Constantine Demetrius Memos

Stamou, A.I., Memos, C. and Spanoudaki, K., 2007. Estimating water renewal time in semi-enclosed coastal areas of complicated geometry using a hydrodynamic model. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 282 – 286. Gold Coast, Australia, ISSN 0749.0208 A methodology is presented to determine water renewal time in semi-enclosed coastal areas with artificial peninsulas or islands of complicated geometry. The methodology is applied in Durrat Alkhobar development in Saudi Arabia. The coastal area consists of the inner and the outer region. The inner region will be dredged and a fingerlike alignment will emerge. A hydrodynamic model was applied to illustrate the future conditions of the Bay regarding water circulation and renewal due to wind and tidal forcing. The model employs the fundamental hydrodynamic equations of continuity and momentum. The inner region of the coastal area was divided into 21 compartments. The communication of the inner region with the outer region is performed via two openings. Calculations showed that average renewal times ranged from 2.3 to 10.1 days for the wind conditions tested; in 12 compartments renewal times were less than 10 days. Furthermore, tide contributed significantly to the renewal of waters. Renewal time decreased with increasing wind velocity; southerly winds were beneficial for water renewal, because they created flow fields with relatively high exchange of flow via the openings.

A two-dimensional high-order Boussinesq-type model was derived to simulate wave propagation and relevant processes in the nearshore zone. Because of its enhanced nonlinear character, the model can describe more accurately the amplitude dispersion compared to its weakly nonlinear counterpart. Extension to the surf zone was accomplished using the eddy-viscosity concept for simulating breaking waves. Swash-zone dynamics were simulated by applying a modified narrow-slot technique. Bottom friction and subgrid turbulent mixing were also incorporated. The model can estimate the wave-induced current field, including the undertow effect. The numerical model relied on a generalized multistep predictor-corrector scheme, and the waves were generated using the source function method. Both the one-horizontal-dimensional (1DH) and two-horizontal-dimensional (2DH) versions were validated against a variety of experimental tests, including regular and irregular wave propagation and breaking on plane beaches and sub...

Three enhanced versions of two existing nonlinear Boussinesq-type models are herein derived. These models, along with two other similar solvers, were investigated with respect to their nonlinear and dispersive characteristics. In particular, this study comprises Fourier analysis at first-order, second-order, and third-order harmonics; an investigation of linear and nonlinear dispersion; linear shoaling analysis; and an estimation of transfer functions for subharmonics and superharmonics. The models are also validated against demanding experimental tests of wave propagation over a submerged bar. Conclusions of both a special and a general nature are drawn and discussed concerning the scope of nonlinear upgrade of Boussinesq-type equations, their numerical implementation, and the limitations of such models.

A simple model for predicting the vertical distribution of wave-induced pore pressures inside submerged porous structures is presented. A Boussinesq-type model coupled with a Darcy–Forchheimer equation was used to derive depth-averaged velocities. Then their profile was obtained by a semi-empirical approach based on energy considerations applied on a vertical distribution of the particle velocities induced by nonlinear waves in a free field. Laboratory measurements of hydrodynamic pressures were undertaken in a flume for breaking and non-breaking regular waves. The proposed model was compared with these measurements and to the results of a Reynolds Averaged Navier–Stokes equations model. Good agreement of the proposed model with the experiments was found and very good behaviour when compared with the RANS code. Increased pore pressures were identified during the experiments close to the downstream slope of the mound and a tendency of the pressures to increase with wave steepness. These effects were satisfactorily captured by the model.

A simple model for predicting the vertical distribution of wave-induced horizontal orbital velocities inside submerged porous structures is presented. A velocity profile is formulated based on the exponential profile of the nonlinear wave theory. This velocity distribution is then fitted to the numerically-predicted depth-integrated velocity given by a Boussinesq model assuming uniform porosity. For the sake of comparison, experimental measurements of horizontal velocities were taken in a laboratory flume. The proposed model was also compared with the results of a version of the commercial program FLOW-3D dealing with linear waves in a simple manner. A good agreement of the model results with the experiments was found as well as an improved behaviour with respect to this program. Moreover, increased velocities were identified at the downstream slope of the rubble mound caused by recirculating flow.

(2011). Introduction. Journal of Hydraulic Research: Vol. 49, Coastal and Maritime Hydraulics (Guest Editor: Constantine Memos), pp. 423-423.

An experimental study carried out in a flume to a scale of 1/20 is presented to assess the wave height attenuation induced by submerged meadows of Posidonia oceanica. After examination of the appropriate scaling laws and selection of the model material, an extensive test programme included both regular and random waves. A semi-empirical formulation for estimating the wave height transformation along the meadow is obtained, based on energy conservation and considering that dissipation is only due to drag forces. The latter were linearized to obtain an exponential decay law. The formulation proposed depends on the drag coefficient and includes also an empirical parameter accounting for wave steepness. The model improves previous results and extends its applicability to random waves. The drag coefficient associated to the meadows is found to be better related to the Keulegan–Carpenter parameter than to the Reynolds number. Its value is given also for models proposed by others.

Limenoscope is a web based database aiming at promoting the cultural heritage regarding ancient Greek harbours and disseminate the relevant information equally to the general public and to researchers with an interest in that particular cognitive field. The scope of the project is the realization of a database, where one can search for concise information relevant to the historical role, the topography, the morphology, as well as the technical works and installations of ancient harbours in the Mediterranean and the Black Sea. The Database started off with the registration of harbours located in the Aegean Sea and Cyprus, dating from Archaic to Byzantine times. Special emphasis is laid on the bibliographical update of the data forms of the harbour sites, as well as on the related references in ancient literature. The database enables the locating of these sites on a general map, where photographs, plans etc. are also archived. The principles of the database structure are briefly presented along with an example, that of the harbour of Phalasarna, among the harbours registered therein.

Rubble-mound breakwaters are subject not only to wave action but, also, to other types of environmental loading, such as earthquakes. High seismic activity combined with soft foundation soil can lead to large settlements and even to failures of these structures. This paper reports on some aspects of the investigation undertaken to study the behaviour of rubble-mound breakwaters under seismic loading. The investigation comprised physical and mathematical modeling of two breakwaters: the first one sitting on a rigid bed, and the second on a yielding base of loose sand. Input earthquakes induced horizontal acceleration with increasing magnitude at consecutive tests. Measurements of hydrodynamic pressures and accelerations were taken. It was found that in general rubble-mound breakwaters resting on rigid bed are quite seismic resistant structures. However, a soft foundation soil plays a dominant role in the seismic behaviour of such breakwaters and may lead to quite high residual deformations. Extra care should be taken during the design phase whenever rubble-mound breakwaters are to be placed on soft soil in areas of high seismicity.