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Technical Paper

Study of the Noise Characteristics of Motorcycle Silencers

2001-03-05
2001-01-1209
This paper describes methodologies developed to reduce the noise radiated from silencers while keeping or improving engine performance; i.e. whilst minimising the pressure loss through the silencer. This work was successfully developed to help motorcycle designers to meet the current legal noise limitations with minimum detriment to engine performance. Innovative designs for reactive silencers have resulted, with improved acoustic and engine performance levels, compared with traditional systems. The methodology was developed using the boundary element method (BEM). This method is able to calculate the acoustic variables in the interior and exterior fluid of the silencer. Furthermore, it is possible to simulate the temperature gradient along the silencer. A further important characteristic of the method is the ability to simulate the proper boundary conditions at the outlet without the need of hand calculations or “guesses”.
Technical Paper

Transfer Path Analysis of Structure-Borne Shock Absorber Noise in a Passenger Car

2001-04-30
2001-01-1441
This paper describes a method to separate structure-borne noise, which comes from the shock absorber, from the measured vehicle interior sound pressure. The transfer path analysis (TPA) was used. Shock absorber was considered as an input source while the sound pressure at the driver seat as its output. It was found that the sound pressure at the driver seat position and accelerations at the shock absorber mounting points are strongly correlated. Using one-third octave band analysis, the contribution of shock absorber structure-borne noise to the driver seat sound pressure was analyzed. Also the relationship between the measured acceleration and sound pressure was studied.
Technical Paper

Application of Mathematical Models to Detect and Diagnose Reciprocating Compressor Valve Leakage

2001-05-14
2001-01-1724
This report presents results from the model simulation of the pressure, vibration, and current signatures as derived in the accompanying publication [1] and compares the simulated data with measured data from an actual laboratory motor-compressor system. The simulations from the models were used to determine the information content of the sensor signals, compare the various diagnostic techniques and develop a multisensor approach based on the integration of these techniques to detect and diagnose reciprocating compressor valve leakage.
Technical Paper

A Comparison of the Hydraulic Performance of Ethylene Glycol and Propylene Glycol Aqueous Solutions as Automotive Coolants

2001-05-14
2001-01-1730
1.0 The present paper presents a theoretical study that enables making a comparison of the performance of the hydraulic performance of ethylene glycol and propylene glycol based aqueous coolants. The analysis establishes equations for calculating and comparing the pressure drop encountered in the flow of coolants in the laminar, transitional and turbulent flow regimes. The study covers a wide range of temperatures.
Technical Paper

Effects of Vehicle Windshield Defrosting and Demisting Process on Passenger Comfort

2001-05-15
2001-01-1729
This paper describes an investigation into the fluid flow and heat transfer on the windshield as well the effect of the air discharge from the defroster vents on passenger comfort. The investigation is both experimental and computational. Full-scale tests are conducted on a current vehicle model using non-intrusive diagnostic methods. The results presented are from numerical simulations validated by experimental measurements. The numerical predictions compare well with the experimental measurements. The locations of maximum velocity and pressure, as well as width and length of re-circulation regions, are correctly predicted.
Technical Paper

Determining Source Fluidborne Noise Characteristics of Automotive Fluid Power Pumps

2001-04-30
2001-01-1612
A new method, the “3 Pressures/ 2 Systems” method, is developed for determining source flow ripple and internal impedance of fluid power pumps. The method integrates exclusively an on-line measurement technique for the speed of sound in the fluid and a technique for eliminating flow disturbance effect on pressure sensors into the basic principle used in the existing “2 Pressures / 2 Systems” method. The new method has an inherent potential to yield results with higher accuracy and higher confidence. The high accuracy of the method is confirmed by the comparison of measured and predicted pressure ripple in a pump-pipe-valve system. Then, the method is applied to automotive fluid power pumps - power steering pumps. The measured results of source flow ripple and internal impedance are presented.
Technical Paper

Active Boom Noise Damping of Dodge Durango

2001-04-30
2001-01-1614
Two active boom noise damping techniques using a Helmholtz resonator-based compensator and a lead compensator called a positive pressure feedback have been developed at the University of Dayton [1]. The two damping techniques are of feedback type and their compensators can be implemented in software or hardware (using inexpensive operational amplifiers). The active damping system would rely on a speaker, a low-cost microphone, two accelerometers, and an electronic circuit (or a micro-controller) to add damping to the offending low-frequency vibroacoustic modes of the cavity. The simplicity of the active boom noise damping system lends itself to be incorporated into a vehicle's sound system. The Helmholtz resonator-based strategy is implemented on a Dodge Durango sport utility vehicle. The control scheme adds appreciable amount of damping to the first cavity mode and the first structurally induced acoustic mode of the cabin.
Technical Paper

Noise Source Identification in a Cab Interior

2001-04-30
2001-01-1630
Nearfield Acoustical Holography (NAH) has traditionally been utilized in the identification of noise sources on separable geometry of the wave equation. Recent advances have utilized the Boundary Element Method (BEM) to extend the source identification to noise sources with arbitrary geometry. However, this generalized NAH leads to the solution of a discrete ill-posed problem that requires solution through Singular Value Decomposition (SVD) in conjunction with numerical regularization. Robust numerical regularization schemes have recently been implemented in commercial software COMET/Acoustics® [1, 2] so as to fully automate the noise source identification procedure, and render it applicable to complex, practical problems. An application involving noise source identification on the interior of an earthmoving equipment cab is presented to demonstrate the capability of generalized NAH. The NAH reconstructed velocities on the surface of the cab are compared with the input velocities.
Technical Paper

A Method to Determine the Power Input Associated with Rain Excitation for SEA Models

2001-04-30
2001-01-1625
Statistical Energy Analysis is used to predict the sound pressure level (SPL) in the interior of the vehicle. This is accomplished by knowing the energy sources (tire, engine, wind, etc) affecting the interior as well as the acoustic performance (absorption and transmission loss) of the interior trim components (headliner, door panels, instrument panel, etc). One of the noise sources that has not been seriously examined to-date is panel excitation by precipitation. The excitation of the roof due to raindrops can be a major noise source. Knowing how to properly model this power input would help analyze different headliners or roof treatments to minimize the SPL in the interior cavity. This will involve computational determination of mass, speed, and energy of standard water droplets for one of rain condition. A power spectrum is presented for one rain intensity condition on a test fixture.
Technical Paper

Sound Through Partial Enclosures with Louvers

2001-04-30
2001-01-1525
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.
Technical Paper

Development of an Air Intake System Using Vibro-Acoustics Numerical Modeling

2001-04-30
2001-01-1519
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.
Technical Paper

Numerical Modeling of Engine Noise Radiation through the use of Acoustic Transfer Vectors - A Case Study

2001-04-30
2001-01-1514
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.
Technical Paper

Combining Vehicle and Test-Bed Diagnosis Information to Guide Vehicle Development for Pass-By Noise

2001-04-30
2001-01-1565
Typically pass-by noise evaluation is performed very late in the vehicle development cycle and any changes or modifications are costly, making an exterior modeling procedure compatible with both test and math-based techniques desirable. This paper demonstrates how the Airborne Source Quantification (ASQ) technique can be applied to modeling vehicle exterior noise. The results of this study also show that the source strength of individual sub-systems, i.e. the engine or transmission, can be determined independently from the full vehicle using a sub-system dynamometer. Results are correlated by assessing source strength and overall pass-by sound pressure level.
Technical Paper

Effect of Seating Foam on the Acoustic Behavior of an Earth-Moving Cab

2001-04-30
2001-01-1560
The designs of vehicle seats have significant impact on interior acoustic modes as well as sound pressure level inside the vehicles. Seats trimmed with elastic porous materials are especially critical to the acoustic behavior of the vehicles due to the sound absorption of the materials. This paper demonstrates how seating materials affect the acoustic performance of an earh-moving cab. To accurarely simulate the sound absorption of the seat, the seat was modeled as a bulk reactive absorber instead of a local reactive absorber.
Technical Paper

Development and Validation of a Computational Process for Pass-By Noise Simulation

2001-04-30
2001-01-1561
The Indirect Boundary Element Analysis is employed for developing a computational pass-by noise simulation capability. An inverse analysis algorithm is developed in order to generate the definition of the main noise sources in the numerical model. The individual source models are combined for developing a system model for pass-by noise simulation. The developed numerical techniques are validated through comparison between numerical results and test data for component level and system level analyses. Specifically, the source definition capability is validated by comparing the actual and the computationally reconstructed acoustic field for an engine intake manifold. The overall pass-by noise simulation capability is validated by computing the maximum overall sound pressure level for a vehicle under two separate driving conditions.
Technical Paper

Sound Quality Equivalent Modeling for Virtual Car Sound Synthesis

2001-04-30
2001-01-1540
The pressure on development cycles in the automotive industry forces the acoustical engineers to create awareness of sound quality in the early stages of development, perhaps even before a physical prototype is available. Currently, designers have few tools to help them listen to their “virtual” models. For the design of a synthesis platform of in-vehicle binaural sound, the sound should be modeled with almost identical sound quality perception. A concept is presented where the total sound of a vehicle is split in a number of components, each with its own sound characteristics. These characteristics are described in a signal model that allows the analysis of an existing sound into a limited number of signal components: orders-frequency spectra, time envelopes and time recordings.
Technical Paper

Determination of the noise contributions of engine surfaces

2001-04-30
2001-01-1482
One of the key elements in efforts to minimize the noise emmissionis of engines and other machinery is the knowledge of the main noise radiating surfaces and the relation between measurable surface vibration and the sound pressure. Under the name of Airborne Source Quantification (ASQ), various techniques have been developed to discretize and quantify the source strength, and noise contributions, of vibrating surface patches of machinery or vehicle components. The noise contributions of patches to the sound pressure at specific locations in the sound field or to the total radiated sound power are identified. The source strength of equivalent point sources, the acoustic transfer from the source surface to critical sound field locations and finally the sound pressure contributions of the individual patches are quantified. These techniques are not unique to engine application, but very relevant for engine development. An example is shown for an engine under artificial excitation.
Technical Paper

Automatic Detection of Buzz, Squeak and Rattle Events

2001-04-30
2001-01-1479
In the world of BSR (Buzz, Squeak and Rattle) testing, there is a high level of sophistication regarding the test machines employed to excite the items under test as well as the techniques used to ensure that the test is representative of real-life operating conditions. However, the object of the measurements, i.e., the identification of transient acoustic events classified as Buzz, Squeak or Rattle, is mostly a subjective procedure with classification in terms of Sound Pressure Level in dB(A) or Stationary Loudness. These “standard” metrics have proven, in general, unreliable in assessing the importance of individual transient events, and inappropriate to describe the vehicle signature from a BSR standpoint.
Technical Paper

Engine Cooling System Stability

2001-05-14
2001-01-1741
Engine cooling systems contain multiple parallel flow paths, which under sub-cooled boiling conditions can experience excursive flow instability. This study presents an analytical model describing the pressure drop in a channel subjected to flow boiling. Using water as the working fluid, results are presented showing the effect of inlet velocity and surface heat flux on the overall pressure drop. The accuracy of this model for water has been verified. The calculations show that for typical engine operating conditions, the cooling passage can contain regions of partially developed and fully developed sub-cooled boiling.
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