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MIXED BRIGHTNESS-INTEGRALS OF CONVEX BODIES
Ni Li,Baocheng Zhu 대한수학회 2010 대한수학회지 Vol.47 No.5
The mixed width-integrals of convex bodies are defined by E. Lutwak. In this paper, the mixed brightness-integrals of convex bodies are defined. An inequality is established for the mixed brightness-integrals analogous to the Fenchel-Aleksandrov inequality for the mixed volumes. An isoperimetric inequality (involving the mixed brightness-integrals) is presented which generalizes an inequality recently obtained by Chakerian and Heil. Strengthened version of this general inequality is obtained by introducing indexed mixed brightness-integrals.
Nili-Ahmadabadi, Mahdi,Nematollahi, Omid,Cho, Dae Seung,Kim, Kyung Chun Elsevier 2018 Applied thermal engineering Vol.137 No.-
<P><B>Abstract</B></P> <P>A real dense gas such as R245fa is mostly used in organic-Rankine-cycle turbine expanders. The dense gas effects should be taken into account, especially in the transonic and supersonic flow regimes. Oblique shock and the interaction of shock and separation on the turbine blades are phenomena that have little deviation between a real gas and an ideal gas. This research numerically simulated the flow passing through a cascade of simple straight blades with keen edges considered for an ideal gas (air) and dense R245fa gas in a supersonic flow regime. The blade geometry was selected so that the deviations between the dense and ideal gas flows would be clearer than that with actual blades. The AUSM density-based method and NIST real gas model were used to model the ideal and dense gas, respectively. A second-order scheme was used for discretization, and the shear stress transport (SST) model was for the turbulence. The results show that an oblique shock is created on the leading edge when the inlet Mach number is 2.18 in dense gas. In ideal gas, a bow shock is created at the front of the leading edge. Moreover, for a wall pressure coefficient distribution, the separation point in dense gas is posterior than that in ideal gas.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Flow passing through a cascade has numerically simulated. </LI> <LI> Simple straight blades with keen edges are considered. </LI> <LI> Ideal gas (air) and R245fa gas in a supersonic flow regime are compared. </LI> <LI> Oblique shock is created in dense gas while a bow shock is in ideal gas. </LI> </UL> </P>
Centrifugal compressor shape modification using a proposed inverse design method
Mahdi Nili-Ahmadabadi,Farzad Poursadegh 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.3
This paper is concerned with a quasi-3D design method for the radial and axial diffusers of a centrifugal compressor on the meridional plane. The method integrates a novel inverse design algorithm, called ball-spine algorithm (BSA), and a quasi-3D analysis code. The Euler equation is solved on the meridional plane for a numerical domain, of which unknown boundaries (hub and shroud) are iteratively modified under the BSA until a prescribed pressure distribution is reached. In BSA, unknown walls are composed of a set of virtual balls that move freely along specified directions called spines. The difference between target and current pressure distributions causes the flexible boundary to deform at each modification step. In validating the quasi-3D analysis code, a full 3D Navier-Stokes code is used to analyze the existing and designed compressors numerically. Comparison of the quasi-3D analysis results with full 3D analysis results shows viable agreement. The 3D numerical analysis of the current compressor shows a huge total pressure loss on the 90° bend between the radial and axial diffusers. Geometric modification of the meridional plane causes the efficiency to improve by about 10%.
Optimization of a seven-stage centrifugal compressor by using a quasi-3D inverse design method
Mahdi Nili-Ahmadabadi,Farzad Poursadegh 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.11
This paper focuses on performance improvement of a centrifugal compressor. An inverse design method for 3D design approaches is formulated to address this concern. The design procedure encompasses two major steps. First, with the use of ball spine algorithm, which is an inverse design algorithm, on the meridional plane of impeller, the hub and shroud of impeller are computed based on a modified pressure distribution along them. Second, an original and progressive algorithm is developed for design of blade camber line profile on the blade-to-blade planes of impeller based on blade loading improvement. Full 3D analysis of the current and designed compressor is accomplished by using a Reynolds-averaged Navier–Stokes equations solver. A comparison between the analysis results of the current and designed compressor shows that the total-to-total isentropic efficiency and pressure ratio of the designed compressor under the same operating conditions are enhanced by more than 4.5% and 5%, respectively.
Mohammad Hosein Nili,Banafsheh Zahraie,Hosein Taghaddos 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.26 No.4
Effective bridge maintenance reduces bridge operation costs and extends its service life. The possibility of storing bridge life-cycle data in a 3D parametric model of the bridge through Bridge Information Modeling (BrIM) provides new opportunities to enhance current practices of bridge maintenance management. This study develops a Decision Support System (DSS), namely BrDSS, which employs BrIM and an efficient optimization model for bridge maintenance planning. The BrIM model in BrDSS extracts basic data of elements required for the optimization process and visualizes the inspection data and the optimization results to the user to help in decision makings. In the optimization module of the DSS, the specifically formulated Genetic Algorithm (GA) eliminates the chances of producing infeasible solutions for faster convergence. The practicality of the presented DSS was explored by utilizing the DSS in the maintenance planning of a bridge under operation in the southwest of Iran.
Shape memory effect in nanocrystalline NiTi alloy processed by high-pressure torsion
Shahmir, H.,Nili-Ahmadabadi, M.,Huang, Y.,Myun Jung, J.,Seop Kim, H.,Langdon, T.G. Elsevier Sequoia 2015 Materials science & engineering. properties, micro Vol.626 No.-
A NiTi alloy was processed by high-pressure torsion for 10 turns followed by post-deformation annealing at 673K for various times. An anneal for 60min gave a nanocrystalline microstructure with a superior shape memory effect and an improvement of more than 40% over the initial state.