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Blower noise is the single most dominating contributor of interior noise for several operating conditions; the worst condition being low engine speed and high HVAC fan speed. The goal of the research presented in this paper is to investigate the application of an acoustical resonator to reduce HVAC blower noise. Resonator systems are constructed and objective bench tests are performed to objectively assess their effectiveness towards a specific acoustical issue within the HVAC system. In addition, HVAC performance is objectively measured to ensure that airflow has not been degraded with the addition of the resonator. Modeling and simulation are used in this research to verify the HVAC system acoustical properties and to optimize the location of the resonator.

This paper considers the use of partial enclosures and absorbing materials inside those enclosures to dissipate energy. Several experiments were conducted where various parameters of an enclosure were altered and the effect on the noise radiating through the opening was measured. From these results, the parameters that play the most important role in sound radiation through the opening of an enclosure were determined. The two-point method and decomposition theory were used to calculate the transmission loss, which was used as the primary variable to analyze the enclosure's performance; the transmission loss is shown to be a better variable than sound pressure or output sound power for this purpose. Numerical simulations were conducted using the indirect boundary element method, and the results were compared with experimental results.

NVH engineers typically are dealing with issues that relate to shake, harshness and low frequency noise and vibration concerns. However there is a greater importance being placed on dealing with high frequency structureborne noise problems which are related to gear meshing forces and drivetrain dynamics. This paper presents a case study of a high frequency structureborne noise problem. The objective of the paper is to show the application and effectiveness of using various testing based techniques such as Transfer Path, Running modes, and Mobility analysis along with acoustic excited operating deflection shapes for solving these problems in a timely and effective manner.

An energy source simulation method (ESSM) has been developed to determine sound energy density. Using this approach, a specified intensity boundary condition on the surface of a vibrating body is approximated by superimposing energy density sources placed inside the body. The unknown strengths for these sources are then found by minimizing the error on the boundary, using a least squares technique. The superposition of these energy density sources should then approximate the sound radiating from the body. The approach was evaluated in two-dimensions for a circle, square, and a more general geometry. The ESSM proved an excellent tool for predicting the energy density provided that power radiated uniformly in all directions. However, the ESSM could not accurately predict the directional characteristics of the energy density field if the power radiated significantly higher from one side of an object than other sides.

In order to meet the customers comfort requirements, reduction of noise in the passenger compartment is one of the primary concerns in the automotive industry. Moreover, for a better reactivity to the market, vehicle development time tends to be shorter and shorter. Instead of constructing many prototypes and running a lot of tests, numerical simulation has to take a bigger part in the design of cars. This would be a cheaper and quicker way of testing many new solutions. We have developed for several years a numerical model, combining by Finite Element Method (FEM) and Boundary Element Method (BEM), for computing the vibro-acoustic behaviour of a fully trimmed car with engine and power train. This model allows prediction of the structure borne sound field due to the engine and wheels excitations at low frequencies (0-200 Hz).

This paper considers two questions: how does one know when a boundary element mesh is reliable, and what are the advantages and potential pitfalls of various methods for sound radiation prediction. To answer the first question, a mesh checking method is used. With this method velocity boundary conditions are calculated on the nodes of the mesh using a point source or sources placed inside the mesh. A boundary element program is then used to calculate the sound power due to these boundary conditions. The result is compared to the known sound power of the point source or sources. This method has been used to determine the maximum frequency of a mesh, how many CHIEF points to use, etc. The second question is answered by comparing the results of several numerical methods to experimental results for a running diesel engine. The methods examined include the direct and indirect boundary element methods and the Rayleigh integral.

Sound transmission through a cylindrical double-walled shell lined with an elastic porous material is studied. Love's equation is applied to describe the shell motions coupled with acoustic wave equations. An interesting method is developed to simplify the analysis of the wave propagation in the elastic porous material, which reduces the model developed by Bolton et al. [2] based on the Biot's theory [1] to a simple one-dimensional wave propagation model. The results from the simplified model are compared with those from the Bolton's model and measurements. Solutions for the sound transmission through the cylindrical double-walled shell lined with an elastic porous material are obtained for various configurations using the simplified method, and compared with measured results. Advantages and limitations of the simplified analysis method developed are explained from the perspective of practical applications.

This paper describes the use of Vibro-Acoustics numerical modeling for prediction of an Air Intake System noise level for a commercial vehicle. The use of numerical methods to predict vehicle interior noise levels as well as sound radiated from components is gaining acceptance in the automotive industry [1]. The products of most industries can benefit from improved acoustic design. On the other hand, sound emission regulation has become more and more rigorous and customers expect quieter products. The aim of this work it is to assess the Vibro-Acoustics behavior of Air Intake System and influence of it in the sound pressure level of the vehicle.

Amongst various sources of noise and vibrations in gear meshing, transmission error and sliding friction between the teeth are two major constituents. As the operating conditions are altered, the magnitude of these two excitations is affected differently and either of them can become the dominant factor. In this article, an experimental investigation is presented for identifying the friction excitation and to study the influence of tribological parameters on the radiated sound. Since both friction and transmission error excitations occur at the same fundamental period of one meshing cycle, they result in similar spectral contents in the dynamic response. Hence specific methods like the variation of parameters are designed in order to distinguish between the individual vibration and noise sources. The two main tribological parameters that are varied are the lubricant and the surface finish characteristics of gear teeth.

Sound transmission through the sidewall of an automotive muffler has been studied theoretically and experimentally. Three wall structures: a single shell, double shell and porous-cored shell constructions are considered. Transmission losses through the sidewalls were measured using the two microphone method. Experimental results are compared to one another, and to the corresponding theoretical analysis results, which shows that the mean flow effect is not a significant factor in designing the muffler sidewall.

Low frequency longitudinal vibrations resulting from driver throttle inputs are a common problem in modern passenger cars. This phenomenon, which is commonly referred to as shuffle or shunt, is due to sudden changes in the engine torque exciting torsional oscillations in the driveline. This paper presents a dynamic model of a vehicle driveline for the optimization of low frequency torsional vibration. The model used is first validated against experimental tests. Parameter sensitivity studies have been carried out using the model to identify the important components affecting shuffle. Three key parameters have been chosen from the parameter study. To optimize these key factors, Genetic Algorithms (GAs) have been used in this multi-parameter optimization problem. The results obtained from GAs have been compared with the calculus based optimization techniques.

This paper presents the numerical modeling of noise radiated by an engine, using the so-called Acoustic Transfer Vectors and Modal Acoustic Transfer Vectors concept. Acoustic Transfer Vectors are input-output relations between the normal structural velocity of the radiating surface and the sound pressure level at a specific field point and can thus be interpreted as an ensemble of Acoustic Transfer Functions from the surface nodes to a single field point or microphone position. The modal counter part establishes the same acoustic transfer expressed in modal coordinates of the radiating structure. The method is used to evaluate the noise radiated during an engine run-up in the frequency domain. The dynamics of the engine is described using a finite element model loaded with a rpm-dependent excitation. The effectiveness of the method in terms of calculation speed, compared with classical boundary element methods, is illustrated.

This paper presents a method applied in the development of an optimized transmission rubber mount of a midsize Diesel pickup. The focus of this optimization were to improve the vibration insulation and consequently improve the NVH (Noise and Vibration Harshness) quality of the vehicle. The paper describes the basic mounting design and manufacturing constrains, the simulation modeling basis, inputs required to perform the computational simulation, the experimental method used to extract the center of gravity and rotational inertia of the powertrain and a general mounting tuning strategy. The mounting dynamic simulation results for the optimized version is also presented compared to the original one. In order to quantify the noise and vibration improvements, the internal noise and vibration transmissibility levels were measured and compared in percentile reduction basis to current vehicle levels

Combustion noise plays a considerable role in the acoustic tuning of gasoline and diesel engines. Even though noise levels of modern diesel engines reach extremely low values, they are still higher than those of conventional gasoline engines. On the other hand, new combustion procedures designed to improve fuel consumption lead to elevated combustion noise excitations as in case of today's direct injecting gasoline engines whose vibration excitation and airborne noise emissions are slightly increased during stratified operation. The partly conflicting development goals resulting from this can only be realized by integrating the NVH specialists' expertise into every development step from concept to SOP.

The new inline six-cylinder engine from BMW notoriously sets new standards on objective performance in power and torque and fuel consumption as well as on “Laufkultur” (engine refinement). It has been a general movement in recent years to design engines that not only perform, but also improve driver's feedback for performance on an emotional level. New is the degree of differentiation of this new engine through distinctive sound design for the whole bandwidth of vehicle categories ranging from a 5-Series luxury sedan to a Z3 roadster, or an X5 sports utility vehicle to a 3-Series compact car. For each BMW class, the intake and exhaust systems of the inline 6-cylinder engines have been tuned to highlight the subjective impression of performance according to the appropriate vehicle type.

Serpentine belt system has been widely used during past years to drive automotive accessories like power steering, alternator, and A/C compressor from a crankshaft pulley. Instead of using multiple belt drives, the serpentine belt system uses a multi-rib flat belt, which wraps around several idlers and accessory pulleys. This design requires the use of a tensioning device to maintain adequate belt tension for preventing slip. Crankshaft torsional vibrations can lead to excessive rotational vibrations in poorly designed accessory systems. This can lead to undesirable noise and excessive slip, which can hamper the belt and bearing life. The value of these rotational frequencies and system response is of utmost interest to the accessory drive designer. While it is not practical to shift these rotational frequencies out of the operating range of an engine, a belt layout with these frequencies at non-dwell engine speed is highly desirable.

With the advance in modularization of engine parts in recent years, there is increased use of plastic-made products in air intake systems. Plastic-made intake manifolds (Fig. 1) provide many advantages including reduced weight, reduced cost, and lower intake air temperatures. However, these manifolds have one disadvantage when compared with conventional aluminum-made intake manifolds, in that they transmit more noise because of their lower material density. For example, plastic intake manifolds of early development often generate flow noise when the throttle is opened quickly. With conventional aluminum intake manifolds, this flow noise had generated, but was not heard. This flow noise is presumed to be generated because of high-speed airflow generated when the throttle is opened quickly, but the mechanism of this noise generation has not been clarified.

In the future, the requirements of acoustic behavior in air intake systems will continue to increase. Active systems will be necessary to reach the higher legislative standards and customer expectations regarding noise levels. The optimization of the Active Noise Control System regarding the sound design in the interior is based on the transfer function between the engine and the passenger compartment as well as the design of the air intake system. This paper shows the development process, with a focus on the investigation of transfer functions in passenger cars and the computational calculation for the system configuration.

An investigation of the disturbing sound elements of automotive exhaust noise will be discussed (e.g. whistle, raspy, boom). The investigation is performed in three steps. First a sound catalogue is established with a definition for each disturbing element. Subsequently, for each of these disturbing elements a metric is determined. This paper is focused on the final step, which consists in determining the link between each metric and the construction of the exhaust system. The case of a whistle generated by a perforated tube will be discussed. Another element that will be discussed is putter, which occurs and the end of the coast-down, before the transition to idle rpm.

The design of an air intake system has to be a compromise between several system targets. In the past these conflicts were solved with experimental test on the first prototype parts. To shorten the development times more and more computational programs in the concept phase are used. 1D simulation programs are based on the transfer matrix method or use the output of gas exchange programs to simulate the acoustic behavior of air intake systems. These tools do usually neglect the coupled fluid/structure modes. Measurements on a simple air cleaner design have shown that these coupling can not be ignored on typical air cleaner designs. The difference between internal and external pressure leads to an increase of the air cleaner volume which shifts the first resonance to a lower engine speed. This paper shows a method which can be used in 1D simulation programs to allow the prediction of orifice noise of air intake systems.