• Steel and Composite Structures
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• 제47권6호
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• pp.795-811
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• 2023

When studying the resonance problem of nanoplates, the existing papers do not consider the influences of geometric nonlinearity and initial geometric imperfection, so this paper is to fill this gap. In this paper, based on the nonlocal strain gradient theory (NSGT), the nonlinear resonances of functionally graded (FG) nanoplates with initial geometric imperfection under different boundary conditions are established. In order to consider the small size effect of plates, nonlocal parameters and strain gradient parameters are introduced to expand the assumptions of the first-order shear deformation theory. Subsequently, the equations of motion are derived using the Euler-Lagrange principle and solved with the help of perturbation method. In addition, the effects of initial geometrical imperfection, functionally graded index, strain gradient parameter, nonlocal parameter and porosity on the nonlinear forced vibration behavior of nanoplates under different boundary conditions are discussed.

• 상하수도학회지
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• 제35권6호
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• pp.507-516
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• 2021

In this study, the machine learning which has been widely used in prediction algorithms recently was used. the research point was the CD(chudong) point which was a representative point of Daecheong Lake. Chlorophyll-a(Chl-a) concentration was used as a target variable for algae prediction. to predict the Chl-a concentration, a data set of water quality and quantity factors was consisted. we performed algorithms about random forest and gradient boosting with Python. to perform the algorithms, at first the correlation analysis between Chl-a and water quality and quantity data was studied. we extracted ten factors of high importance for water quality and quantity data. as a result of the algorithm performance index, the gradient boosting showed that RMSE was 2.72 mg/m³ and MSE was 7.40 mg/m³ and R² was 0.66. as a result of the residual analysis, the analysis result of gradient boosting was excellent. as a result of the algorithm execution, the gradient boosting algorithm was excellent. the gradient boosting algorithm was also excellent with 2.44 mg/m³ of RMSE in the machine learning hyperparameter adjustment result.

• 한국광학회지
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• 제22권1호
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• pp.5-9
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• 2011

다중모드 경사굴절률 플라스틱 광섬유는 경사굴절률을 생성하기 위하여 첨가하는 미세입자, 불균일한 경사굴절률의 분포, 다른 모드 사이의 광학적인 간섭 등으로 인하여 스펙클 잡음이 크기 때문에, 광섬유 출력 단에서 방사되는 기하학적 광 세기 분포를 분석하여 측정하는 기존의 일반적인 수치구경 측정 방법으로는 수치구경 측정이 매우 어려운 문제점이 있다. 따라서 본 논문에서는 이와 같은 다중모드 경사굴절률 플라스틱 광섬유의 수치구경 측정을 위하여 입사 단에서 입사 광의 크기를 조절하여 수치구경을 구하는 새로운 방법을 제안하고, 이를 이용하여 플라스틱 광섬유의 수치구경을 측정하였다. 측정 결과, 기존의 방법으로 측정한 플라스틱 광섬유의 수치구경 값과 비교적 잘 일치함을 확인할 수 있었으며, 제안한 기법이 출력 단에서 방사되는 광세기 분포의 모호함을 배제할 수 있고 입력광의 입사 조건 및 광섬유 결합 효율을 최적화할 수 있는 장점이 있음을 알 수 있었다.

• 한국수자원학회논문집
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• 제32권4호
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• pp.489-499
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• 1999

본 연구는 분포형 수문 모형인 TOPMODEL의 기본 입력자료인 지형지수, 1n(a/tan {{{{{B}_{}}}}}) 산정을 위한 알고리즘과 수로형성면적(CIT)과 구배멱급수(H)를 고려한 개선된 지형지수 산정 알고리즘의 국내 지형에 대한 적용성을 검토하였다. 대상 유역은 청도천 유역의 한제천 소유역 (18.6km2)과 위천 대표 시험유역의 동곡 소유역(33.6km2)으로, 이 두 유역에 대한 10m, 20m, 30m, 50m, 100m의 수치고도자료(Digital elevation model ; DEM)을 구축하였다. 기존 알고리즘에 대해 수로형성면적의 적용 결과, 수로 격자에 대한 지형지수의 적절한 처리를 통해 개선된 계산 결과를 얻을 수 있었고, 구배멱급수(H)의 적용을 통해 기존의 다방향 흐름(MFD) 알고리즘에 비해 유역 내 협곡 지점에 대한 흐름의 수렴 효과를 얻을 수 있었다. 개선된 알고리즘에 의해 계산된 지형지수 분포는 최대값의 감소로 유출 모의시 과도한 초기 유출 계산 문제를 완화시킬 수 있었다. 기존 알고리즘을 사용한 유출 모의와 비교하여 개선된 알고리즘을 활용한 전체적인 모의 효율은 유사하나 수문정보의 공간 분포 산정은 보다 합리적인 결과를 도출하였다,

• 자동차안전학회지
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• 제13권4호
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• pp.129-143
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• 2021

This paper proposes actuator fault detection and adaptive fault-tolerant control algorithms using performance index and human-like learning for longitudinal autonomous vehicles. Conventional longitudinal controller for autonomous driving consists of supervisory, upper level and lower level controllers. In this paper, feedback control law and PID control algorithm have been used for upper level and lower level controllers, respectively. For actuator fault-tolerant control, adaptive rule has been designed using the gradient descent method with estimated coefficients. In order to adjust the control parameter used for determination of adaptation gain, human-like learning algorithm has been designed based on perceptron learning method using control errors and control parameter. It is designed that the learning algorithm determines current control parameter by saving it in memory and updating based on the cost function-based gradient descent method. Based on the updated control parameter, the longitudinal acceleration has been computed adaptively using feedback law for actuator fault-tolerant control. The finite window-based performance index has been designed for detection and evaluation of actuator performance degradation using control error.

• 전자공학회논문지S
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• 제34S권11호
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• pp.138-147
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• 1997

The ultrasonic images are corrupted by the granular pattern noise - a speckle noise. The speckle exist in the type of coherent imaging systems, and the speckle is the signal independent and multiplicative noise. In this paepr, we derive two filters using the gradient and symmetry. One is a noise suppression filter which removes noise while preserves the edges. It is named the ASRF-GS (Adaptive Speckle Removal Filer - Gradient and Symmetry). And the other is a edge detection filter which obtains the thin edge map, called the EDUGS(Edge Detection Using Gradient and Symmetry). The performance of the proposed noise suppression filter is evaluated by the IMPV(SNR improvement) and the Speckle Index(SI), and the perforamnce of the edge detection is evaluated by the edge detection error rate. According to the evaluated method, The SI reduced about 0.035, The IMPV improved about 1.265(dB), and the edge detection error rate is about 17.5%.

• Advances in aircraft and spacecraft science
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• 제7권2호
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• pp.169-186
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• 2020

Based upon differential quadrature method (DQM) and nonlocal strain gradient theory (NSGT), mechanical-hygro-thermal vibrational analyzes of shear deformable porous functionally graded (FG) nanoplate on visco-elastic medium has been performed. The presented formulation incorporates two scale factors for examining vibrational behaviors of nano-dimension plates more accurately. The material properties for FG plate are porosity-dependent and defined employing a modified power-law form. It is supposed that the nano-size plate is exposed to hygro-thermal and variable compressive mechanical loadings. The governing equations achieved by Hamilton's principle are solved implementing DQM. Presented results indicate the prominence of moisture/temperature variation, damping factor, material gradient index, nonlocal coefficient, strain gradient coefficient and porosities on vibrational frequencies of FG nano-size plate.

• Structural Engineering and Mechanics
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• 제88권4호
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• pp.355-368
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• 2023

Employing the non-local strain gradient theory (NSGT), this paper investigates the nonlinear resonance characteristics of functionally graded material (FGM) nanoshells with initial geometric imperfection for the first time. The effective material properties of the porous FGM nanoshells with even distribution of porosities are estimated by a modified power-law model. With the guidance of Love's thin shell theory and considering initial geometric imperfection, the strain equations of the shells are obtained. In order to characterize the small-scale effect of the nanoshells, the nonlocal parameter and strain gradient parameter are introduced. Subsequently, the Euler-Lagrange principle was used to derive the motion equations. Considering three boundary conditions, the Galerkin principle combined with the modified Lindstedt Poincare (MLP) method are employed to discretize and solve the motion equations. Finally, the effects of initial geometric imperfection, functional gradient index, strain gradient parameters, non-local parameters and porosity volume fraction on the nonlinear resonance of the porous FGM nanoshells are examined.

• Advances in nano research
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• 제16권2호
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• pp.175-186
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• 2024

Dynamical behaviors of one-dimensional (1D) nano-sized structures are of great importance in nanotechnology applications. Therefore, the torsional dynamic response of functionally graded nanorods which could be used to model the nano electromechanical systems or micro electromechanical systems with torsional motion about the center of twist is examined based on the theory of strain gradient nonlocal elasticity in this work. The mathematical background is constructed based on both strain gradient theory and Eringen's nonlocal elasticity theory. The equation of motions and boundary conditions of radially functionally graded nanorods are derived using Hamilton's principle and then transformed into the eigenvalue analysis by using Fourier sine series. A general coefficient matrix is obtained to assemble the Stokes' transformation. The case of a restrained functionally graded nanorod embedded in two elastic springs against torsional rotation is then deeply investigated. The effect of changing the functionally graded index, the stiffness of elastic boundary conditions, the length scale parameter and nonlocal parameter are investigated in detail.

• 센서학회지
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• 제27권4호
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• pp.209-215
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• 2018

Recent research in animal behavior has shown that gradient information plays an important role in finding food and home. It is also important in optimization of performance because it indicates how the inputs should be adjusted for maximization/minimization of a performance index. We introduce perturbation as an additional input to obtain gradient information. Unlike the typical approach of calculating the gradient from the derivative, the proposed processing is very robust to noise since it is performed as a summation. Experimental results prove the validity of the process of spatial gradient acquisition. Quantitative indices for measuring the effect of the amplitude and the frequency are developed based on linear regression analysis. Drones are very useful for environmental monitoring and an autonomous path planning is required for unstructured environment. Guiding the drone for finding the origin of the interested physical property is done by estimating the gradient of the sensed value and generating the drone trajectories in the direction which maximizes the sensed value. Simulation results show that the proposed method can be successfully applied to identify the source of the physical quantity of interest by utilizing it for path planning of an autonomous drone in 3D environment.