10,030 research outputs found
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Study on SPH Viscosity Term Formulations
For viscosity-dominated flows, the viscous effect plays a much more important role. Since the viscosity term in SPH-governing (Smoothed Particle Hydrodynamics) equations involves the discretization of a second-order derivative, its treatment could be much more challenging than that of a first-order derivative, such as the pressure gradient. The present paper summarizes a series of improved methods for modeling the second-order viscosity force term. By using a benchmark patch test, the numerical accuracy and efficiency of different approaches are evaluated under both uniform and non-uniform particle configurations. Then these viscosity force models are used to compute a documented lid-driven cavity flow and its interaction with a cylinder, from which the most recommended viscosity term formulation has been identified
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A hybrid stabilization technique for simulating water wave - Structure interaction by incompressible Smoothed Particle Hydrodynamics (ISPH) method
The Smoothed Particle Hydrodynamics (SPH) method is emerging as a potential tool for studying water wave related problems, especially for violent free surface flow and large deformation problems. The incompressible SPH (ISPH) computations have been found not to be able to maintain the stability in certain situations and there exist some spurious oscillations in the pressure time history, which is similar to the weakly compressible SPH (WCSPH). One main cause of this problem is related to the non-uniform and clustered distribution of the moving particles. In order to improve the model performance, the paper proposed an efficient hybrid numerical technique aiming to correct the ill particle distributions. The correction approach is realized through the combination of particle shifting and pressure gradient improvement. The advantages of the proposed hybrid technique in improving ISPH calculations are demonstrated through several applications that include solitary wave impact on a slope or overtopping a seawall, and regular wave slamming on the subface of open-piled structure
Enhanced Magnetization from Proton Irradiated Bulk van der Waals Magnet CrSiTe3
Van der Waals (vdWs) crystals have attracted a great deal of scientific
attention due to their interesting physical properties and widespread practical
applications. Among all, CrSiTe3 (CST) is a ferromagnetic semiconductor with
the Curie temperature (TC) of ~32 K. In this letter, we study the magnetic
properties of bulk CST single-crystal upon proton irradiation with the fluence
of 1x1018 protons/cm2. Most significantly, we observed an enhancement (23%) in
the saturation magnetization from 3.9 {\mu}B to 4.8 {\mu}B and is accompanied
by an increase in the coercive field (465-542 Oe) upon proton irradiation.
Temperature-dependent X-band electron paramagnetic resonance measurements show
no additional magnetically active defects/vacancies that are generated upon
proton irradiation. The findings from X-ray photoelectron spectroscopy and
Raman measurements lead us to believe that modification in the spin-lattice
coupling and introduction of disorder could cause enhancement in saturation
magnetization. This work demonstrates that proton irradiation is a feasible
method in modifying the magnetic properties of vdWs crystals, which represents
a significant step forward in designing future spintronic and
magneto-electronic applications
Flicker Noise in Bilayer Graphene Transistors
We present the results of the experimental investigation of the low -
frequency noise in bilayer graphene transistors. The back - gated devices were
fabricated using the electron beam lithography and evaporation. The charge
neutrality point for the fabricated transistors was around 10 V. The noise
spectra at frequencies above 10 - 100 Hz were of the 1/f - type with the
spectral density on the order of 10E-23 - 10E-22 A2/Hz at the frequency of 1
kHz. The deviation from the 1/f spectrum at the frequencies below 10 -100 Hz
indicates that the noise is of the carrier - number fluctuation origin due to
the carrier trapping by defects. The Hooge parameter of 10E-4 was extracted for
this type of devices. The gate dependence of the noise spectral density
suggests that the noise is dominated by the contributions from the ungated part
of the device channel and by the contacts. The obtained results are important
for graphene electronic applications
Low-noise top-gate graphene transistors
We report results of experimental investigation of the low-frequency noise in
the top-gate graphene transistors. The back-gate graphene devices were modified
via addition of the top gate separated by 20 nm of HfO2 from the single-layer
graphene channels. The measurements revealed low flicker noise levels with the
normalized noise spectral density close to 1/f (f is the frequency) and Hooge
parameter below 2 x 10^-3. The analysis of the noise spectral density
dependence on the top and bottom gate biases helped us to elucidate the noise
sources in these devices and develop a strategy for the electronic noise
reduction. The obtained results are important for all proposed graphene
applications in electronics and sensors.Comment: 9 pages, 4 figure
Incompressible SPH simulation of wave interaction with porous structure
In this paper an incompressible Smoothed Particle Hydrodynamics (ISPH) method is applied to investigate the flow motion in and around the porous structure. In order to describe in a simple and effective way the flow through the interface between the porous region and pure fluid region within the SPH framework, a heuristic boundary treatment method has been proposed. The ISPH model is first verified against a theoretical model of wave propagation over a porous bed and then further validated by comparing the predicted wave surface profiles and flow velocity fields with the experiment data for a typical case of flow motion around and inside a submerged porous structure. The good agreement has demonstrated that the improved ISPH model developed in this work is capable of modelling wave interaction with porous structures
A comparative study on violent sloshing with complex baffles using the ISPH method
The Smoothed Particle Hydrodynamics (SPH) method has become one of the most
promising methods for violent wave impact simulations. In this paper, the incompressible SPH
(ISPH) method will be used to simulate liquid sloshing in a 2D tank with complex baffles. Firstly, the
numerical model is validated against the experimental results and the simulations from commercial
CFD software STAR-CCM+ for a sloshing tank without any baffle. Then various sloshing tanks
are simulated under different conditions to analyze the influence of the excitation frequency and
baffle configuration. The results show that the complex baffles can significantly influence the impact
pressures on the wall caused by the violent sloshing, and the relevant analysis can help find the
engineering solutions to effectively suppress the problem. The main purpose of the paper is to study
the practical importance of this effect
Centrality, system size and energy dependences of charged-particle pseudo-rapidity distribution
Utilizing the three-fireball picture within the quark combination model, we
study systematically the charged particle pseudorapidity distributions in both
Au+Au and Cu+Cu collision systems as a function of collision centrality and
energy, 19.6, 62.4, 130 and 200 GeV, in full pseudorapidity
range. We find that: (i)the contribution from leading particles to
distributions increases with the decrease of the collision
centrality and energy respectively; (ii)the number of the leading particles is
almost independent of the collision energy, but it does depend on the nucleon
participants ; (iii)if Cu+Cu and Au+Au collisions at the same
collision energy are selected to have the same , the resulting of
charged particle distributions are nearly identical, both in the
mid-rapidity particle density and the width of the distribution. This is true
for both 62.4 GeV and 200 GeV data. (iv)the limiting fragmentation phenomenon
is reproduced. (iiv) we predict the total multiplicity and pseudorapidity
distribution for the charged particles in Pb+Pb collisions at TeV. Finally, we give a qualitative analysis of the
and as function of
and from RHIC to LHC.Comment: 12 pages, 8 figure
Cylindrical smoothed particle hydrodynamics simulations of water entry
This paper presents a smoothed particle hydrodynamics (SPH) modeling technique based on the cylindrical coordinates for axisymmetrical hydrodynamic applications, thus to avoid a full three-dimensional (3D) numerical scheme as required in the Cartesian coordinates. In this model, the governing equations are solved in an axisymmetric form and the SPH approximations are modified into a two-dimensional cylindrical space. The proposed SPH model is first validated by a dam-break flow induced by the collapse of a cylindrical column of water with different water height to semi-base ratios. Then, the model is used to two benchmark water entry problems, i.e., cylindrical disk and circular sphere entry. In both cases, the model results are favorably compared with the experimental data. The convergence of model is demonstrated by comparing with the different particle resolutions. Besides, the accuracy and efficiency of the present cylindrical SPH are also compared with a fully 3D SPH computation. Extensive discussions are made on the water surface, velocity, and pressure fields to demonstrate the robust modeling results of the cylindrical SPH
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