Anastasios Nikolaos Georgoulas

The prediction of flow pattern transitions is extremely important to understand the coupling of thermal and fluid dynamic phenomena in two phase systems and it contributes to the optimum design of heat exchangers. Two phase flow regimes have been extensively studied under controlled mass flow rate and velocity. On the other hand, less effort has been spent in the literature on the cases where the flow motion is purely thermally induced and consequently the mass flow rate or the velocity of the phases are not known a priori. In the present work, flow pattern transitions and bubble break-up and coalescence events have been investigated in a passive two phase wickless capillary loop, where the mass flow rate is intrinsically not controllable. Modified Froude, Weber and Bond numbers have been introduced, considering the actual acceleration of the fluid and the length of the bubble as merit parameters for the transitions. The proposed nondimensional investigation was developed by analysing experimental data obtained with ethanol and FC-72, as working fluids, different heat input levels (from 9 to 24 W) as well as three different gravity levels (through a parabolic flight campaign). A new empirical diabatic flow pattern map for accelerated two-phase capillary flows is presented, together with quantitative criteria for the calculation of the flow regime transitions, defining the physic limits for the bubble coalescence and break-up. This kind of new regime maps will be useful to the further development of comprehensive designing tools for passive two-phase wickless heat transfer devices.

This poster presents a droplet of water after impacting on a metallic mesh. The model is using an enhanced VOF-based numerical code where a smoothing approach that filters out spurious current velocities as well as Kistler's dynamic contact angle treatment to accurately account for surface wettability effects have been implemented within the general framework of the open-source CFD toolbox OpenFOAM, for isothermal droplet impact phenomena. The grid generation was performed by using OpenFOAM’s utility snappyHexMesh. The aim of this work is to illustrate that the proposed CFD-based numerical simulation tool can be valuable in extracting quantitative information that cannot be extracted from the experimental measurements and hence give further insight into the complex underpinned mechanisms in the proposed droplet impact phenomenon. An example of these information includes the percentage of liquid that remains entrapped on the metallic mesh, over time. https://doi.org/10.1103/APS.DFD.2018.GFM.P0036

In the present paper, an enhanced Volume Of Fluid (VOF) based numerical simulation framework is applied for the conduction of parametric numerical experiments, aiming to investigate break-up phenomena of elongated vapour slugs, within circular mini-channels. The effect of fundamental controlling parameters, in the resulting break-up characteristics, is examined. In more detail, four different series of parametric numerical experiments of isolated liquid slugs within a mini-channel were performed, investigating the effects of Applied Pressure Drop (APD), Surface Tension Coefficient (STC), Initial Liquid Film Thickness (ILFT) and Applied Heat Flux (AHF), on the vapour slug dynamics. Such break-up phenomena have been observed experimentally, in the past, within mini-channel branches of a hybrid thermosyphon/pulsating heat pipe device, under micro-gravity conditions. The simulation results identify three prevailing regimes. A "full break-up" regime, a "partial break-up" regime and a "no break-up" regime. It is characteristic that an entrainment of liquid droplets at the trailing edge of the vapour slugs, is responsible for their subsequent "full break-up", into a leading and a trailing bubble in each case, as it is identified from the numerical simulations. Moreover, it is quite interesting that the value of the AHF, does not seem to influence the resulting break-up regime and its main characteristics.

The thermo-fluid dynamic behaviour of a Single Loop Pulsating Heat Pipe (SLPHP) has been characterized during the 66 th ESA Parabolic. The SLPHP, with a 2 mm inner diameter, has been tested in bottom heated mode, varying the working fluid (FC-72 and ethanol), the heat power input (from 1W to 24W) and the gravity level (0.01g, 1g and 1.8g). Two transparent tubes connect the evaporator and the condenser, allowing local fluid flow visualization. A set of three-dimensional maps, derived from semi-empirical correlations usually adopted in literature to estimate the critical diameter at different gravity levels are drawn for the different fluids tested, liquid velocities and fluid temperatures. These maps are used to compare the flow velocity observed experimentally with the critical diameter value calculated. Additionally, an enhanced Volume of Fluid (VOF) model is utilised to simulate an imposed slug flow within a straight 2 mm inner diameter channel, replicating the same experimental conditions, with the primary aim to study the effect of the vapour bubble length and the liquid film thickness on the generated elongated bubble dynamics, in microgravity conditions.

Flow boiling in micro-channels constitutes an effective cooling method which has been proven experimentally to be able to remove significantly high heat fluxes, while keeping the component of interest at an appropriate operating temperature. Plenty of experimental works exist in literature so far, but appropriate models to predict flow boiling heat transfer are still lacking or they are based on unrealistic assumptions. In the present investigation, direct numerical simulations of vapour slug growth associated with flow boiling within micro-channels are performed, utilising an enhanced Volume of Fluid (VOF) based method that accounts for spurious currents reduction and phase-change. The effect of various micro-structured finned patterns in the heated wall of the channels is numerically investigated. The main aim is to give further insight on the effect of surface structuring on flow boiling in the slug flow regime. The utilised, enhanced VOF-based model is implemented in OpenFOAM CFD toolbox. Initially, comparison with literature available numerical results for a straight wall circular micro-channel is carried out. After the proposed comparison, different geometrical configurations of the heated part of the utilised channel are implemented, keeping the same operating and initial conditions. In more detail, various fin patterns of rectangular cross-section are introduced in the heated wall of the channel. The analysis of the results reveals in order to have an increase in the heat transfer coefficient an optimum geometric configuration is needed.

Loop Heat Pipes (LHP) and other two-phase passive thermal devices, such as Heat Pipe Loops (HPL), represent a very attractive solution for the energy management of systems with a distributed presence of heating and cooling zones that request fast start-up, reliability, low cost and lightness. Even if the usual application for these devices is in the space sector, there could be a potential significant application for the automotive industry, for the development of embedded thermal networks for Full Electric Vehicles (FEV), in order for example to recover the waste heat for cabin heating and cooling or to improve the aerodynamic efficiency. In the present investigation, the possibility to implement a new thermal control for an electric vehicle comprising from Heat Pumps and Loop Heat Pipes, is here evaluated. In more detail, a 1-D Lumped Parameter Model that is able to predict the transient behaviour of a LHP in response of varying boundary and initial conditions, is developed and validated against literature available experimental data. A novel methodology for treating numerically the condenser is proposed and validated for three different working fluids. An extensive parametric analysis is also conducted, showing the robustness of the thermal solution for different conditions and proving the possibility of using the proposed numerical code both for feasibility studies and for optimization purposes. A feasibility study utilizing the proposed model is also conducted and the results indicate that an array of LHPs can effectively transport heat from the motor section of the vehicle to the underbody, reducing significantly the aerodynamic losses.

A numerical framework for modelling micro-scale multiphase flows with sharp interfaces has been developed. The suggested methodology is targeting the efficient and yet rigorous simulation of complex interface motion at capillary dominated flows (low capillary number). Such flows are encountered in various configurations ranging from micro-devices to naturally occurring porous media. The methodology uses as a basis the Volume-of-Fluid (VoF) method combined with additional sharpening smoothing and filtering algorithms for the interface capturing. These algorithms help the minimisation of the parasitic currents present in flow simulations, when viscous forces and surface tension dominate inertial forces, like in porous media. The framework is implemented within a finite volume code (OpenFOAM) using a limited Multidimensional Universal Limiter with Explicit Solution (MULES) implicit formulation, which allows larger time steps at low capillary numbers to be utilised. In addition, an adaptive interface compression scheme is introduced for the first time in order to allow for a dynamic estimation of the compressive velocity only at the areas of interest and thus has the advantage of avoiding the use of a-priori defined parameters. The adaptive method is found to increase the numerical accuracy and to reduce the sensitivity of the methodology to tuning parameters. The accuracy and stability of the proposed model is verified against five different benchmark test cases. Moreover, numerical results are compared against analytical solutions as well as available experimental data, which reveal improved solutions relative to the standard VoF solver. Keywords CFD; InterFoam; Two-phase flows; Microfluidics; Surface tension forces; Parasitic currents; Micro-scale modelling

Droplet impact on porous media has a broad range of applications such as material processing, drug delivery and ink injection etc. The simulation studies of such processes are rather limited. To represent the spreading and absorption process of the droplet on porous materials, robust numerical schemes capable of accurately representing wettability as well as capillary effects need to be established. The current work, presents one of the first studies of droplet impact on a real porous media geometry model extracted from a micro-CT scan. The process involves processing of CT image and subsequent threshold based on the structures segmentation. The porous geometry is extracted in the form of a STL (STereoLithography) model, which, with the aid of dedicated software like ANSA and SnappyHexMesh, is converted to an unstructured mesh for successful discretization of the flow domain. The solution algorithm is developed within the open source CFD toolbox OpenFOAM. The numerical framework to track the droplet interface during the impact and the absorption phases is based on previous work [1, 2]. The volume-of-fluid (VOF) method is used to capture the location of the interface, combined with additional sharpening and smoothing algorithms to minimise spurious velocities developed at the capillary dominated part of the phenomenon (droplet recession and penetration). A systematic variation of the main factors that affect this process are considered, i.e. wettability, porous size, impact velocity. To investigate the influence of porous structures on droplet spreading, the average porosity of the media is varied between 18.5% and 23.3% . From these numerical experiments, we can conclude that the droplet imbibition mainly depends on the porous wettability and secondly that the recoiling phase can be observed in the hydrophobic case but not in the hydrophilic case.

The present study addresses a detailed experimental and numerical investigation on the impact of water dropletson smooth heated surfaces. High-speed infrared thermography is combined with high-speed imaging to couple the heat transfer and fluid dynamic processes occurring at droplet impact. Droplet spreading (e.g. spreading ratio) and detailed surface temperature fields are then evaluated in time and compared with the numerically predicted results. The numerical reproduction of the phenomena was conducted using an enhanced version of a VOF- based solver of OpenFOAM previously developed, which was further modified to account for conjugate heat transfer between the solid and fluid domains, focusing only on the sensible heat removed during droplet spreading. An excellent agreement is observed between the temporal evolution of the experimentally measured and the numerically predicted spreading factors (differences between the experimental and numerical values were always lower than 3.4%). The numerical and experimental dimensionless surface temperature profiles along the droplet radius were also in good agreement, depicting a maximum difference of 0.19. Deeper analysis coupling fluid dynamics and heat transfer processes was also performed, evidencing a strong correlation between maximum and minimum temperature values and heat transfer coefficients with the vorticity fields in the lamella, which lead to particular mixing processes in the boundary layer region. The correlation between the resulted temperature fields and the droplet dynamics was obtained by assuming a relation between the vorticity and the local heat transfer coefficient, in the first fluid cell i.e. near the liquid-solid interface. The two measured fields revealed that local maxima and minima in the vorticity corresponded to spatially shifted local minima and maxima in the heat transfer coefficient, at all stages of the droplet spreading. This was particularly clear in the rim region,which therefore should be considered in future droplet spreading models.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5024

The “Direct Numerical Simulations” (DNS) of droplet impact processes is of great interest and importance for a variety of industrial applications, where laboratory experiments might be difficult, costly and time-consuming. Furthermore, in most cases after validated against experimental data, they can be utilised to further explain the experimental measurements or to extend the experimental runs by performing “virtual” numerical experiments. In such “DNS” calculations of the dynamic topology of the interface between the liquid and gas phase, the selected dynamic contact angle treatment is a key parameter for the accurate prediction of the droplet dynamics. In the present paper, droplet impact phenomena on smooth, dry surfaces are simulated using three different contact angle treatments. For this purpose, an enhanced VOF-based model, that accounts for spurious currents reduction, which has been previously implemented in OpenFOAM CFD Toolbox, is utilised and further enhanced. Apart from the already implemented constant and dynamic contact angle treatments in OpenFOAM, the dynamic contact angle model of Kistler, that considers the maximum advancing and minimum receding contact angles, is implemented in the code. The enhanced VOF model predictions are initially compared with literature available experimental data of droplets impacting on smooth surfaces with various wettability characteristics. The constant contact angle treatment of OpenFOAM as well as the Kistler’s implementation show good qualitative and quantitative agreement with experimental results up to the point of maximum spreading, when the spreading is inertia dominated. However, only Kistler’s model succeeds to accurately predict both the advancing and the recoiling phase of the droplet impact, for a variety of surface wettability characteristics. The dynamic contact angle treatment fails to predict almost all stages of the droplet impact. The optimum version of the model is then applied for 2 additional series of parametric numerical simulations that identify and quantify the effects of surface tensionand viscosity, in the droplet impact dynamics.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5020

A one dimensional lumped parameter model has been developed within the general framework of the open source software Octave, in order to describe the physical behaviour of a Loop Heat Pipe. By means of the electro-thermal-hydraulic analogy, this model gives the values of temperature and pressure for every part of the device, in response to varying boundary conditions. Furthermore, a novel approach in describing the phase change at the condenser has been adopted, differentiating the vapour quality variation over time. The code is initially validated against both simulation and experimental data found in literature. Since the present work aims to produce a design tool for the automotive industry, a parametric analysis on the geometrical characteristics of a Loop Heat Pipe is then performed, identifying and quantifying the most influential design parameters.

In the present investigation an enhanced Volume Of Fluid (VOF) based numerical simulation framework is applied for the conduction of parametric numerical simulations, aiming to investigate observed break-up phenomena of vapour slugs, within circular mini-channel branches of a hybrid thermosyphon / pulsating heat pipe device, during microgravity experiments. The simulation results identify three prevailing break-up regimes. The effect of fundamental controlling parameters in the resulting break-up characteristics is also examined. An entrainment of a liquid droplet at the trailing edge of the vapour slug, that is responsible for its subsequent " full " break-up, is identified from the simulations. Moreover, it is quite interesting that the value of the applied heat flux, does not seem to influence the break-up regime and its main characteristics.

This study presents the numerical reproduction of the entire surface temperature field resulting from a water droplet spreading on a heated surface, which is compared with experimental data. High-speed infrared thermography of the back side of the surface and high-speed images of the side view of the impinging droplet were used to infer on the solid surface temperature field and on droplet dynamics. Numerical reproduction of the phenomena was performed using OpenFOAM CFD toolbox. An enhanced volume of fluid (VOF) model was further modified for this purpose. The proposed modifications include the coupling of temperature fields between the fluid and the solid regions, to account for transient heat conduction within the solid. The results evidence an extremely good agreement between the temporal evolution of the measured and simulated spreading factors of the considered droplet impacts. The numerical and experimental dimensionless surface temperature profiles within the solid surface and along the droplet radius, were also in good agreement. Most of the differences were within the experimental measurements uncertainty. The numerical results allowed relating the solid surface temperature profiles with the fluid flow. During spreading, liquid recirculation within the rim, leads to the appearance of different regions of heat transfer that can be correlated with the vorticity field within the droplet.

Poster Presented in DIPSI Workshop 2017

The present numerical investigation identifies quantitative effects of fundamental controlling parameters on the detachment characteristics of isolated bubbles in cases of pool boiling in the nucleate boiling regime. For this purpose, an improved Volume of Fluid (VOF) approach, developed previously in the general framework of OpenFOAM Computational Fluid Dynamics (CFD) Toolbox, is further coupled with heat transfer and phase change. The predictions of the model are quantitatively verified against an existing analytical solution and experimental data in the literature. Following the model validation, four different series of parametric numerical experiments are performed, exploring the effect of the initial thermal boundary layer (ITBL) thickness for the case of saturated pool boiling of R113 as well as the effects of the surface wettability, wall superheat and gravity level for the cases of R113, R22 and R134a refrigerants. It is confirmed that the ITBL is a very important parameter in the bubble growth and detachment process. Furthermore, for all of the examined working fluids the bubble detachment characteristics seem to be significantly affected by the triple-line contact angle (i.e., the wettability of the heated plate) for equilibrium contact angles higher than 45°. As expected, the simulations revealed that the heated wall superheat is very influential on the bubble growth and detachment process. Finally, besides the novelty of the numerical approach, a last finding is the fact that the effect of the gravity level variation in the bubble detachment time and the volume diminishes with the increase of the ambient pressure.

The coastal zone is a transitory zone between land and sea. Due to its importance to man, not only for its high food production but also for recreation, sea transportation and industrial activities, coastal zone receives high environmental pressure from him. This paper deals with degradation phenomena of the coastal zone in the west section of the River Nestos Delta, North Aegean Sea, with special stress on the geomorphological changes in the coastline. The length of the coastline in this part of river Nestos Delta (the Kavala- Chrisoupoli part), from Nea Karvali village to the west, up to the river mouth to the east, is around 35 km long. This section constitutes the biggest and more extended sector of the Nestos Delta; it is the section where the main course and the various branches of the river were located, in the past. Along the coastal zone of this section of the delta many lagoons, sand bars, spits, barrier islands, washover fans, etc. were developed in its geologic past. Some of these geoforms still exist, but the majority of them have been destroyed by physical and/or anthropogenic interventions. Two of the last interventions are the diversion and entrenchment of the river to the east, in early 50’s and the construction of two high dams in the river course inland, in 2000. These human interventions deprived this land of flooding waters and sediments resulting in: (a) drying of most of the river channels and courses crossing this area of the river’s delta, (b) erosion of the coastal landforms and retreat of the shoreline in the majority of the delta coasts. There are, of course, a few places along the coastline where deposition and accretion are still taking place. In more detail, along the coastline taken into consideration in the present paper, one can meet: • stretches with high erosion rates, like the Akroneri Cape (spit), the inner coastline of Keramoti bay (Kokala -Piges coast), the Monastiraki coastline, etc, • stretches with high accretion rates like the Keramoti peninsula/spit, and • stretches at equilibrium or low rate of change like the barrier (spit) west of Akroneri Cape up to Nea Karvali coast and a short stretch of the coastline south-east of Keramoti peninsula. Comparing the Delta coastline of 1945 (from available aerial photographs) and the coastline of 2002 (from high resolution satellite images), before the construction of the Thisavros and Platanovrisi high dams (period 1945-2002), it has been estimated that: 88% of the delta and the adjacent coastlines has been accreted while only 12% has been eroded. In other words, there was a surplus of accretion by 76% and the delta was procreated. Comparing the Delta coastline of 2002 (from high resolution satellite images) and the coastline of 2007 (from high resolution D-GPS field measurements), after the construction of the dams (period 2002-2007), it has been estimated that: only 39% of the delta and the adjacent coastlines has been accreted while 61% has been eroded. In other words, there was a surplus of erosion by 22% and the delta began to retreat. This was due to Δελτίο της Ελληνικής Γεωλογικής Εταιρίας, 2010 Bulletin of the Geological Society of Greece, 2010 Πρακτικά 12ου Διεθνούς Συνεδρίου Proceedings of the 12th International Congress Πάτρα, Μάιος 2010 Patras, May, 2010 the great reduction (by almost 80%) of the river’s sediment load reaching to the sea. Thus, up to 2002, or so, the balance accretion – erosion in the whole delta coastline was positive, whereas after 2002 the erosion and retreat predominates in the delta’s coastline. The prevention of sediments and fresh water flooding in the delta area, has also affected the crops production in the fields in the vicinity of the delta as well as the fish output in the lakes and lagoons of the coastal zone.

The ability to accurately predict the dynamics of a droplets impinging on solid and porous surfaces remains of interest due to a number of important applications including material processing, ink printing, drug delivery, fuel injection etc.. In the current work we present the numerical investigation of four cases of such droplets (one based on impact on a solid surface and three on porous materials). Results are compared with experimental data for the time evolution of the droplet spreading and recoil. Our numerical method is based on the one fluid-VOF based-approach of OpenFOAM, however an improved interface capturing framework has been implemented in an effort to capture droplet impact dynamics and penetration even at areas that capillary effects are dominant. Introduction The spreading of liquid droplets on solid and porous surfaces is a widespread phenomenon of both fundamental and industrial interest. A liquid droplet impacting onto a dry substrate generates a radially expanding liquid film (lamella) that can also be bounded by a rim in cases of higher velocities. The kinematics of droplet spreading and receding have been investigated rather extensively and the various outcomes can be summarised as: deposition, prompt splash and corona splash. The specific outcome of the impact depends mostly upon the droplet size, impact velocity, surface tension, viscosity, and also upon the surface roughness, porosity and wettability. Deposition and bouncing depend mostly on the wetting properties of the substrate. while splashing arises from the breakup of a fine liquid sheet that is ejected radially along the substrate at higher impact velocities. Recent comprehensive reviews can be found in [11, 18, 29], and provide insight to the state-of-the art of the droplet impact modelling. It should be noticed though that most of the studies involve high impact velocities although the behaviour of lower impact velocity is equally important.

This paper discusses the implementation of an explicit density-based solver, that utilises the central-upwind schemes for the simulation of cavitating bubble dynamic flows. It is highlighted that, in conjunction with the Monotonic Upstream-Centered Scheme for Conservation Laws (MUSCL) scheme they are of second order in spatial accuracy; essentially they are high-order extensions of the Lax–Friedrichs method and are linked to the Harten Lax and van Leer (HLL) solver family. Basic comparison with the predicted wave pattern of the central-upwind schemes is performed with the exact solution of the Riemann problem, for an equation of state used in cavitating flows, showing excellent agreement. Next, the solver is used to predict a fundamental bubble dynamics case, the Rayleigh collapse, in which results are in accordance to theory. Then several different bubble configurations were tested. The methodology is able to handle the large pressure and density ratios appearing in cavitating flows, giving similar predictions in the evolution of the bubble shape, as the reference.

Micro-droplet formation and mobilization is an emerging area of research due to its wide-ranging usage within microfluidics application relevant to tight porous media (Andrew et al., 2015). Physical understanding of this process at the pore scale is helpful in exploring macroscopic phenomena in oil and gas recovery and also forms the basisofmany potential applications such as synthesis of new materials, formulation of products in pharmaceutical, cosmetics and food industries. The standard two-phase Volume Of Fluid (VOF) and/or Level Set (LS) methods for interface tracking between two immiscible fluids, have been used extensively in the literature to perform numerical simulations of droplet formation in different micromodels (Wörner, 2012). These methods are less successful for the study of phenomena when the combined effect of viscous and capillary forces is dominant. This is mainly due to difficulties in predicting the flow in presence of high capillary forcesencountered in flows at the pore scale, which can introduce non-physical (parasitic) velocities or instabilities in the numerical results. In the present work, a novel dynamic VOF-based framework for reducing parasitic velocities at low capillary number flows (based in the works (Georgoulaset al., 2015; Raeiniet al., 2015)) work for conservative sharp interface trackingis introduced. This framework is compared with the commonly used for the prediction of relaxation of static droplets with varying sizes and they are also utilized to study the dynamics of oil droplet trapping and mobilization within pore throats through a T-junction configuration. The overall numerical model development has been conducted within the open-source, CFD Toolbox, OpenFOAM(version 2.3.x). The Navier–Stokes equations are discretized using a finite volume approach, while the Volume Of Fluid method is used to capture the location of interfaces. The volume fraction (alpha) is advectedimplicitly and additional algorithms for compressing, sharpening and smoothing the interface are implemented in order to guarantee its physical thickness and curvature. Surface tension forces are then computed based on the sharp/smooth (𝛼) field which maintains a steep transition area for capillary pressure. The influence of the static/equilibrium contact angleimposed at the rigid wall is also considered in order to account for various wettability effects. The developed numerical method targets efficient modelling of multiphase flows in the micro-scale with complex interface motion and irregular solid boundaries. It allows correcting surface forces and permits simulations at low capillary numbers dampening out non-physical velocities. Moreover, the addition of the adaptive grid refinement method and the implicit formulation for the equation of volume fraction, allows larger time steps and thus lower computational cost. Overall, the comparison of computational results with analytical models and experiments shows that the introduced framework improves the accuracy of the original VOF method when the surface tension influence is predominant. Some indicative results for a static droplet case (150 micron) are depicted in Figures and below. Keywords; Two-phase flow, Pore-scale modelling, Volume Of Fluid, Parasitic currents

This paper discusses the implementation of an explicit density-based solver, based on the central-upwind schemes originally suggested by Kurganov, for the simulation of cavitating bubble dynamic flows. Explicit density based solvers are suited for highly dynamic, violent flows, involving large density ratios, as is rather common in cavitating flows. Moreover, the central-upwind schemes have the advantage of avoiding direct evaluation of the Jacobian matrix or estimation of the wave pattern emerging from Euler equations. Second order accuracy can be achieved with TVD MUSCL schemes. Basic comparison with the predicted wave pattern of the central-upwind schemes is performed with the exact solution of the Riemann problem showing an excellent agreement. Then several different bubble configurations were tested, similar to the work of Lauer et al. (2012). The central-upwind schemes prove to be able to handle the large pressure and density ratios appearing in cavitating flows, giving similar predictions in the evolution of the bubble shape.

Nestos is one of the most important transboundary rivers flowing through Bulgaria and Greece. In the Greek part of the river, two reservoirs, the Thisavros Reservoir and the Platanovrysi Reservoir, have already been constructed and started operating in 1997 and 1999, respectively. In the first part of the chapter, the reservoir sedimentation effect on the coastal erosion is investigated, for the case of the Nestos River delta and the adjacent shorelines, through a combination of mathematical modeling, modern remote sensing techniques, and field surveying, while in the second part, the mechanical removal as well as the flushing of sediment from the reservoir of Platanovrysi and its disposal in the subbasin downstream of the Platanovrysi Dam up to the Nestos River delta are investigated as potential treatment methods of reducing coastal erosion, using a modification of the same mathematical model that is utilized in the first part of the chapter. The overall findings and conclusions arising from the work presented and discussed in the present chapter contribute to the overall need to thoroughly understand the direct effect of dam construction on coastal erosion, as well as to examine the effectiveness of potential sediment management treatments.

Boiling heat transfer has been a subject of extensive investigation during the last decades. Since the subprocesses in nucleate boiling, involve quite complex physics, the development of comprehensive correlations and/or models has not been possible so far. However, more recently, numerical simulations of the boiling process have proven to be capable of reliably predicting bubble dynamics and heat transfer characteristics. In the present paper, heat transfer and phase-change are coupled with a previously improved and validated Volume Of Fluid (VOF) model for adiabatic bubble dynamics. The model is initially verified with an existing analytical solution for cases of evaporating bubble growth in a superheated liquid domain. Moreover, the predictions of the proposed model regarding the bubble detachment characteristics are also validated against available experimental data on pool boiling of refrigerants. The validated and optimised version of the model is further applied for the conduction of a wide range of parametric numerical simulations, identifying the effects of the initial thermal boundary layer thickness, the contact angle between the liquid/vapour interface and the heated plate, as well as the plate superheat, on the bubble detachment characteristics. It is found that the bubble growth and detachment characteristics are highly sensitive to the initially developed thermal boundary layer thickness, following a linear relationship. This has a strong implication on the experimental activities, since in many cases it is not clear at which time the initial measurements of the pool boiling characteristics have been carried out with respect to the time scale to reach the quasi steady-state condition of the thermal boundary layer, linked to the natural convection. As for the imposed contact angle effect, a threshold value is identified below which, the effect on the bubble detachment characteristics is minimal while above this value the influence is quite significant. Moreover, the bubble detachment characteristics follow an exponential increase with the corresponding increase in the superheat of the heated plate.

Flow Boiling heat transfer within micro-channels has been a subject of extensive investigation during the last decades. Due to the underlined complexity, the development of comprehensive correlations and/or models for flow boiling has not been possible so far. However, more recently, numerical simulations have been proven being capable of reliably predicting bubble dynamics and heat transfer characteristics. Heat transfer and phasechange due to evaporation and/or condensation are coupled with a previously improved and validated, Volume Of Fluid (VOF) model for adiabatic bubble dynamics. Initially the model is validated with an existing analytical solution and with literature available experimental results of pool boiling with an excellent degree of convergence. In the present paper, the proposed VOF model is further applied for 3D numerical simulations of flow boiling in micro-channels, with single and multiple nucleation sites identifying some interesting observations regarding the bubble growth and detachment characteristics within the liquid cross-flow as well as regarding the coalescence of bubbles detaching from different nucleation sites. The analysis of the numerical results reveals that the proposed numerical model constitutes a quite promising tool for the investigation of the complex sub-processes which occur during flow boiling in micro-channels.

The present investigation, identifies the exact quantitative effects of fundamental parameters, on the detachment characteristics of isolated bubbles, emanating quasi-statically from submerged orifices into isothermal liquid pools. For this purpose, a Volume of Fluid (VOF) based interface capturing approach is further improved, for the conduction of axisymmetric and 3D numerical experiments on adiabatic bubble growth dynamics. The predictions of the model, are quantitatively validated against literature available experimental data, showing excellent agreement. Two series of numerical experiments are performed, quantitatively exploring the parametric effects of the liquid phase properties in five different gravity levels, and the effect of the gravity vector direction inclination angle, respectively. It is found that the bubble detachment characteristics, are more sensitive in the variation of the surface tension, liquid phase density and gravity, while the effect of liquid phase dynamic viscosity is generally minimal. From dimensionless analysis, two correlations are derived, which for the examined range of Eötvos numbers, are able to predict the equivalent bubble detachment diameter and the bubble detachment time, respectively. It is also found that the bubble detachment characteristics, reduce significantly as the gravity vector direction gradually deviates from being parallel to the bubble injection orifice, following a non-linear decrease.

The heat transfer mechanism of Nucleate Boiling (NB) is widely used in technological applications. However, there is an incomplete understanding of the fundamental physics of bubble dynamics, at small scales as well as at non-trivial geometrical configurations. In order to investigate bubble dynamics an adiabatic approach is often used, where gas/vapor bubbles are injected into liquids at saturation conditions. So far, there is a great deal of experimental, theoretical and numerical investigations on adiabatic gas/vapor injected bubble growth dynamics. However, according to the authors' best knowledge the majority of these works deal with gas/vapor bubbles injected upwards into stagnant liquid domains, with the injection axis being parallel to the gravitational acceleration direction, using mainly water and air as the working fluids. In the present investigation, an improved algebraic VOF (Volume of Fluid) based interface capturing approach, originally developed in OpenFOAM®, is applied for the conduction of axisymmetric and 3D numerical experiments on adiabatic bubble growth dynamics. The investigation focuses on the influence of different fluid properties and inclination angles of the gas/vapor injection orifice, on the bubble growth and detachment characteristics. Prior to the application, the predictions of the numerical model are validated against literature available experimental data. From the overall results it can be concluded that the bubble growth and detachment characteristics, are strongly dependent not only on the fluid properties but also on the orifice inclination angles due to the induced asymmetry, which mainly results from the formation of asymmetric and unsynchronized vortexes during the bubble growth process.

A steel plate is one of the critical components of a scroll expander system that can experience cavitation micro-pitting while in service. The content of the present paper consists of two distinct but interrelated parts. The first part aims to highlight that the use of computational fluid dynamics (CFD) simulations can constitute a potential tool for the prediction of cavitation erosion areas in scroll expander systems. For this purpose, a three-dimensional CFD, steady-state numerical simulation of the refrigerant working fluid is employed. Numerical results revealed the critical areas where cavitation bubbles are formed. These numerical critical areas are in direct qualitative agreement with the actual eroded regions by cavitation, which were found by microscopic observations across the steel plate on an after use, scroll expander system. The second part of the paper aims to further investigate the behaviour and the durability of the steel plate of the studied scroll expander system subjected to cavitation erosion by using an ultrasonic experimental test rig. Scanning electron microscopy and optical interferometer micrographs of the damaged surfaces were observed, showing the nature of the cavitation erosion mechanism and the morphological alterations of the steel plate samples. Experimental results are explained in terms of the cavitation erosion rates, roughness profile, accumulated strain energy, and hardness of the matrix. The experimental study can serve as a valuable input for future development of a CFD numerical model that predicts both cavitation bubbles formation as well as cavitation damage induced by the bubbles that implode on the steels plates.

Coastal erosion that is generated by the reduction of the annual sediment yield at river outlets, due to the construction of reservoirs, constitutes one of the main environmental problems in many parts of the world. Nestos is one of the most important boundary rivers, flowing through Bulgaria and Greece, characterized by its great biodiversity. In the Greek part of the river, two reservoirs, the Thisavros Reservoir and the Platanovrysi Reservoir, have already been constructed and started operating in 1997 and 1999, respectively. The present paper constitutes the first attempt where the assessment of reservoir sedimentation effect on the coastal erosion for the case of the Nestos River delta and the adjacent shorelines is addressed in detail, through mathematical modeling, modern remote sensing techniques and field surveying. It is found that the construction and operation of the considered reservoirs have caused a dramatic decrease (about 83%) in the sediments supplied directly to the basin outlet and indirectly to the neighbouring coast and that this fact has almost inversed the erosion/accretion balance in the deltaic as well as the adjacent shorelines. Before the construction of the reservoirs, accretion predominated erosion by 25.36%, while just within five years after the construction of the reservoirs, erosion predominates accretion by 21.26%.

An experimental study to evaluate cavitation bubble dynamics is conducted. The aim is to predict the magnitude and statistical distribution of hydrodynamic impact pressure generated from the implosion of various individual acoustic cavitation bubbles near to a rigid boundary, considering geometrical features of the pitted area. A steel sample was subjected to cavitation impacts by an ultrasonic transducer with a 5mm diameter probe. The pitted surface was then examined using high-precision 3D optical interferometer techniques. Only the incubation period where surface is plastically deformed without material loss is taken into account. The exposure time was adjusted in the range of 3-60s to avoid pit overlapping and a special procedure for pit analysis and characterisation was then followed. Moreover, a high-speed camera device was deployed to capture the implosion mechanisms of cavitation bubbles near to the surface. The geometrical characteristics of single incubation pits as well as pit clusters were studied and their deformation patterns were compared. Consequently, a reverse engineering approach was applied in order the hydrodynamic impact pressure from the implosion of an individual cavitation bubble to be determined. The characteristic parameters of the cavitation implosion process such as hydrodynamic impact pressure and liquid micro-jet impact velocity as well as the hydrodynamic severity of the cavitation impacts were quantified. It was found that the length of the hypotenuse of the orthographic projections from the center of the pit, which basically represents the deformed area of the pit, increases with the hydrodynamic impact aggressiveness in a linear rate. Majority of the hydrodynamic impacts were in the range of 0.4-1GPa while the corresponding micro-jet velocities were found to be in the range of 200-700m/s. Outcomes of this study, contribute to further understanding the cavitation intensity from the implosion of acoustically generated bubbles and could certainly represent a significant step towards developing more accurate cavitation models.

This study investigates the long-term capacity of the North Aegean coastal systems to transport and store conservative pollutants that originate from the Black Sea. Emphasis is placed on modeling the dispersion and accumulation of a passive tracer that represents a Black Sea pollutant (BSP) substance that continuously discharges from the Dardanelles exit into the North Aegean, for a long period of time (16 years). The effects of the Black Sea water (BSW) inflows, meteorological forcing, and seasonal stratification are assessed with a 3D hydrodynamic model (Estuary, Lake and Coastal Ocean Model), after validation with available field data. The salinity, water temperature, and discharge from the Dardanelles Strait are taken to be seasonally varied. According to the authors' best knowledge, the present paper constitutes the first numerical modeling attempt in the literature that apart from the long-term hydrodynamic characteristics that have also been studied in previous works, a suitable tracer is introduced in order to predict the long-term fate, distribution, and accumulation of pollutants that originate from the Black Sea into the North Aegean coastal regions. The overall results of the present investigation indicate that the BSP concentration is very high at the coastal waters of Thassos, Samothraki, and Limnos islands, as well as along the mainland coastal waters between Alexandroupolis and Strymonikos Gulf, during summer and autumn when strong water column stratification occurs. In general, the BSP concentration in the North Aegean surface waters reaches considerable high values (47–58 % of the initial pollutant concentration at Dardanelles inflow) within 16 years. Even for depths more than 500 m the BSP concentration is still remarkable, slightly increasing with time. The increase of the BSP concentration with respect to time at various depths (from free surface up to 750 m) is also investigated.

A steel plate is one of the critical components of a scroll expander system that usually experiences cavitation in service. An experimental study is conducted to study the behaviour of the scroll's steel plate subjected to cavitation erosion. For this purpose an ultrasonic transducer is utilised to produce cavitation bubbles. Micrographs of damaged surfaces were observed, showing the nature of the cavitation mechanism and the morphology alterations across the steel sample. Experimental results are explained in terms of the cavitation erosion rates, roughness profile, accumulated strain energy, and hardness of the matrix.

A numerical simulation of the surface buoyant plume that is formed from the Black Sea brackish water discharge into the North Aegean Sea, through the Dardanelles Straits, has been performed using the ELCOM hydrodynamic model after validation with available field and remote sensing data. Important climatological factors, such as air temperature, relative humidity, wind speed, wind direction, solar radiation, atmospheric pressure and rainfall that affect the water circulation in North Aegean as well as the Coriolis force effect, are taken into account. The seasonal characteristics of the water circulation in the North Aegean are examined using a horizontal grid resolution of 4 km by 4 km. The salinity, the water temperature and discharge from the Dardanelles straits are taken to be seasonally varied. The simulation was conducted for a total flow time of 6 years. According to the authors best knowledge the present paper constitutes the first numerical modeling attempt in the literature that apart from the long-term hydrodynamic characteristics that have also been studied in previous works, suitable tracers are introduced in order to predict the long term fate and distribution of pollutants that are transported from the Black sea into the North Aegean. The overall results of the present investigation indicate that a substantial percentage of pollutants originating from the Black Sea, accumulate in the North part of the Aegean Sea. The Black Sea Pollutant (BSP) concentration in the North Aegean surface waters reaches relatively high values (20–34%) of its initial assumed value (100%) at the Dardanelles exit to the North Aegean, in a relatively short period of 6 years. Even at 500 m depth the BSP accumulation is more than 5% of its initial value.

During floods, the density of river water usually increases due to the increase in the concentration of the suspended sediment that the river carries, causing the river to plunge underneath the free surface of a receiving water basin and form a turbidity current that continues to flow along the bottom. The study and understanding of such complex and rare phenomena is of great importance, as they constitute one of the major mechanisms for suspended sediment transport from rivers into the ocean, lakes or reservoirs. In the present paper a previously tested and verified numerical model [1] is applied in laboratory scale numerical experiments of continuous, high density turbidity currents. The turbidity currents are produced by the steady discharge of fresh water – suspended sediment mixtures, into an inclined channel which is connected at its downstream end to a wide horizontal tank. Both, channel and tank are initially filled with fresh water. This configuration serves as a simplified experimental analog of natural, hyperpycnal turbidity currents that are formed at river outflows in the sea, lakes or reservoirs and usually travel within subaqueous canyon-fan complexes. The main aim is to investigate the exact qualitative and quantitative effect of fundamental, flow controlling parameters in the hydrodynamic and depositional characteristics of continuous, high density turbidity currents. According to the authors’ best knowledge, the present paper constitutes the first attempt in the literature, where the isolated effects of each individual controlling parameter as well as their relative importance on the hydrodynamic characteristics of continuous, high-density turbidity currents are quantitatively evaluated in detail. The numerical model used, is based on a multiphase modification of the Reynolds Averaged Navier–Stokes equations (RANS). For turbulence closure the Renormalization-group (RNG) k–ε model is applied, which is an enhanced version of the widely used standard k–ε model.

During floods, the density of river water usually increases due to a subsequent increase in the concentration of the suspended sediment that the river carries, causing the river to plunge underneath the free surface of a receiving water basin and form a turbidity current that continues to flow along the bottom. The study and understanding of such complex phenomena is of great importance, as they constitute one of the major mechanisms for suspended sediment transport from rivers into oceans, lakes or reservoirs. Unlike most of the previous numerical investigations on turbidity currents, in this paper, a 3D numerical model that simulates the dynamics and flow structure of turbidity currents, through a multiphase flow approach is proposed, using the commercial CFD code FLUENT. A series of numerical simulations that reproduce particular published laboratory flows are presented. The detailed qualitative and quantitative comparison of numerical with laboratory results indicates that apart from the global flow structure, the proposed numerical approach efficiently predicts various important aspects of turbidity current flows, such as the effect of suspended sediment mixture composition in the temporal and spatial evolution of the simulated currents, the interaction of turbidity currents with loose sediment bottom layers and the formation of internal hydraulic jumps. Furthermore, various extreme cases among the numerical runs considered are further analyzed, in order to identify the importance of various controlling flow parameters. KeywordsTurbidity currents-Hyper-pycnal flows-CFD numerical modelling-Suspended sediment transport

In this paper, hypopycnal and hyperpycnal particulate currents that are formed at river outflows in the sea are studied. The main aim is the use of CFD methods, in order to investigate the plunging mechanism in the case of hyperpycnal currents. Two series of numerical experiments are conducted. The first series, aims to validate the numerical model by checking its ability in capturing the critical suspended sediment concentration for plunging. The second series, aims to investigate the dependence of the plunge depth from the initial flow conditions, in the case of hyperpycnal currents. From the analysis of the results, an empirical equation is derivedwhich relates the plunge depth with the initial conditions. It is also found that secondary hyperpycnal currents, can be generated indirectly, from hypopycnal currents, due to descending sediment fingers. The model predictions, in the present paper are in agreement with previous investigations.

The coastal zone is a transitory zone between land and sea. Due to its importance to man, not only for its high food production but also for recreation, sea transportation and industrial activities, coastal zone receives high environmental pressure from him. This paper deals with degradation phenomena of the coastal zone in the west section of the River Nestos Delta, North Aegean Sea, with special stress on the geomorphological changes in the coastline. The length of the coastline in this part of river Nestos Delta (the Kavala-Chrisoupoli part), from Nea Karvali village to the west, up to the river mouth to the east, is around 35 km long. This section constitutes the biggest and more extended sector of the Nestos Delta; it is the section where the main course and the various branches of the river were located, in the past. Along the coastal zone of this section of the delta many lagoons, sand bars, spits, barrier islands, washover fans, etc. were developed in its geologic past. Some of these geoforms still exist, but the majority of them have been destroyed by physical and/or anthropogenic interventions. Two of the last interventions are the diversion and entrenchment of the river to the east, in early 50's and the construction of two high dams in the river course inland, in 2000. These human interventions deprived this land of flooding waters and sediments resulting in: (a) drying of most of the river channels and courses crossing this area of the river's delta, (b) erosion of the coastal landforms and retreat of the shoreline in the majority of the delta coasts. There are, of course, a few places along the coastline where deposition and accretion are still taking place. In more detail, along the coastline taken into consideration in the present paper, one can meet:  stretches with high erosion rates, like the Akroneri Cape (spit), the inner coastline of Keramoti bay (Kokala-Piges coast), the Monastiraki coastline, etc.  stretches with high accretion rates like the Keramoti peninsula/spit, and  stretches at equilibrium or low rate of change like the barrier (spit) west of Akroneri Cape up to Nea Karvali coast and a short stretch of the coastline southeast of Keramoti peninsula. Comparing the Delta coastline of 1945 (from available aerial photographs) and the coastline of 2002 (from high resolution satellite images), before the construction of the Thisavros and Platanovrisi high dams (period 1945-2002), it has been estimated that: 88% of the delta and the adjacent coastlines has been accreted while only 12% has been eroded. In other words, there was a surplus of accretion by 76% and the delta was procreated. Comparing the Delta coastline of 2002 (from high resolution satellite images) and the coastline of 2007 (from high resolution D-GPS field measurements), after the construction of the dams (period 2002-2007), it has been

Observations of cavitation damage within a lubricated expander system are studied experimentally. Typical experimental analysis is used to observe cavitation erosion features such as SEM, light-microscopy and lightinterferometer. An experimental test-rig is used to study bubble characteristics within fluids to compare the theoretical analysis and practical in-service results from the expander system. Using an ultra-sonic methodology and high-speed camera techniques the bubbles are observed within the working fluids. A 2D numerical simulation of the scroll was performed to explore the mechanism which generates scroll cavitation. It is found that the pressure is high enough to liquefy instantaneously part of the refrigerant close to the bottom boundary, creating conditions for the generation of cavitation bubbles within the liquefied refrigerant. This finding resolves the puzzle how the refrigerant which enters the scroll in gas phase produces cavitation.

BEACHMED-e: “Strategic management of beach protection measures for the sustainable development of Mediterranean coastal areas BEACHMED-e is a Regional Framework Operation part-fi nanced by the European Union (European Regional Development Fund) within the INTERREG IIIC south Programme

Coastal zones all over the world are part of a unique and sensitive environment that is the stage of a myriad of uses – and therefore confl icts – which can be brought into pacifi c coexistence through a very slow but dynamic and articulated process of decision-making called Integrated Coastal Zone Management1. The Mediterranean, for centuries celebrated as the cradle of western civilisation, has one of the most threatened coastlines in the world, and because of its physical peculiarities and the contrasting socio-economic realities of its bordering countries it must undergo vital management challenges regarding the impacts over natural resources and the eff ects of coastal urbanisation (Hinrichsen, 1998). In fact, two related aspects of the developed, often urbanised, Mediterranean coasts draw the immediate attention of non-Mediterranean visitors: the economic value of the sandy stretch that we, as scientists or tourists, call the beach, and how strenuously this is being defended from events that in many other places of the world are just part of a balance that is allowed to proceed naturally. It is a fact that the management of such Mediterranean beaches is of key importance because of the threat they bear, the highly-priced uses they host and what such a value may represent to local, regional and national economies. This confl ict gives birth to a signifi cant line of research and specifi c policies on beach defence and its optimisation in terms of time and costs - beach monitoring and defence strategies imply high investments and have specifi c timings according to the type of environment and the scope of monitoring.The planning and management of the coastal zone requires therefore an accurate and updated knowledge of the processes in act, and in particular of those responsible for changes to beach morphology. Shoreline evolution determines the shape and extension of the emerged beach – the part of the territory with the highest economic value – and therefore must be studied in detail by those in charge of planning and managing the diff erent uses that are made of this part of the territory. Such is a focus of beach management as an important component of the broader coastal zone management: as beaches bear (and cause) eff ects that are produced (and felt) in adjacent environments, beach management is actually one “slice” of coastal management, and therefore in defi ning the most eff ective policies for the management of the beach it is necessary to frame it within the macro-scale of coastal management and sustainable use of the coastal zone. The coastal zone subject to management can be understood as a transition space between the sea and the adjacent land, which stretches alongshore across diff erent countries. Because of its nature many of the coastal issues that countries must face are of international scope, and the eff ects that coastal uses will have on nearby countries must be considered when planning them (Clark, 1998). The Mediterranean sea, due to its geographical enclosure and socio-political peculiarities, represents a particular case where the already “hard-to-defi ne” boundaries of the coastal zone show a special blur:if the marine environment, shorelines and coastal zones are part of a cross and longshore “continuum”, calling for integration also at the international level, here neighbouring countries that share such a particularly and tightly connected environment must depend deeply on transboundary policies in order to reach a coherent and eff ective approach to coastal management. Coastal management and planning at international scale is in fact highly strategic and focuses on developing broad strategies and action plans to ensure common eff orts between coastal nations, including programmes that are developed between groups of countries (Kay and Alder, 1999). The sustainable development of the Mediterranean coastal zone is a transnational issue, and therefore programmes that can sustain public policies on solving confl icts over the beach – and reach real change as eff ects – tend to be more eff ective if they involve diff erent neighbouring countries. In this context, methodologies for surveying, data processing and analysis of trends in act must take into consideration all new technologies available in order to increase accuracy and cost/benefi t ratio of operative monitoring activities. Certifi ed and shared techniques are necessary for creating regional, national and international scenarios that are capable of dealing with diff erent realities. Such a confrontation, if using homogeneous data, allows not only to evaluate the eff ect that diff erent natural and anthropogenic processes have on diff erent realities but also to analyse the need for intervention (normative or structural) in order to plan the available resources – being aware though that the priority for interventions should not be based on physical data only. Statistics that refer to coastal evolution processes, realised at national (e.g. for Italy - GNRSC, 2006), continental (e.g. for Europe – EUROSION, 2004) or global (e.g. for worldwide coasts - Bird, 1996), present data that are obtained with criteria and methodologies that are extremely diverse, elaborated in different forms and often with diff erent scopes. Among the most relevant diff erences, we can point those that refer to time intervals, survey scales and accuracy on the positioning of the shoreline. The “perception” of how severe the phenomenon is can be highly subjective, and often infl uenced by local realities – minimal shoreline retreat (that could be maybe due to nearly annual oscillations) can be considered as being relevant and therefore noted wherever the general trend shows equilibrium or accretion. On the other hand, in regions that are characterised by shoreline retreat of some tens of metres per year, erosive processes of small proportions can be underestimated. In such evaluations, the economic value of the beach has an important weight, and limited erosion of beaches that are heavily used by the tourist industry will receive higher attention if compared to consistent shoreline retreat in coasts that undergo lower anthropogenic impact. The need for developing and validating new monitoring techniques, and sharing them among countries that border the Mediterranean - where similar environmental characteristics allow an easier standardisation of the methodologies - had already been identifi ed by the Regions who proposed Interreg III B Medocc Beachmed (2002 – 2004), and such approach had been developed during that project (Beachmed, 2005). The results obtained, together with the continuing technological evolution in this sector, and the need to target other competent authorities, have led Regions to propose the new Interreg III C Regional Framework Operation Beachmed-e2 where a signifi cant part of the budget was dedicated to this aspect, calling for the proposal of OpTIMAL. Beachmed-e concentrated on the strategic management of beach protection for the sustainable development of the Mediterranean coastal zone, and included diff erent 8 regions from 4 Mediterranean countries as offi cial partners, having had participants from many other regions as observers. OpTIMAL, one of the nine Beachmed-e subprojects, aimed at the optimisation of beach monitoring, and had the participation of 10 institutes representing all those 8 regions. Each of them had to face the same problem of dealing with the reality - and complexity - of beach erosion within a diff erent technical, social, cultural, administrative, legal and economical context. In spite of that, methodologies applied during this project at diff erent sites have shown similar results regarding their accuracy, and this increases our hope to analyse the Mediterranean coasts in a more homogenous way in order to obtain eff ectively comparable results in the near future. References Beachmed (2005) - Le projet Beachmed : Récupération environnementale et entretien des littoraux en érosion avec l’utilisation des dépôts sablonneux marins (Convention 2002-01-4.3-I-028) - 3ème cahier technique (phase C). Roma, 324 pp. Bird E.C.F. (1996) - Beach management. Wiley and Sons, Chichester, 292 pp. Cicin-Sain B. and Knecht R.W. (1998) - Integrated coastal and ocean management: concepts and practices. Island Press. Washington D.C. 517 pp. Clark J. (1998) - Coastal seas: the conservation challenge. Blackwell Science. Oxford. 134 pp. EUROSION (2004) - Living with coastal erosion in Europe: Sediment and Space for Sustainability. European Commission, pp. 38. GNRAC (2006) - Lo stato dei litorali italiani. Studi costieri, 10: 1-174. Hinrichsen D. (1998) - Coastal waters of the world: trends, threats and strategies. Island Press. Washington D.C. 276 pp. Kay R. and Alder J. (1999) - Coastal planning and management. E&FN Spon. London. 375 pp.

Nowadays, one of the most important sources of pollution for the North Aegean Sea is the water inflow from the Dardanelles straits and by extension from the Black Sea. The main aim of the current work is the study of the surface buoyant plume that is formed from the discharge of the brackish waters from the Dardanelles into the North Aegean Sea taking into account the effect of the Coriolis force in the root and dispersion pattern of the proposed plume. The study is carried out using both an experimental and a numerical model. For the experimental work a physical model of the North Aegean Sea constructed in a rotating tank is used and the experiments are carried out following the method of Flow Visualization. A comparison is made with properly processed satellite data in order to validate the experimental results. The numerical simulation of the proposed phenomenon is carried out using the ELCOM hydrodynamic model. From the comparison of the experimental, satellite and numerical data, it is concluded that the North Aegean Sea, is highly influenced by the Dardanelles outflow.

Coastal morphology alterations at the Nestos River estuary are studied in the present work, due to the three large dams’ construction at the sites of Dospati in Bulgaria and Thisavros / Platanovrysi in Greece. The above mentioned interventions’ impact is estimated using the commercial software package CEDAS, along with the processing of satellite images and field measurements in order to extract past and contemporary shorelines of the area. The computational models of CEDAS produce estimates of the wave climate and the shoreline change in coastal areas, given the field morphological characteristics and the wave characteristics for deep or intermediate water conditions. The extracted shorelines are used as reference shorelines in the sensitivity tests and the calibration of the above models (Fig.2), also taking into account the riverine sediment discharge for the present conditions, as estimated from other researchers. Finally, the input wave data are application results of the model WAM performed for the Aegean Sea by H.C.M.R.. The application results of CEDAS demonstrate a sediment budget deficit in the direct vicinity of Nestos’ mouth (eroded areas’ overbalance of 25.8%) and a displacement of the river’s delta peak to the Εast (Fig.4). They are deemed to be clearly indicative of the impact the works in the Nestos’ hydrological basin had on the coastal area and constitute a guide for the advisable restoration practices.