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A Unified Computational Method for Simulating Dynamic Behavior of Planing Vessels

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China Ocean Engineering 2009年第3期23卷 517-528页

作者： Mohammad Saeed SEIF Ebrahim JAHANBAKHSH Roozbeh PANAHI Mohammad Hossein KARIMI sharif University of Technology Transportation research institute

High speed planing hulls have complex hydrodynamic behaviors. The trim angle and drafts are very sensitive to speed and location of the center of gravity. Therefore, motion simulation for such vessels needs a strong coupling between rigid body motions and hydrodynamic analysis. In addition, free surface should be predicted with good accuracy for each time step. In this paper, velocity and pressure fields are coupled by use of the fractional step method. On the basis of in- tegration of the two-phase viscous flow induced stresses over the hull, acting loads （forces and moments） are calculated. With the strategy of boundary-fitted body-attached mesh and calculation of 6-DoF motions in each time step, time history of ship motions including displacements, speeds and accelerations are evaluated. For the demonstration of the software capabilities, circular cylinder slamming is simulated as a simple type of water slamming. Then, a high-speed planing catamaran is investigated in the case of steady forward motion. All of the results are in good concordance with experimental data. The present method can be widely implemented in design as well as in the performance prediction of high-speed vessels.

关键词： ship motions slamming planing vessel

Feeding More People on an Increasingly Fragile Planet: China's Food and Nutrition Security in a National and Global Context

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Journal of Integrative Agriculture 2014年第6期13卷 1193-1205页

作者： Shenggen Fan Joanna Brzeska International Food policy research institute

Developing and developed countries alike are increasingly facing the dififcult question of how to feed more people amidst a host of emerging demographic, environmental, and health challenges. At the same time, in addition to food quantity, increased attention is being given to food quality attributes, in particular nutrition and safety. This is especially evident in China, where concerns are on the rise regarding the ability of China’s food production systems to deliver nutritious and safe food to a growing, urbanizing and more aflfuent population. These food and nutrition concerns come at a time when China is an increasingly inlfuential actor within the global food security network through activities such as production, consumption and trade. We argue that China has the opportunity to increase food and nutrition security both nationally and globally through a comprehensive policy agenda that focuses on institutional reforms, investments for and in agriculture, productive social safety nets, mutually beneifcial trade, and the exchange of know-how and technologies among developing countries and donors. This agenda will help China adapt its food production systems to the changing face of agriculture and to play a vital role in addressing the emerging challenges facing food and nutrition security within and beyond China in the coming decades.

关键词： food security nutrition China agricultural development

Electrochemically Assisted Photocatalytic Oxidation of Methanol on TiO_2 Nanotube Arrays

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Journal of Materials Science & Technology 2010年第6期26卷 535-541页

作者： R.Mohammadpour A.Iraji zad N.Taghavinia M.Rahman M.M.Ahadian institute for Nanoscience and Nanotechnology Sharif University of Technology Department of Physics Sharif University of Technology

The influence of an externally applied bias on photocatalytic performance of crystallized TiO2/Ti nanotubular electrode formed by anodization in fluoride-based electrolyte were investigated and compared to the behavior of multiporous TiO2 electrode. The photoelectrocatalytic oxidation behavior of methanol over the nanotubular electrode has been studied by measuring photocurrent response, potentiodynamic polarization spectroscopy and using electrochemical impedance spectroscopy （EIS）. It was found that the photoelectrocatalytic oxida- tion and the charge transfer rate constant of reaction on TiO2/Ti nanotubular electrode can significantly be increased by applying electrochemical bias. Moreover, TiO2 electrodes have considerably better performance alytic performance. based on the results, it was found that the nanotubular in comparison with porous samples in photoelectrocatalytic performance.

关键词： TiO2 nanotube Photoelectrocatalyst Electrochemical impedance spectroscopy Methanol

Cobalt supported on CNTs-covered γ-and nano-structured alumina catalysts utilized for wax selective Fischer-Tropsch synthesis

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Journal of Natural Gas Chemistry 2012年第6期21卷 713-721页

作者： Mohammad Reza Hemmati Mohammad Kazemeini Farhad Khorasheh Jamshid Zarkesh Alimorad Rashidi sharif University of Technology(SUT) Department of Chemical & Petroleum Engineering research institute of Petroleum Industry(RIPI)

Cobalt supported on carbon nanotubes （CNTs）-covered alumina has been recently developed and successfully utilized as a catalyst in Fischer-Tropsch synthesis （FTS）. Problems associated with shaping of Co/CNTs into extrudates or pellets as well as catalyst attrition rendered these materials unfavorable for industrial applications. In this investigation regular γ- and nano-structured （N-S） alumina as well as CNTs-covered regular γ- and N-S-alumina supports were impregnated by cobalt nitrate solution to make new cobalt-based catalysts which were also promoted by Ru. The catalysts were characterized and tested in a micro reactor to evaluate their applicability in FTS. γ-Al2O3 was prepared by calcination of bohemite and N-S-Al2O3 was prepared by sol-gel method using aluminum chloride as starting material. Catalyst evaluations indicated that N-S-Al2O3 was superior to regular γ-Al2O3 and that CNTs-covered alumina supports were favored over non-covered ones in terms of activity and heavy hydrocarbon selectivity. These were justified by porosimetric characteristics of the catalysts and existence of CNTs points of view. CNTs-covered catalysts also showed higher wax selectivity and better resistance to deactivation. Furthermore, TPR analysis indicated that the cobalt aluminate phase, which is responsible for the permanent deactivation of alumina supported Co-based catalysts, did not form on alumina supported Co-based catalysts covered with CNTs due to weaker interactions between cobalt and alumina.

关键词： Fischer-Tropsch synthesis nano-structured alumina gamma alumina carbon nanotubes catalyst deactivation

Experimental study of the boundary layer over an airfoil in plunging motion

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Acta Mechanica Sinica 2012年第2期28卷 372-384页

作者： F.Rasi Marzabadi M.R.Soltani Aerospace research institute TehranIran Department of Aerospace Engineering Sharif University of TechnologyTehranIran

This is an experimental study on the bound- ary layer over an airfoil under steady and unsteady conditions. It specifically deals with the effect of plunging oscil- lation on the laminar/turbulent characteristics of the bound- ary layer. The wind tunnel measurements involved surface- mounted hot-film sensors and boundary-layer rake. The ex- periments were conducted at Reynolds numbers of 0.42 x 106 to 0.84 X l06 and the reduced frequency was varied from 0.01 to 0.11. The results of the quasi-wall-shear stress as well as the boundary layer velocity profiles provided impor- tant information about the state of the boundary layer over the suction surface of the airfoil in both static and dynamic cases. For the static tests, boundary layer transition occurred through a laminar separation bubble. By increasing the an- gle of attack, disturbances and the transition location moved toward the leading edge. For the dynamic tests, earlier transi- tion occurred with increasing rather than decreasing effective angle of attack. The mean angle of attack and the oscillating parameters significantly affected the state of the boundary layer. By increasing the reduced frequency, the boundary layer transition was promoted to the upstroke portion of the equivalent angle of attack, but the quasi skin friction coeffi- cient was decreased.

关键词： Boundary layer Unsteady - Plunging Wind tunnel Airfoil

Effect of Sintering Temperature on Microstructure and Hydrogen Permeation Properties of Perovskite Membrane

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Journal of Materials Science & Technology 2013年第2期29卷 137-141页

作者： Marzieh Heidari Akbar Zamaniyan Aliakbar SafeKordi Ensieh Ganji Babakhani Mahdi Amanipour Chemical Engineering Department Sharif University of Technology Gas Department Research Institute of Petroleum Industry

The BaCe0.9Y0.1O3-δ （BCY） perovskite membrane was successfully synthesized by liquid citrate method. The phase structure of the powder was characterized by X-ray diffraction （XRD）. Scanning electron microscopy （SEM） was used to characterize microstructures of the membrane sintered under various conditions. Sintering temperatures and dwell time during sintering influence the final microstructure of the ceramic. Results showed that increasing sintering temperature resulted in a dense membrane with clear grains. An increase of dwell time was favorable to produce membranes with larger grains in the sintered ceramics. A density of 5.87 g/cm3 was reached for the membrane after sintering at 1200 ℃ with dwell time of 10 h. This resulted in the formation of dense membranes with clear structure and average grain size of 0.27 μm. The influence of microstructure on the hydrogen permeation flux through BCY was observed by measuring the hydrogen permeation flux, and the results showed that hydrogen permeation flux increases with increasing the average grain size of the membrane. From H2 permeation rates, it was found that bulk diffusion rather than surface reaction played the dominant role in H2 transport.

关键词： Ceramic membrane Perovskite Sintering Microstructure Hydrogen permeation

Managing Climate Change Risk in China's Agricultural Sector: The Potential for an Integrated Risk Management Framework

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Journal of Integrative Agriculture 2014年第7期13卷 1418-1431页

作者： Kevin Z.Chen Claire Hsu International Food policy research institute-Beijing Office

Climate change poses a serious threat to the future food security of China, which is among the most disaster-prone countries in the world. This paper discusses the implications of climate change for China＇s agricultural sector. Its main objectives are to identify the agricultural risks associated with climate change, to introduce a conceptual framework for agricultural climate risk management and to enumerate key adaptation strategies, challenges, and recommendations.

关键词： climate change food security risk management agricultural development

Dissociation of polar oil components in low salinity water and its impact on crude oil-brine interfacial interactions and physical properties

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Petroleum Science 2019年第2期16卷 328-343页

作者： Rasoul Mokhtari Shahab Ayatollahi School of Chemical and Petroleum Engineering Shiraz University sharif Upstream Petroleum research institute (SUPRI) Chemical and Petroleum Engineering Department Sharif University of Technology

Despite many efforts into the study of fluids interaction in low salinity water flooding, they are not probing the basics of transport phenomena between the involved phases. This work is aimed to bring new understanding of fluid-fluid interaction during low salinity water flooding through a series of organized experiments in which a crude oil sample with known properties was kept in contact with different brine solutions of various ionic strengths. Measuring brine pH, conductivity and crude oil viscosity and density for a period of 45 days illustrates the strong effect of the contact time and ionic strength on the dissociation of polar components and physical properties of the crude oil and brine. Besides, the interfacial tension(IFT) measurements show that the interfacial interactions are affected by several competitive interfacial processes. By decreasing the ionic strength of the brine, the solubility of naphthenic acids in the aqueous solution increases, and hence,the conductivity and the pH of the aqueous phase decrease. To verify this important finding, UV-Vis spectroscopy and 'H NMR analysis were also performed on aged brine samples. Notably, there is an ionic strength of brine in which the lowest IFT is observed, while the other physical properties are remained relatively unchanged.

关键词： Ionic strength Oil-brine interaction Physical properties Contact time Polar components

Optimal Equilibrium Selection of Price-maker Agents in Performance-based Regulation Market

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Journal of Modern Power Systems and Clean Energy 2022年第1期10卷 204-212页

作者： Mohammad Rayati Aras Sheikhi Ali Mohammad Ranjbar Wei Sun Department of Electrical Engineering Sharif University of TechnologyTehranIran sharif Energy research institute(SERI) Sharif University of TechnologyTehranIran Department of Electrical Engineering and Computer Science University of Central FloridaOrlandoFL 32816USA

This paper analyzes the oligopolistic equilibria of multiple price-maker agents in performance-based regulation(PBR)*** these markets,there are price-maker agents representing some frequency regulation(FR)providers and a number of independent price-taker FR providers.A model of equilibrium problem with equilibrium constraints(EPECs)is employed in this paper to study the equilibria of a PBR market in the presence of price-maker agents and price-taker FR *** to the incorporation of the FR providers’dynamics,the proposed model is reformulated as a mixed-integer linear programming(MILP)problem over innovative mathematical *** optimal equilibrium point is also selected for the market,where none of the agents is the unique deviator and the dynamic performance of power system is improved *** effectiveness of the proposed optimal equilibrium point is evaluated by comparing the outputs with the conventional optimal dispatches of the FR providers.

关键词： Performance-based regulation(PBR)market multi-agent system equilibrium problem with equilibrium constraint(EPEC) frequency regulation(FR) mixed-integer linear programming(MILP)