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On dynamic stiffness of spacecraft flexible appendages in deployment phase
, Article Aerospace Science and Technology ; Volume 47 , 2015 , Pages 1-9 ; 12709638 (ISSN) ; Malaek, S. M ; Sharif University of Technology
Abstract
Deployment inertial effects of a spacecraft appendage on its flexible dynamics are investigated. The Euler-Bernoulli beam theory and the actual deployment profile, in which appendage axial motion accelerates from static state and then decelerates to end at zero velocity and acceleration, are employed. The study is concentrated on the arm dynamic stiffness introduced by inertial effects of the arm deployment, and the resultant effects on the arm flexible motions. Lagrange's equations and some appropriate shape functions in the series approximation method are employed to study the arm lateral elastic displacements. Finally a system of ordinary differential equations with time varying...
Economically optimal uncertainty set characterization for power system operational flexibility
, Article IEEE Transactions on Industrial Informatics ; Volume 15, Issue 10 , 2019 , Pages 5456-5465 ; 15513203 (ISSN) ; Hosseini, S. H ; Fotuhi Firuzabad, M ; Sharif University of Technology
IEEE Computer Society
2019
Abstract
Assessing the operational flexibility of the grid with high penetration of renewable resources remains an issue of critical importance. Operational flexibility insufficiency may bring about two major problems: 1) there may exist no feasible solution for operation under uncertain conditions due to insufficient available flexibility capacity; 2) even if the solution feasibility criterion is ensured, dispatch limitations of the flexible resources may force the system operating point to deviate from the optimal economic point with increased redispatch. In this paper, an optimal uncertainty set at the unit commitment time scale is proposed and characterized as a reliable operational metric. A...
Experimental Study on Aerodynamic Deformation of Flexible Wings of an Ornithopter
, M.Sc. Thesis Sharif University of Technology ; Mazaheri, Karim (Supervisor)
Abstract
Flapping motions of flexible wings generate dynamic forces. These forces include aerodynamic forces and inertial forces due to angular acceleration of wing mass, that cause aeroelastic deformation of wings. In this thesis a method is presented by use of a software and some experimental test conditions to study elastic behaviors and aerodynamic forces of flexible wings. A high speed camera records motion of wings in hovering condition and then these images is processed with software to recognize deformations (such as deflection, torsion, etc.) and aerodynamic forces due to them. Afterwards aerodynamic model and deformations is combined for better modeling. Finally we can compare results with...
Control of Two-Arm Flexible Robot Carrying Fluid Tank With Constraint on the Elevation of the Liquid Free-Surface
, M.Sc. Thesis Sharif University of Technology ; Haddadpour, Hassan (Supervisor) ; Kouchakzadeh, Mohammad Ali (Supervisor)
Abstract
Control of two-arm flexible robot is studied in this research. The goal is to control the robot in order to carry a fluid tank installed in the top of the last arm, while the vibration of fluid must be damped. The equations governing the system are extracted by the energy method while Euler-Bernoulli beam is selected to model the elastic members. In order to develop the equations, all of the potential and kinematic energies due to rigid and elastic motions are calculated, then a proper controller is designed for the system to accomplish the considered missions. Since the system is classified as an under-actuated system, the exact feedback linearization method is not practical to control the...
Valuation High_Tech Start up Projects with Real Options Method (Polymer Industry Case Study)
, M.Sc. Thesis Sharif University of Technology ; Zamani, Shiva (Supervisor) ; KeyMaram, Farid (Supervisor)
Abstract
The Real Option Theory (ROT) offers a modern methodology for the valuation of an investment project because it considers the value of managerial flexibility facing project uncertainties. The present work seeks to study the Expand and Swich options value for a polymer plant investment project. Perhaps the most critical step of ROT is the estimation of the project volatility. This work also makes an effort to estimate the project volatility in different cases considering different possibilities of modeling the uncertain variables. The main uncertain variables that can positively affect the project value are the price of the raw material, the price of the product and the demand growth of the...
Modeling of Local Joint Flexibility in Opensees Software by a New Element Added to the Library of Software
, M.Sc. Thesis Sharif University of Technology ; golafshani, Ali akbar (Supervisor)
Abstract
Jacket type offshore platforms are classified as expensive and also strategic structures, and the cost of their maintanace is considerable. Therefore, any inspection and retrofit plans for life extension of the existing structures is economically and logically preferable rather than making decision for design and construction of new structures. The first stage of assessment plan is monitoring the performance of structure during critical loadings for which the structure is designed. One of the critical loads that should be considered in assessment of jacket structures is seismic loading. Due to dynamic nature of the applied loads in seismic assessment of jacket structures the accuracy of...
Minimizing total completion time in the flexible flowshop sequence-dependent group scheduling problem
, Article Annals of Operations Research ; Volume 226, Issue 1 , March , 2014 , pp. 351-377 ; ISSN: 02545330 ; Salmasi, N ; Varmazyar, M ; Sharif University of Technology
Abstract
This research considers a flexible flowshop sequence-dependent group scheduling problem with minimization of total completion time. A mixed integer linear mathematical model for the research problem is developed. Since the research problem is shown to be strongly NP-hard, a metaheuristic algorithm based on memetic algorithm (MA) is proposed. A lower bounding method based on the Branch and Price algorithm is also proposed to evaluate the quality of the MA. In order to evaluate the performance of the proposed algorithms, random test problems, ranging in size from small, medium, to large are generated and solved by the MA and the lower bounding method. The results show that the average...
Design and dynamic modeling of planar parallel micro-positioning platform mechanism with flexible links based on Euler Bernoulli beam theory
, Article Journal of Solid Mechanics ; Volume 5, Issue 2 , 2013 , Pages 174-192 ; 20083505 (ISSN) ; Zohoor, H ; Kargarnovin, M. H ; Sharif University of Technology
Islamic Azad University
2013
Abstract
This paper presents the dynamic modeling and design of micro motion compliant parallel mechanism with flexible intermediate links and rigid moving platform. Modeling of mechanism is described with closed kinematic loops and the dynamic equations are derived using Lagrange multipliers and Kane's methods. Euler-Bernoulli beam theory is considered for modeling the intermediate flexible link. Based on the Assumed Mode Method theory, the governing differential equations of motion are derived and solved using both Runge-Kutta- Fehlberg4, 5th and Perturbation methods. The mode shapes and natural frequencies are calculated under clamped-clamped boundary conditions. Comparing perturbation method with...
Vibration analysis of a new type of compliant mechanism with flexible-link, using perturbation theory
, Article Mathematical Problems in Engineering ; Volume 2012 , February , 2012 ; 1024123X (ISSN) ; Zohoor, H ; Kargarnovin, M. H ; Sharif University of Technology
2012
Abstract
Vibration analysis of a new type of compliant parallel mechanism with flexible intermediate links is investigated. The application of the Timoshenko beam theory to the mathematical modeling of the intermediate flexible link is described, and the equations of motion of the flexible links are obtained by using Lagrange's equation of motion. The equations of motion are obtained in the form of a set of ordinary differential equations by using assumed mode method theory. The governing differential equations of motion are solved using perturbation method. The assumed mode shapes and frequencies are to be obtained based on clamped-clamped boundary conditions. Comparing perturbation method with...
Planning a capacitated road network with flexible travel times: a genetic algorithm
, Article Journal of Mathematical Modelling and Algorithms in Operations Research ; Volume 14, Issue 4 , December , 2015 , Pages 425-451 ; 2214-2487 (ISSN) ; Mahdavi Amiri, N ; Mahdavi, I ; Sharif University of Technology
Botanical Society of America Inc
2015
Abstract
We are concerned with a capacitated location-multi allocation-routing problem in a road network with flexible travel times. It is assumed that all links are two-way and capacities of the server nodes and arcs for accepting of population are limited. The aim of our work is to find numbers and locations of server nodes, allocation of the existing population in existing demand nodes on the network to the servers and the allocation of existing population in each node to different routes to determine the decided server for each member so that total transportation time is minimized. Here, two basic concepts are considered: multi allocation and flexible travel times. The concept of multi allocation...
Investigating stage construction in high concrete arch dams
, Article Indian Journal of Science and Technology ; Volume 8, Issue 14 , July , 2015 ; 09746846 (ISSN) ; Ghaemian, M ; Sharif University of Technology
Indian Society for Education and Environment
2015
Abstract
Concrete arch dam is a complex geometric structure and designing such a structure requires experience and high knowledge. One of the important parameters in designing concrete arch dams is the tensile stress in arch concrete material. The static analysis results of high arch dam structure depend on structure analysis model, intensively. Stage construction is needed to be focused in modeling high arch dams. In this study, the necessity of considering stage construction in static analysis of dam structure is focused. Modeling stage construction uses Birth and Death technique of elements. Therefore, six stage construction models are provided including applying dam wall weight outright, two...
SnO2 nanowires on carbon nanotube film as a high performance anode material for flexible Li-ion batteries
, Article Journal of Nanostructures ; Volume 8, Issue 3 , 2018 , Pages 288-293 ; 22517871 (ISSN) ; Faramarzi, M. S ; Sanaee, Z ; Ghasemi, S ; Sharif University of Technology
University of Kashan
2018
Abstract
Today, Li-ion batteries (LIBs) are the most common rechargeable batteries used in electronic devices. SnO2 with theoretical specific capacity of 782 mAh/g is among the best anode materials for LIBs. In this report, Threedimensional SnO2 nanowires (NWs) on carbon nanotube (CNT) thin film (SnO2 / CNT) is fabricated using a combination of vacuum filtration and thermal evaporation techniques. The resulting 3D heterostructure SnO2/CNT was characterized by X-ray diffraction, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). This fabricated SnO2/CNT electrode has been tested as a flexible and binderfree anode for LIB, which exhibits high initial discharge/charge...
Utilising flags to reduce drag around a short finite circular cylinder
, Article Journal of Turbulence ; Volume 19, Issue 3 , 2018 , Pages 229-251 ; 14685248 (ISSN) ; Kiani, F ; Tahaye Abadi, M ; Sharif University of Technology
Taylor and Francis Ltd
2018
Abstract
This paper utilises flags to decrease the drag around a short finite circular cylinder. Wall-adapted large eddy simulation and two-way fluid–structure interaction methods were applied to resolve unsteady turbulent flow structure. The far-field Reynolds number of the current configuration based on the cylinder diameter was chosen to be 20,000. In addition, the length-to-diameter ratio of the cylinder was assumed to be L/D = 2 whereas the flexible flag had a width-to-diameter ratio of W/D = 1.5. The results were compared with the regular short finite circular cylinder and the rigid flagged cylinder in our previous work. The results indicate that utilising flags inside the near-wake region of...
Vanadium dioxide-anchored porous carbon nanofibers as a Na+ intercalation pseudocapacitance material for development of flexible and super light electrochemical energy storage systems
, Article Applied Materials Today ; Volume 10 , 2018 , Pages 72-85 ; 23529407 (ISSN) ; Shahrokhian, S ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
The development of a flexible binder free electrode based on 3D vanadium dioxide (VO2) nano-architectures has materialized as an effective strategy for fabrication of advanced wearable, portable, and stretchable electronic devices. However, most of the stretchable energy storage devices based on VO2 suffer from a relatively low operating voltage, high weight, low specific capacitance, and thus low energy density. Here, a novel binder free supercapacitor electrode composed of hierarchical VO2 nanosheet arrays grown on porous carbon nanofibers (VO2@PCNFs) is designed using a simple hydrothermal method followed by annealing treatment. The electrochemical evaluation confirmed that the energy...
Reliability optimization of tools with increasing failure rates in a flexible manufacturing system
, Article Arabian Journal for Science and Engineering ; Volume 44, Issue 3 , 2019 , Pages 2579-2596 ; 2193567X (ISSN) ; Akhavan Niaki, S. T ; Haleh, H ; Naderi, B ; Sharif University of Technology
Springer Verlag
2019
Abstract
Tool reliability is one of the most important issues in a flexible manufacturing system. If a tool fails to operate correctly, the performance of the manufacturing system is reduced, the due date may be violated, or the product quality falls behind the standards. This paper develops a bi-objective mathematical model for tool selection in a flexible manufacturing system in order to optimize both reliability and cost. The tools in these environments are considered to have increasing failure rates as they are used over time; a case closer to reality. This paper aims to evaluate the availability of different tools used in a production system, in which the reliability of a tool is dependent on...
Numerical modeling of sloshing frequencies in tanks with structure using new presented DQM-BEM technique
, Article Symmetry ; Volume 12, Issue 4 , 2020 ; Feng, J ; Ghalandari, M ; Maleki, A ; Abdelmalek, Z ; Sharif University of Technology
MDPI AG
2020
Abstract
The sloshing behavior of systems is influenced by different factors related to the liquid level and tank specifications. Different approaches are applicable for the assessment of sloshing behavior in a tank. In this paper, a new numerical model based on the differential quadrature method and boundary element approaches is adopted to investigate the sloshing behavior of a tank with an elastic thin-walled beam. The model is developed based on small slope considerations of the free surface. The main assumption of fluid modeling is homogeneity, isotropy, inviscid, and only limited compressibility of the liquid. Indeed, the formulation is represented based on the reduced-order method and then is...
Multiferroic behavior of the functionalized surface of a flexible substrate by deposition of Bi2O3 and Fe2O3
, Article Microscopy Research and Technique ; 2021 ; 1059910X (ISSN) ; Sobola, D ; Ţălu, Ş ; Orudzev, F ; Arman, A ; Kaspar, P ; Dallaev, R ; Ramazanov, G ; Sharif University of Technology
John Wiley and Sons Inc
2021
Abstract
Thin films of bismuth and iron oxides were obtained by atomic layer deposition (ALD) on the surface of a flexible substrate poly(4,4′-oxydiphenylene-pyromellitimide) (Kapton) at a temperature of 250°C. The layer thickness was 50 nm. The samples were examined by secondary-ion mass spectrometry, and uniform distribution of elements in the film layer was observed. Surface morphology, electrical polarization, and mechanical properties were investigated by atomic force microscope, piezoelectric force microscopy, and force modulation microscopy. The values of current in the near-surface layer varied in the range of ±80 pA when a potential of 5 V was applied. Chemical analysis was performed by...
Localization analysis in softening RC frame structures
, Article Earthquake Engineering and Structural Dynamics ; Volume 32, Issue 2 , 2003 , Pages 207-227 ; 00988847 (ISSN) ; Tariverdilo, S ; Sharif University of Technology
2003
Abstract
This paper discusses the sensitivity of softening reinforced concrete frame structures to the changes in input ground motion and investigates the possibility of localizations for this type of structure in static and dynamic analysis. A finite element model is used in which the sections resisting force are calculated using a proposed differential hysteretic model. This model is especially developed for modelling softening behaviour under cyclic loading. To obtain parameters of the differential model the moment-curvature of each section is evaluated using a microplane constitutive law for concrete and bi-linear elasto-plastic law for reinforcements. The capability of the procedure is verified...
Adaptive-passive structural vibration attenuation using distributed absorbers
, Article Proceedings of the Institution of Mechanical Engineers, Part K: Journal of Multi-body Dynamics ; Volume 216, Issue 3 , 2002 , Pages 223-235 ; 14644193 (ISSN) ; Esmailzadeh, E ; Sharif University of Technology
Professional Engineering Publishing
2002
Abstract
A distributed dynamic vibration absorber with adaptive capability is presented to improve vibration suppression characteristics of harmonically excited structures. A double-ended cantilever beam carrying intermediate lumped masses forms the absorber subsection. The adaptive capability is achieved through concurrent adjustment of the positions of the moving masses, along the beam, to comply with the desired optimal performance. The necessary and sufficient conditions for the existence of periodic oscillatory behaviour, along with some physical bounds placed on the absorber parameters, form a constrained optimization problem for the optimum tuning strategy. Through numerical simulations it is...
A new management framework for mitigating intense ramping in distribution systems
, Article Energy ; Volume 254 , 2022 ; 03605442 (ISSN) ; Abbaspour, A ; Fotuhi Firuzabad, M ; Lehtonen, M ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
Nowadays, the increasing integration of variable renewable energies (VREs) in power systems have resulted in operational transformations of energy systems. Respectively, the high-amount of integrated VREs could cause severe-ramping in the net-load of energy systems due to abrupt changes in their power production. Accordingly, based on the limited flexibility capacity in transmission systems, severe ramping-up/down (RU/RD) in distribution systems should be addressed by employing local flexible resources (LFRs). Nevertheless, evolution of multi-agent structured distribution systems has limited the direct access of distribution system operators (DSOs) in scheduling of LFRs. Consequently, this...