共查询到20条相似文献，搜索用时 109 毫秒
1.
Several independent sets of field data have been analyzed in order to estimate the frequency of sediment movement on the continental shelf off Washington over an annual period and to identify the major components of the bottom velocity field causing this motion. Sediment motions resulting from: (1) bottom currents caused by surface wind stress and tides, and (2) wave-induced oscillatory bottom currents have been investigated. Analysis of a 260-day current record from 3 m off the seabed at 80 m depth on the continental shelf and a 205-day open-ocean wave record collected on Cobb Seamount 465 km west of the Washington coast suggest that the threshold of sediment motion was exceeded for approximately 22 days per year as a result of mean currents (20 min time averaged) and approximately 53 days per year from wave-induced oscillatory currents. Substantial variations can be expected from year to year, so these values represent order of magnitude estimates. 相似文献
2.
Jeffrey H. List 《Coastal Engineering》1991,15(5-6)
This paper proposes a new definition of the groupiness factor, GF, based on the envelope of the incident-wave time series. It is shown that an envelope-based GF has several important advantages over the SIWEH-based groupiness factor, including objective criteria for determining the accuracy of the envelope function and well-defined numerical limits.Using this new GF, the variability of incident wave groupiness in the field is examined both temporally, in unbroken waves at a fixed location, and spatially, in a cross-shore array through the surf zone. Contrary to previous studies using the SIWEH-based GF, results suggest that incident wave groupiness may not be an independent parameter in unbroken waves; through a wide range of spectral shapes, from swell to storm waves, the groupiness did not vary significantly. As expected, the groupiness decreases rapidly as waves break through the surf zone, although significant wave height variability persists even through a saturated surf zone. The source of this inner surf zone groupiness is not identified; however, this observation implies that models of long wave generation must account for nonsteady radiation stress gradients landward of some narrow zone near the mean breakpoint. 相似文献
3.
在对南海石油平台所处的南海北部海域海底地形、平均海平面、风浪时空分布等进行分析基础上,利用南海石油平台水位计对Jason-2卫星高度计进行了测高绝对定标,定标结果为30.9 cm±7.8 cm,分析发现南海北部中尺度涡可能对定标结果产生影响;利用南海石油平台测波雷达对Jason-1高度计有效波高进行了精度检验,Jason-1高度计Ku波段和C波段有效波高测量的均方根误差分别为0.43 m和0.45 m。分析和检验结果表明,南海石油平台所处海洋环境条件、平台上装载的水位计和测波雷达均满足卫星雷达高度计定标与检验要求。南海石油平台定标场预期可用于中国海洋二号卫星和其他卫星高度计的定标与检验。 相似文献
4.
On the basis of the wave energy balance equation, the response model of mean directions of locally wind-generated waves in slowly turning wind fields has been derived. The results show that in a homogeneous field, the time scale of the response is not only related to the rate of wave growth, but also to the directional energy distribution and the angle between the wind direction and the mean wave direction. Furthermore, the law of change in the mean wave direction has been derived. The numerical computations show that the response of wave directions to slowly turning wind directions can be treated as the superposition of the responses of wave directions to a series of sudden small-angle changes of wind directions and the turning rate of the mean wave direction depends on the turning rate and the total turning angles of the wind direction. The response of wave directions is in agreement with the response for a sudden change of wind directions if the change in wind directions is very fast. Based on the no 相似文献
5.
Stanislaw R. Massel 《Ocean Engineering》1998,25(9):735-752
The vertical acceleration threshold concept has been applied to evaluate the limiting wave height in the train of wind-induced waves propagated over a horizontal bottom. This concept yields very simple computation of the probability of breaking for stochastic sea in deep and finite water depths. The computations confirmed the available field and laboratory observations that the limiting wave steepness in the deep water is lower than the steepness predicted by Stokes. For shallow water depth, the limiting wave height is smaller than 0.55h. This conclusion is consistent with field as well as wave tank observations. 相似文献
6.
Magdalena Andres Jae-Hun Park Mark Wimbush Xiao-Hua Zhu Kyung-Il Chang Hiroshi Ichikawa 《Journal of Oceanography》2008,64(6):937-950
Data from satellite altimeters and from a 13-month deployment of in situ instruments are used to determine an empirical relationship between sea-level anomaly difference (SLA) across the Kuroshio
in the East China Sea (ECS-Kuroshio) and net transport near 28°N. Applying this relationship to the altimeter data, we obtain
a 12-year time series of ECS-Kuroshio transport crossing the C-line (KT). The resulting mean transport is 18.7 ± 0.2 Sv with
1.8 Sv standard deviation. This KT is compared with a similarly-determined time series of net Ryukyu Current transport crossing
the O-line near 26°N southeast of Okinawa (RT). Their mean sum (24 Sv) is less than the mean predicted Sverdrup transport.
These KT and RT mean-flow estimates form a consistent pattern with historical estimates of other mean flows in the East China
Sea/Philippine Basin region. While mean KT is larger than mean RT by a factor of 3.5, the amplitude of the KT annual cycle
is only half that of RT. At the 95% confidence level the transports are coherent at periods of about 2 years and 100–200 days,
with RT leading KT by about 60 days in each case. At the annual period, the transports are coherent at the 90% confidence
level with KT leading RT by 4–5 months. While the bulk of the Kuroshio enters the ECS through the channel between Taiwan and
Yonaguni-jima, analysis of satellite altimetry maps, together with the transport time series, indicates that the effect of
mesoscale eddies is transmitted to the ECS via the Kerama Gap southwest of Okinawa. Once the effect of these eddies is felt
by the ECS-Kuroshio at 28°N, it is advected rapidly to the Tokara Strait. 相似文献
7.
I. Rychlik 《Ocean Engineering》1996,23(6):447-454
In this note conservative bounds for significant crest height and amplitude obtained from the crossing intensity of a sea are presented. For Gaussian models of a sea level, the Rayleigh approximation for the distributions of amplitude and crest height is proved to provide conservative values for the expected significant wave characteristics. The results are illustrated by examples in which both Gaussian and non-Gaussian models for a sea are considered. 相似文献
8.
For morphological studies in coastal areas the wave-driven currents are often of primary importance. As the computation of the wave-driven current field requires the computation of the driving forces from a wave propagation model, the quality of these forces is basic to the success of the morphological study. It is shown in the paper that, under the common conditions of slowly varying wave fields, the driving force per unit mass is closely proportional to the wave energy dissipation per unit area and that diffraction-related terms give insignificant contributions. This result holds good for wave fields without current refraction. Examples show that formulation of the driving forces in terms of the wave dissipation yields more trustworthy results than those obtained by numerical differentiation of the radiation stress tensor. 相似文献
9.
The Edgeworth’s form of a cumulative expansion of the probability density function (PDF) of surface elevation expands the maximum wave height distribution to predict the occurrence probability of freak waves. This study investigated the enhancement of the occurrence probability of freak waves due to the fourth order moment of surface elevation, kurtosis, change and found that the nonlinear effects on the occurrence probability of a freak wave linearly depends on kurtosis for a small number of waves N=250. The statistical theory was compared with field data, and freak waves sometimes appear when not expected by the Rayleigh theory, but they were predicted by the proposed theory. 相似文献
10.
Non-linear waves have been a research topic for a long time, but have not yet entered common ocean engineering practice. In this article the problem of calculating the probability density function (pdf) for non-linear waves is investigated. The ‘saddle point approximation’ is applied to a second-order wave model to estimate the pdf. The performance of the approximation is compared with the performances of the more commonly used methods for different types of input spectra. In addition, a non-parametric transformation method, with extrapolation of the level crossing intensity, is proposed to estimate the pdf. One simulation and three different data sets are used to investigate the performance of the model. 相似文献
11.
Waves impinging on rubble mound breakwaters and seawalls induce a mean flow within the breakwater, analogous to the so-called undertow within the surf zone. Here, using a plane wave approximation (kh<1.5), a second-order problem is solved for an idealized breakwater with a rectangular cross-section to show the origin and the nature of the mean flow within the porous structure. The mean flow is expressed in terms of a mean stream function analytically derived, obtained based on the mass flux balance between the incident, reflected and transmitted waves. Furthermore, the evolution of other second-order magnitudes such as mean water level and mass flux is analyzed under different incident wave conditions, structure geometry and porous material characteristics. Results show that the evolution of the different mean quantities is controlled mainly by reflection and consequently depends highly on structure geometry and porous material characteristics. Furthermore, it is shown that the return flow is stronger with increasing mass flux decay. Some qualitative experiments to show the described mechanism are also presented. 相似文献
12.
Swagata Bisoi 《Marine Georesources & Geotechnology》2017,35(7):905-920
Global warming is expected to change the wind and wave patterns at a significant level, which may lead to conditions outside current design criteria of monopile supported offshore wind turbine (OWT). This study examines the impact of climate change on the dynamic behavior and future safety of an OWT founded in clay incorporating dynamic soil–structure interaction. A statistical downscaling model is used to generate the time series of future wind speed and wave height at local level. The responses and fatigue life of OWT are estimated for present and future periods and extent of change in design is investigated at offshore location along the west coast of India. Wind speed, wave height, and wave period data are collected from the buoy deployed by Indian National Centre for Ocean Information Services and the future climate for the next 30 years is simulated using the general circulation model corresponding to Special Report on Emission Scenarios A1B scenario. The OWT is modeled as Euler–Bernoulli beam and soil–structure interaction is incorporated using nonlinear p-y springs. This study shows that changes in design of OWT are needed due to increased responses owing to the effect of climate change. Fatigue life is found to be decreased because of climate change. 相似文献
13.
Arvid Naess 《Ocean Engineering》1983,10(5):313-324
A general method for investigating the extreme values of certain types of stochastic processes is described through the study of Morison-type wave loading on piles. By using this method, previously published results concerning the level upcrossing frequency of the Morison-type loading function are rederived. Further, the expected largest value of the loading function during a given time interval has been calculated. 相似文献
14.
鱼类在单向脉冲电场中明显地趋向阳极,称为趋阳反应。这是目前国内外广泛采用的电渔法的生物学依据。在甲壳类动物中,有些具有与鱼类一致的趋向性,有些则正好相反。而国内电捕虾则是根据趋阳性设计的。至于中国对虾(Penaeus orientalis)在脉冲电场下的趋向性,至今尚未见报道。 随着国内对虾养殖业的迅速发展,对养殖技术提出了越来越高的要求。为了探索在养虾池内用电场进行对虾集群、驱赶以及鱼、虾分 相似文献
15.
16.
We consider steady, slowly varying water waves propagating on a steady current over a gently sloping bed, so-called current depth refraction. All expressions are correct to second order in wave amplitude. Formulating the energy equation for the fluctuating motion in terms of wave action (wave energy divided by intrinsic angular frequency) results in an expression, where the dissipative term is strikingly similar to wave action itself. It is simply the ‘extra’ dissipation (per unit area) caused by the fluctuating motion (i.e. total dissipation minus the effect of current acting on total mean bed shear stress) divided by the intrinsic angular frequency. We call it ‘wave action dissipation’. An inconsistency in Phillips' (1977) book is pointed out. A new formula for the calculation of wave amplitudes along rays is set forth. 相似文献
17.
18.
Abstract A necessary stage in calculations for prediction purposes is the study of the tsunami recurrence function which yields mean recurrence of tsunami with maximum wave height not greater than a specified level h. The major problem in using these functions for prediction purposes is the fact that a well‐grounded approximation of empirical data on wave heights is difficult to obtain, because the mathematical model for prediction is an extrapolation of this function for tsunami heights whose recurrence remains uncertain. We shall show that the natural relation of observable tsunamis statistics to extremum statistics leads to the discovery of at least two and possibly three temporal scale intervals with different tsunami modes. It has also been clarified that for the 10 years < T < 103 years range of time periods, which is the most important one for tsunami wave height prediction purposes, the tsunami recurrence is described by two parameters: frequency A of occurrence of large tsunamis and coefficient k of wave ampliflcation near the shore. As an example, a diagram of tsunami hazard zoning of the eastern Honshu coast has been plotted. 相似文献
19.
The boundary layer characteristics beneath waves transforming on a natural beach are affected by both waves and wave-induced
currents, and their predictability is more difficult and challenging than for those observed over a seabed of uniform depth.
In this research, a first-order boundary layer model is developed to investigate the characteristics of bottom boundary layers
in a wave–current coexisting environment beneath shoaling and breaking waves. The main difference between the present modeling
approach and previous methods is in the mathematical formulation for the mean horizontal pressure gradient term in the governing
equations for the cross-shore wave-induced currents. This term is obtained from the wave-averaged momentum equation, and its
magnitude depends on the balance between the wave excess momentum flux gradient and the hydrostatic pressure gradient due
to spatial variations in the wave field of propagating waves and mean water level fluctuations. A turbulence closure scheme
is used with a modified low Reynolds number k-ε model. The model was validated with two published experimental datasets for normally incident shoaling and breaking waves
over a sloping seabed. For shoaling waves, model results agree well with data for the instantaneous velocity profiles, oscillatory
wave amplitudes, and mean velocity profiles. For breaking waves, a good agreement is obtained between model and data for the
vertical distribution of mean shear stress. In particular, the model reproduced the local onshore mean flow near the bottom
beneath shoaling waves, and the vertically decreasing pattern of mean shear stress beneath breaking waves. These successful
demonstrations for wave–current bottom boundary layers are attributed to a novel formulation of the mean pressure gradient
incorporated in the present model. The proposed new formulation plays an important role in modeling the boundary layer characteristics
beneath shoaling and breaking waves, and ensuring that the present model is applicable to nearshore sediment transport and
morphology evolution. 相似文献
20.
Examination of wind-wave interaction source term in WAVEWATCH III with tropical cyclone wind forcing
Results of drag coefficient(CD) from field observations and laboratory wave tank experiments indicate that the operational wave model can overestimate wind energy input under high wind conditions. The wind-wave interaction source term in WAVEWATCH Ⅲ has been modified to examine its behavior with tropical cyclone wind forcing. Using high resolution wind input,numerical experiments under idealized wind field and tropical cyclone Bonnie(1998) were designed to evaluate performance of the modified models. Both experiments indicate that the modified models with reduced CD significantly decrease wind energy input into the wave model and then simulate lower significant wave height(SWH) than the original model. However,the effects on spatial distribution of SWH,mean wavelength,mean wave direction,and directional wave spectra are insignificant. Due to the reduced wind energy input,the idealized experiment shows that the modified models simulate lower SWH than the original model in all four quadrants. The decrease in the front quadrants is significantly larger than that in the rear quadrants;it is larger under higher winds than lower winds. The realistic experiment on tropical cyclone Bonnie shows that the modified model with the various downward trends of CD in high winds creates a simulation that agrees best with scanning radar altimeter observations. 相似文献