• 한국전산유체공학회:학술대회논문집
• /
• 2008.03b
• /
• pp.385-388
• /
• 2008

The objective of this paper is simulating blood flow through the branched and stenotic tube numerically. SC-Tetra, which is one of the commercial code using FVM method, was utilized for this analysis. The flow is assumed as an incompressible laminar flow with the additional condition of non-Newtonian fluid. As the constitutive equation for the fluid viscosity, the following models were solved with governing equations ; Cross Model, Modified Cross Model, Carreau Model and Carreau-Yasuda Model. Final goal was achieved to get analytic data about shear stress, at specific points, changing the geometry with various factors like the bifurcation angle, diameter of the branches, the ratio of stenosis, and etc. The material property of blood was referred from the related papers. Furthermore, to verify results they were compared with those of the published papers. There were some discrepancies based on the different solver and the different data post-processing method. However, many parameters like the location of low shear stress, which arised from bifurcation or stenosis, and the tendency of various factors were found to be very similar.

• Journal of Environmental Science International
• /
• v.25 no.8
• /
• pp.1165-1176
• /
• 2016

The accuracy of digital elevation models (DEMs) is crucial for properly estimating flood inundation area. DEM pixel size is especially important when generating flood inundation maps of small streams with a channel width of less than 50 m. In Korea, DEMs with large spatial resolutions of 30 m have been widely applied to generate flood inundation maps, even for small streams. Additionally, when making river master plans, field observations of stream cross-sections, as well as reference points in the middle of the river, have not previously been used to enhance the DEM. In this study, it was graphically demonstrated that high-resolution DEMs can increase the accuracy of flood inundation mapping, especially for small streams. Also, a methodology was proposed to modify the existing low-resolution DEMs by adding additional survey reference points, including river cross-sections, and interpolating them into a high spatial resolution DEM using the inverse distance weighting method. For verification purposes, the modified DEM was applied to Han stream on Jeju Island. The modified DEM showed much better accuracy when describing morphological features near the stream. Moreover, the flood inundation maps were formulated with the original 30 m pixel DEM and the modified 0.1 m pixel DEM using HEC-RAS modeling of the actual flood event of Typhoon Nari, and then compared with the flood history map of Nari. The results clearly indicated that the modified DEM generated a similar inundation area, but a very poor estimate of inundation area was derived from the original low-resolution DEM.

• Journal of The Korean Astronomical Society
• /
• v.52 no.6
• /
• pp.217-225
• /
• 2019

We apply a modified Convolutional Neural Network (CNN) model in conjunction with transfer learning to predict whether an active region (AR) would produce a ≥C-class or ≥M-class flare within the next 24 hours. We collect line-of-sight magnetogram samples of ARs provided by the SHARP from May 2010 to September 2018, which is a new data product from the HMI onboard the SDO. Based on these AR samples, we adopt the approach of shuffle-and-split cross-validation (CV) to build a database that includes 10 separate data sets. Each of the 10 data sets is segregated by NOAA AR number into a training and a testing data set. After training, validating, and testing our model, we compare the results with previous studies using predictive performance metrics, with a focus on the true skill statistic (TSS). The main results from this study are summarized as follows. First, to the best of our knowledge, this is the first time that the CNN model with transfer learning is used in solar physics to make binary class predictions for both ≥C-class and ≥M-class flares, without manually engineered features extracted from the observational data. Second, our model achieves relatively high scores of TSS = 0.640±0.075 and TSS = 0.526±0.052 for ≥M-class prediction and ≥C-class prediction, respectively, which is comparable to that of previous models. Third, our model also obtains quite good scores in five other metrics for both ≥C-class and ≥M-class flare prediction. Our results demonstrate that our modified CNN model with transfer learning is an effective method for flare forecasting with reasonable prediction performance.

• KSBB Journal
• /
• v.26 no.4
• /
• pp.352-356
• /
• 2011

The detection of biomarkers is an important issue for disease diagnosis. However, many systems are not suitable to detect the biomarker itself directly. For direct detection of biomarker proteins in human serum, a new affinity-capture method using aptamers combined with the mass spectrometry was suggested. Since signals from protein samples cannot be amplified, modified chromatin immunoprecipitation (ChIP) and subsequent cross-linking with formaldehyde between aptamers and target proteins were used not to lose the captured target proteins, which allowed us to perform a harsh washing step to remove the non-specifically bound proteins. As a model system, a thrombin aptamer was used as a bait and thrombin as a target protein. Using our modified ChIP and affinity-capture method, non-specific binding proteins on the beads decreased significantly, suggesting that our new method is efficient and can be applied to developing diagnosis systems for various biomarkers.

• Journal of Institute of Control, Robotics and Systems
• /
• v.14 no.10
• /
• pp.991-997
• /
• 2008

A new RMRAC scheme far the PMSM current regulation is proposed in a synchronous frame, which is completely free from the parameter's uncertainty. A current regulator of PMSM is the inner most loop of electromechanical driving systems and plays a foundation role in the control hierarchy. When the PMSM runs in high speed, the cross-coupling terms must be compensated precisely for large system BW. In the proposed RMRAC, the input signal is composed of a calculated voltage defined by MRAC law and an output of the disturbance compensator. The gains of feed forward and feedback controller are estimated by the proposed modified gradient method, where the system disturbances are assumed as filtered current regulation errors. After the compensation of the system disturbance from error information, the corresponding voltage is fed forward to control input to compensate for real disturbances. The proposed method robustly compensates the system disturbance and cross-coupling terms. It also shows a good realtime performance due to the simplicity of control structure. Through real experiments, the efficiency of the proposed method is verified.

• Journal of Bio-Environment Control
• /
• v.30 no.4
• /
• pp.278-286
• /
• 2021

In this study, based on the Computational Fluid Dynamics (CFD) simulation model developed through previous study, inner environmenct of the modified glass greenhouse was predicted. Also, suggested the optimal shape of the greenhouse and location of the heat exchangers for heat energy management of the greenhouse using the developed model. For efficient heating energy management, the glass greenhouse was modified by changing the cross-section design and the location of the heat exchanger. The optimal cross-section design was selected based on the cross-section design standard of Republic of Korea's glass greenhouse, and the Fan Coil Unit(FCU) and the radiating pipe were re-positioned based on "Standard of greenhouse environment design" to enhance energy saving efficiency. The simulation analysis was performed to predict the inner temperature distribution and heat transfer with the modified greenhouse structure using the developed inner environment prediction model. As a result of simulation, the mean temperature and uniformity of the modified greenhouse were 0.65℃, 0.75%p higher than those of the control greenhouse, respectively. Also, the maximum deviation decreased by an average of 0.25℃. And the mean age of air was 18 sec. lower than that of the control greenhouse. It was confirmed that efficient heating energy management was possible in the modified greenhouse, when considered the temperature uniformity and the ventilation performance.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.34 no.12
• /
• pp.48-58
• /
• 2006

The spray and combustion characteristics of liquid jet in cross flow with variation of injection angle are numerically studied. Numerical analysis was carried out using KIVA code, which may be used to generate numerical solutions to spray and chemical reactive fluid problem in three space dimensions and modified to be suitable for simulating liquid jet ejected into the cross flow. Wave model and Kelvin- Helmholtz(KH) /Rayleigh-Taylor(RT) hybrid model were used for the purpose of analyzing liquid column, ligament, and the breakup of droplet. Penetration length increases as flow velocity decreases and injection velocity increases. Numerical error increases as inflow velocity increases. The results of flame propagation contour in combustion chamber and local temperature distribution, combustion emissions were obtained.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.59 no.6
• /
• pp.1126-1130
• /
• 2010

Speech production can be viewed as a filtering operation in which a sound source excites a vocal tract filter. The vocal tract is modeled as a chain of cylinders of varying cross-sectional area in linear prediction acoustic tube modeling. In this modeling the most common implementation assumes equal length of tube sections. Therefore, to model complex vocal tract shapes, a large number of tube sections are needed. This paper proposes a new vocal tract model with unfixed sectionlengths, which uses the reduced lattice filter for modeling the vocal tract. This model transforms the lattice filter to reduced structure and the Burg algorithm to modified version. When the conventional and the proposed models are implemented with the same order of linear prediction analysis, the proposed model can produce more accurate results than the conventional one. To implement a system within similar accuracy level, it may be possible to reduce the stages of the lattice filter structure. The proposed model produces the more similar vocal tract shape than the conventional one.

• Steel and Composite Structures
• /
• v.46 no.3
• /
• pp.353-366
• /
• 2023

This paper presents a finite-element analysis (FEA) of aluminum alloy rectangular hollow sections (RHSs) and square hollow sections (SHSs) with circular through-openings under three-point and four-point bending. First, a finite-element model (FEM) was developed and validated against the corresponding test results available in the literature. Next, using the validated FE models, a parametric study comprising 180 FE models was conducted. The cross-section width-to-thickness ratio (b/t) ranged from 2 to 5, the hole size ratio (d/h) ranged from 0.2 to 0.8 and the quantity of holes (n) ranged from 2 to 6, respectively. Third, results obtained from laboratory test and FEA were compared with current design strengths calculated in accordance with the North American Specifications (NAS), the modified direct strength method (DSM) and the modified Continuous strength method (CSM). The comparison shows that the modified CSM are conservative by 15% on average for aluminum alloy RHSs and SHSs with circular through-openings subject to bending. Finally, a new design equation is proposed based on the modified CSM after being validated with results obtained from laboratory test and FEA. The proposed design equation can provide accurate predictions of flexural capacities for aluminum alloy RHSs and SHSs with circular through-openings.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.3 no.3
• /
• pp.124-131
• /
• 1979

An optimim reduction gear ratio problem for a subway rapid transit car in Seoul was solved by using a computer program package, which is a modified and extened version of the simple model by Mischke. The optimum value of reduction gear ratio was evaluated by minimizing the total start-to stop time.The validity of the computer program package was verified by cross-checking the calculated values of gear ratio and dynamic characteristics with the actual and measured values.