Browse Topic: Noise pollution
There is an increasing effort to reduce noise pollution across different industries worldwide. From a transportation standpoint, pass-by regulations aim to achieve this and have been implementing increasingly stricter emissions limits. Testing according to these standards is a requirement for homologation, but does little to help manufacturers understand why their vehicles may be failing to meet limits. Using a developed methodology such as Pass-by Source Path Contribution (SPC, also known as TPA) allows for identification of dominant contributors to the pass-by receivers along with corresponding acoustic source strengths. This approach is commonly used for passenger vehicles, but can be impractical for off-highway applications, where vehicles are often too large for most pass-by-suitable chassis dynamometers. A hybrid approach is thereby needed, where the same techniques and instrumentation used in the indoor test are applied to scenarios in an outdoor environment. This allows for determination of all the useful contribution results in a more representative environment and without limitations associated with indoor facilities. This paper demonstrates the application of this method on an off-highway vehicle for several scenarios.
Decarbonizing regional and long-haul freight is challenging due to the limitations of battery-electric commercial vehicles and infrastructure constraints. Hydrogen fuel cell medium- and heavy-duty vehicles (MHDVs) offer a viable alternative, aligning with the decarbonization goals of the Department of Energy and commercial entities. Historically, alternative fuels like compressed natural gas and liquefied propane gas have faced slow adoption due to barriers like infrastructure availability. To avoid similar issues, effective planning and deploying zero-emission hydrogen fueling infrastructure is crucial. This research develops deployment plans for affordable, accessible, and sustainable hydrogen refueling stations, supporting stakeholders in the decarbonized commercial vehicle freight system. It aims to benefit underserved and rural energy-stressed communities by improving air quality, reducing noise pollution, and enhancing energy resiliency. This research also provides a blueprint for replacing diesel in over-the-road Class 8 freight truck applications with hydrogen fueling solutions. The study focuses on the Texas Triangle Megaregion (I-45, I-35, and I-10), the I-10 corridor between San Antonio, TX, and Los Angeles, CA, and the I-5/CA-99 corridors between Los Angeles, CA, and San Francisco, CA. This area represents a significant portion of U.S. heavy-duty freight movement, carrying ~8.5% of the national freight volume. Using the OR-AGENT (Optimal Regional Architecture Generation for Efficient National Transport) modeling framework, the study conducts an advanced assessment of commercial vehicles, road and freight networks, and energy systems. The framework integrates data on freight mobility, traffic, weather, and energy pathways to deliver a region-specific, optimized vehicles powertrain architectures, infrastructure deployment solutions, operational logistics, and energy pathways. By considering all vehicle origin-destination pairs utilizing these corridors and all feasible fueling station location options, the framework's genetic algorithm identifies the minimum number and optimal locations of hydrogen refueling stations, ensuring no vehicle is stranded. It also determines fuel schedules and quantities at each station. A roadmap for station deployment based on multiple adoption trajectories ensures a strategic rollout of hydrogen refueling infrastructure.
Small multirotor vehicles, for example, designed for package delivery, are expected to operate in close proximity to populated areas, raising concerns about noise pollution. This study utilizes acoustic flight tests and computational modeling of an instrumented research hexacopter developed at Penn State to investigate noise generation during takeoff and landing maneuvers, considering varying flight path angles and vehicle speeds. Flight tests were conducted at Mid-State Regional Airport and corresponding predictions were made using the Penn State Noise Prediction System. The predicted vehicle states and noise levels are first validated against the flight test data. The validated model and flight test data are then utilized to study the noise emissions of the aircraft. Measurements and predictions of the acoustic characteristics of the vehicle are analyzed using conventional noise metrics, frequency content, and directivity features. Descent maneuvers are found to be noisier than climb maneuvers. Noise generation decreases with an increase in forward speed during both climb and descent and also with an increase in vertical speed during climb. However, during descent, noise generation increases with an increase in sink rate.
Worldwide automotive sector regulatory norms have changed and become more stringent and complex to control environmental noise and air pollution. To continue this trend, the Indian Ministry of Road Transport is going to impose new vehicle exterior pass-by noise regulatory norms IS 3028:2023 (Part2) to control urban area noise pollution. This paper studies the synthesis of M1 category vehicle driving acceleration, dominant noise source, and frequency contribution in exterior PBN level. A vehicle acceleration analysis study was carried out to achieve an optimized pass by noise (PBN) level based on the vehicle’s PMR ratio, reference, and measured test acceleration data. Based on the analysis, test gear strategy was decided to achieve a lower PBN level. This strategy involved increasing the effective final drive ratio and optimizing engine calibration, resulting in improvement with acceleration in the ith gear. This increased acceleration surpassed the upper limit of the reference acceleration range; hence, the vehicle was tested in a combination of both gear (ith and ith+1) conditions. With this approach, a significant noise improvement could be achieved in overall PBN level. Furthermore, an analysis of exterior pass-by noise sources was conducted during acceleration and constant speed test conditions. Using a masking technique, each major noise source contribution to the overall pass-by noise level was identified. The powertrain emerged as the primary noise source, with its mid-frequency noise making a substantial contribution to pass-by noise. A frequency analysis was also performed to address higher intake noise. These innovative approaches resulted in a considerable reduction in the overall pass-by noise level. Additionally, by implementing these strategies, OEMs could meet the new PBN regulatory standards for all their existing and upcoming vehicle models.
Global warming, pollution, dependence on foreign oil resources and rising petroleum prices are major issues the nations facing today. Increasing density of IC engine powered vehicles, urban air pollution, traffic congestion and wastage of valuable land for parking have negative impact economically, ecologically and politically. Moreover, an increasing preference for personal mobility, owing to the pandemic and social distancing norms has witnessed notable growth in automobile sales. Hence, a strategy to replace conventional vehicles is urgently required by electric vehicles, which is one of the most promising alternative technologies. Governments also recognized the value of electric mobility in building a cleaner, smarter and more sustainable future cities. Adoption of low-cost, light weight and low power electric vehicles designed for the city environment can considerably reduce the impact of personal mobility not only by reducing energy consumption but also by minimizing the use of parking and driving space in comparison with conventional vehicles. This paper proposes and develops an environmentally friendly low-cost electric microcar that maneuvers easily in city heavy traffic with zero emissions and benefits the high energy efficiency, energy security and noise pollution reduction. An analytical modeling is carried out for sizing of powertrain elements. CAD modeling of chassis frame using solid works followed by analysis using ANSYS is also performed. A double seater low-cost electric microcar with comprehensible mechanism has demonstrated a range of 75 km on full charging. A simple fuel and emission analysis has observed that around 851.66 liters of petroleum fuel saving and corresponding 2.077 tonnes of carbon dioxide reduction annually with this prototype.
This column presents technologies that have applications in commercial areas, possibly creating the products of tomorrow. To learn more about each technology, see the contact information provided for that innovation.
Noise pollution resulting from technological development, urbanization and economic growth is one of the major sources of complaints in urban areas. The sound generated by transportation systems, is one of the most important causes of noise-induced annoyance, since the exposure to high levels for long periods of time can be detrimental to health. Freight railway systems have great potential of noise emission, since they are designed to meet safety requirements, rather than comfort, and are subject to more severe operations and cruder maintenance procedures than passenger cars. Among the different types of noise that originate from a railroad, the squealing generated in curves is one that stands out since it can exceed regular rolling noise in 30 dB and often occurs in frequencies where the human hearing is more sensitive. Analytical models have been developed over the years to help understanding and predicting squeal. This paper aims to validate, at a freight railroad, an analytical model created to predict squeal sound pressure level (SPL) from subways and urban trains. The model was implemented on numerical computation software, taking into account wheel and bogie characteristics, train speed and curve radius. The estimated data were compared with measurements of SPL carried out at the railway during regular traffic. The squeal was heard during the measurement, and the noise peak was later identified during the data analysis. Measurements were carried out at three curves with different radii to investigate if the model accuracy was influenced by this variable. Nonetheless, since the occurrence of squeal noise results from the interplay of many parameters, it was not heard in some of the measurements. Even though, the results suggest that the model may be a useful tool to predict and understand the relationship between train speed, curve radius and squeal SPL.
One major problem of big cities is the congested traffic situation and the noise pollution generated by the traffic participants, i.e., cars, busses, and trams. Those ground-bound transport systems are already reaching their limits. The use of aerial taxi services has the potential to use the third, vertical dimension. Vertical take-off and landing systems, shortened to VTOL systems, possibly autonomous and electrified, with low noise emission and little ground space requirements are preferred. Applying an MBSE-based approach like our methodology called 'Compositional Unified system-Based Engineering', in short CUBE, enables to control the complexity of the challenge to develop appropriate VTOLs. This methodology has already proven itself in the automotive industry and its system development processes. In this paper the CUBE methodology will be transferred to the aerospace system development process to demonstrate its general usability. The fully systematical and model-based description of the System of Systems (SoS, meaning urban infrastructure here) is used to condense the requirements for the System of Interest (SoI, meaning VTOL) regarding many possibilities and limitations. This concept is a promising approach to create system-based and model-based specifications of requirements for the VTOL systems, which later shall operate seamlessly as part of the SoS.
Battery Electric Vehicles (BEVs) are gaining momentum all around the world and India is not far behind in terms of EV sales. The principle difference between BEVs and Internal Combustion Engine based Vehicles (hereafter known as ICEs) is that BEVs run on electric motors and don’t have Internal Combustion based engines that generate significant noise while running. The engine noise contributes to noise pollution, but it is useful in alerting the pedestrians about the incoming vehicle and can function as a passive safety system. The lack of such noise can be a safety threat to pedestrians, cyclists, wildlife etc. Many countries around the world have mandated, or are in the process of mandating, a pass-by noise generating system to alert pedestrians about the incoming vehicle. This paper is an attempt to study various pass-by noise generating systems used worldwide in electric four-wheelers. A majority of those systems use speakers located on the exterior of the cabin to mimic noise generated by IC engines. This paper describes a detailed comparison of the pseudo-sound generating devices, enlists advantages and disadvantages of each system and also suggests a proposed pass-by noise generation system (PSGS) considering Indian road conditions. In the future, this paper can be used as a reference for the development of pass-by noise generating systems.
3-D horn is a vehicle to vehicle communication-based technology which helps in reducing the noise pollution, which occurs, due to honking of automobile horns by letting only the drivers of the automobile to hear the horns and not the whole environment around him. To achieve this, several relatively small horn speakers are placed inside the car. These speakers are controlled by drivers of other cars. In this way honking will be heard only by the drivers. The most unique feature of this technology is the 3-D effect caused by the speakers which will let the driver know the location of the outside car which is honking. The 3-D effect is achieved by varying the intensity and proper allotment of sound to the positioned speakers in such a way that it will give the feel of the location of the outside car to the driver. Human detection is another important feature this technology provides. It will recognize whether the horn is honked for an automobile or for a human. In case of human an external horn will be honked otherwise 3-D horn will be honked. A combination of GPS and RADAR is used to achieve this functionality.
The increasing in popularity of Light Commercial Vehicles (LCV) segment is an emerging trend in the commercial vehicle industry. LCVs are very efficient and cost-effective for transportation of materials and good on short distances or loads of lesser weights. Sensing the market potential, many auto companies have developed LCVs recently. Since LCV segment is price sensitive, low cost single cylinder water cooled diesel engine being used as prime mover. High noise & vibration is inherent feature of diesel engine & it is predominant in single cylinder diesel engine. In order to retain low cost of product, less attention is given on overall noise of vehicle. Also, it is challenging to meet the regulatory limits of Pass-by Noise (PBN) for this category of vehicle. This paper is a development work done for pass-by noise reduction of a diesel powered single cylinder LCV vehicle. A prototype vehicle needs to meet the legislative pass-by noise requirement when tested as per IS0 362 / IS 3028. Initial Pass-by noise test of the proto vehicle clearly demands to reduce the Pass-by noise by 2-3 dB which in turn required to carry out the Noise Source Identification during Pass-by noise test. Pass-by Noise Source Identification resulted with various sources contributing to increase in noise levels. Development iterations were conducted on the vehicle to achieve the significant Pass-by noise reduction.
Noise Pollution has become one of the major environmental concerns for global automotive industry in the current era. Air Induction System (AIS) plays an important role in engine performance and vehicle noise. An ideal design of AIS provides debris free air for combustion and also reduces the engine noise heard at snorkel. Acoustic engineers always face challenges for achieving optimized AIS design with packaging space constraints. Conventionally, AIS optimization is an iterative procedure. This paper emphasizes a one dimensional (1D) approach for optimization of AIS to meet the functional requirements for flow and acoustics. Air flows from the snorkel to the intake manifold whereas the sound propagates in the opposite direction. Suitable design of ducts, air box and resonators are required to attenuate the snorkel noise (SN) to meet the required sound pressure levels. In this paper a detailed methodology is developed to study the AIS with different geometries and their impact on pressure drop and noise attenuation at different engine speed. GEM3D is used as a pre-processor for air box, resonators and duct modeling. The discretization of air box shell and ducts for element generation has played an important role in proper prediction of noise and pressure drop. Transmission loss (TL), pressure restriction and snorkel noise simulation is carried out using GT-POWER® tool. Four pole transfer matrix method is applied for the calculation of TL which allows us to understand attenuation of sound. The effect of TL in wide frequency range (0 to 1000 Hz) is studied. Pressure restriction study enabled us to understand flow characteristics through pressure difference between dirty side duct (DSD) and clean side duct (CSD). The TL and pressure drop plots are found to be in good correlation with test results. The optimized design of AIS will be tested at different engine speeds at full throttle conditions to achieve good correlation for snorkel noise. These optimization techniques shall be useful for future programs at an early stage of product development which reduces development time and cost.
Sintered fiber metal composites are used in aircraft as an acoustic media within environmental ducting, inlet and exhaust systems. The material can be engineered to meet specific acoustic attenuation and noise reduction goals within these applications. Sintered metal fiber composites have proven reliable and effective since the 1950's, but continue to deliver new value through ongoing investment and new use cases. There are four design options for mitigating noise in the turbine gas flow and in the environmental control system (ECS) of aircraft. In some applications, the use of sintered metal fiber composites may be the most cost- or space-effective approach, deliver unique ancillary benefits or perform better than other technologies that can survive the requisite temperatures.
Vehicles powered by electric machines offer the advantage to be more silent than vehicles equipped with an internal combustion engine. On the one hand, the reduced noise levels enable an improvement of the inner-city noise pollution. On the other hand, quiet vehicles entail risks not to be acoustically detected by surrounding pedestrians and cyclists in the lower speed range. The emitted noise can easily be masked by the urban background noise. Therefore, the UNECE has founded an informal working group which is currently developing guidelines in terms of an exterior noise required for detecting Quiet Road Transport Vehicles (QRTV). With the introduction of an Acoustic Vehicle Alerting System (AVAS), not only the exterior noise but also the perceived interior noise for an enhanced driving experience can be considered. Nevertheless, car manufactures have a big interest in maintaining their perceived brand identity. For the solution of this task, a synthetic sound generation system has been developed. Besides the realization of executable software for real-time capable vehicle communication and sound calculation, an implementation on an in-vehicle control unit has been engineered. Special attention has been paid to the aspect “ease of use”. Important control parameters of the sound design can be modified with a graphical user interface directly in a road test from both in- and outside the test vehicle. The methodology of the AVAS, different sound design approaches for various demonstrator vehicles and key results regarding the audibility and sound quality are object of this paper.
Noise pollution is a major concern for global automotive industries which propels engineers to evolve new methods to meet passenger comfort and regulatory requirements. The main purpose of an exhaust system in an automotive vehicle is to allow the passage of non-hazardous gases to the atmosphere and reduce the noise generated due to the engine pulsations. The objective of this paper is to propose a Design for Six Sigma (DFSS) approach followed to optimize the muffler for better acoustic performance without compromising on back pressure. Conventionally, muffler design has been an iterative process. It involves repetitive testing to arrive at an optimum design. Muffler has to be designed for better acoustics performance and reduced back pressure which complicates the design process even more. A hybrid type muffler is the most commonly used muffler in automotive industry and it plays an important role in noise attenuation by using a combination of impedance mismatch and absorption techniques. In this paper a DFSS approach is developed in order to optimize a hybrid muffler design for a passenger car. DFSS approach has an input, output, control factors and the noise factors for the above problem. Exhaust gas mass flow rate at different engine rpm is the input and the tail pipe noise is the output for the analysis. All the design parameters which affects the output is considered as the control factors and the temperature of the exhaust gas is considered as the noise factor since it is not controlled by the design engineer. Commercial 1D simulation software GT-POWER® is used for this analysis. L18 orthogonal array is developed in order to capture the interactions of all controls factors, its levels and noise factor. Simulation is run for the L18 array for different engine rpm and results are plotted between engine rpm versus tail pipe noise. The tail pipe noises for the different design were studied and lowest one across different rpm is selected. Critical design parameter which affects the tail pipe noise is derived from this simulation. DFSS approach adopted in this paper has provided a better correlation of simulation results with test data. The optimized design shows better acoustic and back pressure performance than the original design. Deployment of advanced software and experimental methods leads to First Time Right product development by effectively reducing valuable design cycle time and can be further used in the field of research for future vehicle programs.
The rapid growth of Electric Vehicles (EV’s) and Hybrid Electric Vehicles (HEV’s) has increased the concern that the relative silence of these type of vehicles will result in an increased risk to pedestrian safety. A practical solution to this problem is to add artificial sounds to EV's to aid their detection by pedestrians and other vulnerable road users. Acoustic warning systems for EV’s should increase pedestrian safety and simultaneously produce a small impact on environmental noise levels. This paper shows the main advantage of using a directive acoustic source implemented as a beamforming loudspeaker array in an EV to increase pedestrian safety and control the effect on noise pollution. An example of such a system has been implemented in a Nissan Leaf vehicle and its performance in realistic situations has been assessed. The experimental results show that this type of approach is very effective to increase close-to-accident pedestrian safety near EV’s and simultaneously reduce noise pollution with respect to conventional acoustic warning devices.
There are many environmental issues in India. Air pollution, water pollution, garbage, vibration, noise pollution and pollution of the natural environment are all challenges for India. India has a long way to go to reach environmental quality similar to those enjoyed in developed economies. Pollution remains a major challenge and opportunity for India. The review of trends in farm practices and machinery development suggests that vibration & noise problems are still prevalent in agricultural situations, even though there has been a steady increase in the availability of materials and equipment for vibration & noise control over recent years. Diesel engine is the main source of power for agricultural equipments, such as water pump set, compressor, electric generator and tractor. Even it is one of the sources of vibration & noise in agricultural field. There is reluctance of the agricultural sector to use of vibration & noise control methods. It is difficult to estimate the number of workers (self-employed and employees) in agriculture and forestry who suffer in India. In this project work, the challenge was to predict vibration performance / characteristics of 8 HP, 2100 rpm, single cylinder diesel engine. Also check the effect of up-gradation of same engine to 2600 rpm; which will be done to get more water quantity and at higher level /head. Engine model building was started with 3D CAD modeling using Pro/E software then discritization (Meshing) and Nastran solver deck / model with loads and boundary conditions was developed using Hyper Mesh software. Engine loads was calculated using analytical methods for 2100 rpm & 2600 rpm. Those excitation loads was used to simulate NVH behavior of engine using CAE method. Detailed vibration source identification was carried out by actual vibration measurement using B & K measuring system and NVH CAE simulation methods. Fuel tank and gear cover was potential candidate of vibration. Based on vibration source identification by both methods, design modifications were done and verified using NVHCAE simulation technique for 2100 rpm and 2600 rpm before final recommendation for design changes. Those modifications were showing good amount of vibration reduction for the respective natural frequencies as design changes were strengthening the plane surfaces of sheet metal fuel tank and gear cover. Design modifications were recommended to implement after prototype testing.
Natural gas is increasingly being utilized for vehicle applications both to reduce vehicle emissions and as an alternate energy source to gasoline and diesel fuels. Natural gas can be used to reduce carbon dioxide emissions while the global distribution of natural gas allows energy independence for regions with gas rather than oil reserves. Thus natural gas as alternative vehicle fuel not only provides emission benefits but also provide an economical option in comparison to the Hybrid and Electric Vehicles. An increasing number of vehicles worldwide are being manufactured to run on CNG. CNG/NGV vehicles produce 20-30% less carbon dioxide than gasoline and diesel [1]. The CO2 contributes to global climate change due to greenhouse effect. Further CNG vehicles decrease noise pollution by having a smoother and more silent engine performance compared to gasoline and diesel engines. The CNG injection technology is developed to obtain engine performance equivalent to gasoline engines unlike the conventional venturi system wherein the performance and drivability is compromised. One of the major challenge associated with using injector based CNG system is cabin noise due to the injector noise. The operational metallic and gas pulsation noise associated with sequential functioning of the gas injector is generally higher as compared to liquid fuels like gasoline due to dry nature of the CNG fuel. This paper describes the methodology adopted for reduction of CNG injector noise and suggests an experimental set up to predict the noise at early design stage. Experimental data suggests correlation between bench simulation and actual vehicle noise. The iterative process followed for improving the NVH performance by measurement of operational and gas pulsation noise from CNG injector can thus be avoided to reduce overall development time.
Increasing interest is being paid to noise pollution of internal combustion engines and as a result, recent international standards imposed more severe limitations to acoustic emissions on engine manufacturers. In particular, the noise coming from gas-dynamic interactions has an important influence in determining the final noise level of the engine; as a consequence, the muffler design is currently being considered as one of the most important research threads for engine companies. Within this context, the 1D approach to numerical simulations, which has been successfully applied by industrial designers to the fluid-dynamic design of the engine, is considered to be inaccurate in the evaluation of the acoustic behavior of the muffler for medium-high frequencies. On the other hand, an extension of the applicability of these codes in the medium-high frequencies would be desirable. The direct advantage would be the use of the same software for the simulation of both the fluid-dynamic and acoustic performance of the engine. On these bases, a commercial 1D numerical code was primarily analyzed in terms of accuracy, computational cost and modeling capability of mufflers from the acoustic point of view. As a second step, two non-conventional approaches were developed in order to improve the prediction capabilities of the 1D code and to widen its frequency range of validity, as well. The base scheme of these new approaches was to extend the application of the traditional 1D nonlinear equations not only in the axial direction but also in perpendicular directions within the cross-section of the muffler, achieving a simplified description of the acoustic phenomena in the whole volume. The 1D predictions using these new approaches were compared both with several sets of experimental data collected on a purposefully developed test rig and specific 3D simulations; as a result, their limits in terms of accuracy were highlighted. Moreover, the introduction of the new sub-models increased the accuracy of the simulations and the frequency range of validity, leading to notable results with respect to traditional formulations of the problem.
Noise pollution has become one of the major environmental concerns in present era. With the ever tightening laws and increasingly straight regulations for controlling noise pollution of automotive vehicles, mufflers are important part of engine system and commonly used in exhaust system to minimize noise caused by exhaust gases. Design of mufflers is a complex function that affects the noise characteristics and fuel efficiency of the vehicle. Traditionally, muffler design has been an iterative process by trial and error method. However theories and science that has undergone development in recent years has given a way for an engineer to cut short number of iterations. In today's competitive world market, it is important for a company to shorten product development cycle time and thereby cost. The objective of this paper is to propose a practical approach to design, develop and validate muffler practically which will give advantage over conventional method. This paper also emphasis on how modern CAE tools could be leveraged for optimizing overall system design balancing conflicts like noise and back pressure. The project is considered for validation plan on real time vehicle application to realize objective of design as future scope of work.
Analysis of pressure pulsations in ducts is an active research field within the automotive industry. The fluid dynamics and the wave transmission properties of internal combustion (IC) engine intake and exhaust systems contribute to the energy efficiency of the engines and are hence important for the final amount of CO₂ that is emitted from the vehicles. Sound waves, originating from the pressure pulses caused by the in- and outflow at the engine valves, are transmitted through the intake and exhaust system and are an important cause of noise pollution from road traffic at low speeds. Reliable prediction methods are of major importance to enable effective optimization of gas exchange systems. The use of nonlinear one-dimensional (1D) gas dynamics simulation software packages is widespread within the automotive industry. These time-domain codes are mainly used to predict engine performance parameters such as output torque and power but can also give estimates of radiated orifice noise. However, components with large cross-dimensions, fluid-structural interaction, frequency-dependent damping and boundary conditions are difficult to describe analytically in 1D in the time domain. Since a frequency-domain description in the form of a two-port is normally straightforward to obtain analytically, numerically or experimentally it is of interest to introduce these in time-domain calculations as black box models. This paper suggests the use of Finite Impulse Response (FIR) filters as a method to achieve this improvement. An initial study is presented where tabulated frequency-domain two-port data representing an air cleaner unit on the impedance form is inversely transformed to the time domain and used as FIR filters in nonlinear time-domain 1D calculations with good accuracy. Favorable attenuation, achieved from the filter paper itself, is demonstrated experimentally as well as by the calculations.
Acoustic performance of vehicle engines is a real challenge for powertrain design engineers. Quiet engines are required to reduce noise pollution and satisfy pass-by noise regulations, but also to improve the driving comfort. Simulation techniques such as the Boundary Element Method (BEM) have already been available for some time and allow predicting the vibro-acoustic response of engines. Although the accuracy of these simulation techniques has been proven, a challenge still remains in the required computation time. Given the large amount of speeds for a full engine run-up and the need to cover a large frequency range, computation times are significant, which limits the possibility to perform many design iterations to optimize the system. In 2001, Acoustic Transfer Vectors (ATV) [1] have been presented to adequately deal with multiple rpm. The ATV provide the acoustic response for unit surface velocities and are therefore independent from the engine's actual surface vibrations. As such, the ATV only need to be computed once and can be easily combined afterwards with the actual vibrations at each rpm to obtain the acoustic response for a full engine run-up. This paper presents recent further improvements to reduce the computation time of engine acoustic (ATV) simulation. For BEM, the Fast Multipole BEM method is discussed. For Finite Element Methods (FEM), a new modeling approach based on the Perfectly Matched Layer (PML) technique is presented and an update on state of the art iterative (Krylov) solvers and direct solvers is provided. This paper concludes with a discussion on the results of two industrial simulation cases in which these new techniques have been applied.
Exhaust noise from engines is one of component noise pollution to the environment. Exhaust systems are developed to attenuate noise meeting required db (a) levels and sound quality, emissions based on environment norms. Hence this has become an important area of research and development. Most of the advances in theory of acoustic filters and exhaust mufflers have been developed in last two decades. Mufflers are important part of engine system and commonly used in exhaust system to minimize sound transmissions caused by exhaust gases. Design of mufflers is a complex function that affects noise characteristics, emission and fuel efficiency of engine. Therefore muffler design becomes more and more important for noise reduction. Traditionally, muffler design has been an iterative process by trial and error. However, the theories and science that has undergone development in recent years has given a way for an engineer to cut short number of iteration. In today's competitive world market, it is important for a company to shorten product development cycle time. This paper deals with a practical approach to design, develop and test muffler particularly reactive muffler for exhaust system, which will give advantages over the conventional method with shorten product development cycle time and validation. This paper also emphasis on how modern CAE tools could be leveraged for optimising the overall system design balancing conflicting requirements like Noise & Back pressure.
Environmental pollution is likewise characterized by noise emissions. As a result, according to the European ambient noise directive 2002/49/EG, noise pollution of inner-city areas, in particular congested urban areas, is a major issue of the future European policy. In areas of bus stops and roofed installations, such as bus stations, there are high values of disturbing noise emissions induced by urban bus traffic. Concerning this matter, hybrid urban buses are able to offer promising solutions for an effective noise emissions reduction. At the Institut für Kraftfahrzeuge (ika), RWTH Aachen University, the project "HYBOB," financed by the BMWi (Bundesministerium für Wirtschaft und Technologie), is being conducted in cooperation with the EvoBus GmbH/Daimler Buses. The project is aiming to design and develop a highly sophisticated serial-hybrid diesel-electric propulsion system for urban bus applications. Besides fuel consumption reduction and lower CO2 emissions, the development and implementation of innovative solutions for an effective noise emissions reduction and also enhanced passenger comfort are major NVH-related tasks of this project. Relevant NVH aspects, the development process as well as current optimization results of the ongoing project are represented in this paper.
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