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1.
Numerical flow simulation of flush type intake duct of waterjet 总被引：1，自引：0，他引：1
Waterjet propulsion system is widely used to thrust high speed marine vessels in excess of 30–35 knots by virtue of high propulsive efficiency, good maneuverability, and less vibration. Since, however, approximately 7–9% of the total power is lost in intake duct due to flow separation, nonuniformity, etc., detail understanding of flow phenomena occurring within intake duct is essential to reduce the power loss. The present work solved 3D incompressible RANS equations on multiblocked grid system of the flush type intake duct of waterjet. The numerical results of surface pressure distributions, velocity vectors, and streamlines were compared with experiments and good agreements were obtained for three jet velocity ratios. Strong suction flow through the inlet was shown and the vortex induced by the separation along the corner of the side wall was clearly shown. Flow separation on the lip was also observed. The location of stagnation point on the lip was well predicted, in accordance with PIV measurement. 相似文献
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Experimental Investigation into the performance of the Axial-Flow-Type Waterjet according to the Variation of Impeller Tip Clearance 总被引：1，自引：0，他引：1
The tip clearance inside the duct from the tip of the impeller is very important to the performance of waterjet systems, which fact has been proven in the pump field. The tip clearance is especially important on the model scale because it is very difficult in manufacture to keep the tip clearance constant and minimally small along the inside of the duct. In the present study, a flush-type waterjet propulsion unit (duct, impeller, stator, and nozzle) was designed for an amphibious tracked vehicle. Two impellers of different inner diameter were designed and manufactured in order to investigate the gap effect. Resistance and self-propulsion tests with a 1/5-scale model were conducted in PNU towing tank. The flow rate at the nozzle exit, the static pressure at the various sections along the duct and also the nozzle, the revolution of the impeller, and the torque, thrust, and towing forces at various advanced speeds were measured. Based on these measurements, the performance was analyzed according to the ITTC 96 standard analysis method. Based on this analysis method, the full-scale effective and delivered power of the tracked vehicle was estimated according to the variation of tip clearance. 相似文献
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Attenuations of solitary wave over a patch of submerged canopy are experimentally investigated. The submerged canopy is modeled by a group of circular cylinder array. The decay coefficients of different wave heights in two water depths along the wave flume are measured for six canopy models, including two canopy heights and three styles of arrangements. The relationships among the decay coefficient, and the dimensionless wave height, submergence ratio, relative height and arrangement of the canopy are experimentally studied. 2D PIV technique is employed to measure the representative flow field inside the canopy. A four-deck flow structure is proposed for wave flow field over shallow submerged canopy. The characteristics of shear flow inside the aligned canopy region are discussed. 相似文献
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Experimental measurements of solitary wave attenuation over shallow and intermediate submerged canopy 总被引：1，自引：1，他引：0
Attenuations of solitary wave over a patch of submerged canopy are experimentally investigated. The submerged canopy is modeled by a group of circular cylinder array. The decay coefficients of different wave heights in two water depths along the wave flume are measured for six canopy models, including two canopy heights and three styles of arrangements. The relationships among the decay coefficient, and the dimensionless wave height, submergence ratio, relative height and arrangement of the canopy are experimentally studied. 2D PIV technique is employed to measure the representative flow field inside the canopy. A four-deck flow structure is proposed for wave flow field over shallow submerged canopy. The characteristics of shear flow inside the aligned canopy region are discussed. 相似文献
7.
Similarity methods provide a very powerful technique for modelling offshore platforms. Such methods are preferable for situations where the wave-structure interaction process is complex, and its modelling cannot be expressed by rigorous mathematical formulations.In modelling the interaction between waves and an offshore platform, the dynamic properties of the wave and structure must be considered together to determine the similitude parameters. The paper gives details of such an investigation using a frequency response function approach. Three different models, which are termed general, distorted and nondistorted Froudian models, are developed. From the general model, it was found that the velocity scales of the wave and structure could be treated differently. Internal and external force scales could also be different. It is observed then that a restrictive modelling criterion is used when the velocity scale of a structure is obtained from Froudian scale modelling. Furthermore, detailed scales for practical use are developed. The model parameters for an acrylic plastic tripod tower platform with length scales of 1/50 and 1/70 are given, and the accuracy involved among the three models determined for these scales. The sensitivity of the results to slight variations in thickness and Young's modulus are also discussed. 相似文献
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The flow characteristics of tidal jets induced by a Tidal-Jet Generator (TJG) are investigated using a finite-difference numerical scheme, named Navier–Stokes (NS)–Marker and Cell (MAC)-TIDE, based on the fully 3D NS equations. The TJG is an enclosed rectangular breakwater, which has vertical opening and a large enclosed volume inside. During both phases of tide, strong and uni-directional jets can be obtained locally from the inlet of the TJG, due to the water level difference between the inner and outer sides of TJG.The computed results are extensively compared with three other independently developed numerical models; 3D-ADI, DVM, and CIP-CSF. These models are based on quasi-3D, 2D depth-averaged, and fully 3D NS equations, respectively. It is seen that the present fully 3D numerical model NS–MAC-TIDE can predict the maximum intensity of inlet velocity with higher accuracy than the other numerical models when compared with the empirical function proposed from the experiments. The numerical simulations based on NS–MAC-TIDE can reproduce successfully the processes of generation, development, and dissipation of tidal jets. The effects of gap opening on the main characteristics of the tidal jet flow are assessed. Through numerical assessment, it is also clearly demonstrated that the residual time of a pollutant distributed around the front of the TJG can be decreased by significant amount due to the locally induced tidal jet. The TJG can thus utilize tidal energy for water purification in local marine environment by providing a flushing mechanism. 相似文献
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S. V. Shagalov V. P. Reutov G. V. Rybushkina 《Izvestiya Atmospheric and Oceanic Physics》2010,46(1):95-108
The generation of narrow-band Rossby wave packets and the modulated vortex chains induced by them in a weakly-dissipative
zonal flow on the beta-plane with a velocity profile in the form of a shear layer is studied. The analysis is performed within
the framework of the asymptotic approach based on the distinguishing a thin critical layer inside of which the vortex chains
are formed. The evolution equations, describing the simultaneous development of a wave packet envelope and vorticity perturbations
in a nonlinear critical layer, are derived for a weakly supercritical flow. A transition to the complex dynamics of a wave
packet (low-mode turbulence) is studied within the framework of a numerical solution of the derived equations and its mechanism
is revealed. The onset of chaotic advection and anomalous diffusion of passive scalar in the critical layer is considered,
and the exponent of the diffusion law is calculated. 相似文献
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When a ship model test is performed in a tank, particularly when the tank is small and the ship model is relatively large, the blockage effect will inevitably occur. With increased ship model scale and speed, the blockage effect becomes more obvious and must be corrected. In this study, the KRISO 3600 TEU Container Ship(KCS) is taken as a model and computational fluid dynamics techniques and ship resistance tests are applied to explore the mechanism and correction method of the blockage effect. By considering the degrees of freedom of the sinkage and trim, the resistance of the ship model is calculated in the infinite domain and for blockage ratios of 1.5%, 1.8%, 2.2%, and3.0%. Through analysis of the free surface, pressure distribution, and flow field around the ship model, the action law of the blockage effect is studied. The Scott formula and mean flow correction formula based on the average cross sectional area are recommended as the main correction methods, and these formulas are improved using a factor for the return flow velocity correction based on comparison of the modified results given by different formulas. This modification method is verified by resistance test data obtained from three ship models with different scale ratios. 相似文献
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The lifting motor pump is the core equipment of the deep-sea hydraulic pipeline lifting system, and its research results are one of the important technical reserves for the research and development of marine mineral resources. It is an essential capacity for lifting motor pump to allow coarse particles pass through the flow passages, to realize this requirement, an increased flowrate method is employed to design a wide flow passage for an innovative six-stage lifting motor pump. Based on Computational Fluid Dynamics (CFD), the anti-blocking performance of the lifting motor pump designed by the conventional method and the increased flowrate method are compared, which show that the latter is better than the former. Numerical simulations of the internal two-phase flow inside the innovative pump are presented, and the flow parameters such as pressure, velocity and particle trajectory are obtained. According to the design method of the six-stage lifting motor pump, a two-stage lifting motor pump is manufactured, and the relevant performance experiments are performed. The results obtained by numerical simulation is in a good agreement with the experimental ones, thus the validity and accuracy of the numerical model and method is verified. The innovative two-stage lifting motor pump can operate smoothly with low noise and no blockage occurs, and its performance meets the design goals and requirements. 相似文献
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The main purpose of this article is to systematically investigate the influence of offshore fringing reef topography on the infragravity-period harbor oscillations. The infragravity (IG) period oscillations inside an elongated harbor induced by normally-incident bichromatic wave groups are simulated using a fully nonlinear Boussinesq model, FUNWAVE 2.0. Based on an IG wave decomposition method, effects of plane reef-face slopes, reef-face profile shapes and the existence of reef ridge on bound and free IG waves and their relative components inside the harbor are comprehensively studied. For the given harbor and reef ridge, the range of the reef-face slopes and the various profile shapes studied in this paper, results show that the amplitude of the free IG waves inside the harbor increases with the increasing of the reef-face slope; while the bound IG waves inside the harbor seem insensitive to it. The effects of the profile shapes on the IG period waves inside the harbor are closely related to the width of the reef face. The existence of the reef ridge can relieve the bound IG waves to some extent when the incident short wave amplitudes are relatively large, while its effects on the free IG waves are negligible. 相似文献
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导管推进器是一种普遍应用于无人遥控潜水器（ROV）等潜器中的特种推进器。在桨叶与导管之间的梢隙中存在非常复杂的流动,本研究基于大涡模拟（LES）对导管推进器的梢隙流动进行了数值模拟分析。通过对时间步长的收敛性研究,建立两套基于不同网格类型的计算模型。将计算结果与试验进行对比,比较两种不同类型网格模拟结果的差异发现,切割体网格能够更好地捕捉到泄涡的细节,并结合梢隙流场的原理分析泄涡发展的过程,梢隙涡的驱动力是吸力面与压力面之间的压差。此外,随着进速系数增大,梢隙周向的涡管轴向分布范围减小,主泄涡发生位置延后,泄出涡的长度和数量都有所减少。 相似文献
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The purpose of the present study is to investigate the performance and three-dimensional flow fields in a water-jet pump. TASCflow is employed to simulate the rotator-stator coupling flow field. A standard k-ε turbulence model combined with standard wall functions is used. In order to investigate the effect of a rear stator on flow fields, the flows in two water-jet pumps with and without a rear stator are studied. Computational fluid dynamics (CFD)-predicted overall performances are in good agreement with the experimental results. Then the flow fields, such as the pressure distribution on the blade surfaces, and the axial and tangential velocity distribution, especially the radial loading distribution, are investigated at different flow rates. In addition, the effects of a rear stator and different spacings between the rotor and the stator on the overall performance and the flow fields of the water-jet pump are also investigated. 相似文献
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According to analysis on field data obtained by ADCP(Acoustic Doppler Current Profiler),the flow regime of the Yangtze River Estuary is studied by use of a 3-D numerical model.The flow field characteristics,under the influence of Coriolis force,saltwater intrusion and freshwater inflow and tidal current interaction,are depicted in details.The main driving forces and some important effective factors of lateral,longitudinal and horizontal circulation are also analyzed. 相似文献
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Gridding heterogeneous bathymetric data sets with stacked continuous curvature splines in tension 总被引：3，自引：0，他引：3
Gridding heterogeneous bathymetric data sets for the compilation of Digital bathymetric models (DBMs), poses specific problems
when there are extreme variations in source data density. This requires gridding routines capable of subsampling high-resolution
source data while preserving as much as possible of the small details, at the same time as interpolating in areas with sparse
data without generating gridding artifacts. A frequently used gridding method generalizes bicubic spline interpolation and
is known as continuous curvature splines in tension. This method is further enhanced in this article in order to specifically
handle heterogeneous bathymetric source data. Our method constructs the final grid through stacking several surfaces of different
resolutions, each generated using the splines in tension algorithm. With this approach, the gridding resolution is locally
adjusted to the density of the source data set: Areas with high-resolution data are gridded at higher resolution than areas
with sparse source data. In comparison with some of the most widely used gridding methods, our approach yields superior DBMs
based on heterogeneous bathymetric data sets with regard to preserving small bathymetric details in the high-resolution source
data, while minimizing interpolation artifacts in the sparsely data constrained regions. Common problems such as artifacts
from ship tracklines are suppressed. Even if our stacked continuous curvature splines in tension gridding algorithm has been
specifically designed to construct DBMs from heterogeneous bathymetric source data, it may be used to compile regular grids
from other geoscientific measurements. 相似文献
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In this paper, two modified pressure gradient models based on Taylor series expansion are proposed to enhance the higher order source term MPS (MPS-HS) method. The modified models consist of gradient correction matrices applied to the existing (base) pressure gradient models. To validate the modified pressure gradient models first hydrostatic pressure test is simulated and compared to both the base and modified MPS methods. Using the modified models are shown to reduce unphysical pressure oscillations observed in the base models. Second, an evolution of an elliptical drop in a 2D flow field is examined and shown to verify the models. Third, the proposed models illustrated appropriate stability and consistency properties against analytical solutions when an altered gravitational acceleration was superimposed to the hydrostatic pressure test. In addition, an improved performance is observed when Higher order Laplacian (HL) and Error-Compensating Source (ECS) of the Poisson Pressure Equation (PPE) schemes are coupled with the modified pressure gradient models compared to coupling them with the base gradient models. Finally, the modified MPS methods enhanced performances are validated in a free-surface flow simulation for a dam break problem with impact pressure, and a violent sloshing flow in a rectangular tank when compared to the base MPS methods against an existing experimental data. 相似文献
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A numerical method is proposed to predict the effective wake profiles of high speed underwater vehicles propelled by contra-rotating propellers (CRPs), in which the hydrodynamic effects of the CRPs are simulated by distributed body forces. First, Reynolds-averaged Navier-Stokes (RANS) simulations are conducted for identical body-force distributions in open-water and self-propulsion conditions. The effective wake profiles at the CRP disks are then obtained by subtracting the velocities induced by the body forces in the open water from those induced by the body forces in the self-propulsion condition. The effective wake profiles were then predicted for a generic underwater vehicle with an established CRP design. Next, the hydrodynamic performance of the CRPs in the effective wake was computed using an in-house vortex-lattice code. The potential-flow results agree well with those provided by the RANS simulation under the self-propulsion condition, indicating that the proposed method can predict the effective wake profiles for CRPs with reasonable accuracy. The influences of different wake components on the blade forces were investigated, determining that for CRPs, and especially for the aft propeller, the circumferential wake cannot be neglected in the design. 相似文献
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对安装在海上风电钢管桩基础上的升降式网箱结构的波浪场特性进行研究,掌握升降式网箱结构内部及结构后方水体的运动特征及速度场变化情况。基于OpenFOAM软件包开发了波、流与孔隙介质结构相互作用的数值计算模型,将网箱结构按等效阻力简化为多孔介质结构,开展升降式网箱结构的波浪场特性研究。研究结果表明：网箱结构对流体具有一定的阻流作用,网箱结构内部速度场得到一定程度的减小,网箱结构背浪侧也有一定的速度衰减区域;对比网箱结构顶部不同潜深条件下的网箱结构内部流场特征,网箱结构顶部潜深在1/4D~1/2D（D为水深）范围内网箱结构内部流场速度最小、流场最为稳定、速度分布均匀,网箱结构向浪侧前方和背浪侧后方流场波动较小。所得结论表明在钢管桩基础上安装升降式网箱结构时需要关注的网箱结构对流场特性的影响,充分考虑网箱结构阻力对流速的作用,掌握极端工况下升降式网箱结构保持优良养殖环境需要下潜的高度范围,以保障升降式网箱的安全。 相似文献