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.

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.

scholarly journals Analytical approach for determining the mean water level profile in an estuary with substantial fresh water discharge

2016 ◽  
Vol 20 (3) ◽  
pp. 1177-1195 ◽  
Author(s):  
Huayang Cai ◽  
Hubert H. G. Savenije ◽  
Chenjuan Jiang ◽  
Lili Zhao ◽  
Qingshu Yang
Keyword(s):  
Water Level ◽  
Fresh Water ◽  
River Discharge ◽  
River Flow ◽  
Water Discharge ◽  
Value Theory ◽  
Velocity Amplitude ◽  
Mean Water Level ◽  
The Mean ◽  
Fresh Water Discharge

Abstract. The mean water level in estuaries rises in the landward direction due to a combination of the density gradient, the tidal asymmetry, and the backwater effect. This phenomenon is more prominent under an increase of the fresh water discharge, which strongly intensifies both the tidal asymmetry and the backwater effect. However, the interactions between tide and river flow and their individual contributions to the rise of the mean water level along the estuary are not yet completely understood. In this study, we adopt an analytical approach to describe the tidal wave propagation under the influence of substantial fresh water discharge, where the analytical solutions are obtained by solving a set of four implicit equations for the tidal damping, the velocity amplitude, the wave celerity, and the phase lag. The analytical model is used to quantify the contributions made by tide, river, and tide–river interaction to the water level slope along the estuary, which sheds new light on the generation of backwater due to tide–river interaction. Subsequently, the method is applied to the Yangtze estuary under a wide range of river discharge conditions where the influence of both tidal amplitude and fresh water discharge on the longitudinal variation of the mean tidal water level is explored. Analytical model results show that in the tide-dominated region the mean water level is mainly controlled by the tide–river interaction, while it is primarily determined by the river flow in the river-dominated region, which is in agreement with previous studies. Interestingly, we demonstrate that the effect of the tide alone is most important in the transitional zone, where the ratio of velocity amplitude to river flow velocity approaches unity. This has to do with the fact that the contribution of tidal flow, river flow, and tide–river interaction to the residual water level slope are all proportional to the square of the velocity scale. Finally, we show that, in combination with extreme-value theory (e.g. generalized extreme-value theory), the method may be used to obtain a first-order estimation of the frequency of extreme water levels relevant for water management and flood control. By presenting these analytical relations, we provide direct insight into the interaction between tide and river flow, which will be useful for the study of other estuaries that experience substantial river discharge in a tidal region.

scholarly journals Dynamics of fortnightly water level variations along a tide-dominated estuary with negligible river discharge

2021 ◽  
Author(s):  
Erwan Garel ◽  
Ping Zhang ◽  
Huayang Cai
Keyword(s):  
Water Level ◽  
Phase Difference ◽  
River Discharge ◽  
Water Levels ◽  
Level Increase ◽  
Upstream Direction ◽  
Water Level Variations ◽  
Mean Water Level ◽  
The Mean ◽  
Guadiana Estuary

Abstract. Observations indicate that the fortnightly fluctuations in mean water level increase in amplitude along the lower half of a tide-dominated estuary (The Guadiana estuary) with negligible river discharge but remain constant upstream. Analytical solutions reproducing the semi-diurnal wave propagation shows that this pattern results from reflection effects at the estuary head. The phase difference between velocity and elevation increases from the mouth to the head (where the wave has a standing nature) as the high and low water levels get progressively closer to slack water. Thus, the tidal (flood-ebb) asymmetry in discharge is reduced in the upstream direction. It becomes negligible along the upper estuary half, as the mean sea level remains constant despite increased friction due to wave shoaling. Observations of a flat mean water level along a significant portion of an upper estuary, easier to obtain than the phase difference, can therefore indicate significant reflection of the propagating semi-diurnal wave at the head. Details of the analytical model shows that changes in the mean depth or length of semi-arid estuaries, in particular for macrotidal locations, affect the fortnightly tide amplitude, and thus the upstream mass transport and inundation regime. This has significant potential impacts on the estuarine environment.

Determination of the Spectra of Empirical Wave Force Coefficients

1972 ◽  
Vol 29 (1) ◽  
pp. 19-25
Author(s):  
W. H. Bell
Keyword(s):  
Power Spectra ◽  
Wave Theory ◽  
Wave Force ◽  
Orbital Velocity ◽  
Force Measurements ◽  
Force Coefficients ◽  
Force Equation ◽  
Wave Parameters ◽  
Using Data

A method is proposed for obtaining frequency-dependent values of wave force coefficients for marine structural forms. If orbital velocity (or acceleration) components and wave force measurements are directly available, the coefficients are obtained without recourse to any particular wave theory. However, linearity of the wave-force process is implicit in the use of the Morison force equation. Modifications of the method are indicated for use when velocities must be inferred from measurements of wave parameters other than velocity, or from their power spectra, by means of a chosen wave theory. The feasibility of the method for obtaining wave force coefficients as a function of frequency is demonstrated using data reported by another worker for force measurements on a sphere.

Waves Off Land's End

1965 ◽  
Vol 18 (2) ◽  
pp. 180-187 ◽  
Author(s):  
L. Draper ◽  
H. S. Fricker
Keyword(s):  
Water Level ◽  
First Year ◽  
Zero Crossing ◽  
South West ◽  
Mean Water Level ◽  
The Mean ◽  
Wave Recorder

Since January 1962, waves have been recorded by a shipborne wave recorder (Tucker, 1956) on the Sevenstones light-vessel which is stationed about 20 miles south-west of Land's End in about 200 ft. of water. Records were taken at three-hourly intervals and were mostly of 12 minutes’ duration. The analysis presented here is based on 2920 records taken in the first year of operation; the method of analysis which has been used is that described by Tucker (1961). This gives for each record:(a) H1 = The sum of the distances of the highest crest and the lowest trough from the mean water level.(b) Tz = The mean zero-crossing period.(c) Tc = The mean crest period.

scholarly journals Propagation of bichromatic-bidirectional waves

RBRH ◽  
2019 ◽  
Vol 24 ◽  
Author(s):  
Mario Grüne de Souza e Silva ◽  
Paulo Cesar Colonna Rosman ◽  
Claudio Freitas Neves
Keyword(s):  
Water Level ◽  
Stress Tensor ◽  
Nonlinear Term ◽  
Primary Wave ◽  
Radiation Stress ◽  
Stress Components ◽  
Mean Water Level ◽  
The Mean ◽  
Mohr’S Circles ◽  
Infragravity Wave

ABSTRACT This study aims to investigate the transformations experienced by the mean water level and radiation stress tensor during the propagation of Bichromatic-Bidirectional (Bi-Bi) waves on a slope of 1:22 and water depth varying from 55 cm to 26 cm, simulating laboratory conditions. A computer program written in Python was used to compute those quantities at different combinations of wave angles and periods. The setup and setdown of the mean water level are strongly dependent on the combination of periods and direction of the primary waves, as they propagate along the slope, modifying the bound infragravity wave. Mohr’s circles for the radiation stress tensor showed significant changes of diameter and center at different points along the basin. The radiation stress components for the Bi-Bi waves are the sum of the stresses associated with each primary wave and a nonlinear term which results from the interference between primary waves. Disregarding these nonlinear terms may significantly affect the nearshore hydrodynamics prediction.

Numerical Experiments of Bottom Stress on Wave Setup

2012 ◽  
Vol 212-213 ◽  
pp. 1108-1111
Author(s):  
Shi Chao Liu ◽  
Li Huang
Keyword(s):  
Numerical Experiment ◽  
Water Level ◽  
Numerical Experiments ◽  
Surf Zone ◽  
Current Increase ◽  
Wave Setup ◽  
Bottom Stress ◽  
Mean Water Level ◽  
The Mean ◽  
Wave Induced

Wave-induced setup increases the mean water level in the surf zone and can be influenced by bottom stress in the presence of ambient current. As the numerical experiment shows, the effects of bottom stress on wave setup are associated with wave conditions. An onshore-directed bottom stress caused by offshore ambient current increase the wave setup and an offshore-directed bottom stress caused by onshore ambient current decrease the wave setup. According to the experiment, it is necessary to calculate wave-induced setup including the bottom stress in the presence of ambient current.

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.

scholarly journals MODELING OF THE REYNOLDS STRESS IN THE BURSTING LAYER AFFECTED BY TYPHOON

2011 ◽  
Vol 1 (32) ◽  
pp. 35
Author(s):  
Tomokazu Murakami ◽  
Jun Yoshino ◽  
Takashi Yasuda
Keyword(s):  
Water Level ◽  
Reynolds Stress ◽  
Trough Level ◽  
Wind Waves ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Wave Trough ◽  
Mean Water Level ◽  
The Mean ◽  
Particle Velocities

When large and intensive water surface displacements are caused by developed wind waves due to a typhoon, it is impossible in the Eulerian coordinate system to measure water particle velocities continuously in a domain between the wave trough level and the mean water level. Consequently, the domain between the wave trough level and the mean water level becomes a void zone where the Reynolds stress cannot be described. By treating the sea surface boundary layer including the void zone as a bursting layer, we modeled the Reynolds stress in the bursting layer. Validity of that modeling was verified by performing comparisons with experimentally obtained results.

Numerical Simulation of Random Wave Forces Near the Free Surface

1991 ◽  
Vol 113 (1) ◽  
pp. 14-22 ◽  
Author(s):  
M. Isaacson ◽  
K. Subbiah
Keyword(s):  
Numerical Simulation ◽  
Free Surface ◽  
Standard Deviation ◽  
Probability Density ◽  
Random Wave ◽  
Wave Forces ◽  
Water Particle ◽  
Time Histories ◽  
The Mean ◽  
Water Particle Kinematics

The present paper describes the numerical simulation of random wave forces acting on a section of fixed slender vertical cylinder near the free surface, taking account of the intermittency of submergence. Time histories of water particle kinematics corresponding to a specified wave spectrum are generated using linear numerical transforms and corresponding force time histories at different sections are computed using the Morison equation. Analytical predictions of various statistical properties of water particle kinematics and forces for the intermittent flow are compared with results of the numerical simulations. These include the probability density of particle kinematics, the spectral density of the force, the probability density of force maxima, and the mean and standard deviation of the force maxima. In general, the agreement is found to be quite satisfactory. The effects of simulation time and random phases on the mean and standard deviation of intermittent force maxima are also investigated.

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