Numerical simulations of wave–current flow in an ocean basin     

《Applied Ocean Research》2016

Wave–current flow is a phenomenon that is present in many practical engineering situations. Over the past several decades, this type of flow has been increasingly investigated under controlled laboratory conditions. This paper presents a numerical study of wave–current flow in the ocean basin of the LabOceano (COPPE/UFRJ). A homogeneous multiphase model based on the RANS equations and the k–ɛ turbulence model implemented in ANSYS-CFX code were used. A cross section of the ocean basin was represented. A regular wave with a height of 0.08 m and a period of 1.80 s (i.e., a wave steepness of H/L = 0.016), propagating on favourable currents, was simulated. The behaviour of the free surface elevation over time and the streamlines along the basin for wave and wave–current flows were presented. The numerical results were compared to the non-viscous theory given by the Rayleigh equation applied to the problem of wave–current interaction. Good agreement was found between the wave length estimated by the numerical results and the analytical solutions, with a deviation of less than 2%.  相似文献   

Hydrodynamic analysis of three–unit arrays of floating annular oscillating–water–column wave energy converters     

《Applied Ocean Research》2016

This paper deals with the hydrodynamic analysis of an array of Oscillating Water Column (OWC) devices, made up of coaxial cylinders, which are floating either independently or as a unit forming a floating platform. The platform is considered either free – floating or as TLP configuration connected to the sea bottom. Numerical results concerning the three boundary value problems, namely, the diffraction, the motion – and the pressure – dependent radiation ones are given. They have been obtained through an analytical solution method using matched axisymmetric eigenfunction expansion formulations. In all cases the interaction phenomena with neighbouring bodies have been taken properly into account using the physical idea of multiple scattering. Numerical results for the first – and the mean second – order wave forces, the hydrodynamic interaction coefficients along with pressure hydrodynamic parameters, inner air pressure and free–surface oscillation amplitude inside and outside of each device are parametrically evaluated and supplemented by experimental data.  相似文献   

Ocean robotics in support of fisheries research and management     

S Swart  JJ Zietsman  JC Coetzee  DG Goslett  A Hoek  D Needham 《African Journal of Marine Science》2016,38(4):525-538

South Africa’s small-pelagic fishery is a socio-economically important component of the country’s commercial fisheries sector, second in value only to the demersal trawl fishery. Management of this sector relies on infrequent hydro-acoustic surveys, which provide measures of anchovy Engraulis encrasicolus and sardine Sardinops sagax biomass used in the assessments of stock status and in the development of management plans for the sustainable utilisation of these resources. We demonstrate how technological capabilities in ocean robotics at the Council for Scientific and Industrial Research (CSIR) could augment the current resource-intensive hydro-acoustic ship-based survey programme and create opportunities for expanding its spatial and temporal resolution. We successfully implement and demonstrate an autonomous wave glider, fitted with a hydro-acoustic sensor and compare the data to a collocated ‘traditional’ ship-based acoustics survey. In the future these autonomous systems approaches could be seen as a means to lessen the cost burden of the ship-based survey, while at the same time with the added advantage of continuous collection over much wider spatial and temporal domains. This could enable a more reflexive stock management approach taking into account the seasonal characteristics of the fishery and its ecosystem. Gliders thus have potential to increase dramatically the quantity of information available to fisheries managers, thereby reducing uncertainty and contributing to improved management of valuable fish resources. They are likely to contribute to improved knowledge of the ecology of small pelagic fish species off the coast of South Africa in a changing climate and should potentially also permit the collection of biomass data for other marine resources currently not routinely monitored.  相似文献   

Combined paraxial-consistent boundary conditions finite element model for simulating wave propagation in elastic half-space media     

《Soil Dynamics and Earthquake Engineering》2015

In this paper, a finite element model of a soil island is coupled to both a consistent transmitting boundary and a paraxial boundary, which are then used to model the propagation of waves in semi-infinite elastic layered media. The formulation is carried out in the frequency domain while assuming plane strain conditions. It is known that a discrete model of this type, while providing excellent results for a wide range of physical parameters in the context of a half-space problem, may deteriorate rapidly at low frequencies of excitation. This is so because at low frequencies the various waves in the model eventually attain characteristic wavelengths which exceed the distance of the bottom boundary, which then causes that boundary to fail. Also, the paraxial boundaries themselves break down at very low frequencies. In this paper, this difficulty is overcome and the model׳s performance is improved upon dramatically by incorporating an artificial buffer layer sandwiched between the bottom of the soil medium and the underlying elastic half-space. Applications dealing with rigid foundations resting on homogenous or layered half-space media are shown to exhibit significant improvement. Following extensive simulations, clear guidelines are provided on the performance of the coupled model and an interpretation is given on the engineering significance of the findings. Finally, clear recommendations are provided for the practical use of the proposed modelling strategy.  相似文献   

基于极限强度和逐步坍塌分析的空间框架有限元研究     

韩圣章  闫宏生  王晓波  郭海涛 《海洋技术学报》2005,24(2):98-103

对海洋工程结构基于极限强度和逐步坍塌的理念进行有限元分析中的几个问题进行了探讨,给出了有限元分析的弹性分析理论和塑性考虑方法,并对实施有限元分析过程中的控制进行了分析,对几个主要问题进行了讨论,为提高分析的可靠性奠定了坚实的基础。  相似文献   

冰芯和台站记录的近50 a来东南极冰盖边缘地区气候变化格局   总被引：4，自引：0，他引：4  

效存德  秦大河  任贾文  李忠勤  张明军  孙维贞  王晓香 《冰川冻土》2003,25(1):1-10

对取自东南极冰盖Lambert冰流东、西两侧共支雪芯,恢复了过去50 a来稳定同位素温度序列和积累率序列.对比发现,位于Lambert冰流东侧,即位于Wilks地和Princess Elizabeth 地的5支雪芯(GC₃0, GD03, GD15, DT001和DT085),过去50 a来积累率总体为上升趋势,δ¹⁸O上升速率介于0.34～2.6 kg·m^-2·a^-1; 稳定同位素显示其气温亦呈整体上升趋势, 上升速率介于0‰～0.02‰·a^-1. 但对位于Lamb ert冰流西侧, 即位于Dronning Maud地、Mizuho高原和Kamp地的5支雪芯(Core E,DML 05,W2 00, LGB16和MGA),过去50 a来积累率总体为下降趋势,下降速率介于-0.01～-2.3 6 kg·m^-2·a^-1; 稳定同位素温度变化则十分复杂:Dronning Maud 地西侧为上升, Mizuho高原和Kamp地为下降或变化不明显. 分布于LGB两侧沿岸气象站记录也印证了上述格局. 这种格局可能是南大洋独特的环流形式-环南极波(ACW)-在特殊地形( 如大的冰盆)影响下, 在南极冰盖边缘的表现形式.  相似文献   

Spatio‐temporal distribution of actual evapotranspiration in the Indus Basin Irrigation System          下载免费PDF全文

Umar Waqas Liaqat  Minha Choi  Usman Khalid Awan 《水文研究》2015,29(11):2613-2627

Strategic planning of optimal water use requires an accurate assessment of actual evapotranspiration (ET_a) to understand the environmental and hydrological processes of the world's largest contiguous irrigation networks, including the Indus Basin Irrigation System (IBIS) in Pakistan. The Surface Energy Balance System (SEBS) has been used successfully for accurate estimations of ET_a in different river basins throughout the world. In this study, we examined the application of SEBS using publically available remote sensing data to assess spatial variations in water consumption and to map water stress from daily to annual scales in the IBIS. Ground‐based ET_a was calculated by the advection‐aridity method, from nine meteorological sites, and used to evaluate the intra‐annual seasonality in the hydrological year 2009–2010. In comparison with the advection‐aridity, SEBS computed daily ET_a was slightly underestimated with a bias of ?0.15 mm day^?1 during the kharif (wet; April–September) season, and it was overestimated with a bias of 0.23 mm day^?1 in the rabi (dry; October–March) season. Monthly values of the ET_a estimated by SEBS were significantly (P < 0.05) controlled by mean air temperature and rainfall, among other climatological variables (relative humidity, sunshine hours and wind speed). Because of the seasonal (kharif and rabi) differences in the water and energy budget in the huge canal command areas of the IBIS, ET_a and rainfall were positively correlated in the kharif season and were negatively correlated during the rabi season. In addition, analysis of the evaporation process showed that mixed‐cropping and rice–wheat dominated areas had lower and higher water consumption rates, respectively, in comparison with other cropping systems in the basin. Basin areas under water stress were identified by means of spatial variations in the relative evapotranspiration, which had an average value of 0.59 and 0.42 during the kharif and the rabi seasons, respectively. The hydrological parameters used in this study provide useful information for understanding hydrological processes at different spatial and temporal scales. Results of this study further suggest that the SEBS is useful for evaluation of water resources in semi‐arid to arid regions over longer periods, if the data inputs are carefully handled. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Oblique surface wave propagation over a small undulation on the bottom of an ocean     

S. C. Martha 《地球物理与天体物理流体动力学》2013,107(2):65-80

The problem of oblique water wave diffraction by small undulation of the bottom of a laterally unbounded ocean is considered using linear water wave theory. A perturbation analysis is employed to obtain the velocity potential, the reflection and the transmission coefficients up to the first order in terms of integrals involving the shape functions c(x) representing the bottom undulation. Finite cosine transform is used to find the first order potential, and this potential is utilised in obtaining the first order reflection and transmission coefficients. Some particular forms of the shape function representing an exponentially damped undulation, a single hump and a patch of sinusoidal ripples are considered and the integrals for the reflection and transmission coefficients are evaluated. For the exponentially damped undulation, it is observed that the reflection ceases much before transmission while for the single hump, reflection and transmission go hand in hand up to a certain value of the wavenumber, after which they vanish. For the patch of sinusoidal ripples having the same wavenumber, the reflection coefficient up to the first order is found to be an oscillatory function in the quotient of twice the component of the wavenumber along x-axis and the ripple wavenumber. When this quotient becomes one, the theory predicts a resonant interaction between the bed and free surface, and the reflection coefficient becomes a multiple of the number of ripples. High reflection of the incident wave energy occurs if this number is large. Also, when a patch of ripples having different wavenumbers is considered the same result follows. Known results for the normal incidence are recovered as special cases for the patch of sinusoidal ripples. The theoretical observations are shown computationally.  相似文献   

波力发电方案的工程性探讨   总被引：4，自引：1，他引：4  

陈加菁  王龙文 《海洋工程》1995,(1)

本文从工程角度出发，分析了波力发电的困难，从而指出，在目前技术水平下，一个现实性的波力发电装置必需具备的条件，并结合原理性，分析了值得重视的二类波力发电装置。进而推介了一种工程性较强的柱式波力发电系统。  相似文献   

Numerical analysis of seasonal heat storage in an energy pile foundation     

《Computers and Geotechnics》2014

The use of concrete geostructures for energy extraction and storage in the ground is an environmentally friendly and easy way of cooling and heating buildings. With such energy geostructures, it is possible to transfer energy from the ground to buildings by means of fluid-filled pipes cast in concrete. By injecting thermal energy in summer and extracting it in winter, the ground in the area of a building’s piles can be used for seasonal energy storage, as long as the underground water flow in the storage remains low. This paper is a contribution to the improvement of the knowledge in the field of energy geostructures. The behaviour of a multi-pile seasonal storage system subjected to thermo-mechanical loading is examined numerically from both thermal and mechanical perspectives. The purpose of this paper is (i) to propose a thermo-hydro-mechanical 2D solution to the 3D problem, (ii) to explore the thermal behaviour of this type of storage and (iii) to evaluate its structural consequences. Coupled multi-physical finite element modelling is conducted. The efficiency of the storage is not dramatically affected by an increase in the annual mean temperature of the storage. It is shown that induced mechanical loads are less important when considering a wholly heated pile structure than when considering a single heated pile in a foundation. The evolution of stresses in the piles and in the soil during heating–cooling cycles also reveals possible critical phenomena.  相似文献