Experimental Determination of the Effect of Bow Shape on the Wave Drift Load

2017 ◽  
Author(s):  
Anne Boorsma ◽  
Kees Aalbers ◽  
Riaan van ‘t Veer ◽  
René Huijsmans
Keyword(s):  
Linear Theory ◽  
Wave Height ◽  
Measurement Data ◽  
Ship Motions ◽  
Hull Form ◽  
Small Motion ◽  
Water Line ◽  
Wave Drift ◽  
Wave Heights ◽  
The Mean

In the last forty years wave drift loads have been calculated with methods based on the near-field theory (hull pressure integration, Pinkster [4]) and/or the far field method (linear momentum theory). Both methods use linear theory and through its formulation ignore the ship’s hull form above the mean water line. It is evident that in survival sea-states the small motion assumptions are violated and the hull form above the mean water line can affect the motion characteristics of the ship and the drift loads. In order to get more insight in this effect, SBM has conducted a systematic model test campaign at the TU Delft using an Aframax size tanker. The campaign included tests with two different bow shapes: the original bow with flare, and a wall-sided bow. Horizontal loads on the complete vessel and a section of the bow only were measured accompanied by measurements of the ship motions and relative wave heights. Measurements were performed for various wave heights and periods. Numerous repeat tests were conducted to establish the confidence level of the measurement data. Measurements have shown motions and relative wave heights are dependent on wave height. It was suggested that viscous damping may play a part in this. The relative wave height in high waves is affected by bow shape; namely the finite draft, the flare and the bulb. How this departure from linear theory affects the forces on the vessel should be investigated further.

Distribution of Wave Height Maxima in Storm Sea States

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Z. Cherneva ◽  
C. Guedes Soares ◽  
P. Petrova
Keyword(s):  
Wave Height ◽  
Exceedance Probability ◽  
Third Order ◽  
Wave Statistics ◽  
The North ◽  
Empirical Probability ◽  
Probability Densities ◽  
Wave Heights ◽  
The North Sea ◽  
The Mean

The effect of the coefficient of kurtosis, as a measure of third order nonlinearity, on the distribution of wave height maxima has been investigated. Measurements of the surface elevation during a storm at the North Alwyn platform in the North Sea have been used. The mean number of waves in the series is around 100. The maximum wave statistics have been compared with nonlinear theoretical distributions. It was found that the empirical probability densities of the maximum wave heights describe qualitatively the shift of the distribution modes toward higher values. The tendency for the peak of distribution to diminish with an increase in the coefficient of kurtosis up to 0.6 is also clearly seen. However, the empirical peak remains higher than the theoretically predicted one. The exceedance probability of the maximum wave heights was also estimated from the data and was compared with the theory. For the highest coefficients of kurtosis, estimated at nearly 0.6, the theoretical distribution approximates very well the empirical data. For lower coefficients of kurtosis, the theory tends to overestimate the exceedance probability of the maximum wave heights.

scholarly journals Assessment of Current Influence on the Wind Wave Parameters in the Black Sea based on Numerical Modeling

2020 ◽  
Author(s):  
А. D. Rybalko ◽  
S. A. Myslenkov ◽  
◽  
◽  
◽  
...  
Keyword(s):  
Wave Height ◽  
Black Sea ◽  
Wind Waves ◽  
The Black Sea ◽  
Spatial And Temporal Variability ◽  
Positive Contribution ◽  
Wave Parameters ◽  
Wave Heights ◽  
The Mean ◽  
Average Wave

Currents affect wind waves parameters. The issue of significance of this influence for the Black Sea has not been studied properly. The purpose of this paper is to study the scale, spatial and temporal variability of influence of sea currents on the wave height in the Black Sea. The research was carried out based on simulation using SWAN wave model and an irregular computational grid. Two datasets were used as input data: the NCEP/CFSv2 wind reanalysis and current data taken from the Remote Sensing Department's archive of the Marine Hydrophysical Institute of RAS. It is shown that the average wave height mainly decreases when sea current is considered. These changes are insignificant relative to the average values of wave heights. The greatest negative changes are typical of the western and northeast parts of the Black Sea. Here, the consideration of circulation reduces the average annual wave heights by up to 0.1 m. A slight increase in the average wave height is typical of the southern and southeast parts of the sea as well as the northwest shelf. The positive contribution to the mean annual wave heights is up to 0.02 m. When taken into account, currents change wave parameters at a maximum in winter months and at a minimum in late spring and summer. Currents change the mean monthly wave heights by –0.04…0.06 m in January and February in most parts of the sea. The contribution of currents is close to zero in June and July. The maximum changes in wave height reach 6–10 % of the monthly average.

scholarly journals WAVE INVESTIGATIONS IN SHALLOW WATER

1970 ◽  
Vol 1 (12) ◽  
pp. 10 ◽  
Author(s):  
Winfried Siefert
Keyword(s):  
Shallow Water ◽  
Wave Height ◽  
Wind Direction ◽  
Tidal Flat ◽  
Propagation Direction ◽  
Elbe Estuary ◽  
Zero Crossing ◽  
Wave Heights ◽  
The Mean ◽  
The Waves

Examination of the significant heights of zero-crossing waves in the Elbe Estuary has yielded two noteworthy results: 1 In the deeper water of the estuary, the value of the quotient relating the significant and the mean wave heights is larger than on the bordering tidal flat. 2. The value of this function is dependent on the height of the waves; on the tidal flat this dependency is considerably more sensitive than in deeper water. With increasing wave height the value of significant wave height divided by mean height becomes smaller The propagation direction of waves moving onto the tidal flat is contingent upon the position of intertidal channels Such channels sharply reduce the possible propagation directions The waves nearly always move up-channel regardless of the wind direction It is possible to derive special wave period and wave height distributions representing the conditions m very shallow water.

Distribution of Wave Height Maxima in Storm Sea States

2008 ◽  
Author(s):  
Zhivelina Cherneva ◽  
C. Guedes Soares ◽  
Petya Petrova
Keyword(s):  
Wave Height ◽  
Exceedance Probability ◽  
Third Order ◽  
Wave Statistics ◽  
The North ◽  
Probability Densities ◽  
Distribution Mode ◽  
Wave Heights ◽  
The North Sea ◽  
The Mean

The effect of the coefficient of kurtosis as a measure of the nonlinearity of third order on the distribution of the wave height maxima has been investigated. Measurements of the surface elevation during a storm at the North Alwyn platform in the North Sea have been used. The mean number of waves in the series is around 100. The maximum wave statistics have been compared with nonlinear theoretical distributions. It was found that the empirical probability densities of the maximum wave heights describe qualitatively the shift of the distribution mode towards higher values. The tendency for the peak of distribution to diminish with increase of the coefficient of kurtosis up to 0.6 is also clearly seen. However, the empirical peak remains higher than the theoretically predicted one. Exceedance probability of the maximum wave heights was also estimated from the data and was compared with the theory. For the highest coefficients of kurtosis nearly 0.6 the theoretical distribution approximates very well the empirical data. For lower coefficients of kurtosis the theory tends to overestimate the exceedance probability of the maximum wave heights.

Low-Frequency Phenomena Associated With Vessels Moored at Sea

1975 ◽  
Vol 15 (06) ◽  
pp. 487-494 ◽  
Author(s):  
J.A. Pinkster
Keyword(s):  
Wave Height ◽  
Low Frequency ◽  
Second Order ◽  
Irregular Waves ◽  
Ship Motions ◽  
Wave Forces ◽  
Mooring System ◽  
Frequency Wave ◽  
First Order ◽  
The Mean

Abstract The influence of the low-frequency-wave-drifting force on the motions of moored vessels and the loads in the mooring system is demonstrated from results of model tests in irregular waves. The origin of the wave drifting force is discussed and methods for calculating the mean drifting force are reviewed. To facilitate calculation of the low-frequency-wave drifting force on an object in irregular waves, an existing method using the mean drifting force in regular waves is generalized. The results of calculations using the method introduced in this paper are compared with previously published test results. Finally, some remarks are added concerning effects that have not been accounted for in existing calculation methods. Introduction A vessel moored at sea in stationary conditions with regard to waves, wind, and current is subjected to forces that tend to shift it from the desired position. For a given vessel and position in the position. For a given vessel and position in the horizontal plane, the motions depend on both the mooring system and the external forces acting on the vessel. In steady conditions, the forces caused by a constant wind and current are constant quantities for a given heading angle of the vessel. The forces caused by a stationary irregular sea are of an irregular nature and may be split into two parts: first-order oscillatory forces with wave parts: first-order oscillatory forces with wave frequency, and second-order, slowly varying forces with frequencies much lower than the wave frequency.The first-order oscillatory wave forces on a vessel cause the well known ship motions whose frequencies equal the frequencies present in the spectrum of the irregular waves. These are the linear motions of surge, sway, and heave and the three angular motions of roll, pitch, and yaw. In general, the first-order wave forces are proportional to the wave height, as are the ensuing motions. The magnitude of the linear oscillatory motions is in the order of the height of the waves.The second-order wave forces, perhaps better known as the wave drifting forces, have been shown to be proportional to the square of the wave height. These forces, though small in magnitude, are the cause of the low-frequency, large-amplitude, horizontal motions sometimes observed in large vessels moored in irregular waves. Tests run in irregular waves in wave tanks of the Netherlands Ship Model Basin revealed a number of properties and effects of the low-frequency-wave properties and effects of the low-frequency-wave drifting force that are discussed here using the results of two test programs.The first of these programs concerns tests run with the model of a 125,000-cu m LNG carrier moored in head seas with an ideal linear mooring system. The second program deals with a 300,000-DWT VLCC moored with a realistic nonlinear bow hawser to a single-buoy mooring in waves, wind, and current coming from different directions.The results of the tests with the LNG carrier are shown in Figs. 1 through 3, while the results of the tests with the 300,000-DWT VLCC are shown in Fig. 4. All results are given in full-scale values. Fig. 1 shows the wave trace and the surge motion of the LNG carrier to a base of time. SPEJ P. 487

scholarly journals Wave height and period on 16 March, 21 April, and 22 September 2019, in the Ujung Batee coastal waters and Lampanah coastal waters, Aceh Besar District, Indonesia

2021 ◽  
Vol 869 (1) ◽  
pp. 012040
Author(s):  
I Setiawan ◽  
S M Yuni ◽  
M Ulfah ◽  
S Purnawan ◽  
H A Haridhi ◽  
...  
Keyword(s):  
Wave Height ◽  
Coastal Waters ◽  
Measurement Data ◽  
Research Station ◽  
Wave Data ◽  
Wave Measurements ◽  
Wave Measurement ◽  
Wave Heights ◽  
Station Location ◽  
Sea Wave

Abstract Waves are one of the sea parameters that affect the rate of retreat of the coastline. This research investigation was carried out in the coastal waters of Ujong Batee and Lampanah, Aceh Besar District on 16 March, 21 April, and 22 September 2019, with the aim of examining wave parameters, namely wave height and period. Then the wave measurement data sampled at the research station location was carried out by purposive random sampling method. Sea wave data were taken using a scale board that has been labeled with numbers and a stopwatch. Wave measurements were carried out approximately 1000 times. Then the sea wave data is processed to obtain the wave height and period and then analyzed. The results obtained that the wave heights on 16 March, 21 April, and 22 September 2019 were 67 cm, 83 cm, and 80 cm in Ujong Batee and 55 cm, 67 cm, and 66 cm in Lampanah. While the wave period is 12 seconds on March 16, April 21, and September 22 in Ujong Batee and Lampanah. Thus, the wave height and period at both locations ranged from 50 cm to 80 cm and 12 s.

Estimating wave heights from pressure data at the bed

2014 ◽  
Vol 743 ◽  
Author(s):  
A. Constantin
Keyword(s):  
Linear Theory ◽  
Wave Height ◽  
Water Wave ◽  
Small Amplitude ◽  
Wave Amplitude ◽  
Pressure Measurements ◽  
Two Dimensional ◽  
Pressure Data ◽  
Hydrostatic Approximation ◽  
Wave Heights

AbstractWe provide some estimates for the wave height of a two-dimensional travelling gravity water wave from pressure measurements at the flat bed. The approach is applicable without limitations on the wave amplitude. It improves the classical estimates available if one relies on the hydrostatic approximation or on the linear theory of waves of small amplitude.

scholarly journals CRITICAL TRAVEL DISTANCE OF WAVES IN SHALLOW WATER

1974 ◽  
Vol 1 (14) ◽  
pp. 24
Author(s):  
Winfried Siefert
Keyword(s):  
Shallow Water ◽  
Wave Height ◽  
Water Wave ◽  
Characteristic Parameter ◽  
Wave Climate ◽  
Height Distribution ◽  
Shallow Water Wave ◽  
German Coast ◽  
Wave Heights ◽  
The Mean

A new criterion for shallow water wave analysis is evaluated from prototype data off the German coast on the reef and wadden sea areas south of the outer Elbe river. Correlations of mean wave heights H with mean wave peri- - H ods T, and wave height distribution factors C. /•, = —l/3 t-^ respectively show that the mean periods and both complete height and period distributions of waves in shallow water can be expressed as functions of mean height and topography. So the mean wave height H proves to be the characteristic parameter for the description of the complete shallow water wave climate. The upper envelop of the values H = f (meteorology, topography) is defined as the case of fully developed sea, which leads to the function of the highest mean wave heights Hmax.

Spatial Variability of Physical Parameters and Processes in Two Field Soils

1991 ◽  
Vol 22 (5) ◽  
pp. 327-340 ◽  
Author(s):  
K. Høgh Jensen ◽  
J. C. Refsgaard
Keyword(s):  
Transport Model ◽  
Flow Direction ◽  
Measurement Data ◽  
Flow Simulation ◽  
Solute Concentration ◽  
Conclusive Evidence ◽  
Physical Parameters ◽  
Effective Parameters ◽  
The Mean ◽  
Tracer Experiments

A numerical analysis of solute transport in two spatially heterogeneous fields is carried out assuming that the fields are composed of ensembles of one-dimensional non-interacting soil columns, each column representing a possible soil profile in statistical terms. The basis for the analysis is the flow simulation described in Part II (Jensen and Refsgaard, this issue), which serves as input to a transport model based on the convection-dispersion equation. The simulations of the average and variation in solute concentration in planes perpendicular to the flow direction are compared to measurements obtained from tracer experiments carried out at the two fields. Due to the limited amount of measurement data, it is difficult to draw conclusive evidence of the simulations, but reliable simulations are obtained of the mean behaviour within the two fields. The concept of equivalent soil properties is also tested for the transport problem in heterogeneous soils. Based on effective parameters for the retention and hydraulic conductivity functions it is possible to predict the mean transport in the two experimental fields.

scholarly journals Estimation of Significant Wave Heights from ASCAT Scatterometer Data via Deep Learning Network

2021 ◽  
Vol 13 (2) ◽  
pp. 195
Author(s):  
He Wang ◽  
Jingsong Yang ◽  
Jianhua Zhu ◽  
Lin Ren ◽  
Yahao Liu ◽  
...  
Keyword(s):  
Deep Learning ◽  
Wave Height ◽  
Significant Wave Height ◽  
Incidence Angle ◽  
Ocean Waves ◽  
Global Scale ◽  
Learning Technology ◽  
Sea State ◽  
Significant Wave ◽  
Wave Heights

Sea state estimation from wide-swath and frequent-revisit scatterometers, which are providing ocean winds in the routine, is an attractive challenge. In this study, state-of-the-art deep learning technology is successfully adopted to develop an algorithm for deriving significant wave height from Advanced Scatterometer (ASCAT) aboard MetOp-A. By collocating three years (2016–2018) of ASCAT measurements and WaveWatch III sea state hindcasts at a global scale, huge amount data points (>8 million) were employed to train the multi-hidden-layer deep learning model, which has been established to map the inputs of thirteen sea state related ASCAT observables into the wave heights. The ASCAT significant wave height estimates were validated against hindcast dataset independent on training, showing good consistency in terms of root mean square error of 0.5 m under moderate sea condition (1.0–5.0 m). Additionally, reasonable agreement is also found between ASCAT derived wave heights and buoy observations from National Data Buoy Center for the proposed algorithm. Results are further discussed with respect to sea state maturity, radar incidence angle along with the limitations of the model. Our work demonstrates the capability of scatterometers for monitoring sea state, thus would advance the use of scatterometers, which were originally designed for winds, in studies of ocean waves.

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