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- 저자 : Hongnian Liu (검색결과 4 건)
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Pengcheng Liu,Hongnian Yu,Shuang Cang 제어·로봇·시스템학회 2018 International Journal of Control, Automation, and Vol.16 No.5
Motivated by the desire to optimally control the friction-induced stick-slip locomotion and sufficiently improve the energy efficacy, a novel trajectory synthesis and optimization scheme is proposed in this paper for a underactuated microrobotic system with dynamic constraints and couplings. The nonlinear microrobotic model utilizes combined tangential-wise and normal-wise vibrations for underactuated locomotion, which features a generic significance for the studies on microrobotic systems. Specifically, an analytical two-stage velocity trajectory is constructed under control indexes and physical constraints. Subsequently, the dynamic coupling behavior and the qualitative variation laws are characterized through rigorous bifurcation analysis. The synthesized trajectory is optimized and tuned via rigorous analysis based on the robot dynamics. The proposed trajectory planning mechanism provides a promising approach in determining the optimal viscoelastic parameters and trajectory parameters such that the optimal locomotion indexes can be met. Simulation results are presented to demonstrate the efficacy and feasibility of the proposed scheme.
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Dehai Jiang,Weimei Jiang,Hongnian Liu,Jianning Sun 한국풍공학회 2008 Wind and Structures, An International Journal (WAS Vol.11 No.4
Large eddy simulations have been performed within and over different types of urban building arrays. This paper adopted three dimensionless parameters, building frontal area density (λf), the variation degree of building height (σh), and the staggered degree of building range (rs), to study the systematic influence of building spacing, height and layout on wind and turbulent characteristics. The following results have been achieved: (1) As λf decrease from 0.25 to 0.18, the mean flow patterns transfer from “skimming” flow to “wake interference” flow, and as λf decrease from 0.06 to 0.04, the mean flow patterns transfer from “wake interference” flow to “isolated roughness” flow. With increasing σh, wind velocity within arrays increases, and the vortexes in front of low buildings would break, even disappear, whereas the vortexes in front of tall buildings would strengthen and expand. Tall buildings have greater disturbance on wind than low buildings do. (2) All the wind velocity profiles and the upstream profile converge at the height of 2.5H approximately. The decay of wind velocity within the building canopy was in positive correlation with λf and rs. If the height of building arrays is variable, Macdonald’s wind velocity model should be modified through introducing σh, because wind velocity decreases at the upper layers of the canopy and increases at the lower layers of the canopy. (3) The maximum of turbulence kinetic energy (TKE) always locates at 1.2 times as high as the buildings. TKE within the canopy decreases with increasing λf and rs but the maximum of TKE are very close though σh varies. (4) Wind velocity profile follows the logarithmic law approximately above the building canopy. The Zero-plane displacement zd heighten with increasing λf, whereas the maximum of and Roughness length z0 occurs when λf is about 0.14. zd and z0 heighten linearly with σh and rs, If σh is large enough, zd may become higher than the average height of buildings.
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Jiang, Dehai,Jiang, Weimei,Liu, Hongnian,Sun, Jianning Techno-Press 2008 Wind and Structures, An International Journal (WAS Vol.11 No.4
Large eddy simulations have been performed within and over different types of urban building arrays. This paper adopted three dimensionless parameters, building frontal area density (${\lambda}_f$) the variation degree of building height (${\sigma}_h$), and the staggered degree of building range ($r_s$), to study the systematic influence of building spacing, height and layout on wind and turbulent characteristics. The following results have been achieved: (1) As ${\lambda}_f$ decrease from 0.25 to 0.18, the mean flow patterns transfer from "skimming" flow to "wake interference" flow, and as ${\lambda}_f$ decrease from 0.06 to 0.04, the mean flow patterns transfer from "wake interference" flow to "isolated roughness" flow. With increasing ${\lambda}_f$, wind velocity within arrays increases, and the vortexes in front of low buildings would break, even disappear, whereas the vortexes in front of tall buildings would strengthen and expand. Tall buildings have greater disturbance on wind than low buildings do. (2) All the wind velocity profiles and the upstream profile converge at the height of 2.5H approximately. The decay of wind velocity within the building canopy was in positive correlation with ${\lambda}_f$ and $r_s$. If the height of building arrays is variable, Macdonald's wind velocity model should be modified through introducing ${\sigma}_h$, because wind velocity decreases at the upper layers of the canopy and increases at the lower layers of the canopy. (3) The maximum of turbulence kinetic energy (TKE) always locates at 1.2 times as high as the buildings. TKE within the canopy decreases with increasing ${\lambda}_f$ and $r_s$ but the maximum of TKE are very close though ${\sigma}_h$ varies. (4) Wind velocity profile follows the logarithmic law approximately above the building canopy. The Zero-plane displacement $z_d$ heighten with increasing ${\lambda}_f$, whereas the maximum of and Roughness length $z_0$ occurs when ${\lambda}_f$ is about 0.14. $z_d$ and $z_0$ heighten linearly with ${\sigma}_h$ and $r_s$, If ${\sigma}_h$ is large enough, $z_d$ may become higher than the average height of buildings.
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