Study on Wave Spectra in South Coastal Waters of Jiangsu

2012 ◽  
Vol 212-213 ◽  
pp. 193-200 ◽  
Author(s):  
Wei Bin Feng ◽  
Bin Yang ◽  
Hai Jing Cao ◽  
Xing Ye Ni
Keyword(s):  
Wave Height ◽  
Water Waves ◽  
Significant Wave Height ◽  
Spectral Characteristics ◽  
Peak Frequency ◽  
Spectral Peak ◽  
Wave Spectra ◽  
Spectral Parameters ◽  
Significant Wave ◽  
Better Than

The paper examined the spectral characteristics of shallow water waves, which was based on the wave data collected along the south coast of Jiangsu. It proposes a tentative spectra model which can work better than Joint North Sea Wave Project (JONSWAP)spectra. Both of the value of tentative spectral parameters (α and γ) increase with significant wave height and spectral peak frequency. According to a regression analysis, empirical equations are achieved, which is related to the parameters with significant wave height and spectral peak frequency. The study shows that the measured wave spectra can be represented by tentative spectra, and the fitting results in high-frequency tail of tentative spectra are better than that of JONSWAP spectrum with modified parameters.

On the Performance of the MPI Algorithm for the Retrieval of Significant Wave Height From ERS Synthetic Aperture Radar

2003 ◽  
Author(s):  
Nelson Violante-Carvalho ◽  
Ian S. Robinson
Keyword(s):  
Synthetic Aperture Radar ◽  
Wave Height ◽  
Significant Wave Height ◽  
Synthetic Aperture ◽  
Wave Spectra ◽  
Sar Images ◽  
Significant Wave ◽  
Directional Wave ◽  
Better Than ◽  
Aperture Radar

Spaceborne Synthetic Aperture Radar (SAR) is to date the only source of two dimensional directional wave spectra with continuous and global coverage when operated in the so-called SAR Wave Mode (SWM). Since the launch in 1991 of the first European Remote Sensing Satellite ERS-1 and more recently with ENVISAT millions of SWM imagettes containing detailed spectral information are now available in quasi-real time. This huge amount of directional wave data has opened up many exciting possibilities for the improvement of our knowledge of the dynamics of ocean waves. However the retrieval of wave spectra from SAR images is not a trivial exercise due to the nonlinearities involved in the mapping mechanism. The Max-Planck Institut (MPI) scheme was the first ever proposed and most widely used algorithm to retrieve directional wave spectra from SAR images. In this work significant wave height retrieved from SAR images using the MPI scheme are compared against one year of directional buoy measurements obtained in deep water and against WAM spectra. Our results show that for periods shorter than 12 seconds the WAM model performs better than the MPI method, even considering the fact that the model is used as first guess to the MPI scheme. However, for periods longer than 12 seconds (the part of the spectrum directly observed by SAR) the MPI method performs better than WAM. This is in contrast with the results obtained by Voorrips et al. (2001), who found that the performance of the WAM model is superior even when only the low wavenumber part of the spectrum is considered.

Semi-Empirical Crest Distributions of Long-Crest Nonlinear Waves of Three-Hour Duration

2017 ◽  
Author(s):  
Zhenjia (Jerry) Huang ◽  
Qiuchen Guo
Keyword(s):  
Nonlinear Wave ◽  
Wave Height ◽  
Model Test ◽  
Significant Wave Height ◽  
Spectral Peak ◽  
Wave Crest ◽  
Empirical Formulas ◽  
Peak Period ◽  
Significant Wave ◽  
Semi Empirical

In wave basin model test of an offshore structure, waves that represent the given sea states have to be generated, qualified and accepted for the model test. For seakeeping and stationkeeping model tests, we normally accept waves in wave calibration tests if the significant wave height, spectral peak period and spectrum match the specified target values. However, for model tests where the responses depend highly on the local wave motions (wave elevation and kinematics) such as wave impact, green water impact on deck and air gap tests, additional qualification checks may be required. For instance, we may need to check wave crest probability distributions to avoid unrealistic wave crest in the test. To date, acceptance criteria of wave crest distribution calibration tests of large and steep waves of three-hour duration (full scale) have not been established. The purpose of the work presented in the paper is to provide a semi-empirical nonlinear wave crest distribution of three-hour duration for practical use, i.e. as an acceptance criterion for wave calibration tests. The semi-empirical formulas proposed in this paper were developed through regression analysis of a large number of fully nonlinear wave crest distributions. Wave time series from potential flow simulations, computational fluid dynamics (CFD) simulations and model test results were used to establish the probability distribution. The wave simulations were performed for three-hour duration assuming that they were long-crested. The sea states are assumed to be represented by JONSWAP spectrum, where a wide range of significant wave height, peak period, spectral peak parameter, and water depth were considered. Coefficients of the proposed semi-empirical formulas, comparisons among crest distributions from wave calibration tests, numerical simulations and the semi-empirical formulas are presented in this paper.

scholarly journals Performance of Linear Generator Designs for Direct Drive Wave Energy Converter under Unidirectional Long-Crested Random Waves

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 5098
Author(s):  
Budi Azhari ◽  
Fransisco Danang Wijaya ◽  
Edwar Yazid
Keyword(s):  
Output Power ◽  
Wave Height ◽  
Wave Energy ◽  
Significant Wave Height ◽  
Analytical Calculation ◽  
Weight Ratio ◽  
Peak Frequency ◽  
Random Waves ◽  
Direct Drive ◽  
Significant Wave

For generating electricity, direct-drive wave energy converters (WECs) with linear permanent magnet generators (LPMGs) have advantages in terms of efficiency, simplicity, and force-to-weight ratio over WEC with rotary generators. However, the converter’s work under approaching-real wave conditions should be investigated. This paper studies the performance of a pico-scale WEC with two different LPMGs under unidirectional long-crested random waves. Different significant wave heights (using data in the Southern Ocean of Yogyakarta, Indonesia) and peak frequencies are tested. The JONSWAP energy spectrum is used to extract the wave elevations, while the MSS toolbox in MATLAB Simulink is employed to solve the floater’s dynamic responses. Next, the translator movements are extracted and combined with the flux distribution from FEMM simulation and analytical calculation, and the output powers are obtained. An experiment is conducted to test the output under constant speed. The results show for both designs, different tested significant wave height values produce higher output powers than peak frequency variation, but there is no specific trend on them. Meanwhile, the peak frequency is inversely proportional to the output power. Elimination of the non-facing events results in increasing output power under both parameters’ variation, with higher significant wave height resulting in a bigger increase. The semi iron-cored LPMG produces lower power loss and higher efficiency.

Spectral Modeling of Sea States With Multiple Wave Systems

1992 ◽  
Vol 114 (4) ◽  
pp. 278-284 ◽  
Author(s):  
C. Guedes Soares ◽  
M. C. Nolasco
Keyword(s):  
Wave Height ◽  
Significant Wave Height ◽  
Theoretical Models ◽  
Wave System ◽  
Spectral Parameters ◽  
Peak Period ◽  
Multiple Wave ◽  
Significant Wave ◽  
General Acceptance ◽  
Spectral Models

The spectral models of individual wave systems have one peak and are described by theoretical models that have gained general acceptance. This work deals with sea states with more than one wave system, leading to spectral models with two or more peaks. Use is made of spectra derived from measurements off the Portuguese Coast and data is provided as to their probability of occurrence as well as about the dependence of the spectral parameters on the significant wave height and peak period. It is shown that wind-dominated and swell-dominated two-peaked spectra tend to occur in different areas of the scatter diagram. The spectral parameters of the two-peaked spectra show little correlation with significant wave height and peak period.

scholarly journals Wave spectral shapes in the coastal waters based on measured data off Karwar, west coast of India

2017 ◽  
Author(s):  
M. Anjali Nair ◽  
V. Sanil Kumar
Keyword(s):  
Wave Height ◽  
Coastal Waters ◽  
High Frequency ◽  
Significant Wave Height ◽  
Wave Spectrum ◽  
Temporal Variations ◽  
Wave Spectra ◽  
Monsoon Period ◽  
Significant Wave ◽  
Spectral Shapes

Abstract. Understanding of the wave spectral shapes is of primary importance for the design of marine facilities. In this paper, the wave spectra collected from January 2011 to December 2015 in the coastal waters are examined to know the temporal variations in the wave spectral shape. For 31.15 % of the time, peak frequency is between 0.08 and 0.10 Hz and the significant wave height is also relatively high (~ 1.55 m) for waves in this class. The slope of the high-frequency tail of the monthly average wave spectra is high during the Indian summer monsoon period (June–September) compared to other months and it increases with increase in significant wave height. There is no much interannual variation in slope for swell dominated spectra during the monsoon, while in the non-monsoon period when wind-seas have much influence, the slope varies significantly. Since the high-frequency slope of the wave spectrum is within the range 3–4 during the monsoon period, Donelan spectrum shows better fit for the wave spectra in monsoon months compared to other months.

Gap-Filling and Predicting Wave Parameters Using Support Vector Regression Method

2011 ◽  
Author(s):  
Maziar Golestani ◽  
Mostafa Zeinoddini
Keyword(s):  
Support Vector Regression ◽  
Wave Height ◽  
Significant Wave Height ◽  
Rational Design ◽  
Wave Spectrum ◽  
Support Vector ◽  
Wave Spectra ◽  
Significant Wave ◽  
Wave Parameters ◽  
Data Gaps

Knowledge of relevant oceanographic parameters is of utmost importance in the rational design of coastal structures and ports. Therefore, an accurate prediction of wave parameters is especially important for safety and economic reasons. Recently, statistical learning methods, such as Support Vector Regression (SVR) have been successfully employed by researchers in problems such as lake water level predictions, and significant wave height prediction. The current study reports potential application of a SVR approach to predict the wave spectra and significant wave height. Also the capability of the model to fill data gaps was tested using different approaches. Concurrent wind and wave records (standard meteorological and spectral density data) from 4 stations in 2003, 2007, 2008 and 2009 were used both for the training the SVR system and its verification. The choice of these four locations facilitated the comparison of model performances in different geographical areas. The SVR model was then used to obtain predictions for the wave spectra and also time series of wave parameters (separately for each station) such as its Hs and Tp from spectra and wind records. New approach was used to predict wave spectra comparing to similar studies. Reasonably well correlation was found between the predicted and measured wave parameters. The SVR model was first trained and tested using various methods for selecting training data. Also different values for SVM parameters (e.g. tolerance of termination criterion, cost, and gamma in kernel function) were tested. The best possible results were obtained using a Unix shell script (in Linux) which automatically implements different values for different input parameters and finds the best regression by calculating statistical scores like correlation of coefficient, RMSE, bias and scatter index. Finally for a better understanding of the results, Quantile-Quantile plots were produced. The results show that SVR can be successfully used for prediction of Hs and wave spectrum out of a series of wind and spectral wave parameters inputs. Also it was noticed that SVR is an efficient tool to be used when data gaps are present in the data.

scholarly journals The Influence of Air–Sea Roughness, Sea Spray, and Storm Translation Speed on Waves in North Atlantic Storms

2008 ◽  
Vol 38 (4) ◽  
pp. 817-839 ◽  
Author(s):  
Weiqing Zhang ◽  
William Perrie
Keyword(s):  
Wave Height ◽  
Significant Wave Height ◽  
Storm Track ◽  
Wave Drag ◽  
Sea Spray ◽  
Wave Spectra ◽  
Translation Speed ◽  
Significant Wave ◽  
Directional Wave ◽  
The Impact

Abstract A coupled atmosphere–wave–sea spray model system is used to evaluate the impact of sea spray and wave drag on storm-generated waves, their height variations, and directional wave spectra in relation to the storm location and translation speed. Results suggest that the decrease or increase of significant wave height due to spray and wave drag is most significant in high-wind regions to the right of the storm track. These processes are modulations on the maximum-wave region and tend to occur several hours after the peak wind events, depending on the storm translation velocity. The translation speed of the storm is important. The directional variation between local winds and wind-generated waves within rapidly moving storms that outrun the waves is notably different from that of trapped waves, when the dominant waves’ group velocity approximates the storm translation speed. While wave drag and spray can increase or reduce the magnitudes of wind and significant wave height, their nondirectional formulations allow them to have little apparent effect on the directional wave spectra.

scholarly journals The wave spectrum in archipelagos

Ocean Science ◽  
2019 ◽  
Vol 15 (6) ◽  
pp. 1469-1487
Author(s):  
Jan-Victor Björkqvist ◽  
Heidi Pettersson ◽  
Kimmo K. Kahma
Keyword(s):  
Wave Height ◽  
Significant Wave Height ◽  
Wave Spectrum ◽  
Spectral Width ◽  
Peak Frequency ◽  
Wide Frequency Range ◽  
Systematic Research ◽  
Significant Wave ◽  
Average Value ◽  
Starting Point

Abstract. Sea surface waves are important for marine safety and coastal engineering, but mapping the wave properties at complex shorelines, such as coastal archipelagos, is challenging. The wave spectrum, E(f), contains a majority of the information about the wave field, and its properties have been studied for decades. Nevertheless, any systematic research into the wave spectrum in archipelagos has not been made. In this paper we present wave buoy measurements from 14 locations in the Finnish archipelago. The shape of the wave spectrum showed a systematic transition from a single-peaked spectrum to a spectrum with a wide frequency range having almost constant energy. The exact shape also depended on the wind direction, since the fetch, island, and bottom conditions are not isotropic. The deviation from the traditional spectral form is strong enough to have a measurable effect on the definitions of the significant wave height. The relation between the two definitions in the middle of the archipelago was H1/3=0.881Hs, but the ratio varied with the spectral width (Hs was defined using the variance). At this same location the average value of the single highest wave, Hmax∕Hs, was only 1.58. A wider archipelago spectrum was also associated with lower confidence limits for the significant wave height compared to the open sea (6 % vs. 9 %). The challenges caused by the instability of the peak frequency for an archipelago spectrum are presented, and the mean frequency, weighted with E(f)4, is proposed as a compromise between stability and bias with respect to the peak frequency. The possibility of using the frequency and width parameters of this study as a starting point for a new analytical parameterisation of an archipelago type spectrum is discussed.

scholarly journals The wave spectrum in archipelagos

2019 ◽  
Author(s):  
Jan-Victor Björkqvist ◽  
Heidi Pettersson ◽  
Kimmo K. Kahma
Keyword(s):  
Wave Height ◽  
Significant Wave Height ◽  
Wave Spectrum ◽  
Spectral Width ◽  
Peak Frequency ◽  
Wide Frequency Range ◽  
Systematic Research ◽  
Significant Wave ◽  
Average Value ◽  
Sea Surface Waves

Abstract. Sea surface waves are important for marine safety and coastal constructions, but mapping the wave properties at complex shorelines, such as coastal archipelagos, is challenging. The wave spectrum, E(f), contains a majority of the information about the wave field, and its properties have been studied for decades. Nevertheless, any systematic research into the wave spectrum in archipelagos has not been made. In this paper we present wave buoy measurements from 14 locations in the Finnish archipelago. The shape of the wave spectrum showed a systematic transition from a single peaked spectrum, to a spectrum with a wide frequency range having almost constant energy. The exact shape also depended on the wind direction, since the fetch, island, and bottom conditions are not isotropic. The deviation from the traditional spectral form is strong enough to have a measurable effect on the definitions of the significant wave height. The relation between the two definitions in the middle of the archipelago was H1/3 = 0.881 Hs, but the ratio varied with the spectral width (Hs was defined using the variance). At this same location the average value of the single highest wave, Hmax/Hs, was only 1.58. A wider archipelago spectrum was also associated with lower confidence limits for the significant wave height compared to the open sea (6 % vs. 9 %). The challenges regarding the instability of the peak frequency and the difficulties in finding a good characteristic frequency for an archipelago spectrum is discussed. The mean frequency, weighted with E(f)4, is proposed as a compromise between stability, and bias with respect to the peak frequency.

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