• Structural Engineering and Mechanics
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• v.82 no.3
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• pp.283-294
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• 2022

An inerter is a passive mechanical element whose inertance can be thousands of times its own physical mass. This paper discusses the application of an inerter-based passive control system, termed rotational inertial double-tuned mass damper (RIDTMD), to mitigate human-induced floor vibrations. First, the acceleration frequency response function of the floor with an RIDTMD is first derived. It is then employed to determine the optimal design parameters of the RIDTMD using the extended fixed-points technique. Based on a theoretical analysis, design-oriented empirical functions are proposed for the RIDTMD optimal parameters, whose performance for floor vibration control is evaluated by numerical examples, in which three typical human-induced load types are considered: walking, jumping, and bouncing. The results indicate that the applicability and effectiveness of the RIDTMD for human-induced floor vibration control are robust for various load types, load frequencies, and floor natural frequencies. For the same mass ratio, the RIDTMD is better than the TMD in reducing the floor vibration amplitude and improving the effective frequency suppression bandwidth, and for the same vibration suppression effect, the mass of the RIDTMD is much lighter than that of the TMD.

• Journal of The Korean Astronomical Society
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• v.55 no.2
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• pp.37-57
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• 2022

Using I-band images of 35 nearby (z < 0.1) type 1 active galactic nuclei (AGNs) obtained with Hubble Space Telescope, selected from the 70-month Swift-BAT X-ray source catalog, we investigate the photometric properties of the host galaxies. With a careful treatment of the point-spread function (PSF) model and imaging decomposition, we robustly measure the I-band brightness and the effective radius of bulges in our sample. Along with black hole (BH) mass estimates from single-epoch spectroscopic data, we present the relation between BH mass and I-band bulge luminosity (M_BH-M_I,bul relation) of our sample AGNs. We find that our sample lies offset from the M_BH-M_I,bul relation of inactive galaxies by 0.4 dex, i.e., at a given bulge luminosity, the BH mass of our sample is systematically smaller than that of inactive galaxies. We also demonstrate that the zero point offset in the M_BH-M_I,bul relation with respect to inactive galaxies is correlated with the Eddington ratio. Based on the Kormendy relation, we find that the mean surface brightness of ellipticals and classical bulges in our sample is comparable to that of normal galaxies, revealing that bulge brightness is not enhanced in our sample. As a result, we conclude that the deviation in the M_BH-M_I,bul relation from inactive galaxies is possibly because the scaling factor in the virial BH mass estimator depends on the Eddington ratio.

• International Journal of High-Rise Buildings
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• v.9 no.3
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• pp.273-282
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• 2020

An innovative high-rise timber-concrete hybrid structure was proposed in previous research, which is composed of the concrete frame-tube structure and the prefabricated timber modules as main structure and substructures, respectively. Considering that the timber substructures are built on the concrete floors at a different height, the floor response spectrum is more effective in estimating the seismic response of substructures. In this paper, the floor response spectra of the hybrid structure with different structural parameters were calculated using dynamic time-history analysis. Firstly, one simplified model that can well predict the seismic response of the hybrid structure was proposed and validated. Then the construction site, the mass ratio and the frequency ratio of the main-sub structure, and the damping ratio of the substructures were discussed. The results demonstrate that the peaks of the floor response spectra usually occur near the vibration periods of the whole structure, among which the first two peaks stand out; In most cases, the acceleration amplification effect on substructures tends to be more evident when the construction site is farther from the fault rupture; On the other hand, the acceleration response of substructures can be effectively reduced with an appropriate increase in the mass ratio of the main-sub structure and the damping ratio of the substructures; However, the frequency ratio of the main-sub structure has no discernible effect on the floor response spectra. This study investigates the characteristics of the floor response spectrum of the novel timber-concrete structure, which supports the future applications of such hybrid structure in high-rise buildings.

• Steel and Composite Structures
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• v.42 no.3
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• pp.375-388
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• 2022

In this work, limit elastic speed analysis of functionally graded porous rotating disks has been reported. The work proposes an effective approach for modeling the mechanical properties of a porous functionally graded rotating disk. Four different types of porosity models namely: uniform, symmetric, inner maximum, and outer maximum distribution are considered. The approach used is the variational principle, and the solution has been achieved using Galerkin's error minimization theory. The study aims to investigate the effect of grading indices, aspect ratio, porosity volume fraction, and porosity types on limit angular speed for uniform and variable disk geometries of constant mass. To validate the current study, finite element analysis has been used, and there is good agreement between the two methods. The study yielded a decrease in limit speed as grading indices and aspect ratio increase. The porosity volume fraction is found to be more significant than the aspect ratio effect. The research demonstrates a range of operable speeds for porous and non-porous disk profiles that can be used in industries as design data. The results show a significant increase in limit speed for an exponential disk when compared to other disk profiles, and thus, the study demonstrates a range of FG-based structures for applications in industries that will not only save material (lightweight structures) but also improve overall performance.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.933-938
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• 2001

A 5-valve(intake 3-valve) engine has been developed to increase engine performance. These vehicles have a high power caused by the decrease of inertia mass of an intake valve and the increase of intake effective area. In this study, velocity profiles at near intake valves were inspected by using a two-color PIV and laser sheet method with tumble control valve(TCV). In addition, steady flow tests were performed to quantify tumble ratio on flow-fields generated with a TCV. These experimental results show that the tendency of the tunble ratio in intake 3-valve engine is different from the one in intake 2-valve engine. From this results, the intake flow characteristics around intake valves were made clear.

• Journal of Korean Association for Spatial Structures
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• v.2 no.1 s.3
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• pp.41-49
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• 2002

In this paper, a study of 2-step damage detection for space truss structures using the extended Kalman filter theory is presented. Space truss structures are composed of many members, so it is difficult to find damaged member from the whole system. Therefore, 2-step damage identification method is applied to detect the damaged members. First, kinetic energy change ratio is used to find damage region including damaged member and then detect damaged member using extended Kalman filtering algorithm in damage region. The effectiveness of proposed method is verified through the numerical examples.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.921-926
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• 2002

In this study, we investigate the plugging effect on the CE type steam generator tube. The natural frequency and mode shape will be changed due to decrease of the effective mass distribution along the tube. We compared the variation of stability ratio for plugged tube with that for unplugged one. The natural frequency increased because of removing the cooling water inside the steam generator tube, but the stability ratio decreased inversely because of changing the vibrational model shape. We also investigated the turbulent excitation effect.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.390.1-390
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• 2002

In this study, we investigate the plugging effect on the CE type steam generator tube. The natural frequency and mode shape will be changed due to decrease of the effective mass distribution along the tube. We compared the variation of stability ratio for plugged tube with that fur unplugged one. The natural frequency increased because of removing the cooling water inside the steam generator tube, but the stability ratio decreased inversely because of changing the vibrational mode shape. We also investigated the turbulent excitation effect.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.8 no.3
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• pp.13-20
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• 2009

Development of a dynamic engine model is essential to predict and analyze of dynamic characteristics from a natural gas engine. Reducing the harmful exhaust emissions can be accomplished by a precise air-fuel ratio control. In this paper, the dynamic engine model was proposed and included mixture formation and intake process because the dynamic characteristics can be affected by the mixture components such as an air and a gaseous fuel. The air mass flow, the partial pressure ratio, and the gas constant are changed by variations of the components in the mixture formation and intake process. The dynamic engine model is applied to the natural gas engine for validation test. Experimental results show that the dynamic engine model is effective to predict the dynamic characteristics of the natural gas engine.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.3
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• pp.1-10
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• 2000

In order to predict the performance of subsonic/sonic ejector system and to provide fundamental data for a cost effective design, one dimensional gas dynamics theory was applied to the subsonic and sonic ejector systems with the second throat. In the current theoretical analyses, ejector throat area ratio, mass flow ratio and secondary stagnation pressure were derived as a function of the operating pressure ratio of the ejector, and the discharge coefficient of the primary nozzle and the loss coefficient of the diffuser were incorporated into the whole performance of the ejector system. The results of theoretical analysis can be applied to practical industrial use of subsonic and sonic gas ejector systems.