Fatigue life and reliability of aero-engine blade are always of important significance to flight safety.The establishment of damage model is one of the key factors in blade fatigue research.Conventional linear Miner＇...Fatigue life and reliability of aero-engine blade are always of important significance to flight safety.The establishment of damage model is one of the key factors in blade fatigue research.Conventional linear Miner＇s sum method is not suitable for aero-engine because of its low accuracy.A back propagation neutral network（BPNN） based on the combination of Levenberg-Marquardt（LM） and finite element method（FEM） is used to describe process of nonlinear damage accumulation behavior in material and predict fatigue life of the blade.Fatigue tests of standard specimen made from TC4 are carried out to obtain material fatigue parameters and S-N curve.A nonlinear continuum damage model（CDM）,based on the BPNN with one hidden layer and ten neurons,is built to investigate the nonlinear damage accumulation behavior,in which the results from the tests are used as training set.Comparing with linear models and previous nonlinear models,BPNN has the lowest calculation error in full load range.It has significant accuracy when the load is below 500 MPa.Especially,when the load is 350 MPa,the calculation error of the BPNN is only 0.4%.The accurate model of the blade is built by using 3D coordinate measurement technology.The loading cycle in fatigue analysis is defined from takeoff to cruise in 10 min,and the load history is obtained from finite element analysis（FEA）.Then the fatigue life of the compressor blade is predicted by using the BPNN model.The final fatigue life of the aero-engine blade is 6.55 104 cycles（10 916 h） based on the BPNN model,which is effective for the virtual design of aero-engine blade.展开更多
To comprehensively consider the effects of strength degeneration and failure correlation, an improved stress–strength interference （SSI） model is proposed to analyze the reliability of aeroengine blades with the fa...To comprehensively consider the effects of strength degeneration and failure correlation, an improved stress–strength interference （SSI） model is proposed to analyze the reliability of aeroengine blades with the fatigue failure mode. Two types of TC4 alloy experiments are conducted for the study on the damage accumulation law. All the parameters in the nonlinear damage model are obtained by the tension–compression fatigue tests, and the accuracy of the nonlinear damage model is verified by the damage tests. The strength degeneration model is put forward on the basis of the Chaboche nonlinear damage theory and the Griffith fracture criterion, and determined by measuring the fatigue toughness during the tests. From the comparison of two kinds of degeneration models based on the Miner’s linear law and the nonlinear damage model respectively, the nonlinear model has a significant advantage on prediction accuracy especially in the later period of life. A time-dependent SSI reliability model is established. By computing the stress distribution using the finite element （FE） technique, the reliability of a single blade during the whole service life is obtained. Considering the failure correlation of components, a modified reliability model of aero-engine blades with common cause failure （CCF） is presented. It shows a closer and more reasonable process with the actual working condition. The improved reliability model is illustrated to be applied to aero-engine blades well, and the approach purposed in this paper is suitable for any actual machinery component of aero-engine rotor systems.展开更多
The performance and particulate emission of a diesel engine are affected by the consumption of lubricating oil. Most studies on oil consumption mechanism of the cylinder have been done by using the experimental method...The performance and particulate emission of a diesel engine are affected by the consumption of lubricating oil. Most studies on oil consumption mechanism of the cylinder have been done by using the experimental method, however they are very costly. Therefore, it is very necessary to study oil consumption mechanism of the cylinder and obtain the accurate results by the calculation method. Firstly, four main modes of lubricating oil consumption in cylinder are analyzed and then the oil consumption rate under common working conditions are calculated for the four modes based on an engine. Then, the factors that affect the lubricating oil consumption such as working conditions, the second ring closed gap, the elastic force of the piston rings are also investigated for the four modes. The calculation results show that most of the lubricating oil is consumed by evaporation on the liner surface. Besides, there are three other findings： （1） The oil evaporation from the liner is determined by the working condition of an engine; （2） The increase of the ring closed gap reduces the oil blow through the top ring end gap but increases blow-by; （3） With the increase of the elastic force of the ring, both the left oil film thickness and the oil throw-off at the top ring decrease. The oil scraping of the piston top edge is consequently reduced while the friction loss between the rings and the liner increases. A neural network prediction model of the lubricating oil consumption in cylinder is established based on the BP neural network theory, and then the model is trained and validated. The main piston rings parameters which affect the oil consumption are optimized by using the BP neural network prediction model and the prediction accuracy of this BP neural network is within 8%, which is acceptable for normal engineering applications. The oil consumption is also measured experimentally. The relative errors of the calculated and experimental values are less than 10%, verifying the validity of the simulation results. Applying the established simulation model and the validated BP network model is able to generate numerical results with sufficient accuracy, which significantly reduces experimental work and provides guidance for the optimal design of the piston rings diesel engines.展开更多
以某燃料电池载重车为研究对象,建立了包括燃料电池、储氢罐、电动机及变速箱、动力电池和DC/DC(direct current to direct current)变换器等全部动力系统子结构在内的28自由度动力学模型,并结合实车道路测试进行了模型验证。通过动力...以某燃料电池载重车为研究对象,建立了包括燃料电池、储氢罐、电动机及变速箱、动力电池和DC/DC(direct current to direct current)变换器等全部动力系统子结构在内的28自由度动力学模型,并结合实车道路测试进行了模型验证。通过动力学模拟和试验设计探究了动力系统子结构位置、悬置刚度和阻尼对驾驶室和燃料电池振动的影响。结果显示:驾驶室振动在2、4、9、12 Hz有明显的能量集中,除受到悬架偏频和簧下偏频的影响外,储氢罐位置和燃料电池位置分别对驾驶室2~4 Hz和9~12 Hz振动影响最大,燃料电池振动受其本身悬置刚度的影响最大,动力系统其他结构对上述振动也有一定影响。以动力系统安装空间与悬置变形量为约束,以动力系统位置、子结构悬置刚度和阻尼为优化变量,进行驾驶室多频率振动和燃料电池加速度均方根的多目标优化设计。优化结果表明:在不同车速下,驾驶室4~12 Hz振动均降低40%,燃料电池振动降低45%以上,驾驶舒适性和燃料电池振动安全性均得到显著提升。展开更多
胰十二指肠切除术(pancreaticoduodenectomy,PD)术后胰漏(postoperative pancreatic fistula,POPF)是胰腺术后最危险的并发症和主要致死原因,严重的POPF还引起腹腔感染、出血、胃排空障碍及败血症等[1]。2016年国际胰腺外科研究组织(int...胰十二指肠切除术(pancreaticoduodenectomy,PD)术后胰漏(postoperative pancreatic fistula,POPF)是胰腺术后最危险的并发症和主要致死原因,严重的POPF还引起腹腔感染、出血、胃排空障碍及败血症等[1]。2016年国际胰腺外科研究组织(international study group on pancreatic surgery,ISGPS)将POPF分为A、B、C级。A级:生化漏,对临床进程无明显影响;B级:胰漏需要术后处理,改变医疗进程。展开更多
基金supported by National Natural Science Foundation of China (Grant No. 60879002)Tianjin Municipal Science and Technology Support Plan of China (Grant No. 10ZCKFGX03800)
文摘Fatigue life and reliability of aero-engine blade are always of important significance to flight safety.The establishment of damage model is one of the key factors in blade fatigue research.Conventional linear Miner＇s sum method is not suitable for aero-engine because of its low accuracy.A back propagation neutral network（BPNN） based on the combination of Levenberg-Marquardt（LM） and finite element method（FEM） is used to describe process of nonlinear damage accumulation behavior in material and predict fatigue life of the blade.Fatigue tests of standard specimen made from TC4 are carried out to obtain material fatigue parameters and S-N curve.A nonlinear continuum damage model（CDM）,based on the BPNN with one hidden layer and ten neurons,is built to investigate the nonlinear damage accumulation behavior,in which the results from the tests are used as training set.Comparing with linear models and previous nonlinear models,BPNN has the lowest calculation error in full load range.It has significant accuracy when the load is below 500 MPa.Especially,when the load is 350 MPa,the calculation error of the BPNN is only 0.4%.The accurate model of the blade is built by using 3D coordinate measurement technology.The loading cycle in fatigue analysis is defined from takeoff to cruise in 10 min,and the load history is obtained from finite element analysis（FEA）.Then the fatigue life of the compressor blade is predicted by using the BPNN model.The final fatigue life of the aero-engine blade is 6.55 104 cycles（10 916 h） based on the BPNN model,which is effective for the virtual design of aero-engine blade.
基金National Science Foundation of China and Civil Aviation Administration Foundation of China(No.U1233201)National Natural Science Foundation of China(No.60879002)Tianjin Municipal Science and Technology Support Plan of China(No.10ZCKFGX03800)
文摘To comprehensively consider the effects of strength degeneration and failure correlation, an improved stress–strength interference （SSI） model is proposed to analyze the reliability of aeroengine blades with the fatigue failure mode. Two types of TC4 alloy experiments are conducted for the study on the damage accumulation law. All the parameters in the nonlinear damage model are obtained by the tension–compression fatigue tests, and the accuracy of the nonlinear damage model is verified by the damage tests. The strength degeneration model is put forward on the basis of the Chaboche nonlinear damage theory and the Griffith fracture criterion, and determined by measuring the fatigue toughness during the tests. From the comparison of two kinds of degeneration models based on the Miner’s linear law and the nonlinear damage model respectively, the nonlinear model has a significant advantage on prediction accuracy especially in the later period of life. A time-dependent SSI reliability model is established. By computing the stress distribution using the finite element （FE） technique, the reliability of a single blade during the whole service life is obtained. Considering the failure correlation of components, a modified reliability model of aero-engine blades with common cause failure （CCF） is presented. It shows a closer and more reasonable process with the actual working condition. The improved reliability model is illustrated to be applied to aero-engine blades well, and the approach purposed in this paper is suitable for any actual machinery component of aero-engine rotor systems.
基金supported by National Natural Science Foundation of China (Grant No. 50975192)Specialized Research Foundation for the Doctoral Program of Higher Education of China (Grant No.20090032110001)
文摘The performance and particulate emission of a diesel engine are affected by the consumption of lubricating oil. Most studies on oil consumption mechanism of the cylinder have been done by using the experimental method, however they are very costly. Therefore, it is very necessary to study oil consumption mechanism of the cylinder and obtain the accurate results by the calculation method. Firstly, four main modes of lubricating oil consumption in cylinder are analyzed and then the oil consumption rate under common working conditions are calculated for the four modes based on an engine. Then, the factors that affect the lubricating oil consumption such as working conditions, the second ring closed gap, the elastic force of the piston rings are also investigated for the four modes. The calculation results show that most of the lubricating oil is consumed by evaporation on the liner surface. Besides, there are three other findings： （1） The oil evaporation from the liner is determined by the working condition of an engine; （2） The increase of the ring closed gap reduces the oil blow through the top ring end gap but increases blow-by; （3） With the increase of the elastic force of the ring, both the left oil film thickness and the oil throw-off at the top ring decrease. The oil scraping of the piston top edge is consequently reduced while the friction loss between the rings and the liner increases. A neural network prediction model of the lubricating oil consumption in cylinder is established based on the BP neural network theory, and then the model is trained and validated. The main piston rings parameters which affect the oil consumption are optimized by using the BP neural network prediction model and the prediction accuracy of this BP neural network is within 8%, which is acceptable for normal engineering applications. The oil consumption is also measured experimentally. The relative errors of the calculated and experimental values are less than 10%, verifying the validity of the simulation results. Applying the established simulation model and the validated BP network model is able to generate numerical results with sufficient accuracy, which significantly reduces experimental work and provides guidance for the optimal design of the piston rings diesel engines.
文摘以某燃料电池载重车为研究对象,建立了包括燃料电池、储氢罐、电动机及变速箱、动力电池和DC/DC(direct current to direct current)变换器等全部动力系统子结构在内的28自由度动力学模型,并结合实车道路测试进行了模型验证。通过动力学模拟和试验设计探究了动力系统子结构位置、悬置刚度和阻尼对驾驶室和燃料电池振动的影响。结果显示:驾驶室振动在2、4、9、12 Hz有明显的能量集中,除受到悬架偏频和簧下偏频的影响外,储氢罐位置和燃料电池位置分别对驾驶室2~4 Hz和9~12 Hz振动影响最大,燃料电池振动受其本身悬置刚度的影响最大,动力系统其他结构对上述振动也有一定影响。以动力系统安装空间与悬置变形量为约束,以动力系统位置、子结构悬置刚度和阻尼为优化变量,进行驾驶室多频率振动和燃料电池加速度均方根的多目标优化设计。优化结果表明:在不同车速下,驾驶室4~12 Hz振动均降低40%,燃料电池振动降低45%以上,驾驶舒适性和燃料电池振动安全性均得到显著提升。
文摘胰十二指肠切除术(pancreaticoduodenectomy,PD)术后胰漏(postoperative pancreatic fistula,POPF)是胰腺术后最危险的并发症和主要致死原因,严重的POPF还引起腹腔感染、出血、胃排空障碍及败血症等[1]。2016年国际胰腺外科研究组织(international study group on pancreatic surgery,ISGPS)将POPF分为A、B、C级。A级:生化漏,对临床进程无明显影响;B级:胰漏需要术后处理,改变医疗进程。
