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Showing 4 results for Excitation Frequency
Effects of Duty Cycles of the Plasma Actuators on Improvement of the Pressure Distribution over NLF0414 Airfoil
Seyyed Arash Seyyed Shams Taleghani, Abdollah Shadaram, ,
Volume 12, Issue 1 (4-2012)
Abstract
This paper deals with the effects of duty cycle on improvement of pressure distribution over a NLF0414 airfoil using the plasma actuators. Three Dielectric barrier discharges as the plasma actuators are flush mounted on the airfoil surface in different positions to improve pressure distribution at post-stall angles of attack. The experiments were performed in wind tunnel with pressure tabs measurements at Re_c=7.5×〖10〗^5. The main objective of these experiments is to find the most effective duty cycles for different excitation frequencies and different angles of attack. Results show that the plasma actuators in unsteady excitations are more effective in lower duty cycles on low excitation frequencies but the lower duty cycles lose their effectiveness on higher excitation frequencies.
Experimental Investigation of Geometric and Electrical Characteristics by measurements of the induced flow velocity
Seyyed Arash Seyyed Shams Taleghani, , ,
Volume 12, Issue 5 (1-2013)
Abstract
This paper deals with experimental measurements of the instantaneous ionic wind velocity induced by Dielectric barrier discharge (DBD) plasma actuator in quiescent air at atmospheric pressure. A parametric study has been performed in order to increase the velocity of the ionic wind induced by the DBD actuators. The electrical and mechanical characteristics of the plasma actuator have been studied under different conditions. The main objective of this work was to help to optimize the geometrical and electrical parameters to obtain more effective ionic wind for flow control. The time averaged velocity profiles of the ionic wind show that the position of the maximum velocity come near the surface by increasing the excitation frequency. Our results indicate that the DBD plasma actuators generate vortices at the same frequency of the excitation frequency of the applied high voltage. The power, of the vortices that are shed from the actuators, increases by increasing duty cycle percentage. Unlike other similar works in this field, this study has examined the behavior of unsteady plasma actuator.
Designing virtual vibration absorber with adaptable stiffness for vibrations control under harmonic excitation with noise in time-varying frequency
Soheil Salighe, Hossein Mohammadi,
Volume 17, Issue 7 (9-2017)
Abstract
In the present article, a real mass-spring system under external excitation with time-varying frequency is studied. The external excitation causes additional oscillations in the real mass-spring system response which disrupt the path tracking procedure. Adaptive control law, which is considered for annihilating the additional oscillations, is equal to a virtual vibration absorber which its stiffness regardless of the real system and external excitation uncertainties, can be updated based on the linear absorber theory until the natural frequency of the absorber reaches the excitation frequency. The variation of the frequency is based on the step and ramp function which relatively are equal to the sudden and transient change from the initial value to the final value of the frequency. Besides, the effects of the noise with various amplitudes existed in the transient variation of the frequency on updating the virtual absorber stiffness is developed. Simulation results are presented to demonstrate that the determined adaptation law guarantees the adaptation of virtual absorber stiffness considering excitation frequency variation based on both step function and ramp function and eliminates additional vibrations of the real system.
Effect of frequency dependency of impedance functions on seismic damage index of soil-structure systems

Volume 24, Issue 6 (11-2024)
Abstract
In seismic analysis and design of conventional structures, it is generally assumed that the soil beneath the foundation is rigid and, thus, its flexibility is not taken into account. Soil flexibility can affect the response of structures through complex phenomenon of dynamics soil-structure interaction (SSI) effect. It is believed that effective soil and structural parameters could in some case significantly influence seismic response of structures in different manners and conditions. In this study, through an intensive parametric study, the effect of frequency dependency of impedance functions on constant-ductility damage index parameter of soil-structure SDOF systems subjected to ordinary strong ground motions were investigated. To this end, the soil-structure system was modeled by sub-structure method and the foundation was modeled as a homogeneous elastic half-space using the concept of the cone model. The soil-structure systems with shallow foundation were modeled based on various SSI key parameters, and were then analyzed under 15 earthquake ground motions recorded on soft soils.  Results of this study show that, in average, the maximum effect of excitation frequency dependency on seismic damage index is referred to the intensive SSI models, slender structures and with low level of inelastic behavior, which, in critical case, will occur in one or limited values of fundamental period. The maximum mean value is about 13.56% which cannot be considered as a criterion for practical application. Therefore, to have a logical criterion for practical purpose, the average values of entire periodic region in 15 earthquake ground motions were computed and, then, the maximum value, i.e., 5.76, was considered to make a decision. Overall, the results indicate that for soil-structure SDOF systems with shallow foundation, frequency dependency of impedance functions on damage index of structures subjected to earthquake ground motions would not have a remarkable effect and thus can be practically ignored in seismic analysis and design of soil-structures systems with shallow foundations. This finding being debated by researchers can lead to using a simple soil-structure system with less computational time and effort.
 

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