scholarly journals METHOD FOR ESTIMATING DIRECTIONAL WAVE SPECTRUM IN INCIDENT AND REFLECTED WAVE FIELD

1984 ◽  
Vol 1 (19) ◽  
pp. 32 ◽  
Author(s):  
Masahiko Isobe ◽  
Kosuke Kondo
Keyword(s):  
Wave Field ◽  
Wave Spectrum ◽  
Likelihood Method ◽  
Phase Lag ◽  
Reflected Waves ◽  
Directional Spectrum ◽  
Reflected Wave ◽  
Interaction Terms ◽  
Modified Maximum Likelihood ◽  
High Resolution Power

The relationship between the directional spectrum and the crosspower spectra in an incident and reflected wave field differs from the situation with no reflected waves because the phase lag between the incident and reflected waves is not random. Extra terms, which may be called phase interaction terms, exist. Hence standard methods for estimating the directional spectrum are not applicable. In the present study, the MLM is modified for this situation and the method is termed the MMLM (Modified Maximum Likelihood Method). The validity of the MMLM is examined by numerical simulation. The results indicate that the MMLM has a high resolution power. Formulas to determine the reflection coefficient are derived and their accuracy and suitability are examined.

scholarly journals ENHANCEMENT OF DIRECTIONAL WAVE SPECTRUM ESTIMATES

1974 ◽  
Vol 1 (14) ◽  
pp. 14
Author(s):  
Narayana N. Panicker ◽  
Leon E. Borgman
Keyword(s):  
Practical Importance ◽  
Wave Spectrum ◽  
Wave Force ◽  
Entropy Method ◽  
Likelihood Method ◽  
Smoothing Function ◽  
Random Waves ◽  
Directional Distribution ◽  
Directional Spectrum ◽  
Data Limitations

Determination of the directional distribution of ocean surface waves is of practical importance and analytical schemes for it are developed and discussed here. Based on a generalized representation of wave properties such as surface elevation, subsurface pressure or horizontal components of water particle velocity, acceleration or wave force, two general schemes of analysis are developed. In one scheme the predictive equations for the directional distribution of both the amplitude and phase of waves are derived. Distribution of energy as a function of direction for random waves is obtained in the other scheme. Fourier series parameterization is used to represent directional spectrum. The truncation of the series dictated by data limitations introduce directional spread and negative side lobes for the estimated directional spectrum. A procedure to remove these undesirable side lobes by a non-negative smoothing function is described. The smoothing causes further directional spread. Methods for obtaining better directional resolution are discussed. Data adaptive spectral analysis techniques such as Maximum Likelihood Method and Maximum Entropy Method are suggested.

scholarly journals Estimating nearshore waves by assimilating buoy directional spectrum data in SWAN

2021 ◽  
Author(s):  
David T. Walker ◽  
Kelsey Brunner
Keyword(s):  
Wave Field ◽  
Single Point ◽  
Wave Spectrum ◽  
Observation Data ◽  
Directional Spectrum ◽  
Near Shore ◽  
Nearshore Waves ◽  
Mean Wave Period ◽  
Standard Output ◽  
The Relationship

AbstractThis paper describes a variational data assimilation algorithm based on the SWAN near shore wave-spectrum model. The approach allows single-point wave spectrum observations to be used to estimate the wave field for a nearshore region under stationary conditions, assuming a spatially uniform incident wave spectrum at the offshore boundary. The assimilated data are in the form of Fourier directional coefficients, the standard output from operational wave buoys, and are used directly by incorporating the relationship between directional spectrum and the Fourier coefficients into the formulation. The algorithm was tested on data from nearshore buoys deployed off the coast of North Carolina in May 2012, and the estimated wave field is compared to both the input data and to independent observation data. The results compare favorably to the independent data with overall RMS errors of 10–20 percent for significant wave height, about half a second for mean wave period, and as much as 3–4 SWAN spectral grid cells for mean direction. Overall, the results show that the algorithm can be effectively used to estimate the offshore boundary spectrum and accurately reproduce wave conditions in the domain.

Numerical Study of the Characteristics of Wave-Wave Interactions in Multiphase Wave Field Near Coastal Area

2011 ◽  
Vol 255-260 ◽  
pp. 2313-2317
Author(s):  
Ruey Syan Shih
Keyword(s):  
Wave Field ◽  
Coastal Area ◽  
High Frequency ◽  
Surf Zone ◽  
Numerical Study ◽  
Wave Interactions ◽  
Incoming Wave ◽  
Reflected Waves ◽  
Irregular Wave ◽  
Reflected Wave

Numerical investigations of multiphase irregular wave field are presented by using the BEM, which incorporates the interaction between incoming wave and reflected wave in the coastal area. This study discusses the case of multi-component wave generation using the 2D-NWT, which incorporates the wave-wave interactions between various conditions of incoming waves and high frequency reflected waves, including the variation of wave field and particle trajectory. The surf beats in the surf zone is mainly the cause of the cross-shore motion, and the generations of high frequency harmonics waves, these phenomena will be study accordingly in this preliminary study for the modeling of oscillations cause by surf beat and back swash, the generation of high frequency multi-phase reflected wave are carried out to investigate the deformation of wave profile, wave field and particle path-line.

Reflection of a longitudinal travelling wave from the notch in a rod

2007 ◽  
Vol 5 ◽  
pp. 212-220 ◽  
Author(s):  
M.A. Ilgamov ◽  
A.G. Khakimov
Keyword(s):  
Inverse Problem ◽  
Longitudinal Wave ◽  
Travelling Wave ◽  
Observation Point ◽  
Reflected Waves ◽  
Reflected Wave ◽  
Using Data

This article investigates the reflection of a longitudinal wave from the transverse notch and its movement along an infinite rod. The dependence is obtained between the reflected wave and parameters of the notch. The statement of the inverse problem allows defining the coordinate of the notch and the parameter that contains its depth and length using data on both the incident and reflected waves at the observation point.

Interaction of High Frequency Lamb Waves with Surface-Mount Sensor Adhesives

2013 ◽  
Vol 558 ◽  
pp. 489-500 ◽  
Author(s):  
Patrick Norman ◽  
Claire Davis ◽  
Cédric Rosalie ◽  
Nik Rajic
Keyword(s):  
Wave Field ◽  
Lamb Waves ◽  
Base Material ◽  
Adhesive Layer ◽  
Scattered Wave ◽  
Phase Lag ◽  
Wave Fields ◽  
Surface Mount ◽  
Frequency Regime ◽  
Fibre Bragg Gratings

The application of Lamb waves to damage and/or defect detection in structures is typicallyconfined to lower frequencies in regimes where only the lower order modes propagate in order to simplifyinterpretation of the scattered wave-fields. Operation at higher frequencies offers the potentialto extend the sensitivity and diagnostic capability of this technique, however there are technical challengesassociated with the measurement and interpretation of this data. Recent work by the authorshas demonstrated the ability of fibre Bragg gratings (FBGs) to measure wave-fields at frequencies inexcess of 2 MHz [1]. However, when this work was extended to other thinner plate specimens it wasfound that at these higher frequencies, the cyanoacrylate adhesive (M-Bond 200) used to attach theFBG sensors to the plate was significantly affecting the propagation of the waves. Laser vibrometrywas used to characterise the wave-field in the region surrounding the adhesive and it was found that theself-adhesive retro-reflective tape applied to aid with this measurement was also affecting the wavefieldin the higher frequency regime. This paper reports on an experimental study into the influence ofboth of these materials on the propagating wave-field. Three different lengths of retro-reflective tapewere placed in the path of Lamb waves propagating in an aluminium plate and laser vibrometry wasused to measure the wave-field upstream and downstream of the tape for a range of different excitationfrequencies. The same experiment was conducted using small footprint cyanoacrylate film samplesof different thickness. The results show that both of these surface-mount materials attenuate, diffractand scatter the incoming waves as well as introducing a phase lag. The degree of influence of thesurface layer appears to be a function of its material properties, the frequency of the incoming waveand the thickness and footprint of the surface layer relative to the base material thickness. Althoughfurther work is required to characterise the relative influence of each of these variables, investigationsto date show that for the measurement of Lamb Waves on thin structures, careful considerationshould be given to the thickness and footprint of the adhesive layer and sensor, particularly in the highfrequency regime, so as to minimise their effect on the measurement.

scholarly journals OBSERVATION OF DIRECTIONAL WAVE SPECTRA AND REFLECTION COEFFICIENT OF BREAKWATER IN A HARBOR

1988 ◽  
Vol 1 (21) ◽  
pp. 3
Author(s):  
Tetsunori Ohshimo ◽  
Kosuke Kondo ◽  
Tsunehiro Sekimoto
Keyword(s):  
Reflection Coefficient ◽  
Wave Diffraction ◽  
Maximum Likelihood Method ◽  
Wave Spectrum ◽  
Field Investigation ◽  
Likelihood Method ◽  
Electromagnetic Current ◽  
Wave Spectra ◽  
Field Investigations ◽  
Directional Wave

Field investigations were performed in order to show the effect of wave diffraction by breakwaters through directional wave spectra measurements in a harbor, and to estimate the reflection coefficient by resolving the incident and reflected wave energy in front of a composite type breakwater. Combinations of an ultrasonic wave gage (USW) and an electromagnetic current meter (EMC) were used to measure the synchronized data of the water surface elevation and two horizontal velocities. The EMLM (Extended Maximum Likelihood Method) was applied for the calculation of the directional wave spectrum, and the modified EMLM for an incident and reflection wave field was applied for the estimation of the reflection coefficient. Through the estimated directional wave spectra, the effect of wave diffraction by breakwaters were discussed and the reflection coefficient was estimated at about 0.9. As a result, the applicability of the field investigation method and the modified EMLM were verified.

The reflexion of internal/inertial waves from bumpy surfaces. Part 2. Split reflexion and diffraction

1971 ◽  
Vol 49 (1) ◽  
pp. 113-131 ◽  
Author(s):  
P. G. Baines
Keyword(s):  
Wave Field ◽  
Logarithmic Singularity ◽  
Fluid Velocity ◽  
Wave Theory ◽  
Dispersive Wave ◽  
Inertial Waves ◽  
Incident Wavelength ◽  
Wave Fields ◽  
Reflected Wave ◽  
Square Root Singularity

This paper considers the linear inviscid reflexion of internal/inertial waves from smooth bumpy surfaces where a characteristic (or ray) is tangent to the surface at some point. There are two principal cases. When a characteristic associated with the incident wave is tangent to the surface we have diffraction; when the tangential characteristic is associated with a reflected wave we have split reflexion, a phenomenon which has no counterpart in classical non-dispersive wave theory. In both these cases the problem of determining the wave field may be reduced to a set of coupled integral equations with two unknown functions. These equations are solved for the simplest topography for each case, and the properties of the wave fields for more general topographies are discussed. For both split reflexion and diffraction, the fluid velocity has an inverse-square-root singularity on the tangential characteristic, and the energy density has a corresponding logarithmic singularity. The diffracted wave field penetrates into the shadow region a distance which is of the order of the incident wavelength. Possibilities for instability and mixing are discussed.

Interaction Effects in a Transonic Turbine Stage

2000 ◽  
Author(s):  
J. W. Barter ◽  
P. H. Vitt ◽  
J. P. Chen
Keyword(s):  
Analytical Techniques ◽  
Interaction Effects ◽  
Phase Lag ◽  
Turbine Stage ◽  
Reflected Waves ◽  
Blade Row ◽  
Transonic Turbine ◽  
Unsteady Loading ◽  
Unsteady Pressure Measurements ◽  
Blade Row Interaction

A 3D, viscous, time-accurate code has been used to predict the time-dependent flowfield in a transonic turbine stage. Two analytical techniques are used to understand the unsteady physics. One technique takes into account interaction effects associated with reflected waves bouncing between blade rows while the other neglects them. Both techniques model the exact blade counts using phase-lag boundary conditions. The analytical techniques are validated by comparing to unsteady pressure measurements which have been made on the vane and blade surfaces at midspan. The analytical results are then used to understand the importance of interaction effects when the blade rows are close-coupled and when they are more widely spaced. The results show that interaction effects must be taken into account in order to accurately predict the unsteady loading on the upstream blade row. However, for the downstream blade row, interaction effects are second order and do not routinely need to be taken into account in the design process.

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