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MODELING DAM-BrEAK FLOOD OVEr NATUrAL rIVErS USING DISCONTINUOUS GALErKIN METHOD

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Journal of Hydrodynamics 2012年第4期24卷 467-478页

作者： khan abdul A. Glenn Department of Civil Engineering Clemson University

A well-balanced numerical model is presented for two-dimensional, depth-averaged, shallow water flows based on the Discontinuous Galerkin （DG） method. The model is applied to simulate dam-break flood in natural rivers with wet/dry bed and complex topography. To eliminate numerical imbalance, the pressure force and bed slope terms are combined in the shallow water flow equations. For partially wet/dry elements, a treatment of the source term that preserves the well-balanced property is presented. A treatment for modeling flow over initially dry bed is presented. Numerical results show that the time step used is related to the dry bed criterion. The intercell numerical flux in the DG method is computed by the Harten-Lax-van Contact （HLLC） approximate riemann solver. A two-dimensional slope limiting procedure is employed to prevent spurious oscillation. The robustness and accuracy of the model are demonstrated through several test cases, including dam-break flow in a channel with three bumps, laboratory dam-break tests over a triangular bump and an L-shape bend, dam-break flood in the Paute river, and the Malpasset dam-break case. Numerical results show that the model is robust and accurate to simulate dam-break flood over natural rivers with complex geometry and wet/dry beds.

关键词： Discontinuous Galerkin (DG) method shallow water flows dam-break flood well-balanced scheme

Systematic Geometric Error Modeling for Workspace Volumetric Calibration of a 5-axis Turbine Blade Grinding Machine

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Chinese Journal of Aeronautics 2010年第5期23卷 604-615页

作者： abdul Wahid khan School of Mechanical Engineering and Automation Beijing University of Aeronautics and Astronautics

A systematic geometric model has been presented for calibration of a newly designed 5-axis turbine blade grinding machine. This machine is designed to serve a specific purpose to attain high accuracy and high efficiency grinding of turbine blades by eliminating the hand grinding process. Although its topology is rPPPr （P： prismatic; r： rotary）, its design is quite distinct from the competitive machine tools. As error quantification is the only way to investigate, maintain and improve its accuracy, calibra- tion is recommended for its performance assessment and acceptance testing. Systematic geometric error modeling technique is implemented and 52 position dependent and position independent errors are identified while considering the machine as five rigid bodies by eliminating the set-up errors of workpiece and cutting tool. 39 of them are found to have influential errors and are accommodated for finding the resultant effect between the cutting tool and the workpiece in workspace volume. rigid body kinematics techniques and homogenous transformation matrices are used for error synthesis.

关键词： 5-axis machine tools calibration modeling geometric errors kinematics homogenous transformation matrices

Thermospheric neutral wind studies over the equatorial region:A review

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Earth and Planetary Physics 2025年第1期9卷 81-100页

作者： Siti Syazwani Nasuha Idahwati Sarudin Nurul Shazana abdul Hamid Ahmad Fairuz Omar School of Physics Universiti Sains Malaysia11800 USMPulau PinangMalaysia Department of Applied Physics Faculty of Science and TechnologyUniversiti Kebangsaan Malaysia43600 UKM BangiSelangorMalaysia Space Science Centre(ANGKASA) Institute of Climate ChangesUniversiti Kebangsaan Malaysia43600 UKM BangiSelangorMalaysia

Thermospheric neutral winds(TNWs)refer to the neutral gases in the thermosphere circulating as tides,which play a crucial role in the dynamics of the thermosphere-ionosphere system(TIS).Global geospace neutral winds,particularly over the magnetic equator,have been a subject of study for several ***,despite the known importance of neutral winds,a comprehensive understanding and characterization of the winds is still *** ground-based and satellite missions have provided valuable information on the contribution of neutral winds to the global atmospheric ***,efforts in the global monitoring of neutral winds are still lacking,and the drivers behind the behavior of TNWs as well as their influence on the TIS remain *** address these knowledge gaps in the global circulation of TNWs,it is crucial to develop a deep understanding of the neutral wind characteristics over different *** low-latitude equatorial region in particular has been observed to exert complex influences on TNWs because of the unique effects of the Earth’s magnetic field at the dip *** neutral winds over this region will provide valuable insights into the unique dynamics and processes that occur in this region,thereby enhancing our understanding of their role in the overall dynamics of the ***,through empirical observations,an improved ability to accurately model and predict the behavior of this region can be *** review article addresses challenges in understanding equatorial winds by reviewing historical measurements,current missions,and the interactions of ionospheric and thermospheric phenomena,emphasizing the need for comprehensive measurements to improve global atmospheric dynamics and weather forecasting.

关键词： thermospheric neutral wind thermosphere-ionosphere system dip equator equatorial region

Optical Characterization of rf-Magnetron Sputtered Nanostructured SnO2 Thin Films

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Chinese Physics Letters 2009年第7期26卷 316-319页

作者： abdul Faheem khan National Centre for Nanotechnology Department of Chemical and Materials Engineering Pakistan Institute of Engineering and Applied Sciences (PIEAS) Islamabad 45650 Pakistan Department of Physics Bahauddin Zakariya University Multan 60800 Pakistan NILOP Islamabad 45650 Pakistan

Tin oxide （Sn02 ） thin films are deposited by rf-magnetron sputtering and annealed at various temperatures in the range of 100-500 ℃ for 15 min. raman spectra of the annealed films depict the formation of a small amount of SnO phase in the tetragonal Sn02 matrix, which is verified by x-ray diffraction. The average particle size is found to be about 20-30 nm, as calculated from x-ray peak broadening and SEM images. Various optical parameters such as optical band gap energy, refractive index, optical conductivity, carrier mobility, carrier concentration etc. are determined from the optical transmittance and reflectance data recorded in the wavelength range 250-2500 nm. The results are analyzed and compared with the data in the literature.

关键词： Condensed matter: electrical magnetic and optical Semiconductors Surfaces interfaces and thin films Nanoscale science and low-D systems Condensed matter: structural mechanical & thermal

Model Predictions of Charged-Particle Azimuthal Distributions and Forward-Backward Correlations in pp Interactions at s1/2= 900 GeV

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Communications in Theoretical Physics 2019年第10期71卷 1172-1178页

作者： r.khan M.Ajaz Y.Ali H.Younis G.khan Z.Wazir A.Zaman A.khan Department of Physics Abdul Wali Khan UniversityMardan23200Pakistan Department of Physics COMSATS UniversityIslamabad44000Pakistan Department of Physics International Islamic UniversityIslamabad44000Pakistan

We report inelastic interactions of protons at the center of mass energy s1/2 = 900 Ge V, by using different event generators to study the forward-backward(FB) correlation in summed transverse momentum and multiplicity of produced charged particles. The transverse momentum, p T ≥ 100 Me V, and pseudorapidity, | η |r both the correlations. The simulation results are compared with the ATLAS experimental data, obtained with the same values of | η | and p T at s1/2 = 900 Ge V. We also measure the jet and jet-like structure as a function of azimuthal distributions in the events relative to the highest transverse momentum particle. Three overlapping regions of pseudorapidity, | η |re used with transverse momentum, p T > 500 Me V. For FB correlations, EPOS, and Sybill2.3 c results are in a good agreement with the data as compared to the other ***, for the azimuthal distribution, EPOS-LHC, DPMJETIII, and Sibyll2.3 c show good agreement with the data for full η region. In general, EPOS provides a better description of the data for both the quantities studied in this paper.

关键词： forward-backward correlation CrMC models LHC ATLAS

Time stepping in discontinuous Galerkin method

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Journal of Hydrodynamics 2013年第3期25卷 321-329页

作者： LAI Wencong khan abdul A Glenn Department of Civil Engineering Clemson University Clemson S.C. USA

The time discretization in the Discontinuous Galerkin （DG） scheme has been traditionally based on the Total Variation Diminishing （TVD） second-order runge-Kutta （rK2） scheme. Computational efficiency and accuracy with the Euler Forward （EF） and the TVD second-order rK2 time stepping schemes in the DG method are investigated in this work. Numerical tests are condu- cted with the scalar Burgers equation, 1-D and 2-D shallow water flow equations. The maximum Courant number or time step size required for stability for the EF scheme and rK2 scheme with different slope limiters are compared. Numerical results show that the slope limiters affect the stability requirement in the DG method. The rK2 scheme is generally more diffusive than the EF scheme, and the rK2 scheme allows larger time step sizes. The EF scheme is found to be more efficient and accurate than the rK2 scheme in the DG method in computation.

关键词： Discontinuous Galerkin (DG) method Euler Forward (EF) scheme second-order runge-Kutta scheme

Numerical solution of the Saint-Venant equations by an efficient hybrid finite-volume/finite-difference method

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Journal of Hydrodynamics 2018年第2期30卷 189-202页

作者： Wencong Lai abdul A.khan Glenn Department of Civil Engineering Clemson University

A computationally efficient hybrid finite-volume/finite-difference method is proposed for the numerical solution of SaintVenant equations in one-dimensional open channel flows. The method adopts a mass-conservative finite volume discretization for the continuity equation and a semi-implicit finite difference discretization for the dynamic-wave momentum equation. The spatial discretization of the convective flux term in the momentum equation employs an upwind scheme and the water-surface gradient term is discretized using three different schemes. The performance of the numerical method is investigated in terms of efficiency and accuracy using various examples, including steady flow over a bump, dam-break flow over wet and dry downstream channels, wetting and drying in a parabolic bowl, and dam-break floods in laboratory physical models. Numerical solutions from the hybrid method are compared with solutions from a finite volume method along with analytic solutions or experimental measurements. Comparisons demonstrates that the hybrid method is efficient, accurate, and robust in modeling various flow scenarios, including subcritical, supercritical, and transcritical flows. In this method, the QUICK scheme for the surface slope discretization is more accurate and less diffusive than the center difference and the weighted average schemes.

关键词： Hybrid numerical method Saint-Venant equations shallow water flow

Biodiesel synthesis via metal oxides and metal chlorides catalysis from marine alga Melanothamnus afaqhusainii

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Chinese Journal of Chemical Engineering 2016年第3期24卷 388-393页

作者： abdul Majeed khan Noureen Fatima research Laboratory of Bioenergy Department of ChemistryFederal Urdu University of ArtsSdence and TechnologyCulshan-e-lqbal CampusUniversity RoadKarachi-75300Pakistan

This research article demonstrates the most comprehensive comparative catalytic study of different metal oxides and metal chlorides towards the methanolysis of triglycerides of marine red macroalga Melanothamnus alhqhusainii. CaO was found to be the most reactive metal oxide that yielded 80% biodiesel while ZnCI2 was the most reactive metal chloride that produced 60% biodiesel by mechanical stirring for 6 h at 100-110 ℃. The overall reactivity order of the catalysts was found to be CaO 〉 MgO 〉 Pb02 〉 ZnC12 〉 TIC14 〉 PbO 〉 HgC12 〉 ZnO 〉 AIC13 〉 SnCI2 〉 TiO2 whereas, CaCI2, MgCI2, A1203, HgO, PbCI2, MnO2, MnC12, Fe203 and FeCI3 were found to be non-reactive for transesterification of triglycerides. In addition, a detailed study of the screening of mobile phases and spraying reagents was conducted which showed that petroleum ether ： chloroform ： toluene （7：2：1 ） is the best mobile phase, whereas iodine crystals/silica gel is the best visualizing agent for the thin layer chroma- tography （TLC） examination ofbiodiesel. Biodiesel production was confirmed by comparative TLC examination. It was further supported by the determination of fuel properties of biodiesel, which were found to be similar to the standard limits of American Society for Testing and Materials （ASTM）,

关键词： Biomass Methanolysis Triglycerides Biodiesel Catalysts

1-D coupled non-equilibrium sediment transport modeling for unsteady flows in the discontinuous Galerkin framework

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Journal of Hydrodynamics 2016年第4期28卷 534-543页

作者： Farzam Safarzadeh MALEKI abdul A.khan Engineering Department Massachusetts Maritime Academy Glenn Department of Civil Engineering Clemson University

A high-resolution, 1-D numerical model has been developed in the discontinuous Galerkin framework to simulate 1-D flow behavior, sediment transport, and morphological evaluation under unsteady flow conditions. The flow and sediment concentration variables are computed based on the one-dimensional shallow water flow equations, while empirical equations are used for entrainment and deposition processes. The sediment transport model includes the bed load and suspended load components. New formulations for Harten-Lax-van Leer （HLL） and Harten-Lax-van Contact （HLLC） are presented for shallow water flow equations that include the bed load and suspended load fluxes. The computational results for the flow and morphological changes after two dam break events are compared with the physical model tests. results show that the modified HLL and HLLC formulations are robust and can accurately predict morphological changes in highly unsteady flows.

关键词： dam break flow sediment transport modeling Harten-Lax-van Leer (HLL) and Harten-Lax-van Contact (HLLC) fluxfunctions discontinuous Galerkin scheme