• Journal of Biomedical Engineering Research
• /
• v.25 no.6
• /
• pp.565-573
• /
• 2004

In this paper, we proposed a heart activity control model for simulation of the aortic sinus baroreceptor, which was the most representative baroreceptor sensing the variance of pressure in the cardiovascular system. And then, the heart activity control model composed electric circuit model of the cardiovascular system with baroreflex control and time delay sub-model to observe the effect of time delay in heart period and stroke volume under the regulation of baroreflex in the aortic sinus. The mechanism of time delay in the heart activity baroreflex control model is as follows. A control function is conduct sensing pressure information in the aortic sinus baroreceptor to transmit the efferent nerve through central nervous system. As simulation results of the proposed model, we observed three patterns of the cardiovascular system variability by the time delay. First of all, if the time delay over 2.5 second, aortic pressure and stroke volume and heart rate was observed non-periodically and irregularly. However, if the time delay from 0.1 second to 0.25 second, the regular oscillation was observed. And then, if time delay under 0.1 second, then heart rate and aortic pressure-heart rate trajectory were maintained in stable state.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2009.05a
• /
• pp.656-661
• /
• 2009

상수도시설은 준공후 관련지자체에 이관 관리하는 시설로서 사용관종이 현재 다양하게 생산 보급되고 있어 관종 선정시 다각적인 측면에서 검토하여 채택하여야 한다. 최근 한국토지공사에서 사용하고 있는 상수도 관종은 대부분 택지개발계획 등 인허가 당시부터 관리주체인 지방자치단체 등과의 협의과정을 거쳐 선정되는 경우가 많아 자재선택에 한계성이 있다. 이를 극복하기 위해서는 자재 성능에 대한 공사내 명확한 기준이 제시되어야 한다. 상수관종을 선정하기 위한 가장 중요한 요소는 경제성으로 판단되는데, 관종의 경제성은 시공비와 자재비를 포함한 단순 공사비에만 국한되는 것이 아니라 유지관리비용을 포함한 생애주기비용(LCC: Life Cycle Cost)을 평가하여야 한다. 따라서 본 연구에서는 한국토지공사에서 택지지구 조성을 위해 사용한 배수관.급수관용 상수관종에 대한 경제성 평가기준을 제시하였고, 평가기준에 따라 각각의 택지지구 조성사례별로 종합적인 경제성 평가를 수행하였다. 보다 풍부한 자료를 바탕으로 객관적인 경제성평가 기준을 수립하기 위한 전(前)과정으로 이해되길 바라며, 설계시부터 객관적인 평가기준을 통해 합리적인 상수관을 선정하여 지금까지의 상수관종 자재선택의 한계를 최소한으로 축소하고자 하는데 가장 큰 목표를 가지고 있다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2006.05a
• /
• pp.314-318
• /
• 2006

The interest on the detonation in small tubes, which can be applied to the ignition devices of propulsion system, is increasing. However, the propagation dynamics of detonation waves in small tubes has not been investigated clearly yet. In the present experiments, propagations of detonation waves in stoichiometric propane-oxygen mixture through transparent tubes were recorded using a high speed camera and average velocities were measured as well. In terms of average velocity, there exists a transition regime where the waves show smooth transition from the normal Chapman-Jouguet(CJ) detonation to the low velocity detonation$(\sim0.5V_{CJ})$ along the decreasing initial pressure. In this transition regime, the detonation waves are highly unstable and show cyclic or intermittent longitudinal velocity fluctuation.

• Proceedings of the KSME Conference
• /
• 2001.11b
• /
• pp.859-866
• /
• 2001

During the Pre-service Inspection for Wolsong Unit 3&4 in 1997/1998 respectively, 17 Distorted Roll Transition indications(over expanded beyond tubesheet secondary face) were identified at the Unit 4 (S/G B, D). Six(6) tubes out of these tubes were plugged in 1998. However the first Periodic Inspection identified additional 110 indications in 1999 and 2000. The additionally identified 110 indication call, not reported at the Pre-service Inspection, are; 2 Not-Finally-Expanded-Tubes and 108 Distorted Roll Transition tubes. Design limit of each Steam Generator tube Plugging is 6.4%. Plugging was performed by the Steam Generator manufacturer under the warranty. When Distorted Roll Transition indications were first identified on the Unit 4 in 1998 the degree of Over-expansion was measured using an inner dial-gage to make the disposition of Nonconformance report. 2 Not-Finally-Expanded-Tubes were plugged and 10 tubes out of 108 Distorted Roll Transition Tubes were also plugged as a preventive measure.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.19 no.7
• /
• pp.500-511
• /
• 2007

The Optimal solutions of the design variables in internally finned tubes have been obtained for three-dimensional periodically fully developed turbulent flow and heat transfer. For a trapezoidal fin profile, performances of the heat exchanger are determined by considering the heat transfer rate and pressure drop, simultaneously, that are interdependent quantities. Therefore, Pareto frontier sets of a heat exchanger can be acquired by integrating CFD and a multi-objective optimization technique. The optimal values of fin widths $(d_1,\;d_2)$, fin height(h) and helix angle$(\gamma)$ are numerical1y obtained by minimizing the pressure loss and maximizing the heat transfer rate within ranges of $d_1=0.5\sim1.5mm$, $d_2=0.5\sim1.5mm$, $h=0.5\sim1.5mm$, and $\gamma=0\sim20^{\circ}$. For this, a general CFD code and a global genetic algorithm(GA) are used. The Pareto sets of the optimal solutions can be acquired after $30^{th}$ generation.

• Korean Journal of Ichthyology
• /
• v.25 no.2
• /
• pp.74-81
• /
• 2013

Factors influencing spawning or respawning conditions of the bitterling, Acheilognathus signifer were investigated in the aquariums. Inducing the female spawning was more sensitive to the mussel than the male. The ovipositor of the female was periodically elongated and reduced from 4 to 6 days with the presence of mussel. During of the elongated state of the ovipositor was 1 to 2 days. As the result of natural spawning in the aquariums, it takes 1 to 3 days (mean 1.6) to spawn. The most important factor to respawn spawned females again was the mussel. It takes 11 to 53 days (mean 29.5) from extraction to reextraction of females which have elongated ovipositor. The egg numbers of reextraction were 2 to 41 (mean 19). This experiments showed the tendency the more standard length of females grows, the more the number of extracted eggs increases.

• Journal of the Korean Data and Information Science Society
• /
• v.27 no.5
• /
• pp.1241-1251
• /
• 2016

We consider a correlated discrete-time random walk in which the current jump size depends on the previous jump size and a noncorrelated discrete-time random walk where the jump size is determined independently. By using the strong law of large numbers of Markov chains we derive the formula for the asymptotic means of the random mixture and the periodic pattern of these two random walks and then we show that there exists Parrondo's paradox where each random walk has mean 0 but their random mixture and periodic pattern have negative or positive means. We describe the parameter sets at which Parrondo's paradox holds in each case.

• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.1418-1423
• /
• 2004

Optimization of a heat exchanger with internally finned circular tubes has been performed for three-dimensional periodically fully developed turbulent flow and heat transfer. The design variables of fin number N, fin width ($d_1,d_2$) and fin height(H), are numerically optimized for the limiting conditions of $N=22{\sim}37$, $d_1=0.5{\sim}1.5$ mm, $d_2=0.5{\sim}1.5$ mm, $H=0.1{\sim}1.5$. Due to the periodic boundary conditions along main flow direction, the three layers of meshes are considered. The CFD and the mathematical optimization are coupled to optimize the heat exchanger. The flow and thermal fields are predicted using the finite volume method and the optimization is carried out by using the sequential quadratic programming (SQP) method which is widely used in the constrained nonlinear optimization problem.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.17 no.10
• /
• pp.938-946
• /
• 2005

Shape optimization of internally finned circular tube has been peformed for periodically fully developed turbulent flow and heat transfer. The physical domain considered in this study is very complicated due to periodic boundary conditions both streamwise and circumferential directions. Therefore, Pareto frontier sets of a heat exchanger can be acquired by coupling the CFD and the multi-objective genetic algorithm, which is a global optimization technique. The optimal values of fin widths $(d_1,\;d_2)$ and fin height (H) are numerically obtained by minimizing the pressure loss and maximizing the heat transfer rate within ranges of $d_1=0.2\sim1.5\;mm,\;d_2=0.2\sun1.5\;mm,\;and\;H=0.2\sim1.5\;mm$. The optimal values of the design variables are acquired after the fifth generation and also compared to those of a local optimization algorithm for the same geometry and conditions.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.4 s.235
• /
• pp.460-468
• /
• 2005

Analyses of flow and heat transfer characteristics and shape optimization of internally finned circular tubes have been performed for three-dimensional periodically fully developed turbulent flow and heat transfer. CFD and mathematical optimization are coupled in order to optimize the shape of heat exchanger. The design variables such as fin widths $(d_{1},\;d_{2})$ and fin height (h) are numerically optimized by minimizing the pressure loss and maximizing the heat transfer rate for limiting conditions of $d_{1}=0.2\~1.5\;mm,\;d_{2}=0.2\~1.5\;mm,$ and $h=0.2\~1.5mm$. Due to the periodic boundary conditions along main flow direction, the three layers of meshes are considered. The flow and thermal fields are predicted using the finite volume method and the optimization is carried out by means of the sequential quadratic programming (SQP) method which is widely used in the constrained nonlinear optimization problem.