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Technical Paper

System Component Coupling for Structure Borne Noise Isolation Studies

1997-05-01
971460
Control of structure borne noise transmission into an aircraft cabin generated from component excitation, such as rotor/engine vibration imbalance or firing excitations or from auxiliary equipment induced vibrations, can be studied empirically via impedance characterization of the system components and application of appropriate component coupling procedures. The present study was aimed at demonstrating the usefulness of such impedance modeling techniques as applied to a Bell 206B rotorcraft and a Cessna TR182 general aviation aircraft. Simulated rotor/engine excitations were applied to the assembled aircraft systems to provide baseline structure borne noise transmission data. Thereafter, impedance tests of the system components were carried out to provide a data base from which system component coupling studies were carried out.
Technical Paper

Electromagnetic Compatibility in the Off-Highway Vehicle Part III: Electromagnetic Emissions (EME)

1992-09-01
921654
Electromagnetic emissions (EME) from vehicles and their effect on broadcast radio and television were studied as early as 1944. Their original effect was significantly reduced by the early 1960s. Today, ignition noise (broadband) and vehicular micro-processor-controlled system noise (narrowband) are interfering with Land Mobile (two-way) communication services and other devices such as computers. Two SAE test methods, J551 and J1816, are used to measure this EME. Under development are methods to measure conducted EME on vehicle signal wiring and power input leads. This paper discusses EME measurement methods, provides insight into the sources of EME problems, and gives information on the test instrumentation used to make these measurements. This paper is the third in a series of papers on electromagnetic compatibility (EMC) in the off-highway vehicle. The first paper was an overview of a complete EMC program with discussion of several important segments.
Technical Paper

Noise Reduction Techniques as They Apply to Engine-Generator Design and Treatment

1969-02-01
690755
Small engines may require soundproofing to eliminate one or more of the following effects: hearing loss, speech interference, community annoyance, detectability, and psychological disorientation. Detectability criteria are frequently associated with military applications and may require the use of a soundproof enclosure in addition to other engine treatments. Acoustical noise sources are conveniently classed as either aerodynamic or mechanical. Aerodynamic sources are predominant on small engines. Treatment of exhaust noise by individual components, e.g., muffler, is inadequate; a system approach, through the use of an electro-acoustic analog computer, has proved to be a much more satisfactory procedure.
Technical Paper

A Bench Test Facility for Engine Muffler Evaluation

1963-01-01
630283
The problem associated with laboratory evaluation of muffler acoustical characteristics are complicated both by the acoustical considerations involved in obtaining an adequate noise source and by the ambiguities involved in defining what constitutes quality in a muffler built for general application. In order to quantitatively define the characteristics of quality mufflers, an extensive series of field tests were conducted on a variety of sizes and types of mufflers in conjunction with four engine configurations. Work then turned to the development of a wide band siren noise source and acoustical test system which would simulate the high impedance character of an engine exhaust noise source, and in addition generate the necessary intensity and spectral characteristics required to obtain test data over the range of noise conditions encountered in the field.
Technical Paper

Advanced Nondestructive Testing Methods for Bearing Inspection

1972-02-01
720172
The principles of the magnetic-perturbation method of flaw detection and the Barkhausen noise residual stress measurement method are briefly reviewed. It is suggested that they provide very powerful tools for assuring improved ball bearing performance. The methods are applied for the evaluation of ball bearing races. Typical experimental results are presented along with metallurgical sectioning correlation.
Technical Paper

A Multi-Variable Experimental Study of Diesel Geartrain Rattle

2011-05-17
2011-01-1561
Geartrain noise can be a significant contribution to the overall sound level of diesel engines. Some engine manufacturers employ isolation solutions such as sound deadening covers and foam panels to combat the problem, but these add cost. Little has been published on geartrain noise reduction, and public standards for diesel geartrain design and development are not available. This paper describes an experimental study of the relative influence of gear design parameters on the rattle noise of a diesel engine timing geartrain. The geartrains of several diesel engines were benchmarked to determine the noise reduction strategies employed. A total of three gear sets were designed and tested in a 3.3L four cylinder normally aspirated diesel engine. The experimentation quantified the influence of an anti backlash idler gear in reducing gear rattle noise, and revealed that a key path for gear rattle noise transmission is through an idler gear journal bearing shaft.
Technical Paper

Noise Benchmarking of the Detroit Diesel DD15 Engine

2011-05-17
2011-01-1566
Several new or significantly upgraded heavy duty truck engines are being introduced in the North American market. One important aspect of these new or revised engines is their noise characteristics. This paper describes the noise related characteristics of the new DD15 engine, and compares them to other competitive heavy truck engines. DD15 engine features relevant to noise include a rear gear train, isolated oil pan and valve cover, and an amplified high pressure common rail fuel system. The transition between non-amplified and amplified common rail operation is shown to have a significant noise impact, not unlike the transition between pilot injection and single shot injection in some other engines.
Technical Paper

Diesel Combustion Mode Switching - A Substantial NVH Challenge

2009-05-19
2009-01-2080
Tier 2, bin 5 diesel engines may use multiple combustion modes to achieve stringent emissions requirements. Unfortunately, switching between different combustion modes can cause step changes in noise that will be unacceptable to consumers. In this paper, several sound quality metrics are evaluated for their ability to quantify the NVH issues that arise during a rich pulse event. In addition, techniques are presented that allow an engine developer to reduce the NVH effects caused by changing combustion modes. Careful calibration tuning in close cooperation with performance and emissions development engineers is required to solve noise problems that arise from combustion mode switching events, since an NVH improvement may often come at the expense of a performance or emissions issue.
Technical Paper

Calibrating and Protecting Microphones to Allow Acoustic Measurements in Hazardous Environments

2009-05-19
2009-01-2163
Performing acoustic measurements on or near engines, transmissions, as well as in other circumstances where the environment is hazardous and harsh for microphones requires special precautions. Fluids inevitably leak, and the possibility of transducer damage can be very high without proper protection. Properly protecting microphones during testing allows for consistent data quality in these hazardous and difficult environments. While this paper will present the use of a 5 mil Nitrile cover which protects against many fluids within the scope of automotive testing, including water, hydrocarbons, and alcohols, as well as having good heat resistance and high strength, the concepts developed are applicable to other types of microphone protective mechanisms. Acoustic sensitivity was measured and used to calculate the change of the microphone's response after the treatment is applied, as well as after being exposed to various contaminants.
Technical Paper

Sound Quality Jury Analysis versus Sound Pressure Measurement in Snowmobiles

2009-05-19
2009-01-2231
Restrictions on noise and gaseous emissions of snowmobiles have been a topic of much attention for the past decade. Concerns with snowmobiles in our national parks and with private land owners have resulted in new park legislations as well as legal disputes regarding recreational vehicle rights-of-way. The most widely used standard for snowmobile testing is SAE J192 Exterior Sound Level for Snowmobiles, SAE Recommended Practice. This is a wide-open throttle test with sound level meters 50 feet on either side of the snowmobile. The sound pressure cannot exceed a certain level for the snowmobile to pass. Perceived noise also plays an important role in the objections to snowmobiles. This paper considers the role of Sound Quality methods, specifically Jury Analysis, in understanding the difference between objective noise analysis and subjective noise preferences; also considering the underlying snowmobile attributes that control snowmobile noise.
Technical Paper

Determination of Source Contribution in Snowmobile Pass-by Noise Testing

2009-05-19
2009-01-2228
As noise concerns for snowmobiles become of greater interest for governing bodies, standards such as SAE J192 are implemented for regulation. Specific to this pass-by noise standard, and unlike many other pass-by tests, multiple non-standardized test surfaces are allowed to be used. Manufacturers must understand how the machines behave during these tests to know how to best improve the measured noise levels. Data is presented that identifies the contributions of different sources for different snowmobiles on various test surface conditions. Adaptive resampling for Doppler removal, frequency response functions and order tracking methods are implemented in order to best understand what components affect the overall measurement during the pass-by noise test.
Technical Paper

Modeling Interior Noise in Off-Highway Trucks using Statistical Energy Analysis

2009-05-19
2009-01-2239
The objective of this project was to model and study the interior noise in an Off-Highway Truck cab using Statistical Energy Analysis (SEA). The analysis was performed using two different modeling techniques. In the first method, the structural members of the cab were modeled along with the panels and the interior cavity. In the second method, the structural members were not modeled and only the acoustic cavity and panels were modeled. Comparison was done between the model with structural members and without structural members to evaluate the necessity of modeling the structure. Correlation between model prediction of interior sound pressure and test data was performed for eight different load conditions. Power contribution analysis was performed to find dominant paths and 1/3rd octave band frequencies.
Technical Paper

Sound Power Measurement in a Semi-Reverberant, Volume Deficient Chamber

2015-06-15
2015-01-2359
Sound power can be determined using a variety of methods, but precision methods require the volume of the noise source to be less than 1% of the chamber volume leading to relatively large test chambers. Automotive torque converter performance and noise testing is completed in an enclosed metallic test fixture which inhibits the use of precision methods due to volume and space limitations. This paper describes a new method developed to accurately determine sound power of an automotive torque converter in a relatively small enclosure through characterization of the test environment. The test environment was characterized using two reference noise sources designed to represent torque converter noise output and physical geometry. Sound pressure levels of the sources were measured at multiple microphone locations and at three source amplitude levels to characterize the environment.
Technical Paper

Continued Drive Signal Development for the Carbon Nanotube Thermoacoustic Loudspeaker Using Techniques Derived from the Hearing Aid Industry

2017-06-05
2017-01-1895
Compared to moving coil loudspeakers, carbon nanotube (CNT) loudspeakers are extremely lightweight and are capable of creating sound over a broad frequency range (1 Hz to 100 kHz). The thermoacoustic effect that allows for this non-vibrating sound source is naturally inefficient and nonlinear. Signal processing techniques are one option that may help counteract these concerns. Previous studies have evaluated a hybrid efficiency metric, the ratio of the sound pressure level at a single point to the input electrical power. True efficiency is the ratio of output acoustic power to the input electrical power. True efficiency data are presented for two new drive signal processing techniques borrowed from the hearing aid industry. Spectral envelope decimation of an AC signal operates in the frequency domain (FCAC) and dynamic linear frequency compression of an AC signal operates in the time domain (TCAC). Each type of processing affects the true efficiency differently.
Technical Paper

Torsional Vibration Analysis of Six Speed MT Transmission and Driveline from Road to Lab

2017-06-05
2017-01-1845
When a manual transmission (MT) powertrain is subjected to high speeds and high torques, the vehicle driveshaft, and other components experience an increase in stored potential energy. When the engine and driveshaft are decoupled during an up or down shift, the potential energy is released causing clunk during the shift event. The customer desires a smooth shift thus reduction of clunk will improve experience and satisfaction. In this study, a six-speed MT, rear-wheel-drive (RWD) passenger vehicle was used to experimentally capture acoustic and vibration data during the clunk event. To replicate the in-situ results, additional data was collected and analyzed for powertrain component roll and pitch. A lumped parameter model of key powertrain components was created to replicate the clunk event and correlate with test data. The lumped parameter model was used to modify clutch tip-out parameters, which resulted in reduced prop shaft oscillations.
Technical Paper

Evaluation of Off-Highway Vehicle Cab Noise and Vibration Using Inverse Matrix Techniques

1999-09-14
1999-01-2815
Noise Path Analysis techniques (NPA) have been developed and refined by the automotive industry for structure-borne noise and vibration evaluation of their products. Off-highway vehicles, particularly those with enclosed cabs, are excellent candidates for the application of these techniques. Like automobiles, many off-highway machines are typically driven by a rotating power source, have a well-defined acoustic receiver space, and use some form of isolation between source and receiver sub-systems. These structural characteristics make NPA a useful tool for identifying dominant sources and energy transfer paths. The objectives of this paper are to revisit the fundamental theory of matrix inversion as it applies to NPA techniques, and to address the common setup and measurement issues encountered when acquiring noise path data on off-highway machines. A general overview of the procedures involved in applying NPA to an off-highway machine will be presented.
Technical Paper

Summary and Characteristics of Rotating Machinery Digital Signal Processing Methods

1999-09-14
1999-01-2818
Several very different order tracking and analysis techniques for rotating equipment have been developed recently that are available in commercial noise and vibrations software packages. Each of these order tracking methods has distinct trade-offs for many common applications and very specific advantages for special applications in sound quality or noise and vibrations troubleshooting. The Kalman, Vold-Kalman, Computed Order Tracking, and the Time Variant Discrete Fourier Transform as well as common FFT based order analysis methods will all be presented. The strengths and weaknesses of each of the methods will be presented as well as the highlights of their mathematical properties. This paper is intended to be an overview of currently available technology with all methods presented in a common format that allows easy comparison of their properties. Several analytical examples will be presented to thoroughly document each methods' behavior with different types of data.
Technical Paper

Vibrational and Sound Radiation Properties of a Double Layered Diesel Engine Gear Cover

1999-05-17
1999-01-1773
The introduction of a thin fluid layer between two layers of sheet metal offers a highly effective and economical alternative to the use of constrained viscoelastic damping layers in sheet metal structures. A diesel engine gear cover, which is constructed of two sheet metal sections spot welded together, takes advantage of fluid layer damping to produce superior vibration and sound radiation performance. In this paper, the bending of a double layered plate coupled through a thin fluid layer is modeled using a traveling wave approach which results in a impedance function that can be used to assess the vibration and sound radiation performance of practical double layered plate structures. Guided by this model, the influence of fluid layer thickness and inside-to-outside sheet thickness is studied.
Technical Paper

Application of Indirect Force Estimation Techniques to the Automotive Transfer Case

1999-05-17
1999-01-1764
In the NVH design optimization of automotive structures, the spectral properties of dynamic forces transmitted from rotating machinery to its housing is of primary interest. This paper describes the application of an indirect dynamic force estimation technique, more commonly known as transfer path analysis, to an operational transfer case. Through the implementation of an inverse transfer matrix technique, dynamic forces transmitted to a transfer case housing are estimated at a discrete number of locations. This paper describes the experimental and analytical methodology employed for dynamic force estimation as well as statistical techniques for solution optimization. Good correlation is shown to exist between frequencies of known physical phenomena and estimated dynamic forces for a total of nine (9) operational variations of transfer case speed and torque.
Technical Paper

Interior Noise Source/Path Identification Technology

2000-05-09
2000-01-1709
Excessive interior noise and vibration in propeller driven general aviation aircraft can result in poor pilot communications with ground control personnel and passengers, and, during extended flights, can lead to pilot and passenger fatigue. Noise source/path identification technology applicable to single engine propeller driven aircraft were employed to identify interior noise sources originating from structure-borne engine/propeller vibration, airborne propeller transmission, airborne engine exhaust noise, and engine case radiation. The approach taken was first to conduct a Principal Value Analysis (PVA) of an in-flight noise and vibration database acquired on a single engine aircraft to obtain a correlated data set as viewed by a fixed set of cabin microphones.
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