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941.
Liquid sloshing is a kind of very complicated free surface flow and exists widely in many fields. In order to calculate liquid
sloshing damping precisely a volume of fluid method based on finite volume scheme is used to simulate free surface flows in
partly filled cylindrical containers. A numerical method is presented to simulate the movement of the free surface flow, in
which a piecewise linear interface construction scheme and an unsplit Lagrangian advection scheme instead of Eulerian advection
scheme are used. The damping performance of liquid sloshing in cylindrical containers under fundamental sloshing mode is investigated.
There are four factors determining the surface-wave damping: free surface, boundary-layer, interior fluid and contact line.
In order to study different contributions from these four factors to whole damping, several examples are simulated. No-slip
and slip wall boundary conditions on both side wall and bottom wall of the cylindrical containers are studied to compare with
the published results obtained by solving Stokes equations. In the present method the first three main factors can be considered.
The simulation results show that the boundary-layer damping contribution increases while the interior fluid damping contribution
decreases with increase of Reynolds number.
Supported by the National Natural Science Foundation of China (Grant No. 10532010) 相似文献
942.
Field measurement on wind characteristic and buffeting response of existing bridge is of great value to the development of
bridge wind engineering, and the structural health monitoring system (SHMS) employed in many long-span bridges provide a research
basis for the field measurement. In order to provide reliable basis for wind resistant evaluation of Runyang Suspension Bridge
(RSB), two anemometers and 85 accelerometers were installed in the SHMS of RSB. In August 2005, Typhoon Matsa crossed over
Jiangsu, the SHMS timely recorded the typhoon and structural vibration responses. In this paper by using the time-frequency
technique and statistical theory, the recorded data were analyzed to obtain the strong wind characteristics, the buffeting
response characteristics of the cable and deck, and the variation of buffeting response RMS versus wind speed. Results obtained
in this study can be employed to validate the credibility of current buffeting response analysis theory techniques, and provide
reference values for wind resistant evaluation of other long-span bridges.
Supported by the National Hi-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA04Z416), the
Key Project of the National Natural Science Foundation of China (Grant No. 50538020) and the Outstanding Youth Fund of the
National Natural Science Foundation of China (Grant No. 50725828) 相似文献
943.
JunHu Ma HeQing Yang YuZhe Song Li Li XiaoLi Xie RuiNi Liu LinFang Wang 《中国科学E辑(英文版)》2009,52(5):1264-1272
Large-scale oriented ZnO nanocone arrays were directly grown on zinc substrate through a hydro-thermal reaction of Zn foil with aqueous butylamine solution(3 mol/L) at 100—180 ℃ for 12 h.The syn-thesized products were characterized with X-ray diffraction,Raman spectrum,scanning electron mi-croscopy and transmission electron microscopy.The results showed that the ZnO nanocones were single crystalline with the wurtzite structure and grown along the [0001] direction.The diameter of nanocones is decreased with ... 相似文献
944.
Poly(vinyl alcohol)/Hydroxylapatite (PVA/HA) composite hydrogel was prepared with poly(vinyl alcohol) and hydroxylapatite
as raw materials, using the method of repeated freezing and thawing. The morphologies of PVA/HA composite hydrogel were observed
by means of high-accuracy 3D profiler and scanning electron microscope (SEM). The compressive elastic modulus and the stress
relaxation characteristics of PVA/HA composite hydrogel were measured using the flat-head cylinder indenter. The friction
and wear tests between PVA/HA composite hydrogel and bovine knee articular cartilage were performed on the micro-tribometer.
The worn morphologies of PVA/HA composite hydrogel were observed with environmental scanning electron microscope (ESEM). The
results showed that PVA/HA composite hydrogel has the cross-link network microstructure which is similar to that of the natural
bovine knee articular cartilages. With the increase of freezing-thawing cycles and the HA content, the degree of cross-link
and the crystallization of PVA/HA composite hydrogel both increase, the elastic modulus increases evidently, the rate of stress
relaxation is improved and the value of balance stress decreases. The friction coefficient decreases with the increase of
the freezing-thawing cycles and the HA content. The more the freezing-thawing cycles are, the earlier the friction coefficient
reaches the stable balance value. The friction deformation depth between PVA/HA composite hydrogel and bovine knee articular
cartilage is inversely proportional to freezing-thawing cycles and the HA content. The main wear mechanisms of PVA/HA composite
hydrogel are plastic flowing and adhesive flaking. The wear severity degree decreases with the increase of freezing-thawing
cycles and the HA content.
Supported by Key Program of the National Natural Science Foundation of China (Grant No. 50535050), Program for New Century
Excellent Talents in University (Grant No. NCET-06-0479) and Natural Science Foundation of Jiangsu Province (Grant No. BK2005403) 相似文献
945.
Electroosmotic flow (EOF) is a promising way for driving and mixing fluids in microfluidics. For the parallel-plate microchannel
with the hydrophobic surface, this paper solved the governing equations using the finite element method (FEM), and the effects
of microchannel height, electric strength and ionic concentration on EOF were thus investigated. The simulation indicates
that the transient characteristics of EOF are similar in hydrophobic and hydrophilic microchannels, the steady time of EOF
is proportional to the square of microchannel height, and the scale is microsecond. EOF velocity is proportional to the electric
strength and independent of the channel height, and decreases slowly with the ionic concentration, which is lower than that
in hydrophilic microchannel due to the presence of slip length in hydrophobic microchannel. The results can provide valuable
insights into the optimal design of microchannel surfaces to achieve accurate EOF control in hydrophobic microchannel.
Supported by the National Natural Science Foundation of China (Grant No. 50730007) 相似文献
946.
Copolymers of 9,9-dioctylfluorene (DOF) and 2-thienyl-benzothiadiazole (DBT) were synthesized by Suzuki reaction and end-capped
by N-hexyl-carbazole and benzene, which were abbreviated as PDOF-DBT-Cz and PDOF-DBT-B, respectively. The photophysical, electrochemical
and thermal properties of the copolymers were studied. The results indicated that replacement of N-hexyl-carbazole as end-capping
group of PDOF-DBT can vary light color and improve luminescence efficiency.
Supported by the Major Project of Science Foundation Ministry of Education of China (Grant No. 207015) and the National Natural
Science Foundation of China (Grant No. 20671068) 相似文献
947.
Ultralight X-type lattice sandwich structure (I): Concept,fabrication and experimental characterization 总被引:1,自引:1,他引:0
ZHANG QianCheng HAN YunJie CHEN ChangQing & LU TianJian State Key Laboratory for Mechanical Behavior of Materials School of Material Science Engineering Xi’an Jiaotong University Xi’an China MOE Key Laboratory for Strength Vibration School of Aerospace Department of Engineering Mechanics AML Tsinghua University Beijing 《中国科学E辑(英文版)》2009,52(8):2147-2154
A new type of ultra-lightweight metallic lattice structure (named as the X-type structure) is reported. This periodic structure
was formed by two groups of staggered struts in the traditional pyramid structure, and fabricated by folding expanded metal
sheet along rows of offset nodes and then brazing the folded structure (as the core) with top and bottom facesheets to form
sandwich panels. The out-of-plane compressive and shear properties of the X-type lattice sandwich structure were investigated
experimentally and compared to those of the sandwich having a pyramidal truss core. It is found that the formation of the
2-dimensional staggered nodes can effectively make the X-type structure more resistant to inelastic and plastic buckling under
both compression and shear loading than the pyramidal lattice truss. Obtained results show that the compressive and shear
peak strengths of the X-type lattice structure are about 30% higher than those of the pyramidal lattice truss having the same
relative density.
Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2006CB601202), the National Natural Science
Foundation of China (Grant Nos. 10632060,10825210), the National “111” Project of China (Grant No. B06024) and the National
High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA03Z519) 相似文献
948.
Hydrogen atom adsorption and diffusion properties on clean and vacancy defective Mg (0001) surface have been investigated
systematically by using a first-principles calculations method based on the density functional theory. The calculation results
of adsorption energy and diffusion energy barrier show that hydrogen atom is apt to be adsorbed at fcc and hcp sites on clean
Mg (0001) surface, and fcc adsorption site is found to be more preferred. The highest diffusion energy barrier is estimated
as 0.6784 eV for the diffusion of hydrogen from clean Mg (0001) surface into its bulk. Surface effects, which affect hydrogen
diffusion obviously, results in a slow diffusion velocity of hydrogen from surface to subsurface, while a fast one from subsurface
to bulk, indicating the range of surface effects is only restricted within two topmost layers of Mg (0001) surface. Comparatively,
Mg atom vacancy on Mg (0001) surface not only enhances the chemisorption interaction between H and Mg surface, but also benefits
H atom diffusion in Mg bulk with relatively more diffusion paths compared with that of clean surface. Besides, hydrogen atom
is found to occupy mostly the tetrahedral interstice when it diffuses into the Mg bulk. Further analysis of the density of
states (DOS) shows that the system for hydrogen atom to be adsorbed at fcc site has a lower DOS value (N (E
F)) at Fermi level and more bonding electrons at the energy range blow the Fermi level of H/Mg (0001) system as compared with
that at hcp site. On the other hand, the enhanced chemisorption interaction between hydrogen and defective surface should
be attributed to the fact that the electronic structures of Mg (0001) surface are modified by an Mg vacancy, and the bonding
electrons of the topmost layer Mg atoms are transferred from low energy range to Fermi level, which is in favor of improving
the surface activity of Mg (0001) surface.
Supported by the PhD Programs Foundation of Ministry of Education of China (Grant No. 200805321032), the Science and Technology
Program Project of Hunan Province (Grant No. 2008GK3083) and the Program for Changjiang Scholars and the Innovative Research
Team in university (Grant No. 531105050037) 相似文献
949.
Separation of nanocolloids driven by dielectrophoresis: A molecular dynamics simulation 总被引:1,自引:0,他引:1
The nonequilibrium molecular dynamics (MD) method was used to model the nanocolloids and the solvent particles. By introducing
a non-uniform electric field, colloids were polarized to have opposite polarities. Separation of colloids driven by dielectrophoresis
(DEP) could be seen clearly under a strong electric field at low temperatures. Analyzing the ratio of DEP velocities of colloids
to thermal velocities of neutral solvent particles showed that when the ratio was correspondingly big, collision between colloids
and solvent particles would be intense, making the DEP velocity of colloids fluctuate frequently. By changing the electric
field strength, it was found that the enhancement of electric field strength would quicken the separation of colloids. But
when the electric field strength increased to a certain degree, the separation motion would be slow because of the strong
friction resistance of the solvent particles to the colloids. Moreover, studying the separation reason of colloids based on
the potential energy showed that after colloids were polarized, the attractive potential energy among the colloids would be
weaker than before, while the increase of temperature would reduce the attractive potential energy and increase the repulsive
potential energy, which accorded with the DLVO theory.
Supported by the National Hi-Tech Research and Derelopment Program of China (“863” Project) (Grant No. 2006AA04Z351) and the
National Natural Science Foundation of China (Grant Nos. 50675033, 30770553) 相似文献
950.
Tao Zhang JunHong Jin DaYong Hu ShengLin Yang Guang Li JianMing Jiang 《中国科学E辑(英文版)》2009,52(4):906-909
The effect of coagulation temperature on the morphology, microstructures and mechanical properties of dihydroxy poly(p-phenylene benzobisoxazole) (DHPBO) fibers was investigated during dry-jet wet-spinning process, in which the coagulation
bath concentration and drawn ratio were kept as 10 wt% of PPA in water and 1.7, respectively. The structures and mechanical
properties of the as-spun DHPBO fibers were characterized by FTIR, XRD, SEM, and single fiber tensile testing. The results
indicated that in PPA/H2O coagulation system, when the coagulation temperature was 25°C, highly crystallized DHPBO as-spun fibers possessing fine
crystallites, circular and smooth morphology, and excellent mechanical properties could be achieved.
Supported by the National Natural Science Foundation of China (Grant No. 50673017), Shanghai Leading Academic Discipline Project
(Grant No. B603) and the Program of Introducing Taleuts of Discipline to University of People’s Republic of China (“111” Program)
(Grant No. 111-2-04) 相似文献