• Journal of Korean Institute of Industrial Engineers
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• v.40 no.3
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• pp.305-312
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• 2014

This research deals with a problem that minimizes makespan in a non-identical parallel machine system with sequence and machine dependent setup times and machine dependent processing times. We first present a new mixed integer programming formulation for the problem, and using this formulation, one can easily find optimal solutions for small problems. However, since the problem is NP-hard and the size of a real problem is large, we propose four heuristic algorithms including genetic algorithm based heuristics to solve the practical big-size problems in a reasonable computational time. To assess the performance of the algorithms, we conduct a computational experiment, from which we found the heuristic algorithms show different performances as the problem characteristics are changed and the simple heuristics show better performances than genetic algorithm based heuristics for the case when the numbers of jobs and/or machines are large.

• Korean Journal of Construction Engineering and Management
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• v.6 no.6 s.28
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• pp.133-141
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• 2005

In the resent years, the importance of VE (value engineering) and LCC (life cycle cost) analysis for apartment building construction projects has been fully recognized. Accordingly theoretical models, guidelines, and supporting software systems were developed for the value engineering and life cycle cost analysis for construction management including large building systems. However, the level of consensus on VE and LCC analysis results is still low due to the lack of reliable data on maintenance. This paper presents time dependent LCC model based value analysis method for rational investment decision making and design alternative selection for construction of apartment building. The proposed method incorporates a time dependent LCC model and a performance evaluation technique by fuzzy logic theory to properly handle the uncertainties associated with statistics data and to analyze the value of alternatives more rationally. The presented time dependent VE and LCC analysis procedure were applied to a real world project, and this case study is discussed in the paper. The model and the procedure presented in this study can greatly contribute to design value engineering alternative selection, the estimation of the life cycle cost, and the allocation of budget for apartment building construction projects.

• Journal of the Korea Concrete Institute
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• v.25 no.2
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• pp.145-153
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• 2013

Recently, accelerated chloride diffusion coefficients are used for an evaluation of chloride behavior. Similar as apparent diffusion coefficients, accelerated diffusion coefficients decrease with time. In this study, decrease in diffusion coefficient with time is simulated with porosity. Utilizing DUCOM-program, porosities from 15 mix proportions are obtained and diffusion coefficients are modelled with regression analysis of porosity for 270 days. Considering non-linear binding capacity which means the relation between free and bound chloride ion, chloride behavior in high performance concrete is evaluated. Through utilizing the previous test results for concrete under chlorides for 180 days, the applicability of the proposed technique is verified. The proposed technique is evaluated to reasonably predict the chloride behavior in concrete with various w/c (water to cement) ratios and mineral admixtures (GGBFS and FA). It is also shown that decrease in chloride diffusion should be considered for chloride prediction in concrete with mineral admixture since it has very clear decrease in diffusivity with time.

• Proceedings of the ESK Conference
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• 1995.04a
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• pp.3-14
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• 1995

To investigate the effect of illumination conditions on visual inspection performance for TV panel glasses, three dependent variables, inspection time, error, and preference , were measured and analyzed through two consecutive experiments. The first experiment for reflection inspection was conducted using two independent variables, position and brightness. The second experiment for transparent inspection was made using two independent variables, height and brightness. The summary of the results of the experiment for reflection inspection are as follows ; The inspection performance of the position right above the subject (Position 1) was the best among the conditions in terms of errors, while the performance of the position slightly in front of and above the subject(Position 2) was the best in terms of inspection times. Inspection time was statistically different according to the brightness conditions specifically at the position in front of the subject(Position 3). The results of the second experimen for transparent inspection are that the inspection performance at medium height (Height 2) was the best among the three conditions in terms of errors while the performance at lower height(Height 3) was the best in subject preference. Based upon both results with respect to actual field conditions, two alternative inspection station designs were proposed for each lighting conditon.

• Earthquakes and Structures
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• v.25 no.4
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• pp.223-234
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• 2023

The use of displacement-dependent rotational friction dampers (RFD) as fuses or interchangeable elements in the moment-resisting frames (MRF) is one of the newest methods for improving seismic performance. In the present study, the performance of rotational friction dampers in MRF has been investigated. Evaluation of MRF with and without RFD models was performed using the finite element method by ABAQUS. For validation, an MRF and MRF with rotational friction dampers were modeled that had been experimentally tested and reported in previous experimental research and a good agreement was observed. The behavior of these dampers in frames of 3-, 6-, and 9-story was studied by modeling the damper directly. Nonlinear time history dynamic analysis was used. It was observed that by increasing the number of stories in the buildings, rotational friction dampers should be used to perform properly against earthquakes. The installation of rotational friction dampers in steel moment-resisting frames shows that the drift ratio between the floors is reduced and the seismic performance of these frames is improved.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.9B
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• pp.823-833
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• 2003

To satisfy the requirements of the real-time Internet services, queue management and scheduling schemes should be enhanced to accommodate the delay and jitter characteristic of them. Although the existing queue management schemes can address the congestion problems of TCP flows, they have some problems in supporting real-time services. That is, they show performance degradation when burst traffics are continuously going into the system after the queue is occupied at a predefined threshold level. In addition, under the congestion state, they show large jitter, which is not a desirable phenomenon for real-time transmissions. To resolve these problems, we propose a SDRED (State Dependent Random Early Detection) and dynamic scheduling scheme that can improve delay and jitter performances by adjusting RED parameters such as ma $x_{th}$ and $w_{q}$ according to the queue status. The SDRED is designed to adapt to the current traffic situation by adjusting the max,$_{th}$ and $w_{q}$ to four different levels. From the simulation results, we show that the SDRED decreases packet delays in a queue and has more stable jitter characteristics than the existing RED, BLUE, ARED and DSRED schemes.mes.mes.

• Journal of the Korean Operations Research and Management Science Society
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• v.22 no.2
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• pp.99-123
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• 1997

Performance analysis of NTT/BT protocol is investigated, which is a GFC (Generic Flow Control) ptotocol in ATM (Asynchronous Transfer Mode ) network and is based on cyclic reset mechanism. THe mean cell delay time is proposed as a performance measure of NTT/BT protocol. The mean cell delay time is defined as the duration from the instant the cell arrives at the transmission buffer until the cell is fully transmitted. The process of cell transmission can be described as a single server queueing modle with two dependent services. By utilizing this model, mean cell delay time is obtained and sensitivity of the factors such as window size and reset period is also analysed.

• Journal of applied mathematics & informatics
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• v.2 no.2
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• pp.21-46
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• 1995

Congestion and memory occupancy in computer system may be reduced further if new jobs are admitted only when the num-ber of jobs queued at CPU is below CPU run queue cutoff (RQ). In this paper we prove that response time of a job is invariant with respect to RQ if jobs do not communicate each other. We also demonstrate this invariance property numerically using marix-geometric methods and present an approximate method for the delay due to context switch-ing under time slicing. The approximation suggests that time slicing with constant overhead yields a throughput similar to an FCFS system without overhead.

• Journal of the Korea Institute of Military Science and Technology
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• v.11 no.3
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• pp.67-75
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• 2008

In this paper, we analyze the performance of Follower Noise Jamming(FNJ) considering three practical tracking parameters such as tracking bandwidth, tracking time and tracking success probability. The performance of FNJ is compared with that of Partial-Band Noise Jamming(PBNJ) in terms of Symbol Error Rate(SER) at the communication receiver under the assumed typical operation model. It is observed that the performance of FNJ is non-linearly dependent on the tracking bandwidth, the tracking time and the tracking success probability. As we can easily expect, it is also observed that the performance of FNJ is better than that of the PBNJ. Finally, it is shown that, for a fixed tracking bandwidth, the combinations of the required tracking time and the tracking success probability which satisfy a certain required SER.

• Smart Structures and Systems
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• v.31 no.5
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• pp.437-454
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• 2023

Real-time hybrid simulation (RTHS), which has the advantages of a substructure pseudo-dynamic test, is widely used to investigate the rate-dependent mechanical response of structures under earthquake excitation. However, time delay in RTHS can cause inaccurate results and experimental instabilities. Thus, this study proposes a model-based adaptive control strategy using a Kalman filter (KF) to minimize the time delay and improve RTHS stability and accuracy. In this method, the adaptive control strategy consists of three parts-a feedforward controller based on the discrete inverse model of a servohydraulic actuator and physical specimen, a parameter estimator using the KF, and a feedback controller. The KF with the feedforward controller can significantly reduce the variable time delay due to its fast convergence and high sensitivity to the error between the desired displacement and the measured one. The feedback control can remedy the residual time delay and minimize the method's dependence on the inverse model, thereby improving the robustness of the proposed control method. The tracking performance and parametric studies are conducted using the benchmark problem in RTHS. The results reveal that better tracking performance can be obtained, and the KF's initial settings have limited influence on the proposed strategy. Virtual RTHSs are conducted with linear and nonlinear physical substructures, respectively, and the results indicate brilliant tracking performance and superb robustness of the proposed method.