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Efficiency of employing fiber-based finite-length plastic hinges in simulating the cyclic and seismic behavior of steel hollow columns compared with other common modelling approaches

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Earthquake Engineering and Engineering Vibration 2019年第4期18卷 777-794页

作者： mojtaba Farahi Saeed Erfani Department of Civil Engineering Amirkabir University of Technology

The accuracy and effi ciency of the modelling techniques utilized to model the nonlinear behavior of structural components is a signifi cant issue in earthquake engineering. In this study, the suffi ciency of three diff erent modelling techniques that can be employed to simulate the structural behavior of columns is investigated. A fi ber-based fi nite length plastic hinge (FB-FLPH) model is calibrated in this study. In order to calibrate the FB-FLPH model, a novel database of the cyclic behavior of hollow steel columns under simultaneous axial and lateral loading cycles with varying amplitudes is used. By employing the FB-FLPH model calibrated in this study, the interaction of the axial force and the bending moment in columns is directly taken into account, and the deterioration in the cyclic behavior of these members is implicitly considered. The superiority of the calibrated FB-FLPH modelling approach is examined compared with the cases in which conventional fi ber-based distributed plasticity and concentrated plasticity models are utilized. The effi ciency of the enumerated modelling techniques is probed when they are implemented to model the columns of a typical special moment frame in order to prove the advantage of the FB-FLPH modelling approach.

关键词： cyclic behavior seismic behavior fi ber-based fi nite-length plastic hinge model fi ber-based modelling techniques cyclic strength deterioration axial force-bending moment interaction

A Probability Measure for Entanglement of Pure Two-Qubit Systems and a Useful Interpretation for Concurrence

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Chinese Physics Letters 2011年第7期28卷 16-19页

作者： Abbass Sabour mojtaba Jafarpour Department of Physics Shahid Chamran UniversityAhvazIran

A new probability measure for the quantification of entanglement of pure states is *** computations indicate that the derived measure is equal to concurrence,up to the precision of the computer program *** it also pro... 详细信息

关键词： Probability concurrence pure

Numerical evaluation of passive control of shock wave/boundary layer interaction on NACA0012 airfoil using jagged wall

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Acta Mechanica Sinica 2016年第5期32卷 792-804页

作者： mojtaba Dehghan Manshadi Ramin Rabani Mechanical and Aerospace Engineering Department Malek-Ashtar University of TechnologyEsfahan Iran Department of Mechanical Engineering Yazd University

Shock formation due to flow compressibility and its interaction with boundary layers has adverse effects on aerodynamic characteristics, such as drag increase and flow separation. The objective of this paper is to appraise the practicability of weakening shock waves and, hence, reducing the wave drag in transonic flight regime using a two-dimensional jagged wall and thereby to gain an appropriate jagged wall shape for future empirical study. Different shapes of the jagged wall, including rectangular, circular, and triangular shapes, were employed. The numerical method was validated by experimental and numerical studies involving transonic flow over the NACA0012 airfoil, and the results presented here closely match previous experimental and numerical results. The impact of parameters, including shape and the length-to-spacing ratio of a jagged wall, was studied on aerodynamic forces and flow field. The results revealed that applying a jagged wall method on the upper surface of an airfoil changes the shock structure significantly and disintegrates it, which in turn leads to a decrease in wave drag. It was also found that the maximum drag coefficient decrease of around 17 % occurs with a triangular shape, while the maximum increase in aerodynamic efficiency（lift-to-drag ratio）of around 10 % happens with a rectangular shape at an angle of attack of 2.26？.

关键词： Jagged wall Passive flow control Shock wave/boundary layer interaction Aerodynamic efficiency

Aerodynamic Characteristics of Conventional and Innovative High Lift Swept Wings

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Journal of Bionic Engineering 2019年第3期16卷 432-441页

作者： mojtaba Ramezani Voloojerdi Mahmoud Mani Aerospace Engineering Department Amirkabir University of Technology 424 Hafez Ave Tehran 158757413 Iran

The new bird inspired wing sweep was introduced and compared with straight and conventional swept wings in gliding flight by an experimental test setup. Due to the similarity with the birds, wing, all test models have S1223 airfoil. Swept models inspired from the bird consist of two parts: the straight part near the root and the swept part near the tip. Aerodynamic forces on each wing were measured from 0° to 24° angles of attack and Reynolds numbers of 4.3×10^4, 8.6×10^4, 1.3×10^5, and 1.7× 10^5. Wind tunnel test results show that wings with an innovative sweep at α> 0 have more lift for Reynolds numbers between 4.3× 10^4 and 8.6×10^4. Also, innovative sweep increases the stall angle, and the wing did not stall until α = 24° for Reynolds between 1.3×10^5 and 1.7×10^5. An increase in lift and having sufficient aerodynamic performance in low Reynolds numbers for birds' inspired wing sweep in gliding flight may be the answer to why the wing sweep of birds is not like conventional sweeps.

关键词： bio-inspired wing wing sweep wing aerodynamics bird wing low Reynolds number

Performance improvement of a crumb rubber modified bitumen using recycled glass powder

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2013年第11期14卷 805-814页

作者： mojtaba GHASEMI Seyed Morteza MARANDI Department of Civil Engineering Shahid Bahonar UniversityKerman 761691 4111 Iran

In this study, the efficiency of bitumen and asphalt mixtures modified with crumb rubber(CR) and recycled glass powder(RGP) is evaluated. From an environmental point of view, the application of RGP in asphalt mixtures is considered beneficial since it prevents accumulation of waste glass in the natural environment. Rheological and mechanical properties of modified bitumen samples were investigated by laboratory methods such as bitumen conventional tests and dynamic shear rheometer(DSR), and also by asphalt mixture performance tests including Marshall stability, indirect tensile strength(ITS),compressive strength, and indirect tensile stiffness modulus. The results showed that the application of RGP in place of CR has no negative impact on the efficiency of bitumen and asphalt mixtures and even improves their engineering properties except for the toughness index(TI). Moreover, a modification with 5% CR and 5% RGP in asphalt mixtures results in the best overall performance.

关键词： Crumb rubber (CR) Recycled glass powder (PGP) Rheological properties Performance testing Stone matrixasohalt (SMA)

Mechanochemical sulfidization of a mixed oxide-sulphide copper ore by co-grinding with sulfur and its effect on the flotation efficiency

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Chinese Journal of Chemical Engineering 2020年第3期28卷 743-748页

作者： mojtaba Masdarian Asghar Azizi Zahra Bahri Faculty of Mining Petroleum and GeophysicsShahrood University of TechnologyShahroodIran Department of Control and Modeling of Mineral Processing Systems Institute of Mineral ProcessingACECR at Tarbiat ModaresTehranIran

Mechanochemical sulfidization of a mixed sulfide/oxide copper ore by co-grinding with sulfur and additives including Mg(NO3)2 and Fe(NO3)3 salts and iron,aluminum and magnesium powders was investigated for the first ***,the influence of sulfidization during the wet-milling process was examined on the separation efficiency and recovery of copper in *** results demonstrated that co-grinding with sulfur solely had the best flotation performance at the value of 0.5 wt.%and it was attributed to the possible existence of S\\O bonding on copper oxides *** addition,adding magnesium nitrate salt,magnesium powder,iron nitrate salt and aluminum powder as additive associated with 0.5 wt%sulfur into ball milling caused the flotation improvement at the amounts of 0.2 wt%,0.2 wt%,0.5 wt%and 0.5 wt%,***,the effect of grinding time and sulfidization pH with 0.5 wt%sulfur solely was determined and pH s of 7.5 to 8.5 gave the best *** highest recovery(75.76%)and separation efficiency(63.44%)were achieved at pH of 7.5 and 8.5,respectively.

关键词： Sulphide/oxide copper ore Floatability Mechanochemical sulfidization Reductive additives Recovery

Assessment of the kinetic–frictional model for dense granular flow

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Particuology 2008年第1期6卷 50-58页

作者： Boon Ho Ng mojtaba Ghadiri Institute of Particle Science&Engineering University of LeedsLeeds LS2 9JTUK

This paper aims to quantitatively assess the application of kinetic-frictional model to simulate the motion of dry granular materials in dense condition, in particular, the annular shearing in Couette configuration. The weight of frictional stress was varied to study the contribution of the frictional stress in dense granular flows. The results show that the pure kinetic-theory-based computational fluid dynamics （CFD） model （without frictional stress） over-predicts the dominant solids motion of dense granular flow while adding frictional stress [Schaeffer, D. G. （1987）. Instability in the evolution equations describing incompressible granular flow. Journal of Differential Equations, 66（1）, 19-50] with the solids pressure of [Lun, C. NTK., Savage, S. B., Jeffrey, D. J., ＆ Chepurniy, N. （1984）. Kinetic theories for granular flow： Inelastic particles in Couette flow and slightly inelastic particles in a general flow field. Journal of Fluid Mechanics, 140, 223-256] in the CFD model improves the simulation to better conform available experimental results. The results also suggest that frictional stress transmission plays an important role in dense granular flow and should not be neglected in granular flow simulations. Compatible simulation results to the experimental data are seen by increasing the weight of frictional stress to a factor of 1.25-1.5. These improved simulation results suggest the current constitutive relations （kinetic-frictional model） need to be improved in order to better reflect the real dense granular flow.

关键词： Gas-solids flow CFD Constitutive relations Couette flow Kinetic theory Kinetic-frictional model

Characterisation of flowability of cohesive powders by testing small quantities of weak compacts

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Particuology 2008年第4期6卷 282-285页

作者： Ali Hassanpour mojtaba Ghadiri Institute of Particle Science and Engineering University of LeedsLeeds LS2 9JTUnited Kingdom

Characterisation of flowability of small quantities of cohesive powders is of great industrial interest, particularly for the pharmaceutical sec- tors, where a limited amount of material is available or the material is not easily accessible. In this paper, ball indentation on a powder bed is evaluated for flow characterisation of small quantities of cohesive powders at low levels of consolidation pressures. In parallel, the bulk powder is subjected to the common test method of unconfined direct compression. Analogous to indentation hardness testing, for which the indentation pressure is related to the flow stress, a constraint factor (C) is defined relating the unconfined yield stress and indentation pres- sure. The constraint factors for the test powders have been evaluated, enabling an easy method to characterize the flow behaviour of cohesive powders.

关键词： Flowability Cohesive powder Indentation on powder bed Constraint factor

PID-type Terminal Sliding Mode Control for Permanent Magnet Synchronous Generator-based Enhanced Wind Energy Conversion Systems

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CSEE Journal of Power and Energy Systems 2022年第4期8卷 993-1003页

作者： mojtaba Nasiri Saleh Mobayen Ali Arzani the Solar Energy Applications Group Trinity College DublinDublin 2D02 PN40Ireland Department of Electrical Engineering University of ZanjanZanjanIran the Future Technology Research Center National Yunlin University of Science and TechnologyDouliuYunlin County 64002TaiwanChina the Center for Energy Systems Research(CESR) Tennessee Technological UniversityCookevilleTN 38505USA

The provision of wind farm(WF)grid codes(GCs)has become imperative for sustained grid operations,especially for WFs with permanent-magnet synchronous generator(PMSG)wind energy conversion *** techniques have been developed for executing GC requirements in the event of grid *** the methods,an intriguing strategy is to enhance the performance of back-to-back(BTB)converter *** this research,the PID-type terminal sliding mode control(PID-TSMC)scheme is implemented for both machine-side and grid-side converter-modified controllers of BTB-converter,to reinforce the nonlinear relationship among the state-variable and the control *** application of this control scheme decreases the response time and improves the robustness of the BTB-converter controllers regarding uncertainty of parameters and external *** grid-side converter tracks the maximum power point,contributing to the rapid decrease of generator active power output during *** frees up converter capacity for injecting GC-compliant reactive current into the ***,the machine-side converter regulates DC-link voltage,in which its variations during external disturbances decrease substantially with the *** discussions on the simulations contemplate on the robustness and efficiency of the implemented PID-TSMC strategy in comparison to other BTB-converter control strategies.

关键词： Back-to-back converter grid code PMSG-based wind turbine terminal sliding mode control