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1

A cost-effective method for estimating long-term effects of waves on beach erosion with application to Sitia Bay, Crete

Karathanasi Flora E., Belibassakis Kostas A.

Oceanologia

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2019

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No. 61 (2)

276--290

EN

Considering the significant role of beaches for the sea environment and welfare of coastal communities, a variety of process-based models are applied in order to examine and understand the interaction of hydrodynamic processes with seabed material at different time scales. However, a long-term view of this interaction requires a great amount of computational time. In this work a cost-effective methodology is proposed to surpass this shortcoming and estimate bed level evolution. The technique is relied on an objective criterion to assess spectral wave time series of wave height, period and direction and identify the wave conditions that contribute to the initiation of sediment movement. After implementing the so-called Shields criterion, the full wave climate is reduced to two classes of representative wave conditions: the over-critical ones, mainly responsible for long-term erosion, and the sub-critical wave conditions. By applying a well-known process-based model, the representative wave conditions are used as input for the wave-current-sediment transport simulation and rates of bed level changes are obtained, on the basis of which the long-term effects of waves on beach erosion are estimated. Taking into account that erosion is a threatening phenomenon along the sandy beaches of Mediterranean Sea, the present method is demonstrated at a sandy coast of Sitia Bay, Crete. The bed levels derived from the proposed methodology and the full time series are compared. The results indicate reasonable agreement at the selected locations with deviations under 7%, and conformity of the tendency of seabed evolution, rendering the new methodology a useful tool.

2

Modelling nearshore hydrodynamics and circulation under the impact of high waves at the coast of Varkiza in Saronic-Athens Gulf

Belibassakis K. A., Karathanasi F. E.

Oceanologia

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2017

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No. 59 (3)

350--364

EN

A plethora of physical parameters, such as hydro-, litho- and morpho-dynamic characteristics, are essential for understanding the response of coastal systems to intense sea states in terms of sediment transport and shoreline evolution. Nowadays, numerical models are extensively applied to meet the above needs and support coastal planning and management. In the present work, a 2DH dynamic modelling system is used for simulating the hydrodynamic and meteorological/oceanographic characteristics of the Saronic Gulf, in order to examine circulation patterns and predict sediment transport phenomena under high wave conditions at the coast of Varkiza, a sandy beach in the southern Attica, Greece. Time series of wind and wave data were used as input at the open boundaries of the model domain while the model was calibrated and validated through (linear and directional) statistical measures with respect to in situ wave measurements, since there was lack of hydrodynamic data at the site of interest. The simulation period of the model was between January 3 and February 19, 2013, with consecutive high waves in-between. The good agreement of the numerical results from the wave and hydrodynamic model with in situ measurements confirmed the suitability of the model for the support of sediment transport rates at Varkiza coastal segment. Model results reveal that there is a counter-clockwise water circulation during high waves that contribute to the erosion of the examined beach, which is also confirmed by independent field measurements.

3

Equivalent electromagnetic model for current leads made of HTS tapes

Czerwiński D., Jaroszyński L., Kozak J., Majka M.

Przegląd Elektrotechniczny

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2012

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R. 88, nr 9b

230-233

EN

An equivalent electromagnetic model that describes the behaviour of a current lead build of HTS tapes has been proposed. Electromagnetic filed analysis of HTS lead using FEM environment was made. The model is based on the physical structure and behaviour of HTS tapes. It was possible to calculate the magnetic filed distribution in the lead. Obtained results can be very useful in the analysis of quench states of the superconducting current leads.

PL

W niniejszym opracowaniu został przedstawiony elektromagnetyczny model przepustów prądowych wykonanych z taśm nadprzewodnikowych HTS drugiej generacji. Model opiera się na fizycznej strukturze i zachowaniu taśmy HTS. Dzięki temu było możliwe obliczenie rozkładu pola elektromagnetycznego w przepuście. Uzyskane wyniki mogą być bardzo przydatne w analizie stanów przejściowych przepustów HTS oraz optymalizacji budowy przepustu ze względu na wydzielane w nim dodatkowe straty mocy.

4

Numeryczne metody modelowania uzwojeń transformatorów dużych mocy

Drzymała P., Welfle H.

Przegląd Elektrotechniczny

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2011

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R. 87, nr 2

191-194

PL

W pracy przedstawione zostały nowoczesne metody budowy trójwymiarowych modeli obliczeniowych uzwojeń transformatorów dużych mocy w oparciu o konstrukcję transformatora 426 MVA. Zaprezentowano zarówno metody budowy modeli o wymuszeniu prądowym jak i napięciowym. Modele prądowe opracowano stosując złączenie elementów skończonych z całkowitym potencjałem magnetycznym w aktywnych obszarach magnetycznych i zredukowanym potencjałem magnetycznym w obszarach uzwojeń. Modele polowo - obwodowe opracowano stosując złączenie elementów skończonych i elementów krawędziowych o dodatkowych stopniach swobody dla obszarów uzwojenia.

EN

The paper presents the modern methods of construction of three-dimensional computational models of large power transformer windings based on a 426 MVA transformer design. It presents both methods for building models current and voltage of excitation. Current models were developed using finite elements based on the total magnetic potential in the active areas of magnetic and reduced potential in the areas of magnetic coils. Field-circuit models were developed using finite elements and edge elements with additional degrees of freedom for the winding areas.