• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 22-24 Oct. 1991
• /
• pp.1133-1138
• /
• 1991

A control of nonlinear system is motivated by the fact that all real plants are nonlinear systems and model identification introduces parameter errors. The purpose of this study is to design a Discrete Variable Structure Controller(DVSC) for single-rod hydraulic cylinder system. The model contains uncertain parameters which we known to lie upper and lower bounds. In the design of DVSC, the boundary layer concept was adopted to reduce cattering. The DVSC was evaluated through digital computer simulation and compared with a VSC (analog controller).

• 한국전산유체공학회지
• /
• 제3권1호
• /
• pp.82-88
• /
• 1998

As a par of a project related to the development of the design algorithm of a compact heat exchanger for the application of the electronic home appliances, the effect of the discreteness of the airflow boundary generated on the cooling fin surface on the heat transfer and pressure drop characteristics of the heat exchanger was studied numerically. In general, there are two critical design parameters seriously considered in the design of the heat exchanger; heat transfer rate(Q) and pressure drop coefficient(C/sub p/). Even though the higher heat transfer rate with lower pressure drop characteristics is required in a design of the heat exchanger, it is not an easy job to satisfy both conditions at the same time because these two parameters are phenomenally inversely proportional. To control the boundary layer thickness and its length along the streamline, the surface of the flat fin was modified to accelerate the heat transfer rate on the fin surface. To understand the effect of the discreted fin size(S/sub w/) and its location(S/sub h/) on the performance of the heat exchanger in the airflow field, the flat fin was modified as shown in Fig. 1. From this study, it was found that the smaller and more number of slits on the fin surface showed the higher energy diffusion rate. It means that the discreteness of the boundary layer is quite important on the heat transfer rate of the heat exchanger. On the other hand, if the fin surface configuration is very complex than needed, higher static pressure drop occurs than required in a system and it may be a reason of the induced aerodynamic noise in the heat exchanger.

• 한국추진공학회지
• /
• 제9권1호
• /
• pp.9-16
• /
• 2005

제트베인은 로켓추진기관의 발사초기 자세제어와 조정 안정성의 확보를 위해 로켓노즐 출구부에 장착되어지며, 발사 수초 후까지 연소가스와의 접촉으로 인해 구동부를 가열시키고, 그 자체도 화학적 혹은 기계적으로 삭마된다. 본 연구는 제트베인의 열해석을 위한 기초연구로서 균일 초음속 유동장내에 위치한 단일 제트베인으로의 열전달 특성 해석을 수행하여 보았다. 경계층 적분법과 유한차분법의 연립해석이 이루어 졌으며, 벽근방에서 도출된 경계조건을 바탕으로 베인 내부의 비정상 열전도 해석도 수행되었다.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume I
• /
• pp.21-24
• /
• 2006

Processes controlling the interannual variation of mixed layer temperature (MLT) averaged over the NINO3 domain ($150-90^{\circ}W$, $5^{\circ}N-5^{\circ}S$) are studied using an ocean data assimilation product that covers the period of 1993 to 2003. Advective tendencies are estimated here as the temperature fluxes through the domain's boundaries, with the boundary temperature referenced to the domain-averaged temperature to remove the dependence on temperature scale. The overall balance is such that surface heat flux opposes the MLT change but horizontal advection and subsurface processes assist the change. The zonal advective tendency is caused primarily by large-scale advection of warm-pool water through the western boundary of the domain. The meridional advective tendency is contributed mostly by Ekman current advecting large-scale temperature anomalies though the southern boundary of the domain. Unlike many previous studies, we explicitly evaluate the subsurface processes that consist of vertical mixing and entrainment. In particular, a rigorous method to estimate entrainment allows an exact budget closure. The vertical mixing across the mixed layer (ML) base has a contribution in phase with the MLT change. The entrainment tendency due to temporal change in ML depth is negligible comparing to other subsurface processes. The entrainment tendency by vertical advection across the ML base is dominated by large-scale changes in wind-driven upwelling and temperature of upwelling water. Tropical instability waves (TIWs) result in smaller-scale vertical advection that warms the domain during La Ni? cooling events. When the advective tendencies are evaluated by spatially averaging the conventional local advective tendencies of temperature, the apparent effects of currents with spatial scales smaller than the domain (such as TIWs) become very important as they redistribute heat within the NINO3 domain. However, such internal redistribution of heat does not represent external processes that control the domain-averaged MLT.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
• /
• 제5B권1호
• /
• pp.70-77
• /
• 2005

This paper presents sensorless speed control of a cylindrical permanent magnet synchronous motor (PMSM) using the adaptive integral binary observer. In view of the composition with a main loop regulator and an auxiliary loop regulator, the normal binary observer has the feature of chattering alleviation in the constant boundary layer. However, the steady state estimation accuracy and robustness are dependent upon the thickness of the constant boundary layer. In order to improve the steady state performance of the binary observer, a new binary observer is formed by the addition of extra integral dynamics to the existing switching hyperplane equation. Also, because the parameters of the dynamic equations such as machine inertia or viscosity friction coefficient are not well known and these values can be changed during normal operations, there are many restrictions in the actual implementation. The proposed adaptive integral binary observer applies an adaptive scheme so that the observer may overcome the problems caused by using dynamic equations. The rotor speed is constructed by using the Lyapunov function. The observer structure and its design method are described. The experimental results of the proposed algorithm are presented to prove the effectiveness of the approach.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2008년도 춘계학술대회논문집
• /
• pp.101-104
• /
• 2008

The sailfish is the fastest sea animal, reaching its maximum speed of 110km/h. On its skin, a number of V-shaped protrusions pointing downstream exist. Thus, in the present study, the possibility of reducing the skin friction using its shape is investigated in a turbulent boundary layer. We perform a parametric study by varying the height and width of the protrusion, the spanwise and streamwise spacings between adjacent ones, and their overall distribution pattern, respectively. Each protrusion induces a pair of streamwsie vortices, producing low and high shear stresses at its center and side locations, respectively. These vortices also interact with those induced from adjacent protrusions. As a result, the drag is either increased or unchanged for all the cases considered. In some cases, the skin friction itself is reduced but total drag including the form drag on the protrusions is larger than that of a smooth surface. Since the shape of present protrusions is similar to that used by Sirovich and Karlsson [Nature 388, 753 (1997)] where V-shaped protrusions pointing upstream were considered, we perform another set of experiments following their study. However, we do not obtain any drag reduction even with random distribution of those V-shaped protrusion.

• 한국지능시스템학회논문지
• /
• 제12권2호
• /
• pp.164-170
• /
• 2002

슬라이딩 모드 제어방식은 가변구조 제어이론의 하나로서 불확실성을 가진 비선형 시스템에 대한 강인한 특성을 가지고 있지만 제어입력에 채터링 현상을 발생시키기 때문에 그 적용에 한계를 가지고 있다. 채터링을 제거하는 방식에는 여러 가지 방식이 있으나 본 논문에서는 특수한 비선형 함수와 퍼지시스템 이용하여 기존의 고정 경계층 이용방식에 비하여 정상상태 오타를 줄일 수 있는 개선된 채터링 제거전략을 제안한다. 제안된 제어방식에서는 퍼지시스템의 출력변수 상에 설정된 퍼지집합의 구간 범위를 조절함으로써 trade-off관계에 있는 정상상태 오타와 채터링의 크기를 적절히 조절할 수 있다. 제안된 전략의 타당성을 보이기 위해 기존의 고정 경계층 방식을 간단히 분석하고 컴퓨터 시뮬레이션을 통하여 이를 비 교 분석 한다.

• International Journal of Aeronautical and Space Sciences
• /
• 제2권1호
• /
• pp.12-19
• /
• 2001

Study of turbulent mixing layers has been a popular subject from the point of view of both practical application and phenomenological importance in engineering field. Turbulent mixing layers can be applied in many fields where rapid transition to turbulence is desirable in order to prevent boundary layer separation or to enhance mixing. The ability to control mixing, structure and growth of the shear flow would obviously have a considerable impact on many engineering applications. In addition to practical applications, free shear flows are one of the simplest flows to understand the fundamental mechanism in the transition process to turbulence. After the discovery of large-scale vortical structure in free shear flows many researchers have investigated the physical mechanism of generation and dissipation processes of the vortical structure. This study investigated the role of the large-scale vortical structures in the turbulent mixing layer using LES(Large-Eddy Simulation). The result shows that the pairing interaction of the vortical structure plays an important role in the growth rate of a mixing layer. It is found that the turbulence quantities depend strongly on the velocity ratio. It is also found that the vorticity in the high-velocity-side can extract energy from the mean flow, while the vorticity in the low-velocity-side lose energy by the viscous dissipation. Finally the results suggest the guideline to obtain the desired flow by control of the velocity ratio.

• Smart Structures and Systems
• /
• 제6권8호
• /
• pp.921-938
• /
• 2010

Most of studies on control of beams containing piezoelectric sensors and actuators have been based on linear quadratic regulator (LQR) with state feedback or output feedback law. The aim of this study is to develop velocity-acceleration feedback law in the optimal control of smart piezoelectric beams. A new controller which is an optimal control system with velocity-acceleration feedback is presented. In finite element modeling of the beam, the variation of mechanical displacement through the thickness is modeled by a sinus model that ensures inter-laminar continuity of shear stress at the layer interfaces as well as the boundary conditions on the upper and lower surfaces of the beam. In addition to mechanical degrees of freedom, one electric potential degree of freedom is considered for each piezoelectric element layer. The efficiency of this control strategy is evaluated by applying to an aluminum cantilever beam under different loading conditions. Numerical simulations show that this new control scheme is almost as efficient as an optimal control system with state feedback. However, inclusion of the acceleration in the control algorithm increases practical value of a system due to easier and more accurate measurement of accelerations.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2006년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
• /
• pp.229-231
• /
• 2006

The paper presents a sensorless speed control of interior permanent magnet synchronous motors using an adaptive integral binary observer in view of composition with a main loop regulator and an auxiliary loop regulator. The binary observer has a property of the chattering alleviation in the constant boundary layer; however, the steady state estimation accuracy and robustness are dependent upon with width of the constant boundary. In order to improve the steady state performance of the binary observer, the binary observer is formed by adding extra integral dynamic to the switching hyperplane equation.