The propagation of acoustic waves in a slowly varying duct with radially sheared axial mean flow

We consider the propagation of acoustic waves along a cylindrical duct carrying radially sheared axial mean flow, in which the duct radius is allowed to vary slowly along the axis. In previous work [A.J. Cooper & N. Peake, Journal of Fluid Mechanics 445 (2001) 207-234.] radially sheared axial mean flow with nonzero swirl in a slowly varying duct was considered, but in this paper we set the swirl to zero, thereby allowing simplification of the calculations of both the mean and unsteady flows. In this approach the acoustic wavenumber and corresponding eigenfunction are determined locally, while the wave amplitude is found by solving an evolution equation along the duct. Sample results are presented, including a case in which, perhaps surprisingly, the number of cut-on modes increases as the duct radius decreases. © 2013 Elsevier Ltd. All rights reserved.

生活周期毒性试验动物─—方形网纹溞的生物学

在实验室条件下研究方形网纹的生物学。试验时水温２５±１℃，饲以斜生栅藻。初生幼体平均体长０．４０ｍｍ，第１成龄０．９６ｍｍ，最大体长可达１．４５ｍｍ，体长增长（１＿ｔ，单位ｍｍ）与年龄（ｔ，ｄ）的关系可以表达为１＿ｔ＝１．４３－ｅ￣（－０．２６８ｔ），平均寿命２２．７３（１７．１０－２５．００）ｄ，其中包括３个幼龄和１３个成龄。在３．９１ｄ达到性成熟。７ｄ内生殖３胎，产仔４０（１９－４７）个。一生生殖２２２．０个幼体，平均每胎１８．５（４．８－２３．６）个。生殖量最大出现在第６成龄。这时的年龄１１．０５ｄ

Design and testing of a medium-speed 250 kW Brushless DFIG

This paper presents the design and testing of a 250 kW medium-speed Brushless Doubly-Fed Generator (Brushless DFIG), and its associated power electronics and control systems. The experimental tests confirm the design, and show the system's steady-state and dynamic performance. The medium-speed Brushless DFIG in combination with a simplified twostage gearbox promises a low-cost low-maintenance and reliable drive train for wind turbine applications.