Wave Spectral Characteristics Research Articles

A numerical study for assessing the spectral wave characteristics during Hurricane Fiona

A numerical study for assessing the spectral wave characteristics during Hurricane Fiona

Analysis of Unidirectional Wave Spectral Characteristics in the Northeastern Waters of Taiwan

Marine energy development has been actively promoted in recent years. Analyzing wave data in the surrounding sea areas is crucial for improving wave power generator efficiency. This study collected unidirectional wave spectrum data from the northeast coastal area of Taiwan (e.g., Pengjia Islet, Fugui Cape, and NTOU). It aimed to analyze the main wave types (i.e., wind waves, swell, or mixed sea) and their proportions during the northeast and non-northeast monsoon periods. The results indicate that swell waves dominate at the NTOU buoy, while wind waves dominate at the other two stations. In addition, the analysis of wave spectra ratios revealed a low percentage of unimodal spectra (only about 0.5%), and bimodal and unformed spectra presented as predominant. Furthermore, this study also introduced a brand new JW-J wave spectrum, which combines the JW and JONSWAP spectra to describe low-frequency (swell) and high-frequency (wind wave) systems, showing superior performance compared to the Torsethaugen spectrum. Finally, this research analyzed the JW-J spectrum parameters from the Pengjia Islet and Fugui Cape stations and applied these results to the NTOU bouy for effectively describing wind/swell wave variations.

NOWCASTING INFRAGRAVITY WAVE HEIGHT WITHIN A HARBOUR USING AN ARTIFICIAL NEURAL NETWORK

Infragravity (IG) waves, sometimes known as “long waves” “low frequency waves” or “subharmonic gravity waves” are waves that are forced in deeper water through subharmonic interactions of sea and swell wave components. These waves are typically quite small (a few centimetres to decimetres) but can excite harbour seiching and amplification due to resonance. This can cause vessels to surge and sway at their berth, straining mooring lines and making loading and unloading difficult. This paper describes the design, training and application of a Bayesian regularized Artificial Neural Network (ANN) to accurately predict (“nowcast”) IG wave height outside and inside Port Kembla from deep-water swell wave spectral characteristics measured at Port Kembla Waverider Buoy (PKWRB), NSW coast (Williams, 2019).

Adaptation of functional systems in different generations of Caucasians in the North-East of Russia

BACKGROUND: A substantial body of research has focused on adaptation of the new residents of the European and Asian Far North. However, these publications fail to address the changes occurring in successive generations of native Caucasians who migrated to the regions with harsh climatic conditions.
 AIM: To study functional adaptations exhibited by individuals born in the Magadan Region to various generations of Caucasians permanently living in the area.
 METHODS: A total of 1632 male volunteers, all students aged 181.1 years, and of Caucasian ethnicity, participated in this study. These individuals were either migrants or residents of Russia's North-East, born within the first to third generations. We investigated anthropometric characteristics, cardiohemodynamic parameters, and gas exchange to understand the adaptive readjustments that take place within the body's functional systems.
 RESULTS: Migrants and first-generation residents in the Magadan region experience constant stress and inadequate functioning of their cardiohemodynamic and energy exchange systems under extreme conditions. However, the third-generation subjects exhibited optimal performance of the cardiovascular system. Remarkably, the third-generation residents demonstrate an increased systolic volume at lower arterial pressure and lower total peripheral resistance. Furthermore, they had elevated proportion of the high frequency component and total power of the heart rhythm spectrum. This represents a new level of changed influence on the heart rhythm, as seen in the altered balance of its statistical and spectral wave characteristics. Moreover, the adaptability of the cardiovascular system to the harsh conditions of the North is reflected not only in the physiological indicators of the body but also in the integral structure of their correlations. This includes the magnitude and sign of the correlation coefficients and their significance.
 CONCLUSIONS: Our main findings suggest that adaptive changes in cardiohemodynamic and gas exchange exhibited by the migrants and several generations of residents of the Far North-East of Russia are directed to minimization of the total energy expenditure in functional systems. Additionally, the parasympathetic contribution increases fostering a novel interaction between the components of autonomic nervous regulation reflected by both qualitative and quantitative alterations in the structure and patterns of correlation clusters. These findings contribute to our understanding of the physiological mechanisms behind the morphofunctional readjustments of Caucasian men in the process of adaptation to the harsh climatic conditions of the Russian North-East.

Shallow water wave spectral characteristics in southwest Bay of Bengal using measurements from a moored buoy

Shallow water wave spectral characteristics in southwest Bay of Bengal using measurements from a moored buoy

Dependence of Quasi‐Electrostatic Magnetosonic Wave Generation on Plasma Density and Suprathermal Protons

AbstractMagnetosonic (MS) wave is one of the most common electromagnetic emissions in the magnetosphere, while quasi‐electrostatic magnetosonic (QEMS) waves are seldom observed. Here we present an interesting QEMS event detected by Van Allen Probe A on 9 January 2014, in which the presence of multi‐band QEMS emissions shows evident correlations with relatively low plasma densities (∼10 cm−3) and enhancements of suprathermal (∼10 − 100 eV) proton fluxes. Based on the observed proton distributions, simulations demonstrate very similar profiles to the observed QEMS in the wave spectral characteristics. Parametric studies indicate that the QEMS growth rate can increase by ∼20 times with the plasma density decreasing from 50 to 10 cm−3. Effective growth rates of higher‐band QEMS occur when the suprathermal proton population is sufficiently large. This study reveals that low densities and large suprathermal proton populations are favorable for generating distinct multi‐band QEMS in the magnetosphere.

Increasing trends in spectral peak energy and period in a semi-closed sea

This study aims to investigate long-term trends in the Black Sea's spectral wave peak energy and periods. Improved Visualization of the Innovative Trend Analysis and the Mann-Kendal methods was applied to the maximum and mean spectral peak energies and peak periods between 1979 and 2020. Long-term spectral data are obtained from the ERA5 reanalysis and two spectral wave models, SWAN and WWIII. The innovative trend analysis method has the particularity to examine trends in higher and lower value categories. Studies of long-term changes in spectral wave characteristics are rare, and trends in spectral peak parameters are evaluated in this study for the first time in the Black Sea. It was detected that both spectral peak energies and peak periods tend to increase predominantly over most of the time scales. Furthermore, while the change rates for peak energies do not exceed 40% annually and seasonally, change rates exceeding 100% are observed on a monthly basis. Besides, the change rates of the peak periods vary in the ±5% band and usually do not exceed 15%. Moreover, despite a few differences, trend analysis results obtained using SWAN and WWIII models were close to the global ERA5 results. The results may provide insight into the design and durable development of coastal and marine structures as well as the evaluation of wave climate change based on spectral wave data.

Whitecapping term analysis of extreme wind wave modelling considering spectral characteristics and water depth

The Simulating WAves Nearshore (SWAN) model can be used to simulate extreme wind waves such as tropical cyclone waves, which are of great significance for the study of coastal processes and the protection of coastal engineering. In this study, the basic setting and whitecapping term of the SWAN model are analysed to model tropical cyclone waves, with spectral characteristics and water depth taken into account. By investigating the temporal variation of bulk wave parameters and wave spectral characteristics of key nodes, the optimal values of 4 basic setting parameters are determined. By analysing the sensitivity of tuning effects of key coefficients in different whitecapping formulations, calibration criteria of these parameters are provided, and the coefficients Stpm and Powk in the Komen formulation are found to be most sensitive to the outputted significant wave height and mean wave period, respectively. To further study the sensitivity of these coefficients, especially their relationship with water depth, spatial analyses of sensitivity variations are performed in the coastal region, which show that the sensitivity of these coefficients increases first and then tends to be stable with the increase of water depth, indicating a critical water depth between 20 m and 50 m. This study provides insights for more effective and directional modelling of tropical cyclone waves in coastal and shelf seas.

Two types of wave-current interactions and their effects on extreme waves in directional seas

The nonlinear wave-current interactions can influence and change extreme wave probability, spectral characteristics, and average shape of extreme waves significantly (Wang, J., Ma, Q. W., & Yan, S. (2021). On Extreme Waves in Directional Seas with Presence of Oblique Current. Applied Ocean Research, 112, pp. 102586). There are different scenarios of wave-wave interactions in reality. This study identifies two types of wave-current interactions: Type-I (waves propagating from current-negligible region to current-significant region) and Type-II (waves propagating from current-significant region to current-negligible region). The impacts of the two types of wave-current interactions on extreme wave probability and the spectral properties will be investigated by using fully nonlinear potential flow model. The numerical results reveal that the changes in extreme wave probability and spectral properties due to Type-I are more evident than those induced by Type-II. It is recommended that a proper type of wave-current interaction scenario should be selected in the design of the numerical modelling or laboratory experiments for wave-structure interactions to achieve more accurate representations of the local wave climate and flow conditions.

Precise prediction of the collapse column based on channel wave spectral disparity characteristics and velocity tomography imaging

Abstract Collapse columns are complex geological anomalies that present safety hazards in coal mines. In practice, the boundaries and internal features are difficult to finely characterize. In this study, we use the Jeffrey divergence to reveal the spectral disparity when the channel wave seismic ray path encounters a collapse column. We use the forward mode and applications for verification. We find that the centroid peak frequency shifts toward lower frequencies, the frequency band narrows and the rays through a collapse column cause attenuation of energy. When a seismic ray path encounters a large collapse column, no channel wave appears in the seismic record, the dispersion curve velocity is greater than the velocity of a normal coal seam, the centroid peak frequency drops and the frequency band shrinks. When a seismic ray passes through the boundary of a collapse column, the dispersion curve shows two parallel velocity phases. When a seismic ray path passes through a small collapse column, the decrease in the centroid frequency becomes the only identifying feature. The proposed channel wave spectral disparity characteristic and velocity tomography imaging method can effectively identify small collapse columns and improve the accuracy and precision of the location of collapse column boundaries, with a position deviation of less than 10 m.

Deep-water wave spectral characteristics in East-Central Arabian Sea

Deep-water wave spectral characteristics in East-Central Arabian Sea

A novel 8-channel DWDM demultiplexer on silicon photonic crystal slab: Design and analysis

In this work an 8-channel DWDM demultiplexer is proposed with multiple designs and numerical analysis. Photonic crystal ring resonators of airholes on a 220 nm thick silicon slab are used as wavelength selective elements. Demultiplexers of three different designs are considered and their characteristics are analyzed. For all the three designs, the resolved wavelengths are in the range of 1530–1540 nm, where Erbium Doped Fiber Amplifiers are applicable. For the optimized device, the average coupling efficiency, cross talk are found to be 70.4% and − 16.76 dB, respectively. Maximum and minimum coupling efficiencies of 79% and 56% are achieved. Photonic bandgap computation is performed by using plane wave expansion method and spectral characteristics are obtained by applying 3D finite difference time domain method.

Spectral wave characteristics in the coastal waters of the central west coast of India during tropical cyclone Kyarr

Spectral wave characteristics in the coastal waters of the central west coast of India during tropical cyclone Kyarr

Assessment of Polymer Concrete Sample Geometry Effect on Ultrasonic Wave Velocity and Spectral Characteristics.

In this paper an analysis of the influence of polymer concrete sample shape and dimensions on ultrasonic wave propagation is carried out. Compositions of tested fly ash polymer concretes were determined using a material optimization approach. The tests were carried out on the samples of three shapes: cubes, beams, and plates. The ultrasonic testing was done by a direct method (transmission method) using a digital ultrasonic flow detector and piezoelectric transducers of 100 kHz central frequency. Propagation of the ultrasonic wave was characterized by pulse velocity. Frequency spectra and time-frequency spectrograms obtained using Fourier transform and Fourier-based synchrosqueezing transform were also presented. The correlation analysis showed that neither the path length nor the lateral dimension to the direction of wave propagation are not statistically significant for the UPV variability. However, a general trend of decrease in the UPV with increasing the path length was noticed. The analysis of the signal in time-frequency domain seemed to be useful in the analysis of particulate composites properties, especially when UPV changes are not clear enough, since it revealed greater differences in relation to changes in sample geometry than frequency spectra analysis.

Directional wave buoy data measured near Campbell Island, New Zealand

The New Zealand Defence Force (NZDF) has established a permanent wave observation station near Campbell Island, south of New Zealand (52 45.71 S, 169 02.54E). The site was chosen for logistical convenience and its unique location adjacent to the highly energetic Southern Ocean; allowing instrumentation typically deployed on the continental shelf to be used in this rarely observed southern environment. From February 2017, a Triaxys Directional Wave Buoy was moored in 147 m depth, some 17 km to the south of the island, with satellite telemetry of the 2D wave spectra at 3-hourly intervals. To date there have been three deployments on locations, yielding some 784 days of data. Validation of the measured significant wave height against co-located satellite altimeter observations suggests that the predominant wave directions are not attenuated by the island. The data provide a valuable record of the detailed wave spectral characteristics from one of the least-sampled parts of the Global Ocean.

Prediction of Ship Motions in Irregular Waves Based on Response Amplitude Operators Evaluated Experimentally in Noise Waves

Abstract The most common methods for predicting ship roll motions in a specified sea state are direct measurements of motions in a representative irregular wave realisation (time domain) or calculations of motions from response amplitude operators (RAOs) in the frequency domain. The result of the first method is valid only for the tested sea state, whilst the second method is more flexible but less accurate. RAO-based predictions are calculated assuming a linear model of ship motions in waves. RAO functions are usually evaluated by means of tests in regular waves for a limited number of frequencies and a constant wave amplitude. This approach is time-consuming and the discrete form of the RAO functions obtained for a limited number of frequencies may lead to discrepancies in the prediction of seakeeping and often does not allow the actual amplitude of the response in resonant frequency to be determined. Another challenge is the appropriate selection of wave amplitude for tests due to the considerable influence of viscous damping on roll response in irregular sea waves. There are alternative methods for the experimental determination of RAO functions and one of them is presented in this study. The presented approach allows RAO functions to be evaluated in one run by the generation of irregular waves characterised by a white or coloured noise spectrum. This method reduces the experiment duration, with almost continuous RAO characteristics obtained. The flat (white noise) and linear (coloured noise) wave spectral energy characteristics are considered in the experiment and the obtained predictions are compared with the results of accurate measurements in irregular waves.

Performance Assessment of ERA5 Wave Data in a Swell Dominated Region

The present paper deals with a performance assessment of the ERA5 wave dataset in an ocean basin where local wind waves superimpose on swell waves. The evaluation framework relies on observed wave data collected during a coastal experimental campaign carried out offshore of the southern Oman coast in the Western Arabian Sea. The applied procedure requires a detailed investigation on the observed waves, and aims at classifying wave regimes: observed wave spectra have been split using a 2D partition scheme and wave characteristics have been evaluated for each wave component. Once the wave climate was defined, a detailed wave model assessment was performed. The results revealed that during the analyzed time span the ERA5 wave model overestimates the swell wave heights, whereas the wind waves’ height prediction is highly influenced by the wave developing conditions. The collected field dataset is also useful for a discussion on spectral wave characteristics during monsoon and post-monsoon season in the examined region; the recorded wave data do not suffice yet to adequately describe wave fields generated by the interaction of monsoon and local winds.

Field Observations of Wind Waves in Upper Delaware Bay with Living Shorelines

Constructed oyster reefs (CORs) provide shore protections and habitats for fish and shellfish communities via wave energy attenuation. However, the processes and mechanism of CORs on wave attenuation remain unclear, thus limiting the effective assessment of CORs for shoreline protection. This paper presents results of a field investigation on wave characteristics and wave spectral variations along a shoreline with CORs in an estuary with a large tidal range as well as large wind waves and swell energy. Six pressure transducers were deployed from January 31 to April 2, 2018, in Gandy’s Beach, New Jersey, in upper Delaware Bay. CORs were constructed at the study site in 2016 as living shoreline structures after Hurricane Sandy. The data collected from the study site exhibits the wave variations and spectral characteristics over the span of 2 months, including four winter storms (i.e., nor’easters). The spatial variations of wave heights measured on both sides of CORs show a strong dependence on the ratio between the freeboard of CORs and the offshore wave heights. Due to the large tidal range (> 2 m), the crests of CORs remain submerged over 85% of the time. The submerged CORs only provide partial attenuation of wave energy. The wave environment in the estuary is complex, especially during nor’easters. For instance, winds with rapid changing fetches could lead to bi-modal wind seas. Due to the complex wave spectra, the bulk wave heights such as the significant wave heights cannot be adopted to adequately reveal the capacity of CORs to attenuate wave energy. Spectral analysis is conducted to investigate the spatial and temporal variations of wave energy in targeted frequency bins. The spectral analysis results reveal the energy transfer from the primary waves to the high harmonics after waves propagate over the submerged CORs. Moreover, it is found that swell energy originated from the Atlantic Ocean can penetrate CORs without any dampening even when CORs are emergent. This study could help resource managers for in-depth evaluation of living shoreline effectiveness and improvement of living shoreline structures such as CORs.

A Hybrid Physical-Statistical Algorithm for SAR Wave Spectra Quality Assessment

A new approach for assessing the quality of Synthetic Aperture Radar (SAR) wave spectra is presented here. The algorithm addresses two specific issues, related to the 180° directional ambiguity in the propagation direction inherent to SAR measurements, and the removal of noise. In spite of several and progressive advances in the mapping and retrieval of SAR wave spectra, these issues are persistent in the existing official databases and hinder the use of these data for practical uses. This new algorithm is based on a recently developed database of long-term global wave spectral characteristics, which allows estimating the occurrence probability of every individual wave system found in the observed spectra, and that of its ambiguous pair. In addition, assuring the spatial consistency of the wave systems along track, helps obtaining more robust results. In this sense, wave spectra within a track are processed in several steps, so that wave systems with more likelihood of being correct are processed first, and consequently used to evaluate the more challenging components. Accordingly, a specific quality label is assigned to every wave system depending on the certainty achieved. An Envisat track over a challenging area with multiple crossing swells is used to illustrate the performance of the algorithm.

Pulsed spin wave propagation in a magnonic crystal

Amplitude, frequency, and time domain characteristics have been mapped for short spin wave pulses inside a magnonic crystal. A space- and time-resolved magnetoinductive probing system has been used to detail the spin wave spectral, propagation, and evolution characteristics in a geometrically structured yttrium iron garnet film. Experiments have been performed using magnetostatic surface spin waves excited in a chemically-etched magnonic crystal, ultrafast pulsed excitation of the spin waves, and direct spin wave detection using a scannable magnetoinductive probe connected to a synchronized fast oscilloscope. The results show how the frequency discriminating effect of a magnonic bandgap decreases as the excitation pulse width decreases. They also show how the use of rectangular pulses compromise the magnonic crystal performance because of the high frequency components of such pulses. Space and time maps show how these components are transmitted without additional damping.