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Seismic performance assessment of fixed offshore structures by endurance time method
, Article Ships and Offshore Structures ; Volume 14, Issue 7 , 2019 , Pages 709-722 ; 17445302 (ISSN) ; Mehdigholi, H ; Seif, M. S ; Sharif University of Technology
Taylor and Francis Ltd
2019
Abstract
The aim of this paper is to consider the ability of endurance time (ET) method to estimate the seismic response of fixed offshore platforms at various excitation levels. In this way, various sources of nonlinear behaviour and challenging issues in the ET approach are included in the three-dimensional model of a real jacket platform utilising the finite element method. In addition to common-designed, over-designed and under-designed cases of this platform have been investigated to examine the effects of the structural characteristics on the ET response. To consider the accuracy and reliability of this approach, results of the ET method are compared with results of nonlinear time history...
Seismic performance assessment of fixed offshore structures by endurance time method
, Article Ships and Offshore Structures ; Volume 14, Issue 7 , 2019 , Pages 709-722 ; 17445302 (ISSN) ; Mehdigholi, H ; Seif, M. S ; Sharif University of Technology
Taylor and Francis Ltd
2019
Abstract
The aim of this paper is to consider the ability of endurance time (ET) method to estimate the seismic response of fixed offshore platforms at various excitation levels. In this way, various sources of nonlinear behaviour and challenging issues in the ET approach are included in the three-dimensional model of a real jacket platform utilising the finite element method. In addition to common-designed, over-designed and under-designed cases of this platform have been investigated to examine the effects of the structural characteristics on the ET response. To consider the accuracy and reliability of this approach, results of the ET method are compared with results of nonlinear time history...
Response spectrum method for extreme wave loading with higher order components of drag force
, Article Journal of Marine Science and Application ; Volume 16, Issue 1 , 2017 , Pages 27-32 ; 16719433 (ISSN) ; Dezfouli, Mani, F ; Dastan Diznab, M. A ; Mohajernasab, S ; Seif, S. M ; Sharif University of Technology
2017
Abstract
Response spectra of fixed offshore structures impacted by extreme waves are investigated based on the higher order components of the nonlinear drag force. In this way, steel jacket platforms are simplified as a mass attached to a light cantilever cylinder and their corresponding deformation response spectra are estimated by utilizing a generalized single degree of freedom system. Based on the wave data recorded in the Persian Gulf region, extreme wave loading conditions corresponding to different return periods are exerted on the offshore structures. Accordingly, the effect of the higher order components of the drag force is considered and compared to the linearized state for different sea...
Assessment of offshore structures under extreme wave conditions by Modified Endurance Wave Analysis
, Article Marine Structures ; Volume 39 , December , 2014 , Pages 50-69 ; ISSN: 09518339 ; Mohajernassab, S ; Seif, M. S ; Tabeshpour, M. R ; Mehdigholi, H ; Sharif University of Technology
2014
Abstract
Recently, various approaches have been introduced to estimate the response of offshore structures in different sea states by stepwisely intensifying records. In this article, a more practical approach entitled Modified Endurance Wave Analysis (MEWA) considering the random and probabilistic nature of wave loading and utilizing optimal time duration is introduced. Generation procedure of this approach is described based on two practical wave theories: random and constrained new-wave. In addition, assessment of a simplified model representing a typical fixed offshore platform under extreme wave conditions in the Persian Gulf is performed making use of MEWA. A comparative analysis has been also...
Developing Dynamic Increasing Amplitude and Period (DIAP)Method for Evaluation of Offshore Structures
, M.Sc. Thesis Sharif University of Technology ; Tabeshpour, Mohammad Reza (Supervisor) ; Dastan Diznab, Mohammad Ali (Co-Advisor)
Abstract
In this study, Wave Endurance Time (WET) is introduced as an applicable method for assessment of offshore structures under extreme waves. In this method, artificial records called Wave Functions (WFs) are used instead of usual extreme wave records. WFs are designed so that their excitations gradually increase with time. Therefore, one WF can be replaced by a large number of sea surface records with different excitation levels. The main advantage of proposed method is that it assesses the structural performance under various extreme waves with low computational cost especially in comparison with three-hour simulasions. Moreover, reliability of structures can be evaluated based on the time...
Modeling of Dynamic Behavior of Fixed Offshore Platforms and their Performance Improvement by Endurance time Method
, Ph.D. Dissertation Sharif University of Technology ; Seif, Mohammad Saeed (Supervisor) ; Mehdigholi, Hamid (Supervisor) ; Tabeshpour, Mohammad Reza (Co-Advisor)
Abstract
In this thesis, multi-degree-of-freedom and finite element methods are utilized to simulate the dynamic behavior of fixed offshore structures under the wave and the earthquake excitations. In the field of seismic loading, seismic response of the platform is determined with the response spectrum analysis (RSA), time history analysis (THA) and endurance time (ET) methods. The accuracy and the computational cost of the ET method are compared with the RSA and THA methods. The results indicate that despite the RSA method, the ET method can estimate the nonlinear behavior of these types of structures. Moreover, in comparison with the THA method, the computational burden decreases to about 5% while...
Computer simulations of pressure and velocity fields in a human upper airway during sneezing
, Article Computers in Biology and Medicine ; Volume 71 , 2016 , Pages 115-127 ; 00104825 (ISSN) ; Haghighi, A ; Dastan, A ; Abouali, O ; Farid, M ; Ahmadi, G ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
In this paper, the airflow field including the velocity, pressure and turbulence intensity distributions during sneezing of a female subject was simulated using a computational fluid dynamics model of realistic upper airways including both oral and nasal cavities. The effects of variation of reaction of the subject during sneezing were also investigated. That is, the impacts of holding the nose or closing the mouth during sneezing on the pressure and velocity distributions were studied. Few works have studied the sneeze and therefore different aspects of this phenomenon have remained unknown. To cover more possibilities about the inlet condition of trachea in different sneeze scenarios, it...
Performance-based assessment of steel jacket platforms by wave endurance time method
, Article Ships and Offshore Structures ; Volume 12, Issue 1 , 2017 , Pages 32-42 ; 17445302 (ISSN) ; Dastan Diznab, M. A ; Mehdigholi, H ; Tabeshpour, M. R ; Seif, M. S ; Sharif University of Technology
2017
Abstract
In this article, wave endurance time (WET) is addressed as an applicable method for performance-based assessment of fixed offshore structures under extreme waves. In this method, inspired by the endurance time method in the field of earthquake engineering, artificial wave records called wave functions are designed so that their excitations gradually increase with time. Therefore, the main advantage of the proposed method is that it can assess the structural performance under various wave load conditions through a single time-history analysis. Moreover, the reliability of structures can be evaluated on the basis of the time that the structural response is still acceptable. In this study,...
Modification of endurance wave analysis based on New-wave theory
, Article Ships and Offshore Structures ; Volume 12, Issue 3 , 2017 , Pages 330-340 ; 17445302 (ISSN) ; Dastan Diznab, M. A ; Mehdigholi, H ; Seif, M. S ; Tabeshpour, M. R ; Sharif University of Technology
Taylor and Francis Ltd
2017
Abstract
The main objective of this investigation is to modify endurance wave analysis (EWA) based on New-wave theory for convenient assessment of offshore structures under extreme waves. EWA is a novel time history based approach to evaluate structural performance in various excitation levels of wave loading by intensifying wave records. In this article, modifications are proposed to determine appropriate time duration and intensifying trend for reliable and practical assessment of offshore structures. In this way, a simplified model of a real jacket platform is utilised to investigate the application of this approach under extreme wave conditions in the Persian Gulf and results are compared with...
Stereometric analysis of TiO2 thin films deposited by electron beam ion assisted
, Article Optical and Quantum Electronics ; Volume 52, Issue 5 , 2020 ; Arman, A ; Ţălu, Ş ; Dastan, D ; Luna, C ; Rezaee, S ; Sharif University of Technology
Springer
2020
Abstract
The micromorphology and semiconductor properties of TiO2 thin films growth using different ion beam energies have been finely analyzed using atomic force microscopy (AFM), ultra-violet visible (UV–visible) spectroscopy and stereometric analysis. The AFM measurements and surface stereometric analysis are essential for the accurate characterization of the 3-D surface topographic features and allow the determination of the 3-D surface texture parameters that influence the optical properties of the material. The samples were divided into four groups to discuss the obtained results, according to the ion beam energy applied in the sample preparation. The results obtained from experimental...
Statistical, morphological, and corrosion behavior of PECVD derived cobalt oxide thin films
, Article Journal of Materials Science: Materials in Electronics ; Volume 30, Issue 24 , 2019 , Pages 21185-21198 ; 09574522 (ISSN) ; Alam, M. H ; Dastan, D ; Ziakhodadadian, S ; Shi, Z ; Garmestani, H ; Weidenbach, A. S ; Ţălu, Ş ; Sharif University of Technology
Springer
2019
Abstract
Experimental parameters have direct influences on materials properties and therefore their applications. The effect of plasma power on the properties of cobalt oxide thin films, prepared using plasma-enhanced chemical vapor deposition technique, on stainless steel substrates have been addressed in this paper. The structural, morphological, and compositional properties of these films were investigated by means of X-ray diffraction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) technique. The XRD patterns demonstrated the growth of polycrystalline Co3O4 thin film with a cubic spinel structure such that the intensity of (511) and (311) peaks increase as the...
Evaluation of Synchronization Mechanisms of Dual HW-RAID controllers in Data Storage Systems
, M.Sc. Thesis Sharif University of Technology ; Asadi, Hossein (Supervisor)
Abstract
Using single RAID HW-Controller in data storage systems can become a single point-of-failure. Hence, it will affect system availability. As a result, in enterprise-class storage systems, utilizing dual-HW-Controller architecture for managing redundant array of independent disks is prevalent to enhance performance and reliability. Employing such architecture, however, faces major challenges. One of these challenges is the synchronization of dual-HW-based controllers in case RAID arrays revealing erratic behaviours. No thorough study has been done for evaluating dual-controller architecture synchronization mechanisms and its performance. In this thesis, different configurations of enterprise...
Symptom prediction and mortality risk calculation for COVID-19 using machine learning
, Article Frontiers in Artificial Intelligence ; Volume 4 , June , 2021 ; 26248212 (ISSN) ; Asgary, A ; Tavakoli, N ; Zali, A ; Dastan, F ; Daaee, A ; Badakhshan, M ; Esmaily, H ; Jamaldini, S. H ; Safari, S ; Bastanhagh, E ; Maher, A ; Babajani, A ; Mehrazi, M ; Sendani Kashi, M. A ; Jamshidi, M ; Sendani, M. H ; Rahi, J ; Mansouri, N ; Sharif University of Technology
Frontiers Media S. A
2021
Abstract
Background: Early prediction of symptoms and mortality risks for COVID-19 patients would improve healthcare outcomes, allow for the appropriate distribution of healthcare resources, reduce healthcare costs, aid in vaccine prioritization and self-isolation strategies, and thus reduce the prevalence of the disease. Such publicly accessible prediction models are lacking, however. Methods: Based on a comprehensive evaluation of existing machine learning (ML) methods, we created two models based solely on the age, gender, and medical histories of 23,749 hospital-confirmed COVID-19 patients from February to September 2020: a symptom prediction model (SPM) and a mortality prediction model (MPM)....
Studying the Effect of Applying Different Refrigerants in Ground Source Heat Exchangers
, M.Sc. Thesis Sharif University of Technology ; Hakkaki-Fard, Ali (Supervisor)
Abstract
Economical strategy of developed countries imposes to improve energy efficiency and a rational renewable energies usage in the buildings. Ground source heat pumps are one of the most important tools in the way moving toward this goal. This study focuses on studying the effect of applying different refrigerants in the direct expansion ground source heat exchangers. In order to compare the performance of the ground source heat pumps using different refrigerants, a specific methodology is presented and implemented. First on this study, the thermal performance of a geothermal borehole filled with both CO2 and a zeotropic mixture of CO2 and R32 (20/80) is studied and the quality, temperature, and...
Facile deposition of porous fluorine doped tin oxide by Dr. Blade method for capacitive applications
, Article Ceramics International ; 2020 ; Tajabadi, F ; Dastan, D ; Sangpour, P ; Shi, Z ; Taghavinia, N ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Three-dimensional macroporous fluorine-doped tin oxide (p-FTO) films were successfully deposited using commercial ink of FTO powder and SnCl2 salt via Dr. Blade method. Various features of p-FTO thin films were studied as a function of the ink composition and sintering temperature. The morphological studies corroborated formation of porous, uniform, and crack-free FTO films after annealing at 300 °C for 10 min in air. X-ray diffraction pattern demonstrated development of highly crystalline FTO films. The lowest sheet resistance of 47 Ω/□ was obtained for the p-FTO film with a thickness of 21 μm. The capacitance of thin p-FTO films was investigated using a three-electrode system and the...
Facile deposition of porous fluorine doped tin oxide by Dr. blade method for capacitive applications
, Article Ceramics International ; Volume 47, Issue 4 , 2021 , Pages 5487-5494 ; 02728842 (ISSN) ; Tajabadi, F ; Dastan, D ; Sangpour, P ; Shi, Z ; Taghavinia, N ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
Three-dimensional macroporous fluorine-doped tin oxide (p-FTO) films were successfully deposited using commercial ink of FTO powder and SnCl2 salt via Dr. Blade method. Various features of p-FTO thin films were studied as a function of the ink composition and sintering temperature. The morphological studies corroborated formation of porous, uniform, and crack-free FTO films after annealing at 300 °C for 10 min in air. X-ray diffraction pattern demonstrated development of highly crystalline FTO films. The lowest sheet resistance of 47 Ω/□ was obtained for the p-FTO film with a thickness of 21 μm. The capacitance of thin p-FTO films was investigated using a three-electrode system and the...
Theoretical study of high repetition rate short pulse generation with fiber optical parametric amplification [electronic resource]
, Article Journal of Lightwave Technology ; May 2012, Volume 30, Issue 9, PP. 1263-1268 ; Ariaei, A. M ; Jadidi, M. M ; Salehi, J. A ; Sharif Unversity of Technology
Abstract
In this paper, we study theoretically the generation of high repetition rate short pulses using fiber optical parametric amplification. We show that the pulse shape and duration depend on the signal location relatively to the pump frequency. We demonstrate that in order to get the shortest pulse width, the signal must be located at one of the extremities of the gain spectrum associated with the pump peak power. We derive the analytical expression of the pulse shape in this case and compare it to the exponential gain regime case. Using numerical simulations, we also analyze the impact of walk-off and pump phase modulation that is required to suppress Stimulated Brillouin Scattering and derive...
A novel omega shaped microwave absorber with wideband negative refractive index for C-band applications
, Article Optik ; Volume 242 , 2021 ; 00304026 (ISSN) ; Baqir, M. A ; Iftikhar, A ; Ali, M. M ; Rahim, A. A ; Niaz Akhtar, M ; Mughal, M. J ; Naqvi, S. A ; Sharif University of Technology
Elsevier GmbH
2021
Abstract
This paper reports a polarization controllable and angle-insensitive perfect metamaterial absorber (PMA). The proposed PMA consists of periodically arranged asymmetric omega-shaped resonators made of metallic copper. The absorptivity was analyzed considering the microwave C-band from 4 GHz to 8 GHz. The proposed PMA shows an absorption peak with almost 100% absorptivity at 6.2 GHz. Also, wideband negative index of refraction is observed. Further, the absorber is inspected for the different rotation angles of the top metasurface (omega-shaped ring) along the optical axis, and obliquity of incidence angle for both TE and TM polarized waves. Moreover, surface electric field and surface current...
Formal process algebraic modeling, verification, and analysis of an abstract Fuzzy Inference Cloud Service
, Article Journal of Supercomputing ; Vol. 67, issue. 2 , February , 2014 , pp. 345-383 ; Online ISSN: 1573-0484 ; Rahmani, A. M ; Movaghar, A ; Teshnehlab, M
2014
Abstract
In cloud computing, services play key roles. Services are well defined and autonomous components. Nowadays, the demand of using Fuzzy inference as a service is increasing in the domain of complex and critical systems. In such systems, along with the development of the software, the cost of detecting and fixing software defects increases. Therefore, using formal methods, which provide clear, concise, and mathematical interpretation of the system, is crucial for the design of these Fuzzy systems. To obtain this goal, we introduce the Fuzzy Inference Cloud Service (FICS) and propose a novel discipline for formal modeling of the FICS. The FICS provides the service of Fuzzy inference to the...
Impact of holmium on structural, dielectric and magnetic properties of Cu–Zn spinel ferrites synthesized via sol–gel route
, Article Journal of Materials Science: Materials in Electronics ; Volume 32, Issue 2 , 2021 , Pages 2205-2218 ; 09574522 (ISSN) ; Khan, M. A ; Hussain, A ; Akhtar, M. N ; Ahmad, M ; Javid, M. A ; Sharif University of Technology
Springer
2021
Abstract
The mixed nano-ferrites materials Cu0.6Zn0.4HoxFe2−xO4 (0.00 ≤ x ≤ 0.12) were prepared via the sol–gel auto combustion technique. The TGA curve established the annealing temperature (500 °C) for phase formation. The single exothermic peak on the DSC plot occurred at 341 °C temperature. XRD patterns of these nano ferrites verified single phase formation of the FCC cubic structure. The lattice constant a was increased from 8.4244 to 8.4419 Å and then its value decreased to 8.4319 Å. Crystallite size was found in the range of 7 to 16 nm. The surface morphology of the samples was observed from the scanning electron microscope (SEM) images. The grain size was found within the range of 90 nm to...