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IEEE JOURNAL OF OCEANIC ENGINEERING 1

Development and Performance Validation ofa Cylindrical Buoy for Deep-Ocean

Tsunami MonitoringR. Venkatesan, S. A. Sannasiraj, M. V. Ramanamurthy, P. Senthilkumar, and G. Dhinesh

Abstract—This paper describes the development and perfor-mance validation of a cylindrical surface buoy (CSB) used formonitoring tsunamis in Indian seas. The buoy design with mul-tiple compartments provides damage-tolerance curved top surfaceprofile, the subsurface access ensures vandalism resistance, andthe shape provides enough space for the power and control sys-tems for an offshore endurance of two years. The scaled-downCSB is numerically modeled and experimentally validated for itsstability in a wave basin. The validated numeric model is extendedto a diameter of 2.4 m and the mooring loads are analyzed. Thefield scale prototype CSB is deployed in the open ocean, where thewater depth is 2500 m. The performance of the CSB is validatedfrom one year of failure-free performance and capability to remainwithin the watch circle under all environmental conditions, and ithas detected the water level change events during the operationalperiod.

Index Terms—Cylindrical buoy, tsunami, vandal-resistantfeatures.

I. INTRODUCTION

THE Indian Tsunami Buoy System (ITBS) developed andoperated by the National Institute of Ocean Technology

(NIOT) is used for monitoring the water level changes in deepoceans during the propagation of a tsunami wave. The waterlevel data serve as one of the critical inputs to the Indian TsunamiEarly Warning System (ITEWS) for confirming a tsunami, es-timating its travel time to shore, and assessing possible impactson the coastline of the Indian Ocean rim countries during atsunamigenic earthquake. The ITBS comprises a network offive buoys, with four buoys in the Bay of Bengal (BoB) andone in the Arabian Sea. These are used to detect, measure, andmonitor tsunamis from the two tsunamigenic source regions ofthe Indian Ocean in real time using satellite communication [1],[2]. By incorporating state-of-the-art developments in the ar-eas of onboard energy storage, satellite-based communication,deep ocean moorings, and data analysis tools, the mean timebetween failure (MTBF) of a tsunami buoy operating in the

Manuscript received October 18, 2016; revised June 14, 2017 and November25, 2017; accepted March 20, 2018. This work was supported by the Ministry ofEarth Sciences, Government of India. (Corresponding author: S. A. Sannasiraj.)

Associate Editor: M. Atmanand.R. Venkatesan, M. V. Ramanamurthy, P. Senthilkumar, and G. Dhinesh

are with the National Institute of Ocean Technology, Ministry of Earth Sci-ences, Chennai 600100, India (e-mail:,[email protected]; [email protected];[email protected]; [email protected]).

S. A. Sannasiraj is with the Department of Ocean Engineering, Indian Instituteof Technology Madras, Chennai 600036, India (e-mail:,[email protected]).

Digital Object Identifier 10.1109/JOE.2018.2819238

Fig. 1. Operating principle of a tsunami buoy.

BoB and communicating to the NIOT-mission control center(NIOT-MCC) has increased from 0.3 years in 2007 to 0.9 yearsin 2013. The four-node network in the BoB has recorded anMTBF of 1.62 years, with an availability of 98.3% [3]. Thesurface buoy is a critical component of the moored system, asit houses the subsystems for communication with the satelliteand with seabed located bottom pressure recorder (BPR), andto remain stable within the defined location so as to have effec-tive acoustic communication with the BPR [4]. The principle ofoperation of the tsunami buoy, is shown in Fig. 1.

Reliability analysis done for the ITBS based on the fieldfailure data, which indicates that the presently operating2.2-m diameter discus-shaped surface buoy has an MTBF of

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2 IEEE JOURNAL OF OCEANIC ENGINEERING

Fig. 2. Description of the cylindrical shape buoy.

four years with an annual failure probability of 22%. The studyalso revealed that majority of the failures in the ITBS were dueto the act of vandalism in the offshore moored discus-shapedsurface buoy, which resulted in damage of the buoy commu-nication system and associated data outages [3]. The reportedfailures have prompted the development of a cylindrical sur-face buoy (CSB), which is more damage tolerant and vandalismresistant, with a design capable of having increased space to ac-commodate increased energy storage redundant electronics andcommunication systems so as to have an offshore endurance ofup to two years [5]. In this study, the performance of the CSBwas analyzed through the scaled-down model tests and valida-tion of the numerical model based on the experimental results.The extended numerical analysis carried out on the prototypeCSB and the mooring load analysis with the CSB was described.The deployment of the field-scale prototype CSB was furtherdescribed and the performance results discussed.

II. OPERATING AND IMPROVED DESIGN

A. Operating Discus-Shaped Buoy

The buoy used in the ITBS has a discus-shaped hull compris-ing two split halves for ease of assembly and transportation. Thecentral instrument housing is used for placing the energy storagebatteries, electronics modules, and the onboard communicationsystems used for communicating with the satellite through IN-MARSAT and acoustically with the BPR [6], [7]. A keel weightand a keel frame are connected below the instrument housing

Fig. 3. Scaled model of buoy configurations (1:6).

Fig. 4. Experimental setup of the model in the laboratory wave tank.

TABLE IDETAILS OF THE SCALED DOWN MODEL

to prevent capsizing of the buoy and to facilitate the subsurfacesensor mounting. The hull, which is 2.2 m in diameter and 7 min height, weighs about 1264 kg, when assembled with its mastand keel frame. The central instrument housing, lower mast,upper mast, and sensor arm are madeup of aluminum alloy Al6061 T6, whereas the hull is made up of glass fiber reinforcedplastic and filled with polyurethane foam of density 64 kg/m3.Fenders made of extruded rubber are mounted on the outer pe-riphery of the hull to safeguard the discus-shaped buoy duringdeployment and retrieval operations [4].

B. New Cylindrical Shaped Buoy

The new CSB, as shown in Fig. 2, is used to overcome thelimitations in the presently operating discus-shaped buoy. It


VENKATESAN et al.: DEVELOPMENT AND PERFORMANCE VALIDATION OF A CYLINDRICAL BUOY FOR DEEP-OCEAN TSUNAMI 3

TABLE IIPARAMETERS OF THE CSB

Fig. 5. Section lay out the wave flume and model position.

consists of hull and instrument housing as two major compo-nents. The hull acts as buoyancy chamber and the instrumenthousing is used to accommodate all the electronics, communi-cation, and energy storage systems. To have damage tolerance,the hull is made up of FRP material as a single unit with six wa-ter tight compartments. Its outer layer has average thickness of4.5–5 mm with alternate layers of 450 gram square meter (GSM)chopped strand mat (CSM) and 610 GSM woven roving withisophthalic polyester resin and gel coat with an initial layer ofone surface mat and one 300 GSM CSM. The instrument hous-ing is made up of steel with stiffening ribs on the bottom of thehousing, which is covered by three layers of FRP and its innerdiameter is 850 mm. All the carbon steel buoy subcomponentswere hot dip galvanized to avoid the corrosion in hostile envi-ronment. The CSB has provision to have twin modems, primaryand secondary battery systems, health monitoring systems, gasdetection and temperature sensors, moon pool for instrumentmountings and two round fenders on the outer edge of the hullto avoid damages to the CSB during deployment, and retrievaloperations. The space available for housing enough batteriesis used to serve the power supply needs for two years and tocontrol biofouling; the wetted surface of the buoy assembly wascovered with marine grade antifouling paint, which is a decid-ing factor in buoy maintenance. To avoid transmission lossesbetween the acoustic transponder located in the BPR and thesurface modem due to the disturbance caused by sea surfacewaves and swells, the surface acoustic modem is kept at a depth

Fig. 6. Measured heave RAO of the model.

of 3 m below the water surface using a 2-m galvanized iron(GI) pipe and keel frame. It is also used for routing the surfaceacoustic modem cable to the instrument container so as to avoiddamage to communication cables and to give better stability tothe CSB.



Fig. 7. Measured pitch RAO of the model.

Fig. 8. Experimental and numerical results for the heave RAO of the model.

III. SCALED DOWN EXPERIMENTS AND NUMERICAL

MODEL VALIDATION

A. Scaled Down Experiment

To evaluate the hydrodynamic response of the CSB experi-mentally, a scaled-down model was developed (see Fig. 3). A

Fig. 9. Experimental and numerical results for the pitch RAO of the model.

Fig. 10. Mooring load on the buoy.

Froude scale of ratio 1:6, as shown in Table I, was adopted tomaintain the floating body characteristics including the meta-centric height as given in Table II. Fig. 4 shows the experimentalsetup of the model in the laboratory wave tank located at the De-partment of Ocean Engineering, Indian Institute of TechnologyMadras, Chennai, India [8]. The heave and pitch responses un-der the action of regular and random waves were measured. Thefrequency characteristics of the system were reported and heavepitch responses for the buoy were studied for the wide range of



Fig. 11. Prototype CSB stability test and location at sea.

Fig. 12. Actual location of CSB deployment.

wave frequencies, which is represented as a response amplitudeoperator (RAO). RAO refers to the normalized response of afloating structure as a function of the wave period.

The buoy model was subjected to regular waves with a periodranging from 0.8 to 5.0 s and each period was associated withheight varying from 0.05 to 0.15 m. In the random wave test,the buoy model was subjected to JONSWAP wave spectrum, inwhich the peak period of the wave varied from 1.0 to 3.0 s, andfor each of peak period, the significant wave heights varyingfrom 0.05 to 0.1 m were employed.

The schematic outline of the wave tank with the model in-stallation is shown in Fig. 5.

In the wave generation system, a servo-controlled piston-typewave maker was used. In the basic servo loop, the servo con-troller compares the desired wave maker position signal receivedfrom the control computer with the actual position of the wavemaker, and based on the deviation between two signals, it sendsa corrected final signal to the servo actuator.

The wave elevation was traced using resistance-type wavegauges. The responses of the buoy model were measured using

potentiometers accelerometers [9]. The heave and pitch RAOsare shown in Figs. 6 and 7.

B. Numerical Approach

In the numerical model, all the CSB components are modeledin 3-D using Pro-E wildfire 4.0 and the relevant material proper-ties are applied to get the combined center of gravity and radiusof gyration. The developed model of the hull is analyzed usingthe AnsysAqwa software, by the potential flow model using thepanel method [10]. The Pro-E output values are fed as inputsto the model configuration file for frequency domain analysisin AnsysAqwa and to find the motions of CSB under variousenvironmental conditions [11], [12]. The results obtained fromfrequency domain analysis for the CSB in the heave and pitchdegrees of freedom are shown in Figs. 8 and 9.

It is noted from the experimental and numerical approachesthat the heave RAO is maximum for a wave period of 2 s. Asthe results are in close agreement, the numerical model is ex-tended to analyze the performances of the actual 2.4-m diameterprototype CSB.



Fig. 13. Buoy watch circle log.

IV. NUMERICAL ANALYSIS OF THE PROTOTYPE CSB

The CSB consists of a subsurface acoustic transducer anda transmitting antenna, which is connected with mooring toposition the buoy in a location within the watch circle to havethe reliable communication with BPR. To get the uninterrupteddata from the buoy system, the acoustic transducer and thetransmitting antenna should be in proper orientation, which canbe maintained only when CSB is stable.

Numerical studies are carried out to estimate the hydrostaticand dynamic behavior including heave, pitch, and roll responsefor 2.4-m CSB. The peak RAO is used for estimating the heaveand pitch frequencies for the prototype.

The peak period for the heave is at 4.7 s, which is away fromthe predominant wave periods experienced in the Indian Ocean(which are between 6 and 18 s) [13]. The variation in the RAOcomparison between the analysis and experiment results of CSBis due to the variation in the physical size of the buoy.

V. ANALYSIS OF THE MOORED BUOY

Various types of oceanographic moorings are used for databuoy application to collect the met, ocean, and Tsunami data[14]. The NIOT Ocean Observation System (OOS) uses Met-Ocean and Tsunami buoy moorings, which are derived from theinverse catenary mooring type.

The buoy mooring configuration consists of a chain, a com-bination rope, a nylon rope, and a sinker weight along with adrag anchor. From the CSB, mooring starts with a 25.4-mm di-ameter GI chain of length 3 m followed by the 18-mm diametercombination wire rope (with a submerged weight of 0.75 kg/m)

for a length of 550 m, followed by a 16-mm diameter nylonrope (with a submerged weight of 0.14 kg/m) of 320 m and theremaining length of mooring covered by the 18-mm diameterpolypropylene rope (with a submerged weight of 0.16 kg/m),and finally, 3 m of a 25.4-mm diameter chain (with a submergedweight of 13.7 kg/m) connected to a sinker weight (2t) alongwith a 150-kg drag anchor.

OrcaFlex V9.6 is used for calculating the mooring loads onCSB when subjected to the extreme environmental conditions.The OrcaFlexis marine hydrodynamics program was developedby Orcina for static and dynamic analysis of a wide range ofoffshore systems, including rigid and flexible marine risers,moorings, installation, and towed systems [15], [16]. The analy-sis considered following marine environment conditions: waterdepth of 2500 m, flat seabed condition, current speed varyingwith water column with maximum of 2 m/s at the surface, whilecurrent and monochromatic wave acting in the same direction,and wave height of 8 m with the period of 12 s [17].

The mooring load analysis results for CSB are shown in Fig.10. The weight of the CSB is 1989 kg and its radii of gyration inX, Y, and Z directions are 1306, 1306, and 388 mm, respectively.Analysis showed that the highest tension in the mooring line isabout 9 kN (917 kgf). Based on the guidelines for moorings[18], [19], the minimum factor of safety of two is adopted and,hence, a 2t anchor is chosen.

VI. DEPLOYMENT OF FIELD SCALE PROTOTYPE

The CSB was fabricated as per the design. The instrumen-tation cylinder, which would hold the electronics, was tested



Fig. 14. The 17 N/89 E location buoy triggered the seismic event on April 25, 2015.

Fig. 15. The 17 N/89 E location buoy triggered the seismic event on May 12, 2015.

for 1.2-bar internal pressure with leak tightness. The buoyancymodule underwent periodic inspection during the various phasesincluding material selection, mould preparation, internal stiff-ener setup, foam filling, and final dimension inspection. Finally,the same was certified by the classification society. Field trialfor the realized prototype CSB was conducted (see Fig. 11) at17° 52.410’ N, 89° 41.430’ E in the BoB, and CSB was foundto be stable at sea during the field trials.

After the field trial, the CSB was integrated with the sys-tems of tsunami buoy ITB09. The actual deployment of CSBwith the mooring system was carried out in the BoB at theITBS09 location (17° 29.275’ N, 89° 46.860’ E) on April6, 2014. The measured sea depth at the deployment loca-tion (see Fig. 12) was 2280 m and the buoy draft was 0.4m. The deployed CSB was working satisfactorily for a pe-riod of more than two years and transmitting real-time data toNIOT-MCC [6].

VII. PERFORMANCE RESULTS AND DISCUSSIONS

Since the discus buoy was prone to vandalism, the CSB wasdesigned with increased endurance and features that can resistvandalism. The numerical analysis and the model test were car-

ried out to study the behavior of the system before deployment.The buoy integration mounting arrangement was positioned be-low the water surface to avoid the dismantling at site and theservicing endurance was increased from one year to two years.

The performance of the CSB was evaluated from failure-free continuous performance at sea, capability to remain withinthe watch circle so as to have continuous communication withthe BPR, and the successful capturing and transmission of thewater level change events. The deployed location of the tsunamibuoy can expect rough weather conditions with the onset ofmonsoon as well as during frequent cyclonic disturbances [20].The moored buoys close to the location equipped with sensorsto measure wind speed and surface current recorded a maximumwind speed of 20 m/s and a surface current speed up to 1.2 m/sat the peak of the southwest monsoon season. The region alsoexperienced huge waves with a wave height of more than 6 m.Fig. 13 shows the watch circle, which is the location of theCSB logged in the NIOT-MCC and it can be seen that CSB hasremained operational within the defined location over the entireyear.

The system also successfully recorded pressure changesdue to the seismic Rayleigh waves during the two earthquakeevents of magnitudes 7.5 and 7.2 on a Ritcher scale in Nepal



on April 25, 2015 and May 12, 2015, respectively. Duringboth events, ITB09 with CSB worked satisfactorily and thedata ware reported to the NIOT-MCC and ITEWS. After thatevent, the buoys switched back to the normal mode. Duringthe seismic events, 146 and 74 data sets were sent includingevent mode data and extended event reporting mode data. Theevents recorded by ITB09 during the two events are shown inFigs. 14 and 15.

VIII. SUMMARY

The performance of the newly designed cylindrical surfacebuoy was found to be good through a laboratory scale model andfield observations of the prototype for two years. The stabilitywas enhanced and the instrumentation modules were designedin such a way so as to reduce the vandalism. During the severemonsoon waves with a wave height of 6 m, the CSB was found tobe performing well. The new buoy at BoB had encountered twoseismic events, which were captured successfully. The successof these deployments would pave a way for many such designsin the future.

ACKNOWLEDGMENT

The authors are indebted to the Directors of the NationalCentre for Antarctic and Ocean Research, Goa and INCOIS,Hyderabad, for their support. The authors would also like tothank the staff of the OOS’s group, Vessel Management Cell ofthe NIOT, and the ship staff for their excellent help and supportonboard.

REFERENCES

[1] T. Srinivasa Kumar, R. Venkatesan, N. Vedachalam, S. Padmanabhan,and R. Sundar, “Assessment of the reliability of the Indian tsunamiearly warning system,” Mar. Technol. Soc., vol. 50, no. 3, pp. 92–108,May/Jun. 2016.

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[5] R. Venkatesan, N. Vedachalam, M. Arul Muthiah, B. Kesavakumar, R.Sundar, and M. A. Atmanand, “Evolution of reliable and cost-effectivepower systems for buoys used in monitoring Indian seas,” Mar. Technol.Soc. J., vol. 49, no. 1, pp. 71–82, Jan./Feb. 2015.

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[8] S. A. Sannasiraj, R. Venkatesan, and M. V. Ramanamurthy, “Physicalmodel testing of moored surface buoy,” in Proc. IEEE Underwater Tech-nol., Chennai, India, 2015, pp. 1–7.

[9] R. Balaji, S. A Sannasiraj, and V. Sundar, “Physical model studies ondiscus buoy in regular random and double peak spectral wave,” Indian J.Mar. Sci., vol. 36, no. 1, pp. 18–26, 2007.

[10] AQWA Reference Manual, Ansys, Inc., South Pointe, PA, USA, 2012.[11] S. L. Lau, Z. Ji, and C. O. Ng, “Dynamics of an elastically moored floating

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[12] S. A. Malik, P. Guang, and L. Yanan, “Numerical simulations for theprediction of wave forces on underwater vehicle using 3D panel methodcode,” J. Appl. Sci. Eng. Technol., vol. 5, no. 21, pp. 5012–5021, 2011.

[13] V. Sanil Kumar, J. Singh, P. Pednekar, and R. Gowthaman, “Wave in thenear shore water of northern Arabian Sea during the summer monsoon,”Ocean Eng., vol. 38, no. 2, pp. 382–388, 2011.

[14] R. P. Trask and R. A. Weller, “Moorings,” in Woods Hole OceanographicInstitute, Cambridge, MA, USA: Academic, 2001, pp. 1850–1860.

[15] OrcaFlex User Manual, Orcina, Ltd., Cumbria, U.K., 2010.[16] H. O. Berteaux, Oceanographic Buoy System, in Buoy Engineering, 2nd

ed. New York, NY, USA: Wiley, pp.197–265, 1976.[17] O. M. Faltinsen, “Sea Environment,” in Sea Load on Ship and Offshore

Structures, Cambridge, U.K.: Cambridge Univ. Press, 1990, pp.13–34.[18] Amer. Bur. Shipping, “Rules for building and classing single point moor-

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R. Venkatesan received the Ph.D. degree in study onbehavior of materials in deep sea in materials engi-neering from the Indian Institute of Science Banga-lore, Bengaluru, India, in 2001.

He is currently the Head of the Ocean Observa-tion Group, National Institute of Ocean Technology,Chennai, India. He is also the Vice Chairman-Asiaof the Data Buoy Cooperation Panel and the Chair ofthe International Tsunameter Partnership. He was theRegional Coordinator of South Asian Seas programof UNEP, SACEP, Sri Lanka. His research interests

include ocean observations methods as well as ocean policy and management.Dr. Venkatesan was the recipient of the Certificate of Merit by the World

Meteorological Organization and UNESCO IOC for his outstanding services inglobal ocean data collection and the prestigious MTS Lockheed Martin Awardand the National Geoscience Award from the Honourable President of India.

S. A. Sannasiraj received the B.E. degree in civilengineering, the M.E. degree in civil structures, andthe Ph.D. degree in ocean engineering.

He is currently a Professor and the Head of theDepartment of Ocean Engineering, Indian Instituteof Technology Madras, Chennai, India. His areas ofspecialization include wave hydrodynamics, wind-wave modeling, numerical simulation of nonlinearwave-structure interaction and, coastal erosion andprotection. Since 2003, he has completed 14 re-search projects and executed more than 200 industrial

projects of nature port and harbours, intake/outfall systems, design of coastalprotection structures, and wind-wave prediction.

M. V. Ramanamurthy received the B.E. degree incivil engineering from Nagarjuna University, Nam-buru, India, in 1987, the M.Tech. degree in planningfrom CEPT University, Ahmedabad, India, in 1991,and the M.Tech. and Ph.D. degrees in ocean engi-neering from Indian Institute of Technology Madras,Chennai, India, in 1997 and 2008, respectively.

He is currently a Scientist-G with the Ministryof Earth Sciences heading the Integrated Coastal andMarine Area Management Project Directorate andalso looks after the programs of Ocean Structures and

Island Desalination, National Institute of Ocean Technology, Chennai, India. Hisareas of specialization include integrated coastal and marine area management,port and harbour structures, wave structure interaction studies, offshore andcoastal hydrodynamics, coastal engineering and measurements and coastal pro-cess modeling including tsunami and storm surge.



P. Senthilkumar received the B.E. degree in in-dustrial engineering from the College of Engineer-ing, Anna University, Chennai, India, in 2006 andthe M.E. degree in computer-aided design fromSathyabama University, Chennai, India, in 2015.

He is currently a Project Scientist in Ocean Ob-servation Systems at the National Institute of OceanTechnology, Chennai, India. His areas of specializa-tion include design and development of buoy compo-nents, analysis of deep sea moorings, and corrosionand bio-fouling study.

G. Dhinesh received the B.E degree in mechanicalengineering from Madras University, Chennai, India,in 2002, the M.E. degree in water resources from theCollege of Engineering, Anna University, Chennai,India, in 2004, and the Ph.D. degree in ocean engi-neering from Indian Institute of Technology, Madras,India, in 2009.

He is currently a Scientist-D in ocean structuresand island desalination with the National Instituteof Ocean Technology, Chennai, India. His areas ofspecialization include analysis of deep sea moorings,

deep sea water intake subsea pipeline analysis, vortex induced vibration onmarine pipelines, marine outfall systems, ship hydrodynamics, propulsion dy-namics, computational fluid dynamics applications related to all floating bodies,and experimental hydrodynamics.

ieee journal of oceanic engineering 1 ......2 ieee journal of oceanic engineering fig. 2....

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