排序方式: 共有30条查询结果,搜索用时 15 毫秒
1.
Petar Liovic Murray Rudman Jong-Leng Liow Djamel Lakehal Doug Kothe 《Computers & Fluids》2006,35(10):1011-1032
A new volume tracking method is introduced for tracking interfaces in three-dimensional (3D) geometries partitioned with orthogonal hexahedra. The method approximates interface geometries as piecewise planar, and advects volumes in a single unsplit step using fully multidimensional fluxes that have their definition based in backward-trajectory remapping. By using multidimensional unsplit advection, the expense of high-order interface reconstruction is incurred only once per timestep. Simple departures from strict backward-trajectory remapping remove any need for consideration of volume computations involving shapes consisting of non-planar ruled surfaces. Second-order accuracy of the method is demonstrated even for vigorous 3D deformations. 相似文献
2.
The paper explores liquid drop dynamics over a solid surface, focusing on adherence and bouncing phenomena. The study relies
on detailed interface tracking simulations using the Level Set approach incorporated within a Navier–Stokes solver. The investigation
deals with moderate Reynolds number droplet flows, for which two-dimensional axisymmetric simulations can be performed. The
modelling approach has been validated against experiments for axisymmetric and full three-dimensional impact upon dry surfaces.
A drop-impact regime map is generated for axisymmetric conditions, in which the impact dynamics is characterized as a function
of Weber number and equilibrium contact angle, based on about 60 simulations. The detailed simulations also helped validate
a new mechanistic model based on energy-balance analysis, delimiting the boundary between adherence and bouncing zones at
low Weber numbers. The mechanistic model is only valid for moderate droplet Reynolds numbers and it complements existing models
for higher Reynolds numbers. 相似文献
3.
4.
Djamel Lakehal 《Nuclear Engineering and Design》2010,240(9):2096-2106
The paper centres on the use of the so-defined LEIS approach (Large-Eddy & Interface Simulation) for turbulent multifluid flows present in thermal-hydraulics applications. Interfacial flows involving deformable, sheared fronts separating immiscible fluids are shown to be within reach of this new approach, featuring direct resolution of turbulence and sheared interface deformations within the interface tracking (ITM) framework, such as level sets and VOF. In this technique supergrid turbulence and interfacial scales are directly solved whereas the sub-grid (SGS) parts are modelled, at least the turbulence part of it. First results are shown (feasibility), and difficulties and open issues are discussed. The connection between these two particular scales will also be discussed, and potential modelling routes evoked, including combining two-fluid and ITM, local grid refinement, or combing particle tracking and ITM for sub-grid inclusions smaller than the grid size. 相似文献
5.
Speech coders operating at low bit rates necessitate efficient encoding of the linear predictive coding (Lpc) coefficients. Line spectral Frequencies (Lsf) parameters are currently one of the most efficient choices of transmission parameters for theLpc coefficients. In this paper, an optimized trellis coded vector quantization (Tcvq) scheme for encoding theLsf parameters is presented. When the selection of a proper distortion measure is the most important issue in the design and operation of the encoder, an appropriate weighted distance measure has been used during theTcvq construction process. We further applied the optimizedTcvq system for encoding theLsf parameters of the us Federal Standard (Fs1016) 4.8 kbps speech coder. At lower bit rates, objective and subjective evaluation results show that the incorporatedLsf tcvq encoder performs better than the 34 bits/frameLsf scalar quantizer used originally in the fs1016 coder. The subjective tests reveal also that the 27 bit/frame scheme produces equivalent perceptual quality to that when theLsf parameters are unquantized. 相似文献
6.
Merouane Bouzid 《电信纪事》2007,62(3-4):426-463
In this paper, we present an optimized trellis coded vector quantization (tcvq) coding system designed for the effective and robust coding of lsf spectral parameters at low bit rate. The aim of this system, called at the beginning « lsf-otcvq Encoder », is to achieve a low bit rate transparent quantization of lsf parameters of the us Federal Standard (fs1016) speech coder. Once the effectiveness of our lsf-otcvq encoders (with weighted distance) was proven in the case of ideal transmissions over noiseless channel, we were interested after in the improvement of their robustnesses for real transmissions over noisy channel. To implicitly protect the transmission indices of our lsf-otcvq coders incorporated in the Fsl016, we used a joint source-channel coding carried out by the channel optimized vector quantization (covq) method. In the case of transmissions over noisy channel, we will show that our new encoding system, called “covq-lsf-otcvq Encoder”, would be able to contribute significantly in the improvement of the fs1016 performances by ensuring a good coding robustness of its lsf spectral parameters. 相似文献
7.
Abdesselam Lakehal Ioannis Parissis 《Software Testing, Verification and Reliability》2009,19(2):133-154
LUSTRE is a data‐flow synchronous language, on which is based the SCADE tool‐suite, widely used for specifying and programming critical reactive applications in the areas of avionics, energy or transport. Therefore, testing LUSTRE programs, that is, generating test data and assessing the achieved test coverage, is a major issue. Usual control‐flow‐based test coverage criteria (statement coverage, branch coverage, etc.) are not relevant for LUSTRE programs. In this paper, a new hierarchy of adequacy criteria tailored to the LUSTRE language is presented. These criteria are defined on operator networks, which are usual models for LUSTRE programs. The criteria satisfaction measure is automated in LUSTRUCTU , a non‐intrusive tool (no instrumentation of the code), based on the symbolic computation of path activation conditions. The applicability and the relevance of the criteria are assessed on a case study. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
8.
M. Otter G. Athanasopoulos N. Hlubek M. Montagnese M. Labois D.A. Fishman F. de Haan S. Singh D. Lakehal J. Giapintzakis C. Hess A. Revcolevschi P.H.M. van Loosdrecht 《International Journal of Heat and Mass Transfer》2012,55(9-10):2531-2538
A transient thermal imaging technique is used to monitor heat diffusion at the surface of the antiferromagnetic spin ladder material Ca9La5Cu24O41. This material shows highly anisotropic thermal conductivity due to a large uni-directional magnetic heat transport along the ladders. The thermal conductivity is measured using optical heating as well as electrical heating, yielding 37 ± 3 W m?1 K?1 for the fast (ladder) direction and 2.5 ± 0.5 W m?1 K?1 for the slow direction, respectively. The fast direction result is in agreement with the thermal conductivity measured using other dynamic methods, but about 60% lower than the thermal conductivity measured using steady state methods. 相似文献
9.
Mehdi Merouane 《Automatic Control and Computer Sciences》2017,51(1):13-23
Nowadays, Denial of Service (DoS) attacks have become a major security threat to networks and the Internet. Therefore, even a naive hacker can launch a large-scale DoS attack to the victim from providing Internet services. This article deals with the evaluation of the Snort IDS in terms of packet processing performance and detection. This work describes the aspect involved in building campus network security system and then evaluates the campus network security risks and threats, mainly analyses the attacks DoS and DDoS, and puts forward new approach for Snort campus network security solutions. The objective is to analyze the functional advantages of the solution, deployment and configuration of the open source based on Snort intrusion detection system. The evaluation metrics are defined using Snort namely comparison between basic rules with new ones, available bandwidth, CPU loading and memory usage. 相似文献
10.
Salima Lakehal Nadia Ouddai 《中国稀土学报(英文版)》2010,28(2):161-165
Density functional theory (DFT) calculations were carried out on the compounds Cp2Ln-guan for Ln=Y, Lu, Yb, Dy and Gd, [guan=(iPrN)2CN(iPr)2]. The results were compared with the X-ray structures that were available from the literature; the calculations reproduced quite well the experimental structural features in these complexes exhibiting distorted tetrahedron geometry. The calculated evolution of the Ln-guan bond as a function of the cation showed that lanthanide-ligand distances increased with the increa... 相似文献