STUDIES TO IMPROVE EXHAUST SYSTEM ACOUSTIC PERFORMANCE BY DETERMINATION AND ASSESSMENT OF THE SOURCE CHARACTERISTICS AND IMPEDANCE OPTIMIZATION

It is shown that the relationship between an impedance change and the dynamic response of a linear system is in the form of the Moebius transformation. The Moebius transformation is a conformal complex transformation that maps straight lines and circles in one complex plane into straight lines and circles in another complex plane. The center and radius of the mapped circle can be predicted provided that all the complex coefficients are known. This feature enables rapid determination of the optimal impedance change to achieve desired performance. This dissertation is primarily focused on the application of the Moebius transformation to enhance vibro-acoustic performance of exhaust systems and expedite the assessment due to modifications. It is shown that an optimal acoustic impedance change can be made to improve both structural and acoustic performance, without increasing the overall dimension and mass of the exhaust system. Application examples include mufflers and enclosures. In addition, it is demonstrated that the approach can be used to assess vibration isolators. In many instances, the source properties (source strength and source impedance) will also greatly influence exhaust system performance through sound reflections and resonances. Thus it is of interest to acoustically characterize the sources and assess the sensitivity of performance towards source impedance. In this dissertation, the experimental characterization of source properties is demonstrated for a diesel engine. Moreover, the same approach can be utilized to characterize other sources like refrigeration systems. It is also shown that the range of variation of performance can be effectively determined given the range of source impedance using the Moebius transformation. This optimization approach is first applied on conventional single-inlet single-outlet exhaust systems and is later applied to multi-inlet multi-outlet (MIMO) systems as well, with proper adjustment. The analytic model for MIMO systems is explained in details and validated experimentally. The sensitivity of MIMO system performance due to source properties is also investigated using the Moebius transformation

Development of Wireless Techniques in Data and Power Transmission - Application for Particle Physics Detectors

Wireless techniques have developed extremely fast over the last decade and using them for data and power transmission in particle physics detectors is not science- fiction any more. During the last years several research groups have independently thought of making it a reality. Wireless techniques became a mature field for research and new developments might have impact on future particle physics experiments. The Instrumentation Frontier was set up as a part of the SnowMass 2013 Community Summer Study [1] to examine the instrumentation R&D for the particle physics research over the coming decades: {\guillemotleft} To succeed we need to make technical and scientific innovation a priority in the field {\guillemotright}. Wireless data transmission was identified as one of the innovations that could revolutionize the transmission of data out of the detector. Power delivery was another challenge mentioned in the same report. We propose a collaboration to identify the specific needs of different projects that might benefit from wireless techniques. The objective is to provide a common platform for research and development in order to optimize effectiveness and cost, with the aim of designing and testing wireless demonstrators for large instrumentation systems

Active Noise Control Over Space: A Wave Domain Approach

Noise control and cancellation over a spatial region is a fundamental problem in acoustic signal processing. In this paper, we utilize wave-domain adaptive algorithms to iteratively calculate the secondary source driving signals and to cancel the primary noise field over the control region. We propose wave-domain active noise control algorithms based on two minimization problems: first, minimizing the wave-domain residual signal coefficients, and second, minimizing the acoustic potential energy over the region, and derive the update equations with respect to two variables, the loudspeaker weights and wave-domain secondary source coefficients. Simulation results demonstrate the effectiveness of the proposed algorithms, more specifically the convergence speed and the noise cancellation performance in terms of the noise reduction level and acoustic potential energy reduction level over the entire spatial region.DP14010341

Wide-band channel sounding in the bands above 2GHz

Modem telecommunication services require increasing data rates for both mobile and fixed applications. At frequencies in the range 2.5 GHz to 6 GHz physical constraints on the size of equipment result in antenna with moderate directivity typically with an antenna beam width of 20 degrees or greater. Thus building and ground clutter is present within the first Fresnel zones of the antenna system which gives rise to multi-path propagation. This multi-path propagation (average delay and RMS delay spread) has been investigated using a wideband FMCW channel sounder that is capable of operation at a number of frequencies. The channel sounder has been based upon a parallel architecture sounder operating within the 2 GHz band with a number of frequency conversion modules to translate operation to the new frequency bands under study. Two primary configurations have been explored. In the first of these, propagation has been measured simultaneously within the 2.5 GHz, 3.4 GHz and 5.7 GHz bands. This is believed to be novel and original. In the second configuration four parallel channels operating within the 5.7 GHz band may be operated simultaneously. This configuration supports multiple antennas at the receiver. To support the work in the bands from 2.5 GHz to 6 GHz wideband discone antenna have been designed and fabricated. A system to provide relative gain and phase calibration for up to four antennas has been developed and demonstrated. This is also believed to represent a novel method of performing antenna and array calibration. Finally, the frequency converters have been used in conjunction with additional components to provide an FMCพ sounder operating within the 60 GHz Oxygen absorption band. This work is novel in that up to 1 GHz of spectrum can be swept. To support this work a significant number of microwave components have been designed and developed. In particular a novel wide band balanced X3 multiplier and a novel impedance-matched amplitude-equaliser (to provide amplifier gain-slope equalisation) has been developed. Channel soundings have been performed at three frequencies simultaneously using band specific and common antenna. The average delay and RMS delay spread have been demonstrated to be essentially frequency independent for the environments evaluated

Active vibration control of doubly-curved panels

This thesis considers active control of the vibration of doubly-curved panels. Such panels are widely used in vehicles such as cars and aircraft, whose vibration is becoming more problematic as the weight of these vehicles is reduced to control their CO2 emissions. The dynamic properties of doubly-curved panels are first considered and an analytic model which includes in-plane inertia is introduced. The results of this analytical model are compared with those from numerical modelling. Of particular note is the clustering of lower-order modes as the curvature becomes more significant. The influence of these changes in dynamics is then studied by simulating the performance of a velocity feedback controller using an inertial actuator. The feasibility of implementing such an active control system on a car roof panel is then assessed.Experiments and simulations are also conducted on a panel, mounted on one side of a rigid enclosure, which is curved by pressurising the enclosure. The active control of vibration on this panel is then implemented using compensated velocity feedback control and novel inertial actuators. It is found that the performance of the feedback control initially improves as the curvature increases, since the fundamental natural frequency of the panel becomes larger compared with the actuator resonance frequency, but then the performance is significantly degraded for higher levels of curvature, since the natural frequencies of many of the panel modes cluster together. Finally, the integration of a compensator filter in the control system ensures the robustness of the system, despite changes in curvature, which makes it a good candidate for future multi-channel implementations

Active feedback control of acoustic noise in 3 - D enclosures

Active Noise Control (ANC) strategies using feedback control methods are investigated for reducing acoustic noise in 3-D enclosures. It has been shown that robust control design techniques are effective in broadband control of noise especially in low frequency range. The work presented includes modeling, system identification, controller design, and experimental validation of different active control methodologies. The finite dimensional approximate models were obtained using both analytical as well as system identification-based methods. The analytical model was derived using basic 3-D wave equation and assumed modes method. The system identification-based model was derived using ERA-based system-id toolbox (SOCIT). The controller designs presented include LQG, passivity-based, and an H-infinity designs. The LQG design which used the state-weighting matrix derived directly from the energy function of the enclosure performed very effectively. The passivity-based controllers gave the most satisfactory closed-loop performance. These controllers are based on energy-extraction principle, and therefore, are the most desirable candidates for ANC systems. These controllers have excellent stability robustness properties as well. With high modal density and resonant peaks in the frequency response the design of H-infinity controllers becomes very difficult. For single and multi-tone cases, both LQG as well as passivity-based controllers gave significantly large noise reductions. For broadband white noise disturbance the noise reduction up to 6 dB was obtained without destabilization

Modeling and analysis of secondary sources coupling for active sound field reduction in confined spaces

This article addresses the coupling of acoustic secondary sources in a confined space in a sound field reduction framework. By considering the coupling of sources in a rectangular enclosure, the set of coupled equations governing its acoustical behavior are solved. The model obtained in this way is used to analyze the behavior of multi-input multi-output (MIMO) active sound field control (ASC) systems, where the coupling of sources cannot be neglected. In particular, the article develops the analytical results to analyze the effect of coupling of an array of secondary sources on the sound pressure levels inside an enclosure, when an array of microphones is used to capture the acoustic characteristics of the enclosure. The results are supported by extensive numerical simulations showing how coupling of loudspeakers through acoustic modes of the enclosure will change the strength and hence the driving voltage signal applied to the secondary loudspeakers. The practical significance of this model is to provide a better insight on the performance of the sound reproduction/reduction systems in confined spaces when an array of loudspeakers and microphones are placed in a fraction of wavelength of the excitation signal to reduce/reproduce the sound field. This is of particular importance because the interaction of different sources affects their radiation impedance depending on the electromechanical properties of the loudspeakers