Relevance of the dissertation is determined by the object of research – the influence of logistical factors on transport flows distribution. The growth of world economics, business globalization, progress in technology skills extends the distances between geographical points of raw materials resources, manufacturers and consumers. Due to the membership in the European Union (EU) Lithuania has got new opportunities for international trade growth, and all the Eastern Baltic countries have become the buffer region for the EU trading with the countries of the Eastern Europe and Asia. A proper transport policy and infrastructure development would increase significantly the GNP in warehousing, transport and distribution sectors. Forecasting of potential transport flows according to logistical requirements of freight suppliers is most important for transport network optimization. Scientific problem. Contemporary transport engineering theory approaches the peculiarities of transport flows formation too narrowly, only as an analysis of internal factors determining freight flows. There is no analysis of external factors. Many researchers assume that transport flows are determined only by the existing transport network and its characteristics. Other researchers consider transport flows as a result of logistic elements only. The estimating of internal and external logistical factors provides a possibility to forecast the transport flows. Aim of the research is to create a model of... [to full text] / Pasaulio ekonomikos augimas, spartėjantis globalizacijos procesas, technologijų pažanga didina atstumus tarp žaliavų gavimo, gamybos ir pagamintų prekių vartojimo taškų. Lietuva tapusi Europos Sąjungos nare, tampa Europos Sąjungos buferine zona prekybiniams mainams su Rytų Europos ir Azijos šalimis. Lietuvos transporto sistemą būtina pritaikyti esamiems ir potencialiems tarptautiniams krovinių srautams aptarnauti. Transporto srautų formavimosi išorinių veiksnių nustatymas ir įvertinimas Lietuvos transporto strategijoje gali suteikti šaliai didžiulį ekonominį potencialą.

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This thesis investigates several aspects of stratified flow over isolated topography in ocean, lake, and atmospheric settings. Three major sub-topics are addressed: steady, inviscid internal waves trapped over topography in a pycnocline stratification, topographically generated internal waves and their interaction with the viscous bottom boundary layer, and flow over large-scale crater topography in the atmosphere. The first topic examines the conditions that lead to very large internal waves trapped over topography in a fluid with a pycnocline stratification. This type of stratification is connected to ocean or lake settings. The steady-state Euler equations of motion are used to derive a single partial differential equation for the isopycnal displacement in supercritical flows under two conditions: a vertically varying background current under the Boussinesq approximation and a constant background current under non-Boussinesq conditions. A numerical method is developed to solve these equations for an efficient exploration of parameter space. Very large waves are found over depression topography when the background flow speed is close to a limiting value. Variations in the background current are examined, as well as comparisons between Boussinesq and non-Boussinesq results. The second topic aims to extend the above subject by considering unsteady, viscous flows. Once again, supercritical flow over topography in a pycnocline stratification generates internal waves. These internal waves interact with the viscous bottom boundary layer to produce bottom boundary instabilities. The three-dimensional aspects of these instabilities are studied under changes in viscosity. The boundary layer instabilities have important implications for sediment transport in the coastal oceans or lakes. Lastly, the final topic is motivated by the connection between dust streaks on the Martian surface and crater topography. Flow over a large 100-km diameter crater is examined with numerical simulations conducted using the Weather Research and Forecasting model. Modifications to the stratification and topography are applied. It is found that a large hydraulic structure of amplitude comparable to the crater depth forms in many cases. This structure may have important implications for dust transport in the atmosphere. In addition, Martian atmospheric parameters are used to study the flow properties under Mars-like conditions.

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Botnets are becoming the predominant threat on the Internet today and is the primary vector for carrying out attacks against organizations and individuals. Botnets have been used in a variety of cybercrime, from click-fraud to DDOS attacks to the generation of spam. In this thesis we propose an approach to detect botnet activity using two different strategies both based on machine learning techniques. In one, we examine the network flow based metrics of potential botnet traffic and show that we are able to detect botnets with only data from a small time interval of operation. For our second technique, we use a similar strategy to identify botnets based on their potential fast flux behavior. For both techniques, we show experimentally that the presence of botnets may be detected with a high accuracy and identify their potential limitations. / Graduate

In the present study a parallel three dimensional Volume of Fluid (VOF) method is developed to simulate Marangoni force in immiscible fluids with variable surface tension. Conservation equations are solved based on cell-averaged one-field volume tracking scheme. Evaluating the convective term in the energy equation along the boundary between the fluids highly depends on the position and orientation of the interface; hence, using average cell values simply ignores the interface shape and leads to computational uncertainty. As a remedy to this issue, the original idea behind the volume tracking method is used not only to advect mass and momentum but also energy across cells. To verify the proposed algorithm, results are compared against theoretically predicted thermocapillary migration velocity of a droplet at the limit of zero Marangoni number. However, at relatively high Marangoni numbers, thermal boundary layers are very thin and challenging to resolve. To demonstrate the capabilities of the heat transfer module, simulations of a Fluorinert droplet moving in silicon oil under applied temperature gradient in microgravity are compared against the available experimental results and the migration velocity of the droplet are reported.

Significant progress has been made towards developing an effective solution method for predicting low-speed flows through vertical-axis wind turbines. A Godunov-type finite-volume scheme has been developed for the solution of the Euler equations in two-dimensions on a multi-block mesh. The proposed algorithm features a parallel block-based adaptive mesh refinement scheme and a mesh adjustment procedure to enable straightforward meshing of irregular solid boundaries. A low-Mach-Number preconditioner is used in conjunction with a dual timestepping scheme to reduce the computational costs of simulating low-speed unsteady flows. A second-order backwards differencing time-marching scheme is used for the outer physicaltime discretization, and an explicit optimally-smoothing multi-stage time-stepping scheme with multigrid acceleration is used for the inner pseudo-time loop. Results are presented for various low-speed flows that demonstrate the suitability of the algorithms for wind turbine flows. Additional theory and discussion are also presented for extension of the schemes to the full Navier-Stokes equations.

In the present study a parallel three dimensional Volume of Fluid (VOF) method is developed to simulate Marangoni force in immiscible fluids with variable surface tension. Conservation equations are solved based on cell-averaged one-field volume tracking scheme. Evaluating the convective term in the energy equation along the boundary between the fluids highly depends on the position and orientation of the interface; hence, using average cell values simply ignores the interface shape and leads to computational uncertainty. As a remedy to this issue, the original idea behind the volume tracking method is used not only to advect mass and momentum but also energy across cells. To verify the proposed algorithm, results are compared against theoretically predicted thermocapillary migration velocity of a droplet at the limit of zero Marangoni number. However, at relatively high Marangoni numbers, thermal boundary layers are very thin and challenging to resolve. To demonstrate the capabilities of the heat transfer module, simulations of a Fluorinert droplet moving in silicon oil under applied temperature gradient in microgravity are compared against the available experimental results and the migration velocity of the droplet are reported.

Significant progress has been made towards developing an effective solution method for predicting low-speed flows through vertical-axis wind turbines. A Godunov-type finite-volume scheme has been developed for the solution of the Euler equations in two-dimensions on a multi-block mesh. The proposed algorithm features a parallel block-based adaptive mesh refinement scheme and a mesh adjustment procedure to enable straightforward meshing of irregular solid boundaries. A low-Mach-Number preconditioner is used in conjunction with a dual timestepping scheme to reduce the computational costs of simulating low-speed unsteady flows. A second-order backwards differencing time-marching scheme is used for the outer physicaltime discretization, and an explicit optimally-smoothing multi-stage time-stepping scheme with multigrid acceleration is used for the inner pseudo-time loop. Results are presented for various low-speed flows that demonstrate the suitability of the algorithms for wind turbine flows. Additional theory and discussion are also presented for extension of the schemes to the full Navier-Stokes equations.

Discontinuous dynamical system defined by impulsive autonomous differential equation is a field that has actually been considered rarely. Also, the properties of such systems have not been discussed thoroughly in the course of mathematical researches so far. This thesis comprises two parts, elaborated with a number of examples. In the first part, some results of the previous studies on the classical dynamical system are exposed. In the second part, the definition of discontinuous dynamical system defined by impulsive autonomous differential equation is formulated, and its properties are investigated, in the view of the known results of the studies on the classical dynamical system and impulsive differential equations.