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This paper describes the validation of the Comfort Assessment function of RAMSIS performed at Saab Automobile AB. The purpose was to find out if the effects of a change in design on comfort can be predicted by RAMSIS. An interior mock-up of a car was used, in which seat, steering wheel, accelerator pedal, brake pedal and clutch pedal could be adjusted independently. In this mock-up 21 test subjects (10 men, 11 women) were told to adjust the steering wheel and the seat in the way that they obtained a good driving position. Pedals were fixed at a pre-defined position. The test subjects were told to judge the discomfort of the driving position on a scale from 1 to 10 with 1 meaning “not at all comfortable” and 10 meaning “very comfortable”. Then the test subjects were told to adjust the pedals and seat to improve the driving position, and asked to judge the discomfort of the new driving position. The seat, steering wheel and pedal positions were recorded for the two driving positions.

Exhaust acoustics simulation is an important part of the exhaust system process. Especially important is the trend towards a coupled approach to performance and acoustics design. The present paper describes a new simulation tool developed for such coupled simulations. This tool is based on a one-dimensional fluid dynamics solution of the flow in the engine manifolds and exhaust and intake elements. To represent the often complex geometries of mufflers, an easy-to-use graphical pre-processor is provided, with which the user builds a model representation of mufflers using a library of basic elements. A comparison made to two engines equipped with exhaust silencers, shows that the predictions give good results.

This paper explores the performance of light weight attenuators, which take a dissipative approach to sound abatement in the motor vehicle. An analytical model is used to predict the sound transmission loss and random incidence sound absorption of attenuators, absorbers and sandwich insulation systems. Then, a mathematical expression is developed which combines the dissipative and sound transmission loss performance to determine the total noise reduction provided in the vehicle. Using this equation, the performance of multi-layered attenuators is shown to be comparable to, or better than that of sandwich insulators. Finally, test results from various studies in vehicles show that significant weight savings can be realized by using these multi-layered attenuators, which take a dissipative approach to vehicle sound insulation, rather than the traditional sandwich insulation system.

A new method for evaluating the acoustical properties of porous materials is described here. To implement the procedure, a two-microphone standing wave tube was modified to include: a new sample holder; a section that accommodated a second pair of microphones downstream of the sample holder; and an approximately anechoic termination. A four-point sound pressure method was then used to estimate the two-by-two transfer matrix of the material. The transfer matrix can then be used to determine the wave number and characteristic impedance of the material. The procedure has been used to estimate the acoustical properties of two glass fiber materials.

Cavity reinforcement materials are used in the automotive industry to stiffen hollow cavities in unibody constructions. Typical areas of use include the engine rails, rocker panels, roof support or any other cavity in need of reinforcement. Use of these materials can allow for reductions in vehicle weight without sacrificing long-term durability and stiffness. Additional NVH benefits could be gained through the change in stiffness and through acting as a physical barrier to the propagation of noise, water and dust. The objective of this paper is to describe the properties of a new type of cavity reinforcing material and to identify key properties of reinforcing materials.

During numerical analysis of an exhaust system, the use of shell elements gives accurate results. However, it requires a lot of modeling and calculation time and a big computer system. In this paper, bar elements have been utilized for the numerical analysis of the exhaust system. It shows that the adoption of bar elements providing appropriate results can reduce modeling efforts and computing costs since less than 200 bar elements are enough during the numerical analysis of the exhaust system. To find the equivalent bar properties of curved pipe, the strain energy concept is utilized. The bellows of the exhaust system is simplified with modification of stiffness of bar elements. The developed model can be utilized to find possible hanger position with the analysis of vibration mode. The prediction of endurance performance is another benefit of the developed numerical model with bar elements.

Low density polyurethane foam, applied in general assembly, is being used as a replacement for rubber-based heat reactive baffles in automobile cavities to inhibit noise transmittance. Most chemically reactive urethane foam systems used in barrier applications are MDI-based (diphenylmethane diisocyanate). The use of classical MDI-based technology in assembly plants typically requires substantial levels of ventilation [1]. High capital and operating expenses associated with plant ventilation systems have hindered the growth of polyurethane technology. This paper describes benefits of using a low MDI polyurethane foam system in place of classical two-component MDI-based foam systems and conventional rubber-based heat reactive baffles. Severe industrial hygiene testing has indicated that ventilation requirements to use the low MDI foam system in assembly plants may be greatly reduced.

Sound absorption is one way to control noise in automotive passenger compartments. Fibrous or porous materials absorb sound in a cavity by dissipating energy associated with a propagating sound wave. The objective of this study was to evaluate the acoustic performance of a cotton fiber absorbing material in comparison to a new polypropylene fibrous material, called ECOSORB ®. The acoustical evaluation was done using measurements of material properties along with sound pressure level from road testing of a fully-assembled vehicle. The new polypropylene fibrous material showed significant advantages over the cotton fiber materials in material properties testing and also in-vehicle measurements. In addition to the performance benefits, the polypropylene absorber provided weight savings over the cotton fiber material.

A hardware / software package is presented that is used to determine the dynamic mechanical properties of viscoelastic materials as a function of temperature and frequency. The material properties can then be used to aid in the design of surface damping treatments for various engineering structures.

The high-frequency performance of automotive sound packages may be predicted by combining transmission loss and absorption calculations with statistical energy analysis (SEA) models. Vehicle SEA modeling therefore requires analytical tools that accurately describe the acoustic properties of layered structures such as trim panels. While widely accepted prediction models for fibrous materials exist, less work has been done on foam layers. This paper presents a numerical calculation of sound transmission through layered structures using a direct global matrix (DGM) solution. This numerical technique is used to compare several models for acoustic propagation in foams. Predictions are compared to transmission loss measurements for several panel configurations. A rigid porous model compares well with data up to 1 kHz for the foams studied, while foam elasticity appears to be important at higher frequencies.

A programmed heat-activated foam technology has recently been introduced for making baffles to seal hollow car body channels[1,2]. First, we summarize the key characteristics of the programmed foams. Some unique design features such as maximum gap to allow easy E-coat drainage, multiple section design for complex channels, allowance for passage of drainage hose and double-layered baffle are presented. Then, we examine the important design parameters affecting the acoustic performance of baffles based on the programmed foams. The insertion loss(IL) was measured for various baffles expanded in a test channel. The effects of foam expansion ratio, surface density, etc., on the acoustic performance of various single-layered and double-layered baffles are reported.

A new multifunctional material was developed to provide corrosion protection, anti-chip protection and vibration damping equal to or better than the existing materials today. This multifunctional coating, applied robotically or manually with airless spray equipment, is a one component system and provides the following characteristics: high vibration damping, low viscosity-easy to process, low shrinkage-no small molecules given off, no solvents, excellent adhesion to oily steel and electrocoat, excellent stone-chip resistance, high stiffness and low density. This paper describes the application and performance benefits of utilizing this sprayable, chip-resistance damper.

Constrained layer damping (CLD) is a well known technique to efficiently damp low frequency vibration. CLD employs a viscoelastic material sandwiched between two very stiff, typically metal, layers. While effective over essentially flat surfaces, CLD has not been applicable to cylindrical shapes. In order to damp low frequency vibration in metal pipes, users have been forced to rely on extensional layer damping, typically consisting of thick layers of extruded or molded rubbers. This paper discusses a novel product to damp cylindrical articles such as metal pipes with a constrained layer heat shrink tubing. This product utilizes a stiff heat shrinkable polymeric jacket bonded on the inside with a viscoelastic layer. When shrunk on a metal pipe or rod, a CLD system is produced. The product is typically thinner than an extensional layer damper and is more effective. It also meets the other physical and environmental requirements for a pipe covering.

In noise and vibration control, damping treatments are applied on panel surfaces to dissipate the energy of flexural vibrations. Presence of damping treatment on the surface of a panel also plays an important role in the resulting vibro-acoustic characteristics of the composite system. The focus of this study is to explore possibilities of reducing the weight of damping treatments by means of perforation without sacrificing performance. The power injection concept from Statistical Energy Analysis (SEA) is used in conjunction with Finite Element Analysis (FEA) to predict the effect of perforated unconstrained layer treatments on flat rectangular panels. Normalized radiated sound power of the treated panels are calculated to assess the effect of varying percentage of perforation on structural-acoustic coupling.

Damping material for automotive structures is often quantified in terms of composite loss factor or damping ratio by using ASTM/SAE beam or modal tests. Simplified expressions have also been used to estimate certain material properties. However, none of these tests provide any information on the properties of viscoelastic core material such as rubber or adhesive in practical structures. To overcome this deficiency, a refined estimation procedure is proposed. A new sandwich beam model has been developed which describes all layers of an arbitrarily applied damping patch. By using both analytical predictions and modal experiments on a cantilever beam, spectrally-varying loss factor and shear modulus of the unknown core are determined.

In this study, a simplified approach to modeling the dynamics of damping treatments in FEA (Finite Element)/ SEA (Statistical Energy) models is presented. The basic idea is to represent multi-layered composite structures with an equivalent layer. The properties of the equivalent layer are obtained by using the RKU (Ross, Kerwin and Ungar) method. The procedure presented here does not require any special pre-processing of the finite element input file and it does not increase the number of active degrees of freedom in the model, thereby making it possible to include the effect of these treatments in large system/subsystem level models. The equivalent properties obtained from RKU analysis can also be used in the SEA system models. In this study, both unconstrained and constrained layer damping treatments applied to simple structures (e.g., flat panels) as well as production vehicle components are examined.

Substantial activity in the field of recycling has made industry increasingly aware of the need to find novel ways of reusing post industrial and post consumer waste to produce useful products for our markets. The traditional approaches have been to use the scrap material as is into the original markets targeted for virgin materials, and finding areas that can accept the resultant downgraded properties. This approach has created difficulties in the recycling of automotive painted thermoplastic polyolefin (TPO) fascia and trim products. The presence of the paint contaminant has substantially degraded the physical properties of the plastic. This paper reviews the use of painted TPO scrap as a raw material for automotive sound barrier applications whereby the inherent material characteristics of TPO are capitalized on. The material modifications and functional characteristics as they relate to this application are described.

The influence of manifold geometry on exhaust noise is studied. First, a linear description of the problem is presented, so that potential relevant factors may be identified. Then a full non-linear simulation is performed, for a simple geometry, in order to check, in more realistic conditions, the ideas obtained from the linear theory. The results indicate that, although some qualitative trends may be obtained from the linear analysis, the role of back-reaction of the manifold on the engine (a non-linear coupling effect) may be determinant.

Flow noise from exhaust systems is a noise source that contributes to drive-by noise measurements. A prediction tool that allows us to choose the right duct dimensions would be very helpful. Therefore we integrated a flow noise module in a given linear acoustic prediction software. A flow noise source is modelized as an acoustic source. The source spectra is a function of the Strouhal number. The noise level depends on flow speed. A flow noise measurement with cold flow gives a set of source describing parameters. Using these parameters and the flow noise source model, a prediction of flow noise for mufflers is possible.

This paper describes a method to determine an objective measure of disturbing sounds of automotive exhaust noise (e.g. booming noise, whistle, flow noise,…). First, a disturbing sound catalogue is established. Then the approach used to make the different disturbing sounds measurable is presented. By making the perception of the disturbing sounds objective, it becomes easy to determine when they appear and to what extent. Finally, the contribution of this research in the framework of the global integration of sound quality in the design process of exhaust systems will be discussed.