Showing papers on "Wave height published in 1973"

Probabilities for Highest Wave in Hurricane

Abstract: The function, which is called the extremal Rayleigh distribution, is found to be an accurate approximation to the probability distribution function for the maximum pro a hurricane with time-varying intensity A formula is developed for the maximum wave distribution function in time-varying storms and computed for a large number of historical hurricanes The extremal Rayleigh function was found to be a very accurate approximation in all cases Two parameters are shown to be interpretable in terms of an equivalent uniform intensity storm as the reciprocal of the logarithm square wave height and the logarithm of the number of waves in the storm, respectively Data from Hurricane Carla was analyzed to determine the parameters which best described the probability behavior of the larger waves in each 20 min record Statistical formulas and tables are given to facilitate probability use of the extremal Rayleigh probability law in coastal engineering and hurricane research

Long-Term Wave Probabilities Based on Hindcasting of Severe Storms

Abstract: Presents new procedures that can be used to estimate long-term wave probabilities on the basis of oceanographer's hindcasts of sea-states generated during the most severe storms on record for the area of interest. The method is particularly applicable to areas where available wave data are insufficient for reliable extrapolation to the long return periods that are of interest in the design of offshore facilities. Special emphasis is placed on wave crest statistics, since crest height is a more important design parameter than wave height in many applications involving bottom-founded structures such as oil production platforms. Wave height statistics are also treated.

Two frequency radar interferometry applied to the measurement of ocean wave height

Abstract: A technique is developed for measuring the rms wave height averaged over an area of the sea that is much greater than any horizontal scale of the surface waves. The method involves a nadir looking radar which transmits and receives two monochromatic signals simultaneously. Signal processing at the receiver involves the computation of the correlation between the two returning signals as a function of theft variable frequency separation. The cross correlation between the amplitude and phase functions of the individual returning carriers depends on the distribution of discrete scatterers along the direction of propagation. This information can be used to determine the rms surface elevation (about the mean); it does not depend on the temporal or spatial frequency spectrum of the wave height or slope. Under conditions which are typical for a microwave signal being normally incident and reflected by the sea, the two frequency correlation function R(\Delta k) is seen to be equal to the characteristic function of the surface elevation of specular points. Laboratory measurements have been conducted on wind driven waves, and the measured correlation function compares favorably with the theory developed here.

Optical Wave Measurement Technique and Experimental Comparison with Conventional Wave Height Probes

Abstract: An optical system developed to measure wave slope is described. When the phase speed of a wave train propagating in a single direction is known, the measured slope can be integrated to give wave height directly. Results obtained under these conditions are compared with those from a capacitive wave height probe and demonstrate the accuracy of the system. These experiments also indicate a rather severe limitation of the wave height probe due to a lack of spatial resolution because of the mensicus on the probe. Confirmation is also given that the correct value of surface tension to use in the wave dispersion relation can be obtained from a static measurement, in this case by a du Nouy tensiometer.

Hydraulic roughness of ice covers

Abstract: Cold region rivers and canals covered with ice have been found to develop ripple-like reliefs on the ice underside causing head losses considerably in excess of those of smooth boundaries. Observations showed that ice thickness near the banks was several times that of the conveying part of the waterway. It is postulated that these features are caused by heat transferred from the bottom of the waterway. Note that observed ratios of wave height to wave length of the ripples do not exceed approximately 0.12. This is the approximate upper limit of wave index number of separation free flow over sinusoidal waviness. Some measured values of ice roughness coefficient (Mannings n) are given. A graph presenting a dimensionless solution for composite roughness coefficient as a function of ice underside and channel bed coefficients is included.

Synthetic Aperture Observations of Directional Height Spectra for 7 s Ocean Waves

Abstract: Directional wave-height spectra of 7 s period ocean waves in equilibrium with the wind have been measured using Bragg scattering of LORAN-A transmissions and synthetic aperture techniques. The spectra measured have a resolution of approximately 10° and a dynamic range of at least 25 dB. Observations were carried out over an 8 d period in November 1972, during which sea and wind conditions varied slowly over periods of 24 to 48 h. The ratio of mean-square heights of wave propagating directly downwind to those propagating directly upwind is at least 300:1. The directional spectra were extremely broad, with spectral width between 90° and 180° and varied with the wind.

Waves off Mangalore Harbor—West Coast of India

Abstract: Detailed statistical investigations of recorded waves off Mangalore on the West Coast of India are presented. Rayleigh distribution is found to describe adequately the distribution of wave heights and this distribution is not found to be especially sensitive to the spectral width parameter. Wave height parameters are in good agreement with the Longuet–Higgins' theoretical results, over a wide range of ocean wave environment. The highest waves reaching the coast are not found to be associated with the longest periods. The wave height and period variations are studied for different seasons. Severe waves occur only during the monsoon season and the sea is practically calm during the fair-weather season. Based on a study of weather data and cyclone tracks for the Arabian Sea, it is recommended that the design wave could be based on the annual wave evaluated from recorded data. Wave characteristics evaluated using Tucker's Method of Analysis compared favorably with computed data

Statistics of ocean wave groups

Abstract: Statistical parameters are derived to describe a group of consecutive waves that are large compared with the average wave height. The parameters describing the statistics of ocean wave groups can be derived from the energy spectrum of the waves; they are then compared with those found for actual wave data. Wave groups are an important consideration in designing mooring systems for large vessels subjected to long-period surge motions.

Wave height and wave resistance in the presence of a viscous wake

Abstract: The wave disturbance set up by the uniform motion of a Lagerstrom “singular needle” on or below the free surface of an incompressible viscous fluid is analyzed. Since the motion of this singularity generates a viscous wake, the interaction of the latter with the free surface is automatically included in the analysis. Based on formal expressions derived in earlier work, asymptotic representations for the wave height are derived which are valid for large Reynolds number relative to wavelength and for large distances downstream of the singularity. These representations explicitly show the effect of the viscous wake on the amplitude and phase of the surface waves. A definition of wave resistance is formulated appropriate to the large Reynolds number case, and curves of the wave resistance of the singularity versus speed are calculated.

Extreme Wave Height Distributions over Oceans

Abstract: The scale and shape parameters of the extreme wind speed distribution are transformed to scale and shape parameters of the extreme wave distribution for extratropical storm areas This provides the means of obtaining the extreme wave distribution anywhere in deep water in these areas Estimates of the extreme wave period are obtained from applying known empirical relationships to estimated significant wave height quantiles A method is explored for obtaining extreme wave height quantiles for tropical cyclone areas from available extreme wind quantiles through applying empirical relationships involving duration of high winds

Extreme wave height distributions over oceans

Abstract: The scale and shape parameters of the extreme wind speed distribution are transformed to scale and shape parameters of the extreme wave distribution for extratropical storm areas. This provides the means of obtaining the extreme wave distribution anywhere in deep water in these areas. Estimates of the extreme wave period are obtained from applying known empirical relationships to estimated significant wave height quantiles. A method is explored for obtaining extreme wave height quantiles for tropical cyclone areas from available extreme wind quantiles through applying empirical relationships involving duration of high winds.

Two Frequency Radar Interferometry Applied to the Measurement of Ocean Wave Height

Abstract: A technique is developed for measuring the rms wave height averaged over an area of the sea that is much greater than any horizontal scale of the surface waves. The method involves a nadir looking radar which transmits and receives two monochromatic signals simultaneously. Signal processing at the receiver involves the computation of the correlation between the two returning signals as a function of their variable frequency separation. The cross correlation between the amplitude and phase functions of the in- dividual returning carriers depends on the distribution of discrete scatterers along the direction of propagation. This information can be used to determine the rms surface elevation (about the mean); it does not depend on the temporal or spatial frequency spectrum of the wave height or slope. Under conditions which are typical for a microwave signal being normally incident and reflected by the sea, the two frequency correlation function R(Ak) is seen to be equal to the characteristic function of the surface elevation of specular points. Laboratory measurements have been conducted on wind driven waves, and the measured correlation function compares favorably with the theory developed here. F I. IKTRODUCTION OR THE SEVERAL spacecraft and aircraft ocean- ography and met'eorology programs now under way and for those being developed, a need always exists for real time sea t>ruth data for the area being surveyed in order to test and eva.Iuate t,he experimental and t,heoret- ical tools being developed. The particular surface param- et.ers associat,ed n4t.h "sea trruth" nil1 vary from one t.ype of program to another, e.g., radiomet.ry, satellite altimehry, microwave backscat,t,er, etc. The study reported here sug- gests a t>echnique, which can be used to observe one impor- $ant para.meter a.lone, one which is frequently useful in interpreting observations with ot,her sensors as well as being an indicat.or of sea statme by it.self. For insta.nce, when wind condit.ions are such that, the Phillips saturat,ion spectrum (l) describes t.he sea surface t,he rms height is proportional to t,he squa.re of the wind speed. This result has been deduced and explained by Munk and Nierenberg (2). This strong dependence could be useful for wind speed measurements. This study mas directed at the development, of a t.ech- nique for measuring the rms wave height. avera.ged over an area of the sea that is much great,er than any horizont,al scale of t-he surface waves. The measurement. method developed here involves a nadir looking rada.r that, trans-

Shipboard observations of wave spectra with a bow-mounted wave height sensor

Abstract: Wave height spectra were observed from the bow of the U.S.N.S. Kane with a semiportable bow-mounted wave system. Distance from the sea surface to a transducer at the bow of the Kane was measured with an infrared height sensor. Displacement of the bow associated with surface wave motion was obtained with a static pressure measuring device. Wave height spectra were estimated by cross-spectrum analysis of signals from these two devices. Reasonably good agreement was obtained with predictions of Phillips' equilibrium range and Pierson-Moskowitz wave spectra.

Near-Shore Ripples: Some Hydraulic Relationships

Abstract: An analysis of sand ripples in shallow water, small fetch environments was made in a wave tank to investigate some aspects of the relationship between ripple geometry and movement and a variety of hydraulic parameters. Although stepwise regression and simple correlation procedures were employed, the effects of autocorrelation and multicollinearity casts some doubt upon these results. Power spectral analysis demonstrated that ripple height and wavelength increase with wave height and decrease with water depth, such that although random fluctuations are present, ripple geometry will tend to increase towards the breaker point. The effect of bed mounds which tend to cause ripples to increase in size on the waveward side and decrease on the leeward side was also noted. Ripple velocity was he least well explained of the ripple parameters investigated, although velocity was shown to be related to water depth and wave height.

Breakwaters for long, short and/or complex water waves

Abstract: This invention relates to a breakwater, expecially for use where a large range of wavesteepness (i.e., ratio of wave height to wave length) is encountered, such as in coastal regions of oceans and large lakes. This new breakwater is a composite device and comprises two different kinds of breakwaters. The component located first in the path of approaching waves is a breakwater particularly adapted to dampen waves of large wave steepness by creating numerous starting and stopping vortices. This first breakwater may take the form of a series of vanes at different depths. The second breakwater in the path of the approaching waves is adapted to dampen waves of a large range of wave steepness. This second type of wavebreaker is preferably a curved plate with the convex side up as viewed from above, and is preferably in the form of a continuous surface. These two types of breakwaters have now been coordinated to create mutual interaction such that the first breakwater reduces wave energy sufficiently so that the second type of breakwater can safely complete the desired wave attenuation, even in stormy weather.

Marine Conditions and Automated Forecasts for the Atlantic Coastal Storm of February 18 20, 1972

Abstract: The storm surge and ocean waves associated with the Atlantic coastal storm of Feb. 18–20, 1972, caused extensive damage along beaches of Long Island and New England. Meteorological conditions of the storm, along with resulting tides, surges, and waves, are described. Comparison is made with forecasts of the storm produced by the primitive-equation model of the National Meteorological Center, as well as with automated forecasts of storm surge and wave height. It is concluded that the meteorological forecasts and the resulting storm surge and wave forecasts were quite good.

Wave Climate at Moffat Beach

Abstract: The analysis of a series of wave recordings made at Moffat Beach, Queensland using an OSPOS wave recorder during 1963-1964 is described. This analysis included (i) the establishment of representative parameters for each wave recording; (ii) the determination of the frequency of occurrence of the representative parameters over the total recording period and (iii) the comparison of the recorded data with visual observations at Cape Moreton and the adjustment of the frequency curves to a longer more Queensland coast cannot be recommended.representative period of time.The results of the analysis provide confirmation of the applicability of the Rayleigh distribution to the short term wave height distribution within a given wave recording. On the other hand no definite conclusions are made concerning which theoretical representation of the long term wave height frequency of occurrence is to be preferred.The data analysed shows that at least four distinct types of wave conditions make up the overall wave climate in this area. The general wave height and period characteristics representative of these conditions together with seasonal variations are presented.The Moffat Beach wave data is compared with that obtained off the Gold Coast using Wave Rider buoys. Generally similar values of significant wave height are found but the wave periods are appreciably different. An analysis of possible explanations for this difference suggests that the filter effect due to pressure attenuation almost completely removes local wind generated seas from the OSPOS records. The question of a representative wave period for a given wave recording is considered and it is concluded that the use of the zero crossing period Tz for the analysis of unfiltered surface wave recordings of simultaneous sea and swell such as generally occurs off the southern Queensland coast cannot be recommended.

Floating Breakwaters - A Wave Tank study

Abstract: As examples of the direct application of a floating breakwater, the author cities the desired protection of certain offshore operations, such as pipeline laying and tanker loading and unloading. This paper describes a laboratory study undertaken to establish which parameters affecting a breakwaters' performance are most important. Results show that wave reduction was not greatly affected by wave height. With regard to the breakwater itself, a square cross-section gives slightly better wave reduction than a triangular, circular, or trapeziodal one. Permeable and impermeable coverings give essentially the same results. Concentrating the ballast low in the profile and using two-thirds to full submergence yielded best results. As indicated by the author, probably one of the most serious and least understood problems is that of the mooring of breakwaters. The result of this study indicates that mooring line forces can be reduced by using horizontal lines and by the proper choice of attachment point.

Processed Wind and Wave Measurements from Ocean Weather Station PAPA

Abstract: : As part of an investigation into the environmental conditions existing in the North Pacific Ocean, observational data collected from ships occupying Ocean Weather Station PAPA were obtained from the Canadian Atmospheric Environment Service. Wind and wave data for the fall and winter months over the period 1951 through 1971 were processed. Wind speed and wave height were examined using a computer program to construct histograms displaying data distribution a monthly basis. Data were divided into two intervals (1951 through 1961, and 1962 through 1971) to compare the two periods since their is a general belief that wind/wave severity has diminished during the past 20 years. The histograms included in the report show that maximum wind speed data and the mean wave height data as reported indicate a definite lessening in environmental severity at the location. Mean wind speed data show a similar trend, but of a much smaller extent.

The Probabilistic Interpretation of Wave-height Data from the Botany Bay Hydraulic Model

Abstract: This paper describes a method by which data measured in a large wave model can be analysed to produce a statistical estimate of the probability of occurrence of large wave-heights.

Determination of Ocean Surface Descriptors Using Sea Photo Analysis Techniques

Abstract: : The techniques of Sea Photo Analysis have been used to obtain surface truth descriptors of the open ocean from an aircraft. Aerial photographs were taken such that the density fluctuations of the negatives were related to surface slope. The slope spectra, obtained by Fourier analysis of the negatives, were fitted to an equivalent form of the Pierson-Moskowitz wave height spectrum. The photographs, the wave height spectrum, and the rms slope equations determined by Cox and Munk then yielded the averaged heading of the waves, the equivalent wind speed, the rms wave height, and the rms slope for clean and slick surfaces. The optical techniques of Sea Photo Analysis used in this program and digital analysis, used when whitecaps were present in the photographs, are discussed. The empirical equations used to determine rms wave height and slope and auxiliary rms slope and wave height spectrum equations are given. Surface descriptors were inferred for seas driven by winds from 3 to 21 knots occurring on 16 separate days.

100 year extremes of some ocean phenomena: Method and coastal California predictions

Abstract: For many reasons, e.g., port operations, coastal construction planning, undersea structure survival, underwater transport, man wishes to know the extreme values that are likely to occur in physical oceanographic variables. This paper presents a hybrid statistics/computer simulation method that uses common oceanographic observations to estimate confidence levels on the most extreme values likely to occur over a given period in the future. The method is applied to the California coast for a period of 100 years on the following variables: wave height by water depth, wave length by water depth, wave period, bottom surge particle velocity by water depth, current velocity, regions of high density, regions of low density, and earthquake magnitude. Values are given for the 99 % and 99.9% probability levels.