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Junlei Sun,Heping Wang,Zhou Zhou,Shan Lei 한국항공우주학회 2018 International Journal of Aeronautical and Space Sc Vol.19 No.3
Aerodynamic numerical simulation of low Reynolds number long-endurance Diamond Joined-Wing configuration unmanned aerial vehicle was performed. First, low Reynolds number aerodynamic characteristics of a typical wing are numerically simulated by solving the Reynolds averaged Navier–Stokes (RANS) equations based on the structural grid technology and the k–kL–ω transition model. To prove the accuracy of this method, experimental data and numerical simulation results were compared. Second, the performance of low Reynolds number Diamond Joined-Wing configuration UAV (unmanned aerial vehicle) aerodynamic characteristics and control surfaces was studied by numerical simulation and theoretical analysis. The analysis of the interference between the Frt-wing (front wing) and the Aft-wing (after wing) of the Diamond Joined-Wing configuration UAV and the reason for the change in the pitching moment in the lateral-directional motion is carried out. The results show that the Diamond Joined-Wing configuration UAV has a typical low Reynolds number surface flow characteristics, Frt-wing and Aft-wing flow interference are relatively minor at a small angle of attack, which has a high basic aerodynamic performance in addition to good stall characteristics, with longitudinal and lateral-directional static stability. The performance of control surfaces and flaps is higher to meet the design requirements. Finally, the accuracy of the numerical simulation results was verified by vehicle aerodynamic testing.
Yongjie Zhao,Rongxia Huang,Rongzheng Liu,Heping Zhou,Wei Zhao 한국물리학회 2013 Current Applied Physics Vol.13 No.9
In the present work, lead-free K0.48Na0.52NbO3 (KNN) ceramics were synthesized by conventional ceramicsprocesses. The excess 3.3 mol% Na2CO3 and 1.1 mol% K2CO3 were added to decrease the sinteringtemperature to 990 ℃ and effectively promote the densification of KNN ceramics. X-ray diffraction resultsindicated that the excess Na2CO3 and K2CO3 would induce the formation of the A-site riched secondaryphase with the sintering temperature. Compositional segregation phenomenon enhanced bydifferent sintering temperature, spurs the formation of secondary phase in KNN-AEe ceramics. Inaddition, the difference between ferroelectric domain structure of the poled and as-sintered KNN-AEesamples for 990 ℃ was investigated. Via XRD analysis and SEM observation, it was found that the domainorientation was urged during the poling process.
Zhao, Wei,E, Lei,Ya, Jing,Liu, Zhifeng,Zhou, Heping Korean Chemical Society 2012 Bulletin of the Korean Chemical Society Vol.33 No.7
Perovskite structured barium titanate particles ($BaTiO_3$) platelets were synthesized by molten salt synthesis and topochemical microcrystal conversion. As the precursors of $BaTiO_3$, plate-like $BaBi_4Ti_4O_{15}$ particles were first synthesized by the reaction of $Bi_4Ti_3O_{12}$, $BaCO_3$, and $TiO_2$ at $1080^{\circ}C$ for 3 h in $BaCl_2$-KCl molten salt. After the topochemical reactions, layer-structured $BaBi_4Ti_4O_{15}$ particles transformed to the perovskite $BaTiO_3$ platelets. $BaTiO_3$ particles with thickness of approximately $0.5{\mu}m$ and a length of $10-15{\mu}m$ retained the morphology feature of the $BaBi_4Ti_4O_{15}$ precursor. For <001> $Pb(Mg_{1/3}Nb_{2/3})O_3-32.5PbTiO_3$ (PMNT)-5 wt % PbO piezoelectric ceramics textured with 5 vol % of $BaTiO_3$ templates, the Lotgering factor reached 0.82, and $d_{33}$ was 870 pC/N.
Wei Zhao,Lei E,Jing Ya,Zhifeng Liu,Heping Zhou 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.7
Perovskite structured barium titanate particles (BaTiO3) platelets were synthesized by molten salt synthesis and topochemical microcrystal conversion. As the precursors of BaTiO3, plate-like BaBi4Ti4O15 particles were first synthesized by the reaction of Bi4Ti3O12, BaCO3, and TiO2 at 1080 °C for 3 h in BaCl2-KCl molten salt. After the topochemical reactions, layer-structured BaBi4Ti4O15 particles transformed to the perovskite BaTiO3 platelets. BaTiO3 particles with thickness of approximately 0.5 μm and a length of 10-15 μm retained the morphology feature of the BaBi4Ti4O15 precursor. For <001> Pb(Mg1/3Nb2/3)O3-32.5PbTiO3 (PMNT)-5 wt % PbO piezoelectric ceramics textured with 5 vol % of BaTiO3 templates, the Lotgering factor reached 0.82, and d33 was 870 pC/N.
Rongxia Huang,Yuzhen Zhao,Yongjie Zhao,Rongzheng Liu,Heping Zhou 한국물리학회 2011 Current Applied Physics Vol.11 No.5
Lead-free (K_0.462Na_0.48Li_0.058)_(1+x)NbO_3(0 ≤ x ≤ 0.03) ceramics with excessive alkaline elements were synthesized by conventional ceramics processes as functions of sintering temperatures and quantities of excess alkaline elements. X-ray diffraction results reveal a transformation from tetragonal phase to orthorhombic phase with increasing the contents of excessive alkaline elements. The grain size and the piezoelectric properties were enhanced when a certain amount of excessive alkaline elements were added. Further elevation in the amount of alkaline elements added resulted in excessive liquid phase in the ceramics and deteriorated the piezoelectric properties. With x = 0.01, the ceramics sintered at 1050 ℃ show better properties of planar electromechanical coupling factor k_p = 43.4%, piezoelectric constant d_33 = 204 pC/N, dielectric constant ε^T_33/ε_0 = 704.4, and loss tangent tan δ = 2.8%.