• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.2
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• pp.179-187
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• 2013

Floating production storage and offloading (FPSO) facilities are used at most of the offshore oil fields worldwide. FPSO usage is expected to grow as oil fields move to deeper water, thus requiring the reliability and stability of mooring wires and risers in extreme environmental conditions. Except for the case of predictable attack angles of external loadings, FPSO facilities with turret single point mooring (SPM) systems are in general use. There are two types of turret systems: permanent systems and disconnectable turret mooring systems. Extreme environment criteria for permanent moorings are usually based on a 100-year return period event. It is common to use two or three environments including the 100-year wave with associated wind and current, and the 100-year wind with associated waves and current. When fitted with a disconnectable turret mooring system, FPSOs can be used in areas where it is desirable to remove the production unit from the field temporarily to prevent exposure to extreme events such as cyclones or large icebergs. Static and dynamic mooring analyses were performed to evaluate the stability of a spider buoy after disconnection from a turret during cyclone environmental conditions.

• Journal of Internet Computing and Services
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• v.17 no.6
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• pp.103-111
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• 2016

Offloading tasks from mobile devices to available cloud servers were improved since the introduction of the cloudlet. With the implementation of dynamic offloading algorithms, mobile devices can choose the appropriate server for the set of tasks. However, current task distribution approaches do not consider the number of VM, which can be a critical factor in the decision making. This paper proposes a dynamic task distribution on clustered data centers. A proportional VM migration approach is also proposed, where it migrates virtual machines to the cloud servers proportionally according to their allocated CPU, in order to prevent overloading of resources in servers. Moreover, we included the resource capacity of each data center in terms of the maximum CPU in order to improve the migration approach in cloud servers. Simulation results show that the proposed mechanism for task distribution greatly improves the overall performance of the system.

• Proceedings of the Korea Information Processing Society Conference
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• 2011.11a
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• pp.1315-1318
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• 2011

모바일 컴퓨팅의 보편화에 따라 엔터프라이즈 모바일 컴퓨팅을 위한 복잡한 모바일 어플리케이션의 사용이 점점 요구된다. 그러나, 모바일 디바이스는 제한된 자원을 가지므로 기능도가 복잡한 어플리케이션을 실행하는 것은 어렵다. 본 연구에서는 안드로이드 모바일 디바이스를 이용하여 현재 자원 상태에 따라 일부 기능을 외부 서버로 오프로드 하여 복잡한 어플리케이션 실행을 가능하게 하는 실용적이고 구현 가능한 프레임워크를 제안한다.

• Journal of Communications and Networks
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• v.18 no.3
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• pp.513-522
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• 2016

We propose a mechanism for monitoring load in quality of service (QoS)-enabled wireless networks and show how it can be used for network management as well as for dynamic pricing. Mobile network traffic, especially video, has grown exponentially over the last few years and it is anticipated that this trend will continue into the future. Driving factors include the availability of new affordable, smart devices, such as smart-phones and tablets, together with the expectation of high quality user experience for video as one would obtain at home. Although new technologies such as long term evolution (LTE) are expected to help satisfy this demand, the fact is that several other mechanisms will be needed to manage overload and congestion in the network. Therefore, the efficient management of the expected huge data traffic demands is critical if operators are to maintain acceptable service quality while making a profit. In the current work, we address this issue by first investigating how the network load can be accurately monitored and then we show how this load metric can then be used to provide creative pricing plans. In addition, we describe its applications to features like traffic offloading and user satisfaction tracking.

• Journal of Information Processing Systems
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• v.17 no.2
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• pp.297-305
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• 2021

Large amount of data is being generated in gaming servers due to the increase in the number of users and the variety of game services being provided. In particular, load balancing schemes for gaming servers are crucial consideration. The existing literature proposes algorithms that distribute loads in servers by mostly concentrating on load balancing and cooperative offloading. However, many proposed schemes impose heavy restrictions and assumptions, and such a limited service classification method is not enough to satisfy the wide range of service requirements. We propose a load balancing agent that combines the dynamic allocation programming method, a type of greedy algorithm, and proximal policy optimization, a reinforcement learning. Also, we compare performances of our proposed scheme and those of a scheme from previous literature, ProGreGA, by running a simulation.

• Ocean Systems Engineering
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• v.8 no.3
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• pp.247-279
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• 2018

This study aims to investigate the behavioral characteristics of the LWSCR (lazy-wave steel catenary riser) for a turret-moored FPSO (Floating Production Storage Offloading) by using fully-coupled hull-mooring-riser dynamic simulation program in time domain. In particular, the effects of initial geometric profile on the global performance and structural behavior are investigated in depth to have an insight for optimal design. In this regard, a systematic parametric study with varying the initial curvature of sag and arch bend and initial position of touch down point (TDP) is conducted for 100-yr wind-wave-current (WWC) hurricane condition. The FPSO motions, riser dynamics, constituent structural stress results, accumulated fatigue damage of the LWSCR are presented and analyzed to draw a general trend of the relationship between the LWSCR geometric parameters and the resulting dynamic/structural performance. According to this study, the initial curvature of the sag and arch bend plays an important role in absorbing transferred platform motions, while the position of TDP mainly affects the change of static-stress level.

• Journal of Ocean Engineering and Technology
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• v.24 no.5
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• pp.16-21
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• 2010

During the loading/offloading operation of a liquefied natural gas carrier (LNGC) that is moored in a side-by-side configuration with an offshore plant, sloshing that occurs due to the partially filled LNG tank and the interactive effect between the two floating bodies are important factors that affect safety and operability. Therefore, a time-domain software program, called CHARM3D, was developed to consider the interactions between sloshing and the motion of a floating body, as well as the interactions between multiple bodies using the potential-viscous hybrid method. For the simulation of a floating body in the time domain, hydrodynamic coefficients and wave forces were calculated in the frequency domain using the 3D radiation/diffraction panel program based on potential theory. The calculated values were used for the simulation of a floating body in the time domain by convolution integrals. The liquid sloshing in the inner tanks is solved by the 3D-FDM Navier-Stokes solver that includes the consideration of free-surface non-linearity through the SURF scheme. The computed sloshing forces and moments were fed into the time integration of the ship's motion, and the updated motion was, in turn, used as the excitation force for liquid sloshing, which is repeated for the ensuing time steps. For comparison, a sloshing motion coupled analysis program based on linear potential theory in the frequency domain was developed. The computer programs that were developed were applied to the side-by-side offloading operation between the offshore plant and the LNGC. The frequency-domain results reproduced the coupling effects qualitatively, but, in general, the peaks were over-predicted compared to experimental and time-domain results. The interactive effects between the sloshing liquid and the motion of the vessel can be intensified further in the case of multiple floating bodies.

• Ocean Systems Engineering
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• v.2 no.3
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• pp.217-228
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• 2012

As the size of container ships continues to increase, not many existing harbors can host the super-container ship due to its increased draft and the corresponding dredging requires huge budget. In addition, the minimization of waiting and loading/offloading time is the most important factor in harbor competitiveness. In this regard, mobile-harbor concept has been developed in Korea to achieve much improved harbor capacity and efficiency. In developing the concept, one of the most important elements is the operability of crane between two or more floating bodies in side-by-side arrangement. The container ship is to be stationed through a hawser connection to an outside-harbor fixed-pile station with the depth allowing its large draft. The mobile harbors with smart cranes are berthed to the sides of its hull for loading/offloading containers and transportation. For successful operation, the relative motions between the two or more floating bodies with hawser/fender connections have to be within allowable range. Therefore, the reliable prediction of the relative motions of the multiple floating bodies with realistic mooring system is essential to find the best hull particulars, hawser/mooring/fender arrangement, and crane/docking-station design. Time-domain multi-hull-mooring coupled dynamic analysis program is used to assess the hydrodynamic interactions among the multiple floating bodies and the global performance of the system. Both collinear and non-collinear wind-wave-current environments are applied to the system. It is found that the non-collinear case can equally be functional in dynamics view compared to the collinear case but undesirable phenomena associated with vessel responses and hawser tensions can also happen at certain conditions, so more care needs to be taken.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.3
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• pp.298-307
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• 2016

In the building process of FPSOs(floating production, storage and offloading units) is the increasing demand of high performance piping joints that can be installed on its turret system and maintain smooth and long-term flow of ultra-high pressure crude oil, being subjected to external excitations such as wind and wave on the sea. Following such a trend, in this paper, a new-type piping joint of four effective degrees of freedom has been designed, and its dynamic characteristics predicted through mathematical modeling and computer simulations. Moreover, via an example it was shown how the yaw motion in particular can be independently controlled for future durability test despite strong kinetic couplings.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.317-325
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• 2011

Vehicle model validation for the static vehicle testing has been done by comparison of the simulation results and test results and the parameters of the vehicle model to be used in the simulation have been adjusted to reflect the measured behaviour. The vehicle model fort the simulation should be validated by suitable tests and/or practical experience. The static vehicle test used to validate the vehicle model are the weight measurement, the wheel offloading test, the bogie rotational resistance test and the sway test. Finally, the computer simulation model has been validated and using the validated vehicle model the acceptance of the vehicle safety of the resistance to flange climbing derailment at low speed can be examined.