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Nam Hoang

Bio: Nam Hoang is an academic researcher from University of Tokyo. The author has contributed to research in topics: Damper & Vibration. The author has an hindex of 7, co-authored 8 publications receiving 573 citations. Previous affiliations of Nam Hoang include Vietnam National University, Ho Chi Minh City & Asian Institute of Technology.

Papers
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Journal ArticleDOI
TL;DR: In this paper, a study on the optimal design of a TMD for a single-degree-of-freedom structure under seismic loads was conducted in which the floor decks and isolation system together can be viewed as a giant tuned mass damper to reduce the seismic force of the truss.

293 citations

Journal ArticleDOI
TL;DR: In this paper, a method to design multiple tuned mass dampers (multiple TMDs) for minimizing excessive vibration of structures has been developed using a numerical optimizer, which can be easily extended to general structures with different combinations of loading conditions and target controlled quantities.
Abstract: A new method to design multiple tuned mass dampers (multiple TMDs) for minimizing excessive vibration of structures has been developed using a numerical optimizer. It is a very powerful method by which a large number of design variables can be effectively handled without imposing any restriction before the analysis. Its framework is highly flexible and can be easily extended to general structures with different combinations of loading conditions and target controlled quantities. The method has been used to design multiple TMDs for SDOF structures subjected to wide-band excitation. Some novel results have been obtained. To reduce displacement response of the structure, the optimally designed multiple TMDs have distributed natural frequencies and distinct damping ratios at low damping level. The obtained optimal configuration of TMDs was different from the earlier analytical solutions and was proved to be the most effective. A robustness design of multiple TMDs has also been presented. Robustness is defined as the ability of TMDs to function properly despite the presence of uncertainties in the parameters of the system. Numerical examples of minimizing acceleration structural response have been given where the system parameters are uncertain and are modeled as independent normal variates. It was found that, in case of uncertainties in the structural properties, increasing the TMD damping ratios along with expanding the TMD frequency range make the system more robust. Meanwhile, if TMD parameters themselves are uncertain, it is necessary to design TMDs for higher damping ratios and a narrower frequency range. Copyright © 2004 John Wiley & Sons, Ltd.

135 citations

Journal ArticleDOI
TL;DR: In this article, accurate asymptotic formulas are derived for the modal damping ratio of a general cable, and important formulas relevant to the design of both types of dampers are tabulated.
Abstract: The performance of a damper in controlling large-amplitude vibrations of a stay cable in a bridge is influenced by essential parameters such as the amount of sag and flexural rigidity of the cable, and the stiffness of the damper support. In this paper, accurate asymptotic formulas are analytically derived for the modal damping ratio of a general cable. The formulation includes the parameters mentioned above and is appropriate for a damper having a finite support stiffness. For a viscous damper, the influential parameters are explicitly incorporated as reduction and modification factors in the modal damping formula, which significantly simplifies the design procedure for stay cables. The analytical results are also extended to high-damping rubber dampers which have recently been encountered in practice. Finally, important formulas relevant to the design of both types of dampers are tabulated.

114 citations

Journal ArticleDOI
TL;DR: In this paper, the effects of bending on the modal properties of a stay cable with a transverse damper were analyzed and an explicit asymptotic formula for modal damping with a general type of damper was derived.
Abstract: The effects of bending on the modal properties of a stay cable with a transverse damper are analytically studied. Considering that the value of the flexural rigidity in the stay cable is small in practice, an explicit asymptotic formula for the modal damping of a cable with a general type of damper is derived. For a viscous damper, the asymptotic formula obtained is compact, accurate, and thus is very suitable for practical design. Furthermore, for the first few vibration modes of interest, the asymptotic solution is independent of the modal index. It is shown that flexure in the cable reduces the maximum attainable modal damping, possibly up to 20%, while it significantly increases the optimal damping coefficient of the damper.

70 citations

Journal ArticleDOI
TL;DR: In this paper, the combined effect of two dampers, either on the same end or opposite ends of a stay cable, is analytically studied, and it is shown that when the dampers are installed at opposite ends, the total damping effect is asymptotically the sum of the contributions from single dampers.
Abstract: The combined effect of two dampers, either on the same end or opposite ends of a stay cable, is analytically studied in this paper. By considering small distances of the dampers from the anchorages, an asymptotic formula for the modal damping ratio of the cable is derived from which the total damping effect is presented in an explicit form. It is shown that when two dampers are installed at opposite ends of the cable, the total damping effect is asymptotically the sum of the contributions from single dampers. On the contrast, if two dampers are at the same end, there is no advantage of increasing the maximum modal damping in the cable over the use of a single damper.

37 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, the authors proposed the use of a novel type of passive vibration control system to reduce vibrations in civil engineering structures subject to base excitation, based on the inerter, a device that was initially developed for high-performance suspensions in Formula 1 racing cars.
Abstract: SUMMARY: This paper proposes the use of a novel type of passive vibration control system to reduce vibrations in civil engineering structures subject to base excitation. The new system is based on the inerter, a device that was initially developed for high-performance suspensions in Formula 1 racing cars. The principal advantage of the inerter is that a high level of vibration isolation can be achieved with low amounts of added mass. This feature makes it an attractive potential alternative to traditional tuned mass dampers (TMDs). In this paper, the inerter system is modelled inside a multi-storey building and is located on braces between adjacent storeys. Numerical results show that an excellent level of vibration reduction is achieved, potentially offering improvement over TMDs. The inerter-based system is compared to a TMD system by using a range of base excitation inputs, including an earthquake signal, to demonstrate how the performance could potentially be improved by using an inerter instead of a TMD. © 2013 John Wiley & Sons, Ltd.

493 citations

Journal ArticleDOI
TL;DR: In this article, a tuned mass-damper-inerter (TMDI) was proposed to suppress the oscillatory motion of stochastically support excited mechanical cascaded (chain-like) systems.

449 citations

Journal ArticleDOI
TL;DR: In this paper, a study on the optimal design of a TMD for a single-degree-of-freedom structure under seismic loads was conducted in which the floor decks and isolation system together can be viewed as a giant tuned mass damper to reduce the seismic force of the truss.

293 citations

Journal ArticleDOI
TL;DR: The review clearly demonstrates that the TMDs have a potential for improving the wind and seismic behaviors of prototype civil structures and shows that the MTMDs and d-MTMDs are relatively more effective and robust, as reported.

263 citations

Journal ArticleDOI
TL;DR: In this article, the optimum parameters of tuned mass dampers (TMD) are proposed under seismic excitations, and a Matlab program is developed for numerical optimization and time domain simulation.

206 citations