1,720,969 research outputs found
Semi-Analytical Model for the Evaluation of Shoreline Recession Due to Waves and Sea Level Rise
Full text linkThe climate change process is leading to an increase in the sea level and the storm intensity. The associated shoreline recession can damage coastal facilities and also beaches protected by submerged/emerged breakwaters whose defense action can become ineffective. The application of cross-shore numerical models does not allow the performance of long-term analyses. In this paper, a semi-analytical model for the evaluation of shoreline recession due to waves and sea-level rise for free and protected beaches is proposed. The model is an extension of the Dean's approach in which some limitations on the beach profile are overcome and the effects of breakwaters on the wave height (wave transmission) and on the water level (piling-up) are considered. The model takes into account a wide range of parameters for wave, sea level, beach profile, and breakwater characteristics. Among the breakwater parameters, the freeboard and the berm width are found to mainly affect the shoreline recession. For submerged breakwaters, an optimal value of the freeboard can be computed depending on the sea level and the offshore wave characteristics. The results of the model are then used to find prediction relations of the shoreline recession, with r(2) > 0.99, for both free and protected beaches, depending on the main hydrodynamic/geometrical characteristics
Experimental investigation on wave set-up and nearshore velocity field in presence of a BDS
No full textExperimental investigation on wave set up and nearshore velocity field in presence of a BDS
No full textAn extensive full scale laboratory investigation on a 2D physical model of a Beach Drainage System (BDS) was performed at the GWK in Hannover, Germany. The experiments aimed at improving the knowledge of the hydrodynamic and morphodynamic behaviour of a drained beach in order to allow the definition of the main design criteria. The present paper deals with the nearshore hydrodynamic aspects of a beach equipped with BDS. The adopted BDS consisted by 4 pipes installed below the swash zone and at a variable distance from the shoreline. Several drain configurations were considered under three wave energy conditions, paying attention to water table oscillations, wave set up, undertow currents and high-order velocity moments influenced by the system start up. The results show that the drains lead to a reduction in the water table level and, as a consequence, a lowering of wave set up on the beach. This effect induced a decrease in undertow currents and high-order velocity moments in the surf and swash zones. The observed flow characteristics can be used for energetic-based transport models able to predict erosional/accretionary trends in the nearshore morphodynamic changes under the influence of a BDS. The analyses yield useful hydrodynamic information on the general efficiency of a BDS in different wave conditions
Hydraulic Performance of Geotextile Sand Containers for Coastal Defenses
Full text linkLaboratory experiments were performed in the wave flume of the Laboratorio di Idraulica e Costruzioni Marittime of the Universita Politecnica delle Marche (Ancona, Italy) to study the hydrodynamic performance of coastal protection structures made of a new type of geotextile sand containers (GSCs). Such structures are used as softer and flexible alternatives to traditional hard coastal defenses made of concrete or rubble mound material. The GSC structures can also be used as temporary coastal protections during the winter period. The physical model reproduced two main configurations: in the former one, the GSCs were used as coastal revetments with three different slopes. In the latter one, the GSCs were applied to make detached submerged breakwaters with different submergences and berm widths. The geometric scale of the models was 1:10, and the weight of each GSC in the prototype was 5 t. The geotextile material of the containers and the wave characteristics were reproduced by using the Reynolds and the Froude similarity criteria, respectively. Reflection coefficients and hydraulic stability behaviors for the revetments, as well as transmission coefficients and piling-up amount for breakwaters, were obtained
Experimental investigation on wave set up and nearshore velocity field in presence of a BDS
No full textAn extensive full scale laboratory investigation on a 2D physical model of a Beach Drainage System (BDS) was performed at the GWK in Hannover, Germany. The experiments aimed at improving the knowledge of the hydrodynamic and morphodynamic behaviour of a drained beach in order to allow the definition of the main design criteria. The present paper deals with the nearshore hydrodynamic aspects of a beach equipped with BDS. The adopted BDS consisted by 4 pipes installed below the swash zone and at a variable distance from the shoreline. Several drain configurations were considered under three wave energy conditions, paying attention to water table oscillations, wave set up, undertow currents and high-order velocity moments influenced by the system start up. The results show that the drains lead to a reduction in the water table level and, as a consequence, a lowering of wave set up on the beach. This effect induced a decrease in undertow currents and high-order velocity moments in the surf and swash zones. The observed flow characteristics can be used for energetic-based transport models able to predict erosional/accretionary trends in the nearshore morphodynamic changes under the influence of a BDS. The analyses yield useful hydrodynamic information on the general efficiency of a BDS in different wave conditions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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