It is well known that interactions between the leading edge of a blade and incoming vortical structures produce a sharp rise in fluctuating pressure nearby,contributing significantly to the noise production in various...It is well known that interactions between the leading edge of a blade and incoming vortical structures produce a sharp rise in fluctuating pressure nearby,contributing significantly to the noise production in various types of rotorcrafts.To suppress this fluctuating pressure and subsequently induced noise,as the first step,active control of interactions between an airfoil and incoming cylinder-generated vortices,which mimics the practical phenomenon,was experimentally investigated.The essence of the control is to create a local perturbation,using piezo-ceramic actuators,on the surface near the leading edge of the airfoil,thus modifying the airfoil-vortex interactions.Both open-and closed-loop methods were used,where the surface perturbation was controlled by an external sinusoidal wave and a feedback pressure signal from a pressure transducer installed at the leading edge,respectively.It was observed that the closed-loop control was superior to the open-loop one;the closed-and open-loop controls achieve a maximum reduction in the pressure fluctuation at the dominant vortex frequency by 32% and 11%,respectively.The detailed physics behind the observations was discussed.展开更多
By using the soil static and dynamic universal triaxial and torsional shear apparatus, a series of combined cyclic shear tests are performed to simulate the rotation in the principal stress direction induced by ocean ...By using the soil static and dynamic universal triaxial and torsional shear apparatus, a series of combined cyclic shear tests are performed to simulate the rotation in the principal stress direction induced by ocean wave. The tests include the cyclic preloading tests and liquefaction tests in the second loading on saturated loose sand with a relative density of 30%. The all tests are consolidated under isotropic condition. The effect of the cyclic preloading on the resistance to liquefaction of saturated loose sands under the condition of continuous rotation in the principal stress direction is investigated. Experimental data indicate that the void ratio of saturated sands has a negligible reduction after cyclic preloading. With the increase of the intensity of cyclic preloading (in the amplitude and in the number of cycles), the resistance to liquefaction in the second loading is increased continuously under the condition that the liquefaction does not occur during the cyclic preloading. The reason is that the construction of more stable structure due to the uniformity of the void and the better interlocking of the particles when the cyclic preloading is applied to the saturated sand.展开更多
The conductance spectra of a graphene ribbon and graphene-superconductor （G-S） junctions are investi- gated, using the tight-binding model and non-equilibrium Green＇s function formalism. It is found that the quanti...The conductance spectra of a graphene ribbon and graphene-superconductor （G-S） junctions are investi- gated, using the tight-binding model and non-equilibrium Green＇s function formalism. It is found that the quantized conductance related to graphene＇s edge-states is robust against perturbations in the model parameters for a graphene monolayer ribbon with the zigzag boundary. With appropriate a new bound state with odd-frequency symmetry is found in conductance amplitude is followed model parameter of the spin-orbit interaction strength, the G-S junction. An enhancement in the zero-energy展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 51076153, 50836006) and‘Hundred Talent Program’ of Chinese Academy of Sciences
文摘It is well known that interactions between the leading edge of a blade and incoming vortical structures produce a sharp rise in fluctuating pressure nearby,contributing significantly to the noise production in various types of rotorcrafts.To suppress this fluctuating pressure and subsequently induced noise,as the first step,active control of interactions between an airfoil and incoming cylinder-generated vortices,which mimics the practical phenomenon,was experimentally investigated.The essence of the control is to create a local perturbation,using piezo-ceramic actuators,on the surface near the leading edge of the airfoil,thus modifying the airfoil-vortex interactions.Both open-and closed-loop methods were used,where the surface perturbation was controlled by an external sinusoidal wave and a feedback pressure signal from a pressure transducer installed at the leading edge,respectively.It was observed that the closed-loop control was superior to the open-loop one;the closed-and open-loop controls achieve a maximum reduction in the pressure fluctuation at the dominant vortex frequency by 32% and 11%,respectively.The detailed physics behind the observations was discussed.
基金the National Natural Science Foundation of China (Nos. 50579006 and 50639010)
文摘By using the soil static and dynamic universal triaxial and torsional shear apparatus, a series of combined cyclic shear tests are performed to simulate the rotation in the principal stress direction induced by ocean wave. The tests include the cyclic preloading tests and liquefaction tests in the second loading on saturated loose sand with a relative density of 30%. The all tests are consolidated under isotropic condition. The effect of the cyclic preloading on the resistance to liquefaction of saturated loose sands under the condition of continuous rotation in the principal stress direction is investigated. Experimental data indicate that the void ratio of saturated sands has a negligible reduction after cyclic preloading. With the increase of the intensity of cyclic preloading (in the amplitude and in the number of cycles), the resistance to liquefaction in the second loading is increased continuously under the condition that the liquefaction does not occur during the cyclic preloading. The reason is that the construction of more stable structure due to the uniformity of the void and the better interlocking of the particles when the cyclic preloading is applied to the saturated sand.
基金Supported by the National Natural Science Foundation of China under Grant No.61271163
文摘The conductance spectra of a graphene ribbon and graphene-superconductor （G-S） junctions are investi- gated, using the tight-binding model and non-equilibrium Green＇s function formalism. It is found that the quantized conductance related to graphene＇s edge-states is robust against perturbations in the model parameters for a graphene monolayer ribbon with the zigzag boundary. With appropriate a new bound state with odd-frequency symmetry is found in conductance amplitude is followed model parameter of the spin-orbit interaction strength, the G-S junction. An enhancement in the zero-energy
