Isoparametric Boundary Element Method Applied to the Rectangular and Delta Hydrofoils near the Free Surface     

Hassan GHASSEMI  Ahmad Reza KOHANSAL 《中国海洋工程》2010,24(2):321-331

In this paper, the hydrodynamic characteristics and flow field around rectangular and delta hydrofoils, moving with a constant speed beneath the free surface are numerically studied by means of isoparametric boundary element method (IBEM). The quantities (source and dipole strengths) and the geometry of the elements are represented by a linear distribution. Two types of three-dimensional hydrofoils (rectangular and delta) are selected with NACA4412 and symmetric Joukowski sections. Some numerical results of pressure distribution, lift, wave-making drag coefficients and velocity field around the hydrofoils are presented. Also, the wave pattern due to moving hydrofoil is predicted at different operational conditions. Comparisons are made between computational results obtained through this method and those from the experimental measurements and other numerical results which reveal good agreement.  相似文献   

基于大涡模拟的波状前缘水翼空化抑制研究     

马楷东  曹留帅  万德成 《海洋工程》2023,41(6):112-123

为了降低空化造成的水动力性能损失,基于仿生学原理,参考座头鲸鳍肢剖面形状,将前缘波浪构型引入到水翼设计中,研究波状前缘水翼的非定常空化特性,并探究前缘参数改变对空化控制的效果和规律。选用NACA63₄-021水翼为基准模型,进行前缘参数化重构,设计出3种不同的波状水翼进行对比研究。采用大涡模拟（LES）方法对空化流场进行精细化数值模拟,针对基准水翼和不同波幅与波长参数下的波状水翼开展了空化周期、升阻力系数、压力脉动以及流向涡结构的对比分析。结果发现,波状水翼在抑制空化和降低压力脉动方面都取得了显著效果。其中,3种不同的波状水翼空化抑制率分别为15.7%、18.6%和27.9%,压力脉动幅值分别降低了55.3%、67.3%和74.6%。分析表明,波浪前缘的引入使得空化的分区效应更加凸显,空化从波谷处初生,增大波幅或减小波长都可以加强对空化的抑制效果,并可以提高升力系数以及显著降低水翼表面的压力脉动。前缘波浪构型还将诱发向下游发展的对转涡结构,不同前缘参数的波状水翼涡结构的演化是相似的,空泡发展与溃灭的整个过程对涡结构的发展也具有显著影响。  相似文献   

Ibiza Absolute Calibration Experiment: Survey and Preliminary Results     

J. J. MARTINEZ-BENJAMIN  M. MARTINEZ-GARCIA  S. GONZALEZ LOPEZ  A. NUÑEZ ANDRES  F. BUILL POZUELO  M. ESPINO INFANTES 《Marine Geodesy》2013,36(3-4):657-681

Within the framework of a project comprising part of the Spanish Space Program related to the JASON-1 CNES (Centre National d'Etudes Spatiales)/NASA (National Aeronautics and Space Administration) mission, a campaign was conducted from June 9–17, 2003, on the Absolute Calibration Site of the island of Ibiza. The objective was to determine the local marine geoid slope under the ascending (187) and descending (248) Jason-1 ground tracks, in order to allow a better extrapolation of the open-ocean altimetric data with on-shore tide gauge locations, and thereby improve the overall precision of the calibration process. For this we have used a catamaran with two GPS antennas onboard, following the Corsica/Senetosa design (Bonnefond et al. 2003a Bonnefond, P., Exertier, P., Laurain, O., Menard, Y., Orsoni, A., Jeansou, E., Haines, B., Kubitschek, D. and Born, G. 2003a. Leveling Sea Surface using a GPS catamaran. Marine Geodesy, 26(3–4): 319–334. [Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]). Five GPS reference stations were deployed in order to reduce the distance between the areas covered by the catamaran and the fixed GPS receiver used in the kinematic process. The geodetic activities (e.g., GPS, leveling) have enabled the building of a very accurate (few mm) network in a reference frame compatible with the satellite altimetry missions (ITRF 2000). The GPS kinematic data were processed using two different software programmes, allowing checking of the consistency of the solutions. If the standard deviation of the differences (3.3 cm) is close to the kinematic process precision, they exhibit some large values (up to 14 cm). These large discrepancies have been reduced using a weighting based on the crossover differences. Inasmuch as the distances between the tide gauges and the areas covered by the GPS catamaran were becoming large, we have used the MOG2D ocean model (Carrère and Lyard 2003 Carrère, L. and Lyard, F. 2003. Modelling the barotropic response of the global ocean to atmospheric wind and pressure forcing—comparisons with observations. Geophys. Res. Letters, 30(6) [Google Scholar]) to correct the sea surface from tides. In the farthest areas, the crossover differences show an improvement by a factor of two. Finally, we also present preliminary results on Jason-1 altimeter calibration using the derived marine geoid. From this analysis, the altimeter bias is estimated to be 120 ± 5 mm. The quality of this first result validates the whole GPS-based marine geoid processing, for which the accuracy is estimated to be better than 3 cm rms at crossovers.  相似文献   

Experiments with flexible shrouds to reduce the vortex-induced vibration of a cylinder with low mass and damping     

《Applied Ocean Research》2017

Experiments employing a low-mass-damping cylinder have been conducted to determine the vortex-induced vibration (VIV) response of four suppressors of the flexible-shroud family. The VIV suppressors were inspired in the concept of the Ventilated Trousers (VT), a flexible shroud composed of a flexible net fitted with three-dimensional bobbins. Reynolds number varied between 5 × 10³ and 25 × 10³, while reduced velocity varied from 2 to 26. The VIV dynamic response showed that the VT suppressed the peak amplitude of vibration down to 40% of that of a bare cylinder. Other flexible shrouds also achieved suppression, but not as efficiently. Drag was reduced during the VIV synchronization range, but remained above the value for a bare static cylinder thereafter. Spectral analysis of displacement and lift revealed that, depending on the geometry and distribution of the bobbins, the flexible shroud can develop an unstable behavior, capturing energy from the wake and sustaining vibrations for higher reduced velocities. PIV measurements of the wake revealed that the entrainment flow through the mesh is necessary to extend the vortex-formation length of the wake; this mechanism only occurs for the VT mesh.  相似文献   

Polar lows and tropical hurricanes: Their energy and sizes and a quantitative criterion for their generation     

G. S. Golitsyn 《Izvestiya Atmospheric and Oceanic Physics》2008,44(5):537-547

Similarity and dimension considerations applied to convection in a rotating fluid allows one to estimate the sizes and horizontal velocities of generated vortices. To do this, it is necessary to know the buoyancy flux in the fluid and the angular velocity of fluid rotation [1, 2]. The author’s preliminary efforts [3] have shown that the sizes, wind speeds, and total kinetic energy can thus be estimated correctly for tropical cyclones (TCs), as well as for polar lows (PLs) (which are often called explosive mesocyclones because they take just a few hours to develop). In this study, the sensible and latent heat fluxes for U = 33 m/s and the related buoyancy fluxes are estimated on the basis of climatology, bulk formulas, and the velocity scale of convection in a rotating fluid. In the tropics, at hurricane wind speeds U ≥ 33 m/s and climatological air humidity r = 80%, the total heat flux at the water surface temperature T _s ≥ 26°C becomes equal to or greater than 700 W/m². Due to the Clausius-Clapeyron equation, the latent heat flux to the atmosphere (the main part of the flux in the tropics) decreases substantially at lower values of T _s. Thus, an energy flux from the ocean to the atmosphere of 700 W/m² or greater should be regarded as the first necessary condition for TC genesis instead of the temperature T _s. Low static stability, which must be at least half its climatological value as estimated here, is another necessary condition [4]. In polar regions, total fluxes roughly twice those in the tropics are needed for the formation of explosive mesocyclones, PLs, which is explained by the much smaller role of latent heat, greater geostrophicity, and stronger static stability of the atmosphere there. Enthalpy fluxes and wind speeds are interrelated: the larger the flux is, the stronger the convection, the higher the concentration of angular momentum in an ascending convective air column, and the greater the azimuthal velocity in the vortex are, which in turn enhances the transfer of energy from the ocean. Considering the problem with the use of simple analytic relations makes it possible, for the first time, to find a numerical criterion for their generation. It is hoped that this material may be useful for educational purposes as well.  相似文献   

Solar-, monsoon- and Kuroshio-influenced thermocline depth and sea surface salinity in the southern Okinawa Trough during the past 17,300 years     

Libo Wang  Jun Li  Jingtao Zhao  Helong Wei  Bangqi Hu  Yanguang Dou  Zhilei Sun  Liang Zou  Fenglong Bai 《Geo-Marine Letters》2016,36(4):281-291

Factors influencing millennial-scale variability in the thermocline depth (vertical mixing) and sea surface salinity (SSS) of the southern Okinawa Trough (OT) during the past 17,300 years were investigated based on foraminifer oxygen isotope records of the surface dweller Globigerinoides ruber sensu stricto and the thermocline dweller Pulleniatina obliquiloculata in the AMS ¹⁴C dated OKT-3 core. The thermocline depth is influenced by surface thermal buoyancy (heat) flux, in turn controlled by the annual mean insolation at 30°N and the strength of the East Asian winter monsoon (EAWM). Strong insolation and weak EAWM tend to increase buoyancy gain (decrease buoyancy loss), corresponding to shallow thermocline depths, and vice versa. Regional SSS is influenced by the global ice volume, the Kuroshio Current (KC), and vertical mixing. A deep thermocline coincides with a high SSS because strong vertical mixing brings more, saltier subsurface KC water to the surface, and vice versa. Local SSS (excluding the global ice volume effect) became lower in the northern OT than in the southern OT after ~9.2 ka, implying that Changjiang diluted water had stronger influence in the northern sector. SSS show no major changes during the Bølling/Allerød and Younger Dryas events, probably because the KC disturbed the North Atlantic signals. This argues against earlier interpretations of sea surface temperature records of this core. Wavelet and spectral analyses of the Δδ¹⁸O_P-G (δ¹⁸O of P. obliquiloculata minus G. ruber s.s.) and δ¹⁸O_local records display 1,540-, 1,480-, 1,050-, 860-, 640-, and 630-year periods. These are consistent with published evidence of a pervasive periodicity of 1,500 years in global climate as well as EAWM and KC signatures, and a fundamental solar periodicity of 1,000 years and intermediary derived periodicity of 700 years.  相似文献   

Direct measurements of diapycnal mixing in a fjord reach—Puget Sound's Main Basin     

J. B. Mickett  M. C. Gregg  H. E. Seim   《Estuarine, Coastal and Shelf Science》2004,59(4):539

In the spring of 1988, time series of microstructure and ADCP current profiles were collected at four locations in the North Main Basin of Puget Sound, Washington. Depth and time averages of diapycnal diffusivity at the four stations (1.8−67.0×10⁻⁴ m² s⁻¹) were one to three decades above typical open-ocean thermocline levels. The buoyancy frequency-squared N² was near open-ocean levels, but unlike the open-ocean where N²S², finescale shear-squared S² was three to six times N² over significant portions of the water column at two of the stations. The time and space mean of all measurements ( ) is close to inferred vertical eddy diffusivity from a primitive equation model for Puget Sound (K_z=3×10⁻³ m² s⁻¹) (J. Geophys. Res. 96 (1991) 16779). Large time and space variability of K_ρ was found, with differences of inter-station, depth–time means over one decade. A simple scaling argument using the observed K_ρ suggests significant exchange of mass between the layers of the subtidal flow over the basin's residence time. Additionally, measurements show that local mixing may be comparable to volume-weighted sill mixing in modifying the Main Basin's stratification. Both are contrary to the “advective reach” simplification of fjord dynamics. The mixing levels were dominated by the passage of a mid-depth, southward-flowing density intrusion and what we interpret as a strongly advected, non-linear internal tide. These mechanisms elevated profile-averaged K_ρ by more than 10 times background levels, with sustained patches of K_ρ≥1×10⁻² m² s⁻¹. Critical 8-m gradient Richardson numbers (Ri₈<0.25) matching regions of overturns (>20 m) and strong turbulence suggest that shear instabilities dominated the turbulence production, though there was support for double-diffusive convection in the warm core of the density intrusion.  相似文献   

Turbulent heat transfer in a tube fitted with serrated twist tape under rolling and pitching environments with applications to shipping machineries     

Shyy Woei Chang  Tong-Miin Liou  Kun-Tse Chen 《Ocean Engineering》2008,35(16):1569-1577

Turbulent heat transfer in a swinging tube with a serrated twist tape insert was experimentally examined to reveal the effects of swinging oscillations on heat transfer for such a swirl tube under sea-going conditions. This swirl tube swings about two orthogonal axes under single and compound rolling and pitching oscillations. A selection of Nusselt number (Nu) measurements illustrates the influences of swinging oscillations with and without buoyancy interaction on heat transfer performances. Single rolling or pitching oscillation with the swinging frequencies ranging from 0.333 to 1 Hz reduces heat transfer levels from the static references. Synergistic effects of compound rolling and pitching oscillations with either harmonic or non-harmonic rhythms improve heat transfer performances. Buoyancy effects in the swinging swirl tube elevate local Nu, but are weakened as the relative strength of swinging force increases. A set of heat transfer correlations is derived that permits the individual and interactive effects of single and compound swinging force effects with buoyancy interactions on the developed flow heat transfer value () to be quantified.  相似文献   

Flow around an array of four equispaced square cylinders     

《Applied Ocean Research》2019

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Motions and slamming impact on catamaran   总被引：1，自引：0，他引：1  

Kamlesh S. Varyani  Rama M. Gatiganti  Miroslaw Gerigk 《Ocean Engineering》2000,27(7)

Prediction of craft motions and the dynamic loads acting on a catamaran hull are of great importance to the designer. This paper presents the motions of a Vosper International catamaran in head seas with and without forward speed. Two approaches are used—strip theory and the 3D pulsating source method. A method to predict slamming loads acting on this catamaran section using Computational Fluid Dynamics is presented. The loads acting on catamaran hulls and the cross structure are illustrated.  相似文献   

Primary productivity in a cold water mass and the neighborhood area occurring off Enshu-nada in the late summer of 1989     

Akihiro Shimoto  Satsuki Matsumura 《Journal of Oceanography》1992,48(1):105-115

Primary productivity off Enshu-nada was measured by the¹³C method in September 1989. Primary productivity was estimated in a cold water mass developed off Enshu-nada for the first time. The obtained value was 469 mgC·m^–2·d^–1 and higher than those in the pelagic area of Kuroshio, but equivalent to those in the neritic and the Oyashio areas. It was indicated that cold water mass is the place where organic matter is produced actively. Extremely high chlorophylla of more than 5g·l^–1 were found in the cold water mass. The high productivity was due to high standing crop of phyoplankton. Furthermore, calculated light efficiency and quantum yield showed consistent increase with depth and showed a maximum at 10% light level. Both were larger on the coastal side than those on the oceanic side of the Kuroshio current.  相似文献   

Interface depth used in a two-layer model of nonlinear internal waves     

Guan-Yu Chen  Chung-Lin Wu  Yu-Hwui Wang 《Journal of Oceanography》2014,70(4):329-342

A two-layer model includes three parameters: interface depth h ₁, upper layer density \(\rho_{1}\) , and lower layer density \(\rho_{2}\) . Many theoretical and laboratorial studies of internal waves, as well as most numerical models, are based on the two-layer assumption. However, these three parameters cannot be directly measured because a pycnocline in the real ocean has finite thickness, and the densities in both the mixed layer and the deep ocean are not constant. In the present study, seven different methods are used to determine the interface depth of the two-layer model and compared with the depth of maximum vertical displacement: the depth of maximum buoyancy frequency (Ν _max), the depth where the first mode eigenfunction has its maximum (Φ_max), the depth where the lowest mode temperature empirical orthogonal function has its maximum, the depth where either the two-layer Korteweg–de Vries (KdV) or Benjamin–Ono equation has closest coefficients with their continuously stratified counterparts, and the same KdV approach with stratification replaced by two idealized distributions. The multi-ship measurement conducted near the Luzon Strait is used for deep ocean comparison, and two measurements conducted in the east of Dongsha Atoll are used for shallow water comparison. The results show that in the deep ocean, the KdV approach with idealized type I stratification gives the interface closest to the depth of maximum vertical displacement. In shallow waters, the KdV approach agrees with the measurement best.  相似文献   

Benthic foraminifera of bathyal hydrocarbon vents of the Gulf of Mexico: Initial report on communities and stable isotopes     

Barun K. Sen Gupta  Paul Aharon 《Geo-Marine Letters》1994,14(2-3):88-96

Substrates associated with active hydrocarbon vents in bathyal Gulf of Mexico support numerous foraminiferal species, with a few of them showing unusually high relative abundances. In the 584- to 695-m-depth range,Bolivina ordinaria, Gavelinopsis translucens, andCassidulina neocarinata strongly dominate the vent community, whereasBolivina subaenariensis andUvigerina laevis play this role around a vent at 216 m water depth. The bathymetric imprint on the foraminiferal record is also seen in the ¹⁸O compositions of some species, includingUvigerina peregrina. The adaptation of foraminiferal communities to bacterial (Beggiatoa) mats, in which the redox boundary is very close to the sediment—water interface, and anomalous depletions of¹³C inU. peregrina (relative to the same species from nonventing sites) indicate that several species are probably facultative anaerobes and tolerant of H₂S toxicity.  相似文献   

Modeling and simulation of a novel autonomous underwater vehicle with glider and flapping-foil propulsion capabilities     

田文龙  宋保维  杜晓旭  毛昭勇  丁浩 《中国海洋工程》2012,26(4):603-622

HAISHEN is a long-ranged and highly maneuverable AUV which has two operating modes: glider mode and flapping-foil propulsion mode. As part of the vehicle development, a three-dimensional mathematical model of the conceptual vehicle was developed on the assumption that HAISHEN has a rigid body with two independently controlled oscillating hydrofoils. A flapping-foil model was developed based on the work done by Georgiades et al. (2009). Effect of controllable hydrofoils on the vehicle stable motion performance was studied theoretically. Finally, a dynamics simulation of the vehicle in both operating modes is created in this paper. The simulation demonstrates that: (1) in the glider mode, owing to the independent control of the pitch angle of each hydrofoil, HAISHEN travels faster and more efficiently and has a smaller turning radius than conventional fix-winged gliders; (2) in the flapping-foil propulsion mode, HAISHEN has a high maneuverability with a turning radius smaller than 15 m and a forward motion velocity about 1.8 m/s; (3) the vehicle is stable under all expected operating conditions.  相似文献   

Rapid and precise measurement method for adsorbed