• Structural Engineering and Mechanics
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• 제60권5호
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• pp.891-902
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• 2016

The beam structure with breathing cracks subjected to harmonic excitations was modeled by FEM based on Euler-Bernoulli theory, and a piecewise dynamical system was deduced. The precise integration method (PIM) was employed to propose an algorithm for analyzing the dynamic responses of the deduced system. This system was first divided into linear sub-systems, between which there are switching points resulted from the breathing cracks. The inhomogeneous terms due to the external excitations were tackled by introducing auxiliary variables to express the harmonic functions, hence the sub-systems are homogeneous. The PIM was then applied to solve the homogeneous sub-systems one by one. During the procedures, a predictor-corrector algorithm was presented to determine the switching points accurately. The presented method can provide solutions with an accuracy to a magnitude of $10^{-12}$ compared with exact solutions obtained by the theories of ordinary differential equations. The PIM results are much more accurate than Newmark ones with the same time step. Moreover, it is found that the PIM can maintain a high level of accuracy even when the time step increases within a relatively wide range.

• BMB Reports
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• 제36권6호
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• pp.558-564
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• 2003

In microarray data mining, one of the key problems is how to handle weak signals. Based on a bent piecewise linear accumulated distribution generally found in the microarray data, a new detectable threshold finding method is proposed to filter genes with unreliable information in this paper. More reliable and reproducible data is produced for the subsequent data mining.

• 한국주조공학회지
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• 제31권3호
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• pp.124-129
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• 2011

We applied two numerical schemes to improve accuracy of the solution in the flow simulation of molten metal. One method is Piecewise Linear Interface Calculation (PLIC) method and the other is Donor-Acceptor (D-A) method. In the present work, we have tested simple problems to verify the module of the interface reconstruction algorithms. After validations, accuracy and efficiency of these two methods have compared by simulating various real products. On the numerical simulation of free surface flow, it is possible for PLIC method to track very accurately the interface between phases. PLIC method, however, has the weak point where a lot of computational time hangs, though it shows the more accurate interface reconstruction. Donor-Acceptor method has enough effectiveness in the macro observation of mold filling sequence though it shows the inferior accuracy.

• Journal of Power Electronics
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• 제11권4호
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• pp.542-550
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• 2011

This paper describes the design and hardware implementation of a Single Input Fuzzy Logic Controller (SIFLC) to regulate the output voltage of a boost power converter. The proposed controller is derived from the signed distance method, which reduces a multi-input conventional Fuzzy Logic Controller (CFLC) to a single input FLC. This allows the rule table to be approximated to a one-dimensional piecewise linear control surface. A MATLAB simulation demonstrated that the performance of a boost converter is identical when subjected to the SIFLC or a CFLC. However, the SIFLC requires nearly an order of magnitude less time to execute its algorithm. Therefore the former can replace the latter with no significant degradation in performance. To validate the feasibility of the SIFLC, a 50W boost converter prototype is built. The SIFLC algorithm is implemented using an Altera FPGA. It was found that the SIFLC with asymmetrical membership functions exhibits an excellent response to load and input reference changes.

• 한국통신학회논문지
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• 제34권3C호
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• pp.322-328
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• 2009

본 논문은 BER 성능을 높인 LDPC 복호를 위한 새로운 SSP 알고리즘을 제안한다. 제안하는 SSP 알고리즘은 추가적인 연산 없이 곱셈 연산과 나눗셈 연산을 덧셈 연산과 뺄셈 연산으로 대체가 가능하다. 제안하는 SSP 알고리즘은 In[tanh(x)] 함수와 $tanh^{-1}[exp(x)]$ 함수를 각각의 양자화 테이블을 사용하여 단순화하기 때문에 연산 복잡도를 줄일 수 있다. 시뮬레이션 결과 제안하는 SSP 알고리즘은 기존의 근사화 SP 알고리즘과 비교하여 BER 성능을 $0.3\;{\sim}\;0.8\;dB$ 향상시킨 것을 보여준다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.10-10
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• 2009

파이프 용접은 중력의 영향으로 인하여 위치에 따라 같은 용접변수라도 비드 형상이 매우 달라 지게 된다. 또한 지금까지 많은 용접 기술자들이 위험하고 까다로운 환경에서 수작업으로 용접을 실행하였다. 따라서 이러한 이유로 용접 자동화 공정이 반드시 필요하게 된다. 본 연구에서는 FCAW를 사용하여 파이프 모재 대신 필릿 평판을 아래보기, 위보기 자세를 포함하여 9개 자세에서 실행하였다. 용접 자세를 비롯한 용접 변수와 비드 형상 변수간의 관계를 비선형 회귀 분석과 구간적 3차 에르미트 보간법을 이용하여 주어진 용접 변수에서의 비드 단면의 형상을 예측하고, 비드의 결함 유무를 파악하였다. 이러한 방법을 통하여 자세에 따라서 용접 결함이 없는 용접 변수를 구할 수 있었다. 시각센서를 이용하여 용접 후 비드 형상에 대해 모니터링을 실시하였다. 모니터링의 알고리즘은 영상획득, 이진화, 세선화, 적응형 미디언 필터링, 적응형 허프 변환, 용접 결함 검출의 순서로 구성되어 있으며, 본 연구에서는 보다 빠른 영상처리를 위하여 적응형 미디언 필터링을 제시하였다. 모니터링을 통하여 2차원 비드 단면뿐만 아니라, 디루니 삼각법을 적용하여 3차원으로 비드 표면을 표현할 수 있다. 보간법을 사용하여 얻은 비드 형상과 시각 센서를 통하여 얻은 비드 형상간의 비교를 통하여 본 연구의 적합성 여부를 확인하였다.

• 대한기계학회논문집B
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• 제30권10호
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• pp.1003-1011
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• 2006

Droplets are ejected onto a substrate through a nozzle by pushing liquids in flow channels of drop-on-demand devices. The behavior of ejection and formation of droplets is investigated to enhance the physical understanding of the hydrodynamics involved in inkjet printing. The free surface phenomenon of a droplet is described using $CFD-ACE^{TM}$ which employs the volume-of-fluid (VOF) method with the piecewise linear interface construction (PLIC). Droplet formation characteristics are analyzed in various flow regimes with different Ohnesorge numbers. The computational results show that the droplet formations are strongly dependent on the physical properties of working fluids and the inlet flow conditions. In addition, the wetting characteristics of working fluids on a nozzle influence the volume and velocity of a droplet produced in the device. This study may provide an insight into how a liquid droplet is formed and ejected in a piezoelectric inkjet printing device.

• 융합신호처리학회 학술대회논문집
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• 한국신호처리시스템학회 2001년도 하계 학술대회 논문집(KISPS SUMMER CONFERENCE 2001
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• pp.101-104
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• 2001

본 논문에서는 5GHz 대역을 사용하는 무선 LAN의 표준안인 IEEE 802.11a-1999를 위한 디지털 자동 이득 제어기를 제안한다. 송수신간의 동기화를 위한 신호인 Training symbol을 이용하여 수신기에 입력되는 신호의 이득을 측정한다. 측정된 이득을 이상적인 이득과 비교하여 갱신할 이득을 구한다. 갱신 이득은 신호를 증폭하는GCA(Gain Controlled Amplifier)의 입력 전압으로 변환되어 신호의 증폭도를 제어하게 된다. 본 논문에서는 하드웨어 부담을 줄이기 위해 부분 선형 근사방법을 이용하여, 갱신 이득을 GCA의 입력 전압으로 변환한다. 보다 정확한 제어를 위하여 이득 측정 및 제어 값의 갱신을 7회 반복하여 수행한다. 본 논문에서 제안한 디지털 자동 이득 제어기는 VHDL을 이용하여 설계하였으며, Xilinx CAD Tool을 이용하여 Timing Verification을 수행하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권6호
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• pp.1546-1564
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• 2012

Pattern-based query processing has not attracted much attention in wireless sensor network though its counterpart has been studied extensively in data stream. The methods used for data stream usually consume large memory and much energy. This conflicts with the fact that wireless sensor networks are heavily constrained by their hardware resources. In this paper, we use piece wise representation to represent sensor nodes' collected data to save sensor nodes' memory and to reduce the energy consumption for query. After getting data stream's and patterns' approximated line segments, we record each line's slope. We do similar matching on slope sequences. We compute the dynamic time warping distance between slope sequences. If the distance is less than user defined threshold, we say that the subsequence is similar to the pattern. We do experiments on STM32W108 processor to evaluate our strategy's performance compared with naive method. The results show that our strategy's matching precision is less than that of naive method, but our method's energy consumption is much better than that of naive approach. The strategy proposed in this paper can be used in wireless sensor network to process pattern-based queries.

• 제어로봇시스템학회논문지
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• 제17권4호
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• pp.289-294
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• 2011

Digital redesign is yet another efficient tool to convert a pre-designed analog controller into a sampled-data one to maintain the analog closed-loop performance in the sense of state matching. A rising difficulty in developing a digital redesign technique for trackers with time-varying references is the unavailability of a closed-form discrete-time model of a system, even if it is linear time-invariant. A way to resolve this is to approximate the time-varying reference as a piecewise constant one, which deteriorates the state matching performance. Another remedy may be to decrease a sampling period, which however could numerically destabilize the optimization-based digital redesign condition. In this paper, we develop a digital redesign condition for time-varying trackers by approximating the time-varying reference through a triangular hold and by introducing delta-operated discrete-time models. It is shown that the digitally redesigned sampled-data tracker recovers the performance of the pre-designed analog tracker under a fast sampling limit. Simulation results on the formation flying of satellites convincingly show the effectiveness of the development.