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Design of Acoustic Metamaterials for Noise Mitigation with Ventilation

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Dr. Heow Pueh Lee is currently the Deputy Head for Research for the Department of Mechanical Engineering, College of Design and Engineering, National University of Singapore. He obtained his Bachelor degree from the University of Cambridge, Master of Engineering from the National University of Singapore, Master of Science and PhD from Stanford University. His research efforts concentrate on characterization of sound and the design of acoustic meta-structures (manmade and non-existence in nature), in particular for low frequency regime where existing acoustic mitigation solutions fail. While he emphasizes on new insights of meta- materials designs from physics-based approaches, he also actively pursues the potential applications of technology for mitigation of environmental noise in densely populated cities. His is an Associate Editor for Applied Acoustics (Elsevier), and Member of Editorial Board for Acta Mechanica Sinica (Springer), Design (MDPI) , and Acoustics (MDPI).

Heow Pueh Lee
Department of Mechanical Engineering College of Design and Engineering,
National University of Singapore

Noise in major cities has become a major issue that affects the health and quality of life. In typical noise mitigation measures, acoustic panels or barriers are typically used to shield the noise source or the recipients. Such measures are effective for mid to high frequency noise but are usually not good for mitigating low frequency noise, which has attracted increasing attention due to the increased awareness of potential health effect on human physiological functions. On the other hand, the usual installation of noise shields and noise barriers will drastically cut down the ventilation which will be required for preventing heat built-up or for providing sufficient air change for preventing the transmission of infectious diseases. The enabling of natural ventilation will also cut down the energy usage for providing forced ventilation. Daylight will typically come with natural ventilation and that will cut down the energy usage for providing lighting. Acoustic metamaterials can be designed for targeting the mitigation of mid to low frequency noise, for supplementing the performance of typically noise absorption materials which are good for mid to high frequencies. In this study, various designs of acoustic metamaterials which enable ventilation would be presented. The designs are in the form of stackable or re-configurable designs with the provision of opening for ventilation. As noise could also enter via the openings, other strategies such as the incorporation of Helmholtz's resonators or labyrinth absorbers could be used to mitigation the noise that enters via these ventilation openings. Various other designs in the form of cages with the associated guiding design principles will also be presented. The cages not only could shield the noise form machines or noise source, they are also be used for providing a quiet corner or spot within a noisy environment.

Thermoacoustic Instability: A Complex Systems Perspective

R. I. Sujith
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Prof. R. I. Sujith received his undergraduate degree in Aerospace Engineering from IIT Madras in 1988. He then graduated with an M. S. degree in 1990 and a Ph. D. in 1994, from the Georgia Institute of Technology, Atlanta, USA. He has over 360 technical publications (including 190 refereed journal publications), 12 patents and published a book on Thermoacoustic Instability. He is a recipient of the Alexander von Humboldt Fellowship and the Hans Fischer Senior Fellowship of the Institute for Advanced Study (IAS) of the Technical University of Munich. Sujith was the founding Editor-in-Chief of the International Journal of Spray and Combustion Dynamics from 2009-2015, and is currently a member of the editorial advisory board of Chaos. He has won the Young Engineer Award of the Indian National Academy of Engineering. He has been awarded the Swarnajayanti Fellowship and the J. C. Bose Fellowship by the Department of Science & Technology. He is a distinguished fellow if the International Institute of Acoustics and Vibration (IIAV) and a fellow of the Combustion Institute. He is a fellow of the Indian National Academy of Engineering and the Indian Academy of Sciences, and has been conferred the title of "TUM ambassador" of the Technical University of Munich. Prof. Sujith currently works on the application of dynamical systems and complex systems theory to study and mitigate thermoacoustic instability.

Prof. R.I. Sujith
Department of Aerospace Engineering,
IIT Madras,
Chennai, India

Large amplitude self-sustained oscillations resulting from thermoacoustic instability is a serious problem in the development of modern gas turbine and rocket engines. Thermoacoustic instability is a consequence of the nonlinear interaction between the sound waves, hydrodynamics and the unsteady flame. However, it has been traditionally studied in a linear framework with a reductionist approach where the activity in hydrodynamic and acoustic fields and the flame dynamics are studied separately. Recently, researchers have advocated that a thermoacoustic system such as a turbulent combustor can be viewed as a complex system by analysing all of its components simultaneously. Then, its dynamics can be perceived as the emergent behavior of this complex system owing to the interaction between constituent components. We will discuss some strategies to forewarn and mitigate thermoacoustic instability derived based on complex system theory.

Concepts for Frequency Sweep and Efficient Repeated Analysis in the context of Vibroacoustic Optimization and Uncertainty Quantification

Steffen Marburg
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Professor Steffen Marburg obtained his PhD from the Technische Universität (TU) Dresden in Germany. From 2010 until 2015, he held the Chair for Engineering Dynamics at the Universität der Bundeswehr (University of the Federal Armed Forces) in Munich, Germany. In July 2015, he took over the Chair of Vibroacoustics of Vehicles and Machines of the Technical University of Munich. His research interests include simulation and simulation methods of vibroacoustics, uncertainty quantification, experimental identification of parameters and parameter distributions, damage detection, and other problems of vibroacoustics. In recent years, even data-based approaches using machine/deep learning techniques and sound due to non-linear vibration phenomena have accounted for interesting new fields of his research. Steffen Marburg is one of the Co-Editors-in-Chief of the Journal of Theoretical and Computational Acoustics, Associate Editor of the Journal of the Acoustical Society of America and Editor of Mechanical Systems and Signal Processing and Acoustics Australia. He is author of approximately 170 peer reviewed journal papers and 8 book chapters. Furthermore, he is editor of a book on finite and boundary element methods and has worked as a guest editor for nine special issues of the Journal of Theoretical and Computational Acoustics. Professor Marburg is a well-known expert in computational acoustics.

Steffen Marburg
Professorial Faculty
Technical University of Munich

This presentation aims at passive noise control for vibroacoustic problems which are analyzed by finite and boundary element techniques. The author distinguishes interior and exterior problems mainly because of the quantities used as the objective function to assess the acoustic quality. For interior problems, it is common to use local quantities such as the sound pressure at a field point or, in rare cases, energy density at a field point. The situation is different for exterior problems where the radiated sound power accounts for a suitable and global quantity to assess the emission from a vibrating structure. For most engineering purposes, the assessment requires frequency sweeps in which the problem needs to be solved at many discrete frequencies. In vibroacoustic optimization and in sampling based uncertainty quantification, it is very common that structural parameters are varied while the acoustic field remains the same throughout the entire process. In this talk, we will review concepts and recent developments of efficient frequency sweeps and repeated analysis with unmodified fluid domain. For many practical cases, the situation for interior problems is rather simple to survey. Either authors have applied a modal analysis and use a modal superposition for frequency sweep and repeated analysis or the concept of unmodified acoustic transfer vectors is applied. Both concepts are quite successful as long as certain conditions are fulfilled. For exterior problems, a modal superposition is possible but, so far, only for a limited number of cases practically applicable as will be discussed herein. The concept of using acoustic transfer vectors becomes inefficient since the evaluation of the radiated sound power as an integral over a closed enveloping surface would require an excessively high amount of storage capacity. Therefore, other concepts are being followed. For frequency sweeps, a number of methods is using a frequency interpolation based on a few discrete sample frequencies. Often, these techniques are used together with Krylov-subspace model order reduction techniques. In recent years, a number of so-called low rank approximations have been developed and applied to frequency sweeps. The field of efficient repeated analysis shows some interesting developments which can be easily applied to sampling based uncertainty quantification but do not seem to be easily and generally applied for optimization.

Rotor Dynamics in a Multi-Field Environment (Virtual Presentation)

Fulei Chu
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Professor Fulei Chu received his PhD from Southampton University in UK. He is now a professor of mechanical engineering at Tsinghua University in Beijing. He is the Vice President of the Chinese Society for Vibration Engineering (CSVE) and Chairman of the Technical Committee for Machine Fault Diagnostics of CSVE. He is also a Distinguished Fellow of the International Institute of Acoustics and Vibration and a member of IFToMM Technical Committee for Rotor Dynamics. He serves as members of the editorial board for many journals, including Journal of Sound and Vibration, Journal of Mechanical Engineering Science, Journal of Vibration Engineering and others. His research interests include rotor dynamics, machine condition monitoring and fault diagnostics, nonlinear vibration and vibration control. His research results have been extensively used in the condition monitoring of water turbines and wind turbines in China. He has published more than 300 papers in peer review journals with citations of over 11000 times. He has received many awards in China, including the Outstanding Young Researcher Award from Natural Science Foundation of China and the State Natural Science Award.

Fulei Chu
Department of Mechanical Engineering,
Tsinghua University, Beijing

Traditional rotor dynamics investigates unbalance response, stability, balancing of the rotor system. As the rotating machines become high efficiency with high operation precision, more accurate prediction of the vibration level is required. There is a need to consider the effects of the fluid excitation (fluid structure interaction), thermal effect, magnetic influence, and acoustic excitation in the vibration analyses. This presentation will discuss vibration modeling and analysis for a rotating system excited by a single factor or co-excited by two factors from fluid excitation, thermal effect, magnetic influence, and acoustic excitation. For the fluid structure interaction, analytical expressions of the resistant fluid forces on the cylinder and the disk are obtained according to the vector analysis method of fluid mechanics. The vibration characteristics of the rotor system under the action of the fluid forces are analyzed. For the thermal effect, the equivalent thermally induced forces and moments are obtained and the thermal vibrations for a simplified rotor shaft are discussed under the environment where there exists the temperature gradient. For the magnetic influence, a unified expression for the non-uniform air gap length considering both the dynamic and static eccentricities is established, and the unbalanced magnetic pull (UMP) is then obtained numerically. The nonlinear vibrations induced by UMP are analyzed.

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