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Viewing 1 to 30 of 101162
Technical Paper
2015-05-09
Kazumoto Morita, Michiaki Sekine
The number of elderly drivers is increasing in Japan and ensuring the safety of elderly drivers is becoming an important issue. The authors previously conducted an analysis of the characteristics of accidents and traffic violations by elderly drivers based on the number of accidents in which they were rear-ended. This method was used in order to exclude the influence of driving frequency. As a result of that analysis, it was found that the likelihood of violations committed by elderly drivers was not particularly higher than in other age groups, while the likelihood of accidents caused by them was higher. The risk of causing an accident was judged to be about two times higher in elderly drivers than in the 35–44 year age group. However, the methodology presupposed that collisions in which a driver is rear-ended are accidents that occur haphazardly, and that they occur with the same probability in each age group. To verify the results of that study, we attempted a new analytical method that uses the number of stop sign violations, which are considered to occur with the same probability among age groups, as an indicator of driving frequency in place of rear-ended collisions.
Technical Paper
2014-09-16
Zachary A. Collier, Steve Walters, Dan DiMase, Jeffrey M. Keisler, Igor Linkov
Counterfeit electronic components entering into critical infrastructure and applications through the global supply chain threaten the economy and national security. In response to the growing threat from counterfeits, the Society of Automotive Engineers G-19 Committee is developing AS6171. This aerospace standard is focused on testing facilities with a goal of standardizing the process of counterfeit detection. An integral part of the standard is a semi-quantitative risk assessment method. This method assigns risk scores to electronic components based on a number of relevant criteria, and places the components into one of five risk tier levels corresponding to an appropriate level of laboratory testing to ensure the authenticity of the component. In this way, the methodology aims at standardizing the risk assessment process and bases the identified risk as guidance for commensurate testing protocols. This paper outlines the risk assessment method contained within AS6171 and briefly explores other complementary efforts and research gaps within the G-19 and electronics community.
Technical Paper
2014-09-15
Kai Chen
The synthetic paraffinic kerosine (SPK) produced via HEFAs is of great interest for civil aviation industry as it exhibits an excellent thermal oxidative stability with significantly lower particulate matter emission. However, due to its aromatic free characteristics, the widespread use of SPK is limited by its compatibility with non-metal materials such as fuel tank elastomers. In this research the compatibility of SPK and its blends with widely used aircraft fuel tank elastomers were systematically studied. Experimental results demonstrated the volume swellability of all selected materials showed a linear relationship with volume percentage of No.3 jet fuel in SPK blend. The increase of volume percentage of No.3 jet fuel in the SPK blend increased volume swellability for all materials except fluorosilicone gasket. The alkyl benzenes and naphthalenes in the blend acted as the hydrogen donors, which facilitated the formation of polymer matrix and led to the increase of the distance between polymer chains.
Technical Paper
2014-06-30
Kasper Steen Andersen, Fuyang Liu
Keywords Aftertreatment system, Exhaust, Silencer, Transfer Matrix, Coupling Introduction The tailpipe noise from an aftertreatment system must comply with legislation and meet customer expectations. The approach to capture the influence of complicated geometries and the ceramic substrates included in full aftertreatment systems is possible by coupling the 1D analytical solution of the substrates with the 3D FEM solution. The originality of the paper This paper present simulation and measurement results for a complete aftertreatment system including DOC, DPF, SCR, mixers and acoustic features with and without mean flow, where the transfer matrix of the aftertreatment system founds the basis for both transmission loss, insertion loss and tail pipe noise calculations. The transfer matrix of the aftertreatment system is extracted after solving the finite element model only once, when applying the appropriate boundary conditions and taking advantage of a symmetric transfer matrix with a determinant of one.
Technical Paper
2014-06-30
Koen Vansant, Hadrien Bériot PhD, Claudio Bertolini, Giuseppe Miccoli
As the legislation for pass-by-noise (PBN) has recently become more stringent, it is clear that car manufacturers face again a challenging task to reach the new SPL objective (70dB(A)). Following the well-known scheme of source-transmission-receiver, we can see how a good design of the engine bay is required to sufficiently attenuate the noise coming from sources as the engine and the intake. This involves proper design of the engine bay’s panels including apertures, and a good selection of the type and location of acoustic treatments. Such optimization or redesign can be inspired by a new target SPL, but can also be initiated by a change in source: the radiated noise from an electric motor differs from that of a conventional IC engine. For a given engine bay design, the PBN SPL results can be obtained with a PBN test or by an equivalent simulation. The conditions for a good PBN test setup are well described but not always easy to obtain. Using simulation models however it is possible to create the perfect test environment virtually and moreover to obtain acoustic results for a large number of designs upfront of any actual testing or prototype.
Technical Paper
2014-06-30
Albert Albers, Jan Fischer, David Landes, Matthias Behrendt
Albert Albers 1, *Jan Fischer 1, David Landes 1, Matthias Behrendt 1 1 IPEK - Institut für Produktentwicklung am Karlsruher Institut für Technologie (KIT) * Contact author: Kaiserstr. 10, 76131 Karlsruhe; jan.fischer@kit.edu The driving comfort is an important factor for buying decisions. Especially for battery electric vehicles (BEV) the acoustic quality is an elementary distinguishing feature, since the masking of an internal combustion engine (ICE) is no longer present. Opposing the importance of the acoustic quality is the lack of knowledge of how to measure and interpret the high frequency noise generated by an electric powertrain with respect to the NVH behavior influencing the passengers [1, 2]. In this contribution a method for measuring and interpreting the transfer path of acoustic phenomena from the drivetrain of a battery electric vehicle into the passenger cabin is presented. Due to the lack of masking by the ICE in case of BEV, high frequency phenomena must be considered as well.
Technical Paper
2014-06-30
Ze Zhou, Jonathan Jacqmot, Gai Vo Thi, ChanHee Jeong, Kang-Duck Ih
Abstract: The NVH study of trimmed vehicle body is essential in improving the passenger comfort and optimizing the vehicle weight. Efficient modal finite-element approaches are widely used in the automotive industry for investigating the frequency response of large vibro-acoustic systems involving a body structure coupled to an acoustic cavity. In order to accurately account for the localized and frequency-dependant damping mechanism of the trim components, a direct physical approach is however preferred. Thus, a hybrid modal-physical approach combines both efficiency and accuracy for large trimmed body analysis. Dynamic loads and exterior acoustic loads can then be applied on the trimmed body model in order to evaluate the transfer functions between these loads and the acoustic response in the car compartment. The scenario study of installing different trim components into the vehicle provides information on the acoustic absorption and dynamic damping with regard to added vehicle weight by the trim.
Technical Paper
2014-06-30
Daniel Fernandez Comesana, Emiel Tijs, Daewoon Kim
For (benchmark) tests it is not only useful to study the acoustic performance of the whole vehicle, but also to assess separate components such as the engine. Reflections inside the engine bay bias the acoustic radiation estimated with sound pressure based solutions. Consequently, most current methods require dismounting the engine from the car and installing it in an anechoic room to measure the sound emitted. However, this process is laborious and hard to perform. In this paper, two particle velocity based methods are proposed to characterize the sound radiated from an engine while it is still installed in the car. Particle velocity sensors are much less affected by reflections than sound pressure microphones when the measurements are performed near a radiating surface due to the particle velocity's vector nature, intrinsic dependency upon surface displacement and directivity of the sensor. Therefore, the engine does not have to be disassembled, which saves time and money. An array of special high temperature particle velocity probes is used to measure the radiation simultaneously at many positions near the engine of a compact class car.
Technical Paper
2014-06-30
Hiromichi Tsuji, Kimihiko Nakano PhD
In the early stage of digital phase and prototype experimental phase, the identification of the operational force on the components and the most important paths of the vibration correlated to the one of the evaluation points, such as steering, seats, and passenger ears, is required for optimizing the dynamic characteristics of the subsystem components of the vehicle. The transfer path analysis (TPA) with the impedance matrix of the component joints is widely used and reliable method to identify the force and the paths of the noise and vibration. However, the conduction of this TPA costs a lot of times. In addition, the estimated force includes not contributing to the evaluation responses. The uncorrelated force to the evaluation responses causes the design errors of the dynamic characteristics in the digital development phase when it has high value at the certain frequency range. To solve the problems, a new force estimation technique is presented in this paper. The proposed technique is based on TPA with the impedance matrix in the frequency domain.
Technical Paper
2014-06-30
Mahdi Mohammadpour, Ramin Rahmani, Homer Rahnejat
The over-riding objective in modern engine development is fuel efficiency. This has led to a host of pursued measures, including down-sizing (a lower number of cylinders), high output power-to-weight ratio, variable valve activation or cylinder de-activation (CDA) as well as a gradual trend towards mild or micro-hybrid technology. Furthermore, The main aim is to combine a suitable combination of the aforementioned methods with various driving conditions in order to reduce thermal and frictional losses as well as meeting the ever stringent emission directives as outlined in the NEDC. Another imperative is to ensure good NVH refinement which can be adversely affected by application of the above trends, such as light weight constructions and exacerbated power torque variations with CDA. The highlighted issues affect all the load bearing conjunctions in an engine. In particular, increased load fluctuations with CDA can also affect the whirl stability of big-end bearings. Therefore, the current paper concentrates on the issues that affect the big-end bearing thermo-frictional characteristics and dynamic stability in NEDC cycle.
Technical Paper
2014-06-30
Roland Sottek, Bernd Philippen
In the engine development process, the ability to judge NVH comfort as early as possible is a great benefit. The prediction of engine noise on the basis of a prototype engine without the need to install it in a real car significantly speeds up the development process and leads to a cost reduction, as prototype modifications can be evaluated faster. Meaningful predictions of the perceived NVH comfort cannot be achieved just by comparing order levels, but require listening to an auralization of the engine noise at the driver’s position. With the methods of Transfer Path Analysis and Synthesis (TPA/TPS) a prototype engine can be virtually installed in a car using test-bench data. The interior noise can be estimated by combining source signals containing near-field airborne radiation and mount forces together with transfer functions describing the transmission to the target position in the cabin. Even the transfer functions of a predecessor car could be used if the new car body is not yet available.
Technical Paper
2014-06-30
Sameh AFFI
In order to face new standards restrictions (ex: EURO6, CAFE), car manufacturers are looking for reducing both fuel consumption and toxic emission. That's why, they are heading much more for hybrid technology with preferably simple and low cost solutions. In this case, Stop & Start system may be adopted without heavy modifications of existent architecture (12V board system and conventional ring gear starter). Such technology results in higher ICE (internal combustion engine) restart occurrence, which impacts customers' acceptance of its NVH aspect. Indeed, engine restart should be imperceptible especially when it steps in without driver's will because it may surprise or even annoy. Besides, noise perception is directly related to engine restart duration. Therefore, the shorter the restart, the better the perception will be at equal noise level. This paper provides NVH analysis of engine restart sequence with conventional ring gear starter. Some optimized solutions for hybrid application was tested and their contribution on reducing restart noise and duration was quantified by a test bench.
Technical Paper
2014-06-30
Rujia Wang, Diange Yang, Ziteng Wang
Identification and quantitative measurement of the pass-by noise radiated by moving vehicles exterior sources correctly and quickly is very important in controlling vehicle noise. In the recent years, acoustical holography has been widely applied for noise sources location and sound field quantitative measurement. Based on this theory, we developed several methods which can effectively achieve identification of moving sound sources and improve the accuracy of quantitative measurement: the diffraction acoustical holography method, dynamic wave super position method, and hybrid acoustical holography method which is the acoustical holography based on wave superposition (WSAH). In this paper, the theoretical analysis and simulations of the comparative study of the above methods were taken; experiments were also carried out based on these methods. With the comparison among these methods, the research conclusions are drawn that the hybrid acoustical holography method performs best in quantitative measurement, which not only provide better identification results for locating sound sources accurately but also reduce the side lobe significantly and solve the ghost sources problem successfully.
Technical Paper
2014-06-30
Ennes Sarradj, Thomas Geyer, Christoph Jobusch, Sebastian Kießling, Alexander Neefe
The development of energy-efficient and lightweight vehicles is a major challenge for researchers and engineers in the automotive industry, with one solution being the use of micro gas turbines in serial hybrid vehicles. Among other advantages, the use of a micro gas turbine instead of a reciprocating engine, enables a high reliability and low emissions. What makes the concept of using a gas turbine even more interesting are its special NVH characteristics, which are quite different from those of a reciprocating engine. Besides the fact that a gas turbine in general produces less noise and vibration than a diesel engine of the same power, the characteristic noise spectrum is also very different. In this paper, the noise characteristics of a micro gas turbine are compared to those typical for a common reciprocating engine and the sources of the noise are considered. The data that form the basis for these analyses were obtained using measurements on a 70 kW micro gas turbine that is designed to be used in a serial hybrid concept for buses.
Technical Paper
2014-06-30
Barry M. James, Andreas Hofmann
The noise performance of electric vehicles is essential to ensure that they gain market acceptance. This can be a challenge for several reasons. Firstly, there is no masking from the internal combustion engine. Next, there is pressure to move to motor designs such as Switch Reluctance Motors, which have worse dynamic properties than their Permanent Magnet counterparts. Finally, there is the drive towards higher speed motors with their greater power density. Experience has shown that this challenge is frequently not met. It is known that reputable motor suppliers reputable transmission suppliers have designed and developed their "quiet" sub-systems to conventional, state of the art levels, only to discover that the assembled E-powertrain is unacceptably noisy. This paper follows an EU-funded project that is part of the FP7 programme that is focussed on the design of a highly integrated driveline for a passenger car. The consortium is led by Bosch but includes the likes of Renault, Romax Technology, Fuchs and GKN Driveline.
Technical Paper
2014-06-30
Vishal Parmar, Daniele Di Rocco, Martin Sopouch, Philippe Albertini
Over the past 30 years simulation of the N&V (Noise and Vibration) behavior of automotive drivelines became an integral part of the powertrain development process. With current and future HEVs (Hybrid-Electrical Vehicles) additional phenomena and effects have been entered the scene and need to be taken into account during layout/design as well as optimization phase. Beside effects directly associated with the e-components (namely electric whistle and whine), torque changes caused by activation/deactivation of the e-machine give rise to vibration issues (e.g. driveline shuffle or clonk) as well. This is in particular true for transient operation conditions like boosting and recuperation. Moreover, aspects of starting the Internal Combustion Engine (ICE) using the built-in e-machine in conjunction with the dynamic behavior of torsional decoupling devices become increasingly important. In order to cope with above mentioned effects a multi-physics simulation approach is required. The following paper proposes a simulation approach which incorporates the domains of the ICE thermodynamics, the mechanical driveline system, the electric components, the vehicle, as well as the fundamental control functions.
Technical Paper
2014-06-30
Janko Slavic, Martin Cesnik, Miha Boltezar
Car components are exposed to the random/harmonic/impact excitation which can result in component failure due to vibration fatigue. The stress and strain loads do depend on local stress concentration effects and also on the global structural dynamics properties. Standardized fatigue testing is long-lasting, while the dynamic fatigue testing can be much faster; however, the dynamical changes due to fatigue are usually not taken into account and therefore the identified fatigue and structural parameters can be biased. In detail: damage accumulation results in structural changes (stiffness, damping) which are hard to measure in real time; further, structural changes change the dynamics of the loaded system and without taking this changes into account the fatigue load in the stress concentration zone can change significantly (even if the excitation remains the same). This research presents a new approach for accelerated vibration testing of real structures. The new approach bases on phase locked harmonic excitation and can be used for identification of natural frequencies and damping while the damage due to vibration is being accumulated.
Technical Paper
2014-06-30
Jean-Baptiste Dupont, Racha Aydoun, Pascal BOUVET
The noise radiated by an electrical motor is very different from the one generated by an internal combustion engine. It is characterized by the emergence of high frequency pure tones that can be annoying and badly perceived by future drivers, even if the overall noise level is lower than that of a combustion engine. A simulation methodology has been proposed, consisting in a multi-physical approach to simulate the dynamic forces and noise radiated by electric motors. The principle is first to calculate the excitation due to electromagnetic phenomena (Maxwell forces) using an electromagnetic finite element solver. This excitation is then projected onto the structure mesh of the stator in order to calculate the dynamic response. Finally, the radiated sound power is calculated with the aid of a standard acoustic finite element method. The calculation methodology assumes a weak coupling between the different physical levels. It has been validated by comparison with the experiment. This simulation only considers the excitation generated by a perfect machine.
Technical Paper
2014-06-30
Alois Sontacchi, Matthias Frank, Franz Zotter, Christian Kranzler, Stephan Brandl
Today, the number of downsized engines with two or three cylinder engines is increasing due to an increase in fuel efficiency. However, downsized engines exhibit unbalanced interior sound in the range of their optimal engine speed, largely because of their dominant engine orders. In particular, the sound of two-cylinder engines yields half the perceived engine speed of an equivalent four-cylinder engine at the same engine speed. As a result when driving, the two-cylinder engine would be shifted to higher gears much later, diminishing the expected fuel savings. This contribution presents an active in-car sound generation system that makes a two-cylinder engine sound like the more familiar four-cylinder engine. This is done by active, load-dependent playback of signals extracted from the engine vibration through a shaker mounted on the firewall. A blind test with audio experts indicates a significant reduction of the engine speed when shifting to a higher gear. In the blind test, experts favored the interior sound of the proposed sound generation system and perceived better interaction with the vehicle.
Technical Paper
2014-06-30
Matthias Frank, Franz Zotter, Alois Sontacchi, Stephan Brandl, Christian Kranzler
When employing in-car active sound generation (ASG) and active noise cancellation (ANC), the accurate knowledge of the vehicle interior sound pressure distribution in magnitude as well as phase is paramount. Revisiting the ANC concept relevant boundary conditions in spatial sound fields will be addressed. Moreover, within this study the controllability and observability requirements in case of ASG and ANC were examined in detail. This investigation focuses on sound pressure measurements using a 24 channel microphone array at different heights near the head of the driver. A shaker at the firewall and four loudspeakers of an ordinary in-car sound system have been investigated in order to compare their sound fields. Measurements have been done for different numbers of passengers, with and without a dummy head and real person on the driver seat. Transfer functions have been determined with a log-swept sine technique. According to the measurements, the shape of the sound field produced by the shaker is more balanced than one produced by the loudspeakers, albeit the shaker’s frequency response is limited to low frequencies.
Technical Paper
2014-06-30
Thilo Bein, Dirk Mayer, Jonathan Militzer
The automotive industry is more and more facing the problem of reducing the weight of the vehicle but guaranteeing an equivalent level of comfort in terms of noise, vibration, and harshness (NVH). Improvement of vehicle noise and vibration without affecting other per-formances is proving to be extremely difficult if not impossible with state-of-the-art technolo-gy. Besides advanced passive material systems, active or smart concepts are being increasingly considered for the NVH optimization of vehicles. However, to overcome contradicting re-quirements traditional design and material choices must be revisited. Frequently, new tech-nologies in the fields of smart materials and active control provide potential solutions although they have mainly been proved in the laboratory. Although the principles of controlling NVH in cars was demonstrated some time ago, its commercial application has been slower than in the aviation field, because of the greater cost sensitivity of the automotive industry.
Technical Paper
2014-06-30
Yuan feng Xia, Jian Pang, Chengtai Hu, Cui Zhou, Cong Wu
The paper analyzes the characteristics of driveline torsional vibration of a RWD vehicle and provides the control methods of transmission rattle noise caused by the system torsional resonances. A driveline dynamic model of the RWD vehicle is established by multi-body dynamic method. The natural frequencies and modal shapes are calculated for each gear position and torsional vibration responses are predicted by forced vibration analysis. The system sensitivity and DOE are analyzed based on the parameterized stiffness, inertia and damping. The 3rd order modal results show that the transmission shaft possesses the maximum amplitudes and its corresponding modal frequencies vary with different gear position. The sensitivity analysis results show that the system torsional vibration is significantly reduced by reducing clutch stiffness, increasing driveshaft stiffness, rising the input shaft inertia and increasing the clutch damping. The DOE analysis results show that the clutch stiffness and damping, tire stiffness, and the inertia of rear axle play an important role in reducing torsional vibration of the transmission gear shafts.
Technical Paper
2014-06-30
Xiaohong Kuang, Jian Pang, Haiyan Zhang, Liang Yang, Jiang-hua FU
The paper describes the identification and control methods of turbocharger surge noise. Some parameters, such as temperature, flow quantity, pressure, vibration, engine rpm and noise, are provided to identify surge noise. The advantages and disadvantages for each parameter are analyzed. The paper identifies that some special noise inside vehicle is turbocharger surge noise by using correlation analysis of the turbocharger inlet temperature, outlet pressure and vehicle internal noise. Spectral filtration analysis shows that the surge noise frequency components are above 1000Hz with wide frequency band. Quarter waver’s effective frequency range is found to be consistent with the surge noise frequency band. A panfluter-resonator which is a combination of several special quarter wave tubes is invented to diminish the wide band high frequency noise. After the panfluter-resonator is installed on a turbocharger system, the vehicle internal surge noise is significantly reduced.
Technical Paper
2014-06-30
Denis Blanchet, Anton Golota, Nicolas Zerbib, Lassen Mebarek
Recent developments in the prediction of the contribution of windnoise to the interior SPL have opened a realm of new possibilities in terms of i) how the convective and acoustic sources terms can be identified, ii) how the interaction between the source terms and the side glass can be described and finally iii) how the transfer path from the sources to the interior of the vehicle can be modeled. This paper discusses in details these three aspects of windnoise simulation and recommends appropriate methods to deliver required results at the right time based on i) simulation and experimental data availability, ii) design stage and iii) time available to deliver these results. Several simulation methods are used to represent the physical phenomena involved such as CFD, FEM, BEM, FE/SEA Coupled and SEA. Furthermore, a 1D and 2D wavenumber transformation is used to extract key parameters such as the convective and the acoustic component of the turbulent flow from CFD and/or experimental data whenever available.
Technical Paper
2014-06-30
Jan Hendrik Elm, Jens Viehöfer, Jan-Welm Biermann
List of authors: Prof. Dr.-Ing. habil. J.-W. Biermann, Dipl.-Ing. Jan Hendrik Elm, Dipl.-Ing. Jens Viehöfer Abstract: The automotive industry permanently enhances Downsizing concepts due to environmental commitments and energy consumption concerns. Even in the category of city- and supermini-cars, great efforts are done for the development of highly charged engines with small displacement. So far the main focus of these developments is set on the reduction of CO2 emissions and fuel consumption. However these are not the only aspects, which have to be fulfilled by the vehicle in order to meet the demands of the customers and to be successful in competition. The NVH-characteristics of such Downsizing vehicles have to match a class-specific level, which can only be achieved by additional measures. Regarding this, a view of the dynamic behavior of the entire vehicle is required. At the Institut für Kraftfahrwesen Aachen (ika) the potential for reducing fuel consumption and CO2 emissions of a Downsizing concept is investigated using a city-car as reference.
Technical Paper
2014-06-30
Farokh Kavarana, Kin Yu, Tyler Robbins, John DeYoung
The advantages of hydraulic mounts over conventional elastomeric mounts for NVH refinement are well known, particularly in the area of engine and suspension mounts. Recently, hydraulic mounts have been successfully employed as body mounts between the frame and cab, principally to control freeway hop in pickup trucks. Due to their ability to provide increased damping at small displacements, hydraulic body mounts also have good potential to reduce smooth road shake. This paper documents the reduction in smooth road shake performance of a full size pickup truck. Hydraulic body mounts tuned to the frequency of the smooth road shake sensitivity area were added to the rearmost cab mount location. Both tire-wheel balance and uniformity were set to the highest production level specification allowed and the effect of hydraulic cab mount was measured experimentally during smooth road driving at medium to high speeds. Hydraulic body mounts were found to be successful in reducing smooth road floor shake by up to 6 dB, thereby considerably refining the vehicle vibration due to first order tire-wheel input forces.
Technical Paper
2014-06-30
Alessandro Zanon, Michele De Gennaro, Helmut Kuehnelt, Domenico Caridi, Daniel Langmayr
In hybrid and electrical vehicles new challenges in meeting the drivers’ expectation with regards to acoustic comfort arise. The absence of low frequency internal combustion engine noise has given way to other noise sources, e.g. from the Heating, Ventilation and Air-Conditioning (HVAC) system. Therefore the research in efficient and reliable numerical models able to predict flow-induced broadband noise has become a major topic in vehicle industry. The Zonal LES coupled with the Ffowcs Williams-Hawkings (FWH) acoustic analogy can provide reliable predictions of the broadband noise emitted by a low speed fan in reasonable computational time, as shown by the authors in previous publications. The proposed approach consists of a fully resolved LES, which embeds the acoustic generation region, merged with a RANS solution in the outer flow domain. However, the complexity of the phenomena involved requires a careful setup of the numerical simulation (mesh generation, definition of the boundary conditions).
Technical Paper
2014-06-30
Bryce Gardner, Tiago Macarios
Speech transmissibility is a critical factor in the design of public address systems for passenger cabins in trains, aircraft and coaches. Speech transmissibility is primarily affected by the direct field, early low order reflections, and late reflections (reverberation) of the source. The direct and low order reflections are affected by the relative location of speakers and seats as well as the acoustic properties of the reflecting walls. To properly capture these early reflections, measures of speech transmissibility typically require time domain information. However, another important factor for speech transmissibility is background noise due to broadband exterior sources such as a flow noise sources. The background noise is typically modeled with broadband steady state assumptions such in statistical energy analysis (SEA). This works presents an efficient method for predicting speech transmissiblity by combining ray tracing with SEA. In this method, the direct field and low order reflections are modelled using raytracing, while the reverberant field and background noise are modelled using SEA.
Technical Paper
2014-06-30
Augusto Medeiros, Tiago Macarios, Gregorio Azevedo, Bryce Gardner
Transmission loss (TL) is a common metric for the comparison of the acoustic performance of mufflers. Muffler TL can be computed from a Boundary Element Method (BEM) model. Perforated tube elements are commonly used in automotive muffler applications. These can be modeled with a detailed BEM model that includes each individual hole in the perforated tube. The main drawback with such a straightforward BEM approach is that the discretionary of the perforated surfaces can result in computationally expensive models. The current work demonstrates an approach to develop a more computationally-efficient, yet, precise way of modeling complex mufflers that contain perforated surfaces with BEM. In this approach, instead of explicitly modeling the perforations explicitly they are taken into account as equivalent transfer impedances. There are several models in the literature that can be used to develop the transfer impedance model of the perforated surface. This paper demonstrates how these models can be used in a BEM prediction and also how one needs to be careful in selecting the cases used to evaluate the models.
Technical Paper
2014-06-30
Gregor Tanner, David J. Chappell, Dominik Löchel, Niels Søndergaard
Title: Discrete Flow Mapping - a mesh based simulation tool for mid-to-high frequency vibro-acoustic excitation of complex automotive structures Authors: Gregor Tanner, University of Nottingham, UK David J Chappell, Nottingham Trent University, UK Dominik Loechel and Niels Soendergaard, inuTech GmbH, Germany Modelling the vibro-acoustic properties of mechanical built-up structures is a challenging task - especially in the mid to high frequency regime - even with the computing powers available today. Standard modelling tools comprise for complex vehicle parts are finite and boundary element methods (FEM & BEM) as well as Multi-Body Simulations (MBS). All these methods are, however, robust only in the low frequency regime; in particular FEM is not scalable to higher frequencies due to the prohibitive increase in model size. We have recently developed a new method called Discrete Flow Mapping (DFM), which extends existing high frequency methods, such as Statistical Energy Analysis or the so-called Dynamical Energy Analysis (DEA), to work on meshed structures.
Viewing 1 to 30 of 101162