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The WEPTOS is a well-known wave energy converter (www.weptos.com), formed by several rotors, with a shape that draws upon the reputable Salters Duck geometry. The WEPTOS has a large efficiency under waves of one particular frequency, i.e. when resonance conditions occur. In order to extend the range of resonance conditions, the possible use of a negative stiffness in the rotor system is analysed. This note presents some considerations on the effectiveness of negative stiffness based on physical model experiments and on the numerical simulations used to interpret the test results. More specifically, the aim of the work is to evaluate how the WEPTOS performance is affected by the presence of a spring into the system that enhances the rotor oscillations applying a negative (un-stabilizing) torque proportional to the degree of rotation. Experiments were carried out in the deepwater wave basin of Aalborg University, on a 1:30 scale model of one rotor of the WEPTOS. Three different configurations were analysed, providing different values of the negative stiffness. A set of 16 regular and 5 irregular wave conditions were tested, with maximum heights up to approximately 6 m at prototype scale, periods ranging from 5 to 9 s. The incident wave characteristics, the device rotations and the power dissipated by a dummy power converter were accurately measured. The effect of the negative stiffness was partly hindered by the presence of friction, so that no conclusive evidence could be drawn. A simple numerical model, where the rotor was interpreted as an oscillating mass-damper- spring system, was set up and calibrated to the experimental results. Reasonably good agreement between predictions and measurements were found at model scale. The numerical simulations at prototype dimensions, where friction effects have a relatively lower importance, revealed that the springs responsible of the negative stiffness increase in fact the efficiency of the device.

Summary report of the MedDelt project. This project has studied the impact of climate change on the deltas in the northwestern Mediterranean sea., Meddelt

With the present paper we aim at summarizing the work undertaken in the MEDDELT Project on the characterisation of the dynamical processes of the Po Delta Fringe and particulalry highlight the conceptual developments achieved about the integrated modelling. We assume to be in a region of the deltaic area where there is tipically a direct influence of sea dynamics on the evolution of the morphological characters on a time scale of decades. In practice in the Po Delta such area is delimited by sea dikes. This assumption rises the requirement to consider not just the direct natural mechanisms of influence but also the direct human induced ones particularly in the long term evolution of the Po Delta fringe. We briefly describe the problem of definition of scales, the computation of budget and the physiographic unit approach with reference to climatic change related phenomena impacting on the Po Delta fringe. As a first approach we go deeper into the application of the classical Bruun approach in the evaluation of the effects of relative sea level rise in the coastal area. We then focus on the modelling of the formation and reduction processes and on the application of the physiographic unit approach. We conclude by discussing the topic of predictability and application of the models in an integrated framework as decision support tools., Hydraulic Engineering, Civil Engineering and Geosciences

We have formulated an aggregated-scale behaviour-model for the interaction between a tidal basin and its adjacent coastal environment, without adopting a priory assumptions about their independent dynamic equilibrium behaviour. Necessarily so, the model combines observations and findings resuhing from analogical model applications. The model formulation is based on earlier concepts regarding the response of individual tidal system elements on a disturbance from their dynamic equilibrium state. Here, we have extended the earlier work by including interactions with the ebb-tidal delta and the directly adjacent coast. Results for schematized and real cases are discussed., Hydraulic Engineering, Civil Engineering and Geosciences

With the present paper we aim at summarizing the work undertaken in the MEDDELT Project on the characterisation of the dynamical processes of the Po Delta Fringe and particulalry highlight the conceptual developments achieved about the integrated modelling. We assume to be in a region of the deltaic area where there is tipically a direct influence of sea dynamics on the evolution of the morphological characters on a time scale of decades. In practice in the Po Delta such area is delimited by sea dikes. This assumption rises the requirement to consider not just the direct natural mechanisms of influence but also the direct human induced ones particularly in the long term evolution of the Po Delta fringe. We briefly describe the problem of definition of scales, the computation of budget and the physiographic unit approach with reference to climatic change related phenomena impacting on the Po Delta fringe. As a first approach we go deeper into the application of the classical Bruun approach in the evaluation of the effects of relative sea level rise in the coastal area. We then focus on the modelling of the formation and reduction processes and on the application of the physiographic unit approach. We conclude by discussing the topic of predictability and application of the models in an integrated framework as decision support tools., Hydraulic Engineering, Civil Engineering and Geosciences

We have formulated an aggregated-scale behaviour-model for the interaction between a tidal basin and its adjacent coastal environment, without adopting a priory assumptions about their independent dynamic equilibrium behaviour. Necessarily so, the model combines observations and findings resuhing from analogical model applications. The model formulation is based on earlier concepts regarding the response of individual tidal system elements on a disturbance from their dynamic equilibrium state. Here, we have extended the earlier work by including interactions with the ebb-tidal delta and the directly adjacent coast. Results for schematized and real cases are discussed., Hydraulic Engineering, Civil Engineering and Geosciences