• Coupled systems mechanics
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• v.3 no.2
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• pp.171-193
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• 2014

The dynamic characterization is important in making accurate predictions of the seismic response of the hybrid structures dominated by different damping mechanisms. Different damping characteristics arise from the construction of hybrid structure with different materials: steel for the upper part; reinforced concrete for the lower main part and interaction with supporting soil. The process of modeling damping matrices and experimental verification is challenging because damping cannot be determined via static tests as can mass and stiffness. The assumption of classical damping is not appropriate if the system to be analyzed consists of two or more parts with significantly different levels of damping. The dynamic response of structures is critically determined by the damping mechanisms, and its value is very important for the design and analysis of vibrating structures. A numerical algorithm capable of evaluating the equivalent modal damping ratio from structural components is desirable for improving seismic design. Two approaches are considered to explore the dynamic response of hybrid tower of cable-stayed bridges: The first approach makes use of a simplified model of 2 coupled lumped masses to investigate the effects of subsystems different damping, mass ratio, frequency ratio on dynamic characteristics and equivalent modal damping; the second approach employs a detailed numerical step-by step integration procedure.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.1
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• pp.75-82
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• 2004

With an aim at eliminating the numerical dispersion error arising from the numerical simulation of stress wave propagation, numerical dispersion characteristics of the wave equation based one-dimensional finite element model are analyzed and some dispersion control scheme are proposed in this paper The dispersion analyses are carried out for two types of mass matrix, namely the consistent and the lumped mass matrices. Based on the finding of the analyses, dispersion correction techniques are developed for both the implicit and explicit schemes. For the implicit scheme, either the weighting factor for the spatial derivatives of each time level or the lumping coefficient for mass matrix is adjusted to minimize the numerical dispersion. In the case of the explicit scheme an artificial dispersion term is introduced in the governing equation. The validity of the dispersion correction techniques proposed in this study is demonstrated by comparing the numerical solutions obtained using the Present techniques with the analytical ones.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.10a
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• pp.186-192
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• 1999

Safety-related equipments of nuclear power plant must be seismically qualified to demonstrate their ability to function as required during and/or after the earthquake, The seismic qualification is usually achieved through analysis and testing. Analysis method is preferably adopted for structurally simple equipments which are easy to be mathematically modeled. However even for relatively complex equipments analysis method is occasionally used for computing the input motion or supporting information for the component test followed. Electrical cabinet is a typical example for which analysis method is combinedly used with test to get modal properties of the enclosing cabinet structure. Usually the structural elements and doors of the cabinet are loosely interconnected with small-size bolts or spot welding. Therefore cabinet-type equipment usually has high and complex nonlinear properties which are not easily idealized by simple practical modeling techniques. in this paper with respect to a typical cabinet-type structure(instrumentation cabinet of nuclear power plant) a comparative study has been performed between three different state-of-the -art modeling techniques: lumped mass model frame model and FEM modal. Form the study results it has been found that modal properties of the cabinet-type structure in the elastic behavior range can be reasonably computed through any type of modeling techniques in the practice with slight modification of model properties to get better accuracy. However it needs additional modeling techniques to get reasonable results up to nonlinear range.

• Structural Engineering and Mechanics
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• v.54 no.5
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• pp.909-922
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• 2015

The dynamic response and the mooring line tension of a 1/75 scale model of spar-type platform for 2.5 MW floating offshore wind turbine subject to one-dimensional regular harmonic wave are investigated numerically and verified by experiment. The upper part of wind turbine which is composed of three rotor blades, hub and nacelle is modeled as a lumped mass the scale model and three mooring lines are pre-tensioned by means of linear springs. The coupled fluid-rigid body interaction is numerically simulated by a coupled FEM-cable dynamics code, while the experiment is performed in a wave tank with the specially-designed vision and data acquisition system. The time responses of surge, heave and pitch motions of the scale platform and the mooring line tensions are obtained numerically and the frequency domain-converted RAOs are compared with the experiment.

• Smart Structures and Systems
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• v.14 no.2
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• pp.191-207
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• 2014

In this research, an internal model based method is proposed to estimate the structural displacements and velocities under ambient excitation using only acceleration measurements. The structural response is assumed to be within the linear range. The excitation is assumed to be with zero mean and relatively broad bandwidth such that at least one of the fundamental modes of the structure is excited and dominates in the response. Using the structural modal parameters and partial knowledge of the bandwidth of the excitation, the internal models of the structure and the excitation can be respectively established, which can be used to form an autonomous state-space representation of the system. It is shown that structural displacements, velocities, and accelerations are the states of such a system, and it is fully observable when the measured output contains structural accelerations only. Reliable estimates of structural displacements and velocities are obtained using the standard Kalman filtering technique. The effectiveness and robustness of the proposed method has been demonstrated and evaluated via numerical simulations on an eight-story lumped mass model and experimental data of a three-story frame excited by the ground accelerations of actual earthquake records.

• Proceedings of the ESK Conference
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• 1993.10a
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• pp.243-251
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• 1993

With the recent issuance of a dynamic side impact test regulation in the Federal Motor Vehicle Safety Standard in the United States of America, many aspects of occupant protection in side impact crashes have been under investigation. Many investigations of real world accidents, crash test results and simulation studies have established that in side impact crashes of passenger cars, thoracic and pelvic injuries of occupant are, large part, caused by occupants' impact against the interior side of the vehicle, primarily the door. This paper is concerned with the development of a lumped mass computer model, which simulates the interaction of a struck car door and an adjacent seated occupant in side impacr, based CTP code which has been successfully used in vehicle and occupant simulation. New model developments include elimination of influence of vehicle side structure stiffness in the occupant injury responses. The model was used to investigated the effect of various door padding characteristics on occupant responses to improve vehicle safety performance. The evaluation of different crush properties of door padding have also focused to understand of behavior of impacted occupant. Results from simulations, The effects of both material coefficients $C_{f}$ and p were illustrated in terms of occupant injury criteria TTI and pelvis.

• The Journal of the Acoustical Society of Korea
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• v.21 no.1E
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• pp.12-17
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• 2002

Two improvements are discussed in measurement of the complex Young's modulus of the acoustic materials by using the transfer function method. It is found that the accelerometer misalignment might result in the severe measurement error, particularly in high frequency range. The supporting structure is modified to attach the upper and lower accelerometers along the vertical axis. Secondly, the method fur solving the equation associated with wave model is described. The solution of the lumped mass-spring model is chosen as the starting value for low frequency range, while in the mid and high frequency, the solution to the previous frequency step is used as the initial values. Measurements are done for hard and soft rubber specimens. It is shown that the erroneous peaks in the transfer function, due to the measurement error, cause highly incorrect Young's modulus and loss factors.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.3
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• pp.251-258
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• 2009

At the stage conceptual design, combat vehicle is classified into three general categories of fire power, mobility and physical properties of system. The present research is restricted to fire power and its optimization. At the stage of conceptual designing of system, it is appropriate to consider major variables affecting fire power - including the weight of bullet, which exerts a direct influence on destroying effect, maximum range which takes long range firing in consideration. To estimate the maximum firing range, a simple interior ballistic and an exterior ballistic model were built by using the lumped parameter method, Le Duc method and point mass trajectory model. Design of experiment and regression analysis was used to derive simulations of fire power. Finally, response surface models were built and design variables were analyzed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.3
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• pp.343-353
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• 1997

This paper presents a theoretical model for predicting transient behaviors during storage process of the cool storage system using the R141b clathrate. Introduction of the lumped capacitance method along with a brine reservoir having large thermal capacity yields a set of simplified energy equations. Based on the Arrhenius equation and the known experimental findings, the formation rate of clathrate for which the degree of subcooling is properly accounted is newly developed. An effective nondimensionalization of the model equations facilitates the closure of modeling as well as parametric study. Calculated results for a specific case not only simulate a typical pattern of temperautre variation in the tank successfully, but also agree reasonably well with available data. The effect of each characteristic parameter on the system performance is also investigated. It is revealed that the dominant among relevant parameters are the activation energy of reaction, the degree of subcoling and the initial mass fraction of refrigerant. Finally, the uncertainty associated with modeling of the shaft work variation appears to need further studies.

• Smart Structures and Systems
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• v.6 no.8
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• pp.953-974
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• 2010

The performance of variable dampers for seismic protection of the benchmark highway bridge (phase I) under six real earthquake ground motions is presented. A simplified lumped mass finite-element model of the 91/5 highway bridge in Southern California is used for the investigation. A variable damper, developed from magnetorheological (MR) damper is used as a semi-active control device and its effectiveness with friction force schemes is investigated. A velocity-dependent damping model of variable damper is used. The effects of friction damping of the variable damper on the seismic response of the bridge are examined by taking different values of friction force, step-coefficient and transitional velocity of the damper. The seismic responses with variable dampers are compared with the corresponding uncontrolled case, and controlled by alternate sample control strategies. The results of investigation clearly indicate that the base shear, base moment and mid-span displacement are substantially reduced. In particular, the reduction in the bearing displacement is quite significant. The friction and the two-step friction force schemes of variable damper are found to be quite effective in reducing the peak response quantities of the bridge to a level similar to or better than that of the sample passive, semi-active and active controllers.