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Free vibration analysis of concrete arch dams by quadratic ideal-coupled method
Rezaiee-Pajand, Mohammad,Sani, Ahmad Aftabi,Kazemiyan, Mohammad Sadegh Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.1
This paper is devoted to two new techniques for free vibration analysis of concrete arch dam-reservoir systems. The proposed schemes are quadratic ideal-coupled eigen-problems, which can solve the originally non-symmetric eigen-problem of the system. To find the natural frequencies and mode shapes, a new special-purpose eigen-value solution routine is developed. Moreover, the accuracy of the proposed approach is thoroughly assessed, and it is confirmed that the new scheme is very accurate under all practical conditions. It is also concluded that both decoupled and ideal-coupled strategy proposed in the previous works can be considered as special cases of the current more general procedure.
Mojtaba Moussemi,Davoud Nezamolmolki,Ahmad Aftabi Sani 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.3
This article deals with the free vibration analysis and determination of seismic parameters of a T-Shape frame which consists of a continuous beam and a column connected to each other by means of a semi-rigid Khorjini connection. The individual members of the frame are assumed to be governed by the transverse vibration theory of an Euler-Bernoulli beam and the semirigid Khorjini connection is modeled employing a rotational spring. First of all, a closed-form solution is proposed and then, a numerical analysis is performed for some comparison and validation purposes. The closed-form solution is developed by solving the frame equations of motion, directly. For this reason, some mathematical techniques such as Fourier transform and the well-known complementary solutions are utilized. In this process, some differential equations must be solved, and several boundary conditions should be satisfied. Afterward, the free vibration parameters of the frame are attained. These parameters are also obtained using finite element method as a numerical analysis and it is observed that the results obtained by this approach are completely coincident with the result of closed-form solution. Also, seismic parameters of the frame and seismic behavior of the semi-rigid Khorjini connection for different cases are investigated and their results are compared. Finally, two special cases are presented and, furthermore, the connection mass effect on system frequency is investigated.
Forced vibration analysis of a dam-reservoir interaction problem in frequency domain
Keivani, Amirhossein,Shooshtari, Ahmad,Sani, Ahmad Aftabi Techno-Press 2014 Coupled systems mechanics Vol.3 No.4
In this paper, the forced vibration problem of an Euler-Bernoulli beam that is joined with a semi-infinite field of a compressible fluid is considered as a boundary value problem (BVP). This BVP includes two partial differential equations (PDE) and some boundary conditions (BC), which are introduced comprehensively. After that, the closed-form solution of this fluid-structure interaction problem is obtained in the frequency domain. Some mathematical techniques are utilized, and two unknown functions of the BVP, including the beam displacement at each section and the fluid dynamic pressure at all points, are attained. These functions are expressed as an infinite series and evaluated quantitatively for a real example in the results section. In addition, finite element analysis is carried out for comparison.
Forced vibration analysis of a dam-reservoir interaction problem in frequency domain
Keivani, Amirhossein,Shooshtari, Ahmad,Sani, Ahmad Aftabi Techno-Press 2013 Interaction and multiscale mechanics Vol.6 No.4
In this paper, the forced vibration problem of an Euler-Bernoulli beam that is joined with a semi-infinite field of a compressible fluid is considered as a boundary value problem (BVP). This BVP includes two partial differential equations (PDE) and some boundary conditions (BC), which are introduced comprehensively. After that, the closed-form solution of this fluid-structure interaction problem is obtained in the frequency domain. Some mathematical techniques are utilized, and two unknown functions of the BVP, including the beam displacement at each section and the fluid dynamic pressure at all points, are attained. These functions are expressed as an infinite series and evaluated quantitatively for a real example in the results section. In addition, finite element analysis is carried out for comparison.
Ebrahim Sotoudehnia,Farzad Shahabian,Ahmad Aftabi Sani 국제구조공학회 2019 Smart Structures and Systems, An International Jou Vol.23 No.1
This paper is devoted to proposing a new approach for damage detection of structures. In this technique, the biconjugate gradient method (BCG) is employed. To remedy the noise effects, a new preconditioning algorithm is applied. The proposed preconditioner matrix significantly reduces the condition number of the system. Moreover, based on the characteristics of the damage vector, a new direct search algorithm is employed to increase the efficiency of the suggested damage detection scheme by reducing the number of unknowns. To corroborate the high efficiency and capability of the presented strategy, it is applied for estimating the severity and location of damage in the well-known 31-member and 52-member trusses. For damage detection of these trusses, the time history responses are measured by a limited number of sensors. The results of numerical examples reveal high accuracy and robustness of the proposed method.
Vibration suppression of a double-beam system by a two-degree-of-freedom mass-spring system
Rezaiee-Pajand, Mohammad,Sani, Ahmad Aftabi,Hozhabrossadati, Seyed Mojtaba Techno-Press 2018 Smart Structures and Systems, An International Jou Vol.21 No.3
This paper investigates the free vibration analysis of double-beam system coupled by a two-degree-of-freedom mass-spring system. In order to generalize the model, the main beams are assumed to be elastically restrained against translation and rotation at one end and free at the other. Furthermore, the mass-spring system is elastically connected to the beams at adjustable positions by means of four translational and rotational springs. The governing differential equations of the beams and the mass-spring system are derived and analytically solved by using the Fourier transform method. Moreover, as a second way, a finite element solution is derived. The frequency parameters and mode shapes of some diverse cases are obtained using both methods. Comparison of obtained results by two methods shows the accuracy of both solutions. The influence of system parameters on the free vibration response of the studied mechanical system is examined.
Vibration suppression of a double-beam system by a two-degree-of-freedom mass-spring system
Mohammad Rezaiee-Pajand,Ahmad Aftabi Sani,Seyed Mojtaba Hozhabrossadati 국제구조공학회 2018 Smart Structures and Systems, An International Jou Vol.21 No.3
This paper investigates the free vibration analysis of double-beam system coupled by a two-degree-of-freedom mass-spring system. In order to generalize the model, the main beams are assumed to be elastically restrained against translation and rotation at one end and free at the other. Furthermore, the mass-spring system is elastically connected to the beams at adjustable positions by means of four translational and rotational springs. The governing differential equations of the beams and the mass-spring system are derived and analytically solved by using the Fourier transform method. Moreover, as a second way, a finite element solution is derived. The frequency parameters and mode shapes of some diverse cases are obtained using both methods. Comparison of obtained results by two methods shows the accuracy of both solutions. The influence of system parameters on the free vibration response of the studied mechanical system is examined.
Free vibration analysis of concrete arch dams by quadratic ideal-coupled method
Mohammad Rezaiee-Pajand,Ahmad Aftabi Sani,Mohammad Sadegh Kazemiyan 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.1
This paper is devoted to two new techniques for free vibration analysis of concrete arch dam-reservoir systems. The proposed schemes are quadratic ideal-coupled eigen-problems, which can solve the originally non-symmetric eigen-problem of the system. To find the natural frequencies and mode shapes, a new special-purpose eigen-value solution routine is developed. Moreover, the accuracy of the proposed approach is thoroughly assessed, and it is confirmed that the new scheme is very accurate under all practical conditions. It is also concluded that both decoupled and ideal-coupled strategy proposed in the previous works can be considered as special cases of the current more general procedure.
Dynamic Investigation of a Two Story-Two Span Frame Including Semi-rigid Khorjini Connections
Mojtaba Moussemi,Davoud Nezamolmolki,Ahmad Aftabi Sani 한국강구조학회 2017 International Journal of Steel Structures Vol.17 No.4
In this paper, the free vibration analysis and determination of dynamic parameters of a two story-two span frame is investigated. The frame is consisted of two continuous beams and three columns, in which the middle connections of the continuous beams to the column are provided by means of semi-rigid Khorjini connections. The individual members of the frame are assumed to be governed by the transverse vibration theory of an Euler-Bernoulli beam and the semi-rigid Khorjini connections are modeled employing rotational springs. First of all, a closed-form solution is proposed and then, a numerical analysis is performed for some comparison and validation purposes. At the closed-form solution, some differential equations must be solved, and several boundary conditions should be satisfied. Herein, 40 boundary conditions should be provided. Afterward, the eigenvalues of the frame are obtained. These eigenvalues are also obtained using finite element method as a numerical analysis and it is observed that the results obtained by this approach are completely identical with the result of closedform solution. Also, the eigenvalues and mode shapes of the frame for different values of the semi-rigid Khorjini connections stiffnesses are obtained and some comparisons are made.
A closed-form solution for a fluid-structure system: shear beam-compressible fluid
Keivani, Amirhossein,Shooshtari, Ahmad,Sani, Ahmad Aftabi Techno-Press 2013 Coupled systems mechanics Vol.2 No.2
A closed-form solution for a fluid-structure system is presented in this article. The closed-form is used to evaluate the finite element method results through a numeric example with consideration of high frequencies of excitation. In the example, the structure is modeled as a cantilever beam with rectangular cross-section including only shear deformation and the reservoir is assumed semi-infinite rectangular filled with compressible fluid. It is observed that finite element results deviate from the closed-form in relatively higher frequencies which is the case for the near field earthquakes.