• Journal of Ocean Engineering and Technology
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• v.36 no.2
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• pp.91-100
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• 2022

In general, the effect of roll motion is not considered in the study on maneuverability in calm water. However, for high-speed twin-screw ships such as the DTMB 5415, the coupling effects of roll and other motions should be considered. Therefore, in this study, the estimation of maneuverability using a 4-degree-of-freedom (DOF; surge, sway, roll, yaw) maneuvering mathematical group (MMG) model was conducted for the DTMB 5415, to improve the estimation accuracy of its maneuverability. Furthermore, a study on the change in turning performance according to the fin angle was conducted. To accurately calculate the lift and drag forces generated by the fins, it is necessary to consider the three-dimensional shape of the wing, submerged depth, and effect of interference with the hull. First, a maneuvering simulation model was developed based on the 4-DOF MMG mathematical model, and the lift force and moment generated by the side fins were considered as external force terms. By employing the CFD model, the lift and drag forces generated from the side fins during ship operation were calculated, and the results were adopted as the external force terms of the 4-DOF MMG mathematical model. A 35° turning simulation was conducted by altering the ship's speed and the angle of the side fins. Accordingly, it was confirmed that the MMG simulation model constructed with the lift force of the fins calculated through CFD can sufficiently estimate maneuverability. It was confirmed that the heel angle changes according to the fin angle during steady turning, and the turning performance changes accordingly. In addition, it was verified that the turning performance could be improved by increasing the heel angle in the outward turning direction using the side fin, and that the sway speed of the ship during turning can affect the turning performance. Hence, it is considered necessary to study the effect of the sway speed on the turning performance of a ship during turning.

• Korean Journal of Construction Engineering and Management
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• v.15 no.5
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• pp.40-48
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• 2014

As CBR(Chemical, Biological, and Radiological) attack increases, the importance of CBR protective facilities is being emphasized. When CBR warfare emerges, a task force team, who exist outside of CBR protective facility, should enter the CBR protective facility through neutralizing process in CCA(Contamination Control Area) and TFA(Toxic Free Area). If a bottleneck occurs in the process or zones, the task force team cannot enter the CBR protective facility efficiently and may cause inefficiency in its operation performance or result in casualties. The current design criteria of the CBR protective facility is only limited to ventilation system and it does not consider how much time it takes to enter the facility. Therefore, this research aims to propose the entering time estimation model with discrete event simulation. To make the simulation model, the procedure performed through CCA and TFA is defined and segmented. The actual time of the procedure are measured and adapted for the simulation model. After running the simulation model, variables effecting the entering time are selected for alternatives with adjustments. This entering time estimation model for CBR protective facility is expected to help take time into consideration during the designing phase of CBR protective facility and help CBR protective facility managers to plan facility operation in a more realistic approach.

• Journal of the Korean Institute of Landscape Architecture
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• v.37 no.3
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• pp.61-68
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• 2009

The objective of this study was to examine the possibility of utilizing the immersion stereoscopic image with a curved-screen-display as a tool for evaluating the landscape. The curved-screen-display ensures the continuity of the image and can be simultaneously evaluated by many people. Fifty-meter-wide Gangnamdaero Boulevard in Seoul was selected for this study, and the simulation was done using computer graphics. With the computer simulation, a questionnaire on landscape preferences was conducted according to different visual environments (immersion, non-immersion) and different projection types(stereoscopic or plane image). In the results of this study, the landscape preference was largely dependent on the immersion environment. Using the immersion-type simulation, the observer can easily evaluate the preference with higher judgment power. The stereoscope or plane projection type does not have any significant result in terms of its judgment power. This result implies that it is very important to strengthen the sense of immersion by expanding the screen into an angled view in which the observer can become immersed while making and projecting the simulation to evaluate the landscape. As a landscape evaluation tool for examining the efficiency and usefulness of immersion simulation, this study has limitations in that it controls many factors in street landscape that adversely affect judgment. Accordingly, a detailed comparison and verification of the stereoscopic image in various environments, including street width and building height ratio, must be conducted.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.4
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• pp.78-85
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• 2008

This paper presents a high-level design methodology applied on an SoC using SystemC. The topic will emphasize on high-level design approach for intensive architecture exploration and verifying cycle accurate SystemC models comparative to real Verilog RTL models. Unlike many high-level designs, we started the poject with working Verilog RTL models in hands, which we later compared our SystemC models to real Verilog RTL models. Moreover, we were able to use the on-chip test board performance simulation data to verify our SystemC-based platform. This paper illustrates that in high-level design, we could have the same accuracy as RTL models but achieve over one hundred times faster simulation speed than that of RTL's. The main topic of the paper will be on architecture exploration in search of performance degradation in source.

• Architectural research
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• v.16 no.4
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• pp.203-210
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• 2014

The packaged terminal air conditioner, the typical cooling system for the residential buildings, consumes a large amount of electricity in a short period time during peak hours. In order to reduce the peak load and conserve the electricity, the thermally activated building system can be used as a secondary system to handle the partial cooling load. However, the thermally activated building system may cause condensation and under-cooling. Thus, design of both systems should be performed with careful investigation in characteristics of both systems to amplify the advantages. Since the thermally activated building system has the time-delay effect which may cause under-cooling, the system is designed to handle the base load of the building. Hence, simple simulation with EnergyPlus was performed to observe the characteristics of cooling load in residential buildings. Once the possible range of the load handling ratio of the thermally activated building system was decided, characteristics of system was analyzed in terms of hardware component and operation parameters. The hardware components were analyzed in plant and system aspects and the operation parameter was evaluated in the thermal comfort aspect. As the load handling ratio increased, the thermal comfort increased due to the lower radiant mean temperatures. Within the range of thermal comfort, the several adjustments were made in setpoint temperature and electricity consumptions of difference cases were observed to decide which components and parameters were important for designing the systems.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.2
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• pp.158-164
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• 2011

The study on the improvement of resistance performance is very important for coastal fishing boats in Korea, because the prices of fuel oil are gradually risen and the demand of high-speed fishing boats is increased lately. This study is concerned with the improvement of the resistance performance for Korean high-speed small coastal fishing boats. A semi-planing hull form of Korean small coastal fishing boat is selected in the role of initial hull. From the modification of the hull form parameters and the local characteristics of the hull form, the improvement of the resistance performance is achieved. The resistance performances of the initial and the modified hull forms are estimated by using a numerical simulation method. Also, ship model tests are carried out in ship model basin.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.8B
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• pp.647-656
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• 2012

TDMA MAC protocol in MANET requires precise network synchronization between nodes though network topology changes continuously due to node mobility and the effect of propagation environment. In this paper we propose in-band cross-layer network synchronization architecture for TDMA-based MANETs. In the proposed architecture TDMA MAC protocol and proactive routing protocol cooperate closely to rapidly detect network partition and merge caused by node mobility and to precisely maintain network synchronization. We also implement the proposed synchronization architecture in OPNET simulator and evaluate the performance of it in various simulation scenarios. Simulation results show that our architecture stably maintains network time synchronization in both network partition and merge situations.

• Journal of Ocean Engineering and Technology
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• v.34 no.5
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• pp.285-293
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• 2020

This study evaluated the Hook-up installation of an offshore site construction process, which is the final step in an offshore site installation process. During Hook-up installation, the offshore structure can have a detrimental effect on the work stability due to low-frequency motion. Moreover, economic costs can be incurred by the increase in available days of a tugboat. Therefore, this study developed a numerical analysis program to assess the dynamic behavior of mooring systems during hook-up installation to analyze the generally performed installation process and determine when the tugboat should be released. In this program, the behavior of an offshore structure was calculated using Cummin's time-domain motion equation, and the mooring system was calculated by Lumped mass method (LMM). In addition, a tugboat algorithm for hook-up installation was developed to apply the Hook-up procedure. The model used in the calculations was the barge type assuming FPSO (Floating production storage and off-loading) and has a taut mooring system connected to 16 mooring lines. The results of the simulation were verified by comparing with both MOSES, which is a commercial program, and a calculation method for restoring coefficient matrix, which was introduced by Patel and Lynch (1982). Finally, the offset of the structure according to the number of tugboats was calculated using the hook-up simulation, and the significant value was used to represent the calculation result.

• Computers and Concrete
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• v.23 no.3
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• pp.161-170
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• 2019

This paper aims at presenting a numerical method for estimating the elastic modulus of recycled concrete with crushed aggregates. In the method, polygonal aggregates following a given sieve curve are generated, and placed into a square simulation element with the aid of the periodic boundary condition and the overlap criterion of two polygonal aggregates. The mesostructure of recycled concrete is reconstructed by embedding an old interfacial transition zone (ITZ) layer inside each recycled aggregate and by coating all the aggregates with a new ITZ layer. The square simulation element is discretized into a regular grid and a representative point is selected from each sub-element. The iterative method is combined with the fast Fourier transform to evaluate the elastic modulus of recycled concrete. After the validity of the numerical method is verified with experimental results, a sensitivity analysis is conducted to evaluate the effects of key factors on the elastic modulus of recycled concrete. Numerical results show that the elastic modulus of recycled concrete increases with the increase of the total aggregate content and the elastic moduli of old and new ITZ but decreases with increasing the replacement ratio of recycled aggregate and the thicknesses of old and new ITZ. It is also shown that, for a replacement ratio of recycled aggregate smaller than 0.3, the elastic modulus of recycled concrete is reduced by no more than 10%.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.624-637
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• 2019

A semi-submersible offshore platform always operates under complex weather conditions, especially wind and waves. It is vital to analyze the structural dynamic responses of the platform in short-term sea states under the combined wind and wave loads, which touches upon three following work. Firstly, a derived relationship between wind and waves reveals a correlation of wind velocity and significant wave height. Then, an Improved Mixture Simulation (IMS) method is proposed to simulate the time series of wind/waves accurately and efficiently. Thus, a wind-wave scatter diagram is expanded from the traditional wave scatter diagram. Finally, the time series of wind/wave pressures on the platform in the short-term sea states are converted by Workbench-AQWA. The numerical results demonstrate that the proposed numerical methods are validated to be applicable for wind and wave simulations in structural analyses. The structural dynamic responses of the platform members increase with the wind and wave strength. In the up-wind and wave state, the stresses on the deck, the connections between deck and columns, and the connection between columns and pontoons are relatively larger under the vertical bending moment. These numerical methods and results are wished to provide some references for structural design and health monitoring of several offshore platforms.