Wave radiation due to oscillation of two parallel spaced cylinders

The radiation problem for two parallel-spaced cylinders is studied. The solution is expressed explicitly in terms of well-behaved convergent series with elementary functions, which are convenient for numerical computation and readily applicable for two-dimensional two-body potential problems. The added mass and damping coefficients together with the phase angles of radiated wave potentials for the forced heave and sway motions of two identical submerged cylinders are presented. The results are useful for determination of the hydrodynamic properties of multi-hull semi-submersibles. In view of the close relationship between a radiation and a scattering problem, the application of the results to the problem of energy extraction from water waves is also noted.     

Stationary variational expressions for radiated and scattered acoustic power and related quantities

The construction of stationary expressions for quantities of physical interest such as radiated power and target strength is discussed broadly for acoustic problems involving radiation or scattering from finite objects of arbitrary shape. The Kirchhoff-Helmholtz integral corollaries of the wave equation, which express acoustic pressure at either interior or exterior points in terms of pressure and its normal derivative over any closed surface, yield for both interior and exterior problems two mathematically dissimilar but related functional relations between surface field quantities. One of these is the better known surface Helmholtz integral equation; the other is a differential-integral relation which involves the tangential derivatives of pressure on the surface. The four linear operators involved in these functional relations are studied and it is found that two are self-adjoint, while the other two are an adjoint pair. A general technique for constructing variational expressions recently developed by Gerjuoy et al. [28] is adapted to acoustic radiation and scattering problems with the functional relations taken as the primary governing relations. Included examples are stationary expressions for the radiated power when either the normal velocity or the pressure are specified on the surface (the other quantity being unknown) and the target strength for scattering from a rigid object. The adjoint relations allow simple physical interpretations for the Lagrange multipliers that arise in the theory, such that the guesses for good trial functions can take advantage of existing physical insight. It is demonstrated with a specific example (transversely vibrating disk) that the resulting estimate for radiated power is substantially more accurate than that of the trial function for surface pressure which was inserted into the stationary expression.     

Fluctuation-dissipation relationships used for calculating the response of the soil moisture content to atmospheric actions

Methods of stochastic dynamics based on the application of fluctuation theorems (FTs) are used for describing nonstationary responses of natural objects to specified finite, but not necessarily small, changes in external factors in the presence of random disturbances. Nonlinear fluctuation-dissipation relationships (FDRs) are obtained on the basis of one of the FTs. These FDRs are used for calculating the soil moisture content response to specified changes in the mean precipitation in the presence of synoptic disturbances. The model under consideration, in spite of its coarseness, includes an important nonlinear effect of the moisture excess discharge into a reservoir. An approximate analytical theory is constructed. This theory makes it possible to take into account nonlinear effects when response functions are determined.     

Estimation of the oxygen and CO2 mean exchange between the ocean and the atmosphere in key areas of the ocean

Current estimations of gas exchange between the ocean and the atmosphere are based on the concepts about diffusive gas transfer across the interface and about a stationary character of the processes; however, under a strong wind, these concepts are invalid. Transfer equations for gas constitutents of the air are incorporated into a numerical model of a nonstationary upper layer of the ocean. These equations contain the source function—gas transfer by bubbles, which becomes noticeable even at a wind speed of 8–10 m/s. The fluxes of oxygen and CO₂ are calculated at a specified wind speed, dependences of these fluxes on the wind speed are constructed, and estimates for the average annual fluxes are obtained for several areas of the Gulf Stream and Kuroshio. A substantial change in the difference of the air-water gas contents under a strong wind, caused by the turbulent exchange growth and appreciably affecting the gas exchange, is noted. The influence of the carbonate system of seawater on the CO₂ transfer during a storm is estimated. The results obtained are compared to the estimates based on the traditional approach.     

Investigation of the influence of wind action upon the currents and propagation of impurities in the azov sea

The surge phenomena and currents in the Azov Sea caused by variable winds in the presence of stationary currents are studied by using a three-dimensional nonlinear mathematical model. The specific features of the transformations of impurities in the water area of the Azov Sea under the joint action of stationary and nonstationary winds are investigated. On the basis of the results of numerical calculations, we make conclusions concerning the dependence of the period of dissipation of impurities on the wind velocity and the location of the regions with impurities. It is shown that the variable wind significantly increases the deviations of the sea level and the area of distribution of the impurity as compared with the action solely of the stationary currents.     

Modeling of the breeze circulation of waters in the Kerch Strait

The problem of the numerical analysis of currents in the Kerch Strait is studied within the framework of a linear nonstationary two-dimensional model in the nondivergent approximation. We describe the actual situation when the motion is induced by a breeze against the background of the daily average northeast wind. The breeze is specified as acting in a narrow coastal strip and can be classified as a zonal wind. The variations of circulation near the Tuzla Island are studied in detail. It is shown that the contribution of the breeze circulation to the total circulation can be significant for the explanation of the processes running in the Kerch Strait. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 16–27, November–December, 2007.     

Indices of the factors that form climate changes of different scales

Radiative forcing, the global warming potential, and the recently proposed global temperature potential are widely used not only in scientific studies but also in a number of economic and political evaluations of the effects of an increase in the contents of greenhouse gases and aerosols and other factors that form climate and its changes. New indices have appeared, and, to calculate them, information is required on the quantitative characteristics of the climate system’s components—current and expected—within standard periods of 20, 100, and 500 years. The calculations of some of these indices and potentials require consideration for variations in the rate of energy exchange between the atmosphere and the underlying surface (ocean) within the indicated periods. This leads to a more general problem of analyzing the sensitivity of the climate system to external (radiative) forcing and its response to such a forcing for the conditions of both stationary (equilibrium) and nonstationary “greenhouse” climates. A brief review of the few existing studies of such a response is given.     

The potential of wetlands in reducing storm surge

A critical component of flood protection in some coastal areas is expected to be the potential contribution of wetlands to the lowering of surges as they propagate inland from the coast. Consequently, an accurate method to quantify the effect of wetlands on coastal surge levels is required. The degree to which wetlands attenuate surge is the subject of debate and difficult to assess. The potential of wetlands to reduce storm surge has typically been expressed as a constant attenuation rate, but the relationship is much more complex. A numerical storm surge model was applied to assess the sensitivity of surge response to specified wetland loss. Results suggest that wetlands do have the potential to reduce surges but the magnitude of attenuation is dependent on the surrounding coastal landscape and the strength and duration of the storm forcing. Numerical models that simulate the relevant physical processes can provide valuable information on how to best integrate wetlands into coastal protection plans. However, while the model applied for this study has displayed skill in estimating surges over wetlands, the formulations are missing key processes and model advancements are necessary.     

Wild and farmed salmon in Norway—A review

The Salmon industry in Norway includes three sectors, namely sea and river fishing for wild salmon, and salmon farming, or aquaculture. The three sectors provide different social, economic and cultural benefits to society, but also face many problems and challenges. They have different interests, practices, traditions and audiences, and are also administered by different authorities and regulated under varying management regimes and legislations. On the one hand, they complement each other in terms of product supply, employment creation and income; on the other hand, they face conflicts over management objectives and strategies. This paper provides an overview of the salmon sectors associated with their status, challenges and management regimes. It further analyzes their interests and conflicts over economic contribution and management. Finally, some potential solutions are suggested in an attempt to solve these conflicts.     

Cloud Formation over the Ocean upon Cold Air Intrusion

The problem of stationary vertical distribution of saturated moist air thermodynamic parameters that takes place, for example, in an eyewall cloud of a tropical cyclone is considered. Based on these distributions, the cloud-growth dynamics problem is also considered. The heat and moisture fluxes from the ocean surface are determined by the wind and temperature difference and subcloud layer condition and last after the beginning of cloud formation. They change the condition of both the cloud and the subcloud layer. The coexistence and interaction of the two different regions require additional conditions. We assume continuity of the temperature and humidity profiles at the lower cloud boundary. The problem of cloud formation over the warmer ocean with account for water-phase transformations is considered in the present study. The cloud boundaries (the upper and the lower) in the process are determined and the temperature and moisture profiles within the cloud are also investigated. The lower boundary dipping is determined while taking the subcloud moisture into account. An approximate analytical model of these processes is formulated, and the corresponding equations are solved numerically. Approximate equations govern the vertical cloud structure well.     

Optimal estimation of ship's attitudes and attitude rates

Estimation of ship rotational motions induced by ocean waves plays a central role in many navigation and fire control applications. Inertial-type instruments are available which give good measurements of the attitude, but some form of signal processing is necessary to obtain angular rates or predict attitudes. Using optimal moving-average (or transversal) filters, we can obtain very good estimates of attitude rates as well as predictions of these values. Filter parameters can be changed adaptively to maintain good performance as the ship changes heading or velocity. The problem of designing these optimal filters is examined in detail and numerical results are given for a particular set of conditions. Two implementations of the adaptive filter are discussed. One is based on a recursive estimation of the process autocorrelations with the filter coefficients being recomputed at periodic intervals or whenever nonstationary conditions are detected. The second implementation is based on Widrow's LMS algorithm. Both alternatives for the adaptive filter implementation are quite reasonable in terms of their computational requirements. The steady-state performance analysis can be considered to be a lower bound on the errors incurred by an adaptive filter.     

Undifferenced Cycle Slip Estimation of Triple-Frequency BeiDou Signals with Ionosphere Prediction

With the rapid development of BeiDou satellite navigation system (BDS), high-quality service has been provided in the Asia-Pacific region currently, which will be extended to the whole world very soon. BDS is the first Global Navigation Satellite System that all satellites broadcast the triple-frequency signals. The triple-frequency signals in theory can improve the cycle slip detection that is one of the preconditions in precise positioning by making use of carrier phase. This paper discusses the development of a cycle slip detection method for undifferenced BDS triple-frequency observations in kinematic scenario. In this method, two geometry-free extra-wide-lane combinations and one geometry-free narrow-lane (NL) combinations are employed. The key is to mitigate the between-epoch ionospheric biases in the geometry-free NL combinations. We propose to predict the ionospheric biases of current epoch by using those from its consecutive foregoing epochs. The method is tested with extensive experiments in varying observation scenarios. The results show that in case of sampling interval as small as 5 s, the between-epoch ionospheric biases can be ignored and the correct cycle slips can be determined. Meanwhile in case of lower sampling frequency, one needs to compensate the ionospheric biases of current epoch by using the predicted ionospheric biases. The presented method can correctly detect all cycle slips even if they are as small as 1 cycle.     

Diffusion reduction in an arbitrary scale third generation wind wave model

The numerical schemes for the geographic propagation of random, short-crested, wind-generated waves in third-generation wave models are either unconditionally stable or only conditionally stable. Having an unconditionally stable scheme gives greater freedom in choosing the time step (for given space steps). The third-generation wave model SWAN (“Simulated WAves Nearshore”, Booij et al., 1999) has been implemented with this type of scheme. This model uses a first order, upwind, implicit numerical scheme for geographic propagation. The scheme can be employed for both stationary (typically small scale) and nonstationary (i.e. time-stepping) computations. Though robust, this first order scheme is very diffusive. This degrades the accuracy of the model in a number of situations, including most model applications at larger scales. The authors reduce the diffusiveness of the model by replacing the existing numerical scheme with two alternative higher order schemes, a scheme that is intended for stationary, small-scale computations, and a scheme that is most appropriate for nonstationary computations. Examples representative of both large-scale and small-scale applications are presented. The alternative schemes are shown to be much less diffusive than the original scheme while retaining the implicit character of the particular SWAN set-up. The additional computational burden of the stationary alternative scheme is negligible, and the expense of the nonstationary alternative scheme is comparable to those used by other third generation wave models. To further accommodate large-scale applications of SWAN, the model is reformulated in terms of spherical coordinates rather than the original Cartesian coordinates. Thus the modified model can calculate wave energy propagation accurately and efficiently at any scale varying from laboratory dimensions (spatial scale O(10 m) with resolution O(0.1 m)), to near-shore coastal dimension (spatial scale O(10 km) with resolution O(100 m)) to oceanic dimensions (spatial scale O(10 000 km) with resolution O(100 km).     

High-speed submerged and surface piercing cavitating hydrofoils, including tandem case

The iterative method that is originally developed before both for two- and three-dimensional single cavitating hydrofoils moving with a constant speed under free surface is applied to the case of high-speed (Froude number up to 6.5) and some figures are given. The method is also extended to include the surface piercing hydrofoils (vertical struts) and the case of tandem hydrofoils into the calculations. The iterative nonlinear method based on the Green's theorem allows separating the cavitating hydrofoil problem(s) and the free surface problem. These two (or three in the case of tandem hydrofoil) problems are solved separately, with the effects of one on the other being accounted for in an iterative manner. The cavitating hydrofoil surface(s) and the free surface are modeled with constant strength dipole and constant strength source panels. The source strengths on the free surface are expressed in terms of perturbation potential by applying the linearized free surface conditions. No radiation condition is enforced for downstream and transverse boundaries. The cavitation number is expressed in terms of Froude number and the submergence depth of the hydrofoil from the free surface. An algebraic grid on the free surface has been described to get a smooth transition between the panels along the direction of uniform inflow and to have a long distance in the downstream direction depending on the wave-length (or Froude number) while keeping the number of panels fixed. First, the method is validated in the case of surface piercing hydrofoil. Then, the effects of high Froude number and the submergence depth of the hydrofoil from free surface on the results are discussed and some figures are given for interested engineers and designers. The method is later applied to the case of tandem hydrofoils and the effects of one hydrofoil on the other are discussed.     

等量纬度展开式的新解法

对地图投影学中经常遇到的等量纬度正反解展开式进行了新的研究。借助M athem atica计算机代数系统强大的数学分析功能,给出了新的正解公式,发现并纠正了前人正解公式中的错误;并且以此为基础,导出了用第一偏心率幂级数形式表示的反解展开式和三种主要的参考椭球下的实用反解计算式。本文研究表明计算机代数系统的应用不但极大地提高了公式推演的效率和准确度,而且反解系数从此可以表示为更简单和更便于记忆的符号形式。     

Identifying and quantifying nonconservative energy production/destruction terms in hydrostatic Boussinesq primitive equation models

This paper seeks to illustrate the point that physical inconsistencies between thermodynamics and dynamics usually introduce nonconservative production/destruction terms in the local total energy balance equation in numerical ocean general circulation models (OGCMs). Such terms potentially give rise to undesirable forces and/or diabatic terms in the momentum and thermodynamic equations, respectively, which could explain some of the observed errors in simulated ocean currents and water masses. In this paper, a theoretical framework is developed to provide a practical method to determine such nonconservative terms, which is illustrated in the context of a relatively simple form of the hydrostatic Boussinesq primitive equation used in early versions of OGCMs, for which at least four main potential sources of energy nonconservation are identified; they arise from: (1) the “hanging” kinetic energy dissipation term; (2) assuming potential or conservative temperature to be a conservative quantity; (3) the interaction of the Boussinesq approximation with the parameterizations of turbulent mixing of temperature and salinity; (4) some adiabatic compressibility effects due to the Boussinesq approximation. In practice, OGCMs also possess spurious numerical energy sources and sinks, but they are not explicitly addressed here.Apart from (1), the identified nonconservative energy sources/sinks are not sign definite, allowing for possible widespread cancellation when integrated globally. Locally, however, these terms may be of the same order of magnitude as actual energy conversion terms thought to occur in the oceans. Although the actual impact of these nonconservative energy terms on the overall accuracy and physical realism of the oceans is difficult to ascertain, an important issue is whether they could impact on transient simulations, and on the transition toward different circulation regimes associated with a significant reorganization of the different energy reservoirs. Some possible solutions for improvement are examined. It is thus found that the term (2) can be substantially reduced by at least one order of magnitude by using conservative temperature instead of potential temperature. Using the anelastic approximation, however, which was initially thought as a possible way to greatly improve the accuracy of the energy budget, would only marginally reduce the term (4) with no impact on the terms (1), (2) and (3).     

两层流体中矩形箱浮体的附加质量和阻尼系数

研究了两层流体中矩形箱浮体的辐射问题。基于特征函数匹配理论,针对矩形箱浮体的三种振荡运动模式(横荡、垂荡和横摇),建立两层流体中矩形箱浮体辐射势的求解方法,导出矩形箱浮体附加质量和阻尼系数的计算公式。对所建立的求解模型进行了数值计算分析,结果表明在矩形箱浮体的某个振荡频率范围内,流体的分层效应对其附加质量和阻尼系数有显著影响的。     

A numerical storm surge forecast model with Kalman filter

ImUcrIONThe deterministic storm stirge nurnrical fOrecast Tnedel has played an imPOrtant role inroutine storm surge real-time fOrecast. But somtimes the error of forecast is still large by usingdeterministic medels (Je1esnianshi et al., l992). The source of these errors mainly comesfrom (1 ) errors of wind stress and medel's open boundary, (2) non--optimized medel param-eter, (3) error of model equations, (4) error of medel's numrical methed, etc. The effec-ti ve methed to solve this probl…     

一个稳态Kalman滤波风暴潮数值预报模式

利用Kalman滤波资料同化技术将海洋站水位观测资料融入二维线性风暴潮模式中,研制具有资料同化能力的风暴潮预报模式,改进风暴潮模式计算结果.通过在风暴潮模式的动量方程中加入模式噪声项来修正模式本身和气象强迫力的不确定性.确定性模式的输出通过带有观测噪声的观测方程与可利用的海洋站的潮位观测资料联系起来.假定初始的模式噪声和观测噪声满足均值为0的高斯分布,用迭代法得到计算区域的状态向量的稳态Kalman滤波,进而得到风暴潮模式输出的最优线性校正结果.利用这种资料同化技术,对1956年发生在东海的一次强风暴潮过程进行了后报试验,结果表明,该同化方法对短期风暴潮水位后(预)报有一定的改进.     

Wave diffraction by elliptical breakwaters in shallow water

The scattering of waves by both floating and submerged stationary elliptical breakwaters is investigated by means of linearised shallow water wave theory. This formulation leads to solutions for the fluid velocity potential in terms of Mathieu functions of real argument. Expressions are derived for the wave-induced forces and moments on the structures and their total and differential scattering cross-sections. Numerical results are presented for a range of wave and structural parameters.The present analysis serves as a prelude to a more comprehensive study of the problem without the shallow water restriction.