Design and Optimization of the Electromagnetic Actuator in Active-Passive Hybrid Vibration Isolator

The design and optimization of actuators are difficult andcritical for the active-passive hybrid vibration control system. Inthis paper, an electromagnetic actuator model is establishedbased on Ohm’s Law for magnetic circuit considering theleakage flux. The 600N electromagnetic actuators are designedand optimized based on ANSYS simulation according to theengineering request. Its transient characteristics are studied. Theeffects of different structural parameters on its output force areanalyzed. The experimental results show that the structureparameters and output force characteristics of the designedelectromagnetic actuators satisfy the practical requirement.

Experimental study on dynamic stall control based on AC-DBD actuation

To explore AC-DBD's ability in controlling dynamic stall,a practical SC-1095 airfoil of a helicopter was selected,and systematic wind tunnel experiments were carried out through direct aerodynamic measurements.The effectiveness of dynamic stall control under steady and unsteady actuation is verified.The influence of parameters such as constant actuation voltage,pulsed actuation voltage,pulsed actuation frequency and duty ratio on dynamic stall control effect is studied under the flow condition of k=0.15 above the airfoil,and the corresponding control mechanism is discussed.Steady actuation can effectively reduce the hysteresis loop area of dynamic lift,and control the peak drag and moment coefficient.For unsteady actuation,there is an optimal duty ratio DC=50%,which has the best effect in improving the lift and drag characteristics,and there is a threshold of pulsed actuation voltage in dynamic stall control.The optimal dimensionless frequency will not be found;different F+have different control advantages in different aerodynamic coefficients of different pitching stages.Unsteady actuation has obvious control advantages in improving the lift-drag characteristics and hysteresis,while steady actuation can better control the large nose-down moment.

Array Shape Estimation Using Partitioned Eigenstructure Method with Sources in Unknown Localizations

Advanced array processing approaches require accurate knowledge of the location of individual element in a sensor array.Most array shape estimation methods require the directions of sources.In this paper,an array shape estimation method based on eigen-decomposition is presented.The directions of sources do not need to be considered in advance and optimal array shape is generated through a series of iterations.To further improve the accuracy of this algorithm,a partitioned eigenstructure method is introduced.Numerical simulations using non-partitioned and partitioned method are conducted to verify the performance of the proposed technique.

Sound absorption characteristics of underwater flexible micro-perforated sound absorption structures

A mathematical model for the micro-perforated panel in water medium is established using mode superposition method,and an equivalent circuit model is acquired based on electro-acoustic analogy method.Effects of the flexible micro-perforated panel(FMPP) and the flexible back panel(FBP) on normal incidence sound absorption coefficient are analyzed.Unlike micro-perforated panel in air medium,the underwater micro-perforated panel cannot achieve any satisfactory sound absorption effect due to insufficient structural impedance.To this end,a strengthened micro-perforated sound absorption structure is proposed.Theoretical results are verified in a water-filled impedance tube.Within the range from 20 Hz to 2,000 Hz the average absorption coefficient of the strengthened flexible micro-perforated panel are improved obviously.The absorption coefficient curve gradually approaches rigid micro-perforated panel as the bending stiffness increases.The flexible back panel can reduce the resonance frequency of the absorption curve and improve the low-frequency sound absorption performance.

Theory and calculation for acoustic radiation mode of weak coupled enclosure

Active structural acoustic control(ASAC)is an efficient method in acoustic radiation control of coupled enclosure.In the past research of ASAC,the concept of 'acoustic radiation mode(ARM)of coupled enclosure'was proposed,which was a set of basis functions of structural mode amplitude.However,there was an incompatibility with the ARM definition in free space radiation case which was a set of basic functions of normal velocity or pressure on the vibrating surface.Also,there was severe inconvenience for application as structural modes were required while accurate and useful structural modes were difficult to be extracted in practice.To overcome these problems,by analogy to ARM theory of free space,the acoustic potential energy was expressed in quadratic form of normal velocity on coupling surface and ARM of coupled enclosure was redefined.Furthermore,theoretic derivation showed that ARM of coupled enclosure could be replaced simply by corresponding acoustic mode projection of enclosure when the coupling surface was discretized into equal size elements.Therefore,the ARM theory of coupled enclosure which was consistent with that of free space and convenient for application was formed.Finally,numerical calculation was performed and the results proved that the presented theory was very efficient in ARM calculation of coupled enclosure and ASAC.

Transmission loss of a flexible micro-perforated muffler with a flexible back cavity for water-filled pipelines

To reduce low-frequency noise of the water-filled pipeline system,a compact flexible micro-perforated muffler with a flexible back cavity(FMPMFBC) is proposed.The flexible pipe wall is made of a rubber-cord composite material.A numerical solution for the transmission loss is derived.Firstly,the flexible micro-perforated panel(FMPP) is equivalent to a flexible porous material based on Biot-Allard porous-elastic theory.Then,a periodic structural unit of the aramid fabric cloth is established with the two-scale method,and the equivalent stiffness matrix is obtained.Besides,a multi-layer composite model for the flexible pipe wall is constructed according to the lamination theory.Coupling with the internal sound field,the transmission loss of the FMPMFBC is calculated.On a water-filled impedance tube,the transmission loss curves of the FMPMFBC prototypes are measured with the two source-location method,and compared with those of a flexible micro-perforated muffler with a rigid back cavity(FMPMRBC)and an expansion muffler.Theoretical results are experimentally verified.The FMPMFBC is a hybrid muffler combining reflection with dissipation,capable of attenuating broadband lowfrequency noise.The transmission loss of prototype B2 in the frequency bands of [40 300] Hz and [40 1200] Hz is 36 dB and 30 dB,respectively,while the transmission loss of the same-sized expansion muffler in the corresponding frequency bands is 7 dB and 11 dB,respectively.