• Journal of Navigation and Port Research
• /
• v.47 no.6
• /
• pp.315-323
• /
• 2023

Marine accidents due to loss of stability of small ships have continued to increase over the past decade. In particular, since sudden winds have been pointed out as main causes of most small ship accidents, safety measures have been established to prevent them. In this regard, to prevent accidents caused by sudden winds, a systematic analysis technique is required. The aim of the present study was to develop a probabilistic approach to estimate extreme value and evaluate effects of wind on motion characteristics of ships. The present study included studies of motion analysis, extraction of extreme values, and motion characteristics. A series analysis was conducted for three conditions: wave only, wave with uniform wind speed, and wave with the NPD wind model. Hysteresis filtering and Peak-Valley filtering techniques were applied to time-domain motion analysis results for extreme value extraction. Using extracted extreme values, the goodness of fit test was performed on four distribution functions to select the optimal distribution-function that best expressed extreme values. Motion characteristics of a fishing boat were evaluated for three periodic motion conditions (Heave, Roll, and Pitch) and results were compared. Numerical analysis was performed using a commercial solver, ANSYS-AQWA.

• Korean Journal of Medicinal Crop Science
• /
• v.12 no.4
• /
• pp.328-341
• /
• 2004

Presowing seed treatments used to enhance the rates of germination and afterward seedling emergence have not occasionally shown the same rate in indoor and field. The treatments considering germination mechanism and factors affecting germination must be totally included in indoor experiments so that the results drawn can be reproduced in the field. Seed germination is controlled by Phytochrome-mediated action changed with composition rates of red and far-red lights. Sunlight can penetrate soil into $6{\sim}9\;mm$ depth, which in turn means that seeds having $2{\sim}3\;mm$ in their width may receive the light if soil was covered 3 times over them. The penetrating light, moreover, turns to more far-red light than red light reverse to the sunlight. For germination tests after the artificial presowing seed treatments, therefore, seeds of smaller than 2 mm (< 2 mm), $2{\sim}3\;mm$, and larger than 3 mm (> 3 mm) must be done with incandescent lamp (IL) having more far-red light, with IL or in darkness, and in darkness, respectively. The 96 papers published in 13 Korean scientific journals up to the end of 2003 were analysed on the basis of the above explanation. 91 species were used 147 times as experimental materials; 101 times for < 2 mm seeds, 24 times for $2{\sim}3\;mm$ seeds and 22 times for > 3 mm seeds. If they were analysed as the light sources used for germination tests, correct applications reached more and less than 60% in both $2{\sim}3\;mm$ and > 3 mm seeds but 23% in < 2 mm seeds, conclusionally meaning that when the experimental results in the scientific papers were applied into farming practices, care was taken of their application because most of medicinal plant seeds were very small.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.39 no.12
• /
• pp.1207-1212
• /
• 2015

A vibro ripper utilizes high-frequency vibration for rock fragmentation. This concept is different from those used by other existing breakers. The gearbox-shank welded joint of a vibro ripper is a very important part. Because it delivers the vibromotive force to the tooth, it is important to predict its soundness. This study was conducted to predict the fatigue life under welding conditions. The shank materials were Hardox-Hituf and AR400, and the filler metals were CSF-71T and CSF-81T. Fatigue tests were conducted under each set of conditions. P-S-N curves are presented based on the statistical testing method recommended by JSME-S002, and a comparison is made of the results under each set of conditions. The life was estimated using a P-S-N curve.

• The Korean Journal of Applied Statistics
• /
• v.22 no.4
• /
• pp.793-804
• /
• 2009

The hypotheses of difference, ratio and odds ratio between two proportions are used for the non-inferiority trial. The approximate unconditional test suggested by Kang and Chen (2000) based on difference and ratio have the potential problem against the failure rate. When the sample size is small, the type I errors of the asymptotic test using the normal approximation suggested by Chen et al. (2000) tends to exceed the nominal level. Therefore, we propose the approximate unconditional test based on odds ratio and compare the test with the asymptotic test. And we compare the three hypotheses used in the approximate unconditional tests of two proportions with respect to the type I errors and power.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.21 no.10
• /
• pp.35-39
• /
• 2007

Home appliances, like air-conditionals, washers, refrigerators, etc., can cause voltage fluctuations and light flicker. A standardized flicker test has been established in Europe(IEC 61000-3-3, IEC 61000-3-11). The supply impedance of power supply system varies from plate to place, and for the flicker test in KOREA, the appliance manufacturers do need standardized impedance like the one indicated in IEC 61000-3-3 for 230[V]/50[Hz]. Without it, the same appliance will have different flicker level at different places. For appliance manufacturers, the flicker limit should be related to the reference impedance. However, the European flicker test is designed for 230[V]/50[Hz] power and needs to be modified for a 1P2W(220[V]/60[Hz]) supply system in KOREA. In this paper, the reference impedance for KOREA(220[V]/60[Hz]) systems is proposed. The measured result provided in this paper was served as a proposal for establishing KOREA reference impedance for 220[V]/60[Hz] and has been published in IEC 60725.

• Journal of the Korean GEO-environmental Society
• /
• v.19 no.3
• /
• pp.25-33
• /
• 2018

Piping is one of the most frequently occurring collapse type of a levee, and is often caused by roofing (backward erosion piping) at the ground-structure interface. Roofing is generally evaluated using creep ratio. However, creep ratio does not take into account the characteristics of the ground-structure interface. In this study, the roofing risk was investigated by using model test and numerical analysis considering the ground-structure interface characteristics. In the model test, it was confirmed that the piping potential decreased as the interface roughness increased, and this was applied to the numerical analysis. Existing numerical methods can not adequately simulate the particle behavior at the ground-structure interface because only the water level difference is considered. In this paper, particle behavior at the interface was investigated by performing seepage analysis and then, carrying out particle analysis technique simulating the boundary condition of the ground-structure interface. Analysis results have shown that the roofing resistance decreases as the ground-structure interface roughness decreases.

• Aerospace Engineering and Technology
• /
• v.11 no.1
• /
• pp.103-110
• /
• 2012

In the COMS satellite mission operation, more large meteorological images such as Full Disk(FD) image or 2 adjacent Extended Northern Hemisphere(ENH) images can be taken by the time shift of East West Station Keeping(EWSK) maneuver when the EWSK conflicts with the large images. In this study an analytical approach based on probability of the conflict is proposed for theoretical analysis about the EWSK time shift to avoid the conflict with FD or 2 ENH images. The EWSK time shift has been applied to the COMS operation as a test, too. The theoretical study result and test operation outcome are synthesized to provide the analysis of impact on the COMS fuel consumption by the EWSK time shift. This study is expected to contribute to the maximization of COMS meteorological mission application.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.39 no.6
• /
• pp.611-615
• /
• 2015

Anti-aircraft gun system is used for low-level air defense system and has more than twin guns with high firing rate in order to maximize the capability of defense. Gun's vibration and bullet's variance has a critical effect on accuracy and hit probability of weapon system such as anti-aircraft gun system with high firing rate. Typical mechanism to reduce the amount of vibration and shock during gun-fire process is very important design factor. In this paper, the suspension characteristics of the vehicle are studied for the improvement of isolating performance of gun firing system with high firing rate. Gun fire test for the vehicle is conducted and computational models using Recurdyn and Adams are created based on test results. Through this study, results of computational analysis are compared with the real test results, which includes type, location and quantity of suspension and gun mechanism are selected for anti-aircraft gun. From the result of this study, we could make basic design and consider the proper component of the system such as suspension and gun spring.

• Journal of the Korean Society of Groundwater Environment
• /
• v.5 no.2
• /
• pp.80-87
• /
• 1998

Since groundwater flow paths have one of the major roles to transport the radioactive nuclides from the radioactive waste repository to the biosphere, the discrete fracture network model is used for the rock block scale flow instead of the porous continuum model. This study aims to construct a three dimensional discrete fracture network to interpret the groundwater flow system in the study site. The modeling work includes the determination of the probabilistic distribution function from the fracture geometric and hydraulic parameters, three dimensional fracture modeling and model calibration. The results of the constant pressure tests performed in a fixed interval length at boreholes indicate that the flow dimension around boreholes shows mainly radial to spherical flow pattern. The fracture transmissivity value calculated by Cubic law is 6.12${\times}$10$\^$-7/ ㎡/sec with lognormal distribution. The conductive fracture intensity estimated by FracMan code is 1.73. Based on this intensity, the total number of conductive fractures are obtained as 3,080 in the rock block of 100 m${\times}$100 m${\times}$100 m.

• Journal of Korean Society of Steel Construction
• /
• v.10 no.2 s.35
• /
• pp.153-160
• /
• 1998

The sectional dimensions and initial crookedness of the RHS(rectangular hollow section, ${\boxe}-75{\times}75{\times}3.2,\;{\boxe}-100{\times}100{\times}4.2,\;{\boxe}-125{\times}125{\times}6.0$) were measured. The axial compressive strength tests for columns with slenderness $46{\sim}84$ were performed as well as stub tests and tensile tests. FEM analysis was also used. The measurement shows that the errors of sectional dimensions are negligible. For the column length corresponding to ${\lambda}=100$, the initial crookedness with the 2.5% probability estimated from the measured results is 1/490, 1/1121 1/1395 for each section respectively. The yield strengths obtained from tensile test are higher than the specified minimum value by more than 30%. The column test shows that the maximum axial resistances are almost same as, or a little higher than the FEM results and the specified strength curves of AISC Specification and Eurocode, when the maximum strengths from the stub tests are used as the yield strength of the steel. But the test results show much higher column strength than those specified in the Standard and Code, when the specified minimum yield strength of the steel is used.