scholarly journals HIGHER ORDER WAVE SPECTRA

1978 ◽  
Vol 1 (16) ◽  
pp. 19
Author(s):  
Paul C. Liu ◽  
Albert W. Green
Keyword(s):  
Energy Content ◽  
Wind Waves ◽  
Ocean Waves ◽  
Higher Order ◽  
Bispectral Analysis ◽  
Wave Interactions ◽  
Single Station ◽  
Frequency Components ◽  
Theoretical Considerations ◽  
Nonlinear Energy

As part of an effort aimed at examining the empirical aspects of nonlinear processes of wind-generated waves, this paper presents calculations and examples of bispectra and trispectra and indicates applications of these results to the study of wave growth processes. Recent publications on wave studies have indicated that the growth process of wind waves is primarily associated with the nonlinear energy flux due to wave-wave interactions. While most of these studies are conjectures from theoretical considerations, it is of interest to explore the nonlinear studies empirically. From available wave data largely recorded at a single station, a first step is to perform bispectral and trispectral analyses of the data. Since the unispectrum provides information on the energy content of the frequency components, the bispectrum and trispectrum generally provide information on the interactive relations between two and three frequency components, respectively. These higher order interactive relations can thus be considered as estimates or characterizations of nonlinear interactions. Hasselmann, Munk, and McDonald (1962), perhaps the first to use bispectral analysis, demonstrated that calculations of observed bispectra of ocean waves correlate reasonably well with theoretically derived bispectra. Other ocean wave bispectra were presented by Garrett (1970) and Houmb (1974). Trispectral analysis has not yet been attempted in practical problems.

scholarly journals RAPID CALCULATION OF NONLINEAR WAVE-WAVE INTERACTIONS

2011 ◽  
Vol 1 (32) ◽  
pp. 36 ◽  
Author(s):  
Lihwa Lin ◽  
Zeki Demirbilek ◽  
Jinhai Zheng ◽  
Hajime Mase
Keyword(s):  
Energy Transfer ◽  
Shallow Water ◽  
Nonlinear Wave ◽  
Ocean Waves ◽  
Wave Transformation ◽  
Calculation Algorithm ◽  
Wave Interactions ◽  
Nonlinear Energy Transfer ◽  
Rapid Calculation ◽  
Nonlinear Energy

This paper presents an efficient numerical algorithm for the nonlinear wave-wave interactions that can be important in the evolution of coastal waves. Indeed, ocean waves truly interact with each others. However, because ocean waves can also interact with the atmosphere such as under variable wind and pressure fields, and waves will deform from deep to shallow water, it is generally difficult to differentiate the actual amount of the nonlinear energy transfer among spectral waves mixed with the atmospheric input and wave breaking. The classical derivation of the nonlinear wave energy transfer has involved tedious numerical calculation that appears impractical to the engineering application. The present study proposed a theoretically based formulation to efficiently calculate nonlinear wave-wave interactions in the spectral wave transformation equation. It is approved to perform well in both idealized and real application examples. This rapid calculation algorithm indicates the nonlinear energy transfer is more significant in the intermediate depth than in deep and shallow water conditions.

scholarly journals Laboratory study of non-linear wave-wave interactions of extreme focused waves in the nearshore zone

2020 ◽  
Author(s):  
Iskander Abroug ◽  
Nizar Abcha ◽  
Armelle Jarno ◽  
François Marin
Keyword(s):  
Peak Frequency ◽  
Linear Wave ◽  
Bispectral Analysis ◽  
Phase Coupling ◽  
Wave Interactions ◽  
Wave Groups ◽  
Wave Flume ◽  
Frequency Components ◽  
Wave Trains ◽  
Short Time

Abstract. Extreme waves play a crucial role in marine inundation hazards and coastal erosion. In this article, we experimentally study nonlinear wave-wave interactions of large amplitude focused wave groups propagating in a two-dimensional wave flume over a mild slope (β = 1:25). The influence of the frequency spectrum and the steepness on the nonlinear interactions of focused waves are examined. The generated wave trains correspond to Pierson-Moskowitz and JONSWAP (γ = 3.3 or γ = 7) spectra. Subsequently, we experimentally approach this problem by the use of a bispectral analysis applied on short time series, via the wavelet-based bicoherence parameter, which identifies and quantifies the phase coupling resulting from non-resonant or bound triad interactions with the peak frequency. The bispectral analysis shows that the number of frequency components involved in the focusing process and the resulting phase coupling increases gradually and approaches 1 just prior to breaking, accordingly with the spectrum broadening and the energy increase in high frequency components. Downstream breaking, the values of phase coupling between the peak frequency and its higher harmonics decrease drastically and the bicoherence spectrum becomes less structured.

Noise Reduction of Blade-Passing Frequency Components in a Centrifugal Blower

2004 ◽  
Author(s):  
Yutaka Ohta ◽  
Eisuke Outa
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Noise Source ◽  
Higher Order ◽  
Pressure Level ◽  
Source Distribution ◽  
Centrifugal Blower ◽  
Blade Passing Frequency ◽  
Active Cancellation ◽  
Frequency Components

A hybrid-type noise control method is applied to fundamental and higher-order blade-passing frequency components, abbreviated to BPF components, radiated from a centrifugal blower. An active cancellation of the BPF noise source is conducted based on a detailed investigation of the noise source distribution by using correlation analysis. The sound pressure level of 2nd- and/or 3rd-order BPF can be reduced by more than 15 decibels and discrete tones almost eliminate from the power spectra of blower-radiated noise. On the other hand, the sound pressure level of the fundamental BPF is difficult to reduce effectively by the active cancellation method because of the large amplitude of the noise source fluctuation. However, the fundamental BPF is largely influenced by the frequency-response characteristics of the noise transmission passage, and is passively reduced by appropriate adjusting of the inlet duct length. Simultaneous reduction of BPF noise, therefore, can be easily made possible by applying passive and active control methods on the fundamental and higher-order BPF noise, respectively. We also discuss the distribution pattern of BPF noise sources by numerical simulation of flow fields around the scroll cutoff.

Observation of wave propagation in ice using stereo imaging in the Sea of Okhostk

2021 ◽  
Author(s):  
Alberto Alberello ◽  
Takehiko Nose ◽  
Tsubasa Kodaira ◽  
Keita Nishizawa ◽  
Filippo Nelli ◽  
...  
Keyword(s):  
Sea Of Okhotsk ◽  
Wave Attenuation ◽  
Wind Waves ◽  
Arctic Basin ◽  
Ocean Waves ◽  
The Arctic ◽  
Camera System ◽  
The Sea Of Okhotsk ◽  
Wave Models ◽  
Seasonal Ice Zone

<p>Sea ice seasonally covers the Sea of Okhotsk, a marginal Arctic basin nested between Russia and Japan, but its extent is predicted to decrease by 40% by 2050 leaving larger ice free areas over which waves can form. In the highly dynamical seasonal ice zone, i.e. where waves and ice interact, ice formation and breakup, and wave attenuation mutually affect each other via complex feedback mechanisms. To shed light into these interactions, wave measurements were conducted in the winter seasonal ice zone in the Southern Okhotsk Sea, North of Hokkaido, from onboard the P/V Soya using a stereo camera system. Data show that wave energy penetrates even in high ice concentration (>85%), where contemporary wave models predict complete attenuation of wind waves. Consistently with physical experiments and field observations of waves in the Arctic and Antarctic marginal ice zones, the measurements also show that the ice cover is more effective in attenuating short wave components and, consequently, the dominant wave period in ice is significantly increased compared to corresponding open ocean waves. The present data can inform calibration of wave models in the rapidly evolving seasonal ice zone in the Sea of Okhotsk.</p>

Response-Based Estimation of Sea State Parameters

2007 ◽  
Author(s):  
Ulrik D. Nielsen
Keyword(s):  
Closed Form ◽  
Energy Content ◽  
Wave Spectrum ◽  
Final Outcome ◽  
Bayesian Modelling ◽  
Sea State ◽  
Safe Navigation ◽  
Wave Radar ◽  
Frequency Components ◽  
Analytical Expressions

Reliable estimation of the on-site sea state parameters is essential to decision support systems for safe navigation of ships. The sea state parameters can be estimated by Bayesian Modelling which uses complex-valued frequency response functions (FRF) to estimate the wave spectrum on the basis of measured ship responses. It is therefore interesting to investigate how the filtering aspect, introduced by FRF, affects the final outcome of the estimation procedures. The paper contains a study based on numerical generated time series, and the study shows that filtering has an influence on the estimations, since high frequency components of the wave excitations are not estimated as accurately as lower frequency components. Moreover, the paper investigates how the final outcome of the Bayesian Modelling is influenced by the accuracy of the FRF. Thus, full-scale data is analysed by use of FRF calculated by a 3-D time domain code and by closed-form (analytical) expressions, respectively. Based on comparisons with wave radar measurements and satellite measurements it is seen that the wave estimations based on closed-form expressions exhibit a reasonable energy content, but the distribution of energy appears to be incorrect.

Using Remote Sensed Data for Wave Energy Resource Assessment

2008 ◽  
Author(s):  
M. T. Pontes ◽  
M. Bruck
Keyword(s):  
Wave Height ◽  
Wave Energy ◽  
Wind Waves ◽  
Energy Resource ◽  
Ocean Waves ◽  
Resource Assessment ◽  
Altimeter Data ◽  
Zero Crossing ◽  
Frequency Wave ◽  
Buoy Data

The conversion of the energy contained in ocean waves into an useful form of energy namely electrical energy requires the knowledge at least of wave height and period parameters. Since 1992 at least one altimeter has been accurately measuring significant wave height Hs. To derive wave period parameters namely zero-crossing period Tz from the altimeter backscatter coefficient various models have been proposed. Another space-borne sensor that measures ocean waves is SAR (or the advanced ASAR) from which directional spectra are obtained. In this paper various models proposed to compute Tz from altimeter data are presented and verified against a collocated set of Jason altimeter and NDBC buoy data. A good fitting of altimeter estimates to buoy data was found. Directional spectra obtained from ENVISAT ASAR measurements were compared against NDBC buoy data. It was concluded that for the buoys that are more sensitive to long low-frequency wave components the fitting of wave parameters and spectral form is good for short spatial distances. However, since the cut-off ASAR frequency is low (reliable information is provided only for long waves) their use for wave energy resource assessment in areas where wind-waves are important is limited.

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