基于顶点度的多分辨率表示     

秦勃  纪筱鹏 《中国海洋大学学报(自然科学版)》2004,34(2):303-308

针对边收缩算法在计算大曲率面距离公差时计算量大 ,且收缩大曲率面所含的线段时易使关键点发生偏移而引起模型变动过大、简化不够准确的问题 ,本文在边收缩算法基础上提出了加入顶点度控制的算法 ,以减少大曲率面距离公差的冗余计算 ,并提高模型简化质量。实验表明该算法能提高模型简化质量 ,并加快图形收缩的生成速度。  相似文献   

Performance assessment of a concept propulsor: the thrust-balanced propeller     

Ali Can Takinaci  Mehmet Atlar   《Ocean Engineering》2002,29(2):129-149

This paper presents the results of a numerical performance analysis to demonstrate the worthiness of a recently patented new concept propulsor, the so-called “thrust-balanced propeller (TBP)”. The main advantage of this unconventional propulsor is its inherent ability to reduce the unsteady effect of blade forces and moments when it is operating in a non-uniform wake flow. The propulsor comprises a pair of diametrically opposed blades that are connected to one another and mounted so as to be rotatable together through a limited angle about their spindle axis. A quasi-hydrodynamic approach is described and applied to perform the numerical analysis using a state-of-the-art lifting surface procedure for conventional propellers. Performance comparisons with a conventional fixed-pitch propeller are made for the blade forces and moments, efficiency, cavitation extents and fluctuating hull pressures. Bearing in mind the quasi-static nature of the analyses, the results present favourable performance characteristics for the thrust-balanced propeller and support the worthiness of the concept. However, the concept needs to be proved through physical model tests, which are planned to take in a cavitation tunnel.  相似文献   

Acoustic plane-wave scattering from a rough surface over a random fluid medium     

Jin-Yuan Liu  Chen-Fen Huang  Ping-Chang Hsueh 《Ocean Engineering》2002,29(8):915-930

Acoustic plane-wave scattering from a rough surface overlying a fluid half-space with a sound-speed distribution subject to a small random variation is considered. Under the assumption that the surface roughness and medium randomness are statistically independent, the scattered field may be derived by first solving for the mean field in the medium, and then incorporating with boundary-perturbation method to obtain the total mean field and the power spectral density of the scattered field. The employed algorithm is compatible to the analysis available in the existing literature so that the formulations are conveniently integrated. The results for the power spectral density have shown that the effects of medium inhomogeneities on the rough surface scattering are limited in a spectral regime where the scattered components have shallow grazing angles. The distribution of the power spectral density over the space is primarily governed by the power spectrum and correlation lengths of the rough surface.  相似文献   

Prediction of hydrodynamic loading on a mini TLP with free surface effects     

Bassam A. Younis  Vlado P. Przulj 《Ocean Engineering》2006,33(2):181-204

This paper describes the extension of a fluid-flow simulations method to capture the free surface evolution around a full-scale Tension Leg Platform (TLP). The focus is on the prediction of the resulting hydrodynamic loading on the various elements of the TLP in turbulent flow conditions and, in particular, on quantifying the effects of the free surface distortion on this loading. The basic method uses finite-volume techniques to discretize the differential equations governing conservation of mass and momentum in three dimensions. The time-averaged forms of the equations are used, and the effects of turbulence are accounted for by using a two-equation, eddy-viscosity closure. The method is extended here via the incorporation of surface-tracking algorithm on a moving grid to predict the free-surface shape. The algorithm was checked against experimental measurements from two benchmark flows: the flow over a submerged semi-circular cylinder and the flow around a floating parabolic hull. Predictions of forces on a model TLP were then obtained both with and without allowing for the deformation of the free surface. The results suggest that the free surface effects on the hydrodynamic loads are small for the values of Froude number typically encountered in offshore engineering practice.  相似文献   

厦门港疏浚弃土吹填造陆物理模型试验研究   总被引：2，自引：0，他引：2  

徐啸  崔峥  毛宁 《台湾海峡》2004,23(3):360-368

通过厦门港潮汐水流整体物理模型试验，掌握了厦门港十万吨级深水航道二期工程疏浚弃土吹填造陆各方案实施前后港池航道水流流态，为规划设计单位和决策部门利用疏浚弃土吹填造陆提供可靠的科学依据，试验结果表明，海沧吹填工程可作为一期吹填方案，鸡屿西吹填造陆工程可作为海沧吹填工程的后续工程，仅从水流角度考虑，象鼻嘴吹填造陆方案1是可行的。  相似文献   

A Preliminary Study of Shear Wave in Seafloor Surface Sediments   总被引：1，自引：0，他引：1  

Bo Lu  Ganxian Li  Shaojian Huang 《Marine Georesources & Geotechnology》2006,24(1):17-28

This article preliminarily reports and analyses the transmission characteristics and behaviors of shear wave in the offshore seafloor surface sediments in China, discusses the relationships between the physical and mechanical features of the shear wave and the compression wave, and compares the testing results with that of Hamilton and Chen et al. The result shows that the shear wave can be tested if the seafloor surface sediment has tangent modulus. The shear wave velocity ranges from 50-600 m/s and the measuring frequency from 50-200 kHz. The sound velocity rate of shear wave and compression wave can be used to appraise the stress-strain feature of seafloor surface sediments. This study provides a basis for further describing and appraising the seafloor sedimentary acoustic-mechanical feature and building a geological-acoustic model on China's offshore sea area.  相似文献   

Shallow-Water Gasohydrothermal Vents of Ushishir Volcano and the Ecosystem of Kraternaya Bight (The Kurile Islands)   总被引：2，自引：0，他引：2  

V. G. Tarasov    M. V. Propp    L. N. Propp    A. V. Zhirmunsky    B. B. Namsakakv    V. M. Gorlenko  D. A. Starynin 《Marine Ecology》1990,11(1):1-23

Abstract. A marine ecosystem in the crater of the Ushishir Volcano (Kraternaya Bight, Yankich Island, the Kuriles) showing gasothcrmal activity was studied for hydrographical, hydrochemical, and biological characteristics. Maximal changes in chemical and biological characteristics were observed in the surface water layer of 0–5 m. This layer had higher water temperature, was saturated with volcanogcnic carbon dioxide (up to 2000 10^-6 torr), ovcrsaturatcd with oxygen (up to 200 %), and contained high concentrations of chlorophyll a. Hydrogen sulfide was found in the surface water layer and at a depth of 15 m in the area of maximal effect of volcanic effluents.
The planktonic community is characterized by high rates of production and destruction of organic matter only in the 0–5 m layer. Daily vertical migrations of the ciliatc Mesodinium rubrum were observed, which caused "red tides".
Bacterial, algobacterial, and diatom mats developed on the bottom of the bight in the zone of gasohydrothermal vents and in areas of volcanic water seeping. The rate of organic matter production in algobacterial mats reached 33.4g C-rrr²-d^-l, chcmolithotrophy predominating. Bottom settlements had high population density and great animal biomass, which reached 10 kg m^-2 in gasohydrothermal fields. They obtain sufficient energy from primary production of microphy-tobenthos, algobacterial, and bacterial mats. Bcnthic species dominant in the bight were not found off the Ushishir Islands.
Some species of macrobenthos inhabiting the Kraternaya Bight differ markedly in size and biomass from the same species found beyond the bight.  相似文献   

Elucidating the dynamics and mixing agents of a shallow fjord through age tracer modelling     

Karin E. Gustafsson  Jrgen Bendtsen 《Estuarine, Coastal and Shelf Science》2007,74(4):641

The mixing agents and their role in the dynamics of a shallow fjord are elucidated through an Eulerian implementation of artificial tracers in a three-dimensional hydrodynamic model. The time scales of vertical mixing in this shallow estuary are short, and the artificial tracers are utilized in order to reveal information not detectable in the temperature or salinity fields. The fjord's response to external forcing is investigated through a series of model experiments in which we quantify vertical mixing, transport time scales of fresh water runoff and estuarine circulation in relation to external forcing.Using age tracers released at surface and bottom, we quantify the time scales of downward mixing of surface water and upward mixing of bottom water. Wind is shown to be the major agent for vertical mixing at nearly all depth levels in the fjord, whereas the tide or external sea level forcing is a minor agent and only occasionally more important just close to the bottom. The time scale of vertical mixing of surface water to the bottom or ventilation time scale of bottom water is estimated to be in the range 0.7 h to 9.0 days, with an average age of 2.7 days for the year 2004.The fjord receives fresh water from two streams entering the innermost part of the fjord, and the distribution and age of this water are studied using both ageing and conservative tracers. The salinity variations outside this fjord are large, and in contrast to the salinity, the artificial tracers provide a straight forward analysis of river water content. The ageing tracer is used to estimate transport time scales of river water (i.e. the time elapsed since the water left the river mouth). In May 2004, the typical age of river water leaving the fjord mouth is 5 days. As the major vertical mixing agent is wind, it controls the estuarine circulation and export of river water. When the wind stress is set to zero, the vertical mixing is reduced and the vertical salinity stratification is increased, and the river water can be effectively exported out of the fjord.We also analyse the river tracer fields and salinity field in relation to along estuary winds in order to detect signs of wind-induced straining of the along estuary density gradient. We find that events of down estuary winds are primarily associated with a reduced along estuary salinity gradient due to increased surface salinity in the innermost part of the fjord, and with an overall decrease in vertical stratification and river water content at the surface. Thus, our results show no apparent signs of wind-induced straining in this shallow fjord but instead they indicate increased levels of vertical mixing or upwelling during down estuary wind events.  相似文献   

Applied hydrodynamic wave-resistance computation by Fourier transform     

Jorge D'Elia  Mario A. Storti  Sergio R. Idelsohn 《Ocean Engineering》2002,29(3):261-278

An applied Fourier transform computation for the hydrodynamic wave-resistance coefficient is shown, oriented to potential flows with a free surface and infinity depth. The presence of a ship-like body is simulated by its equivalent pressure disturbance imposed on the un-perturbed free surface, where a linearized free surface condition is used. The wave-resistance coefficient is obtained from the wave-height downstream. Two examples with closed solutions are considered: a submerged dipole, as a test-case, and a parabolic pressure distribution of compact support. In the three dimensional case, a dispersion relation is included which is a key resource for an inexpensive computation of the wave pattern far downstream like fifteen ship-lengths.  相似文献   

Comparison among four kinds of data of sea surface wind stress in the South China Sea   总被引：1，自引：0，他引：1  

Xie Qiang  Wang Weiqiang  Mao Qingwen 《海洋学报(英文版)》2002,21(2):263-273

By using remote sensing (ERS) data, FSU data, COADS data and Hellerman & Rosen-stein objective analysis data to analyze the sea surface wind stress in the South China Sea, it is found that the remote sensing data have higher resolution and more reasonable values. Therefore we suggest that remote sensing data be chosen in the study of climatological features of sea surface wind stress and its seasonal variability in the South China Sea, especially in the study of small and middle scale eddies.  相似文献