Development of an On-Board Wave Estimation System Based on the Motions of a Moored FPSO: Commissioning and Preliminary Validation

2012 ◽  
Author(s):  
Alexandre N. Simos ◽  
Eduardo A. Tannuri ◽  
José J. da Cruz ◽  
Asdrubal N. Queiroz Filho ◽  
Iuri B. da Silva Bispo ◽  
...  
Keyword(s):  
Bayesian Estimation ◽  
Full Range ◽  
Wave Spectrum ◽  
Measurement Unit ◽  
Small Scale ◽  
Automation System ◽  
Wave System ◽  
Small Motion ◽  
Estimation System ◽  
Period Wave

This paper addresses the development, installation and initial tests of a system for wave spectra estimation from the measurements of the first order motions of a moored FPSO located in Campos Basin, Brazil. The estimation is based on Bayesian inference algorithms, previously validated by means of numerical and small-scale experimental analysis. A 6-dof inertial measurement unit (IMU) is used for monitoring the motions of the platform, and this information is sent to a remote data-base, also accessed by the wave-estimation system. The algorithm also requires the Response Amplitude Operators (RAOs), and they depend on the loading conditions of the FPSO. A previous analysis considering typical loading configurations of the tanks showed that the wave estimation is mainly dependent on the total displacement of the vessel, and not on the load distribution among the tanks. Hence, the RAOs for the full-range of drafts (or total displacements) were numerically generated, considering a uniform distribution of the load among the tanks. Since the draft of the platform was not directly measured, the loading levels of the tanks are obtained from the automation system of the platform, and the draft is then estimated. Finally, the heading is measured by a gyrocompass, and it is necessary for the definition of the global wave direction. The Bayesian estimation is executed at time-spans of 30min. A parametric optimization algorithm is then applied for the calculation of the wave spectrum parameters from the raw-spectrum obtained by the Bayesian estimation. A user-friendly interface was also developed, with on-line information about platform motions, estimated wave spectrum, peak statistics and data history. Since all information is accessed by network, the wave system can be installed either on-board or in the on-shore monitoring center. The system was commissioned and a partial 3-month validation campaign was executed. The spectrum results were compared to NOAA estimates. As expected, low-period wave components (smaller than 8s) could not be estimated with accuracy, since the FPSO presents small motion response for these components. Swell and high-period wave components estimates presented good qualitative and quantitative agreement with satellite prediction.

Development of an On-Board Wave Estimation System Based on the Motions of a Moored FPSO: Preliminary Assessments From a Field Campaign

2013 ◽  
Author(s):  
Eduardo A. Tannuri ◽  
Iuri B. da Silva Bispo ◽  
Alexandre N. Simos ◽  
Asdrubal N. Queiroz Filho ◽  
José J. da Cruz ◽  
...  
Keyword(s):  
Estimation Method ◽  
Measurement Unit ◽  
Small Scale ◽  
Preliminary Evaluation ◽  
Statistical Parameters ◽  
Inference System ◽  
Field Campaign ◽  
Estimation System ◽  
Heave Motion ◽  
Two Parameters

This paper addresses a wave inference system developed for on-site estimation of directional wave spectra from the measurements of the wave-frequency motions of moored vessels. As a preliminary evaluation of the system’s performance, the results obtained in a 9-month field campaign based on an FPSO operating in Brazil’s Campos Basin are compared to hindcast predictions for the same region displayed by NOAA. The estimation method is based on Bayesian inference algorithms, previously validated by means of numerical and small-scale experimental analysis. A 6-dof inertial measurement unit (IMU) is used for monitoring the motions of the platform. The algorithm also requires the Response Amplitude Operators (RAOs), which in turn depend on the loading conditions of the FPSO. Those are defined before each estimation is performed by means of readings of the tanks’ levels. The accuracy of the predictions also depends on the calibration of two parameters (the so-called hyperparameters of the Bayesian method) and those are specified with respect to the mean period of heave motion. The system is able to identify unimodal or bimodal (cross) spectra using a bimodality criterion combined to an iterative algorithm for separating each component of the global spectrum. As a result, besides the global energy matrix, the statistical parameters required for reproducing the measured directional spectra by means of Jonswap and cosine2s models are provided. The system was commissioned and a 9-month validation campaign was executed. It is shown that the estimated parameters show quite reasonable correlation with satellite-based hindcasts from NOAA for sea states with peak periods larger than 8sec.

Parametric instability of internal gravity waves

1975 ◽  
Vol 67 (4) ◽  
pp. 667-687 ◽  
Author(s):  
A. D. McEwan ◽  
R. M. Robinson
Keyword(s):  
Internal Wave ◽  
Large Scale ◽  
Wave Spectrum ◽  
Parametric Instability ◽  
Mathieu Equation ◽  
Internal Gravity Waves ◽  
Small Scale ◽  
Preliminary Calculation ◽  
Theoretical Predictions ◽  
Oceanic Internal Wave

A continuously stratified fluid, when subjected to a weak periodic horizontal acceleration, is shown to be susceptible to a form of parametric instability whose time dependence is described, in its simplest form, by the Mathieu equation. Such an acceleration could be imposed by a large-scale internal wave field. The growth rates of small-scale unstable modes may readily be determined as functions of the forcing-acceleration amplitude and frequency. If any such mode has a natural frequency near to half the forcing frequency, the forcing amplitude required for instability may be limited in smallness only by internal viscous dissipation. Greater amplitudes are required when boundaries constrain the form of the modes, but for a given bounding geometry the most unstable mode and its critical forcing amplitude can be defined.An experiment designed to isolate the instability precisely confirms theoretical predictions, and evidence is given from previous experiments which suggest that its appearance can be the penultimate stage before the traumatic distortion of continuous stratifications under internal wave action.A preliminary calculation, using the Garrett & Munk (197%) oceanic internal wave spectrum, indicates that parametric instability could occur in the ocean at scales down to that of the finest observed microstructure, and may therefore have a significant role to play in its formation.

scholarly journals A Low-Cost Motion Capture System for Small-Scale Wave Energy Device Tank Testing

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Francesco Paparella ◽  
Satja Sivcev ◽  
Daniel Toal ◽  
John V. Ringwood
Keyword(s):  
Wave Energy ◽  
Motion Tracking ◽  
Tracking System ◽  
Low Cost ◽  
Measurement Unit ◽  
Small Scale ◽  
Energy Device ◽  
Optical Motion ◽  
Optical Motion Tracking ◽  
Motion Tracking System

The measurement of the motion of a small-scale wave energy device during wave tank tests is important for the evaluation of its response to waves and the assessment of power production. Usually, the motion of a small-scale wave energy converter (WEC) is measured using an optical motion tracking system with high precision and sampling rate. However, the cost for an optical motion tracking system can be considerably high and, therefore, the overall cost for tank testing is increased. This paper proposes a low-cost capture system composed of an inertial measurement unit and ultrasound sensors. The measurements from the ultrasound sensors are combined optimally with the measurements from the inertial measurement unit through an extended Kalman filter (EKF) in order to obtain an accurate estimation of the motion of a WEC.

Critical Conditions for Liquid Mediated Collapse of Two-Dimensional Rough Surfaces

2007 ◽  
Author(s):  
Jeffrey L. Streator ◽  
Robert L. Jackson
Keyword(s):  
Liquid Droplet ◽  
Rough Surfaces ◽  
Full Range ◽  
Surface Profile ◽  
Adhesive Force ◽  
Scale Model ◽  
Critical Conditions ◽  
Liquid Volume ◽  
Small Scale ◽  
Unit Depth

Small-scale devices are particularly vulnerable to adverse effects of adhesion because of large surface-area-to-volume ratios. Additionally, small gaps can be easily bridged at high humidity or when there are other contaminant liquids present. The bridging of a portion of the interface by a liquid droplet of given volume, tends to pull surfaces in closer proximity due to the sub-ambient pressures that arise. In turn, regions spanned by the bridge will increase in size and lead to a greater adhesive force. In the present work we develop a model for these effects in the presence of surface roughness. The influence of asperities on the surface is treated by means of a recently-developed multi-scale model that considers the full range of wavelengths comprising the surface profile. In the simulations, two nominally flat rough surfaces with profiles that vary only in one direction are brought together under a prescribed load. A liquid bridge of given volume (per unit depth) is then introduced into the contact, assuming an initial areal coverage. The interface configuration is then iterated until one is found that satisfies the equations of elasticity and capillarity for a given liquid volume. As a result of the simulation, critical values are found for combinations of parameters that delineate stable and unstable conditions.

On the Estimation of Directional Wave Spectrum Based on Stationary Vessels 1st Order Motions: A New Set of Experimental Results

2008 ◽  
Author(s):  
Joa˜o V. Sparano ◽  
Eduardo A. Tannuri ◽  
Alexandre N. Simos ◽  
Vini´cius L. F. Matos
Keyword(s):  
Bayesian Inference ◽  
Wave Spectrum ◽  
Small Scale ◽  
Large Set ◽  
Wave Spectra ◽  
Inference Method ◽  
Peak Period ◽  
Wave Basin ◽  
Bayesian Inference Method ◽  
Directional Wave

The practicability of estimating directional wave spectra based on a vessel 1st order response has been recently addressed by several researchers. The interest is justified since on-board estimations would only require only a simple set of accelerometers and rate-gyros connected to an ordinary PC. The on-board wave inference based on 1st order motions is therefore an uncomplicated and inexpensive choice for wave estimation if compared to wave buoys and radar systems. The latest works in the field indicate that it is indeed possible to obtain accurate estimations and a Bayesian inference model seems to be the preferable method adopted for performing this task. Nevertheless, most of the previous analysis has been based exclusively on numerical simulations. At Polytechnic School, an extensive research program supported by Petrobras has been conducted since 2000, aiming to evaluate the possibility of estimating wave spectrum on-board offshore systems, like FPSO platforms. In this context, a series of small-scale tests has been performed at the LabOceano wave basin, comprising long and short crested seas. A possible candidate for on-board wave estimation has been recently studied: a crane barge (BGL) used for launching ducts offshore Brazil. The 1:48 model has been subjected to bow and quartering seas with different wave heights and periods and also different levels of directional spreading. A Bayesian inference method was adopted for evaluating the wave spectra based on the time-series of motions and the results were directly compared to the wave spectra measured in the basin by means of an array of wave probes. Very good estimations of the statistical parameters (significant wave height, peak period and mean wave direction) were obtained and, in most cases, even the directional spreading could be properly predicted. Inversion of the mean direction (180° shift), mentioned by some authors as a possible drawback of the Bayesian inference method, was not observed in any case. Sensitivity analysis on errors in the input parameters, such as the vessel inertial characteristics, has also been performed and attested that the method is robust enough to cope well with practical uncertainties. Overall results once again indicate a good performance of the inference method, providing an important additional validation supported by a large set of model tests.

High Performance Structural Vibration Control by a Preview of the Future Seismic Waveform Generated With a Wave Transmission Network and an AI-Based Estimation System

2019 ◽  
Author(s):  
Kazuhiko Hiramoto ◽  
Taichi Matsuoka ◽  
Katsuaki Sunakoda
Keyword(s):  
Vibration Control ◽  
Control Method ◽  
Small Scale ◽  
Control Law ◽  
Time Interval ◽  
Transmission Network ◽  
Control Performance ◽  
Seismic Waveform ◽  
The Future ◽  
Estimation System

Abstract We propose a new active vibration control strategy based on the future seismic waveform information obtained in remote observation sites. The waveform information in the remote site is transmitted by a waveform transmission network to the structure under control. The waveform transmission network is realized by interconnecting multiple controlled structures and observation sites. By using the future waveform information obtained through the network, we propose a control law realizing fairly higher control performance over the conventional structural control methodologies. A preview control law consisting of the state-feedback and feedforward control (preview action) is adopted. For the preview action, future values of the disturbance in some time interval are necessary. However, because the future value of the earthquake waveform is unknown, the preview action contributing the performance improvement is generally impossible. To get over this difficulty, an AI-based wave estimation system to estimate the future earthquake waveform is proposed. The wave estimation system is a multi-layered artificial neural network (ANN). Through a small scale simulation study with a recorded earthquake event in Japan, we show that the proposed control method achieves much higher control performance over the conventional LQ-based active control.

Mining and Indigenous Peoples

2020 ◽  
Author(s):  
Nicholas Bainton
Keyword(s):  
Indigenous People ◽  
Indigenous Peoples ◽  
Social Relations ◽  
Full Range ◽  
Indigenous Communities ◽  
Heritage Management ◽  
Resource Extraction ◽  
Small Scale ◽  
The Social ◽  
The Relationship

Anthropologists have been studying the relationship between mining and the local forms of community that it has created or impacted since at least the 1930s. While the focus of these inquiries has moved with the times, reflecting different political, theoretical, and methodological priorities, much of this work has concentrated on local manifestations of the so-called resource curse or the paradox of plenty. Anthropologists are not the only social scientists who have tried to understand the social, cultural, political, and economic processes that accompany mining and other forms of resource development, including oil and gas extraction. Geographers, economists, and political scientists are among the many different disciplines involved in this field of research. Nor have anthropologists maintained an exclusive claim over the use of ethnographic methods to study the effects of large- or small-scale resource extraction. But anthropologists have generally had a lot more to say about mining and the extractives in general when it has involved people of non-European descent, especially exploited subalterns—peasants, workers, and Indigenous peoples. The relationship between mining and Indigenous people has always been complex. At the most basic level, this stems from the conflicting relationship that miners and Indigenous people have to the land and resources that are the focus of extractive activities, or what Marx would call the different relations to the means of production. Where miners see ore bodies and development opportunities that render landscapes productive, civilized, and familiar, local Indigenous communities see places of ancestral connection and subsistence provision. This simple binary is frequently reinforced—and somewhat overdrawn—in the popular characterization of the relationship between Indigenous people and mining companies, where untrammeled capital devastates hapless tribal people, or what has been aptly described as the “Avatar narrative” after the 2009 film of the same name. By the early 21st century, many anthropologists were producing ethnographic works that sought to debunk popular narratives that obscure the more complex sets of relationships existing between the cast of different actors who are present in contemporary mining encounters and the range of contradictory interests and identities that these actors may hold at any one point in time. Resource extraction has a way of surfacing the “politics of indigeneity,” and anthropologists have paid particular attention to the range of identities, entities, and relationships that emerge in response to new economic opportunities, or what can be called the “social relations of compensation.” That some Indigenous communities deliberately court resource developers as a pathway to economic development does not, of course, deny the asymmetries of power inherent to these settings: even when Indigenous communities voluntarily agree to resource extraction, they are seldom signing up to absorb the full range of social and ecological costs that extractive companies so frequently externalize. These imposed costs are rarely balanced by the opportunities to share in the wealth created by mineral development, and for most Indigenous people, their experience of large-scale resource extraction has been frustrating and often highly destructive. It is for good reason that analogies are regularly drawn between these deals and the vast store of mythology concerning the person who sells their soul to the devil for wealth that is not only fleeting, but also the harbinger of despair, destruction, and death. This is no easy terrain for ethnographers, and engagement is fraught with difficult ethical, methodological, and ontological challenges. Anthropologists are involved in these encounters in a variety of ways—as engaged or activist anthropologists, applied researchers and consultants, and independent ethnographers. The focus of these engagements includes environmental transformation and social disintegration, questions surrounding sustainable development (or the uneven distribution of the costs and benefits of mining), company–community agreement making, corporate forms and the social responsibilities of corporations (or “CSR”), labor and livelihoods, conflict and resistance movements, gendered impacts, cultural heritage management, questions of indigeneity, and displacement effects, to name but a few. These different forms of engagement raise important questions concerning positionality and how this influences the production of knowledge—an issue that has divided anthropologists working in this contested field. Anthropologists must also grapple with questions concerning good ethnography, or what constitutes a “good enough” account of the relations between Indigenous people and the multiple actors assembled in resource extraction contexts.

Wave Spectrum Analysis of Kerry Deepwater Port Sea in Cameroon

2014 ◽  
Vol 638-640 ◽  
pp. 1280-1284
Author(s):  
Hui Xiao ◽  
Yi Feng Zhang ◽  
Hong Bo Zhao
Keyword(s):  
Fourier Transform ◽  
Spectrum Analysis ◽  
Wave Spectrum ◽  
Transform Method ◽  
Long Period ◽  
Fast Fourier Transform Method ◽  
Spectrum Characteristics ◽  
One Year ◽  
Sea Area ◽  
Period Wave

According to the measured wave data for one year in Kerry deepwater port sea area, Cameroon, the wave spectrum characteristics calculate using fast Fourier transform method; the result shows that the bimodal spectrum is given priority to this sea area, and the big wave appears in summer and autumn, the long period wave influence is opposite bigger that should be pay attention.

Task-Allocation and Control of a Ground Robots Collective for Warehouse Automation

2015 ◽  
Author(s):  
Mehmet Ali Guney ◽  
Ioannis Raptis
Keyword(s):  
System Architecture ◽  
Task Allocation ◽  
Arbitrary Number ◽  
Small Scale ◽  
Automation System ◽  
Test Bed ◽  
Allocation Algorithm ◽  
Automation Systems ◽  
Algorithmic Design ◽  
And Control

In the last years, there have been several attempts to deploy Autonomous Guided Vehicles (AGVs) to automate the operation of warehouse environments. The implementation of AGVs has numerous advantages over conventional warehouse automation systems in terms of cost and scalability. In this work, we present the development of a test-bed platform for the utilization of an AGV collective to a warehouse automation system. The system architecture has plug-and-play algorithmic design which makes it extremely modular. In this system, small-scale robotic forklifts are used to transport an arbitrary number of circular pallets to predefined locations. The forklift robots are able to move in the arena without colliding each other due to the implementation of a centralized deconfliction algorithm. A task allocation algorithm prevents the forklift drives from being trapped by a fence of pallets. The performance of the proposed system is validated by both simulation and experimental results.

scholarly journals Scattering of surface gravity waves by bottom topography with a current

2007 ◽  
Vol 576 ◽  
pp. 235-264 ◽  
Author(s):  
FABRICE ARDHUIN ◽  
RUDY MAGNE
Keyword(s):  
Gravity Waves ◽  
Bottom Topography ◽  
Wave Spectrum ◽  
Action Spectrum ◽  
Wave Action ◽  
Surface Gravity ◽  
Small Scale ◽  
Surface Gravity Waves ◽  
Reflected Wave ◽  
A Current

A theory is presented that describes the scattering of random surface gravity waves by small-amplitude topography, with horizontal scales of the order of the wavelength, in the presence of an irrotational and almost uniform current. A perturbation expansion of the wave action to order η2 yields an evolution equation for the wave action spectrum, where η = max(h)/H is the small-scale bottom amplitude normalized by the mean water depth. Spectral wave evolution is proportional to the bottom elevation variance at the resonant wavenumbers, representing a Bragg scattering approximation. With a current, scattering results from a direct effect of the bottom topography, and an indirect effect of the bottom through the modulations of the surface current and mean surface elevation. For Froude numbers of the order of 0.6 or less, the bottom topography effects dominate. For all Froude numbers, the reflection coefficients for the wave amplitudes that are inferred from the wave action source term are asymptotically identical, as η goes to zero, to previous theoretical results for monochromatic waves propagating in one dimension over sinusoidal bars. In particular, the frequency of the most reflected wave components is shifted by the current, and wave action conservation results in amplified reflected wave energies for following currents. Application of the theory to waves over current-generated sandwaves suggests that forward scattering can be significant, resulting in a broadening of the directional wave spectrum, while back-scattering should be generally weaker.

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