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transient-conditions
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Wind turbine transformer improved design method entailing resonance blocking
, Article IET Electric Power Applications ; Volume 12, Issue 9 , 2018 , Pages 1337-1343 ; 17518660 (ISSN) ; Vakilian, M ; Lehtonen, M ; Sharif University of Technology
Institution of Engineering and Technology
2018
Abstract
A wind turbine transformer resonance can occur due to high frequency transients at its terminal i.e.; under its energization through a length of cable. Occurrence of resonance can be addressed by a sophisticated transformer design procedure. The goal is to obtain an optimum design capable of controlling the frequency response of the winding in such a way to avoid occurrence of any resonance under transient conditions. Three insulation clearances parameters which are employed for the wind turbine transformer winding design have been investigated in design of a (800 kVA, 690/20,000 V) wind turbine transformer to determine effect of their variation on its frequency response. It is shown that...
Modeling of multiple noncatalytic gas-solid reactions in a moving bed of porous pellets based on finite volume method
, Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; Volume 43, Issue 9 , 2007 , Pages 881-894 ; 09477411 (ISSN) ; Saboohi, Y ; Sharif University of Technology
2007
Abstract
A mathematical model is presented to simulate the multiple heterogeneous reactions with complex set of physicochemical and thermal phenomena in a moving bed of porous pellets. This model is based on both heat and mass transfer phenomena of gaseous species in a porous medium including chemical reactions at interfaces whose areas vary during the conversion. This model accounts for both the exothermic and endothermic reactions which can be equimolar or nonequimolar. Furthermore it considers simultaneously the reactions in the nonisothermal transient condition. A powerful technique based upon finite volume fully implicit approach has been implemented to solve the complicated governing equations...
A comparison between partial discharge propagation in multiple-α and single-α transformer winding
, Article Electrical Insulation Conference and Electrical Manufacturing Expo, 2005, Indianapolis, IN, 23 October 2005 through 26 October 2005 ; Volume 2005 , 2005 , Pages 108-111 ; 0780391454 (ISBN); 9780780391451 (ISBN) ; Vakilian, M ; Blackburn, T. R ; Phung, B.T ; Zhang, H ; Nam O, H ; Naderi, M. S ; Sharif University of Technology
2005
Abstract
Power transformers are in service in different environmental, electrical and mechanical conditions. Many experiences have proved that the inner insulation system degradation may pose the transformer to fail while in service. On the other hand, partial discharges (PD) are recognized as the main cause of insulation deterioration process. Therefore, reaching the optimum inner insulation system is one of the challenges a transformer designer is faced with. The solution lies in the correct and accurate modelling of different types of transformer windings. Transformer strength especially during transient conditions is a criterion for transformer insulation designers. This challenge has made...
Improving the performance of the finned absorber inclined rooftop solar chimney combined with composite PCM and PV module
, Article Solar Energy ; Volume 228 , 2021 , Pages 562-574 ; 0038092X (ISSN) ; Hakkaki Fard, A ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
Solar Chimney (SC) can play a significant role in energy consumption reduction of ventilation applications. The primary purpose of this study is to ameliorate the performance of an inclined rooftop SC integrated with the Phase Change Material (PCM) and Photovoltaic (PV) module, called the SC-PCM-PV system. To this aim, the effects of using finned absorbers and composite PCMs on the performance of the SC-PCM-PV system are investigated for the first time. A 3D-CFD model is developed via the finite volume method to examine the impact of various design parameters, including fin number, fin thickness, PCM type, and PCM mass on natural ventilation duration, ventilation capacity, and power output....
Development of a qualified nodalization for small-break LOCA transient analysis in PSB-VVER integral test facility by RELAP5 system code
, Article Nuclear Engineering and Design ; Volume 240, Issue 10 , October , 2010 , Pages 3309-3320 ; 00295493 (ISSN) ; Jafari, J ; Boroushaki, M ; D'Auria, F ; Sharif University of Technology
2010
Abstract
This paper deals with development and qualification of a nodalization for modeling of the PSB-VVER integral test facility (ITF) by RELAP5/MOD3.2 code and prediction of its primary and secondary systems behaviors at steady state and transient conditions. The PSB-VVER is a full-height, 1/300 volume and power scale representation of a VVER-1000 NPP. A RELAP5 nodalization has been developed for PSB-VVER modeling and a nodalization qualification process has been applied for the developed nodalization at steady state and transient levels and a qualified nodalization has been proposed for modeling of the PSB ITF. The 11% small-break loss-of-coolant-accident (SBLOCA), i.e. rupture of one of the...
The potential impact of Fully Ceramic Microencapsulated (FCM) fuel on thermal hydraulic performance of SMART reactor
, Article Nuclear Engineering and Design ; Volume 339 , 2018 , Pages 39-52 ; 00295493 (ISSN) ; Salehi, A. A ; Khalafi, H ; Mataji Kojouri, N ; Jahanfarnia, G ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
One of emerging advanced fuel materials for the next generations of the nuclear reactors is Fully Ceramic Microencapsulated (FCM) fuel. FCM fuel structure is comprised of TRISO particles dispersed randomly in a SiC matrix. In the present study, the thermal hydraulic performance of a SMART reactor is investigated and the results are compared with the case that conventional UO2 fuel is loaded into the core. At the beginning of the cycle, the reactor is simulated in normal operational and transient conditions. MCNPX 2.6 stochastic code is utilised to calculate neutronic parameters. COMSOL and RELAP5 codes are used for thermal hydraulic analysis. The reactor dynamics is simulated based on...
Application of optimal PWM of induction motor in synchronous machines at high power ratings
, Article 2007 IEEE/ASME International Conference on Advanced Intelligent Mechatronics, AIM, Zurich, 4 September 2007 through 7 September 2007 ; 2007 ; 1424412641 (ISBN); 9781424412648 (ISBN) ; Aflaki, M ; Rezazade, A ; Sharif University of Technology
2007
Abstract
The proposed current harmonic model for high-power synchronous machines is dependent on the inductances of quadrature and direct axes. Variation of these parameters, as a consequence of modification in operating point, aging and temperature rise, in-progress pulse patterns, are no longer optimal solutions for minimization of harmonic losses. On the other hand, offline calculation of optimal pulse patterns for slight changes in these parameters, and storing them in read-only memories to serve as look-up tables, give rise to immoderate computational burden and unmanageable look-up tables. Notwithstanding performing online identification process and offline calculation of optimal pulse...
Effects of unsteady friction factor on gaseous cavitation model
, Article Scientia Iranica ; Volume 17, Issue 1 B , 2010 , Pages 13-24 ; 10263098 (ISSN) ; Firooz Abadi, B ; Sharif University of Technology
Abstract
The condition known as a water-hammer problem is a transient condition that may occur as a result of worst-case loadings, such as pump failures, valve closures, etc. in pipeline systems. The pressure in the water hammer can vary in such a way that in some cases it may increase and cause destruction to the hydraulic systems. The pressure in the water hammer can also be decreased to the extent that it can fall under the saturation pressure, where cavitation appears. Therefore, the liquid is vaporized, thus, making a two-phase flow. This pressure decrease can be as dangerous as the pressure rise. As a result of the pressure drop and vaporization of the liquid, two liquid regions are separated,...
A multiphysics model for analysis of droplet formation in electrohydrodynamic 3D printing process
, Article Journal of Aerosol Science ; Volume 135 , 2019 , Pages 72-85 ; 00218502 (ISSN) ; Movahhedy, M. R ; Khodaygan, S ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
Electrohydrodynamic (EHD) printing is a novel technology used for fabricating high-resolution part features from a wide range of materials. Due to the multiphysics dynamics and the multiphase nature of the microdroplet formation in the EHD printers, modeling of this phenomenon is complicated. In this paper, the formation of a droplet in an EHD printer—under a pulsed electrical field—is simulated using a new numerical model which couples the fluid flow, the electric field distribution and the movement of the electric charges under dynamic and transient conditions. The level-set method is applied to the entire multiphysics domain in order to study the formation of the droplet. The presented...