According to the hypothesis that the dissipation of turbulent kinetic energy satisfies log-normal distribution, a stochastic model of dissipation is provided and the Langevin modef[6] of velocity is modified. Then a j...According to the hypothesis that the dissipation of turbulent kinetic energy satisfies log-normal distribution, a stochastic model of dissipation is provided and the Langevin modef[6] of velocity is modified. Then a joint Pdf equation of turbulent velocity and dissipation is derived. We solve numerically the joint Pdf equation using Monte Carlo method and obtain satisfactory results for decaying turbulence and homogeneous turbulent shear flow. The preliminary results show that the model is well working.展开更多
该文提出一种多文档关键词抽取方法,该方法提出ATF×PDF(Average Term Frequency×ProportionalDocument Frequency)来计算词语权重,并根据候选关键词之间的语义相似度,采用联合权重方法重新计算候选关键词的权重来抽取关键词...该文提出一种多文档关键词抽取方法,该方法提出ATF×PDF(Average Term Frequency×ProportionalDocument Frequency)来计算词语权重,并根据候选关键词之间的语义相似度,采用联合权重方法重新计算候选关键词的权重来抽取关键词。该方法综合考虑了词语的频率,词性以及词语之间的语义相似性等信息,实验表明,该方法能有效抽取多个文档的关键词,同基于关键词的聚类标记方法相比,其准确率提高3%,召回率提高7%,F-measure提高4.4%。展开更多
Based on the direct numerical simulation （DNS）, the developing planar jets under different initial conditions, e.g., the con- ditions of the exit Reynolds number and the exit mean velocity profile, are investigated....Based on the direct numerical simulation （DNS）, the developing planar jets under different initial conditions, e.g., the con- ditions of the exit Reynolds number and the exit mean velocity profile, are investigated. We mainly focus on the characteristics of the invariants of the velocity gradient tensor, which provides insights into the evolution of the dynamics and the geometry of the planar jets along with the flow transition. The results show that the initial flow near the jet exit is strongly predominated by the dissipation over the enstrophy, the flow transition is accompanied by a severe rotation and straining of the flow elements, where the vortex structure evolves faster than the fluid element deformation, in the fully-developed state, the irrotational dissipation is dominant and the most probable geometry of the fluid elements should remain between the biaxial stretching and the axisymmetric stretching. In addition, with a small exit Re and a parabolic profile for the exit mean streamwise velocity, the decay of the mean flow field and the magnitude of the turbulent variables will be strengthened in the process of the flow transition, however, a large exit Re will promote the flow transition to the fully-developed state. The cross-impact between the exit Re and the exit mean velocity profile is also observed in the present study.展开更多
文摘According to the hypothesis that the dissipation of turbulent kinetic energy satisfies log-normal distribution, a stochastic model of dissipation is provided and the Langevin modef[6] of velocity is modified. Then a joint Pdf equation of turbulent velocity and dissipation is derived. We solve numerically the joint Pdf equation using Monte Carlo method and obtain satisfactory results for decaying turbulence and homogeneous turbulent shear flow. The preliminary results show that the model is well working.
文摘该文提出一种多文档关键词抽取方法,该方法提出ATF×PDF(Average Term Frequency×ProportionalDocument Frequency)来计算词语权重,并根据候选关键词之间的语义相似度,采用联合权重方法重新计算候选关键词的权重来抽取关键词。该方法综合考虑了词语的频率,词性以及词语之间的语义相似性等信息,实验表明,该方法能有效抽取多个文档的关键词,同基于关键词的聚类标记方法相比,其准确率提高3%,召回率提高7%,F-measure提高4.4%。
基金Supported by the Research Foundation Program for Doctor of Liaoning Province(20170520084)Fundamental Research Funds for the Central Universities(DUT16RC3018)
基金supported by the Collaborative Research Project of the Institute of Fluid Science, Tohoku Universitysupported by Grants-in-Aid (Grant Nos. 25289030, 25289031) from the Ministry of Education, Culture, Sports, Science and Technology in Japan
文摘Based on the direct numerical simulation （DNS）, the developing planar jets under different initial conditions, e.g., the con- ditions of the exit Reynolds number and the exit mean velocity profile, are investigated. We mainly focus on the characteristics of the invariants of the velocity gradient tensor, which provides insights into the evolution of the dynamics and the geometry of the planar jets along with the flow transition. The results show that the initial flow near the jet exit is strongly predominated by the dissipation over the enstrophy, the flow transition is accompanied by a severe rotation and straining of the flow elements, where the vortex structure evolves faster than the fluid element deformation, in the fully-developed state, the irrotational dissipation is dominant and the most probable geometry of the fluid elements should remain between the biaxial stretching and the axisymmetric stretching. In addition, with a small exit Re and a parabolic profile for the exit mean streamwise velocity, the decay of the mean flow field and the magnitude of the turbulent variables will be strengthened in the process of the flow transition, however, a large exit Re will promote the flow transition to the fully-developed state. The cross-impact between the exit Re and the exit mean velocity profile is also observed in the present study.
