An Empirical Method for the Estimation of Towing Resistance of a Life Raft in Various Sea States

Current IMO regulations require life rafts to be tow tested only in calm water. In real evacuation situations, life rafts are deployed in the prevailing environmental conditions, with wind and waves. Added wave resistance is small at low wave heights but increases nonlinearly with increased wave height. If life rafts are to be towed in moderate seas (up to 4 m significant wave height), tow force estimates based only on calm water tow resistance become less reliable. Tow patches, towline, towing craft etc. also need to be designed to withstand dynamic wave loading in addition to mean load. Therefore, mean tow force, tow force variation and maximum tow force are important. A full-scale 16-person, commercially available, SOLAS approved life raft was towed in the tank, in upwind, head seas with significant wave height of 0.5 m. The measured tow force showed that it could be treated as a linear system with wave amplitude, by demonstrating that tow force is mainly inertial and follows a Rayleigh distribution. Therefore, extreme-value statistics used for waves can be applied to developing equations for predicting tow force. A method is proposed to predict life raft tow force at different tow speeds and in various sea states, with waves and wind. The method involved using tank experiments to obtain tow force response for one sea state. The information can then be used to predict life raft tow force in wind and waves for different sea states. Three equations are proposed to demonstrate that a simple tank experiment could provide valuable information necessary to empirically estimate the mean tow force, tow force variation and maximum tow force for a specific life raft in different sea states. The equations are developed for upwind, head seas. These equations were extensively validated using tow force measured in the tank. They were partially validated with limited sea trial data, by towing the same 16-person life raft and a 42-person life raft in upwind, head seas with significant wave height of 1.3 m. The equations were able to predict maximum tow forces to within 15% of the measured.

Download Full-text

Estimation of Significant Wave Heights from ASCAT Scatterometer Data via Deep Learning Network

Remote Sensing ◽

10.3390/rs13020195 ◽

2021 ◽

Vol 13 (2) ◽

pp. 195

Author(s):

He Wang ◽

Jingsong Yang ◽

Jianhua Zhu ◽

Lin Ren ◽

Yahao Liu ◽

...

Keyword(s):

Deep Learning ◽

Wave Height ◽

Significant Wave Height ◽

Incidence Angle ◽

Ocean Waves ◽

Global Scale ◽

Learning Technology ◽

Sea State ◽

Significant Wave ◽

Wave Heights

Sea state estimation from wide-swath and frequent-revisit scatterometers, which are providing ocean winds in the routine, is an attractive challenge. In this study, state-of-the-art deep learning technology is successfully adopted to develop an algorithm for deriving significant wave height from Advanced Scatterometer (ASCAT) aboard MetOp-A. By collocating three years (2016–2018) of ASCAT measurements and WaveWatch III sea state hindcasts at a global scale, huge amount data points (>8 million) were employed to train the multi-hidden-layer deep learning model, which has been established to map the inputs of thirteen sea state related ASCAT observables into the wave heights. The ASCAT significant wave height estimates were validated against hindcast dataset independent on training, showing good consistency in terms of root mean square error of 0.5 m under moderate sea condition (1.0–5.0 m). Additionally, reasonable agreement is also found between ASCAT derived wave heights and buoy observations from National Data Buoy Center for the proposed algorithm. Results are further discussed with respect to sea state maturity, radar incidence angle along with the limitations of the model. Our work demonstrates the capability of scatterometers for monitoring sea state, thus would advance the use of scatterometers, which were originally designed for winds, in studies of ocean waves.

Download Full-text

Development of Operational Limit Diagrams for Offshore Lifting Procedures

Volume 1: Offshore Technology; Offshore Geotechnics ◽

10.1115/omae2015-42270 ◽

2015 ◽

Author(s):

Leonardo Roncetti ◽

Fabrício Nogueira Corrêa ◽

Carl Horst Albrecht ◽

Breno Pinheiro Jacob

Keyword(s):

Wave Height ◽

Significant Wave Height ◽

Technological Development ◽

Automatic Generation ◽

Dynamic Responses ◽

Offshore Platforms ◽

Peak Period ◽

Significant Wave ◽

Wave Heights ◽

Offshore Crane

Lifting operations with offshore cranes are fundamental for proper functioning of a platform. Despite the great technological development, offshore cranes load charts only consider the significant wave height as parameter of environmental load, neglecting wave period, which may lead to unsafe or overestimated lifting operations. This paper aims to develop a method to design offshore crane operational limit diagrams for lifting of personnel and usual loads, in function of significant wave height and wave peak period, using time domain dynamic analysis, for a crane installed on a floating unit. The lifting of personnel with crane to transfer between a floating unit and a support vessel is a very used option in offshore operations, and this is in many cases, the only alternative beyond the helicopter. Due to recent fatal accidents with lifting operations in offshore platforms, it is essential the study about this subject, contributing to the increase of safety. The sea states for analysis were chosen covering usual significant wave heights and peak periods limits for lifting operations. The methodology used the SITUA / Prosim software to obtain the dynamic responses of the personnel transfer basket lifting and container loads on a typical FPSO. Through program developed by the author, it was implemented the automatic generation of diagrams as a function of operational limits. It is concluded that using this methodology, it is possible to achieve greater efficiency in the design and execution of personnel and routine load lifting, increasing safety and a wider weather window available.

Download Full-text

Neural Networks Based Simulation of Significant Wave Height

Volume 4: Materials Technology; Ocean Engineering ◽

10.1115/omae2007-29171 ◽

2007 ◽

Cited By ~ 3

Author(s):

H. Bazargan ◽

H. Bahai ◽

A. Aminzadeh-Gohari ◽

A. Bazargan

Keyword(s):

Neural Networks ◽

Wave Height ◽

Significant Wave Height ◽

Optimization Technique ◽

Conditional Probability Density ◽

Significant Wave ◽

The Pacific ◽

Wave Heights ◽

Significant Wave Heights ◽

Long Term Forecasting

A large number of ocean activities call for real time or on-line forecasting of wind wave characteristics including significant wave height (Hs). The work reported in this paper uses statistics, and artificial neural networks trained with an optimization technique called simulated annealing to estimate the parameters of a probability distribution called hepta-parameter spline for the conditional probability density functions (pdf’s) of significant wave heights given their eight immediate preceding 3-hourly observed Hs’s. These pdf’s are used in the simulation of significant wave heights related to a location in the Pacific. The paper also deals with short and long term forecasting of Hs for the region through generating random variates from the spline distribution.

Download Full-text

Capability of Jason-2 Subwaveform Retrackers for Significant Wave Height in the Calm Semi-Enclosed Celebes Sea

Remote Sensing ◽

10.3390/rs12203367 ◽

2020 ◽

Vol 12 (20) ◽

pp. 3367

Author(s):

Kaoru Ichikawa ◽

Xi-Feng Wang ◽

Hitoshi Tamura

Keyword(s):

Wave Height ◽

Significant Wave Height ◽

Leading Edge ◽

Sea State ◽

Significant Wave ◽

Contamination Sources ◽

The Pacific ◽

Unique System ◽

Calm Water ◽

Good Agreement

Satellite altimetry is a unique system that provides repeated observations of significant wave height (SWH) globally, but its measurements could be contaminated by lands, slicks, or calm water with smooth surface. In this study, capability of subwaveform retrackers against 20 Hz Jason-2 measurements is examined in the calm Celebes Sea. Distances between contamination sources and Jason-2 observation points can be determined using sequentially assembled adjacent waveforms (radargram). When no contamination sources are present within a Jason-2 footprint, subwaveform retrackers are in excellent agreement with the Sensor Geophysical Data Records (SGDR) MLE4 retracker that uses full-length waveforms, except that Adaptive Leading Edge Subwaveform (ALES) retracker has a positive bias in a calm sea state (SWH < 1 m), which is not unusual in the Celebes Sea. Meanwhile, when contamination sources exist within 4.5 km from Jason-2 observation points, SGDR occasionally estimates unrealistically large SWH values, although they could be partly eliminated by sigma0 filters. These datasets are then compared with WAVEWATCH III model, resulting in good agreement. The agreement becomes worse if swells from the Pacific is excluded in the model, suggesting constant presence of swells despite the semi-enclosed nature. In addition, outliers are found related with locally-confined SWH events, which could be inadequately represented in the model.

Download Full-text

Uncertainties in Extreme Wave Height Estimates for Hurricane-Dominated Regions

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.2746401 ◽

2007 ◽

Vol 129 (4) ◽

pp. 300-305 ◽

Cited By ~ 18

Author(s):

Philip Jonathan ◽

Kevin Ewans

Keyword(s):

Wave Height ◽

Significant Wave Height ◽

Small Data ◽

Extreme Wave ◽

Significant Wave ◽

Wave Characteristics ◽

Height Estimates ◽

Wave Heights ◽

Using Data ◽

High Percentile

Inherent uncertainties in estimation of extreme wave heights in hurricane-dominated regions are explored using data from the GOMOS Gulf of Mexico hindcast for 1900–2005. In particular, the effect of combining correlated values from a neighborhood of 72 grid locations on extreme wave height estimation is quantified. We show that, based on small data samples, extreme wave heights are underestimated and site averaging usually improves estimates. We present a bootstrapping approach to evaluate uncertainty in extreme wave height estimates. We also argue in favor of modeling supplementary indicators for extreme wave characteristics, such as a high percentile (95%) of the distribution of 100-year significant wave height, in addition to its most probable value, especially for environments where the distribution of 100-year significant wave height is strongly skewed.

Download Full-text

Ocean State Forecast along Ship Routes: Evaluation Using ESSO-INCOIS Real-Time Ship-Mounted Wave Height Meter and Satellite Observations

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-15-0047.1 ◽

2015 ◽

Vol 32 (11) ◽

pp. 2211-2222 ◽

Cited By ~ 1

Author(s):

R. Harikumar ◽

N. K. Hithin ◽

T. M. Balakrishnan Nair ◽

P. Sirisha ◽

B. Krishna Prasad ◽

...

Keyword(s):

Indian Ocean ◽

Correlation Coefficient ◽

Wave Height ◽

Significant Wave Height ◽

Satellite Observations ◽

Southern Indian Ocean ◽

Significant Wave ◽

Safe Navigation ◽

Wave Heights ◽

The Indian Ocean

AbstractOcean state forecast (OSF) along ship routes (OAS) is an advisory service of the Indian National Centre for Ocean Information Services (INCOIS) of the Earth System Science Organization (ESSO) that helps mariners to ensure safe navigation in the Indian Ocean in all seasons as well as in extreme conditions. As there are many users who solely depend on this service for their decision making, it is very important to ensure the reliability and accuracy of the service using the available in situ and satellite observations. This study evaluates the significant wave height (Hs) along the ship track in the Indian Ocean using the ship-mounted wave height meter (SWHM) on board the Oceanographic Research Vessel Sagar Nidhi, and the Cryosat-2 and Jason altimeters. Reliability of the SWHM is confirmed by comparing with collocated buoy and altimeter observations. The comparison along the ship routes using the SWHM shows very good agreement (correlation coefficient > 0.80) in all three oceanic regimes, [the tropical northern Indian Ocean (TNIO), the tropical southern Indian Ocean (TSIO), and extratropical southern Indian Ocean (ETSI)] with respect to the forecasts with a lead time of 48 h. However, the analysis shows ~10% overestimation of forecasted significant wave height in the low wave heights, especially in the TNIO. The forecast is found very reliable and accurate for the three regions during June–September with a higher correlation coefficient (average = 0.88) and a lower scatter index (average = 15%). During other months, overestimation (bias) of lower Hs is visible in the TNIO.

Download Full-text

Wave directional measurement in Patos Lagoon, RS, Brazil

RBRH ◽

10.1590/2318-0331.011716053 ◽

2017 ◽

Vol 22 (0) ◽

Author(s):

Natália Lemke ◽

◽

Lauro Julio Calliari ◽

José Antônio Scotti Fontoura ◽

Déborah Fonseca Aguiar

Keyword(s):

Wave Height ◽

Significant Wave Height ◽

Wave Climate ◽

Coastal Protection ◽

Peak Period ◽

Patos Lagoon ◽

Significant Wave ◽

Wave Parameters ◽

Wave Heights ◽

Significant Wave Heights

ABSTRACT The wave climate characterization in coastal environments is essentially important to oceanography and coastal engineering professionals regarding coastal protection works. Thus, this study aims to determine the most frequent wave parameters (significant wave height, peak period and peak direction) in Patos Lagoon during the period of operation of a directional waverider buoy (from 01/27/2015 to 06/30/2015). The equipment was moored at approximately 14 km from the São Lourenço do Sul coast at the geographic coordinates of 31º29’06” S and 51º55’07” W, with local depth of six meters, registering significant wave height, peak period and peak direction time series. During the analyzed period, the greatest wave frequencies corresponded to short periods (between 2 and 3.5 seconds) and small values of significant wave heights (up to 0.6 meters), with east peak wave directions. The largest wave occurrences corresponded to east peak wave directions (33.3%); peak wave periods between 2.5 and 3 seconds (25.6%) and between 3 and 3.5 seconds (22.1%); and to significant wave heights of up to 0.3 meters (41.2%) and from 0.3 to 0.6 meters (38%). This research yielded unprecedented findings to Patos Lagoon by describing in detail the most occurring wave parameters during the analyzed period, establishing a consistent basis for several other studies that might still be conducted by the scientific community.

Download Full-text

Climatology, Variability and Extrema of Ocean Waves: The Web-Based KNMI/ERA-40 Wave Atlas

Volume 3: Safety and Reliability; Materials Technology; Douglas Faulkner Symposium on Reliability and Ultimate Strength of Marine Structures ◽

10.1115/omae2006-92568 ◽

2006 ◽

Author(s):

Andreas Sterl ◽

Sofia Caires

Keyword(s):

Wave Height ◽

Significant Wave Height ◽

Wave Model ◽

Ocean Waves ◽

Wave Period ◽

Web Based ◽

Significant Wave ◽

Wave Parameters ◽

Wave Heights ◽

The Web

The European Centre for Medium Range Weather Forecasts (ECMWF) has recently finished ERA-40, a reanalysis covering the period September 1957 to August 2002. One of the products of ERA-40 consists of 6-hourly global fields of wave parameters like significant wave height and wave period. These data have been generated with the Centre’s WAM wave model. From these results the authors have derived climatologies of important wave parameters, including significant wave height, mean wave period, and extreme significant wave heights. Particular emphasis is on the variability of these parameters, both in space and time. Besides for scientists studying climate change, these results are also important for engineers who have to design maritime constructions. This paper describes the ERA-40 data and gives an overview of the results derived. The results are available on a global 1.5° × 1.5° grid. They are accessible from the web-based KNMI/ERA-40 Wave Atlas at http://www.knmi.nl/waveatlas.

Download Full-text