• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.5
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• pp.331-338
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• 2020

In this study, the characteristic of a 3-D micro-woven material, which is one of the newly developed periodic open-cell structure, is analyzed through various computational simulations. To increase the accuracy of the numerical simulations, the distance between each directional wire is parameterized using six design variables, and its model geometry is precisely discretized using tetrahedron elements. Using the improved computational model, the material properties of the mechanical, thermal, and fluidic behavior are investigated using commercial software and compared with the previous experimental results. By changing the space between the x- and y-directional wires, a parametric test is performed to determine the tendency of the change in the material properties. In addition, the correlation between two different material properties is investigated using the Ashby chart. The result can further be used in determining the optimal pattern and wire spacing in 3-D micro-woven materials.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.5
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• pp.343-352
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• 2016

In this study, a pre-swirl duct for the 180,000 DWT bulk carrier has been designed from a propulsion standpoint using CFD. The stern duct - designed by NMRI - was selected as the initial duct. The objective function is to minimize the value of delivered power in model scale. Design variables of the duct include duct angle, diameter, chord length, and vertical and horizontal displacements from the center. Design variables of the stators are blade number, arrangement angle, chord length, and pitch angle. A parametric design was carried out with the objective function obtained using CFD. Reynolds averaged Navier-Stokes equations have been solved; and the Reynolds stress model applied for the turbulent closure. A double body model is used for the treatment of free-surface. MRF and sliding mesh models have been applied to simulate the actuating propeller. A self-propulsion point has been obtained from the results of towing and self-propelled computations, i.e., form factor obtained from towing computation and towing forces obtained from self-propelled computations of two propeller rotating speeds. The reduction rate of the delivered power of the improved stern duct is 2.9%, whereas that of the initial stern duct is 1.3%. The pre-swirl duct with one inner stator in upper starboard and three outer stators in portside has been designed. The delivered power due to the designed pre-swirl duct is reduced by 5.8%.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.6
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• pp.341-348
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• 2019

The purpose of this study is to model and analyze retractable large spatial structures by applying parametric modeling techniques. The modeling of wind loads in the analysis of typical structures including curved surfaces can be error-prone, and the processing time increases dramatically when there are many types of variables. However, the method based on StrAuto that was developed in previous research, facilitates the efficacious assignment of wind loads to structures and the rapid arrival of conclusions. As a result, it is possible to compare alternatives with various loads, including wind loads, to determine an optimal alternative much faster than the existing process. Further, it is almost impossible to directly input the wind load by calculating the area of an irregularly curved surface. However, the proposed method automatically assigns the wind load, which allows for automatic optimization in a structural analysis system. The approach was applied and optimized using several models, and the results are presented.

• Journal of the Korean Data and Information Science Society
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• v.23 no.4
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• pp.683-691
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• 2012

In $4{\times}4$ graeco-latin square design, powers of rank transformed statistic for testing the main effect are superior to powers of parametric statistic without regard to the effect structure with equally or unequally spaced effect levels as well as the type of population distributions such as exponential, double exponential, normal and uniform distribution. As numbers of block effect or effect sizes are decreased, powers of rank transformed statistic are much higher than powers of parametric statistic. In case that block effects are smaller than a main effect or one block effect is higher than other block effects, powers of rank transformed statistic are much higher than powers of parametric statistic in $4{\times}4$ graeco-latin square design with three block effects and one main effect.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.5
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• pp.1055-1063
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• 2012

The noise of image is added by many environmental factors. Therefore, we need to remove these noises using the conventional filtering methods, which are optimized based on the statistical characteristic of noise. In direct restoration method, there is an inverse filter and the wiener filter. Here, the wiener filter is the optimized filter in the view of least square method. First, we are going to study the inverse filter, wiener filter, constraint least square filter. Second, in order to control the quantity, we use the parameters instead of the power spectrum ratio. But, these parameters have the conflicting condition, therefore, we optimized the variables using parametric wiener filter which adjust the application appropriately. In the simulation results, the contrast of the degraded image was enhanced and the noise was removed. Comparative experimentation was demonstrated edge preserving and noise removing property.

• Current Optics and Photonics
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• v.5 no.2
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• pp.186-190
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• 2021

In this study, a compact, picosecond, mid-infrared 3.8 ㎛ MgO:PPLN optical parametric oscillator (OPO) laser output with high peak power is realized using a master oscillator power amplifier (MOPA) 1 ㎛ solid-state laser seeded by a picosecond fiber laser as the pump source. The pump source was a 50 MHz and 10 ps fiber seed source. After AOM pulse selection and two-stage solid-state amplification, a 1,064 nm laser output with a repetition frequency of 1-2 MHz, pulse width of 9.5 ps, and a maximum average power of 20 W was achieved. Furthermore, a compact short cavity with a unsynchronized pump is adopted through the design of an OPO cavity structure. When the injection pump power was 15 W and the repetition frequency was 1 MHz, the average output power of idler light was 1.19 W, and the corresponding peak power was 119 kW. The optical conversion efficiency was 7.93%. When the repetition frequency was increased to 2 MHz, the average output power of idler light was 1.63 W, the corresponding peak power was 81.5 kW, and the optical conversion efficiency was 10.87%. At the same time, the output wavelength was measured at 3,806 nm, and the beam quality was MX2 = 3.21 and MY2 = 3.34.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.632-637
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• 2019

The cable tray design of an offshore plant production design is to optimally arrange the 3D modeling so that the cable can be installed without interfering with the structural members and various outfit equipment, and it is performed using a PDMS (Plant design management system), which is a 3D CAD system for an offshore plant layout. This study reviewed the development of PML (Programmable macro language) for a PDMS supporting offshore plant cable tray design and examined the efficiency compared to the existing method. Cable tray design PML developed in this paper enables fully parametric design using electrical outfit template library, allowing a rapid response to frequent modifications due to design changes and minimizing repetitive work fatigue by reflecting the accumulated design experience. In addition, the developed system was applied to the offshore plant structure module and it improved the work efficiency by more than 50% compared to the existing method.

• Journal of Korean Society on Water Environment
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• v.27 no.5
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• pp.634-645
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• 2011

A newly developed rainwater harvesting (RWH) system reliability model is evaluated for roof area of buildings in Haeundae District of Busan. RWH system is used to supply water for toilet flushing, back garden irrigation, and air cooling. This model is portable because it is based on a non-parametric precipitation generation algorithm using a markov chain. Precipitation occurrence is simulated using transition probabilities derived for each day of the year based on the historical probability of wet and dry day state changes. Precipitation amounts are selected from a matrix of historical values within a moving 30 day window that is centered on the target day. Then, the reliability of RWH system is determined for catchment area and tank volume ranges using synthetic precipitation data. As a result, the synthetic rainfall data well reproduced the characteristics of precipitation in Busan. Also the reliabilities of RWH system for each of demands were computed to high values. Furthermore, for study area using the RWH system, reduction efficiencies for rooftop runoff inputs to the sewer system and potable water demand are evaluated for 23%, 53%, respectively.

• Journal of the Society of Naval Architects of Korea
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• v.59 no.2
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• pp.96-108
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• 2022

In this paper, we propose a systematic hull form variation technique which automatically satisfies the displacement constraint and guarantees a high level of fairness. This method is possible through multiple parameter correction curves. The present method is to improve the hull form variation method based on parametric modification function and consists of two sub-categories: SAC variation and section lines modification. For SAC variation, the utilization of two B-Spline curves satisfying GC¹ condition led to the satisfaction of displacement constraint and high level of fairness at the same time. Section lines modification methods involves in using two fuctions: the first is the waterplane modification function combining two cubic splines. the other function is the sectional area modification function consisting of 2nd order polynomial over the DLWL(Design Load Waterline) and 3rd order polynomial below the DLWL, This function enables not only the fundamental U-V section shape variation but also systematically modified section lines. The present method is expected to be more useful in the hull form optimization process using CFD compared to the existing method.

• Journal of Soil and Groundwater Environment
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• v.11 no.2
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• pp.56-67
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• 2006

Trends of variation in groundwater levels, electrical conductivities and water temperatures obtained from the national groundwater monitoring stations (95 shallow and 169 deep wells) of Korea were evaluated. For the analysis, both parametric (linear regression) and non-parametric (Mann-Kendall test, Sen's test) methods were adopted. Results of linear regression analysis indicated that about 50% of the monitoring wells showed increasing trends of groundwater levels, electrical conductivities, and water temperatures and the others showed decreasing trends. However, the non-parametric analyses with monthly median values revealed that $14.8{\sim}20.0%$ of water levels were decreased, $24.2{\sim}36.9%$ of electrical conductivities were increased, and $27.4{\sim}32.5%$ of water temperatures were increased at a confidence level of 99%. Highly proportions of increasing or decreasing trends were unexpected and they resulted from the relatively short term of data collection (maximum 6 years). Meanwhile, the investigation of groundwater around the national groundwater monitoring stations showed that the decreasing or increasing trends of water levels, electrical conductivities, themselves, didn't indicate directly groundwater hazards such as groundwater depletion or groundwater contamination. Both the values and variation rates (slopes) of water level, electrical conductivity and temperature in the longer period are considered simultaneously. This study is the first comprehensive work in analyzing trends of groundwater data obtained from the national groundwater monitoring stations. Based on this study, the periodical and regular analysis of groundwater data is essentially required to grasp the overall variational trend of groundwater resources in the country.