Evaluation of an Extended Operational Boussinesq-Type Wave Model for Calculating Low-Frequency Waves in Intermediate Depths

2011 ◽  
Author(s):  
Martijn P. C. de Jong ◽  
Mart Borsboom ◽  
Jan A. M. de Bont ◽  
Bas van Vossen
Keyword(s):  
Low Frequency ◽  
Wave Model ◽  
Coastal Engineering ◽  
Extended Model ◽  
Depth Range ◽  
Frequency Range ◽  
Frequency Wave ◽  
Type Wave ◽  
Wave Heights ◽  
Low Frequency Waves

The motions of (LNG) vessels moored offshore at depths ranging from about 20 to 100 m may depend significantly on the presence of (bound) low-frequency waves with periods in the order of 100 s. This is because these moored vessels show a large motion response in this frequency range and because the energy contents of low-frequency waves at these ‘intermediate’ depths is relatively large. As part of the Joint Industry Project HawaI, the operational Boussinesq-type wave model of Deltares, TRITON, was used to investigate whether this type of wave models could predict bound low-frequency waves (setdown waves) at intermediate depths. Comparison to measured and theoretical data, however, showed an underestimation of the computed levels of bound low-frequency wave heights for this depth range by a factor 2 to 4. Recently, additional tests were made with TRITON in situations for which the model has been designed: coastal engineering applications in shallow water (depths up to at most 20 m). These also showed an underestimation of the bound low-frequency wave heights, albeit smaller, up to a factor 2. In view of the importance of the energy contained in the low-frequency range for certain nearshore and shoreline processes, such as morphological processes, this underestimation is also of concern in coastal engineering. This triggered the development of a higher-order extension of the TRITON model equations (Borsboom, 2008, Wellens, 2010), with the aim to improve the accuracy of the model for long waves while still keeping computational times within acceptable (operational) limits. This paper reports on the usefulness of the extended model for the field of application considered in JIP HawaI/II: providing wave data for calculating the motions of vessels moored in intermediate depths. The results show a significant improvement of the modeling of nonlinear wave dynamics, including the prediction of bound low-frequency waves. This means that the model extension is an important step towards an operational Boussinesq-type wave model with sufficient accuracy in both the wave-frequency (sea, swell) and the low-frequency range for applications in intermediate depths.

scholarly journals SHORT WAVE BREAKING EFFECTS ON LOW FREQUENCY WAVES

2011 ◽  
Vol 1 (32) ◽  
pp. 20 ◽  
Author(s):  
Christopher Daly ◽  
Dano Roelvink ◽  
Ap Van Dongeren ◽  
Jaap Van Thiel de Vries ◽  
Robert McCall
Keyword(s):  
Wave Breaking ◽  
Surf Zone ◽  
Low Frequency ◽  
Breaking Waves ◽  
Short Wave ◽  
Frequency Wave ◽  
Wave Heights ◽  
Wave Groupiness ◽  
Set Up ◽  
Low Frequency Waves

The effect of short wave breaking on low frequency waves is investigated using two breaker formulations implemented in a time-dependent numerical model (XBeach): (1) an advective-deterministic approach (ADA) and (2) the probabilistic breaker formulation of Roelvink (1993). Previous research has shown that the ADA breaker model gives different results for the cross-shore pattern of the fraction of breaking waves, which is now shown to affect not only the short wave height but also the short wave groupiness. While RMS short wave heights are comparable to measurements using both breaker models, the ADA breaker model allows higher levels of short wave groupiness into the surf zone. It is shown that this acts as an additional forcing mechanism for low frequency waves in the shoaling and nearshore zone, which, in addition to greater levels of breaking, leads to higher values of wave set-up. These findings are dependent on the complexity of the local bathymetry. For a plane slope, the differences in the low frequency wave heights and set-up predicted by both breaker models are negligible. Where arbitrary breakpoints are present in the field of wave propagation, such as nearshore bars or reefs, the ADA model predicts higher localized set-up, indicative of greater flow over such features. Differences are even more pronounced when the incident wave regime is highly energetic.

scholarly journals Two-point observations of low-frequency waves at 67P/Churyumov-Gerasimenko during the descent of PHILAE: comparison of RPCMAG and ROMAP

2016 ◽  
Vol 34 (7) ◽  
pp. 609-622 ◽  
Author(s):  
Ingo Richter ◽  
Hans-Ulrich Auster ◽  
Gerhard Berghofer ◽  
Chris Carr ◽  
Emanuele Cupido ◽  
...  
Keyword(s):  
Low Frequency ◽  
Minimum Variance ◽  
Wave Source ◽  
Frequency Wave ◽  
Final Destination ◽  
Connection Line ◽  
New Type ◽  
Current Instability ◽  
Comet 67P ◽  
Low Frequency Waves

Abstract. The European Space Agency's spacecraft ROSETTA has reached its final destination, comet 67P/Churyumov-Gerasimenko. Whilst orbiting in the close vicinity of the nucleus the ROSETTA magnetometers detected a new type of low-frequency wave possibly generated by a cross-field current instability due to freshly ionized cometary water group particles. During separation, descent and landing of the lander PHILAE on comet 67P/Churyumov-Gerasimenko, we used the unique opportunity to perform combined measurements with the magnetometers onboard ROSETTA (RPCMAG) and its lander PHILAE (ROMAP). New details about the spatial distribution of wave properties along the connection line of the ROSETTA orbiter and the lander PHILAE are revealed. An estimation of the observed amplitude, phase and wavelength distribution will be presented as well as the measured dispersion relation, characterizing the new type of low-frequency waves. The propagation direction and polarization features will be discussed using the results of a minimum variance analysis. Thoughts about the size of the wave source will complete our study.

Shallow subsurface mapping by electromagnetic sounding in the 300 kHz to 30 MHz range: Model studies and prototype system assessment

Geophysics ◽  
1994 ◽  
Vol 59 (8) ◽  
pp. 1201-1210 ◽  
Author(s):  
Duff C. Stewart ◽  
Walter L. Anderson ◽  
Thomas P. Grover ◽  
Victor F. Labson
Keyword(s):  
Dielectric Permittivity ◽  
High Frequency ◽  
Low Frequency ◽  
Computer Programs ◽  
Thin Layers ◽  
Depth Range ◽  
Frequency Range ◽  
Model Studies ◽  
New Instrument ◽  
Displacement Currents

A new instrument designed for frequency‐domain sounding in the depth range 0–10 m uses short coil spacings of 5 m or less and a frequency range of 300 kHz to 30 MHz. In this frequency range, both conduction currents (controlled by electrical conductivity) and displacement currents (controlled by dielectric permittivity) are important. Several surface electromagnetic survey systems commonly used (generally with frequencies less than 60 kHz) are unsuitable for detailed investigation of the upper 5 m of the earth or, as with ground‐penetrating radar, are most effective in relatively resistive environments. Most computer programs written for interpretation of data acquired with the low‐frequency systems neglect displacement currents, and are thus unsuited for accurate high‐frequency modeling and interpretation. New forward and inverse computer programs are described that include displacement currents in layered‐earth models. The computer programs and this new instrument are used to evaluate the effectiveness of shallow high‐frequency soundings based on measurement of the tilt angle and the ellipticity of magnetic fields. Forward model studies indicate that the influence of dielectric permittivity provides the ability to resolve thin layers, especially if the instrument frequency range can be extended to 50 MHz. Field tests of the instrument and the inversion program demonstrate the potential for detailed shallow mapping wherein both the resistivity and the dielectric permittivity of layers are determined. Although data collection and inversion are much slower than for low‐frequency methods, additional information is obtained inasmuch as there usually is a permittivity contrast as well as a resistivity contrast at boundaries between different materials. Determination of dielectric permittivity is particularly important for hazardous waste site characterization because the presence of some contaminants may have little effect on observed resistivity but a large effect on observed permittivity.

Low-Frequency Oscillations Within the Hambantota Port During the Southwest Monsoon, 2019

2020 ◽  
Author(s):  
Zhenjun Zheng ◽  
Xiaozhou Ma ◽  
Xuezhi Huang ◽  
Yujin Dong ◽  
Guohai Dong
Keyword(s):  
Wind Waves ◽  
Low Frequency ◽  
Southwest Monsoon ◽  
Long Waves ◽  
Frequency Wave ◽  
Low Frequency Oscillations ◽  
Mild Slope Equation ◽  
Spectrum Density ◽  
Forcing Mechanisms ◽  
Low Frequency Waves

Abstract Long waves with periods greater than tens of seconds propagating into a harbor may be trapped and significantly amplified, thereby resulting in detrimental effects on port operations. The water surface elevation in the Hambantota Port, Sri Lanka, was measured to investigate the low-frequency oscillations and their forcing mechanisms. Results show that the port is protected well from short waves with periods less than 30 s; however, the protection against long waves with periods larger than 30 s is inadequate. The spectral analyses identified four dominant periods within the low-frequency wave range. Modal analysis based on the extended mild-slope equation shows that the measured spectrum density for some dominant periods is low because the measurement point is close to the corresponding modal lines. Correlation analysis shows that low-frequency oscillations inside the Hambantota Port are excited directly by the low-frequency waves contained within the incident waves. The low-frequency waves outside the Hambantota Port are generated from the higher-frequency gravity waves (swell and wind waves) due to nonlinear interactions. Empirical formula is adopted to estimate the low-frequency wave height outside the Hambantota Port.

Growth of low-frequency waves due to a photon beam in a magnetized electron–positron plasma

1997 ◽  
Vol 58 (2) ◽  
pp. 345-366 ◽  
Author(s):  
QINGHUAN LUO ◽  
D. B. MELROSE
Keyword(s):  
High Frequency ◽  
Random Phase ◽  
Low Frequency ◽  
Photon Beam ◽  
Radio Waves ◽  
Wave Interactions ◽  
Frequency Wave ◽  
Pair Plasma ◽  
Electron Positron ◽  
Low Frequency Waves

The effect of a beam of radio waves of very high brightness passing through a cold, magnetized, electron–positron plasma is discussed. The properties of the natural wave modes in such a plasma are summarized, and approximate forms for the nonlinear response tensor are written down. Photon-beam-induced instabilities of low-frequency waves in the pair plasma are analysed in the random-phase approximation. When three-wave interactions involve two high-frequency waves in the same mode and a low-frequency wave in a different mode, wave–wave interactions are similar to wave–particle interactions in that photons act like particles that emit and absorb low-frequency waves. The absorption coefficients for various low-frequency waves due to a photon beam are evaluated. In a pure electron–positron plasma, photon-beam-induced instabilities can be effective only when either the high-frequency or the low-frequency waves are strongly modified by the magnetic field. The growth of the low-frequency waves is most effective when the high-frequency photon beam has a frequency close to the cyclotron frequency.

Induced Three-wave Interactions in Eclipsing Pulsars

1995 ◽  
Vol 12 (1) ◽  
pp. 71-75
Author(s):  
Qinghuan Luo ◽  
D. B. Melrose
Keyword(s):  
Thermal Effects ◽  
Cold Plasma ◽  
Low Frequency ◽  
Wave Interaction ◽  
Wave Interactions ◽  
Frequency Wave ◽  
Frequency Branch ◽  
High Frequency Waves ◽  
The Magnetic Field ◽  
Low Frequency Waves

AbstractThree-wave interactions involving two high-frequency waves (in the same mode) and a low-frequency wave are discussed and applied to pulsar eclipses. When the magnetic field is taken into account, the low-frequency waves can be the ω-mode (the low-frequency branch of the ordinary mode) or the z-mode (the low-frequency branch of the extraordinary mode). It is shown that in the cold plasma approximation, effective growth of the low-frequency waves due to an anisotropic photon beam can occur only for z-mode waves near the resonance frequency. In the application to pulsar eclipses, the cold plasma approximation may not be adequate and we suggest that when thermal effects are included, three-wave interaction involving low-frequency cyclotron waves (e.g. Bernstein modes) is a plausible candidate for pulsar eclipses

scholarly journals Upstream Ultra-Low Frequency Waves Observed by MESSENGER's Magnetometer: Implications for Particle Acceleration at Mercury's Bow Shock

2020 ◽  
Author(s):  
Norberto Romanelli ◽  
Gina DiBraccio ◽  
Daniel Gershman ◽  
Guan Le ◽  
Christian Mazelle ◽  
...  
Keyword(s):  
Solar Wind ◽  
Wave Amplitude ◽  
Solar Wind Speed ◽  
Low Frequency ◽  
Space Environment ◽  
Occurrence Rate ◽  
Frequency Range ◽  
S Waves ◽  
Mercury Surface ◽  
Low Frequency Waves

<p>In this work we perform the first statistical analysis of the main properties of waves observed in the 0.05–0.41 Hz frequency range in the Hermean foreshock by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Magnetometer. Although we find similar polarization properties to the '30 s' waves observed at the Earth's foreshock, the normalized wave amplitude (∼0.2) and occurrence rate (∼0.5%) are much smaller. This suggests significant lower backstreaming proton fluxes, due to the relatively low solar wind Alfvenic Mach number around Mercury. These differences could also be related to the relatively smaller foreshock size and/or more variable solar wind conditions. Furthermore, we estimate that the speed of resonant backstreaming protons in the solar wind reference frame (likely source for these waves) ranges between 0.95 and 2.6 times the solar wind speed. The closeness between this range and what is observed at other planetary foreshocks suggests that similar acceleration processes are responsible for this energetic population and might be present in the shocks of exoplanets.</p>

scholarly journals Event-Based Validation of Swell Arrival Time

2016 ◽  
Vol 46 (12) ◽  
pp. 3563-3569 ◽  
Author(s):  
Haoyu Jiang ◽  
Alexander V. Babanin ◽  
Ge Chen
Keyword(s):  
Arrival Time ◽  
Wave Model ◽  
Coastal Engineering ◽  
Early Arrival ◽  
Wave Heights ◽  
Numerical Wave ◽  
Event Based ◽  
Buoy Data ◽  
Good Agreement

AbstractThe arrival time of ocean swells is an important factor for offshore and coastal engineering and naval and recreational activities, which can also be used in evaluating the numerical wave model. Using the continuity and pattern of wave heights during the same swell event, a methodology is developed for identifying swell events and verifying swell arrival time in models from buoy data. The swell arrival time in a WAVEWATCH III hindcast database is validated with in situ measurements. The results indicate that the model has a good agreement with the observations but usually predicts an early arrival of swell, about 4 h on average. A histogram shows that about one-quarter of swell events arrive early and three-quarters late by comparison with the model. Many processes that may be responsible for the arrival time errors are discussed, but at this stage it is not possible to distinguish between them from the available data.

scholarly journals SEPARATION OF LOW-FREQUENCY WAVES BY AN ANALYTICAL METHOD

2011 ◽  
Vol 1 (32) ◽  
pp. 64
Author(s):  
Yuxiang Ma ◽  
Guohai Dong ◽  
Xiaozhou Ma
Keyword(s):  
Fluid Mechanics ◽  
Gravity Waves ◽  
Present Method ◽  
Low Frequency ◽  
Wave Generation ◽  
Coastal Engineering ◽  
Wave Groups ◽  
International Conference ◽  
Long Wave ◽  
Low Frequency Waves

A new method for separating low-frequency waves in time domain is proposed by constructing the analytical signals of the measured waves. Using three simultaneous wave records, the time series of incident bound, free and reflected low-frequency waves can be obtained by the present method. This method is only suitable for separating monochromatic low-frequency waves. The applicability of the method is examined by numerical tests. The results show that the present method can give accurate results over sloping beaches when water depth (kh) is larger than 0.2. Then, the present method is used to study an experiment of low-frequency waves over a mild slope beach. References Bakkenes, H.J. 2002. Observation and separation of bound and free low-frequency waves in the nearshore zone, in Faculty of Civil Engineering and Geosciences. Delft University of Technology: Delft. Baldock, T.E., D.A., Huntley, P.A.D., Bird, T.O., Hare, and G.N., Bullock. 2000. Breakpoint generated surf beat induced by bichromatic wave groups. Coastal Engineering. 30 (2-4): 213-242. http://dx.doi.org/10.1016/S0378-3839(99)00061-7 Battjes, J.A., Bakkenes, H.J., Janssen, T.T., van Dongeren, A.R. 2004. Shoaling of subharmonic gravity waves. J. Geophys. Res., 109(C2): C02009. http://dx.doi.org/10.1029/2003JC001863 Bowers, E.C. 1977. Harbour resonance due to set-down beneath wave groups. Journal of Fluid Mechanics. 79: 71-92. http://dx.doi.org/10.1017/S0022112077000044 Cohen, L. 1995. Time Frequency Analysis: Theory and Applications. Prentice Hall Englewood Cliffs, New Jersey. Dong, G.H., X.Z., Ma, M., Perlin, Y.X., Ma, B., Yu, and G., Wang. 2009. Experimental Study of long wave generation on sloping bottoms. Coastal Engineering, 56(1), 82-89. http://dx.doi.org/10.1016/j.coastaleng.2008.10.002 Kamphuis, J.W. 2000. Designing for low frequency waves. Proceedings of 27th International Conference on Coastal Engineering. Sydney, Australian. 1434-1447. Kostense, J.K. 1984. Measurements of surf beat and set-down beneath wave groups. Proceedings of 19th International Conference on Coastal Engineering. Houston, USA. 724-740. Longuet-Higgins, M.S. and R.W., Stewart. 1962. Radiation stress and mass transport in gravity waves with application to 'surfbeat'. Journal of Fluid Mechanics. 13: 481-504 http://dx.doi.org/10.1017/S0022112062000877 Mallat, S. 1999. A Wavelet Tour of Signal Processing. Academic Press. PMCid:407895 Nagai, T., N., Hashimoto, T., Asai, et al. 1994. Relationship of a moored vessel in a harbor and a long wave caused by wave groups. Proceedings of 17th International Conference on Coastal Engineering. Kobe, Japan. 847-861. Schäffer, H.A. 1993. Second-orderwavemaker theory for irregularwaves.Ocean Engineering. 23 (1), 47–88. http://dx.doi.org/10.1016/0029-8018(95)00013-B Symonds, G.D.A., D.A., Huntley, and A.J., Bowen. 1982. Two-dimensional surf beat-long-wave generation by a time-varying breakpoint. Journal of Geophysical Research. 87(C1): 492-498. http://dx.doi.org/10.1029/JC087iC01p00492 Yu, J. and C.C., Mei. 2000. Formation of sand bars under surface waves. Journal of Fluid Mechanics. 416: 315-348. http://dx.doi.org/10.1017/S0022112000001063

scholarly journals ANTIREFLECTIVE VERTICAL STRUCTURE EXTENDED FOR ATTENUATION OF LOW FREQUENCY WAVES

2012 ◽  
Vol 1 (33) ◽  
pp. 49
Author(s):  
Jose Alberto Gonzalez-Escriva ◽  
Josep Ramon MEDINA
Keyword(s):  
Large Scale ◽  
Vertical Structure ◽  
Wave Reflection ◽  
Wind Waves ◽  
Low Frequency ◽  
Scale Model ◽  
Frequency Wave ◽  
Large Scale Model ◽  
Multiple Unit ◽  
Low Frequency Waves

A new maritime vertical structure was designed to improve the antireflective performance for wave reflection of wind waves and oscillations associated with intense storms, resonance waves in port basins, etc. Multiple unit chambers formed with long cell circuits (Medina et al., 2010) are responsible for the low frequency wave absorption that was studied through large-scale model testing.

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