• 산업기술연구
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• 제21권A호
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• pp.123-127
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• 2001

This paper proposed for allotment of group key's rekey interval required from secure multicast environment. New group key distribution occurs in two cases: one is periodical update and the other is permitted or unpermitted withdrawal of group member. In later case, the group controller distributes new group key to member except withdrawal member because it can't predict precisely. In former case, the group member who cheated the group can adjust the rekey interval. Using relation between security level, overhead and cost from rekey interval, this paper suggests effective rekey interval allotment through probable performance analysis in large dynamic group.

• 설비공학논문집
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• 제22권5호
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• pp.275-281
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• 2010

Car HVAC is one of main factors influencing a potential customer's first impression. It should be fault-free, which requires the most stable control performance. So, the control algorithm consists of a proportional feedback only, not with an integral action needed for elimination of steady-state errors. To reduce the errors and make the response faster, feedforward algorithm based on predicted thermal load is added. To evaluate the performance, car HVAC is dynamically modelled and its control logic is simulated. The results shows that the proportional feedback leads to about $4^{\circ}C$ of steady-state error. When the feedback is combined with the feedforward algorithm and with a set value update based on disturbances, it predicts less than $1^{\circ}C$ of control error and improved thermal comfort.

• 한국공간정보시스템학회:학술대회논문집
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• 한국공간정보시스템학회 2004년도 국내 LBS 기술개발 및 표준화 동향세미나
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• pp.69-74
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• 2004

Selectivity estimation for spatial query is very important process in finding the most efficient execution plan. Many works have been performed to estimate accurately selectivity. Although they deal with some problems such as false-count, multi-count, they require a large amount of memory to retain accurate selectivity, so they can not get good results in little memory environments such as mobile-based small database. In order to solve this problem, we propose a new technique called MW histogram which is able to compress summary data and get reasonable results. It also has a flexible structure to react dynamic update. The experimental results showed that the MW histogram has lower relative error than MinSkew histogram and gets a good selectivity in little memory.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 D
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• pp.2424-2426
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• 2002

This paper proposes an adaptive control method of partially known system and shows its application result to control for two-wheeled WMR. The controlled system is stable in the sense of Lyapunov stability. To design a tracking controller for welding path reference, an error configuration is defined and the controller is designed to drive the error to zero as fast as desired. Moments of inertia of system are considered to be unknown system parameters. Their values are estimated using update laws in adaptive control scheme. The effectiveness of the proposed controller is shown through simulation results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 B
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• pp.474-477
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• 1997

In this paper, an efficient attitude determination algorithm based on the Kalman Filter which combines earth/sun sensor data with gyro data in a mutually compensating manner is presented. Quaternion is used as the attitude state to save computation time and to prevent the gimbal-lock situation associated with Euler angles. Gyro data allows the use of the kinematic equation instead of space vehicle's dynamic equation which is usually based on approximation of the actual dynamics and inaccurate torque information. The gyro data are used to propagate the attitude through kinematic equation and the earth/sun sensor data are used to update the attitude and estimate the gyro bias. Simulation results for the KOMPSAT attitude determination system are presented.

• ETRI Journal
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• 제38권6호
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• pp.1190-1196
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• 2016

We propose a new bandpass filter (BPF)-based online channel normalization method to dynamically suppress channel distortion when the speech and channel noise components are unknown. In this method, an adaptive modulation frequency filter is used to perform channel normalization, whereas conventional modulation filtering methods apply the same filter form to each utterance. In this paper, we only normalize the two mel frequency cepstral coefficients (C0 and C1) with large dynamic ranges; the computational complexity is thus decreased, and channel normalization accuracy is improved. Additionally, to update the filter weights dynamically, we normalize the learning rates using the dimensional power of each frame. Our speech recognition experiments using the proposed BPF-based blind channel normalization method show that this approach effectively removes channel distortion and results in only a minor decline in accuracy when online channel normalization processing is used instead of batch processing

• 제어로봇시스템학회논문지
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• 제12권5호
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• pp.444-449
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• 2006

Path planning is a key element in navigation of a mobile robot. Several algorithms such as a gradient method have been successfully implemented so for. Although the gradient method can provide the global optimal path, it computes the navigation function over the whole environment at all times, which result in high computational cost. This paper proposes a high-speed path planning scheme, called a gradient method with topological information, in which the search space for computation of a navigation function can be remarkably reduced by exploiting the characteristics of the topological information reflecting the topology of the navigation path. The computing time of the gradient method with topological information can therefore be significantly decreased without losing the global optimality. This reduced path update period allows the mobile robot to find a collision-free path even in the dynamic environment.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.497-502
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• 2004

This paper presents applications of the objective stress rates to stress update algorithms for transient shell dynamic analysis within the context of explicit time integration. The hypo elasto-plastic materials are assumed in establishing constitutive equations. The derivation of the objective stress rates are investigated by use of the Lie derivative. Comparison results are given between the Kirchhoff and Cauchy stress formulation. The Jacobian determination algorithm proposed in this paper is presented in association with the Belytschko-Lin-Tsay shell theory. Several numerical examples are demonstrated including contact and non-contact examples, by which proposed algorithms are compared with respect to the accuracy and effectiveness.

• 융합신호처리학회논문지
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• 제2권1호
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• pp.95-100
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• 2001

본 논문에서는 불확실성을 갖는 비선형 시스템에 제어기를 설계하기 위해서 출력제환 선형화 방법을 통하여 비선형 시스템을 선형시스템으로 변환하고 슬라이딩 모드 제어기법을 사용하여 파라미터들을 갱신하고 이를 통하여 제어입력을 갱신하는 강인성제어기를 제안하고자 한다. 비선형시스템은 최소 위상시스템이고, 시스템의 상대차수는 r＜n 이며, 제로 다이나믹스는 안정하다고 가정한다. 제안된 제어기에 대해서 대역적 점근적 안정도가 보장됨을 보였으며, 제안된 제어기에 대해서 컴퓨터 시뮬레이션을 통하여 타당성을 검증하였다.

• 한국소음진동공학회논문집
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• 제26권6_spc호
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• pp.736-743
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• 2016

This study describes optimization methods for adjustment of helicopter main rotor tracking and balancing (RTB). RTB is a essential process for helicopter operation and maintenance. Linear and non-linear models were developed with past RTB test results for estimation of RTB adjustment. Then global and sequential optimization methods were applied to the each of models. Utilization of the individual optimization method with each model is hard to fulfill the RTB requirements because of different characteristics of each blade. Therefore an ensemble model was used to integrate every estimated adjustment result, and an adaptive method was also applied to adjustment values of the linear model to update for next estimations. The goal of this developed RTB adjustment optimization program is to achieve the requirements within 2 run. Additional tests for comparison of weight factor of the ensemble model are however necessary.