• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.10
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• pp.934-939
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• 2007

Thrust vector control(TVC) is the method which generates the side force and moment by controlling the exhausting gas directly from the supersonic nozzle to change the trajectory of a missile quickly. In this paper, performance study on the tapered ramp tabs asymmetrically installed in the supersonic nozzle exhaust for the thurst vector control has been carried out using the supersonic cold flow system. To study the shock wave structure and location of the oblique shock wave produced by the ramp tab, the flow field visualization using the schlieren system is conducted. This paper provides the thrust spoilage, three directional forces and moments and distribution of surface pressure on the region enclosed by the tapered ramp tabs.

• International Journal of Reliability and Applications
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• v.15 no.2
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• pp.125-150
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• 2014

Accelerated life tests (ALTs) are extensively used to determine the reliability of a product in a short period of time. Test units are subject to elevated stresses which yield quick failures. ALT can be carried out using constant-stress, step-stress, progressive-stress, cyclic-stress or random-stress loading and their various combinations. An ALT with linearly increasing stress is ramp-stress test. Much of the previous work on planning ALTs has focused on constant-stress, step-stress, ramp-stress schemes and their various combinations where the stress is generally increased. This paper presents an optimal design of ramp soak-stress ALT model which is based on the principle of Thermal cycling. Thermal cycling involves applying high and low temperatures repeatedly over time. The optimal plan consists in finding out relevant experimental variables, namely, stress rates and stress rate change points, by minimizing variance of reliability function with pre-specified mission time under normal operating conditions. The Burr type XII life distribution and time-censored data have been used for the purpose. Burr type XII life distribution has been found appropriate for accelerated life testing experiments. The method developed has been explained using a numerical example and sensitivity analysis carried out.

• The KSFM Journal of Fluid Machinery
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• v.18 no.5
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• pp.49-53
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• 2015

Thrust vector control is the method which generates the side force and roll moment by controlling exhausted gas directly in a rocket nozzle. TVC is classified by mechanical and fluid dynamic methods. Mechanical methods can change the flow direction by several objects installed in a rocket nozzle exhaust such as tapered ramp tabs and jet vane. Fluid dynamic methods control the flight direction with the injection of secondary gaseous flows into the rocket nozzle. The tapered ramp tabs of mechanical methods are used in this paper. They installed at the rear in the rocket nozzle could be freely moved along axial and radial direction on the mounting ring to provide the mass flow rate which is injected from the rocket nozzle. TVC of the tapered ramp tabs has the potential to produce both large axial thrust and high lateral force. We have conducted the experimental research and flow analysis of ramp tabs to show the performance and the structural integrity of the TVC. The experiments are carried out with the supersonic cold flow system and the schlieren graph. This paper provides to analyze the location of normal shock wave and distribution of surface pressure on the region enclosed by the tapered ramp tabs.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.5
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• pp.533-536
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• 2014

In this paper, a near optimal decentralized observer-controller design method is proposed for ramp metering systems based on SDRE (State Dependent Riccati Equation) approach. The optimal nonlinear observer gain is parameterized in terms of the solution matrix of an SDRE. This paper gives a simple algorithm to compute the near optimal observer gain. The optimal control design problem is also considered. Finally, numerical simulation results are given to illuminate the effectiveness and practicality of the proposed design method.

• Proceedings of the KIEE Conference
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• 1999.11c
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• pp.506-508
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• 1999

In the distributed control systems where the control components, controllers and sensors are distributed on a communications network, there exist network time delays on communication lines between the system components. This paper deals with the ramp tracking controller design issue for such systems. Time delay terms are converted into the rational terms using Pade approximation method and the system is augmented with two integrators for ramp tracking. For this system, $\mu$-controller design method, which enables to meet not only performance requirements but robust stabilities simultaneously, is employed.

• Proceedings of the KIEE Conference
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• 2001.11c
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• pp.57-60
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• 2001

In the distributed control systems where the control components, controllers and sensors are distributed on a communications network, there exit network time delays on communication lines between the system components. This paper deals with the 2 D.O.F. ramp tracking controller design issue for such system. Time delay terms are converted into rational terms using Pade approximation method and the system is augmented with two integrators for ramp tracking. For this system, $\mu$-controller design method, which enables to meet not only performance requirements but robust stabilities simultaneously, is employed.

• Proceedings of the KIEE Conference
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• 1999.07b
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• pp.951-953
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• 1999

In the distributed control systems where the control components, controllers and sensors are distributed on a communications network, there exist network time delays on communication lines between the system components. This paper deals with the ramp tracking controller design issue for such systems. Time delay terms are converted into the rational terms using Pade approximation method and the system is augmented with two integrators for ramp tracking. For this system, ${\mu}$-controller design method, which enables to meet not only performance requirements but robust stabilities simultaneously, is employed.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.3
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• pp.102-111
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• 1996

For the air-fuel ratio control in a fuel injection SI engine, the Jump-Ramp control algorithm has been widely adopted by using the on/off type oxygen sensor. But the Jump-Ramp control method has limitation on treating the frequency and amplitude of the air-fuel ratio oscillation. This study suggests another feedback control logic named modulated fuel feedback control, which has a concept of pre-tuned air-fuel ratio oscillation. In the modulation method, the oxygen sensor output is not treated as on/off signal but as analog signal for feedback. By using the modulation method, the frequency and the amplitude of air-fuel ratio oscillation can be adjustable to some extent for improving the conversion efficiency of the Three-Way Catalyst. The result shows that the performance of the modulation method is better than that Jump-Ramp control method in reducing the amplitude of the air-fuel ratio oscillation as well as in increasing the frequency of the air-fuel ratio oscillation.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3068-3073
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• 2007

Aerodynamic forces and moments have been used to control rocket propelled vehicles. If control is required at very low speed, Those systems only provide a limited capability because aerodynamic control force is proportional to the air density and low dynamic pressure. But thrust vector control(TVC) can overcome the disadvantages. TVC is the method which generates the side force and roll moment by controlling exhausted gas directly in a rocket nozzle. TVC is classified by mechanical and fluid dynamic methods. Mechanical methods can change the flow direction by several objects installed in a rocket nozzle exhaust such as tapered ramp tabs and jet vane. Fluid dynamic methods control the flight direction with the injection of secondary gaseous flows into the rocket nozzle. The tapered ramp tabs of mechanical methods are used in this paper. They installed at the rear in the rocket nozzle could be freely moved along axial and radial direction on the mounting ring to provide the mass flow rate which is injected from the rocket nozzle. In this paper, the conceptual design and the performance study on the tapered ramp tabs of the thurst vector control has been carried out using the supersonic cold flow system and shadow graph. Numerical simulation was also performed to study flow characteristics and interactions between ramp tabs. This paper provides to analyze the location of normal shock wave and distribution of surface pressure on the region enclosed by the tapered ramp tabs.

• Journal of Korean Society of Transportation
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• v.26 no.5
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• pp.17-28
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• 2008

This study examines the ramp-up analysis techniques which have been introduced till now and presents the strength and weakness of each method. The applicability of each technique was reviewed using a case study involving the data of Cheonan-Nonsan motorway usages where seasonal variations of the data were removed. The results showed that all the techniques except F-test have the same ramp-up period of 12 months. The level of Tamp-up was 65%-72% compared to that of the real traffic volume at the beginning of opening. The demand recovered to the stabilized level as time goes on. To apply the methodology to practical demand forecasts actual surveys of real data of traffic demand should be performed. With these efforts to the patronage ramp-up, more reliable demand analyses can be accompanied.