Wave Elevation on Large Circular Cylinders Excited by Wind-Generated Random Waves

1988 ◽  
Vol 110 (1) ◽  
pp. 48-54 ◽  
Author(s):  
P. S. V. Rao ◽  
H. Raman
Keyword(s):  
Large Diameter ◽  
Diffraction Theory ◽  
Irregular Waves ◽  
Circular Cylinders ◽  
Density Functions ◽  
Random Waves ◽  
Principle Of Superposition ◽  
Wave Elevation ◽  
Spectral Density Functions ◽  
Institute Of Technology

Wave elevation on large cylinders due to irregular waves have been calculated based on the McCamy and Fuchs linear diffraction theory and on the principle of superposition. Experiments have been conducted in the Hydraulic Engineering Laboratory, Indian Institute of Technology, Madras, to examine the wave elevation excited by wind-generated irregular waves on circular cylinders of large diameter. The wave elevation around the cylinders at representative locations were measured and compared with calculated wave elevations. The spectral density functions computed from wave elevation time series measured in the laboratory were compared with calculated time elevation spectral densities on the cylinder.

scholarly journals Water wave diffraction by a cylinder array. Part 2. Irregular waves

2001 ◽  
Vol 442 ◽  
pp. 33-66 ◽  
Author(s):  
C. O. G. OHL ◽  
P. H. TAYLOR ◽  
R. EATOCK TAYLOR ◽  
A. G. L. BORTHWICK
Keyword(s):  
Incident Wave ◽  
Extreme Events ◽  
Diffraction Theory ◽  
Irregular Waves ◽  
Circular Cylinders ◽  
Random Wave ◽  
Wave Groups ◽  
Cylinder Array ◽  
Random Seas ◽  
Focused Wave

Diffraction of irregular waves, focused wave groups, and random seas by an array of vertical bottom-mounted circular cylinders is investigated using theoretical, computational and experimental methods. This is an extension of our study of such an array in regular waves, reported in Part 1. Linear focused wave group theory is reviewed as a method for predicting the probable shape of extreme events from random wave spectra. Measurements are presented of the free surface elevation distribution in the vicinity of a multi-column structure in an offshore basin when subjected to irregular waves having peak frequencies and significant wave heights in the range 0.449 < kpa < 0.555 and 0.114 < Hs < 0.124 respectively, where a is the cylinder radius. Analytical linear diffraction theory is extended for application to focused wave groups and random seas. Experimental irregular wave data are analysed for comparison with this theory. Linear diffraction theory for random seas is shown to give an excellent prediction of incident wave spectral diffraction, while linear diffraction theory for focused wave groups works well for linearized extreme events. Due to the phase shifting of incident wave spectral components, diffraction is shown to generate focused wave groups in the vicinity of the cylinder array.

Air Gap Response of Floating Structures: Statistical Predictions Versus Observed Behavior

2001 ◽  
Vol 123 (3) ◽  
pp. 118-123 ◽  
Author(s):  
Steven R. Winterstein ◽  
Bert Sweetman
Keyword(s):  
Diffraction Theory ◽  
Air Gap ◽  
Statistical Analyses ◽  
Irregular Waves ◽  
Wave Crest ◽  
Detailed Model ◽  
Floating Structures ◽  
Amplification Factors ◽  
Wave Elevation ◽  
Time Histories

The air gap response of a specific semi-submersible platform subjected to irregular waves is considered. Detailed model tests for this structure are studied in depth. Using time-histories of both motions and air gap, statistical analyses both for the absolute near-structure wave elevation (with respect to a fixed observer), and the relative wave elevation (with respect to the moving structure) are performed. Statistics of wave crest amplification, due to diffraction, are established. Corresponding amplification factors are derived from linear diffraction theory, and the results of theory and observations are critically compared.

scholarly journals WAVE FORCES INDUCED BY IRREGULAR WAVES ON A VERTICAL CIRCULAR CYLINDER

1978 ◽  
Vol 1 (16) ◽  
pp. 144 ◽  
Author(s):  
Hajime Ishida ◽  
Yuichi Iwagaki
Keyword(s):  
Circular Cylinder ◽  
Laboratory Experiments ◽  
Large Diameter ◽  
Small Diameter ◽  
Diffraction Theory ◽  
Irregular Waves ◽  
Wave Forces ◽  
Irregular Wave ◽  
Water Level Variations ◽  
Particle Velocities

In order to examine the irregular wave forces on a small diameter cylinder, laboratory experiments have been conducted on water particle velocities and wave forces with various kinds of irregular waves. As the results, it is indicated that the time variation and the spectral distribution of wave forces can be calculated adequately from the water level variations by using the methods proposed by Reid1' and Borgman2' respectively. Moreover, with respect to the irregular wave forces on a large diameter cylinder, a new calculation method was shown by means of applying Reid's linear filters1' to MacCamy and Fuchs's diffraction theory.

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.

A New Spectral Method for Modeling Dynamic Ice Actions

2004 ◽  
Author(s):  
Tuomo Ka¨rna¨ ◽  
Yan Qu ◽  
Walter L. Ku¨hnlein
Keyword(s):  
Dynamic Response ◽  
Spectral Density ◽  
Time Correlation ◽  
General Purpose ◽  
Density Functions ◽  
Offshore Structure ◽  
Spectral Density Functions ◽  
Ice Force ◽  
Ice Forces ◽  
Scale Data

This paper presents a method of evaluating the response of a vertical offshore structure that is subjected to dynamic ice actions. The model concerns a loading scenario where a uniform ice sheet is drifting and crushing against the structure. Full scale data obtained at the lighthouse Norstro¨msgrund is used in the derivation of a method that applies both to narrow and wide structures. A large amount of events with directly measured local forces was used to derive formulas for spectral density functions of the ice force. A non-dimensional formula that was derived for the autospectrum applies for all ice thicknesses. Coherence functions are used to define the cross-spectra of the local ice forces. The two kind of spectral density functions for local forces can be used to evaluate the spectral density of the total ice force. The method takes account of both the spatial and time correlation between the local forces. Accordingly, the model provides a tool to consider the non-simultaneous characteristics of the local ice pressures while assessing the total ice force. The model can be used in conjunction with general purpose FE programs to evaluate the dynamic response of an offshore structure.

Influence of Red Blood Cell Concentrations on the Measurement of Turbulence Using Hot-Film Anemometer

1983 ◽  
Vol 105 (4) ◽  
pp. 406-410 ◽  
Author(s):  
A. M. Sallam ◽  
N. H. C. Hwang
Keyword(s):  
Phosphate Buffer Solution ◽  
Experimental Information ◽  
Characteristic Change ◽  
Density Functions ◽  
Buffer Solution ◽  
Number Range ◽  
Flow Phenomenon ◽  
Human Red Blood Cells ◽  
Spectral Density Functions ◽  
Hot Film

Measurement of local velocity fluctuations was made with an L-shaped conical hot-film probe in a submerged circular jet. The experiment was carried out in solutions of washed human red blood cells (RBC) in a phosphate buffer solution (PBS), at hematocrit concentrations (Ht percent) of 10, 19, 29, and 38 percent. The viscosity of the testing solutions was kept at 3.2 c.p. by adding proper amount of dextran. The experiment was conducted at Reynolds numbers (NR) 674, 963, 1255 and 1410, based on the jet exit velocity and exit diameter. Statistical analyses were performed on the recorded instantaneous velocity signals to obtain the root-mean-square (rms) values, the probability density functions (PDF) and the power spectral density functions (PSDF) of the signals. Within the range tested, we noticed an incidental rise in rms values at 19 to 29 Ht percent for NR = 963 similar to those reported earlier in the literature. Further analyses using PDF and PSDF, however, showed neither a trend nor any physical significance of this rise. Based on the analyses of both the PDF and the PSDF, we believe that the incidental rise in rms value can be partially attributed to the high spikes registered by the probe in a high RBC concentrations fluid flow. The bombardment of RBC on the probe thermal boundary layer may cause a characteristic change in the probe response to certain flow phenomenon, at least within the Reynolds number range used in this study. Additional theoretical and experimental information is needed to pin point the nature of this response. We thus suggest that the second and higher moments of the HFA signals obtained in a fluctuating flow field involving a liquid with relatively high contaminant concentrations cannot be interpreted as a simple flow phenomenon.

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