• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.5
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• pp.558-570
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• 2015

A study on the green ship design for Ultra Large Container Ship (ULCS, 18,000 TEU Class Container Ship) was performed based on the four step procedures of the initial design and hull form optimization to maximize economic and propulsive performance. The first, the design procedure for ULCS was surveyed with economic evaluation considering environmental rules and regulations. The second, the characteristics of single and twin skeg container ships were investigated in view of initial design and performances. The third, the hull form optimization for single and twin skeg ships with the same dimensions was conducted to improve the resistance and propulsive performances at design draught and speed by several variations and the results of the optimization were verified by numerical calculations of CFD and model test. The last, for the estimated operating profile of draught and speed, the hull forms of single and twin sked ships were optimized by CFD. From this study, the methodologies to optimize the hull form of ULCS were proposed with considerations during the green ship design and the improvement of the energy efficiency for the optimized hull forms was confirmed by the proposed formula of the total energy considering design conditions, operating profile and fuel oil consumption.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.1
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• pp.44-52
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• 2016

Kelvin's (1887) theory that predicts position of ship wave crest can be applied only in deep water. Havelock's (1907) theory that predicts cusp locus angle can be applied in whole water depths but cannot predict the position of ship wave crest. In this study, using the linear dispersion fully, we develop the equations to predict ship wave crest in whole water depths and, using the developed equations, we predict cusp locus angle. We simulate ship wave propagation using FLOW-3D in the condition of Johnson's (1985) hydraulic experiment and find that the cusp locus angles predicted by the present theory are close to numerical results of FLOW-3D and hydraulic experimental data. We also simulate for various conditions and compare numerical results of distances between adjacent wave crests and values predicted by the present theory. For Froude number less than unity, the numerical results are close to the values predicted by the theory. For Froude number greater than unity, the constant value of $C_1$ which determines the distance between the ship and the first ship wave crest is almost equal to zero and the numerical results of distances between adjacent ship waves excluding the first ship are close to the values predicted by the theory.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.4
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• pp.313-325
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• 2011

Finite element grid system using h-refinement on the Yellow Sea was constructed based on previous study (Suh, 1999b) from 14 K to 210 K and special attention was concentrated on refining the coastal zone. In grid generation, depth change between adjacent points and non-dimensional tidal wave length ratio were considered. As a result approximately a quarter of the total nodes are located nearby 5 m of shallow area. Accurate bathymetry data using 30's and ETOPO1 with open boundary conditions of 8 major tidal constituents extracted automatically from FES2004 have been applied. In tidal simulation a 3-dimensional nonlinear harmonic model was setup and tidal amplification due to changes in vertical turbulent and bottom friction were simulated. In this study not only 8 major tidal constituents but also nonlinear shallow tides $M_4,$, $MS_4$ and long period $M_f,$, $M_{sf}$ were reproduced. It is found that implication of spatial variation of friction coefficient plays a very important role in reproduction of astronomical and shallow tides which are computed by iterative computation of nonlinear terms. Also it should be considered differently with respect to tidal periods. To understand the distribution of tidal asymmetry, amplitude ratio of $M_4/M_2$ and phase differences $2g(M_2)-g(M_4)$ were calculated. Tidal distortion ratio marks up to 0.2 on the west coast showing shallow coastal characteristics and somewhat wide range of ebb-dominances in front of Mokpo area are reproduced.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.1
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• pp.9-16
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• 2014

Using a level set method and topological derivatives, a topological shape optimization method that is independent of an initial design is developed for linearly elastic structures. In the level set method, the initial domain is kept fixed and its boundary is represented by an implicit moving boundary embedded in the level set function, which facilitates to handle complicated topological shape changes. The "Hamilton-Jacobi(H-J)" equation and computationally robust numerical technique of "up-wind scheme" lead the initial implicit boundary to an optimal one according to the normal velocity field while minimizing the objective function of compliance and satisfying the constraint of allowable volume. Based on the asymptotic regularization concept, the topological derivative is considered as the limit of shape derivative as the radius of hole approaches to zero. The required velocity field to update the H-J equation is determined from the descent direction of Lagrangian derived from optimality conditions. It turns out that the initial holes are not required to get the optimal result since the developed method can create holes whenever and wherever necessary using indicators obtained from the topological derivatives. It is demonstrated that the proper choice of control parameters for nucleation is crucial for efficient optimization process.

• Journal of the Korean Society for Marine Environment & Energy
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• v.11 no.3
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• pp.164-174
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• 2008

In this study we try to identify the three-dimensional mixing characteristics of Seomjin River discharges in Seomjin River Estuary and Gwangyang Bay using a seasonal field observation (CTD) during spring tide and a three-dimensional numerical model with EFDC (Environmental Fluid Dynamics Code). The tidal elevation conditions of the four main tidal harmonic constituents on the open boundary and river discharges and thermal effluents at the specific boundary are considered. The calculated harmonic constants of tide and tidal current agreed well with those of observations at two stations for tide and two stations for tidal current. The model successfully reproduced well known the estuarine circulation in Seomjin River Estuary where tide and river discharges are dominant forcings. In the winter mean discharges case, tidal currents move Seomjin River discharges in Seomjin River mouth and in the summer mean discharges case, river flows move Seomjin River discharges near ae Seomjin River Estuary. A three-dimensional mixing characteristics of Seomjin River Estuary show well a three-dimensional estuarine circulation and thermal effluents effect to the seasonal variation of river discharges.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.7
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• pp.953-960
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• 2019

The Miller cycle is a diesel engine that has been developed in recent years that it can reduce NOx and improve fuel consumption by reducing the compression ratio through intake valve closing (IVC) time control. The Miller cycle can be divided into the early Miller method of closing the intake valve before the bottom dead center (BDC) and the late Miller method of closing the intake valve after the BDC. At low speeds, the late Miller method is advantageous as it can increase the volumetric efficiency; while at medium and high speeds, the early Miller method is advantageous because of the high internal temperature reduction effect due to the expansion of the intake air during the piston lowering from IVC to BDC. Therefore, in consideration of the ef ects of the early and late Miller methods, it is necessary to adopt the most suitable Miller method for the operating conditions. In this study, a two-stage turbo charge system was applied to four-stroke engines and the process of enhancing the Miller effect through a reduction of the intake and exhaust valve overlap as well as the valve change adjustment mechanism were considered. As a result, the ef ects of fuel consumption and Tmax reduction were confirmed by adopting the Miller cycle with a two-stage supercharge, a reduction of valve overlap, and an increase of suction valve lift.

• Journal of Navigation and Port Research
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• v.41 no.6
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• pp.395-400
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• 2017

As a serial communications protocol, Modbus has become a practically standard communication protocol and is now a commonly available means of connecting industrial electronic devices. Therefore, all devices can be connected using the Modbus protocol with the measurement and remote control on ships, buildings, trains, airplanes and more. The existing Modbus that has been used is based on serial communication. Modbus TCP uses Ethernet communication based on TCP / IP which is the most widely used Internet protocol today; so, it is faster than serial communication and can be connected to the Internet of Things. In this paper, we designed an algorithm to control LED lighting in a wireless Wi-Fi environment using the Modbus TCP communication protocol, and designed and implemented a LED controller circuit that can check external environmental factors and control remotely through the integrated management system of a ship. Temperature, humidity, current and illuminance values, which are external environmental factors, are received by the controller through the sensors, and these values are communicated to the ship's integrated management system via the Modbus protocol. The Modbus can be connected to Master devices via TCP communication to monitor temperature, humidity, current, illuminance status and LED output values, and also users can change the RGB value remotely in order to change to the desired color. In addition, in order to confirm the implementation of the controller, we developed a simulated ship management system to monitor the temperature, humidity, current and illumination conditions, and change the LED color of the controller by changing the RGB value remotely.

• Journal of Navigation and Port Research
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• v.41 no.6
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• pp.415-422
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• 2017

In a situation where there is excessive competition among logistics centers due to the low price of logistics centers for attracting freight volume, the conditions provided by the logistics centers are similar. Therefore, in order to determine the logistics center, we want to find out what kind of differentiated service the shippers desire, as well as what level of service they want in addition to al ow price. There are currently no studies about the service quality of logistics centers. The components of the service quality of the logistics center were extracted by applying them to the logistics center based on the existing service quality theory. Factor analysis revealed five dimensions of service quality: tangibility, reliability, empathy, assurance, and know-how. It was found that service quality had a statistically significant influence on customer satisfaction, from the investigation of the causal effect relationship. In addition, 'Know-How' among these factors has more influence on customer satisfaction, so it is important to accumulate differentiated 'Know-How' only in logistics centers.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.1
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• pp.1-10
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• 2003

In this paper, the laboratory test results with middle-sired ,soil box test in modeling the in-situ installing of horizontal drains are discussed the estimation of the optimum negative pressure. The test was carried out in the different vacuum pressure conditions together with the measurement for the settlement and volume change of drained water by the installed drains during the consolidation process. After the test, the water content was measured to both directions of lateral distance from the drain and depth of the soil, to find out the distribution of ground improvement and strength enhancement. From the analysis on the distribution of water content, the gradual application of vacuum pressure to higher level by pre-determined stages starting from low vacuum pressure is found to be effective and desirable. In the comparison of the degrees of consolidation with elapsed time, the calculated value by the prediction method based on the Barren's conventional theory showed a good agreement with the measured value. With this, It is positively considered that the applicability of the prediction method based on Barren's theory to the practical design of horizontal drains can be justified such as in the calculation of drain spacing and consolidation period.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.1
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• pp.75-90
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• 1995

A mathematical model for the dynamic analysis of a riser system with the inclusion of internal flow and nonlinear effects due to large structural displacements is developed to investigate the effect of internal flow on marine riser dynamics. The riser system accounts fir the nonlinear boundary conditions and includes a steady flow inside the pipe which is modeled as an extensible or inextensible. tubular beam subject to nonlinear three dimensional hydrodynamic loads such as current or wave excitation. Galerkin's finite element approximation and time incremental operator are implemented to derive the matrix equation of equilibrium for the finite element system and the extensibility or inextensibility condition is used to reduce degree of freedom of the system and the required computational time in the case of a nonlinear model. The algorithm is implemented to develop computer programs used in several numerical applications. The investigations of the effect of infernal flow on riser vibration due to current or wave loading are performed according to the change of various parameters such as top tension, internal flow velocity, current velocity, wave period, and so on. It is found that the effect of internal flow can be controlled by the increase of top tension. However, careful consideration has to be given in the design point particularly for the long riser under the harmonic loading such as waves. And it is also found that the consideration of nonlinear effects due to large structural displacements increases the effect of internal flow on riser dynamics.