| 1. |
- Aare, Magnus, 1974-
(author)
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Prevention of Head Injuries - focusing Specifically on Oblique Impacts
- 2003
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Doctoral thesis (other academic/artistic)abstract
- The massive number of injuries sustained in trafficaccidents is a growing problem worldwide, especially indeveloping countries. In 1998, more than one million peoplewere killed in traffic accidents worldwide, while about tentimes as many people were injured. Injuries to the centralnervous system and in particular to the headare especiallycritical to human life. This thesis contains five researchpapers looking at head injuries and head protection, proposingnew and more efficient ways of protecting the head, especiallyin traffic accidents.In order to define the national dimensions of the patternsof injuries incurred in motorcycle and moped accidents inSweden, a statistical survey was performed on data spanning a13-year period (Paper A). In Sweden, 27,100 individualsreceived in-patient care for motorcycle and moped accidentinjuries between 1987 and 1999. The motorcycle and moped injuryrate reduced in the second half of the study period, so toowere the total number of days of treatment per year. Males hadeight times the incidence of injuries of females. Head injurieswere the single most frequent diagnosis, followed by fracturesof the lower limbs. Concussion was the most frequent headinjury. These statistics clearly show the need for better headinjury prevention systems.According to the statistics, the most common type of impactto the head in motorcycle and moped accidents is an obliqueimpact. Oblique impacts generate rotations of the head, whichare a common cause of the most severe head injuries. Thereforea new test rig was constructed to reproduce oblique impacts toa helmeted dummy head, simulating those occurring in real lifeaccidents (Paper B). The new test rig was shown to provideuseful data at speeds of up to 50 km/h and with impact anglesvarying from purely tangential to purely radial. Thisinnovative test rig appears to provide an accurate method formeasuring accelerations in oblique impacts to helmets.When testing the performances of motorcycle helmets,discrepancies are usually seen in the test results. In order toevaluate these discrepancies, the finite element method (FEM)was used for simulations of a few oblique helmet impacts (PaperC). Amongthe parameters studied, the coefficients of frictionbetween the impacting surface and the helmet and between thehead and the helmet had the most significant influence on therotational accelerations. Additionally, a thinner andconsequently also weaker shell and a weaker liner, providedbetter protection for the impacts studied.Since there are no generally accepted global injurythresholds for oblique impacts to the human head, a study wasdesigned to propose new injury tolerances accounting for bothtranslations and rotations of the head (Paper D). In thatstudy, FE models of (a) a human head, (b) a Hybrid III dummyhead, and (c) the experimental helmet were used. Differentcriteria were proposed for different impact scenarios. Both thetranslational and the rotational effects were found to beimportant when proposing a predictor equation for the strainlevels experienced by the human brain in simulated impacts tothe head.In order to reduce the level of head injuries in society andto better understand helmet impacts from different aspect, aballistic impact was also studied (Paper E). The effects ofdifferent helmet shell stiffness and different angles ofimpacts were simulated. In this study, the same FE head modelfrom Paper D was used, however here it was protected with amodel of a composite ballistic helmet. It was concluded thatthe helmet shell should be stiff enough to prevent the insideof the shell from striking the skull, and that the strainsarising in the brain tissue were higher for some obliqueimpacts than for purely radial ones.In conclusion, this thesis describes the injury pattern ofmotorcycle and moped accidents in Sweden. This thesis showsthat the injuries sustained from these accidents can bereduced. In order to study both translational as well asrotational impacts, a new laboratory test rig was designed. Byusing the finite element method, it is possible to simulaterealistic impacts to the head and also to predict how severehead injuries may potentially be prevented.
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| 2. |
- Agebro, Markus, 1975-
(author)
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Driver Preferences of Steering Characteristics
- 2007
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Licentiate thesis (other academic/artistic)abstract
- The future of vehicle steering systems lies within by-wire technology. With by-wire technology mechanical or hydraulic systems are replaced by electronic systems. Removal of the steering column and possibly other linkage and gears yields vast potential of further improvement of performance, comfort and safety. Steer-by-wire technology also enables the manufacturer to tailor the steering feel to better suit the individual drivers’ need and preference. Since a driver gains critical information about the vehicle from feedback through the steering wheel, steering feel will play a very important part in consumer acceptance of steer-by-wire systems. It will also be possible to customize steering characteristics to the individual driver. This thesis presents a methodology for investigating steering characteristics through analysis of simulator experiments and to find the impact of specific steering characteristics on drivers of varying skill. There are many key aspects to consider when designing simulator experiments. A validated vehicle model is required. Evaluation criteria need to be well defined as well as concise and simple. The utilized scenario has to be able to capture the selected evaluation criteria. Recruitment of test subjects should represent the target population. How to utilize the available time in the simulator most effectively and how to analyze the results are also important. In this work three studies are performed. Paper A investigates how steering gear ratio and steering wheel effort of a passenger car affect preferences of high and low mileage drivers. Paper B is an extended study of Paper A, where the resolution is higher, speed dependence is investigated and performance of the drivers is also evaluated. In Paper C the impact of four important steering system characteristics on driver performance and preference is evaluated. The major conclusions drawn from this work are that variation of steering gear ratio has considerable impact on perceived steering feel and manoeuvrability as well as on driver performance. Variation in steering wheel effort affect perceived steering feel and stability, but no significant influence is detected in perceived manoeuvrability or driver performance. There are distinguishable differences in preferences of the investigated evaluation criteria between driver categories of varying skill. However, general trends of the preferences for the categories are fairly similar. Low skilled drivers prefer lower effort and higher ratio than high skilled drivers, especially at the highest investigated speed, 100 km/h. The developed methodology for performing simulator experiments to evaluate steering characteristics has proven satisfactory through findings of three different studies. This work also shows that there are several important steering characteristics that need to be considered when designing steering systems, particularly steering systems with by-wire applications and especially considering drivers of varying skill.
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| 3. |
- Alenius, Emma, 1983-
(author)
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CFD of Duct Acoustics for Turbocharger Applications
- 2010
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Licentiate thesis (other academic/artistic)abstract
- The search for quieter internal combustion engines drives the quest for a better understanding of the acoustic properties of engine duct components. In this work the main focus is the turbocharger compressor and a discussion of turbocharger acoustics and earlier work within the area is presented, giving an insight into its sound generating mechanisms and the damping effect it has on pressure pulses, i.e. incoming waves. However, despite the fact that turbo-charging was developed during the first part of the 20th century, there is not much research results available within the area of centrifugal compressor acoustics. To improve the understanding of the acoustics of engine duct components, methods based on compressible Large Eddy Simulation (LES) are explored. With these methods it is possible to capture both the complex flow, with sound generating mechanisms, and acoustic - flow interactions. It is also possible to get a detailed insight into some phenomena by access to variables and/or areas where it is difficult to perform measurements. In order to develop these methods the linear scattering of low frequency waves by an orifice plate have been studied, using an acoustic two-port model. This simple geometry was chosen since the flow has several of the characteristics seen in a compressor, like unsteady separation, vortex generation and shock waves at high Mach numbers. Furthermore the orifice plate is in itself interesting in engine applications, where constrictions are present in the ducts. The results have been compared to measurements with good agreement and the sensitivity to different parameters has been studied, showing an expected dependence on inlet Mach number and difficulties to simultaneously keep the amplitude low enough for linearity and high enough to suppress flow noise with the short times series available in LES. During the development of new engines the industry uses 1D engine CFD tools. These tools are developed to give performance data, but sometimes also the acoustic pulsations are studied. The duct components are modelled and the turbocharger is often modelled with a map, representing its fluid mechanical properties measured under steady state conditions. An aim in this work has been to study the limitations of the models available in the commercial software GT-Power. The scattering of incoming waves was simulated and the results were compared to measurements, showing a large discrepancy for the compressor and a significant discrepancy for the orifice plate.
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| 4. |
- Allam, Sabry, 1965-
(author)
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Acoustic modelling and testing of advanced exhaust system components for automotive engines
- 2004
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Doctoral thesis (other academic/artistic)abstract
- The increased use of the diesel engine in the passenger car, truck and bus market is due to high efficiency and lower fuel costs. This growing market share has brought with it several environmental issues for instance soot particle emission. Different technologies to remove the soot have been developed and are normally based on some kind of soot trap. In particular for automobiles the use of diesel particulate traps or filters (DPF:s) based on ceramic monolithic honeycombs are becoming a standard. This new exhaust system component will affect the acoustics and also work as a muffler. To properly design exhaust systems acoustic models for diesel particulate traps are needed. The first part of this thesis considers the modelling of sound transmission and attenuation for traps that consist of narrow channels separated by porous walls. This work has resulted in two new models an approximate 1-D model and a more complete model based on the governing equations for a visco-thermal fluid. Both models are expressed as acoustic 2-ports which makes them suitable for implementation in acoustic software for exhaust systems analysis. The models have been validated by experiments on clean filters at room temperature with flow and the agreement is good. In addition the developed filter models have been used to set up a model for a complete After Treatment Device (ATD) for a passenger car. The unit consisted of a chamber which contained both a diesel trap and a Catalytic Converter (CC). This complete model was also validated by experiments at room temperature. The second part of the thesis focuses on experimental techniques for plane wave decomposition in ducts with flow. Measurements in ducts with flow are difficult since flow noise (turbulence) can strongly influence the data. The difficulties are also evident from the lack of good published in-duct measurement data, e.g., muffler transmission loss data, for Mach-numbers above 0.1-0.2. The first paper in this part of the thesis investigates the effect of different microphone mountings and signal processing techniques for suppressing flow noise. The second paper investigates in particular flow noise suppression techniques in connection with the measurement of acoustic 2-ports. Finally, the third paper suggests a general wave decomposition procedure using microphone arrays and over-determination. This procedure can be used to determine the full plane wave data, e.g., the wave amplitudes and complex wave numbers k+ and k-. The new procedure has been applied to accurately measure the sound radiation from an unflanged pipe with flow. This problem is of interest for correctly determining the radiated power from an engine exhaust outlet. The measured data for the reflection coefficient and end correction have been compared with the theory of Munt [33] and the agreement is excellent. The measurements also produced data for the damping value (imaginary part of the wavenumber) which were compared to a model suggested by Howe [13]. The agreement is good for a normalized boundary layer thickness less than 30-40
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| 5. |
- Amlinger, Hanna
(author)
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Reduction of Audible Noise of a Traction Motor at PWM Operation
- 2018
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Licentiate thesis (other academic/artistic)abstract
- A dominating source for the radiated acoustic noise from a train at low speeds is the traction motor. This noise originates from electromagnetic forces acting on the structure resulting in vibrations on the surface and thus radiated noise. It is often perceived as annoying due to its tonal nature. To achieve a desirable acoustic behavior, and also to meet legal requirements, it is of great importance to thoroughly understand the generation of noise of electromagnetic origin in the motor and also to be able to control it to a low level.In this work, experimental tests have been performed on a traction motor operated from pulse width modulated (PWM) converter. A PWM converter outputs a quasi-sinusoidal voltage created from switched voltage pulses of different widths. The resulting main vibrations at PWM operation and their causes have been analyzed. It is concluded that an appropriate selection of the PWM switching frequency, that is the rate at which the voltage is switched, is a powerful tool to influence the noise of electromagnetic origin. Changing the switching frequency shifts the frequencies of the exciting electromagnetic forces. Further experimental investigations show that the trend is that the resulting sound power level decreases with increasing switching frequency and eventually the sound power level reaches an almost constant level. The underlying physical phenomena for the reduced sound power level is different for different frequency ranges. It is proposed that the traction motor, similar to a thin walled cylindrical structure, shows a constant vibration over force response above a certain frequency. This is investigated using numerical simulations of simplified models. Above this certain frequency, where the area of high modal density is dominating, the noise reducing effect of further increasing the switching frequency is limited.
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| 6. |
- Andersson, Evert, et al.
(author)
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Energy Consumption and Related Air Pollution for Scandinavian Electric Passenger Trains
- 2006
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Reports (other academic/artistic)abstract
- Energy consumption of a number of modern Scandinavian electric passenger train operations is studied. The trains are X 2000, Regina, OTU (Øresundstoget), Type 71 “Flytoget”and Type 73 “Signatur”. Energy measurements are made in regular train operations inSweden, Denmark and Norway. For Regina and Flytoget long time series (at least oneyear) are available, while shorter time series are available for the other train types. Energydata for new trains (introduced since 1999) are collected in the years 2002-2005. Energydata from 1994 are used for X 2000 and are corrected for operational conditions of 2004.For comparison, energy data for an older loco-hauled train of 1994 is also used.In the present study energy consumption for propulsion, on-board comfort and catering, aswell as idling outside scheduled service, is determined. The energy consumption includeslosses in the railway’s electrical supply, i.e. the determined amount of energy is as suppliedfrom the public electrical grid.Emissions of air pollutants, due to production of the electric energy used, are alsodetermined, in this case CO2, NOx, HC and CO. Three alternative determinations are made:(1) Pollution from average electric energy on the common Nordic market;(2) Pollution from “Green” electric energy from renewable sources;(3) Marginal contribution for an additional train or passenger, short-term and long-term.The newly introduced EU Emissions Trading Scheme with emission allowances willmost likely limit the long-term emissions independently of the actual amount ofelectric energy used by electric trains.It is shown that the investigated modern passenger train operations of years 2002- 2005 usea quite modest amount of energy, in spite of the higher speeds compared with trains of1994. For comparable operations the energy consumption is reduced by typically 25 – 30 %per seat-km or per passenger-km if compared with the older loco-hauled trains. The reasonsfor the improved energy performance are:(1) Improved aerodynamics compared with older trains (reduced air drag);(2) Regenerative braking (i.e. energy is recovered when braking the train);(3) Lower train mass per seat;(4) Improved energy efficiency in power supply, partly due to more advancedtechnologies of the trains.Energy consumption per passenger-km is very dependent of the actual load factor (i.e. ratiobetween the number of passenger-km and the offered number of seat-km). For longdistance operations load factors are quite high, typically 55 - 60 % in Scandinavia. In thismarket segment energy consumption is determined to around 0.08 kWh per pass-km. Forfast regional services with electric trains, the load factors vary from typically 20 to about40 %, while the energy consumption varies from 0.07 kWh per pass-km (for the highestload factor) to 0.18 kWh/pass-km.However, also in the latter cases the investigated trains are very competitive to other modesof transport with regard to energy consumption and emissions of air pollutants.
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| 7. |
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| 8. |
- Andreasson, Johan, 1976-
(author)
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On Generic Road Vehicle Motion Modelling and Control
- 2006
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Doctoral thesis (other academic/artistic)abstract
- With the increased amount of on-board electric power driven by the ongoing hybridization, new ways to realize vehicles are likely to occur. This thesis outlines a future direction of vehicle motion control based on the assumptions that: 1) future vehicle development will face an increased amount of available actuators for vehicle propulsion and control that will open up for an increased variety of possible configurations, 2) the onboard computational power will continue to increase and allow higher demands on active safety and drivability that will require a tighter interaction between sensors and actuators, 3) the trend towards more individualized vehicles on common platforms with shorter time-to-market require design approaches that allow engineering knowledge to be transferred conveniently from one generation to the next. A methodology to facilitate the selection of vehicle configurations and the design of the corresponding vehicle motion controllers is presented. This includes a method to classify and map configurations and control strategies onto their possible influence on the vehicle's motion. Further, a structured way of implementing and managing vehicle and subsystem models that are easy to reconfigure and reuse is suggested and realised in the developed VehicleDynamics Library. In addition, generic ways to evaluate vehicle configurations, especially the use of the adhesion potential to identify safety margin and expected limit behaviour are presented. Special attention is given to how the characteristics of a vehicle configuration can be expressed so that it can be used in vehicle motion control design. A controller structure that enables a generic approach to this is introduced and within this structure, two methods for control allocation are proposed, via tyre forces and directly. The first method uses a developed mapping of available actuators as constraints onto the achievable tyre forces and inverse tyre models to calculate the actuator inputs. The second method allocates the actuator inputs directly for an adapted problem that is linearized around the current operating point. It is shown that the methods are applicable to a variety of different vehicle configurations without redesign. Therefore, the same controller can manage a variety of vehicle configurations and there is no need to recognize and treat each different situation separately. Finally, a road map on how to continue this research towards a possible industry implementation is given. Also suggestions on more detailed improvements for modelling and vehicle motion control are provided.
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| 9. |
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| 10. |
- Backström, Daniel, 1978-
(author)
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Vibration of sandwich beams
- 2006
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Doctoral thesis (other academic/artistic)abstract
- Some aspects and properties of the lateral vibration of sandwich beams are investigated, including the concept of apparent bending stiffness and shear modulus, allowing the sandwich beam dynamics to be approximately described by classical beam theory. A sixth order beam model is derived including boundary conditions, and the free and forced response of some beam configurations analyzed. The possibility of computing material parameters from measured eigenfrequencies, i. e. inverse analysis, is considered. The higher order model is also utilized for investigation of the energy propagation through sandwich composite beams and the transmission over different junctions.
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