• Journal of Ocean Engineering and Technology
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• v.25 no.4
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• pp.42-47
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• 2011

In this paper, wake equalizing duct (WED) form optimization was carried out using computational fluid dynamics (CFD) techniques. A WED is a ring-shaped flow vane with a foil-type cross-section fitted to a hull in front of the upper propeller area. The main advantage of a WED is the power savings resulting from the uniformity of the velocity distribution on the propeller plane, a reduction in the flow separation at the aft-body, and lift generation with a forward force component on the foil section. This paper intends to evaluate these functions and find an optimized WED form for minimizing the viscous resistance and equalizing the wake distribution. In the optimization process, the study uses four WED parameters: the angle of the section, longitudinal location, and angles of the axes for the half rings against the longitudinal and transverse planes of the ship. KRISO 300K VLCC2 (KVLCC2) is chosen as an example ship to demonstrate the WED optimization. The optimization procedure uses genetic algorithms (GAs), a gradient-based optimizer for the refinement of the solution, and Non-dominated Sorting GA-II(NSGA-II) for Multiobjective Optimization. The results show that the optimized WED can reduce the viscous resistance at the expense of the uniformity of the wake distribution.

• Composites Research
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• v.27 no.6
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• pp.207-212
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• 2014

The shape optimization of composite flexbeam sections of a bearingless helicopter rotor is studied using a finite element (FE) sectional analysis integrated with an efficient evolutionary optimization algorithm called particle swarm assisted genetic algorithm (PSGA). The sectional optimization framework is developed by automating the processes for geometry and mesh generation, and the sectional analysis to compute the elastic and inertial properties. Several section shapes are explored, modeled using quadratic B-splines with control points as design variables, through a multiobjective design optimization aiming minimum torsional stiffness, lag bending stiffness, and sectional mass while maximizing the critical strength ratio. The constraints are imposed on the mass, stiffnesses, and critical strength ratio corresponding to multiple design load cases. The optimal results reveal a simpler and better feasible section with double-H shape compared to the triple-H shape of the baseline where reductions of 9.46%, 67.44% and 30% each are reported in torsional stiffness, lag bending stiffness, and sectional mass, respectively, with critical strength ratio greater than 1.5.

• Nuclear Engineering and Technology
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• v.56 no.6
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• pp.2019-2028
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• 2024

Advanced nuclear reactors, especially the newly developed small and micro-reactors have complex neutron spectrum, which makes the deterministic reactor core calculations sensitive to the energy group structure of few-group cross-sections. To avoid significantly increasing the cost of energy discretization in the core calculation, two energy group structures with 31 groups and 33 groups were adopted for typical thermal and fast reactor cores, respectively. Then, an adaptive scheme of group division for reactor cores with a medium neutron spectrum was proposed. The works were based on the full spectrum nuclear reactor analysis code SARAX/TULIP. An equivalent one-dimensional model of the core was proposed to capture the key neutron spectrum features of the reactor core. Such features were used to adaptively determine a few-group structure for the following reactor core calculations. Then, the neutron spectrum in different zones with more details was calculated. With this spectrum, the cross-sections were condensed into the determined energy groups. Three tests based on different neutron spectrum were calculated to verify the schemes. The results show that using the adaptive energy group division scheme, the following core calculation can meet the accuracy requirement of different reactors with different neutron spectra.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.7
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• pp.914-920
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• 2011

For a hydro turbine electricity generation system in river or bay, a venturi system could be applied to accelerate flow speed at the inlet of the turbine system in a flow field. In this study, a steady flow simulation was conducted to understand the effect of venturi system on the acceleration of current speed at the inlet of a hydro turbine system. According to the continuity equation, the flow speed is inversely proportional to the cross-section area in a conduit flow; however, it would be different in an open region because the venturi system would be an obstruction in the flow region. As the throat area is 1/5 of the inlet area of the venturi, the flow velocity is accelerated up to 2.1 times of the inlet velocity. It is understood that the venturi system placed in an open flow region gives resistance to the upcoming flow and disperses the flow energy around the venturi system. The result of the study should be very important information for an optimum design of a hydro turbine electricity generation system.

• Laser Solutions
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• v.13 no.4
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• pp.14-20
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• 2010

Robot path generation and laser welding technology for manufacturing automotive body are studied. Laser welding and industrial robot systems are used with the robot based laser welding system. The laser system used in this study is 1.6kW Fiber laser, while the robot system is 6 axes Industrial robot (payload: 130kg). The robot based laser welding system is equipped with laser scanner system for remote laser welding. The laser source, robot and laser scanner system are used to increase the processing speed and to improve the process efficiency. The welding joints of steel plate are butt and lapped joints. The quality test of the laser welding are through the observation the shape of bead on plate and cross-section of welding part. The 3 dimensional laser welding for non-linear pipe welding line is performed. This paper introduces the robot based laser welding system to resolve the limited welding speed and accuracy of the conventional spot welding system.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.335-340
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• 2010

In this paper development of an automatic grid generation program for flow field calculation around 3D wing is described and its application is also introduced. The program is developed by using JAVA programming language and a graphic library, JOGL, and it can be usee either as an application program on a local computer or as a applet in the network environment. Currently, The program provides NACA series 4-digit airfoils as the wing cross-section shape and it offers a non-complicated GUI program which can easily generate structured grids for wings based on user's parameter input. Grid generated by the program can be selected as one of two types; O-type and C-type. In this research advancing layer method(ALM) augmented by elliptic smoothing method is used for the FLUENT. It is shown that by using current program high-quality structured grids around 3D wings can be easily generated, and typical grid generation results and flow solutions are demonstrated. Study on effects of geometric parameters on flow field is also tried by changing major wing parameters such as incidence angle type of wing-tip and sweepback angle.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.360-360
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• 2011

In this work, SUS310S used for valve plate assembly was electron beam (EB) welded to determine the influence of the parametric conditions on the characteristics of the weld and to minimize porosity and micro-fissures among others. The evolution in the weld geometry and microstructure was examined as a function of the process conditions such as beam current and focusing current under a constant welding speed and accelerating voltage. The integrity of the EB welds in SUS310S was examined for defects (e.g. cracking, porosity, etc.), adequate penetration depth, and tolerable weld width deviation for the various welding conditions. Optical microscopy (OM), x-ray photoelectron spectroscopy analysis (XPS), scanning electron microscopy (SEM) and 3D micro-computed tomography (Micro-CT) for the cross section analysis of the electron beam welded SUS310S were utilized. The tensile strength and hardness were analyzed for the mechanical properties of the EB weld. At the 6 kV accelerating voltage, it was determined that a satisfactory penetration depth and desirable weld width deviation requires a beam current of 30 mA and a focusing current of 0.687 A at the welding speed of 25 mm/sec.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05b
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• pp.445-450
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• 1997

Self-Powered Neutron Detectors(SPNDs) are currently used to estimate the power generation distribution and fuel burn-up in several nuclear power reactors in Korea. In this paper, Monte Carlo simulation is accomplished to calculate the escape probability of beta particle as a function of their birth position fur the typical geometry of rhodium-based SPNDs. Also, a simple numerical method calculates the initial generation rate of beta particles and the change of generation rate due to rhodium burn-up. Using the simulation and the numerical method, the burn-up profile of rhodium density and the neutron sensitivity are calculated as a function of burn-up time in the reactor. The sensitivity of the SPNDs decreases non-linearly due to the high absorption cross-section and the non-uniform burn-up of rhodium in the emitter rod. In addition, for improvement of some properties of rhodium-based SPNDs which are currently used, this paper presents a new material. The method used here can be applied to the analysis of other types of SPNDs and will be useful in the optimum design of new SPNDs for long term usage.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1097-1106
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• 2007

Rail provides running tract for train and broadly and widely conveys the weight of the train exerted from the train wheels that the rail directly supports onto the cross tie and roadbed, and supports the cross-sectional pressure exerted by centrifugal force at curvatures. That is, stationary rail provides surface on which dynamic train runs and guarantees cross-sectional resistance to enable the vertical snake motion of the train wheels as well as to maintain lateral force at curvatures. Rail provides running surface on which train wheels can run smoothly, and secures vertical and lateral force. However, it undergoes continuous destructive reactions (wearing and damages) and abrasion of the cladding by the train wheels. It is obvious that wearing will result when two metal parts act against each other. However, occurrence of abnormal wearing such as rapid wearing of the rail side due to complex generation of various mechanisms at the contact surface between the rail and train wheel flange. It is not easy to simply examine the causes of occurrence of abnormal wearing of rail and train wheel flange. Although countless number of academicians and specialists are conducting researches on abnormal wearing of rail and vertical wearing of train wheels, I believe it is too early to argue on pros and cons due to insufficiency of officially verified information on the issue. This review will be focusing on the examples of repairs that reduced the generation of abnormal wearing of rail by reviewing and improving characteristics of wearing and slack, speed of the train and cant as well as status of lubricator by choosing the compound curves present in the section between the $Anguk{\sim}Jongno3-ga$ Stations of the Route No. 3 among the compound curve tracks of the Seoul Metro Routes No. 3 & 4 at which abnormal wearing is generated continuously.

• Structural Engineering and Mechanics
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• v.82 no.1
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• pp.107-120
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• 2022

The bracing members capable of active control against seismic loads to reduce earthquake damage have been widely utilized in construction projects. Effectively reducing the structural damage caused by earthquake events, bracing systems equipped with retrofitting damper devices, which take advantage of the energy dissipation and impact absorption, have been widely used in practical construction sites. Shape Memory Alloys (SMAs) are a new generation of smart materials with the capability of recovering their predefined shape after experiencing a large strain. This is mainly due to the shape memory effects and the superelasticity of SMA. These properties make SMA an excellent alternative to be used in passive, semi-active, and active control systems in civil engineering applications. In this research, a new system in diagonal braces with slit damper combined with SMA is investigated. The diagonal element under the effect of tensile and compressive force turns to shear force in the slit damper and creates tension in the SMA. Therefore, by creating shear forces in the damper, it leads to yield and increases the energy absorption capacity of the system. The purpose of using SMA, in addition to increasing the stiffness and strength of the system, is to create reversibility for the system. According to the results, the highest capacity is related to the case where the ratio of the width of the middle section to the width of the end section (b₁/b) is 1.0 and the ratio of the height of the middle part to the total height of the damper (h₁/h) is 0.1. This is mainly because in this case, the damper section has the highest cross-section. In contrast, the lowest capacity is related to the case where b₁/b=0.1 and the ratio h₁/h=0.8.