Numerical study of abutment scour in cohesive soils

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

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

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.

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)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

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)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

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)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

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.

Chern-Simons theory of knots invariants

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

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

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.

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

Chen UMI 1990 국내박사

Factors Associated With Inappropriate Gestational Weight Gain

Lin, Chen Xi University of California, San Francisco ProQuest D 2023 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Background: Inadequate gestational weight gain (GWG) has become a prevalent health concern, raising risks for both maternal and neonatal health. Numerous studies have explored various factors associated with GWG across individual, familial, and societal domains, yet the findings remain inconclusive.. Method: This study aimed to investigate the factors associated with GWG, with a particular emphasis on the association between social/institutional, interpersonal/family, and maternal factors and excessive gestational weight gain and the relationship between antenatal depression and GWG. A systematic review and meta-analysis approach was cinducted. The Oregon Pregnancy Risk Assessment Monitoring System (PRAMS) for 2016-2021 was utilized for secondary data analysis.Results: The results of the meta-analysis showed that antenatal depression was associated with a higher risk of EGWG (pooled OR = 1.13, 95% CI, 1.04–1.22) and IGWG (pooled OR=1.09, 95% CI, 1.02-1.16). The association between antenatal depression and GWG varied at different stages of pregnancy. No association was found between antenatal depression occurring later in pregnancy and insufficient or excessive GWG. The secondary analysis of PRAMS dataset found no social/institutional and interpersonal/family factors were observed to be associated with EGWG.Having gestational diabetes is associated with a lower risk of EGWG (OR=0.43, 95% CI= 0.22-0.84). No associations were found between any of the depression parameters and GWG, EGWG, or IGWG. Conclusion: It is important to monitor blood sugar levels and pay close attention to depression, especially when it occurs in the first half of pregnancy. To clarify the association between antenatal depression and GWG, further trimester-specific studies are needed.

Integrated Multi-Physics Modeling of Steelmaking Process in Electric ARC Furnace

Chen, Yuchao Purdue University ProQuest Dissertations & Theses 2022 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

The electric arc furnace (EAF) is a critical steelmaking facility that melts the scrap by the heat produced from electrodes and burners. The migration to EAF steelmaking has accelerated in the steel industry over the past decade owing to the consistent growth of the scrap market and the goal of "green" steel production. The EAF production already hit a new high in 2018, contributing to 67% of total short tons of U.S. crude steel produced. The EAF steelmaking process involves dynamic complex multi-physics, in which electric arc plasma and coherent jets coexist resulting in an environment with local high temperature and velocity. Different heat transfer mechanisms are closely coupled and the phase change caused by melting and re-solidification is accompanied by in-bath chemical reactions and freeboard post-combustion, which further creates a complicated gas-liquid-solid three-phase system in the furnace. Therefore, not all conditions and phenomena within the EAF are well-understood. The traditional experimental approach to study the EAF is expensive, dangerous, and labor-intense. Most of the time, direct measurements and observations are impossible due to the high temperature within the furnace. To this fact, the numerical model has aroused great interest worldwide, which can help to gain fundamental insights and improve product quality and production efficiency, greatly benefiting the steel industry. However, due to the complexity of the entire EAF steelmaking process, the relevant computational fluid dynamics (CFD) modeling and investigations of the whole process have not been reported so far.The present study was undertaken with the aim of developing the modeling methodologies and the corresponding comprehensive EAF CFD models to simulate the entire EAF steelmaking process. Two state-of-the-art comprehensive EAF CFD models have been established and validated for both the lab-scale direct current (DC) EAF and the industry-scale alternating current (AC) EAF, which were utilized to understand the physical principles, improve the furnace design, optimize the process, and perform the trouble-shootings.For the lab-scale DC EAF, a direct-coupling methodology was developed for its comprehensive EAF CFD model which includes the solid steel melting model based on the enthalpy-porosity method and the electric arc model (for lab-scale DC arc) based on the Magneto Hydrodynamics (MHD) theory, so that the dynamic simulation of the steel ingot melting by DC arc in the lab-scale furnace can be achieved, which considered the continuous phase changing of solid steel, the ingot surface deformation, and the phase-to-phase interaction. Both stationary DC arc and the arc-solid steel interface heat transfer and force interaction were validated respectively against the experimental data in published literature. For the given lab-scale furnace, the DC arc behavioral characteristics with varying arc lengths generated by the moving electrode were analyzed, and the effects of both the initial arc length and the dynamic electrode movement on the steel ingot melting efficiency were revealed.For the industry-scale AC EAF, an innovative integration methodology was proposed for its comprehensive EAF CFD model, which relies on the stage-by-stage approach to simulate the entire steelmaking process. Six simulators were developed for simulating sub-processes in the industry-scale AC EAF, and five models were developed for the above four simulators, including the scrap melting model, the electric arc model (for industry-scale AC arc), the coherent jet model, the oxidation model, and the slag foaming model, which can be partially integrated according to the mass, energy, and momentum balance.

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

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

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

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.