• 대한기계학회논문집A
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• 제28권5호
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• pp.503-510
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• 2004

In this paper, the well-conditioned observer for a stochastic system is designed so that the observer is less sensitive to the ill-conditioning factors in transient and steady-state observer performance. These factors include not only deterministic uncertainties such as unknown initial estimation error, round-off error, modeling error and sensing bias, but also stochastic uncertainties such as disturbance and sensor noise. In deterministic perspectives, a small value in the L$_{2}$ norm condition number of the observer eigenvector matrix guarantees robust estimation performance to the deterministic uncertainties. In stochastic viewpoints, the estimation variance represents the robustness to the stochastic uncertainties and its upper bound can be minimized by reducing the observer gain and increasing the decay rate. Both deterministic and stochastic issues are considered as a weighted sum with a LMI (Linear Matrix Inequality) formulation. The gain in the well-conditioned observer is optimally chosen by the optimization technique. Simulation examples are given to evaluate the estimation performance of the proposed observer.

• 한국정보전자통신기술학회논문지
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• 제2권2호
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• pp.37-43
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• 2009

본 논문에서는 저 전력 시스템에 적합한 고정 소수점 연산기로 구현된 다중 채널 디지털 보청기 알고리즘의 최적화 기법을 제시한다. 먼저 입력 신호를 고속 MDCT(modified discrete cosine transform) 방법을 사용하여 주파수 대역 분할함으로써 알고리듬의 복잡도를 최소화 하였고, MDCT 출력을 비선형 대역 분할 과정을 거쳐 채널별 그룹핑을 한 다음, 각 채널 신호를 난청인의 청각 손실 정도에 따라 구성한 라우드니스 보상 함수(loudness compensation function: LCF)표를 이용하여 이득을 조절하고, 최종적으로 TDAC 기법을 구현하는 IMDCT(Inverse MDCT) 변환을 거쳐 보상된 출력을 합성한다. 모든 과정은 16비트 정수 연산으로 구현되며, 이득을 계산하기 위해 측정되는 로그 단위의 연산 과정은 미리 계산된 테이블과 고속 탐색 알고리듬을 이용하여 구현된다. 구성된 보청기 알고리즘의 성능을 컴퓨터 시뮬레이션을 통해 평가하였다.

• 조명전기설비학회논문지
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• 제28권1호
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• pp.9-15
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• 2014

This paper focuses on the heat gain of a lighting system, one of the most-used appliances in buildings, and its thermal effect within a low energy building. In this study, a dynamic thermal model of a lighting system is first established based on the first principle of thermodynamics. Then, thermal parameters of this model are estimated by experiments and an optimization process. Afterward, the obtained model of the system is validated by comparing simulation results to experimental one. Finally it is integrated into a low energy building model in order to quantify its thermal influence within a low energy building. As a result, heat flux of the lighting system, indoor temperature and heating energy demands of the building are obtained and compared with the results obtained by the conventional model of a lighting system. This paper helps to understand thermal dynamics of a lighting system and to further apply lighting systems for energy management of low energy buildings.

• 동력기계공학회지
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• 제17권4호
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• pp.109-114
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• 2013

In this study, the microstructure, mechanical properties and high temperature oxidation characteristics of HiSiMo and HiSiMoM ductile iron for exhaust manifold were investigated. The HiSiMoM ductile iron was developed by optimization of alloying element addition and casting design. The exhaust manifold prototype was fabricated using the HiSiMoM iron and this resulted in the weight saving of 0.73kg. The microstructures of the HiSiMo and HiSiMoM irons were similar each other and graphite nodularity was 89% and 93% respectively. Tensile strengths of them were 663.5 and 674.4 MPa and Brinell hardness were 235.3 and 243.9 respectively. Both irons showed parabolic weight gain behavior in high temperature oxidation atmosphere. Oxidation layer was divided into external and internal layers. The weight gain of the HiSiMoM iron was lower than that of the HiSiMo iron after isothermal oxidation test at $900^{\circ}C$. This should be rationalized by higher Si enrichment at the interface of the matrix and internal layer of the HiSiMoM iron.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권6호
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• pp.2240-2254
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• 2021

We investigate the channel allocation problem in an ultra-dense device-to-device (D2D) enabled cellular network in underlaying mode where multiple D2D users are forced to share the same channel. Two kinds of low complexity solutions, which just require partial channel state information (CSI) exchange, are devised to resolve the combinatorial optimization problem with the quality of service (QoS) guaranteeing. We begin by sorting the cellular users equipment (CUEs) links in sequence in a matric of interference tolerance for ensuring the SINR requirement. Moreover, the interference quota of CUEs is regarded as one kind of communication resource. Multiple D2D candidates compete for the interference quota to establish spectrum sharing links. Then base station calculates the occupation of interference quota by D2D users with partial CSI such as the interference channel gain of D2D users and the channel gain of D2D themselves, and carries out the channel allocation by setting different access priorities distribution. In this paper, we proposed two novel fast matching algorithms utilize partial information rather than global CSI exchanging, which reduce the computation complexity. Numerical results reveal that, our proposed algorithms achieve outstanding performance than the contrast algorithms including Hungarian algorithm in terms of throughput, fairness and access rate. Specifically, the performance of our proposed channel allocation algorithm is more superior in ultra-dense D2D scenarios.

• 한국콘텐츠학회논문지
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• 제9권4호
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• pp.27-33
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• 2009

비디오 부호화에서의 라그랑지안 계수의 선정은 Rate-Distortion Optimization의 성능을 결정하는 중요한 요소이다. H.264의 참조소프트웨어인 JM에서는 모든 매크로블록에 하나의 RDO모델을 사용한다. 그러나 각각의 매크로블록의 특성은 다르기 때문에 그에 맞는 RDO모델을 적용함으로써 성능향상을 기대할 수 있다. 본 논문에서는 매크로블록의 특성에 따라서 적응적인 RDO알고리즘을 제안한다. 우리는 실험적으로 각 매크로블록의 특성에 따른 최적의 라그랑지안 계수를 얻었다. 성능평가를 위하여 제안한 알고리즘은 참조 소프트웨어 JM10.2에 적용되었고, 실험결과 약 0.2dB정도의 화질 향상을 얻을 수 있었다.

• Journal of Power Electronics
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• 제12권1호
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• pp.104-112
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• 2012

In this paper a new method for the design of a simple PI controller is presented and it has been applied in the control of a Boost based PFC rectifier. The Strength Pareto evolutionary algorithm, which is based on the Pareto Optimality concept, used in Game theory literature is implemented as a multi-objective optimization approach to gain a good transient response and a high quality input current. In the proposed method, the input current harmonics and the dynamic response have been assumed as objective functions, while the PI controller's gains of the PFC rectifier (Kpi, Tpi) are design variables. The proposed algorithm generates a set of optimal gains called a Pareto Set corresponding to a Pareto Front, which is a set of optimal results for the objective functions. All of the Pareto Front points are optimum, but according to the design priority objective function, each one can be selected. Simulation and experimental results are presented to prove the superiority of the proposed design methodology over other methods.

• 한국유체기계학회 논문집
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• 제5권3호
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• pp.40-45
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• 2002

Since the previous cut-and-try design algorithm requires much cost and time, the automated design technique with the CFD and optimum design algorithm has recently been concerned. In this work, the Navier-Stokes equation was solved to gain more detailed viscous flow information of cascade with rotor-stator interactions. The H-grid embedded by O-grid was generated to obtain more accurate solution by eliminating the branch cut of H-grid near airfoil surface. To handle the relative motion of the rotor to the stationary stator, the sliding multiblock method was applied and the cubic-spline interpolation was used on the block interface boundary. To validate present procedure, the time-averaged aerodynamic loads were compared with experimeatal data. A good agreement was obtained. The Modified Method of Feasible Direction (MMFD) was used to carry out the sensitivity analysis of the change of aerodynamic performance by the changes of the cascade geometry. The present optimization of the cascade gave a dramatic reduction of the drag while the lift maintains at the value within the user-specified tolerance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권9호
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• pp.4044-4062
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• 2016

We investigate the optimization of energy consumption in Mobile Cloud environment in this paper. In order to optimize the energy consumed by the CPUs in mobile devices, we put forward using the asymptotic time complexity (ATC) method to distinguish the computational complexities of the applications when they are executed in mobile devices. We propose a multi-scale scheme to quantize the channel gain and provide an improved dynamic transmission scheduling algorithm when offloading the applications to the cloud center, which has been proved to be helpful for reducing the mobile devices energy consumption. We give the energy estimation methods in both mobile execution model and cloud execution model. The numerical results suggest that energy consumed by the mobile devices can be remarkably saved with our proposed multi-scale scheme. Moreover, the results can be used as a guideline for the mobile devices to choose whether executing the application locally or offloading it to the cloud center.

• 한국CDE학회논문집
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• 제19권2호
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• pp.91-102
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• 2014

The outer surface of an irregular structure contains panels with two-directional curvature called NURBS. To construct these forms of exterior materials, complex geometric surface should be divided into forms and sizes that can be manufactured and constructed. Because the bigger the curvatures of these divided exterior panel, the more expensive the construction costs, these complex two-directional curvatures should go through optimal process of reinterpretation to minimize the curved surfaces with complex two-directional curvatures. Yet, to gain higher ground in technological competition in the field of irregular structure construction, companies do not share know-how that they obtained. Accordingly, small construction and design companies have trouble calculating even rough estimate and cannot adjust expected construction cost based on comparison of design alternatives. Given this situation, this study conducted the research that can support decision-making in the design stage of the construction and provide basic material for optimal range to reduce manufacturing cost by the minimizing the distorted plane of the irregular structure.