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dynamic-response
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Total 179 records
Stability assessment of bowed asymmetric rotors on nonlinear supports
, Article Journal of the Brazilian Society of Mechanical Sciences and Engineering ; Volume 44, Issue 12 , 2022 ; 16785878 (ISSN) ; Mousavi, S. M. R ; Firouz Abadi, R. D ; Farajolahi, M ; Chasalevris, A ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2022
Abstract
This paper investigates the influence of residual bow on the stability of a rotating system consisting of an unbalanced Jeffcott rotor with anisotropy and two nonlinear journal bearing supports. The motion equations of the rotor system are formulated and analyzed considering most common faults and features including coupling effects of unbalance, anisotropy and residual shaft bow, by applying Lagrangian dynamics and Floquet theory. Time varying system properties of stiffness and damping are introduced into the equations of motion affecting the rotor behavior, and the influence is studied with respect to the extent of the bearing nonlinearity and the rotor anisotropy. Increasing area of...
In-plane vibration analysis of horizontally curved beams resting on visco-elastic foundation subjected to a moving mass
, Article Mechanical Systems and Signal Processing ; Volume 172 , 2022 ; 08883270 (ISSN) ; Abdoos, H ; Khaloo, A. R ; Mofid, M ; Sharif University of Technology
Academic Press
2022
Abstract
This paper deals with the in-plane dynamics of Horizontally Curved Beams (HCBs) supported by a visco-elastic foundation under the excitation induced by a moving mass. What has been included as worthy of detailed exposition is the inevitable contribution of the inertial actions of the mass object into the problem formulation. By taking into account the effect of Coriolis acceleration, centrifugal force and rotary inertia, the governing coupled non-linear differential equations of equilibrium for a simply supported HCB are derived. In the proposed solution, a new system of linear ordinary differential equations is distilled from the governing differential equations of motion, which can be...
A DC power system stabilizer based on passivity-oriented DC bus impedance shaping
, Article Scientia Iranica ; Volume 29, Issue 4 , 2022 , Pages 2029-2039 ; 10263098 (ISSN) ; Mokhtari, H ; Sharif University of Technology
Sharif University of Technology
2022
Abstract
High penetration of Power Electronic (PE) converters in DC power grids causes new stability challenges due to dynamic interactions among the subsystems of a network. Such dynamic interactions can be avoided by the impedance coordination among the subsystems through the modification of control loops or passive elements inside a grid. Impedance coordination is a very complex and time-consuming task with no adaptations to dynamic changes in a power grid. The current study delved into the concepts of dynamic interaction and passivity and they were combined to provide an online stability measure concerning the DC bus impedance characteristics. In this regard, a novel DC Power System Stabilizer...
Controlling the seismic response of structures under near-field earthquakes with fluid/structure interaction of cylindrical liquid tanks
, Article European Journal of Environmental and Civil Engineering ; Volume 26, Issue 2 , 2022 , Pages 570-593 ; 19648189 (ISSN) ; Attari, N. K. A ; Rofooei, F. R ; Sharif University of Technology
Taylor and Francis Ltd
2022
Abstract
In this paper, the effectiveness of using nonlinear fluid/structure interaction for controlling the seismic response of the structures under near-field earthquake is investigated. For this purpose an SDOF Structure is considered which is equipped with the circular cylindrical liquid tank. Considering its fundamental mode of vibration, the structure is an idealised model of multi-degree of freedom system. Under 72 horizontal near-field earthquake excitations, the dynamic response of this system is examined studying three liquid sloshing modes. The dynamic response is investigated in the neighbourhood of 1:1 resonance between first unsymmetrical sloshing mode and SDOF structural mode. For this...
Probabilistic seismic performance assessment of optimally designed highway bridge isolated by ordinary unbonded elastomeric bearings
, Article Engineering Structures ; Volume 247 , 2021 ; 01410296 (ISSN) ; Khansefid, A ; Khaloo, A ; Ehteshami Moeini, M ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
Following the idea of using unbonded isolators to eliminate the tensile stress and providing a cost-effective isolation system, recent experimental research has shown ordinary unbonded steel reinforced elastomeric bearings (SREBs) as an attractive option for seismic isolation of highway bridges. The focus of current research work is on the evaluation of the seismic vulnerability of a highway bridge isolated by unbonded SREBs through developing fragility curves of the structure. This assessment considers parameters playing a key role in the isolation system behavior, namely the friction coefficient, as well as the isolator aging effects. In this regard, a typical three-span highway bridge is...
On optimal proportions of structural member cross-sections to achieve best seismic performance using value based seismic design approach
, Article Engineering Structures ; Volume 231 , 2021 ; 01410296 (ISSN) ; Estekanchi, H. E ; Sarcheshmehpour, M ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
The value-based seismic design framework is a new design method that efficiently balances the construction resources and the seismic consequences, through reliable evaluation of the building performance at an affordable computational cost. This paper employs the value-based design approach to optimize the cross-section proportions of the steel wide-flange members. An optimization problem is proposed within the framework of value-based design. Construction cost and seismic consequences are selected as the value components. Moreover, the minimum code requirements are formulated as the design constraints. FEMA-P58 framework is exploited for the prediction of the seismic consequences including...
On the nonlinear dynamics of a multi-scale hybrid nanocomposite disk
, Article Engineering with Computers ; Volume 37, Issue 3 , 2021 , Pages 2369-2388 ; 01770667 (ISSN) ; Ebrahimi, F ; Habibi, M ; Safarpour, H ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2021
Abstract
This is the first research on the nonlinear frequency analysis of a multi-scale hybrid nanocomposite (MHC) disk (MHCD) resting on an elastic foundation subjected to nonlinear temperature gradient and mechanical loading is investigated. The matrix material is reinforced with carbon nanotubes (CNTs) or carbon fibers (CF) at the nano- or macroscale, respectively. We present a modified Halpin–Tsai model to predict the effective properties of the MHCD. The displacement–strain of nonlinear vibration of multi-scale laminated disk via third-order shear deformation theory (TSDT) and using Von Karman nonlinear shell theory is obtained. Hamilton’s principle is employed to establish the governing...
Optimal tuner selection using Kalman lter for a real-time modular gas turbine model
, Article Scientia Iranica ; Volume 27, Issue 2 , 2021 , Pages 806-818 ; 10263098 (ISSN) ; Vossughi, G ; Alasty, A ; Sharif University of Technology
Sharif University of Technology
2021
Abstract
In this study, a real-time exible modular modeling approach to simulating the dynamic behavior of gas turbine engines based on nonlinear thermodynamic and dynamic laws is addressed. The introduced model, which is developed in the Matlab-Simulink environment, is an object-oriented high-speed real-time computer model and is capable of simulating the dynamic behavior of a broad group of gas turbine engines due to its modular structure. Moreover, a Kalman lter-based model tuning procedure is applied to decrease the modeling errors. Modeling errors are de ned as the mismatch between simulation results and available experimental data. This tuning procedure is an underdetermined estimation problem,...
Conceptual study on dynamic response of semi-submersible
, Article Proceedings of the Institution of Civil Engineers: Maritime Engineering ; 2021 ; 17417597 (ISSN) ; Hajnoruzi, F ; Sharif University of Technology
ICE Publishing
2021
Abstract
Hydrodynamic analysis of semi-submersible offshore structures has been the topic of many researches performed numerically and experimentally in the past. In this paper, the effect of structure alignment and mooring lines on dynamic behaviour of semi-submersible platforms has been taken into account. The contribution of pitch and roll in heave motion of side points is also investigated. Mooring lines are connected to semi-submersible at sides and therefore total displacement of side points is related to total displacement of mooring lines and total tension as well. A three dimensional boundary element model of Amirkabir platform in Caspian Sea is implemented using boundary element method...
On the out-of-plane dynamic response of horizontally curved beams resting on elastic foundation traversed by a moving mass
, Article Journal of Sound and Vibration ; Volume 479 , 2020 ; Khaloo, A. R ; Foyouzat, M. A ; Sharif University of Technology
Academic Press
2020
Abstract
In this paper, the dynamic behavior of Horizontally Curved Beams (HCBs) resting on an elastic foundation and subjected to a moving mass is investigated. The governing coupled non-linear differential equations of equilibrium are derived, where Coriolis acceleration, centrifugal force and rotary inertia are incorporated in the problem formulation. In the proposed analytical solution, by employing the transition matrix technique, the governing differential equations of motion are subsequently transformed into a new system of linear ordinary differential equations which can be solved using standard numerical procedures. The accuracy as well as the robustness of the solution is ascertained...
Effects of motion and structural vibration–induced loadings on the coupled dynamic response of a mono-column tension-leg-platform floating wind turbine
, Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; Volume 234, Issue 2 , 2020 , Pages 426-445 ; Abbaspour, M ; Tabeshpour, M. R ; Karimirad, M ; Sharif University of Technology
SAGE Publications Ltd
2020
Abstract
Floating wind turbines are subjected to highly dynamic and complicated environmental conditions leading to significant platform motions and structural vibrations during operation and survival conditions. These motions and vibrations alter the induced loading characteristics; and consequently, affect the dynamic behavior of the system. In order to better understand the influence of such motions and structural vibrations, herein elastic structural disturbance of tower, on the system behavior, the spectral and statistical characteristics of a floating wind turbine dynamic responses under operational and survival conditions are fully explored using a fully coupled...
On the nonlinear dynamics of a multi-scale hybrid nanocomposite disk
, Article Engineering with Computers ; 2020 ; Ebrahimi, F ; Habibi, M ; Safarpour, H ; Sharif University of Technology
Springer
2020
Abstract
This is the first research on the nonlinear frequency analysis of a multi-scale hybrid nanocomposite (MHC) disk (MHCD) resting on an elastic foundation subjected to nonlinear temperature gradient and mechanical loading is investigated. The matrix material is reinforced with carbon nanotubes (CNTs) or carbon fibers (CF) at the nano- or macroscale, respectively. We present a modified Halpin–Tsai model to predict the effective properties of the MHCD. The displacement–strain of nonlinear vibration of multi-scale laminated disk via third-order shear deformation theory (TSDT) and using Von Karman nonlinear shell theory is obtained. Hamilton’s principle is employed to establish the governing...
Nonlinear dynamics of viscoelastic pipes conveying fluid placed within a uniform external cross flow
, Article Applied Ocean Research ; Volume 94 , 2020 ; Haddadpour, H ; Hosseini Kordkheili, S. A ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
This paper investigates the nonlinear dynamic response of a viscoelastic pipe conveying fluid subjected to a uniform external cross flow based on the Euler-Bernoulli theory. The main objective of this work is to find the proper viscoelastic coefficients to mitigate the dynamic response of a marine riser. A nonlinear oscillator is utilized to simulate the mean drag force and the vortex-induced lift force. Also, the pipe material is assumed to be viscoelastic and consisted of the Kelvin-Voigt type. The extended Hamilton's principle along with the Galerkin discretization are employed to construct the nonlinear model of the coupled fluid-structure system. Moreover, the assumed mode method along...
Dynamic performance enhancement of RC slabs by steel fibers vs. externally bonded GFRP sheets under impact loading
, Article Engineering Structures ; Volume 213 , 2020 ; Khaloo, A ; Sadraie, H ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Recently, to improve the dynamic behavior of Reinforced Concrete (RC) slabs under impact load, the methods of externally bonding Glass Fiber Reinforced Polymer (GFRP) sheets to slab and internally reinforcing concrete by steel fibers have been proposed. Nevertheless, it is required to investigate the comparison between these two methods on response of RC slabs under impact loads. In this study, the influence of volume fraction of steel fibers, the number of GFRP sheet layers (one or two) and the arrangement of GFRP sheets (covering the whole or parts of surface), are examined. Performance of fourteen 1000 × 1000 × 75 mm concrete slabs including one plain slab, one steel RC slab, three steel...
A semi-active SMA-MRF structural stability element for seismic control in marine structures
, Article Applied Ocean Research ; Volume 100 , 2020 ; Zabihollah, A ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
The stability and integrity of structures under indeterminant external loadings, particularly earthquakes, is a vital issue for the design and safe operation of marine and offshore structures. Over the past decades, many structural control systems, such as viscous-based systems, have been developed and embedded in marine and offshore structures, particularly oil platforms to maintain the stability and mitigate the seismic hazards. Rapid improvement in intelligent materials, including shape memory alloys (SMAs) and Magnetorheological fluid (MRF), have led to the design and development of efficient structural control elements. The present work aims to establish a framework for the structural...
Applicability of rigid block based approaches in predicting sandy slope displacements by 1g shaking table tests
, Article Soil Dynamics and Earthquake Engineering ; Volume 126 , 2019 ; 02677261 (ISSN) ; Farahi Jahromi, H ; Rajabigol, M ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
Various approaches have been developed by researchers to predict earthquake induced landslide displacements. This study evaluates the applicability of these approaches on sandy slopes. For this purpose, nine physical models are constructed inside a rigid box and thirty-six shaking table tests are conducted. Dynamic responses are then converted to the full scale model by applying similitude laws. Five statistical criteria are applied to compare the measured and predicted displacements and evaluate the precision of the approaches. By combining the outcomes and using a scoring procedure, the approaches are scored. Consequently, the approaches of Fotopoulou and Pitilakis [23] and Hsieh and Lee...
Introducing a response-based duration metric and its correlation with structural damages
, Article Bulletin of Earthquake Engineering ; Volume 17, Issue 11 , 2019 , Pages 5987-6008 ; 1570761X (ISSN) ; Harati, M ; Ashoori Barmchi, M ; Estekanchi, H. E ; Sharif University of Technology
Springer Netherlands
2019
Abstract
This study proposes a response-based parameter for strong motion duration which is computed for structures and is the total time they are nonlinear during an earthquake. Correlation between structural response and duration for structures, subjected to a set of spectrum matched ground motions, is employed to examine the efficiency of the proposed method. The spectral matching procedure ensures that the influence of amplitude and frequency content of motions on structural response variability is significantly removed. Four concrete building type systems are studied and correlation coefficients of structural response with the proposed duration definition are examined. Comparison of the proposed...
Dynamic performance of concrete slabs reinforced with steel and GFRP bars under impact loading
, Article Engineering Structures ; Volume 191 , 2019 , Pages 62-81 ; 01410296 (ISSN) ; Khaloo, A ; Soltani, H ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
Reinforced concrete slabs are common structural elements that could be exposed to impact loading. Although use of reinforced concrete slabs and utilization of Fiber Reinforced Polymer (FRP) as alternative to traditional steel reinforcement slabs are growing, but the influence of various parameters on their response under impact loads is not properly evaluated. This study investigated the effect of rebar's material, amount and arrangement of reinforcements, concrete strength and slab thickness on dynamic behavior of reinforced concrete slabs using both laboratory experiments and numerical simulations. Performance of fifteen 1000 × 1000 mm concrete slabs, including two 75 mm thick plain slabs,...
Predictive equations for drift ratio and damage assessment of RC shear walls using surface crack patterns
, Article Engineering Structures ; Volume 190 , 2019 , Pages 410-421 ; 01410296 (ISSN) ; Dolatshahi, K. M ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
The purpose of this paper is to quantify the extent of damage of rectangular reinforced concrete shear walls after an earthquake using surface crack patterns. One of the most important tasks after an earthquake is to assess the safety and classify the performance level of buildings. This assessment is usually performed by visual inspection that is prone to significant errors. In this research, an extensive database on the images of damaged rectangular reinforced concrete shear walls is collected from the literature. This database includes more than 200 images from experimental quasi-static cyclic tests. Using the concept of fractal geometry, several probabilistic models are developed by...
Strain gradient based dynamic response analysis of heterogeneous cylindrical microshells with porosities under a moving load
, Article Materials Research Express ; Volume 6, Issue 3 , 2019 ; 20531591 (ISSN) ; Mohasel Afshari, B ; Barati, M. R ; Hamouda, A. M. S ; Sharif University of Technology
Institute of Physics Publishing
2019
Abstract
Forced vibration of a porous functionally graded (FG) cylindrical microshell due to a moving point load with constant velocity is studied for the first time. Through the thickness of microshell, there are even-type or uneven-type porosities. Therefore, material properties of the microshell become porosity-dependent and are described via modified power-law function. For micro-scale shells, small size effects due to non-uniform strain field can be considered via strain gradient theory (SGT). At first, the governing equations of the microshell are converted to new equations in Laplace domain. Then, time response of the microshell will be obtained implementing inverse Laplace transform...