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Speech Title: Control Issues in Active Magnetic Suspension Technology

Abstract:The noncontact suspension of an object is still fascinating people. A typical method of achieving such suspension is magnetic suspension in which the object (floator) is kept in air by magnetic force. There is no contact between stator and floator. No mechanical friction and wear are expected during operation even without lubrication. These advantages have already given rise to many industrial applications such as Maglev systems for transportation, and magnetic bearings for the suspension of rotating object (rotor).

Among various methods of magnetic suspension, active electromagnetic suspension is most widely used in industrial applications. In this technology, active control plays a critical role mainly because this type of magnetic suspension system is inherently unstable.

In this speech, several approaches of control are introduced. First, an overview of technological fundamentals is explained. Then, the pioneer and/or recent works of the author are presented.

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Speech Title: Future Perspective of Carbon-Free Hydrogen/Ammonia in Energy System

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Bio: Xingjian Jing(M’13, SM’17) received the B.S. degree from Zhejiang University, China, the M.S. degree and PhD degree in Robotics from Shenyang Institute of Automation, Chinese Academy of Sciences, respectively. He also achieved the PhD degree in nonlinear systems and signal processing from University of Sheffield, U.K., in 2008. He is now a Professor with the Department of Mechanical Engineering, City University of Hong Kong. Before joining in CityU, he was a Research Fellow with the Institute of Sound and Vibration Research, University of Southampton, followed by assistant professor and associate professor with Hong Kong Polytechnic University. His current research interests include: Nonlinear dynamics, Vibration, Control and Robotics, with a series of 200+ publications of 8000+ citations and H-index 47 (in Google Scholar), with a number of patents filed in China and US.

Speech Title: The X-Structure/Mechanism Approach to Beneficial Nonlinear Design in Engineering

Abstract: Nonlinearity can take an important and critical role in engineering systems and thus cannot be simply ignored in structural design, dynamic response analysis, and parameter selection. A key issue is how to analyze and design potential nonlinearities introduced to or inherent in a system of under study. This is a must-do task in many practical applications involving vibration control, energy harvesting, sensor systems and robots etc. This paper presents an up-to-date review on a cutting-edge method for nonlinearity manipulation and employment developed in recent several years, named as the X-shaped structure or mechanism approach. The method is inspired from animal leg/limb skeletons and can provide passive low-cost high-efficiency adjustable and beneficial nonlinear stiffness (high static & ultra-low dynamic), nonlinear damping (dependent on resonant frequency and vibration excitation amplitude) and nonlinear inertia (low static & high dynamic) individually or simultaneously. The X-shaped structure or mechanism is a generic structure or mechanism representing a class of beneficial geometric nonlinearity with realizable and flexible linkage mechanism or structural design of different variants or forms (quadrilateral, diamond, polygon, K/Z/S/V-shape, or others) which all share similar geometric nonlinearity and thus similar nonlinear stiffness/damping properties, flexible in design and easy to implement. This paper systematically reviews the research background & motivation, essential bio-inspired ideas, advantages of this novel method, beneficial nonlinear properties in stiffness, damping and inertia, and potential applications, and ends with some remarks and conclusions.

Bio: Alam Md. Mahbub is a professor at Harbin Institute of Technology (China) since 2012. He worked as a senior lecturer at the University of Pretoria (South Africa), research and postdoctoral fellows at the Hong Kong Polytechnic University, and lecturer at the Rajshahi University of Engineering and Technology (Bangladesh). More than 350 technical articles are authored and co-authored, including 166 SCI journal papers. Most of the papers have been published in the top-notched journals, including Journal of Fluid Mechanics, Journal of Fluids & Structures, Ocean Engineering, Physics of Fluids, and Journal of Sustainable and Energy Reviews. His papers are well-cited, 4255 (h-index 38) in WoS database and 6535 (h-index 42) in the google database. He has been listed as a highly cited researcher for 2018 - 2021 (single year) by Web of Science, ranked top 2%. He is the author of two books. He has edited four special issues in ‘Wind and Structures, an International Journal’. He has delivered 25 Keynote speeches at international conferences. His research has mostly involved flow-induced vibrations, bluff-body wake, wind load on structures, fluid-structure interactions, hydrodynamics of swimming animals, flow control, and energy harvesting from wind and ocean current. Prof Alam has received a number of awards: Japan Government Scholarship (monbusho) for Masters and PhD studies; JSPS (Japan Society for Promotion of Science) Postdoctoral fellowship; South Africa National Research Foundation (NRF) rating ‘Promising Young Researcher, Y1’; China 1000-young-talent scholar; Shenzhen High-Level Overseas Talent; 2015 Shenzhen Outstanding Teacher; and 2017 Nanshan-District High-Level Talent. He is an editorial board member of ‘Wind and Structures, an International Journal’.

Speech Title: Hydrodynamics of aquatic animal swimming

Abstract:“How does a fish swim?’ is essentially a fascinating question. For hundreds of millions of years, adaptation and evolution have enabled fish to achieve excellent propulsion performance with their fast speed and high efficiency. During this long history of evolution, swimming animals have mastered an exquisite capacity to control their body and the flow around themselves to efficiently cruise in water. The distinctive swimming abilities of fish have inspired scientists and engineers to analyze locomotive mechanisms and to design fish-like robots. There is no doubt that human beings admire the swimming skills of aquatic animals and hope to have a similar capacity. With the development of science and technology, researchers have conscientiously considered swimming performance to be scientific as explained in light of fluid dynamics. Generally, natural swimmers share two major propulsive strategies, including caudal-fin pitching propulsion (e.g. salmon, tuna, dolphins, and sharks) and travelling wave propulsion (e.g. eels and lampreys). When animals and humans swim, the motion of their limbs from the equilibrium to the extreme and from the extreme to the equilibrium may not be symmetric. We expect slower motion in the stroke from the equilibrium to the extreme (forward stroke) and a faster motion in the stroke from the extreme to the equilibrium (retract stroke). This novel waveform is examined in our recent work. We home in on the insight into the relationship between the kinematics and thrust or efficiency. This lecture will encompass (i) the hydrodynamic performance of a traveling wavy foil with varying foil kinematics (Strouhal number), fluid properties (Reynolds number), and foil deforming characteristics (wavelength), and (ii) enhancement of both thrust and efficiency using the hypothesized waveform.

Bio: Prof. Dr. Chunning Ji, is a full professor of computational fluid dynamics, Tianjin University, China. He was awarded a PhD degree in Port, Coastal and Offshore Engineering by Tianjin University in 2006. He worked as a Marie Curie Fellow in Queen Mary, University of London, United Kingdom, from 2009 to 2011. After that, he worked as a visiting professor in University of Michigan from 2015 to 2016.
He has a broad research interests, e.g., computational fluid dynamics, fluid-structure interaction, multi-phase flow, sediment transport in an open channel, vortex-induced vibration of marine risers, marine current energy harnessing, computational bio-fluids, etc. On these subjects, he has produced more than 140 peer-reviewed papers published by international journals and conference proceedings. He was awarded the best paper prize by the 35th IAHR world congress and the Tianhe Star prize by the Chinese National Super Computing Center.
His research focuses on the sediment transport in turbulent boundary layer and the underlying mesoscopic scale physics by using the cutting-edge direct numerical simulation of turbulent flows. In 2011, this research was evaluated by the UKTC (UK Turbulence Consortium) as ‘pushing the boundary of science’. His research also focuses on the design and optimization of an aquatic clean energy converter (VIVACE) - a new concept to generate clean renewable electricity from river and ocean flow utilizing vortex-induced vibration of cylinder schools. A series of work have been done experimentally and numerically in seeking the optimal designs of VIVACE in cross-flow with high (turbulent flow) and low (laminar flow) Reynolds number. Three related patents have been awarded. He also investigated the stability of marine structures, such as the vortex-induced vibrations of marine risers, the local scouring around piles, pipelines and etc.

Speech Title: Transitions in vibration mode and wake structure of a near-wall flexible cylinder at various yaw angles

Abstract:The multi-mode transition and vortex structures in the VIV of a near-wall flexible cylinder under different yaw angles are investigated through three-dimensional direct numerical simulation. Yaw angles α = 0°-60°, gap ratio G/D = 0.8, and Re = 500 are adopted. With the increase of α, the dominated vibration mode decreases from the 6th to 1st mode in the in-line (IL) direction and the 3rd to 2nd mode in the cross-flow (CF) direction. For the IL vibration, no mode transition occurs at α = 0°, whereas frequently mode transition is observed at α > 0°, due to the intermittent participation and spanwise competition of different modes, thus showing an intensified traveling-wave characteristic. For the CF vibration, mode transition is not excited at any α case even with spanwise mode competitions, due to the significant weight of the dominated mode, thus showing a strong standing-wave characteristic. The asymmetrical distributions of vibration displacements and force coefficients are established because of irregular energy transfer along the span. The spanwise vortex tubes at α = 0°-30° are separated into several cells associated with the dominated vibration mode, showing a locally parallel vortex shedding. However, positively-yawed and negatively-yawed vortex shedding are observed at α = 45° and 60°, respectively. The vortex strengths vary along the cylinder, where large-scale and small-scale vortices are observed at the CF anti-node and node planes, respectively. The Independence Principle (IP) is only valid at α < 15° for predicting the multi-mode vibrations and hydrodynamics, significantly reduced than that of α < 45° in the wall-free case or the mono-mode VIV case.