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Study on three-dimensional expansion characteristics of four wall combustion-gas jets in confined liquid space

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Acta Mechanica Sinica 2017年第2期33卷 341-355页

作者： Zhitao Hu Yonggang Yu School of Energy and Power Engineering Nanjing University of Science and Technology Nanjing 210094 China

To explore further the launch mechanism of the new underwater launching technology proposed in this paper, the expansion characteristics of four wall combustion-gas jets in confined liquid space must be studied firstly. The experimental device is designed, and the high-speed digital photographic system is adopted to obtain the expansion sequence processes of Taylor cavities formed by the four wall jets. Meanwhile, the influence of the injection pressure on the axial expansion property of the four wall jets is discussed. Based on the experiments, a three-dimensional unsteady mathematical model is established to simulate the turbulent flow process of the four wall jets expanding in liquid, and the temporal and spatial distribution laws of phase, pressure, temperature, and velocity and the evolution rules of vortices are illustrated in detail. Results show that, accompanied by the jets expanding downstream, the four wall combustion-gas jets get close to each other and achieve convergence eventually under induction of the interference effect between multiple jets. Meanwhile, the heads of the Taylor cavities separate from the observation chamber wall and offset to the central axis of the observation chamber with time going on. The numerical simulation results of the four wall combustion-gas jets coincide well with the experimental data.

关键词： Wall jet Taylor cavity Kelvin-Helmholtz instability interference effect

An Experimental Study on Dynamics Features of Three Side-by-Side Flexible Risers Undergoing Vortex-Induced Vibrations in A Uniform Flow

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China Ocean Engineering 2020年第4期34卷 500-512页

作者： LIU Yu LI Peng WANG Yu LIU Li-hua WANG Fei GUO Hai-yan FU Qiang College of Architecture and Civil Engineering Shandong University of Science and TechnologyQingdao 266590China Shandong Provincial Key Laboratory of Civil Engineering Disaster Prevention and Mitigation Qingdao 266590China College of engineering Ocean University of ChinaQingdao 266100China Yantai China International Marine Containers Raffles Offshore Ltd Yantai 264000China

A vortex-induced vibration(VIV)experiment on three side-by-side risers subjected to a uniform flow was carried out in a combined wave-current *** dynamic features of interference effect on three side-by-side risers were investigated by varying fluid velocity and inter-riser *** distributions of dimensionless displacement,dominant frequency,and displacement trajectory of the model risers were measured using mode decomposition and wavelet transform *** coupled interference of inter-riser fluid to adjacent risers at different spacings was disclosed by introducing the"interference ratio"*** results show that at spacings smaller than 6.0 D,the three model risers display appreciable deviations in their displacement responses in cross-flow or in-line direction,attributable to the strong proximity disturbance and wake interference between the *** the spacing is increased to 8.0 D,wake interference still makes great difference to the dynamic response of the risers in both *** reduced velocity increases,the three risers show higher agreement with an isolated riser in overall dominant vibration frequency in CF direction than that in IL direction at all spacings and the side risers,although symmetrically placed,do not vibrate symmetrically,as a result of the steady deflection of clearance flow within the riser *** effect results in a remarkable unsteady mode competition within the risers;quantitation of the interference levels for the three risers at different spacings with interference ratio revealed that under low flow velocities and large spacing ratios,clearance flow constitutes a non-neglectable interferer for three side-by-side risers.

关键词： three-riser group VIV side-by-side arrangement interference effect clearance flow mode competition

Visually constructing the chemical structure of a single molecule by scanning Raman picoscopy

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National Science Review 2019年第6期6卷 1169-1175页

作者： Yao Zhang Ben Yang Atif Ghafoor Yang Zhang Yu-Fan Zhang Rui-Pu Wang Jin-Long Yang Yi Luo Zhen-Chao Dong J.G.Hou Hefei National Laboratory for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics University of Science and Technology of China

The strong spatial confinement of a nanocavity plasmonic field has made it possible to visualize the inner structure of a single molecule and even to distinguish its vibrational modes in real space. With such ever-improved spatial resolution, it is anticipated that full vibrational imaging of a molecule could be achieved to reveal molecular structural details. Here we demonstrate full Raman images of individual vibrational modes at the ■ level for a single Mg-porphine molecule, revealing distinct characteristics of each vibrational mode in real space. Furthermore, by exploiting the underlying interference effect and Raman fingerprint database, we propose a new methodology for structural determination, which we have called 'scanning Raman picoscopy', to show how such ultrahigh-resolution spectromicroscopic vibrational images can be used to visually assemble the chemical structure of a single molecule through a simple Lego-like building process.

关键词： scanning Raman picoscopy tip-enhanced Raman spectroscopy structure determination vibrational mode imaging interference effect

Study on Multiplexing Ability of Identical Fiber Bragg Gratings in a Single Fiber

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Chinese Journal of Aeronautics 2011年第5期24卷 607-612页

作者： LIU Jiansheng ZHANG Jing LI Xin ZHENG Zheng School of Electronics and lnformation Engineering Beihang University Beijing 100191 China

The multiplexing ability of a novel multiplexing fiber Bragg grating （FBG） method based on Optical Time Domain Reflecto meter （OTDR） and Time Division Multiplexing TDM technologies has been theoretically analyzed and studied. This method permits the interrogation of hundreds of identical FBGs with low reflectivity in a single fiber, making the FBG sensors more applicable in the aerospace health monitoring engineering. The analysis shows that the multiplexing ability can be greatly improved if the FBG reflectivity is sufficiently low. And hence, an inexpensive large-scale distributed sensing system based on this method can be realized, When evaluating the multiplexing ability of this system, we propose for the first time that the interference effect of multi-reflections among FBGs should be taken into consideration.

关键词： Bragg gratings multiplexing low reflectivity multi-reflection interference effect

Theoretical analysis on fully differential cross sections for C^(6+)impact ionization of helium

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Chinese Physics B 2014年第6期23卷 188-192页

作者：方小英张瑞芳段慧晓孙世艳贾祥富 Center for Molecules Research School of Physics and Information Engineering Shanxi Normal University

Fully differential cross sections （FDCS） are calculated within a four-body model for single ionization of helium by C6＋ impact at the incident energy of 100 MeV/a.u. （atomic unit）. The results are compared with experimental data and other theoretical predictions. It is shown that our results are in very good agreement with experiment for three small momentum transfers in the scattering plane; however, some significant discrepancies are still present at the largest momentum transfer in both the scattering plane and the perpendicular plane. In actuality, the problem has not been explained by the theory during the last decade. Accordingly, the contributions of different scattering amplitudes to FDCS are analyzed. It is found that for the largest momentum transfer the cross section arising from a destructive interference of the three amplitudes is much smaller than the experimental data. However, the cross section due to the constructive interference of two scattering amplitudes between projectile-ionized electron interaction and projectile-passive electron interaction almost approaches the experimental data.

关键词： ion-impact ionization fully differential cross section four-body model interference effect

Experimental study of wind loads on cylindrical reticulated shells

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Applied Mathematics and Mechanics(English Edition) 2013年第3期34卷 281-296页

作者：黄鹏周晅毅顾明 State Key Laboratory of Disaster Reduction in Civil Engineering Tongji University

The cylindrical reticulated shell structures without side walls, which are normally arranged in pairs, are usually used as dry-coal sheds in a thermal power plant. The wind loads of these shells do not exist in standards or codes. Therefore, this study investigates the mean and fluctuating wind loads on a cylindrical reticulated shell with a rise-to-span ratio of 0.39 through a series of wind tunnel tests. The characteristics of the wind pressures on the upper and lower surfaces and the net pressures are presented. The results show that the wind direction and another shell structure significantly affect the wind loads on the principal shell. The most unfavorable wind direction is around 30~, whereas the effects of the wind field and the height of the coal stack are small. The surfaces of the shells are divided into nine blocks, and the block mean and fluctuating （rms） pressure coefficients suitable for engineering applications are given as references for wind load codes.

关键词： cylindrical reticulated shell dry-coal shed wind tunnel test block pressurecoefficient fluctuating pressure interference effect