Spectral analyses of sea-state wave data for the development of a regional-sensitive spectral model

2012 ◽  
pp. 211-214
Author(s):  
M Liew ◽  
M Wahap ◽  
E Lim ◽  
N Abdullah
Keyword(s):  
Spectral Model ◽  
Sea State ◽  
Spectral Analyses ◽  
Wave Data ◽  
State Wave

An Idealization of Wave Scatter Diagram for Spectral Fatigue Analysis

2009 ◽  
Author(s):  
Min Han Oh ◽  
Ki Myung Lee ◽  
Young Sik Jang
Keyword(s):  
Fatigue Analysis ◽  
Scatter Diagram ◽  
Analysis Method ◽  
Sea State ◽  
Environmental Loads ◽  
Wave Data ◽  
Wave Measurements ◽  
Spectral Models ◽  
Wave Heights ◽  
Significant Wave Heights

A spectral fatigue analysis method is most popularly applied for the detailed design of FPSOs. As the environmental loads at the installation site are directly calculated in the spectral analysis, this method gives the most reliable results although it needs much time-consuming works to fully reflect the environmental loads. As the technology of wave measurements advances, the measured wave data increase. Also their spectral models are very complicated because these include many wave components such as swells and wind seas. Since much time and effort are needed to treat these enormous and complicated wave data for the spectral fatigue analysis, a rational idealization of wave data is definitely required. In this paper, wave scatter diagram at Offshore Nigeria was reviewed and their idealization method was proposed. The influence level of each sea state of the wave scatter diagram was identified considering the fatigue damage levels estimated from the significant wave heights and dominant fatigue load RAOs. The sea states giving small fatigue damages were lumped symmetrically by merging or disregarding while those giving large fatigue damages were kept as original. For the validation of this method, the comparisons of dominant fatigue loads and representative fatigue damages were presented for the idealized wave scatter diagram and the original one. From these comparison works, it was confirmed that the idealized wave scatter diagram gives reliable results with reduced amount of calculation work.

The Inertial Pressure Concept for Determining the Wave Forces on Submerged Bodies

1982 ◽  
Vol 104 (1) ◽  
pp. 47-52
Author(s):  
T. E. Horton ◽  
M. J. Feifarek
Keyword(s):  
Three Dimensional ◽  
Offshore Structures ◽  
Empirical Approach ◽  
Wave Forces ◽  
Morison Equation ◽  
Sea State ◽  
Wave Kinematics ◽  
State Wave

A new concept is presented which is aimed at improving the methodology for determining the wave forces on offshore structures. The Inertial Pressure Concept (IPC) is based on a direct, empirical approach to calculating forces. The resulting method can be formulated to include realistic sea state wave kinematics while not being dependent on a particular kinematic representation. Futhermore, the method should be as easy to apply as the Morison equation, but will allow diffraction and three-dimensional aspects to be considered.

scholarly journals ANALYTICAL MODELLING OF SEAKEEPING QUALITIES OF CONTAINER VESSEL

2020 ◽  
Vol 30 (1) ◽  
pp. 78-87
Author(s):  
N. M. Konon ◽  
◽  
◽  
◽  
Keyword(s):  
Wave Height ◽  
Wave Spectrum ◽  
Ship Design ◽  
Design Parameters ◽  
Ship Motions ◽  
Height Distribution ◽  
Added Resistance ◽  
Sea State ◽  
Wave Data ◽  
Deck Wetness

The design of ships or any other floating systems intended to operate on or close to the surface of the sea is controlled to a large extent by what is usually referred to as seakeeping, or, in more common terminology, safety at sea. This is a primary consideration and criteria, which has to be fully met. Safety of a ship naturally includes the crew, cargo and the hull itself. Seakeeping is, indeed, a generalized term and reflects the ship's capability to survive all hazards at sea such as collision, grounding, fire, as well as heavy-weather effects related to the environment in general and waves in particular. The two most likely types of failure under these conditions are due to structural causes and capsizing resulting from insufficient stability under severe weather conditions. Such criteria as economical navigation of the ship as related to speed-keeping abilities, fuel consumption, avoidance of damage to ship components and cargo, and comfort to crew or passengers, or both, are key items. The operational limits of electronic equipment, mechanical components and weapon systems on board warships are other aspects of sea keeping. In this work it is highlighted that seakeeping is a generalized term that includes a wide variety of subjects such as ship motions (amplitudes, accelerations, phases), deck wetness, slamming, steering in waves, added resistance, hydrodynamic loadings (pressures, forces, moments) and transient loads. Since the ship environmental operability or its sea keeping characteristics are closely linked to the severity of the sea, the description of the seaway is usually considered as an integral part of sea keeping. It is taken into consideration that the severity of the sea cannot be considered in absolute terms, since for each floating system, be it a ship, a platform or a buoy, the intensity of the sea state can only be determined in terms of the system's responses. Hence, different thresholds apply to different problems, and sea state 4 may be just as severe for a small patrol craft as sea state 8 may be for a larger containership. Hence, the characteristics and frequency of occurrence of waves in specific sea zones are required if a possible reduction in the system environmental operability is expected. It is demonstrated that most texts or papers, which deal with the overall question of sea keeping, devote some attention to the basic phenomena, that is, the seaway and the motions of the ship or other floating platforms as a result of the excitation imposed by the seaway. Ship motions, as such, do not always constitute the criteria for sea keeping, and much more often other responses directly related to the magnitude and phasing of the motions or the resulting velocities and accelerations constitute the prime cause for exhibiting good or bad sea keeping qualities. Such responses could be a function of the motion only, as in the case of added resistance or hydrodynamic pressures, or they could be a function of motion and other design parameters, such as freeboard in the case of deck wetness or the longitudinal weight distribution in the case of vertical bending moments. In this work, latest methods of modeling and computation for body-wave interactions described and compared with data observed for container carrier. The foregoing calculation routine Судноводіння | Shipping & Navigation ISSN 2306-5761 | 2618-0073 30-2020 Національний університет «Одеська морська академія» 79 is fairly well accepted today among naval architects specializing in the sea keeping aspects of the ship design process. Differences between the results obtained by various techniques as presented by the available computer programs are insignificant. However, since the regular-wave results are of little or no value except as input for the more realistic long- and short-term response predictions in a real seaway environment, it is important to determine which wave data information and what statistical extrapolation techniques are used to obtain the latter. The format used to describe the seaway in most ship response calculations is the wave spectrum. However, since measured spectrum for a specific sea zone or route are very rarely available, it is often necessary to use spectrum measured in one location for predictions in another location. In such a case, while the basic spectruml shape and scatter remain unchanged, the percentage of wave height distribution would vary to represent realistic conditions for the sea area in question. Such data usually are based on observations, and assuming the sample is large enough the distribution of expected wave heights should be quite reliable. An alternative approach often used in ship design is to utilize one of several theoretical spectruml formulations [2, 3, 4] such as the Pierson-Moskowitz one-parameter spectrum, the ISSC spectrum, the JONSWAP spectrum, and other. In each of these cases, some input parameters are required usually in the form of wave height, period, peak frequency, fetch, etc. The reliability of the wave data depends in these cases both on the quality of the input parameter and the adequacy of the theoretical formulation.

Theoretical Analysis of Average Wave Steepness Related to Peak Period or to Mean Period

2010 ◽  
Author(s):  
Felice Arena ◽  
Carlos Guedes Soares ◽  
Petya Petrova
Keyword(s):  
Theoretical Analysis ◽  
North Sea ◽  
Significant Wave Height ◽  
Extreme Values ◽  
Wave Steepness ◽  
Sea State ◽  
Peak Period ◽  
Wave Data ◽  
Average Wave ◽  
Jonswap Spectrum

The average wave steepness may be defined as the ratio between the significant wave height Hs and the wavelength associated to either the zero-up-crossing mean period Lm or the peak period Lp (Bitner Gregersen et al., 1998). This parameter may be calculated from wave data at fixed locations, as well as by starting from theoretical spectra. In this paper the average wave steepness is firstly analyzed by considering a JONSWAP spectrum. It is shown that for this spectrum the ratio Sm = Hs/Lm, as well as Sp = Hs/Lp, depends upon the values of the spectrum parameters. The theoretical values are then compared with wave data in the Mediterranean Sea, Pacific Ocean, Atlantic Ocean and North Sea. The values of Sm and Sp are deeply investigated for severe sea states, with large values of Hs. It is obtained that in severe sea state the observed values of wave steepness, defined as either Sm or Sp, are always in the range defined by theoretical spectra; therefore, the extreme values of Sm and Sp, which are of interest for naval architecture, may be obtained from theoretical analysis, as a function of extreme values of Hs.

A unified two-parameter wave spectral model for a general sea state

1981 ◽  
Vol 112 (-1) ◽  
pp. 203 ◽  
Author(s):  
Norden E. Huang ◽  
Steven R. Long ◽  
Chi-Chao Tung ◽  
Yeli Yuen ◽  
Larry F. Bliven
Keyword(s):  
Spectral Model ◽  
Sea State ◽  
Two Parameter ◽  
Parameter Wave

Comments on Hoffman and Karst: “The Theory of the Rayleigh Distribution and Some of Its Applications”

1976 ◽  
Vol 20 (04) ◽  
pp. 235-238
Author(s):  
J. Dattatri ◽  
N. Jothi Shankar ◽  
H. Raman
Keyword(s):  
West Coast ◽  
Additional Data ◽  
Rayleigh Distribution ◽  
Southwest Monsoon ◽  
The West ◽  
Sea State ◽  
West Coast Of India ◽  
Wave Data ◽  
Wide Range ◽  
Strong Winds

Hoffman and Karst have recently reported, in the title paper, an excellent review of the Rayleigh distribution and some of its applications. They mention that for many ocean zones there is a lack of measured wave data. The primary purpose of this note is to supplement their conclusions with some additional measured ocean wave data. These data, from the west coast of India near Mangalore, where a new major port has recently been commissioned, were obtained over a period of 18 months during 1968–1969, using a frequency-modulated subsurface pressure-type recorder. The analysis of this data has been reported in an earlier paper [1]. 3 More recently, during 1974, some additional data were obtained using an accelerometer-type Wave Rider buoy. The data obtained from the subsurface recorder need to be modified to account for the pressure response and instrument factors, and considerable uncertainties are involved in this computation. On the other hand, the Wave Rider data need no such modifications and can be considered to be more representative of the sea state at the locality. As such, the surface recorder data (Wave Rider data) have been utilized mainly in the preparation of this note, and the subsurface recorder data are furnished for the purpose of comparison. The west coast of India is under the influence of the southwest monsoon during the months of June to September, when the prevailing strong winds cause heavy seas. During the nonmonsoon period, the Arabian Sea is practically calm, with long low swells. Hence the data used herein cover a wide range of conditions from the 'sea' to the 'swell.'

Vuv Spectra Y to Mo

1988 ◽  
Vol 102 ◽  
pp. 239
Author(s):  
M.S.Z. Chaghtai
Keyword(s):  
Excited States ◽  
Spectral Analyses ◽  
Vuv Spectra

Using R.D. Cowan’s computations (1979) and parametric calculations of Meinders et al (1982), old analyses are thoroughly revised and extended at Aligarh, of Zr III by Khan et al (1981), of Nb IV by Shujauddin et Chaghtai (1985), of Mo V by Tauheed at al (1985). Cabeza et al (1986) confirmed the last one largely.Extensive studies have been reported of the 1–e spectra, Zr IV (Rahimullah et al 1980; Acquista and Reader 1980), Nb V (Shujauddin et al 1982; Kagan et al 1981) and Mo VI (Edlén et al 1985). Some interacting 4p54d2levels of these spectra have been reported from our laboratory, also.Detailed spectral analyses of transitions between excited states have furnished complete energy values for J ≠ 1 levels of these spectra during 1970s and 80s. Shujauddin et al (1982) have worked out Nb VI and Tauheed et al (1984) Mo VII from our lab, while Khan et al (1981) share the work on Zr V with Reader and Acquista (1979).

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