In the paper,the Matlab-Simulink model of simulation of operation of theŽS 413/417 series EMU(electric multiple unit)in traction and braking mode is exposed where changes are observed:stator currents of three-phase tr...In the paper,the Matlab-Simulink model of simulation of operation of theŽS 413/417 series EMU(electric multiple unit)in traction and braking mode is exposed where changes are observed:stator currents of three-phase traction motors,traction electric motor speeds and EMU,electromagnetic torque on the rotor shaft of the traction electric motor and DC(direct current)bus voltage.The model allowed review of the listed parameters for:different allowed values of contact network voltage and total voltage distortion at the place of connection of the EMU to the contact network,different mechanical loads of EMU and traction electric motor and different train speeds and rotation of traction electric motors.Appropriate conclusions were made through the analysis of the simulation results obtained.展开更多
Some research results are given in this paper about burnthrough and hydrogen cracking with a flowing chamber and a loop. Many factors including plate thickness, running rate, heat input and so forth have been studied....Some research results are given in this paper about burnthrough and hydrogen cracking with a flowing chamber and a loop. Many factors including plate thickness, running rate, heat input and so forth have been studied. By experiments it can be found that occurrence of hydrogen cracking can be effectively reduced by properly increasing heat input and using the tempering bead technique.展开更多
Hydrogen induced cracking (HIC) is one of the main problems of in-service welding onto active pipeline. Microstructure and hardness of welded joint have a vital effect on hydrogen induced cracking. The microstructur...Hydrogen induced cracking (HIC) is one of the main problems of in-service welding onto active pipeline. Microstructure and hardness of welded joint have a vital effect on hydrogen induced cracking. The microstructure and hardness of welded joint of XTO pipeline steel were studied using simulation in-service welding device. The results show that the main microstructures of in-service welded seam are grain boundary ferrite , intracrystalline acicular ferrite , as well as small amount of widmanztatten structure. The main microstructures of coarse grain heat-affected zone (CGHAZ) are coarse granular bainite, lath ferrite and martensite. Metastable phases such as martensite and lath ferrite are found in CGHAZ because of the too quick cooling velocity a'nd the hardness of the CGHAZ is high.展开更多
The special subject 'research on life prediction technology of important in-service pressure' mainly analyzes the failure mechanism of large-sized important and criticalin-service pressure vessels under the ac...The special subject 'research on life prediction technology of important in-service pressure' mainly analyzes the failure mechanism of large-sized important and criticalin-service pressure vessels under the action of working medium and investigates safety assessmentand life prediction technology with a view to enhance the operation reliability of in-servicepressure vessels in China. Based on a series of accident investigation and test & measuringresearch, the cause of cracking of catalytic regenerator is analyzed and the in-line non-destructiveexamination method and failure prevention measures for the cracking of catalytic regenerator areproposed.展开更多
The chamber device was designed and set up to simulate the in-service welding. The results show : the t8/5 , t8/3 and inner wall peak temperature Tp decrease with the cooling rate increases. The welding energy is car...The chamber device was designed and set up to simulate the in-service welding. The results show : the t8/5 , t8/3 and inner wall peak temperature Tp decrease with the cooling rate increases. The welding energy is carried off by flowing medium, the cooling rate increases, and many unbalanced microstructures such as granular bainite, martensite and M-A generate ; it worsens the properties of HAZ. Under air-cooling, the cooling rate is slow, the austenite grain grows obviously, the lath ferrite crosses the whole austenite, and it causes the hardness value is also big. The change of HAZ width is not obvious with the increase of cooling rate; and burn-through is not susceptible to the cooling rate. The quench microstructures increase and the hydrogen does not outflow from the HAZ easily when increase the cooling rate, so the susceptibility of hydrogen cracking increases.展开更多
Elbows are the most vulnerable parts in pipeline network systems. The residual stress for in-service welding repair has significant impacts on the mechanical properties of straight pipes and elbows. In this paper,the ...Elbows are the most vulnerable parts in pipeline network systems. The residual stress for in-service welding repair has significant impacts on the mechanical properties of straight pipes and elbows. In this paper,the thermal elastic-plastic finite element method is employed to investigate the mechanical field during the in-service welding. The prediction of residual stress and deformation in the straight pipe and elbow is performed based on the validation of the numerical models. And the effects of the curvature radius and defects on the elbow are investigated. The results show that the residual stress distribution is uneven along various directions after welding. And the mechanical properties of the elbow decrease when the curvature radius is small. Compared to the intact elbow,the residual stress of the elbow with defects concentrates in the defective area. The depth of defect is the main factors affecting the mechanical properties of the elbow. A systematic analysis of the mechanical properties of straight pipes and elbows is proposed to provide guidance to the in-service welding.展开更多
SYSWELD was used to simulate in-service welding process of gas pipeline of X70 pipeline steel. Welding thermal cycle, stress and deformation of in-service welded joint were studied. The results show that peak temperat...SYSWELD was used to simulate in-service welding process of gas pipeline of X70 pipeline steel. Welding thermal cycle, stress and deformation of in-service welded joint were studied. The results show that peak temperature of coarse grain heat-affected zone (CGHAZ) of in-service welding onto gas pipeline is the same with routine welding, but ts/5, ts/3 and ts/1 decrease at certain degree. For the zone near welded seam, axial stress and hoop stress in the inner pipe wall are compressive stress when welding source passes through the cross-section that is studied, but residual axial stress and residual hoop stress after welded are all tensile stress. Transient deformation and residual deformation are all convex deformation compared with the original pipe diameter size. Deformation achieves maximum when welding thermal source passes through the cross-section that is studied and then decreases during the cooling process after welding.展开更多
The software of SYSWELD was used to build model and simulate thermal cycle of in-service welding onto active gas pipeline. Influence of pipe diameter, wall thickness and heat input on thermal cycle was studied. The re...The software of SYSWELD was used to build model and simulate thermal cycle of in-service welding onto active gas pipeline. Influence of pipe diameter, wall thickness and heat input on thermal cycle was studied. The results show that t8/5 , t8/3 and peak temperature of inner surface decrease when wall thickness increases from 5 mm to 12 mm. But t8/1 will increases with the increase of wall thickness and will decrease after the wall thickness is larger than 7 mm. Pipe diameter has little influence on thermal cycle and that influence can be ignored when pipe diameter is greater than 273 mm. t8/5 , t8/3 , t8/1 and peak temperature of inner surface will increase with the increase of heat input.展开更多
Malaria is generally considered a major public health problem in Somalia. Providing early diagnosis and effective treatment is the key element of malaria control strategies in malaria-endemic countries, including Soma...Malaria is generally considered a major public health problem in Somalia. Providing early diagnosis and effective treatment is the key element of malaria control strategies in malaria-endemic countries, including Somalia. This required to advocate and ensure health worker’s adherence to the national malaria guidelines at all levels of health care service. A well-designed in-service training program may improve the level of health worker’s adherence to national malaria treatment guidelines, although results have been inconsistent. This is an interventional health facility-based pre and post comparative study aimed to assess the effect of an in-service training program on the practice of healthcare workers toward malaria prevention and treatment guidelines, during in pregnancy in health facilities in Jowhar district, Middle Shabelle region of Somalia. The study was implemented in three phases: pre-intervention phase, intervention phase and post-intervention phase. The sample size consisted of (n = 150) health workers who were selected from ten public health facilities using proportional to size sampling;the data collection adopted in this research is composed of a structured interview questionnaire and observational checklist. Data was analyzed through the application of descriptive statistical analysis that includes frequency and percentage and the Chi-square (x<sup>2</sup>) test was used to test the associations among variables using SPSS software version 25. The study showed that the level of health workers’ awareness of the national malaria guidelines in the treatment and prevention of malaria in pregnancy was found to be good before the intervention 89 (59.3%) and this proportion increased to 150 (100%) post-intervention of the training program. A significance difference has been observed between health workers’ awareness and their adherence to the malarial guidelines at pre-test and post-test with a p-value 0.000. The proportion of health workers who attended previous training on national malaria guidelines in the treatment and prevention of malaria in pregnancy increased from 46 (30.7%) at the pre-test to 150 (100%) after the post-test. A significant difference was observed in the training status among different categories of health worker and their adherence to the guidelines during the pre- and post-intervention of the training program, with a p-value of 0.000. The result showed that health workers were adhering to the guidelines at the pre-test 33 (22%), this increased after the post-test to 87 (58%). The knowledge of the need to adhere led to an increase in the adherence rate after the training program intervention. The study reveals that inadequate awareness was most reason for the non-adherence in the majority of the health workers as indicated by 89 (59.3%) at the pre-test and 56 (37.3%) in the post-test. However, difference was not significant between the availability of anti-malaria drugs in the facilities and the health workers’ adherence to the guidelines p-value 0.355 at the pretest and p-value 0.258 at post-test. The study concluded that the in-service training program significantly improved health workers’ knowledge and practice to the national malaria guidelines in the treatment, and prevention of malaria in pregnancy. The researcher recommends that the national malaria control programme (NMCP) of the Federal Ministry of Health should provide continuous regular in-service training to frontline healthcare workers at (facility and Community-based) to upgrade their skills and knowledge towards the malaria guidelines, disseminate job aids to the health facilities and undertake regular monitoring to ensure effective implementation of the national malaria treatment guidelines in the treatment and prevention of malaria in pregnancy in achieving desired proper case-management practices of malaria in pregnancy at all levels of health care service.展开更多
<strong>Objective:</strong> To investigate and analyze the current status of continuing nursing education (CNE) of in-service nurses in Tibet and their demand for continuing education. <strong>Method...<strong>Objective:</strong> To investigate and analyze the current status of continuing nursing education (CNE) of in-service nurses in Tibet and their demand for continuing education. <strong>Methods:</strong> 663 active nurses in Tibet were taken as the research objects, and the self-developed questionnaire was used to investigate the current status and needs of CNE, and the correlation between the CNE needs of active nurses and their personal conditions was analyzed. <strong>Results:</strong> This study shows that 65.61% (435/663) of active nurses have not participated in any CNE, and 91.86% (609/663) of active nurses believe that they need to participate in CNE. The problems faced by active nurses in participating in CNE include funding restrictions, time limitation and ability limitation. Logistic stepwise regression analysis reveals that the age of active nurses and working years of nurses are negatively correlated with the funding restrictions for participating in CNE (P < 0.05). It is relatively more difficult for young nurses with less working experience to obtain funding for participating in CNE. Moreover, there is a negative correlation between age, educational level and the ability of nurses to participate in CNE (P < 0.05). Younger nurses with lower educational level are more difficult to participate in CNE due to personal ability. There is a positive correlation between the length of working experience and the time limitation faced to participate in CNE (P < 0.05). Senior nurses are too busy with their work to participate in CNE due to limited time. <strong>Conclusion:</strong> The problems faced by active nurses in Tibet in participating in CNE come from funding, time and ability. Young nurses with limited working experience cannot participate in CNE resulting from limited ability and funds;while senior nurses are mainly restricted by time. It is recommended that hospitals and nursing management in Tibet should solve these problems faced by nurses in participating in CNE by implementing a flexible scheduling system, and providing funding or implementing an incentive system, to enhance the confidence of active nurses in participating in CNE.展开更多
In-service structural health monitoring(SHM) technologies are critical for the utilization of composite aircraft structures. We developed a Lamb wave-based in-service SHM technology using built-in piezoelectric actu...In-service structural health monitoring(SHM) technologies are critical for the utilization of composite aircraft structures. We developed a Lamb wave-based in-service SHM technology using built-in piezoelectric actuator/sensor networks to monitor delamination extension in a full-scale composite horizontal tail. The in-service SHM technology combine of damage rapid monitoring(DRM) stage and damage imaging diagnosis(DID) stage allows for real-time monitoring and long term tracking of the structural integrity of composite aircraft structures. DRM stage using spearman rank correlation coeffi cient was introduced to generate a damage index which can be used to monitor the trend of damage extension. The DID stage based on canonical correlation analysis aimed at intuitively highlighting structural damage regions in two-dimensional images. The DRM and DID stages were trialed by an in-service SHM experiment of CFRP T-joint. Finally, the detection capability of the in-service SHM technology was verified in the SHM experiment of a full-scale composite horizontal tail. Experimental results show that the rapid monitoring method effectively monitors the damage occurrence and extension tendency in real time; damage imaging diagnosis results are consistent with those from the failure model of the composite horizontal tail structure.展开更多
Low-frequency carbody swaying phenomenon often occurs to railway vehicles due to hunting instability,which seriously deteriorates the ride comfort of passengers.This paper investigates low-frequency carbody swaying th...Low-frequency carbody swaying phenomenon often occurs to railway vehicles due to hunting instability,which seriously deteriorates the ride comfort of passengers.This paper investigates low-frequency carbody swaying through experimental analysis and numerical simulation.In the tests,the carbody acceleration,the wheel-rail profiles,and the dynamic characteristics of dampers were measured to understand the characteristics of the abnormal carbody vibration and to find out its primary contributor.Linear and nonlinear numerical simulations on the mechanism and optimization measures were carried out to solve this carbody swaying issue.The results showed that the carbody swaying is the manifest of carbody hunting instability.The low equivalent conicity and the decrease of dynamic damping of the yaw damper are probably the cause of this phenomenon.The optimization measures to increase the equivalent conicity and dynamic damping of the yaw damper were put forward and verified by on-track tests.The results of this study could enrich the knowledge of carbody hunting and provide a reference for solving abnormal carbody vibrations.展开更多
The complexity of the actual operating environment of EMU trains and the interaction between the reliability of system components have become a huge challenge for the maintenance scheduling of EMU trains. In response ...The complexity of the actual operating environment of EMU trains and the interaction between the reliability of system components have become a huge challenge for the maintenance scheduling of EMU trains. In response to these problems, the evolution of reliability and failure rate under the influence of environmental factors, failure correlations and economy correlations is analyzed. We assume bogie systems form the EMU train in series. The failure correlation matrix of the bogie systems is modeled. With the lowest total maintenance cost as the optimization objective, a decision-making model for EMU train maintenance is established. A dynamic maintenance strategy is proposed for the model, which can improve maintenance plans efficiently. Artificial bee colony algorithm is applied to further iteratively optimize the threshold parameters in the strategy. The results are calculated and verified by a numerical example. The results show the effectiveness of the maintenance decision model. The dynamic maintenance strategy in this paper is compared with the traditional opportunistic maintenance strategy. The proposed maintenance strategy outperforms the traditional opportunistic maintenance strategy in the numerical example.展开更多
文摘In the paper,the Matlab-Simulink model of simulation of operation of theŽS 413/417 series EMU(electric multiple unit)in traction and braking mode is exposed where changes are observed:stator currents of three-phase traction motors,traction electric motor speeds and EMU,electromagnetic torque on the rotor shaft of the traction electric motor and DC(direct current)bus voltage.The model allowed review of the listed parameters for:different allowed values of contact network voltage and total voltage distortion at the place of connection of the EMU to the contact network,different mechanical loads of EMU and traction electric motor and different train speeds and rotation of traction electric motors.Appropriate conclusions were made through the analysis of the simulation results obtained.
文摘Some research results are given in this paper about burnthrough and hydrogen cracking with a flowing chamber and a loop. Many factors including plate thickness, running rate, heat input and so forth have been studied. By experiments it can be found that occurrence of hydrogen cracking can be effectively reduced by properly increasing heat input and using the tempering bead technique.
文摘Hydrogen induced cracking (HIC) is one of the main problems of in-service welding onto active pipeline. Microstructure and hardness of welded joint have a vital effect on hydrogen induced cracking. The microstructure and hardness of welded joint of XTO pipeline steel were studied using simulation in-service welding device. The results show that the main microstructures of in-service welded seam are grain boundary ferrite , intracrystalline acicular ferrite , as well as small amount of widmanztatten structure. The main microstructures of coarse grain heat-affected zone (CGHAZ) are coarse granular bainite, lath ferrite and martensite. Metastable phases such as martensite and lath ferrite are found in CGHAZ because of the too quick cooling velocity a'nd the hardness of the CGHAZ is high.
基金important scientech problemtackling subject foundation under the state 9th 5-year plan(no.96-918-02-04).
文摘The special subject 'research on life prediction technology of important in-service pressure' mainly analyzes the failure mechanism of large-sized important and criticalin-service pressure vessels under the action of working medium and investigates safety assessmentand life prediction technology with a view to enhance the operation reliability of in-servicepressure vessels in China. Based on a series of accident investigation and test & measuringresearch, the cause of cracking of catalytic regenerator is analyzed and the in-line non-destructiveexamination method and failure prevention measures for the cracking of catalytic regenerator areproposed.
文摘The chamber device was designed and set up to simulate the in-service welding. The results show : the t8/5 , t8/3 and inner wall peak temperature Tp decrease with the cooling rate increases. The welding energy is carried off by flowing medium, the cooling rate increases, and many unbalanced microstructures such as granular bainite, martensite and M-A generate ; it worsens the properties of HAZ. Under air-cooling, the cooling rate is slow, the austenite grain grows obviously, the lath ferrite crosses the whole austenite, and it causes the hardness value is also big. The change of HAZ width is not obvious with the increase of cooling rate; and burn-through is not susceptible to the cooling rate. The quench microstructures increase and the hydrogen does not outflow from the HAZ easily when increase the cooling rate, so the susceptibility of hydrogen cracking increases.
基金supported by the Natural Science Foundation of Shandong Province(No.ZR2018MEE012)China University of Petroleum(East China)Graduate Innovation Project(No.YCX2017052)
文摘Elbows are the most vulnerable parts in pipeline network systems. The residual stress for in-service welding repair has significant impacts on the mechanical properties of straight pipes and elbows. In this paper,the thermal elastic-plastic finite element method is employed to investigate the mechanical field during the in-service welding. The prediction of residual stress and deformation in the straight pipe and elbow is performed based on the validation of the numerical models. And the effects of the curvature radius and defects on the elbow are investigated. The results show that the residual stress distribution is uneven along various directions after welding. And the mechanical properties of the elbow decrease when the curvature radius is small. Compared to the intact elbow,the residual stress of the elbow with defects concentrates in the defective area. The depth of defect is the main factors affecting the mechanical properties of the elbow. A systematic analysis of the mechanical properties of straight pipes and elbows is proposed to provide guidance to the in-service welding.
文摘SYSWELD was used to simulate in-service welding process of gas pipeline of X70 pipeline steel. Welding thermal cycle, stress and deformation of in-service welded joint were studied. The results show that peak temperature of coarse grain heat-affected zone (CGHAZ) of in-service welding onto gas pipeline is the same with routine welding, but ts/5, ts/3 and ts/1 decrease at certain degree. For the zone near welded seam, axial stress and hoop stress in the inner pipe wall are compressive stress when welding source passes through the cross-section that is studied, but residual axial stress and residual hoop stress after welded are all tensile stress. Transient deformation and residual deformation are all convex deformation compared with the original pipe diameter size. Deformation achieves maximum when welding thermal source passes through the cross-section that is studied and then decreases during the cooling process after welding.
基金Sponsored by Scientific Research Fund for Doctors(Y040312)Innovation Fund for Doctors(B2005-3) of China University of Petroleum
文摘The software of SYSWELD was used to build model and simulate thermal cycle of in-service welding onto active gas pipeline. Influence of pipe diameter, wall thickness and heat input on thermal cycle was studied. The results show that t8/5 , t8/3 and peak temperature of inner surface decrease when wall thickness increases from 5 mm to 12 mm. But t8/1 will increases with the increase of wall thickness and will decrease after the wall thickness is larger than 7 mm. Pipe diameter has little influence on thermal cycle and that influence can be ignored when pipe diameter is greater than 273 mm. t8/5 , t8/3 , t8/1 and peak temperature of inner surface will increase with the increase of heat input.
文摘Malaria is generally considered a major public health problem in Somalia. Providing early diagnosis and effective treatment is the key element of malaria control strategies in malaria-endemic countries, including Somalia. This required to advocate and ensure health worker’s adherence to the national malaria guidelines at all levels of health care service. A well-designed in-service training program may improve the level of health worker’s adherence to national malaria treatment guidelines, although results have been inconsistent. This is an interventional health facility-based pre and post comparative study aimed to assess the effect of an in-service training program on the practice of healthcare workers toward malaria prevention and treatment guidelines, during in pregnancy in health facilities in Jowhar district, Middle Shabelle region of Somalia. The study was implemented in three phases: pre-intervention phase, intervention phase and post-intervention phase. The sample size consisted of (n = 150) health workers who were selected from ten public health facilities using proportional to size sampling;the data collection adopted in this research is composed of a structured interview questionnaire and observational checklist. Data was analyzed through the application of descriptive statistical analysis that includes frequency and percentage and the Chi-square (x<sup>2</sup>) test was used to test the associations among variables using SPSS software version 25. The study showed that the level of health workers’ awareness of the national malaria guidelines in the treatment and prevention of malaria in pregnancy was found to be good before the intervention 89 (59.3%) and this proportion increased to 150 (100%) post-intervention of the training program. A significance difference has been observed between health workers’ awareness and their adherence to the malarial guidelines at pre-test and post-test with a p-value 0.000. The proportion of health workers who attended previous training on national malaria guidelines in the treatment and prevention of malaria in pregnancy increased from 46 (30.7%) at the pre-test to 150 (100%) after the post-test. A significant difference was observed in the training status among different categories of health worker and their adherence to the guidelines during the pre- and post-intervention of the training program, with a p-value of 0.000. The result showed that health workers were adhering to the guidelines at the pre-test 33 (22%), this increased after the post-test to 87 (58%). The knowledge of the need to adhere led to an increase in the adherence rate after the training program intervention. The study reveals that inadequate awareness was most reason for the non-adherence in the majority of the health workers as indicated by 89 (59.3%) at the pre-test and 56 (37.3%) in the post-test. However, difference was not significant between the availability of anti-malaria drugs in the facilities and the health workers’ adherence to the guidelines p-value 0.355 at the pretest and p-value 0.258 at post-test. The study concluded that the in-service training program significantly improved health workers’ knowledge and practice to the national malaria guidelines in the treatment, and prevention of malaria in pregnancy. The researcher recommends that the national malaria control programme (NMCP) of the Federal Ministry of Health should provide continuous regular in-service training to frontline healthcare workers at (facility and Community-based) to upgrade their skills and knowledge towards the malaria guidelines, disseminate job aids to the health facilities and undertake regular monitoring to ensure effective implementation of the national malaria treatment guidelines in the treatment and prevention of malaria in pregnancy in achieving desired proper case-management practices of malaria in pregnancy at all levels of health care service.
文摘<strong>Objective:</strong> To investigate and analyze the current status of continuing nursing education (CNE) of in-service nurses in Tibet and their demand for continuing education. <strong>Methods:</strong> 663 active nurses in Tibet were taken as the research objects, and the self-developed questionnaire was used to investigate the current status and needs of CNE, and the correlation between the CNE needs of active nurses and their personal conditions was analyzed. <strong>Results:</strong> This study shows that 65.61% (435/663) of active nurses have not participated in any CNE, and 91.86% (609/663) of active nurses believe that they need to participate in CNE. The problems faced by active nurses in participating in CNE include funding restrictions, time limitation and ability limitation. Logistic stepwise regression analysis reveals that the age of active nurses and working years of nurses are negatively correlated with the funding restrictions for participating in CNE (P < 0.05). It is relatively more difficult for young nurses with less working experience to obtain funding for participating in CNE. Moreover, there is a negative correlation between age, educational level and the ability of nurses to participate in CNE (P < 0.05). Younger nurses with lower educational level are more difficult to participate in CNE due to personal ability. There is a positive correlation between the length of working experience and the time limitation faced to participate in CNE (P < 0.05). Senior nurses are too busy with their work to participate in CNE due to limited time. <strong>Conclusion:</strong> The problems faced by active nurses in Tibet in participating in CNE come from funding, time and ability. Young nurses with limited working experience cannot participate in CNE resulting from limited ability and funds;while senior nurses are mainly restricted by time. It is recommended that hospitals and nursing management in Tibet should solve these problems faced by nurses in participating in CNE by implementing a flexible scheduling system, and providing funding or implementing an incentive system, to enhance the confidence of active nurses in participating in CNE.
基金Funded by the National Natural Science Foundation of China(Nos.11172053 and 91016024)the New Century Excellent Talents in University(NCET-11-0055)the Fundamental Research Funds for the Central Universities(DUT13ZD(G)06)
文摘In-service structural health monitoring(SHM) technologies are critical for the utilization of composite aircraft structures. We developed a Lamb wave-based in-service SHM technology using built-in piezoelectric actuator/sensor networks to monitor delamination extension in a full-scale composite horizontal tail. The in-service SHM technology combine of damage rapid monitoring(DRM) stage and damage imaging diagnosis(DID) stage allows for real-time monitoring and long term tracking of the structural integrity of composite aircraft structures. DRM stage using spearman rank correlation coeffi cient was introduced to generate a damage index which can be used to monitor the trend of damage extension. The DID stage based on canonical correlation analysis aimed at intuitively highlighting structural damage regions in two-dimensional images. The DRM and DID stages were trialed by an in-service SHM experiment of CFRP T-joint. Finally, the detection capability of the in-service SHM technology was verified in the SHM experiment of a full-scale composite horizontal tail. Experimental results show that the rapid monitoring method effectively monitors the damage occurrence and extension tendency in real time; damage imaging diagnosis results are consistent with those from the failure model of the composite horizontal tail structure.
基金supported by the National Key R&D Program of China under grant number 2018YFB1201701.
文摘Low-frequency carbody swaying phenomenon often occurs to railway vehicles due to hunting instability,which seriously deteriorates the ride comfort of passengers.This paper investigates low-frequency carbody swaying through experimental analysis and numerical simulation.In the tests,the carbody acceleration,the wheel-rail profiles,and the dynamic characteristics of dampers were measured to understand the characteristics of the abnormal carbody vibration and to find out its primary contributor.Linear and nonlinear numerical simulations on the mechanism and optimization measures were carried out to solve this carbody swaying issue.The results showed that the carbody swaying is the manifest of carbody hunting instability.The low equivalent conicity and the decrease of dynamic damping of the yaw damper are probably the cause of this phenomenon.The optimization measures to increase the equivalent conicity and dynamic damping of the yaw damper were put forward and verified by on-track tests.The results of this study could enrich the knowledge of carbody hunting and provide a reference for solving abnormal carbody vibrations.
基金Sponsored by the National Natural Science Foundation of China(Grant No. 72061022)。
文摘The complexity of the actual operating environment of EMU trains and the interaction between the reliability of system components have become a huge challenge for the maintenance scheduling of EMU trains. In response to these problems, the evolution of reliability and failure rate under the influence of environmental factors, failure correlations and economy correlations is analyzed. We assume bogie systems form the EMU train in series. The failure correlation matrix of the bogie systems is modeled. With the lowest total maintenance cost as the optimization objective, a decision-making model for EMU train maintenance is established. A dynamic maintenance strategy is proposed for the model, which can improve maintenance plans efficiently. Artificial bee colony algorithm is applied to further iteratively optimize the threshold parameters in the strategy. The results are calculated and verified by a numerical example. The results show the effectiveness of the maintenance decision model. The dynamic maintenance strategy in this paper is compared with the traditional opportunistic maintenance strategy. The proposed maintenance strategy outperforms the traditional opportunistic maintenance strategy in the numerical example.