Theoretical model of acoustic scattering from a flat plate with serrations

2017 ◽  
Vol 819 ◽  
pp. 228-257 ◽  
Author(s):  
Xun Huang
Keyword(s):  
Theoretical Model ◽  
Practical Importance ◽  
Acoustic Scattering ◽  
Low Noise ◽  
Test Cases ◽  
Sound Waves ◽  
Rigorous Description ◽  
Parametric Studies ◽  
Closed Form Analytical Solution ◽  
Hopf Method

A theoretical model is proposed in this work to study the scattering of sound waves from a serrated flat plat in the presence of a uniform flow, which is of both scientific significance and practical importance. The key contribution is the analytic and rigorous description of the scattering from the laterally periodic serrations by incorporating Fourier series expansions and the Wiener–Hopf method, which collectively give a closed-form analytical solution. To validate and demonstrate the model, a couple of test cases with some representative sinusoidal- and sawtooth-shaped serrations are studied by comparing with a commercial finite element solver. The comparisons show quite good agreement for various set-ups. The subsequent parametric studies further demonstrate the efficiency of the model and the effect of the serrations for noise control. Overall, the proposed theoretical model should be able to assist in studies of low-noise aerofoils and the silent flying capabilities of owls.

Tonal Fan-Noise Radiation From Aero-Engine Bypass With Serrated End Treatments

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Hanbo Jiang ◽  
Xun Huang
Keyword(s):  
Theoretical Model ◽  
Mode Conversion ◽  
Jet Noise ◽  
Acoustic Mode ◽  
Low Noise ◽  
Fan Noise ◽  
Engine Design ◽  
Aero Engine ◽  
Parametric Studies ◽  
Hopf Method

Abstract Chevrons, which are also known as serrations, are initially developed to suppress jet noise radiating from aero-engine nozzles. The associated fluid mechanics are already well known. Compared with jet noise, turbomachinery fan noise has become relatively more important along with the ever-increasing bypass ratio. However, it is still unclear whether the trailing-edge chevrons on the bypass duct would attenuate fan noise and, if the answer is yes, what is the associated mechanism. In this work, we first use a theoretical model based on the Wiener–Hopf method to rapidly conduct parametric studies across a number of different setups. The results from such a theoretical model suggest that the chevrons are also effective in the reduction of fan noise scattering. Next, we perform high-fidelity computational fluid and acoustic simulations for a realistic aero-engine with some representative setups, and the results further confirm the effectiveness of chevrons. Both analytical and numerical results show the associated noise control mechanism, that is, chevrons would induce acoustic mode conversion (especially from low modes to high modes), which shall further result in evanescent waves in the radial direction and the final noise reduction at various radiation angles. The findings may find applications in the next-generation low-noise aero-engine design.

Sound wave scattering in a flow duct with azimuthally non-uniform liners

2018 ◽  
Vol 839 ◽  
pp. 644-662 ◽  
Author(s):  
Hanbo Jiang ◽  
Alex Siu Hong Lau ◽  
Xun Huang
Keyword(s):  
Current Model ◽  
Practical Importance ◽  
Closed Form Solution ◽  
Form Solution ◽  
Theoretical Modelling ◽  
Sound Waves ◽  
Matrix Kernel ◽  
Set Up ◽  
Hopf Method ◽  
Flow Duct

Novel acoustic liner designs often incorporate new materials with non-uniform impedance distributions. Therefore, new methods are required for their modelling and analysis. In this paper, a theoretical model is developed to investigate the scattering of sound waves from an axially symmetrical flow duct with a semi-infinite, azimuthally non-uniform acoustic lining on the duct wall. More specifically, the incorporation of Fourier series expansions into the Wiener–Hopf method leads to an analytical model with a matrix kernel, which is further factorised by using the pole-removal method to obtain a closed-form solution. A new mathematical method is developed to solve the residues associated with the pole-removal technique. The proposed model has been verified and validated by comparing with corresponding computational results. In addition to shedding light on the possible physical effect of azimuthally non-uniform liners along with an axial hard–soft interface, the current model enhances the theoretical modelling capability for a complicated set-up of practical importance, and can be used to investigate new liner designs for passive noise control in flow ducts.

Radiation modes of propeller tonal noise

2021 ◽  
pp. 1-25
Author(s):  
Hanbo Jiang ◽  
Siyang Zhong ◽  
Han Wu ◽  
Xin Zhang ◽  
Xun Huang ◽  
...  
Keyword(s):  
Spherical Harmonics ◽  
Sound Field ◽  
Low Noise ◽  
Noise Model ◽  
Sound Waves ◽  
Tonal Noise ◽  
Noise Sources ◽  
Separate Source ◽  
Radial Forces ◽  
Flow Variables

Abstract This paper focuses on the radiation modes and efficiency of propeller tonal noise. The thickness noise and loading noise model of propellers has been formulated in spherical coordinates, thereby simplifying numerical evaluation of the integral noise source. More importantly, the radiation field can be decomposed and projected to spherical harmonics, which can separate source-observer positions and enable an analysis of sound field structures. Thanks to the parity of spherical harmonics, the proposed model can mathematically explain the fact that thrusts only produce antisymmetric sound waves with respect to the rotating plane. In addition, the symmetric components of the noise field can be attributed to the thickness, as well as drags and radial forces acting on the propeller surface. The radiation efficiency of each mode decays rapidly as noise sources approach the rotating centre, suggesting the radial distribution of aerodynamic loadings should be carefully designed for low-noise propellers. The noise prediction model has been successfully applied to a drone propeller and achieved a reliable agreement with experimental measurements. The flow variables employed as an input of the noise computation were obtained with computational fluid dynamics (CFD), and the experimental data were measured in an anechoic chamber.

A New Method for Dynamic Analysis of Mistuned Bladed Disks Based on the Exact Relationship Between Tuned and Mistuned Systems

2002 ◽  
Vol 124 (3) ◽  
pp. 586-597 ◽  
Author(s):  
E. P. Petrov ◽  
K. Y. Sanliturk ◽  
D. J. Ewins
Keyword(s):  
Dynamic Analysis ◽  
Frequency Response Function ◽  
New Method ◽  
Test Cases ◽  
Finite Element Models ◽  
Bladed Disks ◽  
Sector Model ◽  
Bladed Disk ◽  
Parametric Studies ◽  
Exact Relationship

A new method for the dynamic analysis of mistuned bladed disks is presented. The method is based on exact calculation of the response of a mistuned system using response levels for the tuned assembly together with a modification matrix constructed from the frequency response function (FRF) matrix of the tuned system and a matrix describing the mistuning. The main advantages of the method are its efficiency and accuracy, which allow the use of large finite element models of practical bladed disk assemblies in parametric studies of mistuning effects on vibration amplitudes. A new method of calculating the FRF matrix of the tuned system using a sector model is also developed so as to improve the efficiency of the method even further, making the proposed method a very attractive tool for mistuning studies. Various numerical aspects of the proposed method are addressed and its accuracy and efficiency are demonstrated using representative test cases.

Minding the Mechanisms: A Discussion of How Mindfulness Leads to Positive Outcomes at Work

2015 ◽  
Vol 8 (4) ◽  
pp. 620-629 ◽  
Author(s):  
Dexter Miksch ◽  
Meghan I. H. Lindeman ◽  
Lebena Varghese
Keyword(s):  
Theoretical Model ◽  
Empirical Research ◽  
Practical Importance ◽  
Work Outcomes ◽  
Future Research ◽  
Positive Outcomes ◽  
Mindfulness Practices ◽  
Mediating Mechanisms ◽  
The Many ◽  
Positive Work

Hyland, Lee, and Mills (2015) asserted that the many benefits of mindfulness practices have been underutilized and understudied at work. We agree with the focal article's stance that more research is needed on mindfulness at work. We extend this argument to include a request that future research pays attention to the mechanisms responsible for the effects of mindfulness at work. In this commentary, we (a) briefly discuss the practical importance of understanding the mechanisms by which mindfulness practices lead to positive outcomes, (b) outline the mediating mechanisms proposed by the leading theoretical model of mindfulness effects and how those mediators apply to work, and (c) argue that more rigorous, empirical research is needed to understand the mechanisms through which mindfulness practices lead to positive work outcomes.

Theoretical model of scattering from flow ducts with semi-infinite axial liner splices

2015 ◽  
Vol 786 ◽  
pp. 62-83 ◽  
Author(s):  
Xin Liu ◽  
Hanbo Jiang ◽  
Xun Huang ◽  
Shiyi Chen
Keyword(s):  
Fourier Series ◽  
Theoretical Model ◽  
Numerical Solutions ◽  
Practical Importance ◽  
Numerical Test ◽  
Closed Form Solution ◽  
Fourier Series Expansion ◽  
Constant Matrix ◽  
Acoustic Effect ◽  
Matrix Kernel

In this paper we present a theoretical model to study sound scattering from flow ducts with a semi-infinite lining surface covered by some equally spaced rigid splices, which is of practical importance in the development of silent aeroengines. The key contribution of our work is the analytical and rigorous description of axial liner splices by incorporating Fourier series expansion and the Wiener–Hopf method. In particular, we describe periodic variations of the semi-infinite lining surface by using Fourier series that accurately represent the layout of rigid splices in the circumferential direction. The associated matrix kernel involves a constant matrix and a diagonal matrix. The latter consists of a series of typical scalar kernels. A closed-form solution is then obtained by using standard routines of Wiener–Hopf factorisation for scalar kernels. A couple of appropriate approximations, such as numerical truncations of infinite Fourier series, have to be adopted in the implementation of this theoretical model, which is validated by comparing favorably with numerical solutions from a commercial acoustic solver. Finally, several numerical test cases are performed to demonstrate this theoretical model. It can be seen that the proposed theoretical model helps to illuminate the essential acoustic effect jointly imposed by axial and circumferential hard–soft interfaces.

Wire Stress Calculations in Helical Strands Undergoing Bending

1992 ◽  
Vol 114 (3) ◽  
pp. 212-219 ◽  
Author(s):  
M. Raoof ◽  
Y. P. Huang
Keyword(s):  
Theoretical Model ◽  
Axial Stress ◽  
Operating Conditions ◽  
Radius Of Curvature ◽  
Axial Component ◽  
Practical Applications ◽  
Bending Stresses ◽  
Parametric Studies ◽  
Steel Cables ◽  
The Individual

Steel cables play an important role in many offshore applications. In many cases, an understanding of the magnitude and pattern of bending stresses in the individual component wires of a bent strand is essential for minimizing the risk of their failure under operating conditions. Following previously reported experimental observations, a theoretical model is proposed for obtaining the magnitude of wire bending stresses in a multi-layered and axially preloaded spiral strand fixed at one end and subsequently bent to a constant radius of curvature. The individual wire bending stresses are shown to be composed of two components. The first component is the axial stress generated in the wires due to interwire/interlayer shear interactions between the wires in a bent cable, and the second component is associated with the wires bending about their own axes. Using the theoretical model, which includes the effects of interwire friction, parametric studies on a number of realistic helical strands with widely different cable (and wire) diameters and lay angles subjected to a range of practical mean axial loads, and subsequently bent to a range of radii of curvature with one end of the cable fixed against rotation, have been carried out. It is shown that for most practical applications, the axial component of wire stresses due to friction is much greater than the second component of bending stresses associated with the individual wires bending about their own axes.

Prediction of axial hysteresis in locked coil ropes

1996 ◽  
Vol 31 (5) ◽  
pp. 341-351 ◽  
Author(s):  
M Raoof ◽  
I Kraincanic
Keyword(s):  
Theoretical Model ◽  
Cross Section ◽  
Axial Load ◽  
Dynamic Instability ◽  
Contact Forces ◽  
Damping Capacity ◽  
Outermost Layer ◽  
Parametric Studies ◽  
Load Perturbations ◽  
Practical Implications

In published literature, the strand constructions dealt with have almost invariably involved only wires which are circular in cross-section. There are, however, instances when shaped wires are used in, for example, half-lock and full-lock coil constructions. The paper reports details of a theoretical model which enables an insight to be gained into various characteristics of axially loaded lock coil ropes. The model is based on an extension of a previously reported orthotropic sheet concept and provides a fairly simple means of estimating wire kinematics, interwire/interlayer contact forces, effective axial stiffnesses and axial hysteresis in axially preloaded locked coil ropes experiencing uniform cyclic axial load perturbations. The theory takes interwire contact deformations and friction into account. Final numerical results based on theoretical parametric studies on some substantial cables highlight the substantial role that the outermost layer(s) with shaped wires play as regards the overall axial damping capacity of fully bedded-in (old) locked coil ropes, and it is found that (for the same lay angles and outer diameters) axial hysteresis in locked coil ropes is generally higher than spiral strands which are composed of only round wires. This finding may have significant practical implications in terms of the design against dynamic instability of structures supported by such cables.

Post Fire Transient Temperature Distribution in Drum Type Packages in the Absence of Heat Generation

2003 ◽  
Author(s):  
Allen C. Smith
Keyword(s):  
Thermal Conductivity ◽  
Temperature Distribution ◽  
Heat Generation ◽  
Heat Storage ◽  
Internal Heat ◽  
Thermal Response ◽  
Transient Temperature ◽  
Test Cases ◽  
Transient Temperature Distribution ◽  
Parametric Studies

This study investigates the temperature distribution in an idealized cylindrical package subjected to the HAC Fire transient, with no internal heat generation. Cases for overpack materials with thermal conductivity spanning two orders of magnitude are considered. The results show that the peak internal temperature is determined by the thermal conductivity of the overpack material, for this case. The thermal wave effect, where the interior temperature continues to rise after the end of the fire exposure, is present in all three of the test cases. For contents with no heat generation, the most desirable overpack materials would have low thermal conductivity and low heat storage capability. The study complements the parametric studies of effects of thermal properties on thermal response of packages which were previously reported.

scholarly journals The Friedrichs-Lee Model and Its Singular Coupling Limit

Proceedings ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 17 ◽  
Author(s):  
Davide Lonigro ◽  
Paolo Facchi ◽  
Marilena Ligabò
Keyword(s):  
Form Factor ◽  
Theoretical Model ◽  
Bosonic Field ◽  
Lee Model ◽  
Field Coupling ◽  
Mathematical Properties ◽  
Rigorous Description ◽  
Singular Coupling Limit ◽  
Integrable Form ◽  
Field Theoretical Model

Lee’s field-theoretical model describes the interaction between a qubit and a structured bosonic field. We study the mathematical properties of the Hamiltonian of the single-excitation sector of the theory, including a possibly “singular” qubit-field coupling (i.e., mediated by a non-square integrable form factor). This result allows for a rigorous description of qubit-field interactions in many physically interesting systems and may be extended to higher-excitation sectors of the theory.

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