• Journal of Mechanical Science and Technology
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• v.17 no.12
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• pp.1977-1985
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• 2003

In the present study, the dynamic modelling of planar mechanisms that consist of a system of rigid bodies is carried out using point coordiantes. The system of rigid bodies is replaced by a dynamically equivalent constrained system of particles. Then for the resulting equivalent system of particles, the concepts of linear and angular momentums are used to generate the equations of motion without either introducing any rotational coordinates or distributing the external forces and force couples over the particles. For the open loop case, the equations of motion are generated recursively along the open chains. For the closed loop case, the system is transformed to open loops by cutting suitable kinematic joints with the addition of cut-joints kinematic constraints. An example of a multi-branch closed-loop system is chosen to demonstrate the generality and simplicity of the proposed method.

• Journal of KSNVE
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• v.10 no.1
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• pp.153-159
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• 2000

This paper presents a new method for including the dynamic stiffness of the stationary parts in rotordynamic analysis. As a consequence of the support dynamics, critical speeds are varied and/or additional critical speeds are introduced. Therefore, dynamic effects of the support are often significant in high speed turbomachinery, but most of analysis has considered the support as a rigid body or a simple structure. The proposed method is based on the coupled characteristics of the driving point and transfer frequency response functions of the support system to model the equivalent spring-mass series in finite element analysis. To demonstrate the applicability of the simulation procedures provided, it is applied to the rotor model of the double suction centrifugal pump. Results of the suggested equivalent-support rotor model including coupled effects agree well with the entire pump model.

• Proceedings of the KIEE Conference
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• 1989.07a
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• pp.226-229
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• 1989

With the increasing number of power plants in modern electric power systems, power system dynamics studies become more complex. Frequently, only some part of the power system is interesting. So it becomes necessary to reduce the size of dynamics or to introduce the dynamic equivalencing techniques. The major approach of dynamic equivalencing techniques are two: one is coherency approach, which seperates machines in groups and combines machines within each group closely swinging together into one equivalent and the other is modal approach which neglects the fast modes of external system. In this paper, a new dynamic equivalencing approach which seperates machines in coherent groups as the coherency method but doesn't predetermine the structure of the equivalent.

• Proceedings of the KSR Conference
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• 1998.11a
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• pp.345-352
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• 1998

The dynamic analysis of a train system has tended to analyze one vehicle or subsystem of that rather than to analyze entire vehicles. But, the speeding and lightening of a train requires more accurate analysis. Thus, the analysis of entire vehicles is required but it spends much time. Therefore, it is needed to find out the new analytic method which is more accurate and efficient. This paper suggests a new method for analyzing a multi-vehicle system more efficiently, using‘mechanical impedance’At first, get the impedance of vehicles which influence the dynamics of the object car, through analyzing the dynamics of a vehicle. ‘Equivalent system’, a simple mechanical system, of which the impedance is similar to that ,is proposed. Then, the equivalent system was applied to a vehicle and it showed that the equivalent system works like a real vehicle system. Finally, we tried non-linear analysis of a vehicle to which the equivalent system is applied.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.11
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• pp.1434-1440
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• 1999

For the real-time power system analysis, there exists a limitation to the scale of the system to be simulated, hence it is necessary for the real-time simulation to develop reduced equivalent systems which preserve the desired property of the original system. In this paper, a procedure for developing an equivalent system whose scale is reduced within the hardware capacity of a real-time simulator is proposed. Also, the proposed procedure is applied to a KEPCO's system. The comparison between the original system and equivalent systems illustrates the capabilities of the proposed procedure.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.7
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• pp.1654-1663
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• 1994

Even if the ball bearing was conservatively designed considering the dynamic capacity and the rating life, sometimes the bearing was early failed on account of the misalignment and the lubricant contaminations etc. Misalignment was generated when bearing-shaft system transmitted large power and when the bearing was inadequately mounted. It was possible to predict the fatigue life of ball bearing under the misalignment considering the motions of ball, cage and raceway, and the factors of the effect on fatigue life. Misalignment affected on ball bearing as radial and moment load and the relationships between misalignment and moment were obtained. In this paper, the analysis of the load distributions between ball and raceway, and the prediction of fatigue life of deep groove ball bearing under radial and moment loads were carried out. And, the new formulation of equivalent dynamic load considering the effects of moment load was proposed.

• Journal of Ocean Engineering and Technology
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• v.12 no.3 s.29
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• pp.19-30
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• 1998

In this paper, the dynamic analysis of a dolphin system for mooring a floating structure such as barge mounted plant is studied. The characteristics of the soil-pile system are simplified by a set of equivalent spring elements at the mudline. To evaluate the equivalent spring constants, the finite difference method is used. Since the characteristics of the soil-pile system are nonlinear in case of soft foundation, the nonlinear dynamic analysis technique is needed. The Newmark $beta$ method incorporating the modified Newton-Raphson method(initial stiffness method) is used. A numerical analysis is performed on two mooring dolphin systems on soft foundation and rock foundation. In case of the rock foundation, the characteristics are found to be nearly linear, so the linear dynamic analysis may be sufficient to consider the foundation effect. But in case of soft foundation, the non-linearity of the foundation appears to be very signigicant, so the nonlinear dynamic analysis si needed.

• KIEE International Transactions on Power Engineering
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• v.12A no.1
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• pp.1-5
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• 2002

This paper presents the procedure to construct equivalent model of large power system based on nonlinear time simulation responses. It consists of coherency identification, generator aggregation and network reduction. Coherency index that can be directly implemented to this procedure is proposed. Generator aggregation based on detailed model is performed. This procedure can be used to construct equivalent model in PSS/E. It is also possible to reduce the large power system directly from the nonlinear time responses. This procedure is applied to the transient stability analysis of Korea power system that now experiences rapid changes. The equivalent model is compared with the original model in its size, accuracy, speed and performance. This paper shows that the developed equivalent model is a good estimate of the original system.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1262-1269
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• 2003

In structural optimization, static loads are generally utilized although real external forces are dynamic. Dynamic loads have been considered in only small-scale problems. Recently, an algorithm for dynamic response optimization using transformation of dynamic loads into equivalent static loads has been proposed. The transformation is conducted to match the displacement fields from dynamic and static analyses. The algorithm can be applied to large-scale problems. However, the application has been limited to size optimization. The present study applies the algorithm to shape optimization. Because the number of degrees of freedom of finite element models is usually very large in shape optimization, it is difficult to conduct dynamic response optimization with the conventional methods that directly threat dynamic response in the time domain. The optimization process is carried out via interfacing an optimization system and an analysis system for structural dynamics. Various examples are solved to verify the algorithm. The results are compared to the results from static loads. It is found that the algorithm using static loads transformed from dynamic loads based on displacement is valid even for very large-scale problems such as shape optimization.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.8
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• pp.1363-1370
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• 2003

In structural optimization, static loads are generally utilized although real external forces are dynamic. Dynamic loads have been considered in only small-scale problems. Recently, an algorithm for dynamic response optimization using transformation of dynamic loads into equivalent static loads has been proposed. The transformation is conducted to match the displacement fields from dynamic and static analyses. The algorithm can be applied to large-scale problems. However, the application has been limited to size optimization. The present study applies the algorithm to shape optimization. Because the number of degrees of freedom of finite element models is usually very large in shape optimization, it is difficult to conduct dynamic response optimization with the conventional methods that directly threat dynamic response in the time domain. The optimization process is carried out via interfacing an optimization system and an analysis system for structural dynamics. Various examples are solved to verify the algorithm. The results are compared to the results from static loads. It is found that the algorithm using static loads transformed from dynamic loads based on displacement is valid even for very large-scale problems such as shape optimization.