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Direct frequency domain analysis of concrete arch dams based on FE-(FE-HE)-BE technique
Vahid Lotfi 한국계산역학회 2004 Computers and Concrete, An International Journal Vol.1 No.3
A FE-(FE-HE)-BE procedure is presented for dynamic analysis of concrete arch dams. In this technique, dam body is discretized by solid finite elements, while the reservoir domain is considered by a combination of fluid finite elements and a three-dimensional fluid hyper-element. Furthermore, foundation rock domain is handled by three- dimensional boundary element formulation. Based on thismethod, a previously developed program is modified, and the response of Morrow Point arch dam is studied for various conditions. Moreover, the effects of canyon shape on response of dam, is also discussed
Frequency domain analysis of concrete arch dams by decoupled modal approach
Vahid Lotfi 국제구조공학회 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.21 No.4
A modal approach is proposed for dynamic analysis of concrete arch dam-reservoir systems in frequency domain. The technique relies on mode shapes extracted by considering the symmetric parts of total mass and stiffness matrices. Based on this method, a previously developed program is modified, and the response of Morrow Point arch dam is studied for various conditions. The method is proved to be very effective and it is an extremely convenient modal technique for dynamic analysis of concrete arch dams.
Frequency domain analysis of concrete arch dams by decoupled modal approach
Lotfi, Vahid Techno-Press 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.21 No.4
A modal approach is proposed for dynamic analysis of concrete arch dam-reservoir systems in frequency domain. The technique relies on mode shapes extracted by considering the symmetric parts of total mass and stiffness matrices. Based on this method, a previously developed program is modified, and the response of Morrow Point arch dam is studied for various conditions. The method is proved to be very effective and it is an extremely convenient modal technique for dynamic analysis of concrete arch dams.
Lotfi, Vahid,Zenz, Gerald Techno-Press 2018 Coupled systems mechanics Vol.7 No.3
The Wavenumber or more accurately Wavenumber-FD approach was initially introduced for two-dimensional dynamic analysis of concrete gravity dam-reservoir systems. The technique was formulated in the context of pure finite element programming in frequency domain. Later on, a variation of the method was proposed which was referred to as Wavenumber-TD approach suitable for time domain type of analysis. Recently, it is also shown that Wavenumber-FD approach may be applied for three-dimensional dynamic analysis of concrete arch dam-reservoir systems. In the present study, application of its variation (i.e., Wavenumber-TD approach) is investigated for three-dimensional problems. The method is initially described. Subsequently, the response of idealized Morrow Point arch dam-reservoir system is obtained by this method and its special cases (i.e., two other well-known absorbing conditions) for time harmonic excitation in stream direction. All results for various considered cases are compared against the exact response for models with different values of normalized reservoir length and reservoir base/sidewalls absorptive conditions.
Direct frequency domain analysis of concrete arch dams based on FE-BE procedure
Lotfi, Vahid Techno-Press 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.26 No.4
A FE-BE procedure is presented for dynamic analysis of concrete arch dams. In this technique, dam body is discretized by finite elements, while foundation rock is handled by three dimensional boundary element formulation. This would allow a rigorous inclusion of dam-foundation rock interaction, with no limitations imposed on geometry of canyon shape. Based on this method, a previously developed program is modified, and the response of Morrow Point arch dam is studied for various ratios of foundation rock to dam concrete elastic moduli under an empty reservoir condition. Furthermore, the effects of canyon shape on response of dam, is also discussed.
Direct frequency domain analysis of concrete arch dams based on FE-BE procedure
Vahid Lotfi† 국제구조공학회 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.26 No.4
A FE-BE procedure is presented for dynamic analysis of concrete arch dams. In this technique, dam body is discretized by finite elements, while foundation rock is handled by three dimensional boundary element formulation. This would allow a rigorous inclusion of dam-foundation rock interaction, with no limitations imposed on geometry of canyon shape. Based on this method, a previously developed program is modified, and the response of Morrow Point arch dam is studied for various ratios of foundation rock to dam concrete elastic moduli under an empty reservoir condition. Furthermore, the effects of canyon shape on response of dam, is also discussed.
Significance of rigorous fluid-foundation interaction in dynamic analysis of concrete gravity dams
Lotfi, Vahid Techno-Press 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.21 No.2
Dynamic analysis of dam-reservoir-foundation system is usually carried out by employing a simplified and approximate one-dimensional model to account for fluid-foundation interaction. The approximation introduced on this basis is examined thoroughly in this paper by comparing the method with the rigorous approach. It is concluded that the errors due to approximate method could be very significant both for horizontal and vertical ground motions.
An efficient three-dimensional fluid hyper-element for dynamic analysis of concrete arch dams
Lotfi, Vahid Techno-Press 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.24 No.6
The accurate dynamic analysis of concrete arch dams relies heavily on employing a three-dimensional semi-infinite fluid element. The usual method for calculating the impedance matrix of this fluid hyper-element is dependent on the solution of a complex eigen-value problem for each frequency. In the present study, an efficient procedure is proposed which simplifies this procedure amazingly, and results in great computational time saving. Moreover, the accuracy of this technique is examined thoroughly and it is concluded that efficient procedure is incredibly accurate under all practical conditions.
Time harmonic analysis of dam-foundation systems by perfectly matched layers
Adib Khazaee,Vahid Lotfi 국제구조공학회 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.50 No.3
Perfectly matched layers are employed in time harmonic analysis of dam-foundation systems. The Lysmer boundary condition at the truncation boundary of the PML region has been incorporated in the formulation of the dam-foundation FE model (including PML). The PML medium is defined in a way that the formulation of the system can be transformed into time domain. Numerical experiments show that applying Lysmer boundary conditions at the truncation boundary of the PML area reduces the computational cost and make the PML approach a more efficient technique for the analysis of dam-foundation systems.