• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.161-170
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• 2007

In general, deflection limit criteria of bridge design specifications would have been considered based on the static serviceability and structural stability. Dynamic serviceability induced from bridge vibration, as a comfort limit, actually has not been included in the criteria. Thus, it is necessary for dynamic serviceability to be considered in bridge vibration problems and for comfort limit on vibration to be needed for evaluating dynamic serviceability of bridges. In this paper, comfort limits of bridge structures considering the time duration exposed by vibration were examined with frequency and time dependent comfort limits, and they were evaluated by using the vibration signals measured from the existing bridges. Therefore, it is resulted that the time-dependent comfort limit considering the duration of vibration is an efficient estimate for evaluating dynamic serviceability of bridges.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.17 no.31
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• pp.115-123
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• 1994

Group scheduling, which is a kind of operations scheduling based on the GT concept is analyzed in a multi-stage manufacturing system. The purpose of this research is to develop and evaluate a heuristic algorithm for determining gro up sequence and job sequence within each group to minimize a complex cost function, i.e. the sum of the total pe-nalty cost for tardiness and the total holding cost for flow time, in a multi-stage manufacturing system with group setup time dependent upon group sequence. A heuristic algorithm for group sc heduling is developed, and a numerical example is illustrated. For the evaluation of the pro-posed heuristic algorithm, the heuristic solution of each of 63 problems is compared with that of random scheduling. The result shows that the proposed heuristic algorithm provides better solution in light of the proposed cost function.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.19 no.2
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• pp.103-121
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• 2015

In this paper, we briefly review and describe a projection algorithm for numerically computing the two-dimensional time-dependent incompressible Navier-Stokes equation. The projection method, which was originally introduced by Alexandre Chorin [A.J. Chorin, Numerical solution of the Navier-Stokes equations, Math. Comput., 22 (1968), pp. 745-762], is an effective numerical method for solving time-dependent incompressible fluid flow problems. The key advantage of the projection method is that we do not compute the momentum and the continuity equations at the same time, which is computationally difficult and costly. In the projection method, we compute an intermediate velocity vector field that is then projected onto divergence-free fields to recover the divergence-free velocity. Numerical solutions for flows inside a driven cavity are presented. We also provide the source code for the programs so that interested readers can modify the programs and adapt them for their own purposes.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.10
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• pp.923-935
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• 2007

In general, deflection limit criteria of bridge design specifications would have been considered based on the static serviceability and structural stability. Dynamic serviceability induced from bridge vibration, as a comfort limit, actually has not been included in the criteria. Thus, it is necessary for dynamic serviceability to be considered in bridge vibration problems and for comfort limit on vibration to be needed for evaluating dynamic serviceability of bridges. In this paper, comfort limits of bridge structures considering the time duration exposed by vibration were examined with frequency and time dependent comfort limits, and they were evaluated by using the vibration signals measured from the existing bridges. Therefore, it is resulted that the time-dependent comfort limit considering the duration of vibration is an efficient estimate for evaluating dynamic serviceability of bridges.

• Publications of The Korean Astronomical Society
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• v.5 no.1
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• pp.1-16
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• 1990

Some important problems for the bimodal initial mass function(IMF) of field stars in the solar neighborhood, the relation of the IMF of field stars with the combined IMF of open star clusters and the time-dependent IMF of young star clusters are discussed particularly by comparing their observed and computed present day mass functions.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.38 no.3
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• pp.169-180
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• 2015

Recently, scheduling problems with position-dependent processing times have received considerable attention in the literature, where the processing times of jobs are dependent on the processing sequences. However, they did not consider cases in which each processed job has different learning or aging ratios. This means that the actual processing time for a job can be determined not only by the processing sequence, but also by the learning/aging ratio, which can reflect the degree of processing difficulties in subsequent jobs. Motivated by these remarks, in this paper, we consider a two-agent single-machine scheduling problem with linear job-dependent position-based learning effects, where two agents compete to use a common single machine and each job has a different learning ratio. Specifically, we take into account two different objective functions for two agents: one agent minimizes the total weighted completion time, and the other restricts the makespan to less than an upper bound. After formally defining the problem by developing a mixed integer non-linear programming formulation, we devise a branch-and-bound (B&B) algorithm to give optimal solutions by developing four dominance properties based on a pairwise interchange comparison and four properties regarding the feasibility of a considered sequence. We suggest a lower bound to speed up the search procedure in the B&B algorithm by fathoming any non-prominent nodes. As this problem is at least NP-hard, we suggest efficient genetic algorithms using different methods to generate the initial population and two crossover operations. Computational results show that the proposed algorithms are efficient to obtain near-optimal solutions.

• Journal of the Korean Operations Research and Management Science Society
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• v.30 no.3
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• pp.119-135
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• 2005

Design of location erea(LA) in a cellular network is to partition the network into clusters of cells so as to minimize the cost of location updating and paging. Most research works dealing with the LA design problem assume that the call. arrival rate and mobile flow rate are fixed parameters which can be estimated independently. In this aspect, most Problems addressed so far are deterministic LA design problems(DLADP), known to be NP hard. The mobile flow and call arrival rate are, however, varying with time and should be treated simultaneously because the call arrival rate in a cell during a day is influenced by the change of a population size of the cell. This Paper Presents a new model on IA design problems considering the time-dependent call arrival and mobile flow rate. The new model becomes a stochastic LA design problem(SLADP) because It takes into account the possibility of paging waiting and blocking caused by the changing call arrival rate and finite paging capacity. Un order to obtain the optimal solution of the LA design problem, the SIADP is transformed Into the DLADP by introducing the utilization factor of paging channels and the problem is solved iteratively until the required paging quality is satisfied. Finally, an illustrative example reflecting the metropolitan area, Seoul, is provided and the optimal partitions of a cell structure are presented.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.423-426
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• 2005

Steel reinforced concrete (SRC) columns, which are widely employed in high-rise buildings, exhibit particular time-dependent behavior due to creep and shrinkage of the concrete, and this behavior may cause problems related to serviceability and structural stability. SRC columns also exhibit a time-dependent, cross-sectional relative humidity distribution that differs from reinforced concrete (RC) columns, due to the presence of an inner steel plate, which interferes with the moisture diffusion of concrete. This differential moisture distribution of SRC columns may reduce the drying shrinkage and the drying creep as contrasted with RC columns. Therefore, we propose that the differential moisture distribution be taken into account to accurately predict SRC column shortening.

• Structural Engineering and Mechanics
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• v.76 no.5
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• pp.599-611
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• 2020

A state-space method is developed to investigate the time-dependent behaviors of an angle-ply cylindrical shell in cylindrical bending with surface-bonded piezoelectric layers. Both the interfacial diffusion and sliding are considered to describe the properties of the imperfect interfaces. Particularly, a matrix reduction technique is adopted to establish the transfer relations between the elastic and piezoelectric layers of the laminated shell. Very different from our previous paper, in which an approximate numerical technique, i.e. power series expansion method, is used to deal with the time-dependent problems, the exact solutions are derived in the present analysis based on the piezoelasticity equations without any assumptions. Numerical results are finally obtained and the effects of imperfect interfaces on the electro-mechanical responses of the laminated shell are discussed.

• Structural Engineering and Mechanics
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• v.52 no.6
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• pp.1069-1084
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• 2014

The long-term performance of plates resting on viscoelastic foundations is a major concern in the analysis of soil-structure interaction. As a powerful mathematical tool, fractional calculus may address these plate-on-foundation problems. In this paper, a fractionalized Zener model is proposed to study the time-dependent behavior of a uniformly loaded rectangular thin foundation plate. By use of the viscoelastic-elastic correspondence principle and the Laplace transforms, the analytical solutions were obtained in terms of the Mittag-Leffler function. Through the analysis of a numerical example, the calculated plate deflection, bending moment and foundation reaction were compared to those from ideal elastic and standard viscoelastic models. It is found that the upper and lower bound solutions of the plate response estimated by the proposed model can be determined using the elastic model. Based on a parametric study, the impacts of model parameters on the long-term performance of a foundation plate were systematically investigated. The results show that the two spring stiffnesses govern the upper and lower bound solutions of the plate response. By varying the values of the fractional differential order and the coefficient of viscosity, the time-dependent behavior of a foundation plate can be accurately captured. The fractional differential order seems to be dependent on the mechanical properties of the ground soil. A sandy foundation will have a small fractional differential order while in order to simulate the creeping of clay foundation, a larger fractional differential order value is needed. The fractionalized Zener model is capable of accounting for the primary and secondary consolidation processes of the foundation soil and can be used to predict the plate performance over many decades of time.