Acoustic Loading Research Articles

Prediction of Aircraft Surface Noise in Supersonic Cruise State

The aerodynamic noise of an aircraft leads to vibration fatigue damage to structures. Herein, a prediction method for aircraft surface noise under the comprehensive effect of mixed acoustic sources during flight, primarily surface aerodynamic, air intake, and tail nozzle jet noises, was studied. In the supersonic cruising state, the internal and external flow fields of the aircraft were solved using the Reynolds-averaged Navier–Stokes equations to obtain the statistical average solution of the initial turbulence. The non-linear disturbance equation was used to obtain the surface acoustic load of the aircraft. The calculation results revealed that the main source of aircraft surface noise is aerodynamic noise. The sound pressure level on the fuselage increases gradually from front to rear along the aircraft, and the OASPL at the air intake and tail nozzle is relatively large. The jet noise has little effect on the sound pressure level at the front of the fuselage and only contributes to the OASPL at the tail nozzle of the fuselage. The intensity of pressure pulsations from the engine exhaust in the tail section is 93.3% of the total intensity of pressure pulsations.

Nonlinear thermo-acoustic response and fatigue prediction of three-dimensional braided composite panels in supersonic flow

In this paper, a novel aerodynamic-acoustic coupling model to investigate the influence of aeroelastic effects on the thermo-acoustic response of three-dimensional, four-directional braided composite panel is proposed, and the fatigue life under the combined aerodynamic load and acoustic load is discussed by using a rainflow cycle counting method. Assuming that the fibers are transversely isotropic and the matrix is isotropic, the fiber inclination model was used to predict the effective stiffness matrices of the composite panels. The piston theory and Gaussian random acoustic excitation were used to simulate the aerodynamic load and acoustic load, the thermal load is assumed to be a uniform distribution in steady state, and the material properties are assumed to be independent of temperature. Based on the von-Karman strain–displacement relation, the governing equations of the panel were formulated, and the response solutions of the four sides simply supported panel were obtained using Galerkin method and Runge-Kutta method. The aeroelastic effect on the thermos-acoustic response of the braided composite panel was investigated in time and frequency domains, and the life of different load conditions was predicted. The results show that the aeroelastic not only transforms the movement form, but also affects fatigue life of the panel.

Analysis of etiopathogenetic factors in the development and progression of perceptual hearing loss

Relevance: Sensorineural deafness is a polyetiological disease. The most studied etiopathogenesis factors are vascular, acoustic and age. Despite numerous studies, the factors of the development and progression of chronic sensorineural hearing loss, as well as tinnitus, remains unclear in 25-30% of cases. Purpose: to determine the most influential factors in the development and progression of sensorineural hearing loss in patients who work in conditions of increased sound load. Methods and materials: The study was conducted on the basis of the Kyiv Clinical Hospital on Railway Transport No. 2, as a division of the Department of Otolaryngology of the O.O. Bogomolets National Medical University. We conducted an examination of 678 patients who work under conditions of increased acoustic load (drivers, drivers' assistants, fitters, railway track fitters) with the aim of identifying perceptual disorders and analyzing the etiopathogenesis factors of chronic sensorineural hearing loss. Further examinations were carried out in 89 patients who had perceptual disorders. Results: The first degree of deafness was detected in 75.3% of patients, the second and third - in 12.35% each. The largest number was made up of patients aged 56 to 65 years, but even among those examined up to 45 years of age, there were 2 cases of third-degree hearing loss. The correlation between age and the degree of deafness in patients with perceptual disorders, as well as age and decreased whisper perception was weakly positive: 0.167 and 0.261, respectively; The relationship between indicators of work experience and the degree of hearing loss, as well as work experience and a decrease in the perception of whispered speech – the average degree of severity is 0.382 and 0.476, respectively. These data were confirmed with the help of two-factor analysis. Conclusions: Among patients with perceptual disorders who work in conditions of increased sound load, the largest number was aged 56-65 with more than 30 years of experience and had the first degree of hearing loss. The relationship between hearing impairment and age and work experience was found to be weak and medium, respectively. 11.1% of cases of third-degree hearing loss were found among patients under 45 years of age and with a work experience of up to 30 years. This may indicate the presence of other factors in them, for example, genetic disorders, which significantly affect the development and progression of sensorineural hearing loss and require further research.

Design and acoustic tests of the ATHENA WFI filter wheel assembly development model towards TRL5

The filter wheel (FW) assembly (FWA), developed by the CBK Institute, is one of the critical subsystems of the wide field imager (WFI) instrument on board the Advanced Telescope for High Energy Astrophysics—mission of the ESA Cosmic Vision 2015-25 space science program (launch scheduled around 2035). The instrument has to collect soft x-rays with very high quantum efficiency, thus WFI requires extremely thin optical blocking filter (OBF). Due to its thickness (∼150 nm) and large area (∼170 mm × 170 mm) needed to achieve a 40 ′ × 40 ′ instrument field of view, the filter is extremely vulnerable to acoustic loads generated during Ariane 6 rocket launch. On the other side, FW mechanism has to provide high overall reliability, so it is more favourable to launch the instrument in atmospheric pressure (without vacuum enclosure for filter protection). Design efforts of the FW subsystem were focused on two issues: providing maximal possible sound pressure level suppression and smallest possible differential pressure across the OBF, which should prevent filters from damaging. We describe the design of a reconfigurable acoustic-demonstrator model (DM) of WFI FWA created for purposes of acoustic testing. Also, the acoustic test campaign is described: test methodology, test criteria, and results discussion and its implication on future FWA design. In general, tests conducted with the FWA DM showed that current design of WFI is feasible and the project can be continued without introducing a vacuum enclosure, which would significantly increase system complexity and mass.

Analytical method for modal analysis of submerged electric motor stator

Modal analysis of the stator is important for reducing motor noise and diagnosing motor faults. An accurate analytical model is beneficial for the establishment of the relationship between the motor stator parameters and the natural frequencies, which will further aid in optimizing machine designs. Up to now, the existing modal analysis models are mainly aimed at onshore motors. When the motor is submerged in dense fluid, such as those used in the rim-driven thrusters, the vibration behaviors are quite different due to the high characteristic impedance of the fluid. In a bid to analyze the wet natural frequencies of motor stator, this paper proposes analytical models with one, three and five degrees of freedom for different application scenarios based on Donnell, Love and Soedel’s theories. The coupling between the structure and fluid is realized by the acoustic pressure load derived from the acoustic wave function. The resulting non-linear dispersion equations are then solved by Newton’s iterative method. The proposed models are applied to analyze the natural frequencies of motor stators of various sizes and with a wide range of thickness-to-radius and length-to-radius ratios. The results show that the analytical models are insensitive to the stator radius but sensitive to the thickness-to-radius and length-to-radius ratios. For thick and short motor stators, it is necessary to consider the shear deformation and rotatory inertia in the analytical model to compute the natural frequency accurately, especially when the fluid loading is taken into account.

Fatigue Life Prediction for the Skin Structures of Aircraft Sensor Pod Under Acoustic Load with Mean Stress

The skin structure of sensor pod mounted on the exterior of aircraft can be exposed to the acoustic dynamic load and static load such as aerodynamic pressure and inertial load during flight. Fatigue life prediction of structural model under acoustic load should be performed and also differential stiffness of model modified by static load should be considered. The acoustic noise test spectrum of MIL-STD-810G was applied to the structural model and the stress response power spectral density (PSD) was calculated. The frequency response analysis was performed with or without prestress induced by inplane static load, and the response spectrum was compared. Time series data was generated using the calculated PSD, and the time and frequency domain fatigue life were predicted and compared. The variation of stress response spectrum due to static load and predicted fatigue life according to the different structural model considering mean stress were examined and decreasing fatigue life was observed in the model with prestress of compressive static load.

Aeroelastic modeling and analysis of honeycomb plates in high-speed airflow with acoustic load and general boundary conditions

Aeroelastic modeling and analysis of honeycomb plates in high-speed airflow with acoustic load and general boundary conditions

Supersonic flow unsteadiness induced by control surface deflections

Control surface deployment in a supersonic flow has many applications, including flow control, mixing, and body-force regulation. The extent of control surface deflections introduces varying flow unsteadiness. The resulting fluid dynamics influence the downstream flow characteristics and fluid–structure interactions significantly. In order to understand the gas dynamics, an axisymmetric cylindrical body with a sharp-tip cone at zero angles of attack (α=0°) is examined in a free stream Mach number of M∞=2.0 and Reynolds number of ReD=2.16×106 (D = 50 mm). Four static control surface deflection angles (θ=π/36,π/6,π/3, and π/2 rad) are considered around the base body. The cases are computationally investigated through a commercial flow solver adopting a two-dimensional detached eddy simulation strategy. Recirculation bubble length, drag coefficient's variation, wall-static pressure statistics, acoustic loading on the model and the surroundings, x − t trajectory and x − f spectral analysis, pressure fluctuation's correlation coefficient on the model, and modal analysis are obtained to understand the flow unsteadiness. At θ=[π/36], the wall-static pressure fluctuations behind the control surface are minimal and periodic, with a mere acoustic load of about 50 dB. At θ=[π/2], a violent periodic fluctuation erupted everywhere around the control surface, leading to a higher acoustic load of about 150 dB (three times higher than the previous). For θ=[π/6] and [π/3], high-frequency fluctuations with small- and large-scale structures continuously shed along the reattaching shear layer, thereby causing a broadened spectra in the control surface wake.

Study of traffic noise exposure on street and road networks in a megapolis

The article analyses the regularities of the acoustic impact of motor transport on the inhabited territory of a large city. It is noted that noise from motor transport has a noticeable negative impact on human health, especially in large cities, industrial centres and transport hubs. The results of field research on automobile noise level are presented in sections of a road network of a large city characterised by a high level of road accidents. Accident sites are shown to be characterised by high values of the equivalent level of sound and exposure to traffic noise. The values of equivalent sound level in the investigated sections during the period of maximum intensity of traffic significantly exceed the maximum permissible level. Exposure values of vehicular noise to which road users as well as residents of nearby neighbourhoods are exposed on the studied sections of the street and road network vary in the range from 1-3 to 320 Pa2∙s. The results of the correlation and regression analysis are presented. Measures are proposed to reduce the degree of acoustic load caused by road transport in the residential area.

Напівемпіричне оцінювання акустичних навантажень на головну частину ракети при нестандартній конфігурації стартових споруд

The paper deals with assessing the acoustic loads on the surface of a launching rocket obtained using the semiempirical technique NASA SP-8072 adapted for a launch pad located above the water area. The features of the launch facilities include the reduced length of the gas duct and the presence of a wedge-shaped gas-dynamic deflector divided into two symmetrical oppositely directed slopes. The calculations are made with the allowance for the limited length of the rocket jet's laminar core during take-off due to interaction with the gas-dynamic deflector. A corrected dependence is used for the overall acoustic energy distribution along the supersonic jet for the first time in domestic practice. The contributions of the sound sources associated with different jet sections and acoustic reflection from the water surface are assessed, depending on the current height of the rocket lift. A significant dependence of the resulting acoustic field around the rocket head on the length of the horizontal section of the gas duct is noted.

Using of acoustic resonance for detection and identification of hidden defects in polymer layered composites

A method of non-destructive testing is proposed, which combines the acoustic load of the object of inspection and interferometric control of its surface displacements, formed as a result of an acoustic wave resonance in a hidden defect. The method is aimed at solving the problem of detection and identification of subsurface defects formed in structural elements made of polymer layered composite materials or contain protective paint coatings. At the same time, the defect is considered as an acoustic resonator filled with a medium in which only a longitudinal acoustic wave propagates. Usually such media are air or water. The novelty of the method is that it allows us not only to detect a hidden defect and establish its location, but also to determi¬ne its dimensions. The scheme of the experimental installation is given and the method is described. The research of the detection and identification of subsurface defects that most often occur in practice was conducted with the help of the model of the experimental installation. In products made of polymer layered composites, such defects are unbounded areas between layers during construction, internal damages such as cracks and areas of crumpling during its operation. The results of the experiments proved the effectiveness of the proposed method. The described method is also suitable for detection and identification of blistering of protective paint coatings, provided that they are filled with liquids or gases in which transverse acoustic waves do not propagate.

Patterns of changes in the acoustic characteristics on public transport linear segments

The problem of noise pollution in cities becomes quite acute as soon as it comes to increasing the level of motorization. However, most researchers study the negative impact of traffic noise in general. In the era of sustainable mobility, there will be a trend to reduce the number of private vehicles on city streets. Still, the problem of acoustic load in residential areas will not be solved since public transport is a rather powerful source of traffic noise. The article solves the problem of determining the patterns of changes in the acoustic load from public transport vehicles at different speed modes and road surface. The article's objects of research are straight sections of public transport lines. The subject of the study is the patterns of changes in the noise level from public transport vehicles at different speeds, their position, and the type of surface. The obtained results indicate that the main range of noise pollution from public transport on straight sections is 75-85 dBA, and this level can vary by 15-20% depending on the type of line (trolley bus, bus, tram) and the type of road surface. The regularities of changes in the level of noise pollution, which were revealed in work, indicate that for each type of surface and type of public transport line, there are such values of traffic speeds, when they are reached, there is an overtime acoustic load on residential areas at specific distances from them. The obtained results differ from the currently existing scientific studies in that they consider the acoustic characteristics of clear public transport lines and not the traffic flow as a whole. Therefore, it becomes possible to determine the maximum and not the equivalent level of noise from public transport. The field of application of the results is transport planning of both new residential areas and areas of existing adjacent buildings. Thus, in the first case, recommendations were made regarding territorial gaps from the construction line to arterial streets with high volume of public transport, depending on its type and surface. On the other hand, recommendations have been established regarding the speed regime of public transport at different distances from existing buildings' lines.

Simulations of a full sonoreactor accounting for cavitation.

In spite of the increasing interest in ultrasound processing applications, industrial scale-up remains limited, in particular by the unavailability of predictive computer tools. In this study, using a previously published model of cavitating liquids implementable as a non-linear Helmholtz equation, it is shown that a full sonoreactor can be modelled and simulated. The model includes the full transducer and the vibrations of the vessel walls, using the physics of elastic solids and piezo-electricity. The control-loop used by the generator to set the optimal frequency is also accounted for. Apart from the geometry, the unique input of the model is the current feeding the transducer whereas the dissipated electrical power, transducer complex impedance and working frequency are available as outputs. The model is put to the test against experiments realized in different geometries, varying either the input current or the transducer immersion depth. Despite the overestimation of the power dissipated in the liquid, the evolution of the acoustic load in both cases is reasonably well reproduced by simulation, which partially validates the method used.

Control of High-Temperature Impinging Jet Issued from Overexpanded Rocket Nozzle

High-speed impinging jets issued from the exhaust of a launch vehicle are highly oscillatory and create hazardous conditions for the vehicle structure, affecting the sensitive payloads and personnel due to intense acoustic loads. Therefore, to reduce the unsteadiness of a jet and mitigate its adverse effects, a fundamental understanding of the associated flow and acoustic field is of utmost importance. The present experimental study is one such step to characterize the aeroacoustic properties of a high-temperature jet issued from an overexpanded rocket nozzle. Further, the effectiveness of microjet-based active flow control in reducing the flow unsteadiness and near-field noise levels is also explored. The experiments were performed at different jet stagnation temperatures, and the results were quantified at different impingement heights simulating the takeoff and landing environment of reusable launch vehicles. Mean pressure measurements were mapped on the ground plane using discrete pressure taps. The time-varying pressure component was measured using an unsteady pressure transducer located at the impingement point, and near-field acoustic measurements were carried out using a microphone. In addition, the velocity field was mapped using planar particle image velocimetry. The near-field pressure spectra are broadband, and the magnitude of noise content is a function of jet stagnation temperature. Furthermore, the injection of microjets resulted in a significant attenuation of near-field noise, impingement point pressure fluctuations, and turbulent kinetic energy.

Determination of Critical Stresses in Frozen Soils Under Wave Acoustic Loading

The issues related to the development of permafrost and seasonally frozen soils without their preliminary loosening by various earthmoving machines with active working bodies, magnetostrictive vibrators, that soften dense and frozen soils using acoustic elastic waves, are considered. The analytical studies allowed us to establish the regularities of the process of destruction of frozen soil by active teeth of bucket working bodies, according to which, the formulas for calculating the critical tensile stress and shear resistance were obtained. The research results allow us to determine the main parameters of wave loading for both a single radiation source and a group of "n" in-phase radiation sources. The intensity of the acoustic field from the group of "n" emitters increases in proportion to the number of vibration exciters.

Performance Investigation of Superplastic Shape Memory Alloy-Based Vibration Isolator for X-Band Active Small SAR Satellite of S-STEP under Acoustic and Random Vibration Environments

In a launch environment, all satellites are subjected to severe random vibration and acoustic loads owing to rocket separation, airflow, and injection/combustion of the fuel. Structural vibrations induced by mechanical loads cause the malfunction of vibration-sensitive components in a satellite, leading to failures during the launch process or an on-orbit mission. Therefore, in this study, a shape memory alloy-based vibration isolator was used on the connection between the launch vehicle and satellite to reduce the vibration transmission to a satellite. The vibration isolator exhibited a high performance in the vibration isolation, owing to the dynamic properties of super-elasticity and high damping. The vibration-reduction performance of the vibration isolator was experimentally verified using random vibration and acoustic tests in a structural thermal model of the satellite developed in the synthetic aperture radar technology experimental project. Owing to the super-elasticity and high attenuation characteristics of the vibration isolator, it was possible to significantly reduce the random vibration of the satellite in the launch environment. Although the mechanical load of the acoustic test mainly excited the antenna on the upper side of the satellite rather than the bottom side, the results of the acoustic test showed the same trend as the random vibration test. From this perspective, the vibration isolator can contribute to saving the costs required for satellite development. These advantages have made it possible to develop satellites according to the new space paradigm, which is a trend in the space industry worldwide.

A fast direct solver for non-intrusive reduced order modeling of vibroacoustic problems

This paper proposes a fast model order reduction method for large-scale three-dimensional vibro-acoustic coupling problems, which proceeds in three perspectives. Firstly, part of the coupling matrices is neglected and another part of the coupling matrices is treated as the partial right-hand side of the Schur complement of the corresponding subsystem in order to implement model reduction quickly. Secondly, the proposed fast method does not require the use of the underlying complex-valued and dense boundary element full-order model for the construction of a global orthonormal basis in the offline phase. Rather, its sparse approximation is exploited, which benefits from the consistent amplitude decay property of the kernel functions. This way it can be regarded as a non-intrusive method. Lastly, in addition to structural loads, acoustic loads, such as the load from incident waves impinging on the flexible structure from the outside, can be handled as well. Application of this solution method to the frequency sweep analyses of coupled structural acoustic systems, i.e. simple sphere and complex geometrical model submerged in an infinite fluid with the number of degrees of freedom ranging from hundreds of thousands up to millions, shows the improved computational efficiency and reduced memory requirement as compared to the brute force approach based on the direct evaluation of original high-dimensional models and also the previous acceleration scheme.

Analysis on Vibroacoustic Fatigue Life of Empennage in a Hypersonic Vehicle

In this study, the fatigue life prediction in hypersonic vehicle noise environment is researched under the structural vibration caused by the engine jet noise and the aerodynamic noise. A finite element analysis model is first established, and then natural frequency and vibration mode are obtained. According to the modal analysis, the vibroacoustic coupling calculation is finished in the dynamic analysis software. Modal participation factor, modal displacement, and the power spectral density of the stress response on the coupled surface are acquired. The finite element, border component, and vibrating stress analytical techniques are also employed in this research to predict the acoustical fatigue performance of the tail fins of a specific type of spacecraft. On the basis of vibration fatigue theory, identified material S–N curve, and linear cumulative damage theory, the Dirlik model in the frequency domain method for vibration fatigue is used to predict the fatigue life of empennage. According to the characteristics of the acoustic load, effects of the load characteristics, and damping ratios on the fatigue conditions, the design of the antifatigue design is put forward.

A Review on Vibro-Acoustic Analysis of a Launch Vehicle Structure

Abstract: Space vehicles are subjected to significant dynamic pressure loads when their rocket propulsion systems are in use during flying missions. During the aerodynamic and launch phases, launch vehicles, payloads, and their parts are subjected to extremely high random acoustic loads. The noise from the engine exhaust gas, aerodynamic boundary layer noise, transonic buffering, structure-borne vibration, engine thrust fluctuation, etc. is the source of these loads, which also result in a secondary acoustic load. When the vehicle is lifting off and traveling at a speed greater than Mach number, acoustic stresses to the spacecraft and payload are very harsh and significant. This loading causes the structure to vibrate randomly, which could be dangerous for some vehicle parts, avionics, propulsion systems, and payloads like satellites. This paper discusses the vibration of the structure subjected to acoustic excitation on a diffuse acoustic field and the software used for the analysis.

Improving the thermal properties of aircraft cabin interiors with the integration of vacuum insulation panels

Commercial aircrafts require insulation to protect passengers in the cabin from thermal and acoustic loads. The conventional insulation in aircrafts consists of blankets made from layers of glass wool wrapped in foil that keeps the glass wool from being adversely affected by the environment. There is a potential to improve the thermal and acoustic properties of the cabin by replacing the interior panels with conventional secondary insulation by new panels combined with vacuum insulation panels (VIP). This article is focusing on the study of the VIP integration into the interior panels. First, the new structure solutions are defined on the basis of a requirement analysis for interior panels and VIP and theoretical analysis. Second, the manufacturing feasibility study for the new solutions is performed. The results show that the new structures can be manufactured. Third, the thermal properties of the new structure solutions are measured. The test results show a decrease of thermal conductivity of the new panels by a factor of 3–6 compared to the conventional solutions. Finally, the impact of the hot molding press on the vacuum maintaining inside the VIP is investigated. The trials demonstrate that the high barrier films can withstand high-temperature and pressure conditions and that the thermal conductivity of the test specimens didn’t worsen after 1 year.