共查询到20条相似文献，搜索用时 320 毫秒
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A methodology to define discrete waves from free sea surface elevation time series is presented. The method allows an objective discrimination of false waves among small waves, avoiding the use of arbitrary criteria associated with zero-up-crossing, zero-down-crossing, or other definitions. The method uses the Hilbert Transform and the representation of the time series in the complex plane. A discrete wave corresponds to a 2π phase-advance in the complex plane. The waves between zero crossings which do not show 2π phase advance are considered false waves. Wave rider buoy records, measured off the west coast of Portugal, were employed in assessing some of the statistical implications of this methodology. 相似文献
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Traditional wave steepness s=H/L does not define steep asymmetric waves in a random sea uniquey. Three additional parameters characterising single zero-downcross waves in a time series are crest front steepness, vertical asymmetry factor and horizontal asymmetry factor. Results for steepness and asymmetry from zero-downcross analysis of wave data obtained from full scale measurements in deep water on the Norwegian continental shelf in 58 time series are presented. The analysis demonstrates clearly the asymmetry of both “extreme waves” and the highest waves. The period and height of the highest waves are also given together with their correlation to spectral parameters. The measured maximum wave heights are also compared with predicted values of maximum wave heights showing good agreement. 相似文献
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A. V. Babanin P. P. Verkeev B. B. Krivinsky V. G. Proshchenko 《Physical Oceanography》1993,4(5):399-407
An accelerometer buoy wave gauge developed in the Marine Hydrophysical Institute of the Ukrainian Academy of Sciences is described. This allows measurement of acceleration and the sea surface elevation in the system of reference connected with a buoy. The integral and frequency spectral characteristics of waves can be computed from the records of the wave gauge signal. The use of a buoy accelerometer at sea provides a possibility to derive effective information on the wind waves.Translated by Mikhail M. Trufanov. 相似文献
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To plan for proper mitigation measures, one should have an advanced knowledge of the phenomenon of tsunami propagation from the deep ocean to coastal waters. There are a few methods to predict tsunamis in the ocean waters; one method is the effective use of data buoy measurements. Although data buoys have been used along the Indian waters there has been a tremendous growth in the number of buoy deployment recently. Under the National Data Buoy Programme (NDBP) of India, the 2.2 m diameter discus data buoys were deployed along the east and west coasts of India for measuring meteorological and ocean parameters. It would be advantageous if these buoys could be efficiently used to measure rare events such as tsunamis. Understanding the dynamic behavior of the buoy is of prime importance if a tsunami warning system is to be successful. This may be accomplished through experimental or numerical studies. A comprehensive experimental study has been conducted to understand the dynamic behavior of a wave rider buoy exposed to a variety of waves. It is common that tsunami waves are represented in terms of shallow water waves, namely solitary and cnoidal waves. Hence, in the present study, the discus type data buoy is scale modeled and tested under the action of solitary and cnoidal waves in the laboratory. The time histories of wave elevations, as well as heave and pitch motions of the buoy model, were analyzed through a spectral approach as well as through wavelet transformations. The wavelet approach gives more detailed insight into the spectral characteristics of the buoy motion in the time scale. The harmonic analyses were performed for the cnoidal wave elevations and subsequent motion characteristics that give an insight into the energy variations. The details of the model, instrumentation, testing conditions and the results are presented in this paper. 相似文献
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This paper investigates latching type control on a floating wave energy converter in deep water. An on-board, actively controlled motion-compensated platform is used as a reference (‘active reference’) for power absorption and latching. A variational formulation is used to evaluate an optimal control sequence in the time domain. Time domain simulation results are presented for a heaving buoy in small-amplitude waves. Results are compared with an equivalent system where latching and power absorption are from a sea-bottom-fixed reference. 相似文献
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Point absorber wave energy device with multiple degrees of freedom (DOF) is assumed to have a better absorption ability of mechanical energy from ocean waves. In this paper, a coaxial symmetric articulated point absorber wave energy converter with two degrees of freedom is presented. The mechanical equations of the oscillation buoy with power take-off mechanism (PTO) in regular waves are established. The three-dimensional numerical wave tank is built in consideration of the buoy motion based upon the CFD method. The appropriate simulation elements are selected for the buoy and wave parameters. The feasibility of the CFD method is verified through the contrast between the numerical simulation results of typical wave conditions and test results. In such case, the buoy with single DOF of heave, pitch and their coupling motion considering free (no PTO damping) and damped oscillations in regular waves are simulated by using the verified CFD method respectively. The hydrodynamic and wave energy conversion characteristics with typical wave conditions are analyzed. The numerical results show that the heave and pitch can affect each other in the buoy coupling motion, hydrodynamic loads, wave energy absorption and flow field. The total capture width ratio with two coupled DOF motion is higher than that with a single DOF motion. The wave energy conversion of a certain DOF motion may be higher than that of the single certain DOF motion even though the wave is at the resonance period. When the wave periods are high enough, the interaction between the coupled DOF motions can be neglected. 相似文献
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Nearshore directional wave measurements by surface-following buoy and acoustic Doppler current profiler 总被引：1，自引：0，他引：1
Directional energy spectra of nearshore surface waves were measured for a 3-year period (2004–2007) at a site with mean depth 14 m and mean tidal range 2.1 m. Triaxys surface-following wave buoys reported hourly directional wave energy spectra and wave parameters near the offshore end of the Savannah River Entrance Channel, Georgia, USA. An acoustic Doppler current profiler (ADCP) was located beside the wave buoy for 3 months. Directional and non-directional surface wave energy spectra and the corresponding bulk wave parameters (height, period, and direction) are compared for the two systems. Most parameters derived from the spectra agree closely; the most significant differences were found at the upper and lower frequency measurement limits, where signal-to-noise ratios were lower. The wave buoy consistently reports a small amount of energy below 0.05 Hz that does not appear in the ADCP-derived spectra and does not appear to be related to the mooring system. This leads to larger mean and peak periods reported by the buoy. All directional spectra were computed using the Maximum Entropy Method for both instruments, but the buoy, with spectra derived from six independent time series, provides lower directional resolving power than the ADCP, which utilizes twelve time series. Both systems gave similar results defining mean and peak wave directions, with the primary difference being that the ADCP indicates energy to be more tightly concentrated around the peak direction. 相似文献
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We made and set a spar buoy in September 1975 at Tsuyazaki for the purpose of developing the buoy system to acquire the oceanographical data. Motions of the buoy were also measured in terms of three components of acceleration, roll, and pitch. The buoy was removed from the site in May 1978.A method of eliminating influence of the buoy motion on the measured wave data was invented and examined by using the field data. It was found that the influence of the buoy motion on the wave data was so small that the amount of correcting the motion was negligible. In addition wave data obtained at the buoy were compared with those obtained at the fixed type platform, which was built in 1974 to get the reference data of wind, waves and currents. The agreement was found to be good. The performance of the buoy was as good as intended. Thus, it was shown that the buoy so far developed could be used as the platform for oceanographic research such as measuring wind and waves with higher precision. 相似文献
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The seakeeping characteristics of various boom geometries in irregular waves and currents are investigated. The response of a floating boom section on the open sea is a function of a number of parameters, such as boom geometry, distribution of mass, buoyancy/weight ratio, and wave and current characteristics. To understand the relationship between these design parameters more clearly, a series of regular and irregular wave tests were conducted with six different 1:4 scale models for three current velocities and six different wave conditions. To simplify the problem, only rigid boom sections consisting of a buoyancy cylinder and vertical skirt were used. In parallel with this experimental program, a numerical model for the responses of two-dimensional floating boom sections in small-amplitude waves is also developed. The numerical results are compared with our large-scale experimental results. The boom effectiveness on the open sea is evaluated based on the concept of “effective draft” and “effective freeboard” assuming that drainage and oversplashing failures are the prime mechanisms of containment failure. Using the present results, a guideline for the optimum design/selection of future booms is developed. 相似文献
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A new model is presented for the propagation of monochromatic surface waves over a region of arbitrary, one-dimensional bottom topography. The smoothly varying bed profile is divided into a series of shelves separated by abrupt steps. The wave fields on either side of each step are related by a “transfer matrix”, and the propagation of waves along the shelf between adjacent steps is described by a “rotation matrix”. Starting from a point where the surface wavefield is known, the step by step application of the appropriate combination of these matrices allows computation of the wavefield over the region of interest. If the individual steps are small then the transfer matrix reduces to a simpler plane-wave form, with considerable savings in computational effort. Comparisons are made with an exact potential solution for single and double steps in order to investigate the accuracy and validity of the matrix method. Finally, the model is applied to the case of wave reflection by fixed sinusoidal bottom undulations, and good agreement is found between its predictions and existing laboratory data. 相似文献
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The small-scale roughness of the sea surface acts as an important link in air-sea interaction processes. Radar and sonar waves are scattered by short surface waves providing the basis for remote sensing methods of the sea surface. At high wind speeds, breaking waves occur. Bubbles penetrate into the water and drastically increase acoustical reverberation, transmission loss and ambient noise. Thus, the development of short waves and wave breaking have to be known to apply radar remote sensing to the surface and to deduce from radar backscatter which sonar conditions prevail. To measure the wind dependence of short waves an experimental device was constructed for use from stationary platforms. It is nearly all-weather capable and can easily be handled by a crane. On the other hand, frequencies of short waves measured in a fixed position are extremely frequency shifted by currents. This limits the usefulness of tower-based measurements, e.g., the short wave modulation by wind and waves or currents can only be estimated in a rough approximation. Consequently, a buoy was developed to reduce the frequency shifts. The principle of the buoy is to drift in the local surface current and to follow the amplitudes of long waves. Therefore, short waves are measured in facets of long waves and the Doppler shifts are minimized. The wind is measured at a constant height above the long wave profile and relative to the moving facets. The paper describes the conventional measuring device and points out the necessity of the drifting buoy system. Examples of wind and wave spectra are presented and short wave modulations by long waves are depicted, too. From these measurements, new insights in short wave behaviour have to be expected 相似文献
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The Breaking Celerity Index (BCI) is proposed as a new wave breaking criterion for Boussinesq-type equations wave propagation models (BTE).The BCI effectiveness in determining the breaking initiation location has been verified against data from different experimental investigations conducted with incident regular and irregular waves propagating along uniform slope [Utku, M. (1999). “The Relative Trough Froude Number. A New Criteria for Wave Breaking”. Ph.D. Dissertation, Dept. of Civil and Enviromental Engineering, Old Dominion University, Norfolk, VA; Gonsalves Veloso dos Reis, M.T.L. (1992). “Characteristics of waves in the surf zone”. MS Thesis, Department of Civil Engineering, University of Liverpool., Liverpool; Lara, J.L., Losada, I.J., and Liu, P.L.-F. (2006). “Breaking waves over a mild gravel slope: experimental and numerical analysis”. Journal of Geophysical Research, VOL 111, C11019] and barred beaches [Tomasicchio, G.R., and Sancho, F. (2002). “On wave induced undertow at a barred beach”. Proceedings of 28th International Conference on Coastal Engineering, ASCE, New York, 557–569]. The considered experiments were carried out in small-scale and large-scale facilities. In addition, one set of data has been obtained by the use of the COBRAS model based upon the Reynolds Averaged Navier Stokes (RANS) equations [Liu, P.L.-F., Lin, P., Hsu, T., Chang, K., Losada, I.J., Vidal, C., and Sakakiyama, T. (2000). “A Reynolds averaged Navier–Stokes equation model for nonlinear water wave and structure interactions”. Proceedings of Coastal Structures ‘99, Balkema, Rotterdam, 169–174; Losada, I.J., Lara, J.L., and Liu, P.L.-F. (2005). “Numerical simulation based on a RANS model of wave groups on an impermeable slope”. Proceedings of Fifth International Symposium WAVES 2005, Madrid].Numerical simulations have been performed with the 1D-FUNWAVE model [Kirby, J.T., Wei, G., Chen, Q., Kennedy, A.B., and Dalrymple, R.A. (1998). “FUNWAVE 1.0 Fully Nonlinear Boussinesq Wave Model Documentation and User's Manual”. Research Report No CACR-98-06, Center for Applied Coastal Research, University of Delaware, Newark]. With regard to the adopted experimental conditions, the breaking location has been calculated for different trigger mechanisms [Zelt, J.A. (1991). “The run-up of nonbreaking and breaking solitary waves”. Coastal Engineering, 15, 205–246; Kennedy, A.B., Chen, Q., Kirby, J.T., and Dalrymple, R.A. (2000). “Boussinesq modeling of wave transformation, breaking and run-up. I: 1D”. Journal of Waterway, Port, Coastal and Ocean Engineering, 126, 39–47; Utku, M., and Basco, D.R. (2002). “A new criteria for wave breaking based on the Relative Trough Froude Number”. Proceedings of 28th International Conference on Coastal Engineering, ASCE, New York, 258–268] including the proposed BCI.The calculations have shown that BCI gives a better agreement with the physical data with respect to the other trigger criteria, both for spilling and plunging breaking events, with a not negligible reduction of the calculation time. 相似文献
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I.D. James 《Ocean Engineering》1986,13(2)
The sea surface displacements measured by a wave staff, fixed in horizontal position, and a wave rider buoy, which moves with the water particles, are compared. Second-order theory shows that, to this approximation, the second harmonic in the surface displacement is not measured by the wave rider. Here a simple approximation to maximum amplitude gravity waves is considered; then a freely floating wave rider gives an approximately sinusoidal record at a lower frequency than the wave, while a tethered wave rider gives results depending on the mooring system. The horizontal motion of a tethered buoy still affects the measurements, particularly of the second and higher harmonics. 相似文献
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The motions and time-mean horizontal drift forces of floating backward-bent duct buoy wave energy absorbers in regular waves are calculated taking account of the oscillating surface-pressure due to the pressure drop in the air chamber above the oscillating water column within the scope of the linear wave theory. The present numerical results show that the time-mean drift forces of backward-bent duct buoys are in the reverse direction of propagation of the incident waves over specific frequency ranges as found by McCormick through his experimental work. The drift force has been calculated by the near-field method. A brief discussion on Maruo’s formula which shows that the time-mean drift force must be in the direction of propagation of the incident waves, has also been presented. 相似文献
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A.G. Davies 《Ocean Engineering》1991,18(1-2)
Previous studies of combined wave and current bottom boundary layer flow have concentrated on the final converged state of the flow following the addition of waves to a current. While this final state is of primary interest to modellers and engineers, it pre-supposes that such a state is actually attained in reality, and this may not always be the case. In addition, it overlooks the interesting and complicated transient effects which occur as a wave-current flow evolves from one state to another. The present study concentrates attention on the transient effects predicted by a “one-equation” turbulence closure model. Results of case studies are presented in which waves are superimposed co-linearly on a current (“forward problem”), and are then removed from the converged wave-current flow (“backward problem”). Two formulations of the “forward” and “backward” problems are discussed. In the first the steady component of the pressure gradient driving the mean flow is held constant throughout, and in the second the steady component of the mass flux is held constant. In each case the detailed evolution of the profiles of mean velocity, turbulent energy, mixing length, eddy viscosity and shear stress are discussed. More generally, the question of the convergence timescale of a combined wave-current flow is considered, and a convergence criterion is proposed. 相似文献
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A submarine-launched wave measuring buoy 总被引：1，自引：0，他引：1
A wave buoy, the Submarine Deployed Sea State Sensor (SUDSS), was developed to directly measure surface waves from a submerged moving submarine. The SUDSS is adapted from the Submarine Launched Expendable Bathythermograph (SSXBT) by replacing its temperature probe with a vertical sensing accelerometer. The SUDSS, launched from the aft signal ejector, utilizes the SSXBT cylinder, its lifting body, and filament wire spool-out mechanisms. Upon surfacing it oscillates vertically in phase with waves of frequencies below 0.5 Hz producing a voltage signal that is conducted via the filament wire back to the submarine and processed to produce a 10–12 minute wave record. On-board data analysis determines spectra, sea state, and the partial variance of spectral energy which between 0.2–0.5 Hz estimates the local wind speed.An accelerometer calibrator for wave frequencies was assembled consisting of a computer-controlled motor-driven swing arm which rotates an accelerometer as a simple harmonic oscillator; different rotation rates providing a variety of frequencies. Absolute accelerations are determined from the arm radius and its angular velocity. Wilcoxen accelerometers were chosen, providing a linear output of 1 v/g0 (sensitivity) for simulated waves from 0.09–0.25 Hz (4–11 s periods).The SUDSS fitted with a buoyant tether signal cable, can be deployed from a surface ship for rapid wave/sea state measurements. 相似文献
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为验证研制的国产气象水文传感器的性能,设计了直径3 m的圆盘式小型浮标,拟搭载所有传感器在2000 m以深海域开展应用试验。统计了试验海域的有义波高、波浪周期、最大风速和表层流速等环境参数,计算了浮标的质量、重心、吃水、受力投影面积和惯性矩等设计参数。以三维势流理论和波浪辐射-绕射理论为基础,使用AQWA软件在频域内对浮标进行水动力计算,仿真了浮标工作时所受的一阶波浪力、附加质量、附加阻尼和运动幅值响应因子,通过仿真结果对浮标设计方案进行优化,优化后的浮标计算结果随波浪频率变化平缓,幅值合理且无激增点,表明该浮标与工作海域内的波浪没有发生明显谐振,对环境载荷有足够的承受能力,方案可用于浮标研制。 相似文献