Non linear highest sea wave groups in an undisturbed field and in front of a vertical wall

In this paper some non-linear effects for the mechanics of sea wave groups with large waves are investigated, either for waves in an undisturbed field or for waves in front of a vertical wall. To the first-order in a Stokes expansion, Boccotti s quasi-determinism theory enables us to foresee the mechanics of wave groups, either in undisturbed or in diffracted fields, when a large wave occurs. The first formulation of this theory shows the random group mechanics when a large crest height occurs (New wave); the second theory formulation gives the random group mechanics when a large crest-to-trough wave height occurs. The quasi-determinism theory in both formulations, for undisturbed fields, was extended recently to the second-order by the author. In this paper the procedure to derive the second-order solution is analyzed and is applied to random wave groups in front of a vertical wall. The non-linear effects are then investigated in space-time domain, and it is obtained a good agreement of analytical predictions with both field data and data from numerical simulation

Operational modal analysis of a spar-type floating platform using frequency domain decomposition method

System identification of offshore floating platforms is usually performed by testing small-scale models in wave tanks, where controlled conditions, such as still water for free decay tests, regular and irregular wave loading can be represented. However, this approach may result in constraints on model dimensions, testing time, and costs of the experimental activity. For such reasons, intermediate-scale field modelling of offshore floating structures may become an interesting as well as cost-effective alternative in a near future. Clearly, since the open sea is not a controlled environment, traditional system identification may become challenging and less precise. In this paper, a new approach based on Frequency Domain Decomposition (FDD) method for Operational Modal Analysis is proposed and validated against numerical simulations in ANSYS AQWA v.16.0 on a simple spar-type structure. The results obtained match well with numerical predictions, showing that this new approach, opportunely coupled with more traditional wave tanks techniques, proves to be very promising to perform field-site identification of the model structures

Nonlinear Stochastic Dynamics of an Oscillating Water Column (U-OWC) Harvester: A Frequency Domain Approach

This paper deals with the problem of examining the nonlinear dynamic of a U-Oscillating Water Column (U-OWC) Wave Energy Converter. The U-OWC dynamic response is governed by a set of non-linear differential equations. In the paper, an approximate linear solution is sought by using the technique of statistical linearization. The linearization scheme is implemented by identifying a surrogate linear system equivalent to the nonlinear one in a mean-square sense. In this context, frequency-domain analyses of the U-OWC response are readily implemented via standard linear input-output relationship. Comparisons between the nonlinear response computed via numerical simulations and by the approximate one assess the reliability of the method. The proposed approach is applied to a small-scale U-OWC model installed in the Natural Engineering Laboratory (NOEL) in Reggio Calabria, Italy

From green-energy to green-logistics: a pilot study in an Italian port area

Abstract An ongoing two-year research is performing with the general objective to assess the feasibility of a system integrating the production of green-energy and its consumption inside and close to port areas for mobility services. The system is composed by two elements: (a) a "sea-to-grid" technological component harvesting and producing electrical energy from sea waves; and (b) a "green" logistic service based on the use of Fully Electric Vehicles (FEVs). A pilot study will be conducted near an Italian port area supporting passengers and freight mobility between a port and a backward (sub)-urban area. The proposed system is within the environmental goals set by the EU (Europe 2020 Strategy) and the Italian Government (National Energy Masterplan). Indeed, the energy-producing technology reduces dependence from traditional energy sources (coal, gas, oil) and consequently reduces their negative effects (greenhouse gases, air pollution, etc.). Considering that the energy is produced by sea waves, the system transfers the entire amount of produced (green) energy to the electric vehicles. The system will be experimented in a medium size urbanized area and the energy will be produced in a small size port

Analysis of the coupled dynamics of an offshore floating multi-purpose platform, part B : hydro-elastic analysis with flexible support platform

A multi-purpose platform (MPP) is an offshore system designed to serve the purposes of more than one offshore industry. Indeed, over the past decades, a number of industries have expanded, or are expanding, from onshore to offshore locations (renewables, aquaculture, tourism, mineral extractions, etc), and the research on these type of platform is increasing. In the present work, a MPP able to accommodate wind turbines, wave energy converters, and aquaculture systems is considered. For an overview of the MPP platform considered and its research context, please refer to the EU H2020 project overview (OMAE 2019-96104). This work presents the second part (Part B) of the analyses of the dynamics of the floating support structure for this MPP, focusing on the hydro-elastic analysis, while its complementary rigid-body hydrodynamic analysis is presented in Part A (OMAE2019-96212). The aim here is to assess if the support platform structural elasticity has a substantial impact on the dynamic response of the platform. A beam model and a 3D solid model of the support structure have been developed, and the inertial forces, hydrodynamic added mass forces, hydrostatic and mooring restoring forces have been considered in the hydro-elastic analyses performed. The results show that the dynamic response to the wave loads is not substantially influenced by the elasticity of the support structure, and that, at first approximation, a rigid-body approach is acceptable

OMAE2010-20811 THEORETICAL ANALYSIS OF AVERAGE WAVE STEEPNESS RELATED TO PEAK PERIOD OR TO MEAN PERIOD

ABSTRACT The average wave steepness may be defined as the ratio between the significant wave height H s and the wavelength associated to either the zero-up-crossing mean period m L or the peak period p