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Abbas Heydari,Mahdi Shariati 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.6
The current study presents a new technique in the framework of the nonlocal elasticity theory for a comprehensive buckling analysis of Euler-Bernoulli nano-beams made up of bidirectional functionally graded material (BDFGM). The mechanical properties are considered by exponential and arbitrary variations for axial and transverse directions, respectively. The various circumstances including tapering, resting on two-parameter elastic foundation, step-wise or continuous variations of axial loading, various shapes of sections with various distribution laws of mechanical properties and various boundary conditions like the multi-span beams are taken into account. As far as we know, for the first time in the current work, the buckling analyses of BDFGM nano-beams are carried out under mentioned circumstances. The critical buckling loads and mode shapes are calculated by using energy method and a new technique based on calculus of variations and collocation method. Fast convergence and excellent agreement with the known data in literature, wherever possible, presents the efficiency of proposed technique. The effects of boundary conditions, material and taper constants, foundation moduli, variable axial compression and small-scale of nano-beam on the buckling loads and mode shapes are investigated. Moreover the analytical solutions, for the simpler cases are provided in appendices.
Abbas Zamani,Hossein Bolandi 제어·로봇·시스템학회 2022 International Journal of Control, Automation, and Vol.20 No.4
This paper develops a novel robust tracking predictive controller for continuous-time nonlinear systems capable to deal with changing setpoints and unknown non-additive bounded disturbance. The sudden changes in a setpoint and/or existence of disturbance may lead to feasibility and stability issues if a stabilizing terminal constraint-based predictive controller is used. The robust tracking MPC presented in this paper extends the artificial reference-based nonlinear MPC for continuous-time systems and disturbance rejection. Closed-loop input-to-state stability and recursive feasibility of the optimization problem are guaranteed by tightening the terminal region, input constraint, and appropriate terminal cost function. An explicit formula that specifies the bound of sampling time interval is also introduced. We show that the proposed controller can reach an offset-free tracking if the disturbance is slowly time varying. However, in the case of non-slowly varying disturbance, a specific bound on tracking error will be guaranteed using an appropriate disturbance observation error based Lyapunov function. The satellite attitude control system simulation results are provided to show the efficiency of the proposed controller.
Abbas Mahmood Oghor Anwer,Fuad Alhaj Omar,Ahmet Afsin Kulaksiz 제어·로봇·시스템학회 2020 International Journal of Control, Automation, and Vol.18 No.11
The permanent magnet synchronous motors (PMSM) are widely employed in industrial, robotic, water pumping and HVAC applications due to their numerous benefits such as small size, high-energy efficiency, high performance, low inertia and the ability to operate in full load at low speeds. In case the PMSM drive system is supplied from photovoltaic (PV) modules, it can be a perfect match for water pumping or HVAC applications. In such a system, in order to extract full energy from PV modules, a maximum power point tracking (MPPT) algorithm must be employed. This article presents a PV system-fed PMSM drive system with sensorless speed control. The proposed system consists of two main parts. The first part deals with MPPT algorithm based on fuzzy logic controller and the second part deals with PMSM drive system with a sensorless speed estimator by using Model Reference Adaptive System (MRAS) approach to eliminate the use of an encoder. The operation of PMSM is accomplished by using the vector control method to obtain a similar dynamic of the DC motor. The overall system is modelled in Matlab/Simulink environment and simulation results are collected under various operating conditions.
Abbas Aminifard,Seyed Komail Tayebi 한국경제연구학회 2011 Korea and the World Economy Vol.12 No.2
In this paper, we have examined the long-run currency relationship, based on purchasing power parity (PPP), between the five major ASEAN countries (Malaysia, Indonesia, the Philippines, Singapore and Thailand) plus China, South Korea and Japan (as the East Asian side) and Iran (as the West Asian side) by using panel data methods to test for unit roots over the period 2000-2009. If the test rejects the unit root hypothesis, the long-run PPP holds. We six thus used five panel unit roots tests: Levin, Lin, and Chu (2002), Breitung (2000), Im, Pesaran and Shin (2003), Maddala and Wu (1999) and Hadri (2000). By the use of real effective exchange rates, such methods test the PPP hypothesis showing whether real exchange rates among East Asian countries and also between two Asian sides (East and West) are stationary. Of these tests, only the LLC (Levin, Lin, and Chu method) holds the hypothesis in which the PPP holds. The results are consistent with those obtained by O’Connell (1998).
A Cost/Worth Approach to Evaluate UPFC Impact on ATC
Abbas Rajabi-Ghahnavieh,Mahmud Fotuhi-Firuzabad,Mohammad Shahidehpour,Rene Feuillet 대한전기학회 2010 Journal of Electrical Engineering & Technology Vol.5 No.3
Available transfer capability (ATC) is a measure of the transfer capability remaining in a transmission system. Application of unified power flow controllers (UPFCs) could have positive impacts on the ATC of some paths while it might have a negative impact on the ATC of other paths. This paper presents an approach to evaluate the impacts of UPFCs on the ATC from a cost/worth point of view. The UPFC application worth is considered as the maximum cost saving in enhancing the ATC of the paths due to the UPFC implementation. The cost saving is considered as the cost of optimal application of other system reinforcement alternatives (except for UPFC) to reach the same ATC level obtained by UPFC application. UPFC application costs include the maximum cost of alleviating the probable negative impact on the ATC of some paths caused by implementing UPFCs. Optimal system reinforcement is used for systems with UPFCs to determine the aforementioned cost. The proposed method is applied to the IEEERTS and the results are evaluated through a sensitivity analysis. The cost/worth of UPFC application is also used to develop an index for optimal UPFC location and the results are compared with those of other indices. A comparison is finally made with the results obtained using an existing ATC allocation profit-based approach to determine UPFC application worth.
Meta-synthesis of COVID-19 lessons: charting sustainable management of future pandemics
Abbas Ziafati Bafarasat 서울시립대학교 도시과학연구원 2021 도시과학국제저널 Vol.25 No.3
Development of the COVID-19 vaccines has been creating a lot of hope for an ultimate return to normality, but returning to normality as we had before would mean we will continue to ignore life-ravaging lessons, as we did for severe acute respiratory syndrome, Ebola, and Middle East respiratory syndrome. This meta-synthesis of COVID-19 lessons charts sustainable pandemic management in terms of choosing strategies that are situated in their contextual specifications and beginning preparations for future application of such strategies from now. To guide selection of a situated strategy, the paper provides a comprehensive list of epidemiological determinants (e.g. communicativeness, poverty, supply chain, density, wind, remoteness); consolidates knowledge about strategies of elimination, suppression and mitigation; and proposes a quantified SWOT analysis of epidemiological determinants that produces coordinates for strategy identification in a Cartesian plane divided into twelve strategy quarters. To guide prior preparations for future application of pandemic management strategies, the paper consolidates lessons learned in implementation of situated strategies and proposes preparations at the national level for elimination, at the local/community level for suppression, and at the regional level for mitigation.
Nonlinear Finite Element Model for the Optimization of Post-Tensioned One-Way Concrete Slab
Abbas H. Mohammed,Dia Eddin Nassani,Nildem Tayşi,Ali K. Hussein 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.7
Optimization in its wide sense can be used to solve many engineering problems and to find the best solutions so that designers cangain a maximum benefit from the available resources. In this research a nonlinear Finite Element (FE) model was developed for theoptimization of Unbonded Post-Tensioned (UPT) one-way slab. ANSYS program was used to find the optimum total weight of Post-Tensioned Tendon (PTT). In the optimization analysis, the objective function is the total weight of PTTs. The area of PTT, tendoninitial stress, and tendon eccentricity are considered as the design variables. Concrete normal stress, steel tendon stress, concrete shearstress, and mid-span deflection of concrete slab are considered as constraints. The optimization result indicates that the total weight ofPTTs can be reduced about 33% for the UPT slabs using an appropriate optimization algorithm.