• Advances in aircraft and spacecraft science
• /
• v.9 no.5
• /
• pp.463-477
• /
• 2022

This study compares various ways of calculating flows for the problems with the presence of shock waves by first-order schemes and higher-order DG method on the tests from the Quirk list, namely: Quirk's problem and its modifications, shock wave diffraction at a 90 degree corner, the problem of double Mach reflection. It is shown that the use of HLLC and Godunov's numerical schemes flows in calculations can lead to instability, the Rusanov-Lax-Friedrichs scheme flow can lead to high dissipation of the solution. The most universal in heavy production calculations are hybrid schemes flows, which allow the suppression of the development of instability and conserve the accuracy of the method.

• Journal of the Korean Society for Precision Engineering
• /
• v.14 no.6
• /
• pp.114-120
• /
• 1997

To assess the validity of the previously computed finite element analysis results, the photoelastic experiment was carried out to determine stress intensity factors for crack originating from thin section of integrally stiffened plates having discontinuous thickness interface. The stress intensity factors were deter- mined by using linear slope method of photoelastic data. Results are presented as variable thickness geometry factor. $F_{IV}$ , for various crack lengths and thickness ratios. The experimental values of F/ sub IV/are compared with 3-D finite element analysis results. The correlation between experimental values and analysis results is resonably good.

• Proceedings of the KIPE Conference
• /
• 2020.08a
• /
• pp.261-262
• /
• 2020

본 논문은 DC/DC 위상천이 풀브릿지 컨버터의 과도상태 개선을 위한 듀얼모드 제어를 제안한다. 기존의 discontinuous conduction mode (DCM)과 continuous conduction mode (CCM)을 이용하여 운용하는 위상천이 풀브릿지 컨버터는 각 모드의 상이한 전압게인의 특성을 고려하지 않아 급격한 로드 변동시 출력 전압의 언더슈트 혹은 오버슈트가 크게 발생한다. 제안하는 듀얼모드 제어는 DCM과 CCM 각 모드 별개로 제어가 적용되고 출력 전류의 변화에 대응하는 적응형 feed-forward 제어가 적용되어 컨버터의 과도상태를 개선할 수 있다. 듀얼모드의 제어 방법의 성능과 타당성을 시뮬레이션을 통해 입증한다.

• Proceedings of the KIPE Conference
• /
• 2020.08a
• /
• pp.427-428
• /
• 2020

본 논문에서는 최소손실 불연속 변조 기법에 따른 2레벨 3상 전압원 인버터의 DC 링크 전압 리플을 분석하고 이를 통해 DC 링크 커패시터 전기 용량을 선정하는 방법을 제시하였다. 커패시터 전기 용량은 클수록 전압 리플을 제한하는 데 유리하지만, 이는 인버터 제작비용을 증가시키고 전력 밀도를 낮춘다. 따라서 DC 링크 커패시터 전기 용량을 적절히 선정하는 것이 중요하다. PSIM을 이용한 매입형 영구자석 동기 전동기 구동모의실험으로 제시한 분석 방법의 타당성을 검증하였다.

• Journal of Korean Association for Spatial Structures
• /
• v.24 no.2
• /
• pp.43-52
• /
• 2024

Phayathonzu temple in Myanmar was made of masonry bricks, and so it was vulnerable to lateral load such as earthquake. Especially, it has many difficulties in structural modeling and dynamic analysis because the discontinuous characteristics of masonry structure should be considered. So, it is necessary to provide the seismic performance evaluation technology through the inelastic dynamic modeling and analysis under earthquake loads for the safety security of masonry brick temple. Therefore, this study analyzes the seismic behavior characteristics and evaluates the seismic performance for the 479 structure with many cracks and deformations. Through the evaluation results, we found out the structural weak parts on earthquake loads.

• Journal of the Korean Society for Railway
• /
• v.20 no.5
• /
• pp.668-682
• /
• 2017

Alignments of railways recently constructed in Korea have been straightened due to the advent of high-speed rail, which means increasing the numbers of tunnels and bridges. Overbreak during tunnel construction may be unavoidable, and is very influential on overall stability. Over-excavation in tunneling is also one of the most important factors in construction costs. Overbreak problems around crown areas have decreased with improvements of excavation methods, but overbreak problems around bottom areas have not decreased because those areas are not very influential on tunnel stability compared with crown areas. The filling costs of 10 cm thickness of overbreak at the bottom of a tunnel are covered under construction costs by Korea Railway Authority regulations, but filling costs for more than the covered thickness are considered losses of construction cost. The filling material for overbreak bottoms of tunnels should be concrete, but concrete and mixed granular materials with fractured rock are also used for some sites. Tunnels in which granular materials with fractured rock are used may have a discontinuous section under the concrete slab track. The discontinuous section influences the propagation of waves generated from train operation. When the bottom of a tunnel is filled with only concrete material, the bottom of the tunnel can be considered as a continuous section, in which the waves generated from a train may propagate without reflection waves. However, a discontinuous section filled with mixed granular materials may reflect waves, which can cause resonance of vibration. The filled materials and vibration propagation characteristics are studied in this research. Tunnel bottom filling materials that have ratios of granular material to concrete of 5.0 %, 11.5 %, and 18.0 % are investigated. Samples were made and tested to determine their material properties. Static numerical analyses were performed using the FEM program under train operation load; test results were found to satisfy the stability requirements. However, dynamic analysis results show that some mixed ratios may generate resonance vibration from train operation at certain speeds.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.10 no.2
• /
• pp.119-128
• /
• 2008

In the case of a circular shaft, it is expected that asymmetric loads should apply on the surface rather than symmetric loads due to geographical factors and the non-homogeneity of the jointed rock masses. In this study, discontinuous numerical analysis was carried in order to analyze the characteristics of asymmetric load distribution on the wall of the circular shaft due to anisotropy caused by heterogeneity of rock masses affected by the discontinuities like as a Joint. And it was also analyzed that the effect of the mechanical properties varied with the rock mass rating and horizontal stress with depth had influence in the asymmetric load on the wall of the shaft. In the case of considering the effect of the joint as variable, asymmetric load ratio $(R_p)$, which was defined as the ratio of the load subtracted minimum from maximum to minimum, was below 25% in the hard rock. As regarding the variation of the rock mass rating with depth as variable, the value of $R_p$ was below than 25% in the hard rock, and the value between 30% and 40% in the soft rock. On the other hand, the $R_p$ of fractures rock was between $45{\sim}50%$ which value was much higher than that in better rock mass rating.

• Korean Journal of Biological Psychiatry
• /
• v.8 no.1
• /
• pp.20-36
• /
• 2001

The debate about whether depressive disorders should be divided into categories or arrayed along a continuum has gone for decade, without resolution. In our review, there is more evidence consistent with the spectrum concept than there is with the idea that depressive disorders constitute discrete clusters marked by relatively discontinuous boundaries. First, "depression spectrum", "is there a common genetic factors in bipolar and unipolar affective disorder", "threshold model of depression" and "bipolar spectrum disorder" are reviewed. And, a new subtype of depression is so called SeCA depression that is a stressor-precipitated, cortisol-induced, serotonin-related, anxiety/aggression-driven depression. SeCA depression is discussed. But, there is with the idea that depressive disorders constitute discrete subtypes marked by relatively discontinuous boundaries. This subtypes of depressive disorder were reviewed from a variety of theoretical frames of reference. The following issues are discussed ; Dexamethasone suppression test(DST), TRH stimulation test, MHPG, Temperament Character Inventory(TCI), and heart rate variability(HRV).

• Reproductive and Developmental Biology
• /
• v.35 no.1
• /
• pp.61-65
• /
• 2011

The objective of this study was to examine the effect of various discontinuous Percoll washing conditions on motile sperm recovery rate and motion kinematics. Frozen semen samples from 3 bulls (0.5 ml plastic straws, 6% glycerol in egg yolk-Tris-glycerol extender) were thawed in $37^{\circ}C$ water bath for 1 min. After thawing, the mixed semen samples were randomly allocated to 12 treatment groups. Briefly, the spermatozoa were centrifuged for three different time lengths (10, 20, and 30 min) at two gravities ($300{\times}g$ and $700{\times}g$) through two concentrations of discontinuous Percoll density gradient of 1 ml 90%: 1 ml 45% Percoll and 2 ml 90%: 2 ml 45% Percoll to remove extender, debris, and dead spermatozoa. Motile sperm recovery rate and motion kinematics were evaluated by computer assisted sperm analyzer using Makler counting chamber. Sperm motility (%) and motile sperm recovery rate showed similar pattern in all treatment groups. However, sperm motility (%) and motile sperm recovery rate were highest at $700{\times}g$ for 30 min through a discontionous Percoll density gradient of 1 ml 90%: 1 ml 45% Percoll. There were no significant differences in motion kinematics after various Percoll washings. These results suggest that force of centrifugation, centrifugation time, and Percoll volume significantly affect motile sperm recovery rate.

• Animal Systematics, Evolution and Diversity
• /
• v.21 no.1
• /
• pp.45-56
• /
• 2005

Three species of Gastrostyla ciliates collected from the sewage treatment plant and a puddle in the valley from Korea were identified as Gastrostyla minima Hemberger, 1985, G. steinii Engelmann, 1862 and G. setifera (Engelmann, 1862). The description was based on the observation of living specimens, protargol impregnated specimens and biometric analysis. The morphological variations among the populations of these species were investigated with morphometry. These species have not been reported in Korea and their diagnostic characteristics are as follows: G. minima normally has two oval macronuclei (Ma) with one spherical micronucleus (Mi) respectively, continuous ventral cirral row (VCR) with additional one postoral ventral cirrus (poVC), five transverse cirri (TC), six dorsal kineties (DK) with broken 4th kinety, and cortical granules. G. steinii has four oval Ma with three to five Mi, discontinuous VCR with additional one poVC, four TCs, six DKs, and no cortical granules. G. setifera has two oval Ma with one spherical Mi respectively, five TCs which distinctly separate in two groups, six DKs, discontinuous VCR with additional two poVCs, and no cortical granules.