• Journal of Ship and Ocean Technology
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• v.9 no.2
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• pp.21-28
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• 2005

Recently moored offshore vessels like as FPSO(Floating Production Storage Offloading) are frequently deployed in seas for a long time. For successful operation, the motion behavior of such a vessel in waves must be clarified in advance either theoretically or experimentally. It is of particular interest to examine the behavior, when swells are superposed to seas with different incident angle. Such a situation is actually reported in some offshore oilfield. In this paper, the motion of a FPSO in irregular waves including swells is studied in time domain. Hydrodynamic coefficients and wave forces are calculated in frequency domain using three-dimensional singularity distribution method. Time memory function and added mass at infinite frequency are derived by Fourier transform utilizing hydrodynamic damping coefficients. In the process, the numerical accuracy of added mass at infinite frequency is carefully examined in association with free decay simulations. It is found from numerical simulations that swells significantly affect the vertical motion of FPSO mainly because of their longer period compared to the ordinary sea waves. In particular, the roll motion is largely amplified because the dominant period of swell is closer to the roll natural period than that of seas.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.6
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• pp.824-831
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• 2014

In this study, structural variations and overlay errors caused by multiple patterning lithography techniques to print narrow parallel metal interconnects are investigated. Resistance and capacitance parasitic of the six lines of parallel interconnects printed by double patterning lithography (DPL) and triple patterning lithography (TPL) are extracted from a field solver. Wide parameter variations both in DPL and TPL processes are analyzed to determine the impact on signal propagation. Simulations of 10% parameter variations in metal lines show delay variations up to 20% and 30% in DPL and TPL, respectively. Monte Carlo statistical analysis shows that the TPL process results in 21% larger standard variation in delay than the DPL process. Crosstalk simulations are conducted to analyze the dependency on the conditions of the neighboring wires. As expected, opposite signal transitions in the neighboring wires significantly degrade the speed of signal propagation, and the impact becomes larger in the C-worst metals patterned by the TPL process compared to those patterned by the DPL process. As a result, both DPL and TPL result in large variations in parasitic and delay. Therefore, an accurate understanding of variations in the interconnect parameters by multiple patterning lithography and adding proper margins in the circuit designs is necessary.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.37.2-37.2
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• 2014

Gas in disk galaxies interacts nonlinearly with a underlying stellar spiral potential to form galactic spiral shocks. Numerical simulations typically show that these shocks are unstable to the wiggle instability, forming non-axisymmetric structures with high vorticity. While previous studies suggested that the wiggle instability may arise from the Kelvin-Helmholtz instability or orbit crowding of gas elements near the shock, its physical nature remains uncertain. It was even argued that the wiggle instability is of numerical origin, caused by the inability of a numerical code to resolve a shock that is inclined to numerical grids. In this work, we perform a normal-mode linear stability analysis of galactic spiral shocks as a boundary-value problem. We find that the wiggle instability originates physically from the potential vorticity generation at a distorted shock front. As the gas follows galaxy rotation, it periodically passes through multiple shocks, successively increasing its potential vorticity. This sets up a normal-mode that grows exponentially, with a growth rate comparable to the orbital angular frequency. We show that the results of our linear stability analysis are in good agreement with the those of local hydrodynamic simulations of the wiggle instability.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.1
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• pp.114-125
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• 2017

This paper addresses a study of inner-tank sloshing effect on motion responses of a Floating Liquefied Natural Gas (FLNG) system, through experimental analysis and numerical modeling. To investigate hydrodynamic characteristics of FLNG under the conditions of with and without LNG-tank sloshing, a series of numerical simulations were carried out using potential flow solver SESAM. To validate the numerical simulations, model tests on the FLNG system was conducted in both liquid and solid ballast conditions with 75% tank filling level in height. Good correlations were observed between the measured and predicted results, proving the feasibility of the numerical modeling technique. On the verified numerical model, Response Amplitude Operators (RAOs) of the FLNG with 25% and 50% tank filling levels were calculated in six degrees of freedom. The influence of tank sloshing with varying tank filling levels on the RAOs has been presented and analyzed. The results showed that LNG-tank sloshing has a noticeable impact on the roll motion response of the FLNG and a moderate tank filling level is less helpful in reducing the roll motion response.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.1
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• pp.11-24
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• 2017

The present work focuses multi-objective optimization of blade sweep for a Wells turbine. The blade-sweep parameters at the mid and the tip sections are selected as design variables. The peak-torque coefficient and the corresponding efficiency are the objective functions, which are maximized. The numerical analysis has been carried out by solving 3D RANS equations based on k-w SST turbulence model. Nine design points are selected within a design space and the simulations are run. Based on the computational results, surrogate-based weighted average models are constructed and the population based multi-objective evolutionary algorithm gave Pareto optimal solutions. The peak-torque coefficient and the corresponding efficiency are enhanced, and the results are analysed using CFD simulations. Two extreme designs in the Pareto solutions show that the peak-torque-coefficient is increased by 28.28% and the corresponding efficiency is decreased by 13.5%. A detailed flow analysis shows the separation phenomena change the turbine performance.

• Journal of the Semiconductor & Display Technology
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• v.12 no.2
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• pp.19-25
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• 2013

Extrusion is one of the most important operations in the polymer-processing industry. Balancing the distribution of flow through a die to achieve a uniform velocity distribution is the primary objective and one of the most difficult tasks of extrusion die design. If the manifold in a coat-hanger die is not properly designed, the exit velocity distribution may be not uniform; this can affect the thickness across the width of the die. Yet, no procedure is known to optimize the coat hanger die with respect to an even velocity profile at the exit. While optimizing the exit velocity distribution, the constraint optimization used in this work with allowable pressure drop in the die; according to this constraint we can control the pressure in the die. The computational approach incorporates three-dimensional finite element simulations software STAR-CCM+. These simulations are used with numerical optimization to design polymer coat hanger dies with pressure drop, uniform velocity and temperature variation across the die exit.

• Bulletin of the Korean Chemical Society
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• v.30 no.3
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• pp.623-629
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• 2009

We have performed replica-exchange molecular dynamics simulations on 41 residue peptide mainly composed of NAC (non A$\beta$ component) sequence in $\alpha$-Synuclein. To investigate conformational characteristics of intrinsically unstructured peptides, we carried out structural analysis on the ‘representative structures’ for ensemble of structures occurring at different temperatures. The secondary structure profile obtained from our simulations suggests that the NAC region of $\alpha$-synuclein can be divided into roughly three helical-like segments. It is found that the overall helix-turn-helix like topology is conserved even though the conformational fluctuations grow as the temperature increases. The coordinate-based and the distance-based representative structures exhibit noticeable differences at higher temperatures while they are similar at lower temperatures. It is found that structural variations for the coordinate-based representative structures are much larger, suggesting that distance-based representative structures provide more reliable information concerning characteristic features of intrinsically unstructured proteins. The present analysis also indicates that the conformational features of representative structures at high temperatures might be related to those in membrane or low pH environment.

• Korean Journal of Agricultural Science
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• v.47 no.3
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• pp.509-517
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• 2020

Geographic information system (GIS) sewer network data are a fundamental input material for urban inundation modeling, which is important to reduce the increasing damages from urban inundation due to climate change. However, the essential attributes of the data built by a local government are often missing because the purpose of building the data is the maintenance of the sewer system. Inconsistent simplification and supplementation of the sewer network data made by individual researchers may increase the uncertainty of flood simulations and influence the inundation analysis results. Therefore, it is necessary to develop a basic algorithm to convert the GIS-based sewage network data into input data that can be used for inundation simulations in consistent way. In this study, the format of GIS-based sewer network data for a watershed near the Sadang Station in Seoul and the Oncheon River Basin in Busan was investigated, and a missing data supplementing algorithm was developed. The missing data such as diameter, location, elevation of pipes and manholes were assumed following a consistent rule, which was developed referring to government documents, previous studies, and average data. The developed algorithm will contribute to minimizing the uncertainty of sewer network data in an urban inundation analysis by excluding the subjective judgment of individual researchers.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.1
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• pp.59-71
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• 2008

In this paper, a software framework that integrates computational and experimental simulation has been developed to simulate and test a large-scale structural system under earthquake loading. The proposed software framework does not need development of the computer codes for both dynamic and static simulations. Any general-purpose software can be utilized with a main control module and interface APIs. This opens up a new opportunity to facilitate use of sophisticated finite elements into hybrid simulation regime to enhance accuracy and efficiency of simulations. The software framework described in the paper is modular and uses object oriented programming concepts. A series of illustrative examples demonstrate that the system is fully-functional and is capable of running any number of experimental and/or analytical components.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.2
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• pp.113-124
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• 2017

Recently, ship owners are requiring an assessment of sailing safety of a ship from an analysis considering maneuverability and environmental loads etc. In this paper, we propose a new approach to assess sailing safety by considering the prescribed parameters. The concept of sailing safety is developed from DP capability analysis and is based on the maneuvering simulations. While the ship is continuously disturbed due to irregular environmental loads during the simulations, it is steered to keep its course along the way points assumed along a straight path. After relative distances between four edges of the ship and allowable safety boundaries are calculated for 3 hours, the minimum values are obtained. The minimum distances are marked on a polar chart and we call this a quantified safe operation judgment chart which indicates quantified sailing safety.