Aeroacoustics damping performances of double-layer perforated pipes at low grazing-bias flow Mach number

2021 ◽  
Vol 149 (4) ◽  
pp. A140-A140
Author(s):  
Dan Zhao ◽  
YX Gay
Keyword(s):  
Mach Number ◽  
Double Layer ◽  
Bias Flow

scholarly journals Sound propagation in a lined nozzle with shear and bias flows

2018 ◽  
Vol 18 (1) ◽  
pp. 3-48
Author(s):  
LMBC Campos ◽  
C Legendre
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Boundary Layers ◽  
Lower Boundary ◽  
Cross Flow ◽  
Core Flow ◽  
The Core ◽  
Wide Range ◽  
Bias Flow ◽  
Number Formula

In this study, the propagation of waves in a two-dimensional parallel-sided nozzle is considered allowing for the combination of: (a) distinct impedances of the upper and lower walls; (b) upper and lower boundary layers with different thicknesses with linear shear velocity profiles matched to a uniform core flow; and (c) a uniform cross-flow as a bias flow out of one and into the other porous acoustic liner. The model involves an “acoustic triple deck” consisting of third-order non-sinusoidal non-plane acoustic-shear waves in the upper and lower boundary layers coupled to convected plane sinusoidal acoustic waves in the uniform core flow. The acoustic modes are determined from a dispersion relation corresponding to the vanishing of an 8 × 8 matrix determinant, and the waveforms are combinations of two acoustic and two sets of three acoustic-shear waves. The eigenvalues are calculated and the waveforms are plotted for a wide range of values of the four parameters of the problem, namely: (i/ii) the core and bias flow Mach numbers; (iii) the impedances at the two walls; and (iv) the thicknesses of the two boundary layers relative to each other and the core flow. It is shown that all three main physical phenomena considered in this model can have a significant effect on the wave field: (c) a bias or cross-flow even with small Mach number [Formula: see text] relative to the mean flow Mach number [Formula: see text] can modify the waveforms; (b) the possibly dissimilar impedances of the lined walls can absorb (or amplify) waves more or less depending on the reactance and inductance; (a) the exchange of the wave energy with the shear flow is also important, since for the same stream velocity, a thin boundary layer has higher vorticity, and lower vorticity corresponds to a thicker boundary layer. The combination of all these three effects (a–c) leads to a large set of different waveforms in the duct that are plotted for a wide range of the parameters (i–iv) of the problem.

Switching LPV Control with Double-Layer LPV Model for Aero-Engines

2016 ◽  
Vol 0 (0) ◽  
Author(s):  
Lili Tang ◽  
Jinquan Huang ◽  
Muxuan Pan
Keyword(s):  
Mach Number ◽  
Double Layer ◽  
Rotational Speed ◽  
State Feedback ◽  
Operating Conditions ◽  
Flight Altitude ◽  
Robust Controller ◽  
Aero Engine ◽  
Lpv Control ◽  
Aero Engines

AbstractTo cover the whole range of operating conditions of aero-engine, a double-layer LPV model is built so as to take into account of the variability due to the flight altitude, Mach number and the rotational speed. With this framework, the problem of designing LPV state-feedback robust controller that guarantees desired bounds on both

scholarly journals Dust ion-acoustic solitary structures in non-thermal dusty plasma

2011 ◽  
Vol 78 (2) ◽  
pp. 149-164 ◽  
Author(s):  
ANIMESH DAS ◽  
ANUP BANDYOPADHYAY ◽  
K. P. DAS
Keyword(s):  
Mach Number ◽  
Solitary Wave ◽  
Double Layer ◽  
Solitary Waves ◽  
Negative Potential ◽  
Present System ◽  
Charged Dust ◽  
Solitary Structures ◽  
Ion Acoustic ◽  
Layer Solution

AbstractDust ion-acoustic solitary structures have been investigated in an unmagnetized non-thermal plasma consisting of negatively charged dust grains, adiabatic positive ions, and non-thermal electrons. Whenever the non-thermal parameter exceeds a critical value, the present system supports negative potential double layer solution. However, this double layer solution is unable to restrict the occurrence of negative potential solitary waves of the present system. As a result, the occurrence of one type of negative potential solitary wave is restricted by Mc < M < MD, whereas the second type of solitary wave exists for all M > MD, where Mc is the lower bound of the Mach number M and MD (> Mc) is the Mach number corresponding to a negative potential double layer. A finite jump between the amplitudes of negative potential solitary waves at M = MD − ϵ1 and M = MD + ϵ2 has been observed, where 0 < ϵ1 < MD − Mc and ϵ2 > 0. Depending on the analytical theory presented in this paper, a numerical scheme has been provided to find the value of the Mach number at which double layer solution exists, and also the amplitude of that double layer. Although the occurrence of coexistence of solitary structures of both polarities is restricted by Mc < M ≤ Mmax, only negative potential solitary wave still exists for all M > Mmax, where Mmax is the upper bound of M for the existence of positive potential solitary waves only. Qualitatively different compositional parameter spaces showing the nature of existing solitary structures of the energy integral have been found. These solution spaces are capable of producing new results and physical ideas for the formation of solitary structures whenever one can move the solution spaces through the family of curves parallel to the curve M = Mc.

Cracking at the fold in double layer coated paper: the influence of latex and starch composition

TAPPI Journal ◽  
2019 ◽  
Vol 18 (2) ◽  
pp. 93-99
Author(s):  
SEYYED MOHAMMAD HASHEMI NAJAFI ◽  
DOUGLAS BOUSFIELD, ◽  
MEHDI TAJVIDI
Keyword(s):  
Mechanical Properties ◽  
Double Layer ◽  
Starch Content ◽  
Single Layer ◽  
Double Layers ◽  
Coated Paper ◽  
Coated Papers ◽  
Coating Layers ◽  
Scanned Images ◽  
Packaging Paper

Cracking at the fold of publication and packaging paper grades is a serious problem that can lead to rejection of product. Recent work has revealed some basic mechanisms and the influence of various parameters on the extent of crack area, but no studies are reported using coating layers with known mechanical properties, especially for double-coated systems. In this study, coating layers with different and known mechanical properties were used to characterize crack formation during folding. The coating formulations were applied on two different basis weight papers, and the coated papers were folded. The binder systems in these formulations were different combinations of a styrene-butadiene latex and mixtures of latex and starch for two different pigment volume concentrations (PVC). Both types of papers were coated with single and double layers. The folded area was scanned with a high-resolution scanner while the samples were kept at their folded angle. The scanned images were analyzed within a constant area. The crack areas were reported for different types of papers, binder system and PVC values. As PVC, starch content, and paper basis weight increased, the crack area increased. Double layer coated papers with high PVC and high starch content at the top layer had more cracks in comparison with a single layer coated paper, but when the PVC of the top layer was low, cracking area decreased. No measurable cracking was observed when the top layer was formulated with a 100% latex layer.

A Survey on Crypto-Steganographic Schemes and A Use Case in Healthcare System

2019 ◽  
Vol 1 (2) ◽  
pp. 25-33
Author(s):  
Mei Ling Phang ◽  
Swee Huay Heng
Keyword(s):  
Social Networking ◽  
Information Sharing ◽  
Healthcare System ◽  
Double Layer ◽  
21St Century ◽  
Electronic Devices ◽  
Third Party ◽  
Use Case ◽  
Comparison Analysis ◽  
Information Assets

Information sharing has become prevalent due to the expansion of social networking in this 21st century. However, electronic devices are vulnerable to various kinds of attacks. Information might be disclosed, modified and accessed by an unauthorised third party which consequently leads to the breach of confidentiality, integrity and availability of the information. Therefore, it is of utmost importance to employ the technology of cryptography and steganography to protect information assets. Cryptography and steganography have weaknesses when they are working alone. Therefore, crypto-steganography, the combination of cryptography and steganography are introduced to overcome the weaknesses in order to provide a double layer of security and protection. This paper provides a general overview of steganography and cryptography as well as a comparison analysis of different crypto-steganographic schemes. A secure crypto-steganographic system for healthcare is then developed with the implementation and integration of the secure crypto-steganographic scheme proposed by Juneja and Sandhu. This healthcare system enables users to store and deliver message in a more secure way while achieving the main goals of both cryptography and steganography.

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