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137 results on '"Tutunea-Fatan, O Remus"'

15. Preliminary Analysis of Hydrodynamic Drag Reduction and Fouling Resistance of Surfaces Inspired by the Mollusk Shell, Dosinia juvenilis.

Author

Hamilton, Benjamin W., Tutunea-Fatan, O. Remus, and Bordatchev, Evgueni V.

Subjects
*DRAG reduction, *SEASHELLS, *SURFACE resistance, *TURBULENT boundary layer, *LARGE eddy simulation models
Abstract

Many species of plants and animals show an ability to resist fouling with surface topographies tailored to their environments. The mollusk species Dosinia juvenilis has demonstrated the ability to resist the accumulation of fouling on its outer surface. Understanding the functional mechanism employed by nature represents a significant opportunity for the persistent challenges of many industrial and consumer applications. Using a biomimetic approach, this study investigates the underlying hydrodynamic mechanisms of fouling resistance through Large Eddy simulations of a turbulent boundary layer above a novel ribletted surface topography bio-inspired by the Dosinia juvenilis. The results indicate a maximum drag reduction of 6.8% relative to a flat surface. The flow statistics near the surface are analogous to those observed for other ribletted surfaces in that the appropriately sized riblets effectively reduce the spanwise and wall-normal velocity fluctuations near the surface. This study supports the understanding that nature employs ribletted surfaces toward multiple functionalities including the considered drag reduction and fouling resistance. [ABSTRACT FROM AUTHOR]

Published
2024
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24. Parametric analysis of hydrodynamic drag reduction effects determined by streamwise triangular riblets

Author

Gordon, William, Tutunea-Fatan, O. Remus, Bordatchev, Evgueni V., Gordon, William, Tutunea-Fatan, O. Remus, and Bordatchev, Evgueni V.

Abstract

Significant research efforts were recently made in studying hydrodynamics of a turbulent water flow over surfaces structured with various micro-scale features. Past studies have demonstrated drag reduction, self-cleaning, and fouling-resistant effects of streamwise triangular riblets (STR) as well as several other riblet designs. The goal of this study was to numerically simulate and parametrically analyze the effect of included angle (?) as well as other geometric characteristics of STRs on potential drag reduction effects. The CFD simulations performed within the scope of the current study were focused on the effect of design parameters on turbulent flow hydrodynamics as well as their effect on drag reduction performance. The analysis considered several different values of the included angle namely ? = 15°, 30°, and 60° as well as several flow velocity magnitudes. The flow conditions – particularly the turbulent structures formed adjacent to riblet peaks and valleys – have been analyzed in details and have been compared with results associated with previously investigated fouling resistant microstructures. In agreement with previously reported data, CFD simulations were run by means of the LES WALE model encompassing an unstructured mesh. The examination of the turbulent flow patterns near riblet tips and valleys revealed that the flow exhibits characteristics consistent with those published in the past for 60° STR. Moreover, as ? decreases, the range of non-dimensional riblet spacing (s+) exhibiting drag reducing effects reduces while the range of Reynolds number increases. The smaller value of the analyzed included angle seemed to be associated with maximum drag reduction (10%) for smaller s+ values. The preliminary results also suggested that in case of comparable Reynolds numbers, the largest drag reduction effects are associated with intermediate included angle values. This research could bring significant contributions various industry sectors for, Résumé de la communication présentée lors du congrès international tenu conjointement par Canadian Society for Mechanical Engineering (CSME) et Computational Fluid Dynamics Society of Canada (CFD Canada), à l’Université de Sherbrooke (Québec), du 28 au 31 mai 2023.

Published
2023

26. Applicability of Laser Polishing on Inconel 738 Surfaces Fabricated Through Direct Laser Deposition.

Author

Cvijanovic, Srdjan, Bordatchev, Evgueni V., and Tutunea-Fatan, O. Remus

Subjects
INCONEL, FINISHES & finishing, SURFACE finishing, SURFACE roughness, LASER deposition, LASERS
Abstract

Today's manufacturing industry requires novel technologies capable to improve process versatility, rapidity as well as the surface quality of the parts fabricated through additive manufacturing. A cost/process-effective manufacturing solution capable to meet these requirements is represented by the direct laser deposition (DLD) technology. DLD is essentially an additive manufacturing (AM) process that can accurately fabricate complex freeform geometries. The main drawback of DLD is constituted by the reduced surface quality that is in fact an unavoidable characteristic of the AM processes. It was found that the best areal surface roughness (Sa) occurs on the front wall characterized by a +90° angle (or clockwise rotation) between DLD feed and flow vectors. More specifically, while the front wall is characterize by Sa = 0.704µm, the rear/back wall (-90° or counterclockwise rotation) is characterized by Sa = 3.861µm because powder is distributed and affixed in an already solidifying molten pool. To counteract this DLD process inconsistency, high-speed laser polishing (LP) can be used as a post processing technique capable to significantly improve the post-DLD surface quality. Along these lines, LP can eliminate and/or reduce the time and the cost of post-DLD surface finishing operations. Preliminary experimental results demonstrate that LP improves the quality of DLDgenerated surfaces by decreasing with up to 70% the surface roughness (Sa LP(90deg) = 0.211 µm, Sa LP(-90deg) = 0.444 µm) through a redistribution of melted micro-peaks into micro-valleys. The combination of these two laser-based technologies offers an economic, ergonomic, and ecologic fabrication option and opens up avenues for future implementations of computer-based adaptive control, self-optimization, and online monitoring techniques. [ABSTRACT FROM AUTHOR]

Published
2023
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27. Clustering-based shape segmentation for surface unfolding, model retrieval, and 3D printing applied in bolus shaping

Author

Xing, Malcolm (Mechanical Engineering), Leung, Carson (Computer Science), Tutunea-Fatan, O. Remus (Mechanical and Materials Engineering, Western University), Peng, Qingjin, Li, Rui, Xing, Malcolm (Mechanical Engineering), Leung, Carson (Computer Science), Tutunea-Fatan, O. Remus (Mechanical and Materials Engineering, Western University), Peng, Qingjin, and Li, Rui

Abstract

Bolus is used to cover treatment areas of the patient skin to improve the dose distribution. The existing method of bolus shaping is a manual process to cut the material into pieces, then wrap and cover them on the target area, which is time-consuming and inaccurate. This research proposes clustering-based surface segmentation methods to improve accuracy and efficiency of the bolus shaping. Segmentation methods are developed for accurate shape unfolding, efficient model retrieval, and optimal 3D printing direction. For the accurate shape unfolding, surface flattenability is improved using a spectral clustering method based on features combined topology and segmentation saliency. A 3D mesh surface is optimized using a particle swarm optimizer with four requirements and one constraint to further improve surface unfolding accuracy. The 3D mesh surface is unfolded into 2D planes in a coordinate transformation process to improve the iterative efficiency using a mass-spring model with crossed springs. For the efficient model retrieval, an image-based method is proposed using visual entropies and feature skeletons of images and models. For the optimal 3D printing direction, an improved spectral clustering method is developed by combining the surface topology and printing features to improve surface quality and reduce support material. High-level features of the topology and printing are abstracted by Stacked Auto-encoders. Case studies verify the proposed segmentation and optimization methods. The shape unfolding method significantly reduces processing errors. The image-based model retrieval method shows its accuracy and efficiency in different applications. The surface segmentation increases surface quality and reduces support material of the 3D printed product.

Published
2022

29. Single point diamond cutting of high-aspect ratio V-grooves: alternative flank cutting strategy and preliminary burr formation analysiS

Author

Rangel, Otoniel F., Tutunea-Fatan, O. Remus, and Bordatchev, Evgueni V.

Abstract

The preliminary analysis of the top burr demonstrates that the material being removed from the groove during double flank cutting moves concurrently both in longitudinal and transversal directions. This material movement leads to the formation of the chip and side bulge/Poisson burrs, respectively. Moreover, the analysis performed suggests that the depth of cut has a more significant effect on the burr formation than the cutting speed. It is expected that that these results will enable a more in-depth analysis of the mechanics and dynamics associated with single point cutting of high-aspect/high-precision trilateral structures to eventually advance their use in surface functionalization applications., 36th Annual Meeting of the American Society for Precision Engineering, ASPE 2021, November 1-15, 2021, Minneapolis, Minnesota, USA

Published
2021

33. Determination of geometry-based errors for interpolated tool paths in five-axis surface machining

Author

Tutunea-Fatan, O. Remus and Feng, Hsi-Yung

Subjects
Machining -- Research, Production engineering -- Research, Manufacturing software, Bills of material (BOM) software, Technology application, Engineering and manufacturing industries, Science and technology
Abstract

Five-axis computer numerical control (CNC) machining is characterized with a multitude of errors. Among them an important component comes from the computer-aided manufacturing software known as the geometry-based errors. A new and accurate method to determine these errors is presented in this paper as opposed to the conventional chordal deviation method. The present method allows establishing the exact linearly interpolated tool positions between two cutter contact points on a given tool path, based on the inverse kinematics analysis of the machine tool. A generic procedure has been developed to ensure wide applicability of the proposed method. Analytical derivation of the geometry-based errors provides insights regarding the origin of these errors and their affecting parameters. Due to the highly non-linear characteristics of the problem, analytical solutions can only be obtained for simple surface geometry. Numerical computation is able to determine the errors for general surface shapes but it would be difficult to uncover further insightful information from the calculated error values. Besides the local surface geometry, the configuration of the kinematic chain of the CNC machine has been found to be the primary factor controlling the resulting value and type of the geometry-based errors. Implementations with a typical complex free-form surface demonstrated that the conventional chordal deviation method was not reliable and could significantly underestimate the geometry-based errors. [DOI: 10.1115/1.1831285]

Published
2005

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