scholarly journals SCOUR ABOUT A SINGLE, CYLINDRICAL PILE DUE TO COMBINED RANDOM WAVES AND A CURRENT

1986 ◽  
Vol 1 (20) ◽  
pp. 136 ◽  
Author(s):  
Robert W. Eadie ◽  
John B. Herbich
Keyword(s):  
Random Wave ◽  
Two Dimensional ◽  
Random Waves ◽  
Sediment Size ◽  
Waves And Currents ◽  
Using Data ◽  
Almost All ◽  
A Current ◽  
Water Depths ◽  
Monochromatic Waves

There have been many studies of scour around piles caused by waves, and some studies of scour by waves and currents combined. However, almost all of the studies were conducted with monochromatic waves. The purpose of this investigation was to study what scouring effects various currents and random waves have on a single, cylindrical pile. These results were then compared with the results from previous studies of scour resulting from currents and monochromatic waves at Texas A&M University (Armbrust, 1982 and Wang, 1983). Experiments were conducted in a two-dimensional wave tank. The pile used in this study had a diameter of 1.5 inches. Two water depths, four currents, one sediment size and four random wave spectra were utilized. Using data obtained from the experiments, an attempt was made to describe scour in terms of relevant dimensionless parameters.

scholarly journals RANDOM BREAKING WAVES HORIZONTAL SEABED

1986 ◽  
Vol 1 (20) ◽  
pp. 68 ◽  
Author(s):  
Hans Peter Riedel ◽  
Anthony Paul Byrne
Keyword(s):  
Wave Height ◽  
Water Depth ◽  
Breaking Waves ◽  
Random Wave ◽  
Random Waves ◽  
Flume Experiments ◽  
Depth Ratio ◽  
Wave Trains ◽  
Monochromatic Waves

According to wave theories the depth limited wave height over a horizontal seabed has a wave height to water depth ratio (H/d) of about 0.8. Flume experiments with monochromatic waves over a horizontal seabed have failed to produce H/d ratios greater than 0.55. However designers still tend to use H/d 0.8 for their design waves. Experiments have been carried out using random wave trains in the flume over a horizontal seabed. These experiments have shown that the limiting H/d ratio of 0.55 applies equally well to random waves.

scholarly journals Method of the Laboratory Wave Generation for Two Dimensional Hydraulic Model Experiment in the Coastal Engineering Fields: Case of Random Waves

2021 ◽  
Vol 33 (6) ◽  
pp. 383-390
Author(s):  
Jong-In Lee ◽  
Il Rho Bae ◽  
Young-Taek Kim
Keyword(s):  
Wave Generation ◽  
Hydraulic Model ◽  
Coastal Engineering ◽  
Experimental Results ◽  
Random Wave ◽  
Two Dimensional ◽  
Random Waves ◽  
Coastal Structures ◽  
Successful Execution ◽  
The Stability

The experiments in coastal engineering are very complex and a lot of components should be concerned. The experience has an important role in the successful execution. Hydraulic model experiments have been improved with the development of the wave generator and the advanced measuring apparatus. The hydraulic experiments have the advantage, that is, the stability of coastal structures and the hydraulic characteristics could be observed more intuitively rather than the numerical modelings. However, different experimental results can be drawn depending on the model scale, facilities, apparatus, and experimenters. In this study, two-dimensional hydraulic experiments were performed to suggest the guide of the test wave(random wave) generation, which is the most basic and important factor for the model test. The techniques for generating the random waves with frequency energy spectrum and the range for the incident wave height [(HS)M/(HS)T = 1~1.05] were suggested. The proposed guide for the test wave generation will contribute to enhancing the reliability of the experimental results in coastal engineering.

scholarly journals SIMULTANEOUS WAVE AND CURRENT FORCES ON A PIPELINE

1980 ◽  
Vol 1 (17) ◽  
pp. 106
Author(s):  
David A. Knoll ◽  
John B. Herbich
Keyword(s):  
Small Diameter ◽  
Horizontal Cylinder ◽  
Random Wave ◽  
Ocean Bottom ◽  
Hydrodynamic Loads ◽  
Fluid Force ◽  
Interaction Of Waves ◽  
Drag Forces ◽  
Waves And Currents ◽  
A Current

The hydrodynamic loads on an offshore pipeline resting on the ocean bottom are a function of parameters associated with waves and currents acting near the pipeline. There have been many studies conducted to develop the criteria needed to estimate the hydrodynamic loads imposed by waves and currents. Many of these studies have investigated the effect of these phenomena individually, but to date only limited research has been directed towards evaluating the combined effect. In general, the investigations of the interaction of waves and currents and their effect on the fluid force have been directed toward vertical piles1'2'3'1*'5 and structures in a random wave field with a current present;6'7'8'9 however, the fluid force of waves in the presence of currents on pipelines has not been directly addressed. The purpose of this research was to investigate the interaction of waves and currents and its relationship to the forces on submerged pipelines. A model pipeline in a wave-flume was used to obtain experimental values which were compared to values predicted by the Morison equation in conjunction with the superposition of the waves and a current. The Morison equation10 was used to evaluate the forces on a horizontal cylinder resting on the bottom. The two major input parameters required by this equation are (1) the water particle kinematics of velocity and acceleration; and (2) the coefficients of drag and inertia. The testing program investigated the drag forces developed by the combined waves and a current. The inertia forces were assumed small when compared to the drag forces since a relatively small diameter cylinder was used in the experiments, thus the accelerations were small.

scholarly journals NEAR BOTTOM VELOCITIES IN WAVES WITH A CURRENT; ANALYTICAL AND NUMERICAL COMPUTATIONS

1984 ◽  
Vol 1 (19) ◽  
pp. 79 ◽  
Author(s):  
W.G.M. Van Kesteren ◽  
W.T. Bakker
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Bottom Friction ◽  
Bottom Boundary Layer ◽  
Two Dimensional ◽  
Layer Model ◽  
Bottom Boundary ◽  
Waves And Currents ◽  
A Current ◽  
Bottom Velocities

In this paper, starting from the Prandtl hypothesis a three-dimensional numerical bottom boundary layer model has been developed, which allows to calculate bottom friction by a combination of waves and currents. The model has been compared with two-dimensional analytical computations which gave similar results. The bottom friction values found are comparable to the ones, found by Lundgren (1972), however in the most relevant cases somewhat less. Furthermore in the two-dimensional case the model has been compared with measurements of Bakker and Van Doom (1978). With respect to the oscillatory motion, still some minor deviations occur between theory and measurements, due to deficiencies of the Prandtl theory.

scholarly journals PROBABILITY OF EXCEEDING THE CRITICAL SHEAR STRESS FOR SAND MOTION IN SPECIFIC WAVE AND CURRENT CONDITIONS

2012 ◽  
Vol 1 (33) ◽  
pp. 4
Author(s):  
Pierre-Yves Henry ◽  
Alf Tørum ◽  
Øivind Artsen ◽  
Dag Myrhaug ◽  
Muk Chen Ong
Keyword(s):  
Shear Stress ◽  
Critical Shear Stress ◽  
Bed Shear Stress ◽  
Random Waves ◽  
Flow Conditions ◽  
Flume Experiments ◽  
Natural Sand ◽  
Waves And Currents ◽  
Mobility Parameter ◽  
A Current

This study is focusing on the threshold of sand motion under random waves combined with a following current. The analysis is based on some flume experiments realized over a natural sand bed for different flow conditions (waves and currents). The main result comes as a map of the probability to exceed the threshold of sand motion, as a function of a wave and a current mobility parameter. These observations are compared to methods predicting the bed shear stress using an equivalent monochromatic wave, and links between the probability of exceeding the critical shear stress for initiation of sand motion and the calculated maximum bed shear stress are found.

scholarly journals A MODEL FOR OFFSHORE SEDIMENT TRANSPORT

1984 ◽  
Vol 1 (19) ◽  
pp. 97 ◽  
Author(s):  
M.J.F. Stive ◽  
J.A. Battjes
Keyword(s):  
Sediment Transport ◽  
Equilibrium State ◽  
Return Flow ◽  
Random Wave ◽  
Two Dimensional ◽  
Random Waves ◽  
Water Motion ◽  
First Approximation

Observation of the two-dimensional breaking of random waves on a beach suggests that under conditions of active surf an important mechanism in the process of offshore sediment transport is the transport by the undertow or return flow, induced by the breaking of waves. It is found that a model incorporating this mechanism exclusively is able to describe the local sediment transport and the resulting bottom variation of a beach under random wave attack to a first approximation. A laboratory verification is made based on measurements of both the dynamics of the water motion and the bottom profile. Finally, a realistic equilibrium state is shown to result from the model

scholarly journals Time Scale for Scour Beneath Pipelines Due to Long-Crested and Short-Crested Nonlinear Random Waves Plus Current

2021 ◽  
Vol 9 (2) ◽  
pp. 114
Author(s):  
Dag Myrhaug ◽  
Muk Chen Ong
Keyword(s):  
Time Scale ◽  
Current Flow ◽  
Irregular Waves ◽  
Wave Crest ◽  
Random Wave ◽  
Random Waves ◽  
Flow Conditions ◽  
Regular Waves ◽  
Nonlinear Random Waves ◽  
2D And 3D

This article derives the time scale of pipeline scour caused by 2D (long-crested) and 3D (short-crested) nonlinear irregular waves and current for wave-dominant flow. The motivation is to provide a simple engineering tool suitable to use when assessing the time scale of equilibrium pipeline scour for these flow conditions. The method assumes the random wave process to be stationary and narrow banded adopting a distribution of the wave crest height representing 2D and 3D nonlinear irregular waves and a time scale formula for regular waves plus current. The presented results cover a range of random waves plus current flow conditions for which the method is valid. Results for typical field conditions are also presented. A possible application of the outcome of this study is that, e.g., consulting engineers can use it as part of assessing the on-bottom stability of seabed pipelines.

Risk Analysis for Knowledge Sharing in Tax Payment

2016 ◽  
Vol 6 (1) ◽  
pp. 20-37
Author(s):  
Zahra Kazemi ◽  
Ahmad Jafari Samimi ◽  
Hamed Fazlollahtabar
Keyword(s):  
Knowledge Sharing ◽  
Tax Evasion ◽  
Developed Countries ◽  
Government Expenditures ◽  
Positive Effects ◽  
The People ◽  
Using Data ◽  
Tax Payments ◽  
Almost All ◽  
Tax Payers

One way to finance government expenditures is to collect taxes. Regarding to this financial source compared with other sources positive tax knowledge sharing amongst people or tax payers lead to effective investment. Unlike developing countries in developed countries - that taxes have little effects - almost all government expenditures is financed by taxes. One of the main challenges in the tax system is how to collect taxes due to tax evasion. The main reason is the uncertainty surrounding how government uses the taxes paid by the people. A major factor in the outbreak of the sense of failure to pay taxes, is the discussion and sharing the viewpoint of each other. If there is any positive tax effect prevalence of speech among people motivate them to pay more and if not, paying taxes is impaired. Therefore in order to avoid disorderliness in paying taxes that lead to a reduction in the development growth rate of investing taxes in industry and services sectors procedures should be designed so that taxes spread in speech with more quality. In this article five categories that people share their knowledge about them with each other, have been proposed. Defining risk structure and using data from surveying form the risk values of tax payment the results indicate that sharing tax knowledge amongst people have positive effects on tax payments.

Sign in / Sign up

Export Citation Format

Share Document