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Behrooz?HassaniEmail author Mostafa?Khanzadi S.?Mehdi?Tavakkoli 《Structural and Multidisciplinary Optimization》2012,45(2):223-233
The Isogeometric Analysis (IA) method is applied for structural topology optimization instead of finite elements. For this
purpose, a control point based Solid Isotropic Material with Penalization (SIMP) method is employed and the material density
is considered as a continuous function throughout the design domain and approximated by the Non-Uniform Rational B-Spline
(NURBS) basis functions. To prevent the formation of layouts with porous media, a penalization technique similar to the SIMP
method is used. For optimization an optimality criteria is derived and implemented. A few examples are presented to demonstrate
the performance of the method. It is shown that, dissimilar to the element based SIMP topology optimization, the resulted
layouts by this method are independent of the number of the discretizing control points and checkerboard free. 相似文献
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Alireza Tavakkoli Mircea Nicolescu George Bebis Monica Nicolescu 《Machine Vision and Applications》2009,20(6):395-409
Most methods for foreground region detection in videos are challenged by the presence of quasi-stationary backgrounds—flickering
monitors, waving tree branches, moving water surfaces or rain. Additional difficulties are caused by camera shake or by the
presence of moving objects in every image. The contribution of this paper is to propose a scene-independent and non-parametric
modeling technique which covers most of the above scenarios. First, an adaptive statistical method, called adaptive kernel
density estimation (AKDE), is proposed as a base-line system that addresses the scene dependence issue. After investigating
its performance we introduce a novel general statistical technique, called recursive modeling (RM). The RM overcomes the weaknesses
of the AKDE in modeling slow changes in the background. The performance of the RM is evaluated asymptotically and compared
with the base-line system (AKDE). A wide range of quantitative and qualitative experiments is performed to compare the proposed
RM with the base-line system and existing algorithms. Finally, a comparison of various background modeling systems is presented
as well as a discussion on the suitability of each technique for different scenarios. 相似文献
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Jahangiry Hassan A. Gholhaki Majid Naderpour H. Tavakkoli S. Mehdi 《International Journal of Mechanics and Materials in Design》2021,17(4):947-967
International Journal of Mechanics and Materials in Design - This article aims to utilize IsoGeometric analysis (IGA) and Level set method for topology optimization of elastoplastic plane stress... 相似文献
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Sushilov NV Tavakkoli J Cobbold RS 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2001,48(1):274-284
Based on the method proposed by Donnelly and Ziolkowski [1], [2], a new general solution has been obtained for the isotropic/homogeneous scalar wave equation in cylindrical coordinates. It is shown that well-known limited diffraction beams such as Durnin's Bessel beams [4], Lu and Greenleaf's X-wave [15], localized waves of Donnelly and Ziolkowski [1], [2], and limited-diffraction, band-limited waves of Li and Bharath [19], [20] can be obtained from this generic solution as particular cases. In addition, we have obtained new X-wave solutions and have calculated the field characteristics for one of them using a finite aperture realization. It is shown that with a proper choice of the free parameter values, well-behaved X-waves with narrow beamwidths and large depths of field can be achieved. For similar source spectra, the results are compared with Lu and Greenleaf's zeroth-order X-wave, and it is shown that the depth of field and beamwidth are very comparable. 相似文献
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Fate of Zinc Oxide Nanoparticles during Anaerobic Digestion of Wastewater and Post-Treatment Processing of Sewage Sludge 总被引:1,自引:0,他引:1
E Lombi E Donner E Tavakkoli TW Turney R Naidu BW Miller KG Scheckel 《Environmental science & technology》2012,46(16):9089-9096
The rapid development and commercialization of nanomaterials will inevitably result in the release of nanoparticles (NPs) to the environment. As NPs often exhibit physical and chemical properties significantly different from those of their molecular or macrosize analogs, concern has been growing regarding their fate and toxicity in environmental compartments. The wastewater-sewage sludge pathway has been identified as a key release pathway leading to environmental exposure to NPs. In this study, we investigated the chemical transformation of two ZnO-NPs and one hydrophobic ZnO-NP commercial formulation (used in personal care products), during anaerobic digestion of wastewater. Changes in Zn speciation as a result of postprocessing of the sewage sludge, mimicking composting/stockpiling, were also assessed. The results indicated that "native" Zn and Zn added either as a soluble salt or as NPs was rapidly converted to sulfides in all treatments. The hydrophobicity of the commercial formulation retarded the conversion of ZnO-NP. However, at the end of the anaerobic digestion process and after postprocessing of the sewage sludge (which caused a significant change in Zn speciation), the speciation of Zn was similar across all treatments. This indicates that, at least for the material tested, the risk assessment of ZnO-NP through this exposure pathway can rely on the significant knowledge already available in regard to other "conventional" forms of Zn present in sewage sludge. 相似文献
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In this study, the nonlinear partial differential equations governing two phase flow through porous media are solved using two different methods, namely, finite difference and finite element. The capillary pressure term is considered in the mathematical model. The numerical results on a 2-D test case are then compared with the experimental drainage process and water flooding performed on a glass type micromodel. Based on the obtained results, finite difference technique needs less computational time for solving governing equations of two phase flow, but findings of this method show less agreement with the experimental data. The finite element scheme was found to be more adequate and its results are matched well with the obtained experimental data. 相似文献