• Journal of the KSME
• /
• v.26 no.2
• /
• pp.138-144
• /
• 1986

지금까지 몇가지의 차등법들을 계산의 정확도 및 안정성에 관하여 검토하였다. 상류 차등법과 왜도 차등법은 좋은 안정성을 가지고 있으나 그 정확도가 미흡한게 결점이고 중앙 차등법은 비 교적 좋은 정확드를 가지고 있으나 불안정한게 큰 결점이다. QUICK 차등법의 경우에는 보다 정확한 수치해를 얻기위해 종속 변수를 보다 고차의 근사치로 표시하였는데 정확도가 증가함에 따라 몇가지의 불이익이 생기게 된다. 그 불이익으로는 제일 먼저 계산 비용의 증가를 들 수 있으며 수치 계산이 불안정하게 되고 경계 조건의 표시가 어려워 진다. 또한 난류 에너지 방 정식과 같이 종속 변수가 반드시 양수값을 갖는 방정식에서 그 차등방정식의 종속 변수도 양수 치를 가져야 한다는 제한 조건을 만족시키는데 일반적으로 어려움이 많다. 그 이유는 QUICK 차등법을 이용한 차등방정식은 흔히 음수치의 원천항을 갖기 때문에 차등방정식을 푼 후 그 종속 변수가 음수치를 갖기 때문이다. 아직도 고차의 정확도를 갖는 차등법이 연구 개발중이며 종속 변수가 반드시 양수치인 유동방정식을 푸는 좋은 차등법은 아직까지도 없는 실정이어서 2차 이 상의 정확도와 절대 안정성 (absolute stability)을 갖는 새로운 차등법의 개급이 시발하다 하겠다.

• Proceedings of the KAIS Fall Conference
• /
• 2000.10a
• /
• pp.218-222
• /
• 2000

본 논문에서는 피드백 사용형 2차 반복 학습제어 방법이 수렴 성능의 향상과 외란에 대한 강인성 향상에 덧붙여 학습제어의 피드백 항을 이용함으로써 초기 조건 오차가 있음에도 불구하고 이를 극복할 뿐만 아니라 기존의 알고리즘보다 더 빠른 수렴 능력이 있음을 확인한다. 또한 불안정한 결과를 낳는 높은 학습 제어 게인의 경우에도 피드백 항을 추가한 본 학습제어 방법에 의해 안정화됨으로써, 빠른 응답 특성과 강인성 향상을 가져올 수 있음을 보인다. 그리고 본 알고리즘을 선형 시변 연속 시스템이 적용된 모델 시스템을 설계하여 이를 통한 시뮬레이션 결과로서 초기 조건 오차의 극복 능력이 뛰어남을 확인하고 시스템의 안정화와 강인성 향상에 기여함을 확인한다.

• Food Science of Animal Resources
• /
• v.28 no.5
• /
• pp.549-554
• /
• 2008

Liposomes were prepared from egg yolk phospholipids to study their physical properties and stability at various storage conditions. Under storage conditions at different pH levels, the particle sizes of liposomes increased at the range of pH 1-2, and the absolute values of $\xi$-potentials were reduced at the range of pH 1-4. The leakage of sulforhodamine B (SRB), a fluorescent dye which is encapsulated in the liposome, increased greatly at pH 2-4. At different storage temperatures, the particle size of liposomes increased from the 10 days of storage at $4^{\circ}C$ and the 40 days at 20 and $35^{\circ}C$. The $\xi$-potentials decreased slightly later during storage under 4, 20 and $35^{\circ}C$. At the storage temperature of $50^{\circ}C$, the leakage of SRB was the greatest. Therefore, we concluded that the pH conditions lower than pH 6 and high temperature of $50^{\circ}C$ are not conducive to storing liposomes. The results obtained here may prove helpful in developing liposome-based encapsulation and diagnostic reagents.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.13 no.4
• /
• pp.290-295
• /
• 2001

Subsets pipelines are exposed to several potential risks of damage due to corrosion, soil instability, anchor impact and other hazards. One of the main risk factors for the safety of a subsea pipeline is its free spanning. This paper examines the safety of subsea pipelines with free span under axial compressive load. The variation of allowable lengths of dynamic free span is examined for generalized boundary conditions. The free span is modelled as a beam with an elastic foundations and the boundary condition is replaced by linear and rotational springs at each end. A dynamic free span curve is obtained with a function of non-dimensional parameters and can be used usefully for the design of subsea pipelines with a free span. A case study is carried out to introduce the application method of the curve.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.33 no.6
• /
• pp.2473-2481
• /
• 2013

The two characteristics of two-lane-and-two-way traffic flow are platoon and overtaking triggered by low-speed vehicle. It is crucial to develop a robust model which simultaneously generates the behaviors of platoon by low-speed vehicle and overtaking using opposite lane. Hence, a microscopic two-lane and two-way vehicle model was introduced (B. Yoon, 2011), which is based on CA (Cellular Automata) which is one of discrete time-space models, in Korea. While the model very reasonably explains the behaviour of overtaking low-speed vehicle in stable traffic flow below critical density, it has shortcomings to the overtaking process in unstable traffic flow above the critical density. Therefore, the objective of this study is to develope a vehicle model to more realistically explain overtaking process in unstable traffic flow state based on the model developed in the previous study. The experimental results revealed that the car-following model robustly generates the various macroscopic relationships of traffic flow generating stop-and-go traffic flow and the overtaking model reasonably explains the behaviors of overtaking under the conditions of both opposite traffic flow and stochastic parameter to consider overtaking in unstable traffic flow state. The vehicle model presented in this study can be expected to be utilized for the analysis of two-lane-and-two-way traffic flows more realistically than before.

• The Journal of the Korea Contents Association
• /
• v.9 no.12
• /
• pp.348-356
• /
• 2009

The purpose of this study was to examine the effect of bridging using Swiss ball, whole body vibration (WBV), and mat on trunk and lower extremity muscle activity and postural stability. The results were as follows: 1) EMG activity of internal oblique increased significantly in WBV condition compared with mat condition (p<.05). 2) EMG activity of rectus femoris and medial gastrocnemius increased significantly in Swiss ball condition and WBV condition compared with mat condition (p<.05). 3) The muscle activity of medial hamstrings increased significantly in Swiss ball condition compared with mat condition (p<.05). 4) The limit of stability in three groups increased significantly in all directions after 4-week intervention (p<.05). 5). There were no significant differences in the limit of stability among three groups after 4-week intervention (p>.05). Therefore the trunk and lower extremity muscle activity increased in Swiss ball and WBV conditions, and postural stability was improved in three groups after intervention period.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.12 no.1
• /
• pp.29-36
• /
• 2008

Spray characteristics for APU gas turbine engine are investigated. In the test, four flight conditions such as sea level idle, sea level max power, 20,000 feet idle, 20,000 feet max power are used as spray experimental conditions. Spray visualization was performed by using ND-YAG laser bean PDPA(Phase Doppler Particle Analyzer) was used for measuring the particle diameter and velocity from 20 mm to 100 mm from discharge orifice. From the test result, SMD is $90{\sim}95\;{\mu}m$ 맛 20,000 ft idle condition and SMD is $60{\sim}75\;{\mu}m$ at sea level idle condition. Also SMD is $55{\sim}65\;{\mu}m$ at 20,000 ft max power condition and SMD is $30{\sim}70\;{\mu}m$ at sea level max power condition. In the case of 20,000 ft idle condition, combustion instability could be occurred due to the higher drop diameter. Therefore it is necessary to decrease the droplet diameter in the high altitude condition.

• Korean Journal of Food Science and Technology
• /
• v.32 no.1
• /
• pp.117-124
• /
• 2000

Considering the thermal unstableness of ginseng components, microwave-assisted extraction(MAE) was performed under the atmospheric pressure condition. The monitoring of extraction characteristics and the optimization of extraction conditions were made by response surface methodology. The extraction efficiency of soluble ginseng components was high at lower ethanol concentration and at higher microwave power, while crude saponin content was easily extracted at higher ethanol concentration. Estimated conditions for the maximized extraction of soluble components including crude saponin, total phenolics and electron donating ability were $54{\sim}60%$ in ethanol concentration, $41{\sim}90$ W in microwave power, and within 4 min in extraction time. Predicted values at the optimum condition(60% ethanol, 80 W microwave power and 4 min extraction time) were in good agreement with observed values.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.17 no.4
• /
• pp.30-37
• /
• 2013

A soft rock fracture zone is an important element for rock slope or earth retaining, however stability studies of earth retaining wall have been lack. Therefore, this study is analyzed for a behavior of earth retaining wall with condition of fracture zone or no fracture zone and then a numerical analysis (Finite Element Method) was performed considering interaction with field monitoring data between ground and structures. As a result, applied horizontal displacement on retaining wall is correspond between result of numerical analysis and field monitoring data and displacement point stress distribution with fracture zone condition analyzed to be stable side but no fracture zone condition is expressed to be unstable side. The results of this study is purpose for applying safety construction as a top priority at field when designing for future.

• Geophysics and Geophysical Exploration
• /
• v.11 no.2
• /
• pp.153-160
• /
• 2008

Seismic modeling is used to simulate wave propagation in the earth. Although the earth's subsurface is usually semi-infinite, we cannot handle the semi-infinite model in seismic modeling because of limited computational resources. For this reason, we usually assume a finite-sized model in seismic modeling. In that case, we need to eliminate the edge reflections arising from the artificial boundaries introducing a proper boundary condition. In this study, we changed three kinds of boundary conditions (sponge boundary condition, Clayton and Engquist's absorbing boundary condition, and Higdon's transparent boundary condition) so that they can be applied in elastic wave modeling for anisotropic media. We then apply them to several models whose Poisson's ratios are different. Clayton and Engquist's absorbing boundary condition is unstable in both isotropic and anisotropic media, when Poisson's ratio is large. This indicates that the absorbing boundary condition can be applied in anisotropic media restrictively. Although the sponge boundary condition yields good results for both isotropic and anisotropic media, it requires too much computational memory and time. On the other hand, Higdon's transparent boundary condition is not only inexpensive, but also reduce reflections over a wide range of incident angles. We think that Higdon's transparent boundary condition can be a method of choice for anisotropic media, where Poisson's ratio is large.