantages that the calculation is simple and the measurement is easy.展开更多
As the outfield load spectrum is so complicated that it cannot be used directly for test study in laboratory.This paper presents a method to determine load spectrum for high and low cycle combined fatigue of turbine m...As the outfield load spectrum is so complicated that it cannot be used directly for test study in laboratory.This paper presents a method to determine load spectrum for high and low cycle combined fatigue of turbine mortise at elevated temperature through experimental and numerical method.First of all,the low cycle load spectrum with duration time is determined through cumulative damage rule.The rain flow counting method is applied to obtain main cycles and sub cycles,and then the stress cycle is converted into pulsation cycle(stress ratio=0)based on the S-N curve and the Goodman curve;Secondly,three groups of different amplitudes tests are established to determine the high cycle amplitude.Finally,another three groups of the high-low combined cycle fatigue(HLCCF)tests for turbine mortise of a certain type engine are carried out.The results show that the macro and micro failure modes are identical with outfield's,which verifies the accuracy of the conversion method.展开更多
The aim of this study was to analyze the effects of the planting distance and depth on the power take-off(PTO)load spectrum of a small riding-type transplanter for the optimal design of the transplanter.To measure loa...The aim of this study was to analyze the effects of the planting distance and depth on the power take-off(PTO)load spectrum of a small riding-type transplanter for the optimal design of the transplanter.To measure load data during actual planting operation,a load measurement system was developed using a torque sensor,a data acquisition system,and an inverter.Field experiments were conducted at four planting distances(26 cm,35 cm,43 cm,and 80 cm)and three planting depths(85 mm,105 mm,and 136 mm)in a field with similar soil conditions.The measured load data were inverted into a load spectrum using rain-flow counting and Smith-Watson-Topper(SWT)methods.The safety factor of a transplanter according to the planting conditions was analyzed using the converted load spectrum and commercial software.The load spectrum for all planting conditions showed torque ratios similar within a high cycle region of 108 to 109.The torque ratio increased when the planting depth increased and planting distance decreased in the low cycle region under less than 108 cycles.The safety factors of the PTO driving gear and the driven gear increased as the planting distance increased at all planting depths.When the planting depth decreased at the same planting distance,the safety factor of the PTO gears increased.The results of this study might provide useful information for a transplanter PTO design considering the working load according to the various planting conditions.展开更多
For complex engineering systems, such as trains, planes, and offshore oil platforms, load spectra are cornerstone of their safety designs and fault diagnoses. We demonstrate in this study that well-orchestrated machin...For complex engineering systems, such as trains, planes, and offshore oil platforms, load spectra are cornerstone of their safety designs and fault diagnoses. We demonstrate in this study that well-orchestrated machine learning modeling, in combination with limited experimental data, can effectively reproduce the high-fidelity, history-dependent load spectra in critical sites of complex engineering systems, such as high-speed trains. To meet the need for in-service monitoring, we propose a segmentation and randomization strategy for long-duration historical data processing to improve the accuracy of our data-driven model for longterm load-time history prediction. Results showed the existence of an optimal length of subsequence, which is associated with the characteristic dissipation time of the dynamic system. Moreover, the data-driven model exhibits an excellent generalization capability to accurately predict the load spectra for different levels of passenger-dedicated lines. In brief, we pave the way, from data preprocessing, hyperparameter selection, to learning strategy, on how to capture the nonlinear responses of such a dynamic system, which may then provide a unifying framework that could enable the synergy of computation and in-field experiments to save orders of magnitude of expenses for the load spectrum monitoring of complex engineering structures in service and prevent catastrophic fatigue and fracture in those solids.展开更多
基金National Natural Science Foundation of China(No.11272082)
文摘The rainflow counting method is a reasonable cyclecounting procedure for fatigue life calculation and simulation testing of structures.It defines cycles as closed stress /strain hysteresis loops.Application of the rainflow counting method requires a data processing of the loading spectrum,which consists of the elimination of non-peak value data points,load time histories adjustment and loop extraction.In the data processing of the loading spectrum,if a stress point is neither the peak nor the valley,it will be identified and eliminated from the loading spectrum.Generally,the loading process is idealized as a single peak-valley straight line.But in actually,there are polylines or nearly straight lines between peaks and valleys which can't be ignored.Therefore,in the process of eliminating such data points,it will produce error in method itself.To reduce the error produced by the traditional method itself,a new method which can well simplify the polylines in data processing of loading spectrum is proposed in this paper.Comparing with the original approximation method,the proposed method has higher precision.
基金sponsored by the National Natural Science Foundation of China(52105269).
文摘For the randomness of crane working load leading to the decrease of load spectrum prediction accuracy with time,an adaptive TSSA-HKRVM model for crane load spectrum regression prediction is proposed.The heterogeneous kernel relevance vector machine model(HKRVM)with comprehensive expression ability is established using the complementary advantages of various kernel functions.The combination strategy consisting of refraction reverse learning,golden sine,and Cauchy mutation+logistic chaotic perturbation is introduced to form a multi-strategy improved sparrow algorithm(TSSA),thus optimizing the relevant parameters of HKRVM.The adaptive updatingmechanismof the heterogeneous kernel RVMmodel under themulti-strategy improved sparrow algorithm(TSSA-HKMRVM)is defined by the sliding window design theory.Based on the sample data of the measured load spectrum,the trained adaptive TSSA-HKRVMmodel is employed to complete the prediction of the crane equivalent load spectrum.Applying this method toQD20/10 t×43m×12mgeneral bridge crane,the results show that:compared with other prediction models,although the complexity of the adaptive TSSA-HKRVMmodel is relatively high,the prediction accuracy of the load spectrum under long periods has been effectively improved,and the completeness of the load information during thewhole life cycle is relatively higher,with better applicability.
基金The Key Technologies R& D Program of Jiangsu Province(No. BE2006036)Transformation Program of Science and Technology Achievements of Jiangsu Province (No. BA2008030)
文摘Based on the basic theory of mechanics,kinematic and dynamic analysis for a slider-crank mechanism with a balance mechanism is performed.The theoretical formula of the load spectrum for the interaction between the crank shaft and the bearing seat of the upper beam is achieved by approximately simplifying the mechanical model of the crank shaft.The simulation for the load spectrum data of combined frame under the operating conditions of blanking or piling is performed using Matlab and the law of the load spectrum curves under these two conditions is analyzed.The simulation results show that under a no-load condition,the load spectrum curves of the interaction between the crank shaft and the bearing seat of the upper beam present a form of periodic sine wave and under the piling condition,the load spectrum curves of the interaction between the crank shaft and the bearing seat of the upper beam present a form of periodic pulse wave.The simulation results can provide a theoretical foundation for the load determination during the process of analyzing the dynamic characteristics on the combined frame of a closed high-speed press through the finite element method.
基金This work was supported by the National Basic Research Program of China,National Nature Science Foundation of China(No.51675266)the Foundation Research Funds for the Center in NUAA(Nos.NJ20160038,NS2017011)Foundation of Graduate Innovation Center in NUAA(No.kfjj20170220)。
文摘A filtering method of aero-engine load spectrum based on the rain flow counting is proposed in this paper.Firstly,the original load spectrum is counted through the rain flow method to get the peak and valley values.Then,some data points in the original load spectrum are added between the peak and valley values.Finally,the filtering spectrum is obtained.The proposed method can reflect the path information of the original load spectrum.In addition,it can also eliminate the noise in the signal and improve the efficiency of signal processing,which is of practical significance for the research of aero-engine.
基金The project was financially supported by the National Natural Science Foundation of China (Grant No. 50078010)
文摘The rain-flow counting method is widely used to compile the fatigue load spectrum, The second stage counting of the rain-flow method is a troublesome process. In order to overcome this drawback, the rain-flow and reverse rain-flow counting method is proposed in this paper. In this counting method, the rule for counting of the rain-flow method is modified, so that the sequence of load-time need not be adjusted. This is a valid and useful method to count cycles and compile the load spectrum and it can be widely used in ocean engineering.
文摘A new, more actual approach for omitting small loads in a loading history was pres-ented according to crack closure, and load interactive effects which are large on damage of com-ponents were studied. Intrinsic periodic spectrum block representing a damage element of a loadhistory, a new concept, was put out. It has been proven by theoretic analysis and tests that themodes of constructing fatigue loading spectrum have little effect on damage of components,which will change the incomplete knowledges on constructing fatigue spectrum ago.
基金Supported by the National Natural Science Foundation of China( 51008034 )Development Plan Project of Jilin Provincial Science and Technology Department ( 201201135)Chunmiao Foundation of Jilin Provincial Education Department( 2013299)
文摘In order to study the fatigue fracture behavior of the rear axle of certain China-made car, the strain loading spectrum near the rear axle fracture location is collected, the modified Neuber rule and the cyclic stress-strain hysteresis loop curve equation are used to convert the nominal strain his- tory into the local stress-strain response. The impact of mean stress on fatigue damage is corrected according to the Manson-Coffin model, and programming calculation of the fatigue damage of the fracture crack is conducted in the INFIELD software, the electromagnetic vibrators are used to sweep the vibration modal frequencies of the rear axle and car body. The enhancement test and fre- quency sweep results show that the rear axle fatigue damage mainly concentrates on the washboard road, and when the forced vibration excitation frequency is 24. 07 Hz, the vibration modal frequency of the rear axle is close to the excitation frequency of the washboard road, leading to resonance and making the rear axle subjected to large strain and fatigue damage, and then vibration fatigue fracture due to high stress concentration.
基金the National High-Tech Research and Development Program of China(No.2002AA331080)the Beijing Important Science Technology Projects(No.H024200050021).
文摘Cavitation erosion is an especially destructive and complex phenomenon. To understand its basic mechanism, the fatigue process of materials during cavitation erosion was investigated by numerical simulation technology. The loading spectrum used was generated by a spark-discharged electrode. Initiation crack life and true stress amplitude was used to explain the cavitation failure period and damage mechanism. The computational results indicated that the components of different materials exhibited various fatigue lives under the same external conditions. When the groove depth was extended, the initiation crack life decreased rapidly, while the true stress amplitude was increased simultaneously. This gave an important explanation to the accelerating material loss rate during cavitation erosion. However, when the groove depth was fixed and the length varied, the fatigue life became complex, more fluctuant than that happened in depth. The results also indicate that the fatigue effect of cavitation plays an important role in contributing to the formation and propagation of characteristic pits.
基金Project 59775004 supported by National Natural Science Foundation of China
文摘Based on the platform of Matlab and the theory of digital signal processing, we propose a method in the cepstrum domain for dynamic load spectra identification of machinery. We demonstrate that the dynamic load spectra can be identified from the response signal of the system, based on cepstra. An ARMA model is built based on the harmonic retrieval by high-order spectra. The coefficients of a Green function are determined and the window width can be estimated. Finally the effectiveness of the method is validated by simulation results.
文摘Drive system is the key device of armored chassis. Its working state and reliability influence the maneuver performance of armored chassis directly. In order to simulate the failure process and evaluate the service reliability of drive system in training or battle missions,a new kind of dynamic simulation model and driving simulation platform of the complete drive system were established based on virtual prototype and finite element technology in this paper. Using the platform, the kinematics and dynamic characteristics of drive system were studied and analyzed in detail,the dynamic load spectrum of key components was obtained,the service life was predicted, and the service reliability evaluation results were provided. A simulation example of transmission gear was shown to illustrate the simulation and evaluation process. The result proves that the simulation method not only can be used to compute and evaluate the service reliability of complex mechanical mechanism, but also has high precision and reasonable computational cost. Therefore,simulation and reliability analysis based on virtual prototype of the armored chassis drive system will provide scientific reference for the formulation of armored chassis reasonable repair cycle.
基金The National Science and Technology Pillar Program of China(No.2015BAF07B00)
文摘In order to predict the extreme load of the mechanical components during the entire life,an automatic method based on the bootstrapping technology(BT)is proposed to determine the most suitable threshold.Based on all the turning points of the load history and a series of thresholds estimated in advance,the generalized Pareto distribution is established to fit the exceedances.The corresponding distribution parameters are estimated with the maximum likelihood method.Then,BT is employed to calculate the mean squared error(MSE)of each estimated threshold based on the exceedances and the specific distribution parameters.Finally,the threshold with the smallest MSE will be the optimal one.Compared to the kurtosis method and the mean excess function method,the average deviation of the probability density function of exceedances determined by BT reduces by 38.52%and 29.25%,respectively.Moreover,the quantile-quantile plot of the exceedances determined by BT is closer to a straight line.The results suggest the improvement of the modeling flexibility and the determined threshold precision.If the exceedances are insufficient,BT will enlarge their amount by resampling to solve the instability problem of the original distribution parameters.
基金supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)National Natural Science Foundations of China(Nos.52075244,52002181)。
文摘The simplification of fatigue load spectrum,which can effectively reduce experimental cost,is of great importance for structural fatigue tests.By introducing random variables,the probabilistic tolerance method of removing small amplitude cycles proposed in this paper takes into account the randomness of both load and fatigue limit.The probability of the damage occurrence caused by the removed small loads is calculated to ensure that it cannot exceed the given probabilistic tolerance.Accordingly,the omission level is obtained and the truncated spectrum is formed.The unnotched aluminum sheet specimens are used to perform the fatigue test on the original fatigue spectrum and truncated fatigue spectrum of a transporter.The test results show that there is no statistical difference between the test life of the truncated spectrum and that of the original spectrum,which demonstrates the validity of the small-load-omitting method that considers randomness.
基金Scientific Research Project of Department of Education of Liaoning Province,China(No.L2014228)
文摘The load spectrum of the main bearing of tunnel boring machine( TBM) is difficult to establish because of the complex factors affecting the driving load of tunneling. In this paper, a simulation model of dynamic load of cutterhead is established,with a view to structural features and special conditions, based on a complex combination stratum, the cutter layout model and cutterhead control parameters,and it is a dynamic load boundary of the main drive bearing. Combined with the load distribution calculation of the main bearing and Hertz contact theory, the prediction model of dynamic load spectrum of the main drive bearing is completed during tunneling,and in accordance with the predicted results,the static and dynamics characteristics of load spectrum for the main drive bearing on the thrust and tilting moment are analyzed. The results of cutterhead load show that,in the certain complex stratum, the fluctuations of load for thrust rollers can reflect formation interface information of complex stratum in current tunneling. The main drive bearing bear the thrust and overturning moment of cutterhead under the composite,the external load has a greater influence on the load-spectrum of reverse thrust roller than that of main thrust roller,and the maximum contact stress of the two row roller is almost the same. The load spectrum,obtained by this method,can provide a meaningful reference for the design and checking of the main drive bearing,and also can be the basis of its fatigue reliability.
文摘The dynamic load spectrum is one of the most important basis of design and dynamic characteristics analysis of machines. But it is difficult to measure it on many occasions, especially for mining machines, due to their bad working circumstances and high cost of measurements. For such situation, the load spectrum has to be obtained by indirect determination methods. A new method to identify the load spectrum, cepstrum analysis method, was presented in this paper. This method can be used to eliminate the filtering influence of transfer function to the response signals so that the load spectrum can be determined indirectly. The experimental and engineering actual examples indicates that this method has the advantages that the calculation is simple and the measurement is easy.
基金This work is supported by National Natural Science Foundation of China(51305012)Doctoral Fund of Ministry of Education of China(20111102120011)National Natural Science Foundation of China(51375031).The writers are grateful。
文摘As the outfield load spectrum is so complicated that it cannot be used directly for test study in laboratory.This paper presents a method to determine load spectrum for high and low cycle combined fatigue of turbine mortise at elevated temperature through experimental and numerical method.First of all,the low cycle load spectrum with duration time is determined through cumulative damage rule.The rain flow counting method is applied to obtain main cycles and sub cycles,and then the stress cycle is converted into pulsation cycle(stress ratio=0)based on the S-N curve and the Goodman curve;Secondly,three groups of different amplitudes tests are established to determine the high cycle amplitude.Finally,another three groups of the high-low combined cycle fatigue(HLCCF)tests for turbine mortise of a certain type engine are carried out.The results show that the macro and micro failure modes are identical with outfield's,which verifies the accuracy of the conversion method.
基金This work was supported by the Industrial Strategic Technology Development Program(10062546,Construction database of work load and development of simulation model for tractor powertrain)funded by the Ministry of Trade,Industry&Energy(MI,Korea).
文摘The aim of this study was to analyze the effects of the planting distance and depth on the power take-off(PTO)load spectrum of a small riding-type transplanter for the optimal design of the transplanter.To measure load data during actual planting operation,a load measurement system was developed using a torque sensor,a data acquisition system,and an inverter.Field experiments were conducted at four planting distances(26 cm,35 cm,43 cm,and 80 cm)and three planting depths(85 mm,105 mm,and 136 mm)in a field with similar soil conditions.The measured load data were inverted into a load spectrum using rain-flow counting and Smith-Watson-Topper(SWT)methods.The safety factor of a transplanter according to the planting conditions was analyzed using the converted load spectrum and commercial software.The load spectrum for all planting conditions showed torque ratios similar within a high cycle region of 108 to 109.The torque ratio increased when the planting depth increased and planting distance decreased in the low cycle region under less than 108 cycles.The safety factors of the PTO driving gear and the driven gear increased as the planting distance increased at all planting depths.When the planting depth decreased at the same planting distance,the safety factor of the PTO gears increased.The results of this study might provide useful information for a transplanter PTO design considering the working load according to the various planting conditions.
基金supported by the Basic Science Center of the National Natural Science Foundation of China for “Multiscale Problems in Nonlinear Mechanics”(Grant No. 11988102)the National Key Research and Development Program of China (Grant Nos. 2017YFB0202800 and2016YFB1200602)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB22020200)the Science Challenge Project (Grant No. TZ2018002)。
文摘For complex engineering systems, such as trains, planes, and offshore oil platforms, load spectra are cornerstone of their safety designs and fault diagnoses. We demonstrate in this study that well-orchestrated machine learning modeling, in combination with limited experimental data, can effectively reproduce the high-fidelity, history-dependent load spectra in critical sites of complex engineering systems, such as high-speed trains. To meet the need for in-service monitoring, we propose a segmentation and randomization strategy for long-duration historical data processing to improve the accuracy of our data-driven model for longterm load-time history prediction. Results showed the existence of an optimal length of subsequence, which is associated with the characteristic dissipation time of the dynamic system. Moreover, the data-driven model exhibits an excellent generalization capability to accurately predict the load spectra for different levels of passenger-dedicated lines. In brief, we pave the way, from data preprocessing, hyperparameter selection, to learning strategy, on how to capture the nonlinear responses of such a dynamic system, which may then provide a unifying framework that could enable the synergy of computation and in-field experiments to save orders of magnitude of expenses for the load spectrum monitoring of complex engineering structures in service and prevent catastrophic fatigue and fracture in those solids.
