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A Semi-Empirical Approach for Modeling Greenhouse Surface Wind Noise

BBN Technologies, an Operating Unit of GTE-William B. Coney
Ford Motor Co.-Jen Y. Her
Published 1999-05-19 by SAE International in United States
A CAE procedure for modeling the aerodynamic excitation of greenhouse surface vibration and its reradiation as noise is described. The procedure begins with a description of the steady flow over the surfaces. This is used as a basis for estimating the spatially varying unsteady pressure loading. The approach is semi-empirical, utilizing normalized pressure data collected through wind tunnel testing of production vehicles. The unsteady pressures are utilized within a normal mode analysis to predict vibration of the greenhouse panels. Interior noise associated with the panel vibration is estimated from a statistical energy analysis model. We show that contributions of multiple surfaces can be significant.
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Coupling of Finite Element and Energy Finite Element Solutions for Calculating the Vibration of Co-linear Beams in the Mid-Frequency Range

The University Of Michigan-Xi Zhao, Nickolas Vlahopoulos
Published 1999-05-19 by SAE International in United States
The theoretical development of a hybrid finite element method is presented. It combines conventional Finite Element Analysis (FEA) with Energy Finite Element Analysis (EFEA) in order to achieve a numerical solution to mid-frequency vibrations. In the mid-frequency range a system is comprised by some members that contain several wavelengths and some members that contain a small number of wavelengths. The former are considered long members and they are modeled by the EFEA. The latter are considered short and they are modeled by the FEA. The new formulation is based on deriving appropriate interface conditions at the joints between sections modeled by the EFEA and the FEA methods. Since the work presented in this paper constitutes a fundamental step in the development of a hybrid method for mid-frequency analysis, the formulation for one flexural degree of freedom in co-linear beams is presented. The excitation is considered to be applied on a long member and the response of the entire system is computed. Uncertainty effects are imposed only on the long members of the system. Validation cases…
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Alternate Fueled Powertrain - An Insight into Its Combustion Related NVH Issues

Raytheon Systems Co.-T. N. Patro, D. A. LaRue
Published 1999-05-19 by SAE International in United States
Over the past two decades, significant work has been accomplished in the development and commercial applications of powertrains fueled by alternate fuels like compressed natural gas, hydrogen, liquefied petroleum gas, and alcohol, etc. These fuels have been proven to be very promising in terms of fuel economy and clean emissions. However, almost no work has been done or reported in terms of the noise and vibration aspects of powertrains being powered by these fuels.In this paper, an attempt has been made to elaborate the noise and vibration behavior of powertrains fueled by various alternate fuels. Some distinct powertrain NVH features due to alternate fuel combustion have been portrayed in detail.*
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Validation of SEA Models using Measured Modal Power

Cambridge Collaborative, Inc-Jerome E. Manning
Published 1999-05-18 by SAE International in United States
Statistical energy analysis is generally used to study the vibroacoustic response of systems with high modal densities. The most accurate predictions are obtained at high frequencies where the modal overlap is high and many modes contribute to the response in each frequency band. Under these conditions, the vibrational response is fairly uniformly distributed over frequency and over the spatial extent of the SEA subsystems. Validation of an SEA model at high frequencies can be accomplished by comparing the predictions of average subsystem response with an average formed from measured data at a relatively small number of locations. At lower frequencies, where the modal overlap is not high, the vibrational response shows significant variability over both frequency and location. Large variability makes validation of the models more difficult. An accurate measurement of the average subsystem response requires that data be collected at a large number of locations and over wide frequency bands. The introduction of “modal power” as a basis of comparison helps to reduce the response variability and thereby allows SEA models to be validated…
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Brake Squeal DOE Using Nonlinear Transient Analysis

CAE Tech., Inc.-Sanjay Mahajan
Ford Motor Company-Yu-Kan Hu, Kevin Zhang
Published 1999-05-18 by SAE International in United States
To reduce warranty cost due to brake squeal and provide guidance for brake design, it is important to understand the contributions of key brake design parameters to brake noise. In this paper, a new technique, which employs the nonlinear transient finite element method as well as Taguchi method, is proposed as a design tool for improving the quality of brake systems. This DOE technique has been implemented to a car program. The final results identified the major parameters associated with the brake noise and also led to an optimal design by selecting appropriate levels of those parameters.
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Vehicle Disc Brake Squeal Simulations and Experiences

CAE Tech., Inc.-Sanjay K. Mahajan
Ford Motor Co.-Yu-Kan Hu, Kevin Zhang
Published 1999-05-18 by SAE International in United States
Brake related warranty costs are a major concern to the automotive industry. Large part of these costs are due to noise, more particularly due to the brake squeal complaints. Computer-aided engineering solutions have attracted a lot of attention from the engineering and development community for more effective brake product development. Recently, three brake squeal analysis methods were implemented on disc type brakes in a vehicle program at Ford. This paper summarizes the results and documents the experience obtained during implementation in the vehicle CAE process.
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Gear Noise Rating Prediction Based on Objective Measurement

New Venture Gear-Steve Becker, Scott X. Yu
Published 1999-05-17 by SAE International in United States
No Abstract Available.
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Sound Transmission Analysis of Vehicle Door Sealing System

Ford Motor Company-Yuksel Gur, Kenneth N. Morman
Published 1999-05-17 by SAE International in United States
A finite element-based acoustic-structure interaction analysis tool has been developed to determine the noise transmission loss characteristics of door seal systems. This tool has been applied to determine the effects of the individual parameters, such as seal material density, seal constitutive model, separation distance between seal layers, external cavity shape, and seal prestress field, on noise transmission characteristics. Our findings indicate that the external and internal cavity shapes, seal material density, and deformed seal geometry are the key factors affecting the noise transmission through seal system. Increasing seal material density decreases the resonance frequencies and increases the overall sound transmission loss. Changing the separation distance between seal layers changes the sound transmission characteristics without changing the compression load deflection behavior of the seal system. Moving the resonant frequencies to desired frequency regions, we can reduce seal system contribution to the vehicle interior noise level. The nature of the resonance frequencies of this coupled system have also been determined. This analysis tool was applied to determine the noise transmission characteristics of a vehicle door seal system,…
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Intake/ Exhaust Noise Reduction with Rig Test Optimization – Case Studies

Industrial Technology Research Institute-Ming-Hung Lu, Ming Une Jen
Published 1999-05-17 by SAE International in United States
The study employed the rig test method for the intake/exhaust noise investigation by using shaker. This article describes two case studies including 1.2 liter minivan and a 250 c.c. motorcycle. For the minivan case, it was verified that along with the reduction of 5∼8 dB(A) of intake noise the interior noise was also improved using the rig test optimization result. For the motorcycle case, It was found that there was very good correlation of the exhaust noise measured among the engine dynamometer, road test and rig test after the temperature effect was compensated. Hence, the study chose the rig test as a development tool to get prompt NVH evaluation results on the different exhaust pipe lengths and keep the development time schedule. From the results, it is concluded that the simple and cheap rig test evaluation technique is vital and a very effective tool to achieve the vehicle NVH development goal.
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Package Tray Optimization Using Experimental and Analytical Techniques

Lear Corporation-Gordon Ebbitt
Published 1999-05-17 by SAE International in United States
The area in the neighborhood of the package tray can be a significant path for road noise and exhaust noise. Air extraction routes and loudspeakers add to the difficulty of effective system design. A variety of designs were prototyped and their transmission loss measured in a standard SAE J1400 sound transmission loss suite. The performance of the various designs was compared to an untrimmed piece of sheet metal with embedded air extraction holes. The addition of trim added from 1 dB to 14 dB to the transmission loss. Statistical energy analysis (SEA) models of a variety of package tray systems will also be shown. Both of these techniques can provide design guidance at an early stage of vehicle program development.
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