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Effects of Degrees of Motion freedom on free-fall of A Sphere in Fluid

China Ocean Engineering 2018年第5期32卷 605-613页

作者： LIU Lei YANG Jian-min LYU Hai-ning TIAN Xin-liang PENG Tao State Key Laboratory of Ocean Engineering Shanghai Jiao Tong UniversityShanghai 200240China Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration(CISSE) Shanghai 200240China

free-fall of a sphere in fluid is investigated at a Galileo number of 204 by direct numerical simulations(DNS). We mainly focus on the effects of different degrees-of-freedom(DOFs) of the sphere motion during free-fall. The characteristics of free-fall are compared with those of flow past a fixed sphere. Additional numerical tests are conducted with constraints placed on the translational or rotational DOFs of the sphere motion to analyze different DOFs of sphere motion. The transverse motion contributes significantly to the characteristics of free-fall; it results in the retardation of the vortex shedding, leading to the decrease of the Strouhal number. In addition, the transversal sphere motion exhibits the tendency to promote the sphere rotation. On the contrary, the effects of the sphere rotation and vertical oscillations during free-fall are negligible.

关键词： free-fall direct numerical simulation degree of motion freedom

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Physical Body Impact After High Altitude Bail-out

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Chinese Journal of Aeronautics 2011年第2期24卷 145-149页

作者： CHEN Xiaopeng GUAN Huanwen ZHUO Congshan FENG Wenchun ZHONG Chengwen School of Mechanics Civil Engineering and Architecture Northwestern Polytechnical University Xi'an 710072 China The First Aircraft Institute Aviation Industry Corporation of China Xi'an 710089 China School of Aeronautics Northwesern Polytechnical University Xi 'an 710072 China

In most of the emergency circumstances,the aircrew leaves the aircraft under unsatisfied conditions,such as too high relative velocity to the ambient air or low partial oxygen pressure.The aircrew must pass through this area as quickly as possible before opening the parachute safely,viz.,free-fall.Numerical simulations are conducted in this paper to explore the major characteris-tics of the aircrew free-fall process by using a commercial computational fluid dynamic（CFD） software,FLUENT.Coupled with the classical pressure-altitude and temperature-altitude relations,Navier-Stokes（N-S） equations for compressible flow are solved by using finite volume method.The body velocity and the attitude are predicted with six-degree of freedom（6DOF） module.The evolution of velocities,including horizontal,vertical components and angular velocity,is obtained.It is also analyzed further according to the particle kinetic theories.It is validated that the theories can predict the process qualitatively well with a modi-fied drag effect,which mainly stems from the velocity pressure.An empirical modification factor is proposed according to the fitting results.

关键词： computational aerodynamics free-fall six-degree of freedom parachute opening life-saving

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Development and Application of an in Situ Penetrator for Rapid Strength Testing of Submarine Sediment

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Journal of Ocean University of China 2019年第2期18卷 328-338页

作者： ZHANG Minsheng WANG Zhenhao WANG Xiuhai WEN Mingzheng HONG Bo School of Transportation Science and Engineering Beihang University Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering Ocean University of China

In marine engineering, the strength of a submarine sediment is an indispensable parameter for assessment of construction. In this study, a free-fall cone penetrator named IPen was developed to realize a rapid and efficient measurement of sediment strength. The equipment is characterized by modular design and self-contained data acquisition. It is equipped with an acceleration sensor, a water pressure sensor, and a piezocone penetration test(CPTu) probe. It is designed to be released from near seabed surface with a releaser and then fall freely to provide a higher penetration velocity. Its maximum working depth is approximately 2500 m and maximum penetration depth is approximately 3 m. To derive the correlation between penetration resistance and sediment strength, a calibrator was devised to determine the penetration-rate factor. In addition, the factor applicable to in situ test points was determined in laboratory experiments. In June 2016, the IPen was tested in situ in the South Yellow Sea, China, during a shared voyage funded by the National Science Foundation. Meanwhile, undisturbed column samples were collected for laboratory tests. Based on the in situ test results, it was demonstrated that the IPen could accurately record the working states of various sensors during the freely falling course. IPen test results reliably reflected the sediment strength at all the testing points when compared with laboratory calibration tests, in situ vane tests and penetration tests, laboratory penetration tests, and unconsolidated and undrained triaxial compression tests.

关键词： submarine sediment free-fall cone penetration test sediment strength the Yellow Sea penetration-rate factor

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Remote Plasma Maintenance in Low-Pressure Discharges with an External Magnetic Field

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Journal of Modern Physics 2012年第10期3卷 1616-1625页

作者： Stiliyan Lishev Antonia Shivarova Khristo Tarnev Department of Applied Physics Technical University-Sofia Sofia Bulgaria Faculty of Physics Sofia University Sofia Bulgaria

The spatial structure of remote plasma regions in rf discharges is analyzed based on a 2D model of free-fall regime discharge maintenance. Since the study is directed towards description of the magnetic filter region in the tandem plasma sources of negative hydrogen ions, hydrogen discharges are considered, with a weak magnetic field located outside the region of the rf power deposition. With the formation of different regions in the discharge—the rf power deposition region, the region with electron magnetization, the transition between them and the region behind the filter—the results display superimposed effects of nonlocal discharge maintenance without and with a magnetic field. Slight decrease of the electron temperature accompanied with strong drop of the electron density is the “pure” effect of the plasma expansion in regions without external magnetic field. Strong drop of the electron temperature accompanied with formation of a maximum of the electron density in the filter region is the “pure” effect of the plasma expansion through a magnetic field. Based on the results for the spatial distribution of the electron density and temperature obtained with shifting the position of the magnetic filter, optimization of the source regarding high yield of volume-produced negative ions is discussed.

关键词： Remote Plasma Maintenance Tandem Plasma Sources Magnetic Filter Hydrogen Discharges free-fall Regime

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