Influence Of Sea State Research Articles

Reconstruction of Wide Swath Significant Wave Height From Quasi‐Synchronous Observations of Multisource Satellite Sensors

AbstractGlobal sea wave monitoring is of utmost importance for tasks such as analysis of ocean climate change, offshore fisheries, and early warning of marine disasters. Significant wave height (SWH) is one of the most vital and widely used metrics for measuring sea waves in marine research. Hence, obtaining high precision and extensive coverage measurements of SWH is of great significance for comprehensive sea wave studies. A data set is constructed by combining wave spectrometer and scatterometer data from China‐French Ocean Satellite, synthetic aperture radar (SAR) wave mode data from Sentinel‐1, and altimeter data from Jason‐3 and HY‐2B through space‐time matching method. The multi‐sources integrated data set is used to complete the reconstruction of the wide swath SWH. A model based on stacked autoencoder and deep neural network (SAE‐DNN) is developed. The SWH reconstructed by the model is evaluated with the training‐independent test set. The results demonstrate that the accuracy of the SAE‐DNN model is significantly improved by incorporating SAR joint quasi‐synchronous observations and the root mean square error can reach 0.217 m, which is comparable to the SWH measured by altimeter and highlights the effectiveness and reliability of the model in accurately reconstructing SWH. We further examine and analysis the distance variations between SWH reconstruction sites and Surface Wave Investigation and Monitoring observations, the influence of different SAR features, and the influence of sea state, highlighting the benefits of incorporating SAR data into SAE‐DNN model.

Jointly optimizing ocean shipping routes and sailing speed while considering involuntary and voluntary speed loss

This study jointly optimizes ocean shipping routes and sailing speed by considering the influence of sea states, such as wind and wave states, on sailing speed. A joint optimization model for ocean shipping routes and sailing speed is established for ocean-going vessels to determine the optimal ocean shipping route and corresponding optimal sailing speed while minimizing fuel consumption, and the involuntary and voluntary speed losses caused by ocean environments and time window constraints are considered. To implement the proposed joint optimization model, a heuristic method based on a difference algorithm is designed to obtain an optimal solution. The proposed model and designed algorithm are applied to a real case study. The results show that the optimization model can efficiently reduce fuel consumption. The maximum and minimum fuel consumption reduction ratios are 5.04% and 0.21%, respectively, and the optimal ocean shipping routes and corresponding optimal sailing speeds that minimize fuel consumption can be determined. Furthermore, comparative experiments are conducted. The results indicate that the fuel consumption savings ratio achieved by the proposed algorithm is considerably higher than the ratios obtained by other algorithms.

Design of Reciprocating Wave Power Generation System

The world’s energy structure, the main energy used by mankind is still oil, natural gas and coal and other non renewable resources. Therefore, renewable energy has a huge development prospect. Wave energy is a renewable energy with a high density. The system mainly depends on the wave energy in the ocean and provides a reciprocating wave power generation system. The influence of sea state on the dynamic characteristics of power tools is analyzed by using the knowledge of dynamics. The mechanical analysis of crank and connecting rod is carried out to understand its vibration characteristics, which provides necessary theoretical basis for power tools such as wave power generation system.

Better together: analysis of integrated acoustic and visual methods when surveying a cetacean community

Understanding the relative performance of data collection methods is critical for the production of robust results in any biological field study. This is particularly relevant for monitoring studies of rare and inconspicuous species, such as some cetaceans. Here, we compared how passive acoustic and visual survey methods performed when surveying a multispecies cetacean community in a large-scale survey area and whether the simultaneous application of these methods leads to complementary results. For both methods we compared (1) frequency of unscheduled survey stoppages, (2) detection ranges, (3) success in identifying species, (4) precedence of either method in synchronous detections, (5) detection rates, and (6) influence of sea state on detection rates. Data were collected during 4 surveys conducted between 2015 and 2017, using simultaneous visual and acoustic methods in the Santos Basin, Brazil. A total of 1492 h of simultaneous sampling yielded 617 detections, of which 46.5% (n = 287) were exclusively acoustic, 18.5% (n = 114) were exclusively visual, and 35% (n = 216) were corresponding detections of the same group made by each method, resulting in 108 paired detections. The simultaneous application of visual and acoustic methods was complementary. Acoustics were more efficient in detecting cetaceans—detecting first and further from the vessel and with a greater detection rate—whereas visual observation was more accurate for species identification. When used together, detection rates per species increased, reducing potential biases. By improving acoustic classification through visually confirmed sightings, this integrated approach has the potential to provide a reliable sound library for cetaceans in the Southwest Atlantic Ocean.

Speed optimization of a container ship on a given route considering voluntary speed loss and emissions

This study performs a speed optimization of a 4250 TEU container ship in which the influence of sea states and voluntary speed loss on ship sailing are considered. A speed optimization model is established for a single voyage, wherein the objectives are minimizing the main engine fuel consumption, and the ship operating costs. Based on the verified speed optimization model, ship speed optimizations with and without voluntary speed loss are performed. The research results show that the optimization results of the model with voluntary speed loss are significantly different from those without voluntary speed loss. To make the optimization results more accurate and more in line with actual navigation conditions, it is necessary to consider voluntary speed loss in the optimization model. In addition, the ship speed optimization is extremely sensitive to the time window. A larger time window constraint can provide more potential for speed reduction and increasing ship energy efficiency, which is consistent with the theory of slow steaming for optimizing energy efficiency. The established model can provide reasonable speed optimization decisions for ship operations.

Influence of Sea State on Sea Surface Height Oscillation from Doppler Altimeter Measurements in the North Sea

This paper reports on an investigation on the influence of waves on the sea surface height error, σh, as measured by Delay Doppler satellite altimetry (DDA). CryoSat-2 altimeter sea surface height (SSH) data in the North Sea, processed in both DDA and pseudo low resolution mode (PLRM), are correlated with European Centre for Medium-Range Weather Forecasts (ECMWF) co-located sea state data. We find a small, but consistent correlation between the 1 Hz standard deviation, σh, of the 20 Hz altimeter SSH and the ECMWF total significant wave height, SWHt. The same analysis carried out between σh and the swell component of the wave spectrum shows a smaller correlation. In contrast, the correlation between the PLRM σh and any component of the SWH spectrum has not been found to be significant. To provide an explanation of these results, the aliasing effect caused by the interaction between the sea wavelength and the altimeter resolution has been considered; a simple model has, therefore, been produced to simulate the dependence of the aliasing-derived, σA, on the sea wavelength. The alias/wavelength curve obtained helps to explain why—at least for the relatively low wavelength sea data considered—the wave direction and its wavelength have little or no influence on σh.

Influence of Sea State and Tidal Height on Wave Power Absorption

The wave energy converter developed at Uppsala University (Uppsala, Sweden) consists of a linear generator placed on the seabed and driven by the motion of a buoy on the water surface. The buoy is connected to the moving part of the linear generator, the translator, which is made of ferrite magnets. The translator moves vertically inducing voltage in the windings of a fixed component, the so-called stator. The energy conversion of the linear generator is affected by the sea state and by variations of mean sea level. The sea state influences the speed and the stroke length of the translator, while the variation of tidal level shifts the average position of the translator with respect to the center of the stator. The aim of this study is to evaluate the energy absorption of the wave energy converter at different locations around the world. This goal is achieved by developing a hydromechanic model which analyses the optimum generator damping factor for different wave climates and the power absorbed by the generator, given a fixed geometry of the buoy and a fixed stroke length of the translator. Economic considerations regarding the optimization of the damping factor are included within the paper. The results suggest a nominal damping factor and show the power absorption losses at various locations, each of them characterized by a different wave climate and tidal range. The power losses reach up to 67% and in many locations a tidal compensation system, included in the design of the wave energy converter, is strongly motivated.

The influence of sea state on dynamic behaviour of offshore pipelines for deepwater S-lay

The dynamic response of offshore pipelines induced by deepwater S-lay is highly noticeable, and directly dominates the design of such structures and the installation feasibility in practice. A comprehensive finite element model for deepwater S-lay systems using the software OrcaFlex is specially developed to explore the influences of sea state on the pipeline dynamic responses, considering surface waves, ocean currents, pipelay vessel motions, clashing contact between the pipeline and rollers. Meanwhile, a non-linear hysteretic soil model is applied to simulate the vertical pipe–seabed interaction, and the modified Coulomb friction model is used to model the lateral pipe–seabed interaction. The numerical model is then used to carry out an illustrative example analysis of a 12-in. gas export pipeline being laid onto the seabed with a water depth of 1500m using the HYSY 201 pipelay vessel in the LW3-1 gas field in the South China Sea under various sea states. The influences of sea state on the pipeline dynamic behaviour on aspects of configuration, lateral displacement, axial tension, bending moment, stress and strain as well as pipeline embedment are estimated quantitatively. The findings show that a strong relevance exists between surface wave and resulting pipelay vessel motions, and pipeline dynamic responses.

The influence of sea state on formation speed of alongshore variability in surf zone sand bars

The formation time of alongshore morphological variability in surf zone sand bars has long been known to differ from one beach to the other and from one post-storm period to another. Here we investigate whether the type of sea state, i.e. distant swell waves or locally generated short period wind sea, affects the formation time of the emerging alongshore topographic variability.A numerical modeling approach is used to examine the emergence of alongshore variability under different shore-normal wave forcing. A research version of Delft3D, operating on the time-scale of wave groups, is applied to a schematised bathymetry with a single bar. The model is then used to investigate several wave scenarios, examining the impact of peak period, frequency spread and directional spread on the formation time of alongshore variability.Results show that an increase in wave period has a large effect, changing the formation time up to O (250%) in case the wave period is changed from a representative value for the Dutch coast (Tp~5–6s) to an Australian South East coast value (Tp~10–12s). In contrast, modifications in the directional and frequency spread of the wave field result only in a minor change in the formation time.Examination of hydrodynamics and potential sediment transport shows that the variations in formation time are primarily related to changes in the magnitude of the time-averaged flow conditions. Variations in the magnitude of very low frequency (f<0.004Hz) or infragravity (0.004<f<0.04Hz) surf zone flow velocities do not affect the mean sediment transport capacity. Consequently the formation speed of patterns is primarily governed by positive feedback between mean flow and morphology, and low frequency flow fluctuations are of minor importance.These findings indicate that the development of alongshore topographic variability may be faster at swell dominated open coasts, primarily due to the occurrence of longer period swell. Also, at a given site, the arrival of a long wave period swell after a storm can accelerate the emergence of variability.

The influence of sea state on atmospheric drag

With the advent of aircraft early in the century, a need arose to relate air flow drag to aircraft surfaces such as the wings and fuselage. It was quickly demonstrated that the drag coefficient of a boundary layer was related to the roughness of the underlying surface [Nikuradse, 1933], and meteorologists soon were able to develop these ideas for calculating the atmospheric drag over land. A popular concept was aerodynamic roughness length, z0, which can be uniquely related to the drag coefficient under the assumption that the velocity profile in air is logarithmically distributed with height above the surface. This appears quite reasonable in near neutral, steady conditions.