scholarly journals Storm Wave Characteristics

1967 ◽  
Vol 7 (01) ◽  
pp. 87-98 ◽  
Author(s):  
R.J. Robinson ◽  
H.R. Brannon ◽  
G.W. Kattawar
Keyword(s):  
Power Spectrum ◽  
Gulf Of Mexico ◽  
Random Noise ◽  
Offshore Structures ◽  
Wave Profile ◽  
Wave Crest ◽  
Wave Characteristics ◽  
Storm Wave ◽  
Wave Profiles ◽  
Wave Shapes

Abstract Accurate prediction of storm wave characteristics are needed for design of offshore structures. Statistical methods of random noise analysis provide techniques for predicting required wave properties. These techniques have been used to analyze and characterize storm wave profiles from Gulf of Mexico recording installations in 34, 65 and 98 ft of water. Correlations based on the results can be used to predict wave crest probabilities and wave shapes for a range of Gull water depths and storm conditions. Example predictions of wave crest probability as a function of water depth for a particular set of storm conditions are given. Introduction Accurate predictions of wave crests and wave shapes are needed for design of offshore structures. With predictions of wave crests, platform deck elevations giving adequate protection from exposure to storm waves can be selected. Use of hydrodynamic wave theories with the wave crest and wave shape predictions permits an estimate of the wave forces an offshore structure must withstand. Observation of ocean waves suggests use of statistical analysis for studying wave characteristics for water depths beyond the breaking wave zone; recent wave generation theories lend support to this approach. One of the most powerful methods of statistically analyzing wave profiles was introduced by Cartwright and Longuet-Higgins; most of the basic relations used were developed by Rice in studies of random noise theory. This method predicts wave crest elevation probabilities from two parameters characterizing a wave profile. The statistical approach also provides a means for predicting wave shapes. In the random noise model of a wave profile, surface elevation is represented as an infinite sum of sine waves with closely spaced frequencies and random phase angles. Power density is proportional to the sum of the squares of the amplitudes of sine waves having frequencies within a narrow band, and the distribution of power density as a function of frequency is called the power density spectrum, or power spectrum. The power spectrum characterizes an irregular sea, and hence finds use in motion studies of ships, barges and semisubmersible drilling platforms. From the power spectrum, a wave profile of any duration of time can, in principle, be calculated; this long wave profile depicts the many wave shapes to which a structure may be exposed. Thus, the statistical methods of wave analysis provide an approach to selecting wave shapes as well as wave crest elevations needed for design of offshore structures. For practical application of these techniques, power spectra and related quantities must be predicted from storm properties. Barber and Tucker have reviewed correlations of wave properties and storm conditions. Their review summarizes work of Darbyshire, among others, in which a correlation of power spectra with wind intensity of the North Atlantic was developed. These results, plus more recent work by Pierson and Moskowitz and Kitaigorodskii, establish feasibility of correlation, but there is no theoretical basis for modifications extending the relations to other area's as remote as the Gulf of Mexico. Hence, to predict characteristics of Gulf of Mexico waves, a study of local observations is needed. This paper presentsa practical approach to computing wave profiles that depict shapes of waves for use in force calculations,a summary of relations for predicting probabilities of wave crest elevations,correlations of parameters needed to apply these methods in the Gulf of Mexico andexamples of application of the techniques. THEORETICAL BACKGROUND The following sections summarize relations needed to calculate wave profiles and to estimate wave crest probabilities. SPEJ P. 87ˆ

scholarly journals Sufficiency of a Gaussian power spectrum likelihood for accurate cosmology from upcoming weak lensing surveys

2021 ◽  
Author(s):  
Robin E Upham ◽  
Michael L Brown ◽  
Lee Whittaker
Keyword(s):  
Power Spectrum ◽  
Random Noise ◽  
Power Spectra ◽  
Stage Iv ◽  
Wishart Distribution ◽  
Weak Lensing ◽  
Dependence Structure ◽  
Gaussian Fields ◽  
Non Gaussian ◽  
Parameter Constraints

Abstract We investigate whether a Gaussian likelihood is sufficient to obtain accurate parameter constraints from a Euclid-like combined tomographic power spectrum analysis of weak lensing, galaxy clustering and their cross-correlation. Testing its performance on the full sky against the Wishart distribution, which is the exact likelihood under the assumption of Gaussian fields, we find that the Gaussian likelihood returns accurate parameter constraints. This accuracy is robust to the choices made in the likelihood analysis, including the choice of fiducial cosmology, the range of scales included, and the random noise level. We extend our results to the cut sky by evaluating the additional non-Gaussianity of the joint cut-sky likelihood in both its marginal distributions and dependence structure. We find that the cut-sky likelihood is more non-Gaussian than the full-sky likelihood, but at a level insufficient to introduce significant inaccuracy into parameter constraints obtained using the Gaussian likelihood. Our results should not be affected by the assumption of Gaussian fields, as this approximation only becomes inaccurate on small scales, which in turn corresponds to the limit in which any non-Gaussianity of the likelihood becomes negligible. We nevertheless compare against N-body weak lensing simulations and find no evidence of significant additional non-Gaussianity in the likelihood. Our results indicate that a Gaussian likelihood will be sufficient for robust parameter constraints with power spectra from Stage IV weak lensing surveys.

Analytical bow waves for fine ship bows with rake and flare

2011 ◽  
Vol 55 (01) ◽  
pp. 1-18
Author(s):  
Francis Noblesse ◽  
Gérard Delhommeau ◽  
Patrick Queutey ◽  
Chi Yang ◽  
Hyun Yul Kim
Keyword(s):  
Parametric Study ◽  
Rake Angle ◽  
Wave Profile ◽  
Wave Crest ◽  
Bow Waves ◽  
Bow Wave ◽  
Hydrodynamic Calculations ◽  
Parametric Studies ◽  
Computational Fluid Dynamics Cfd ◽  
Analytical Relations

The bow wave generated by a steadily advancing ship is considered for a family of fine ruled ship bows with rake and flare. This family of ship bows is defined in terms of four parameters: the ship draft D, the entrance angles a and a' at the top and bottom waterlines, and the rake angle 8. The corresponding bow wave similarly depends on four parameters: the draft-based Froude number F and the three angles a, a', and 8. An extensive parametric study, based on thin-ship theory, is performed to explore the variations of the water height Z0 at the ship stem X = 0, the location X0 (measured from the ship stem) of the intersection of the bow-wave profile with the mean free-surface plane Z = 0, and the bow-wave profile, with respect to the four parameters F, a, a', and 8. This parametric study extends the previously reported similar study of the height Zb of the bow wave and the location Xb of the bow-wave crest. These two complementary parametric studies yield simple analytical relations, which extend relations given previously for wedge-shaped ship bows without rake or flare. In spite of their remarkable simplicity, the analytical relations given here yield bow waves that are comparable to computational fluid dynamics (CFD) waves given by Euler-flow calculations. The analytical relations, which explicitly account for the influence of the four primary parameters F, a, a', and 8, can be used immediately—without hydrodynamic calculations—for ship design, notably at early design stages when the precise hull geometry is not yet known. The study also provides insight for ship bow design. Specifically, it suggests that a bow with positive rake and negative flare may be beneficial, and that a bulb located aft of the stem and integrated with the hull may be an advantageous alternative to a traditional bulb protruding ahead of the bow, in agreement with the results of a hull-form optimization analysis.

Conditional Short-Crested Second Order Waves in Shallow Water and With Superimposed Current

2004 ◽  
Author(s):  
Jo̸rgen Juncher Jensen
Keyword(s):  
Shallow Water ◽  
Wave Spectrum ◽  
Ocean Waves ◽  
Offshore Structures ◽  
Second Order ◽  
Stokes Wave ◽  
Wave Crest ◽  
Wave Kinematics ◽  
Wave Approach ◽  
Non Linear

For bottom-supported offshore structures like oil drilling rigs and oil production platforms, a deterministic design wave approach is often applied using a regular non-linear Stokes’ wave. Thereby, the procedure accounts for non-linear effects in the wave loading but the randomness of the ocean waves is poorly represented, as the shape of the wave spectrum does not enter the wave kinematics. To overcome this problem and still keep the simplicity of a deterministic approach, Tromans, Anaturk and Hagemeijer (1991) suggested the use of a deterministic wave, defined as the expected linear Airy wave, given the value of the wave crest at a specific point in time or space. In the present paper a derivation of the expected second order short-crested wave riding on a uniform current is given. The analysis is based on the second order Sharma and Dean shallow water wave theory and the direction of the main wind direction can make any direction with the current. Numerical results showing the importance of the water depth, the directional spreading and the current on the conditional mean wave profile and the associated wave kinematics are presented. A discussion of the use of the conditional wave approach as design waves is given.

Influence of Wave Group Characteristics on the Motion of a Semisubmersible in Freak Waves

2014 ◽  
Author(s):  
Yanfei Deng ◽  
Jianmin Yang ◽  
Longfei Xiao
Keyword(s):  
Time Lag ◽  
Ocean Waves ◽  
Offshore Structures ◽  
Hydrodynamic Performance ◽  
Wave Crest ◽  
Time Lags ◽  
Wave Group ◽  
Freak Waves ◽  
Motion Responses ◽  
Group Characteristics

In the last few decades, the hydrodynamic performance of offshore structures has been widely studied to ensure their safety as well as to achieve an economical design. However, an increasing number of reported accidents due to rough ocean waves call for in-depth investigations on the loads and motions of offshore structures, particularly the effect of freak waves. The aim of this paper is to determine the sea conditions that may cause the maximum motion responses of offshore structures, which have a significant effect on the loads of mooring systems because of their tight relationship. As a preliminary step, the response amplitude operators (RAOs) of a semisubmersible platform of 500 meters operating depth are obtained with the frequency-domain analysis method. Subsequently, a series of predetermined extreme wave sequences with different wave group characteristics, such as the maximum crest amplitude and the time lag between successive high waves, are adopted to calculate the hydrodynamic performance of the semisubmersible with mooring systems in time-domain. The paper shows that the maximum motion responses not only depend on the largest wave crest amplitude but also the time lags between successive giant waves. This paper will provide an important reference for future designs which could consider the most dangerous wave environment.

Extreme Load-Response Mechanisms of a Tension Leg Platform due to Larger Wave Crests: Some Results of the ‘CresT’ JIP

2011 ◽  
Author(s):  
Janou Hennig ◽  
Jule Scharnke ◽  
Bas Buchner ◽  
Joris van den Berg
Keyword(s):  
Gulf Of Mexico ◽  
Extreme Event ◽  
Offshore Structures ◽  
Wave Load ◽  
Extreme Wave ◽  
Response Process ◽  
Load Response ◽  
Extreme Load ◽  
The Waves ◽  
Crest Height

For the design of ships and offshore structures the largest crest height which can be expected in their lifetime is of key importance. This was confirmed by several incidences e.g. in hurricanes in the Gulf of Mexico during the recent years. This is why MARIN started up the CresT JIP with a number of partners. The CresT JIP is now completed and some results of the extreme wave load and response mechanisms observed during model tests with a TLP will be presented in this paper. First an overview is given of the loading and response process during the most extreme event observed. As a next step the loading and response is related to the time and spatial characteristics of the waves, as it is not per definition the highest local crest or wave height that results in the most extreme dynamic response. Furthermore, the effect of different TLP design variations and short-crestedness will be discussed.

THE COVARIANCE OF EXTERNAL SHOT NOISE AT A SENSOR ARRAY

Geophysics ◽  
1973 ◽  
Vol 38 (5) ◽  
pp. 957-958
Author(s):  
T. S. Edrington
Keyword(s):  
Power Spectrum ◽  
Bessel Function ◽  
Shot Noise ◽  
Sensor Array ◽  
Random Noise ◽  
Zero Order ◽  
Random Combination ◽  
Order Bessel Function ◽  
Single Sensor ◽  
Cross Power Spectrum

Noise (of seismic and other origins) is often modeled as a shot process, i.e., as a random combination of wavelets. Specifically, if X is the random noise process and g is the deterministic waveform of the wavelet, then [Formula: see text]where the [Formula: see text] are Poisson points in time. One useful result (derived by Backus et al., 1964) under this model is that if the wavelets are propagating across a sensor array, and if the wavelet origins are uniformly distributed in azimuth, then the cross‐power spectrum for a pair of sensors is the product of the power spectrum at a single sensor and a zero‐order Bessel function. In the notation of Backus et al., [Formula: see text]

Simplified Method to Assess Dynamic Response of Jacket Type Offshore Platforms Subjected to Wave Loading

2004 ◽  
Author(s):  
B. Asgarian ◽  
A. Mohebbinejad ◽  
R. H. Soltani
Keyword(s):  
Dynamic Response ◽  
Dynamic Characteristics ◽  
Offshore Structures ◽  
Center Of Gravity ◽  
Simplified Model ◽  
Mode Shapes ◽  
Stokes Wave ◽  
Wave Crest ◽  
Offshore Platforms ◽  
Wave Loading

Dynamic response of offshore platforms subjected to wave and current is of fundamental importance in analysis. The first step in dynamic analysis is computing dynamic characteristics of the structure. Because of pile-soil-structure and fluid-structure interactive effects in the dynamic behavior, the model is very complex. In this paper a simplified model for dynamic response of jacket-type offshore structures subjected to wave loading is used. Since wave loads on offshore platforms vary with time, they produce dynamic effects on structures. In the model used in this paper, all of the structural elements are modeled as vertical equivalent cylinders that are in the direction of the wave crest. In the simplified model, the degrees of freedom are considered at the seabed, jacket horizontal elevations and topside center of gravity. The stiffness properties of the model are computed considering the stiffnesses of the vertical bracings, legs and piles. The structural mass is considered as lumped nodal masses at horizontal elevations and topside center of gravity. The hydrodynamic added mass in addition to the structural masses was modeled at jacket horizontal elevations. In the simplified model, for computing wave loading, the projected areas of all members in the direction of the wave crest are considered. For the wave loading calculation, Morison equation is considered. The fluid velocities are calculated for the submerged portions of the structures using a computer program developed for this purpose. In this program both Airy and Stokes wave theories can be used. This model can be used to assess dynamic properties and responses of jacket type offshore structures. The model is used to assess the response of three jacket-type offshore platforms in Persian Gulf subjected to loadings due to several waves. The results in terms of dynamic characteristics and responses were compared with the more accurate analysis results using SACS software. The results are in a good agreement with the SACS analysis outputs, i.e. structural periods, mode shapes and dynamic response.

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