• 한국기계가공학회지
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• 제20권8호
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• pp.93-98
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• 2021

The complex effects of the machining parameters make it is difficult to control and predict surface roughness. The theoretical surface roughness observed during mechanical machining with a round tool is determined by the tool radius and pitch. However, it was revealed that other parameters, such as the depth of cut and cutting speed, also affect surface roughness. This study adapted the Taguchi method, which can analyze the effects of cutting parameters quantitatively with an efficient number of experiments, to optimize the parameters for better surface roughness. Experiments were designed based on an orthogonal array, and the quantitative effects on the surface roughness were analyzed using the S/N ratio. The surface roughness was affected by all parameters, especially the tool radius. The optimum cutting parameter values obtained in this study showed better surface roughness than the other combinations of the parameters.

• Wind and Structures
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• 제32권1호
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• pp.55-69
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• 2021

Ultrapure ferritic stainless steel provides a new generation of long-span metal roof systems with continuous welding technology, which exhibits many unknown behaviors during wind excitation. This study focuses on the wind-resistant capacity of a new continuous welding stainless steel roof (CWSSR) system. Full-scale testing on the welding joints and the CWSSR system is performed under uniaxial tension and static ultimate wind uplift loadings, respectively. A finite element model is developed with mesh refinement optimization and is further validated with the testing results, which provides a reliable way of investigating the parameter effect on the wind-induced structural responses, namely, the width and thickness of the roof sheeting and welding height. Research results show that the CWSSR system has predominant wind-resistant performance and can bear an ultimate wind uplift loading of 10.4 kPa without observable failures. The welding joints achieve equivalent mechanical behaviors as those of base material is produced with the current of 65 A. Independent structural responses can be found for the roof sheeting of the CWSSR system, and the maximum displacement appears at the middle of the roof sheeting, while the maximum stress appears at the connection supports between the roof sheeting with a significant stress concentration effect. The responses of the CWSSR system are greatly influenced by the width and thickness of the roof sheeting but are less influenced by the welding height.

• 한국정보통신학회논문지
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• 제24권3호
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• pp.398-404
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• 2020

본 논문에서는 변형 경사하강검색법을 이용한 새로운 나선 직교진폭변조 신호성상도와 이를 위한 이진사상규칙을 제시한다. 기존 방법과는 달리 새로운 검색법은 반복설계를 위한 파라미터로 최대 반복 횟수와 함께 성상도 최적화 알고리즘을 사용하여 위상잡음에 더욱 강인한 나선 직교진폭변조 성상도를 생성한다. 또한, 제시된 이진사상기법은 신호성상도에서 동일한 경계를 공유하는 필드 수를 조정함으로써 성상도의 평균 해밍거리를 크게 감소시키는 것으로 나타났다. 그 결과, 제안된 나선 직교진폭변조는 매우 심한 수준의 위상잡음 환경에서도 기존 성상도에 비하여 훨씬 향상된 심볼오류성능을 가지는 것으로 확인되었다. 따라서 제안된 나선 직교진폭변조는 위상잡음의 영향이 크게 나타나는 코히어런트 광통신시스템과 직교 주파수분할다중화 시스템에 유용한 변조방법인 것으로 판단된다.

• 융합정보논문지
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• 제11권2호
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• pp.124-129
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• 2021

본 논문에서는 절대 안정도를 보장하는 최적의 제어기 설계에 대해 제안하였다. 논문의 적용 순서는 지연시간의 포함여부를 판단하고, 지연시간이 포함되었을 경우 Pade 근사법을 통해서 지연시간을 근사화 한다. 그 다음 공정모델과 제어기 전달함수에 대한 개루프 전달함수를 구하며, Routh-Hurwitz 판별법에 의해서 절대 안정도 구간을 계산한다. 마지막 단계에서는 앞 단계에서 구한 구간을 활용하여 유전자 알고리즘으로 최적의 PID 제어파라미터 값을 구한다. 그 결과 제안 된 방법은 안정성이 보장되며, 최적의 제어기를 설계하여 기존의 방법보다 성능 지표에서 우월함을 확인하였다. 향후 지연시간에 대한 보상방법이 연구된다면 더욱 좋은 성능지표를 얻을 것으로 판단된다.

• 한국수자원학회논문집
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• 제54권8호
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• pp.617-628
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• 2021

가뭄은 심각한 사회적 경제적 손실을 초래하는 주요 자연재해이다. 지역 가뭄 예측은 가뭄 대비에 중요한 정보를 제공할 수 있다. 본 연구에서는 한반도 동남부 부산-울산-경남 지역에서 1981년부터 2020년까지 10개 관측소의 과거 가뭄지수 및 기상 관측자료를 사용하여 가뭄을 예측하는 새로운 기계학습모델을 제안한다. 베이지안 최적화기법을 이용하여 하이퍼 파라미터가 튜닝된 Random Forest, XGBoost, Light GBM 모델을 구축하여 1개월 뒤의 6개월 시간 척도의 증발 수요 가뭄지수를 예측하였다. 단일 지점별 모델과 지역 모델을 각각 구성하여 모델 성능을 비교하였다. 또한 지역 모델을 기반으로 개별 지점의 자료에 대해 미세조정된 모델을 구성하여 모델 성능을 높일 가능성을 살펴보았다.

• International Journal of Computer Science & Network Security
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• 제22권10호
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• pp.246-256
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• 2022

Recently, parents and teachers consider physical education as a minor subject for students in elementary and secondary schools. Physical education performance has become increasingly significant as parents and schools pay more attention to physical schooling. The sports mining with distribution analysis model considers different factors, including the games, comments, conversations, and connection made on numerous sports interests. Using different machine learning/deep learning approach, children's athletic and academic interests can be tracked over the course of their academic lives. There have been a number of studies that have focused on predicting the success of students in higher education. Sports interest prediction research at the secondary level is uncommon, but the secondary level is often used as a benchmark to describe students' educational development at higher levels. An Automated Student Interest Prediction on Sports Mining using DL Based Bi-directional Long Short-Term Memory model (BiLSTM) is presented in this article. Pre-processing of data, interest classification, and parameter tweaking are all the essential operations of the proposed model. Initially, data augmentation is used to expand the dataset's size. Secondly, a BiLSTM model is used to predict and classify user interests. Adagrad optimizer is employed for hyperparameter optimization. In order to test the model's performance, a dataset is used and the results are analysed using precision, recall, accuracy and F-measure. The proposed model achieved 95% accuracy on 400^th instances, where the existing techniques achieved 93.20% accuracy for the same. The proposed model achieved 95% of accuracy and precision for 60%-40% data, where the existing models achieved 93% for accuracy and precision.

• 대한조선학회논문집
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• 제59권2호
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• pp.96-108
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• 2022

In this paper, we propose a systematic hull form variation technique which automatically satisfies the displacement constraint and guarantees a high level of fairness. This method is possible through multiple parameter correction curves. The present method is to improve the hull form variation method based on parametric modification function and consists of two sub-categories: SAC variation and section lines modification. For SAC variation, the utilization of two B-Spline curves satisfying GC¹ condition led to the satisfaction of displacement constraint and high level of fairness at the same time. Section lines modification methods involves in using two fuctions: the first is the waterplane modification function combining two cubic splines. the other function is the sectional area modification function consisting of 2nd order polynomial over the DLWL(Design Load Waterline) and 3rd order polynomial below the DLWL, This function enables not only the fundamental U-V section shape variation but also systematically modified section lines. The present method is expected to be more useful in the hull form optimization process using CFD compared to the existing method.

• 한국정보전자통신기술학회논문지
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• 제15권5호
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• pp.380-386
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• 2022

본 논문은 적대적 생성 신경망 기법의 하나인 Pix2Pix를 활용하여 컬러색상을 입히는 경우 학습된 이미지의 빛 반사 정도에 따라 예측결과가 손상되어 나오는 부분에 집중하여 Pix2Pix 모델 적용 전 이미지 전처리 프로세스 및 모델 최적화를 위한 파라미터 테이블을 구성한다. 기존 논문에 나온 Pix2Pix 모델을 활용하여 실생활에 적용하기 위해서는 해상도에 대한 확장성을 고려해야한다. 학습 및 예측결과 이미지 해상도를 키우기 위해서는 동시에 모델의 커널 사이즈 등을 같이 맞춰주는 부분을 수정해줘야 하는데 이부분은 파라미터로 튜닝 가능하도록 설계했다. 또한 본 논문에서는 예측결과가 빛 반사에 의해 손상된 부분만 별도 처리하는 로직을 같이 구성하여 예측결과를 왜곡시키지 않는 전처리 로직을 구성하였다. 따라서 활용성을 개선하기 위하여 Pix2Pix 모델의 학습이미지에 공통적인 빛반사 튜닝 필터를 적용하는 부분과 파라미터 구성부분을 추가하여 모델 정확도를 개선하였다.

• Structural Engineering and Mechanics
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• 제81권3호
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• pp.293-303
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• 2022

As infrastructure ages and traffic load increases, serious public concerns have arisen for the well-being of bridges. The current health monitoring practice focuses on large-scale bridges rather than short span bridges. However, it is critical that more attention should be given to these behind-the-scene bridges. The relevant information about the construction methods and as-built properties are most likely missing. Additionally, since the condition of a bridge has unavoidably changed during service, due to weathering and deterioration, the material properties and boundary conditions would also have changed since its construction. Therefore, it is not appropriate to continue using the design values of the bridge parameters when undertaking any analysis to evaluate bridge performance. It is imperative to update the model, using finite element (FE) analysis to reflect the current structural condition. In this study, a FE model is established to simulate a concrete culvert bridge in New South Wales, Australia. That model, however, contains a number of parameter uncertainties that would compromise the accuracy of analytical results. The model is therefore updated with a neural network (NN) optimisation algorithm incorporating Monte Carlo (MC) simulation to minimise the uncertainties in parameters. The modal frequency and strain responses produced by the updated FE model are compared with the frequency and strain values on-site measured by sensors. The outcome indicates that the NN model updating incorporating MC simulation is a feasible and robust optimisation method for updating numerical models so as to minimise the difference between numerical models and their real-world counterparts.

• Geomechanics and Engineering
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• 제27권5호
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• pp.527-535
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• 2021

The creep characteristics of rock is of great significance for the study of long-term stability of engineering, so it is necessary to carry out indoor creep test and creep model of rock. First of all, in different water-bearing state and different positive pressure conditions, the granite is graded loaded to conduct indoor shear creep test. Through the test, the shear creep characteristics of granite are obtained. According to the test results, the stress-strain isochronous curve is obtained, and then the long-term strength of granite under different conditions is determined. Then, the fractional-order calculus software element is introduced, and it is connected in series with the spring element and the nonlinear viscoplastic body considering the creep acceleration start time to form a nonlinear viscoplastic creep model with fewer elements and fewer parameters. Finally, based on the shear creep test data of granite, using the nonlinear curve fitting of Origin software and Levenberg-Marquardt optimization algorithm, the parameter fitting and comparative analysis of the nonlinear creep model are carried out. The results show that the test data and the model curve have a high degree of fitting, which further explains the rationality and applicability of the established nonlinear visco-elastoplastic creep model. The research in this paper can provide certain reference significance and reference value for the study of nonlinear creep model of rock in the future.