Acoustic signature of a submarine hull under harmonic excitation

The presence in operation of many prototypes of UAVs with propeller propellers, the use of such devices at relatively low altitudes and flight speeds makes the problem of noise reduction from UAVs urgent both from the point of view of acoustic imperceptibility and ecology.The aim of the work is to determine a set of methods that help to reduce the visibility of UAVs in the acoustic range. It is shown that the main source of noise from the UAV on the ground is the power plant, which includes the engine and the propeller. The parameters of the power plants influencing the processes that determine the acoustic signature of the UAV were investigated. A comprehensive analysis of the factors affecting visibility was carried out. The power plants include two-stroke and four-stroke engines, internal combustion and two-blade propellers. The use of silencers on the exhaust of the internal combustion engine was considered. The spectral characteristics of the acoustic fields of the propeller-driven power plants for the operating sample of the UAV "Eco" were obtained. The measurements were carried out in one-third octave and 1/48 octave frequency bands under static conditions. The venue is the KhAI airfield. Note that the propellers that were part of the power plants operated at Reynolds numbers (Re0,75<2*105), which can significantly affect its aerodynamic and acoustic characteristics. It is shown that when choosing a UAV control system, one should take into account the fact that two-stroke piston engines are the dominant source in the noise of propeller-driven control systems in the absence of a hood and mufflers in the intake and exhaust tracts. The use of a four-stroke internal combustion engine significantly reduces the noise of the control system. In the general case, the position of the boundaries of the zone of acoustic visibility of a UAV at the location of the observer is determined by the ratio between the intensity of acoustic radiation perceived by the observer from the UAV and the intensity of sound corresponding to the natural acoustic background and depends on the degree of manifestation of acoustic effects accompanying the propagation of sound in a turbulent atmosphere - the refraction of sound waves. Absorption and dissipation of acoustic energy. The calculation and comparison of the UAV detection range was carried out taking into account the existing natural maskers.The results of experimental studies are presented that allow assessing the degree of acoustic signature of the UAV. A set of measures aimed at reducing the intensity of the acoustic signature of the UAV in various regions of the radiation spectrum has been determined.

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Localization of a harmonic excitation load in a bi-clamped beam using finite element method and artificial neural network

10.26678/abcm.cobem2019.cob2019-0629 ◽

2019 ◽

Author(s):

Otavio Duarte Zotelli Boaventura ◽

Daniel Henrique de Sousa Obata ◽

Matheus Proença ◽

Amarildo Tabone Paschoalini

Keyword(s):

Neural Network ◽

Finite Element Method ◽

Artificial Neural Network ◽

Finite Element ◽

Harmonic Excitation ◽

Artificial Neural ◽

Element Method

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Acoustic signature reduction using feedback of piezoelectric layers

10.1117/12.388757 ◽

2000 ◽

Author(s):

Johan Hamberg ◽

Anders Malmgren

Keyword(s):

Acoustic Signature ◽

Piezoelectric Layers

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On the chaotic behavior of graphene-reinforced annular systems under harmonic excitation

Engineering With Computers ◽

10.1007/s00366-020-01210-9 ◽

2021 ◽

Author(s):

Lianghua Ma ◽

Xiaoliang Liu ◽

Zohre Moradi

Keyword(s):

Chaotic Behavior ◽

Harmonic Excitation

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Nonlinear vibration of knitted spacer fabric under harmonic excitation

Journal of Engineered Fibers and Fabrics ◽

10.1177/1558925020983561 ◽

2020 ◽

Vol 15 ◽

pp. 155892502098356

Author(s):

Fuxing Chen ◽

Hong Hu

Keyword(s):

Nonlinear Vibration ◽

Harmonic Balance Method ◽

Harmonic Excitation ◽

Polyurethane Foams ◽

Excitation Level ◽

Harmonic Amplitude ◽

Damping Force ◽

Spacer Fabric ◽

Fabric System ◽

Quadratic Stiffness

Knitted spacer fabrics can be an alternative material to typical rubber sponges and polyurethane foams for the protection of the human body from vibration exposure, such as automotive seat cushions and anti-vibration gloves. To provide a theoretical basis for the understanding of the nonlinear vibration behavior of the mass-spacer fabric system under harmonic excitation, experimental, analytical and numerical methods are used. Different from a linear mass-spring-damper vibration model, this study builds a phenomenological model with the asymmetric elastic force and the fractional derivative damping force to describe the periodic solution of the mass-spacer fabric system under harmonic excitation. Mathematical expression of the harmonic amplitude versus frequency response curve (FRC) is obtained using the harmonic balance method (HBM) to solve the equation of motion of the system. Parameter values in the model are estimated by performing curve fit between the modeled FRC and the experimental data of acceleration transmissibility. Theoretical analysis concerning the influence of varying excitation level on the FRCs is carried out, showing that nonlinear softening resonance turns into nonlinear hardening resonance with the increase of excitation level, due to the quadratic stiffness term and the cubic stiffness term in the model, respectively. The quadratic stiffness term also results in biased vibration response and causes an even order harmonic distortion. Besides, the increase of excitation level also results in elevated peak transmissibility at resonance.

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Vibration Equation of Fractional Order Describing Viscoelasticity and Viscous Inertia

Open Physics ◽

10.1515/phys-2019-0088 ◽

2019 ◽

Vol 17 (1) ◽

pp. 850-856 ◽

Cited By ~ 2

Author(s):

Jun-Sheng Duan ◽

Yun-Yun Xu

Keyword(s):

Fractional Derivative ◽

Fractional Order ◽

Fractional Derivatives ◽

Harmonic Excitation ◽

Steady State Response ◽

Vibration System ◽

Derivative Operator ◽

Vibration Equation ◽

State Response ◽

Frequency Relation

Abstract The steady state response of a fractional order vibration system subject to harmonic excitation was studied by using the fractional derivative operator ${}_{-\infty} D_t^\beta,$where the order β is a real number satisfying 0 ≤ β ≤ 2. We derived that the fractional derivative contributes to the viscoelasticity if 0 < β < 1, while it contributes to the viscous inertia if 1 < β < 2. Thus the fractional derivative can represent the “spring-pot” element and also the “inerterpot” element proposed in the present article. The viscosity contribution coefficient, elasticity contribution coefficient, inertia contribution coefficient, amplitude-frequency relation, phase-frequency relation, and influence of the order are discussed in detail. The results show that fractional derivatives are applicable for characterizing the viscoelasticity and viscous inertia of materials.

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