86,649 research outputs found
Multiscale Smoothed Particle Hydrodynamics based on a domain-decomposition strategy
No full textA multi-resolution algorithm for weakly-compressible Smoothed Particle Hydrodynamics is hereby proposed. The approach chosen is based on a domain decomposition to subdivide the computational domain into regions with different resolutions. Each sub-problem is closed by appropriate Dirichlet boundary conditions that are enforced via buffer regions, populated by particles whose physical quantities are obtained by means of an interpolation over adjacent sub-domains. The algorithm has been implemented into the DualSPHysics open-source code and it has been tested and validated through a series of different study cases. The capability of the numerical scheme to simulate multiscale fluid flow has been demonstrated by solving the flow past a cylinder for a Reynolds number of 9,500 and a ratio between the largest and smallest particle size equal to 28. Furthermore, the proposed SPH multi-resolution algorithm can also be used for flow around moving objects, such as an oscillating cylinder in cross-flow, and free-surface flow, such as the simulation of a triangular wedge impacting on the free surface of a quiescent liquid
Direct numerical simulation of three-dimensional isotropic turbulence with smoothed particle hydrodynamics
No full textAssessment of pre-simulated scenarios as a non-structural measure for flood management in case of levee-breach inundations
No full textLevee breach inundations can entail large flood losses due to the high concentration of exposed assets in levee-protected floodplains and, sometimes, to the inadequacy or absence of early warning systems for this type of events. Since real-time modelling is computationally expensive and presents several uncertainties, which might prevent obtaining a reasonably accurate forecast of the flood propagation, an alternative methodology for the prompt prediction of flooded area, maximum depths, and arrival times during a real event was proposed. The strategy is based on the use of a database of pre-simulated scenarios of levee-breach inundations, obtained adopting a high-resolution two-dimensional shallow water model. The paper aims at the a posteriori assessment of the usefulness of this strategy. To this end, the December 2020 event on the Panaro River (Italy) is thoroughly analyzed. In the study area, the strategy had already been implemented before the event, and pre-simulated scenarios were consulted during the emergency. Post-event observations are also available for the ex-post model validation. The database was obtained considering two inflow synthetic hydrographs and a discrete number of breach locations, and unavoidable differences between real events and hypothetical scenarios were to be expected. However, for this case study, the closest levee-breach scenario in the database (in terms of breach position and inflow) provided reliable predictions of flood extent and maximum depths for the actual inundation. The pre-simulated database also helped identifying some critical spots, where effective emergency operations (sandbagging) helped protecting an urban district during the event. As accurate real-time forecasts of levee-breach inundations are yet to come, a database of pre-simulated scenarios is proven as an effective “surrogate” method for civil protection purposes
Low Complexity Compensation of SOA Nonlinearity for Single-Channel PSK and OOK
No full textCarrier density fluctuations in semiconductor optical
amplifiers (SOAs) impose penalties on phase-shift keying (PSK)
signals due to nonlinear phase noise (NLPN), and on-off keying
(OOK) signals due to self-gain modulation. In this paper, we propose
a simple scheme to equalize the impairments induced by SOA
nonlinearities, derived from the small signal analysis of carrier
density fluctuations. We demonstrate via simulation almost complete
cancelation of the NLPN added by a saturated SOA on a
differential PSK signal. We demonstrate via both simulations and
experiment the effectiveness of the method for mitigation of nonlinear
distortions imposed by SOAs on an OOK signal
Modeling Nonlinearity in Coherent Transmissions with Dominant Interpulse-Four-Wave-Mixing
No full textBy extending a well-established time-domain perturbation approach to dual-polarization propagation, we provide an analytical framework to predict the nonlinear interference (NLI) variance, i.e., the variance induced by nonlinearity on the sampled field, and the nonlinear threshold (NLT) in coherent transmissions with dominant intrachannel four-wave-mixing (IFWM). Such a framework applies to non dispersion managed (NDM) very long-haul coherent optical systems at nowadays typical baudrates of tens of Gigabaud, as well as to dispersion-managed (DM) systems at even higher baudrates, whenever IFWM is not removed by nonlinear equalization and is thus the dominant nonlinearity. The NLI variance formula has two fitting parameters which can be calibrated from simulations. From the NLI variance formula, analytical expressions of the NLT for both DM and NDM systems are derived and checked against recent NLT Monte-Carlo simulations
DQPSK: when is a narrow filter receiver is good enough?
No full textIn this paper, we investigate experimentally and via
simulation the pros and cons of a narrow filter receiver for differential
quadrature phase-shift keying based on a single optical filter
and eschewing the conventional asymmetrical Mach–Zehnder interferometer
structure. We quantify the performance differences
between the two receivers, allowing system designers and operators
to determine when the less complex narrow filter receiver
might be the appropriate choice.We numerically optimize the 3-dB
bandwidth and center frequency of the narrow filter and show
it is more robust to carrier frequency detuning than the conventional
solution. We show that the narrow filter receiver is more
tolerant to chromatic dispersion (CD) than the conventional one,
and equally tolerant to first-order polarization-mode dispersion.
We show the impact of the 3-dB bandwidth on the receiver performance
when CD accumulates. Finally, we show via experiments
and simulations that the 3 dB advantage of the conventional receiver
vanishes when the nonlinear impairments are fiber nonlinearities;
comparing the two receivers at the optimum launch power
for a 25x80 km system, the difference in optical SNR margin is
reduced to 1.6 dB. Experiments are conducted at 42 Gb/s using
a commercially available narrow filter for reception
Formulation and Transdermal Permeation of a New N-Acylethanolamine Acid Amidase (NAAA) Inhibitor
No full textSOA Intensity Noise Suppression: MulticanonicalMonte Carlo Simulator of Extremely Low BER
No full textWe present a thorough numerical study of intensity
noise mitigation of spectrum sliced wavelength-division multiplexing
(SS-WDM) systems employing a nonlinear semiconductor
optical amplifier (SOA) before the modulator. Our simulator of
the SS-WDM link, embedded inside a Multicanonical Monte Carlo
(MMC) platform, estimates the tails of the probability density
functions of the received signals down to probabilities smaller
than 10^-6. We introduce a new, simple, and efficient technique
to handle intersymbol interference (ISI) in MMC simulations.
We address the impact of optical postfiltering on SOA noise suppression
performance. While previous research experimentally
observed the SOA-induced noise cleaning in SS-WDM systems,
this is the first complete simulator able to correctly predict the
ensuing BER improvement. We measure the BER at different
bit-rates and validate predicted BERs with and without post
filtering
Relationship between structure and ex-vivo binding of imidazole H3 antagonists to rat brain H3 receptors
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