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Carrer, J.A.M.,Mansur, W.J. Techno-Press 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.23 No.3
This work presents a time-truncation scheme, based on the Lagrange interpolation polynomial, for the solution of the two-dimensional scalar wave problem by the time-domain boundary element method. The aim is to reduce the number of stored matrices, due to the convolution integral performed from the initial time to the current time, and to keep a compromise between computational economy and efficiency and the numerical accuracy. In order to verify the accuracy of the proposed formulation, three examples are presented and discussed at the end of the article.
A step-by-step approach in the time-domain BEM formulation for the scalar wave equation
Carrer, J.A.M.,Mansur, W.J. Techno-Press 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.27 No.6
This article is concerned with the presentation of a time-domain BEM approach applied to the solution of the scalar wave equation for 2D problems. The basic idea is quite simple: the basic variables of the problem at time $t_n$ (potential and flux) are computed with the results related to the potential and to its time derivative at time $t_{n-1}$ playing the role of "initial conditions". This time-marching scheme needs the computation of the potential and its time derivative at all boundary nodes and internal points, as well as the entire discretization of the domain. The convolution integrals of the standard time-domain BEM formulation, however, are not computed; the matrices assembled, only at the initial time interval, are those related to the potential, flux and to the potential time derivative. Two examples are presented and discussed at the end of the article, in order to verify the accuracy and potentialities of the proposed formulation.
Application of joint time-frequency distribution for estimation of time-varying modal damping ratio
H. Bucher,C. Magluta,W.J. Mansur 국제구조공학회 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.37 No.2
The logarithmic decrement method has been long used to estimate damping ratios in systems with only one modal component such as linear single degree of freedom (SDOF) mechanical systems. This paper presents an application of a methodology that uses joint time-frequency distribution (JTFD) as input, instead of the raw signal, to systems with several vibration modes. A most important feature of the present approach is that it can be applied to a system with time-varying damping ratio. Initially the precision and robustness of the method is determined using a synthetic model with multiple harmonic components, one of them displaying a time-varying damping ratio, subsequently the results obtained from experiments with a reduced model are presented. A comparison is made between the results obtained with this methodology and those using the classical technique of Least Squares Complex Exponential Method (LSCE) in order to highlight the advantages of the former, such as, good precision, robustness and excellent performance in extreme cases, e.g., when very low frequency components and time varying damping ratio are present.
Application of joint time-frequency distribution for estimation of time-varying modal damping ratio
Bucher, H.,Magluta, C.,Mansur, W.J. Techno-Press 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.37 No.2
The logarithmic decrement method has been long used to estimate damping ratios in systems with only one modal component such as linear single degree of freedom (SDOF) mechanical systems. This paper presents an application of a methodology that uses joint time-frequency distribution (JTFD) as input, instead of the raw signal, to systems with several vibration modes. A most important feature of the present approach is that it can be applied to a system with time-varying damping ratio. Initially the precision and robustness of the method is determined using a synthetic model with multiple harmonic components, one of them displaying a time-varying damping ratio, subsequently the results obtained from experiments with a reduced model are presented. A comparison is made between the results obtained with this methodology and those using the classical technique of Least Squares Complex Exponential Method (LSCE) in order to highlight the advantages of the former, such as, good precision, robustness and excellent performance in extreme cases, e.g., when very low frequency components and time varying damping ratio are present.
Quantitative Analysis Tools and Digital Phantoms for Deformable Image Registration Quality Assurance
Kim, Haksoo,Park, Samuel B.,Monroe, James I.,Traughber, Bryan J.,Zheng, Yiran,Lo, Simon S.,Yao, Min,Mansur, David,Ellis, Rodney,Machtay, Mitchell,Sohn, Jason W. SAGE Publications 2015 Technology in cancer research & treatment Vol.14 No.4