Showing papers on "Wave height published in 1972"

Analysis of the resistance increase in waves of a fast cargo ship

Abstract: A new method to calculate the added resistance of a ship in longitudinal waves is discussed. For the particular case of a fast cargo-ship the calculated values are compared with experimental results, and a satisfactory agreement is shown. In addition the experiments with the considered shipform confirm that added resistance varies as the squared wave height for constant speed and wave length.

Airy wave theory and breaker height prediction

Abstract: Using a critical value for Yt> = H./ h. as a wave breaking criterion, where Hb and hb are respectively the wave breaker height and depth, applying Airy wave theory, and assuming conservation of the wave energy flux, one obtains 1/5 2 2/5 Hb = k g (TH. ) relating Hb to the wave period T and to the deep-water wave height H^ . Three sets of laboratory data and one set of field data yield k = 0.39 for the dimensionless coefficient. The relationship, based on Airy wave theory and empirically fitted to the data, is much more successful in predicting wave breaker heights than is the commonly used equation of Munk, based on solitary wave theory. In addition, the relationship is applicable over the entire practical range of wave steepness values.

Maximum breaker height

Abstract: Based on a re-evaluation of available experimental data on breaking waves, a relationship between the breaker height-breaking depth ratio, the incident wave steepness and the beach slope is found. This relationship, when combined with experimental observations of breaker travel, permits an estimate of the maximum breaking wave height a coastal structure might experience given a design wave period and design depth at the structure site. Breaker-type classification according to inshore and offshore parameters as presently defined cannot be reconciled to observations of the relationship between breaker-height index, wave steepness and beach slope. Revised criteria for breaker classification are presented.

Long-term wave height distributions at seven stations around the British Isles

Abstract: Long-term instrumental measurements of significant wave height and mean zero-crossing period at 7 stations are analysed The marginal distribution of significant heights is well described by a Weibull law The long-term distribution of individual wave heights is calculated from the joint distribution of significant wave height and mean wave period It is found to be nearly exponential

Microscale pressure fluctuations near waves being generated by the wind

Abstract: Measurements of static pressure and wave height are used to describe the waveinduced pressure field above generating sea waves. A large hump in the pressure spectra is observed at the wave frequencies. The amplitude of this hump increases and the rate of its vertical decay decreases as the mean wind speed increases. The phase difference between the pressure and the waves during active generation is about 135°, pressure lagging the waves, and does not change vertically for measurements at heights greater than the wave crests. In the present data, active wave generation appears to occur only when the wind at a height of 5 metres is greater than or about equal to twice the phase speed of the waves.

A method of numerical analysis of wave propagation application to wave diffraction and refraction

Abstract: A method is presented to obtain numerically wave patterns in the region of arbitrary shape. The principle is to solve the linearized wave equations under given boundary conditions from a certain initial state. In this paper, two principal applications of our method of numerical analysis are presented in the fundamental fashion. The first application of our method is related to wave diffraction. The distribution of wave height along a semi-infinite breakwater and a detached breakwater is calculated and compared with that obtained from the conventional analytic solutions to confirm the validity of our numerical method. Three examples of application are presented to the wave height distribution along breakwaters of arbitrary shape and of arbitrary reflecting power and to wave force upon a large isolated vertical structure. The second application is to wave refraction. In particular, this method of numerical analysis is applicable to the analysis of wave propagation in the region of ray intersections which are indicated by the conventional geo-optic wave refraction theory. An example of application to a submerged shoal with concentric circular contours where a cusped caustics is formed is presented and the calculated wave height distribution around the shoal is compared with that obtained from hydraulic model experiments. Our method of numerical analysis might be applied to the calculation of wave height distribution in the region of more realistic bottom topography and it is possible to include vertical boundaries of arbitrary shape.

Wave reflection and transmission for pile arrays

Abstract: A group of piles in a specific geometric pattern may represent a part of a foundation supported by multiple pilings or a porous sea wall or other type of porous coastal structure. "Wave characteristics" of such a structure will include not only the wave transmission but also wave reflection characteristics. Most of the experiments in the past on pile groups were mainly concerned with wave transmission characteristics as a function of wave height and period. The main purpose of these previous studies was to evaluate the absorption characteristics of pile groups, and wave reflections were generally not measured, or evaluated. Variables in this study included wave characteristics such as wave height and length and three types of symmetric pile arrays, two providing clear spacing in the direction of the wave between pile rows and one with a staggered arrangement. The results presented in dimensionless form show the effect of pile geometry and wave steepness on the coefficient of reflection and transmissibility.

Reflection and transmission for a porous structure

Abstract: Effects of characteristics of incident waves and of the thickenss of structure on wave reflection by and transmission through a porous structure were studied. Use of an idealized porous structure which is a lattice composed of circular cylinders was made. The relative thickness of structure B/L was found to have appreciable effects on reflected and transmitted wave energies. The reflection coefficient Kr reaches to a maximum of it for B/L of about 0.2 to 0.25, then decreases as B/L increases, and remains approximately uniform for B/L larger than about 0.6. The transmission coefficient Kt, however, decreases nearly exponentially as B/L increases. Measurement of wave height within structure revealed a Dattern of standing waves having a loop at the front face and a node at the rear face of it. That relates to the trend of Kr. Analytical approaches to predict the transmitted wave height, and wave heights before and within porous structures are found to be useful.

Extreme wave conditions in british and adjacent waters

Abstract: Information on extreme wave conditions is needed in the design of offshore structures. This paper present the results of calculations of the parameters in the 50-year storm; the work has been based on extreme wind data and on instrumental wave measurements. The results are complementary, and are combined in two maps, one of extreme wave height and the other of the corresponding wave period.

Attenuation of water waves and control and utilization of wave-induced water movements

Abstract: Curved vane-like structures for positioning beneath or at the surface of a body of water to attenuate incident waves, and change the wave-induced normal orbital water movements to produce currents and other useful hydrodynamic effects or combinations thereof. The vanes in the structures are configured and oriented to intercept the water at various locations in its orbital movements, guide it into new paths defined by the shape of the vanes, and discharge it from the structure as a current flowing in a preselected direction, such as counter to or in the direction of wave movement, towards the water surface, or towards the bottom or floor of the body of water. These effects are utilized to perform useful work, including diminishing wave height, speed and period, moving subsurface and surface debris and contaminants such as spilled oil to a collecting point or facility, transportation and dispersal of waters polluted by thermal, chemical or other discharges, transfer of sand, silt, or other solid material on the bottom from one location to another, and generation of electrical or hydraulic power. Various styles and configurations of these vaned structures, manners in which they can be arranged to perform an intended function, and methods for securing them in operating position also are described.

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.

Experiments on the Transition from Nonbreaking to Postbreaking Wave Pressures

Abstract: Wave pressures upon vertical walls with and without a rubble mound were measured at the relative water depth of h/L=0.10 to 0.30 for the range of the relative wave height of H/h=0.15 to 0.93 in a c...

A wave climatology for u.s. coastal waters

Abstract: In a program conducted by the Coastal Engineering Research Center, cumulative wave height distribution functions, from 10 wave gages operated by this agency over the past 20 years along the Atlantic, Pacific, and Gulf Coasts have been examined in the format of the exponential distribution Based on this study, the authors have determined that one complete year of data at six observations per day, appears to yield a reliable wave height distribution up to the one percent level of occurrence Further, wave data from shipboard weather reports when compared to wave gage data were found to be of some use in describing long term summaries of coastal wave height conditions A brief discussion of data acquisition procedures and interpretation precedes a general discussion of wave climatology

Riprap Stability on Earth Embankments Tested in Large- and Small-Scale Wave Tanks.

Abstract: : Tests of models in wave tanks were made to determine the effectiveness of several riprap designs in protecting embankment slopes from wave action. Models ranging from about 1:20 scale to almost full scale were tested with waves up to about 6 feet high. A range of wave periods were tested, embankment slopes varied from 1 on 2 to 1 on 5, and armor layers were composed of quarried stone, glacial boulders and tribars. Relationships that define the effect of wave height, wave period, embankment slopes and Reynolds number on size of stable armor units were experimentally determined and are given in graphs and tables. (Author)

Wave runup on vertical cylinders

Abstract: Wave height at a point on vertical cylinders is measured as a function of the orientation angle, a, between the normal from the point on the cylinder and the direction of travel of a single periodic train of waves. The wave height distribution, H(a), has a broad maximum around a = 0° (facing into the waves) and a more restricted maximum at a = 180 . The maximum at a = 0° increases with wave height in all cases, and the super elevation has about the magnitude of the velocity head in the wave crest. In 21 different H(a) for which it is possible to determine the axis of symmetry by a simple objective test, 14 H(a) have axes of symmetry within * 3° of the direction of wave travel. Most of the variation in H(a) is due to variation in crest elevation; trough elevation remains relatively constant for the 360° range of a. The shape of H(a) depends more on height and cylinder cross section than on period, although the variation in H(a) as a function of cross section is significantly less than the extreme variations in tested cross sections. Applications of these results to wave direction measurement and to interpretation of wave records from surface-piercing wave gages are discussed.

Bistatic radar sea state monitoring

Abstract: Bistatic radar techniques were examined for remote measurement of the two-dimensional surface wave height spectrum of the ocean. One technique operates at high frequencies (HF), 3-30 MHz, and the other at ultrahigh frequencies (UHF), approximately 1 GHz. Only a preliminary theoretical examination of the UHF technique was performed; however the principle underlying the HF technique was demonstrated experimentally with results indicating that an HF bistatic system using a surface transmitter and an orbital receiver would be capable of measuring the two-dimensional wave height spectrum in the vicinity of the transmitter. An HF bistatic system could also be used with an airborne receiver for ground truth ocean wave spectrum measurements. Preliminary system requirements and hardware configurations are discussed for both an orbital system and an aircraft verification experiment.

Dissipation of wave energy due to opposing current

Abstract: Energy dissipation and wave height attenuation were analysed theoretically for surface waves propagating against uniform flow. Energy dissipation was estimated from evaluation of work "by internal and boundary shear stresses. Experiments were conducted in a test flume of 20m long, 0.8m wide and 0.5m high. Results showed that tested values of rate of wave height attenuation were comparable with theoretical values.

Effects of Irregular Wave Trains on Rubble-Mound Breakwaters

Abstract: Results of model tests on a typical cross section of a rubble-mound breakwater are presented. The structure was protected against wave attack by a cover layer consisting of a double layer of dolos armor units of 43 g. These units were intended to represent 0.19 ton prototype units to a scale of 1/16. All tests were carried out on a slope of 1:1.5. The armor units were first submitted to attack by nonbreaking waves of the regular type and then by nonbreaking waves of the irregular type. Two kinds of irregular waves simulating a narrow-band spectrum and a wide-band spectrum were used. Wave heights and periods were measured with the help of resistance type wave gages. Two types of damage were identified: the stable and the unstable damage. The test results are presented showing the significant wave height and the damage coefficient versus the stable and unstable damage.

Estimating ocean wind wave spectra by means of underwater sound

Abstract: Measurements of the spectrum of ocean surface reradiated acoustic signals generated by an omnidirectional, sinusoidal source are used to estimate the ocean surface wave‐height spectrum, and the results are compared with wave‐staff measurements made simultaneously in the scattering area. Plane‐wave physical optics theory is applied to a long‐crested sea surface model to verify Marsh's hypothesis that for low sea states the spectrum of acoustic waves reradiated by the rough, moving sea surface consists of a specular component at the transmitted frequency and a scattered component, which is the weighted surface wave‐height spectrum. The approach employs theories by Parkins, Clay and Medwin, and Pierson. The weighting function applied to the surface spectrum depends on signal frequency, experimental geometry, and mean‐square wave height. Continuous‐wave signals at 127 and 1702 Hz were transmitted from fixed, omnidirectional sources to receivers 4.5 and 31 km downrange. Additionally, wave height was monitored ...

On the Vertical Distribution of Water Particle Velocity Induced by Waves on Beach

Abstract: As ocean waves progress on the beach, wave characteristics change and waves break finally. On the transformation of wave height, celerity, length, and the breaking wave height and depth, many inves...

Taylor-Görtler vortices expected in the air flow on sea surface waves—II

Abstract: The instability of Taylor-Gortler vortices which are expected in the air flow on water waves was studied in part I, under the assumption that the curvature around the crest or the trough of water waves, where the instability was expected to take place first, was constant, namely that the characteristics of the vortices were affected little by the local change of the curvature along the direction of the progress of water waves (the direction ofx-axis) However, the curvature actually varies from positive to negative, or vice versa. In order to study this effect, the instability of Taylor-Gortler vortices is examined with respect to the range of the part of a constant curvature, in the model in which the curvature is positive constant near the trough and negative constant near the crest, and zero in the intermediate regions, respectively. It is shown that as the region of the constant curvature becomes narrower, the instability tends to weaken. For the same example with part I, namely, when the wind of 12.2 m s−1 is blowing over swells of 15 m in wavelength, if the range of constant curvature near the trough is taken as a quarter of one wave length, the critical wave height becomes 0.96 m instead of 0.50 m, and conversely, the wave length and the height of center of the vortex become 11.9 m and 2.1 m instead of 24 m and 3.7 m, respectively. Further, using the energy equations, quantitative estimates are performed of the intensity of the vortices which develop when the wave height of the swell is 1.05 m in the above described example, and also of the influence of the vortices upon the wind profile when the equilibrium state is reached. When the vortices are generated and grow to attain to an equilibrium state interacting with the mean flow, the maximumx-component of velocity in the vortices is about 1.04 m s−1. Consequently, the wind profile undergoes a considerable distortion from the logarithmic one near the level of 2 m height. This distorted wind profile has a form similar to those sometimes observed above the sea surface.

Wave forces on submerged pipe lines

Abstract: This is a presentation of the analyses of data obtained from a laboratory investigation of horizontal forces produced by oscillatory waves on submerged pipes. The research program was planned to help solve design problems for pipe lines located on or below the bottom in the oceans or the Great Lakes. The project was financed by the National Science Foundation. A continuous record of wave height and horizontal force was obtained for pipes of four diameters, for three wave heights and three wave lengths. Forces were measured at four locations below the water surface, the lowest position being as near the bottom as possible. Other tests were conducted with the pipes located in various positions within trenches of several different shapes. The actual pipe diameters, wave heights and wave periods used in the laboratory tests were such that on the basis of a scale ratio of 1 to 75 the range of prototype parameters would include pipe diameters varying from 8 to 15 feet, wave heights varying from 8 to 23 feet and wave periods in the range from 6 seconds to 12 seconds. Results are presented in the form of coefficients of inertial resistance and drag which can be used with the Airy equations to compute forces.

On the relative wave elevations at the ship's side in oblique seas

Abstract: Model tests of two container ships in oblique regular and irregular waves were carried out at the seakeeping tank of S. R. I., and the relative wave elevations at various positions of the models' hull were measured by means of capacitance wave probes attached on the hull.The relative wave elevation induced by combined ship motions as pitch, heave and roll and the wave elevation can be calculated by the strip method. The deformation of the wave surface near the hull which is induced by hydrodynamic interaction between ship's body and wave is estimated by the Tasai's two dimensional theory, and it is added to the above-mentioned relative wave elevation.The comparison of the test results with the computed values shows that : a) calculations including the hydrodynamic interactions show good agreement with the experiment, generally speaking, in head and bow seas, b) the measured values in beam sea lie between calculated values including and excluding hydrodynamic interactions, c) disagreement between measured and calculated values is most remarkable in quartering sea, except one for the stem provided that the estimation is made excluding hydrodynamic interactions, d) the amplitude distributions of the relative wave elevations measured in irregular waves show good agreement with the estimated one by the linear superposition of the response amplitude operator and sea spectrum.

A study on the formation of continental shelves

Abstract: In view of that continental shelves are essentially the erosional landform and also that the sea level fluctuation after Wurm glacial stage has played an important role i n the for mation of continental shelves, the author completed a model of continental shelf formation, which was based on a combination of coastal cliff recession and the postglacial transgression; the model is summarized in the following two equations: _??_ (1) and Z*=-ha+A(1-2e-at+e-2at), (2) where X* and Z* are the coordinates showing the position of the point P (Fig. 9) and a continental shelf profile may be obtained by finding a locus of this point; c is the recession rate of the present coastal cliff, in meters per year; t is time in years, and t=0 and t=2×104 show 2×104 years B. P. and the present respectively; ha is the critical water depth for submarine bedrock erosion, in meters and may be estimated approximately by _??_ in which H0 and L0 are the deep water wave height and length in meters respectively and H and L are the wave height and length in meters, at the water depth ha respectively, and a nomogram for this equation is shown in Fig. 1; W0 is the width of abrasion platform in meters at t=0 and is written as W0=Wp-2×104c, in which Wp is the present platform width, defined as the horizontal distance from the present coastline to the place where water depth is ha; A and a are constants appeared in the following equation expressing the curve of the postglacial sea level change: Z=A(1-2e-at+e-2at) which is shown in Fig. 8 and A=125 and a=1.98×104 in this case. The validity of this model was examined in three areas facing on the Pacific Ocean (Fig. 10). Physiographical and oceanographical conditions of these areas are listed in Table 2. Figure 15 shows comparisons between the continental shelf profiles in the fields and the ones calculated by using Eqs. (1) and (2); the actual profiles and the calculated ones are in fairly good agreement: this model can explain in full degree the first essentials of continental shelf formation.