• Computers and Concrete
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• 제29권 6호
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• pp.361-374
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• 2022

On the premise of ensuring that the automatic and quantitative discharging function of concrete conveyors is met, the accuracy of the weight forecast by the mathematical model of the screw conveying volume is improved, and the error of the weight of the concrete parts and the accumulation thickness is reduced. In this paper, the discrete element method (DEM) is used to simulate the macroscopic flow of concrete. Using the concrete discrete element model, the size of the screw conveyor is set, and establish the response model between the influencing factors (process and structure) and the concrete mass flow rate according to the design points of the screw discharging experiment. The nonlinear data fitting method is used to obtain the volumetric efficiency function under the influence of process and structural factors, and the traditional screw conveying volume model is improved. The mass flow rate of concrete predicted by the improved mathematical model of screw conveying volume is consistent with the test results. The model can accurately describe the conveying process of concrete and achieve the purpose of improving the accuracy of forecasting the weight of discharged concrete.

• 수산해양기술연구
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• 제59권2호
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• pp.145-154
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• 2023

In this study, to control the heading angle of a ship, which is constantly subjected to various internal and external disturbances during the voyage, an LADRC (linear active disturbance rejection control) design that focuses more on improving the disturbance removal performance was proposed. The speed rate of change of the ship's heading angle due to the turn of the rudder angle was selected as a significant factor, and the nonlinear model of the ship's maneuvering equation, including the steering gear, was treated as a total disturbance. It is the similar process with an LADRC design for the first-order transfer function model. At this time, the gains of the controller included in LADRC and the gains of the extended state observer were tuned to RCGAs (real-coded genetic algorithms) to minimize the integral time-weighted absolute error as an evaluation function. The simulation was performed by applying the proposed GA-LADRC controller to the heading angle control of the Mariner class vessel. In particular, it was confirmed that the proposed controller satisfactorily maintains and follows the set course even when the disturbances such as nonlinearity, modelling error, uncertainty and noise of the measurement sensor are considered.

• Wind and Structures
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• 제37권3호
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• pp.191-209
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• 2023

This work investigates the subcritical free-shear prism wake at Re=22,000 by the Koopman analysis using the Dynamic Mode Decomposition (DMD) algorithm. The Koopman model linearized nonlinearities in the stochastic, homogeneous anisotropic turbulent wake, generating temporally orthogonal eigen tuples that carry meaningful, coherent structures. Phenomenological analysis of dominant modes revealed their physical interpretations: Mode 1 renders the mean-field dynamics, Modes 2 describes the roll-up of the Strouhal vortex, Mode 3 describes the Bloor-Gerrard vortex resulting from the Kelvin-Helmholtz instability inside shear layers, its superposition onto the Strouhal vortex, and the concurrent flow entrainment, Modes 6 and 10 describe the low-frequency shedding of turbulent separation bubbles (TSBs) and turbulence production, respectively, which contribute to the beating phenomenon in the lift time history and the flapping motion of shear layers, Modes 4, 5, 7, 8, and 9 are the relatively trivial harmonic excitations. This work demonstrates the Koopman analysis' ability to provide insights into free-shear flows. Its success in subcritical turbulence also serves as an excellent reference for applications in other nonlinear, stochastic systems.

• Advances in aircraft and spacecraft science
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• 제10권1호
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• pp.19-49
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• 2023

The present study proposes a theoretical and numerical investigation on the dynamic response behaviour of a functional graded (FG) ceramic-metal tapered rotor shaft system, by the differential quadrature finite elements method (DQFEM) to identify the natural frequencies for modelling and analysis of the structure with suitable validations. The purpose of this paper is to explore the influence of heat gradients on the natural frequency of rotation of FG shafts via three-dimensional solid elements, as well as a theoretical examination using the Timoshenko beam mode, which took into account the gyroscopic effect and rotational inertia. The functionally graded material's distribution is described by two distribution laws: the power law and the exponential law. To simulate varied thermal conditions, radial temperature distributions are obtained using the nonlinear temperature distribution (NLTD) and exponential temperature distribution (ETD) approaches. This work deals with the results of the effect on the fundamental frequencies of different material's laws gradation and temperature gradients distributions. Attempts are conducted to identify adequate explanations for the behaviours based on material characteristics. The effect of taper angle and material distribution on the dynamic behaviour of the FG conical rotor system is discussed.

• Structural Engineering and Mechanics
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• 제84권3호
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• pp.361-373
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• 2022

This paper examines the flexural performance of concrete beams reinforced with glass fibre-reinforced polymer (GFRP) bars under fatigue loading. Experiments were carried out on concrete beams of size 1500×200×100 mm reinforced with 10 mm and 13 mm diameter GFRP bars under fatigue loading. Experimental investigations revealed that fatigue loading affects both strength and serviceability properties of GFRP reinforced concrete. Experimental results indicated that (i) the concrete beams experienced increase in deflection with increase in number of cycles and failed suddenly due to snapping of rebars and (ii) the fatigue life of concrete beams drastically decreased with increase in stress level. Analytical model presented a procedure for predicting the deflection of concrete beams reinforced with GFRP bars under cyclic loading. Deflection of concrete beams was computed by considering the aspects such as stiffness degradation, force equilibrium equations and effective moment of inertia. Nonlinear finite element (FE) analysis was performed on concrete beams reinforced with GFRP bars. Appropriate constitutive relationships for concrete and GFRP bars were considered in the numerical modelling. Concrete non linearity has been accounted through concrete damage plasticity model available in ABAQUS. Deflection versus number of cycles obtained experimentally for various beams was compared with the analytical and numerical predictions. It was observed that the predicted values are comparable (less than 20% difference) with the corresponding experimental observations.

• 한국지진공학회논문집
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• 제15권4호
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• pp.45-54
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• 2011

경계요소를 가지는 철근콘크리트 전단벽의 비선형 해석을 위한 간편 모델을 제안하였다. 이 간편 모델은 전단벽의 휨 및 전단 거동을 스프링요소로 나타낸 거시적 모델이다. 휨거동은 벽체의 단면해석을 기초로 한 모멘트강도와 회전능력을 벽체 양단의 수직 스프링요소로 나타내었다. 경계요소를 가지는 전단벽은 휨거동에 의해 지배되므로 전단거동은 휨거동에 바탕하여 변수를 계산하였고 중앙부 수평 스프링요소로 나타내었다. 제안된 모델은 전단벽 정적이력시험 결과와 비교한 후 비선형동적해석을 수행하여 사용된 이력법칙 및 변수들의 타당성을 조사하였다. 비선형동적해석을 이용한 변수연구를 통하여 내진성능평가의 주요변수인 요구값과 성능값에 미치는 영향을 검토하였다. 그 결과 전단력-전단변형 관계에서 약간의 차이가 있지만 전단벽의 전체거동은 잘 일치하였으며, 주요 변수의 변화에 대해 요구값과 성능값도 일정하게 변화하므로 제안된 해석모델은 경계요소를 가진 철근콘크리트 전단벽에 알맞은 것으로 판단된다.

• 한국지반공학회지:지반
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• 제12권6호
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• pp.185-198
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• 1996

EPS(Expanded Polystyrene)를 이용한 하중경감공법은 초경량재(20~30kg/m3)인 EPS를 본 연구는 보강토 토류벽체의 뒤채움재로서 폐 EPS 조각을 혼합한 경량의 성토재료를 개발, 활용하기 위한 기초연구로서, 우리나라에 광범위하게 분포하는 화강풍화토와 폐 EPS조각을 혼합한 경량성토재에 대해 공학적 특성파악을 위한 기본물성시험을 수행하였고, 또한 국내에서 판매되고 있는 두가지 대표적인 강성 및 연성 지오그리드 보강재에 대해 폐 EPS조각의 혼합비를 변화시 켜가며 실내인발시험을 수행하였으며, 이들 시험결과를 토대로 하여 폐 EPS조각 혼합경량토의 토질공학적 특성과 지오그리드-혼합경량토 사이의 마찰특성을 분석.평가하였다. 또한 본 연구에서는, 인장력 이외에도 다짐하중 및 상재하중 등 수직하중에 의한 압축력이 추가로 동시에 작용하는 경우의 지오그리드의 인장력-변형률 관계를 고려할 수 있는 마찰강도 산정방법을 제시하였으며, 이 방법을 토대로 하여 지오그리드-혼합토 사이의 마찰강도 평가시 적용가능한 보정계수 a1 및 a2 값의 범위를 제시하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제34권1호
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• pp.102-108
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• 2010

본 연구에서는 설계사양과 경제성을 고려한 퍼지형 자동조타기를 설계하기 위한 이전 단계로 Bech와 Wagner Smith의 Nomoto 2차 비선형 확장모델을 퍼지모델로 구현하는 것을 다룬다. 우선 퍼지형 자동조타기를 얻기 위해 선박의 동적 특성을 효과적으로 표현 가능한 T-S 퍼지모델을 얻는다. T-S 퍼지모델은 선박의 회두각속도를 설계변수로 간주하고 이것의 변화에 따라 다수개의 지역 선형모델(서브시스템)을 구한 후, "IF-THEN" 퍼지규칙으로 결합한 것이다. 이때 선형모델의 파라미터와 퍼지모델의 소속함수는 선박의 동적인 특성과 일치하도록 입 출력 데이터와 실수코딩 유전알고리즘이 결합된 모델 조정기법을 이용하여 최적으로 추정한다.

• 한국농공학회논문집
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• 제51권5호
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• pp.25-34
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• 2009

The objective of this study is to evaluate the future potential climate and vegetation canopy change impact on a dam watershed hydrology. A $6,661.5\;km^2$ dam watershed, the part of Han-river basin which has the watershed outlet at Chungju dam was selected. The SWAT model was calibrated and verified using 9 year and another 7 year daily dam inflow data. The Nash-Sutcliffe model efficiency ranged from 0.43 to 0.91. The Canadian Centre for Climate Modelling and Analysis (CCCma) Coupled Global Climate Model3 (CGCM3) data based on Intergovernmental Panel on Climate Change (IPCC) SRES (Special Report Emission Scenarios) B1 scenario was adopted for future climate condition and the data were downscaled by artificial neural network method. The future vegetation canopy condition was predicted by using nonlinear regression between monthly LAI (Leaf Area Index) of each land cover from MODIS satellite image and monthly mean temperature was accomplished. The future watershed mean temperatures of 2100 increased by $2.0^{\circ}C$, and the precipitation increased by 20.4 % based on 2001 data. The vegetation canopy prediction results showed that the 2100 year LAI of deciduous, evergreen and mixed on April increased 57.1 %, 15.5 %, and 62.5% respectively. The 2100 evapotranspiration, dam inflow, soil moisture content and groundwater recharge increased 10.2 %, 38.1 %, 16.6 %, and 118.9 % respectively. The consideration of future vegetation canopy affected up to 3.0%, 1.3%, 4.2%, and 3.6% respectively for each component.

• 전력전자학회논문지
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• 제7권6호
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• pp.509-516
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• 2002

본 논문에서는 신경회로망을 이용한 스위치드 릴럭턴스 전동기(Switched Reluctance Motor, SRM)의 간편한 순시토크 추정기법과 스위칭 각 제어에 관해 연구하였다. 간단한 구조와 높은 효율 등의 많은 장점을 가지고 있는 SRM은 부하토크와 회전속도에 따라 운전특성이 달라지므로 최적운전을 위해서는 스위칭 각 제어가 필수적이다. 이러한 스위칭 각은 고정자 및 회전자 극호각, 토크 및 속도 능의 여러 변수들에 따라 달라지기 때문에 적정 스위칭 시점을 결정하는데 있어서 어려움이 있다. 따라서 본 논문에서는 부하토크 및 회전속도에 따라 효율이 가장 높은 적정 스위칭 각을 실험을 통해 선정한 후 신경회로망(Neural Network, NN)을 이용하여 전동기 제어에 적용하는 방안에 관해 고찰하였다. 또한 스위칭 각 제어에 있어서 필수적인 순시토크의 추정에 있어서도 신경회로망을 이용하여 인덕턴스의 비선형적인 특성이 고려되도록 하였다. 구현된 스위칭 각 제어기를 실제 시스템에 적용하였으며, 고효율 측면에서 선정된 스위칭 각 제어기의 동특성을 확인함으로써 스위칭 각 제어기의 적합성을 검증하였다.