• Journal of the Earthquake Engineering Society of Korea
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• v.1 no.4
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• pp.11-20
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• 1997

The aseismic capacity of a traditional three-bay-straw-roof wooden house for rock site condition is quantitatively estimated. One 1/4 scale model was tested for the Nahanni Earthquake with peak ground accelerations from 0.1g to 0.6g. The natural frequency of the wooden house in elastic range is 1.66 Hz and 2.15 Hz in longitudinal and transversal direction, respectively. Damping ratio of the house in elastic range is 7%. The horizontal acceleration response of the house is significantly reduced compared with the input motion due to the nonlinear inelastic characteristics of the Sagae-machum joint of the frame. The traditional wooden house has high aseismic capacity in the rock site condition where high frequency contents of motion are predominant.

• Journal of Industrial Technology
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• v.20 no.B
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• pp.155-162
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• 2000

Although Fuzzy Logic Controller(FLC) adopted three terms as input gives better performance, FLC is in general composed of two-term control because of the difficulty in the construction of fuzzy rule base. In this paper, a three-term FLC which is similar to PID control but acts as a nonlinear controller is proposed. To reduce the complexity of the rule base design and to increase efficiency. a simplified fuzzy PID control is induced from a hybrid velocity/position type PID algorithm by sharing a common rule base for both fuzzy PI and fuzzy PD parts. It is simple in structure, easy in implementation, and fast in calculation. The phase plane technique is applied to obtain the rule base for fuzzy two-term control and the resultant rule base is Macvicar-Whelan type. And the membership function is a Gaussian function. The frequency response information is used in tuning of the membership functions. Also a tuning strategy for the scaling factors is proposed based on the relationship between PID gain and the scaling factors. Simulation results show better performance and the effectiveness of the proposed method.

• Bulletin of the Society of Naval Architects of Korea
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• v.23 no.2
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• pp.33-45
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• 1986

In the present paper, the nonlinear analysis of dynamic response of the jacket type offshore structures subject to nonlinear fluid force is performed. Furthermore, several analysis methods, such as quasi-static analysis, Newmark-$\beta$ method and state vector time integration technique, and described and compared with each others in order to investigate the efficiency numerical of the schemes for this kind of nonlinear structural analysis. In the problem formulation, various environmental forces acting on the jacket type offshore structure have been studied and calculated. Particularly, hydrodynamic forces are calculated by using the Morison type formula, which contains the interaction effect between the motion of the structure and the velocity of fluid particles. Also, Stokes' 5th order wave theory and Airy's linear wave theory are used to predict the velocity distribution of the fluid particles. Finally, the nonlinear equation of motion of the structure is obtained by using three-dimensional finite element formulation. Based on the above procedures, two examples, i.e. a single pile and a typical offshore jacket platform, are studied in details.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.12
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• pp.2353-2363
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• 1994

This paper is concerned with the design of a robust digital controller using reduced-order observer on a robotic manipulator under the disturbance. In most cases of robotic manipulator since all state vectors are not measurable, the unmeasurable state vectors must be estimated or reconstructed. Other problems are caused by the nonlinear element like as nondifferentiable Coulomb friction, disturbance due to the gravitational pull, and the torsional spring effect of a link between the drive motor and the manipulator arm. The controller is based on feeding back the observable variables and the estimated state variables which are generated by the observer, and augmenting the system by additional discrete integrators. The feedback gain parameters are obtained by first applying the optimal control theory and then readjusting the feedback parameters to eliminate the limit cycle by using describing Function for nonlinear hybrid system.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.4 s.304
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• pp.143-152
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• 2005

Optimal methods for designing multiplierless IIR filters with cascaded prefilter-equalizer structures are proposed for narrowband applications. Assuming that an U filter consists of a cyclotomic Polynomial (CP) prefilter and an all-Pole equalizer based on interpolated first order polynomial (IFOP), in the proposed method the prefilter and equalizer are simultaneously designed using mixed integer linear programming (MILP). The resulting filter is a cascaded filter with minimal complexity. In addition, MtP tries to minimize both computational complexity and phase response non-linearity. Design examples demonstrate that the proposed methods produce a more efficient cascaded prefilter-equalizer than existing methods.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.04a
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• pp.267-274
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• 1999

Since the seismic response of dams can be strongly influenced by the dam-reservior interaction in needs to be taken into account in the seismic design of dams. In general a substructure method is employed to solve the dam-reservoir interaction problem in which the dam body is modeled with finite elements and the infinite region of a reservoir using a transmitting boundary. When the water is modeled as a compressible fluid the equation is formulated in frequency domain. But nonlinear behavior of dam body cannot be studied easily in the frequency domain method. In this study time domain formulation of the dam-reservoir-soil interaction is proposed based onthe lumped parameter modeling of the reservoir region, The frequency dependent dynamic-stiffness coefficients of the reservoir are converted into frequency independent lumped-parameters such as masses dampers and springs. The soil-structure interactionis modeled using lumped parameters in similar way. the ground is assumed as a visco-elastic stratum on the rigid bedrock. The dynamic stiffnesses of the rigid surface foundation are calculated using the hyperelement method and are converted into lumped parameters. The application example demonstrated that the lumped parameter model gives almost identical results with the frequency domain formulation.

• Journal of the Earthquake Engineering Society of Korea
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• v.19 no.1
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• pp.1-11
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• 2015

In order to perform a soil-isolation-structure interaction analysis of seismically isolated nuclear power plant (NPP) structures, the nonlinear behavior of a seismic isolation system may be converted to an equivalent linear model used in frequency domain analysis. Seismic responses for seismically isolated NPP containment structures subjected to a simple artificial acceleration history and different site class earthquakes are evaluated for the equivalent-linear and nonlinear models that have been applied to lead-rubber bearing (LRB) modeling. It can be observed that the maximum displacements of the equivalent linear model are larger than that of the nonlinear model. From the floor response spectrum analysis for the top of NPP containment structures, it can be observed that the spectral acceleration of an equivalent linear model at about 0.5 Hz frequency is about 2~3 times larger than that of a nonlinear model.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.172-178
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• 2003

As a typoon gets into harbour, a moored ships shows erratic motions and even mooring line failures is occurred. Such troubles may be caused by harbour resonance phenomena, result in large motion amplitudes at law frequency, which is closed to the natural frequency of the moored ship. The nonlinear motions of a moored ship beside quay are simulated under external forces due to wave, current including mooring forces in time domain. The forces due to waves are obtained from source and dipole distribution method in the frequency domain. The current forces are calculated by using slow motion maneuvering equation in the horizontal plane. The wind forces are calculated from emperical formula of ABS and the mooring forces of ropes and fenders are modeled as linear spring.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.11
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• pp.861-867
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• 2014

In this study, a semi-active isolator was constructed from applying a MR damper that used the MR fluid to an isolator. The parameter identification was also performed to determine the characteristics of this semi-active isolator during which the least squares method and the auxiliary variable method were applied to produce a value closest to the true value. In addition, the MR damper's nonlinear damping force was closely analyzed to greatly reduce the range of error. Based on this analysis, it was discovered that the parameter tended to increase with more electric current. Such analysis of the dynamic properties of semi-active isolator proved that constructing an isolator that provides a more stable operation could be achieved.

• Journal of KSNVE
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• v.9 no.2
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• pp.317-323
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• 1999

Dynamic characteristics of catenary that supplies electrical power to high-speed trains are investigated. A simple catenary is composed of the contact and messenger wires connected by droppers possessing bi-directional stiffness properties. For slender, repeating structures such as catenary, both the wave propagation and vibration properties need to be understood. The influence of parameters that determine catenary dynamics are investiaged through numerical simulations involving finite element models. The effects of the tension and flexural rigidity of the contact wire is first investigated. The effects of dropper characteristics are then investigated. For linear droppers wave propagation as well as modal properties are determined. For large catenary motion, droppers can be modeled as bi-directional elements possessing low stiffness in compression and high stiffness in tension. For this case, impulse response is computed and compared with the cases of linear droppers. It is found that the catenary dynamics are primarily determined by contact wire tension and dropper properties, with large responses observed in 5∼40 Hz frequency range. In particular, the dropper stiffness and spacing are found to have dominant influence on the response frequency and the wave transmission characteristics.