Prediction Of Structure-borne Noise Research Articles

Experimental study of component-based transfer path analysis hybrid methods applied to a helicopter

The noise prevailing inside the helicopter’s cabin always presents a problem for the operators of this vehicle. It is a source of annoyance and represents a pressing problem in the helicopter industry, causing manufacturers to constantly seek new technologies and solutions to reduce noise. This article aims to present a component-based transfer path analysis method (CB-TPA) and its application to the prediction of structure-borne noise transmitted into the cabin of a helicopter due to its main gearbox. The approach characterizes the source using a laboratory test bench and uses various CB-TPA methods to couple the blocked force to the dynamics of the receiving structure. The article details the used methods, their main assumptions, the experimental test configurations, and discusses the results compared to the classical in situ CB-TPA method. The effects of important parameters such as the completeness of the input and transfer mobility matrices are also discussed. It is shown that the presented methodology can correctly and accurately capture the noise in the cabin from a decoupled characterization of the source and the receiving structure.

A Symplectic-Spectral Element Method for High Frequency Vibration Analysis and Its Application in Structure-Borne Noise Prediction

The frequency-domain vibration model of the vehicle-track structure is established based on the symplectic-spectral element method (S-SEM). To this end, the vehicle is considered as 10-degree-of-freedom, and the rail is modeled by an infinite Timoshenko beam supported by discrete sprung fasteners. Further, the track slab and base plate are regarded as two-dimensional Timoshenko beams supported by uniformly distributed sprung elements. Using the pseudo excitation method (PEM), the track irregularity is viewed as the pseudo load. The vibration response and the internal force of the single-layer or multi-layer beam models are obtained by solving the corresponding S-SEM-based equations. The spectral forces are also applied in frequency bands to the finite element (FE) and statistical energy analysis (SEA) acoustic models. The steel-concrete composite bridge deck is simulated with composite plate materials. The effectiveness of the proposed method is verified by comparing the predicted results with those obtained from the field test. The achieved results reveal that multi-layer beam structures effectively consume energy, and elastic fasteners and steel springs are capable of effectively reducing bridge noise.

Computational prediction of structure-borne noise in a two-stage double-helical gearbox using harmonic balance method

The acoustics of gearboxes contribute as a quality feature to the success of a gear design by increasing consumer satisfaction. Particularly in special machine engineering, ensuring quiet operation is a challenging task because the production and testing of a prototype is usually not a feasible option. A suitable calculation methodology is thus crucial for finding the optimal design. Unfortunately, an increase in accuracy most often results in high simulation times and thus complicates a continuous design support. A promising approach regarding computational efficiency for nonlinear periodic systems is the harmonic balance method (HBM). However, its application to gearboxes is still quite rare or even non-existent in terms of this acoustic motivation. Convergence behavior and memory requirements are ambitious aspects for the HBM. Consequently, tracking the vibration propagation from the gear mesh to the housing in one simulation run requires special treatment. This article examines appropriate implementation recommendations and further investigates the applicability of the HBM for gear acoustics from a practical point of view. Experimental data serves as the basis for validation purposes.

An efficient frequency domain analysis method for bridge structure-borne noise prediction under train load and its application in noise reduction

Development of an efficient method for solving the structure-borne noise of the bridge in the frequency domain is of concern. Based on the stochastic theory, the vehicle-track coupling model is established in the frequency domain, and its frequency domain response and the force transmitted to the bridge are analyzed by the pseudo excitation method-symplectic method (PEM-SM). Thereafter, the field vibration and noise test of a 30 m U-shaped concrete subway girder are carried out to compare the cases before and after installing damping fasteners. In the frequency domain, after the input of the force transmitted to the bridge, the finite element–boundary element method (FE-BEM) model of the girder is developed to predict the vibration and structure-borne noise. There is a rationally good agreement between the results of numerical simulations and those of experiment, suggesting an innovative idea for the rapid prediction of structural vibration and noise. Finally, the noise reduction effect and mechanism of the acoustic board and steel spring floating plate beneath the track are discussed. The obtained results reveal that reducing the input of the track system to the bridge is better than preventing the vibration and noise radiation of bridge plates. The above results provide a theoretical and experimental basis for calculating and controlling of vibration and noise in rail transit.

Structure-borne Noise at PWM Excitation using an Extended Field Reconstruction Method and Modal Decomposition

Pulse-Width Modulation (PWM) represents a carrier-frequency-dependent structural excitation. The PWM’s excitation harmonics are also reflected in the air gap’s electromagnetic forces, the vibration response and the resulting structure-borne noise. The last of these can be numerically predicted with a multiphysics finite-element-analysis (FEA) containing electronic, electromagnetic, mechanical and acoustic field problems. The multiphysics FEA are precise, but computationally inefficient and consequently inadequate for parametric studies. This paper introduces a method for a fast structure-borne noise prediction at PWM excitation. The presented approach contains the Extended Field Reconstruction Method (EFRM) to handle the magnetic saturation and slotting effects in magnetics, and the modal decomposition to couple the electromagnetic and mechanical domains. Finally, the structure-borne sound power level is calculated via the vibration-velocity response. Indeed, this approach demands a pre-calculation of the basis functions and modal parameters from the FEA, but afterwards the effect of the different PWM excitation cases can be evaluated in a few seconds. The proposed method can calculate the structure-borne noise at PWM excitation accurately and is more than 104 times faster than the conventional multiphysics FEA approach.

Uncertainties in predicting structure-borne sound power input into buildings

There has been a steady development of methods of measurement and prediction of structure-borne noise in buildings, particularly over the last two decades. In proposing and evaluating these methods, a major consideration has been the likely trade-off between accuracy and simplicity. Structure-borne sound transmission is a more complicated process than airborne sound transmission, but practitioners seek methods of prediction for the former, which are as straightforward as for the latter. In this paper a description is given of a study of multi-contact sources in buildings. The study concentrates on measurement and calculation procedures for sources and calculation procedures for receiver structures, particularly lightweight building elements. Although the study is not exhaustive, the findings point to the limitations of simplified methods, specifically the uncertainties likely as a result of reducing the data sets and computational effort, and the discrepancies resulting from simplifying assumptions.

A Method for Prediction of Structure-borne Noise Radiated from Concrete Railway Viaducts

Prediction of structure-borne noise has been a significant issue for railway viaducts, since it causes an excessive degree of noise attributable to structural member vibration. A new method of flexural vibration analysis expanded to cover whole structure for the prediction of structure-borne noise has therefore been developed. After calculation and measurement of noise in the vicinity of a floor slab of a concrete viaduct constructed on a Shinkansen line, it was revealed that the proposed method can be used as a practical means for predicting structure-borne noise.

643 コンクリート高架橋の振動解析手法の改良

Prediction of structure-borne noise based on an analysis of vibration of structure has been a significant issue for railway viaducts. We have therefore developed a new method of vibration analysis based on a flexural vibration analysis extended to the whole of structure. As the result of the calculation and measurement of the vibration of the floor slab of a concrete viaduct constructed on Shinkansen line, it has been revealed that the developed method has acceptable accuracy. However, the method is a little bit complex because in the method, three layers, namely rail, rail-supporting layer and composite layer composed of the track slab and floor slab are treated as a three layered beam and a property equation of the three layered beam should be solved. In place of that, if each of three layers can be treated as an Euler beam, and only property equation of each beam individually should be solved, the analysis becomes simpler. In this paper, the substituted treatment has been examined and it has been revealed that the difference in accuracy between the solution of three layered model and that of the model in which respective beams are treated individually is substantially small.

Prediction of structure-borne noise caused by the powertrain on the basis of the hybrid transfer path

In the early development stage, the prediction of interior noise due to powertrain vibration is important for enhancement of the noise vibration harshness (NVH) performance. Traditional transfer path analysis (TPA) technology has been used to estimate interior noise on the basis of experiment by using real parts of the powertrain. When a structural modification of the powertrain is necessary to reduce interior noise, it is efficient to use a finite element (FE) model of the powertrain components to identify the effect of that modification. In this paper, hybrid TPA is employed. Until now, no paper has been presented on predicting the interior noise caused by a powertrain on the basis of hybrid TPA with a real vehicle. The hybrid TPA uses a simulated excitation force as the input force, which excites the flexible body of a car at the mount point, whereas the traditional TPA uses the measured force. This simulated force is obtained by numerical analysis for the FE model of a powertrain. The interior noise is predicted by multiplying the simulated force by the vibroacoustic transfer function (VATF) of the vehicle. The trend of the predicted interior noise based on the hybrid TPA corresponds very well to the measured interior noise.

Noise and Vibration Spectrum of Structure-borne Noise from Railway System

In this study, the spectrum and resonance frequencies of the structure-borne noise and vibration excited by the train traffic on concrete viaduct structure are examined. Comparisons of air- and structure-borne noise spectrum between local and overseas trains are taken. Real-time octave band and FFT (Fast Fourier Transform) mode are used to analyze structure-borne noise spectra in details. Based on the spectrum results of the structure-borne noise, air-borne noise lies on high frequency component and structure-borne noise lies between 20 Hz and 200 Hz, which is a tonal noise. From the FFT analysis, the vibration resonance frequencies are 43 Hz and 54 Hz and acoustics coincidence are 121.5 Hz and 128.5 Hz. The theoretical relationships between sound and vibration are in agreement with the experimental results. The results will be useful for the prediction of structure-borne noise from railways.

Characterization of building equipment

The feasibility of a characterization method consisting of measurement of the structure-borne noise generated by building equipment mounted in a laboratory test room and in calibrating the test room by using a reference structure-borne sound source, is presented. The experimental results obtained with different sources (motorized awnings and waste water pipes) mounted on different walls validates the method. In conclusion, some ideas on structure-borne noise prediction in buildings are proposed.

Update on the structureborne noise standard structures

In 1994 the authors, along with a number of interested parties, established a set of structures of increasing complexity intended to be used as standards for investigating structureborne noise prediction techniques. The structures are: a T-beam, a ribbed panel and an acoustic enclosure. This activity was jointly sponsored by Technical Committees of the Institute of Noise Control Engineers (Prediction and Modeling) and the Acoustical Society of America (Structural Acoustics and Vibration). With the assistance of funding from the Structural Acoustics Branch of the NASA Langley Research Center, these structures have been built and experimentally characterized by various interested parties with the intention of providing a baseline check for the various analytical methods. This paper will introduce the structures and present the results which have been obtained thus far in this investigation, thereby creating the framework for viewing the more recent work to be presented by other authors within this session.

A numerical structure-borne noise prediction scheme based on the boundary element method, with a new formulation for the singular integrals

Predicting the noise radiated from vibrating structures is important in the automotive, aerospace, construction equipment, and defense industries. In this paper a numerical implementation of the boundary element method (BEM) in solving the Helmholtz equation for acoustic analysis is presented. The developed code can use the results from a structural dynamic analysis performed by a general-purpose structural finite element code like NASTRAN, to predict the noise emitted from the vibrating structure. A new approach is introduced in this paper to numerically treat the singularity problem inherent in the boundary element methodology for acoustics. The integration scheme and the overdetermination technique used in this development are also presented. The developed computer code is verified by comparison to available analytical solutions. Two practical applications, a vehicle interior noise analysis and a transmission cover noise radiation analysis are presented. Finally, the Rayleigh integral method which is suitable for analyzing plane structures in a baffle is implemented into computer code as an alternative to the BEM formulation, and some verification analyses are presented.

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.