Paris law can reflect the failure mechanism of materials and is usually used to be a method to predict fatigue life or residual fatigue life.But the variable which can represent the health of machine is hardly measure...Paris law can reflect the failure mechanism of materials and is usually used to be a method to predict fatigue life or residual fatigue life.But the variable which can represent the health of machine is hardly measured on line.To a degree,the difficulty of on-line application restricts the scope of application of Paris law.The relationship between characteristic values of vibration signals and the variable in the Paris equation which can describe the health of machine is investigated by taking ball bearings as investigative objects.Based on 6205 deep groove ball bearings as a living example,historical lives and vibration signals are analyzed.The feasibility of describing that variable in the Paris equation by the characteristic value of vibration signals is inspected.After that vibration signals decomposed by empirical mode decomposition（EMD）,root mean square（RMS） of intrinsic mode function（IMF） involving fault characteristic frequency has a consistent trend with the diameter of flaws.Based on the trend,two improved Paris models are proposed and the scope of application of them is inspected.These two Paris Models are validated by fatigue residual life data from tests of rolling element bearings and vibration signals monitored in the process of operation of rolling element bearings.It shows that the first improved Paris Model is simple and plain and it can be easily applied in actual conditions.The trend of the fatigue residual life predicted by the second improved Paris model is close to the actual conditions and the result of the prediction is slightly greater than the truth.In conclusion,after the appearance of detectable faults,these improved models based on RMS can predict residual fatigue life on line and a new approach to predict residual fatigue life of ball bearings on line without disturbing the machine running is provided.展开更多
对双主动全桥DAB(dual active bridge)双向DC/DC变换器的调制方案进行了研究,DAB变换器的主要优势在于具有对称结构、双向潮流能力、宽软开关区域和灵活的控制能力等特点。控制这种拓扑结构最简单的方法是通过控制变换器原副边全桥之间...对双主动全桥DAB(dual active bridge)双向DC/DC变换器的调制方案进行了研究,DAB变换器的主要优势在于具有对称结构、双向潮流能力、宽软开关区域和灵活的控制能力等特点。控制这种拓扑结构最简单的方法是通过控制变换器原副边全桥之间的移相角来控制功率传输的方向和大小。然而在轻载条件下,当变换器的输入或输出电压变化较大时,会产生大量的无功功率,同时部分开关管的零电压开关ZVS(zero voltage switching)操作会丢失而直接导致转换效率变低。因此,为了提高DAB变换器的效率,提出了一种混合单移相调制PSM(phase shift modulation)方案,在保持控制简单的基础上,通过减小电感电流有效值,扩大软开关的范围,提高了变换器的效率。首先,通过让拓展移相EPS(extended phase shift)、双移相DPS(dual phase shift)以及三移相TPS(triple phase shift)调制方案中的可控变量相等,从而形成了4种不同的PSM方案。接着,对这些调制方案进行了稳态特征的比较分析,包括传输功率容量、电感电流水平以及软开关性能等。在此基础上,提出了一种混合PSM方案。最后,通过搭建实验平台验证了所提出调制方案的有效性和正确性。展开更多
A numerical simulation method based on inverse discrete Fourier transform(IDFT)is presented for generating Gaussian rough surface with a desired autocorrelation function(ACF). The probability density function of the h...A numerical simulation method based on inverse discrete Fourier transform(IDFT)is presented for generating Gaussian rough surface with a desired autocorrelation function(ACF). The probability density function of the height distribution of the generated Gaussian surface and the root-mean-square height of the rough surface are also considered. It is found that the height distribution of the generated surface follows the Gaussian distribution, the deviation of the root-mean-square height of the modeled rough surface from the desired value is smaller than that of Patir's method, and the autocorrelation function of the modeled surface is also in good agreement with the desired autocorrelation function. Compared with Patir's method, the modeled surface generated by the IDFT method is in better agreement with the desired autocorrelation function, especially when the correlation length is relatively large.展开更多
Considering the relationship between the nuclear radius and the average bindingenergy of nucleons,a simple semi-empirical formula for the nuclear rms charge radii is suggest-ed together with the formula for light neut...Considering the relationship between the nuclear radius and the average bindingenergy of nucleons,a simple semi-empirical formula for the nuclear rms charge radii is suggest-ed together with the formula for light neutron-rich nuclear rms neutron radii.These formulascan well fit the new experimental values.展开更多
Thin films of three types of fullerene derivatives were prepared through the electrospray deposition (ESD) method. The optimized conditions for the fabrication of the thin films were investigated for different types o...Thin films of three types of fullerene derivatives were prepared through the electrospray deposition (ESD) method. The optimized conditions for the fabrication of the thin films were investigated for different types of fullerene derivatives: [6,6]-phenyl-C61-butyric acid methyl ester, [6,6]-phenyl-C71-butyric acid methyl ester, and indene-C60-monoadduct. The spray diameter during the ESD process was observed as a function of the supply rate achieved by changing the applied voltage. In all cases, the spray diameter increased with increasing applied voltage, reaching the maximum diameter (Dmax) in the voltage range 4 to 6 kV. It was clear that Dmax was influenced by the dipole moments of the fullerene derivatives (as calculated by density functional theory methods). Scanning electron microscopy observation of the?fabricated thin films showed that imbricated structures were formed through the stacking of the fullerene-derivative sheets. Atomic force microscopy images revealed that the density of the imbricated structure was dependent on the spray diameter during the ESD process, and the root-mean-square roughness of the film surface decreased with increasing applied voltage. These findings suggest that the ESD method will be effective for the preparation of fullerene-derivative thin films for the production of organic devices.展开更多
以某室外大跨轻柔钢结构人行桥为案例,介绍了该结构的设计概况及调谐质量阻尼器（tuned mass damper,简称TMD）减振设计,分别在结构施工完成后以及TMD装置安装后对其进行了实地动力测试,测得了该结构减振前后的模态特性以及在多种人行...以某室外大跨轻柔钢结构人行桥为案例,介绍了该结构的设计概况及调谐质量阻尼器（tuned mass damper,简称TMD）减振设计,分别在结构施工完成后以及TMD装置安装后对其进行了实地动力测试,测得了该结构减振前后的模态特性以及在多种人行荷载工况下的振动响应,采用加速度峰值和均方根值为评价指标,分析了钢连桥人致振动情况及特性。结果表明：一端设计为滑动连接的钢连桥人致振动主要由第1阶竖向振型控制,扭动及水平振动响应相对较小;安装经优化设计的TMD装置后,整体连桥的频率特性没有明显变化,分布式TMD对多种频率激励工况均有良好的调谐减振作用,减振率达到35%-70%;共振激励下测得的原结构阻尼比较小,安装TMD后结构的阻尼比提高4倍,并且呈现出在自由振动衰减的前期较大,随着振动幅度变弱阻尼比降低;测试中发现TMD装置的减振效率对其阻尼比的变化不敏感。展开更多
基金supported by National Natural Science Foundation of China (Grant No. 50705096)National Science and Technology Major Project of China(Grant No. 2009zx04014-014)
文摘Paris law can reflect the failure mechanism of materials and is usually used to be a method to predict fatigue life or residual fatigue life.But the variable which can represent the health of machine is hardly measured on line.To a degree,the difficulty of on-line application restricts the scope of application of Paris law.The relationship between characteristic values of vibration signals and the variable in the Paris equation which can describe the health of machine is investigated by taking ball bearings as investigative objects.Based on 6205 deep groove ball bearings as a living example,historical lives and vibration signals are analyzed.The feasibility of describing that variable in the Paris equation by the characteristic value of vibration signals is inspected.After that vibration signals decomposed by empirical mode decomposition（EMD）,root mean square（RMS） of intrinsic mode function（IMF） involving fault characteristic frequency has a consistent trend with the diameter of flaws.Based on the trend,two improved Paris models are proposed and the scope of application of them is inspected.These two Paris Models are validated by fatigue residual life data from tests of rolling element bearings and vibration signals monitored in the process of operation of rolling element bearings.It shows that the first improved Paris Model is simple and plain and it can be easily applied in actual conditions.The trend of the fatigue residual life predicted by the second improved Paris model is close to the actual conditions and the result of the prediction is slightly greater than the truth.In conclusion,after the appearance of detectable faults,these improved models based on RMS can predict residual fatigue life on line and a new approach to predict residual fatigue life of ball bearings on line without disturbing the machine running is provided.
基金Supported by the National Basic Research Program of China("973"Program,No.2013CB632305)
文摘A numerical simulation method based on inverse discrete Fourier transform(IDFT)is presented for generating Gaussian rough surface with a desired autocorrelation function(ACF). The probability density function of the height distribution of the generated Gaussian surface and the root-mean-square height of the rough surface are also considered. It is found that the height distribution of the generated surface follows the Gaussian distribution, the deviation of the root-mean-square height of the modeled rough surface from the desired value is smaller than that of Patir's method, and the autocorrelation function of the modeled surface is also in good agreement with the desired autocorrelation function. Compared with Patir's method, the modeled surface generated by the IDFT method is in better agreement with the desired autocorrelation function, especially when the correlation length is relatively large.
基金The project supported by the National Natural Science Foundation of ChinaShanghai Research Funds for Young Scientists
文摘Considering the relationship between the nuclear radius and the average bindingenergy of nucleons,a simple semi-empirical formula for the nuclear rms charge radii is suggest-ed together with the formula for light neutron-rich nuclear rms neutron radii.These formulascan well fit the new experimental values.
文摘Thin films of three types of fullerene derivatives were prepared through the electrospray deposition (ESD) method. The optimized conditions for the fabrication of the thin films were investigated for different types of fullerene derivatives: [6,6]-phenyl-C61-butyric acid methyl ester, [6,6]-phenyl-C71-butyric acid methyl ester, and indene-C60-monoadduct. The spray diameter during the ESD process was observed as a function of the supply rate achieved by changing the applied voltage. In all cases, the spray diameter increased with increasing applied voltage, reaching the maximum diameter (Dmax) in the voltage range 4 to 6 kV. It was clear that Dmax was influenced by the dipole moments of the fullerene derivatives (as calculated by density functional theory methods). Scanning electron microscopy observation of the?fabricated thin films showed that imbricated structures were formed through the stacking of the fullerene-derivative sheets. Atomic force microscopy images revealed that the density of the imbricated structure was dependent on the spray diameter during the ESD process, and the root-mean-square roughness of the film surface decreased with increasing applied voltage. These findings suggest that the ESD method will be effective for the preparation of fullerene-derivative thin films for the production of organic devices.
文摘以某室外大跨轻柔钢结构人行桥为案例,介绍了该结构的设计概况及调谐质量阻尼器（tuned mass damper,简称TMD）减振设计,分别在结构施工完成后以及TMD装置安装后对其进行了实地动力测试,测得了该结构减振前后的模态特性以及在多种人行荷载工况下的振动响应,采用加速度峰值和均方根值为评价指标,分析了钢连桥人致振动情况及特性。结果表明：一端设计为滑动连接的钢连桥人致振动主要由第1阶竖向振型控制,扭动及水平振动响应相对较小;安装经优化设计的TMD装置后,整体连桥的频率特性没有明显变化,分布式TMD对多种频率激励工况均有良好的调谐减振作用,减振率达到35%-70%;共振激励下测得的原结构阻尼比较小,安装TMD后结构的阻尼比提高4倍,并且呈现出在自由振动衰减的前期较大,随着振动幅度变弱阻尼比降低;测试中发现TMD装置的减振效率对其阻尼比的变化不敏感。
