共查询到20条相似文献，搜索用时 46 毫秒
1.
将置于大尺度密度分层水槽上下层流体中的两块垂直板反方向平推,以基于MCC理论解的内孤立波诱导上下层流体中的层平均水平速度作为其运动速度,发展了一种振幅可控的双推板内孤立波实验室造波方法,并对内孤立波作用下浮式生产储油系统(FPSO)的载荷特性开展了系列实验。结果表明,无因次内孤立波水平力和力矩幅值均与先导内孤立子无因次振幅之间呈线性关系,其斜率与上下层流体深度比有关;在各种上下层流体深度比下,无因次内孤立波垂向力幅值与先导内孤立子振幅之间近似呈幂函数关系。 相似文献
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The variation of the dynamic pressures around a circular cylinder due to regular waves is studied in a wave basin of constant water depth of 3 m. The measuring segment consisted of 12 pressure transducers placed at an elevation of 0.8 m below the still water level. The tests were conducted with the cylinder axis inclined with respect to the vertical plane along and against wave direction. The results on the variation of dimensionless pressures with the non-dimensional input wave parameters are reported for different angles of orientation of the cylinder. The sectional normal force obtained by integrating the pressures is also presented as a function of wave steepness and the effect of angle of orientation of the cylinder is also reported. 相似文献
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An array of large concentric porous cylinder arrays is mounted in shallow water exposed to cnoidal waves. The interactions between waves and cylinders are studied theoretically using an eigenfunction expansion approach. Semi-analytical solutions of hydrodynamic loads and wave run-up on each cylinder are obtained using first approximation to cnoidal waves. The square array configuration of four-legged identical concentric porous cylinder is investigated in present study. Numerical results reveal the variation of dimensionless wave force and wave run-up on individual cylinder with angle of incidence, porosity parameter, spacing between outer and inner cylinders, spacing between concentric porous cylinders and wave parameter. Different mechanism of wave force is found under different range of scattering parameter. 相似文献
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This paper discusses the use of Hermite polynomial in the derivation of statistical properties of waves, wave field kinematics and dynamics and wave forces under various conditions. Specifically, covariance functions and approximate spectra are obtained for (1) wave force on vertical cylinder according to Morison's formula, (2) horizontal fluid particle velocity considering the effects of free surface fluctuations, and (3) elevation of breaking waves. 相似文献
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Experimental Investigation of Irregular Wave Uplift Force on Deck of Exposed High-Pile Jetties 总被引：1，自引：0，他引：1
A laboratory setup was developed to investigate irregular wave uplift loads on exposed high-pile jetties.It is shown that the dimensionless uplift load increases to the maximum with an increasing relative clearance and then decreases.The relative clearance corresponding to the peak force is linked to a range from 0.4 to 0.8.When the relative clearance exceeds a certain value,the wave can not reach the underside of the deck and the force becomes zero.Distinct trends of dimensionless force with a relative width of deck show that the force tends to decrease as the relative deck width increases,and then the decrease slows down after the relative deck width increases or decreases to a certain value.The pressure distribution length associated with the maximum uplift force is equivalent to the wave contact width x.When x is larger than the width of deck B,it is taken as B.The statistical distribution of loads obeys the Weibull distribution.The results from the analyses of the real data suggest a new dimensionless prediction model on wave-in-deck uplift loads and the conversion ratio between wave loads at different exceedance probabilities.A comparison is made between the new prediction model and the existing widely used three prediction models.These results are used as useful references for structural design of the jetty. 相似文献
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从提高锚泊系统收放时效性入手,提出了一种半潜式钻井平台复合式锚泊系统组分配比优化设计方法,旨在尽可能降低复合式锚泊系统的钢链配比长度,提高收放效率。结合锚泊系统设计参数,制定优化设计准则,建立优化分析流程,采用ANSYS-AQWA建立锚泊定位半潜式平台水动力分析模型,获得平台运动参数和锚链动力参数,对平台漂移量、锚链最小安全系数、走锚临界张力、锚链最小卧底长度和起锚力进行无量纲指标分析,并综合考虑张力倾角与预张力对优化结果的影响,获得复合式锚泊系统钢链与钢缆的最优配比关系,确定最优钢链长度为395 m,较原钢链长度缩短225 m,钢链收放时间降低36%,进一步提高锚泊系统收放时效性,并降低平台可变荷载。 相似文献
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B. A. Kagan O. Alvarez E. V. Gorchakov 《Izvestiya Atmospheric and Oceanic Physics》2008,44(6):781-786
The third generation of the SWAN wave model is modified by the incorporation of new resistance laws for hydrodynamically rough, incompletely rough (smoothly rough), and smooth underlying surfaces. A modified model is used to determine the functional dependences of wave parameters (such as the dimensionless energy of waves and the dimensionless spectral peak frequency) on a dimensionless fetch. The results of calculations are compared to the experimental data obtained in Lake George (northeastern Australia), which has a nearly constant depth and extended, nearly rectilinear segments of coast. The SWAN model is shown to depend weakly on hydrodynamic properties of the sea bottom: distinctions arising from changes in hydrodynamic properties of the sea bottom are smaller than the variances of experimental estimates. 相似文献
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Accurate estimation of wave uplift force is essential to the designs of reliable coastal and marine structures.We presents a series of laboratory work here on the impact of regular waves on horizontal panels,from which an empirical formula to estimate accurately the wave uplift force on panels is established.The laboratory measurements show that the wave uplift force depends mainly on the incident wave height,the wave period,the wave length,the panel width,and the clearance between the subsurface of the panel and the still water level.Among these factors,the impact of the panel width on uplift forces is relatively complicated.Result shows that the relative panel width(i.e.,the ratio of panel width to wave length)plays a more important role in estimating the wave uplift force.Based on our comprehensive laboratory measurements,we further developed an empirical formula to compute wave uplift force on horizontal panels through dimensionless analysis.Compared with other empirical formulas,this formula uses dimensionless variables of clear physical meanings,thus can describe the interaction between waves and the panels in a better way.In addition,the efficiency of the formula to estimate wave uplift force on horizontal panels is verified against existing works.Therefore,the findings in this study shall be useful for understanding the mechanism of wave uplift force on horizontal panels and numerical model validation. 相似文献
10.
在集合数据同化中,协方差局地化（covariance localization,CL）方法的使用存在限制。集合转换卡尔曼滤波（ensemble transform Kalman filter,ETKF）作为集合平方根滤波的变种方法,是一种应用较广、计算高效的数据同化方法。本文分析了CL方法应用于ETKF方法的困难,从而改进CL方法使其可以适用于ETKF方法。另外,结合浅水方程,利用Askey函数作为多元局地化函数,提出了一种适用于多元数值模型的CL方法。通过具体实验验证,得到了较好的分析结果。 相似文献
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Propagation of shallow water waves in an open parabolic channel using the WKB perturbation technique
A singular perturbation analysis based on the WKB technique to study the hydrodynamic performance of periodic ocean waves that are incident on an open parabolic channel of constant depth is proposed. We derive a linear model to predict the propagation of the long ocean waves into the channel. In this manner, the spatial distribution for the surface elevation of the ocean waves inside the channel as a function of two dimensionless parameters, namely, a kinematical parameter, κ and a geometrical parameter ε, is governed by a second-order ordinary differential equation. The kinematical parameter κ denotes the ratio of the potential head, due to gravity, to the kinetic head of the ocean waves along the longitudinal axis of the parabolic channel. Meanwhile, ε is a dimensionless geometrical parameter that represents a characteristic ratio of the parabolic channel. Using matching conditions, simple expressions for the reflection and transmission coefficients are obtained. 相似文献
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《Oceanic Engineering, IEEE Journal of》1996,21(1):24-36
The treatment of acoustic energy forward scattered from the sea surface, which is modeled as a random communications scatter channel, is the basis for developing an expression for the time-dependent coherence function across a vertical receiving array. The derivation of this model uses linear filter theory applied to the Fresnel-corrected Kirchhoff approximation in obtaining an equation for the covariance function for the forward-scattered problem. The resulting formulation is used to study the dependence of the covariance on experimental and environmental factors. The modeled coherence functions are then formed for various geometrical and environmental parameters and compared to experimental data 相似文献
13.
波浪与外壁透空双方形沉箱相互作用 总被引：1，自引：1，他引：0
在线性波浪理论下,利用复合边界元素法(composite BEM)数值解析在等水深、规则波浪入射二种外壁透空双方形沉箱的无因次波力及Kd绕射分布图,并分别与其他研究者所作双圆筒内、外圆柱无因次波力及绕射分布图的计算结果进行比较,都说明本模式的合理性和可行性。在考虑不同透水参数下,分别计算波浪作用在内、外结构物的波力及沉箱四周绕射系数大小分布图。计算结果显示:波浪作用于外壁透空全透水双方形沉箱,外方柱无因次最大波力值会随着透水参数增加而降低;内方柱无因次最大波力值则随着透水参数增加而增加。本研究结果可供设计外海透水方形沉箱结构交互作用参考。 相似文献
14.
风浪成长关系的分析及其对3/2指数律的支持 总被引：1，自引：1，他引：1
系统地分析比较了迄今根据观测已提出的一些风浪成长关系。通过研究发现 :这些风浪成长关系式存在较大的不协调性。然而 ,当消去无因次风区后 ,由这些关系式得到的无因次波高与无因次周期关系却与 3/ 2指数律有着非常好的协调一致性。还分析 Wen etal构造出的代表平均状况的风浪成长关系。发现由这一风浪成长关系得到的无因次波高与无因次周期关系是与平均状况的 3/ 2指数律完全一致的。上述风浪成长关系构成对 3/ 2指数律的观测支持 ,从而说明了 3/ 2指数律的普遍性。并提出这些风浪成长关系间不协调性的一个可能解释 相似文献
15.
Analysis of measurements from two long-term moored arrays in and near the Gulf Stream suggests a simple parameterization of eddy spatial covariance statistics: a parameterization that can be referred to as “quasi-homogeneous and isotropic”. Taking the normalized covariance function (i.e. the correlation function) for streamfunction to be homogeneous and isotropic and assuming motions to be horizontally nondivergent and hydrostatic permit the velocity and temperature covariances to be derived from the streamfunction covariance. Statistical tests indicate that deviations from these assumptions are indistinguishable from Gaussian random noise. The spatial correlation function used in Gaussian with a decay scale of about 140 km, which is only weakly depth dependent. A simple form is also suggested for the vertical lag dependence. This parameterization permits calculation of derived quantities such as the eddy vorticity flux divergence which is discussed in the context of the mean potential vorticity balances for the depth integrated circulation and for the subthermocline layer. The divergence of the relative vorticity flux is found capable of driving two counter-rotating gyres of strength 30–40 Sv on either side of the Stream, as are observed. The “thickness flux” dominates the lower layer eddy potential vorticity flux and is of the correct sign to make the recirculation more barotropic. The lower layer eddy forcing is weak and the gyres exist in a region of nearly uniform mean potential vorticity. 相似文献
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MICHAEL K. TIPPETT STEPHEN E. COHN RICARDO TODLING DAN MARCHESIN 《地球，A辑:动力气象学与海洋学》2000,52(5):533-553
Ensemble and reduced‐rank approaches to prediction and assimilation rely on low‐dimensional approximations of the estimation error covariances. Here stability properties of the forecast/analysis cycle for linear, time‐independent systems are used to identify factors that cause the steady‐state analysis error covariance to admit a low‐dimensional representation. A useful measure of forecast/analysis cycle stability is the bound matrix , a function of the dynamics, observation operator and assimilation method. Upper and lower estimates for the steady‐state analysis error covariance matrix eigenvalues are derived from the bound matrix. The estimates generalize to time‐dependent systems. If much of the steady‐state analysis error variance is due to a few dominant modes, the leading eigenvectors of the bound matrix approximate those of the steady‐state analysis error covariance matrix. The analytical results are illustrated in two numerical examples where the Kalman filter is carried to steady state. The first example uses the dynamics of a generalized advection equation exhibiting non‐modal transient growth. Failure to observe growing modes leads to increased steady‐state analysis error variances. Leading eigenvectors of the steady‐state analysis error covariance matrix are well approximated by leading eigenvectors of the bound matrix. The second example uses the dynamics of a damped baroclinic wave model. The leading eigenvectors of a lowest‐order approximation of the bound matrix are shown to approximate well the leading eigenvectors of the steady‐state analysis error covariance matrix. 相似文献
19.
Hastings F.D. Schneider J.B. Broschat S.L. Thorsos E.I. 《Oceanic Engineering, IEEE Journal of》2001,26(1):94-101
A finite-difference time-domain (FDTD) method for scattering by one-dimensional, rough fluid-fluid interfaces is presented, modifications to the traditional FDTD algorithm are implemented which yield greater accuracy at lower computational cost. These modifications include use of a conformal technique, in which the grid conforms locally to the interface, and a correction for the numerical dispersion inherent to the FDTD algorithm, Numerical results are presented for fluid-fluid cases modeling water-sediment interfaces. Two different roughness spectra, the single-scale Gaussian roughness spectrum and a multiscale modified power-law spectrum, are used. The Gaussian results are calculated as a function of the dimensionless parameters kh and kl, where k is the wavenumber in water, h is the rms surface height, and l is the surface correlation length. For the modified power-law spectrum, statistical parameters consistent with an insonification frequency of 7.5 kHz are used. Results are compared with those obtained using an integral equation technique both for scattering from single-surface realizations and for Monte Carlo averages of scattering from an ensemble of surface realizations. Scattering strengths are calculated as a function of scattering angle for an incident angle of 70° (20° grazing). The results agree well over all scattering angles for the cases examined 相似文献
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根据预报值具有最小方差这一要求,详细推导了融合法在观测数据为一维、多维和维数不同的情况下的具体同化表达形式,同时还给出了不同情况下与同化表达式相对应的预报误差公式.利用这些公式,可以用融合法处理常见的海洋观测数据的同化问题.在陆架海模式HAMSOM基础上,以4月份的渤海海表温度为例,我们验证了同化公式的正确性,并给出了同化后较好的同化结果。最后将融合法的同化结果与卡尔曼滤波同化结果进行了对比.比较表明,融合法使用起来更简单,且能有效地处理常见的海洋观测数据. 相似文献