DSpace Collection:http://hdl.handle.net/10203/6252018-02-25T10:06:13Z2018-02-25T10:06:13ZSeries representations for the rectification of a superhelixLim, SungyeopHan, Soonhunghttp://hdl.handle.net/10203/2403662018-02-21T06:38:15Z2018-04-01T00:00:00ZTitle: Series representations for the rectification of a superhelix
Authors: Lim, Sungyeop; Han, Soonhung
Abstract: A superhelix is a curve that is helically coiled around a helix. Despite its importance in relation to the deformation modeling of various shapes, the superhelix is greatly overlooked, in part owing to its complexity and in part due to the lack of an analytical formula for its arc length. Deriving an exact analytical formula is not simple, because one needs to integrate a function without a closed-form integral solution to determine the arc length of a superhelix. In this study, we present a method by which to obtain the integral of the function that has no closed form integral by employing the series expansion approach of Maclaurin, as originally used to express the exact perimeter of an ellipse as an infinite sum. Our final expression of the arc length of a superhelix takes the form of two separate infinite sums, from which the one that converges is chosen to be applied, depending on the range of the geometric variables of the curve. (C) 2017 Elsevier Inc. All rights reserved.2018-04-01T00:00:00ZSchlieren, Shadowgraph, Mie-scattering visualization of diesel and gasoline sprays in high pressure/high temperature chamber under GDCI engine low load conditionKim, DonghoonPark, Stephen SungsanBae, Choongsikhttp://hdl.handle.net/10203/2265982018-01-30T08:52:47Z2018-02-01T00:00:00ZTitle: Schlieren, Shadowgraph, Mie-scattering visualization of diesel and gasoline sprays in high pressure/high temperature chamber under GDCI engine low load condition
Authors: Kim, Donghoon; Park, Stephen Sungsan; Bae, Choongsik
Abstract: Three visualization methods, Schlieren, Shadowgraph, and Mie-scattering, were applied to compare diesel and gasoline spray structures in a constant volume chamber. Fuels were injected into a high pressure/high temperature chamber under the same in-cylinder pressure and temperature conditions of low load in a GDCI (gasoline direct injection compression ignition) engine. Two injection pressures (40 MPa and 80 MPa), two ambient pressures (4.2 MPa and 1.7 MPa), and two ambient temperatures (908 K and 677 K) were use. The images from the different methods were overlapped to show liquid and vapor phases more clearly. Vapor developments of the two fuels were similar; however, different liquid developments were seen. At the same injection pressure and ambient temperature, gasoline liquid propagated more quickly and disappeared more rapidly than diesel liquid phase. At the low ambient temperature and pressure condition, gasoline and diesel sprays with higher injection pressures showed longer liquid lengths due to higher spray momentum. At the higher ambient temperature condition, the gasoline liquid length was shorter for the higher injection pressure. Higher volatility of gasoline is the main reason for this shorter liquid length under higher injection pressure and higher ambient temperature conditions. For a design of GDCI engine, it is necessary to understand the higher volatility of gasoline.2018-02-01T00:00:00ZA Study on Computational Efficiency Improvement of Novel SORM Using the Convolution IntegrationPark, Jeong WooLee, Ikjinhttp://hdl.handle.net/10203/2387392018-01-30T08:55:01Z2018-02-01T00:00:00ZTitle: A Study on Computational Efficiency Improvement of Novel SORM Using the Convolution Integration
Authors: Park, Jeong Woo; Lee, Ikjin
Abstract: This paper proposes to apply the convolution integral method to the novel second-order reliability method (SORM) to further improve its computational efficiency. The novel SORM showed better accuracy in estimating the probability of failure than conventional SORMs by utilizing a linear combination of noncentral or general chi-squared random variables. However, the novel SORM requires significant computational time when integrating the linear combination to calculate the probability of failure. In particular, when the dimension of performance functions is higher than three, the computational time for full integration increases exponentially. To reduce this computational burden for the novel SORM, we propose to obtain the distribution of the linear combination using the convolution and to use the distribution for the probability of failure estimation. Since it converts an N-dimensional full integration into one-dimensional integration, the proposed method is computationally very efficient. Numerical study illustrates that the accuracy of the proposed method is almost the same as the full integral method and Monte Carlo simulation (MCS) with much improved efficiency.2018-02-01T00:00:00ZResonant-Plasmon-Assisted Subwavelength Ablation by a Femtosecond OscillatorShi, LipingIwan, BiancaRipault, QuentinAndrade, Jose R. C.Han, SeunghwoiKim, HyunwoongBoutu, WillemFranz, DominikNicolas, RanaHeidenblut, TorstenReinhardt, CarstenBastiaens, BertNagy, TamasBabuskin, IharMorgner, UweKim, Seung-WooSteinmeyer, GuenterMerdji, HamedKovacev, Milutinhttp://hdl.handle.net/10203/2403742018-02-21T06:38:40Z2018-02-01T00:00:00ZTitle: Resonant-Plasmon-Assisted Subwavelength Ablation by a Femtosecond Oscillator
Authors: Shi, Liping; Iwan, Bianca; Ripault, Quentin; Andrade, Jose R. C.; Han, Seunghwoi; Kim, Hyunwoong; Boutu, Willem; Franz, Dominik; Nicolas, Rana; Heidenblut, Torsten; Reinhardt, Carsten; Bastiaens, Bert; Nagy, Tamas; Babuskin, Ihar; Morgner, Uwe; Kim, Seung-Woo; Steinmeyer, Guenter; Merdji, Hamed; Kovacev, Milutin
Abstract: We experimentally demonstrate the use of subwavelength optical nanoantennas to assist a direct nanoscale ablation using the ultralow fluence of a Ti:sapphire oscillator through the excitation of surface plasmon waves. The mechanism is attributed to nonthermal transient unbonding and electrostatic ablation, which is triggered by the surface plasmon-enhanced field electron emission and acceleration in vacuum. We show that the electron-driven ablation appears for both nanoscale metallic as well as dielectric materials. While the observed surface plasmon-enhanced local ablation may limit the applications of nanostructured surfaces in extreme nonlinear nanophotonics, it, nevertheless, also provides a method for nanomachining, manipulation, and modification of nanoscale materials. Collateral thermal damage to the antenna structure can be suitably avoided, and nonlinear conversion processes can be stabilized by a dielectric overcoating of the antenna.2018-02-01T00:00:00Z