• Fisheries and Aquatic Sciences
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• 제11권1호
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• pp.41-49
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• 2008

Internal waves and internal tides occur frequently along the eastern coast of Korea. During the spring-tide period in April 2003, the East Korean Warm Current (EKWC) flowed near the Korean East Coast Farming Forecast System (KECFFS; a moored oceanographic measurement system), creating a strong thermocline at the intermediate layer. Weakened stratification and well-mixed water appeared frequently around the KECFFS, with duration of approximately 1 day. The results suggest the following scenario. Baroclinic motion related to the internal tide generated high frequency internal waves around the thermocline. The breaking of those waves then created turbulence around the thermocline. After well-mixed water appeared, a current component with perpendicular direction to the EKWC appeared within the inertial period. The change in stratification around the KECFFS locally broke the geostrophic balance as a transient state. This local vertical mixing formed an ageostrophic current within the inertial period.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.504-507
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• 2011

The inertial migration of a two-dimensional elastic capsule in a channel flow was studied over the Reynolds number range $1{\leq}Re{\leq}100$. The lateral migration velocity, slip velocity, and the deformation and inclination angle of the capsule were investigated by varying the lateral position, Reynolds number, capsule-to-channel size ratio(${\lambda}$), membrane stretching coefficient(${\Phi}$), and membrane bending coefficient(${\gamma}$). During the initial transient motion, the lateral migration velocity increased with increasing Re and ${\lambda}$ but decreased with increases in ${\Phi}$, ${\gamma}$ and the lateral distance from the wall. The initial behavior of the capsule was influenced by variation in the initial lateral position ($y_0$), but the equilibrium position of the capsule was not affected by such variation. The balance between the wall effect and the shear gradient effect determined the equilibrium position. As Re increased, the equilibrium position initially shifted closer to the wall and then moved towards the channel center. A peak in the equilibrium position was observed near Re=30 for ${\gamma}=0.1$, and the peak shifted to higher Re as ${\gamma}$ increased. Depending on the lateral migration velocity, the equilibrium position moved toward the centerline for larger ${\gamma}$ but moved toward the wall for larger ${\Phi}$ and ${\gamma}$.

• Structural Engineering and Mechanics
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• 제81권5호
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• pp.633-645
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• 2022

The active tuned mass damper (ATMD) is an efficient and reliable structural control system for mitigating the dynamic response of structures. The inertial force that an ATMD exerts on a structure to attenuate its otherwise large kinetic energy and undesirable vibrations and displacements is proportional to its excursion. Achieving a balance between the inertial force and excursion requires a control law or feedback mechanism. This study presents a technique for the optimum design of a sliding mode controller (SMC) as the control law for ATMD-equipped structures subjected to earthquakes. The technique includes optimizing an SMC under an artificial earthquake followed by testing its performance under real earthquakes. The SMC of a real 11-story shear building is optimized to demonstrate the technique, and its performance in mitigating the displacements of the building under benchmark near- and far-fault earthquakes is compared against that of a few other techniques (proportional-integral-derivative [PID], linear-quadratic regulator [LQR], and fuzzy logic control [FLC]). Results indicate that the optimum SMC outperforms PID and LQR and exhibits performance comparable to that of FLC in reducing displacements.

• 대한기계학회논문집B
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• 제36권4호
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• pp.413-418
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• 2012

본 연구에서는 VIStA (Vortex Inertial Staged Air) 버너를 개조하여 관류보일러에 적용하였다. 2차 공기를 노즐을 통해 공급하던 원형과 달리 선회기를 통해 공급함으로써 화염을 안정화하고 일산화탄소(CO)의 발생량을 저감하였다. 그러나, 이러한 개조과정에서 질소산화물(NOx)의 발생이 증가하는 문제가 발생하였다. CO와 NOx 발생량을 함께 제어하기 위하여 본 연구에서는 화염분할을 적용하였다. VIStA 버너는 2개의 연소실이 있고 각각의 연소실에 공급되는 공기량을 댐퍼로 조절하며 3가지 종류의 화염분할 장치를 설계, 장착하여 공기비, 연소부하에 따른 연소 특성을 파악하였다. 화염분할을 통하여 CO 농도 증가는 10 ppm 이내로 유지하면서 NOx의 발생량은 25%까지 저감하는 결과를 얻었다.

• 한국정밀공학회지
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• 제13권2호
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• pp.76-83
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• 1996

We have developed the unconventional robot arm which is composed of the two main parts, one is a ball screw and the other is a robot arm. The dynamic systems of the robot arm and ball screw are unstable systems coupled with each other. The ball screw mechanism is unstable system but controllable system. The robot arm's dynamics is quasi stable system when ball screw's angular position is zero, else, unstable system. Our system has the duality between stability and controllability at the view point of control. This duality causes difficulty to control of the robot arm using normal control law. We have investigated the location of the characteristic roots of the dynamic equation. And we have found out that the best condition for the control of the arm is quasi stable state. In this paper, we have proposed multiple control laws which are consist of three components to guarantee the stability and controllability simultaneously. The computer simulations were carried out based on VSC about the angular position control of the robot arm, and it is confirmed that the good performances could be obtained by using new controller.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권1호
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• pp.215-236
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• 2017

Obtaining accurate location information is important in practical applications of wireless sensor networks (WSNs). The distance vector hop (DV-Hop) is a frequently-used range-free localization algorithm in WSNs, but it has low localization accuracy. Moreover, despite various improvements to DV-Hop-based localization algorithms, maintaining a balance between high localization accuracy and good stability and convergence is still a challenge. To overcome these shortcomings, we proposed an improved DV-Hop localization algorithm based on the bat algorithm (IBDV-Hop) for WSNs. The IBDV-Hop algorithm incorporates optimization methods that enhance the accuracy of the average hop distance and fitness function. We also introduce a nonlinear dynamic inertial weight strategy to extend the global search scope and increase the local search accuracy. Moreover, we develop an updated solutions strategy that avoids premature convergence by the IBDV-Hop algorithm. Both theoretical analysis and simulation results show that the IBDV-Hop algorithm achieves higher localization accuracy than the original DV-Hop algorithm and other improved algorithms. The IBDV-Hop algorithm also exhibits good stability, search capability and convergence, and it requires little additional time complexity and energy consumption.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1993년도 추계학술대회논문집; 반도아카데미, 26 Nov. 1993
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• pp.77-83
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• 1993

In this paper, the dynamics of a 2-DOF not 1:1 resonant Hamiltonian system are studied. In the first part of the work, the behaviors of special periodic orbits called normal modes are examined by means of the harmonic balance method and their approximate stability ar analyzed by using the Synge's concept named stability in the kinematico-statical sense. Secondly, the global dynamics of the system for low and high energy are studied in terms of a perturbation analysis and Poincare' maps. In this part, one can see that the unstable normal mode generates chaotic motions resulting from the transverse intersections of the stable and unstable manifolds. Although there exist analytic methods for proving the existence of infinitely many periodic orbits, chaos, they cannot be applied in our case and thus, the Poincare' maps constructed by direct numerical integrations are utilized fot detecting chaotic motions. In the last part of the work, the existence of arbitrarily many periodic orbits of the system are proved by using a subharmonic Melnikov's method. We also study the possibility of the breakdown of invariant KAM tori only when h>h$_{0}$ (h$_{0}$:bifurcating energy) and investigate the generality of the destruction phenomena of the rational tori in the systems perturbed by stiffness and inertial coupling.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 1999년도 제13회 학술강연논문집
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• pp.33-33
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• 1999

The Coanda effect is the tendency for a fluid jet to atach itself to an adjacent surface and follow its contour without causing an appreciable flow separation. The jet is pulled onto the surface by the low pressure region which develops as entrainment pumps fluid from the region between the jet and the surface. Then the jet is held to the wall surface by the resulting radial pressure gradient which balance the inertial resistance of the jet to turning. The jet may attach to the surface and may be deflected through more than 180 dog, when the radius of the Coanda surface is sufficiently large compared to the height of the exhaust nozzle. However, if the radius of curvature is small, the jet turns through a smaller angle, or may not attach to the surface at all. In general, the limitations in size and weight of a device will limit the radius of the deflection surface. Thus much effort has been paid to improve the jet deflection in a variety of engineering fields. The Coanda effect has long been applied to improve aerodynamic characteristics, such as the drag/lift ratio of flight body, the engine exhaust plume thrust vectoring, and the aerofoil/wing circulation control. During the energy crisis of the seventies, the Coanda jet was applied to reduce vehicle drag and led to drag reductions of as much as about 30% for a trailer configuration. Recently a variety of industrial applications are exploiting another characteristics of the Coanda jets, mainly the enhanced turbulence levels and entrainment compared with conventional jet flows. Various industrial burners and combustors are based upon this principle. If the curvature of the Coanda surface is too great or the operating pressure too high, the jet flow will break away completely from the surface. This could have catastrophic consequences for a burner or combustor. Detailed understanding of the Coanda jet flow is essential to refine the design to maximize the enhanced entrainment in these applications.