Browsing by Subject "Numerical simulation"
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Item Open Access Clustering of Janus particles in an optical potential driven by hydrodynamic fluxes(Digital Library, 2021-08-01) Callegari, Agnese; Mousavi, S. Masoumeh; Kasianiuk, Iryna; Kasyanyuk, Denis; Velu, Sabareesh K. P.; Biancofiore, Luca; Volpe, GiovanniSelf-organisation is driven by the interactions between the individual components of a system mediated by the environment, and is one of the most important strategies used by many biological systems to develop complex and functional structures. Furthermore, biologically-inspired self-organisation offers opportunities to develop the next generation of materials and devices for electronics, photonics and nanotechnology. In this work, we demonstrate experimentally that a system of Janus particles (silica microspheres half-coated with gold) aggregates into clusters in the presence of a Gaussian optical potential and disaggregates when the optical potential is switched off. We show that the underlying mechanism is the existence of a hydrodynamic flow induced by a temperature gradient generated by the light absorption at the metallic patches on the Janus particles. We also perform simulations, which agree well with the experiments and whose results permit us to clarify the underlying mechanism. The possibility of hydrodynamic-flux-induced reversible clustering may have applications in the fields of drug delivery, cargo transport, bioremediation and biopatterning.Item Open Access A gPC-based approach to uncertain transonic aerodynamics(2010) Simon F.; Guillen P.; Sagaut P.; Lucor, D.The present paper focus on the stochastic response of a two-dimensional transonic airfoil to parametric uncertainties. Both the freestream Mach number and the angle of attack are considered as random parameters and the generalized Polynomial Chaos (gPC) theory is coupled with standard deterministic numerical simulations through a spectral collocation projection methodology. The results allow for a better understanding of the flow sensitivity to such uncertainties and underline the coupling process between the stochastic parameters. Two kinds of non-linearities are critical with respect to the skin-friction uncertainties: on one hand, the leeward shock movement characteristic of the supercritical profile and on the other hand, the boundary-layer separation on the aft part of the airfoil downstream the shock. The sensitivity analysis, thanks to the Sobol' decomposition, shows that a strong non-linear coupling exists between the uncertain parameters. Comparisons with the one-dimensional cases demonstrate that the multi-dimensional parametric study is required to get the correct shape and magnitude of the standard deviation distributions of the flow quantities such as pressure and skin-friction. © 2009 Elsevier B.V.Item Open Access High-energy femtosecond photonic crystal fiber laser(2010) Lecaplain, C.; Ortaç, B.; MacHinet G.; Boullet J.; Baumgart, M.; Schreiber, T.; Cormier, E.; Hideur, A.We report the generation of high-energy high-peak power pulses in an all-normal dispersion fiber laser featuring large-mode-area photonic crystal fibers. The self-starting chirped-pulse fiber oscillator delivers 11 W of average power at 15:5 MHz repetition rate, resulting in 710 nJ of pulse energy. The output pulses are dechirped outside the cavity from 7 ps to nearly transform-limited duration of 300 fs, leading to pulse peak powers as high as 1:9 MW. Numerical simulations reveal that pulse shaping is dominated by the amplitude modulation and spectral filtering provided by a resonant semiconductor saturable absorber. © 2010 Optical Society of America.Item Open Access Microjoule-energy, 1 MHz repetition rate pulses from all-fiber-integrated nonlinear chirped-pulse amplifier(Optical Society of America, 2010-03-23) Kalaycioglu, H.; Oktem, B.; Şenel, Ç.; Paltani, P. P.; Ilday, F. Ö.We demonstrate generation of pulses with up to 4 μJ energy at 1 MHz repetition rate through nonlinear chirped-pulse amplification in an entirely fiber-integrated amplifier, seeded by a fiber oscillator. The peak power and the estimated nonlinear phase shift of the amplified pulses are as much as 57 kW and 22π, respectively. The shortest compressed pulse duration of 140 fs is obtained for 3.1 μJ of uncompressed amplifier output energy at 18 π of nonlinear phase shift. At 4 μJ of energy, the nonlinear phase shift is 22 π and compression leads to 170-fs-long pulses. Numerical simulations are utilized to model the experiments and identify the limitations. Amplification is ultimately limited by the onset of Raman amplification of the longer edge of the spectrum with an uncompressible phase profile.Item Open Access nOBS: an ns2 based simulation tool for performance Evaluation of TCP Traffic in OBS networks(Springer-Verlag France, 2007) Gurel, G.; Alparslan, O.; Karasan, E.Performance evaluation of TCP traffic in OBS networks has been under intensive study, since TCP constitutes the majority of Internet traffic. As a reliable and publicly available simulator, ns2 has been widely used for studying TCP/IP networks; however ns2 lacks many of the components for simulating optical burst switching networks. In this paper, an ns2 based OBS simulation tool (nOBS), which is built for studying burst assembly, scheduling and contention resolution algorithms in OBS networks is presented. The node and link objects in OBS are extended in nOBS for developing optical nodes and optical links. The ingress, core and egress node functionalities are combined into a common optical node architecture, which comprises agents responsible for burstification, routing and scheduling. The effects of burstification parameters, e.g., burstification timeout, burst size and number of burstification buffers per egress node, on TCP performance are investigated using nOBS for different TCP versions and different network topologies.Item Open Access Plasmon and grid resonances in the electromagnetic scattering by finite grids of silver nanowires(IEEE, 2010) Natarov, D. M.; Benson, T. M.; Altıntaş, Ayhan; Sauleau, R.; Nosich, A. I.The problem of the H-polarized wave scattering by finite chains of circular nanowires is considered. A two-dimensional diffraction problem with rigorous boundary conditions is solved by partial separations of variables method using local polar coordinates of each scatterer. The obtained results demonstrate convergence of the algorithm and good agreement with data known for the conducting and dielectric cylinders. Plasmonic and grid resonances are found and calculated for grids from a big number of silver nanowires. This opens a way to the accurate numerical simulation of various finite configurations of wires met in today's nano and microsize photonic devices.Item Open Access Spatio-temporal evolution of ultrashort pulses in graded-index multimode fiber at normal dispersion(IEEE, 2017) Teğin, Uğur; Ortaç, BülendSummary form only given. A novel nonlinear phenomenon at normal dispersion regime inside of graded-index multimode fiber (GRIN MMF), geometric parametric instability (GPI), can be observed while propagating beam experiences spatio-temporal evolution. Longhi theoretically predicted this GPI and associated with periodic refocusing inside GRIN MMF [1]. Later his work is verified by Krupa et al. [2] and Lopez-Galmiche et al. [3] and discrete GPI sidebands are reported with more than 120 THz detuning from to pump frequency. These studies focused on quasi-continues pulse evolution in GRIN MMF and the spatio-temporal evolution of femtosecond pulses at normal dispersion regime remains unknown. Here, we present the first experimental observation of GPI sidebands with ultrashort pulses in GRIN MMF. To gain detailed understanding, we perform numerical simulations and theoretical calculations and obtained results are well-aligned with experimental observations.Item Open Access Sub-80 fe dissipative soliton large-mode-area fiber laser(2010) Baumgartl, M.; Ortaç, B.; Lecaplain, C.; Hideur, A.; Limpert J.; Tünnermann, A.We report on high-energy ultrashort pulse generation from an all-normal-dispersion large-mode-area fiber laser by exploiting an efficient combination of nonlinear polarization evolution (NPE) and a semiconductor-based saturable absorber mode-locking mechanism. The watt-level laser directly emits chirped pulses with a duration of 1 ps and 163 nJ of pulse energy. These can be compressed to 77 fs, generating megawatt-level peak power. Intracavity dynamics are discussed by numerical simulation, and the intracavity pulse evolution reveals that NPE plays a key role in pulse shaping. © 2010 Optical Society of America.Item Open Access Transmission enhancement through deep subwavelength apertures using connected split ring resonators(Optical Society of American (OSA), 2010) Ates, D.; Cakmak, A.O.; Colak, E.; Zhao, R.; Soukoulis, C.M.; Özbay, EkmelWe report astonishingly high transmission enhancement factors through a subwavelength aperture at microwave frequencies by placing connected split ring resonators in the vicinity of the aperture. We carried out numerical simulations that are consistent with our experimental conclusions. We experimentally show higher than 70,000-fold extraordinary transmission through a deep subwavelength aperture with an electrical size of λ/31xλ/12 (width x length), in terms of the operational wavelength. We discuss the physical origins of the phenomenon. Our numerical results predict that even more improvements of the enhancement factors are attainable. Theoretically, the approach opens up the possibility for achieving very large enhancement factors by overcoming the physical limitations and thereby minimizes the dependence on the aperture geometries. © 2010 Optical Society of America.