• Computational Structural Engineering
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• v.10 no.4
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• pp.251-265
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• 1997

A piecewise-linear system is utilized to model the offshore mooring system. The approximated piecewise-linear restoring force is obtained to be compared with the analytically derived restoring force of a mooring system. Two systems are compared to verify the applicability of the piecewise-linear system to evaluate responses of the mooring system. Using the piecewise-linear system, the response behaviors of mooring systems are examined under various excitations. Nonlinearity of the system and effects of both system and excitation parameters are intensively examined. System responses are identified mainly by observing Poincare maps. The mooring system is found to have various types of responses such as regular harmonic, subharmonic and complex nonlinear behaviors, including chaos by utilizing a piecewise-linear system. Various values of parameters are applied to determine the effects of parameters upon system responses. Response domains are determined by establishing parametric maps.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.11
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• pp.1059-1068
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• 2007

Nonlinear response structural optimization is performed using equivalent loads (NROEL). Nonlinear response optimization is extremely cost because many nonlinear analyses are required. In NROEL, the external loads are transformed to the equivalent loads (EL) for linear static analysis and linear response optimization is carried out based on the EL in a cyclic manner until the convergence criteria are satisfied. EL is the load set which generates the same response field of linear analysis as that of nonlinear analysis. The primitive from of theory has been published. In this research, the theory is investigated with large scale example problems. Four examples are solved by using NROEL. Conventional optimization with sensitivity analysis using the finite difference method (FDM) is also applied to the same examples. Moreover, response surface optimization method is applied to the last two examples. The results of the optimizations are compared. In nonlinear response optimization of large scale problems, hundreds (or even thousands) of nonlinear analyses are expected to satisfy the convergence criteria. However, in nonlinear response optimization using equivalent loads, only tens of nonlinear analyses are required. The results are discussed and the usefulness of NROEL is presented.

• Communications for Statistical Applications and Methods
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• v.13 no.2
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• pp.273-283
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• 2006

In bioassay, the response curve is usually assumed monotone increasing, but its exact form is unknown, so it is very difficult to select the proper functional form for the parametric model. Therefore, we should probably use the nonparametric regression model rather than the parametric model unless we have at least the partial information about the true response curve. However, it is well known that the nonparametric regression estimate is not necessarily monotone. Therefore the monotonizing transformation technique is of course required. In this paper, we compare the finite sample properties of the monotone transformation methods which can be applied to the local linear quasi-likelihood response curve estimate.

• Proceedings of the KIEE Conference
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• summer
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• pp.1037-1039
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• 2004

A typical conventional systems of a linear motion use rack and pinions or ball screws to convert rotary motions from DC servo motors. A linear motor has been used a several field for a MEMS technology and a aircraft carrier. We was studied a transient response of a linear actuator with a damping ratio, spring constant and a pressed power.

• Computers and Concrete
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• v.16 no.1
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• pp.17-35
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• 2015

In this study, linear and non-linear response of a masonry wall that includes an opening was presented. The masonry wall was modeled with two-dimensional finite elements. Smeared crack model that includes the strain softening behavior was selected to the masonry wall material. For the numerical application, linear and non-linear analyses of the masonry wall were carried out using east-west and vertical components of the 1992 Erzincan and 2003 $Bing{\ddot{o}}l$ earthquake acceleration records. Linear and non-linear solutions were compared each other. The displacement and stress results at the selected points of the masonry wall and crack propagation in the masonry wall were presented for both earthquake acceleration records.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.694-699
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• 2007

The spacer grid set is a part of a nuclear fuel assembly. The set has a spring and the spring supports the fuel rods safely. Although material nonlinearity is involved in the deformation of the spring,nonlinearity has not been considered in design of the spring. Recently a nonlinear response structural optimization method has been developed using equivalent loads. It is called nonlinear response optimization equivalent loads (NROEL). In NROEL, the external loads are teansformed to the equivalent loads (EL) for linear static analysis and linear response optimization is carried out based on the EL in a cyclic manner until the convergence criteria are satisfied. EL is the load set which generates the same response no EL. The objective function is defined by minimizing the maximum stress in the spring while is limited and the support force of the spring is larger than a certain value. The results are verified by nonlinear. ABAQUS is used for nonlinear response analysis and GENESIS is employed for linear response optimization.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.955-959
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• 2003

A technique for realizing linear phase IIR filters has been proposed by Powell-Chau which gives a real-time implementation of H(z-1).H(z), where H(z) is a causal nonlinear phase IIR filter. Powell-Chau system is linear but not timeinvariant system. Therefore, that system has group delay response that exhibits a minor sinusoidal variation superimposed on a constant value. In the signal processing, this oscillation seriously degrade the signal quality. Unfortunately, that system has a large sample delay of 4L and also more computational complexity. Proposed system is present a reduced computational complexity technique by moved the numerator polynomial of H(1/z) out to cascade with causal filter H(z) and remain only all-pole of H(1/z), then applied truncated infinite impulse response to finite with truncated IIR filtel $H_L$(z) and L sample delay to subtract the output sequence from the top and bottom filter. Proposed system is linear time invariance and group delay response and total harmonic distortion are also improved.

• Journal of the Korean Society of Safety
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• v.33 no.1
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• pp.81-87
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• 2018

The seismic response, the natural frequencies and the mode shapes of an offshore wind turbine with twisted tripod substructure subject to various pile-ground interactions are discussed in this paper. The acceleration responses of the tower head by four historical earthquakes are presented as the seismic response, while the other loads are assumed as ambient loads. For the pile-ground interactions, the fixed, linear and nonlinear models are employed to simulate the interactions and the p-y, t-z and Q-z curves are utilized for the linear and nonlinear models. The curves are designed for stiff, medium and soft clays, and thus, the seven types of the pile-ground interactions are used to compare the seismic response, the acceleration of the tower head. The mode shapes are similar to each other for all types of pile-ground interactions. The natural frequencies, however, are almost same for the three clay types of the linear model, while the natural frequency of the fixed support model is quite different from that of the linear interaction model. The wind turbine with the fixed support model has the biggest magnitude of acceleration. In addition, the nonlinear model is more sensitive to the stiffness of clay than the linear pile-ground interaction model.

• Earthquakes and Structures
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• v.17 no.2
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• pp.191-204
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• 2019

Near-field earthquake records including long-period high-amplitude velocity pulses can cause large isolation system displacements leading to buckling or rupture of isolators. In such cases, providing supplemental damping in the isolation system has been proposed as a solution. However, it is known that linear viscous dampers can reduce base displacements in case of near-field earthquakes but at the potential expense of increased superstructure response in case of far-field earthquakes. But can non-linear dampers with different levels of non-linearity offer a superior seismic performance? In order to answer this question, the effectiveness of non-linear viscous dampers in reducing isolator displacements and its effects on the superstructure response are investigated. A comparison with linear viscous dampers via time history analysis is done using a base-isolated benchmark building model under historical near-field and far-field earthquake records for a wide range of different levels of non-linearity and supplemental damping. The results show that the non-linearity level and the amount of supplemental damping play important roles in reducing base displacements effectively. Although use of non-linear supplemental dampers may cause superstructure response amplification in case of far-field earthquakes, this negative effect may be avoided or even reduced by using appropriate combinations of non-linearity level and supplemental damping.

• Proceedings of the Korean Geotechical Society Conference
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• 2007.09a
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• pp.317-333
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• 2007

The Round-Robin Test (RRT) for ground response analysis was performed by Division of Geotechnical Earthquake Engineering of Korean Geotechnical Society. This research analyzed the influence of analysis methods on variation of ground response by using the results of this RRT. The analysis methods include equivalent linear analysis, non-linear analysis and effective stress analysis. A total of 5 teams among 12 teams applied two kinds of analysis methods. This research compared the results of these 5 teams and analyzed the variation of the results according to analysis methods. The compared results were shear stress-shear strain relation, transfer function, time history and the response spectrum of ground surface acceleration, peak ground acceleration, peak shear strain and maximum excess pore pressure ratio.