Simulation of Water Particle Kinematics in the Near Surface Zone

2009 ◽  
Author(s):  
G. Najafian ◽  
N. I. Mohd Zaki ◽  
G. Aqel
Keyword(s):  
Water Level ◽  
High Frequency ◽  
Wave Theory ◽  
Surface Zone ◽  
Offshore Structure ◽  
Near Surface ◽  
Water Particle ◽  
Frequency Components ◽  
Mean Water Level ◽  
Water Particle Kinematics

Linear Random Wave Theory (LRWT) is frequently used to simulate water particle kinematics at different nodes of an offshore structure from a reference surface elevation record. It is, however, well known that wave kinematics calculated from LRWT suffer from unrealistically large high-frequency components in the vicinity of mean water level. To overcome this deficiency, a common industry practice consists of using linear wave theory in conjunction with empirical techniques, such as the Wheeler or the vertical stretching methods, to provide a more realistic representation of the near-surface water particle kinematics. In this paper, a modified version of LRWT is introduced, which, unlike the standard LRWT, does not lead to unrealistically large high-frequency components in the vicinity of mean water level. The proposed method leads to predicted kinematics in the near surface zone which lie between corresponding values from the Wheeler and the vertical stretching methods, respectively.

Derivation of Water Particle Kinematics in the Near Surface Zone by the Effective Water Depth Procedure

2010 ◽  
Author(s):  
N. I. Mohd Zaki ◽  
G. Najafian
Keyword(s):  
Water Depth ◽  
High Frequency ◽  
Random Wave ◽  
Surface Zone ◽  
Offshore Structure ◽  
Near Surface ◽  
Water Particle ◽  
Frequency Components ◽  
Water Particle Kinematics ◽  
Effective Water

Linear Random Wave Theory (LRWT) is frequently used to simulate water particle kinematics at different nodes of an offshore structure from a reference surface elevation record. However, it is well known that LRWT leads to water particle kinematics with exaggerated high-frequency components in the vicinity of mean water level (MWL). To avoid this problem, empirical techniques (such as Wheeler & vertical stretching methods) are frequently used to provide a more realistic representation of the wave kinematics in the near surface zone. In this paper, a modified version of LRWT, based on the derivation of an effective water depth, is introduced. The proposed technique leads to predicted kinematics (in the near surface zone) which lie between corresponding values from the Wheeler and the vertical stretching methods. Furthermore, it does not suffer from exaggerated high-frequency components in the near surface zone.

scholarly journals Comparison of Extreme Offshore Structural Response from Two Alterna-tive Stretching Techniques

2013 ◽  
Vol 7 (1) ◽  
pp. 273-281 ◽  
Author(s):  
N.I. Mohd Zaki ◽  
M.K. Abu Husain ◽  
G. Najafian
Keyword(s):  
Wave Theory ◽  
Surface Elevation ◽  
Random Wave ◽  
Surface Zone ◽  
Offshore Structure ◽  
Near Surface ◽  
Water Particle ◽  
Wave Kinematics ◽  
Water Particle Kinematics ◽  
Extreme Responses

Linear random wave theory (LRWT) has successfully explained most properties of real sea waves with the ex-ception of some nonlinear effects for surface elevation and water particle kinematics. Due to its simplicity, it is frequently used to simulate water particle kinematics at different nodes of an offshore structure from a reference surface elevation record; however, predicted water particle kinematics from LRWT suffer from unrealistically large high-frequency compo-nents in the vicinity of mean water level (MWL). To overcome this deficiency, a common industry practice for evaluation of wave kinematics in the free surface zone consists of using linear random wave theory in conjunction with empirical techniques (such as Wheeler and vertical stretching methods) to provide a more realistic representation of near-surface wave kinematics. It is well known that the predicted kinematics from these methods are different; however, no systematic study has been conducted to investigate the effect of this on the magnitude of extreme responses of an offshore structure. In this paper, probability distributions of extreme responses of an offshore structure from Wheeler and vertical stretching methods are compared. It is shown that the difference is significant; consequently, further research is required to deter-mine which method is more reliable.

The Effect of Different Methods of Simulating Water Particle Kinematics on the 100-Year Responses

2016 ◽  
Author(s):  
N. I. Mohd Zaki ◽  
M. K. Abu Husain ◽  
N. Abdullah Shuhaimy ◽  
G. Najafian
Keyword(s):  
Wave Theory ◽  
Random Wave ◽  
Offshore Structure ◽  
Near Surface ◽  
Water Particle ◽  
Wave Kinematics ◽  
Realistic Representation ◽  
Frequency Components ◽  
Offshore Industry ◽  
Water Particle Kinematics

Linear random wave theory (LRWT) is frequently used to simulate water particle kinematics at different nodes of an offshore structure from a reference surface elevation record. However, it is well known that LRWT leads to water particle kinematics with exaggerated high-frequency components in the vicinity of mean water level (MWL). A number of empirical techniques have been suggested to provide a more realistic representation of near surface wave kinematics. The empirical techniques popular in the offshore industry include Wheeler stretching, linear extrapolation, delta stretching, and vertical stretching. Each of these methods is intended to calculate sensible kinematics above the MWL, yet they have been found to differ from one another in the results yielded. In this paper, two new methods of simulating water particle kinematics are introduced. In this study, the values of 100-year responses derived from different methods of simulating wave kinematics are compared.

Comparison of Extreme Responses From Wheeler and Vertical Stretching Methods

2013 ◽  
Author(s):  
N. I. Mohd Zaki ◽  
M. K. Abu Husain ◽  
G. Najafian
Keyword(s):  
Wave Theory ◽  
Random Wave ◽  
Surface Zone ◽  
Offshore Structure ◽  
Near Surface ◽  
Water Particle ◽  
Realistic Representation ◽  
The Difference ◽  
Water Particle Kinematics ◽  
Extreme Responses

Linear random wave theory (LRWT) is frequently used to simulate water particle kinematics at different nodes of an offshore structure from a reference surface elevation record. However, it is well known that LRWT leads to water particle kinematics with exaggerated high-frequency components in the vicinity of mean water level (MWL). To avoid this problem, empirical techniques such as Wheeler and vertical stretching methods are frequently used to provide a more realistic representation of the wave kinematics in the near surface zone. In this paper, the Monte Carlo time simulation technique is used to investigate the effect of these two different methods of simulating water particle kinematics on the probability distribution of extreme responses. It is shown that the difference could be significant leading to uncertainty as to which method should be used.

scholarly journals EVALUATION OF A MODIFIED STRETCHED LINEAR WAVE THEORY

1986 ◽  
Vol 1 (20) ◽  
pp. 40
Author(s):  
Jen-Men Lo ◽  
R.G. Dean
Keyword(s):  
Water Level ◽  
Wave Theory ◽  
Wave Force ◽  
Inertia Force ◽  
Water Particle ◽  
Force Coefficients ◽  
Stretching Factor ◽  
Mean Water Level ◽  
The Mean ◽  
Water Particle Kinematics

Many experimental investigations of the drag and inertia force coefficients have relied on the determination of water particle kinematics from measured wave forms. Since the pioneering work of Airy (1845), Stokes (1847, 1880) and others, a number of wave theories have been developed for predicting water particle kinematics. Clearly, the use of a certain wave theory will lead to corresponding force coefficients. Therefore, a wave theory that provides more accurate water particle kinematics is very important. Reid (1958) developed the simple superposition method for predicting water particle kinematics from a measured sea surface that could be either random or periodic. The method is based upon linear long-crested wave theory. Borgman (1965, 1967, 1969a, 1969b) introduced the linearized spectral density of wave force on a pile due to a random Gaussian sea. The drag force component has been approximated in the simplest form by a linear relation. This method, however, cannot calculate properties of the wave field and wave force above the mean water level. Wheeler (1969) applied simple superposition with a stretching factor in the vertical coordinate position for hurricane-generated wave data during Wave Project II. With this method it was possible to evaluate the wave force above the mean water level.

DISPERSION IN SEISMIC SURFACE WAVES

Geophysics ◽  
1951 ◽  
Vol 16 (1) ◽  
pp. 63-80 ◽  
Author(s):  
Milton B. Dobrin
Keyword(s):  
Surface Waves ◽  
Water Waves ◽  
Seismic Refraction ◽  
Wave Theory ◽  
Wave Dispersion ◽  
Surface Zone ◽  
Surface Wave Dispersion ◽  
Near Surface ◽  
Arrival Times ◽  
Ground Roll

A non‐mathematical summary is presented of the published theories and observations on dispersion, i.e., variation of velocity with frequency, in surface waves from earthquakes and in waterborne waves from shallow‐water explosions. Two further instances are cited in which dispersion theory has been used in analyzing seismic data. In the seismic refraction survey of Bikini Atoll, information on the first 400 feet of sediments below the lagoon bottom could not be obtained from ground wave first arrival times because shot‐detector distances were too great. Dispersion in the water waves, however, gave data on speed variations in the bottom sediments which made possible inferences on the recent geological history of the atoll. Recent systematic observations on ground roll from explosions in shot holes have shown dispersion in the surface waves which is similar in many ways to that observed in Rayleigh waves from distant earthquakes. Classical wave theory attributes Rayleigh wave dispersion to the modification of the waves by a surface layer. In the case of earthquakes, this layer is the earth’s crust. In the case of waves from shot‐holes, it is the low‐speed weathered zone. A comparison of observed ground roll dispersion with theory shows qualitative agreement, but it brings out discrepancies attributable to the fact that neither the theory for liquids nor for conventional solids applies exactly to unconsolidated near‐surface rocks. Additional experimental and theoretical study of this type of surface wave dispersion may provide useful information on the properties of the surface zone and add to our knowledge of the mechanism by which ground roll is generated in seismic shooting.

Simulations of high-resolution images of amorphous silicon films

1986 ◽  
Vol 44 ◽  
pp. 544-545
Author(s):  
G. Y. Fan ◽  
J. M. Cowley
Keyword(s):  
Electron Microscope ◽  
High Frequency ◽  
Fourier Transformation ◽  
Amorphous Materials ◽  
Low Frequency ◽  
Chromatic Aberration ◽  
Structure Information ◽  
Frequency Components ◽  
High Resolution Images ◽  
Spatial Frequency Spectrum

It is well known that the structure information on the specimen is not always faithfully transferred through the electron microscope. Firstly, the spatial frequency spectrum is modulated by the transfer function (TF) at the focal plane. Secondly, the spectrum suffers high frequency cut-off by the aperture (or effectively damping terms such as chromatic aberration). While these do not have essential effect on imaging crystal periodicity as long as the low order Bragg spots are inside the aperture, although the contrast may be reversed, they may change the appearance of images of amorphous materials completely. Because the spectrum of amorphous materials is continuous, modulation of it emphasizes some components while weakening others. Especially the cut-off of high frequency components, which contribute to amorphous image just as strongly as low frequency components can have a fundamental effect. This can be illustrated through computer simulation. Imaging of a whitenoise object with an electron microscope without TF limitation gives Fig. 1a, which is obtained by Fourier transformation of a constant amplitude combined with random phases generated by computer.

ИССЛЕДОВАНИЯ АКУСТИЧЕСКИХ ХАРАКТЕРИСТИК ВЕРХНЕГО СЛОЯ МОРЯ МЕТОДОМ МНОГОЧАСТОТНОГО АКУСТИЧЕСКОГО ЗОНДИРОВАНИЯ

2020 ◽  
Author(s):  
V.A. Bulanov ◽  
I.V. Korskov ◽  
A.V. Storozhenko ◽  
S.N. Sosedko
Keyword(s):  
High Frequency ◽  
Wave Motion ◽  
High Spatial Resolution ◽  
Wind Waves ◽  
Acoustic Parameter ◽  
Sea Surface ◽  
Near Surface ◽  
Acoustical Properties ◽  
Acoustic Spectroscopy ◽  
Sea Bottom

Описано применение акустического зондирования для исследования акустических характеристик верхнего слоя моря с использованием широкополосных остронаправленных инвертированных излучателей,устанавливаемых на дно. В основу метода положен принцип регистрации обратного рассеяния и отраженияот поверхности моря акустических импульсов с различной частотой, позволяющий одновременно измерятьрассеяние и поглощение звука и нелинейный акустический параметр морской воды. Многочастотное зондирование позволяет реализовать акустическую спектроскопию пузырьков в приповерхностных слоях моря,проводить оценку газосодержания и получать данные о спектре поверхностного волнения при различных состояниях моря вплоть до штормовых. Применение остронаправленных высокочастотных пучков ультразвукапозволяет разделить информацию о планктоне и пузырьках и определить с высоким пространственным разрешением структуру пузырьковых облаков, образующихся при обрушении ветровых волн, и структуру планктонных сообществ. Участие планктона в волновом движении в толще морской воды позволяет определитьпараметры внутренних волн спектр и распределение по амплитудам в различное время.This paper represents the application of acoustic probingfor the investigation of acoustical properties of the upperlayer of the sea using broadband narrow-beam invertedtransducers that are mounted on the sea bottom. Thismethod is based on the principle of the recording of thebackscattering and reflections of acoustic pulses of differentfrequencies from the sea surface. That simultaneouslyallows measuring scattering and absorption of the soundand non-linear acoustic parameter of seawater. Multifrequencyprobing allows performing acoustic spectroscopy ofbubbles in the near-surface layer of the sea, estimating gascontent, and obtaining data on the spectrum of the surfacewaves in various states of the sea up to a storm. Utilizationof the high-frequency narrow ultrasound beams allows us toseparate the information about plankton and bubbles and todetermine the structure of bubble clouds, created during thebreaking of wind waves, along with the structure of planktoncommunities with high spatial resolution. The participationof plankton in the wave motion in the seawater columnallows determining parameters of internal waves, such asspectrum and distribution of amplitudes at different times.

A Novel Adaptive PET/CT Image Fusion Algorithm

2019 ◽  
Vol 14 (7) ◽  
pp. 658-666
Author(s):  
Kai-jian Xia ◽  
Jian-qiang Wang ◽  
Jian Cai
Keyword(s):  
Lung Cancer ◽  
Image Fusion ◽  
High Frequency ◽  
Malignant Tumors ◽  
Low Frequency ◽  
Combination Method ◽  
Ct Image ◽  
Fusion Algorithm ◽  
Pet Ct ◽  
Frequency Components

Background: Lung cancer is one of the common malignant tumors. The successful diagnosis of lung cancer depends on the accuracy of the image obtained from medical imaging modalities. Objective: The fusion of CT and PET is combining the complimentary and redundant information both images and can increase the ease of perception. Since the existing fusion method sare not perfect enough, and the fusion effect remains to be improved, the paper proposes a novel method called adaptive PET/CT fusion for lung cancer in Piella framework. Methods: This algorithm firstly adopted the DTCWT to decompose the PET and CT images into different components, respectively. In accordance with the characteristics of low-frequency and high-frequency components and the features of PET and CT image, 5 membership functions are used as a combination method so as to determine the fusion weight for low-frequency components. In order to fuse different high-frequency components, we select the energy difference of decomposition coefficients as the match measure, and the local energy as the activity measure; in addition, the decision factor is also determined for the high-frequency components. Results: The proposed method is compared with some of the pixel-level spatial domain image fusion algorithms. The experimental results show that our proposed algorithm is feasible and effective. Conclusion: Our proposed algorithm can better retain and protrude the lesions edge information and the texture information of lesions in the image fusion.

Despeckling of Sar Images Using Shrinkage of Two-Dimensional Discrete Orthonormal S-Transform

2020 ◽  
pp. 2150023
Author(s):  
Priya R. Kamath ◽  
Kedarnath Senapati ◽  
P. Jidesh
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Relevant Information ◽  
Detection Algorithm ◽  
Two Dimensional ◽  
Sar Images ◽  
S Transform ◽  
Processing Step ◽  
Frequency Components ◽  
Shock Filter

Speckles are inherent to SAR. They hide and undermine several relevant information contained in the SAR images. In this paper, a despeckling algorithm using the shrinkage of two-dimensional discrete orthonormal S-transform (2D-DOST) coefficients in the transform domain along with shock filter is proposed. Also, an attempt has been made as a post-processing step to preserve the edges and other details while removing the speckle. The proposed strategy involves decomposing the SAR image into low and high-frequency components and processing them separately. A shock filter is used to smooth out the small variations in low-frequency components, and the high-frequency components are treated with a shrinkage of 2D-DOST coefficients. The edges, for enhancement, are detected using a ratio-based edge detection algorithm. The proposed method is tested, verified, and compared with some well-known models on C-band and X-band SAR images. A detailed experimental analysis is illustrated.

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