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Technical Paper

Acoustic Test Facility Capabilities at Gulfstream Aerospace

2011-05-17
2011-01-1647
Gulfstream Aerospace Corporation (GAC) owns and operates an Acoustic Test Facility (ATF) in Savannah, GA. The ATF consists of a Reverberation Chamber, Hemi-Anechoic Chamber, and a Control Room. Types of testing conducted in the ATF include Transmission Loss, Sound Power, and Vibration testing. In addition to accommodating typical types of acoustic testing, the ATF has some unique capabilities. The ATF can be used to conduct testing at cold temperatures representative of up to 45,000 ft flight altitude, while simultaneously taking Transmission Loss measurements of the chilled test sample. Additionally, the ATF has the capability of conducting Transmission Loss testing of a full mockup of the aircraft sidewall, including a section of fuselage, all the thermal/acoustic materials up to and including the interior decorative panel. A sound source capable of very high amplitudes at high frequencies is required to obtain good measurements from testing multiple wall systems such as this.
Technical Paper

Spirit AeroSystems Acoustics Lab: Measurement and Analysis Capabilities

2011-05-17
2011-01-1643
Previously part of a larger OEM, Spirit AeroSystems became a standalone company 5 years ago and is currently a Tier One supplier of aerostructures. Products include fuselage components, wing structures, engine struts and nacelles, and at the request of various OEMs, fully stuffed fuselages and podded engines where all of the wiring, heating, duct work, etc. is installed prior to delivery. While operating as part of the Propulsion Structures and Systems Business Unit, the design, testing and analysis services provided by the acoustics lab potentially impact all programs at all stages of development because of increasing noise regulations and material certification requirements for implementation in high noise environments.
Technical Paper

Design of a Quiet Inlet for a 6×6 Boundary Layer Flow Duct

2011-05-17
2011-01-1617
The turbulent boundary layer (TBL) that forms on the outer skin of the aircraft in flight is a significant source of interior noise. However, the existing quiet test facilities capable of measuring the TBL wall pressure fluctuations tend to be at low Mach numbers. The objective of this study was to develop a new inlet for an existing six inch square (or 6×6) flow duct that would be adequately free from facility noise to study the TBL wall pressure fluctuations at higher, subsonic Mach numbers. First, the existing flow duct setup was used to measure the TBL wall pressure fluctuations. Then the modified inlet was successfully used to make similar measurements up to Mach number of 0.6. These measurements will be used in the future to validate wall pressure spectrum models for interior noise analysis programs such as statistical energy analysis (SEA) and dynamic energy analysis (DEA).
Technical Paper

Design/Testing of Vibration Isolators for Reaction Wheel of Satellite based on Transmission Force Characterization

2011-05-17
2011-01-1605
Reaction wheels are used to control the attitude of a satellite in space in an almost static manner. Excitation forces at high frequencies as well, however, due to unbalance or bearing faults, can be transmitted to the satellite structure and work badly against missions of the satellite. Hence, counteractions such as vibration isolators are often employed in practice. In this paper, procedures are presented to design and test rubber vibration isolators based on characteristics of the transmission forces without isolators obtained from a previous study. First, a system consisting of reaction wheel, bearing, rigid cover and isolators was modeled with 11 degrees of freedom. Second, stiffness and damping of the isolators were designed such that the forces transmitted onto the satellite structure might satisfy given criteria. Finally, an actual isolation system fabricated using a rubber was tested to check the transmission forces.
Journal Article

Direct Aeroacoustic Simulation of Flow Impingement Noise in an Exhaust Opening

2011-05-17
2011-01-1517
Unusual noises during vehicle acceleration often reflect poorly on customer perception of product quality and must be removed in the product development process. Flow simulation can be a valuable tool in identifying root causes of exhaust noises created due to tailpipe openings surrounded by fascia structure. This paper describes a case study where an unsteady Computational Fluid Dynamics (CFD) simulation of the combined flow and acoustic radiation from an exhaust opening through fascia components provided valuable insight into the cause of an annoying flow noise. Simulation results from a coupled thermal/acoustic analysis of detailed tailpipe opening geometry were first validated with off-axis microphone spectra under wide open throttle acceleration. After studying the visualizations of unsteady flow velocity and pressure from the CFD, a problem that had proved difficult to solve by traditional “cut and try” methods was corrected rapidly.
Technical Paper

Improving SEA Predictions with Experimental Data

2011-05-17
2011-01-1701
Statistical Energy Analysis (SEA) has been used widely by industry and academia for more than 20 years to predict the mid-to-high frequency range behavior of complex acoustic systems. At Gulfstream Aerospace Corporation (GAC), SEA models have been developed to predict the interior cabin noise levels of completed Gulfstream aircraft. These models are also used for acoustic evaluations of design changes prior to implementation as well as a diagnostic tool for investigating noise and vibration issues. Throughout the development of the SEA models, extensive experimental testing in GAC's Acoustic Test Facility (ATF) was conducted on numerous aircraft components represented in the models. This paper demonstrates the importance of using experimental data to improve the accuracy of the SEA predictions by accurately adjusting the material properties and acoustic parameters of the SEA model to better match the ATF experimental data.
Technical Paper

Design of Rotorcraft Gearbox Foundation for Reduced Vibration and Increased Crashworthiness Characteristics

2011-05-17
2011-01-1704
Vehicle design is a complex process requiring interactions and exchange of information among multiple disciplines such as fatigue, strength, noise, safety, etc. Simulation models are employed for assessing and potentially improving a vehicle's performance in individual technical areas. Challenges arise when designing a vehicle for improving mutually competing objectives, satisfying constraints from multiple engineering disciplines, and determining a single set of values for the vehicle's characteristics. It is of interest to engage simulation models from the various engineering disciplines in an organized and coordinated manner for determining a design configuration that provides the best possible performance in all disciplines. The multi-discipline design process becomes streamlined when the simulation methods integrate well with finite element or computer aided design models.
Technical Paper

De-NOx Characteristics of a Combined System of LNT and SCR according to Space Velocity

2011-08-30
2011-01-2088
The purpose of this paper is to investigate the adsorption and desorption characteristics of only LNT and SCR catalysts with respect to SV (Space Velocity) and the de-NOx performance of a combined system of LNT and SCR according to the SV. The adsorption time to reach NOx concentration of 500 ppm at SV = 14,000 1/h of the LNT catalyst was about 1,000 sec. The physically and chemically absorbed NH₃ on the SCR catalyst desorbed in same concentration though various SVs. The NOx conversion of the LNT decreased with SV increased in range of 350° or lower temperature, the formation quantity of NH₃ increased as SV increased in the lower temperature range. The NOx conversion of the SCR with SV = 14,000 1/h showed 95% at 320°, the effect of SV on the NOx conversion was not so much. The NOx conversion of the combined system of LNT and SCR with fresh catalysts appeared maximum value of 70% and hydrothermal aging at 900° decreased about to 25% below range of 300°.
Technical Paper

An Ultimate Engine: designed by Computational Fluid Dynamics

2011-08-30
2011-01-2027
A single lightweight engine capable of operating over a wide range of Mach numbers from startup to the hypersonic regime is proposed for automobiles and airplanes. Traditional piston engines, turbojet engines, and scram jet engines operate only under a narrower range of conditions. A compression system of colliding super multijets is proposed instead of a traditional turbofan. This ultimate engine system can be extended with a special piston system to achieve an improved fuel consumption rate, while maintaining a low noise level.
Technical Paper

Locating Multiple Incoherent Sound Sources in 3D Space in Real Time

2011-05-17
2011-01-1667
A model based approach is developed to track and trace multiple incoherent sound sources in 3D space in real time. This technology is capable of handling continuous, random, transient, impulsive, narrowband and broadband sounds over a wide frequency range (20 to 20,000 Hz). The premise of this technology is that the sound field is generated by point sources located in a free field. To locate these sound sources, iterative triangulations are used based on the signals measured by a microphone array. These signals are preprocessed through de-noising techniques to enhance signal to noise ratios (SNR). Unlike the conventional beamforming, the present technology enables one to pinpoint the exact locations of multiple incoherent sound sources simultaneously by using the Cartesian coordinates, including sources behind measurement microphones. In other words, the microphone array need not face a test object, which is required in the beamforming.
Journal Article

Energy Finite Element Analysis Developments for Vibration Analysis of Composite Aircraft Structures

2011-05-17
2011-01-1734
The Energy Finite Element Analysis (EFEA) has been utilized successfully for modeling complex structural-acoustic systems with isotropic structural material properties. In this paper, a formulation for modeling structures made out of composite materials is presented. An approach based on spectral finite element analysis is utilized first for developing the equivalent material properties for the composite material. These equivalent properties are employed in the EFEA governing differential equations for representing the composite materials and deriving the element level matrices. The power transmission characteristics at connections between members made out of non-isotropic composite material are considered for deriving suitable power transmission coefficients at junctions of interconnected members. These coefficients are utilized for computing the joint matrix that is needed to assemble the global system of EFEA equations.
Technical Paper

Development of a Large-Scale Microphone Array for Aircraft Jet Plume Noise Source Characterization

2011-05-17
2011-01-1733
Military jet aircraft expose both ground maintenance personnel and the community to high levels of noise. The U.S. Department of Defense is funding research to develop advanced modeling tools for noise reduction techniques and community noise exposure. A large-scale microphone array for portable near-field acoustic holography (NAH) and data acquisition system was created for this purpose. The system was designed for measuring high-amplitude jet noise from current and next-generation military aircraft to provide model refinement and benchmarking, evaluate performance of noise control devices, and predict ground maintenance personnel and community noise exposure. The acoustical instrumentation system was designed to be easy to use with scalable data processing as the primary focus. The data acquisition system allowed up to 152 channels simultaneously sampled at a rate of 96 kHz.
Journal Article

Fuzzy Boundary Element Method with Uncertain Shear Modulus in Linear Plane Strain Elasticity

2011-04-12
2011-01-0729
Engineering systems are often too complex and their behavior cannot be determined using closed form or exact methods. To circumvent this problem, numerical methods, such as boundary element method, have been formulated to obtain approximate solutions to partial differential equations, which describe the behavior of the physical engineering systems. However, the inherent uncertainty in constitutive formulation causes uncertainties in the solutions obtained by numerical methods and undermines their validity. Conventional analysis does not account for material uncertainty, which is, however, accounted for in the design phase. This paper addresses the impact of uncertain shear modulus for plane strain linear elasticity problems on the numerical solutions obtained using boundary element method. The uncertainty is modeled using fuzzy approach.
Journal Article

An Improved Finite Element-Based Model for Reliability Assessment of a Profile-Type Automotive Body Experiencing Uncertain Loading Conditions and Material Properties

2011-04-12
2011-01-0731
Beam-type structural elements are generally utilized in construction of majority of the automotive structures, e.g. the buses, trailers, and solid axles. These components are usually subjected to spatially-random or uncertain load conditions during their service lives. Moreover, material properties of the beams-type structural elements may vary from a sample to another in a random manner. The situation will be more complex when both material properties and load conditions exhibit random natures in the spatial domain. In the present paper, an algorithm is presented to assess the probabilistic behavior of the beam-type vehicle's components in relation with the strength and deflection requirements. A consistent finite element reliability model that may be employed for beams with arbitrary inclinations under simultaneous spatially-random loading conditions and random material properties is introduced.
Technical Paper

Interval Optimization of Uncertain Suspension Kinematics Characteristics

2011-04-12
2011-01-0730
The optimization of vehicle suspension kinematics characteristics is an important part in the chassis development. The current optimization algorithms for suspension kinematics parameters are certain optimization method. But vehicles to manufacture in large quantities are uncertainty in the structural parameters. Therefore, suspension kinematics characteristics are all uncertain parameters on vehicles. The paper explored an interval method to describe the uncertainty suspension kinematics characteristics and used improved interval Newton iteration method to optimize it. As we all know, some suspension kinematics characteristics are the curves. When the structural parameters are uncertain variables, these curves are uncertain variables curves.
Journal Article

A Simulation and Optimization Methodology for Reliability of Vehicle Fleets

2011-04-12
2011-01-0725
Understanding reliability is critical in design, maintenance and durability analysis of engineering systems. A reliability simulation methodology is presented in this paper for vehicle fleets using limited data. The method can be used to estimate the reliability of non-repairable as well as repairable systems. It can optimally allocate, based on a target system reliability, individual component reliabilities using a multi-objective optimization algorithm. The algorithm establishes a Pareto front that can be used for optimal tradeoff between reliability and the associated cost. The method uses Monte Carlo simulation to estimate the system failure rate and reliability as a function of time. The probability density functions (PDF) of the time between failures for all components of the system are estimated using either limited data or a user-supplied MTBF (mean time between failures) and its coefficient of variation.
Journal Article

Reliability Prediction for the HMMWV Suspension System

2011-04-12
2011-01-0726
This research paper addresses the ground vehicle reliability prediction process based on a new integrated reliability prediction framework. The integrated stochastic framework combines the computational physics-based predictions with experimental testing information for assessing vehicle reliability. The integrated reliability prediction approach incorporates the following computational steps: i) simulation of stochastic operational environment, ii) vehicle multi-body dynamics analysis, iii) stress prediction in subsystems and components, iv) stochastic progressive damage analysis, and v) component life prediction, including the effects of maintenance and, finally, iv) reliability prediction at component and system level. To solve efficiently and accurately the challenges coming from large-size computational mechanics models and high-dimensional stochastic spaces, a HPC simulation-based approach to the reliability problem was implemented.
Technical Paper

Multi-Criteria Decision Analysis of Heuristically Designed Light-Duty Vehicles Today and in 2035

2011-04-12
2011-01-0727
Evaluating options for reducing the environmental impact of light duty vehicles is complicated by the number of technologies being actively researched. In this work, various alternative transportation fuels such as ethanol, biodiesel, hydrogen, and electricity as well as advanced materials and drive-train concepts are analyzed for their environmental benefits compared to conventional diesel and gasoline vehicles. To objectively evaluate the impact of technology and fuel options on various stakeholder criteria under uncertainty (e.g. fuel and technology costs), it is necessary to consider how the technology may be applied to a broad set of vehicle designs. The heuristic vehicle design method uses rules from first principles and engineering practice to ensure vehicles in the design set (virtual fleet) are composed of self-consistent technology options.
Journal Article

Time-Dependent Reliability of Random Dynamic Systems Using Time-Series Modeling and Importance Sampling

2011-04-12
2011-01-0728
Reliability is an important engineering requirement for consistently delivering acceptable product performance through time. As time progresses, the product may fail due to time-dependent operating conditions and material properties, component degradation, etc. The reliability degradation with time may increase the lifecycle cost due to potential warranty costs, repairs and loss of market share. Reliability is the probability that the system will perform its intended function successfully for a specified time interval. In this work, we consider the first-passage reliability which accounts for the first time failure of non-repairable systems. Methods are available in the literature, which provide an upper bound to the true reliability which may overestimate the true value considerably. Monte-Carlo simulations are accurate but computationally expensive.
Journal Article

Next Generation Engine Start/Stop Systems: “Free-Wheeling”

2011-04-12
2011-01-0712
Engine Start/Stop systems reduce CO₂ emissions by turning off the combustion engine at vehicle standstill. This avoids the injection of fuel that would otherwise be needed simply to overcome internal combustion engine losses. As a next development step, engine losses at higher vehicle speeds are to be addressed. During deceleration, state-of-the-art engine technology turns off fuel injection as soon as the driver releases the gas pedal, thus the combustion engine is motored by the vehicle. The engine's drag torque could be desired by the driver, e.g., as a brake assist during downhill driving. However, quite frequently the driver wishes to coast at almost constant speed. Similar to Start/Stop operation, in such situations fuel is injected to simply overcome the combustion engine's drag torque. An operation mode referred to as "Free-Wheeling" reduces CO₂ emissions under such coasting conditions by disconnecting the combustion engine from the powertrain and by turning it off.
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