• Journal of the Earthquake Engineering Society of Korea
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• v.21 no.4
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• pp.181-188
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• 2017

Current seismic design provisions such as ASCE 7-10 provide criteria for selecting ground motions for conducting response history analysis. This study is the sequel of a companion paper (I - Ground Motion Selection) for assessment of the ASCE 7-10 criteria. To assess of the ASCE 7-10 criteria, nonlinear response history analyses of twelve single degree of freedom (SDF) systems and one multi-degree of freedom (MDF) system are conducted in this study. The results show that the target seismic demands for SDF can be predicted using the mean seismic demands over seven and ten ground motions selected according to the proposed method within an error of 30% and 20%, respectively

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2006.03a
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• pp.519-526
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• 2006

This paper compares the seismic response control performance of linear and non-linear models fer tuned liquid damper (TLD). The existing linear and nonlinear TLD models were used for the numerical analysis of single degree of freedom (SDOF) and multi degree of freedom (MDOF) systems with TLD. The nonlinear model considers the variation of the frequency and damping of the TLD with varying excitation amplitude while the linear one has the invariant parameters. Numerical analysis results from SDOF systems indicate that the nonlinear model shows about 5% better control performance than linear one when the mass ratio is 2% and the optimal parameters for reducing peak responses are dependent on the characteristics of the excitation earthquake loads.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.260-260
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• 2000

In this work, we have developed a 2 degree of freedom(DOF) motion simulator that can generate the sensation of motion in a 6 DOF space. The motion base has the DOF of roll and pitch, and the purpose of the motion base is to create the sensation of riding a vehicle in a 3D space by controlling the motion base. The dynamics of the mechanism was analysed and the optimal design of the motion base mechanism has been reached. The prototype motion base mechanism was developed and tested. The multi-axis motion controller(MMC) was used to control the two ac servo motors that drive the roll and pitch motion.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.746-751
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• 2002

This purpose of this study was to design the effect of recovering of a hand amputees by myoelectronic hand. It was designed with 2 degree of freedom in tile laboratory. Myoelectronic hand had only one degree of freedom and one movement until now. Also this myoelectronic hand had multi-joint system. Myoelectronic hand data was obtained by measuring hand and data was applied when it was designed myoelectronic hand. PID controll of myoelectronic hand was used to it. Displacement control was applied the first link of finger. Experiment was accomlkished in Tip grasp, power grasp and Hook grasp modes. Displacement controll was good in low frequency. Velocity control was applied to each mode. This myoelectronic hand with a hand amputees could do some jobs such as grasping materials. Further studies were needed to evaluate the effect of a myoelectronic hand with more precise laboratory equipment.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.170-177
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• 2004

A single degree of freedom system and transmissibility are key concepts in many problems of vibration isolation. In order to apply this approach, however, several assumptions must be satisfied, which are often not realistic. In this paper, an approach using vibration power flow is introduced to deal with vibration isolations in a more practical way. Procedures of this approach and some results of research are presented. Difficulties in this method are also discussed.

• Structural Engineering and Mechanics
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• v.30 no.4
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• pp.445-466
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• 2008

This paper presents a novel structural damage detection method with a new damage index based on the statistical moments of dynamic responses of a structure under a random excitation. After a brief introduction to statistical moment theory, the principle of the new method is put forward in terms of a single-degree-of-freedom (SDOF) system. The sensitivity of statistical moment to structural damage is discussed for various types of structural responses and different orders of statistical moment. The formulae for statistical moment-based damage detection are derived. The effect of measurement noise on damage detection is ascertained. The new damage index and the proposed statistical moment-based damage detection method are then extended to multi-degree-of-freedom (MDOF) systems with resort to the leastsquares method. As numerical studies, the proposed method is applied to both single and multi-story shear buildings. Numerical results show that the fourth-order statistical moment of story drifts is a more sensitive indicator to structural stiffness reduction than the natural frequencies, the second order moment of story drift, and the fourth-order moments of velocity and acceleration responses of the shear building. The fourth-order statistical moment of story drifts can be used to accurately identify both location and severity of structural stiffness reduction of the shear building. Furthermore, a significant advantage of the proposed damage detection method lies in that it is insensitive to measurement noise.

• Smart Structures and Systems
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• v.31 no.5
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• pp.531-543
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• 2023

Base isolation is one of the most widely implemented and well-known technique to reduce structural vibration and damages during an earthquake. However, while the base-isolated structure reduces storey drift significantly, it also increases the base drifts causing many practical problems. This study proposes the use of Shape Memory Alloys (SMA) wires for the reduction in base drift while controlling the overall structure vibrations. A multi-degree-of-freedom (MDOF) structure along with base isolators and Shape-Memory-Alloys (SMA) wires in diagonal is tested experimentally and analytically. The isolation bearing considered in this study consists of laminates of steel and silicon rubber. The performance of the proposed structure is evaluated and studied under different loadings including harmonic loading and seismic excitation. To assess the seismic performance of the proposed structure, shake table tests are conducted on base-isolated MDOF frame structure incorporating SMA wires, which is subjected to incremental harmonic and historic seismic loadings. Root mean square acceleration, displacement and drift are analyzed and discussed in detail for each story. To better understand the structure response, the percentage reduction of displacement is also determined for each story. The result shows that the reduction in the response of the proposed structure is much better than conventional base-isolated structure.

• Wind and Structures
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• v.21 no.5
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• pp.523-536
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• 2015

To study the vibration frequency of super high-rise buildings in the process of vortex induced vibration (VIV), wind tunnel tests of multi-degree-of-freedom (MDOF) aero-elastic models were carried out to measure the vibration frequency of the system directly. The effects of structural damping, wind field category, mass density, reduced wind velocity ($V_r$), as well as VIV displacement on the VIV frequency were investigated systematically. It was found that the frequency drift phenomenon cannot be ignored when the building is very high and flexible. When $V_r$ is less than 8, the drift magnitude of the frequency is typically positive. When $V_r$ is close to the critical wind velocity of resonance, the frequency drift magnitude becomes negative and reaches a minimum at the critical wind velocity. When $V_r$ is larger than12, the frequency drift magnitude almost maintains a stable value that is slightly smaller than the fundamental frequency of the aero-elastic model. Furthermore, the vibration frequency does not lock in the vortex shedding frequency completely, and it can even be significantly modified by the vortex shedding frequency when the reduced wind velocity is close to 10.5.

• Journal of Ocean Engineering and Technology
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• v.25 no.1
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• pp.67-72
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• 2011

Offshore structures, such as a platform, a buoy, or a floating vessel, are exposed to several dynamic loads, and viscoelastic damping material is used to reduce the vibration of offshore structures. It is important to know the properties of viscoelastic materials because loss factor and Young's modulus of the viscoelastic damping material are dependent on frequency and temperature. In this study, an advanced technique for obtaining accurate loss factor and Young's modulus of the viscoelastic damping material is introduced based on a multi degree of freedom curve-fitting method and the RKU (Ross-Kerwin-Ungar) equations. The technique is based on a modified experimental procedure from ASTM E 756-04. Loss factor and Young's modulus of the viscoelastic damping material are measured for different temperatures by performing the test in a temperature-controlled vibration measurement room where temperature varies from 5 to 45 degrees Celsius.

• Smart Structures and Systems
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• v.3 no.4
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• pp.423-437
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• 2007

The empirical mode decomposition (EMD) method is well-known for its ability to decompose a multi-component signal into a set of intrinsic mode functions (IMFs). The method uses a sifting process in which local extrema of a signal are identified and followed by a spline fitting approximation for decomposition. This method provides an effective and robust approach for decomposing nonlinear and non-stationary signals. On the other hand, the IMF components do not automatically guarantee a well-defined physical meaning hence it is necessary to validate the IMF components carefully prior to any further processing and interpretation. In this paper, an attempt to use the EMD method to identify properties of nonlinear elastic multi-degree-of-freedom structures is explored. It is first shown that the IMF components of the displacement and velocity responses of a nonlinear elastic structure are numerically close to the nonlinear normal mode (NNM) responses obtained from two-dimensional invariant manifolds. The IMF components can then be used in the context of the NNM method to estimate the properties of the nonlinear elastic structure. A two-degree-of-freedom shear-beam building model is used as an example to illustrate the proposed technique. Numerical results show that combining the EMD and the NNM method provides a possible means for obtaining nonlinear properties in a structure.