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Die Errichtung von Bauwerken im küstennahen und Offshore-Bereich erfährt seit einigen Jahren, insbesondere im Hinblick auf die Erschließung neuer, regenerativer Energiequellen, eine zunehmend größere Bedeutung. Vor diesem Hintergrund wurden im Rahmen des vom BMBF geförderten KFKI-Forschungsvorhabens Seegangsbelastungen (SEELE) (FKZ 03KIS107) Untersuchungen zum Einfluss der Interaktion zwischen Seegangs- bzw. Wellenbelastungen und (Tide-) Strömung auf Bauwerke im Küstennahbereich durchgeführt, mit dem Ziel der Erweiterung des wissenschaftlichen und technischen Prozessverständnisses zur schrägen Wellen-Strömungs-Interaktion. Die Basis stellten wissenschaftliche Untersuchungen von physikalischen Modellversuchen im 2013/2014 erweiterten 3D-Wellenbecken des Ludwig-Franzius-Instituts für Wasserbau, Ästuar- und Küsteningenieurwesen in Hannover dar. Der Schwerpunkt der Forschung lag auf der Untersuchung von lang¬kämmigen Wellen, die sich schräg, gleich- oder entgegengesetzt zur Strömungsrichtung ausbreiten. Dabei wurde die Interaktion mit einem Strömungsfeld für unterschiedliche Wassertiefen, Wellenperioden, Wellenhöhen und Strömungsgeschwindigkeiten in einem 3D-Wellen-Strömungsbecken untersucht. Das Ziel des Projekts war eine tiefergehende Einsicht in die Prozesse der Wellen-Strömungs-Interaktion und deren Dokumentation., Natural processes drive the nonlinear interactions between waves and currents. The robust reproduction of systems and states in natural environments is still rather limited and therefore physical model tests of wave-current conditions are required. Usually, assessments of processes and loads on coastal structures are derived from experiments either regarding flow only or waves only scenarios in independent physical models and therefore exclude the interaction between waves and currents as a regular feature. Assessments of loads on coastal structures stemming from oblique wave-current interaction remain a challenging and underresearched topic. For this reason, the KFKI research project “Seegangsbelastungen (Seele)” (Contract No. 03KIS107) was founded by the German “Federal Ministry of Education and Research (BMBF)”. Experiments in a 3D wave-current basin were performed to thoroughly investigate drivers and effects of oblique wave-current interaction. Experiments comprise long-crested regular and irregular wave trains on obliquely opposing and following currents for different wave periods, wave heights and flow rates. To observe the physical processes of wave-current interaction, it was essential to proceed as follows: 1. Detailed flow experiments without waves (current alone, CA) in order to characterise the undisturbed currents. 2. Detailed wave experiments without current (waves alone, WA) in order to characterise the undisturbed waves. 3. Wave-current (WC) experiments in order to determine the deviations from only-current and only-wave conditions in order to identify the wave-current interactions. Following this approach, an accurate evaluation of the processes of wave-current interaction was carried out and includes the investigation of side effects of the testing facility., 3D-Wellenbecken, wasserbauliche Modellversuche, current, waves, oblique wave-current interaction, 3D wave basin, physical model tests

In this study, the wave-induced distribution of 13 microplastic (MP) samples of different size, shape, and density was investigated in a wave flume with a sandy mobile beach bed profile. The particle parameter were chosen based on an occurrence probability investigated from the field. MP abundances were analyzed in cross-shore and vertical direction of the test area after over 40,000 regular waves. It was found, that MP particles accumulated in more shallow waters with increasing size and density. Particles with high density (ρs>1.25 g/cm3) have been partly confined into deeper layers of the sloping beach during the formation of the bed profile. Particles with a density lower than that of water used in the experiments floated constantly in the surf zone or deposited on the beach caused by wave run-up. A correlation was found between the settling velocity of the MP particles and the flow velocity at the accumulation point and a power function equation developed. The obtained results were critically discussed with findings from the field and further laboratory studies.

The wave overtopping discharge at coastal defense structures is directly linked to the freeboard height. By means of physical modelling, experiments on wave overtopping volumes at sloped coastal structures are customarily determined for constant water levels and static wave steepness conditions (e.g., specific wave spectrum). These experiments are the basis for the formulation of empirically derived and widely acknowledged wave overtopping estimations for practical design purposes. By analysis and laboratory reproduction of typical features from exemplarily regarded real storm surge time series in German coastal waters, the role of non-stationary water level and wave steepness were analyzed and adjusted in experiments. The robustness of wave overtopping estimation formulae (i.e., the capabilities and limitations of such a static projection of dynamic boundary conditions) are outlined. Therefore, the classic static approach is contrasted with data stemming from tests in which both water level and wave steepness were dynamically altered in representative arrangements. The analysis reveals that mean overtopping discharges for simple sloping structures in an almost deep water environment could be robustly estimated for dynamic water level changes by means of the present design formulae. In contrast, the role of dynamic changes of the wave steepness led to a substantial discrepancy of overtopping volumes by a factor of two. This finding opens new discussion on methodology and criteria design of coastal protection infrastructure under dynamic exposure to storm surges and in lieu of alterations stemming from projected sea level rise. © 2020 by the authors.

Wave overtopping&mdash, i.e., excess of water over the crest of a coastal protection infrastructure due to wave run-up&mdash, of a smooth slope can be reduced by introducing slope roughness. A stepped revetment ideally constitutes a slope with uniform roughness and can reduce overtopping volumes of breaking waves up to 60% compared to a smooth slope. The effectiveness of the overtopping reduction decreases with increasing Iribarren number. However, to date a unique approach applicable for a wide range of boundary conditions is still missing. The present paper: (i) critically reviews and analyzes previous findings, (ii) contributes new results from extensive model tests addressing present knowledge gaps, and (iii) proposes a novel empirical formulation for robust prediction of wave overtopping of stepped revetments for breaking and non-breaking waves. The developed approach contrasts a critical assessment based on parameter ranges disclosed beforehand between a smooth slope on the one hand and a plain vertical wall on the other. The derived roughness reduction coefficient is developed and adjusted for a direct incorporation into the present design guidelines. Underlying uncertainties due to scatter of the results are addressed and quantified. Scale effects are highlighted.

Due to climatic change and the increased usage of coastal areas, there is an increasing risk of dike failures along the coasts worldwide. Wave run-up plays a key role in the planning and design of a coastal structure. Coastal engineers use empirical equations for the determination of wave run-up. These formulae generally include the influence of various hydraulic, geometrical and structural parameters, but neglect the effect of the curvature of coastal dikes on wave run-up and overtopping. The scope of this research is to find the effects of the dike curvature on wave run-up for regular wave attack by employing numerical model studies for various dike-opening angles and comparing it with physical model test results. A numerical simulation is carried out using DualSPHysics, a mesh-less model and OpenFOAM, a mesh-based model. A new influence factor is introduced to determine the influence of curvature along a dike line. For convexly curved dikes (αd = 210° to 270°) under perpendicular wave attack, a higher wave run-up was observed for larger opening angles at the center of curvature whereas for concavely curved dikes (αd = 90° to 150°) under perpendicular wave attack, wave run-up increases at the center of curvature as the opening angle decreases. This research aims to contribute a more precise analysis and understanding the influence of the curvature in a dike line and thus ensuring a higher level of protection in the future development of coastal structures.

Water 11(7), 1333 (2019). doi:10.3390/w11071333 special issue: "Special Issue "Wave-structure Interaction Processes in Coastal Engineering" / Guest Editor: Prof. Dr. Francesco Aristodemo, Università della Calabria, Department of Civil Engineering (DINCI), Arcavacata di Rende (CS), Italy; Prof. Dr. Marcello Di Risio, University of L'Aquila - Department of Civil, Construction-Architectural and Environmental Engineering Department (DICEAA), Environmental and Maritime Hydraulic Laboratory (LIam), Monteluco di Roio, L'Aquila, Italy", Published by MDPI, Basel