For a cyclone, it is possible to improve separation efficiency and reduce pressure drop by increasing the cyclone height. However, an exceeded height increase could result in a dramatical drop in separation efficiency...For a cyclone, it is possible to improve separation efficiency and reduce pressure drop by increasing the cyclone height. However, an exceeded height increase could result in a dramatical drop in separation efficiency. In this study, experimental and computational fluid dynamics simulation results exhibit that the introduction of an apex cone at the dust outlet could avoid the risk of separation efficiency drop but lead to a continuous reducing of the pressure drop. Generally, the optimal cyclone height should be closely related to the natural vortex length. While, when the vortex end contracts into the separation space in the cyclone with an exceeded height, severe back-mixing of particles always occurs, which will result in the decrease of separation efficiency. Herein, it is found that when an apex cone is installed at the dust outlet, the vortex end can be grasped by the cone so as to weaken the back-mixing of particles.Meanwhile, the introduction of this apex cone can enhance the secondary separation to capture the back-mixed particles again so as to protect the efficiency. In addition, it is found that the enhanced secondary separation could come from either the stagnant current of axial velocity in the center or the improved tangential velocity of inner vortex whereas the forcibly extending the length of vortex to exceed its natural length will not significantly increase efficiency.展开更多
The DF1-1 submarine pipeline was investigated using a dual-frequency side-scan sonar and a swath sounder system.More than a hundred scour pits under the pipeline were found,most of which have caused the span of the pi...The DF1-1 submarine pipeline was investigated using a dual-frequency side-scan sonar and a swath sounder system.More than a hundred scour pits under the pipeline were found,most of which have caused the span of the pipeline to increase and threatened its safety.The maximum allowable free span length (MAFSL) of the pipeline was determined through the limitations regarding maximum allowable stress under static or quasi-static loads and the onset of Vortex Induced Vibrations (VIV) under different hydrodynamic actions.The results show that the MAFSL under static conditions is 56 m.However,the MAFSLs are 30 m and 20 m under ordinary weather conditions and hurricane-induced currents for the 100-year return period,respectively,to avoid VIV as calculated by using the highest safety class factor.It is suggested that spanning pipelines longer than 20 m should be supported.Additionally,eight successive spans which may also threaten the pipeline were proposed.The most hazardous scour pits are along the pipeline section from KP42 to KP51.展开更多
Owing to the complex environmental conditions, suspension could induce complicated forces on submarine pipelines and even cause vortex-induced vibration, resulting in fatigue damage of pipelines. Through aiming at the...Owing to the complex environmental conditions, suspension could induce complicated forces on submarine pipelines and even cause vortex-induced vibration, resulting in fatigue damage of pipelines. Through aiming at the 28-inch submarine pipeline in the East China Sea, the pipeline was segmented according to the similarity, considering the factors of pipe assembly, typhoon, current, wave and seabed topography. The effects of span length on natural frequency in each section of submarine pipeline were analyzed by finite element model. The maximum safe span length allowed by each pipeline section was verified by fatigue cumulative damage theory, and the fatigue life of each pipeline section were predicted. The results showed that each order natural frequency of the pipeline decreased with the increase of span length. The calculated results of empirical formulas were much smaller than those of the FEM analysis. The increase of the gap between the suspended pipeline and the seabed was beneficial to enhance the fatigue life of the suspended pipeline.展开更多
以海洋温差能发电(Ocean Thermal Energy Conversion,OTEC)平台的冷水管为研究对象,根据结构方程和尾流振子方程建立冷水管流固耦合模型,采用有限元方法和Newmark-β法对冷水管涡激振动(Vortex-Induced Vibration,VIV)进行时域分析,并在...以海洋温差能发电(Ocean Thermal Energy Conversion,OTEC)平台的冷水管为研究对象,根据结构方程和尾流振子方程建立冷水管流固耦合模型,采用有限元方法和Newmark-β法对冷水管涡激振动(Vortex-Induced Vibration,VIV)进行时域分析,并在MATLAB软件中开发相应的求解程序。针对冷水管所面临的复杂工况,分别研究外部流场、内部流场、长径比和压载质量等因素对VIV产生的影响。结果表明:随着外流流速和长径比的增大,冷水管横流向VIV模态和振动幅值也发生相应改变,振动强度呈现波动上升;在不发生动态失稳的情况下,内流流速的增加可有效减小冷水管横流向振动幅值,压载质量可大幅减小冷水管自由端的振动位移。展开更多
基金sponsored by the National Natural Science Foundation of China (21506139 and U1710101)。
文摘For a cyclone, it is possible to improve separation efficiency and reduce pressure drop by increasing the cyclone height. However, an exceeded height increase could result in a dramatical drop in separation efficiency. In this study, experimental and computational fluid dynamics simulation results exhibit that the introduction of an apex cone at the dust outlet could avoid the risk of separation efficiency drop but lead to a continuous reducing of the pressure drop. Generally, the optimal cyclone height should be closely related to the natural vortex length. While, when the vortex end contracts into the separation space in the cyclone with an exceeded height, severe back-mixing of particles always occurs, which will result in the decrease of separation efficiency. Herein, it is found that when an apex cone is installed at the dust outlet, the vortex end can be grasped by the cone so as to weaken the back-mixing of particles.Meanwhile, the introduction of this apex cone can enhance the secondary separation to capture the back-mixed particles again so as to protect the efficiency. In addition, it is found that the enhanced secondary separation could come from either the stagnant current of axial velocity in the center or the improved tangential velocity of inner vortex whereas the forcibly extending the length of vortex to exceed its natural length will not significantly increase efficiency.
基金supported by the National Basic Research Program of China (973 Program) (Grant No.2005CB422304)the Ocean University of China Scientific Research Start-up Funds Project for Introduced Talents
文摘The DF1-1 submarine pipeline was investigated using a dual-frequency side-scan sonar and a swath sounder system.More than a hundred scour pits under the pipeline were found,most of which have caused the span of the pipeline to increase and threatened its safety.The maximum allowable free span length (MAFSL) of the pipeline was determined through the limitations regarding maximum allowable stress under static or quasi-static loads and the onset of Vortex Induced Vibrations (VIV) under different hydrodynamic actions.The results show that the MAFSL under static conditions is 56 m.However,the MAFSLs are 30 m and 20 m under ordinary weather conditions and hurricane-induced currents for the 100-year return period,respectively,to avoid VIV as calculated by using the highest safety class factor.It is suggested that spanning pipelines longer than 20 m should be supported.Additionally,eight successive spans which may also threaten the pipeline were proposed.The most hazardous scour pits are along the pipeline section from KP42 to KP51.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.11802168 and 51575331)project funded by China Postdoctoral Science Foundation(No.2019M661458)
文摘Owing to the complex environmental conditions, suspension could induce complicated forces on submarine pipelines and even cause vortex-induced vibration, resulting in fatigue damage of pipelines. Through aiming at the 28-inch submarine pipeline in the East China Sea, the pipeline was segmented according to the similarity, considering the factors of pipe assembly, typhoon, current, wave and seabed topography. The effects of span length on natural frequency in each section of submarine pipeline were analyzed by finite element model. The maximum safe span length allowed by each pipeline section was verified by fatigue cumulative damage theory, and the fatigue life of each pipeline section were predicted. The results showed that each order natural frequency of the pipeline decreased with the increase of span length. The calculated results of empirical formulas were much smaller than those of the FEM analysis. The increase of the gap between the suspended pipeline and the seabed was beneficial to enhance the fatigue life of the suspended pipeline.
文摘以海洋温差能发电(Ocean Thermal Energy Conversion,OTEC)平台的冷水管为研究对象,根据结构方程和尾流振子方程建立冷水管流固耦合模型,采用有限元方法和Newmark-β法对冷水管涡激振动(Vortex-Induced Vibration,VIV)进行时域分析,并在MATLAB软件中开发相应的求解程序。针对冷水管所面临的复杂工况,分别研究外部流场、内部流场、长径比和压载质量等因素对VIV产生的影响。结果表明:随着外流流速和长径比的增大,冷水管横流向VIV模态和振动幅值也发生相应改变,振动强度呈现波动上升;在不发生动态失稳的情况下,内流流速的增加可有效减小冷水管横流向振动幅值,压载质量可大幅减小冷水管自由端的振动位移。
