Panayotis Prinos

Large-scale experiments on wave propagation over Posidonia oceanica

Posidonia oceanica, the most abundant seagrass species in the Mediterranean, supports a highly bio-diverse habitat and is crucial in protecting against coastal erosion. In this work, experiments in a large-scale facility have been performed, for the measurement of wave attenuation, transmission and energy dissipation over artificial Posidonia oceanica. The effects of submergence ratio corresponding to the seagrass height divided by water depth, and seagrass density as the number of stems per square metre on the above characteristics are investigated. Measurements of wave height at different locations along the vegetation meadow indicate the wave attenuation along the Posidonia oceanica for three different submergence ratios and two seagrass densities. Results are also analysed with regard to the wave-induced flow within the meadow, and the effects of the submergence ratio and the seagrass density on the mean flow characteristics, based on data of mean velocities taken at three locations within the seagrass.

Best practice for the estimation of extremes: A review

Task 2: Estimation of Extremes of the European Union research project FLOODsite was dedicated to analysing single and joint probability extremes in river, coastal and estuarine environments. It considers the sources of risk, such as river flow and level, wave height, period and direction, and sea level. Herein the work done within Task 2 is reviewed. Several statistical models and various fitting techniques are described. Planning an appropriate extremes analysis involves an understanding of the problem to be addressed, selection and preparation of source data, selection of methods for analysis and parameter fitting, and use of the derived extremes to address the problem. The applications described illustrate some of the pitfalls and difficulties associated with extreme predictions, particularly for the case of more than one variable. Understanding the assumptions and interpreting the obtained results are important for extreme analysis.

Numerical calculation of submerged hydraulic jumps

The turbulence characteristics of submerged hydraulic jumps have been investigated numerically by means of the standard k-ε turbulence model. The concept of a fractional volume of fluid (VOF) is employed to track the moving free surface. Numerical predictions include surface profiles, hydrodynamic pressures, mean velocities, turbulence intensities and shear stresses, maximum horizontal velocities and friction coefficients along the channel bed. Computational results are presented for Froude numbers ranging from 3.2 to 8.2 and submergence factors ranging from 0.24 to 0.85. The results are compared with available experimental data. They provide insights into both the macroscopic structure and the turbulent structure of submerged hydraulic jumps.

Effect of a vegetation patch on turbulent channel flow

The effect of a vegetation patch (VP) on the flow and turbulence characteristics is studied. Two turbulence models are used to simulate patch presence. Numerical results for both mean and turbulence flow characteristics are compared with available measurements to assess the performance of these models for dense and sparse submerged VPs. The mechanisms which control the turbulent development inside the VP are also discussed, and the patch effect on the downstream flow and turbulence is assessed. The results indicate that the patch length and the vegetation density dominate the turbulent development. An increase in the vegetation density causes acceleration of the development of flow velocity and turbulence characteristics inside the patch and increases the channel length downstream of the patch where its effect is significant. Also areas with increased and decreased values of bed shear stresses are observed at the initial part and at the end of the patch, respectively.

2D-V hydrodynamics of wave–floating breakwater interaction

Wave interactions with a fixed floating breakwater (FB) are investigated both numerically and experimentally. Laboratory experiments of large scale have been performed in the CIEM flume of the Catalonia University of Technology, Barcelona and measurements are compared with numerical results obtained with the use of the COBRAS model. The latter solves the two-dimensional, unsteady Reynolds averaged Navier–Stokes (RANS) equations in the vertical plane (2D-V). The k–ε turbulence model is also used for the computation of the Reynolds stresses as well as the Volume Of Fluid method for “tracking” the variation of the free surface. The effects of relative draught dr/D (dr=structure draught, D = water depth) and the FB configuration (breakwater without and with an attached seaward plate with the same dr/D) on the hydrodynamic characteristics (transmission, velocity, vorticity, turbulence) are investigated. Experimental water surface elevation, velocities at selected locations and pressure distribution around the structure are compared satisfactorily with computed results for dr/D equal to 0.325 and 0.2 and the two FB configurations. Detailed computed velocities, vortices and turbulence kinetic energy in the vicinity of the structure indicate the effects of dr/D and FB configuration on the flow pattern and the turbulence structure at the two sides of the structure.

Climate change effects on the marine characteristics of the Aegean and Ionian Seas

This paper addresses the effects of estimated climate change on the sea-surface dynamics of the Aegean and Ionian Seas (AIS). The main aim is the identification of climate change impacts on the severity and frequency of extreme storm surges and waves in areas of the AIS prone to flooding. An attempt is made to define design levels for future research on coastal protection in Greece. Extreme value analysis is implemented through a nonstationary generalized extreme value distribution function, incorporating time harmonics in its parameters, by means of statistically defined criteria. A 50-year time span analysis is adopted and changes of means and extremes are determined. A Regional Climate Model (RegCM3) is implemented with dynamical downscaling, forced by ECHAM5 fields under 20C3M historical data for the twentieth century and the SRES-A1B scenario for the twenty-first century. Storm surge and wave models (GreCSSM and SWAN, respectively) are used for marine climate simulations. Comparisons of model results with reanalysis and field data of atmospheric and hydrodynamic characteristics, respectively, are in good agreement. Our findings indicate that the dynamically downscaled RegCM3 simulation adequately reproduces the present general circulation patterns over the Mediterranean and Greece. Future changes in sea level pressure and mean wind fields are estimated to be small, yet significant for marine extremes. In general, we estimate a projected intensification of severe wave and storm surge events during the first half of the twenty-first century and a subsequent storminess attenuation leading to the resettlement of milder extreme marine events with increased prediction uncertainty in the second half of the twenty-first century.

Modeling of Nonlinear Wave Attenuation due to Vegetation

ABSTRACT Karambas, T.; Koftis, T., and Prinos, P., 2016. Modeling of nonlinear wave attenuation due to vegetation. In the present work, a nonlinear wave propagation model is developed and is applied for the simulation of the wave dissipation over vegetation. The free-surface flow over the vegetation is simulated using a Boussinesq model, while the flow within the canopy is simulated by solving simultaneously a canopy flow model. The parameters of the canopy flow model are related to the geometric characteristics of the vegetation, while the drag coefficient is taken from existing formulas found in literature and is related to the Reynolds number. The coupling between the Boussinesq and the canopy flow model is simulated by adding two extra terms, due to vegetation, in the continuity and momentum equations of the Boussinesq model. The numerical results are found to be in good agreement with several experimental measurements found in the relevant literature. The advantage of the proposed methodology is based on a nonlinear Boussinesq-type wave model, with wide range of applications for both engineering and scientific purposes, and the use of a canopy flow model with no calibration needed for the model coefficients. Moreover, a simple formula is extracted from the results for the estimation of the wave damping coefficient depending on the meadow and wave parameters.

Innovative Engineering Solutions and Best Practices to Mitigate Coastal Risk

Engineering solutions are widely used for the mitigation of flood and erosion risks and have new challenges because of the expected effects induced by climate change in particular sea level rise and increase of storminess. This chapter describes both active methods of mitigation based on the reduction of the incident wave energy, such as the use of wave energy converters, floating breakwaters and artificial reefs, and passive methods, consisting of increase in overtopping resistance of dikes, improvement of resilience of breakwaters against failures, and the use of beach nourishment as well as tailored dredging operations.Existing coastal management and defense approaches are not well suited to meet the challenges of climate change and related uncertanities. Professionals in this field need a more dynamic, systematic and multidisciplinary approach. Written by an international group of experts, Coastal Risk Management in a Changing Climate provides innovative, multidisciplinary best practices for mitigating the effects of climate change on coastal structures. Based on the Theseus program, the book includes eight study sites across Europe, with specific attention to the most vulnerable coastal environments such as deltas, estuaries and wetlands, where many large cities and industrial areas are located. * Integrated risk assessment tools for considering the effects of climate change and related uncertainties* Presents latest insights on coastal engineering defenses* Provides integrated guidelines for setting up optimal mitigation measures* Provides directly applicable tools for the design of mitigation measures* Highlights socio-economic perspectives in coastal mitigation

Chapter 3 – Innovative Engineering Solutions and Best Practices to Mitigate Coastal Risk

Engineering solutions are widely used for the mitigation of flood and erosion risks and have new challenges because of the expected effects induced by climate change in particular sea level rise and increase of storminess. This chapter describes both active methods of mitigation based on the reduction of the incident wave energy, such as the use of wave energy converters, floating breakwaters and artificial reefs, and passive methods, consisting of increase in overtopping resistance of dikes, improvement of resilience of breakwaters against failures, and the use of beach nourishment as well as tailored dredging operations.Existing coastal management and defense approaches are not well suited to meet the challenges of climate change and related uncertanities. Professionals in this field need a more dynamic, systematic and multidisciplinary approach. Written by an international group of experts, Coastal Risk Management in a Changing Climate provides innovative, multidisciplinary best practices for mitigating the effects of climate change on coastal structures. Based on the Theseus program, the book includes eight study sites across Europe, with specific attention to the most vulnerable coastal environments such as deltas, estuaries and wetlands, where many large cities and industrial areas are located. * Integrated risk assessment tools for considering the effects of climate change and related uncertainties* Presents latest insights on coastal engineering defenses* Provides integrated guidelines for setting up optimal mitigation measures* Provides directly applicable tools for the design of mitigation measures* Highlights socio-economic perspectives in coastal mitigation

Coastal Risk Management in a Changing Climate

Engineering solutions are widely used for the mitigation of flood and erosion risks and have new challenges because of the expected effects induced by climate change in particular sea level rise and increase of storminess. This chapter describes both active methods of mitigation based on the reduction of the incident wave energy, such as the use of wave energy converters, floating breakwaters and artificial reefs, and passive methods, consisting of increase in overtopping resistance of dikes, improvement of resilience of breakwaters against failures, and the use of beach nourishment as well as tailored dredging operations.Existing coastal management and defense approaches are not well suited to meet the challenges of climate change and related uncertanities. Professionals in this field need a more dynamic, systematic and multidisciplinary approach. Written by an international group of experts, Coastal Risk Management in a Changing Climate provides innovative, multidisciplinary best practices for mitigating the effects of climate change on coastal structures. Based on the Theseus program, the book includes eight study sites across Europe, with specific attention to the most vulnerable coastal environments such as deltas, estuaries and wetlands, where many large cities and industrial areas are located. * Integrated risk assessment tools for considering the effects of climate change and related uncertainties* Presents latest insights on coastal engineering defenses* Provides integrated guidelines for setting up optimal mitigation measures* Provides directly applicable tools for the design of mitigation measures* Highlights socio-economic perspectives in coastal mitigation