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gravity-forces
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Forced vibration analysis of rotors with an open edge crack based on a continuous vibration theory
, Article Archive of Applied Mechanics ; Volume 87, Issue 11 , 2017 , Pages 1871-1889 ; 09391533 (ISSN) ; Heydari, M ; Behzad, M ; Sharif University of Technology
Abstract
In this paper, the forced vibration of a cracked rotor with an open edge crack has been studied by a new continuous model for flexural vibration of cracked rotors proposed in Ebrahimi et al. (J Sound Vib 333:3522–3535, 2014). The cracked rotor behavior under the external excitation of gravity and unbalance forces is presented. Since the governing equation is linear, using the superposition principle the responses of the cracked rotor to the gravity and unbalance forces are calculated separately. Then, the total response is calculated by summing these two responses. Each of these two responses is found by using a modified Galerkin method. The effect of the crack in the presence of the gravity...
Optimal vibration control of rotors with an open edge crack using an electromagnetic actuator
, Article JVC/Journal of Vibration and Control ; Volume 24, Issue 1 , 2018 , Pages 37-59 ; 10775463 (ISSN) ; Heydari, M ; Behzad, M ; Sharif University of Technology
SAGE Publications Inc
2018
Abstract
Vibration control, especially in cracked rotors, is an important factor that can prevent the occurrence of disastrous failures. In this paper, vibrational control of a cracked rotor with an electromagnetic actuator has been studied with a continuous model of flexural vibration of cracked rotors. The governing equation of motion for the rotor under the external excitation of the electromagnetic actuator, gravity, and unbalanced forces is presented. A control law for the optimal control method to minimize the vibration of the rotor or stress at the crack section was obtained. To this aim, two cost functions have been introduced, based on the overall vibration of the rotor and the maximum...
Wettability effects in gas gravity-Assisted flow as related to displacement instability
, Article Special Topics and Reviews in Porous Media ; Volume 1, Issue 1 , 2010 , Pages 39-47 ; 21514798 (ISSN) ; Kharrat, R ; Alipour Tabrizy, V ; Khosravi, M ; Ghotbi, C ; Sharif University of Technology
Abstract
The drainage of oil under gravity forces is an efficient method because it can farther reduce the remaining oil saturation to below that obtained after water flooding. This paper describes a series of visual experiments under forced gas invasion with special attention to the effects of wettability. From oil production history and image analysis, we examine a threshold criterion for displacement stability that is consistent with the results of gradient percolation theory. The effect of the destabilized front velocity on oil recovery and residual saturation is investigated for both wettability conditions. Different recovery rates occur with different fluid morphologies, which depend on the...
Seismic Demands on Gravity Only Steel Frames
,
M.Sc. Thesis
Sharif University of Technology
;
Maleki, Shervin
(Supervisor)
Abstract
Nowadays, using perimeter steel moment frames in combination with interior gravity frames have become common practice in structural building design. One of the key benefits of this system is the open space that it provides for the architects. In active seismic regions, special details are required in the design of the seismic force resisting systems to make these frames ductile. However, these details cause excessive displacement for the gravity force resisting system. Although the gravity frames are not designed to endure seismic forces, they collaborate in the system’s response as they are connected to the same floor diaphragm and withstand lateral displacements. Therefore, these systems...
Relationship between wetting properties and macroscale hydrodynamics during forced gravity drainage and secondary waterflood
, Article Petroleum Science and Technology ; Volume 28, Issue 8 , 2010 , Pages 804-815 ; 10916466 (ISSN) ; Kharrat, R ; Ghotbi, C ; Alipour Tabrizy, V ; Sharif University of Technology
Abstract
In order to relate the wetting properties at the pore scale to the macroscale prevailing forces, a series of experiments was performed in vertical porous media under forced gas invasion at various wettability conditions with partially spreading oil. To describe the dynamics of oil recovery in a three-phase flow condition, the downward gas flood experiments were continued by water injection from the bottom. Experimental results obtained in situations where the magnitudes of viscous, capillary, and gravity forces are comparable. We study the transition from flow configurations where the interface is stable with respect to viscous instability to flow configurations where viscous fingering...
Numerical analysis (finite element method) of brace effects on the adolescent idiopathic scoliosis during 24 hours
, Article Biomedical Engineering - Applications, Basis and Communications ; Vol. 26, issue. 3 , June , 2014 ; 10162372 ; Haghpanahi, M ; Parnianpour, M ; Ganjavian, M. S ; Kamyab, M ; Sharif University of Technology
Abstract
In the adolescent idiopathic scoliosis (AIS) treatment, a brace is prescribed to the patients who have 20 to 45° curves on their spines to prevent the disorder's advancement. For the analysis of Milwaukee brace effects during time, finite element models (FEMs) of the spine (the thoracolumbar region) and the ribcage (contained 10 pairs of the ribs and the sternum) were prepared for two patients. For modeling the spine part, a new element was used in which a disc (as viscoelastic 3D beam) and a vertebra (as rigid link) were modeled as an element and the ribs and the sternum modeled by 3D elastic beams. The gravity, Milwaukee brace constraints and the forces of the brace's different regions...
An experimental investigation of the effect of fracture dip angle on oil recovery and drainage rate in free fall gravity drainage in fractured reservoirs using a glass micromodel (A pore level investigation)
, Article Petroleum Science and Technology ; Volume 31, Issue 4 , 2013 , Pages 355-367 ; 10916466 (ISSN) ; Kharrat, R ; Ghazanfari, M ; Sharif University of Technology
2013
Abstract
Gravity drainage is the main production mechanism in the gas invaded zone in naturally fractured reservoirs. However, there are large ambiguities and complexities, resulting from the dynamic of oil depletion from matrix blocks toward the fracture network. Visualization of drained oil at pore scale using glass micromodels provides the opportunity to better understand the effects of different parameters which might affect oil recovery from fractured reservoirs. In this work a micromodel apparatus generated by laser etching is used to perform some gravity drainage tests on the network patterns. The experiments were performed on double block systems using crude oil. The block to block...
Simulating imbibition process using interacting capillary bundle model with corner flow: The role of capillary morphology
, Article Journal of Petroleum Science and Engineering ; Volume 176 , 2019 , Pages 62-73 ; 09204105 (ISSN) ; Khasi, S ; Ghazanfari, M. H ; Sharif University of Technology
Elsevier B.V
2019
Abstract
Interacting capillary bundle model has been much attended for modeling of imbibition process, however, how the tube morphology controls the front displacement is not well discussed in the available literature, especially when corner flow of wetting phase is considered. Tubes with non-circular cross-sections were used for simulating imbibition process performed on drained bundle of tubes. Different combinations of the interacting tubes with equilateral triangular, square, and circular cross sections were used in the bundle model to explore the role of capillary morphology. The evolution of displacement front, as well as transient water saturation profiles along the model, were obtained for...
Experimental investigation of matrix wettability effects on water imbibition in fractured artificial porous media
, Article Journal of Petroleum Science and Engineering ; Volume 86-87 , 2012 , Pages 165-171 ; 09204105 (ISSN) ; Ayatollahi, S ; Rostami, B ; Sharif University of Technology
Abstract
Spontaneous water imbibition into the matrix blocks is known as the main mechanism for increased oil recovery from naturally fractured oil reservoirs. The rate of oil recovery and its ultimate value is mostly affected by wettability of the rocks and their pore structure. Oil viscosity also greatly influences the rate of oil recovery. A novel experimental model was utilized to study the imbibition mechanism under different wettability conditions. Matrix blocks made from different grain types and size distributions of glass beads were saturated with two different types of synthetic oil, to mimic the oil-saturated matrixes. The wetting characteristic of the models used in this study were...
An Analytic Solution for the Frontal Flow Period in 1D Counter-Current Spontaneous Imbibition into Fractured Porous Media Including Gravity and Wettability Effects
, Article Transport in Porous Media ; Volume 89, Issue 1 , 2011 , Pages 49-62 ; 01693913 (ISSN) ; Masihi, M ; Standnes, D. C ; Sharif University of Technology
Abstract
Including gravity and wettability effects, a full analytical solution for the frontal flow period for 1D counter-current spontaneous imbibition of a wetting phase into a porous medium saturated initially with non-wetting phase at initial wetting phase saturation is presented. The analytical solution applicable for liquid-liquid and liquid-gas systems is essentially valid for the cases when the gravity forces are relatively large and before the wetting phase front hits the no-flow boundary in the capillary-dominated regime. The new analytical solution free of any arbitrary parameters can also be utilized for predicting non-wetting phase recovery by spontaneous imbibition. In addition, a new...