Figure - Meeting on Structural Damping
Majority of the IWEF activities involved up to now mostly Japanese and U.S. participants. The IWEF held two technical meetings in 1994. Their brief description is included in the previous issue of the IWEF Newsletter. In this issue of the Newsletter, two IWEF meetings (Meeting on Structural Damping, and Workshop on CFD for Prediction of Wind Effects on Buildings and Structures), held in 1995, are described.
The meeting offered an exciting opportunity to discuss structural damping,the most important,yet most uncertain, parameter affecting the dynamic response of buildings and structures. As it is well known, damping uncertainty significantly reduces the reliability of structural design for dynamic effects. Accurate determination of structural damping is very important not only for evaluation of structural response, but also for design of active, passive and hybrid auxiliary damping devices installed in buildings and structures.
Although the meeting was organized by the International Wind Engineering Forum, representing mainly wind engineering community, it brought together professionals in wind, earthquake and structural engineering. Representatives of both research institutes and structural design firms were among nearly 200 participants. Professionals in other related technical fields were also represented. They included experts in design and evaluation of structural response control systems, and others.
Reliable high-quality full-scale damping data for buildings and structures are desired to aid establishing methods/predictors for assessment of the design values of the damping ratio. Due to high cost and scarcity of full-scale investigations, the data base should be made accessible to any interested researcher and practitioner interested in damping of buildings and structures. From this perspective, there exists a pressing need for international collaboration to exchange and collect reliable damping data. The role of this meeting towards this goal was acknowledged by the workshop participants.
The meeting proceedings, including the presented papers and discussion as well as additional technical papers focused on damping issues, will be published by Elsevier Science Publishers in mid 1996. A follow-up damping meeting is planned to held in the future.
This meeting addressed present status and future outlook for practical application of CFD technology in analysis of wind effects on buildings and structures. Advantages, accuracy and limitations of the computational techniques and turbulence modeling were discussed from the wind and structural engineering point of view. Feasibility for application of this methodology for wind resistant structural design was also addressed. The meeting format was informal and free exchange of diverging views was encouraged during discussion periods.
The workshop was attended by approximately 80 participants representing both practitioners and researchers in wind and structural engineering as well as fluid mechanics. In opening remarks, T. Ohkuma of Kanagawa University presented a brief overview of the IWEF and the scope and objectives of the workshop. In the technical program that followed, lectures were presented by seven invited speakers: B. Bienkiewicz of Colorado State University, J. H. Ferziger of Stanford University, A. Kareem of University of Notre Dame, H. Kawai of Tokyo Denki University, S. Kawamoto of Nippon Sheet Glass Co., T. Nomura of Nihon University, and T. Tamura of Tokyo Institute of Technology.
Regarding turbulence modeling for prediction of wind loading on buildings and structures, Ferziger gave a talk on recent developments in application of large eddy simulation (LES) in computations of separated flows past bluff bodies. Addressing the same issue from a different perspective, Kawamoto discussed practical aspects of modeling turbulent transport, for wind effects simulation using a modified two equation model.
The state of application of CFD in wind engineering problems in Japan and in the U.S. was illustrated in presentations by the remaining three speakers. Kareem shared recent LES results for flow past bluff bodies obtained at University of Notre Dame. Kawai presented an overview of recent initiatives focused on application of CFD for wind-resistant structural design, undertaken by the Architectural Institute of Japan (AIJ). Addressing numerical modeling effort focused on a test low-rise building, the speaker pointed out discrepancy between the compared numerical results obtained for this case by different research groups.Concerns regarding this matter and speculation on origins of this discrepancy was later reflected in a discussion that followed the presentation.
The workshop was concluded with a discussion session, in which all the speakers and members of audience were encouraged to participate. The focus of this exchange was the present status and future outlook for practical use of CFD for numerical prediction of wind loading on buildings and structures. Some of the issues emerging from this discussion are summarized next.
Researchers and practitioners in wind and structural engineering are in general not familiar with CFD technology. They need to be educated and through this process acceleration of diffusion (spread) of emerging computational technology may be achieved. One could start with developing a mechanism which would encourage wind and structural engineers to apply computational tools in analysis of simplified, two-dimensional problems. Opinions regarding this strategy however were divided. Some speakers expressed view that numerical results from two-dimensional numerical simulations might provide useful insight and initial guide for more complex three-dimensional problems. Others claimed that differences between two and three-dimensional problems are often quite pronounced and they should be further studied before an attempt is made to extend the results of preliminary two-dimensional studies to three-dimensional problems.
It was also observed that at the present time it is not entirely clear what level of accuracy should be demanded from CFD computations for prediction of wind loading. Related to this issue is the need to establish the range of the scatter in the computational simulations resulting from application of different numerical models. Once this range is determined, the computational results may be used in actual design, with the scatter margin being accounted for in the design procedures.
It was agreed that interchange of CFD know-how should be promoted within the area of wind engineering and through interdisciplinary exchange involving researchers and practitioners in civil, mechanical and aeronautical engineering, as well as atmospheric scientists. Active promotion of such collaboration would require careful planning and execution of joint projects and programs. An example of such an effort in Japan is the AIJ initiative, referred to earlier. It was also stressed that it is important to clearly convey to wind and structural engineering community specific goals and possible payoffs of such collaborative activities.
A follow-up CFD workshop is planned to be held in summer of 1996, in conjunction with the Second International Symposium on Computational Wind Engineering, scheduled to be held at Colorado State University in August of 1996.
For a free copy of the previous issue of the IWEF Newsletter please contact one of the above offices. A limited number of copies of the proceedings of the IWEF meetings are also available at a nominal price. For information on the proceedings and the price list please contact one of the offices. To be included on the IWEF mailing list, please forward the following information to one of the addresses listed above:
Japan Association for Building Research Promotion
5-26-20 Kenchiku-kaikan, Shiba Minato-ku, Tokyo, 108 JAPAN
Prof. Takeshi Ohkuma Prof. Bogusz Bienkiewicz
Prof. Arthur N.L.Chiu Prof. Hiromasa Kawai
Dr. Kunio Fujii Prof. Ahsan Kareem
Prof. James R.McDonald Dr. Hisashi Okada
Prof. Tetsuro Tamura Prof. Yukio Tamura
Dr. Hiroyuki Yamanouchi