Interior Sound Pressure Research Articles

Measuring in-situ air handling unit sound power levels for use in predicting interior sound pressure levels from replacement units

We were faced with the need to develop a noise analysis for replacement rooftop units at a university academic building. With uncertainty about the accuracy of as-built documentation for some of the distribution ductwork and existing duct silencer performance, there was concern that a traditional hand calculation of sound levels from the new rooftop air handling units may not be a reliable method of evaluation. We developed a test method to document in-situ sound power levels from the existing units and resulting sound pressure levels in interior spaces using a reference sound source. These data were then used to predict interior sound pressure levels from the new units. This paper presents the test method, results, and lessons learned.

Parameter identification and NVH characteristic analysis of automotive suspension rubber bushing

Accurate prediction of the dynamic stiffness of rubber bushings is crucial for optimizing vehicle vibration and noise performance. However, this task is highly challenging due to various influencing factors such as frequency and amplitude. Consequently, there has been limited research conducted in this area thus far. This paper presents a novel approach for predicting the dynamic stiffness of rubber bushings. The frequency and amplitude dependencies of rubber bushings were thoroughly investigated through dynamic loading tests. A comprehensive model for rubber bushings, incorporating parallel connections of elastic elements, friction elements, and higher-order fractional derivative viscous elements, was established. The model parameters were accurately identified using the GA-BP method. The results demonstrate that the proposed model exhibits a high level of precision in estimating dynamic stiffness across a frequency range of 0–200 Hz. In comparison to the conventional model, the proposed approach enables more precise computation of interior sound pressure response and enhances vehicle simulation accuracy.

Mid Frequency Structure-Borne Noise Modeling in a Trimmed Automotive Vehicle

Finite Element Method (FEM) and the Statistical Energy Analysis (SEA) are standard methods in the automotive industry for the prediction of vibrational and acoustical response of vehicles. The FE method, based on a deterministic description of the dynamics is typically used for structure-borne and air-borne problems and is usually limited to below 250 Hz. The method becomes prohibitively expensive in terms of computational costs with increasing frequency as more Degrees-of-Freedom (DOF) are required to correctly represent the dynamic response of the structure. Additionally, the dynamic response becomes sensitive to small perturbations in the model, thus defeating the purpose of a deterministic modeling method. SEA is a statistical method widely applied in automotive industry for air-borne problems at frequencies higher than 300 Hz. The method is highly efficient for the design and optimization of sound packages facing airborne sources, but it lacks accuracy when dealing with structure-borne sources in the mid frequency range. However, both methods are not capable of handling the so called "mid frequency problem", where both short and long wavelength components are present in the same system. A Hybrid method has been recently proposed that rigorously couples SEA and FEM. In this work, the HybridFE-SEA method has been used to create fast/efficient model of structure-borne noise in a fully trimmed vehicle from 200Hz to 1 kHz. This paper first describes simple guidelines used to partition the vehicle into stiff components described with FE and modally dense components described with SEA. It is also demonstrated how detailed local FE models can be used to improve SEA descriptions of car panels and couplings. After review of the Hybrid FE-SEA models of a full vehicle that were built, sample experimental validation results of interior Sound Pressure Levels and panel vibration are shown for both bare and fully trimmed vehicle configurations.

Panel Acoustic Contribution Analysis in Automotive Acoustics Using Discontinuous Isogeometric Boundary Element Method

In automotive industries, panel acoustic contribution analysis (PACA) is used to investigate the contributions of the body panels to the acoustic pressure at a certain point of interest. Currently, PACA is implemented mostly by either experiment-based methods or traditional numerical methods. However, these schemes are effort-consuming and inefficient in solving engineering problems, thereby restraining the further development of PACA in automotive acoustics. In this work, we propose a PACA scheme using discontinuous isogeometric boundary element method (IGABEM) to build an easily implementable and efficient method to identify the relative acoustic contributions of each automotive body panel. Discontinuous IGABEM is more accurate and converges faster than continuous BEM and IGABEM in the interior sound pressure evaluation of automotive compartments. In this work, a contribution ratio is defined to estimate the relative acoustic contribution of the structure panels; it can be calculated by reusing the coefficient matrix that has already been generated in the sound pressure evaluation process. The utilization of the parallel technique enables the proposed method to be more efficient than conventional methods; it is validated in two numerical examples, including a car passenger compartment subjected to realistic boundary conditions. A sound pressure response experiment based on a steel box is conducted to verify the accuracy of the interior sound pressure calculation using discontinuous IGABEM. This work is expected to promote the practical process of IGABEM for application in automotive acoustic problems.

Vehicle vibro-acoustical comfort optimization using a multi-objective interval analysis method

Vehicle interior vibro-acoustical comfort, i.e., noise, vibration and harshness (NVH), is important to consumers and automotive manufacturers because it affects the physical and mental health of passengers and impacts the reputations of automotive manufacturers. Although simulations can predict vehicle interior noise and vibration, acoustic treatment and resulting uncertainty may generate considerable errors between the simulation and actual measurement results. Meanwhile, the recursive invocation of a complex simulation model in an optimization leads to a very time-consuming calculation process. These problems make the optimization of vehicle interior vibro-acoustical comfort a challenge for the automotive industry. In this paper, a new method, the multiobjective interval analysis method, was proposed to solve these problems. To implement this method, we carried out a vehicle road test instead of a complicated simulation model to collect data. The vehicle interior noise and vibration were recorded, and the interior sound pressure level (SPL) and total weighted acceleration root mean square (TWA-RMS) values were calculated and used as objectives. Then, a multiobjective interval analysis method was proposed to compute the midpoint and radius of the objective functions under different uncertainties. The preferred average performance and robustness of the vehicle vibro-acoustical comfort was adjusted by tuning the weighting factor. To accelerate the calculation process, a neural network model was developed as an approximate model to construct the numerical relation between the dynamic parameters and the vibro-acoustic metrics. Finally, the effectiveness and accuracy of the proposed method were verified with experimental results.

Active sound quality control of vehicle interior noise using a dual sampling-rate active noise equalization algorithm

In-vehicle active sound quality control (ASQC) system is an advanced application of active noise control (ANC) technology, which always suppresses the interior sound pressure or improves the psychoacoustic features. However, the connection between the sound quality control state and the vehicle's working state is normally ignored, and the passenger's sound perception typically expects a linear relationship between the vehicle speed and sound loudness. This paper presents a dual sampling-rate active noise equalization algorithm. The low sampling-rate signal is used to improve system computing efficiency, the high sampling-rate signal is used to improve the ASQC effect, and their conversion communication uses a hold (low to high) and a sampler (high to low). The data relating to the ASQC system was collected, and some sound quality evaluations were conducted for determining two appropriate sampling-rate values. Combining a genetic algorithm and the corresponding ASQC simulation system, the algorithmic optimal convergence coefficients and gain coefficients were further determined at different engine speeds. The verification results of ASQC using this proposed algorithm show that the loudness of interior noise is effectively suppressed; the nonlinear index is reduced to 1.37, improving by 37% relative to the original noise and by 20% compared to the ANC system.

Development of High-Fidelity Numerical Methodology for Prediction of Vehicle Interior Noise Due to External Flow Disturbances Using LES and Vibroacoustic Techniques

A pleasant and quiet cabin in driving a car is one of the most critical factors affecting a customer’s choice in a market. As the traditional noise sources such as power trains become less, the relative contribution of aerodynamic noise to the interior noise of a road vehicle becomes even more critical. In this study, a high-fidelity numerical methodology is developed for the reliable prediction and analysis of the interior transmitted noise due to external flow disturbance. The developed numerical methodology is based on the sequential application of the high-resolution LES technique, wavenumber–frequency transform, and vibroacoustic model. First, the compressible LES techniques with high-resolution grids are employed to accurately predict the external turbulent flow and aeroacoustic fields due to the turbulent flow, at the same time, of a vehicle running at a speed of 110 km/h. Second, surface pressure fluctuations on the front windshield and side windows, obtained from the LES simulation, are decomposed into incompressible and compressible ones using the wavenumber–frequency transform. Lastly, the interior sound pressure levels are predicted using the vibroacoustic model, which consists of the finite element (FE) and statistical energy analysis (SEA) methods. For the efficient computation of the vibroacoustic interaction between the vibration of the vehicle windows and the acoustic field inside the cabin room, the FE and SEA methods are applied in low- and high-frequency ranges, respectively. The predicted interior sound pressure spectral levels agree well with the measured ones. In addition, although the magnitudes of the compressible pressure components are generally lower than those of the incompressible ones, the compressible field is found to contribute more to the interior noise in high-frequency bands. The physical mechanism of the higher transmission is shown to be related to the coincident effect between the compressible pressure field and the structural vibration of the vehicle window.

A Method for Quantifying Automobile Brake Creep Groan Intensity Based on Friction-Induced Vibration and Noise

To quantify the intensity of automobile brake creep groan, both experimental and analytical studies are innovatively conducted on the friction-induced vibration and noise of the disc brake in this paper. Experimentally, three factors, brake disc initial temperature, terrain, and gear position, are comprehensively contemplated to design six different test conditions, based on which a creep groan vehicle road test is conducted. Depending on the subjective evaluation and statistical analysis of the annoyance degree caused by vibration and noise in the starting and braking process under different test conditions, the influence of each factor on creep groan intensity is obtained. By processing the brake caliper and lower suspension arm acceleration and the interior sound pressure signals acquired in the test, the occurrence conditions and transient dynamic characteristics of creep groan are explored. One of the creep groan vibration modes is triggered by the rapid removal of the force exerted on the brake pedal when the vehicle starts at an extremely low speed, which presents intermittent impact and chaotic characteristics. The other vibration mode shows periodic harmonic characteristics, whose energy is concentrated on specific frequencies in the form of frequency doubling. This vibration mode occurs when continuously maintaining a low brake oil pressure or slowly releasing the force exerted on the brake pedal during the vehicle low-speed starting process, the velocity-displacement phase-plane portrait of which shows a stable limit cycle of stick-slip motion. Analytically, four vibration indexes and four noise indexes are established to evaluate the intensity of creep groan, the validity of which is verified by linear regression analysis. Finally, by combining all effective indexes, multiple linear regression analysis is performed, based on which the mapping relationship between the subjective evaluation of creep groan and effective indexes is obtained. The results demonstrate that the combination of the logarithmic vibration dose value of maximum brake caliper acceleration pulse and the loudness of interior noise can accurately describe the annoying degree caused by creep groan. The regression model can quantify and predict creep groan intensity of the test vehicle under different test conditions, which has guiding significance for engineering applications.

Experimental and Numerical Analysis of Sunroof Buffeting of a Simplified Mercedes-Benz S-Class

<div class="section abstract"><div class="htmlview paragraph">Sunroof buffeting is examined experimentally and numerically in this paper. Despite the fact that some consider the simulation process for sunroof buffeting to be mature, there remain substantial uncertainties even in recently published methodologies. Capturing the frequencies and especially the sound pressure levels correctly is essential if CFD simulations are intended to be used during early stages of a car development process. Numerous experimental results of sunroof buffeting and the interior low-frequency characteristics of a 2013 Mercedes-Benz S-Class have been used to develop a simplified car model: a full-size S-Class model with slightly simplified geometries in the interior as well as at the exterior. To avoid the effects of numerous different materials in the interior, it is solely made from polyurethane and aluminum and built to maximize its structural rigidity and air-tightness. The air-tightness of the cabin and structural modes of body parts have the greatest impact on the Helmholtz frequencies, which are excited by the vortex shedding in the sunroof opening.</div><div class="htmlview paragraph">With this simplified car model various measurements are carried out to validate the numerical simulation method. The measurement data consists of acoustic data as well as flow quantities. In this paper, Star-CCM+ is used to conduct improved delayed detached eddy simulations with direct noise calculation in order to predict the buffeting frequencies that occur at different wind speeds correctly. Due to the rigid and acoustically hard walls of the simplified car model, which fairly match the numerical boundary conditions, it is possible to predict the interior sound pressure levels correctly as well.</div><div class="htmlview paragraph">The presented results demonstrate that state-of-the-art CFD codes are capable of predicting sunroof buffeting frequencies and noise levels correctly if the experimental and numerical boundary conditions match.</div></div>

Simulations of poroelastic materials in a complex acoustic system using frequency-dependent parameters in the mid-frequency range

Efficiency requirements prompt manufacturers to develop ever lighter acoustic packages in vehicles. Poroelastic materials are essential to achieve the desired interior noise level targets and thus the simulation of their effects is of utmost importance in NVH analyses. However, it is challenging to achieve good validation between finite element method (FEM) based simulation results and measurements in the mid-frequency range (400-1000 Hz). One possible reason could be the lack of using frequency-dependent Biot-paremeters describing the poroelastic materials (PEM) characteristics of trims. The present research aims to employ frequency-dependent Biot-parameters for the PEM materials to investigate the acoustic response of a scaled car-like steel structure composed of flat plates and U-section stiffeners enclosing an air cavity. Porous acoustic material is applied to the walls of the cavity. The focus of the study is to understand the effect of applying frequency-dependent Young's modulus and damping values for the PEM parameters in the 100-1000 Hz range. Simulation results obtained from ESI VPS FEM solver are compared with measurements, with particular focus on the interior sound pressure levels. The simulation methodology, including discretization techniques, structural damping and fluid damping applications are described in detail.

Psycho-acoustic evaluation of the automotive acoustic comfort using vibro-acoustic prediction methods

In the automotive industry, the acoustic comfort is considered as a selling point of utmost importance. To help the OEMs improve the acoustic comfort in cars, as a one-tier supplier of automotive glazing, Saint-Gobain is currently working on the acoustic comfort within the cabin in order to propose the right set of glazing consistent with the OEMs' specifications. The characterization of the acoustic comfort mostly relies on physical demonstrators required for carrying out the relevant measurements. It is however not available early in the project phase, delaying the subjective analysis late in the development phase. To have the opportunity to develop effective solutions, the acoustic comfort has to be investigated as early as possible in the design process. Saint-Gobain is thus currently developing relevant acoustic models in order to predict the mid-high frequency airborne interior noise generated by the wind excitations. The subjective acoustic comfort has then to be assessed using the predicted interior sound pressure levels converted into audio soundtracks for the auralization purposes. In this paper, we briefly present the Statistical Energy Analysis model developed by Saint-Gobain. The psychoacoustic methodology deployed to evaluate its reliability for the subjective evaluation of the automotive acoustic comfort is detailed.

High frequency noise model based on statistical energy method parameter sensitivity analysis

According to the basic principle of statistical energy method, the high frequency SEA model of the full vehicle is established. Through the comparison of simulation and test results, the error of power based noise reduction (PBNR) and interior sound pressure level response is less than three dB, which proves the accuracy of high frequency simulation model. Through the design of different schemes, the sensitivity analysis of parameters such as material parameters, internal loss factor and leakage rate to the model is obtained. The research results show that the accuracy of material parameters, internal loss factor and leakage rate can improve the accuracy of high-frequency simulation model. The sensitivity analysis can provide some ideas for vehicle high frequency noise model adjustment and modification.

Effect of mounting bracket structure and material on automotive air conditioning compressor

ABSTRACT This paper proposes an analysis of Mounting Bracket Structure and Material effects on fixed-displacement swash-plate-type compressor. To decrease the interior sound pressure of a vehicle, both finite-element analysis (FEA) and vibration experiment of the automotive air conditioning compressor with the mounting bracket were conducted, and the effect of the material and structure of the mounting bracket on the noise and vibration of the compressor was analysed. The finite-element model of the fixed-displacement swash-plate-type compressor with a mounting bracket is established. For the mounting bracket with different materials and structures, vibration acceleration level (VAL) of the finite-element model was analysed. Results show that the mounting bracket MB3, which is made of QT400-10, provides the best noise and vibration performance, which is also verified through interior sound pressure level experiment. Abbreviations: FEA: finite-element analysis; VAL: vibration acceleration level; FRA: frequency response analysis; EMA: experimental modal analysis; LTI: Linear Time-Invariant; FEM: finite-element model; AMS: automatic multi-level substructuring; DOF: degree of freedom

Effect of Blade Outlet Angle on Acoustics of Marine Centrifugal Pump

To research the effect of blade outlet angle on acoustics of marine centrifugal pump, the unsteady numerical simulation analysis of the four models is carried out and the dipole source of pump shell is extracted. The constraint modal of pump, interior sound pressure level (SPL), exterior acoustic directivity and sound power level are obtained. The results show that five and six SPL peaks appear at BPF and blade frequency multiplier in the pump inlet and outlet, respectively, the SPL peak value is the largest at blade passing frequency (BPF), and the interior acoustics propagates to inlet and outlet directions, and to outlet more significantly. The exterior acoustic directivity in the four models is the same in all directions, and the blade outlet angle has little influence on the changes of exterior acoustic directivity. The SPL at BPF and 2BPF in Y = 0 plane is significantly smaller than that in X = 0 and Z = 0 planes, and the difference of maximum SPL at BPF is 7.2 dB and 8.0 dB and that at 2BPF is 7.6 dB and 6.4 dB, respectively. The sound power level is maximum at 2BPF, and that at the BPF and 2BPF increases first and then decreases with the blade outlet angle increases. When the blade outlet angle is 40o, the interior and exterior acoustic performances are better. The experimental value of the SPL in model 35 is basically consistent with the simulated value, which fully indicates that the numerical simulation analysis has high accuracy and provides support for the credibility of the acoustic simulation results.

Prediction of the acoustic effect of an interior trim porous material inside a rigid-walled car air cavity model

In this paper, a simplified car air cavity model for predicting the influence of an interior trim material on the cabin interior sound pressure level (SPL) was presented. This work studies a rigid-walled car cabin model with one flexible wall. The interior trim material (a porous sound-absorbing material) was mounted in between the enclosed car air cavity and the flexible wall. A single point acoustic source is used to acoustically excite the rigid-walled car air cavity model, where the loudspeaker is positioned at front corner of the car cabin to simulate noise entering via an airborne path. The variation of the car air cavity interior sound pressure level corresponding to the presence of different porous sound-absorbing materials was experimentally investigated for high frequencies. The acoustical effects of the interior trim porous material on the proposed structural and acoustic coupled system were predicted by using the Statistical Energy Analysis (SEA) method for noise in one third octave bands. The comparison of results revealed that the experimentally acquired car cabin interior sound pressure level agrees fairly well with the simplified SEA model, both with and without the porous sound-absorbing materials, for high frequency one third octave band levels.

Experimental analysis of hydrodynamic and acoustic pressure on automotive front side window

Both the hydrodynamic and acoustic pressure on automotive front side window have the potential contribution to the interior sound pressure of the vehicle. The corrected force analysis technique (CFAT) is employed to extract the acoustic pressure on front side window. The sensitivity of all pressure fluctuation inside and outside the vehicle to the variation of wind speed, yaw angle and the geometry of side mirror is analyzed. The scaling law of both hydrodynamic and acoustic pressure is derived, compared and used to confirm the validation of CFAT. The coherence function and contribution coefficient are used to analyze the relative contribution of hydrodynamic and acoustic pressure on front side window to the interior sound pressure. Results show that in the middle and high frequency range, although the magnitude of acoustic pressure on front side window is much smaller than that of hydrodynamic pressure, the acoustic pressure on front side window contributes much more than the hydrodynamic pressure into the interior sound pressure.

Random vibro-acoustic control of internal noise through optimized Tuned Mass Dampers

Abstract The present work deals with the passive control of interior sound pressure induced by randomly vibrating structure coupled to an enclosure filled with air. The control in the low frequency range is achieved using a Tuned Mass Damper (TMD) device. In order to guarantee an optimal performance of the TMD device, a stochastic acoustic optimization strategy is proposed. In the later, the objective function is the root mean square acoustic pressure measured at a given location inside the cavity. Assuming linear behavior of the vibro-acoustic system, the modal interaction approach is used and the objective function is evaluated by means of spectral analysis. The effectiveness of the proposed strategy is investigated and compared with others from the open literature. The capability of the proposed optimization strategy to deal with multimodal control of interior sound has also been addressed. To this end, multiple TMDs have been used. The optimal TMD parameters have been obtained using a multi-objective optimization approach and the results that have been gathered show significant attenuations in all target resonant modes.

Analysis of Urban Bus Body Vibration and Coupling Interior Noise

Bus body vibration and interior noise caused by vibration directly affect the ride comfort, cause driving fatigue, discomfort, and bring to the urban environmental noise pollution at the same time. Based on urban bus as the research object in the paper, the modal analyses of body structure, interior spoke and solid coupling model have been carried out by LMS. Virtual Lab software, and compared with the results of modal experiment results on body. The interior sound pressure response has been calculated under the engine incentive by using the boundary element method, and the sound pressure response curves for low frequency have been gotten. Finally, the local structure of body has been improved, and this method reaches the purpose of noise reduction by the simulation calculation. At the same time, references have been provided for improving vehicle vibration and noise.

Effect of the Fiber Lamination Angle of a Carbon-Fiber, Laminated Composite Plate Roof on the Car Interior Noise

The paper presents the change of the interior noise according to the lamination angles of the carbon fiber in the carbon-fiber reinforced plastic (CFRP) laminated composite plate. In the previous paper, the charateristics of the sound radiated from a CFRP plate was studied in the free field condition. In this paper, vibro-acoustic interaction for the CFRP plate with various lamination angles was studed considering the application of the CFRP plate to car roof. In order to study the vibro-acoustic interaction, a certain enclosure with flexible wall was required and then the closed rectangular box was prepared. The one flexible wall of the rectangular box consisted of CFRP plate. Three CFRP plates with fiber lamination angles of [-15/15/15/-15]s, [-30/30/30/-30]s, and [-75/75/75/-75]s were fabricated and used as one flexible wall of the closed box. These plates were excited by an impact force, and the interior sound pressure within the closed box was calculated both theoretically and experimentally. Then, the identified vibro-acoustic characteristics were used to apply the CFRP plate to the roof of a car, thereby shifting the resonance frequency of the interior noise.

Numerical optimization of sound pressure responses for the dash panel based on automatically matched layer and genetic algorithm

The sound insulation performance of the dash panel has a direct influence on the level of sound absorption of the whole vehicle. Therefore, it is necessary to adopt proper optimization strategies to optimize the dash panel and interior sound pressure response. Firstly, damping loss factor was imported into the dash panel and the coupling model of interior acoustic cavity to compute the sound pressure response of the driver. Sound pressure response had multiple peak noises in the analyzed frequency band. With the increase of the analyzed frequency, Contours for the noise of interior acoustic cavity became increasingly dispersed. Secondly, reverberation chambers on both sides were coupled with the dash panel respectively to establish AML model. In this way, the computational transmission loss would be more consistent with the actual situation. AML method can directly obtain transmission loss without extracting the transmission sound power to compute transmission loss through relevant formulas. In reported papers, there are big differences between simulation and experiment in the low frequency because it is difficult to simulate the real boundary conditions. The computational results of this paper were more consistent with experimental results in the whole frequency band, which indicated that it was more effective to use AML method to compute the transmission loss of the dash panel. Then, a sound package was applied to the dash panel to conduct parametric analysis. Results showed that the thickness of the sound-absorption layer could effectively improve transmission loss over 250 Hz. When the thickness of the sound-absorption layer was 15 mm, transmission loss was relatively optimal. In addition, the thickness of the air layer had little influence on transmission loss. Finally, genetic algorithm was also used to optimize the parameters of sound package of the dash panel. Results showed that the optimized dash panel had a higher average transmission loss and total mass, and the average sound pressure response of the driver also decreased. Additionally, the transmission loss and sound pressure response of the driver optimized by genetic algorithm at each frequency point were improved in the analyzed frequency band to obtain a low-noise and lightweight dash panel.