How to Understand and Utilize Time Delays in Vibration Control
Professor Haiyan Hu, Beijing Institute of Technology
Dr. Haiyan Hu is a Professor of Mechanics at Beijing Institute of Technology, where he served as the Rector from 2007 to 2017. Prior to that appointment, he was the President of Nanjing University of Aeronautics and Astronautics, China from 2001 to 2007, Professor of Mechanics at that university from 1994 to 2007, and a Humboldt Research Fellow at University of Stuttgart, Germany from 1992 to 1994. Professor Hu has been studying the dynamics and control of aerospace structures since 1982. He proposed a systematic approach to analyze the stability and bifurcations of nonlinear vibration systems under delayed control, found the effects of elastic stops and hysteretic damping on the nonlinear vibration isolation systems, and proposed new methods to design the active flutter suppression for aircrafts. His recent advances in the dynamics of soft multi-body systems guaranteed the success of several large space antennas deployed in the orbit. He has authored and co-authored 3 monographs and around 300 journal papers, which have been cited over 10,000 times by other scientists. Professor Hu received the State Award of National Science of China twice, and some other honors, such as Fellow of Chinese Academy of Science in 2007, Fellow of TWAS in 2010, Honorary Doctor from Moscow State University, Russia in 2015, and Honorary Doctor of Science from University of Reading, UK in 2016.
Abstract: Recent years have witnessed an increasing number of studies on the dynamic system involving time delays, which appear inevitably in most dynamic systems, especially those under feedback controls. This lecture addresses several important issues of properly understanding and utilizing the time delays in vibration control. The lecture begins with what is a short time delay that can be ignored from the viewpoint of the stability of a dynamic system with a state feedback. Then, it presents some theoretical studies on the stability criteria and bifurcation analysis for the dynamic system governed by a set of retarded or neutral differential equations. Afterwards, the lecture illustrates, both numerically and experimentally, the theoretical results through two case studies, including the active stabilization of an inverted double-pendulum moving on a straight rail and the active flutter suppression of an aircraft wing in a wind tunnel test. The case studies show how to make use of the advantages of time delays in the system stabilization and how to avoid the shortcomings of the time delays in controller design based on properly understanding their roles in the dynamic systems.
Acoustic Black Hole Effects for Vibroacoustic Applications
Professor Li Cheng, Hongkong Polytechnic University
Dr. Li Cheng is currently a Chair Professor and Director of Consortium for Sound and Vibration Research (CSVR) at the Hong Kong Polytechnic University. He received his BSc degree from Xi'an Jiaotong University, China and Ph.D. degree from the Institut National des Sciences Appliquées de Lyon (INSA-Lyon), France. He became a faculty member at Laval University, Canada in 1992, rising up to the rank of Full Professor before joining Hong Kong PolyU in 2000. He was the Head of Department of Mechanical Engineering from 2011 to 2014. Dr. Cheng published extensively in the field of sound and vibration, structural health monitoring, smart structure and fluid-structure interaction. He currently serves as Deputy Editor-in-Chief of Journal of Sound and Vibration, Associate Editor of the Journal of the Acoustical Society of America, Associate Editor of Structural Health Monitoring: An International Journal and an editorial board member of a few other journals. Dr. Cheng is an elected Fellow of Canadian Academy of Engineering, a Distinguished Fellow of the International Institute of Acoustics and Vibration (IIAV), a Fellow of the Acoustical Society of America, the Acoustical Society of China, IMechE, Hong Kong Institution of Engineers and Hong Kong Institute of Acoustics. He was the President of the Hong Kong Society of Theoretical and Applied Mechanics. He is now a Board Director of IIAV (International Institutes of Acoustics and Vibration) and the Vice-president Asia Pacific of I-INCE (International Institutes of Noise Control Engineering).
Abstract: Flexural waves propagating inside a vibrating structure can be manipulated through the so-called Acoustics Black Holes (ABH) effects. Upon a proper tailoring of the structural thickness, the phase velocity of the bending wave gradually reduces alongside thickness thinning, thus entailing high energy concentration and effective energy dissipation using a small amount of damping materials. The phenomenon arouses increasing interests from the scientific community and inspires innovative design solutions for light-weight and highly damped structures. In addition, the reduced structural wave velocity allows the creation of acoustically slow waves so that subsonic sound radiation regions can be formed inside a structure vibrating above the critical frequency, the consequent of which is the impaired sound radiation efficiency and reduced sound radiation. These unique features show promise of the ABH-based technology for potential applications such as wave manipulation, vibration suppression, energy insulation, sound radiation reduction, energy harvesting etc. In this talk, some of the recent progress on ABH research made by the team led by the speaker and his close collaborators will be highlighted. Topics to be discuss would cover modelling and analysis methods, exploration of underlying mechanisms of various ABH-specific phenomena, ABH structural design and potential industrial applications.
Control of Vibration Field by Actuator Array for Enhancing the Sound Quality of Panel Speakers
Professor Jeong-Guon Ih, Korea Advanced Institute of Science and Technology
Dr. Jeong-Guon Ih has been a Professor at the Department of Mechanical Engineering of the Korea Advanced Institute of Science and Technology (KAIST) since 1990, and an Adjunct Professor at DTU (Denmark) and ITB (Indonesia). He has been a visiting professor at Loughborough University UK, Seikei University Japan, Canterbury University New Zealand, Danish Technical University Denmark, Bandung Institute of Technology Indonesia, Institut für Technische Akustik, Aachen University Germany, KTH Sweden, and INSA Lyon France supported by various program fundings. He had been the Director of the Center for Noise and Vibration Control at KAIST. During 2012-2014, he served as the Chair of the School of Mechanical, Aerospace, and Systems Engineering. During 2014-2017, he had been the Dean of College of Engineering at KAIST. Before joining KAIST, he worked for the Tech Center of Daewoo Motor Co. at Inchon, Korea in charge of the NVH (Noise, Vibration, and Harshness) Group during 1979 – 1990 involved in various car refinement and development projects. Professor Ih is a founding member of the Acoustical Society of Korea (ASK) and the Korean Society for Noise and Vibration Engineering (KSNVE). Currently, he is the President Emeritus of the ASK, for which he served as the Vice President and President in 2006-2010. He was the Director of the International Institute of Acoustics and Vibration (IIAV). He is a Board Member of the International Commission for Acoustics (ICA), and currently the Vice President of the ICA. He has involved in the Scientific Committees of ICSV, ISNVH, NOVEM, ICA conferences and serves as a Theme Organizer of Inter-Noise and ICA conferences. He served as the Secretary General of the Inter-Noise 2003 held at Korea. He is organizing the ICA2022 to be held at Gyeongju in Korea as the President. Professor Ih has published more than 130 technical articles in the acoustics area, mostly published in J. Acoust. Soc. Am., J. Sound Vib., Applied Acoust., etc., and about 215 papers presented at major international conferences, and about 265 papers at the local conferences. Also, he holds about 35 national and international patents. In particular, he conducted more than 125 contract projects in collaboration with industries in automotive, electronics, heavy machines, soundproofing materials, etc. He has received 22 domestic and international awards, scholarships, and fellowships.
Abstract: The panel speaker radiates sound from a vibration field over the plate, which can be used to replace the conventional moving-coil loudspeakers. Because a thin panel is usually employed, it occupies a small volume, which has significantly merit applying modern machines and devices. It also has excellent potential in the age of the Internet-of-Things if the surface of machine coverings and other built-in structures are used. However, due to its finite panel size, the multi-modal vibration behavior is an inherent problem, resulting in severe fluctuation in the radiated sound spectrum. Commercial panel speakers usually adopt passive measures to modify the plate's physical properties to smooth the irregular spectrum of the radiated sound due to the multi-modal vibration of the panel. Materials with a low density, high elastic modulus, and high damping are used to induce a dampened interaction between adjacent modes. Such methods have been partly successful in controlling the resonant vibration, but the applicable frequency range is limited to a narrow band, and the panel should be small. One can use the control actuator array to control the vibration field within the plate. The vibration rendering for the desired vibration pattern or the elimination of some modes is possible by controlling the modal contribution in the frequency range of interest. The control actuator array is inevitably located at the panel's periphery to prevent the interaction with the other electric circuits or operating parts that should be put in the central part of the machine or device. An inverse formulation for the gain and the desired response over the speaker zone should be specified for determining the control gain of the actuators. The inverse problem should be solved without causing any singularity. Alternatively, one can adopt the traveling wave control concept. This method nullifies the reflection of the bending wave at the edge of the panel, where the control actuators are located. The panel boundary, which is changed to the connecting line of actuator array, can be transformed as the anechoic termination. For alleviating the problem with the increased cost due to many actuators, a strip speaker employing only three actuators in a thin beam and adopting the traveling wave control method can be suggested. The panels other than a rectangular shape can also be employed as the radiator. Materials of the panel can be changed to modify the efficient frequency range and the spectral shape. In this talk, the HiFi panel speaker's recent research progress is to be introduced and the future potentials, including on-going works, will be discussed.
Mechanical Applications of Cepstrum Analysis in Machine and Structural Health Monitoring
Emeritus Professor Robert Randall, The University of New South Wales
Bob Randall is a visiting Emeritus Professor in the School of Mechanical and Manufacturing Engineering at the University of New South Wales (UNSW), Sydney, Australia, which he joined in 1988. Prior to that, he worked for the Danish company Brüel & Kjær for 17 years, developing their condition monitoring systems, after ten years’ experience in the chemical and rubber industries in Australia, Canada and Sweden. His book “Frequency Analysis”, published by Brüel & Kjær with the last edition in 1987, was widely distributed. He was promoted to Associate Professor in 1996 and to Professor in 2001, and was made an Emeritus Professor on his retirement in 2008. He has degrees in Mechanical Engineering and Arts (Mathematics, Swedish) from the Universities of Adelaide and Melbourne, respectively. He is the invited author of chapters on vibration measurement and analysis in a number of handbooks and encyclopedias. He is currently serving on the Advisory Board of Mechanical Systems and Signal Processing (MSSP), and the Editorial Board of Proc. IMechE, Part C, Journal of Mechanical Engineering Science. His book Vibration-based Condition Monitoring was published in 2011 by Wiley with a new edition due in June 2021. He is the author of more than 350 papers in the fields of vibration analysis and machine diagnostics, and has supervised seventeen PhD projects in those areas. He has lectured in English, French, German, Danish, Swedish and Norwegian. From 1996 to 2011 he was Director of the DSTO (Defence Science and Technology Organisation) Centre of Expertise in Helicopter Structures and Diagnostics at UNSW, researching diagnostics and prognostics of gears and bearings in helicopter gearboxes and gas turbine engines. He is still active in research, for example being a co-author of fourteen journal papers in the last two year.
Abstract: It is not widely realised that the first paper on cepstrum analysis was published two years before the FFT algorithm, despite having Tukey as a common author, and its definition was such that it was not reversible, even to the log spectrum. After publication of the FFT in 1965, the cepstrum (now called the “power cepstrum” or “real cepstrum”) was redefined so as to be reversible to the log (amplitude) spectrum, and shortly afterwards Oppenheim and Schafer defined the ‘‘complex cepstrum”, which was reversible to the time domain, but only for transient signals. They also derived the analytical form of the complex cepstrum of a transfer function in terms of its poles and zeros. The cepstrum had been used in speech analysis for determining voice pitch (by accurately measuring the harmonic spacing in voiced speech), but also for separating the formants (transfer function of the vocal tract) from voiced and unvoiced sources, and this led quite early to similar applications in mechanics, viz. identification of uniformly spaced sidebands from local faults in gearboxes (Randall), and extraction of the cylinder pressure signal in a diesel engine from acoustic responses (Lyon and Ordubadi), since the cepstrum of a response is the sum of the cepstra of the forcing and transfer functions. Gao and Randall in 1996 used this and the analytical form of the cepstrum to curve fit modal parameters of mechanical structures in the cepstrum. Thus, the cepstrum has been around for a long time, but not used to its full capacity. A breakthrough occurred in 2011, when it was found that edited time signals could be obtained by combining an edited amplitude spectrum (using the real cepstrum) with the original phase spectrum of (sections of) continuous signals, for example to remove families of harmonics and sidebands, or to separate response signals into components dominated by intrinsic forcing functions or modal properties, in particular for variable speed machines, where forcing functions vary with the speed, but modal frequencies remain independent of the speed. This has already been used for a wide range of mechanical applications. A very powerful processing tool is an exponential ‘‘lifter” (window) applied to the cepstrum, which is shown to extract the modal part of the response. This has already been shown to be valuable for Operational Modal Analysis (OMA), in particular of machines, where both forcing functions and modal properties can contain information about condition, but also for structures with many discrete frequency excitations. This presentation is a survey of the history, latest developments, and potential future applications of cepstrum analysis applied to health monitoring of machines and structures.
Structural Health Monitoring of Wind Turbine Blades by Means of Vibration and Sound Measurements
Professor Fulei Chu, Tsinghua University
Dr. Fulei Chu is a Professor of Mechanical Engineering at Tsinghua University. He received his PhD from Southampton University. His research interests include rotating machinery dynamics, machine condition monitoring and fault diagnostics, nonlinear vibration and vibration control. He proposed several models of typical faults in rotating machinery to investigate the fault features and feature extraction methods for non-stationary signal processing which can effectively ameliorate the deficiencies of the traditional Hilbert-Huang transform. His research results have been extensively used in the condition monitoring of water turbines and wind turbines. Professor Chu has published more than 300 papers in peer review journals, including 38 papers in the Journal of Sound and Vibration. He is the Chair of the Fault Diagnostics Technical Committee of the Chinese Society for Vibration Engineering. He remains in the Elsevier list of Most Cited Chinese Researchers in the field of Mechanical Engineering since 2014.
Abstract: As energy capture components in wind turbines, blades are critical for power generation efficiency and operation security. Blades also account for a substantial proportion of failure rates and maintenance costs. Structural health monitoring of wind turbine blades is a challenging issue due to the enormous blade structures and sophisticated operation conditions. This lecture firstly reviews related studies for blade health monitoring based on vibration measurement. When damages exist in blades, structural properties would be changed, and modal characteristics have been extracted to indicate blade health states in the literature. Besides, with the assistance of advanced approaches for signal processing and statistical analysis, several statistical analysis have been used to reveal damages in wind turbine blades. Recent research progress on blade damage identification with the microphone array made by our team at Tsinghua is presented. Contents to be discussed include identification of blade damages, high-resulution sound field reconstruction methods, and applications for operating wind turbine blades. Apart from vibration-based techniques, active and noncontact damage identification could be achieved by the microphone array. In the developed technique, loudspeakers are positioned in blade cavities to excite damage-related information. Damage localization can be realized.
Vibration-based Structural Damage Detection
Professor Weidong Zhu, University of Maryland, USA
Dr. Weidong Zhu is a Professor in the Department of Mechanical Engineering at the University of Maryland, Baltimore County, and the founder and director of its Dynamic Systems and Vibrations Laboratory and Laser Vibrometry Laboratory. He received his double major BS degree in Mechanical Engineering and Computational Science from Shanghai Jiao Tong University in 1986, and his MS and PhD degrees in Mechanical Engineering from Arizona State University and the University of California at Berkeley in 1988 and 1994, respectively. He is a recipient of the 2004 National Science Foundation CAREER Award. He has been an ASME Fellow since 2010, and has served as an Associate Editor of the ASME Journal of Vibration and Acoustics and the ASME Journal of Dynamic Systems, Measurement, and Control, and as a Subject Editor of the Journal of Sound and Vibration and Nonlinear Dynamics. His research spans the fields of dynamics, vibration, control, applied mechanics, metamaterials, structural health monitoring, and wind energy, and involves analytical development, numerical simulation, experimental validation, and industrial application. He has published 220 SCI-indexed journal papers in these areas and has five issued U.S. patents. He is a recipient of the 2020 University System of Maryland Board of Regents Faculty Award for Excellence in Research.
Abstract: Recent advances in model- and non-model-based damage detection methods using vibration data such as natural frequencies and mode shapes are presented. Two major challenges associated with model-based methods are addressed: accurate modeling of structures and development of a robust inverse algorithm to detect damage, which are defined as the forward and inverse problems associated with model-based damage detection methods, respectively. To resolve the forward problem, new physics-based finite element modeling techniques for fillets in thin-walled beams and bolted joints are developed, so that complex structures with thin-walled beams and/or bolted joints can be accurately modeled with a reasonable model size. To resolve the inverse problem, a robust iterative algorithm that uses Levenberg-Marquardt method is developed to accurately detect locations and extent of damage using a minimum number of measured natural frequencies. Non-model-based methods that use vibration shapes measured from scanning laser vibrometry, without use of any a priori information of undamaged structures that is usually not available in practice, are introduced. Curvature vibration shapes are compared with those from polynomial fits with proper orders to yield curvature damage indices to identify damage. A new multi-scale differential geometry scheme is developed to calculate curvature vibration shapes. Spatially detailed vibration shapes can be measured by a continuously scanning laser Doppler vibrometer system developed in-house in a rapid and accurate manner. Application of the methodology to detect delamination in composite plates are demonstrated. Use of operational modal analysis and digital image correlation to detect damage in membranes is also demonstrated.
Research of sound field control in automotive cabins at Huawei
Dr. Xiaojun Qiu, Huawei Technologies Co., Ltd.
Dr. Xiaojun Qiu is currently a Chief Scientist at Huawei. He received his Bachelor and Master degrees from Peking University in 1989 and 1992, and his PhD from Nanjing University in 1995, all majoring in Acoustics. He worked in the University of Adelaide as a Research Fellow in Active Noise Control from 1997 to 2002, in the Institute of Acoustics of Nanjing University as a Professor of Acoustics from 2002 to 2013, at RMIT University as a Professor of Design on Audio Engineering from 2013 to 2016, and at University of Technology Sydney as a Professor in Audio, Acoustics and Vibration from 2016 to 2020. Before he joined Huawei in late 2020, he was the director of the Centre for Audio, Acoustics and Vibration in University of Technology Sydney. He was a Vice president of Acoustical Society of China and a Director of International Institute of Acoustics and Vibration from 2014 to 2018. He served as the director of Institute of Acoustics of Nanjing University from 2011 to 2013. He is a Fellow of Audio Engineering Society, a Fellow of International Institute of Acoustics and Vibration, and was an Alexander von Humboldt Research Fellow in 2008. He serves as an Associate Editor for the International Journal of Acoustics and Vibration and an Associate Technical Editor for the Journal of Audio Engineering Society. His main research areas include noise control, room acoustics, electro-acoustics, and audio signal processing, particularly applications of active control technologies
Abstract: Sound field control in automotive cabins has many challenges. First, different kinds of noise, including tonal engine noise, broadband road/tire noise and wind noise, exist in a cabin under different driving conditions. Second, a cabin interior acoustic environment is complicated due to its small volume and irregular geometry as well as reflection from the glasses, absorption, scattering, and isolation from many objects such as human bodies, seats and sound packages. Third, there are practical constraints on the locations, size and weights of the loudspeakers that can be used for control and their number is limited. Finally, the locations of the listeners are distributed in a cabin at different places. The objective of sound field control in an automotive cabin is to improve the acoustic comfort inside the cabin and to create an ideal acoustic environment for everyone inside. This means that the noise inside a cabin needs to be controlled first, and then various sound capture and reproduction technologies can be implemented for a better sound field. This presentation reports recent process in research of sound field control in automotive cabins at Huawei, which includes active control of engine and road noise, construction of personalized sound zones, and implementation of multichannel surround sound systems inside automotive cabins. The challenges and physical limitations of sound field control in automotive cabins are analyzed and the future research directions are discussed.
Hyundai’s World’s First Road-Noise Active Noise Control, RANC
Dr. Kang-duck Ih, Hyundai Motor Company
Dr. Kang-duck Ih acquired the bachelor’s degree in engineering from Seoul National University in 1989, and PhD degree from Korea Advanced Institute of Science and Technology (KAIST) in 1996. He then joined the test division of Hyundai Motor company and started his career as a test engineer for moving parts, corrosion, durability, and wind noise of vehicles. In 2010, he was promoted as a research fellow in the company in recognition of his remarkable improvement in the performance of wind noise. He has since been leading the NVH Research Lab to investigate fundamental and convergence technologies in terms of NVH. In 2010, he and his colleagues had developed the world's first broadband ANC system for the production car and opened a new horizon. Dr. Lee is currently the chairman of the academic committee of Acoustical Society of Korea (ASK), and a member of Korean Society of Automotive Engineers (KSAE). Since 2012, he has been participating in various conferences including international automotive conferences, FISITA APAC and ISNVH, and served as an official executive director of HMC. He delivered a keynote speech at Inter-Noise 2015 with the title of “New Roles and Responsibilities of Automotive NVH Engineers in an Era of Change.” Besides, he has published nearly one hundred papers at academic journals and conferences.
Abstract: Increasing the driving range of eco-friendly vehicles is the most important task. To achieve this, there are several factors to be improved such as low friction tires, aerodynamic efficiency, regenerative braking, and acceleration/deceleration pattern optimization. Above all, however, the reduction of vehicle weight is the most decisive factor. Eco-friendly vehicles do not generate engine-induced noise, therefore the dominating noise source at low speed is the road noise, whilst the wind noise becomes significant at high speed. The road noise is caused by the interaction between the tire and the road surface, and the excitation at the tire is transmitted through the suspension system and propagated to the vehicle cabin. The control of the low-frequency structure-borne road noise is normally achieved by a weight increase as the mass effect dominates the low-frequency vibration. On the other hand, to improve the performance of eco-friendly vehicles, the stiffness of rubber bushings of suspension systems needs to be increased to meet the demanding handling and durability. This then increases the force transmission in terms of road noise leading to cabin noise deterioration. Active noise control technique can be employed to reduce the cabin noise without the need to increase the weight or weakening the bush stiffness of the transmission system. In this talk, we introduce an active noise control system for broad-band road noise cancellation. The development process of the system is briefly introduced regarding miniaturization of hardware, system digitization, improvement of control performance, and latency minimization. Through this process, we developed a fully digitalized, high-performance, and mass-producible active noise control system for broad-band road noise reduction.
The future and evolution of noise and vibration design in automobile
Hirotaka Shiozaki, Chief Technology Engineer, Mitsubishi Motors Corporation
Mr. Hirotaka Shiozaki joined the research department of Mitsubishi Motors Corporation in 1987. For the next 13 years , in charge of research on vibration and noise technology, researching low-vibration body structures and developing active vibration and noise technology. In 2000, in charge of CAE technology development in the Digital Engineering Department to strengthen digital development. From that time on, promoting system engineering technology development. In 2008, in charge of new vehicle development and new technology development in the function testing department. Since 2016, in charge of Dynamic performance technology, weight reduction technology, and digital innovation technology as Chief Technology Engineer in Vehicle Engineering Development Division. During that time, assumption of the chairman of the Vibration and Noise Committee of the Society of Automotive Engineers of Japan for two years from 2018.
The current automobile industry is said to be a once-in-a-century revolutionary age. In this age, even in the field of vibration and noise technology, higher vibration and noise performance is required than ever before. Furthermore, there is an increasing demand for weight reduction and efficiency improvement. In this way, there is an increasing degree of difficulty of the noise and vibration design. In this lecture, discussing whether there is a countermeasure for this change in the development environment as an extension of the conventional technology. In addition, discussing whether new measures are needed. Furthermore, considering what will be required of vibration and noise engineers in the future in response to changes in the times.
Abstract Submission Deadline：
31st March 2021
New Deadline 15th April 2021
30th April 2021
Full Paper Submission Deadline：
30th June 2021
Notification of Acceptance:
15th August 2021