Oil Spill Modeling Aiming at the Protection of Ports and Coastal Areas

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Modelling the water mass exchange through navigational channels connecting adjacent coastal basins - application to the Channel of Potidea (North Aegean Sea)

The research objective is the detection of the mechanism of the water mass exchange through a navigational channel connecting two adjacent coastal basins. The research involves the application of a mathematical model in parallel to in-situ measurements. The hydrodynamic circulation in the greater area of the NW Aegean Sea is modeled by means of a barotropic circulation model. Wind, Coriolis and Tide are the main forcings taken into account. The flow through the channel is resolved at a subgrid scale by means of a local open channel flow model. The comparison between field measurements, recorded during a limited period, and the model results supports the model verification. The study is integrated by an operational application of the model under various realistic forcings. The results help to gain a better understanding of the mechanisms regulating the water mass exchange and the consequent interaction between two adjacent connected coastal basins. From the case study of the Potidea channel it is revealed that the water mass exchange under mean wind forcing is of the same order as the one induced by the tidal forcing

Advanced physical techniques for radio channel modeling

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Advanced physical techniques for radio channel modeling.

Wireless technology constitutes the basis of the majority of modem communication systems. The deployment of wireless systems mainly concerns data services such as mobile and broadcasting applications, or target identification and military services. The key element for the successful planning of any kind of wireless network is the detailed and in depth knowledge of the propagation channel. The mobility of the user and the physical obstructions that may intervene in the propagation path between the communication points cause distortion to the transmitted information. The understanding of the propagation conditions and the channel characterisation is achieved either by extensive measurement campaigns or by employing sophisticated propagation algorithms. Since the measurement campaign is an expensive and time consuming task, contemporary research is focused on the development of deterministic models that can accurately predict the channel behaviour in real environments. The demand for high data delivery services in modem communication systems requires the utilisation of large bandwidth at high frequency regions of the available spectrum. Therefore, asymptotic high frequency modelling techniques and relevant algorithms have emerged as the major propagation modelling tools for modern radio systems analysis and design. In this thesis, we address the problem of high frequency diffraction over complex structures and scenarios that incorporate a cascade of physical canonical obstructions in the propagation path between the two ends. New formulations are derived for field predictions over rounded surfaces and a cascade of multi-shape structures. The Uniform Theory of Diffraction (UTD) is applied in all the work and it is further extended to account for transition zone diffraction over scenarios that incorporate arbitrary multiple canonical objects being multi-shaped in nature. The concept of continuity equations and slope diffraction are also emphasized. The simulation results show uniform and accurate field predictions and extensive comparison tests are performed with other diffraction theories and measurements. The developed formulations are incorporated in a propagation tool for irregular terrain channel modelling. An unambiguous terrain modelling algorithm is synthesized and used to assign optimum fitted canonical shapes to the terrain irregularities. The results of the simulations are compared with real measurements over irregular scenarios and a very good fit is observed. The importance of the choice of the used canonical shape to the terrain modelling is also highlighted

Rapport III. 8 Construction d'un algorithme mixte aux éléments finis et aux différences finies pour l'étude de l'étalement d'un panache

Development of a mixed algorithm of finite elements and finite differences in order to study the growing of a buyoant jet. Numerical modeling of thermal wastes in the atmosphere in regional scale has two principal difficulties : the first is related to the proper description of boundary conditions on an irregular topography and the second concerns the assumption of the local incompressibility of the flow. The authors present a mixed algorithm, composed by one-dimensional finite elements along the vertical direction and by finite differences in the horizontal plan, permitting to take in accound easely the irregular topography. At every time the divergence of the velocity vector tends to zero by applying a perturbation over the pressure.La modélisation numérique des rejets thermiques dans 1'atmosphère à 1’échelle régionale présente deux difficultés principales : la première est liée à la description correcte des conditions aux limites sur une topographie de site en gênerai irrégulière et la deuxième concerne 1'hypothèse de 1'incompressibilité locale de 1'écoulement. Les auteurs présentent un algorithme mixte, composé d'éléments finis unidimensionnels dans le sens vertical et de différences finies sur le plan horizontal permettant de tenir compte aisément de la topographie irrégulière. À tout instant, la divergence du vecteur vitesse tend vers zéro en appliquant une perturbation sur la pression.Ganoulis Jacques, Koutitas C. Rapport III. 8 Construction d'un algorithme mixte aux éléments finis et aux différences finies pour l'étude de l'étalement d'un panache. In: Rejets de chaleur à l'atmosphère. Gestion des calories et hydraulique associée. Compte-rendu des XVIes journées de l'hydraulique. Paris, 16-18 septembre 1980. Tome 2, 1980

ANALYTICAL CALCULATION OF THE BUOYANCY AND THE HORIZONTAL FORCE ACTING ON A FLOATING BREAKWATER IN HEAVE MOTION

Στην συγκεκριμένη εργασία εξετάζεται η άνωση και η οριζόντια δύναμη που ασκείται σε πλωτό κυματοθραύστη με κατακόρυφη ελευθερία κίνησης. Για τον υπολογισμό τόσο της οριζόντιας όσο και της κατακόρυφης δύναμης καταστρώνονται αναλυτικές λύσεις. Τα αποτελέσματα συγκρίνονται με δημοσιευμένα αριθμητικό και πειραματικά αποτελέσματα γεγονός που επιβεβαιώνει την αξιοπιστία του μαθηματικού ομοιώματος.ln the present study the buoyancy and the horizontal force acting on a floating breakwater in heave motion are examined. Analytical expressions are derived for both cases. The results of the present study are well comparable to published numerical and experiniental results, a fact that confirms the reliability of the mathematical model

BREAKING WAVES OVER SUBMERGED, MONOLITHIC BREAKWATER

Στη συγκεκριμένη εργασία εξετάζεται η αποτελεσματικότητα των βυθισμένων, αδιαπέρατων, μονολιθικών κυματοθραυστών με κατακόρυφα μέτωπα με ένα μαθηματικό ομοίωμα πεπερασμένων διαφορών το οποίο βασίζεται στις εξισώσεις Boussinesq. Ιδιαίτερη έμφαση δίνεται στην προσομοίωση της Θραύσης των κυματισμών πάνω στη βυθισμένη κατασκευή, η οποία αποτελεί τον κύριο μηχανισμό σκέδασης της ενέργειας. Τα αριθμητικά αποτελέσματα συγκρίνονται με ικανοποιητική ακρίβεια με αντίστοιχα δημοσιευμένα πειραματικά.The efficiency of submerged, monolithic breakwaters is studied in the present paper, using a finite-difference, mathematical model based on the Boussinesq type equations. Emphasis is given on the numerical modeling of wave breaking over the submerged structure which is the main energy dissipation mechanism. Numerical results are compared to experimental results satisfactorily

WAVE AND WAVE INDUCED CURRENT EFFECTS ON THE POLLUTANT DISPERSION IN THE NEARSHORE ZONE

Στην εργασία αυτή εξετάζεται η επίδραση των κυματισμών και των κυματογενών ρευμάτων στη διάχυση και διασπορά των ρύπων στην παράκτια ζώνη. Η επίδρασή τους προσομοιώνεται με τη χρήση δύο μαθηματικών μοντέλων. Στις εφαρμογές θα πρέπει να χρησιμοποιηθούν συντελεστές διασποράς που διαφέρουν ανάλογα με τη κλίμακα των μοντέλων που χρησιμοποιούνται. Στα μοντέλα μικρής κλίμακας ο συντελεστής προσομοιώνει την ανάμιξη λόγω της ύπαρξης των θραυόμενων κυματισμών, ενώ στα μοντέλα μεγάλης κλίμακας την μεταφορά λόγω των κυματογενών ρευμάτων στο εσωτερικό του υπολογιστικού βρόγχου.In the present work the wave and wave-induced current effects on the pollutant diffusion and dispersion in the nearshore are examined. Their effects are simulated using two mathematical models. In the applications two difierent values of the dispersion coefficient, tor large and small scale models, are used. ln the small scale models the coefficient simulates the mixing due to the wave breaking while in the large scale models the effect of advectlon due to nearshore wave induced currents