学术活动发布与订制系统

丹麦技术大学大博士，丹麦技术科学院院士，瑞典皇家科学技术院外籍院士，获ESSO奖和MAX-PLANK奖。曾任国际结构和多学科优化协会(ISSMO）主席，国际理论和应用力学学会(IUTAM)执委会秘书、执行局委员。主要从事结构优化、结构振动和稳定性、结构和声场耦合拓扑优化研究。

Abstract: The design of band-gap structures receives increasing attention for many applications in mitigation of undesirable vibration and noise emission levels. A band-gap structure usually consists of a periodic distribution of elastic materials or segments, where the propagation of waves is impeded or significantly suppressed for a range of external excitation frequencies. Maximization of the band-gap is therefore an obvious objective for optimum design. This problem is sometimes formulated by optimizing a parameterized design model which assumes multiple periodicity in the design. However, it is shown in the present lecture that such an a priori assumption is not necessary since, in general, just the maximization of the gap between two consecutive natural frequencies leads to significant design periodicity.

The aim of this lecture is to maximize frequency gaps by shape optimization of transversely vibrating Bernoulli-Euler beams subjected to free, standing wave vibration or forced, time-harmonic wave propagation, and to study the associated creation of periodicity of the optimized beam designs. The beams are assumed to have variable cross-sectional area, given total volume and length, and to be made of a single, linearly elastic material without damping. Numerical results will be presented for different combinations of classical boundary conditions, prescribed orders of the upper and lower natural frequencies of maximized natural frequency gaps, and a given minimum constraint value for the beam cross-sectional area.

To study the band-gap for travelling waves, a repeated inner segment of the optimized beams is analyzed using Floquet theory and the waveguide finite element (WFE) method. Finally, the frequency response is computed for the optimized beams when these are subjected to an external time-harmonic loading with different excitation frequencies, in order to investigate the attenuation levels in prescribed frequency band-gaps. The results demonstrate that there is almost perfect correlation between the band-gap size/location of the emerging band structure and the size/location of the corresponding natural frequency gap in the finite structure.

Niels Olhoff received his M.Sc. degree in Mechanical Engineering (1965), Ph.D. in 1969, and Dr.Techn. degree in 1979 from the Technical University of Denmark (DTU). He was Assistant Professor 1969-70 and Associate Professor 1970-85 at the Dept. of Solid Mechanics at DTU. Since 1985 he is Professor of Computer Aided Mechanical Engineering Design at the Department of Mechanical and Manufacturing Engineering of Aalborg University, Denmark.

Prof. Olhoff’s fields of research are Engineering Design Optimization, Computer-Aided Design, and Applied and Computational Mechanics, including Solid Mechanics, Structural Vibration and Instability, and Machine Acoustics. He is the author of a large number of scientific papers published in international journals and proceedings on these subjects.

Prof. Olhoff was Vice-President 1995-99 and President 1999-2003 of the International Society for Structural and Multidisciplinary Optimization (ISSMO). He served as Secretary of the Congress Committee and the Executive Committee of the International Union of Theoretical and Applied Mechanics (IUTAM) 1992-2000, was a member of the Bureau of IUTAM 2004-2012, and he is currently a Member-at-Large of the General Assembly of IUTAM.