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SAE International Journal of Passenger Cars Mechanical Systems
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The Effects of Porosity and Inclination on the Pressure Drop across Porous Screens and Honeycombs Used for Heat Exchanger Simulations in Wind Tunnel Studies

SAE International Journal of Passenger Cars - Mechanical Systems

Cranfield University-Klementina Gerova, Stefan Velikov, Kevin P. Garry
  • Journal Article
  • 2012-01-2340
Published 2013-07-15 by SAE International in United States
The simulation of heat exchanger air flow characteristics in a sub-scale wind tunnel test requires an accurate representation of the full-scale pressure drop across the element. In practice this is normally achieved using laminations of various porous materials and honeycombs on the basis of experience and ad hoc data. In view of this, a series of measurements of the pressure drop, in both the near and far field, across screens with porosity (β) in the range 0.41 ≺ β ≺ 0.76 are reported. The aim being to establish a relationship between the porosity and the pressure drop characteristics of a given material at various angles of inclination to the free-stream flow. Furthermore, the effect of screen depth was investigated using honeycombs. This data will facilitate detailed design and accurate representation of the flow characteristics at sub scale.The measurements were made in a simple open return blower wind tunnel within a range of Reynolds number (Re), based on screen thickness of 200 ≺ Re ≺ 2100 and screen inclination to the free stream (α) in the…
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Using the Reciprocal Work Identity to Evaluate the Transmission Loss of Mufflers

SAE International Journal of Passenger Cars - Mechanical Systems

University of Kentucky-L. Zhou, D. W. Herrin, T. W. Wu
  • Journal Article
  • 2013-01-1888
Published 2013-05-13 by SAE International in United States
Transmission loss (TL) is a good performance measure of mufflers since it represents the muffler's inherent capability of sound attenuation. There are several existing numerical methods, which have been widely used to calculate the TL from numerical simulation results, such as the four-pole and three-point methods. In this paper, a new approach is proposed to evaluate the transmission loss based on the reciprocal work identity. The proposed method does not assume plane wave propagation in the inlet and outlet ducts, and more importantly, does not explicitly apply the anechoic termination impedance at the outlet. As a result, it has the potential of extending TL computation above the plane wave cut-off frequency.
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Automotive AC System Induced Refrigerant Hiss and Gurgle

SAE International Journal of Passenger Cars - Mechanical Systems

DENSO International America Inc.-Prakash T. Thawani, Stephen Sinadinos, Justin Black
  • Journal Article
  • 2013-01-1890
Published 2013-05-13 by SAE International in United States
Traditional IC engine powered vehicles readily mask the lower amplitude transients like hiss, clicks and slight tones. However, due to the popularity and expected increase in number of hybrid and electrically driven automobiles all around the world, all the OEMs are concerned about the vehicle interior quietness and sound quality. Refrigerant system induced hiss/gurgle is quite normal phenomenon but its excessive levels and frequent occurrences can be objectionable to demanding customers. Introduction of new environmentally friendly refrigerants (HFO-1234yf), A/C compressors with built-in oil separation (reduced damping in evaporator), and use of IHX with coupled suction and liquid lines, may lead to increased refrigerant system induced hiss and gurgle.Operation of typical A/C system generates steady-state and transient noises that consist of audible tones and high frequency hiss. A/C system usage is seasonal and operation controlled by the customer, hence the noise (if present) is readily perceived and flagged as a concern. This paper focuses on diagnostics of refrigerant system induced noise sources and spectral characteristics. A systematic approach is used to quantify and identify the paths…
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Optimization of Test Parameters and Analysis Methods for Fuel Tank Slosh Noise

SAE International Journal of Passenger Cars - Mechanical Systems

Sound Answers Inc.-Eric Frank, Chris Moon
Testing Services Group LLC-Jason Rae, Michael Popovich
  • Journal Article
  • 2013-01-1961
Published 2013-05-13 by SAE International in United States
As the interior sound levels in cabin compartments of passenger vehicles continue to get quieter, noises from various sources which previously were not objectionable can become an issue. One such source is the “slosh noise” from liquid movement within fuel tanks.Vehicle manufacturers, responding to the phenomena, have turned to their suppliers and worked with them to establish robust test and analysis methods to characterize the NVH performance of their fuel storage and delivery systems. Test facilities have recently made great advancements in the capability to measure and characterize “fuel slosh noise” in tanks. However, the industry today lacks standardized procedures to apply to the issue, including defining test parameters and analysis methods (both of which are complex because of the time-domain nature of slosh events).The purpose of this paper is to identify the current capabilities and discuss optimal parameters of testing component-level fuel slosh noise, and to explore the merits of various NVH analysis methods that can be used to quantify slosh noise.
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Dynamic Stiffness of Hydraulic Bushing with Multiple Internal Configurations

SAE International Journal of Passenger Cars - Mechanical Systems

The Ohio State University-Tan Chai, Rajendra Singh, Jason Dreyer
  • Journal Article
  • 2013-01-1924
Published 2013-05-13 by SAE International in United States
Fluid filled bushings are commonly used in vehicle suspension and sub-frame systems due to their spectrally-varying and amplitude-dependent properties. Since the literature on this topic is sparse, a controlled laboratory prototype bushing is first designed, constructed, and instrumented. This device provides different internal combination of long and short flow passages and flow restriction elements. Experiments with sinusoidal displacement excitations are conducted on the prototype, and dynamic stiffness spectra along with fluid chamber pressure responses are measured. The frequency-dependent properties of several commonly seen hydraulic bushing designs are experimentally studied and compared under two excitation amplitudes. Further, new linear time-invariant models with one long and one short flow passages (in parallel or series) are proposed along with the limiting cases. The analytical models are validated in frequency and time domains using transmitted force and chamber pressure measurements. The proposed formulation provides insights into various performance features.
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Analysis of Speed-Dependent Vibration Amplification in a Nonlinear Driveline System Using Hilbert Transform

SAE International Journal of Passenger Cars - Mechanical Systems

The Ohio State University-Laihang Li, Rajendra Singh
  • Journal Article
  • 2013-01-1894
Published 2013-05-13 by SAE International in United States
The engine start-up process introduces speed-dependent transient vibration problems in ground vehicle drivelines as the torsional system passes through the critical speeds during the acceleration process. Accordingly, a numerical study is proposed to gain more insights about this transient vibration issue, and the focus is on nonlinear analysis. First, a new nonlinear model of a multi-staged clutch damper is developed and validated by a transient experiment. Second, a simplified nonlinear torsional oscillator model with the multi-staged clutch damper, representing the low frequency dynamics of a typical vehicle driveline, is developed. The flywheel velocity measured during the typical engine start-up process is utilized as an excitation. The envelope function of the speed-dependent response amplification is estimated via the Hilbert transform technique. Finally, the envelope function is effectively utilized to examine the effect of multi-staged clutch damper properties.
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Spherical Beamforming with Enhanced Dynamic Range

SAE International Journal of Passenger Cars - Mechanical Systems

Brüel & Kjær Sound/Vib Meas A/S-Jorgen Hald
  • Journal Article
  • 2013-01-1977
Published 2013-05-13 by SAE International in United States
Beamforming with an array of microphones on a sphere is an attractive tool for doing noise source localization in cabin environments. In order to achieve acceptable angular resolution, the array must have some minimum diameter, implying that many microphones are needed to obtain low sidelobe level over the frequency range of interest. For electric cars there is an increased need to cover high frequencies. The present paper describes a method to significantly reduce the sidelobe level over a broad frequency range relative to Spherical Harmonics Beamforming (SHB). For each focus point, a set of Finite Impulse Response (FIR) filters are optimized to minimize the highest sidelobe in a Filter And Sum (FAS) beamformer, while maintaining sensitivity at the focus point and limiting the White Noise Gain (WNG). Similar approaches have been published, but a main issue in connection with applications for noise source mapping is the computational load in performing the optimization of FIR filters for each focus point. The paper describes a method to handle that challenge. Basically, filter coefficient are pre-optimized for a…
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Effect of Local Stiffness Coupling on the Modes of a Subframe-Bushing System

SAE International Journal of Passenger Cars - Mechanical Systems

The Ohio State University-Scott Noll, Jason Dreyer, Rajendra Singh
  • Journal Article
  • 2013-01-1904
Published 2013-05-13 by SAE International in United States
The elastomeric joints (bushings or mounts) in vehicle structural frames are usually described as uncoupled springs (only with diagonal terms) in large scale system models. The off-diagonal terms of an elastomeric joint have been previously ignored as they are often unknown since their properties cannot be measured in a uniaxial elastomer test system. This paper overcomes this deficiency via a scientific study of a laboratory frame that is designed to maintain a high fidelity with real-world vehicle body subframes in terms of natural modes under free boundaries. The steel beam construction of the laboratory frame, with four elastomeric mounts at the corners, permits the development of a highly accurate, yet simple, beam finite element model. This allows for a correlation study between the experiment and model that helps shed light upon the underlying physical phenomenon. In particular, the effect of local stiffness coupling of elastomeric bushings or mounts is demonstrated through computational modeling and experimental validation. It is seen that the joint stiffness matrices strongly influence the modal properties of a laboratory subframe-mount system. For…
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Steps towards Predictive Simulation and Faster Experimental Investigation of Automotive Brake Systems with Respect to Squeal

SAE International Journal of Passenger Cars - Mechanical Systems

Technische Univerität Berlin-Sylwia Agnes Hornig, Daniel Hochlenert, Holger Gödecker, Nils Gräbner, Utz Von Wagner
  • Journal Article
  • 2013-01-1908
Published 2013-05-13 by SAE International in United States
The development process of automotive brakes is known to be challenging and time-consuming. It is an iterative process consisting of interplay between brake squeal simulation and extensive experimental investigations of the brake system at the test rig and in the vehicle. In this context, the complex eigenvalue analysis (CEA) of linearized FE models is a part of standard development process of brake systems. Nevertheless this linear analysis has not reached the status of a predictive tool yet, remaining a tool accompanying experimental investigations of the brake system only. Possible reasons may be inadequate simplifications of frictional contact, damping effects and friction material modeling on one hand and insufficiencies of the mathematical mechanical models themselves, i.e. linear vs. nonlinear stability analyses on the other hand. The extensive experimental investigations apply time consuming standard test procedures and need efficiency improvement. This paper introduces several steps towards improvement of brake development process efficiency with respect to brake squeal and gives an overview on corresponding research at the chair of Mechatronics and Machine Dynamics at TU Berlin. First it…
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Effect of the Tooth Surface Waviness on the Dynamics and Structure-Borne Noise of a Spur Gear Pair

SAE International Journal of Passenger Cars - Mechanical Systems

The Ohio State University-Sriram Sundar, Rajendra Singh, Karthik Jayasankaran, Seungbo Kim
  • Journal Article
  • 2013-01-1877
Published 2013-05-13 by SAE International in United States
This article studies the effects of tooth surface waviness and sliding friction on the dynamics and radiated structure-borne noise of a spur gear pair. This study is conducted using an improved gear dynamics model while taking into account the sliding frictional contact between meshing teeth. An analytical six-degree-of-freedom (6DOF) linear time varying (LTV) model is developed to predict system responses and bearing forces. The time varying mesh stiffness is calculated using a gear contact mechanics code. A Coulomb friction model is used to calculate the sliding frictional forces. Experimental measurements of partial pressure to acceleration transfer functions are used to calculate the radiated structure-borne noise level. The roles of various time-varying parameters on gear dynamics are analyzed (for a specific example case), and the predictions from the analytical model are compared with prior literature.
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