Numerical study of abutment scour in cohesive soils

Chen, Xingnian Texas A&M University 2008 해외박사(DDOD)

This research is part of the extension of the SRICOS-EFA method for predicting the maximum scour depth history around the bridge abutment. The basic objective is to establish the equation for predicting the maximum bed shear stress around the abutment at the initial condition of scouring. CHEN3D (Computerized Hydraulic ENgineering program for 3D flow) program is utilized to perform numerical simulations and predict bed shear stress before scouring. The Chimera technique incorporated in CHEN3D makes the program capable of simulating all kinds of complex geometry and moving boundary. CHEN3D program has been proven to be an accurate method to predict flow field and boundary shear stress in many fields and used in bridge scour study in cohesive soils for more than ten years. The maximum bed shear stress around abutment in open rectangular channel is studied numerically and the equation is proposed. Reynolds number is the dominant parameter, and the parametric studies have been performed based on the dimensional analysis. The influence of channel contraction ratio, abutment aspect ratio, water depth, abutment shape, and skew angle has been investigated, and the corresponding correction factors have been proposed. The study of the compound channel configuration is conducted further to extend the application of the proposed equation. Numerical simulations of overtopping flow in straight rectangular channel, straight compound channel and channel bend have been conducted. The bridge deck is found to be able to change the flow distribution and the bed shear stress will increase significantly once overtopping. The influence of the channel bend curvature, abutment location in the channel bend, and the abutment shape is also investigated. The corresponding variation of the bed shear stress has been concluded. The scour models, including the erosion rate function, roughness effect, and the turbulence kinetic energy, have been proposed and incorporated into the CHEN3D program. One flume test case in NCHRP 24-15(2) has been simulated to determine the parameters for the roughness and the turbulence kinetic energy. The prediction of the maximum scour depth history with the proposed model is in good agreement with the measurement for most cases. The influence of overtopping flow on the abutment scour development is also studied and the corresponding correction factor is proposed.

회복환경지각이 공연 작품성 평가, 몰입, 만족도 및 충성도에 미치는 영향 연구 : 중국 산수 실경공연을 중심으로

Chen, Xiaohua 경희대학교 대학원 2021 국내박사

중국 도시지역 중산층들이 성장하면서 중국 소비자들의 소비성향이 변화하고 이는 곧 새로운 소비구조로 전환되고 있다. '소비승급(消费升级)'은 최근 중국 시장이 변화하면서 나타나게 된 소비 트렌드를 일컫는 말이다. 이러한 소비구조의 전환은 고가의 상품을 생산하는 새로운 산업을 발흥시키고 중국 전체의 산업구조 전환과 고도화를 가져오는데 이는 소비 고급화 추세와도 일맥상통한다. 이러한 중국의 신소비(新消費) 현상은 문화, 관광, 교육, 오락, 교통, 의료 등 서비스 각 분야에서 나타나고 있다. 1인 가구의 확대, 중산층의 성장, 온·오프라인 융합과 물류, 첨단기술(빅데이터, AI 등)을 접목한 신소매(新零售)가 등장하면서 새로운 소비 수요가 뚜렷이 증가하고 있다. 새로운 소비구조에 따른 서비스 업종별 마케팅 전략과 이를 위한 연구가 필요한 실정이다. 이 중 ‘산수 실경공연예술’은 중국 문화 콘텐츠 산업 가운데에서도 인기가 있는 관광 상품으로 중국의 신소비 현상과 소비 고급화 추세를 잘 설명할 수 있는 관광콘텐츠이다. 해마다 문화 소비가 늘고 있는 만큼, 문화 콘텐츠 시장의 규모 확대와 함께 중국 문화산업 전체의 경쟁력이 눈에 띄게 높아지고 있다. 또한 산수실경이란 개념은 일반 공연과 차별화를 두는 기본 전략 중 하나이자 공연장은 실제 자연의 아름다움을 체험할 수 있는 공간을 가리키기도 한다. 본 연구의 목적은 중국의 문화 콘텐츠 산업 중 인기 있는 산수 실경공연을 통하여 중국의 변화하고 있는 새로운 개념의 관광 소비성향을 분석하는 데 있으며 더 나아가 현지 문화와 자연자원을 활용한 지역 산수 실경공연이 경쟁력을 갖도록 강화하는 데 그 방안을 모색하고자 한다. 연구 목표는 다음과 같다. 산수 실경공연의 공연장소인 자연환경으로부터 관람객이 지각하는 회복환경요인이 어떻게 작품성 평가와 몰입도에 영향을 미치는가, 공연의 작품성 평가와 몰입은 관람객의 만족도와 충성도에 어떤 영향을 끼치는가를 분석한다. 이를 통하여 산수 실경공연이 관광자원으로서 흡인력을 갖추기 위해 이론적 토대를 마련하고 현지에서 실질적인 경쟁력을 갖추는 데 일조하고자 한다. 이러한 목표를 달성하기 위하여 본 연구는 환경심리학의 주의력 회복이론(Kaplan, 1995)에 근거하여 산수 실경관람객을 대상으로 공연장의 자연환경이 공연관람객에게 주는 심리적 회복 효과를 확인하였다. 이에 따라 회복환경 지각이 공연의 품질평가, 관람몰입, 만족도 및 충성도에 주는 영향 또한 분석하였다. 더 나아가 산수 실경공연에서 관람객이 지각한 회복환경요인이 품질평가와 관람몰입에 어떻게 미치는지 그 영향을 실증적으로 규명하기 위하여 온라인 설문조사 회사인 ‘바이두 설문(baidu survey)’을 이용하였다. 연구의 대상은 과거 2년 이내 산수 실경공연 관람한 중국인 경험자로서 377명의 유효 데이터를 수집하였다. 수집된 자료는 빈도 분석, 요인분석, 신뢰도검증, 상관분석, 구조방정식 모델을 이용하여 분석하였다. 분석 결과는 대부분의 연구가설이 채택되었는데, 우선 자연환경으로 회복환경 지각요인인 탈-이상성, 매력성, 조화성, 범위, 환경 적합성 5가지 모두 작품성 평가와 몰입에 긍정적인 영향을 미쳤다. 회복환경 지각요인 중 공연 작품성에 미치는 영향력은 매력성, 환경 적합성, 탈 일상성, 범위, 조화성의 순으로 나타났으며 몰입에 미치는 영향력은 탈 일상성, 환경 적합성, 매력성, 범위, 조화성의 순으로 파악되었다. 그리고 공연 작품성이 관람몰입과 만족도에 유의미한 영향을 미치는 것으로 나타났다. 또한 공연 몰입과 만족도가 충성도에 유의미한 영향을 미치지만 공연 작품성은 충성도에 직접적인 영향이 없는 것으로 나타났다. 위 연구의 측정척도의 신뢰도와 타당성이 모두 검증된바, 이 연구를 토대로 향후 관련 후속 연구에까지 활용될 수 있다. 실무적으로도 이 연구의 유용성이 증명되었는데, 산수 실경공연 관람객들은 하나의 회복환경으로서 주변 자연환경을 인식함으로써 그 가치를 인정하였다. 몸과 마음을 치유하는 공간으로서의 자연은 그 공간의 확장이 필요한 실정이다. 산수 실경공연은 기획자의 입장에서 어떻게 자연환경을 활용해야 작품성과 관람객 몰입도가 좋은지, 또는 공연 마케터가 어떻게 상품을 홍보해야 하는지 세부적인 제언을 첨언하였다. 예컨대, 공연장 선정에 있어서 주변 자연환경의 각 요소를 충분히 고려하여 콘텐츠로 만들었는지를 살펴봐야 한다. 마지막으로 향후 연구를 위하여 몇 가지 제안을 하였다. 첫째, 대부분의 대형 산수 실경공연은 외국인 관람객이 다수를 차지한다. 국가별, 문화권별 자연환경에 대해 어떤 다른 인식을 하는지 후속 연구가 필요하다. 둘째, 인공 조경된 실내공연장과 야외 자연 산수를 배경으로 하는 산수 실경공연을 비교 분석하면서 관람객의 회복환경 지각이 차이가 있는지 검증하는 연구가 필요하다. 셋째, 산수 실경공연은 급성장하는 신개념 관광 상품이기 때문에 중요한 새로운 연구 분야가 될 것이다. 지금 공연의 횟수와 관광시장 규모에 비해 관련 주제 연구가 크게 뒤떨어져 있다. 이 연구는 주의력 회복이론을 바탕으로 공연 작품성, 관광몰입, 만족도와 충성도를 연구하였는데, 향후 관련 연구에서는 그 밖에 다른 연구 변수 (예를 들어, 관여도, 긍정적인 감정 등) 을 보완하여 이론적 틀을 더욱 풍부하게 하는 것으로 관람객 행동과 패턴을 이해할 필요가 있다. The effects of performing arts audiences' perception of environmental restorativeness based on the attention restoration theory on the quality evaluation, perceived flow, satisfaction, and loyalty -Focusing on the natural landscape performance in China- by Xiaohua, Chen Doctor of Philosophy in Tourism Graduate School of Kyung Hee University Advised by Dr. Gye Hee, Lee In China, One of the significant issues in the consumer market in recent years is the "consumption upgrade," which refers to the trend of consumer luxury. It is necessary to pay attention to the marketing strategy for expanding the market to increase the service field's consumption, such as culture, tourism, education, entertainment, transportation, and medical services. Natural landscape performance (NLP) in the cultural contents industry is emerging as a popular tourism product. This study analyzed how the audiences' perceived environmental restorativeness of the natural environment affected the performing arts quality evaluation and perceived flow. And also how the quality evaluation and perceived flow affect satisfaction and loyalty. The ultimate goal was to provide a theoretical basis for creating performing arts resources' attractiveness. This research confirmed the psychological restoration effect of the performing arts place's natural environment through a survey on the NLP visitors basing on the attention restoration theory suggested by Kaplan (1995). An online survey was conducted. Three hundred seventy-seven valid data have been collected by setting up the subjects who have experienced the performances during the past two years. The collected data were analyzed using frequency analysis, factor analysis, reliability analysis, correlation analysis, and structural equation modeling. Depending on the results, most of the research hypotheses in this study were supported. First, as a natural environment, all five dimensions of perceived environmental restorativeness (being away, fascination, coherence, scope, compatibility) positively affected the performing arts quality evaluation and perceived flow. And the performing arts quality had a significant influence on the perceived flow and satisfaction. Besides, perceived flow and satisfaction significantly directly impacted destination loyalty, while performing arts quality indirectly affected destination loyalty. Also, there was a partial mediation effect of perceived flow between the performing arts quality and satisfaction. There was a full mediation effect of perceived flow between the performing arts quality and loyalty. Perceived flow included both human sensory experience and cognitive experience, allowed people to focus on the joy and satisfaction of what they are doing. Therefore, the perceived flow of the performing arts could be an essential research variable in understanding audiences' behaviors. Based on the above research results, the surrounding natural environment has proven its worth as a recovery environment for the audiences of the natural landscape performance. Since both the reliability and validity of the research-related measurement scale have been verified, these measurement scales can be used for future research. And this research presented a detailed suggestion to the performance planner about how to use the natural environment to create a performance with high artistic and audience engagement and promote the products for the performance marketers. In other words, it is meaningful to contribute to sustainable development and to enhance the competitiveness of performing arts. This research also made some suggestions for future studies. Firstly, since there are always many foreign visitors to see NLPs, people from different cultures have different cultural backgrounds. So it is also necessary to study whether they have different perceived environmental restorativeness about the same natural environment. Secondly, it will be interesting to examine whether there are some differences in the visitors' environment perception by comparing and analyzing two types of indoor theater performance and natural landscape performance. Thirdly, because NLP is a new concept tourism product, it will become an important new research field. Yet, there has not been much empirical research on related topics. So it is necessary to understand visitors' behavior by adding other constructive research concepts related to these performing arts to enrich the theoretical framework in future research. For example, involvement, positive emotions or consumer engagement.

Intrusion Response via Graph-Based Low-Level System Event Analysis

Chen, Xutong Northwestern University ProQuest Dissertations & T 2021 해외박사(DDOD)

Studies of Enhanced Instructional Modalities and Biosignals On User Performance in Virtual Reality Systems

Chen, Ken North Carolina State University ProQuest Dissertat 2022 해외박사(DDOD)

Virtual reality (VR) is a computer-generated environment that can provide simulated experience of the real world through varied channels of sensory feedback. Visual feedback is the most deployed display in VR systems, which focuses on delivering information and stimuli to the visual sensory channel. In specific, current VR technology can display 3-D instructors and agents to guide users to perform various tasks. While conventional studies on 2-D instructors in desktop applications revealed that users tended to trust the instructors that exhibited similarities with them on appearances and personality, studies on 3-D instructors in VR applications were lacking. For haptic feedback, the interaction with VR objects is usually achieved through controllers and joysticks, which does not require forceful exertions that are necessary in the real world. Therefore, users may perceive less physical fidelity when interacting with the VR objects, which can impede the skill transfer from VR training to the real world. Previous study on pseudo-haptic brought up the concept of “virtual exertions” and used electromyography (EMG) as the haptic cue for VR interactions in a simple virtual dumbbell lifting task. It is worth investigating the idea of virtual exertions in more complicated movements that involved muscles across the full body.The research purpose of this dissertation included: (1) studying the utility of 3-D virtual instructors in VR systems where different ways of designing 3-D humanoid instructors were examined and compared; (2) examining the concept of virtual exertions in a simulated patient transfer task using multi-binary criteria; and (3) applying the methods of virtual exertions in manual material handling (MMH) tasks and exploring new approaches for establishing virtual exertions threshold.Two humanoid instructors were designed and examined in two extended reality (XR) applications. A 3-D humanoid model was developed and implemented in a virtual reality exercise program to guide participants to perform pick and place movements; A point-cloud generated humanoid instructor was built in an augmented reality (AR) posture training platform to demonstrate common manual material handling postures. Both humanoid instructors achieved their instructional functions as expected while demonstrated different characteristics: 3-D model based virtual instructor was more flexible and could be easily animated to convey dynamic movement information to the participants; point cloud generated virtual instructor shared more similarities with real humans on appearances but was difficult to be edited and animated.A simulated patient transfer task was studied in a laboratory setting with EMG sensors attached to participants’ muscles across the whole body. Principal component analysis was utilized to select the major contributing muscles of the task. A virtual patient transfer task was conducted targeting the selected major muscles, participants needed to contract all muscles to reach the respective calibration threshold obtained during the physical transfer tasks. The results showed that participants could only finish the tasks with adjusting factors that scaled down the lifting thresholds, which suggested that the multi-binary criterion was difficult to achieve.The third study used psychophysical methods to evaluate MMH tasks, examined the potential of classifying MMH movements using EMG signal, and finally designed a virtual squat lifting task using regression-based criterion. The results showed that the program could evoke comparable sense of perceived exertions in the virtual lifting task against the physical lifting task.

Chern-Simons theory of knots invariants

Chen, Lin University of California, Los Angeles 2009 해외박사(DDOD)

The (type-A) Chern-Simons partition function of a link (in three sphere) is a generating function of all of its colored HOMFLY polynomials. Physicists (Labastida-Marino-Ooguri-Vafa) proposed a conjectural description of this partition function in terms of the integrality of its reformulated invariant. This conjecture was later proved by Kefeng Liu and Pan Peng. There is also a type-B Chern-Simons theory, which is the Kauffman analog of the LMOV conjecture, studied by Bouchard-Florea-Marino and also Chen-Chen-Reshetikhin. In this thesis, we study links in solid torus and their Chern-Simons partition functions. We prove that most of the structural results of links in three sphere can be generalized to links in solid torus except the integrality of the reformulated invariants, which fails for trivial reasons. From the string theory point of view, the type-A Chern-Simons theory computes conjecturally the Gromov-Witten invariants of Calabi-Yau manifolds. A typical example is the theory of topological vertex. To establish such a correspondence, the key idea is to show that both the Chern-Simons partition function and the Gromov-Witten partition function satisfy the same Cut-Join equation. In this work, we derive a Cut-Join equation for type-B Chern-Simons partition function. Finally, we give a brief survey of Gromov-Witten theory and the Virasoro conjecture.

Seismic Performance Evaluation of Weak-axis Column-tree Steel Moment Connections with Various Reduced Beam Section

Chen, Liuyi 忠南大學校 大學院 2015 국내석사

철골모멘트골조는 내진설계에 가장 많이 사용되는 시스템이다. 철골 모멘트골조 시스템에 대한 내진성능평가 및 내진설계와 관련한 많은 연구는 현재까지도 진행되고 있는 중이다. 그러나 1994년 노스리지 지진 이후, 지진에 대해 우수한 연성능력을 가지고 있는 철골모멘트골조에서 접합부에 예상치 못한 취성파괴가 발생되어 강구조학계에 커다란 충격을 주었다. 이와 관련된 문제를 해결하기 위하여 새로운 접합부 개발의 필요성을 인식하고 철골모멘트 접합부 인증접합부를 개발하였다. 미국에서는 철골모멘트골조의 경우 강축 방향에만 모멘트접합을 사용하고 약축 방향에는 핀접합을 사용하고 있기 때문이다. 하지만 국내의 경우는 철골모멘트골조를 보-기둥 접합을 강축 방향뿐만 아니라 약축 방향에도 적용하고 있는데, 약축 방향 칼럼-트리(column-tree) 형식 접합부의 경우 내진성능 확보 여부가 명확하게 규명되지 않은 상태에서 실무적으로 적용되고 있는 상황이며, 철골모멘트골조 약축 방향 칼럼-트리(column-tree) 형식접합부의 내진성능 평가와 관련한 연구가 시급 한 실정이다. 강축 방향 접합에 대해 설계 할 때 유의할 점은 패널존(panel zone) 및 보-기둥 접합부의 스터브 보에서의 소성회전능력에 대하여 고려해야 한다. 특히 패널존 강도가 모멘트 접합부의 내진성능에 영향을 충분히 규명되어 있다. 하지만 약축 방향 모멘트 접합부에서는 패널존의 강도 및 강성이 높기 때문에 연성능력을 충분히 발휘할 수 없어서 보의 소성회전능력을 감소시킨다. 보와 보의 이음부에서 소성변형을 충분히 발휘하기 위하여 RBS-CT (RBS 개념을 도입한 약축 방향 칼럼-트리 형식)와 CTY-CT (보 이음부에서 플랜지의 두께를 감소시킨 칼럼-트리 형식) 대해 실물대(full scale) 실험을 통한 내진성능을 연구를 수행했고 내진설계에 적용할 수 있는 기초 자료를 제공하는 목적으로 한다. 약축 방향 칼럼-트리 CTY형식 모멘트 접합부의 보 이음부에서 플랜지의 두께를 감소시켜 소성힌지의 위치를 이음부에 둠으로써 내진설계에서 중요한 성능인 연성능력을 확보하고자 한다. FEMA 인증접합 상세 중 RBS접합부는 보 플랜지 일부를 절취하여 ‘fuses’와 같은 기능을 하도록 하여 취성파괴를 방지하고 뛰어난 연성능력을 확보하는 접합부이다. 실험을 통해 평가한 4가지의 실험체는특수모멘트골조의 요구사항을 만족하였다. 칼럼-트리 형식 접합부를 갖는 CTY900 실험체는 소성회전각 4%에서 보 플랜지에 좌굴이 발생하며 완만한 강도저하 를 보여주어 특수모멘트골조의 요구사항을 만족하는 내진성능을 충분히 보여주었다. CTY600 실험체는 플랜지에 좌굴이 분명히 보이지 않았지만 보 이음부에서 플랜지의 두께를 감소시켜 소성힌지의 위치를 이음부에 둠으로써 내진설계에서 중요한 성능인 연성능력을 발휘한 것으로 사료된다. RBS 실험체와 DRBS 실험체는 소성회전각 3%에 보 플랜지에 좌굴이 발생하였으며 항복 이후 연성능력이 더 확보되는 것을 알 수 있다. 모든 실험체에서 볼트 미끄러짐 현상이 발생되었으며 에너지 소산능력에 영향을 미치는지에 대한 실험적, 해석적 연구가 필요할 것으로 사료된다.

Novel Approaches to Creating Synthetic Data from Multivariate Survey Data for Statistical Disclosure Control

Chen, Allshine ProQuest Dissertations & Theses The University of 2020 해외박사(DDOD)

Statistical disclosure is the unauthorized identification of individuals, organizations, or key items through the release of individual-level data or summary statistics. The risks that follow disclosure may cause significant damage when the information is used for malicious purposes, resulting in monetary, emotional, or reputational harm. Data syntheses of partially or fully-synthetic datasets can help guard against disclosure risks when sharing or releasing data. In this dissertation, we propose two new methods to guard against statistical disclosure through the creation of fully-synthetic data to release in place of the originals. Our first proposed fully-synthetic data framework combines multiple-imputation with chained multivariate adaptive regression splines and the addition of random residuals to create multivariate continuous data. We compare our proposed method to the existing multiple-imputation with approximate Bayesian bootstrap approach and test them using two simulated datasets and a publicly-available, 2012-2013 National Youth Fitness Survey dataset in terms of data utility and risk of disclosure. Our first method was shown to have better utility than the approximate Bayesian bootstrap approach while controlling the risk at an acceptable level. In human-population microdata, categorical data also play an important role in characterizing the population but are also instrumental to breaches in privacy or confidential, resulting in statistical disclosure. Our second proposed method involves using chi-square automatic interaction detection modeling towards the creation of fully-synthetic categorical data. In order to test our proposed method, we use simulated data with and without variable-interactions and 2017-2018 NHANES demographics data to compare our approach to logistic regression, classification and regression tree, and random forests using data utility and disclosure risk metrics. In conclusion, our second method provides comparable data utility and risk under the scenario of no variable-interaction while exhibits optimal results when variable-interaction are extant in the data.

Classification of Gravitational Instantons with Faster Than Quadratic Curvature Decay

Chen, Gao State University of New York at Stony Brook ProQue 2017 해외박사(DDOD)

In this dissertation, a gravitational instanton is defined to be a complete non-compact hyperkahler 4-manifold with curvature decaying fast enough at infinity. Many examples of gravitational instantons have been constructed. The main result of this thesis is the proof that there are no more examples.

Affiliation with Aggressive Peer Groups, Autonomy, and Adjustment in Chinese Adolescents

Chen, Lingjun ProQuest Dissertations & Theses University of Penn 2019 해외박사(DDOD)

Affiliating with an aggressive peer group has various negative implications for individual development and adjustment, and adolescents are particularly vulnerable to negative peer influence. It is crucial to identify factors that serve to protect adolescents who are members of aggressive peer groups. Autonomy is an important individual characteristic worth exploration because it captures adolescents' differences in navigating their group experiences and it is closely related to their developmental tasks during this period. Moreover, autonomy has become increasingly important in Chinese society in recent years during the rapid social change. The purpose of the present study was to examine the relations between group-level aggression and social, behavioral, school, and psychological adjustment, as well as the moderating role of individual autonomy in shaping these associations in a sample of Chinese adolescents.Participants included 1742 students (821 boys) in Grade 7 (mean age = 13.40 years, SD = .58) and Grade 10 (mean age = 16.32 years, SD = .54) from six regular public schools in China. Data were collected from multiple sources. The participants completed a measure of peer group networks and self-report measures of autonomy, depression, loneliness, and problem behaviors. In addition, peer nominations and teacher rating were used to assess adolescents' social competence, learning problems, aggression, and externalizing problems. Information on academic achievement was obtained from school records. The results showed that group-level aggression was positively related to maladjustment in social, behavioral, and academic domains and that the positive relation of group-level aggression and deviancy and the negative relation of group-level aggression and academic functioning were moderated by individual autonomy. Group-level aggression was associated with deviancy and academic functioning to a lesser extent among adolescents who were higher on autonomy. These results have implications for parents, educators, and professionals who aim to help adolescents affiliated with aggressive peer groups.

Japanese colonialism in Korea and Formosa : a comparison of its effects upon development of nationalism

Chen UMI 1990 국내박사