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International Journal of Sediment Research 2014年第3期29卷 304-315页

作者： Achilleas g.SAMARAS christopher g koutitas Research Fellow CIRI-ECFluid Dynamics Research UnitUniversity of BolognaVia del Lazzaretto 15/5Bologna 40131Italy Department of Civil Engineering Aristotle University of ThessalonikiUniversity Campus

Climate change is an issue of major concern *** impact on the natural and human environment is studied intensively,as the expected shift in climate will be significant in the next few *** experience shows that the effects will be critical in coastal areas,resulting in erosion and inundation phenomena *** addition to that,coastal areas are subject to "pressures" from upstream watersheds in terms of water quality and sediment *** present paper studies the impact of climate change on sediment transport and morphology in the aforementioned coupled *** study regards a sandy coast and its upstream watershed in Chalkidiki,North greece;it is based on:(a)an integrated approach for the quantitative correlation of the two through numerical modeling,developed by the authors,and(b)a calibrated application of the relevant models Soil and Water Assessment Tool(SWAT)and PELNCON-M,applied to the watershed and the coastal zone,*** examined climate change scenarios focus on a shift of the rainfall distribution towards fewer and more extreme rainfall events,and an increased frequency of occurrence of extreme wave *** indicate the significance of climatic pressures in wide-scale sediment dynamics,and are deemed to provide a useful perspective for researchers and policy planners involved in the study of coastal morphology evolution in a changing climate.

关键词： Climate change Sediment transport Coastal morphology Integrated approach Numerical modeling

Incremental Static Analysis of 2D Flow by Inter-Colliding Point-Particles and Use of Incompressible Rhombic Element

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Open Journal of Civil Engineering 2016年第3期6卷 397-409页

作者： Panagis g. Papadopoulos christopher g. koutitas Panos P. Lazaridis Department of Civil Engineering Aristotle University of Thessaloniki Thessaloniki Greece

A simple method is proposed, for incremental static analysis of a set of inter-colliding particles, simulating 2D flow. Within each step of proposed algorithm, the particles perform small displacements, proportional to the out-of-balance forces, acting on them. Numerical experiments show that if the liquid is confined within boundaries of a set of inter-communicating vessels, then the proposed method converges to a final equilibrium state. This incremental static analysis approximates dynamic behavior with strong damping and can provide information, as a first approximation to 2D movement of a liquid. In the initial arrangement of particles, a rhombic element is proposed, which assures satisfactory incompressibility of the fluid. Based on the proposed algorithm, a simple and short computer program (a “pocket” program) has been developed, with only about 120 Fortran instructions. This program is first applied to an amount of liquid, contained in a single vessel. A coarse and refined discretization is tried. In final equilibrium state of liquid, the distribution on hydro-static pressure on vessel boundaries, obtained by proposed computational model, is found in satisfactory approximation with corresponding theoretical data. Then, an opening is formed, at the bottom of a vertical boundary of initial vessel, and the liquid is allowed to flow gradually to an adjacent vessel. Almost whole amount of liquid is transferred, from first to second vessel, except of few drops-particles, which remain, in equilibrium, at the bottom of initial vessel. In the final equilibrium state of liquid, in the second vessel, the free surface level of the liquid confirms that the proposed rhombing element assures a satisfactory incompressibility of the fluid.

关键词： 2D Flow Simulation Inter-Colliding Point-Particles Incremental Static Analysis Incompressible Rhombic Element Hydro-Static Pressure Distribution Flow from a Vessel to Another One “Pocket” Special Purpose Computer Program

Simplified Coarse-grained Dynamic Model for Real gases

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Open Journal of Physical Chemistry 2017年第2期7卷 50-71页

作者： Panagis g. Papadopoulos christopher g. koutitas Yannis N. Dimitropoulos Elias C. Aifantis Department of Civil Engineering Aristotle University of Thessaloniki Thessaloniki Greece Department of Chemistry University of Ioannina Ioannina Greece

A simplified model is proposed for an easy understanding of the coarse-grained technique and for achieving a first approximation to the behavior of gases. A mole of a gas substance, within a cubic container, is represented by six particles symmetrically moving. The impacts of particles on container walls, the inter-particle collisions, as well as the volume of particles and the inter-particle attractive forces, obeying a Lennard-Jones curve, are taken into account. Thanks to the symmetry, the problem is reduced to the nonlinear dynamic analysis of a SDOF oscillator, which is numerically solved by a step-by-step time integration algorithm. Five applications of proposed model, on Carbon Dioxide, are presented: 1) Ideal gas in STP conditions. 2) Real gas in STP conditions. 3) Condensation for small molar volume. 4) Critical point. 5) Iso-kinetic energy curves and iso-therms in the critical point region. Results of the proposed model are compared with test data and results of the Van der Waals model for real gases.

关键词： Real gases Coarse-grained Molecular Dynamics Particles Volume Inter-Particle Attractive Forces Lennard-Jones Curve Step-by-Step Time Integration Algorithm Condensation Critical Point Iso-Kinetic Energy Curves Iso-Therms Van der Waals Model

Simplified Step-by-Step Nonlinear Static Program Investigating Equilibrium Conditions of Electrons in Atom and Ionization Energies: Case Study on Argon

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Open Journal of Physical Chemistry 2018年第2期8卷 33-56页

作者： Panagis g. Papadopoulos christopher g. koutitas Yannis N. Dimitropoulos Elias C. Aifantis Structural Engineering Division Civil Engineering Department Aristotle University of Thessaloniki Thessaloniki Greece Fluid Mechanics Division Civil Engineering Department Aristotle University of Thessaloniki Thessaloniki Greece Physical Chemistry Division Chemistry Department University of Ioannina Ioannina Greece Aristotle University of Thessaloniki Thessaloniki Greece Michigan Technological University Houghton MI USA Beijing University of Civil Engineering and Architecture Beijing China ITMO University St. Petersburg Russia Togliatti State University Togliatti Russia

For investigation of equilibrium conditions of electrons in an atom, and Ionization Energies of Elements, a simplified deterministic static model is proposed. The electrons are initially uniformly and sparsely arranged on the outer surface of nucleus. Then, by taking into account the nucleus-electron interaction (attractive and repulsive) and the mutual electron-electron repulsions, and by a simple step-by-step nonlinear static analysis program, all the electrons are found to equilibrate on the outer surface of the same sphere, which is concentric and larger than nucleus. In a second stage, starting from an equilibrium sphere of electrons, one of the electrons is subjected to gradual forced removal, radially and outwards with respect to nucleus. Within each removal step, the produced work increment is determined and the increments are summed. When no more significant attraction is exerted by nucleus to removed electron, the total work gives the Ionization Energy. After removing of single electron, the remaining electrons fall on a lower shell, that is, they equilibrate on the outer surface of a smaller concentric sphere. For nucleus-electron interaction, an L-J (Lennard-Jones) type curve, attractive and repulsive, is adopted. When the parameter of this curve is n > 1.0, the Ionization Energy exhibits an upper bound. As parameter n increases from 1.0 up to 2.0, the attractive potential of L-J curve is gradually weakened. The proposed model is applied on Argon. It is observed that, as the number of electrons increases, the radius of equilibrium sphere increases, too, whereas the attractive nucleus-electron potential is reduced;thus the Ionization Energy is reduced, too. Particularly, as the number of electrons and the radius of equilibrium sphere exceed some critical values, the above two last quantities exhibit abrupt falls. A regular polyhedron is revealed, which can accommodate Elements up to atomic number Z = 146, that is 28 more than Z = 118 of existing last Elem

关键词： Ionization Energy Electrostatic Laws Lennard-Jones Curve Incremental Nonlinear Static Analysis Atomic Radius Rhombic Dodecahedron Regular Polyhedron

Simple Rational Model for Discharge of Batteries with Aqueous Electrolytes, Based on Nernst Equation

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Open Journal of Physical Chemistry 2021年第1期11卷 1-11页

作者： Panagis g. Papadopoulos christopher g. koutitas Christos g. Karayannis Panos D. Kiousis Yannis N. Dimitropoulos Department of Civil Engineering Aristotle University of Thessaloniki Thessaloniki Greece Department of Civil Engineering Democritus University of Thrace Xanthi Greece Department of Structural and geotechnical Engineering Colorado School of Mines Golden CO USA Department of Chemistry University of Ioannina Ioannina Greece

A simple rational model is proposed for discharge of batteries with aqueous electrolytes, based on Nernst equation. Details of electrode kinetics are not taken into account. Only a few overall parameters of the battery are considered. A simple algorithm, with variable time step-length Δt, is presented, for proposed model. The model is first applied to Daniel cell, in order to clarify concepts and principles of battery operation. It is found that initial pinching, in time-history curve of voltage E-t, is due to initial under-concentration of product ion. Then, model is applied to a lead-acid battery. In absence of an ion product, and in order to construct nominator of Nernst ratio, such an ion, with coefficient tending to zero, is assumed, thus yielding unity in nominator. Time-history curves of voltage, for various values of internal resistance, are compared with corresponding published experimental curves. Temperature effect on voltage-time curve is examined. Proposed model can be extended to other types of batteries, which can be considered as having aqueous electrolytes, too.

关键词： Battery Aqueous Electrolyte Discharge Nernst Equation Daniel Cell Lead-Acid Battery Temperature Effect

Simple Program for Step-by-Step Time Integration in Chemical Kinetics, Applied to Simple Model for Hydrogen Combustion

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Open Journal of Physical Chemistry 2020年第2期10卷 99-116页

作者： Panagis g. Papadopoulos christopher g. koutitas Panos D. Kiousis Christos g. Karayannis Yannis N. Dimitropoulos Structural Engineering Laboratory Civil Engineering Department Aristotle University of Thessaloniki Thessaloniki Greece Computational Fluid Engineering Laboratory Civil Engineering Department Aristotle University of Thessaloniki Thessaloniki Greece Structural and geotechnical Engineering Laboratory Civil and Environmental Engineering Department Colorado School of Mines Golden USA Concrete Structures Laboratory Civil Engineering Department Democritus University of Thrace Xanthi Greece Physical Chemistry Laboratory Chemistry Department University of Ioannina Ioannina Greece

A simple algorithm is proposed for step-by-step time integration of stiff ODEs in Chemical Kinetics. No predictor-corrector technique is used within each step of the algorithm. It is assumed that species concentrations less than 10-6 mol·L-1 do not activate any chemical reaction. So, within each step, the time steplength Δt of the algorithm is determined from the fastest reaction rate maxR by the formula Δt = 10-6mol·L-1/max R. All the reversible elementary reactions occur simultaneously;however, by a simple book-keeping technique, the updating of species concentrations, within each step of the algorithm, is performed within each elementary reaction separately. The above proposed simple algorithm for Chemical Kinetics is applied to a simple model for hydrogen combustion with only five reversible elementary reactions (Initiation, Propagation, First and Second Branching, Termination by wall destruction) with six species (H2, O2, H, O, HO, H2O). These five reversible reactions are recommended in the literature as the most significant elementary reactions of hydrogen combustion [1] [2]. Based on the proposed here simple algorithm for Chemical Kinetics, applied to the global mechanism of proposed five reversible elementary reactions for hydrogen combustion, a simple and short computer program has been developed with only about 120 Fortran instructions. By this proposed program, the following are obtained: 1) The total species concentration of hydrogen combustion, starting from the sum of initial reactants concentrations [H2] + [O2], gradually diminishes, due to termination reaction by wall destruction, and tends to the final concentration of the product [H2O], that is to the 2/3 of its initial value, in accordance to the established overall stoichiometric reaction of hydrogen combustion 2H2 + O2 → 2H2O. 2) Time-histories for concentrations of main species H2, O2, H, H2O of hydrogen combustion, in explosion and equilibrium regions, obtained by the proposed program, are co

关键词： Chemical Kinetics Step-by-Step Time Integration Elementary Reactions Hydrogen Combustion Ignition Delay Explosion

Oil Spill Dispersion Forecasting with the Aid of a 3D Simulation Model

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Journal of Physical Science and Application 2012年第10期2卷 448-453页

作者： Antigoni Zafirakou-Koulouris christopher koutitas Sarantis Sofianos Anneta Mantziafou Margarita Tzali Sofia C. Dermissi Department of Civil Engineering Aristotle University of Thessaloniki Thessaloniki 54006 Greece Ocean Physics and Modelling group (OPAM) Department of Physics University of Athens Athens 15784 Greece

The simulation of the transport and fate of an oil slick, accidentally introduced in the marine environment, is the focus of this research. An oil spill dispersion forecasting system (DIAVLOS forecasting system), based on wind, wave and ocean circulation forecasting models is developed. The 3-D oil spill model, by the University of Thessaloniki, is based on a Lagrangian (tracer) model that accounts for the transport-diffusion-dispersion and physicochemical evolution of an oil slick. The high resolution meteorological, hydrodynamic and wave models are coupled with the operational systems ALERMO and SKIRON of the University of Athens. The modelling system was successfully assembled and tested under theoretical and realistic scenarios, in order to be applied in forecasting mode and be used by local authorities when an accident occurs. As a result, a 48-hours oil spill dispersion forecasting system was synthesized aiming primarily at the oil spill management at the Burgas-Alexandroupolis oil-pipe terminal, part of a greater busy coastal basin in North Aegean.

关键词：模型预测三维仿真分散性溢油预报系统漏油事件海洋环境石油泄漏