• 한국해양공학회지
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• 제16권1호
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• pp.8-15
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• 2002

This paper presents a neural net based nonlinear adaptive controller for an autonomous underwater vehicle (AUV). AUV's dynamics are highly nonlinear and their hydrodynamic coefficients vary with different operational conditions, so it is necessary for the high performance control system of an AUV to have the capacities of learning and adapting to the change of the AUV's dynamics. In this paper a linearly parameterized neural network is used to approximate the uncertainties of the AUV's dynamic, and the basis function vector of network is constructed according to th AUV's physical properties. A sliding mode control scheme is introduced to attenuate the effect of the neural network's reconstruction errors and the disturbances in AUV's dynamics. Using Lyapunov theory, the stability of the presented control system is guaranteed as well as the uniformly boundedness of tracking errors and neural network's weights estimation errors. Finally, numerical simulations for motion control of an AUV are performed to illustrate the effectiveness of the proposed techniques.

• 한국도로학회논문집
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• 제15권4호
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• pp.43-51
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• 2013

PURPOSES : The main purposes of this study are to examine the influences of polyethylene wax-based WMA additive on the optimum asphalt content of warm-recycled asphalt mixture based on the Marshall mix design and to evaluate performance of warm-recycled asphalt mixture containing 30% RAP with polyethylene wax-based WMA additive. METHODS: Physical and rheological properties of the residual asphalt were evaluated in terms of penetration, softening point, ductility and performance grade (PG) in order to examine the effects of polyethylene wax-based WMA additive on the residual asphalt. Also, To evaluate performance characteristics of the warm-recycled asphalt mixtures using polyethylene wax-based WMA additive along with a control hot-recycled asphalt mixture, indirect tensile strength test, modified Lottman test, dynamic immersion test, wheel tracking test and dynamic modulus test were conduced in the laboratory. RESULTS : Based on the limited laboratory test results, polyethylene wax-based WMA additive is effective to decrease mixing and compacting temperatures without compromising the volumetric characteristics of warm-recycled asphalt mixtures compared to hot-recycled asphalt mixture. Also, it doesn't affect the optimum asphalt content on recycled-asphalt mixture. All performance test results show that the performance of warm-recycled asphalt mixture using polyethylene wax-based WMA additive is similar to that of a control hot-recycled asphalt mixture. CONCLUSIONS: Overall, the performance of warm-recycled asphalt mixture using polyethylene wax-based WMA additive is comparable to hot-recycled asphalt mixture.

• Smart Structures and Systems
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• 제26권3호
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• pp.373-390
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• 2020

Hybrid simulation (HS) is a versatile tool for structural performance evaluation under dynamic loads. Although real structural responses are often multiple-directional owing to an eccentric mass/stiffness of the structure and/or excitations not along structural major axes, few HS in this field takes into account structural responses in multiple directions. Multi-directional loading is more challenging than uni-directional loading as there is a nonlinear transformation between actuator and specimen coordinate systems, increasing the difficulty of suppressing loading error. Moreover, redundant actuators may exist in multi-directional hybrid simulations of large-scale structures, which requires the loading strategy to contain ineffective loading of multiple actuators. To address these issues, lately a new strategy was conceived for accurate reproduction of desired displacements in bi-directional hybrid simulations (BHS), which is characterized in two features, i.e., iterative displacement command updating based on the Jacobian matrix considering nonlinear geometric relationships, and force-based control for compensating ineffective forces of redundant actuators. This paper performs performance validation and application of this new mixed loading strategy. In particular, virtual BHS considering linear and nonlinear specimen models, and the diversity of actuator properties were carried out. A validation test was implemented with a steel frame specimen. A real application of this strategy to BHS on a full-scale 2-story frame specimen was performed. Studies showed that this strategy exhibited excellent tracking performance for the measured displacements of the control point and remarkable compensation for ineffective forces of the redundant actuator. This strategy was demonstrated to be capable of accurately and effectively reproducing the desired displacements in large-scale BHS.

• 한국컴퓨터정보학회논문지
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• 제14권10호
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• pp.225-231
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• 2009

본 논문에서는 시간이 변하는 볼륨 데이터로부터 등위면 콤포넌트를 계산하고 그 움직임을 추적하는 새로운 시각화 알고리즘을 기술한다. 등위면 시각화는 볼륨 데이터를 효과적으로 보여주기 위한 가장 흔한 방법 중 하나이다. 그러나 대부분의 기존 등위면 시각화 알고리즘들은 시간이 정지되어 있는 정적 볼륨 데이터에 국한하여 적용되어왔다. 이미징 기술과 시뮬레이션 기술이 발전함에 따라 대용량의 시변 볼륨 데이터들이 생성되고 있어 이러한 시변볼륨 데이터의 동적인 특성을 이용할 수 있는 효과적인 시변 등위면 시각화 알고리즘이 필요하게 되었다. 우리는 우선 두 연속되는 시변 볼륨 데이터에서 정의되는 등위면 컴포넌트들간의 시간적 일치성을 정의한다. 이 정의에 기반하여 컨투어 트리를 이용하여 얻어진 등위면 컴포넌트로부터 그것과 일치되는 그 다음 시간단계에서의 컴포넌트들을 추적하는 알고리즘을 수행한다. 이러한 과정을 매 시간단계에서 반복하면, 선택된 등위면 컴포넌트의 동적인 변형 모습을 보여주어 효과적인 시각화를 이룰수 있다.

• 대한전자공학회논문지SP
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• 제49권3호
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• pp.51-59
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• 2012

본 논문에서는 마르코프 네트워크로 모델링된 다관절체(Articulated body) 사람을 양안 영상(stereo image)을 통해 획득 되어진 디스패리티 맵(disparity map)을 이용해 효과적으로 추적하는 방법을 제안한다. 기존의 색상 정보만을 사용하여 에너지함수의 우도(likelihood)를 계산하는 방법은 조명 및 그림자의 영향과 배경 색상의 임의성 때문에 강건하지 못 하다. 본 논문에서는 색상 정보에 더불어 디스패리티 정보를 활용하여 우도를 계산하는 방법을 제안한다. 원통형 모양의 사람의 신체 요소(body part)는 2차원 영상으로 사영될 때 직사각형으로 사영되므로 이 직사각형의 디스패리티의 분포가 불연속 하지 않다는 특성을 이용한다. 또한 본 논문에서는 디스패리티 맵을 사용한 조건적 메시지 생성 방법을 제안해 신뢰 전파에서 불필요한 메시지 업데이트 수행을 줄이는 방법을 보여준다. 메시지 업데이트는 신뢰 전파 알고리즘의 전체 수행 시간에 80% 이상을 차지하므로, 조건적 메시지 생성 방법은 기존 대비 9~45%의 속도 향상을 보였다. 또한 사람의 연속적인 움직임 특성을 이용한 다이나믹 모델을 제안해 추적 속도를 향상하였다. 자세한 내용은 4장에 설명되어 있다. 실험 결과 제안하는 디스패리티 정보를 활용한 신뢰 전파를 사용해 다관절체를 추적하는 방법은 기존 대비 강건한 추적 결과와 함께 빠른 속도로 추적할 수 있었다.

• 한국건설순환자원학회논문집
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• 제9권1호
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• pp.109-116
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• 2021

본 연구에서는 제철소에서 발생되는 전기로 산화슬래그로써 제철 슬래그 골재를 사용한 SMA 혼합물에 대한 역학적 특성을 평가하였다. 실험 변수는 일반골재와 제철 슬래그 골재 10mm 및 13mm이다. 슬래그 골재의 기본 물성과 품질(비중, 흡수율등)은 KS기준을 만족하였다. 아스팔트콘크리트 혼합물의 역학적 실험을 수행한 결과, 슬래그 골재 혼합물은 최적아스팔트 함량이 일반 골재 혼합물 대비 낮게 도출되었으나 다른 품질 기준은 모두 만족하였다. 제철 슬래그 골재 혼합물이 일반 골재 혼합물 대비 다소 높은 값으로 측정되었고, 모든 시편에서 동적안정도 시험은 2,000pass/mm 기준을 만족하였다. 또한, 제철 슬래그 골재 혼합물의 회복탄성계수는 일반 골재를 사용한 혼합물에 비해 개선된 값을 나타내었다. 이에, 하중 재하 이후 회복하는 속도가 향상되어 차량의 반복적 통행하중에 따른 공용성능 개선 효과가 있을 것으로 판단된다.

• 한국산학기술학회논문지
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• 제19권5호
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• pp.146-152
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• 2018

본 연구에서는 국내에서 주로 발생하는 소성변형에 대한 아스팔트 혼합물의 성능개선을 위해 분말형 및 액상형 재료를 혼합한 복합 개질제를 이용하였다. 주요 구성 물질은 분말형인 규조토, 운모 및 카본블랙, 액상형 고형분 70% SBR(Styrene-Butanaiene Rubber) 라텍스 등을 이용하였다. 시험에 사용된 2종류의 표층용 혼합물에 대한 인장강도비는 국토교통부(2017) 아스팔트 혼합물 생산 및 시공지침 기준인 0.80 이상을 만족하였다. 복합개질제를 첨가한 경우 건조상태에서의 인장강도 증가효과가 약 14% 이상 나타났다. 휠트레킹 시험 하중에 의한 분당변형속도는 0.07-0.14 정도로 복합 개질제 사용 시 분당 변형속도가 개선되었고, 동적안정도의 경우 295에서 590으로 거의 100% 정도 향상되었다. 또한, 최종 침하량은 11.38mm에서 9.57mm로 저감되었다. 동삼축압축시험을 이용한 소성변형 시험결과, 2단계 구간이 끝나고 3단계 소성변형파괴구간에 진입하는 변형량의 크기는 평균 1.50mm에서 1.76mm,나타났다. 또한, 2단계 구간의 시간당 변형 기울기는 기존 아스팔트 혼합물은 0.007 mm/sec 이고, 복합 개질제를 혼합한 아스팔트 혼합물의 평균기울기는 0.005 mm/sec 정도로 도로포장체가 안정적인 공용성능을 발휘하는 구간에서 교통하중에 의한 소성변형 속도가 상대적으로 작음을 알 수 있다.

• Nuclear Engineering and Technology
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• 제47권7호
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• pp.838-848
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• 2015

One of the most important operations in nuclear power plants is load following, in which an imbalance of axial power distribution induces xenon oscillations. These oscillations must be maintained within acceptable limits otherwise the nuclear power plant could become unstable. Therefore, bounded xenon oscillation is considered to be a constraint for the load following operation. In this paper, the design of a sliding mode control (SMC), which is a robust nonlinear controller, is presented.SMCis ameansto control pressurized water nuclear reactor (PWR) power for the load following operation problem in a way that ensures xenon oscillations are kept bounded within acceptable limits. The proposed controller uses constant axial offset (AO) strategy to ensure xenon oscillations remain bounded. The constant AO is a robust state constraint for the load following problem. The reactor core is simulated based on the two-point nuclear reactor model with a three delayed neutron groups. The stability analysis is given by means of the Lyapunov approach, thus the control system is guaranteed to be stable within a large range. The employed method is easy to implement in practical applications and moreover, the SMC exhibits the desired dynamic properties during the entire output-tracking process independent of perturbations. Simulation results are presented to demonstrate the effectiveness of the proposed controller in terms of performance, robustness, and stability. Results show that the proposed controller for the load following operation is so effective that the xenon oscillations are kept bounded in the given region.

• Molecules and Cells
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• 제44권9호
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• pp.627-636
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• 2021

The three-dimensional organization of chromatin and its time-dependent changes greatly affect virtually every cellular function, especially DNA replication, genome maintenance, transcription regulation, and cell differentiation. Sequencing-based techniques such as ChIP-seq, ATAC-seq, and Hi-C provide abundant information on how genomic elements are coupled with regulatory proteins and functionally organized into hierarchical domains through their interactions. However, visualizing the time-dependent changes of such organization in individual cells remains challenging. Recent developments of CRISPR systems for site-specific fluorescent labeling of genomic loci have provided promising strategies for visualizing chromatin dynamics in live cells. However, there are several limiting factors, including background signals, off-target binding of CRISPR, and rapid photobleaching of the fluorophores, requiring a large number of target-bound CRISPR complexes to reliably distinguish the target-specific foci from the background. Various modifications have been engineered into the CRISPR system to enhance the signal-to-background ratio and signal longevity to detect target foci more reliably and efficiently, and to reduce the required target size. In this review, we comprehensively compare the performances of recently developed CRISPR designs for improved visualization of genomic loci in terms of the reliability of target detection, the ability to detect small repeat loci, and the allowed time of live tracking. Longer observation of genomic loci allows the detailed identification of the dynamic characteristics of chromatin. The diffusion properties of chromatin found in recent studies are reviewed, which provide suggestions for the underlying biological processes.

• 천문학회보
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• 제45권1호
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• pp.38.2-38.2
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• 2020

Horizon Run 5 (HR5) is a cosmological hydrodynamical simulation which captures the properties of the Universe on a Gpc scale while achieving a resolution of 1 kpc. This enormous dynamic range allows us to simultaneously capture the physics of the cosmic web on very large scales and account for the formation and evolution of dwarf galaxies on much smaller scales. Inside the simulation box. we zoom-in on a high-resolution cuboid region with a volume of 1049 × 114 × 114 Mpc3. The subgrid physics chosen to model galaxy formation includes radiative heating/cooling, reionization, star formation, supernova feedback, chemical evolution tracking the enrichment of oxygen and iron, the growth of supermassive black holes and feedback from active galactic nuclei (AGN) in the form of a dual jet-heating mode. For this simulation we implemented a hybrid MPI-OpenMP version of the RAMSES code, specifically targeted for modern many-core many thread parallel architectures. For the post-processing, we extended the Friends-of-Friend (FoF) algorithm and developed a new galaxy finder to analyse the large outputs of HR5. The simulation successfully reproduces many observations, such as the cosmic star formation history, connectivity of galaxy distribution and stellar mass functions. The simulation also indicates that hydrodynamical effects on small scales impact galaxy clustering up to very large scales near and beyond the baryonic acoustic oscillation (BAO) scale. Hence, caution should be taken when using that scale as a cosmic standard ruler: one needs to carefully understand the corresponding biases. The simulation is expected to be an invaluable asset for the interpretation of upcoming deep surveys of the Universe.