Structure-borne Noise Transmission Research Articles

Structure-Borne Noise Transmission into Cylindrical Enclosures of Finite Extent

This paper presents an analytical study of structure-borne noise transmission of finite, double-wall-laminated, fiber-reinforced cylindrical enclosures due to stochastic excitations. The stochastic excitations are either uniform random pressures or random point loads with specified spectral densities. The theoretical solutions of the governing acoustic-structural equations are obtained via modal decomposition and a Galerkin-like approach. Numerical results indicative of the effects of acoustic and structural variations are offered.

Hygrothermal effects on structure-borne noise transmission of stiffened laminated composite plates

This paper examines the effect of elevated temperatures, absorbed moisture, and random external excitation on the dynamic response and structure-borne noise transmission of discretely stiffened flat plates from laminated composite material. An analytical approach using modified transfer matrices for composite stiffened flat panels, including the hygrothermal effects, is developed to obtain the required dynamic response solution. Ingestion of moisture and changes of temperature levels were taken to vary linearly with the swelling, which results in effective force resultants. The dynamic response is calculated from the total hygrothermal and mechanical loading environment. The theoretical solutions of the governing acoustic-structural equations for the transmitted noise are obtained using modal decomposition. The acoustic enclosure is taken to be rectangular in shape, a portion of its boundaries is elastic (composite material), while the remaining surface is acoustically rigid. Numerical results are presented for acousto-structural applications revealing the hygrothermal effect on composite materials.

Installation effects on propeller wake/vortex-induced structure-borne noise transmissions

A laboratory-based test apparatus was employed to investigate the effects of power-plant placement, engine/nacelle mass installation, and wing-to-fuselage attachment methods on propeller-induced structure-borne noise (SBN) transmission levels and their effects on noise-control measures. Data are presented showing SBN transmission is insensitive to propeller spanwise placement, however some sensitivity is seen in propeller-to-wing spacing. Installation of an engine/nacelle mass and variation in wing-to-fuselage attachments have measurable influences on SBN transmission and control measures.

Prediction of aircraft-propeller-induced, structure-borne interior noise

Coupled analytical and empirical structural-acoustic models of an aircraft fuselage and wing structure driven by propeller wake/vortex-induced loading are developed to predict structure-borne noise transmission into the aircraft cabin. Free-interface component coupling functions are used to couple the system components for structure-borne noise prediction. Predicted interior noise levels for the first two propeller tones are compared to laboratory-based test results to assess the predictive procedures. The results of the study indicate that accurate prediction of structure-borne noise transmission requires detail finite element modeling of wing panel motion.

Fuselage Structural-Acoustic Modeling for Structure-Borne Interior Noise Transmission

Detailed finite element models of a fuselage structure and acoustic cabin volume of a laboratory based prototypical aircraft fuselage were generated for the purpose of studying the predictive capabilities of deterministic modeling procedures for structure-borne noise transmission. Comparative predictions are made to measured wing-to-fuselage attach point inertances and interior noise to force responses. Several structural models with increased structural definition were evaluated. It was found that to accurately predict wing-to-fuselage attach point inertances required increased local area structural definition, while interior noise can be reasonably well predicted without paying additional attention to local area structural details.

Structure-borne noise generation and transmission

The structure-borne noise generation and transmission of stiffened and interconnected structures under random loads is presented. The method is based on the transfer matrix for the structural response and on the modal decomposition for the interior acoustic field. The acoustic enclosure is taken to be rectangular in shape of which portion of the boundaries are elastic while the remaining surface is acoustically rigid. Numerical results are presented for a variety of acousto-structural problems.

Detection of in-flight propeller-induced structure-borne noise

A potentially important source of structure-borne interior noise transmission in advanced turboprop aircraft is the impingement of the propeller wake/vortex on downstream aerodynamic surfaces. It can be safely assumed that this potential source of interior noise may well adversely affect achievable interior noise levels unless noise control measures are conscientiously incorporated into the aircraft design. Through the use of a laboratory-based test apparatus, techniques were developed to estimate the level of in-flight structure-borne noise transmission from combined frequency response function ground testing and in-flight structural response measurements. All phases of the procedure were simulated in the laboratory and the expected level of accuracy of the procedure is addressed.

Transmission, reflection, and absorption of structureborne noise by discontinuities on a fluid‐loaded plate

The propagation of structureborne noise over a fluid‐loaded structure with a number of discrete structural discontinuities is modeled. An analysis is presented for an elastic plate excited by a uniform time harmonic line force; the structural discontinuities are each modeled as a translational (zero moment impedance) single degree of freedom (SDOF) vibrational system (mass‐spring‐dashpot) attached to the plate. Wave energy incident on the discontinuities are either reflected, transmitted absorbed by the acoustic medium in the form of radiated sound waves, or absorbed by the dashpot of the attached vibrational system. The reflection, transmission, and absorption coefficients are presented as a function of frequency for a finite number of periodically spaced discontinuities. The frequency dependence of these coefficients are affected by the resonance frequency of the SDOF as well as resonance frequencies associated with the spacing of the discontinuities.

Procedure for evaluation of engine isolators for reduced structure-borne noise transmission

Procedure for evaluation of engine isolators for reduced structure-borne noise transmission

Noise reduction for floating compartment and damped deck treatments in ship living spaces

Airborne and structureborne noise measurements were made in two identical full‐scale ship living compartments in the laboratory at Hopeman Brothers (1) with and without a floating compartment treatment and (2) with and without damping noise reduction treatments applied to the deck. An impact hammer was used to drive the deck from underneath. The structureborne noise transmission losses across the floating deck and the reductions in airborne noise levels inside the space due to the floating compartment are presented. For the damped deck treatment, measured data on airborne and structureborne noise reductions are given, along with measured damping loss factors for the deck, with and without the damping treatment in place. Results from noise measurements conducted on identical ships with and without floating decks and on a ship before and after a deck damping treatment was installed are presented and compared to results measured in the laboratory.

Development of the Proposed Canadian Noise-Level Regulations For Vessels Engaged in Towing

The paper will describe the towboat noise-control experiments, noise-level survey, and general rationale behind the Proposed Canadian Noise-Level Regulations for Vessels Engaged in Towing (1975). The proposed regulations are based on what was determined to be the technically feasible noise levels for the large majority of British Columbia vessels at the time of the study with provisions for reduced levels for vessels constructed in the future when marine-noise-control practices will have advanced and become more widely adopted. The relative importance of airborne and structure-borne noise transmission aboard towboats and the significance of this relation to the general philosophy of towboat noise control will be discussed.

Gear Noise Source Identification and Reduction

Some common sources of noise in large industrial and marine high-speed gears are described. Several methods, including instrumentation and test procedures, for the identification of such noise sources are discussed. Reduction of noise from gears is usually achieved by one or more of three primary methods, which are, in order of preference: (a) reduction of source mechanisms, (b) alteration of structureborne noise transmission paths, and (c) alteration of airborne noise transmission paths. A case history of a typical investigation from identification of the source through the confirmation of the effectiveness of the control measures adopted is presented in detail.