COMPLEX ENVELOPE IDENTIFICATION OF WAVE GROUPS

1986 ◽  
Vol 1 (20) ◽  
pp. 57 ◽  
Author(s):  
Rodney J. Sobey ◽  
Han-Bin Liang
Keyword(s):  
Phase Function ◽  
Intrinsic Property ◽  
Wave Model ◽  
Dominant Frequency ◽  
Envelope Function ◽  
Random Wave ◽  
Function Estimation ◽  
Wave Groups ◽  
Complex Envelope ◽  
Analysis Technique

The complex envelope function is presented as the natural analysis technique for wave records where the identification of wave groups is a dominant interest. Algorithms have been developed and confirmed for separation of the complex envelope function, estimation of the dominant frequency and unwrapping of the phase function. Cross-correlograms and coherence spectra reveal a link between the envelope amplitude and phase traces that appears to be an intrinsic property of wave groups. Nevertheless, the majority of the information in typical wave records can be described as random, accounting for the relative success of the Gaussian random wave model.

scholarly journals WAVE GROUPS IN THE FREQUENCY AND TIME DOMAINS

1984 ◽  
Vol 1 (19) ◽  
pp. 47 ◽  
Author(s):  
Rodney J. Sobey ◽  
W. Wayne Read
Keyword(s):  
Wave Model ◽  
Linear Analysis ◽  
Phase Spectrum ◽  
Envelope Function ◽  
Random Wave ◽  
Wave Groups ◽  
Analysis Techniques ◽  
Time Domains

The identification of wave groups in wave records is sought in terms of the classical linear analysis techniques in the frequency and time domains. Unwrapping and detrending of the phase spectrum identifies apparent order where none is assumed in the Gaussian random wave model. Similarly unexpected order is observed in the tail of the correlogram of both the wave record and the Rice envelope function. These aspects are strongly suggestive of wave grouping.

Morphological characterization of bicontinuous structures in polymer blends and microemulsions by the inverse-clipping method in the context of the clipped-random-wave model

2000 ◽  
Vol 61 (6) ◽  
pp. 6773-6780 ◽  
Author(s):  
Hiroshi Jinnai ◽  
Yukihiro Nishikawa ◽  
Sow-Hsin Chen ◽  
Satoshi Koizumi ◽  
Takeji Hashimoto
Keyword(s):  
Polymer Blends ◽  
Wave Model ◽  
Morphological Characterization ◽  
Random Wave

Numerical and Experimental Analysis of Extreme Slamming Loads on FPSO Bows

2002 ◽  
Author(s):  
Ole A. Hermundstad ◽  
Carl T. Stansberg ◽  
O̸yvind Hellan
Keyword(s):  
Wave Model ◽  
Element Model ◽  
Practical Method ◽  
Second Order ◽  
Random Wave ◽  
Fe Model ◽  
Time Step ◽  
Scaled Model ◽  
Structural Responses ◽  
Relative Motions

A practical method for prediction of slamming loads and structural responses in the bow of an FPSO is presented. Incoming waves are simulated by a second-order random wave model, which describes the water elevation and kinematics. Vessel motions are calculated by linear analysis. The diffracted wave field is calculated taking into account linear 3D diffraction. Relative motions are then estimated by combining the linear vessel motions, second-order incoming waves and linear diffraction. The relative motions and velocities at the bow are used as input to numerical slamming calculations. The bow is divided into 2D sections and a boundary value problem is solved for each section applying the generalized Wagner-method of Zhao & Faltinsen (1993) and Zhao et al (1996). The 2D slamming calculations account for the local pile-up of water on each side of the section during impact. Structural responses are calculated from a finite-element model of the bow using the exact pressure distribution from the slamming calculations. This is achieved by automatic mapping of pressures onto the outer surface of the FE-model and performing a quasi-static structural analysis for each time-step. The methods are implemented into a package of computer tools, allowing the user to perform the various steps in the process with little manual editing of data. The system runs easily on a standard PC. Measurements on a 1:55 scaled model of an FPSO are used for validation of the bow slamming calculations. The model was equipped with five 3.85m × 1.65m (full-scale) panels in the upper part of the bow for slamming force measurements. The tests were run in storm conditions with steep waves. The calculated slamming force on a panel located at the foremost tip of the bulwark, 12.8 meters above the mean waterline, is compared with measured results for selected extreme slamming events. Considering the complexity of this problem and the relative simplicity of the approach, the agreement is very good.

scholarly journals 2DH COMPUTATION OF TRANSIENT SEA BED EVOLUTIONS

1986 ◽  
Vol 1 (20) ◽  
pp. 123 ◽  
Author(s):  
Huib J. De Vriend
Keyword(s):  
Sediment Transport ◽  
Current Model ◽  
Wave Model ◽  
Bottom Slope ◽  
Nearshore Zone ◽  
Sea Bed ◽  
Mathematical System ◽  
Analysis Technique ◽  
Unambiguous Conclusion ◽  
Harmonic Analysis Technique

The interaction between the constituent models for waves, currents, sediment transport and bottom level changes in a class of compound 2DH mathematical models of transient sea bed evolutions in the coastal zone is investigated mathematically, using the theory of characteristics and a harmonic analysis technique. This leads to contrary indications as to the importance of including diffraction in the wave model and to the unambiguous conclusion that the bottom slope effect on the sediment transport is indespensable for the mathematical system to be inherently stable. This conclusion is shown to imply that depth-integrated current model are insufficient to describe the flow in this type of morphological computations for the nearshore zone or complex coastal areas.

Frequency modulation within electrocardiograms during ventricular fibrillation

2000 ◽  
Vol 279 (2) ◽  
pp. H825-H835 ◽  
Author(s):  
Abhijit Patwardhan ◽  
Sachin Moghe ◽  
Ke Wang ◽  
Fabio Leonelli
Keyword(s):  
Ventricular Fibrillation ◽  
Body Surface ◽  
Dominant Frequency ◽  
The Body ◽  
Frequency Variation ◽  
Refractory Periods ◽  
Analysis Technique ◽  
Before And After ◽  
Average Variation ◽  
Dominant Frequencies

Periods of reentrant activation and effective refractory periods are correlated with dominant frequency or reciprocal of cycle periods during ventricular fibrillation (VF). In the present study, we used an analysis technique based on Wigner transforms to quantify time-varying dominant frequencies in electrocardiograms (ECGs) during VF. We estimated dominant frequencies within orthogonal ECGs recorded in 10 dogs during trials of 10 s of VF and in 9 dogs during trials of 30 s of VF. In four additional dogs, we compared dominant frequencies during 10 s of VF before and after administration of amiodarone. Our results showed the following. 1) There was substantial frequency variation or modulation within the ECGs during 10 and 30 s of VF, the average variation being ±15% from the mean frequency. Amiodarone decreased mean frequencies ( P < 0.05) as expected; however, amiodarone also decreased the variation in frequencies ( P < 0.05). 2) During 30 s of VF, the dominant frequencies increased continuously from 7.3 to 8.1 Hz ( P < 0.05). The increase in frequency was almost linear with a rate of 0.022 Hz/s ( r 2 = 0.93, P < 0.0005). 3) Modulation of frequencies during the first and the last one-half of 30 s of VF was not different. Average (in time) mean frequencies and modulation of frequencies were similar in all three ECGs. 4) Although the averages were similar, during any VF episode, dominant frequencies in ECGs recorded from different locations on the body surface were similar to each other at some times and markedly different from each other at other times. We conclude that during VF, 1) frequencies in ECGs vary considerably and continuously, and amiodarone decreases this variation; 2) mean frequencies increase linearly during first 30 s; 3) the variability in frequency does not change during 30 s; and 4) at any given time, the frequencies within spatially different body surface ECGs can be either similar or markedly different.

scholarly journals A NUMERICAL STUDY ON SURFACE WAVE EVOLUTION OVER VISCOELASTIC MUD

2018 ◽  
pp. 64
Author(s):  
Elham Sharifineyestani ◽  
Navid Tahvildari
Keyword(s):  
Surface Wave ◽  
Numerical Study ◽  
Current Model ◽  
Resonance Effect ◽  
Wave Model ◽  
Form Solution ◽  
Random Wave ◽  
Complex Frequency ◽  
Wave Evolution ◽  
Domain Phase

A numerical modeling approach is applied to investigate the combined effect of wave-current-mud on the evolution of nonlinear waves. A frequency-domain phase-resolving wave-current model that solves nonlinear wave-wave interactions is used to solve wave evolution. A comparison between the results of numerical wave model and the laboratory experiments confirms the accuracy of the numerical model. The model is then applied to consider the effect of mud properties on nonlinear surface wave evolution. It is shown that resonance effect in viscoelastic mud creates a complex frequency-dependent dissipation pattern. In fact, due to the resonance effect, higher surface wave frequencies can experience higher damping rates over viscoelastic mud compared to viscous mud in both permanent form solution and random wave scenarios. Thus, neglecting mud elasticity can result in inaccuracies in estimating total wave energy and wave shape.

Extended energy-balance-equation wave model for multidirectional random wave transformation

2005 ◽  
Vol 32 (8-9) ◽  
pp. 961-985 ◽  
Author(s):  
Hajime Mase ◽  
Kazuya Oki ◽  
Terry S. Hedges ◽  
Hua Jun Li
Keyword(s):  
Energy Balance ◽  
Balance Equation ◽  
Wave Model ◽  
Energy Balance Equation ◽  
Wave Transformation ◽  
Random Wave

Mechanics of nonlinear random wave groups interacting with a vertical wall

2008 ◽  
Vol 20 (3) ◽  
pp. 036604 ◽  
Author(s):  
Alessandra Romolo ◽  
Felice Arena
Keyword(s):  
Vertical Wall ◽  
Random Wave ◽  
Wave Groups ◽  
Nonlinear Random Wave

Nonlinear Space–Time Evolution of Wave Groups With a High Crest

2005 ◽  
Vol 127 (1) ◽  
pp. 46-51 ◽  
Author(s):  
Felice Arena ◽  
Francesco Fedele
Keyword(s):  
Time Evolution ◽  
Surface Displacement ◽  
Fixed Time ◽  
Space Time ◽  
Second Order ◽  
Random Wave ◽  
Wave Groups ◽  
Free Surface Displacement ◽  
Nonlinear Free Surface ◽  
Space Time Evolution

The theory of quasi-determinism, for the mechanics of linear random wave groups was obtained by Boccotti in the eighties. The first formulation of the theory deals with the largest crest amplitude; the second formulation deals with the largest wave height. In this paper the first formulation of Boccotti’s theory, particularized for long-crested waves, is extended to the second-order. The analytical expressions of the nonlinear free surface displacement and velocity potential are obtained. The space–time evolution of the nonlinear wave group, when a very large crest occurs at a fixed time and location, is then shown. Finally the second-order probability of exceedance of the crest amplitude is obtained and validated by Monte Carlo simulation.

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