In this paper,the effect of water and air fluids on the behavior of a planing catamaran in calm water was studied separately in calm water by using experimental and numerical methods.Experiments were conducted in a to...In this paper,the effect of water and air fluids on the behavior of a planing catamaran in calm water was studied separately in calm water by using experimental and numerical methods.Experiments were conducted in a towing tank over the Froude number range of 0.49–2.9 with two degrees of freedom.The model vessel displacement of 5.3 kg was implemented in experimental tests.Craft behavior was evaluated at the displacements of 5.3,4.6,and 4 kg by using the numerical method.The numerical simulation results for the hull’s resistance force were validated with similar experimental data.The fluid volume model was applied to simulate two-phase flow.The SST k-ωturbulence model was used to investigate the effect of turbulence on the catamaran.The results showed that in the planing mode,the contribution of air to pressure resistance increased by 55%,40%,and 60%at the mentioned displacements,whereas the contribution of air to friction resistance was less than 15%on average.The contribution of the air to the total lift force at the abovementioned displacements exceeded 70%,60%,and 50%in the planing mode but was less than 10%in the displacement mode.At the displacements of 5.3 and 4 kg,the area under the effect of maximum pressure moved around the center of gravity and caused porpoising longitudinal instability at the Froude numbers of 2.9 and 2.4,respectively.However,at the displacement of 4.6 kg,this effect did not occur,and the vessel maintained its stability.展开更多
Wave glider is the first unmanned autonomous marine robot to use only the ocean’s endless supply of wave energy for propulsion. Wave glider comprises fin system, tether and float which harvest all of its energy from ...Wave glider is the first unmanned autonomous marine robot to use only the ocean’s endless supply of wave energy for propulsion. Wave glider comprises fin system, tether and float which harvest all of its energy from waves and sun to produce forward thrust. As a consequence of the lack of design information and data for the wave glider, the main aim of the study is using computational fluid dynamics (CFD) to present a method to predict calm water resistance for the floating hull through calculations of 3 different hull forms using the same mesh generation under the same conditions. Calculations are carried out using 3 different mesh sizes for Froude number in the range of 0.10 to 0.40 and compared for accuracy of the solution parameters. Wigley parabolic hull, high speed round bilge form (NPL) and Series 60 have been comparatively investigated in order to estimate the hydrodynamics performance of the hull. The linear seakeeping analysis, coupled heave and pitch motions, roll motion, in irregular waves, with one parameter Bretschneider and JONSWAP spectra. Numerical computations have been performed for motion response predictions of the three hulls which cover wave angles from 0? to 180? at 45? intervals for six different forward speeds from 0 to 4.304 knots using Maxsurf Motion software. The close agreement between the numerical predictions shows the importance of CFD applications in estimating the hydrodynamics performance to design the floating hull and the numerical method is useful in glider design. The fine grid is fit to the calculation and shows the most appropriate results because convergent results are obtained as the mesh size decrease so the fine grid is the one which will be applied for the other hulls. Also it can be observed that the added resistance and the RAOs for NPL hull are less than the other hulls. Therefore from the comparisons, the NPL hull is the optimum hull compared to the other hulls from the resistance and seakeeping point of view.展开更多
采用多相URANS(unsteady RANS)方法,针对水上飞机静水起飞过程中的性能分析,提出了一种新的数值模拟研究思路。通过考虑起飞过程中气动力和水动力之间的耦合影响、升力和浮力对水线位置高度变化的影响以及阻力和发动机推力对模型前进速...采用多相URANS(unsteady RANS)方法,针对水上飞机静水起飞过程中的性能分析,提出了一种新的数值模拟研究思路。通过考虑起飞过程中气动力和水动力之间的耦合影响、升力和浮力对水线位置高度变化的影响以及阻力和发动机推力对模型前进速度的影响,得到模型起飞过程中的受力变化趋势。模拟前通过分别计算标准模型的气动力和水动力并与实验数据对比,对数值计算方法进行了验证,模拟过程中通过VOF(volume of fluid)方法实现对自由液面界面的捕捉,最后通过对静水起飞过程中模型受力变化进行分析并与实验结果比较,对本文中的水气耦合数值计算进行了验证,计算结果表明,水上飞机低压载状态起飞过程中所受总阻力是缓慢增加的,并不会出现往复;同时水线高度逐渐下降,下降速度逐渐加快,且不会出现埋艏现象。展开更多
文摘In this paper,the effect of water and air fluids on the behavior of a planing catamaran in calm water was studied separately in calm water by using experimental and numerical methods.Experiments were conducted in a towing tank over the Froude number range of 0.49–2.9 with two degrees of freedom.The model vessel displacement of 5.3 kg was implemented in experimental tests.Craft behavior was evaluated at the displacements of 5.3,4.6,and 4 kg by using the numerical method.The numerical simulation results for the hull’s resistance force were validated with similar experimental data.The fluid volume model was applied to simulate two-phase flow.The SST k-ωturbulence model was used to investigate the effect of turbulence on the catamaran.The results showed that in the planing mode,the contribution of air to pressure resistance increased by 55%,40%,and 60%at the mentioned displacements,whereas the contribution of air to friction resistance was less than 15%on average.The contribution of the air to the total lift force at the abovementioned displacements exceeded 70%,60%,and 50%in the planing mode but was less than 10%in the displacement mode.At the displacements of 5.3 and 4 kg,the area under the effect of maximum pressure moved around the center of gravity and caused porpoising longitudinal instability at the Froude numbers of 2.9 and 2.4,respectively.However,at the displacement of 4.6 kg,this effect did not occur,and the vessel maintained its stability.
文摘Wave glider is the first unmanned autonomous marine robot to use only the ocean’s endless supply of wave energy for propulsion. Wave glider comprises fin system, tether and float which harvest all of its energy from waves and sun to produce forward thrust. As a consequence of the lack of design information and data for the wave glider, the main aim of the study is using computational fluid dynamics (CFD) to present a method to predict calm water resistance for the floating hull through calculations of 3 different hull forms using the same mesh generation under the same conditions. Calculations are carried out using 3 different mesh sizes for Froude number in the range of 0.10 to 0.40 and compared for accuracy of the solution parameters. Wigley parabolic hull, high speed round bilge form (NPL) and Series 60 have been comparatively investigated in order to estimate the hydrodynamics performance of the hull. The linear seakeeping analysis, coupled heave and pitch motions, roll motion, in irregular waves, with one parameter Bretschneider and JONSWAP spectra. Numerical computations have been performed for motion response predictions of the three hulls which cover wave angles from 0? to 180? at 45? intervals for six different forward speeds from 0 to 4.304 knots using Maxsurf Motion software. The close agreement between the numerical predictions shows the importance of CFD applications in estimating the hydrodynamics performance to design the floating hull and the numerical method is useful in glider design. The fine grid is fit to the calculation and shows the most appropriate results because convergent results are obtained as the mesh size decrease so the fine grid is the one which will be applied for the other hulls. Also it can be observed that the added resistance and the RAOs for NPL hull are less than the other hulls. Therefore from the comparisons, the NPL hull is the optimum hull compared to the other hulls from the resistance and seakeeping point of view.
文摘采用多相URANS(unsteady RANS)方法,针对水上飞机静水起飞过程中的性能分析,提出了一种新的数值模拟研究思路。通过考虑起飞过程中气动力和水动力之间的耦合影响、升力和浮力对水线位置高度变化的影响以及阻力和发动机推力对模型前进速度的影响,得到模型起飞过程中的受力变化趋势。模拟前通过分别计算标准模型的气动力和水动力并与实验数据对比,对数值计算方法进行了验证,模拟过程中通过VOF(volume of fluid)方法实现对自由液面界面的捕捉,最后通过对静水起飞过程中模型受力变化进行分析并与实验结果比较,对本文中的水气耦合数值计算进行了验证,计算结果表明,水上飞机低压载状态起飞过程中所受总阻力是缓慢增加的,并不会出现往复;同时水线高度逐渐下降,下降速度逐渐加快,且不会出现埋艏现象。
