• Journal of the Korea Institute of Military Science and Technology
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• v.19 no.4
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• pp.526-535
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• 2016

In this study, the estimating weight data of eight leading ships of Korea navy were processed by comparing with the final weight data of their incline test results statistically, and are analyzed as follows; The maximum criteria of the weight margins of Korea naval ship in the preliminary and detailed design phases seem to be appropriate values, but the minimum criteria would be advisable to update more reasonable values. And, the limitation that the acceptable deviation of lightship weight should be 10 % of the lightship weight on a naval ship's ROC(Required Operational Capabilities) is recommended to be prohibited, because it comes from the weight estimation which has considerable uncertainty and it may also drop off design flexibility. Finally, the SWBS(Ship Work Breakdown System) groups which have larger deviation values in the estimating weight of naval ships are necessary to improve their accuracies, and to upgrade their weight database continuously.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.8A
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• pp.743-751
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• 2010

OFDMA femtocell becomes an effective solution to support indoor high data rate services instead of the macrocell systems. Although the advantage of the femtocell, the co-channel interference between the femocell and the macrocell is the most significant problem that reduces the system performance. Macrocell users who have no permission to access the femtocell suffer from interference of the downlink transmission of femtocell. Therefore, the femtocell should use transmission power as small as possible to reduce interference to macrocell users. In this paper, we define the margin adaptive power allocation problem for the femtocell and propose a heuristic power allocation algorithm to solve the problem. Simulation results show the performance of the proposed algorithm.

• Journal of Institute of Control, Robotics and Systems
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• v.17 no.8
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• pp.807-813
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• 2011

High precision of planning in the preoperative phase can contribute to increase operational safety during computer-aided spinal fusion surgery, which requires extreme caution on the part of the surgeon, due to the complexity and delicacy of the procedure. In this paper, an advanced preoperative planning framework for spinal fusion is presented. The framework is based on spinal pedicle data obtained from CT (Computed Tomography) images, and provides optimal insertion trajectories and pedicle screw sizes. The proposed approach begins with safety margin estimation for each potential insertion trajectory that passes through the pedicle volume, followed by procedures to collect a set of insertion trajectories that satisfy operation safety objectives. The radius of a pedicle screw was chosen as 70% of the pedicle radius. This framework has been tested on 68 spinal pedicles of 8 patients requiring spinal fusion. It was successfully applied, resulting in an average success rate of 100% and a final safety margin of $2.44{\pm}0.51mm$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.10
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• pp.2256-2271
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• 1997

In this paper, we analyze the multipath fading and the inter-satellite interference considering the satellite mobility in the LEO mobile satellite communication networks and evaluate the link perfodrmance for various wave propagation environments and reliabilities of communiation system. Multipath fading is estimated by analyzing the variation of fading margin for the satellite motion in rural, urban and suburban environments. The inter-satellite interferences are classified into 8 bypes with respect to interference path. The interferences evaluated in the paper are as follows:intra-LEO satellite interference, inter-LEO satellite interference, and GEO satellite to LEO satellite interference. As a conclusion, this apaper analyzes the change of elevation anagle and propagation distance with respect to time in the LEO satellite netwoek and prosents the variation of link margin continuously.

• Proceedings of the KIEE Conference
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• 2002.07a
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• pp.229-231
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• 2002

The digital current differential relaying scheme is widely used for primary protection of 765(kV) power transformer. The current differential relay pickup the internal fault at the threshold which is set at 30% of rating current. Margin of 30% include current transformer error 5%, relay error 5%, on load tap changer error 7% and margin factor 140% obtained from the field experience. In this paper transformer protection relay and relay setting rule of high voltage power system are discussed. And we verify the correctness of relay setting rule with current differential relay using Matlab simulation.

• Journal of Ocean Engineering and Technology
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• v.32 no.3
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• pp.208-212
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• 2018

In this paper, we focus on planing avoidance control for a supercavitating underwater vehicle based on the potential function method. The planing margin can be calculated using the relative position between the cavity center and vehicle center at the end of the vehicle. The planing margin was transformed into a limit variable such as the pitch angle and yaw angle limit. To prevent the vehicle attitude from exceeding the limit variable, a potential function based planing envelope protection method was proposed. The planing envelope protection system overrides commands from the tracking controller, and the vehicle attitude converges to a desired angle, in which the potential function is minimized. Numerical simulations were performed to analyze the physical feasibility and performance of the proposed method. The results showed that the proposed methods eliminated the planing, allowing the vehicle to follow tracking commands.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.3
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• pp.149-155
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• 2004

This paper presents how to find proper operating points of FACTS devices to enhance the steady-state security level considering line contigency analysis. Three generic types of FACTS devices such as series controllers, shunt controllers, and series-shunt controllers are introduced and applied to moximize a security margin and to minimize security indices. Security indices related to line flows and bus voltages are utilized and minimized iteratively in this paper. Contingency analysis is performed to detect the most severe single line fault. In various load conditions, FACTS devices are tested to establish appropriate preventive or corrective action without generation re-dispatching or load shedding. The FACTS operation scheme is verified on the IEEE 57-bus system in a line-faulted contingency.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.4
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• pp.91-96
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• 2018

This study is collects design data through the process design of the organic Rankine cycle, which can produce 20kW of electric power through the recovery of waste heat. In this study, the simulation was conducted by using APSEN HYSYS in order to make the model for the process design of the 20kW class waste heat recovery system. For the thermodynamic model, the test was conducted with hot water as the heat source, with the water steam used as the cooling water for the cooler and the refrigerant R245fa in the cycle. In Case 1 and Case 2, it was expected and found that the cycle efficiency was 10.6% and that 36.86kw was produced, considering the margin of 84% of 20kW. In Case 3 and Case 4, it was expected and found from the simulation that the cycle efficiency was 12% and that 30.0kw was produced, considering the margin of 84% of 20kW.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.10
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• pp.940-950
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• 2011

This paper reports a filtered velocity feedback(FVF) controller, which is an alternative to direct velocity feedback(DVFB) controller. The instability problems at high frequencies due to non-collocated sensor/actuator configuration with the DVFB can be alleviated by the proposed FVF controller. The FVF controller is designed to filter out the unstable high frequency response. The dynamics of a clamped plate under forces and moments and the FVF controllers are formulated. The stability of the control system and performance are investigated with the open loop transfer function(OLTF). It is found that the FVF controller has a higher gain margin than the corresponding DVFB controller owing to the rapid roll-off behavior at high frequencies. Although the gain margin cannot be fully utilized because of the enhancement at the high frequencies, the vibration at the modes lower than the tuning frequency is well controlled. This performance of the FVF controller is shown to be improved from that of the DVFB controller. It is, however, noted that the stability around the tuning frequency is very sensitive so that the enhancement in vibration level should be followed. The reduction performance at low frequencies using the FVF controller should be compromised with the enhancement in the vibration at high frequencies while designing the controller.

• Journal of Institute of Control, Robotics and Systems
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• v.22 no.6
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• pp.411-416
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• 2016

This paper presents the design methodology of an unknown input observer for Lipschitz nonlinear systems with unknown inputs in the framework of convex optimization. We use an unknown input observer (UIO) to consider both nonlinearity and disturbance. By deriving a sufficient condition for exponential stability in the linear matrix inequality (LMI) form, existence of a stabilizing observer gain matrix of UIO will be assured by checking whether the quadratic stability margin of the error dynamics is greater than the Lipschitz constant or not. If quadratic stability margin is less than a Lipschitz constant, the coordinate transformation may be used to reduce the Lipschitz constant in the new coordinates. Furthermore, to reduce the maximum singular value of the observer gain matrix elements, an object function to minimize it will be optimally designed by modifying its magnitude so that amplification of sensor measurement noise is minimized via multi-objective optimization algorithm. The performance of UIO is compared to a nonlinear observer (Luenberger-like) with an application to a flexible joint robot system considering a change of load and disturbance. Finally, it is validated via simulations that the estimated angular position and velocity provide true values even in the presence of unknown inputs.