• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.3 s.55
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• pp.53-62
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• 2007

This paper presents a new vibration control method for long-span bridges using complex damper system. The new system presents simple mechanical configuration with oil and elasto-plastic dampers which have velocity and displacement dependency in vibration energy absorbing. This system can produce various damping forces according to the applied external forces by the velocity and displacement-dependent characteristics of the dampers. The oil damper dissipates vibration energy for relatively frequent and small amplitude like in the case for small to moderate earthquakes, whereas the elasto-plastic damper system works for rare and large amplitude vibration such as high seismic excitation. Thus, the proposed system exhibits the advantage of low cost with high performance since the roles of the two different dampers are effectively separated. A numerical model is established for the complex damper system, and the response characteristics and effectiveness of the proposed system are presented through numerical simulations. Numerical results show that the proposed complex damper system can significantly improve the seismic performance of long-span bridge structures with much more effective damping mechanism than single conventional passive damper systems.

• Journal of Satellite, Information and Communications
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• v.11 no.3
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• pp.110-113
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• 2016

In this paper of ka band satellite communication using geostationary satellite is very weak to rainfall. So the rain attenuation reflect the values calculated using the satellite communication links vulnerable when designing a more reliable rainfall area distribution of rain attenuation and accurate predictive models must analyze the link budget. In this paper, by utilizing domestic distribution analysis in the recent local rainfall Crane and regional rainfall in the model and compared with the country of the regional distribution of rainfall in your area to fit the rain attenuation in Ka band frequency characteristics Crane rain attenuation prediction models were analyzed to between geostationary satellites and ground station position, distance and year time percentage(%).

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.4
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• pp.449-456
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• 2015

In this paper, attaching various damping plates to the cylindrical structure and performing numerical simulations try to study heave RAO and natural period for cylinder. Most of all, we identified heave RAO of the cylinder by simulations of the motion and the wave. And then, we performed numerical simulations by changing the size and shape of heave damping plate attached to the cylinder and reviewed the heave RAO and natural period for each case. The conclusions of this research are as follows. Firstly, the natural period of cylindrical structure is increased by attached to the cylinder with heave damping plate and the heave RAO of cylindrical structure is reduced in the peak period for incident wave by attached to the cylinder with from the size of 1.30D for heave damping plate. Secondly, circular plate has long natural period than Y-type plate in all of these sections. Finally, the motion response spectrum considering the marine environment of Piranema field was identified as the heave motion of cylindrical structure is remarkably reduced with both circular plate and Y-type plate in the peak period for incident wave.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.3 s.43
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• pp.9-22
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• 2005

The allowed operation space for the mass damper in an active tuned mass damper (ATMD) system is limited for most civil structures. In this study, a restrained stroke active tuned mass damper (RS-ATMD) system with a end-spring and a holder that reduces the stroke of the mass damper with maintaining the control effect durably is proposed. This new control system functions as a conventional ATMD within the predetermined stroke limitation under small excitation and as an RS-ATMD beyond that limitation under large excitation. A new control algorithm considering such an operation principle of the RS-ATMD are also provided. Parameteric study for the various design factors of the RS-ATMD is conducted and the control effectiveness are investigated in comparison with the ATMD. Exposed to sinusoidal or impact load, the RS-ATMD system shows the considerable reduction of the maximum stroke of the mass damper with the slight diminution in the control effectiveness. Excited by random load, it also shows the considerable reduction of the maximum stroke of the mass damper not allowing the diminution in the control effectiveness.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.2
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• pp.199-208
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• 2010

A friction damper installed at a building shows nonlinear behavior since its stick and slip states are occurred repeatedly depending on the amplitude of external loadings to dissipate input energy. Friction damping is existed for the building with a friction damper. In additionally viscous one is inherently included. Therefore, the building installed in such combined damping is quite involved to find the analytical solution. In this study, first, displacement and acceleration characteristics are identified based on the exact solution for a single-degree-freedom building with a friction damper having both friction and viscous damping. Second, in free vibration, the equivalent viscous damping ratio is obtained by the energy dissipation. Third, numerical analysis is carried out to find response configuration with various friction force ratios. Fourth, corresponding equivalent viscous damping ratio is derived with the finding that the response reaches into steady-state for both friction and viscous damped structure. It is deduced using balance of input external energy and output dissipation energy for steady-state response. Finally, the equivalent viscous damping ratios of free or harmonic vibration are verified through nonlinear analysis.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.2 s.54
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• pp.165-171
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• 2009

This research developed two semi-active MR dampers whose gaps in the orifice area were different from each other, and evaluated their damping performance by loading tests. The Damping performance of MR dampers characteristically depends on various factors like their material and mechanical ones, but most importantly on the size of gap in the orifice area. For this research, we designed the orifice gaps of two dampers as each 1.0mm and 2.0mm, both with the 80mm outer diameter of the orifice. We also designed two loading test sets with different input currents, and acquired different control ability from them. The acquired test results were analyzed and evaluated with their maximum and minimum damping force and also their dynamic range from the force-displacement hysteresis loops and the force-input current relationship curve. This research clearly proved how the damping performance of control devices depends on the gap effect, and also presented a possibility that the two dampers developed in this research could be used for the smart control of construction structures by effectively adapting the input current and the number of coil turns.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.2 s.54
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• pp.172-180
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• 2009

Normally in order to build a semi-active control system equipped with MR damper, the dynamic modeling of the damper is required to numerically predict its dynamic damping force and also its behavioral characteristics. For the dynamic modeling of the MR damper, this paper attempts to predict and evaluate its dynamic behavior by applying specifically both a power model and a Bingham model. Dynamic loading tests were performed on the squeeze type of damper specially designed for this research, and force-displacement hysteresis loops confirmed the effectiveness of the damper as a semi-active control device. In the meantime, in order to evaluate the effectiveness of each model applied, the model parameter for each model was identified. On the basis of the parameter, we derived the error ratio of the force-velocity relationship curve and the dynamic damping force, which was contrasted and compared with the experimental results of the squeeze type of damper. Finally, the squeeze type of MR damper developed in this research was proved to be valid as a semi-active control device, and also the evaluation of the two dynamic models showed they were working fine so that they were likely to be easily utilized to numerically predict the dynamic characteristics of any dampers with MR fluid as well as the squeeze type of MR damper.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.5
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• pp.38-44
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• 2015

In this paper, the vibration control effect of the Exo-type damping system was investigated by applying the Kagome dampers to 15-story and 20-story frame structure apartment. A new Exo-type damping system composed of the dampers and supporting column was proposed in the previous work and numerical analysis were performed to investigate the effects of optimum stiffness ratio between controlled structure and supporting column, the size of damper and yield ratio of the damper. The numerical analysis results of a structure with Exo-type damping system up to the third story showed that the stiffness ratio should be higher than 7.0 and the damper device yield ratio be at least 8.0% ($V_{damper}/V_{base\;shear$) to effectively reduce the base shear and the maximum drift of the uppermost story. When the Exo-type damping system was installed up to the fifth story, the stiffness ratio should be higher than 2.5 and damper device yield ratio needs to be at least 3.5% ($V_{damper}/V_{base\;shear$) for obtaining the target performance.

• Computational Structural Engineering
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• v.6 no.1
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• pp.127-135
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• 1993

This paper summarizes a study on the application of viscoelastic dampers as an energy dissipation device in the frame structure. It can be concluded that, even at high temperatures, the viscoelastically damped structure can achieve a significant reduction of structural response as compared to the case with no dampers added. Empirical formulae for estimating the dynamic properties of the viscoelastic damper are established based on the regression analysis using data obtained from component tests of the damper. The structural damping with added dampers can be satisfactorily estimated by the modal strain energy method and the derived empirical formulae. Numerical simulations using conventional modal analysis methods are also carried out to predict the dynamic response of viscoelastically damped structures under seismic excitations. Comparison between numerical simulations and test results shows very good agreement. Based on the above studies, a design procedure for viscoelastically damped structures is present . This design procedure fits naturally into the conventional structural design flow-chart by including damping ratio an additional design parameter.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.3
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• pp.17-22
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• 2003

This paper presents an experimental investigation of a reversible colloidal seismic damper, which is statically loaded, The porous matrix is composed from silica gel (labyrinth or central-cavity architecture), coated by organo-silicones substances, in order to achieve a hydrophobic surface. Water is considered as associated lyophobic liquid. Reversible colloidal damper static test rig and the measuring technique of the static hysteresis are described. Influence of the pare and particle diameters, particle architecture and length of the grafted molecule upon the reversible colloidal damper hysteresis is investigated, for distinctive types and mixtures of porous matrices, Variation of the reversible colloidal damper dissipated energy and efficiency with temperature, pressure, is illustrated.