Showing papers on "Wave height published in 1974"

Computation of set-up, longshore currents, run-up and overtopping due to wind-generated waves

Abstract: The main problem dealt with in this thesis is the calculation of certain effects caused by random waves breaking on a slope. The solution to this problem is greatly complicated by the fact that wave breaking is a highly nonlinear process. The flow field is further complicated by far stronger in homogeneities than those occurring outside the breaker zone, by air entrainment and by generation of turbulence. No realistic deductive treatment of it has been developed so far. Even for the simpler case of periodic waves, empirical knowledge of certain macroscopic properties of the breakers is still an integral part of calculations relating to the surf zone. An attempt has been made in this thesis to apply this knowledge in a formulation incorporating the stochastic nature of wind-generated waves. The computations are of two distinct categories, those relating to comparatively gentle slopes and those relating to comparatively steep slopes. A summary of the results will be given in the following. The energy variation is calculated in chapter 5 by clipping a fictitious wave height distribution, which theoretically would be present if breaking did not occur, at an upper limit which is determined from an adapted breaking criterion for periodic waves. The computed results are in fair agreement with measurements carried out on a plane slope. Knowledge of the energy variation permits the radiation stresses to be evaluated, which in turn are necessary for the calculation of the set-up and the longshore current velocity profiles. A comparison of the calculated set-up profiles with empirical data has not given conclusive results. Good agreement has been found with field data, but not with laboratory data, which locally showed a systematically smaller rise towards the shore than would be expected on the basis of the measured or calculated wave height variations. However, there is some uncertainty with respect to the system used for measuring the set-up in the laboratory, so that is not known to which extent the differences are real or apparent.

New wave pressure formulae for composite breakwaters

Abstract: A proposal is made for new wave pressure formulae, which can be applied for the whole ranges of wave action from nonbreaking to postbreaking waves with smooth transition between them. The design wave height is specified as the maximum wave height possible at the site of breakwater. The new formulae as well as the existing formulae of Hiroi, Sainflou, and Minikin have been calibrated with the cases of 21 slidings and 13 nonslidings of the upright sections of prototype breakwaters. The calibration establishes that the new formulae are the most accurate ones.

Wave Group Formation among Storm Waves

Abstract: Wave data obtained m the North Sea for stormy weather conditions are analyzed to determine the extent of wave group formation among large waves; i.e. the number of large waves succeeding each other in one single run. Three periods associated with the passage of high sea states are examined. The average correlation between succeeding wave heights is found to be +0.2H, which indicates that wave heights do have a "memory". Wave group formations are found to be more pronounced when the sea is growing than decaying. The average lengths of wave runs are calculated.

A transmission line wave height transducer

Abstract: A simple but accurate wave transducer has been developed for measuring waves on inland and coastal waters, consisting of a tunnel diode oscillator, using an open transmission line to sense the water-level. The output signal is a pulse train with a period linearly proportional to the length of transmission line above the water surface.

Extreme levels arising from meteorological surges

Abstract: The design of coastal works depends on estimating the probabilities of extreme water levels, as well as of waves Previous studies of surge-affected levels have extrapolated observed annual maxima or the n highest levels in n years to predict rarer events In addition to using these well-established methods, m this study of tide levels on the Essex coast of Britain a long term record of extreme levels was synthesised by adding surge residuals at the time of predicted HW to predicted HW levels, treating them as statistically independent events Many more large surge residuals have been measured than extreme water levels as many surges are associated with small tides Events with return periods up to 1000 years may be estimated without extrapolating beyond the range of observed surge residuals and predicted tides This method is assessed in relation to previous methods and information relevant to the design of coastal works in the south western part of the North Sea was obtained In addition to forecasting the probabilities of high tide levels, the study included wave forecasts and the encounter probabilities of combinations of sea level and wave height for various aspects of coastal developments.

A Weather Model for Simulating Offshore Construction Alternatives

Abstract: The time and cost required for offshore construction operations are often dominated by the influence of weather, particularly wave heights. Historical wave height data can be summarized in a simple probabilistic model that can be used in a Monte Carlo simulation of the construction operations. Such a simulation has been used effectively to evaluate alternative bids on pipeline projects in the Gulf of Mexico. This paper describes the Markovian wave height model we have incorporated in the simulation.

Wave statistics for March 1968 North Atlantic storm

Abstract: A recent 1968 North Atlantic storm is investigated. The statistics of the wave parameters, namely, wave height and period, are studied. The wave data are analyzed in the time domain to obtain wave parameters by Tucker's method. Spectrum analysis is undertaken to obtain the same statistical quantities. The parameters calculated by the two methods are compared with each other. Overall, the two methods are found to agree within acceptable limits. The statistical distribution, e.g., Rayleigh, of the individual wave heights and wave periods in a record is studied with reference to the spectral width parameter. The theoretical correlation of the distribution of height is found to be mostly poor, whereas the Rayleigh distribution of the square of the period yielded better correlation coefficients. It is argued that the significant wave height varies either with the square of the mean wave period or with both the period and its square in a linear fashion. The joint distribution of these two quantities for this storm is discussed.

Swimming pool alarm system and method with adjustable sensitivity

Abstract: A swimming pool alarm system which is responsive to the height of waves resulting from unauthorized entry, and which includes provision for changing its sensitivity. An alarm circuit is provided with a switch having a plurality of stationary contacts spaces apart as a function of wave height, and another contact movable by a float positioned in the water. A switch is provided to select the stationary contact which corresponds to a preselected wave height of interest.

Height-Period Joint Probabilities in Hurricane Camille

Abstract: An ocean data gathering program in the Gulf of Mexico obtained continuous wave records from six offshore petroleum production platforms during the passage of several hurricanes and tropical storms. This note describes the joint probability of wave heights and periods as hurricane Camille (August 1969, one of the most severe hurricanes on record) approached and passed near one of the six platforms. This analysis was motivated by a need to estimate probabilities of wave height and period combinations which produce bottom pressures capable of triggering submarine mudslides off the Mississippi River delta. The observed joint probabilities are compared to a frequently used joint distribution. The results presented are useful for calculating other probabilities which are functions of hurricane wave height and period. Applications include determination of differential bottom pressures between wave crests and troughs capable of triggering submarine slumping on continental shelves, calculation of drag and inertial forces exerted on structures, and estimation of vessel motion in high seas.

On Motions of a High Speed Planning Boat in Regular Head Sea

Abstract: Recent advances in the research of ship motion in a seaway have enabled to predict the ship motion. These researches, however, are restricted to those of displacement type ships such as a merchant ship and a destroyer, and as to behaviours of high speed planing boat in a seaway few available researches have been published.In the present study the towing tank test of a torpedo boat model was carried out in regular head wave and experimental data were discussed along with the results calculated by Ordinary Linear Strip Method (O. S. M.).The conclusions deduced from these studies are as follows, 1) High frequency components appear in pitching and heaving oscillations at higher encounter frequency, that is, at higher speed and shorter wave. In these regions, each mean value of the pitching and heaving oscillation becomes larger compared with the trim angle and vertical displacement in still water.2) The motions calculated by the O. S. M. give good agreement with experimental data for Fn< 0.5, but they do not always for higher Froude number.3) In spite of much higher frequency components in the motions, the amplitudes of pitching and heaving motions are almost proportional to those of the wave, that is, the linearity to wave height is nearly conserved.

Fifth Order Stokes Wave Profiles

Abstract: Fifth-order Stokes wave theory is often used to predict particle velocities and accelerations for substitution in wave force equations. As with all wave theories, validity must be checked in shallow water for the particular application and wave parameters: height H , period T , and water depth d . However, it is not clear that a single test of validity is reasonable for diverse engineering applications. In this note, a monotonic wave profile is one that continually decreases with increasing distance from the crest. Figures are presented showing characteristic wave profiles.

Beach foreshore sedimentology and morphology in the Apostle Islands of northern Wisconsin

Abstract: Foreshore sediments and slopes of 39 beaches in the Apostle Islands of northern Wisconsin were found to be related to various measures of wave energy, wave steepness and offshore slope. Stepwise regression analysis was used to link the response variables with the process variables. Wave parameters were hindcast using the S-M-B wave hindcasting procedure and were also inferred from foreshore morphology. Mean grain size of the foreshore sediments appears to be very marginally related to the process variables and is primarily a function of local source materials. Sorting of the sediments shows a strong positive relationship with the percentage of gravel in the sample and a weak positive relationship with angle of wave approach and wave height indicating that coarse sediment, poor sorting, strong longshore movement, and high energy are linked to some degree. Weakly negatively skewed sediments are associated with high energy and/or strong longshore movement which flatten and coarsen the foreshore, serving to weaken the winnowing effect of backwash and increasing the degree of trapping of fines, respectively. Low energy situations with a minimum of longshore drift operate to add finer mat rial to the foreshore and thereby steepen it which facilitates the winnowing process, producing strongly negatively skewed sediments. More platykurtic grain-size distributions are associated with the relatively coarse-textured, less negatively skewed sediments comprising flatter foreshores while the more leptokurtic grain-size distributions typify the relatively fine-textured, more negatively skewed sediments characteristic of steeper foreshores. Foreshore slopes are related to mean grain size, wave energy and wave steepness. Steep foreshore slopes are associated with fine-textured sediments, suggesting the effects of constructive wave activity. Foreshore slopes are also generally inversely related to both wave steepness and wave energy.

Probability distributions of breaking wave heights

Abstract: The motions of hydrofoils and surface effect ships as well as other floating objects, such as oceanographic research buoys, can be severely influenced by large breaking waves. Large breaking waves in deep water occur in severe sea states/ therefore they happen more frequently in some areas of the ocean than in others due to the global distribution of prevailing malevolent climates. If the probability distributions of breaking wave heights can be determined, then, some engineering design problems can be solved in terms of the reliability, safety, or probability of survival of the object. It is known from laboratory testing and occurrences at sea that a floating object may capsize when it is subjected to breaking waves. Given that the conditional probability function is known for capsizing, the unconditional probability distribution for capsizing can be calculated, if the probability distribution function is also known. The purpose is to determine the distribution of breaking wave heights for the eastern North Pacific Ocean, with engineering applications in mind.

Effect of Artificial Sea-Grass on Wave Energy and Near-Shore Sand Transport

Abstract: The emplacement of offshore, artificial sea-grass beds directly influences near-shore sand transport, Artificial sea-grass will decrease wave energy due to bending of the fronds, increased bottom drag, internal deformation and refraction. The latter three effects change as a result of the increased bottom slope caused by the sea-grass beds. In turn, the mean longshore current and longshore component of wave power are reduced. Total wave power and incident angle to the beach specifies the longshore component of wave power (PL) which is equated to the quantity of sand moved per unit distance (dq/dx). The average bending moment per individual frond was calculated to be approximately 2.0 lb.-in. A dense bed of sea-grass has the potential to reduce wave energy by twenty percent, based solely on energy lost to bending. The reduction of wave height, corresponding to the energy loss, results in decreased wave power per unit distance expended at the breaker zone. Ginsburg and Lowenstam (1957), reported that Thallassia testudinum offers a suitable substrate for many benthic communities. Algae, Foraminifera, bryozoans, etc., attach to the fronds, while mollusks, echinoderms and crustaceans use the network of baffles for protection and food gathering. These organisms add substantially to the binding ability of the grass and sediment will be readily accumulated within the bed. Variations in the type of community present will depend on wave energy (turbulence), temperature of the water, tidal range and salinity. In areas of low wave energy, embankments may grow, forming a series of offshore bars which will further influence approaching orthogonals.

Wind Wave Studies. Part 2. The Parabolic Antenna as a Wave Probe

Abstract: : Coherent microwave backscatter is the basis of a probe technique useful for studying surface water waves in a laboratory tank. A parabolic antenna is focused to give a plane wave at short range, typically 1.2 m, and an illuminated area of controllable size. The technique strongly discriminates against all water waves except those which have a particular Bragg resonant wavelength ranging between 0.25 cm and 10 cm and propagate parallel to the plane of incidence. The resulting doppler spectra provide a powerful tool for wind wave, breaking, and spray studies. A unique method for directly measuring the water wavenumber resolution is described, together with a technique for absolute calibration of the backscattered power in terms of wave height.

Analysis of Water-Level Rise Effects on Littoral Transport

Abstract: A computer project has included evaluation of the effects of changes in wave height, wave period, wave approach angle, bottom slope and water depth, on beach erosion. This work is primarily applicable to large lakes where long-term changes in water level may be as much as one or two meters. The change in potential erosion is expressed as a ratio of littoral power values. The most important independent variable entering into this ratio is the change in water level. An increase in level of one or two meters can give ratios in the range of 100 to 250 and even higher. A ratio of 100 means that, after the rise in level, the littoral component of power, and hence the amount of sand eroded and transported, is initially 100 times as great as prior to the rise.

Amplitude fluctuations of low‐frequency underwater acoustic pulses reflected from the ocean surface

Abstract: Measurements made with a fixed‐bottomed source and fixed‐bottomed receivers in water 2400 f deep show that for small ocean wave heights, up to about 3 ft, the fluctuations in amplitude of surface‐reflected sine‐wave signals at frequencies of 400, 750, 1000, and 1500 Hz at grazing angles of 18°, 31°, and 85° are in general agreement with theoretical predictions. In this wave height range, the coefficient of variation increased with increasing frequency, grazing angle, and wave height, reaching a maximum at about 5‐ft wave height for each combination of frequency and grazing angle. As the wave height increased further, up to 30 ft, the coefficient for a given combination of frequency and grazing angle generally decreased. For a given combination of frequency and grazing angle, the average peak level of the reflected pulses does not appear to depend strongly upon wave height.

A dual frequency radar for ocean roughness sampling

Abstract: A microwave technique for determining the roughness (rms wave height) of a randomly varying air-water interface has been developed theoretically, verified with laboratory wavetank studies and is currently being implemented for ocean surface measurements in a series of applications flight experiments. These aircraft observations will be near the Chesapeake Light Tower and will include a range of altitudes and sea conditions. The measurement concept involves cross-correlating the envelope fluctuations on two received carriers that are monochromatic when transmitted in a normal direction to the interface and are observed in a backscatter direction after reflection by the large number of randomly distributed specular points on the surface. The measured correlation coefficient (normalized covariance) as a function of carrier frequency separation will depend on the surface roughness, specifically the probability density function of the specular point height. Details of the flight system are discussed, and preliminary flight results are presented.

An ocean wave measuring buoy

Abstract: The author describes the design, construction, and performance of a surface wave-following buoy that can measure the directional spectrum of 0.06 to 0.5 Hz ocean waves with an accuracy of 10%, and an angular resolution of around 90 degrees. The buoy is disc shaped, 1.5 m (5 feet) in diameter, weighs 150 kgm (300 lb), and is completely self-contained. Wave height is measured by an accelerometer mounted on the inner gimbal of a vertical gyro, wave slopes by the tilt of the buoy about the gyro's vertical axis, and buoy heading by a gyro stabilized compass. Data from the transducers are digitized and recorded on computer compatible magnetic tape. Wave spectra are calculated from the data by computer. The accuracy of the measurements is verified by calibration in a wave tank, and by the internal consistency of the data. (Author)

RESEARCH Of) THE MODEL SHELTERING INVESTIGATION OF A HARBOR

Abstract: The Model Sheltering Experiment deals with the planning arrangement of the proposed harbor and is done by the worst wave condition (with respect to wave direction, wave height, and wave period) which probably occurred on the proposed harbor. The objectives of this experiment are to get the wave pattern of the harbor basin and to understand the various phenomena of the wave refraction, diffraction, and reflection caused by model test due to different harbor arrangement, and to comprehend the sheltering effect of the outer breakwaters. From the analysis of these test results, harbor planning of the most effective arrangement - the most economic length of breakwaters and the most ideal width of harbor entrance could be selected. For the purpose of analyzing results of model tests; comparison of theoretical wave diffraction calculation is proposed.

An investigation of surface and internal wave-induced turbulence in shallow water thermal microstructure.

Abstract: Measurements of temperature, wave height, and orthogonal water particle velocity were made in May 1973 at the NUC Tower located one mile off Mission Beach, California. A detailed analysis of the temperature field was made using digital temperature and isotherm contour plots. Billow turbulence microstructure appeared to be the dominant mechanism with the exception of one run in which evidence of doublediffusion microstructure was found. Spatial correlation lengths, calculated from the plot of the covariances, were of the order of 130 cm and less when the signal was high-pass filtered for waves of 100 seconds and longer. No depth dependence was noticed. Both frequency and wavenumber spectra were calculated and a correspondence between the spectra was noted at the frequency and wavenumber of the surface wave-induced particle displacements. The Thornton, Boston, Whittemore model of wave-induced temperature fluctuations was tested and found to model the temperature spectra quite well, especially in a narrow band of frequencies associated with surface waves. The turbulent temperature spectrum, calculated as the difference between the actual and wave-induced spectra, had a slope near -5/3 above 0.1 Hz and more negative at lower frequencies.

Prediction of lifetime extreme accelerations for design of lng cargo tanks

Abstract: A procedure is developed to predict the extreme accelerations needed for design of the cargo tanks in LNG vessels. Extreme values of accelerations for the lifetime of a ship are obtained by applying short-term statistics to extreme sea conditions collected over many years. The predictions are presented in the form of unit wave height response surfaces as a function of ship heading and wave period. By applying published wave statistics to these response surfaces, extreme response surfaces are determined for selected oceanic locations (shipping routes) in the world. (Modified author abstract)

Critical travel distance of waves in shallow water

Abstract: 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.

Research on the Model Sheltering Investigation of a Harbor

Abstract: The Model Sheltering Experiment deals with the planning arrangement of the proposed harbor and is done by the worst wave condition (with respect to wave direction, wave height, and wave period) which probably occurred on the proposed harbor. The objectives of this experiment are to get the wave pattern of the harbor basin and to understand the various phenomena of the wave refraction, diffraction, and reflection caused by model test due to different harbor arrangement, and to comprehend the sheltering effect of the outer breakwaters. From the analysis of these test results, harbor planning of the most effective arrangement – the most economic length of breakwaters and the most ideal width of harbor entrance could be selected. A comparison of theoretical wave diffraction calculation is proposed for the purpose of analyzing the results of model tests.

Formation and development of beach cusps on Del Monte Beach, Monterey, California

Abstract: Observations and measurements were made daily on Del Monte Beach in order to develop a quantitative description of the parameters affecting tlie formation of beach cusps. Multiple regression techniques were used to formulate an equation relating cusp width to the measured parameters. The life cycle of cusps was studied in order to gain insight into the factors affecting the groirth and decay of oosps. It was determined tiiat cusps are depositional in nature and develop sequentially from preferential areas of accretion on the beach. Cusp spacing was found to be a function primarily of wave height (energy) and wave period. Regularity of the wave regime during formation was found to result in uniform cusp spacing. Little migration was observed in mature cusps, and large changes in tlie wave regime or beach conditions were required to alter the cusp profiles. The action of large wind waves, storm surges, and breakers, was observed to destroy beach cusps.