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Andrea Di Mascio Riccardo Broglia Roberto Muscari 《Journal of Marine Science and Technology》2009,14(1):19-29
Numerical simulations of incompressible flows, with and without free surface, by means of high-order Godunov-type schemes
are presented; the results are compared with the second-order essentially nonoscillatory (ENO) scheme, already implemented
and extensively used by the authors for the simulation of flows around ship hulls. Uncertainty assessment and convergence
properties are discussed for two practical test cases: the steady and unsteady laminar flow past a NACA 0012 profile with
and without incidence, and the steady free surface flow past a ship hull at model Reynolds number. The analysis is aimed to
highlight advantages and drawbacks of the numerical schemes considered herein.
This work was presented in part at the International Conference on Computational Methods in Marine Engineering—MARINE 2007,
Barcelona, June 3–4, 2007. 相似文献
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舵片是保证超空泡航行体运动稳定性和控制航行弹道的重要部分。文章基于均质平衡流模型和SST(Shear Stress Transport)湍流模型,计算了单独舵片的流体动力特性,并与试验数据进行了对比,结果符合较好,验证了计算模型的有效性。基于此方法,计算了单独舵片发生空化后在不同操舵状态下的非定常流体动力变化。结果表明,在攻角相同时,操舵状态下舵片的非定常升力系数和定常结果差别不大,而非定常阻力系数大于定常结果,并且操舵速度越快,阻力系数越大。另外计算了舵片发生空化后的流体动力系数,结果显示在攻角相同时,舵片的阻力系数和升力系数均小于其在全湿状态下的结果;在空化状态下,舵片升力系数的斜率小于全湿状态,并且舵片升力系数的斜率是变化的,存在某临界攻角,攻角大于此临界值时,升力系数的斜率减小,而此临界攻角恰好为舵片的吸力面刚刚出现空化时的攻角;操舵状态下舵片的阻力系数和升力系数的变化规律与定常结果一致,但是数值偏小。 相似文献
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HUANG Sheng WANG Pei-sheng HU Jian 《船舶与海洋工程学报》2007,6(2):6-11
The hydrodynamic performance of a propeller in unsteady inflow was calculated using the surface panel method. The surfaces of blades and hub were discreted by a number of hyperboloidal quadrilateral panels with constant source and doublet distribution. Each panel's corner coordinates were calculated by spline interpolation between the main parameter and the blade geometry of the propeller. The integral equation was derived using the Green Formula. The influence coefficient of the matrix was calculated by the Morino analytic formula. The tangential velocity distribution was calculated with the Yanagizawa method, and the pressure coefficient was calculated using the Bonuli equation. The pressure Kutta condition was satisfied at the trailing edge of the propeller blade using the Newton-Raphson iterative procedure, so as to make the pressure coefficients of the suction and pressure faces of the blade equal at the trailing edge. Calculated results for the propeller in steady inflow were taken as initialization values for the unsteady inflow calculation process. Calculations were carried out from the moment the propeller achieved steady rotation. At each time interval, a linear algebraic equation combined with Kutta condition was established on a key blade and solved numerically. Comparison between calculated results and experimental results indicates that this method is correct and effective. 相似文献
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Using the SKAGEX dataset for evaluation of ocean model skills 总被引:1,自引:0,他引:1
Numerical ocean models are now being applied in numerous oceanographic studies. However, the qualities of the model results are often uncertain and there is a great need for standards and procedures for evaluation of the skills of numerical general circulation models. In this paper measurements from repeated hydrographical sections across Skagerrak taken in 1990, the SKAGEX dataset, are used to evaluate the skills of two σ-coordinate ocean models and to study the sensitivity of these models to model parameters. A methodology for quantification of model skills based on observations from repeated hydrographical sections in general is suggested. Area averages of absolute differences are for Skagerrak completely dominated by the discrepancies in the upper few meters of the ocean and may not be used to assess models' abilities to reproduce the fields in the larger and deeper part of the ocean. Therefore, discrepancies between average values in time from the observed fields and time averaged values from model outputs are related to the natural variability of the fields. The numbers produced with the suggested measure are relative numbers that will be specific for each section and for each series of observation. Ideally we would therefore like to see the measures computed for a number of sections for various models and choices of model parameters in order to assess model skills. The value of the SKAGEX dataset as a tool for model improvements is demonstrated. Evidence to support the importance of applying non-oscillatory, gradient preserving advection schemes in areas with sharp density fronts is given. The method is used to identify that the forcing/initial values/boundary values for the temperature field are inferior to the corresponding values for the salinity field. With the present coarse resolution, 11 layers in the vertical, it is shown that it is far from obvious that the quality of the model results improve when replacing simple Richardson number formulations for vertical mixing processes with higher order turbulence closure in the Skagerrak area. 相似文献
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Gérard C.Nihous 《船舶与海洋工程学报》2014,(2)
A simple approach is described to estimate the wave power absorption potential of submerged devices known to cause wave focusing and flow enhancement.In particular,the presence of a flow-through power take-off(PTO)system,such as low-head turbines,can be accounted for.The wave radiation characteristics of an appropriately selected Lagrangian element(LE)in the fluid domain are first determined.In the limit of a vanishing mass,the LE reduces to a patch of distributed normal dipoles.The hydrodynamic coefficients of this virtual object are then input in a standard equation of motion where the effect of the PTO can be represented,for example,as a dashpot damping term.The process is illustrated for a class of devices recently proposed by Carter and Ertekin(2011),although in a simplified form.Favorable wave power absorption is shown for large ratios of the LE wave radiation coefficient over the LE added mass coefficient.Under optimal conditions,the relative flow reduction from the PTO theoretically lies between 0.50 and 1 2≈0.71,with lower values corresponding to better configurations.Wave power capture widths,the sensitivity of results to PTO damping and sample spectral calculations at a typical site in Hawaiian waters are proposed to further illustrate the versatility of the method. 相似文献
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胡天群 《交通部上海船舶运输科学研究所学报》1991,(1)
作者根据螺旋桨空化噪声或激振力的产生机理,分析了它们的时间域和频率域特性,指出在噪声和激振力的信号处理中,必须实现对采样起始的控制及宽频域的高速采集.文中简要叙述了“高速采集贮存,慢速传送微机”系统的设计思想,介绍了以瞬态波形存贮器和微机为主体的多功能采集处理系统,并绘出了系统运行的一些实例图.文章还就数字信号处理的基本原理和瞬态波形存贮器的特点,论述了系统所具有的若干独特功能及其在水动力学研究中的应用前景. 相似文献
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