10 results found
ALMALKI Y, KARMPADAKIS I, SWAN C, 2023, Experimental investigation on the hydrodynamic performance of a pile-supported OWC-type breakwater, Proceedings of the European Wave and Tidal Energy Conference, Vol: 15, ISSN: 2706-6932
<jats:p> The present study considers the design optimisation of an Oscillating Water Column (OWC) incorporated into a pile-supported breakwater structure. This has been achieved by performing a substantial number of scaled physical model tests and a methodical variation of key device parameters within multiple configurations. The key aspects that have been investigated include: (a) the geometric characteristics of the breakwater structure, (b) the pneumatic efficiency of the OWC, (c) the geometry of the OWC chamber and (d) the relative position of the OWC chamber within the breakwater. The present work considers (monochromatic) regular waves of varying steepness and effective water depth as incident wave conditions. The efficiency of the designed structure in terms of shore protection capacity and wave energy extraction was assessed by quantifying relevant transmission coefficients and the power output metrics. This has been achieved by using a combination of collocated and complementary measuring devices, such as arrays of wave gauges, pressure transducers and a high-definition video camera. The study concluded that systematic refinement of the geometrical parameters can substantially enhance the overall hydrodynamic efficiency of a pile-supported OWC breakwater. Additionally, it was found that a configuration featuring a chamber positioned in front of the breakwater, with a relative chamber breadth of 0.67, outperforms wider breadth configurations in terms of both energy extraction efficiency and reduction of the transmission coefficient. Taken together, the present study provides an in-depth analysis of the effects of key design parameters of a breakwater-integrated OWC, its efficiency and shore protection potential.</jats:p>
Karmpadakis I, Swan C, 2023, Improved Crest Height Predictions for Nonlinear and Breaking Waves in Large Storms, Design and Management of Port, Coastal and Offshore Works, ISSN: 2945-1299
Karmpadakis I, Katsardi V, Swan C, et al., 2023, Statistical Distribution of Free Water Surface over a Mild Bed Slope for Extreme Wavefields, Design and Management of Harbor Coastal and Offshore Works, ISSN: 2945-1299
Karmpadakis I, Swan C, 2022, A new crest height distribution for nonlinear and breaking waves in varying water depths, Ocean Engineering, Vol: 266, Pages: 1-17, ISSN: 0029-8018
The statistical distribution of zero-crossing crest heights represents a critical design input for a wide range of engineering applications. The present paper describes the development and validation of a new crest height model, suitable for application across a broad range of water depths. The purpose of this model is two-fold: first, to describe the amplifications of the largest crest heights arising due to nonlinear interactions beyond a second-order of wave steepness, and second, to incorporate the dissipative effects of wave breaking. Although these two effects act counter to each other, there is substantial evidence to suggest departures from existing models based upon weakly nonlinear second-order theory; the latter corresponding to current design practice. The proposed model has been developed on the basis of a significant collection of experimental results and a small subset of field measurements. It incorporates effects arising at different orders of nonlinearity as well as wave breaking in a compact formulation and covers a wide range of met-ocean conditions. Importantly, the new model has been independently validated against a very extensive database of experimental and field measurements. Taken together, these include effective water depths ranging from shallow water (
Karmpadakis I, Dukker T, Triantafyllou N, et al., 2022, ADAPTIVE DESIGN OF COASTALFLOODING DEFENCES: A COUPLEDEXPERIMENTAL AND NUMERICALAPPROACH, ICE Coasts, Marine Structures & Breakwaters 2023
Karmpadakis I, Swan C, Christou M, 2022, A new wave height distribution for intermediate and shallow water depths, Coastal Engineering, Vol: 175, Pages: 1-15, ISSN: 0378-3839
The present paper addresses the short-term distribution of zero-crossing wave heights in intermediate and shallow water depths. New physical insights are provided regarding the effects of nonlinearity, directionality, reduced effective water depth and finite spectral bandwidth. These are demonstrated through the analysis of a large database of experimental simulations of short-crested sea-states on flat bed bathymetries. A new wave height model is proposed building upon these physical insights and is calibrated using the experimental data. Independent comparisons between field measurements and the proposed model indicate that it is appropriate to a wide range of incident wave conditions and that it provides considerable improvement over existing models.
Karmpadakis I, Swan C, 2020, On the average shape of the largest waves in finite water depths, Journal of Physical Oceanography, Vol: 50, Pages: 1023-1043, ISSN: 0022-3670
This paper investigates the average shape of the largest waves arising in finite water depths. Specifically, the largest waves recorded in time-histories of the water surface elevation at a single point have been examined. These are compared to commonly applied theories in engineering and oceanographic practice. To achieve this both field observations and a new set of laboratory measurements are considered. The latter concern long random simulations of directionally spread sea-states generated using realistic JONSWAP frequency spectra. It is shown that approximations related to the linear theory of Quasi-Determinism (QD) cannot describe some key characteristics of the largest waves. While second-order corrections to the QD predictions provide an improvement, key effects arising in very steep or shallow water sea-states are not captured. While studies involving idealised wave groups have demonstrated significant changes arising as a result of higher-order nonlinear wave-wave interactions, these have not been observed in random sea-states.The present paper addresses this discrepancy by decomposing random wave measurements into separate populations of breaking and non-breaking waves. The characteristics of average wave shapes in the two populations are examined and their key differences discussed. These explain the mismatch between findings in earlier random and deterministic wave studies.
Karmpadakis I, Swan C, Christou M, 2020, Assessment of wave height distributions using an extensive field database, Coastal Engineering, Vol: 157, Pages: 1-15, ISSN: 0378-3839
The present paper investigates the short-term statistical distribution of wave heights. Specifically, some of the most commonly applied wave height distributions are assessed using field measurements. The latter comprise of wave radar observations from 10 different locations in the North Sea and cover water depths between 7.7 m and 45 m. In total, the field database includes more than 200 million waves, making it one of the largest of its kind in this water depth regime. In using these data, the accuracy of existing wave height distributions has been examined and guidance is provided concerning the best performing models and their domain of applicability. Additionally, insights concerning the influence of key met-ocean parameters are also provided. Taken together, the results in this paper present an overview of the statistical behaviour of wave heights in finite water depths, as observed in the field.
Karmpadakis I, Swan C, Christou M, 2019, Laboratory investigation of crest height statistics in intermediate water depths, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 475, Pages: 1-24, ISSN: 1364-5021
This paper concerns the statistical distribution of the crest heights associated with surface waves in intermediate water depths. The results of a new laboratory study are presented in which data generated in different experimental facilities are used to establish departures from commonly applied statistical distributions. Specifically, the effects of varying sea-state steepness, effective water depth and directional spread are investigated. Following an extensive validation of the experimental data, including direct comparisons to available field data, it is shown that the nonlinear amplification of crest heights above second-order theory observed in steep deep water sea states is equally appropriate to intermediate water depths. These nonlinear amplifications increase with the sea-state steepness and reduce with the directional spread. While the latter effect is undoubtedly important, the present data confirm that significant amplifications above second order (5–10%) are observed for realistic directional spreads. This is consistent with available field data. With further increases in the sea-state steepness, the dissipative effects of wave breaking act to reduce these nonlinear amplifications. While the competing mechanisms of nonlinear amplification and wave breaking are relevant to a full range of water depths, the relative importance of wave breaking increases as the effective water depth reduces.
Karmpadakis I, Swan C, Christou M, 2019, Wave height and crest height distributions in shallow water — Analysis of field data, Coastal Structures
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