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Hybrid Numerical-Experimental Simulation of Unsteady Multi-phase Flow through High Pressure Hydro-Pneumatic Systems
, M.Sc. Thesis Sharif University of Technology ; Darbandi, Masoud (Supervisor)
Abstract
The simulation of hydro-pneumatic systems should be considered as a difficult task, because they consist of several different hydraulic and pneumatic components working together and affecting each other. For example, hydraulic and pneumatic components interact strongly in a diaphragm pump. As known, a single liquid phase may unwantedly change to two-phase condition and cause unavoidable problems within the simulation processes. In this research, we simulate the unsteady multiphase flow in high pressure hydro-pneumatic systems using a hybrid numerical-experimental method to study such rather complex effects suitably. For the computational fluid dynamics part of the simulation, we use a single...
Analysis of nanoparticles migration on natural convective heat transfer of nanofluids
, Article International Journal of Thermal Sciences ; Volume 68 , June , 2013 , Pages 79-93 ; 12900729 (ISSN) ; Yaghoubi, M ; Sharif University of Technology
2013
Abstract
Both experimental and numerical studies are unanimous for enhancing Nusselt number for forced convection of nanofluids with slight difference, but there is inconsistency for natural convection heat transfer of nanofluids. In this paper attempt is made to study the effects of nanoparticles migration on the natural convection behavior of nanofluids. For analysis, a mixture model is used by including important phenomena such as Brownian motion and thermophoresis effects. These two mechanisms are taken into account to compute the slip velocities between the base fluid and nanoparticles. The governing equations are solved numerically and good agreements are observed in comparison with...
Silicon morphology modelling during solidification process of A356 al alloy
, Article International Journal of Cast Metals Research ; Volume 25, Issue 1 , 2012 , Pages 53-58 ; 13640461 (ISSN) ; Mazahery, A ; Davami, P ; Razavi, M ; Sharif University of Technology
Abstract
In this paper, an introduction of the finite element approach to microstructure based modelling is provided, and the primary and secondary dendrite arm spacings of A356 alloy in the solidification process are simulated. The simulated results of dendrite morphology and the experimental measurements are presented and compared with the investigations of other researchers, which confirmed the accuracy of this model in its ability to predict the dendrite arm spacing. Each of the length scales, including silicon rod diameter and spacing, is discussed in detail. Analytical equations are generated for the length scales and incorporated in the Sharif University Technology academic software for the...
Performance evaluation of a modular design ofwind tower withwetted surfaces
, Article Energies ; Volume 10, Issue 7 , 2017 ; 19961073 (ISSN) ; Bahadori, M. N ; Dehghani Sanij, A ; Nourbakhsh, A ; Sharif University of Technology
MDPI AG
2017
Abstract
Wind towers or wind catchers, as passive cooling systems, can provide natural ventilation in buildings located in hot, arid regions. These natural cooling systems can provide thermal comfort for the building inhabitants throughout the warm months. In this paper, a modular design of a wind tower is introduced. The design, called a modular wind tower with wetted surfaces, was investigated experimentally and analytically. To determine the performance of the wind tower, air temperature, relative humidity (RH) and air velocity were measured at different points. Measurements were carried out when the wind speed was zero. The experimental results were compared with the analytical ones. The results...
Effect of initial surface treatment on shot peening residual stress field: analytical approach with experimental verification
, Article International Journal of Mechanical Sciences ; Volume 137 , 2018 , Pages 171-181 ; 00207403 (ISSN) ; Farrahi, G. H ; Mahmoudi, A. H ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
Shot peening is the most common surface treatment employed to enhance the fatigue performance of structural metallic materials and often carried out after other surface treatments. This paper mainly focuses on the effects of initial conditions of surface such as initial stress filed and hardness profile on shot peening residual stress field. The residual stress distribution induced by shot peening is obtained using Hertzian contact theory and elastic–plastic evaluation after yielding occurred during impingement and rebound of shots. Elastic plastic calculations are performed using different hardening models considering Bauschinger effect. The present model is able to predict redistribution...
Implementation of Time Splitting Projection Method in water hammer modeling in deformable pipes
, Article International Journal of Pressure Vessels and Piping ; Volume 98 , October , 2012 , Pages 30-42 ; 03080161 (ISSN) ; Borghei, S. M ; Bohluly, A ; Sharif University of Technology
Elsevier
2012
Abstract
In this paper Time Splitting Projection Method (TSPM) has been implemented to model transient flow in a deformable pipe. In addition a quasi-steady model and the Brunone unsteady model have been incorporated into the algorithm to consider the effect of static and dynamic friction on the shape and attenuation of pressure waves. The deformation of the cross section of the pipe due to the change of pressure has been considered using Hooke's Law of elasticity. Numerical results of the model have been compared with a simple analytical test and results of experimental measurements for water hammer problem with different Reynolds numbers in a simple pipeline system; besides, numerical stability...
Broadband omnidirectional and miniature fold-up discone antenna in VHF/UHF band
, Article Electromagnetics ; Volume 32, Issue 5 , Jul , 2012 , Pages 266-273 ; 02726343 (ISSN) ; Karkhaneh, H ; Sadeghpour, T ; Sharif University of Technology
2012
Abstract
In this article, a novel miniature broadband omnidirectional antenna is proposed. This antenna is suitable to use in vehicles, especially in unmanned aerial vehicles, since it will be folded in order to reduce its size when the unmanned aerial vehicle lands. A special kind of wire discone antenna is chosen to achieve all desired goals. Passive broadband impedance matching at the input of the antenna improves the voltage standing-wave ratio. A telescopic fiberglass axis is used in the antenna structure in order to reduce size and increase wind resistance. The assessment of the novel structure in implementing the antenna is confirmed by experimental measurements. The measurement results reveal...
Measurement, analysis and reconstruction of residual stresses
, Article Journal of Strain Analysis for Engineering Design ; Volume 47, Issue 4 , February , 2012 , Pages 254-264 ; 03093247 (ISSN) ; Goudar, D ; Farrahi, G. H ; Smith, D. J ; Sharif University of Technology
2012
Abstract
Residual stresses, created in a steel beam by elastic-plastic bending, are predicted using an approximate analysis and the finite element method. The predictions are compared to experimental measurements obtained from the application of incremental centre hole drilling, deep hole drilling and neutron diffraction methods. Finite element simulations of the incremental centre hole drilling and deep hole drilling methods applied to the predicted residual stresses permitted an assessment of their ability to reconstruct the stresses. An analytical reconstruction analysis using an Airy stress function together with boundary and equilibrium conditions is developed and applied to the predictions and...
Iterative implicit integration procedure for hybrid simulation of large nonlinear structures
, Article Earthquake Engineering and Structural Dynamics ; Volume 40, Issue 9 , October , 2011 , Pages 945-960 ; 00988847 (ISSN) ; Ahmadizadeh, M ; Sharif University of Technology
2011
Abstract
A fully implicit iterative integration procedure is presented for local and geographically distributed hybrid simulation of the seismic response of complex structural systems with distributed nonlinear behavior. The purpose of this procedure is to seamlessly incorporate experimental elements in simulations using existing fully implicit integration algorithms designed for pure numerical simulations. The difficulties of implementing implicit integrators in a hybrid simulation are addressed at the element level by introducing a safe iteration strategy and using an efficient procedure for online estimation of the experimental tangent stiffness matrix. In order to avoid physical application of...
Development of a penetration model for an erosive long rod considering strength effects of colliding materials
, Article Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science ; Volume 225, Issue 4 , August , 2011 , Pages 965-973 ; 09544062 (ISSN) ; Vahedi, K ; Zohoor, H ; Sharif University of Technology
2011
Abstract
In this article a simple penetration model for the terminal ballistic of long rod penetrators is developed. The model is to predict the crater depth of a projectile penetrating into a semi-infinite target. A principle objective was to take an account of strength properties of colliding materials using erosive phenomena. The entire velocity regime from low to hypervelocity is analysed. The effect of the penetrator aspect ratio is also considered in the model. The model developed here is based on the steady-state penetration process and is used to compare with existing experimental measurements. The results of the comparison show very good agreement with experimental investigations of other...
Experimental and numerical investigation of a centrifugal compressor
, Article ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, ESDA2010, 12 July 2010 through 14 July 2010, Istanbul ; Volume 3 , 2010 , Pages 447-458 ; 9780791849170 (ISBN) ; Hajilouy Benisi, A ; Nili Ahmadabadi, M ; Sharif University of Technology
2010
Abstract
In this research, centrifugal compressor of a gas turbine is investigated experimentally and numerically. Operation line of the compressor as a component of the gas turbine is obtained experimentally by measurements of impeller rotational speed, and flow parameters at the compressor inlet and outlet during the gas turbine operation. The flow field inside the impeller and diffusers are analyzed numerically using a full 3D Navier-Stokes program with SST turbulence model. Boundary conditions for the numerical simulation are specified from the experimental measurements. The operation line of the compressor is obtained numerically, which is compared with that of the experimental results, and...
Frequency response behavior of microcantilevers in tapping-mode Atomic Force Microscopy
, Article Proceedings of the ASME Design Engineering Technical Conference, 15 August 2010 through 18 August 2010, Montreal, QC ; Volume 4 , 2010 , Pages 469-476 ; 9780791844120 (ISBN) ; Mahmoodi, S. N ; Jalili, N ; Zohoor, H ; Sharif University of Technology
2010
Abstract
Distributed-parameters vibration model of microcantilevers in tapping-mode Atomic Force Microscopy (AFM) is developed and is shown to be highly nonlinear. The question of why these nonlinearities are important and how they influence the predicted frequency response behavior of the cantilevers is addressed by comparing the results of developed model with a simple lumpedparameters model that has been extensively studied in the literature so far. The interaction forces between the microcantilever tip and the sample is supposed to be the same in both models and consist of attractive and repulsive interaction force regimes. In addition, experimental measurements are provided for a typical...
Linear and nonlinear approaches towards amplitude modulation atomic force microscopy
, Article Current Applied Physics ; Volume 10, Issue 6 , 2010 , Pages 1416-1421 ; 15671739 (ISSN) ; Mahmoodi, S. N ; Jalili, N ; Zohoor, H ; Sharif University of Technology
2010
Abstract
Frequency response behavior of microcantilever is analytically and experimentally investigated in amplitude modulation Atomic Force Microscopy (AFM). AFM microcantilever probe is modeled as a continuous beam, and tip-sample interaction force is considered to include both attractive and repulsive force regimes. The developed model is compared with the linear lumped-parameters model that has been extensively used in the literature so far. Experimental measurements are also provided for the frequency response of a typical microcantilever-sample system to demonstrate the advantages of the developed model over the linear formulation. The results indicate that the nonlinear continuous model is...
Measurement and correlation of surface tension for single aqueous electrolyte solutions
, Article International Journal of Thermophysics ; Volume 31, Issue 4-5 , May , 2010 , Pages 852-859 ; 0195928X (ISSN) ; Taghikhani, V ; Ghotbi, C ; Sharif University of Technology
2010
Abstract
In this study, the values of the surface tension for a number of single aqueous electrolyte solutions were measured at various temperatures and electrolyte concentrations using the well-known and computer-aided pendant-drop method. In order to conduct the experimental measurements, a high-pressure IFT-700 apparatus, equipped with a view cell and a data acquisition system, was used. The systems studied in this study were aqueous solutions of KCl, NaCl, CaCl 2, and Na 2SO 4. The pooled standard deviation and the confidence limit of the surface-tension data for a 95 % confidence level were determined to be 0.17mN · m -1 and σ̄ ± 0.19, respectively. It should be noted that while the surface...
A complete accounting of the monoenergetic electron parameters in an ellipsoidal bubble model
, Article Physics of Plasmas ; Volume 17, Issue 3 , 2010 ; 1070664X (ISSN) ; Rahmatollahpur, S ; Sharif University of Technology
2010
Abstract
A reliable analytical expression for the potential of plasma waves with phase velocities near the speed of light is derived. The presented ellipsoid cavity model is more consistent than the previous spherical model and it explains the monoenergetic electron trajectory more accurately especially in the relativistic regime. The electron energy spectrum is also calculated and it is found that the energy distribution ratio of electrons ΔE/E for the ellipsoid model in the here reported condition is about 10%, which is less than half that of the spherical model (25%) and it is in good agreement with the experimentally measured value of 12% under the same condition. The experimental measurements...
Estimating liquefaction-induced settlement of shallow foundations by numerical approach
, Article Computers and Geotechnics ; Volume 37, Issue 3 , April , 2010 , Pages 267-279 ; 0266352X (ISSN) ; Pak, A ; Sharif University of Technology
2010
Abstract
Occurrence of liquefaction in saturated sand deposits underlying foundation of structure can cause a wide range of structural damages starting from minor settlement, and ending to general failure due to loss of bearing capacity. If the bearing capacity failure is not the problem, reliable estimation of the liquefaction-induced settlement will be of prime importance in assessment of the overall performance of the structure. Currently, there are few procedures with limited application in practice for estimation of settlement of foundations on liquefied ground. Therefore, development of a general relationship is important from the practical viewpoint. In this paper, the dynamic response of...
Experimental measurement and analytical determination of shot peening residual stresses considering friction and real unloading behavior
, Article Materials Science and Engineering A ; Volume 657 , 2016 , Pages 309-321 ; 09215093 (ISSN) ; Farrahi, G. H ; Mahmoudi, A. H ; Ghasemi, A ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
This paper presents an analytical model to predict the residual stress distribution induced by Shot peening. The analytical approach is based on the work of Shen and Atluri (2006) [18] with some modifications. The modifications are related to the elasto-plastic unloading of shot impingements, friction coefficient effect and the fraction of kinetic energy transmitted to the treated material. In order to predict more realistic residual stresses, the elasto-plastic unloading phase of shot impacts is modeled using two nonlinear kinematic hardening models considering the Bauschinger effect. Moreover, the effect of the Coulomb friction between target surface and shots is evaluated. For this...
Enhancement of a horizontal axis wind turbine airfoil performance using single dielectric barrier discharge plasma actuator
, Article Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy ; 2020 ; Davari, A. R ; Sabetghadam, F ; Soltani, M. R ; Sharif University of Technology
SAGE Publications Ltd
2020
Abstract
Wind turbines are of the most promising devices to cut down carbon emissions. However, some phenomena that adversely affect their performance are inevitable. The aim of the present paper is to investigate flow separation prevention exploiting leading edge (LE) single dielectric barrier discharge plasma actuator (SDBD-PA) on an airfoil belonging to a section of a locally developed wind turbine. The numerical results of the surface pressure distribution over the airfoil were compared with the experimental measurements carried out by the authors on the same blade section, and good agreement was found between numerical and experimental data for both plasma-OFF and plasma-ON cases. An in-depth...
Modelling and simulation of equiaxed dendritic structures permeability for Pb-Sn alloys
, Article Materials Science and Technology ; Volume 24, Issue 12 , 2008 , Pages 1444-1451 ; 02670836 (ISSN) ; Khajeh, E ; Sharif University of Technology
2008
Abstract
In this investigation, the permeability of interdendritic liquid flow through the equiaxial mushy zone has been modelled for Pb-Sn alloys based on experimental measurements. In the present work by solving Navier-Stokes equation, the flow pattern around the equiaxed dendrite has been obtained and then permeability has been determined by applying Darcy's law. Numerical determined values of permeabilities have been analysed by the use of Statistical Package for the Social Sciences (SPSS) statistical software. Then an experimental method has been used to measure the permeability for flow through equiaxial mushy zone of Pb-Sn alloys. Results show that increasing the solid fraction and...
A study on residual stresses in gas tungsten arc welding of AA5251
, Article Materials and Manufacturing Processes ; Volume 25, Issue 11 , 2010 , Pages 1242-1250 ; 10426914 (ISSN) ; Serajzadeh, S ; Kokabi, A. H ; Sharif University of Technology
2010
Abstract
In this work, thermo-mechanical behavior of an aluminum alloy during gas tungsten arc welding (GTAW) is studied using a three-dimensional mathematical model. The model can be employed to determine residual stresses and their distribution after the welding operation. The effects of the strain hardening and the temperature dependency of material properties have also been considered in the calculations. Model validation has been performed using experimental measurements of residual stress by means of hole-drilling technique. The measurements have been carried out at the heat affected zone (HAZ) and base metal next to the welding line. In addition, microstructural observations have been made to...