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21.
Sonic jet chargers have originally been used in aerosol measurement devices for particle charging and neutralization. Here, our goal was to study if this charger type could be used in particle control devices in which particle concentrations and gas volumes are much higher. The study includes charging efficiency tests in a laboratory and with a commercial 20 kW wood pellet burner. Actual particle removal efficiency was tested with a laboratory scale parallel plate electrostatic collector. The results show that sonic jet-type chargers also have potential in filtering applications. 相似文献
22.
23.
This work presents sound insulation and sound reflection measurements conducted over sonic crystal noise barriers according to the European standards EN 1793-2, EN 1793-5 and EN 1793-6. In most of the reference literature, sound insulation and reflection properties of sonic crystals are measured or a diffuse sound field or in a direct sound field including the top and side edge diffraction effects together with the transmitted (or reflected) components. The aim of this work is to perform free-field measurements over a real-sized sample in order to window out all diffraction components and to verify the points of strength and weakness of the application of standardised measurements to sonic crystals. Diffuse field measurements in laboratory are also done for comparison purposes. Since the target frequency range for traffic noise spectrum is centred at around 1000 Hz, a finite element based parametric investigation is performed to design unit cells capable of generating band gaps in the one-third octave bands ranging from 800 Hz to 1250 Hz. Then, 3 × 3 m sonic crystal noise barriers are installed in the Laboratory of the University of Bologna and sound insulation and sound reflection measurements are performed according to the mentioned active standards for normal incidence. Sound insulation is measured for diffuse incidence too. The two methods give different results. The method more directly comparable to calculations is the free-field one. However, if on the one hand the application of a time window allows to compute the transmitted or reflected component only, on the other hand the time window itself limits the maximum width of the sample for which all reflections of the n-th order having a significant spectral content are included, and thus results critical in the analysis of this kind of noise barriers. Nevertheless, the standardised measurements allow a direct comparison between the performance of sonic crystals and common noise barriers. 相似文献
24.
《Wave Motion》2017
Multiple-scale asymptotic analysis is applied to small-wavelength, weakly nonlinear propagation of an impulsive acoustic wave in a general (3D, in-motion and time dependent) atmosphere. In keeping with previous work on sonic booms and nonlinear acoustics in general, the result is a combination of ray tracing and a generalised Burgers equation describing evolution of the waveform carried by a ray. This is nonetheless, to our knowledge, the first derivation of such a model based on asymptotic analysis of the governing equations for a general atmosphere. Results are given, discussed and compared with measurements for the particular example of the test explosion known as Misty Picture. 相似文献
25.
Yun WangKe Deng Shengjun XuChunyin Qiu Hai YangZhengyou Liu 《Physics letters. A》2011,375(10):1348-1351
The unwanted reflection seriously baffles the practical applications of sonic crystals, such as for various acoustic lenses designed by utilizing the in-band properties of sonic crystals. Herein we introduce the concept of the antireflection coating into the sonic crystal-based devices. The efficiency of such accessorial structures is demonstrated well by an originally high reflection system. Promising perspectives can be anticipated in extending the antireflection coating layers into more general acoustic applications through a flexible design process. 相似文献
26.
Tanner Robert D. Ko Samuel Loha Veara Prokop Ales 《Applied biochemistry and biotechnology》2000,84(1-9):1079-1086
It has previously been shown that a droplet fractionation process, simulated by shaking a separatory funnel containing a dilute
protein solution, can generate droplets richer in protein than present in the original dilute solution. In this article, we
describe an alternative method that can increase the amount of protein transferred to the droplets. The new metho uses ultrasonic
waves, enhanced by a bubble gas stream to create the droplets. The amount of protein in these droplets increases by about
50%. In this method, the top layer of the dilute protein solution (of the solution-air interface) becomes enriched in protein
when air is bubbled into the solution. This concentrating procedure is called bubble fractionation. Once the protein has passed
through the initial buildup, this enriched protein layer is transferred into droplets with the aid of a vacuum above the solution
at the same time that ultrasonic waves are introduced. The droplets are then carried over to a condenser and coalesced. We
found that this new method provides an easier way to remove the protein-enriched top layer of the dilute solution and generates
more droplet within a shorter period than the separatory funnel droplet generation method. The added air creates the bubbles
and carries the droplets, and the vacuum helps remove the effluent airstream from the condenser. The maximum partition coefficient,
the ratio of the protein concentration in the droplets to that in the residual solution (approx 8.5), occurred at pH 5.0. 相似文献
27.
For the structure of a sonic boom produced by a simple aerofoil at a large distance from its source we take a physical model
which consists of a leading shock (LS), a trailing shock (TS) and a one-parameter family of nonlinear wavefronts in between
the two shocks. Then we develop a mathematical model and show that according to this model the LS is governed by a hyperbolic
system of equations in conservation form and the system of equations governing the TS has a pair of complex eigenvalues. Similarly,
we show that a nonlinear wavefront originating from a point on the front part of the aerofoil is governed by a hyperbolic
system of conservation laws and that originating from a point on the rear part is governed by a system of conservation laws,
which is elliptic. Consequently, we expect the geometry of the TS to be kink-free and topologically different from the geometry
of the LS. In the last section we point out an evidence of kinks on the LS and kink-free TS from the numerical solution of
the Euler’s equations by Inoue, Sakai and Nishida [5]. 相似文献
28.
On the Investigation of Some Parameter Identification and Experimental Modal Filtering Issues for Nonlinear Reduced Order Models 总被引:1,自引:0,他引:1
This paper discusses modal filtering of experimental data and the corresponding identification of linear and nonlinear parameters
in reduced order space. Specifically, several experimental configurations will be discussed in order to provide insight into
such identification issues as spatial discretization, observability, and the linear independence of the assumed filter or
basis. The two experiments considered herein represent different measurement configurations of the same clamped–clamped beam.
First, asymmetric inertial loading via asymmetric sensor location was considered, while the second scenario presents a symmetric
sensor configuration. Several important conclusions can be drawn from the two experimental scenarios. First, by asymmetrically
loading the beam, a corresponding asymmetric beam mode was excited yet not observable. In the second scenario, the symmetric
distribution of sensors minimized the impact of the respective asymmetric mode. The resulting spatial information allowed
for the proper filtering of the remnants of the asymmetric mode. Nonlinear parameters in modal space as well as the underlying
linear parameters were successfully identified simultaneously in both experimental scenarios, although the usefulness of the
asymmetrically loaded beam was limited. Finally, successful comparisons were made between the identified reduced order model
and experimental response at the beam quarter point using the symmetric case and the beam midpoint using both experimental
scenarios. 相似文献
29.
This paper investigates a nonreciprocal sound transmission effect provided by a triangular lattice two-dimensional sonic crystal made of rods in a triangular cross-section. This sonic crystal (SC) device works as a frequency selective acoustic diode operating at a frequency of 8950 Hz. The scatterer matrix of the sonic crystal diode prototype was composed of triangular shaped wood rods that break the symmetry of the spatial inversion and provide nonreciprocal wave transmission with a contrast rate of 89% in experiments. This acoustic diode device can provide a high contrast, narrow band, one-way sound transmission for acoustic wave control applications. 相似文献
30.
《Physics letters. A》2020,384(20):126510
We investigate the topologically protected sound propagation in sonic metamaterials, analogous to quantum spin hall effect (QSHE). The sonic metamaterials consist of circular rods and meta-molecules arranged in air with a honeycomb-lattice. The on-demand inversion in topological phase can be achieved by two ways of scatterer controls at locally resonant frequency and Bragg frequency. The Helmholtz resonators in the structure are contributed to the formation of subwavelength double Dirac cones which are more likely to appear due to local resonance enhancement with more number of resonators. By combining two sonic metamaterials with different topological invariants, we demonstrate the robust sound propagation and pseudospin-dependent one-way acoustic propagation at the interface. Experimental measurement of the topologically protected acoustic wave transmission matches well with the simulation result. 相似文献