Development research of reflection-absorption compound type fluid pulsation attenuator
Based on the disadvantages analysis of the existing fluid pulsation attenuator, two reflection-absorption compound type of fluid pulsation attenuators which are both composed of a chamber and a mass-spring-damping system are developed: in-line reflection-absorption compound type of fluid pulsation attenuators (in-line RAFPA) and side-branch reflection-absorption compound type of fluid pulsation attenuators (side-branch RAFPA). The transfer matrix models of the two attenuators are established as well as expansion chamber attenuator and Helmholtz resonator. Based on the transfer matrix model, the transmission loss of the four attenuators is given out to evaluate their attenuation characteristic. The attenuation characteristic comparisons of in-line RAFPA with expansion chamber attenuator and side-branch RAFPA with Helmholtz resonator are carried out respectively. And the effect of the mass-spring-damping system to in-line RAFPA and side-branch RAFPA is investigated. The simulation reveals the two reflection-absorption compound type of fluid pulsation attenuators have better attenuation characteristic and are more compact than expansion chamber attenuator and Helmholtz resonator.
Comparison and implementation of the various numerical methods used for calculating transmission loss in silencer systems
Issues concerning the design and use of large-scale silencers are more prevalent today then ever before. With the increased use of large industrial machinery (such as gas turbines) and the increase in public awareness and concern for noise control, the desire to be able to properly design silencers for specific applications is increasing. Even today, most silencer design is performed by simply modifying existing designs without full confidence of the new performance characteristics. Due to the size and expense of these silencers, it would be beneficial to have means to predict the insertion loss (IL) or transmission loss (TL) characteristics at the design stage. To properly accomplish this, many factors such as geometry, absorptive material properties, flow effects, break out noise, and self-generated noise must be considered. The use of the finite element method (FEM) and the boundary element method (BEM) can aid in the prediction and design. This paper examines three of the different methods used in calculation of TL values; namely the ‘‘traditional’’ laboratory method, the 4-pole transfer matrix method and the 3-point method. A comparison of these methods based on such criteria as accuracy, computation time, and ease of use was conducted. In addition, the idiosyncrasies and problems encountered during implementation are presented. The conclusions were that the FEM is better suited for this kind of application and that the 3-point method was the fastest method and was easier to use than the 4-pole method. # 2003 Elsevier Science Ltd. All rights reserved.
Miniband formulation in Ge/Si quantum dot array
In this work, we estimate the coupling effect of miniband structure and density of states (DoS) resulting from different qunatum-dot physical parameters in a well-aligned Ge/Si quantum dot (QD) array fabricated by neutral beam etching technology. The density of QDs dominates the coupling effect and miniband’s bandwidth, the radius of QDs affects the magnitude of energy levels and miniband bandwidth, and the thickness of QDs has a great impact on the magnitude of energy levels. Among the different shapes of Ge/Si QDs, discoid QDs exhibit the most band crossing and broadest bandwith under the same physical parameters.