• Journal of Ocean Engineering and Technology
• /
• v.32 no.3
• /
• pp.166-176
• /
• 2018

This paper presents a numerical sensitivity analysis for the simulation of the motion performance of an offshore structure in waves using computational fluid dynamics (CFD). Starting with 2D wave simulations with varying numerical parameters such as grid spacing and CFL value, proper numerical conditions were found for accurate wave propagation that avoids numerical diffusion problems. These results were mapped on 2D error distributions of wave amplitude and wave length against the numbers of grids per wave length and per wave height under a given CFL condition. Finally, the 2D numerical sensitivity result was validated through CFD simulation of the motion of a FPSO in waves showing good accuracy in motion RAOs compared with existing potential flow solutions.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.44 no.10
• /
• pp.178-184
• /
• 2007

A new adaptive alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method is proposed to obtain isotropic wave propagation for all directional angles. We add the square terms of time-step multiplied by the spatial derivatives of x and y as a perturbed term to the conventional ADI-FDTD and can find the optimization coefficient of square terms of time-step to generate the minimum anisotropy. The new ADI-FDTD is also stable, even when its time-step is greater than the Courant-Friedrich-Levy (CFL) limit. The characteristic equation of the dispersion relation governing the new method is derived and compared with the theoretical and numerical results for the conventional ADI-FDTD and perturbed ADI-FDTD methods.

• Environmental Engineering Research
• /
• v.21 no.2
• /
• pp.171-179
• /
• 2016

This study analyzes guidelines to select optimum number of grids to represent behavior of a given water system appropriately. The EFDC model was chosen as a 3-D hydrodynamic and water quality model and salt was chosen as a surrogate variable of pollutant. The model is applied to an artificial canal that receives salt water from coastal area and fresh water from a river from respective gate according to previously developed gate operation rule. Grids are subdivided in vertical and horizontal (longitudinal) directions, respectively until no significant changes are found in salinity concentrations. The optimum grid size was determined by comparing errors in average salt concentrations between a test grid systems against the most complicated grid system. MSE (mean squared error) and MAE (mean absolute error) are used to compare errors. The CFL (Courant-Friedrichs-Lewy) number was used to determine the optimum number of grid systems for the study site though it can be used when explicit numerical method is applied only. This study suggests errors seem acceptable when both MSE and MAE are less than unity approximately.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.12 no.2
• /
• pp.151-159
• /
• 1992

In close-range photogrammetry, to employ non-metric camera especially for the purpose of precise measurement, systematic errors must, first of all, be corrected as they have a great influence on accuracies of results. For it, fiducial marks was built in non-metric camera and the factors such as PPS, PPA, EFL, CFL, and radial lens distortion coefficients for each quadrant were calibrated through collimator test. Also, the coefficients of both radial and tangential lens distortion were calibrated from analytical plumb line method and therefore main systematic errors could be effectively corrected. Using the calibrated non-metric camera, close-range photogrammetry could be successfully accomplished and accuracies could be improved sharply.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.48 no.1
• /
• pp.27-33
• /
• 1999

Compact fluorescent lamps are very sensitive to the variation of ambient temperature. This paper investigates the temperature characteristics of a 15[W] compact fluorescent lamp, and compensates the variation of light output by frequency control of its electronic ballast. Circuit parameters for the inverter of the electronic ballast are obtained by analyzing the R-L-C equivalent circuit for the inverter and the lamp. The optimum ratio of the two capacitance($C_1$/$C_2$), which are connected with the lamp in series and in parallel, respectively, is determined which consideration of the temperature variation within a range of 10~35[$^{\circ}C$]. As a result a value of 10 for the ratio is obtained at an operating frequency of 57[kHz], and with this value the frequency control works well for temperature compensation. Its validity is verified by investigating light output stabilization characteristics resulting from frequency control of the lamp at various temperatures.

• Investigative Magnetic Resonance Imaging
• /
• v.17 no.2
• /
• pp.110-122
• /
• 2013

Purpose : To compare the image quality and ligament traceability in ankle images obtained using Volume Isotropic Turbo Spin Echo Acquisition (VISTA) MRI with and without fat suppression. Materials and Methods: The signal-to-noise ratios (SNRs) in images from a phantom and from the ankle of a volunteer were compared. Ten ankles from 10 non-symptomatic volunteers were imaged for comparisons of contrast ratio (CR) and ligament traceability. All examinations were performed using VISTA sequences with and without fat suppression on a 3T MRI scanner. The SNRs were obtained from images with subjects and without subjects (noise-only). Contrast ratios from images of the 10 ankles were acquired between fluid and tendon (F-T), F-cartilage (C), F-ligament (L), fat (f)-T, f-C and f-L. Two musculoskeletal radiologists independently scored the traceability of 7 ligaments, in sagittal, axial and coronal images respectively, based on a 4-point scale (1 as not traceable through 4 as clearly traceable). The Wilcoxon signed-rank test was used to compare the CR. Fisher's exact test and Pearson's chi-squared test were used to compare the ligament traceability. Results: The SNRs did not differ significantly between the two sequences except in bone marrow. VISTA SPAIR showed the higher CR only in F-T (p = 0.04), whereas VISTA showed higher CR in f-T (p = 0.005), f-C (p = 0.005) and f-L (p = 0.005). The calcaneofibular ligament traceability with VISTA was superior to that obtained with VISTA SPAIR (p < 0.05) in all planes. Conclusion: VISTA showed significant superiority to VISTA SPAIR in tracing CFL due to the superior CR between fat and ligament.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.11 no.9
• /
• pp.3583-3589
• /
• 2010

The semi-implicit scheme proposed by Backhaus is introduced to solve two-dimensional shallow water equation. This mothod is applied for the numerical model solving surface elevation and velocity field of Geum River estuary. For the verification of the method, numerical solutions by this model are compared with ones by Heap's well known explicit model. Solutions of two models resemble each other. The time-step chosen for the semi-implicit scheme turned out to be 3 to 6 times longer than explicit model depending on the stringent CFL criterion. The computation time could be reduced at least 50%. It was proved that this scheme is easy to handle dry banks which can be seen in Geum River estuary and numerical stability is obtained for long time computation.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.38 no.8
• /
• pp.1024-1031
• /
• 2009

Crataegi fructus has been used as an oriental medicine and a folk remedy for the treatment of scurvy, constipation and stomach ailment. This study was aimed to investigate the effect of fermented Crataegi fructus vinegar (FCV) on the improvement of lipid metabolism in rats fed high fat diet (40% kcal% fat, fat source; beef tallow). Sprague-Dawley rats (n=32) were randomly divided into four groups [normal diet (ND), high fat diet (HD), and high fat diet supplemented with low (CFL; 1.5% wt/wt) and high (CFH; 3.0% wt/wt) doses of fermented Crataegi fructus vinegar] and were fed experimental diets for 6 weeks. At the end of the experiment, the body weight in high fat diet groups was higher than that of normal diet group, while the body weights of CFL and CFH group were significantly reduced by 7.2% and 10.0%, respectively, as compared with that of HD group. Moreover, liver and kidney weights in CFL and CFH group were significantly lower than that of HD group (p<0.05). The levels of serum triglyceride, total cholesterol, LDL-C, atherogenic index and hepatic triglyceride, total cholesterol in CFH group were significantly decreased as compared with HD group whereas it increased the serum level of HDL-C than HD group (p<0.05). CFL and CFH groups showed significantly decreased AST, ALT and ALP of serum as compared with HD group. Excretions of fecal saturated fatty acid in CFH group was significantly increased compared with ND and HD groups. These results imply that fermented Crataegi fructus vinegar can be used as possible food resources and functional food materials.

• Asia Pacific Journal of Business Review
• /
• v.2 no.2
• /
• pp.1-15
• /
• 2018

The purpose of this paper is to find out the factors responsible for purchase of LED (light-emitting-diodes) bulbs & tubes among Indian consumers and how much they are ready to replace their existing lighting system with LED fittings. A multiple regression model has been employed to investigate the factors affecting the buying decision of LED lamps in place of CFL and incandescent lamps. Eleven motives for adopting LED lamps has been identified viz. price, quality, energy saving, durability, brand, promotion, CSR, & environmental consciousness. In addition the effect of demographic variables like gender, age, household income on the purchasing decision of LED has also been examined. A total 150 respondents were contacted visiting different outlet of electrical shops of Northern Delhi. The study may helpful for the companies to decide their marketing strategies to promote LED Lamps among the consumers with an aim to save energy and save environment.

• 한국전산유체공학회:학술대회논문집
• /
• 2009.04a
• /
• pp.116-120
• /
• 2009

A two-dimensional unsteady inviscid flow solver has been developed for the simulation of complex geometric configurations on adaptive Cartesian meshes. Embedded condition was used for boundary condition and a predictor-corrector explicit time marching scheme was used for time-accurate numerical simulation. The Cartesian mesh generator, which was previously developed for steady problem, was used grid generation for unsteady flow. The solver was based on ALE formulation for body motion. For diminishing the effects of cut-cells, the cell merging method was used. Using cell merging method, it was eliminated the CFL constraints. The conservation problem, which is caused cell-type variation around region swept by solid boundary, was also solved using cell merging method. The results are presented for 2D circular cylinder and missile launching problem.