In this paper a basic idea of a fault-tolerant monitoring and decision support system will be explained. Fault detection is an important part of the fault-tolerant design for in-service monitoring and decision support systems for ships. In the paper, a virtual example of fault detection will be presented for a containership with a real decision support system onboard. All possible faults can be simulated and detected using residuals and the generalized likelihood ratio (GLR) algorithm.

Steel Catenary Risers (SCR) are critical dynamic structures with a complex fatigue response. The offshore industry lacks verification of analytical models with full-scale response measurements. Only a small number of installed SCRs have any instrumentation to monitor dynamic response. This paper describes an on-line monitoring system deployed on one of the Tahiti infield (production) SCRs. Tahiti is a Truss Spar Floater located in 4,000 ft water depth in the Gulf of Mexico. The system is configured with localized strain and motion measurement devices. Emphasis is placed on the selection of number and location of the monitoring devices to characterize vessel induced riser response, VIV induced riser response, riser-seabed interface, and discontinuities at the riser hang-off locations. Monitoring device sensitivity requirements and qualification programs are also discussed. The monitoring system configuration drivers are reviewed in detail such as; monitoring objectives, instrumentation requirements, specification and architecture, field development integration, and installation. Information provided in this paper would be helpful for configuration of complex monitoring systems for deepwater steel catenary rises.

Wave height, period and direction are basic parameters for designing off-shore structures. Besides this direct application, knowledge of the regional characteristics of a wave field can also help in the selection of optimal regions for wave power energy plant design and installation. A wave climatology based on data generated by a WAVEWATCH III model simulation (NOAA WW3) for the Brazilian coast was analyzed and validated against statistical values derived from opportunity vessel measurements. The hindcast covered the period from January 1997 to December 2005 in a region between 5°N – 40°S and 10°W – 65°W. The grid used was uniform with a 0.25° spacial resolution. The boundary conditions were obtained from NOAA WW3 operational model and the atmospheric forcing from NOAA GFS model. The model results were calibrated with field data and detailed information about the simulation can be obtained in Alves et al. (2008) and Alves et al. (in press). Monthly averages of significant height, period and wavelength were calculated using 3 hour time resolution fields. Since a simple mean direction has small physical representativeness, the predominant direction (moda) and associated persistency were obtained from the data. The results were then compared with values from the U.S. Navy Marine Climate Atlas of the World. This Atlas has four points located within the selected model grid region. These points showed good agreement with wave period, height and direction persistency based on the WW3 simulation results. The wave climatology showed that the predominant wave direction from April to July was from S and SE in southern Brazil, associated with swells related to cold fronts. The S and SE swells were also responsible for the largest mean wave height (2.1 m) observed in the climatology. Another result that was validated with the literature was the E and NE predominant wave direction during the austral summer. This phenomenon is associated with winds originated from the South Atlantic High Pressure Center, which is a semi permanent high pressure center near Trindade Island. The wave climate in northern Brazil showed a predominant direction from the N during January to March, associated with the northern hemisphere winter storms. During the remaining months of the year, the predominant wave direction is E and NE associated with trade winds. The model results are still in a processing phase to produce extreme values, which will be more useful for coastal and off-shore structure design.

This paper presents a methodology to estimate deep water design current profiles using Complex Empirical Orthogonal Function (C-EOF) and a structural reliability response based model. The advantage of C-EOF is the capability of directly obtaining directional extreme current profiles. It is estimated that most of the variability of the southeast Brazil current system can be explained by the first two EOF modes. The first mode associated with the southwestward Brazil Current (BC) and the second mode with the northeastward Intermediate Western Boundary Current (IWBC). Thus, only two series of C-EOF amplitudes can be used in the response based technique to estimate the 100-y extreme current values. The methodology can also be used with more EOF modes if required to properly represent the current data. The probabilistic cumulative functions are based on extreme value distributions such as Gumbel or Weibull, and Lognormal for conditional distributions. The evaluation of estimated distribution parameters are carried out using Kolmogorov-Smirnov goodness-of-fit hypothesis tests and correlation coefficients for each directional sector.

The Nankai Trough is well known as the mega thrust earthquake generating tsunamis, with the interval of 100–200 years. The 1944 Tonankai and the 1946 Nankai earthquakes around the Nankai trough, each hypocenter was located off the Kii peninsula. However, according to Prof. Okamura of KOCHI University, super mega thrust earthquakes such as Hoei earthquake (1707) and Hakuho earthquakes (684) are occurring with an interval of 300–400 years or 700 years. Based on structural research, observational research and simulation researches, we proposed and have been starting to deploy the dense ocean floor observatory network system around the Tonankai seismogenic zone, to monitor crustal activities using broadband seismometer, accelerometer and precise pressure gauges. The probability of next Tonankai earthquake recurrence is estimate as 60–70% (The Headquarters for Earthquake Research Promotion; http://www.jishin.go.jp/main/index-e.html) . Therefore, the ocean floor network is significant ant important to monitor the crustal activities around mega-thrust earthquakes. In this paper, we explain the recent and detailed developing of this oceanfloor network system (DONET). Especially, the installation of sensors and improvement of ROV for the deploying system in the deep seafloor will be developed. Furthermore, the new project including observation simulation and mitigation researches of mega thrust earthquakes around the Nankai trough is starting as 5 years project (2008–20012). Especially, the Ocean floor network data is very important and powerful to progress the new project.

The U.S. National Ocean Service (NOS) of NOAA maintains and operates a Physical Oceanography Real Time System (PORTS®) in the Nation’s major ports, harbors and bays. The traditional method of obtaining real-time data from bottom mounted instruments is via underwater cable link. However, this is vulnerable to damage and costly to install and maintain. This paper describes an approach utilizing acoustic and Iridium satellite links to report in real-time wave and current data. The system consists of an ocean bottom instrumentation platform and a U.S. Coast Guard Aid-to-Navigation buoy for data relay. The bottom platform contains a Nortek 1 MHz Acoustic Wave and Current profiler (AWAC) with an integrated Nortek Internal Processor (NIP), a LinkQuest omni-directional UWM2000H underwater acoustic transmitting modem, an ORE acoustic release-based recovery component, and a Teledyne-Benthos UAT-376/EL acoustic transponder. The surface buoy supports an omni-directional UWM2000H receiving modem, an Iridium antenna, and an electronic box containing an Iridium modem, a controller, battery packs, and temperature and voltage sensors. The AWAC measures current profiles along the vertical water column at 30-minute intervals and surface waves at hourly intervals. The NIP processes a set of user selected wave and current parameters and sends these data to the controller on the surface buoy through acoustic modems. The data are then transmitted via Iridium satellite to remote offices in real-time. Sample measurement results and reference data from a near-by Datawell’s Waverider directional wave buoy are presented. The Waverider is operated by the U.S. Army Corps of Engineers (USACE) and Scripps Institution of Oceanography (SIO). Several unique system design features and interesting wave phenomenon observed at the measurement site are discussed. The goal of this project is to demonstrate the performance of AWAC, NIP, shallow water acoustic modems, and Iridium satellite in real-time data telemetry.

The synergistic use of measured in-situ current data and altimetry derived geostrophic current data provides improved seasonal characterisation of the current regime, West of Shetland. In September 2007, considerable downtime was experienced by an offshore operator, West of Shetland, as a result of unexpectedly high currents persisting for a number of days. This downtime was unanticipated following conclusions derived from one year of in-situ measured data, which suggested a most favourable current regime during the months August to October. Ten years of altimetry derived geostrophic currents were utilised in conjunction with approximately 3 years of in-situ data to assess the validity of the reported seasonal trend. The altimetry derived geostrophic currents correlated well with the dominating long period signal extracted from the in-situ data. Seasonal comparison between the altimetry derived geostrophic currents and the total measured signal showed the previously available measurement year had a relatively benign September. Based on the 10 years of satellite data, the inter-annual variability of the current regime West of Shetland does not show any clear seasonal trend.

The Bayesian modeling procedure is modified for real-time estimation of directional wave spectra using non-stationary ship motion data. The assumption of stationary stochastic processes is applied to the seaway, but not to ship response because it also depends on ship maneuvers. Ship response is strongly affected by changes in the encounter angle and frequency of waves. Therefore, it is need to be a real-time algorithm that can deal with non-stationary stochastic processes and estimate the directional wave spectra. In the proposed algorithm, the iterative calculations of the non-linear equations were optimized and the convergence was not achieved at every time step, but was achieved gradually over several time steps. In order to examine the reliability of the proposed method, real-time estimation was conducted by using the data of onboard experiments. Comparisons between the results of the proposed algorithm and a wave monitoring radar system show good agreements.

Wave measurements were obtained at an Eastern Green Canyon location during hurricane Ike in September 2009. The eye of the hurricane passed approximately 68 nautical miles to the South West of the measurement location. The significant wave height was above 30 ft for about 20 hours and above 40 ft for about 5.5 hours. The wave time series provide an insight into the wave field as the storm approaches and leaves the location. One of the interesting features observed was that there were repetitive sequences, where each sequence consisted of a period of increased wave energy followed by periods of reduced wave energy. Each sequence lasted approximately one hour. Measured wave crest, wave trough and wave height distributions are discussed. One unique wave event was observed. This event was characterized by a predictably-sized crest followed by a very deep trough.

Vortex Induced Motion (VIM) of a Deep Draft Semi® with four square columns has been observed in model tests and in the field for a prototype configuration. The model test observations were developed into design guidance procedures. Some of the assumptions based on the model test results are validated with the field observations. A quantitative description of the field measurements is presented. A comparison between the field observations and the design guidance is provided.

The kinematics of short crested steep and breaking waves in the ocean is a subject that is best studied spatially, in the time domain, to obtain a good understanding of the multi-directional spreading of energy, which is dependant on strongly non-linear wave interactions in the system. The paper will cover the collection, recording and processing of streamed sea surface image data, obtained simultaneously from multiple digital video cameras, for analysis using stereoscopic image processing methods to provide information on the kinematics of ocean wave fields. The data streaming architecture, which will be reviewed, incorporates an advanced laptop computer and two to three stand-alone digital video cameras which are all linked through a gigabit ethernet network connection with sufficient bandwidth to simultaneously transfer the image data from the cameras to hard drive storage. The modifications to the laptop computer comprise the provision of increased processing capacity to enable it to accept and process large IP frames simultaneously. The system has the capacity to continuously record images, at a rate of up to 60 frames per second, for periods of up to one hour. It includes an external triggering mechanism, which is synchronised to a micro-second, to ensure that stereo pairs of images are captured simultaneously. Calibration of the cameras, and their stereoscopic configuration, is a critical part of the overall process and we will discuss how ill-conditioned and singular matrices, which can prevent the determination of required intrinsic and extrinsic parameters, can be avoided. The paper will include examples of wave field image data which has been collected using streamed digital video data and Binocular Stereoscopic Image System (BiSIS) processing methods. It will also give examples digital video images and dimensional wave field data which has been collected and processed using the Automated Trinocular Stereoscopic Imaging Systems (ATSIS) methods. Both of these systems provide a valuable means of analysing irregular, non-linear, short crested waves, which leads to an improved understanding of ocean wave kinematics.

Dynamic strain monitoring provides valuable information about behavior and condition of mechanical parts subjected to the load either under test or realistic working conditions. In many occasions, test points for strain measurement are not easily accessible for temporary or permanent wired connection with standard test and measurement equipment, especially for measurements on moving objects. We developed a configurable portable dynamic strain monitoring system, which is particularly suitable for short-term installations and adaptable for wide range of expected strain values. The high-accuracy measuring module, attached to the test point along with the strain gage sensor, digitizes and transmits measured data over the license-free ISM radio-frequency band to the receiving unit for further signal processing and results representation. The calibration procedure is highly simplified due to the specific design of the input analog measuring chain, which eliminates the need, in several commercially available similar instruments, for manual sensor calibration. The accuracy and the bandwidth of the input measuring chain were optimized to provide means for high quality spectral analysis of acquired dynamic strain waveforms. The system may be simply extended for dynamic torque, power and rotational speed measurements on revolving shafts, by connecting to the inductive proximity switch to the receiver module. Receiving unit also provides means for connection with other test and measurement equipment by standard analog and digital industrial communication protocols (4–20 mA current loop, RS485). The overall system was designed to accommodate to wide variety of test and research applications, as well as monitoring parameter ranges.

We propose a novel variational Wave Acquisition Stereo System (WASS) that exploits new stereo reconstruction techniques for accurate estimates of the spatio-temporal dynamics of ocean waves. WASS has a significant advantage as a low-cost system in both installation and maintenance. A stereo camera view provides three-dimensional data (both in space and time) whose statistical content is richer than that of a time series retrieved from wave gauges, ultrasonic instruments or buoys, the latter being expensive to install and maintain. Indeed, wave spectra can be easily estimated from the multi-dimensional images obtained with WASS. The estimated spectra present an inertial range that decays as k −2.5 , k being the wave number, in agreement with wave turbulence theory (Zakharov 1999, Socquet-Juglard et al. 2005). Further, the empirical probability density functions derived from the reconstructed surface data compare very well with theoretical models (Tayfun & Fedele 2007, Fedele 2008). The variational WASS is a promising technology with broader impacts in offshore engineering since it will enrich the understanding of the statistics of waves for an improved design of offshore structures.

Vortex Induced Motion (VIM) of a Spar platform is an important consideration in the design of Spar moorings and risers. During the design phase, the VIM characteristics of a Spar configuration are evaluated by hydrodynamic model testing. The basis for hydrodynamic model testing is that geometric and dynamic similitude between prototype and model parameters is preserved. Reynolds number and Froude number scaling are the two relevant scaling parameters for Spar VIM model testing. However, simultaneously satisfying Reynolds and Froude scaling for the model and prototype conditions is practically impossible. This leads to compromises in model test Reynolds number scaling and inherent uncertainties in extrapolating the model test VIM predictions to full-scale design conditions. Hence measurement of full-scale Spar VIM responses provides valuable data for validation of design assumptions. BP’s integrity management efforts for its Gulf of Mexico deep water production facilities include monitoring of the environmental conditions, and response of the hull, mooring and riser systems. Field measured data for VIM of BP’s Horn Mountain Truss Spar, presented in this paper, shows that the Horn Mountain Truss Spar VIM response is within original design assumptions. The maximum VIM measured in the field (A/D ≈ 0.26) is well below the acceptable design value of A/D = 0.5. The field data is analyzed and results presented in the form of Spar VIM response time traces, Spar VIM response versus Reduced Velocity and variation of period of VIM oscillation with Spar offsets. The field data shows VIM response characteristics consistent with model test observations.

This paper presents a preliminary examination and analysis of a small suite of 4-D wave data to explore what new insight or inference we can garner — particularly toward the realm where conventional approaches have not been traversed. While we caught a few glimpses that might indicate a need for new conceptualizations, it by no means to negates the vast positive contributions the conventional approaches have been made in the past century. We feel it is timely to encourage further 4-D ocean wave measurement and thereby facilitate fresh new states of study and understanding of ocean waves.

The variability of the amplitude-frequency structure of wind waves in space and time during their transformation in the coastal zone are considered. Wave time series, measured synchronously in 15 points along the wave propagation, obtained at field and laboratory experiments, were used for the analysis. Free surface elevation time series were represented as a sum of first and second harmonics with amplitudes slowly varying in time (or envelopes of the waves of corresponding frequency bands). Relative changes of these amplitudes in space and time were studied also. It was revealed, that at the initial stage of the wave transformation, the changes of amplitudes of the first and the second harmonics are similar and amplitudes of the second harmonics are proportional to the squared amplitudes of the first harmonics. At this stage the variability of parameters of individual irregular waves can be explained by Stokes theory. Nearer to the coast the instantaneous values of the amplitudes of the first and the second harmonics varies in time chaotically and is not possible to construct a simple model of the variability of the parameters of individual irregular waves. The main reason for this effect is the backward energy transfer from the second to the first harmonics of the waves during nearly resonant non-linear triad interactions.

In this paper, an integrated wave monitoring network for the Hellenic Seas is presented and its components are described. The network is comprised from wave buoys and nautical X-band radars covering most of the important areas of the Hellenic seas as regards complicated wave propagation patterns. The buoy wave monitoring network is part of the POSEIDON system for the monitoring, information and forecasting of the state of the Hellenic Seas. The X-band wave radar network is under development within the context of the OKEANOS project in co-operation with the Hellenic Navy Hydrographic Service. The measuring techniques and principles of both types of devices (buoys and X-band radars) are also described. The wave measurements from the network are mainly used for improving the operational wave forecasts provided by the Hellenic Centre for Marine Research (HCMR), for individual planning purposes and in the design and construction of coastal and offshore structures. Two experimental coastal sites have been selected for comparing the radar wave data with data from directional wave buoys and the WAM wave model.

Tensioners are used for supporting various kinds of production and drilling risers on offshore platforms. All permanent production facilities (such as TLP’s and Spar’s) have employed tensioners to support their dry tree production risers. The key design parameters for the tensioners design are stiffness, stroke and friction properties. Full scale onshore testing of production riser tensioners to determine tensioner properties is difficult due to the magnitude of the loads and pressures required for typical deepwater risers, thus designers frequently rely on theoretical values or small scale tests. This paper presents a determination of riser tensioner properties from full scale offshore observations made on the Holstein Spar production facility during 2005 hurricance season. The paper presents a model for the tensioner system that relates the properties needed by platform and riser designers to the physical tensioner systems. The methodology and results from extraction of parameters from the full scale data is presented. The results presented in this paper will provide a better insight to the designers of such systems.

Ocean observation has evolved tremendously, from collection and exchange of weather and sea state information by ocean going ships in the late 19th century to today’s multisensor, multi-platform, multi-disciplinary, large scale observation networks. Data are now transmitted and disseminated automatically in real-time to a variety of user groups with significant social and economical implications. This paper provides an overview of representative advances in in-situ ocean observation during the past decade. Major driving forces and representative advances and trends in in-situ observation are described. Advances are discussed under the categories of observation infrastructure and major measurement system components including sensor, platform, data collection and telemetry, and power supply. The U.S. National Oceanic and Atmospheric Administration (NOAA) is a major participant of the global ocean observation programs and examples of its contributions and activities are introduced.

Squalls control design wind conditions offshore West Africa, where the wind regime is otherwise relatively benign. The West Africa Gust (WAG) Joint Industry Project was initiated in 2004 to make best use of available industry data for characterisation of squalls in engineering design. The WAG phase one report highlighted the need for further measurement to address uncertainties in the horizontal and vertical structure of squall winds. This paper describes the resulting measurement system installed on a platform offshore West Africa.