• Smart Structures and Systems
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• 제29권4호
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• pp.535-547
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• 2022

Failure patterns of rock specimens represent valuable information about the mechanical properties and crack evolution mechanism of rock. Several kinds of research have been conducted regarding the failure mechanism of brittle material, however; the influence of brittleness on the failure mechanism of rock specimens has not been precisely considered. In the present study, experimental and numerical examinations have been made to evaluate the physical and mechanical phenomena associated with rock failure mechanisms through the uniaxial compression test. In the experimental part, Unconfined Compressive Strength (UCS) tests equipped with Acoustic Emission (AE) have been conducted on rock samples with three different brittleness. Then, the numerical models have been calibrated based on experimental test results for further investigation and comparing the micro-cracking process in experimental and numerical models. It can be perceived that the failure mode of specimens with high brittleness is tensile axial splitting, based on the experimental evidence of rock specimens with different brittleness. Also, the crack growth mechanism of the rock specimens with various brittleness using discrete element modeling in the numerical part suggested that the specimens with more brittleness contain more tensile fracture during the loading sequences.

• Advances in nano research
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• 제13권2호
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• pp.165-174
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• 2022

In the present study, a hybrid model of artificial neural network (ANN) and internet of things (IoT) is proposed to overcome the difficulties in deriving governing equations and numerical solutions of the dynamical behavior of the nano-systems. Nano-structures manifest size-dependent behavior in response to static and dynamic loadings. Nonlocal and length-scale parameters alongside with other geometrical, loading and material parameters are taken as input parameters of an ANN to observe the natural frequency and damping behavior of micro sensors made from nanocomposite material with piezoelectric layers. The behavior of a micro-beam is simulated using famous numerical methods in literature under base vibrations. The ANN was further trained to correlate the output vibrations to the base vibration. Afterwards, using IoT, the electrical potential conducted in the sensors are collected and converted to numerical data in an embedded mini-computer and transferred to a server for further calculations and decision by ANN. The ANN calculates the base vibration behavior with is crucial in mechanical systems. The speed and accuracy of the ANN in determining base excitation behavior are the strengths of this network which could be further employed by engineers and scientists.

• Geomechanics and Engineering
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• 제29권4호
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• pp.435-449
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• 2022

In this paper, unreinforced and geogrid-reinforced soil foundations were modeled by discrete element method and this performed under surface strip footing loads. The effects of horizontal position of geogrid, vertical position, thickness, number, confining pressure have been investigated on the footing settlement and propagation of tensile force along the geogrids. Also, interaction between rectangular tunnel and strip footing with and without presence of geogrid layer has been analyzed. Experimental results of the literature were used to validation of relationships between the numerically achieved footing pressure-settlement for foundations of reinforced and unreinforced soil. Models and micro input parameters which used in the numerical modelling of reinforced and unreinforced soil tunnel were similar to parameters which were used in soil foundations. Model dimension was 1000 mm* 600 mm. Normal and shear stiffness of soils were 5*10⁵ and 2.5 *10⁵ N/m, respectively. Normal and shear stiffness of geogrid were 1*10⁹ and 1*10⁹ N/m, respectively. Loading rate was 0.001 mm/sec. Micro input parameters used in numerical simulation gain by try and error. In addition of the quantitative tensile force propagation along the geogrids, the footing settlements were visualized. Due to collaboration of three layers of geogrid reinforcements the bearing capacity of the reinforced soil tunnel was greatly improved. In such practical reinforced soil formations, the qualitative displacement propagations of soil particles in the soil tunnel and the quantitative vertical displacement propagations along the soil layers/geogrids represented the geogrid reinforcing impacts too.

• 한국시뮬레이션학회논문지
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• 제32권1호
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• pp.35-44
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• 2023

최근 텍스트 분석으로 트렌드 분석이나 연구 동향 분석을 하는 연구 사례가 많다. 텍스트 분석을 위한 자료 수집에 사용되는 검색어가 약어일 때 약어의 특성상 의미 중의성 해소가 필요하다. 다수의 연구에서는 연구에 필요한 자료를 찾기 위해 수작업으로 자료를 하나씩 읽어 문서를 분류하고 있다. 약어의 의미 중의성 해소를 위한 연구는 단어의 의미를 명확화하는 연구가 대부분이고 지도학습을 이용하고 있다. 약어 중의성 해소를 위한 선행 방법은 약어로 검색된 자료에서 연구 대상 자료를 찾는 문서 분류에는 적합하지 않으며 관련 연구도 부족하다. 본 연구에서는 데이터 전처리 단계에서 비지도 학습 방법인 비음수 행렬 분해 방법으로 토픽 모델링을 진행하여 약어로 수집된 문서를 반자동으로 분류하는 방법을 제시한다. 이를 검증하기 위해 'MSA'라는 약어 검색어로 학술 데이터베이스에서 논문 자료를 수집했다. 수집된 논문 1,401편에서 제안된 방법으로 316편의 Micro Services Architecture와 관련된 논문을 찾았다. 제안된 방법의 문서 분류 정확도는 92.36%로 측정되었다. 제안된 방법이 수작업에 따른 연구자의 시간과 비용을 줄일 수 있기를 기대한다.

• Journal of the Korean Data and Information Science Society
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• 제21권3호
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• pp.535-546
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• 2010

고객 정보를 활용하는 방법에는 고객의 구매액을 활용한 마일리지 방법과 구매 횟수에 따라 등급을 나누어 활용하는 방법 등이 있다. 본 연구에서는 회사 매출에 직결되는 고객의 재구매 여부에 초점을 맞추어 고객정보와 구매정보를 이용하여 로지스틱 회귀분석을 통한 재구매 예측 모형을 만들었다. 예측 모형 평가 측도로는 하이드게 점수를 사용하였으며 하이드게 점수를 최대로 하는 점수를 기준으로 분계점을 선택하였다. 재구매 예측모형을 이용하여 재구매 지수를 만들어 고객을 등급화하여 보다 효율적인 고객 관리가 가능하게 하였다.

• 한국항행학회논문지
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• 제21권5호
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• pp.450-458
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• 2017

본 연구에서는 곤충모방 날갯짓 비행체의 모델링과 제자리비행을 위한 자세제어 및 고도제어기를 설계하여 동역학 모델을 이용한 시뮬레이션을 수행하고 그 결과를 분석하였다. 곤충모방 날갯짓 비행체의 간략화한 날갯짓 운동, 날갯짓의 병진운동 및 회전운동에 대한 공력, 동체 동역학에 대해 수치모델링을 수행하였다. 제자리비행 자세제어를 위해 날갯짓 비행체가 가지는 시변 비선형 시스템을 선형화하여 설계한 LQR(Linear Quadratic Regulator) 제어기법을 통하여 자세안정화를 적용하였으며 PID 제어기법을 통해 고도제어를 수행하였다. 수치 시뮬레이션을 통해 설계된 모델과 제어기의 성능을 확인하였으며 제자리비행을 위한 자세안정화 및 고도 제어가 안정적으로 수행되는 것을 확인하였다. 또한 날갯짓에 의해 발생하는 주기적인 피칭 모멘트를 주기적인 제어입력을 통해 임계 안정하도록 자세 안정화를 수행하는 것을 확인 하였다.

• 한국항공우주학회지
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• 제49권3호
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• pp.185-195
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• 2021

본 연구의 날갯짓 초소형 비행체는 실제 생명체의 날개를 모방하여, 매우 유연한 재질의 캠버날개를 활용한다. 캠버 날개는 생명체와 유사하게 앞전, 시맥, 박막과 같이 특성이 서로 다른 세가지 재질로 구성되어 있고 다양한 방식으로 구속되어 있다. 날개의 유연성을 활용한 수동 회전(passive rotation) 방식은 앞전과 시맥의 재질이 날갯짓 궤적에 매우 큰 영향을 미치는 요소이기 때문에 적절한 유연성을 갖는 재질의 선정이 필수적이다. 이러한 날개의 재질들과 복잡한 형상을 사실적으로 모델링하여 정밀하게 해석할 수 있는 유체-구조 연성해석 프로그램을 개발하고, 날개의 앞전과 시맥의 탄성 계수의 변화에 따른 공력탄성학 효과를 정밀하게 분석하였다. 결과적으로 재료의 탄성 계수 변화만으로도 날개의 비틀림각 궤적을 적절히 발생시킴으로써 날갯짓 비행체의 추력 및 효율을 크게 증가시킬 수 있음을 보였다.

• Computers and Concrete
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• 제8권2호
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• pp.177-192
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• 2011

This research paper aims at computer based modeling of carbonation induced corrosion under extreme conditions and its experimental verification by incorporating enhanced electrochemical and mass balance equations based on thermo-hygro physics with strong coupling of mass transport and equilibrium in micro-pore structure of carbonated concrete for which the previous research data is limited. In this paper the carbonation induced electrochemical corrosion model is developed and coupled with carbon dioxide transport computational model by the use of a concrete durability computer based model DuCOM developed by our research group at concrete laboratory in the University of Tokyo and its reliability is checked in the light of experiment results of carbonation induced corrosion mass loss obtained in this research. The comparison of model analysis and experiment results shows a fair agreement. The carbonation induced corrosion model computation reasonably predicts the quantitative behavior of corrosion rate for normal air dry relative humidity conditions. The computational model developed also shows fair qualitative corrosion rate simulation and analysis for various pH levels and coupled environmental actions of chloride and carbonation. Detailed verification of the model for the quantitative carbonation induced corrosion rate computation under varying relative conditions, different pH levels and combined effects of carbonation and chloride attack remain as scope for future research.

• Computers and Concrete
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• 제17권3호
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• pp.323-336
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• 2016

Although the self-compacting concrete (SCC) offers several practical and economic benefits and quality improvement in concrete constructions, in comparison with conventionally vibrated concretes confronts with autogenously chemical and drying shrinkage which causes the formation of different cracks and creates different problems in concrete structures. Using different fibers in the mix design and implementation of fibrous concrete, the problem can be solved by connecting cracks and micro cracks together and postponing the propagation of them. In this study an experimental investigation using response surface methodology (RSM) based on full factorial design has been undertaken in order to model and evaluate the polypropylene fiber effect on the fibrous self-compacting concrete and curing time, fiber percentage and fiber amount have been considered as input variables. Compressive strength has been measured and calculated as the output response to achieve a mathematical relationship between input variables. To evaluate the proposed model analysis of variance at a confidence level of 95% has been applied and finally optimum compressive strength predicted. After analyzing the data, it was found that the presented mathematical model is in very good agreement with experimental results. The overall results of the experiments confirm the validity of the proposed model and this model can be used to predict the compressive strength of fibrous self-compacting concrete.

• 제어로봇시스템학회논문지
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• 제8권9호
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• pp.736-746
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• 2002

There has been a great demand for smart actuators in the field of micro-machines. However, the control accuracy of smart actuators, e.g., a shape memory alloy(SMA) and a piezoceramic actuator, is limited due to the inherent hysteresis nonlinearity. The Preisach hysteresis model has emerged as an appropriate model f3r the behavior of those smart actuators. Yet it is still not easy to construct a practical model of hysteresis using the classical Preisach model. Accordingly, in this paper, we propose a new simple method for modeling of the hysteresis nonlinearity of SMA. Using only the proportional relation of the major loop of hysteresis, the proposed method makes the computation of the Preisach model easy. We prove the efficacy of the proposed model through the comparative the experimentation with the classical Preisach model.