Spectral characteristics of high shallow water waves (original) (raw)
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Selection of JONSWAP Spectra Parameters during Water-Depth and Sea-State Transitions
Journal of Waterway, Port, Coastal, and Ocean Engineering, 2020
The design of marine structures requires the simulation of wave parameters that consider sea-state and water-depth transitions. Proper selection of the model coefficients (e.g., alpha and gamma of the JONSWAP spectra) is then required, because of the wave-hydrodynamic nonlinearities during these ocean processes. Therefore, the model coefficient selection should be tested using a nonlinear analysis to assess the effect of the selected spectra coefficients over the modeled wave parameters. The present study performed a design of experiment (DOE)-analysis of variance (ANOVA) and probability analysis to assess the effect of alpha and gamma parameters over the significant wave height (Hs) and peak period (Tp) during sea-state and water-depth transitions. The DOE-ANOVA demonstrated for the mean and extreme wave states of the study area that alpha and gamma parameters positively affect the Hs behavior in deep and intermediate waters. Furthermore, the standardized effects of alpha and gamma over the Tp during extreme wave states suggest quadruplets of wave-wave interactions. The joint and normal probability distributions of alpha and gamma for extreme and normal waves showed a Gaussian distribution, allowing identification of specific alpha and gamma values for the JONSWAP spectra model. The selected alpha and gamma parameters were then validated through the comparison of the modeled Hs (JONSWAP) against other local studies. Considering its relevance in design strategies for offshore structures, this research contributed to the understanding of the nonlinear effects of alpha and gamma parameters over the Hs and Tp during variations of water depth and wave states, easing the selection of the model coefficients.
Ocean Dynamics, 2019
Some efforts have been done by previous researchers and scientists to represent the spectral behavior of wind waves in the Persian Gulf by analyzing real-time data, but in most of them, only wave data collected from nearshore stations with water depths of 25 m or less were considered. Therefore, in order to consider offshore wave characteristics of the region, a 5-month wave data through a mooring buoy around Farzad A natural gas field, at a water depth of 45 m, was collected and analyzed. Spectral analysis of offshore measured data along with the previous spectral analyses of coastal wave stations revealed that the wave spectra in the Persian Gulf are mainly single-peaked during all stages of the storms considering the possible uncertainty existing in the shape of wave spectrums depending on storm stage and can be represented by JONSWAP spectrum model using the newly proposed modified key parameters (i.e., Phillip's constant and peak-enhancement parameters). In addition, the spectral behavior of waves during various stages of extreme events/storms showed that the mean values of the key parameters for growing and developed portions of the storms are slightly different from the traditionally recommended values for the JONSWAP parameters, while the estimated average values of decaying portions are considerably different from generally utilized values.
Spectral Wave Modeling in Very Shallow Water at Southern Coast of Caspian Sea
Journal of Marine Science and Application, 2018
This study evaluates the capability of the Simulating WAves Nearshore (SWAN) wave model (version 41.01) in predicting significant wave height and spectral peak energy content for swell waves in very shallow water of surf zone during depth-induced wave breaking and dissipation. The model results were compared with field measurements at five nearshore stations. The results demonstrated that some breaker index formulations were successful for significant wave height prediction in surf zones. However, an incorrect shape of the energy spectrum and overestimated near spectral peak energy content at shallow water stations were obtained using all of the embedded depth-induced wave breaking formulations in SWAN. The dependent breaker index on relative depth (K p d) formulation, which was successful in predicting near spectral peak energy content, resulted in an average error of 30%. Finally, this formulation was modified to enhance the model performance in reproducing the spectral peak energy content.
Surface wave statistics and spectra for Valiathura coastline, SW coast of India
A series of 12 monthly graphical three-dimensional plots were produced for Valiathura, SW coast of India, taking significant wave height, zero up-crossing period and direction as the three axes. Joint distributions of significant wave height and zero-up crossing period have also been developed for these months to understand the combination of these parameters in random waves. The fair weather period (November-April) was characterized by comparatively moderate wave activity with period ranging from 6 to 17.5 sec and direction of wave approach from 190° to 200°. During rough weather period (May -October), the waves exhibit a wider spread of direction ranging from 190° to 260° with periods ranging from 6 to 13.5 sec and significant wave height ranging from 0.6 to 3.2 m. Wave spectrum curves show that the TMA model gives better results and follows the observed spectra in a large number of cases during fair weather. During rough weather, TMA and Shadrin's models show almost identical behavior.
Spectral Wave Characteristics over the Head Bay of Bengal: A Modeling Study
Pure and Applied Geophysics, 2019
Information on spectral wave characteristics is an essential prerequisite for ocean engineering-related activities and also to understand the complex wave environment at any given location. To the best of our knowledge, there are no comprehensive studies attempted so far to study the wave spectral characteristics over the head Bay of Bengal, a low-lying deltaic environment. The present study is an attempt to describe the spectral characteristics of wave evolution across different locations over this deltaic region based on numerical simulations. Therefore, it implements a multiscale nested modeling approach using two state-of-art wave models, WAM and SWAN, and forced with ERA-Interim winds spanning the year of 2016. Model-computed integrated wave parameters are validated against wave rider buoy data as well as remotely sensed SARAL/AltiKa and merged altimeter data. Analysis of the monthly averaged one-dimensional spectrum reveals a single peak during the southwest monsoon and existence of double peaks from November to January, and occasionally up to March. Variance energy density undergoes inter-seasonal variation and attains its maxima during the month of July. Transformation of swell wave energy as a function of depth is found to be mostly associated with physical processes such as wave-bottom interaction and attenuation by opposing winds during the northeast (NE) monsoon. Fetch restriction for the evolution of wind seas (from the NE), modification in wind shear stress by opposing swells, and bottom effects remarkably contribute to the reduction in wind sea energy at shallow water depths. This study indicates that the influence of swells is higher along the eastern side of the basin as compared to the western side, and marginally higher variance is also observed over the east except during February-April. The twodimensional wave spectra exhibit differential wave systems approaching from various directions attributed to a reflected swell system from the south-southeast throughout the year, southwest swells, reversing wind seas following local winds, and reflected wind seas from the land boundary.
Second-order analysis of shallow-water wave spectra
Il Nuovo Cimento C, 1988
This paper presents a study based on a second-order interpretation of wave ,,energy,, spectra, which may explain the build-up of low-and high-frequency peaks for wave spectra measured in shallow water. A comparison between this interpretative model and laboratory data, which were obtained in a bidimensional wave flume, is also given in the paper.
Analysis of ocean wave characteristic in Western Indonesian Seas using wave spectrum model
MATEC Web of Conferences, 2018
Understanding the characteristics of the ocean wave in Indonesian Seas particularly in western Indonesian Seas is crucial to establish secured marine activities in addition to construct well-built marine infrastructures. Three-years-data (July 1996-1999) simulated from Simulating Waves Nearshore (SWAN) model were used to analyze the ocean wave characteristics and variabilities in eastern Indian Ocean, Java Sea, and South China Sea. The interannual or seasonal variability of the significant wave height is affected by the alteration of wind speed and direction. Interactions between Indian Ocean Dipole Mode (IODM), El Niño Southern Oscillation (ENSO) and monsoon result in interannual ocean wave variability in the study areas. Empirical Orthogonal Functions (EOF) analysis produces 6 modes represents 95% of total variance that influence the wave height variability in the entire model domain. Mode 1 was dominated by annual monsoon and has spatial dominant contribution in South China Sea effected by ENSO and Indian Ocean influenced by IODM. Java Sea was influenced by Mode 2 which is controlled by semi-annual monsoon and IODM. A positive (negative) IODM strengthens (weakens) the winds speed in Java Sea during the East (West) season and hence contributes to Mode 2 in increasing (decreasing) the significant wave in Java Sea.
Journal of Atmospheric and Oceanic Technology, 1997
This paper presents a wavenumber spectral model of the surface water waves in the capillary-gravity regime. The database for the analysis consists of spatial and temporal measurements of surface slopes obtained from a scanning slope sensor buoy operating in free-drift mode in the Atlantic Ocean. These data indicate that the contribution of mean square slopes from capillary-gravity waves (wavelengths from 4 mm to 6 cm) is a significant portion of the total mean square slopes. The resulting mean square slopes derived from the proposed spectral model are in excellent agreement with existing field datasets.
A study on the spectral models for waves in finite water depth
Journal of Geophysical Research, 1983
Spectral models for waves in finite water depths are developed based on an extension of the Wallops Spectrum (Huang et al., 1981a) for the deep water waves. It is found that for intermediate water depth, Stokes wave expansions offer a good approximation. In this case, the spectral function is controlled by three parameters: the significant slope, õ; the nondimensional depth, kh; and the peak frequency, no. For the shallow water waves, solitary and cnoidal wave models have to be used. The controlling parameters now reduce to two again, that is, the Ursell number, u, = [2rtõ/(kh)3], and the peak frequency. The resulting spectral models are designed with a specific emphasis on but not limited to the energy containing range of the spectrum; they are also not limited to any particular sea state. They offer a possible explanation of the variations in the spectral slope observed by previous investigators. Comparisons with observational results from both laboratory and field show good agreements.