航行体出水过程中肩部的自然空化将影响航行体的载荷分布及出水姿态,工程上常采用肩部开孔通气的方式改善航行体表面的力学环境,进而解决此类问题.本文针对水下航行体通气空泡周向融合效果不理想问题,基于有限体积法,采用VOF(volume of ...航行体出水过程中肩部的自然空化将影响航行体的载荷分布及出水姿态,工程上常采用肩部开孔通气的方式改善航行体表面的力学环境,进而解决此类问题.本文针对水下航行体通气空泡周向融合效果不理想问题,基于有限体积法,采用VOF(volume of fluid)多相流模型和动态铺层的动网格技术,数值研究了排气孔下游增加小尺度环形凹槽促进空泡融合的作用机制,以及不同发展阶段、不同工况下环形凹槽对空泡融合的促进作用.结果表明,凹槽可以有效改善通气空泡的融合效果.运动坐标系下来流经过环形凹槽时因为流动膨胀发生了边界层的流动分离,其诱导产生的卷吸作用一方面迟滞了空泡的轴向发展,促进空泡产生周向尺寸更大的剪切涡并沿周向膨胀发展,另一方面将部分通气气体吸入环形凹槽,吸入槽内的气体通过挤压破碎实现了周向融合,且槽内融合气泡溢出下泄促进融合边界上移.此外,凹槽可以通过改善空泡内部的流动状态,使空泡的形态和内部压力在不同工况下都更加稳定.展开更多
为降低水下航行体噪声,研究了艉翼填角的降噪效果。分析了水下航行体艉翼接合部马蹄涡影响螺旋桨伴流场的特征,认为马蹄涡对水下航行体噪声产生了不利影响。针对某无人水下航行体(UUV)设计了一种艉翼填角,运用CFD方法对该艉翼填角优化...为降低水下航行体噪声,研究了艉翼填角的降噪效果。分析了水下航行体艉翼接合部马蹄涡影响螺旋桨伴流场的特征,认为马蹄涡对水下航行体噪声产生了不利影响。针对某无人水下航行体(UUV)设计了一种艉翼填角,运用CFD方法对该艉翼填角优化螺旋桨伴流场的效果进行了数值模拟,结果显示伴流场轴向速度的周向不均匀度系数下降35%-62%。将艉翼填角应用于该UUV,开展航行辐射噪声测量试验,结果显示艉翼填角使UUV航行噪声总声源级降低3.4 d B,尤其对低频噪声抑制较好。展开更多
The low frequency load of an underwater explosion bubble and the generated waves can cause significant rigid motion of a ship that threaten its stability.In order to study the fluid-structure interaction qualitatively...The low frequency load of an underwater explosion bubble and the generated waves can cause significant rigid motion of a ship that threaten its stability.In order to study the fluid-structure interaction qualitatively,a two-dimensional underwater explosion bubble dynamics model,based on the potential flow theory,is established with a double-vortex model for the doubly connected bubble dynamics simulation,and the bubble shows similar dynamics to that in 3-dimensional domain.A fully nonlinear fluid-structure interaction model is established considering the rigid motion of the floating body using the mode-decomposition method.Convergence test of the model is implemented by simulating the free rolling motion of a floating body in still water.Through the simulation of the interaction of the underwater explosion bubble,the generated waves and the floating body based on the presented model,the influences of the buoyancy parameter and the distance parameter are discussed.It is found that the impact loads on floating body caused by underwater explosion bubble near the free surface can be divided into 3 components:bubble pulsation,jet impact,and slamming load of the generated waves,and the intensity of each component changes nonlinearly with the buoyance parameter.The bubble pulsation load decays with the increase in the horizontal distance.However,the impact load from the generated waves is not monotonous to distance.It increases with the distance within a particular distance threshold,but decays thereafter.展开更多
In coastal environment,the motion of unmanned underwater vehicle(UUV)is influenced significantly by complex current.The operational performance of UUV can be greatly improved when the impact of ocean current is consid...In coastal environment,the motion of unmanned underwater vehicle(UUV)is influenced significantly by complex current.The operational performance of UUV can be greatly improved when the impact of ocean current is considered.A global path planning method of the static obstacle environmental space is addressed in the paper.Firstly,according to the typically coastal vortex,a model of ocean current is proposed and the influence to the motion of UUV is analyzed.Secondly,to satisfy the rapid requirement in path planning,a heuristic A*algorithm is used to design global planning path with multiple constraints.Besides,to meet the UUV’s smooth path requirement,Bezier curve theory is applied.Simulation experiments are performed to illustrate the feasibility of the algorithm in the steady current and vortex environment.展开更多
Tip vortex cavitation noise of marine propeller became primary concems to reduce hazardous environmental impacts from commercial ship or to keep the underwater surveillance of naval ships. The investigations of the ti...Tip vortex cavitation noise of marine propeller became primary concems to reduce hazardous environmental impacts from commercial ship or to keep the underwater surveillance of naval ships. The investigations of the tip vortex and its induced noise are normally conducted through the model test in a water cavitation tunnel. However the Reynolds number of model-test is much smaller than that of the full-scale, which subsequently results in the difference of tip vortex cavitation inception. Hence, the scaling law between model- and full-scales needs to be identified prior to the prediction and assessment of propeller noise in full scale. From previous researches, it is generally known that the incipient caivtation number of tip vortex can be represented as a power of the Reynolds number. However, the power exponent for scaling, which is the main focus of this research, has not been clearly studied yet. This paper deals with the estimation of scaling exponent based on tip vortex cavitation inception test in both full- and model-scale ships. Acoustical measurements as well as several kind of signal processing technique for an inception criterion suggest the scaling exponent as 0.30. The scaling value proposed in this study shows slight difference to the one of most recent research. Besides, extrapolation of model-ship noise measurement using the proposed one predicts the full-scale noise measurement with an acceptable discrepancy.展开更多
The tip vortex cavitation（TVC） noise of marine propellers is of interest due to the environmental impacts from commercial ships as well as for the survivability of naval ships. Due to complicated flow and noise fiel...The tip vortex cavitation（TVC） noise of marine propellers is of interest due to the environmental impacts from commercial ships as well as for the survivability of naval ships. Due to complicated flow and noise field around a marine propeller, a theoretical approach to the estimation of TVC noise is practically unrealizable. Thus, estimation of prototype TVC noise level is realized through extrapolation of the model TVC noise level measured in a cavitation tunnel. In this study, for the prediction of prototype TVC noise level from a model test, a novel scaling law reflecting the physical basis of TVC is derived from the Rayleigh-Plesset equation, the Rankine vortex model, the lifting surface theory, and other physical assumptions. Model and prototype noise data were provided by Samsung Heavy Industries（SHI） for verification. In applying the novel scaling law, similitude of the spectra of nuclei is applied to assume the same nuclei distribution in the tip vortex line of the model and the prototype. It was found that the prototype TVC noise level predicted by the novel scaling law has better agreement with the prototype TVC noise measurement than the prototype TVC noise level predicted by the modified ITTC noise estimation rule.展开更多
文摘航行体出水过程中肩部的自然空化将影响航行体的载荷分布及出水姿态,工程上常采用肩部开孔通气的方式改善航行体表面的力学环境,进而解决此类问题.本文针对水下航行体通气空泡周向融合效果不理想问题,基于有限体积法,采用VOF(volume of fluid)多相流模型和动态铺层的动网格技术,数值研究了排气孔下游增加小尺度环形凹槽促进空泡融合的作用机制,以及不同发展阶段、不同工况下环形凹槽对空泡融合的促进作用.结果表明,凹槽可以有效改善通气空泡的融合效果.运动坐标系下来流经过环形凹槽时因为流动膨胀发生了边界层的流动分离,其诱导产生的卷吸作用一方面迟滞了空泡的轴向发展,促进空泡产生周向尺寸更大的剪切涡并沿周向膨胀发展,另一方面将部分通气气体吸入环形凹槽,吸入槽内的气体通过挤压破碎实现了周向融合,且槽内融合气泡溢出下泄促进融合边界上移.此外,凹槽可以通过改善空泡内部的流动状态,使空泡的形态和内部压力在不同工况下都更加稳定.
文摘为降低水下航行体噪声,研究了艉翼填角的降噪效果。分析了水下航行体艉翼接合部马蹄涡影响螺旋桨伴流场的特征,认为马蹄涡对水下航行体噪声产生了不利影响。针对某无人水下航行体(UUV)设计了一种艉翼填角,运用CFD方法对该艉翼填角优化螺旋桨伴流场的效果进行了数值模拟,结果显示伴流场轴向速度的周向不均匀度系数下降35%-62%。将艉翼填角应用于该UUV,开展航行辐射噪声测量试验,结果显示艉翼填角使UUV航行噪声总声源级降低3.4 d B,尤其对低频噪声抑制较好。
基金This work was supported by the National Natural ScienceFoundation of China (Grant No. 51879050, 51609044), the Defense IndustrialTechnology Development Program of China (Grant No. JCKY2017604C002), NaturalScience Foundation of Heilongjiang Province of China (No. E2017021) and ShenzhenSpecial Fund for Future Industries (Grant No. JCYJ20160331163751413).
文摘The low frequency load of an underwater explosion bubble and the generated waves can cause significant rigid motion of a ship that threaten its stability.In order to study the fluid-structure interaction qualitatively,a two-dimensional underwater explosion bubble dynamics model,based on the potential flow theory,is established with a double-vortex model for the doubly connected bubble dynamics simulation,and the bubble shows similar dynamics to that in 3-dimensional domain.A fully nonlinear fluid-structure interaction model is established considering the rigid motion of the floating body using the mode-decomposition method.Convergence test of the model is implemented by simulating the free rolling motion of a floating body in still water.Through the simulation of the interaction of the underwater explosion bubble,the generated waves and the floating body based on the presented model,the influences of the buoyancy parameter and the distance parameter are discussed.It is found that the impact loads on floating body caused by underwater explosion bubble near the free surface can be divided into 3 components:bubble pulsation,jet impact,and slamming load of the generated waves,and the intensity of each component changes nonlinearly with the buoyance parameter.The bubble pulsation load decays with the increase in the horizontal distance.However,the impact load from the generated waves is not monotonous to distance.It increases with the distance within a particular distance threshold,but decays thereafter.
基金supported by National Natural Science Foundation (NNSF) of China under Grant 51179038
文摘In coastal environment,the motion of unmanned underwater vehicle(UUV)is influenced significantly by complex current.The operational performance of UUV can be greatly improved when the impact of ocean current is considered.A global path planning method of the static obstacle environmental space is addressed in the paper.Firstly,according to the typically coastal vortex,a model of ocean current is proposed and the influence to the motion of UUV is analyzed.Secondly,to satisfy the rapid requirement in path planning,a heuristic A*algorithm is used to design global planning path with multiple constraints.Besides,to meet the UUV’s smooth path requirement,Bezier curve theory is applied.Simulation experiments are performed to illustrate the feasibility of the algorithm in the steady current and vortex environment.
文摘Tip vortex cavitation noise of marine propeller became primary concems to reduce hazardous environmental impacts from commercial ship or to keep the underwater surveillance of naval ships. The investigations of the tip vortex and its induced noise are normally conducted through the model test in a water cavitation tunnel. However the Reynolds number of model-test is much smaller than that of the full-scale, which subsequently results in the difference of tip vortex cavitation inception. Hence, the scaling law between model- and full-scales needs to be identified prior to the prediction and assessment of propeller noise in full scale. From previous researches, it is generally known that the incipient caivtation number of tip vortex can be represented as a power of the Reynolds number. However, the power exponent for scaling, which is the main focus of this research, has not been clearly studied yet. This paper deals with the estimation of scaling exponent based on tip vortex cavitation inception test in both full- and model-scale ships. Acoustical measurements as well as several kind of signal processing technique for an inception criterion suggest the scaling exponent as 0.30. The scaling value proposed in this study shows slight difference to the one of most recent research. Besides, extrapolation of model-ship noise measurement using the proposed one predicts the full-scale noise measurement with an acceptable discrepancy.
文摘The tip vortex cavitation（TVC） noise of marine propellers is of interest due to the environmental impacts from commercial ships as well as for the survivability of naval ships. Due to complicated flow and noise field around a marine propeller, a theoretical approach to the estimation of TVC noise is practically unrealizable. Thus, estimation of prototype TVC noise level is realized through extrapolation of the model TVC noise level measured in a cavitation tunnel. In this study, for the prediction of prototype TVC noise level from a model test, a novel scaling law reflecting the physical basis of TVC is derived from the Rayleigh-Plesset equation, the Rankine vortex model, the lifting surface theory, and other physical assumptions. Model and prototype noise data were provided by Samsung Heavy Industries（SHI） for verification. In applying the novel scaling law, similitude of the spectra of nuclei is applied to assume the same nuclei distribution in the tip vortex line of the model and the prototype. It was found that the prototype TVC noise level predicted by the novel scaling law has better agreement with the prototype TVC noise measurement than the prototype TVC noise level predicted by the modified ITTC noise estimation rule.
