• Korean Journal of Metals and Materials
• /
• v.49 no.7
• /
• pp.570-576
• /
• 2011

The shape of a dendrite tip has long been approximated by a paraboloid of revolution, but many attempts have been made as well to more accurately match the dendrite tip profile using other mathematical functions: power function, 4th order polynomial, and hyperbolic function. In the present work, dendrite tip shapes were matched by parabolic function. The differences between the dendrite tip shapes of pivalic acid(PVA)-ethanol(Eth) and succinonitrile(SCN)-salol systems, characterized by anisotropic and isotropic solid-liquid interfacial properties, respectively, were quantitatively treated using shape parameters. The PVA-Eth system showed a slightly higher Z/R value than the SCN-salol system, their Z/R values lying in the range 2-4. (Z is the distance from the tip beyond which the parabolic fit starts to deviate from the profile, and R the tip radius.) ${\lambda}_P$ is the distance from the tip beyond which side branching starts to appear, and is larger in the PVA-Eth system than the SCNsalol system. ${\lambda}_P$ is different for both sides of the 2-dimensional dendrite profile. The difference of ${\lambda}_P$ between both sides of the dendrite is larger for PVA-Eth system than for SCN-salol, implying that the dendrite of PVA-Eth is less symmetric than that of SCN-salol.

• 제어로봇시스템학회:학술대회논문집
• /
• 1993.10b
• /
• pp.312-315
• /
• 1993

Optimal control theories based on the maximum principles have been evolved and applied to distributed parameter systems(DPSs) represented by partial differential equations (PDEs) and integral equations (IEs). This paper intends to show that an optimal control of a tubular reactor described by a one-dimensional partial differential equation was obtained using the distributed parameter control method for parabolic PDEs. In develping an algorithm which implements the calculation, the method of lines (MOL) was adopted through using a package called the DSS/2. For the tubular reactor system chosen for this paper, the optimal control method based on PDEs with the numerical MOL showed to be more efficient than the one based on IEs.

• 한국태양에너지학회:학술대회논문집
• /
• 2008.11a
• /
• pp.25-29
• /
• 2008

Economic assessment of solar thermal power generation systems was carried out by calculating the levelized electricity cost. Four different commercial (or near commercial) solar thermal power systems (parabolic trough system, power tower system with saturated steam, power tower system with molten salts, and dish-stilting system) were considered for assessment. The assessment also included sensitivity analysis covering the effects of system capacity, direct normal insolation, and the system efficiency.

• Journal of Institute of Control, Robotics and Systems
• /
• v.14 no.2
• /
• pp.161-167
• /
• 2008

This article describes the methods of a decision of the location which user points to move by an optical device like a laser pointer and a moving to that location. Using a conic mirror and CCD camera sensor, a robot observes a spot of user wanted point among an initiative, computes the location and azimuth and moves to that position. This system offers the brief data to a processor with simple devices. In these reason, we can reduce the time of a calculation to process of images and find the target by user point for carrying a robot. User points a laser spot on a point to be moved so that this sensor system in the robot, detecting the laser spot point with a conic mirror, laid on the robot, showing a camera. The camera is attached on the robot upper body and fixed parallel to the ground and the conic mirror.

• IEMEK Journal of Embedded Systems and Applications
• /
• v.4 no.4
• /
• pp.180-189
• /
• 2009

Currently, most automobile companies are interested in research on intelligent autonomous vehicle. They are mainly focused on driver's intelligent assistant and driver replacement. In order to develop an autonomous vehicle, lateral and longitudinal control is necessary. This paper presents a lateral and longitudinal control system for autonomous vehicle that has only mono-vision camera. For lane detection, we present a new lane detection algorithm using clothoid parabolic road model. The proposed algorithm in compared with three other methods such as virtual line method, gradient method and hough transform method, in terms of lane detection ratio. For adaptive control, we apply a vanishing point estimation to fuzzy control. In order to improve handling and stability of the vehicle, the modeling errors between steering angle and predicted vanishing point are controlled to be minimized. So, we established a fuzzy rule of membership functions of inputs (vanishing point and differential vanishing point) and output (steering angle). For simulation, we developed 1/8 size robot (equipped with mono-vision system) of the actual vehicle and tested it in the athletics track of 400 meter. Through the test, we prove that our proposed method outperforms 98 % in terms of detection rate in normal condition. Compared with virtual line method, gradient method and hough transform method, our method also has good performance in the case of clear, fog and rain weather.

• 한국태양에너지학회:학술대회논문집
• /
• 2011.11a
• /
• pp.324-327
• /
• 2011

SolarPACES(Solar Power and Chemical Energy systems) is an international organization under the REWP(Renewable Energy Working Party)in the IEA(International Energy Agency) and focuses on the technology development and market expansion of CSP(Concentrating Solar Power). Seventeen countries including Rep. of Korea participate in the ExCo(Executive Committee) of SolarPACES. The ExCo meeting helds two times in a year and the second ExCo meeting opens in company with the five Task meetings. Rep. of Korea takes part in the Task-1officially. The 81th ExCo and Task meetings were held during September 18 and 19 in Spain with SolarPACES conference which also continued in succession to September 23 in this year. This paper introduces the activities which have been under progressed in the Task-1 and Task-3based on this time attendance of the meeting. In accordance with the expansion of CSP market and technology development, the needs for the standardization and project status underway in the world are increasing. Therefore, build an international project database and standard of the CSP technology are the main activities in the Task-1 and the standardization is also connected with the Task-3. In addition, to increase the reliability of the new technology of CSP and to reduce the concern of investors, the Task-1 is making guidelines for CSP performance prediction which can provide medium quality calculated performance data of PTC(Parabolic Trough Concentrator) type technology widely used and occupies over 90% CSP market.

• The Journal of the Acoustical Society of Korea
• /
• v.41 no.2
• /
• pp.131-142
• /
• 2022

In order to examine the possibility of horizontal simulations of acoustic waves on the environments of big water depth variations, this study introduces a 3-dimensional model based on the pababolic equation. The model gives approximated solutions by separating the cross- and non cross-terms in the equation. Assuming artificial bathymetry (25 km × 4 km) with a source frequency 75 Hz, the simulations give clear horizontal refractions on the transmission loss distributions. The degree of refractions shows non-linear increase along the propagating range and proportional increase with water depth along the cross range. Another simulations with the real bathymetry (25 km × 8 km) also give clear horizontal refractions. The horizontal distributions present little difference with the depth resolution variations of the same data source because the model gives interpolations over the depth data before simulations. Meanwhile, the horizontal distributions show big difference with those of different data sources.

• Journal of Power Electronics
• /
• v.16 no.4
• /
• pp.1324-1335
• /
• 2016

This article explores the speed regulation problem of permanent magnet synchronous motor (PMSM) systems subjected to unknown time-varying disturbances. A continuous sliding mode control (CSMC) technique is introduced for the speed loop to enhance the robustness of PMSM systems and eliminate the chattering phenomenon caused by high-frequency switch function in the conventional control law. However, the high control gain of the CSMC law in the presence of strong disturbances leads to large steady-state speed fluctuations for PMSM systems. In many application fields, PMSM systems are affected by time-varying disturbances instead of constant disturbances. For example, electric bicycles are usually affected by changing environmental disturbances, including wind speeds, road conditions, etc. These disturbances may be in the form of constant, ramp, and parabolic disturbances. Hence, a generalized proportional integral (GPI) observer is employed to estimate these types of disturbances. Then, the disturbance estimation method and the aforementioned CSMC method are combined to establish a composite sliding mode control method called the CSMC+GPI method for the speed loop of PMSM systems. Contrary to the conventional sliding mode control technique, the proposed method completely eliminates the chattering phenomenon caused by the switching function in the conventional control law. Moreover, a small control gain for the CSMC+GPI method is chosen by feed-forwarding estimated values to the speed controller. Hence, the steady-state speed fluctuations are small. The effectiveness of the proposed control scheme is verified by simulation and experimental result.

• 제어로봇시스템학회:학술대회논문집
• /
• 2003.10a
• /
• pp.1349-1353
• /
• 2003

CEMTool is a command style design and analyzing package for scientific and technological algorithm and a matrix based computation language. In this paper, we present a compiler based approach to the implementation of the command mode generalized PDE solver in CEMTool. In contrast to the existing MATLAB PDE Toolbox, our proposed FEM package can deal with the combination of the reserved words such as "laplace" and "convect". Also, we can assign the border lines and the boundary conditions in a very easy way. With the introduction of the lexical analyzer and the parser, our FEM toolbox can handle the general boundary condition and the various PDEs represented by the combination of equations. That is why we need not classify PDE as elliptic, hyperbolic, parabolic equations. Consequently, with our new FEM toolbox, we can overcome some disadvantages of the existing MATLAB PDE Toolbox.

• Journal of Industrial Technology
• /
• v.20 no.A
• /
• pp.73-82
• /
• 2000

This study was implemented to find an optimal model for wastewater treatment processes using PHOENICS(Parabolic, hyperbolic or Elliptic Numerical Integration Code Series) and ASM(Activated Sludge Model). PHOENICS is a general software based upon the laws of physics and chemistry which govern the motion of fluids, the stresses and strains in solids, heat flow, diffusion, and chemical reaction. The wastewater flow and removal efficiency of particle in two phase system of a grit chamber in wastewater treatment plant were analyzed to inquire the predictive aspect of the operational model. ASM was developed for a biokinetic model based upon material balance in complex activated sludge systems, which can demonstrate dynamic and spatial behavior of biological treatment system. This model was applied to aeration tank and settling chamber in Choonchun city, and the modeling result shows dynamic transport in aeration tank. PHOENCS and ASM could be contributed for the optimal operation of wastewater treatment plant.