• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.154-164
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• 2019

A rotor dynamic analysis is mandatory for stability and design optimization of submerged propellers and turbines. An accurate simulation requires a proper consideration of fluid-induced reaction forces. This paper presents a bi-directional coupling of a bond graph method solver and an unsteady vortex lattice method solver where the former is used to model the rotor dynamics of the power train and the latter is used to predict transient hydrodynamic forces. Due to solver coupling, determination of hydrodynamic coefficients is obsolete and added mass effects are considered automatically. Additionally, power grid and structural faults like grid fluctuations, eccentricity or failure could be investigated using the same model. In this research work a fast, time resolved dynamic simulation of the complete power train is conducted. As an example, the rotor dynamics of a tidal stream turbine is investigated under two inflow conditions: I - shear flow, II - shear flow + water waves.

• 대한한의학원전학회지
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• 제36권1호
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• pp.79-107
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• 2023

Objectives : This study aims to improve the diagnosis and treatment of contemporary insomnia by examining Zhang Jiebin's discussion on treating insomnia. Methods : The classical texts from the 'Insomnia' chapter of the Jingyue Quanshu were examined threefold in terms of symptom, treatment, and prescription analysis, after which the treatment discussion part was examined within the historical context of discussions on insomnia in major medical texts starting from the Huangdineijing. Results : According to Zhang, the cause of insomnia could be divided into two, after which criteria for diagnosis and treatment were set as excess pathogen and vital qi deficiency. He argued that insomnia could be naturally resolved through improvement of various pathogenic situations. Discussions on insomnia from various medical texts since the Huangdineijing suggest that pathology related to psychological function and emotions gradually increased and expanded over time. Conclusions : Zhang's discussion on symptom, treatment and prescriptions of insomnia suggests a new framework that could improve treatment effects through a Korean Medical Mind-Body approach, rather than the contemporary classification of organic insomnia and non-organic insomnia.

• 대한조선학회논문집
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• 제37권1호
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• pp.67-81
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• 2000

본 연구에서는 2차원 비선형 방사문제에 대한 정확하고 효과적인 수치기법을 개발하였다. 물체운동에 의해서 생성되는 비선형파계는 이상유체라는 가정에 의하여 기술되고, 라프라스 방정식은 고차경계요소법과 GMRES(Generalized Minimal RESidual) 알고리즘을 이용하여 신속하고 효율적인 풀이가 가능하도록 하였다. 자유표면과 물체면의 교차점에서 발생하는 교차선문제는 불연속 요소를 이용하여 원활하게 해결하였다. 자유표면의 비선형운동을 기술하기 위해서 음해적 사다리꼴 법칙(implicit trapezoidal rule)을 사용하여 시적분하였다. 물체에 의해서 발생한 비선형파가 수직 하류면에서 반사하는 것을 줄이기 위하여 하류면에 수치감쇠항을 도입하였다. 수치계산 결과로부터 본 시적분법 및 수치방사조건이 비선형 방사문제에 매우 적합함을 확인하였다. 시적분 과정에서 자유표면의 격자점들을 재배치함으로써 수치해법의 효율성을 배가하였으며, 교차점근처의 유동 또한 정확하게 기술하였다. 가속도 포텐셜(acceleration potential) 기법을 이용하여 정확하고 안정하게 비선형 방사력을 구하였다. 본 수치계산결과는 다른 수치계산 및 실험결과와 비교하여 볼 때, 좋은 일치를 보인다.

• 대한기계학회논문집B
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• 제29권5호
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• pp.633-642
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• 2005

Nucleate pool boiling experiments for R11 under a constant wall temperature condition were carried out. A microscale heater array was used for the heating and the measurement of high temporal and spatial resolution by the Wheatstone bridge circuit. Very sensitive heat flow rate data were obtained by the control for the surface condition with high time resolution. The measured heat flow rate shows a discernable peak at the initial growth stage and reaches an almost constant value. In the thermal growth region, bubble shows a growth proportional to $t^{\frac{1}{5}}$. The bubble growth behavior is analyzed with a dimensionless parameter to compare with the previous results in the same scale. As the wall superheat increases, the departure diameter and the departure time increase, and the waiting time decreases. But the asymptotic growth rate is not affected by the wall superheat change. The effect of the wall superheat is resolved into the suggested growth equation. Dimensionless parameters of time and bubble radius characterize the thermal growth behavior well, irrespective of wall condition. The comparison between the result of this study and the previous results shows a good agreement at the thermal growth region. The quantitative analysis for the heat transfer mechanism is conducted with the measured heat flow rate behavior and the bubble growth behavior. The required heat flow rate for the volume change of the observed bubble is about twice as much as the instantaneous heat flow rate supplied from the wall.

• Archives of Plastic Surgery
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• 제37권1호
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• pp.52-58
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• 2010

Purpose: The digital artery perforator flap was recently introduced and has been proven to be useful for reconstruction of various finger defects. Short operative time, less invasive surgery, and reliable flap circulation are the major advantages of this flap. The authors presented the clinical cases of the digital artery perforator flap and compared them with the distant flaps within a hand (thenar and hypothenar flaps) to reveal their differences. Methods: From May of 2006 to February of 2009, the authors performed reconstructions of finger defects with the digital artery perforator flaps in 10 patients as with the distant flaps within hand in 9 patients (7 thenar and 2 hypothenar flaps). In these two groups of the patients, flap size, use of skin graft, length of stay in hospital, healing time, complications were reviewed retrospectively and compared with statistical analysis (Student's t-test). Results: All flaps survived completely. The mean size of the perforator flap was $0.9{\times}1.9\;cm$ and the mean distant flap within a hand was $1.9{\times}2.0\;cm$. The use of skin graft was reduced in the perforator group because the donor site of the flap was closed primarily. The hospitalization period and healing time also reduced significantly in the perforator group. Minor complications (partial flap loss) were noted in small percentages in both groups but resolved with conservative management. Mean follow-up period was about 6 weeks. Conclusion: The digital artery perforator flap was smaller than the distant flap but its reconstruction of finger defects was reliable and comparable to the conventional distant flaps within a hand. This flap would be not only an alternative method but very useful in the management of various finger defects, because of ease of operative technique, less invasive surgery, decreased need of skin graft, and shorter period of hospitalization and healing time.

• Korean Journal of Radiology
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• 제20권1호
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• pp.126-133
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• 2019

Objective: To compare the lumbar vertebral bone marrow fat-signal fractions obtained from six-echo modified Dixon sequence (6-echo m-Dixon) with those from single-voxel magnetic resonance spectroscopy (MRS) in patients with low back pain. Materials and Methods: Vertebral bone marrow fat-signal fractions were quantified by 6-echo m-Dixon (repetition time [TR] = 7.2 ms, echo time (TE) = 1.21 ms, echo spacing = 1.1 ms, total imaging time = 50 seconds) and single-voxel MRS measurements in 25 targets (23 normal bone marrows, two focal lesions) from 24 patients. The point-resolved spectroscopy sequence was used for localized single-voxel MRS (TR = 3000 ms, TE = 35 ms, total scan time = 1 minute 42 seconds). A 2 × 2 × 1.5 cm³ voxel was placed within the normal L2 or L3 vertebral body, or other lesions including a compression fracture or metastasis. The bone marrow fat spectrum was characterized on the basis of the magnitude of measurable fat peaks and a priori knowledge of the chemical structure of triglycerides. The imaging-based fat-signal fraction results were then compared to the MRS-based results. Results: There was a strong correlation between m-Dixon and MRS-based fat-signal fractions (slope = 0.86, R² = 0.88, p < 0.001). In Bland-Altman analysis, 92.0% (23/25) of the data points were within the limits of agreement. Bland-Altman plots revealed a slight but systematic error in the m-Dixon based fat-signal fraction, which showed a prevailing overestimation of small fat-signal fractions (< 20%) and underestimation of high fat-signal fractions (> 20%). Conclusion: Given its excellent agreement with single-voxel-MRS, 6-echo m-Dixon can be used for visual and quantitative evaluation of vertebral bone marrow fat in daily practice.

• 한국대기환경학회지
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• 제16권5호
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• pp.487-497
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• 2000

Spring time is a favorable season to be easily observed the Yellow Sand phenomenon in East Asia. In particular most of the phenomenon tend to occur in April. However, Yellow Sand phenomenon was observed from almost the whole country of Korea in winter of 1966, 1977 and 1999. The features of the synoptic weather pattern in the source regions, air stream flow between the source region and Korea, the measurement of TSP concentration, aerosol size distribution, and chemical composition of snow samples associated with Yellow Sand phenomenon were investigated. The result showed the characteristic evolutionary feature of the synoptic system associated with Yellow Sand phenomena, that is, a strong low level wind mobilized the dust within 2 or 3 days before Yellow Sand phenomenon being observed in Seoul. The wind was remarkably intensified in the source region on January 24, 1999 under the strong pressure gradient, A trajectory analysis showed that the Yellow Sand particle could be reached to Korea within 2 days from the source region, Gobi desert, through Loess plateau and Loess deposition region. The TSP concentration at the top of Kwanak mountain during the Yellow Sand phenomenon is abruptly increasing than the monthly mean concentration. The size resolved number concentration of aerosols ranging from 0.3 to 25${\mu}{\textrm}{m}$ was analyzed during Yellow Sand episode. It was evident that aerosols were distinguished by particles in the range of 2-3 ${\mu}{\textrm}{m}$ to result in the abrupt increase in January 1999, After Yellow Sand phenomenon, there was heavy snow in Seoul. By the analysis of snow collected during that time, it was observed that both the Ca(sup)2+ concentration and pH were increased abnormally compared to those in the other winter season.

• Journal of the Optical Society of Korea
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• 제17권6호
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• pp.548-558
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• 2013

In this work, laser induced breakdown spectroscopy (LIBS) is used to investigate soil samples collected from different desert areas of Riyadh city in Saudi Arabia. Both qualitative analysis and plasma parameters are studied via the observed LIBS spectra. These experiments have been done using a Spectrolaser-7000 system with 50 mJ fundamental wavelength of Nd:YAG laser and detection delay time of 1 microsecond. Many spectral lines are highly resolved for many elements like Al, Fe, Mg, Si, Mn, Na, Ca and K. The electron temperatures Te and electron densities Ne, for the constituent of generated LIBS plasma, are determined for all the collected samples. It is found that both Te and Ne vary from one desert area to other. This variation is due to the change of the elemental concentration in different desert areas that affects the sample's matrices. Time dependent measurements have also been performed on the soil samples. While the signal-to-base ratio (SBR) reached its optimal value at 1 microsecond, the plasma parameters Ne and Te reach values of $4{\times}10^{17}cm^{-3}$ and 9235 K, respectively, at 2.5 microsecond. The later indicate that the plasma cooling processes are slow in comparison to the previously observed results for metallic samples. The observed results show also that in the future it is possible to enhance the exploitation of LIBS in the remote on-line environmental monitoring application, by following up only the values of Ne and Te for one element of the soil desert sample using an optical fiber probe.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.43.2-43.2
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• 2010

In this study, metallurgical grade (MG) silicon with 99% purity produced by arc furnace process was systematically investigated for slag refining. The most problematic impurities to remove from MG silicon are boron (B) and phosphorus (P). To remove B and P from MG-silicon, we used synthetic slag in the molten state. MG-silicon with synthetic slag of CaO, $SiO_2$, and $CaF_2$ was melted using by high-frequency induction furnace with electrical output of 50kW. Specimens prepared by various refining process conditions(holding time, mixture ratio) were inspected by combined analysis of ICP-MS and XRF. With this approach, B has been reduced to <5ppm, P to <1ppm and other impurities to 0.1~0.2% except for Calcium. Calcium has been increased from 17ppm to 1500ppm. Problem of calcium contamination will be resolved by additional refining processes.

• 한국전자거래학회:학술대회논문집
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• 한국전자거래학회 1997년도 한국전자거래학회 종합학술대회지
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• pp.263-268
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• 1997

Functional Modeling methodology, IDEF0 is widely used for modeling, analysis and description of enterprise system. The limitation of modeling components restricts applicability and give rise to confusion about model. In this paper, we propose new method to extend IDEF0. The first is adding modeling components which are semantic representations. In addition to ICOMs, we add the time and cost component which is required to execute the function. The second is tracing mechanism. When we need some information, we drive the functions related with the information by reverse tracing of the function which produces the information as a output and input. Through the tracing, we find out the bottleneck process or high cost process. Finally, we suggest the final decomposition level. We call the final decomposed function into unit function which has only one output data. We can combine and reconstruct some of functions because an unit function is similar to ‘lego block’. To reach the integrated system, the main problem to be solved is the integration of information produced by different functional subsystem. This can be resolved when the creation of data must be dependent on only one function. Through view integration of function output, we can guarantee the integrity of data.