This article deals with the investigation of the effects of porosity distributions on nonlinear free vibration and transient analysis of porous functionally graded skew(PFGS)plates.The effective material properties of...This article deals with the investigation of the effects of porosity distributions on nonlinear free vibration and transient analysis of porous functionally graded skew(PFGS)plates.The effective material properties of the PFGS plates are obtained from the modified power-law equations in which gradation varies through the thickness of the PFGS plate.A nonlinear finite element(FE)formulation for the overall PFGS plate is derived by adopting first-order shear deformation theory(FSDT)in conjunction with von Karman’s nonlinear strain displacement relations.The governing equations of the PFGS plate are derived using the principle of virtual work.The direct iterative method and Newmark’s integration technique are espoused to solve nonlinear mathematical relations.The influences of the porosity distributions and porosity parameter indices on the nonlinear frequency responses of the PFGS plate for different skew angles are studied in various parameters.The effects of volume fraction grading index and skew angle on the plate’s nonlinear dynamic responses for various porosity distributions are illustrated in detail.展开更多
This paper has an objective to show a developed quantitative criterion,based in two mathematical variables that explicit the deviation degree of a normal situation,applying simultaneously data from terminal impedances...This paper has an objective to show a developed quantitative criterion,based in two mathematical variables that explicit the deviation degree of a normal situation,applying simultaneously data from terminal impedances and frequency response.Based in more than 100-measured equipment,of different applications(step-up transformer,transmission transformer,etc.,),for a period of 10 years,the work presents some examples of practical application of this methodology in Brazilian Electrical System.展开更多
为解决颤振控制TMD(tuned mass damper)设计时更准确地获取拟控制桥梁动力特性的问题,基于Sherman Morrison公式、拟控制桥梁的频响函数以及TMD参数,推导桥梁-TMD耦合系统的模态频率和阻尼。基于航空领域的颤振裕度法,推导两自由度弯扭...为解决颤振控制TMD(tuned mass damper)设计时更准确地获取拟控制桥梁动力特性的问题,基于Sherman Morrison公式、拟控制桥梁的频响函数以及TMD参数,推导桥梁-TMD耦合系统的模态频率和阻尼。基于航空领域的颤振裕度法,推导两自由度弯扭耦合气弹系统附加扭转TMD之后的颤振裕度随风速变化的表达式。提出了一种基于颤振裕度的TMD优化设计方法,以最大化颤振临界风速(颤振裕度等于0)为目标,得到TMD的优化参数。基于一个两自由度桥梁截面数值例子,对比分析了颤振裕度法和传统复特征值法所预测的耦合系统颤振临界风速和最优TMD参数,探讨了基于颤振裕度法的TMD优化设计方法的准确性,对比分析了控制前后4个风速下的时域响应,探讨了最优TMD的控制效果。研究结果表明:颤振裕度法和复特征值法两者计算得到的TMD最优参数一致,基于颤振裕度法预测的桥梁-最优TMD系统的颤振临界风速与基于复特征值法预测的结果仅存在2.2%的误差,且用最优TMD控制后桥梁颤振临界风速提高了50%。研究结果为桥梁颤振控制TMD的优化设计提供了一种新的方法。该方法所使用的频响函数包含了结构和气动力信息,依据应用场景不同,其可以是数值计算的频率响应函数,也可以是实测的频响函数。在实际应用中可通过大型激振器进行实验模态分析测试得到,其更加准确地表征了拟控制桥梁的动力特性,为TMD的精准设计奠定了基础。该方法的实际工程应用值得进一步发展和研究。展开更多
A line contact model of elastic coated solids is presented based on the influence coefficients(ICs) of surface displacement and stresses of coating-substrate system and the traditional contact model. The ICs of displa...A line contact model of elastic coated solids is presented based on the influence coefficients(ICs) of surface displacement and stresses of coating-substrate system and the traditional contact model. The ICs of displacement and stresses are obtained from their corresponding frequency response functions(FRF) by using a conversion method based on fast Fourier transformation(FFT). The contact pressure and the stress field in the subsurface are obtained by employing conjugate gradient method(CGM) and discrete convolution fast Fourier transformation(DC-FFT). Comparison of the contact pressure and subsurface stresses obtained by the numerical method with the exact analytical solutions for Hertz contact is conducted, and the results show that the numerical solution has a very high accuracy and verify the validity of the contact model. The effect of the stiffness and thickness of coatings is further numerically studied. The result shows that the effects on contact pressure and contact width are opposite for hard and soft coatings and are intensified with the increase of coating thickness; the locations of crack initiation and propagation are different for soft and hard coatings; the risk of cracks and delaminations of coatings can be brought down by improving the lubrication condition or optimizing the non-dimensional parameter h/bh. This research offers a tool to numerically analyze the problem of elastic coated solids in line contact and make the blindness and randomness of trial-type coating design less.展开更多
文摘This article deals with the investigation of the effects of porosity distributions on nonlinear free vibration and transient analysis of porous functionally graded skew(PFGS)plates.The effective material properties of the PFGS plates are obtained from the modified power-law equations in which gradation varies through the thickness of the PFGS plate.A nonlinear finite element(FE)formulation for the overall PFGS plate is derived by adopting first-order shear deformation theory(FSDT)in conjunction with von Karman’s nonlinear strain displacement relations.The governing equations of the PFGS plate are derived using the principle of virtual work.The direct iterative method and Newmark’s integration technique are espoused to solve nonlinear mathematical relations.The influences of the porosity distributions and porosity parameter indices on the nonlinear frequency responses of the PFGS plate for different skew angles are studied in various parameters.The effects of volume fraction grading index and skew angle on the plate’s nonlinear dynamic responses for various porosity distributions are illustrated in detail.
文摘This paper has an objective to show a developed quantitative criterion,based in two mathematical variables that explicit the deviation degree of a normal situation,applying simultaneously data from terminal impedances and frequency response.Based in more than 100-measured equipment,of different applications(step-up transformer,transmission transformer,etc.,),for a period of 10 years,the work presents some examples of practical application of this methodology in Brazilian Electrical System.
文摘为解决颤振控制TMD(tuned mass damper)设计时更准确地获取拟控制桥梁动力特性的问题,基于Sherman Morrison公式、拟控制桥梁的频响函数以及TMD参数,推导桥梁-TMD耦合系统的模态频率和阻尼。基于航空领域的颤振裕度法,推导两自由度弯扭耦合气弹系统附加扭转TMD之后的颤振裕度随风速变化的表达式。提出了一种基于颤振裕度的TMD优化设计方法,以最大化颤振临界风速(颤振裕度等于0)为目标,得到TMD的优化参数。基于一个两自由度桥梁截面数值例子,对比分析了颤振裕度法和传统复特征值法所预测的耦合系统颤振临界风速和最优TMD参数,探讨了基于颤振裕度法的TMD优化设计方法的准确性,对比分析了控制前后4个风速下的时域响应,探讨了最优TMD的控制效果。研究结果表明:颤振裕度法和复特征值法两者计算得到的TMD最优参数一致,基于颤振裕度法预测的桥梁-最优TMD系统的颤振临界风速与基于复特征值法预测的结果仅存在2.2%的误差,且用最优TMD控制后桥梁颤振临界风速提高了50%。研究结果为桥梁颤振控制TMD的优化设计提供了一种新的方法。该方法所使用的频响函数包含了结构和气动力信息,依据应用场景不同,其可以是数值计算的频率响应函数,也可以是实测的频响函数。在实际应用中可通过大型激振器进行实验模态分析测试得到,其更加准确地表征了拟控制桥梁的动力特性,为TMD的精准设计奠定了基础。该方法的实际工程应用值得进一步发展和研究。
基金Project(2013CB632305)supported by the National Basic Research Program of ChinaProject(51375108)supported by the National Natural Science Foundation of China
文摘A line contact model of elastic coated solids is presented based on the influence coefficients(ICs) of surface displacement and stresses of coating-substrate system and the traditional contact model. The ICs of displacement and stresses are obtained from their corresponding frequency response functions(FRF) by using a conversion method based on fast Fourier transformation(FFT). The contact pressure and the stress field in the subsurface are obtained by employing conjugate gradient method(CGM) and discrete convolution fast Fourier transformation(DC-FFT). Comparison of the contact pressure and subsurface stresses obtained by the numerical method with the exact analytical solutions for Hertz contact is conducted, and the results show that the numerical solution has a very high accuracy and verify the validity of the contact model. The effect of the stiffness and thickness of coatings is further numerically studied. The result shows that the effects on contact pressure and contact width are opposite for hard and soft coatings and are intensified with the increase of coating thickness; the locations of crack initiation and propagation are different for soft and hard coatings; the risk of cracks and delaminations of coatings can be brought down by improving the lubrication condition or optimizing the non-dimensional parameter h/bh. This research offers a tool to numerically analyze the problem of elastic coated solids in line contact and make the blindness and randomness of trial-type coating design less.
