Effects Of Oblique Waves Research Articles

On the Stability of Rubble Mound Structures under Oblique Wave Attack

Slope stability formulae for rubble mound structures are usually developed for head-on conditions. Often, the effects of oblique waves are neglected, mainly because it is assumed that for oblique wave attack, the reduction in damage compared to perpendicular wave attack is insignificant. When the incident waves are oblique, the required armour size can be reduced compared to the perpendicular wave attack case. Therefore, it is important to consider the wave obliquity influence on slope stability formulae as a reduction factor. One of the most recent formulae for estimating the stability of rock-armoured slopes, referred to as Etemad-Shahidi et al. (2020), was proposed for perpendicular wave attack. The aim of this study is to develop a suitable wave obliquity reduction factor for the above-mentioned stability formula. To achieve this, first, laboratory experiment datasets from existing reliable studies were selected and analysed. Then, previously suggested reduction factors were evaluated and a suitable reduction factor for the mentioned stability formula were suggested. The suggested reduction factor includes the effect of wave obliquity and directional spreading explicitly. It is shown that the stability prediction is improved by using the wave obliquity reduction factor.

The effects of oblique waves and currents on the loadings and performance of tidal turbines

Tidal energy exploitation is at an early deployment stage and costs need to be reduced to improve the long term economic viability of the sector. High costs of tidal turbines are, in part, the result of load uncertainties, which lead to the use of high factors of safety in the design to ensure survival. One of the most important causes of uncertainty is hydrodynamic loadings. To date, most of the scaled model experiments with horizontal axis turbines investigating this issue have been carried out with collinear wave and current directions. To the authors' knowledge, the work presented herein is the first experimental investigation of a horizontal axis turbine model subjected to combined oblique waves and current. Turbine performance and loading are measured for a 1:15 scale model tested in the FloWave circular, combined wave and current basin at the University of Edinburgh (UK). Three different flow directions were tested and each of them were also combined with regular waves in three different directions non-collinear with the flow. Fifteen physical quantities were measured including flow velocity, rotor and foundation loads and turbine speed. Characterisation of loads and turbine performance in those oblique current and wave conditions are presented. Waves affect means and standard deviation of rotor power and thrust, but off-axis waves are associated with lower thrust loads than head-on waves. Compared to current only, rotor torque and thrust standard deviations are higher in the presence of waves and almost twice as high when the wave crest is parallel to the rotor plan. The experimental data associated with this article can be downloaded from http://dx.doi.org/10.7488/ds/2360.

Effects of Obliquely Incident Waves on Overtopping for Vertical Walls

ABSTRACT Kim, Y.T.; Shin, S.W.; Choi, J.W., and Lee, J.I., 2016. Effects of oblique waves on overtopping for vertical walls. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1357 - 1361. Coconut Creek (Florida), ISSN 0749-0208. In determination of the crest height of a vertical structure against attacking of obliquely incident waves, most of existing studies have suggested to use the overtopping reduction factor due to incident angles. However, they have not considered the amplification of wave heights and the spatial distribution of wave overtopping. In this study, a spatial distribution of wave overtopping along a vertical structure is experimentally investigated and also the wave overtopping reduction factors (γ) for incident wave angle is suggested. When the incident angle becomes larger, the wave overtopping reduction factor decreases almost l...

OBLIQUE WAVE ATTACK ON CUBE AND ROCK ARMOURED RUBBLE MOUND BREAKWATERS

Stability formulae for armour layers of rubble mound breakwaters are usually being applied assuming perpendicular wave attack. Often it is assumed that for oblique wave attack the reduction in damage compared to perpendicular wave attack is small. This seems however a very conservative assumption. Wave basin tests at Deltares provide information to assess the effects of oblique waves on the stability of rock slopes and cube armoured rubble mound breakwaters. This includes cubes in a single layer and cubes in a double layer. The results show that the few available formulae that include wave obliquity underestimate the effects of oblique wave attack; the observed damage to breakwaters with armour layers of rock and cubes is lower and therefore new stability increase factors and mass reduction factors have been developed. The tests were performed for wave directions between perpendicular (0ï‚°) and 70ï‚°. The results show that large potential savings in diameter and mass can be obtained for large angles of wave obliquity.

The influence of oblique waves on the azimuthal response of a Ku-band scatterometer: a laboratory study

The authors conducted experiments in the large wind-wave tank at IRPHE to examine the influence of longer waves propagating at oblique angles to the wind direction on microwave backscattering. Measurements were made of wind, wave directional spectra, and cross sections from a 13.5-GHz scatterometer at 30/spl deg/ from nadir incidence angle. the authors characterize the scatterometric azimuthal scans with respect to the magnitude and the direction of the maximum backscattered power. Scans of solely wind waves are used to assess the effects of oblique waves, for which the scans yield trends that are related to the oblique-wave direction relative to the wind and the oblique-wave steepness. In particular, cross-section maxima are enhanced by oblique waves and the direction of maxima rotates from the wind axis toward the oblique-wave direction. These scatterometer data, in addition to other oblique-wave studies, led the authors to conclude that wind vectors produced from standard retrieval algorithms for scatterometers should be used with prudence in regions with significant veering winds, such as near meteorological fronts.