Theofanis V. Karambas

2DH NON-LINEAR DISPERSIVE WAVE MODELLING AND SEDIMENT TRANSPORT IN THE NEARSHORE ZONE

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.

Modelling of climate change impacts on coastal flooding/erosion, ports and coastal defence structures

AbstractIn the present work, a numerical model for the redesign of the existing and future ports and coastal defence structures is presented. The model is mainly based on the higher order Boussinesq equations and describes nonlinear wave transformation in the surf and swash zone, wave structure interaction, breaking wave induced currents and morphological changes. The existing model is adapted to describe climate change impacts on coastal flooding/erosion, ports and coastal defence structures. Model applications result to the estimation of: wave overtopping over the breakwaters crests, wave entering the harbour basin through diffraction, coastal erosion and storm surge/wave flooding. The model provides coastal engineers with a useful tool for the redesign of the existing coastal structures.

Integrated Overtopping Wave Energy Converter in a Hybrid Offshore Wind Turbine Power Generation System

Marine construction technologies could be designed to offer power generation in addition to their sea defence and coastal erosion prevention function. This paper aims to evaluate and optimize the performance of an Overtopping Wave Energy Converter (OWEC) as part of a hybrid generation system integrated into an offshore wind turbine. For that purpose, two configurations have been investigated. A 100kW OWEC was combined with a micro-gas turbine of 80kW at the first configuration and the same OWEC with a wind turbine (WT) of 200kW at the second. The preliminary design of an integrated offshore OWEC/WT is presented.The findings of the present investigation have been applied to a specific test case of a small, off–grid island, in the Aegean archipelago. Regarding its power requirement, Donoussa island currently relies exclusively on fossil fuel. At the same time, a high wave and wind power potential is available. A representative set of wind data have been obtained and numerically analyzed. A wave simulation, overtopping prediction and power output has been carried out. Moreover, a techno-economic and environmental assessment of the proposed offshore integrated design is presented. The stand alone coastal OWEC, and a single offshore wind turbine have been evaluated versus the proposed offshore hybrid power generation scheme.The OWEC is expected to generate 320MWh per year, thus covering half of the island’s estimated power demand. Using both wave and wind power generation, energy autonomy of the island could be achieved. In order to cover the requirements of extreme cases, a micro gas-turbine power generation unit has been considered, in parallel to the existing fossil fuel power generation unit. From the techno-economic assessment point of view, the coastal OWEC construction has a shorter return on investment time of 11 years as compared to 13 years of the proposed integrated design but lower profitable investment. Besides providing sufficient electrical power for the island, the additional environmental benefit of the proposed system is that it can be used to counter coastal erosion.The integrated offshore OWEC/WT design could potentially double the power output of each and every offshore wind turbine installation. This result could therefore be interpreted either as halving of the required number of offshore wind turbines erections or as doubling of the power output of an offshore wind park.Copyright