Buoy Model Research Articles

Detection of wave groups from the motion behaviour of a discus buoy

A scale modeled discus data buoy was tested for its motion characteristics under the action of wave groups of different frequencies in a wave tank. The wave groups were theoretically simulated based on the methodology of Xu et al., (1993, Statistical simulation of wave groups, Applied Ocean Research, 15, 217–226) and then converted to paddle displacement signals to drive the wave maker. The motion responses of the buoy model were measured using potentiometers as well as with a non-contact motion tracking camera system. The details of the model, instrumentation, testing conditions and the analysis are presented. The displacement and wave elevation time histories were analysed through statistical, envelope, wavelet transform and phase-time approaches to detect the wave groupiness. The effect of groupiness parameters on the surge, heave and pitch motions of the buoy are detailed in this paper.

Effect of shoreline meteorological measurements on NOAA Buoy model prediction of coastal air–sea gas transfer

The NOAA Buoy model is currently used to estimate the air–sea transfer rates of highly soluble gases over coastal water bodies, such as Tampa Bay, using offshore meteorological measurements. Since a goal of the BRACE study was to improve estimates of nitrogen deposition over Tampa Bay, our objective was to investigate if the model accurately predicts gas transfer when shoreline input data are used in lieu of offshore measurements. To accomplish this objective, we compared over-water measurements of sensible heat with NOAA Buoy model predictions using both offshore and shoreline meteorology. In the summer months, the apparent daytime influence of land surface heating on air temperature produces a higher air than water temperature at the shoreline. For the NOAA Buoy model, this yields stable atmospheric conditions and thus under-predicts the over-water exchange rates for a shallow estuary. If the data records are removed from the model for periods when air temperature is 4.8 K greater than the water temperature, the shoreline and over-water transfer rates are in reasonable agreement.

Modeling air/sea flux parameters in a coastal area: A comparative study of results from the TOGA COARE model and the NOAA Buoy model

Because estuaries and coastal regions are particularly susceptible to nutrient over-enrichment due to their close proximity to source-rich regions, a goal of the BRACE study was to improve estimates of nitrogen air/sea transfer rates in the Tampa Bay Estuary. Our objective was to critically evaluate two air/sea gas exchange models to determine their efficacy for use in a coastal region, with the ultimate goal of improving nitrogen exchange estimates in Tampa Bay. We used meteorological data and oceanographic parameters collected hourly at an instrumented tower located in Middle Tampa Bay, Florida. The data was used to determine the friction velocity and the turbulent flux of heat and moisture across the air/sea interface and then compared with modeled parameters at the same offshore site. On average both models underpredicted sensible heat flux and there was considerable scatter in the data during stable conditions, indicating that nitrogen gas exchange rates may also be underestimated. Model improvement, however, was observed with friction velocity comparisons. Model inter-comparisons of sensible heat flux and friction velocity suggest excellent agreement between the TOGA COARE and the NOAA Buoy models, but model estimated heat transfer coefficients and latent heat fluxes did not agree as well. Based on our analysis, we conclude that both models are suitable for use in a coastal environment to estimate nitrogen air/sea gas exchange, although the NOAA Buoy model requires fewer meteorological inputs. However, if the purpose is to conduct more sophisticated microscale modeling of air/sea interactions, we recommend the TOGA COARE model.

Tsunami Wave Interaction with Data Buoys

To plan for proper mitigation measures, one should have an advanced knowledge of the phenomenon of tsunami propagation from the deep ocean to coastal waters. There are a few methods to predict tsunamis in the ocean waters; one method is the effective use of data buoy measurements. Although data buoys have been used along the Indian waters there has been a tremendous growth in the number of buoy deployment recently. Under the National Data Buoy Programme (NDBP) of India, the 2.2 m diameter discus data buoys were deployed along the east and west coasts of India for measuring meteorological and ocean parameters. It would be advantageous if these buoys could be efficiently used to measure rare events such as tsunamis. Understanding the dynamic behavior of the buoy is of prime importance if a tsunami warning system is to be successful. This may be accomplished through experimental or numerical studies. A comprehensive experimental study has been conducted to understand the dynamic behavior of a wave rider buoy exposed to a variety of waves. It is common that tsunami waves are represented in terms of shallow water waves, namely solitary and cnoidal waves. Hence, in the present study, the discus type data buoy is scale modeled and tested under the action of solitary and cnoidal waves in the laboratory. The time histories of wave elevations, as well as heave and pitch motions of the buoy model, were analyzed through a spectral approach as well as through wavelet transformations. The wavelet approach gives more detailed insight into the spectral characteristics of the buoy motion in the time scale. The harmonic analyses were performed for the cnoidal wave elevations and subsequent motion characteristics that give an insight into the energy variations. The details of the model, instrumentation, testing conditions and the results are presented in this paper.

浮流重油自動追従ブイシステムの開発（第１報）

In recent years, the congested tanker route and abnormal weather unfortunately raise the possibility of sea accidents. Spilled oil from a stranded ship pollutes the ocean environment and also does damage to the regional economics. Therefore, in order to prevent damages spreading, it is very important for us to take adequate measures as soon as possible. Under the circumstances, we are developing an autonomous buoy, which is dropped into the sea and chases spilled oil autonomously when the ship accident occurs. This buoy is expected to inform us in real time of the location of the spilled oil and meteorological and oceanographic data around it. This paper is the first report on the development of a spilled oil chasing autonomous buoy system. This paper firstly introduces the total system of a spilled oil chasing buoy, and secondly shows the experimental and numerical results of maneuverability of the buoy model."

Scatterometer wind fields: A new release over the decade 1991‐2001

The global surface wind fields calculated from scatterometer observations have been updated to cover the decade 1991‐2001. This involves an enhancement of the remotely sensed wind retrievals, quality control, and objective method. This paper presents the improvements with respect to the first release and provides the main characteristics of the surface parameter fields. The accuracy of the resulting weekly and monthly surface wind fields is studied through comparisons with buoy and numerical model averaged wind estimates.

A Study for Development of a Wave Observation Platform

A wave observation buoy has been developed, which uses a system where incident wave height in the ocean can be obtained from the heave motion of the buoy measured using a gyro system and the heave response function determined through theoretical calculations and model experiments.The accuracy of the theoretical calculation of the response function of the buoy motion was first confirmed by model experiments in a wave tank. Next, the validity of the method was verified by comparing the time series of irregular wave profiles measured with a wave height meter fixed in the wave tank and a reproduced series using the heave motion of the buoy model measured with a motion sensor and the response function.A real buoy was designed and constructed based on these studies and has been moored in the sea near Ishigaki Island since March of 2001.Finally, the wave data obtained using the above method were compared with those directly obtained from motions measured with a gyro and the relative wave height measured with a wave sensor fixed to the buoy, and the results were discussed.

Large angular motions of tethered surface buoys

A three-dimensional coupled analysis of the interaction of a floating buoy and its mooring is studied. External loads include hydrodynamic forces, tether tensions, wind loads and system weight and buoyancy. Nonlinearities include large rotational and translational motions and non-conservative fluid loads. The mooring problem is formulated as a nonlinear two-point-boundary-value-problem. At each instant in time, the mooring problem is solved by direct integration using a successive iterative algorithm to satisfy boundary conditions. Buoy kinetic and kinematic equations are derived assuming large angles represented by Euler parameters. Coupling between the buoy and the mooring is enforced by matching the velocities of the tether and buoy at the attachment point. A predictor-corrector coupling algorithm is used with multiple sizes of time steps used to provide stability for the separate mooring and buoy models. Numerical results are compared to experimental responses of three types of buoys (sphere, spar and disc) subject to both regular and irregular waves.

Experimental and numerical investigations of tethered spar and sphere buoys in irregular waves

A series of large-scale experiments were conducted to examine the motions of buoys in a variety of wave climates. In conjunction with these experiments, numerical simulations of selected tests were conducted to test the present ability of a particular computer program to model buoy responses. This paper considers individual wave tests for two of the buoy models used in the experiments, a spar buoy and a sphere buoy. The wave field is generated using a JONSWAP spectrum. A description of the experiments shows that each buoy is subject to significant resonant responses, in heave for the spar and surge for the sphere, even though wave forcing is not present at or immediately adjacent to the resonant frequencies. The numerical simulations show generally good comparisons with the experimental data.

Objective analysis of simulated equatorial Atlantic Ocean data on seasonal time scales

In this study we objectively analyze simulated equatorial Atlantic Ocean data on seasonal time scales using a technique based on optimal interpolation. The purpose is twofold: (1) to estimate the accuracy of the FOCAL/SEQUAL (Programme Francais Ocean-Climat en Atlantique Equatorial/Seasonal Equatorial Atlantic Response Program) array for mapping large-scale seasonal variations in the depth of the isotherm, and (2) to examine the potential of 20 FOCAL drifting buoys drogued with thermistor chains for enhancing that mapping accuracy. This latter point leads to the development of a heuristic model for drifter motion in order to identify the most favorable time and location for buoy deployments. Results are discussed for a number of assumptions about oceanic variability required by both the optimal interpolation procedure and the drifting buoy model. From these we conclude that with data provided by the FOCAL/SEQUAL array, excluding FOCAL drifters, one can expect to map large-scale seasonal variations in the depth of the 20°C isotherm to within 5 m over about 65% of the equatorial Atlantic. This region of expected 5 m accuracy expands to nearly 90% of the equatorial Atlantic if FOCAL drifters are deployed between 2 and 4OS at 5OW in four quarterly installments of five each. Drifters deployed further to the east or .to the west will be less useful in defining large-scale, low-frequency thermal variations since they do not disperse as widely as do those deployed at 5 OW.

Development of wave power generators

The Japan Marine Science and Technology Center (JAMSTEC) started a study on “Wave Power Generator” in 1974. After two years of water tank experiments, the ship type buoy model seemed to be the best compared to the other models with respect to converting efficiency of wave energy into air output, easy construction and safe mooring. JAMSTEC has ordered a prototype of the system which is a massive floating structure, 80 m in length, 12 m in width, 5 m in height and 500 tons in weight. The structure consists of buoyancy rooms and air rooms, and the bottom of the air room is opened to the sea water. When a wave passes through an air room, air is pushed out of the room and sucked into the air, as the water levels rises and falls. Thus electric power is generated with the air turbine generator by the air motion in and out of the air room. The output power of the generated electricity is assumed to be about 2,000 kW, in case of 3 m wave height and 6 sec wave period, according to our theoretical calculation. The system is moored with a chain to the seabed. We have prepared many anchors and a 94-mm chain for the main mooring line of a safety load of 650 tons. A 1/10 scale model test in the water tank showed that the drag force was not so large, and it was about 100 tons to the full scale structure in the rough sea. The first open sea test will be carried out in 1978.