The calculation principle of sampled FBG, which is called transfer matrix method, is analyzed and the simulation software is designed. The sampled FBG is simulated with the software we designed and is fabricated by ou...The calculation principle of sampled FBG, which is called transfer matrix method, is analyzed and the simulation software is designed. The sampled FBG is simulated with the software we designed and is fabricated by ourselves.The experiment result fits well with the simulated one.It is concluded that to improve the refractive modulation index is an effective way to fabricate a sampled FBG with high-reflectivity.展开更多
The effect of frequency and sample shape on fatigue behaviors of DZ125 superalloy are systematically studied.The results show that fatigue fracture still occurs above the cycle of 10~8 for tests carried out at the fre...The effect of frequency and sample shape on fatigue behaviors of DZ125 superalloy are systematically studied.The results show that fatigue fracture still occurs above the cycle of 10~8 for tests carried out at the frequency of f=20 kHz and stress ratio R =-1,so the traditional fatigue limit at cycle of 10~7 is not appropriate for fatigue design.Fatigue fracture surfaces are perpendicular to stress axis for cylindrical and plate specimens,and the fatigue cracks originate from the extra surface of the specimens.Fatigue crack is apt to propagate from cutting direction to forward direction,which occurs mainly in the second propagation stage at higher stress amplitude. There is an obvious frequency effect for DZ125 superalloy.The higher the test frequency is,the more serious the effect of frequency on fatigue behaviors of the alloy.After the frequency correction,the ultra-high cycle fatigue S-N curve well coincide with the traditional fatigue S-N curve.展开更多
It is assumed that the storm wave takes place once a year during the design period, and Nhistories of storm waves are generated on the basis of wave spectrum corresponding to the N-year design period. The responses of...It is assumed that the storm wave takes place once a year during the design period, and Nhistories of storm waves are generated on the basis of wave spectrum corresponding to the N-year design period. The responses of the breakwater to the N histories of storm waves in the N-year design period are calculated by mass-spring-dashpot mode and taken as a set of samples. The failure probability of caisson breakwaters during the design period of N years is obtained by the statistical analysis of many sets of samples. It is the key issue to improve the efficiency of the common Monte Carlo simulation method in the failure probability estimation of caisson breakwaters in the complete life cycle. In this paper, the kernel method of importance sampling, which can greatly increase the efficiency of failure probability calculation of caisson breakwaters, is proposed to estimate the failure probability of caisson breakwaters in the complete life cycle. The effectiveness of the kernel method is investigated by an example. It is indicated that the calculation efficiency of the kernel method is over 10 times the common Monte Carlo simulation method.展开更多
In this paper, the influence of sampling intervals on the chattering in sliding mode （SM） control systems is considered. The describing function （DF） approach is employed to analyze the chattering characteristics ...In this paper, the influence of sampling intervals on the chattering in sliding mode （SM） control systems is considered. The describing function （DF） approach is employed to analyze the chattering characteristics in the sampling SM control. By the DF calculations and limit cycle existence conditions, an unstable limit cycle and two stable limit cycles are found in the SM control system. The frequencies and amplitudes of the two limit cycles can also be estimated by graphical calculations. The estimation accuracy of chattering parameters is evaluated by the simulations. The results of simulations show that the system could converge to a large and a small limit cycle from different initial conditions.展开更多
文摘The calculation principle of sampled FBG, which is called transfer matrix method, is analyzed and the simulation software is designed. The sampled FBG is simulated with the software we designed and is fabricated by ourselves.The experiment result fits well with the simulated one.It is concluded that to improve the refractive modulation index is an effective way to fabricate a sampled FBG with high-reflectivity.
文摘The effect of frequency and sample shape on fatigue behaviors of DZ125 superalloy are systematically studied.The results show that fatigue fracture still occurs above the cycle of 10~8 for tests carried out at the frequency of f=20 kHz and stress ratio R =-1,so the traditional fatigue limit at cycle of 10~7 is not appropriate for fatigue design.Fatigue fracture surfaces are perpendicular to stress axis for cylindrical and plate specimens,and the fatigue cracks originate from the extra surface of the specimens.Fatigue crack is apt to propagate from cutting direction to forward direction,which occurs mainly in the second propagation stage at higher stress amplitude. There is an obvious frequency effect for DZ125 superalloy.The higher the test frequency is,the more serious the effect of frequency on fatigue behaviors of the alloy.After the frequency correction,the ultra-high cycle fatigue S-N curve well coincide with the traditional fatigue S-N curve.
基金financially supported by the National Natural Science Foundation of China(Grant No.51279128)the Innovative Research Groups Science Foundation of China(Grant No.51321065)the Construction Science and Technology Project of Ministry of Transport of the People's Republic of China(Grant No.2013328224070)
文摘It is assumed that the storm wave takes place once a year during the design period, and Nhistories of storm waves are generated on the basis of wave spectrum corresponding to the N-year design period. The responses of the breakwater to the N histories of storm waves in the N-year design period are calculated by mass-spring-dashpot mode and taken as a set of samples. The failure probability of caisson breakwaters during the design period of N years is obtained by the statistical analysis of many sets of samples. It is the key issue to improve the efficiency of the common Monte Carlo simulation method in the failure probability estimation of caisson breakwaters in the complete life cycle. In this paper, the kernel method of importance sampling, which can greatly increase the efficiency of failure probability calculation of caisson breakwaters, is proposed to estimate the failure probability of caisson breakwaters in the complete life cycle. The effectiveness of the kernel method is investigated by an example. It is indicated that the calculation efficiency of the kernel method is over 10 times the common Monte Carlo simulation method.
基金supported by Industrial Research Projects in department of education of Shaanxi province(2014K05-29)Science Research Projects in department of education of Shaanxi province(14JK1669,14JF028)
文摘In this paper, the influence of sampling intervals on the chattering in sliding mode （SM） control systems is considered. The describing function （DF） approach is employed to analyze the chattering characteristics in the sampling SM control. By the DF calculations and limit cycle existence conditions, an unstable limit cycle and two stable limit cycles are found in the SM control system. The frequencies and amplitudes of the two limit cycles can also be estimated by graphical calculations. The estimation accuracy of chattering parameters is evaluated by the simulations. The results of simulations show that the system could converge to a large and a small limit cycle from different initial conditions.
