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Abstract Buoys carrying scientific equipment usually need continuous power supply for the operation of these equipments. These buoys can be equipped with actuators and controlled to harvest power from the heaving motion of the buoy. A two-body wave energy converter can be designed such that the buoy heaves to harvest energy while the second (lower) body carries the science equipments. This paper presents a control approach for this type of two-body wave energy converter. This control approach is a multi resonant control that attempts to maximize the harvested energy from the buoy (upper body). In this model, the actuator is attached to both bodies. The lower body however is required to have minimal heave motion. The proposed multi resonant control utilizes measurements of the buoy position. The frequencies of the measured buoy position are estimated, along with the motion amplitudes of these frequencies, and used for feedback control. Estimation is carried out using two approaches; the first uses a linear Kalman filter while the second uses an extended Kalman filter. A new method for handling the motion and actuation limitations, suitable for the multi resonant control, is proposed. Various numerical simulation results are presented in the paper. Simulation results show that the linear Kalman filter estimation approach is more robust and computationally efficient compared to the extended Kalman filter.

Black Carbon (BC) is an absorbing aerosol which has significant impact on the Earth - Atmosphere radiation balance and hence on climate. The variation of BC mass concentration and contribution of fossil fuel and biomass burning have been investigated over the Indian ocean sector of the Southern Ocean during austral summer. BC mass was in the range of 300-500 ng m-3 between 23.3oS to 24.5oS followed by decrease in BC to 150 ng m-3 as moving to higher southern latitudes till 41oS latitude. An increase in BC mass from 250 to 450 ng m-3 was found between 41 and 50oS due to trap of air masses by cyclonic wind and transport of aerosols from the southern part of African and eastern Madagascar regions. Higher BC concentration (250-350 ng m-3) was observed in the latitude range of 57-60oS which can be attributed to convergence of north-westerly and south-easterly winds. The dominant contributor to BC was fossil fuel, which was > 80% during half of the total observations, while > 20% biomass burning contributed to one fifth of observations. The coastal Antarctic region showed higher BC mass concentration with mixed type of contributions of biomass and fossil fuel. Such accumulation of BC near the Antarctic coast can have a crucial impact on the sea-ice albedo which significantly affect the Antarctic climate system locally and global climate in general.

Abstract The performance evaluation of a wave energy converter in wave channel is influenced by the hydrodynamic effects caused by the near presence of the side walls. Since this phenomenon is not observed in the open ocean, it is important to assess the walls influence in the converter dynamics when analysing experimental results. This paper studies the dynamics and power extraction of an axisymmetric floating oscillating water column (OWC) device, the Spar-buoy OWC, using experimental data obtained in a wave channel. A two heaving body model (spar-buoy and OWC) based on linear forces is formulated in the frequency domain. Linear hydrodynamic coefficients are obtained from a boundary integral equation method. The presence of the channel side walls is simulated approximately by a periodic array of devices, and alternatively by two finite-length walls. Linearized drag forces are derived from small-scale model tests. Power extraction results are presented for regular and irregular waves. The numerical simulations show that the wall effect may amplify the power capture up to a maximum of 15% for regular waves and 10% for irregular wave conditions, for a channel-width-to-device-diameter ratio equal to 5.25.

A one-dimensional wave model was used to investigate the reef top wave dynamics across a large suite of idealized reef-lagoon profiles, representing barrier coral reef systems under different sea-level rise (SLR) scenarios. The modeling shows that the impacts of SLR vary spatially and are strongly influenced by the bathymetry of the reef and coral type. A complex response occurs for the wave orbital velocity and forces on corals, such that the changes in the wave dynamics vary reef by reef. Different wave loading regimes on massive and branching corals also leads to contrasting impacts from SLR. For many reef bathymetries, wave orbital velocities increase with SLR and cyclonic wave forces are reduced for certain coral species. These changes may be beneficial to coral health and colony resilience and imply that predicting SLR impacts on coral reefs requires careful consideration of the reef bathymetry and the mix of coral species.

Abstract The transformation of small-amplitude surface gravity waves as they propagate into a shoaling sea water with a wind-driven current is investigated. The current may vary horizontally on a scale larger than the wave length. Neglecting turbulent dissipation, wave diffraction and breaking, the combined motion of waves and currents is modeled mathematically. The model consists of the linear wave theory expressions of frequency, group velocity, energy and radiation stress together with equations that describe the mass and momentum exchange between waves and current and the conservation of wave crests and wave action under current effects. The boundary value problem for the wave-current interaction inside an infinitely long-shore sea region (outside the surf zone) with parallel depth contours is solved analytically for steady wind-driven currents and obliquely incident waves. The solution clarifies the manner by which wind-driven currents, together with bathymetry variation and coastal boundary limitations, transform the characteristics of the propagating waves and how this, in turn, affects the sea surface displacement (set-up).

Abstract The effectiveness of isolation of CO 2 injected in the North Pacific Ocean was discussed in the seasonal flow fields, which were computed on the bases of the seasonal change of wind, water temperature and salinity. A periodic annual flow field was estimated, where the seasonal change of flow was taken into account using the computed flow fields in four seasons. Particle tracking was also carried out in the periodic flow field over 200 years. The effectiveness of isolation was discussed, in comparison with the computational results in the annual mean flow fields.

Abstract This paper describes the analysis of the spatial properties of ocean waves using measurements from an array of four directional wave buoys installed in a square formation, with side 500 m, in the Celtic Sea, UK. Wave measurements in this area have been installed to support resource assessment and design for wave energy devices at the Wave Hub site off the North Cornwall coast. This unique deployment of multiple directional sensors provides high quality direct measurements of the spatial properties of the wave field. Spectral parameters measured simultaneously by all four buoys within the array are compared and it is demonstrated that wave conditions cannot be considered stationary across the measurement area. Differences in the measured wave fields were observed primarily in the low frequencies and are observed to be of a level sufficient to impact the assessment of site characteristics. Theoretical estimations of refraction and bottom friction indicate that these physical processes contribute to the observed measurements. The results demonstrate the potential effect of spatial variability in wave fields on the monitoring of wave energy sites, and highlight the requirement for accurate evaluation of physical processes.

This study first reviews the various stages of development of recent International Maritime Organisation (IMO) guidelines for the assessment of the minimum propulsion power for safe navigation of ships in adverse conditions, while complying with the requirements of energy efficiency in the frame of the IMO strategy for Green House Gas (GHG) emission reduction from ship operations. It summarizes the underwent key revisions of the guidelines after their original introduction in 2010 (MEPC 61) referring to key elements in the assessment method, such as the definition of the adversity of the operational conditions and ship's navigation speed, to the variety of methods for the prediction of the added resistance in waves, to the recommended thrust deduction fraction and wake fraction, etc., as outlined in the latest version of the guidelines adopted at IMO-MEPC76 (June 2021). An inconsistency in the recommended alternative methods for the added resistance prediction is demonstrated by the analysis of a series of typical tanker and bulk carrier designs. A minimum propulsion power assessment is conducted for the KVLCC2 standard tanker ship to show the impact of the recommended new guidelines on the ship powering requirement. Lastly, the uncertainties involved in the assessment procedure are discussed. ; Ministry of Education (MOE) ; This study is partly supported by the Ministry of Education,Singapore, under its Academic Research Fund Tier 1 (Award Number: #020211-00001; Award Title: “Investigation of the self-propulsion factors for determining minimum propulsion power to ensure safe ship operation at low speeds”).

A three dimensional rectangular grid model is applied to resolve the temperature-salinity dynamics of Ruwais, a segment of the UAE coast which is well known as dense water formation zone. The model employs a heat flux module and a turbulence closure scheme that facilitate realistic calculation of temperature-salinity dynamics. A field survey campaign is carried out to support the modeling study, involving measurements of tide, currents, temperature, and salinity. Investigation is done for two meteorologically extreme conditions, i.e. summer and winter. The model study showed that the western flux develops an anticlockwise circulation in the study area. The water industrial discharges elevated the temperature and salinity of the water near the southeastern shoreline. This water mass propagated towards north under the influence of gravity.