Earticle

연구목적: 직접 알고리즘을 이용한 역해석 기법의 적정성과 현장 적용성을 평가하여 역해석 기법을 통해 흙막이 벽체의 거동을 예측하고 이를 바탕으로 직접 알고리즘 역해석 기법의 실효성을 검증하고자 한다. 연구방법: 단일 및 다층 지반조건을 가정한 가상 지반 모델을 사용하여 역해석을 수행하였으며, 탄소성보 법을 통해 얻은 결과를 계측값으로 활용하였다. 또한, 3개의 실제 현장 계측 결과를 바탕으로 역해석을 진 행하여 현장 적용성을 분석하였다. 연구결과: 역해석 기법은 지반정수 및 벽체 거동 예측에서 매우 높은 정확도를 보였으며, 특히 굴착 후반 단계의 계측 결과와의 일치도가 높았다. 그러나 지층 조건이 양호하 고 벽체 변위가 적은 경우에는 적용성이 떨어지는 것으로 나타났다. 결론: 직접 알고리즘을 활용한 역해 석 기법은 대부분의 조건에서 타당한 결과를 제공하지만, 지반 조건에 따라 적용이 제한될 수 있다. 이러 한 결과는 지반 공학 분야에서의 역해석 기법 적용 시 중요한 참고자료로 활용될 수 있을 것이다.

Purpose: The purpose of this study is to evaluate the adequacy and field applicability of the back analysis method using the direct algorithm. By predicting the behavior of retaining walls through back analysis, this study aims to verify the effectiveness of the direct algorithm-based back analysis method. Method: Back analysis was performed using a virtual ground model assuming single and multi-layered soil conditions, with measurement values obtained from normal analysis using the elastic-plastic beam theory. Additionally, the field applicability was analyzed by conducting back analysis based on measurement results from three actual sites. Result: The back analysis method demonstrated very high accuracy in predicting ground parameters and wall behavior, particularly showing strong alignment with measurement results during the later stages of excavation. However, in cases where the ground conditions are favorable and wall displacements are minimal, the applicability of the method was found to decrease. Conclusion: The back analysis method using the direct algorithm provides valid results under most conditions, but its application may be limited depending on specific ground conditions. These findings can serve as important reference material for the future application of back analysis methods in the field of geotechnical engineering.

In H.264 video compression standard, B frame bi-directional predictions and its DIRECT mode coding are included to enhance video compression efficiency. However, such tools require a complex mode decision process and result in a long computation time. Therefore, fast algorithms are crucial in implementing H.264. In this paper, to save B frame encoding time, a fast DIRECT mode prediction algorithm is proposed, which determines DIRECT mode at an early stage by optimal mode pattern matching. Simulations show that the proposed algorithm can determine DIRECT mode without a complex mode decision process for 42% more macroblocks and, on mis-determination for DIRECT mode, cut down its rate-distortion (RD) cost increment by half, compared with Jin’s algorithm. This enables a fast B frame encoding with less quality degradation.

This paper proposes an optimal damping control algorithm of the DTI (Direct Two-level Inverter) to miniaturize and reduce the weight of auxiliary power supply for railway vehicles. The conventional auxiliary power supply for railway vehicles uses a DC-DC converter to maintain the inverter input power from the line voltage smoothly. The proposed topology does not use a DC-DC converter for reducing of manufacturing and maintenance costs. It also proposes a DTI topology removed damping resistors that generate ground signal noise in a certain period. At this time, a resonance phenomenon of DC-link voltage occurs due to variation of the inductive load, and a method of controlling the resonance phenomenon of DC-link voltage is required. In order to suppress the resonance phenomenon of the DC-link voltage, at a point before resonance occurs, this paper introduces an algorithm to suppress the resonance phenomenon of DC-link voltage by compensating the resonance component of the q axis voltage of the synchronous reference frame. The proposed algorithm verifies the effect through simulation and experiment.

The information on the cloud presence within a instantaneous field of view is the first step toward the derivation of many other geophysical parameters. Here, we first applied the current MODIS cloud detection algorithm developed by University of Wisconsin and compared the results to a visual interpretation of composite data, especially during the daytime. Most of cases, the detection algorithm performs very well, except a few cases with over-detection. One of the reasons for the false detection is due to the time independent use of land information which affects the threshold values of visible channel test. In the presentation, we show detailed analysis of the current cloud detection algorithm and suggest possible way to overcome the current shortfall.

To achieve fast control action, direct control methods should be used. "Direct Mean Torque Control" (DMTC) combines the good dynamic performance of Direct Torque Control (DTC) with the advantages of inherently constant switching frequency and time equidistant control for implementation in a digital signal processor. Since DMTC is a predictive control algorithm, the model and its correction deserves special investigations. This paper proposes a steady-state Kalman filter which is well suited for fast computation.mputation.

Direct torque control based on space vector modulation (SVM-DTC) protects the DTC transient merits. Furthermore, it creates better quality steady-state performance in a wide speed range. The modified method of DTC using SVM improves the electrical magnitudes of asynchronous machines, such as minimizing the stator current distortions, the stator flux with electromagnetic torque without ripple, the fast response of the rotor speed, and the constant switching frequency. In this paper, the proposed method is based on two new control strategies for direct torque control with space vector modulation. First, fuzzy logic control is used instead of the PI torque and a PI flux controller to minimizing the torque error and to achieve a constant switching frequency. The voltages in the direct and quadratic reference frame ($V_d$, $V_q$) are achieved by fuzzy logic control. In this scheme, the switching capability of the inverter is fully utilized, which improves the system performance. Second, the close loop of stator flux estimation based on the voltage model and a low pass filter is used to counteract the drawbacks in the open loop of the stator flux such as the problems saturation and dc drift. The response of this new control strategy is compared with DTC-SVM. The experimental and simulation results demonstrate that the proposed control topology outperforms the conventional DTC-SVM in terms of system robustness and eliminating the bad outcome of dc-offset.

B frame bi-directional predictions and the DIRECT mode coding of the H.264 video compression standard necessitate a complex mode decision process, resulting in a long computation time. To make H.264 feasible, this paper proposes an image backtrack-based fast (IBFD) algorithm and evaluates the performances of two promising fast algorithms (i.e., AFDM and IBFD). Evaluation results show that an image backtrack-based fast (IBFD) algorithm can determine DIRECT mode macroblocks with 13% higher accuracy, as compared with the AFDM. Furthermore, IBFD is shown to reduce the motion estimation time of B frames by up to 23% with a negligible quality degradation.

Optimal design of the direct-driven PM Wind Generator, combined with DEAS(Dynamic Encoding Algorithm for Searches) and FEM(Finite Element Method), has been proposed to maximize the Annual Energy Production(AEP) over the whole wind speed characterized by the statistical model of wind speed distribution. In particular, DEAS has been contributed to reducing the excessive computing time for the optimization process.

CRC (Cyclic Redundancy Codes)는 데이터 전송 시 오류 발생 유무를 검출하기 위한 하나의 방법으로, 정지궤도복합위성(GEO-KOMPSAT 2B) 개발에서는 정지궤도환경탑재체와 위성 간의 GRDDP (GOES-R Reliable Data Delivery Protocol)에 사용되고 있다. 본 논문에서는 CRC를 구현할 때 널리 사용하는 테이블 기반 CRC의 원리를 소개하고, 이를 기반으로 환경탑재체 개발에서 사용 중인 CRC8을 소프트웨어로 구현한 결과를 설명한다.

CRC (Cyclic Redundancy Codes) is a error detection method for the date transmission, which is applied to the GRDDP (GOES-R Reliable Data Delivery Protocol) between satellite and GEMS (Geostationary Environmental Monitoring Sensor) on the GEO-KOMPSAT 2B development. This paper introduces a principle of the table based CRC, and explains software implementation results of the CRC8 applied to GEMS.

This paper describes the development of algorithm for direct data transmission between Raw VLBI Data Buffer (RVDB) and Huge Capacity Data Server (HCDS) operated in Korea-Japan Correlation Center (KJCC). The transmitted data is the VLBI observation data, which is recorded at each radio telescope site, and the data transmitting rate is varying from 1 Gbps, in usual case, upto 8 Gbps. The developed algorithm for data transmission enables the direct data transmission between RVDB and HCDS through 10 Gbps optical network using VLBI Data Interchange Format (VDIF). Proposed method adopts the conventional UDP/IP protocol, but in order to prevent the loss of data during data transmission, the packet error monitoring and data re-transmission functions are newly designed. The VDIF specification and VDIFCP (VDIF Control Protocol) are used for the direct data transmission between RVDB and HCDS. To validate the developed algorithm for data transmission, we conducted the data transmission from RVDB to HCDS, and compared to the transmitted data with the original data bit by bit. We confirmed that the transmitted data is identical to the original data without any loss and it has been recovered well even if there were some packet losses.

비디오 데이터의 효율적인 저장, 관리를 위해서는 장면 전환 검출을 통한 비디오 분할 기술에 대한 연구가 필요하므로, 최근 들어 압축 비디오상의 특징 정보를 직접 추출하여 장면 전환 검출에 사용하는 방법에 대한 연구가 많이 이루어지고 있다. 본 논문에서는 MPEG 압축 비디오 상의 에지 정보를 복호화 과정을 거치지 않고 직접 추출하여 장면 전환 검출에 사용하는 새로운 방법을 제안하였다. 이산 여현 변환(DCT)된 블록내 AC 계수의 부호를 통해 에지의 모양을 알아내었으며, AC 계수간의 상관 관계를 통해 에지의 방향과 세기를 측정하여 프레임을 정합하는 방법을 사용하였다. 실험 결과 사용한 특징 정보가 명도나 색상 변환에 무관하여 잘못 검출하는 비율이 현저히 적었으며, 영상을 완전 복호화한 후 에지를 구하여 장면 전환 검출을 하는 방법에 비해 약 5-6배 속도가 빠름을 확인할 수 있었다.

본 연구에서는 정상상태에서 고조파 전류와 순시전압 강하에 대한 보상성능이 우수한 3상 전압 Sag 및 고조파 전류 보상 시스템을 제안하고 있다. 제안된 시스템의 보상 알고리즘으로는 구현하기 쉽고 간단한 직접 필터링 알고리즘이 사용되고 있으며 하이브리드 직렬형 능동전력필터에 적용하였다. 제안된 알고리즘은 전원전압이 순간적으로 왜형과 sag가 발생되더라도 비선형 부하에 인가되는 전압은 일정한 정현파로 제어 가능하며 동시에 전원전류의 고조파와 기본파 무효전류도 보상 가능하다. 정상상태와 과도상태에서 전력전자전용 시뮬레이터인 PSIM에 의해 제안된 이론의 타당성을 입증하였다.

본 논문에서는 모델과 플랜트의 완전 모델 추종 제어 조건이나 명확한 매개변수 추정자를 필요로 하지않는 직접적응제어방식을 이용한 직류전동기의 정밀속도 제어장치가 제안되었다. MC-68000 microcomputor를 이용한 실제적 시스템뿐만 아니라 컴퓨터 시뮬레이션 역시 이산적인 직접적응제어 알고리듬으로 구성되었으며, 전동기의 출력이 부하에 의한 외란과 매개변수의 변동에서도 기준 입력을 잘 추동함을 알 수 있었다. 적용된 알고리듬은 소프트웨어와 하드웨어적으로 모두 간단하며 효과적인 특성을 가지고 있다.

In this paper, a precisely speed-controlled DC servo motor system utilizing direct adaptive control (DAC) algorithm which require that neither satisfaction of the perfect model following conditions (PMFC) nor explicit parameter identification is proposed. Computer simulation as well as experiments using MC-68000 are implemened with the above input trajectory fairly well in spite of load disturbances and parameter variations. Presented algorithm is simple and effective both in software and hardware applications.

단상태 소나는 음원의 송신시간과 반사파의 수신시간 정보를 이용하여 표적의 위치를 산출한다. 그러나 음원의 송신시간 정보를 수신센서와 공유하지 않는 비동기 양상태 소나 시스템에서는 표적의 위치를 산출하기 위해 수신센서에서 음원의 직접파(direct blast)를 탐지해야한다. 본 논문에서는 직접파에 대한 PRI(Pulse Repetition Interval)와 적응적인 임계치 추정을 통해 직접파 탐지를 수행하는 기법을 제안한다. 모의 신호 및 해상 실험 데이터를 이용하여 제안하는 기법의 성능을 분석하였고 그 결과 강한 배경소음 및 직접파와 유사한 다수의 표적 반사파가 존재하는 환경에서도 강인한 직접파 탐지 성능을 보여주었다.

Monostatic sonar systems localize targets using the time information of pulse transmission and receipt. Whereas, in asynchronous bistatic sonar systems, receivers need to detect direct blast to localize targets, since a source doesn't share pulse information with receivers. In this paper, we propose a direct blast detection algorithm, which estimates PRI (Pulse Repetition Interval) of direct blast and adaptive thresholds. Experimental results show the proposed algorithm has robust direct blast detection performance in the environment where strong background noise and target signal exist.

This paper presents direct load control algorithm based locational and electric load characteristics. Direct load control is defined that demand-side management program activities that can interrupt consumer load at the time of annual peak load by direct control of the utility system operator by interruption power supply to individual appliances or equipment on consumer premises. Korean power system is divided into 14-areas considering branches operating in KEPCO, and electric loads are classified into 19 load groups considering interruption costs in this paper. The purpose of proposed method is to decrease social losses by controlling electric loads mainly whose interruption costs are low. It is expected that the proposed algorithm can be used as the countermeasure for the emergency state of the electric power dispatch in a operation point of view.

본 논문은 직접해법 기반 FETI 알고리즘의 개선 방안을 제시하였다. 개선 대상은 FETI-local로, 해당 알고리즘은 국부 Lagrange 승수를 통해 부영역 간 경계 문제를 정의한다. 부영역 경계 강성 및 하중 계산 단계의 경우, 전체 역행렬 계산 등 과도한 비용을 요구했던 기존 알고리즘을 Boolean 행렬 특성을 활용한 선택적 역행렬 성분 계산으로 개선하였다. 전역 경계 행렬식 계산 단계의 경우, 기존 단일 프로세서 연산을 다중 프론탈 기법 기반 병렬 연산으로 대체하였다. 제시된 FETI-local 알고리즘의 성능 개선은 64만 자유도 수치 예제를 통해 검증되었으며, 기존 대비 최대 97.8%의 계산 시간 감소가 달성되었다. 또한, 기존 대비 안정적이고 개선된 확장성이 가속 지표를 통해 확인되었다. 추가로, 432만 자유도의 대용량 계산 성능 비교가 제시된 알고리즘과 상용 프로그램인 ANSYS 간에 수행되었다. 그 결과, 계산 시간 측면에선 ANSYS가 우수하였으나, 프로세서 수에 따른 가속 성능 증가율 측면에선 제시된 알고리즘이 우수한 것이 확인되었다.

This paper presents an improved computational framework for the direct-solution-based finite element tearing and interconnecting (FETI) algorithm. The FETI-local algorithm is further improved herein, and localized Lagrange multipliers are used to define the interface among its subdomains. Selective inverse entry computation, using a property of the Boolean matrix, is employed for the computation of the subdomain interface stiffness and load, in which the original FETI-local algorithm requires a full matrix inverse computation of a high computational cost. In the global interface computation step, the original serial computation is replaced by a parallel multi-frontal method. The performance of the improved FETI-local algorithm was evaluated using a numerical example with 64 million degrees of freedom (DOFs). The computational time was reduced by up to 97.8% compared to that of the original algorithm. In addition, further stable and improved scalability was obtained in terms of a speed-up indicator. Furthermore, a performance comparison was conducted to evaluate the differences between the proposed algorithm and commercial software ANSYS using a large-scale computation with 432 million DOFs. Although ANSYS is superior in terms of computational time, the proposed algorithm has an advantage in terms of the speed-up increase per processor increase.