40 research outputs found
The impact of watershed management on coastal morphology: A case study using an integrated approach and numerical modeling.
No full textCoastal morphology evolves as the combined result of both natural- and human- induced factors that cover a wide range of spatial and temporal scales of effect. Areas in the vicinity of natural stream mouths are of special interest, as the direct connection with the upstream watershed extends the search for drivers of morphological evolution from the coastal area to the inland as well. Although the impact of changes in watersheds on the coastal sediment budget is well established, references that study concurrently the two fields and the quantification of their connection are scarce. In the present work, the impact of land-use changes in a watershed on coastal erosion is studied for a selected site in North Greece. Applications are based on an integrated approach to quantify the impact of watershed management on coastal morphology through numerical modeling. The watershed model SWAT and a shoreline evolution model developed by the authors (PELNCON-M) are used, evaluating with the latter the performance of the three longshore sediment transport rate formulae included in the model formulation. Results document the impact of crop abandonment on coastal erosion (agricultural land decrease from 23.3% to 5.1% is accompanied by the retreat of ~ 35 m in the vicinity of the stream mouth) and show the effect of sediment transport formula selection on the evolution of coastal morphology. Analysis denotes the relative importance of the parameters involved in the dynamics of watershed–coast systems, and – through the detailed description of a case study – is deemed to provide useful insights for researchers and policy-makers involved in their study
Rapport III. 8 Construction d'un algorithme mixte aux éléments finis et aux différences finies pour l'étude de l'étalement d'un panache
No full textDevelopment 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
Final phase-resolving Boussinesq-type models (D42)
No full textThe design of structures to be built in the nearshore region generally involves the evaluation of different possible layouts, under the effects of local wave and cunents conditions, with the aim of minimizing costs and maximizing the desired results. In particular the design of lowcrested structures involves optimisation of several parameters, which influence both the position, and the shape of the structures. The possible layout of the structures to be designed can be tested experimentally in wave tanks and wave flumes using adequate scale models. An alternative and attractive procedure is to employ suitable numerical and mathematical models. In principle, a very advanced numerical model, able to conectly simulate all the nearshore phenomena (turbulence, waves, currents, sediment transport, etc.) could be equivalent or even superior to a physical model. In practice, the numerical models currently employed in engineering activities, use several assumptions and simplifications: the phenomena that can be simulated strictly depend on the governing equations solved by the model. Indeed, the great advantage of numerical and mathematica! models is that their application is usually much less expensive than physical ones: it is certainly more economie to modify a computer file describing the bathymetry of the area under investigation than rebuild a physical model layout. This report is structured into two discrete sections, the first one contributed by AUTh and the second one by UR3. In the first section a 2DH higher-order Boussinesq-type model combined with a porous flow model, developed tor simulating flow around porous submerged structures is presented. On the other hand, in the second section enhancements on the applicability of Boussinesq-type equations (BTE) into the surf and swash zone are described.Delo
A Model and a Numerical Solver for the Flow Generated by an Air-Bubble Curtain in Initially Stagnant Water
No full textAdvanced physical techniques for radio channel modeling.
No full textWireless 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
Advanced physical techniques for radio channel modeling
No full textEThOS - Electronic Theses Online ServiceGBUnited Kingdo
BREAKING WAVES OVER SUBMERGED, MONOLITHIC BREAKWATER
No full textΣτη 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
ANALYTICAL CALCULATION OF THE BUOYANCY AND THE HORIZONTAL FORCE ACTING ON A FLOATING BREAKWATER IN HEAVE MOTION
No full textΣτην 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
