• 한국지능시스템학회논문지
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• 제20권6호
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• pp.831-836
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• 2010

실제 시스템 적용에 있어서, 수중음향 통신(underwater acoustic communication)에 기반한 이종 해양로봇의 협력제어(coordinated control)를 위한 경로 계획 및 추종(path planning and following) 시스템은 다음의 문제점을 가지고 있다. 즉, 수상 및 수중로봇은 기동 특성이 상이하며, 수중로봇은 더욱 효과적인 운용이 요구되며, 음파의 전달 손실(Transmission Loss : TL)로 통신 거리 제한을 가지며, 음파의 도플러 변형(Doppler distortion)으로 통신 오류를 갖는다. 나아가, 구조와 파라메터의 관점에 있어서 용이한 설계 절차를 요구한다. 이러한 문제들을 해결하기 위해서 시스템 모델링에 기초하여 진화 전략(Evolution Strategy : ES) 및 퍼지논리 제어기(Fuzzy Logic Controller : FLC)를 이용하는 지능형 경로 계획 및 추종 알고리즘을 제안하였다. 제안된 알고리즘의 성능을 검증하기 위해 수상로봇의 기동에 따른 수중로봇의 경로 계획 및 추종이 수행되었다. 시뮬레이션 결과는 제안된 알고리즘이 제기된 문제점들을 효과적으로 해결하고 있음을 보여준다.

• 로봇학회논문지
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• 제2권4호
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• pp.304-309
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• 2007

This paper describes an efficient path generation method for area coverage. Its applications include robots for de-mining, cleaning, painting, and so on. Our method is basically based on a divide and conquer strategy. We developed a novel cell decomposition algorithm that divides a given area into several cells. Each cell is covered by a robot motion that requires minimum time to cover the cell. Using this method, completeness and time efficiency of coverage are easily achieved. For the completeness of coverage in dynamic environments, we also propose a path following method that makes the robot cover missed areas as a result of the presence of unknown obstacles. The effectiveness of the method is verified using computer simulations.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 춘계학술대회 논문집
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• pp.383-387
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• 1996

This paper presents a steering control strategy applicable to vehicle path following problems. This control strategy is based on realistic nonlinear equations of motion of multibody systems described in terms of relative joint coordinates. The acceleration of the steering angle is selected as a control input of the system. This input is obtained by considering position and slope errors at current and at advance times. This steering control strategy is tested in circular and lane change maneuvers with a nonlinear vehicle model.

• 제어로봇시스템학회논문지
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• 제15권12호
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• pp.1232-1239
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• 2009

This paper proposes an exploration strategy to efficiently find a specific place in large unknown environments with wall-following based path planning. Many exploration methods proposed so far showed good performance but they focused only on efficient planning for modeling unknown environments. Therefore, to successfully accomplish the room finding task, two additional requirements should be considered. First, suitable path-planning is needed to recognize the room number. Most conventional exploration schemes used the gradient method to extract the optimal path. In these schemes, the paths are extracted in the middle of the free space which is usually far from the wall. If the robot follows such a path, it is not likely to recognize the room number written on the wall because room numbers are usually too small to be recognized by camera image from a distance. Second, the behavior which re-explores the explored area is needed. Even though the robot completes exploration, it is possible that some rooms are not registered in the constructed map for some reasons such as poor recognition performance, occlusion by a human and so on. With this scheme, the robot does not have to visit and model the whole environment. This proposed method is very simple but it guarantees that the robot can find a specific room in most cases. The proposed exploration strategy was verified by various experiments.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.606-623
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• 2019

The path following problem of a ship sailing in restricted waters under wind effect is investigated based on Robust $H_{\infty}$ Guaranteed Cost Control (RHGCC). To design the controller, the ship maneuvering motion is modeled as a linear uncertain system with norm-bounded time-varying parametric uncertainty. To counteract the bank and wind effects, the integral of path error is augmented to the original system. Based on the extended linear uncertain system, sufficient conditions for existence of the RHGCC are given. To obtain an optimal robust $H_{\infty}$ guaranteed cost control law, a convex optimization problem with Linear Matrix Inequality (LMI) constraints is formulated, which minimizes the guaranteed cost of the close-loop system and mitigates the effect of external disturbance on the performance output. Numerical simulations have confirmed the effectiveness and robustness of the proposed control strategy for the path following goal of a ship sailing in restricted waters under wind effect.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권4호
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• pp.2149-2170
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• 2017

Application-layer Distributed Denial-of-Service (DDoS) attack is one of the leading security problems in the Internet. In recent years, the attack strategies of application-layer DDoS have rapidly developed. This paper introduces a new attack strategy named Path Vulnerabilities-Based (PVB) attack. In this attack strategy, an attacker first analyzes the contents of web pages and subsequently measures the actual response time of each webpage to build a web-resource-weighted-directed graph. The attacker uses a Top M Longest Path algorithm to find M DDoS vulnerable paths that consume considerable resources when sequentially accessing the pages following any of those paths. A detection mechanism for such attack is also proposed and discussed. A finite-state machine is used to model the dynamical processes for the state of the user's session and monitor the PVB attacks. Numerical results based on real-traffic simulations reveal the efficiency of the attack strategy and the detection mechanism.

• 드라이브 ㆍ 컨트롤
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• 제17권4호
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• pp.80-86
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• 2020

Autonomous driving is one of the most important new technologies of our time; it has benefits in terms of safety, the environment, and economic issues. Path following algorithms, such as automated lane keeping systems (ALKSs), are key level 3 or higher functions of autonomous driving. Pure-Pursuit and Stanley controllers are widely used because of their good path tracking performance and simplicity. However, with the Pure-Pursuit controller, corner cutting behavior occurs on curved roads, and the Stanley controller has a risk of divergence depending on the response of the steering system. In this study, we use the advantages of each controller to propose a hybrid control strategy that can be stably applied to complex driving environments. The weight of each controller is determined from the global and local curvature indexes calculated from HD map information and the current driving speed. Our experimental results demonstrate the ability of the hybrid controller, which had a cross-track error of under 0.1 m in a virtual environment that simulates K-City, with complex driving environments such as urban areas, community roads, and high-speed driving roads.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 심포지엄 논문집 정보 및 제어부문
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• pp.261-262
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• 2007

This paper proposed a model algorithm control (MAC) method for trajectory tracking control of the differentially steeredwheeled mobile robots (WMRs) subject to nonholonomic constraint. The dynamic model of the wheeled mobile robot is presented and used as the model to be controlled. The performance of the proposed control algorithm is verified via computer simulations in which the WMR is controlled to track several different reference paths. It is shown that the control strategy is feasible.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.771-776
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• 2001

By matching a well established fast throughflow code, with standard loss correlations, and an efficient optimization algorithm, a new design system has been developed, which optimizes inlet and exit flow-field parameters for each blade row of a multistage axial flow turbine. The compressible steady state inviscid throughflow code based on streamline curvature method is suitable for fast and accurate flow calculation and performance prediction of a multistage axial flow turbine. A general purpose hybrid constrained optimization package, iSIGHT has been used, which includes the following modules: genetic algorithm, simulated annealing, modified method of feasible directions. The design system has been demonstrated using an example of a 5-stage low pressure steam turbine for 800MW thermal power plant previously designed by HANJUNG. The comparison of computed performance of initial and optimized design shows significant improvement in the turbine efficiency.

• Journal of Contemporary Eastern Asia
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• 제21권2호
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• pp.13-26
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• 2022

This study explores the following research question to address issues linked to emotions, identity, and institutions: how has the cult (institution) of the three Kims affected North Koreans' strong sense of nationalism (emotion), which is based on their Juche ideology (identity)? This paper investigates four fundamental elements of historical institutionalism: time boundedness, path dependency, institutional changes, and the shadow of the past. First, time boundedness illustrates how culture and education have been used to build trust and loyalty in the general public to construct individual and family cults. Second, path dependence reveals how the Songbun system has resulted in strong nationalism throughout Rodongdang's institutionalization. Third, institutional changes highlight the significance of age divides, as different age groups do not always support the three Kims' cult. Finally, the shadow of the past helps us understand the primary processes for generating mass ardent nationalism in the form of powerful impulses for self-sacrifice.