Moored Buoy System Research Articles

Indigenization of Buoy Components Using Additive Manufacturing Technique

The Ocean Observation Systems (OOS) group of the National Institute of Ocean Technology (NIOT) is involved in the design, development and sustenance of moored data buoys in the Indian Seas. The moored buoy systems deployed in the Northern Indian Ocean provide real-time, continuous observation of surface meteorological and oceanographic parameters which help in monitoring extreme weather events and natural disasters such as cyclones and tsunamis. Buoy components are of different sizes and shapes and are made of various materials, including metals and plastics. However, due to unique and critical design requirements, the development of deep-sea components faces hurdles caused by manufacturing limitations. The advent of additive manufacturing (AM) has met the demand for quickly producing parts. Due to the high pressure and low temperature conditions, it is extremely difficult to design and develop deep sea components. Consequently, High Impact Polystyrene (HIPS) material has been selected for the subsurface floats. The float is manufactured using the Fused Deposition Modeling (FDM) additive manufacturing technique in the Fabheads 1K FDM printer with pellet based extrusion method. These subsurface floats are used at a water depth of 500 m in NIOT buoy systems, with a working pressure of approximately 50 bar. Taking a factor of safety of two into account, the part is designed to withstand 100 bar. To assess the component's performance under deep-sea hydrostatic conditions, it underwent testing in the hyperbaric chamber test facility at NIOT. During the qualification process, the component successfully withstood the design pressure of 100 bar and imploded at 102 bar. This study is part of NIOT's ongoing efforts to indigenize deep-sea components using AM and assess its future prospects.

Coupled CFD-FEM simulation for the wave-induced motion of a CALM buoy with waves modeled by a level-set approach

The Finite-Analytic Navier-Stokes (FANS) computational fluid dynamics (CFD) code was coupled with an in-house nonlinear finite element (FEM) mooring analysis program, MOORING3D, to study the dynamic responses of a catenary anchor leg mooring (CALM) buoy system in waves. The hydrodynamic loading on the moored buoy was estimated by the CFD module, in which large eddy simulation (LES) was used as the turbulence model. The FANS code was solved in conjunction with the level-set (LS) formulation to model waves. A motion solver in six degrees of freedoms (DoFs) was coupled with the MOORING3D and the CFD to achieve the coupled analysis. Model-scale simulations of free-decay motions of the buoy were performed and validated by experimental comparison. Simulations of the wave-induced motion of the buoy were performed, and the response amplitude operators (RAOs) were compared to experiments. The agreement with experiments manifested the advantages of the coupled CFD-mooring method in addressing viscous and turbulent effects and nonlinear hydrodynamic effects due to free surface. The sensitivity study of the skirt demonstrates the skirt exerting limited influence on the buoy RAOs, which appeared to be dominated by the inertial and viscous effects of the buoy hull. The conclusions demonstrate that the coupled FANS-MOORING3D code provides accurate prediction of wave-induced motion of floating systems.

Best Practices for the Ocean Moored Observatories

Real-time spatio-temporal meteorological and oceanographic data from the Ocean moored observatories are essential for precise forecast of ocean state, climate variability studies and reliable weather prediction. Precise spatio-temporal measurement of subsurface parameters such as temperature, salinity and current are essential for understanding the intra-seasonal and inter-annual evolution of the monsoons and tropical cyclones. To cater to this time-critical information, moored observatories have to be continuously operational in the harsh marine environment by measuring these Essential Ocean Variables, though bio-fouling and corrosion limits the life time and accuracy of the highly precise measuring instruments. Thus, best practices in the moored observations are essential for accurate and cost-effective long term ocean observation. The Indian moored buoy network which is operational since 1997, has been providing quality data over the past one decade. This paper describes the best operational practices and quality control processes followed in the Indian moored buoy system design, sensor calibration, testing, integration, deployment, retrieval and data quality control over the past two decades, which has helped to achieving an average meteorological data return of 90 % .

Analysis of drift characteristic in conductivity and temperature sensors used in Moored buoy system

Conductivity and Temperature (CT) sensors are attached in the Ocean Moored buoy network in Northern Indian Ocean (OMNI) at different depths upto 500 m below the sea surface. Drift in these sensors were analyzed based on the result of calibration. For detailed investigation, the sensor's drift is categorized based on the position of sensors in the mooring as surface layer (above 50 m), thermocline layer (50–200 m) and deep layer (200–500 m) and analysis was carried out at both Arabian Sea (AS) and Bay of Bengal BoB. The drift analysis revealed that over the time of deployment the drift in temperature sensor was very minimal and well within the accuracy limit. However, the drift in the conductivity sensors was more significant. Drift in the conductivity sensor decreases as the deployment depth of the sensor increases and also drift in the sensors which were deployed in AS is high as compared to the sensors deployed in BoB. Biofouling of the sensor is measured spatially in AS and BoB and it indicates that biofouling and Abrasive scouring of cells are due to the flow of high concentrations of plankton in the euphotic zone(top layer), which may cause the drift in the conductivity sensor.

Vertical structure and variation of currents observed in autumn in the Korea Strait

To observe vertical structure and temporal variations of currents in the Tsushima Warm Current region of the Korea Strait, a moored buoy system was deployed in autumn 2009. The moored buoy system measured vertical profiles of current, temperature, and salinity for 24 days and a background hydrographic survey was performed. Along-strait northeastward currents were dominant in the upper layer (8–35 m). The mean current veers counterclockwise from 48 m to 74 m as much as 50°, and its speed is reduced with depth. There were distinct northward onshore currents near the bottom (65–80 m). It was demonstrated that thermal wind relation holds in the inclined pycnocline layer, which generates the counterclockwise veering current structure. Density gradient along the strait is a main factor producing the cross-strait onshore current component below the upper-layer and the cross-strait density gradient reduces the along-strait current component with depth. Previous studies have never focused on the effect of the along-strait density structure on current structure. The first Empirical Orthogonal Function mode (CM1) of current variability explains 70% of local current variations and its vertical structure is close to the mean current structure. The correlation analysis among variations of CM1 current, slope of sea level anomaly (SSLA) and local wind anomaly revealed that the variation of CM1 current is mainly related to the variation of SSLA across the strait (c-SSLA), which is known to be controlled by remote and local wind forcing. Similarity between vertical structures of mean and CM1 current suggests that thermal wind relation is the main dynamics maintaining the counterclockwise turning of CM1 current below the upper layer although the upperlayer CM1 current is controlled by c-SSLA through barotropic geostrophic relation. Time series of temperature and salinity indicate that the thermohaline front between Korean Coastal Water and Tsushima Warm Current Water meanders in time and migrates over the mooring station back and forth. The front meandering and migration also affect the local SSLA and CM1 current variations in autumn in the Korea Strait.

三宅島近海流況観測とそれに基づく海流エネルギー資源量推定

Ocean current near Miyake Island was measured by an Acoustic Doppler Current Profiler equipped on a moored buoy system from March 2013 to March 2014 for an ocean current energy converter development project. Current variations associated with the Kuroshio,tide and wind,were found in the observed record and are described in the paper.Based on the Kuroshio axis location,periods with and without the Kuroshio intrusion into the island were identified. Spectral analysis of the current speed revealed that the diurnal variation is enhanced when the Kuroshio does not intrude.This enhancement of diurnal current variation is possibly related to the generation of the Island-Trapped Waves.By combining the fine-scale observation data and the long-term coarse-resolution Kuroshio axis data,inter-annual variability of the current power was estimated.The estimated current power is about three times larger than the one estimated from an ocean reanalysis.The result implies that coarse-resolution non-tidal numerical models possibly underestimate current power in coastal ocean.

Dynamics of Deployment for Mooring Buoy System Based on ADAMS Environment

Buoy is widely applied in oceanographic research, ocean engineering and so on. The high cable tension and location derivation of its anchor can greatly affected the working condition of buoy. Multi-body software ADAMS is used to analyze the dynamics of deployment for buoy. Firstly, model of mooring buoy is developed. The forces on components of buoy are given such as drag forces, inertia force and impact force between bottom and anchor. The program is developed by macro commands in ADAMS environment. The trajectory and tension force of different nodes on buoy are calculated. This method can simulate the dynamics of deployment process for buoy system. And it is also helpful for guidance for buoy design and deployment process planning.

Design and Calculation of Double Buoys Mooring System in Estuary of Yalu River

In order to design a double buoys mooring system in the estuary of Yalu River for loading work of 40,000 tons of bulk cargo ship, the article mainly based on the practicality of the meteorological condition of this sea area and the data of the vessel as well as the national criterion, do some calculations of wind force, current force, wave force as well as the total force on the ship, with the calculation result to make a designation of double mooring buoy system, decide the size of the mooring buoy, the size and length of the chain, the size and the depth of the Deadman. The construction according to the designation has a good effect; the method of calculation and the designation are proved useful.

Analysis for the deployment of single-point mooring buoy system based on multi-body dynamics method

Deployment of buoy systems is one of the most important procedures for the operation of buoy system. In the present study, a single-point mooring buoy system which contains surface buoy, cable segments with components, anchor and so on is modeled by applying multi-body dynamics method. The motion equations are developed in discrete node description and fully Cartesian coordinates. Then numerical method is used to solve the ordinary differential equations and dynamics simulations are achieved while anchor is casting from board. The trajectories and velocities of different nodes without current and with current in buoy system are obtained. The transient tension force of each part of the cable is analyzed in the process of deployment. Numerical results indicate that the transient payload increases to a peak value when the anchor is touching the seabed and the maximum tension force will vary with different floating configuration. This work is helpful for design and deployment planning of buoy system.

Deployment Simulation of Mooring Buoy System

Deployment of buoy systems is one of the most important procedures for buoy system’s operation. In this paper, buoy system with surface buoy, cable segments with components, anchor and so on is modeled by applying multibody dynamics method. Then numerical method is used to solve the ordinary differential equations and dynamics simulations are achieved while anchor is casting from board. The trajectories, velocity and acceleration of different nodes in buoy system are obtained. The transient tension force of each part of cable is analyzed in the process of deployment. This work is helpful for design and deployment planning of buoy system.

Variability of Upper Ocean Heat Balance in the Shikoku Basin during the Ocean Mixed Layer Experiment (OMLET)

The heat balance of the surface layer in the vicinity of the former Ocean Weather Station “Tango” (OWS-T; 29°N, 135°E), where a large amount of heat is transported by the Kuroshio and transferred to the atmosphere, was studied by during Ocean Mixed Layer Experiment (OMLET) as an oceanographic component of the Japanese World Climate Research Program (1987–1991). Temperature and velocity in the upper ocean measured using a surface moored buoy system deployed by the Ocean Research Institute, the University of Tokyo, in total 668 days of four time series namely the periods of April 1988–November 1988 (OMELET-88), August 1989–February 1990 (OMLET-89), April 1990–September 1990 (OMLET-901) and September 1990–January 1991 (OMLET-902). We have analyzed the moored buoy data of the upper 100 m for the latter three time series (OMLET-89, -901 and -902) and here we discuss the heat balance of the upper 100 m, in combination with surface heat flux and oceanographic data provided by the Japan Meteorological Agency. A large fluctuation of oceanic heat convergence/divergence of 200–300 W/m2 in amplitude with predominant period of 20–30 days occurred in the first half of OMLET-89 period, which was just the early stage in the formation process of a large meander path of the Kuroshio. A large amount of heat convergence of 71 and 79 W/m2 on average was detected in observation period of OMLET-89 and -901, respectively. During OMLET-902, relatively small heat convergence of 13 W/m2 was obtained. It is suggested that these variations of oceanic heat convergence in this region were closely related to the fluctuation of the Kuroshio axis to the south of Japan.

Propagation of semi-diurnal internal tides observed off fukushima, along the east coast of Japan

Analysis of current velocity and temperature records obtained from moored buoy systems deployed off the east coast of Japan reveals the intermittent occurrence of semi-diurnal internal tides and their manner of propagation. The internal tidal waves clearly propagate toward the shore, which is confirmed by cross-correlation of the onshore current velocity and temperature between neighboring stations. The propagation speed of the internal tide increases with water depth except in the area furthest offshore. In this area, motions near the second mode seem to occur occasionally, while in the nearshore area the motions for the most part consist of the first mode.

Computation of errors in current meters attached to near‐surface moorings

Current measurements from moored buoy systems are contaminated by mooring motion. A few examples of moored buoy systems are studied to illustrate the use of computer simulations for computing errors introduced by surface waves in the current meters attached to near‐surface moorings. Results presented show that for all cases studied the standard deviations of true flow components (relative to the current meters) are greater than the standard deviations of wave orbital velocities, except near the surface. Also, in one case which is closest to a surface‐following mooring, the standard deviations of true flow components (relative to the current meters) increase, rather than decrease, with depth over the upper 40–45 m depth. Effect of mooring line characteristics, environment and vertical cosine response on the simulated current meter error is shown. In all cases, for current meters located near the ocean surface, the error is comparable to the surface wave induced Stokes drift. Significant errors (>1 cm s−1) were computed at depths greater (up to 2 and 3 times) than the depth where Stokes drift becomes negligible. Simulations also show a great deal of variation (several centimeters per second, the order of Stokes drift) in the error due to variations in mooring line characteristics and environments.

びわ湖における連続測流 Ｉ 測流の方法と流況の概要

A method of continuous measurements of lake currents and some results obtained in the north basin of Lake Biwa are presented. Two types of current meters were used, both being able to record the current speed and direction and equipped with either a water temperature sensor or a pressure sensor : one is an Aanderaa RCM-4 current meter and another one is a DCM-3B current meter manufactured at Osaka Electro-Communication University. Adopting the subsurface mooring buoy system, observations have been carried out at several locations in the northern part of the north basin of Lake Biwa, mainly in summer and winter since 1981. Analysis of the current measurement data shows the following features of lake currents : (1) In summer, when the lake water is stratified, a counter-clockwise gyre develops above the thermo cline. Surface currents are prominent and stable. (2) In winter, when the lake water is not stratified, surface currents are weak and usually controlled by wind stresses over the lake, so that current directions are deflected to the right-hand side from down wind directions. (3) Both in summer and winter, deep currents are, in general, very weak and have no stable directions. Sometimes, however, the current speed becomes greater than 10 cm·s-1 after a strong wind in summer.

Buoy Systems for Acquiring Data in a Marine Environment

Automatic, unmanned buoys are being used increasingly for acquiring meteorological, oceanographic, and water-quality data from the marine environment. This paper discusses large discus buoys moored in the deep ocean, small buoys used as drifters in open waters and polar ice regions, and moored buoys along the continental shelf. Introduction The mission of the NOAA Data Buoy Office (NDBO) is to develop and apply buoy systems for gathering and processing meteorological, oceanographic, and waterquality data to meet current and near-term user needs. Among existing and potential users are national and international weather services, the scientific research community, offshore industries, fisheries, environmental protection groups, and recreational interests. The Office is part of the National Oceanic and Atmospheric Admin. (NOAA) and is located in Bay St. Louis, Miss. NDBO buoy systems involve a family of automatic and unmanned environmental buoys of differing capabilities, supported by communication/data processing facilities and servicing ships. Basically, processing facilities and servicing ships. Basically, this family can be divided into large moored buoys for use in the deep ocean, smaller moored buoys for application along the continental shelf, and small drifting buoys for use throughout the marine environment. Our most developed area of technology applies to large discus buoys moored in the deep ocean for extended periods in frequently severe environments. Less developed periods in frequently severe environments. Less developed areas of technology, now receiving increasing emphasis, are associated with the more limited smaller buoys for mooring on the continental shelf and for drifting applications. Supporting these technology areas is our ongoing program for developing or improving sensors for meteorological, oceanographic, wave, and water-quality measurement, with oceanographic-sensor development posing the greatest challenge. Deep-Ocean Moored-Buoy Systems A large portion of the NDBO effort has been in the development of deep-ocean moored-buoy systems for acquiring meteorological and oceanographic data in a severe environment, primarily in support of the National Weather Service but designed also to support the scientific community and other interests. Starting with an experimental engineering program for testing and evaluating hardware, coupled wit operational reporting to the National Weather Service and augmented by a payload simplification program, development has payload simplification program, development has progressed to the next-generation prototype environmental progressed to the next-generation prototype environmental buoy recently procured. Experimental Engineering Program A significant achievement in buoy development was realized in mid-1974 with the completion of our largebuoy experimental engineering program. This program was intended to improve the state-of-the-art program was intended to improve the state-of-the-art hardware, to gain experience in its at-sea operation and maintenance, and to set the stage for prototype development. A thick discus moored buoy, as shown in Fig. 1, was the result of this program. This buoy is 40 ft in diameter with a 100-ton displacement and a meteorological sensor suite located at 5 and 10 m above the water. It was designed to be moored to depths of 20,000 ft in a survival environment of a 6.2-knot current, a 155-knot wind, and a significant wave height of 45 ft. The mooring line was designed with an integral data line for accommodating inductively coupled oceanographic sensors at various levels in the upper 500 m. JPT P. 468

Three firms compete in design of environmental buoys

The National Oceanic and Atmospheric Administration has announced the award of competitive design contracts for two types of buoy systems for gathering ocean and weather data. One system is to be moored in a fixed position, while the other will drift freely.Under a $425,000 contract, the Re‐Entry and Environmental Systems Division of General Electric in Philadelphia, will design both a drifting and a moored buoy system. Lockheed Missiles and Space Company, a Division of Lockheed Aircraft Corporation, Sunnyvale, California, was awarded a $270,000 contract for design of a moored buoy system. The Magnavox Company, Government and Industrial Division, ASW Operation, Fort Wayne, Indiana, has a $260,000 contract for designing a drifting buoy system.