• Proceedings of the KIEE Conference
• /
• 1990.07a
• /
• pp.158-161
• /
• 1990

Recently, the phenomena of voltage instability have become major concern in power system. These phenomena are closely related to what are called multiple load flow solutions and calculation methods on these solutions have developed. But conventional methods require much run time. In this paper, by using sign of |J| and weighting factor considering system configuration, fast calculation method on the multiple load flow solutions is presented.

• Journal of the Korean Wood Science and Technology
• /
• v.47 no.5
• /
• pp.567-578
• /
• 2019

A common problem with fast-growing hardwoods is dimensional instability that limits use of their wood. In this study, we investigated the effects of pre-drying methods, temperatures, and heating duration on the specific gravity, water absorption, and dimensional stability of three tropical fast-growing hardwoods, jabon (Neolamarckia cadamba Roxb.), sengon (Falcataria moluccana Miq.), and mangium (Acacia mangium Willd.). Wood samples were pre-dried by two methods (fan and oven at $40^{\circ}C$), and heat treatments were performed at three temperatures (120, 150, and $180^{\circ}C$) for two different time periods (2 and 6 hours). The specific gravity, water absorption, dimensional stability, and structural changes of the samples were evaluated. The results revealed that heat treatments slightly reduced the specific gravity of all three wood species. In addition, the heat treatments reduced water absorption and significantly improved dimensional stability of the samples. Oven pre-drying followed by heat treatment at $180^{\circ}C$ for 6 hours resulted in good physical improvement of jabon and sengon wood. Fan pre-drying followed by heat treatment at $180^{\circ}C$ for 2 hours improved the physical properties of mangium wood. The heat treatment shows a promising technique for improving the physical characteristic of fast growing hardwoods.

• Tribology and Lubricants
• /
• v.33 no.6
• /
• pp.309-314
• /
• 2017

This paper presents a theoretical investigation of the dynamic characteristics of externally pressurized air pad bearings with closed loop grooves. These grooves are made on the surface of bearings to reduce the number of supply holes so that manufacturing costs can be reduced. The semi-implicit method is applied to calculate the time varying pressure profile on the air bearing surface owing to the advantages of numerical stability and fast time tracing characteristics. The static pressure of the groove bearings is much higher than that without grooves, so the groove bearings can provide high load carrying capacity. The equation of motion considering vertical motion and tilting motion are also solved using the Runge-Kutta 4th order method. By combining the semi-implicit method and the Runge-Kutta method, fast calculations of the dynamic behavior of the air bearing can be achieved. The variations of bearing reaction force, air film reaction moment, height, and tilting angle are investigated for the step force input, which is 20% higher than the bearing reaction, when the nominal clearance is 6 mm. The effect of the groove width and the groove depth are investigated by calculating the dynamic behavior. The possibility of the air hammering with the depth of the groove is found and discussed.

• Journal of Mechanical Science and Technology
• /
• v.15 no.5
• /
• pp.569-579
• /
• 2001

This study investigates the effects of operating conditions on the chattering of an automotive disk brake by experimental and computational methods. Design factors, which cause chattering in automobiles, have attracted great attentions for long time; but they are not well understood yet. For this study, we construct a brake dynamometer for measuring the disk surface temperature during chattering, and propose an efficient hybrid algorithm (combining FFT-FEA and traditional FEA program) for analyzing the thermo-elastic behavior of three-dimensional brake system. We successfully measure the judder in a brake system via the dynamometer and efficiently simulate the contact pressure variation by the hybrid algorithm. The three-dimensional simulation of thermo-mechanical interactions on the automotive brake, showing the transient thermo-elastic instability phenomenon, is presented for the first time in this academic community. We also find from the experimental study that the disk bulk temperature strongly influences the brake chattering in the automotive disk brakes.

• Proceedings of the KIEE Conference
• /
• 1987.07b
• /
• pp.1276-1279
• /
• 1987

Cardiac arrhythmias are associated with electrical Instability and, hence, with abnormal mechanical activity of the heart in many cases, arrhythmias can be treated with drugs or electric shock to control and/or stop them. Hence fast arrhythmia detection is very important. In this paper RR interval, QRS width, and morphology are used for diagnosis and QRS complex is detected by hardware system. hence diagnosing time is shorten. Moreover doctors or nurses who have little knowledge of computer manipulation can get the Information of Patient's ECG by showing characteristics of abnormal waveform and by mapping graphs of RR interval .vs. QRS width and RR interval .vs. morphology on screen.

• Proceedings of the KIEE Conference
• /
• 2005.07a
• /
• pp.12-14
• /
• 2005

Security problem has been a fundamental issue in the operation and planning of power system. Voltage instability is widely recognized as an important issue of power system blackout. As far as real-time operation is concerned, there is a need for appropriate tools to identify dangerous contingencies, assess security margins and suggest corrective actions. In this paper, we propose the framework design of Voltage Security Assessment(VSA) using QSS(Quasi Steady-State) analysis method in order to implement fast time domain simulation engine as a major part of VSA.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.57 no.4
• /
• pp.567-575
• /
• 2008

Transient security assessment(TSA) is becoming an essential requirement not only for security monitoring but also for stabilizing control of power systems under new electricity environments. It has already been pointed out that fast transient stability study is an important part for monitoring and controlling system security. In this paper, we discuss an energy function method for stabilizing control of transiently unstable systems by introducing generator tripping system to enhance the transient stability of power systems. The stabilization with less tripped power can be obtained by tripping the generators faster than out-of-synchronism relay. Fast transient stability assessment based on the state estimation and direct transient energy function method is an important part of the stabilizing scheme. It is possible to stabilize the transiently unstable system by tripping less generators before the action of out-of-synchronism relay, especially when a group of generator are going to be out-of-synchronism. Moreover, the amount of generator output needed for tripping can be decided by Transient Energy Function(TEF) method. The main contribution of this paper is on the stabilizing scheme which can be running in the Wide Area Control System.

• International Journal of Aeronautical and Space Sciences
• /
• v.1 no.1
• /
• pp.1-12
• /
• 2000

The wake geometries of a two-bladed rotor in axial flights using a time-marching free-wake method without a non-physical model of the far wake are calculated. The computed free-wake geometries of AH-1G model rotor in climb flight are compared with the experimental visualization results. The time-marching free-wake method can predict the behavior of the tip vortex and the wake roil-up phenomena with remarkable agreements. Tip vortices shed from the two-bladed rotor can interact with each other significantly. The interaction consists of a turn of the tip vortex from one blade rolling around the tip vortex from the other. Wake expansion of wake geometries in radial direction after the contraction is a result of adjacent tip vortices begging to pair together and spiral about each other. Detailed numerical results show regular pairing phenomenon in the climb flights, the hover at high angle of attack and slow descent flight too. On the contrary, unstable motions of wake are observed numerically in the hover at low angle of attack and fast descent flight. It is because of the inherent wake instability and blade-vortex-interaction rather then the effect of recirculation due to the experimental equipment.

• Journal of the Korea Computer Graphics Society
• /
• v.5 no.1
• /
• pp.27-33
• /
• 1999

In this paper, we propose an efficient technique for the animation of flexible thin objects. Mass-spring model was employed to represent the flexible objects. Till now, many techniques have used the mass-spring model to generate plausible animation of soft objects. A straight-forward approach to the animation with mass-spring model is explicit Euler method, but the explicit Euler method has serious disadvantage that it suffers from 'instability problem'. The implicit integration method is a possible solution to overcome the instability problem. However, the most critical flaw of the implicit method is that it involves a large linear system. This paper presents a fast animation technique for mass-spring model with approximated implicit method. The proposed technique stably updates the state of n mass-points in O(n) time when the number of total springs are O(n). We also consider the interaction of the flexible object and air in order to generate plausible results.

• Journal of the Korean Society of Combustion
• /
• v.9 no.4
• /
• pp.35-46
• /
• 2004

Activation energy asymptotics (AEA) for Linan#s premixed-flame regime is revisited in this paper. First, the detailed AEA procedure for the premixed-flame regime is demonstrated, so that the practitioners of AEA could easily apply the method to their own problems. In addition, the controversies surrounding the premixed-flame regime, namely the closure controversy and fast-time instability paradox, are explained. Finally, the limitation of AEA, mainly arising from the wrong prediction of fuel leakage through the reaction zone, is examined and the Zel#dovich-Linan kinetics is introduced as an alternative to meet the needs of modern combustion analysis, where the detailed chemical structure of flame is demanded.