Waverider Research Articles

Observed typhoon wave spectrum in northern South China Sea

To describe both the way in which a wave spectrum grows and the growth processes of realistic wave conditions, the dependence relationship between the spectrum parameters and wind parameters must be obtained. Based on data measured in 2010 by a Wave Rider buoy, which was deployed in the South China Sea at coordinates 21.89°N, 115.13°E, we evaluated the wave spectrum in the sea area when affected by three typhoons: Conson, Chanthu, and Megi. The Joint North Sea Wave Project spectrum was parameterized based on the observed wave spectrum. We proposed a spectrum with three parameters: the dimensionless lowest moment of the spectrum, dimensionless peak frequency, and spectrum width. The relationships between these spectral parameters and the dimensionless fetch were also discussed.

The new wave: are artificial waves the future of surfing?

Surfers are used to hanging around at the beach waiting for the magic words Surfs Up!, but for many wave riders these days there is no real need to hang around for your wave at all, or even travel to the beach to surf it. Wave pools and wave parks allow landlocked surfers to ride the curl whenever they like, whilst even natural swells that hit the coastline can theoretically be improved with the development of artificial surfing reefs.

Wave energy park power quality impact and collection grid economic assessment

In this study, a wave park is analysed from the economic and electrical points of view. The system under consideration goes from each wave energy unit up to the point of common connection with the main grid. Time series are obtained from simulation models for a scaled prototype and include data for mild, medium and strong sea states. The simulation models have been validated against the small scale tank testing of a prime mover, a wave rider buoy and a scaled testing of the power take-off in a land-based test rig. The design of the proposed wave park layout aims to minimise its cost and power losses. A life-cycle analysis of the park is performed showing that around 30 €/MWh will be the share of the electricity price required to install and operate the wave park grid. The power quality of the wave park and its compliance with regulations are also analysed. Special emphasis is put in the study of flicker emissions concluding that the proposed wave park is within the grid code limitations and even a reduction of a 66% in the flicker coefficients is reported when considering the aggregation of several units in one model.

Surface Current and Wave Measurement during Cyclone Phailin by High Frequency Radars along the Indian Coast

Cyclone Phailin originated in the east central Bay of Bengal (BoB) and crossed into the Indian mainland after traversing through the BoB. High frequency radar (HFR) operated by the National Institute of Ocean Technology could track the surface currents and high wave activity within its measuring limits. The radar data provide valuable information on the surface dynamics during the cyclone period. The HFR observations compare well with those of wave rider buoy. This opens up opportunities for observing the wave conditions during the cyclonic period over longer distances from the shore. This method is relatively more robust as HFR is less likely to be disrupted due to the passage of cyclones, unlike moored systems.

Inter-annual variations in wave spectral characteristics at a location off the central west coast of India

Abstract. The inter-annual variations in wave spectrum are examined based on the wave data measured at 9 m water depth off the central west coast of India from 2009 to 2012 using a wave rider buoy. The temporal variation of the spectral energy density over a calendar year indicates similar variation in all the four years studied. The inter-annual variations in wave spectrum are observed in all months with larger variations during January to February, May and October to November due to the changes in wind-sea. The seasonal average wave spectrum during the monsoon (June–September) is single-peaked and the swell component is high in 2011 compared to other years. The annual averaged wave spectrum had higher peak energy during 2011 due to the higher spectral energy present during the monsoon period. During the non-monsoon period, two peaks are predominantly observed in the wave spectra; with the average peak at 0.07 Hz corresponding to the swells from the Indian Ocean and another at 0.17 Hz due to the local wind field.

Inter-annual Variations in Wave Characteristics off Ratnagiri, Northeast Arabian Sea

The wave data measured using the Datawell directional wave rider buoy at 13 m water depth off Ratnagiri during 2010 to 2013 is used to study the inter-annual variations in the wave characteristics. The percentage occurrence of waves with significant wave height (Hs) less than 1 m is the same in all 3 years, but the occurrence of high waves (Hs > 1 m) is not same in all the years. The extreme wave events occur during the monsoon period and if these wave events persists for longer periods cause coastal erosion and hence we have examined the events lasting more than 5h with different threshold limits of wave height (2.5, 3 and 3.5 m). Average Hs during the monsoon is around 3 times that in non-monsoon period. Average of the maximum wave spectral energy density is 12 times higher in monsoon than in non-monsoon. Inter-annual variations in monthly average Hs is maximum (0.5 m) in June and September due to the change in the monsoon intensity. The inter-annual variation in annual average Hs is around 0.1 m and the annual average peak period is 0.1 to 0.5 s. The monsoon average peak period is slightly higher than the values during the non-monsoon period. The joint distribution of the peak wave period and the mean wave direction indicate three peaks; one corresponding to the southwest swells during the post-monsoon season, the second for the southwest-westerly monsoon waves and the third for the northwest waves during the pre-monsoon season.

Impacts of Ports on Shoreline Change Along Odisha Coast

Ports involve construction of coastal structures such as groin, sea wall, breakwater, jetty etc. which result in modification of the shoreline and coastal geomorphology Paradip and Dhamara are two major operational ports along Odisha coast while Gopalpur port isbeing developed as all weather open sea direct berthing port.The coastal structures associated with Paradipport at present are two breakwaters and northern sea wall while Dhamara port is built in an estuarine environment with one jetty. At Gopalpur Port, southern (530m)and northern (362m) groinswere constructed during 2007-2009 along both sides of the previously existing piers. Other developments include intermediate (360m)and southern(1735m)breakwaters during November 2011 to December, 2012 on the south and groin field (ten groins of different dimension) on the north during September, 2011 to December, 2012. Impacts of these coastal structures aremonitored every month from June, 2008 to April, 2014 by observing shoreline change, beach profile andLittoral Environment along 30km stretch on the north and south of Gopalpur port along with one year (June 2008-May 2009) wave and tide measurements by deploying tide gauge and wave rider buoy at 23mdepth off Gopalpur port. Besides, seasonal observations on beach profile and shoreline near ParadipPort(August, 2010 to August, 2013) and long term (1975-2014)shoreline change study at Gopalpur, Paradip and Dhamara Portare carried out with topo-sheet data as base line information. The shoreline change rate (m/yr) in the pre and post construction phases are estimated which show distinct difference between the two phases and also on the north and south of the ports.

Real Time Wave Forecasting Using Wind Time History and Genetic Programming

The significant wave height and average wave period form an essential input for operational activities in ocean and coastal areas. Such information is important in issuing appropriate warnings to people planning any construction or instillation works in the oceanic environment. Many countries over the world routinely collect wave and wind data through a network of wave rider buoys. The data collecting agencies transmit the resulting information online to their registered users through an internet or a web-based system. Operational wave forecasts in addition to the measured data are also made and supplied online to the users. This paper discusses operational wave forecasting in real time mode at locations where wind rather than wave data are continuously recorded. It is based on the time series modeling and incorporates an artificial intelligence technique of genetic programming. The significant wave height and average wave period values are forecasted over a period of 96 hr in future from the observations of wind speed and directions extending to a similar time scale in the past. Wind measurements made by floating buoys at eight different locations around India over a period varying from 1.5 yr to 9.0 yr were considered. The platform of Matlab and C++ was used to develop a graphical user interface that will extend an internet based user-friendly access of the forecasts to any registered user of the data dissemination authority.

MODELLING THE MORPHOLOGICAL RESPONSE OF AN EBB TIDAL DELTA TO STORM WAVE FORCING

The Nerang river outlet - located on the Australian east coast - was stabilised with two entrance jetties in 1986. The entrance, now known as the Gold Coast Seaway, has been the subject of growing concern about the ongoing growth of the ebb tidal delta. Historical analysis of surveying data confirmed the gradual growth of ebb tidal delta, although a sand bypassing system was implemented upstream when the entrance was stabilised. The dredging of the Seaway ebb delta is inevitable to keep the navigation channel open and safe. However, the dredging operation is both time and budget consuming and therefore having a more accurate model which can predict the pattern of morphological changes precisely seems essential. A coupled wave, flow and sediment transport model was developed using MIKE 21 Coupled Model to investigate the sediment transport pattern mainly in the area of the ebb-tidal delta and its linkage with littoral drift in the adjacent open coast. The hydrodynamics of the model were calibrated and verified against current measurements inside the Seaway and offshore wave data obtained from the Gold Coast Wave Rider Buoy. The pattern of the simulated morphological changes was qualitatively similar to that of the observations, and the model’s results show that the storm waves forcing govern the growth of the ebb-tidal delta, and also leads to severe bathymetry changes along the adjacent ocean beaches. The model was found to underestimated the volume of sediment transport in the domain and so further model sensitivity analysis is ongoing in an effort to reach to a quantitatively calibrated morphological model.

KuROS: A New Airborne Ku-Band Doppler Radar for Observation of Surfaces

Abstract This study presents the new airborne Doppler radar Ku-Band Radar for Observation of Surfaces (KuROS), which provides measurements of the normalized radar cross section σ° and of the Doppler velocity over the sea. The system includes two antennas rotating around a vertical axis, although only the results from the lower incidence (14°) antenna are presented here. Also given are the first results from observations performed during two field campaigns held in 2013: the Hydrological Cycle in Mediterranean Experiment (HyMeX) and the Prévision Océanique, Turbidité, Ecoulements, Vagues et Sédimentologie (PROTEVS). Sea wave directional spectra computed by the radar from tilt modulation of σ° are consistent with those given by the directional wave rider moored in the Mediterranean basin, both in terms of significant wave height Hs and main features of the wavenumber spectrum. As concerns the azimuthal distribution, two methods are tested to remove the 180° ambiguity of the radar-derived directional spectrum. The first method is based on the correlation between the modulations of σ° and Doppler velocity, which reflects the correlation between the sea surface slope and orbital velocity. The second method does not use the Doppler velocity but computes the cross spectrum between the modulations of σ° between two power profiles separated by some time lag ΔT, from which the phase velocity of sea waves is deduced. Comparing the sea wave directional spectra disambiguated by both methods, with the directional spectrum given by the wave rider, it is concluded that the first method (using Doppler velocity) is more efficient to remove the 180° ambiguity and should be preferred to the second method.

Ambient noise during rough weather and cyclones in the shallow Bay of Bengal

This paper presents ambient noise analysis during rough weather, using time series measurements from an automated noise measurement system in the shallow southwest Bay of Bengal during October–November 2010. The period witnessed low-pressure events including depressions and cyclones, with JAL cyclone passing close to the measurement site. The time series noise level shows a shift in mid-October, after which deep depressions and cyclones formed, with an average increase of 5–10 dB in the lower band and 2–3 dB in the higher band of frequencies. Furthermore, correlation between noise level and wave height (data from wave rider buoy deployed at the site) for sea state scale 3 and above shows good correlation with an increase in noise level with increase in wave height, the effect being most pronounced at 0.5 kHz. The noise captured during JAL was analysed to identify the spectrum components due to convective precipitation and heavy wind/wave activity and shows anomalously high levels during the crossing of the cyclone. Rain noise spectra from the rain bands associated with the wall of the cyclone are reported. This has been correlated with radar reflectivity measurements to ascertain the presence of rain, and discriminate between convective and stratiform types. Also, vertical directionality pattern of ambient noise during JAL showed clearly distinct surface contributions. On the whole, knowledge of ambient noise fields during high sea states and precipitation is useful in optimizing SONAR performance. The findings at the study site have been compared with measurements from other shallow water locations during rough weather.

A New Platform for the Determination of Air–Sea Fluxes (OCARINA): Overview and First Results

AbstractThe present paper describes a new type of floating platform that was specifically designed for estimating air–sea fluxes, investigating turbulence characteristics in the atmospheric surface boundary layer, and studying wind–wave interactions. With its design, it can be deployed in the open ocean or in shallow-water areas. The system is designed to be used from a research vessel. It can operate for ~10 h as a drifting wave rider and 3 h under power. Turbulence and meteorological instrument packages are placed at a low altitude (1–1.5 m). It was deployed for validation purposes during the Front de Marée, Variabilité (FROMVAR), 2011 experiment off the west coast of Brittany, France. Wind friction velocity and surface turbulent buoyancy flux were estimated using eddy covariance, spectral, bulk, and profile methods. The comparisons of the four methods show a reasonable agreement except for the spectral buoyancy flux. This suggests that the platform design is correct. Also, the wind measured at a fixed height above the sea shows spectral coherence with wave heights, such that wind and swell are in phase, with the largest wind values on top of swell crests. This result in qualitative agreement with current model predictions supports the capability of the Ocean Coupled to Atmosphere, Research at the Interface with a Novel Autonomous platform (OCARINA) to investigate wind–swell interactions.

Hydrodynamics of a small trained tidal inlet (Currumbin Creek, Australia)

Abstract. Small tidal inlets are important features of coastal areas, in terms of provision of access from a back barrier water-body to the ocean as well as periodic circulation of fresh nutrients for the local ecology. Usually, dimensional and geometrical characteristics contribute significantly to morphological stability or instability of a particular inlet and necessitate an individual investigation of any desired location. In other words, generalized usage of previous empirical and experimental research of a different position can hardly be used for other places. In this regard, one of the powerful tools to understand the physical processes of a particular region is to collect as much field data as possible. Such a dataset is used to further analyse and explore the governing processes and can also be used for building a numerical computer model for supplementary studies. In this research, the results of a comprehensive field measurement at Currumbin Creek, Queensland, Australia are presented. This study is part of broader research to investigate the long term evolution of the Currumbin entrance and its adjacent beaches. Currently, an annual dredging campaign is needed to reduce the risk of flooding due to excess rainfall inundations and to maintain water quality. The majority of data were collected over a three month period consistent with the time of the 2012 dredging operation. However, due to the loss of some instrumentation, data collection for some of the parameters was repeated till the middle of May 2013. All collected data included: (1) nearshore waves and tide; (2) creek tidal variation; (3) creek flow discharge and velocity; (4) bathymetric survey of the creek; (5) beach profile evolution survey; and (6) sediment sampling. The measurement showed that the creek entrance is tidally dominated, with flood events having a major role in sediment transport into the creek. The nearshore stations' wave data illustrated the marginal effect of the beach curvature between updrift and downdrift stations. Thus, the historical dataset available from the updrift wave rider buoy will be selected to be used for future numerical modelling. Although changes of some beach profiles were comparatively insignificant, the dramatic changes of the profile lines nearby the inlet channel and also rapid bathymetric change of the flood shoal following the dredging completion are valuable information to better calibrate and interpret a local sediment modelling study for the next phase. Essentially, this evaluation needs to be considered for proposing any alternative maintenance activities.

Coastal processes and longshore sediment transport along Kundapura coast, central west coast of India

Longshore sediment transport (LST) is one of the main factors influencing coastal geomorphology. This study examines the variation in the LST estimate using four well known formulae and the sensitivity of wave parameters on LST determination. The study was done along the Kundapura coast, central west coast of India. The Delft3D-wave module was used for obtaining the nearshore wave characteristics from the wave data measured using Datawell directional wave rider buoy at 12m water depth for a period of one year. Diurnal change and seasonal variation in LST were examined. The study shows that the net LST was toward north for most of the time (non-monsoon period) during the year when predominant wave direction was between SWS and SW, whereas the LST was toward south during the monsoon season when the wave direction was from the west. It was found that the influence of breaker height was more during the non-monsoon period whereas during the monsoon period, breaker angle shows more influence on LST. Estimated annual net LSTR for the region is 3.6, 3.0, 1.6, and 2.6×105m3 based on the CERC, Walton and Bruno, Kamphuis and Komar formulae. The LSTR estimate based on the Kamphuis formula, which also includes the wave period, beach slope, and sediment grain size, was found to be a reliable estimate for the study region. The variation in LSTR estimate considering different data intervals was also examined and found that the difference in monthly LSTR for data intervals of 6, 12 and 24h with respect to the 3h interval was up to 11, 13 and 24%. For better and more accurate estimates of LSTR, the data interval should be 3h or less.

Wave forecasting system for operational use and its validation at coastal Puducherry, east coast of India

An incredible demand for coastal sea-state forecast in recent years has led to development and implementation of wave forecasting system in operational centers, having wide practical applications relevant to marine industry. The wave forecasting system takes advantage of parametric techniques, by nesting global ocean wave models to coastal and near-shore high-resolution wave models. The Indian National Centre for Ocean Information Services (INCOIS) at Hyderabad has a mandate for operational marine weather forecast services that envisages integration and coupling state-of-the-art weather models for operational oceanographic needs. In the present study, two state-of-art wave models viz; WAVEWATCH III (WW3) and Simulating WAves Nearshore (SWAN) are nested and forced with French Research Institute for Exploitation of the Sea/Laboratory of Oceanography From Space (IFREMER/CERSAT) blended surface winds. The objective is to investigate wave evolution at a coastal location off Puducherry in the east coast of India. To evaluate model performance, a detailed validation study is performed by comparing model-simulated wave parameters and wave spectra with corresponding in-situ wave rider buoy observations for four prominent seasons viz; northeast monsoon, southwest monsoon, pre- and post-monsoon. The study signifies applicability of nested wave model for operational use during normal weather condition at coastal Puducherry.

Comment on “Wave‐turbulence interaction and its induced mixing in the upper ocean” by Huang and Qiao

Comment on “Wave‐turbulence interaction and its induced mixing in the upper ocean” by Huang and Qiao

Adaptive Pole Assignment Control for Generic Elastic Hypersonic Vehicle

This paper uses robust pole assignment method to design an adaptive velocity and altitude tracking control algorithm for the longitudinal model of a wave rider configuration air-breathing hypersonic vehicle, which has strong coupling between structure, propulsion and aerodynamics. Base on the elastic hypersonic vehicle model CSUAL_GHV, the simulations using adaptive robust pole assignment control method and adaptive non-robust pole assignment control method are carried out respectively. The results show that, compared with the non-robust pole assignment control method, control system using adaptive robust pole assignment control method not only achieves the velocity and altitude tracking goal with tracking error less than 1%, but also the vibration motion of the hypersonic vehicle is suppressed sufficiently.  Air-breathing hypersonic vehicle is a kind of aircraft flying in the near space atmosphere, which is powered by scramjet and flying faster than 5 Mach. Because of its high speed, the hypersonic vehicle can be used as a military rapid combat platform as well as a fast civilian global transportation, and thus have received much attention. The last successful flight test of the U.S. X-51A Waverider hypersonic vehicle indicates that the hypersonic flight technology has been developed gradually from the experimental stage to the practical stage. Due to the use of airframe/engine integration design technology, the hypersonic vehicle exhibits strong coupling between structural, propulsion and aerodynamics. The hypersonic

Monsoon and cyclone induced wave climate over the near shore waters off Puduchery, south western Bay of Bengal

Seasonal and annual variations in wave characteristics are studied based on measurements during 2009–2011 using wave rider buoy. Presence of swells generated by the south Indian Ocean cyclones are found over the south western Bay of Bengal during pre-monsoon season. Maximum significant wave height is measured 6m during Thane cyclone in December, 2011. Long period waves are observed mostly during the summer (SW) monsoon and are negligible in the winter (NE) monsoon period. Short period waves dominate (63%) the wave climate during the NE monsoon. Wave spectra during the SW monsoon are multi peaked whereas during the post monsoon season single peaked spectra are found. Single peaked spectra observed during SW monsoon of 2011 coincides with the presence of positive Indian Ocean Dipole. Waves during the pre monsoon and SW monsoon season are influenced by sea breeze. Analysis indicates that directional width is minimum for waves from the NE since they are wind waves and maximum for waves from SE since they are swells. Study indicates that wave climate of the south western Bay of Bengal is in contrast to that in eastern Arabian Sea during the SW monsoon.

Surpact: A SMOS Surface Wave Rider for Air-Sea Interaction

A new small wave rider called Surpact was developed for air-sea investigations. It was designed to attach to a drifter or a mooring and to float upon the surface waves in order to measure sea state and atmospheric sea level pressure as well as temperature and salinity at a small fixed depth from the surface. Wind speed is derived from Surpact sea state measurements, and the data are calibrated with co-located Special Sensor Microwave Imager Sounder (SSMIS) wind retrievals during a four-month deployment in the North Atlantic subtropics. Individual 15-minute wind estimates present a root mean square difference on the order of 15% with the SSMIS wind retrievals for wind speeds less than 12 m s-1. The wind retrievals might lag the actual wind changes for moderate to strong winds by an hour. This article discusses the accuracy of these wind retrievals based on in situ data collected during the Strasse cruise in August and September 2012. Temperature and salinity data are also examined. The authors find, under some sunny conditions, radiative warming of the temperature probe reduces the accuracy of some of the daytime temperature data and also affects corresponding salinity estimates. Nonetheless, small realistic daily cycles of near-surface salinity (0.01 psu amplitude) were observed. Also, examples of wind time series collected during salinity drops caused by rainfall during late 2012 in the North Atlantic subtropics indicate no intensification of wind during these rain events.

Observation-based evaluation of surface wave effects on currents and trajectory forecasts

Knowledge of upper ocean currents is needed for trajectory forecasts and is essential for search and rescue operations and oil spill mitigation. This paper addresses effects of surface waves on ocean currents and drifter trajectories using in situ observations. The data set includes colocated measurements of directional wave spectra from a wave rider buoy, ocean currents measured by acoustic Doppler current profilers (ADCPs), as well as data from two types of tracking buoys that sample the currents at two different depths. The ADCP measures the Eulerian current at one point, as modelled by an ocean general circulation model, while the tracking buoys are advected by the Lagrangian current that includes the wave-induced Stokes drift. Based on our observations, we assess the importance of two different wave effects: (a) forcing of the ocean current by wave-induced surface fluxes and the Coriolis–Stokes force, and (b) advection of surface drifters by wave motion, that is the Stokes drift. Recent theoretical developments provide a framework for including these wave effects in ocean model systems. The order of magnitude of the Stokes drift is the same as the Eulerian current judging from the available data. The wave-induced momentum and turbulent kinetic energy fluxes are estimated and shown to be significant. Similarly, the wave-induced Coriolis–Stokes force is significant over time scales related to the inertial period. Surface drifter trajectories were analysed and could be reproduced using the observations of currents, waves and wind. Waves were found to have a significant contribution to the trajectories, and we conclude that adding wave effects in ocean model systems is likely to increase predictability of surface drifter trajectories. The relative importance of the Stokes drift was twice as large as the direct wind drag for the used surface drifter.