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Title: Frictional behavior of bronze-graphite composite as sliding element in the base isolation system
Creator: You, Da
Date: 2021
Description: There are many calamities around the world, one of the most dangerous disasters is earthquake which threatens the safety of people and the...
Show moreThere are many calamities around the world, one of the most dangerous disasters is earthquake which threatens the safety of people and the structures. Almost every year, there are a lot of property losses and casualties caused by earthquakes. To mitigate the bad effect of the earthquake, the base isolation system was proposed by previous researchers. With the contribution of many researchers, several seismic isolations have been developed. Until now, many structures have installed seismic isolations to resist seismic energy and vibration. The seismic isolation system works well during the earthquake period, and it does help reduce the casualty and property loss induced by earthquakes. There are two main types of bearings used in the seismic isolation system. One is the elastomeric bearings and the other is the sliding bearings. The mechanics of the seismic isolation system preventing the influence of the earthquake and reducing the horizontal acceleration of the structure is to elongate the natural frequency of structure. As for the sliding bearings, the simplest way to increase the period is to reduce the friction coefficient of the two sliding elements. In conventional, two stainless steel plates are commonly used in the pure flat sliding bearing. This study tries to use bronze-graphite composite in the sliding bearing to decrease the friction coefficient.Consequently, the testing results suggest that the bronze-graphite composite has a lower friction coefficient, especially the graphite acting as a lubricant. The friction coefficient of the bronze-graphite plate is in the range of 0.12 to 0.23 under the load of 160 kg - 800kg. With a higher ratio of graphite to bronze at the sliding surface, the effect of reducing the friction coefficient more obviously. And the friction coefficient changes during the increasing loads period. It decreases at the beginning, and starts to increase at a certain load applied on it. Finally, it is reasonable to bronze-graphite composite in a low rise structure which has a relatively low weight. Because the load applied in the test is not high enough, the consequence may not work for high or heavy structure. Taken together, the use of new material with similar properties in the seismic isolation system can help improve the performance of resisting the earthquake. It should be accounted for further research in this field.
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Title: HIGH-THROUGHPUT FIRST-PRINCIPLES STUDY ON HIGH-ENTROPY ALLOYS
Creator: Zhang, Jie
Date: 2021
Description: This research thesis discusses the current ecosystem surrounding a new type of alloy: high entropy alloys (HEA) or multi-element crystalline...
Show moreThis research thesis discusses the current ecosystem surrounding a new type of alloy: high entropy alloys (HEA) or multi-element crystalline materials and lays out the high-throughput first-principles calculation as a valuable approach to study these materials. The density function theory (DFT) from computational material science prospect was implemented to investigate the HEAs. Using EMTO-CPA algorithm, high-throughput DFT calculations were conducted. A total of 1958 HEA systems including equimolar and non-equimolar systems were studied with respect to the varies properties, including lattice parameters, bulk moduli, elastic constants, and elastic anisotropy. The first-principles HEA dataset was employed as the training set for the DeepSets a machine learning model. DeepSets, in combination with EMTO-CPA high-throughput calculation, successfully predicted the mechanical properties of specific HEA composition. This paves a promising new path of designing, investigating, and validating the HEA system compared to the time-consuming conventional HEA design method. The doping effect of Vanadium (V) and Titanium (Ti) to NbMoTaW HEA, as well as V or Ti as the fifth element with different molar fraction to the NbMoTaW HEA system, were studied. The phase stability of the new systems was discussed and concluded that all proposed systems tend to form single-phase solid solution. Though the addiction of V only slightly enhances the system’s ductility, the addition of Ti not only enhances the quinary system NbMoTaWTiX (X =0.25, 0.5,0.75, 1.0) ductility, but enables the system to be closer to fully isotropic.
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Title: ASSET PRICING AND RETURN REVERSAL IN KOREAN AND JAPANESE STOCK MARKET
Creator: Kim, Pil Joon
Date: 2020
Description: The stock market in Asia achieved a rapid development in the 1980’s, mainly in Japan and Korea. In particular, stock market in Japan and Korea...
Show moreThe stock market in Asia achieved a rapid development in the 1980’s, mainly in Japan and Korea. In particular, stock market in Japan and Korea is deeply related to the US stock market. However, in 1997, a major financial crisis hit Asia, and IMF decided to provide financial support to Korea. In addition, in 2011, a nuclear accident at the Fukushima Daiichi Nuclear Power Plant was the most severe nuclear accident since the 26 April 1986 Chernobyl disaster. Nevertheless, the Japanese and Korean markets experienced stable growths. Were Japanese and Korean stock markets truly stable and efficient? This study empirically studied market efficiency through stock market return reversal in the Japanese and Korean stock market and the characteristics of these two stock markets were compared and analyzed.Significant return reversal phenomenon was observed as a result of validating return reversal phenomenon against the stock markets in Korea and Japan. Furthermore, return reversal level differed based on the abnormal (excess) return calculation method used in the test model. Return reversal phenomenon can be found more clearly in loser portfolio than in winner portfolio in general. In particular, when the abnormal (excess) return was calculated using CAPM model, different result from existing research was observed. I also found that the Fama-French 3 factor model can compensate for the CAPM problem. I concluded that this phenomenon is observed in Korea and Japan stock market supporting DeBondt & Talher that CAPM misleads theoretical stock price return reversal and Brown and Warner (1980), who found that sophisticated CAPM do not perform better than simple model like market adjusted returns model. This is interpreted that the stock markets in Korea and Japan are not efficient and continue to have unstable factors. These findings provide full of suggestions to further research. CAPM is to explain market equilibrium price as a one-factor model, the Fama-French 3 factor model is a multi-factor model, and it can be said to more accurately describe the equilibrium price by adding size and gross value factor in describing the market equilibrium price. These results show that if Fama-French 3 factor model uses, it can solve the problem when using CAPM.The January effect is found significantly in both the Korean and Japanese markets. In the Korean stock market, the short-term seasonal reversal effect is more pronounced than in the long-term, and in the Japanese stock market, the long-term seasonal reversal effect is more pronounced than in the short-term.
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Title: MARKOV SWITCHING MODELS OF POPULAR FOREIGN EXCHANGE CARRY TRADE STRATEGIES
Creator: Miller, Larissa J.
Date: 2016, 2016-07
Description: The nature of the carry trade produces periods of steady profitability and periods of extreme terror. The 1980s proved to be a particularly...
Show moreThe nature of the carry trade produces periods of steady profitability and periods of extreme terror. The 1980s proved to be a particularly profitable time period. However, during market crashes in the either equity or bond market, the carry trade is marked with short periods of substantial losses (Menkhoff, Saro, Schmeling, Scrimpf 2012). The global financial crisis of 2007 – 2008 was associated with large losses to carry trades. History repeatedly suggests these two bull and bear states in the economic environment (Fabozzi, Francis 1977). An additional state of market neutrality or stability could also be considered. The purpose of this dissertation is to develop a model of the carry trade with multiple states using the Markov switching methodology. To accomplish this, we use two different popular carry trade strategies: (a) logistic regression and (b) mean-variance optimization. As a benchmark, we include an equally weighted portfolio of long positions in foreign currencies against the dollar. We develop a single state model as well as a normal mixture model for each of the two carry trade strategies. The mixture models assume a static probability of the economy being in either state. However, the financial markets are not static. Applying a Markov chain allows us to build a dynamic model, which allows for new information to determine the probability of the next state. We applied a Markov chain to determine the probability of the current state and the next state to improve trading results. We found the application of a Markov chain did not improve trading performance. The portfolio consists of 12 different currencies including both mature and emerging markets. The training period for determining the weights is 1998 through 2002. Using daily data from 2002 through 2015, we evaluate the performance of each strategy using cumulative returns. These results demonstrate the periods of profitability followed by short periods of terror. Next we evaluate the performance of each strategy with an applied mixture-model. The mixture-model improves the results of each strategy. Applying a Markov chain allows for better determination of both the bear and bull states. We use only the two state environment as the three state environment was unstable.
Ph.D. in Management Science, July 2016
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Title: FLOW IN PARTIALLY CONSTRICTED PLANAR CHANNELS - ORIGINS OF VORTEX SHEDDING AND GLOBAL STABILITY OF NAVIER{STOKES SOLUTIONS
Creator: Boghosian, Michael Edward
Date: 2011-04-17, 2011-05
Description: Vortex shedding is a well-known unsteady uid-dynamic phenomenon occur- ring in a variety of ows in nature including stenosed blood vessels. We...
Show moreVortex shedding is a well-known unsteady uid-dynamic phenomenon occur- ring in a variety of ows in nature including stenosed blood vessels. We nd that current hypotheses regarding the origin of vortex shedding do not apply for the inter- nal ow in a partially constricted two-dimensional channel. As a result, we postulate a novel mechanism to explain the origin of vortex splitting and shedding in this ge- ometry. Numerical simulations of the unsteady, two-dimensional, incompressible Navier{ Stokes equations are performed in a channel having a constriction modeled by a two- parameter Gaussian distribution on both channel walls. Reynolds numbers from 1 to 3000 based on inlet half-channel height and mean inlet velocity and constriction ratios of 0:25, 0:5 and 0:75 are considered. The Navier{Stokes solutions are observed to experience a number of bifurca- tions including unsteady behaviour with shear-layer uctuations and vortex shedding downstream of the constriction. A sequence of events is presented describing how a sustained shear layer instability leads to the unsteady vortex shedding phenomenon via a convective instability and a proposed streamwise pressure-gradient mechanism. In addition, a global linear stability analysis is performed on several station- ary Navier{Stokes solutions to determine the long-term temporal behavior of small amplitude perturbations. Finally, the implications of this research on the hemodynamics in the cephalic vein and potential failure of the brachiocephalic stula are addressed.
Ph.D. in Mechanical Engineering, May 2011
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Title: DUAL-BASED APPROXIMATION ALGORITHMS FOR MULTIPLE NETWORK DESIGN PROBLEMS
Creator: Grimmer, Benjamin
Date: 2016, 2016-05
Description: We study a variety of NP-Complete network connectivity problems. Our pri- mary results come from a novel Dual-Based approach to approximating...
Show moreWe study a variety of NP-Complete network connectivity problems. Our pri- mary results come from a novel Dual-Based approach to approximating network de- sign problems with cut-based linear programming relaxations. This approach gives a 3=2-approximation to Minimum 2-Edge-Connected Spanning Subgraph that is equivalent to a previously proposed algorithm. One well-studied branch of network design models ad hoc networks where each node can either operate at high or low power. If we allow unidirectional links, we can formalize this into the problem Dual Power Assignment (DPA). Our Dual-Based approach gives a 3=2-approximation to DPA, improving the previous best known approximation of 11=7 1:57. Another standard network design problem is Minimum Strongly Con- nected Spanning Subgraph (MSCS). We propose a new problem generalizing MSCS and DPA called Star Strong Connectivity (SSC). Then we show that our Dual-Based approach achieves a 1.6-approximation ratio on SSC. As a result of our Dual-Based approximations, we prove new upper bounds on the integrality gaps of these problems. For completeness, we present a family of instances of MSCS (and thus SSC) with integrality gap approaching 4=3.
M.S. in Computer Science, May 2016
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Title: TOPICS IN COUNTERPARTY RISK AND DYNAMIC CONIC FINANCE
Creator: Iyigunler, Ismail
Date: 2012-11-02, 2012-12
Description: This thesis consists of three essays about modeling counterparty risk and pricing derivative securities. In the rst essay, we analyze the...
Show moreThis thesis consists of three essays about modeling counterparty risk and pricing derivative securities. In the rst essay, we analyze the counterparty risk embedded in CDS contracts, in presence of a bilateral margin agreement. We focus on the pricing of collateralized counterparty risk, and we derive the bilateral Credit Valuation Adjustment (CVA), unilateral Credit Valuation Adjustment (UCVA), and Debt Valuation Adjustment (DVA). We propose a model for the collateral by incorporating all related factors such as the thresholds, haircuts and margin period of risk. We derive the dynamics of the bilateral CVA in a general form with related jump martingales. Counterparty risky and the counterparty risk-free spread dynamics are derived and the dynamics of the Spread Value Adjustment (SVA) is found as a consequence. We nally employ a Markovian copula model for default intensities and illustrate our ndings with numerical results. In the second essay we address the issue of computation of the bilateral CVA under rating triggers in presence of ratings-linked margin agreements. We consider collateralized OTC contracts, that are subject to rating triggers, between two parties { an investor and a counterparty. Moreover, we model the margin process as a function of the credit ratings of the counterparty and the investor. We employ a Markovian approach for modeling of the rating transitions and of the default probabilities of the counterparties. In this framework, we derive the representation for bilateral CVA. We also introduce a new component in the decomposition of the counterparty risky price: namely the rating valuation adjustment (RVA) that accounts for the rating triggers. We consider several dynamic collateralization schemes where the margin thresholds are linked to the credit ratings of the counterparties. We account for the rehypothecation risk in the presence of independent amounts. Our results are ix illustrated in terms of a CDS contract and an IRS contract. In the third essay, we study the problem of pricing in incomplete markets with risk measures and acceptability indices. We propose a model for nding the dynamic ask and bid prices of derivative securities using Dynamic Coherent Acceptability Indices (DCAI) in the presence of transaction costs. In this framework, we de ne and prove a representation theorem for dynamic bid ask prices. We show that our prices can be computed using dynamic Gain-Loss Ratio (dGLR), which is a DCAI. To illustrate our results, we provide several numerical examples, by pricing barrier options with dGLR.
PH.D in Applied Mathematics, December 2012
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Title: NETWORK CONGESTION / RESOURCE ALLOCATION GAME
Creator: Shin, Junghwan
Date: 2013, 2013-12
Description: We first consider the K-user(player) resource allocation problem when the resources or strategies are associated with homogeneous functions....
Show moreWe first consider the K-user(player) resource allocation problem when the resources or strategies are associated with homogeneous functions. Further, we consider the K-user(player) matroid resource allocation problem satisfying the specified requirements of the users, which are maximal independent sets of a matroid. The objective is to choose strategies so as to minimize the average maximum cost incurred by a user where the cost of a strategy is the sum of the costs of the elements comprising the strategy. For k commodity networks with heterogeneous latency functions, we consider the price of anarchy (PoA) in multi-commodity selfish routing problems where the latency function of an edge has a heterogeneous dependency on the flow commodities, i.e. when the delay is dependent on the flow of individual commodities, rather than on the aggregate flow. Further we consider the price of anarchy (PoA) in multi-commodity atomic flows where the latency function of an edge has a heterogeneous dependency on the flow commodities, i.e. when the delay is dependent on the flow of individual commodities, rather than on the aggregate flow. Lastly, we show improved bounds on the price of anarchy for uniform latency functions where each edge of the network has the same delay function. We prove bounds on the price of anarchy for the above functions. Our bounds illustrate how the PoA is dependent on θ and the coefficients gij . At the end, we consider security aspects of network routing in a game-theoretic framework where an attacker is empowered with the ability for intrusion into edges of the network; on the other hand, the goal of the designer is to choose routing paths.
PH.D in Computer Science, December 2013
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Title: RISK SHIFTING, MANAGER SENTIMENT AND NEW INVESTMENT EFFICIENCY IN MANAGED FUTURES
Creator: Jiang, Cheng
Date: 2017, 2017-05
Description: This dissertation focuses on a subset of hedge fund, Commodity Trading Advisors (CTAs), which has grown in the past 35 years and highlighted...
Show moreThis dissertation focuses on a subset of hedge fund, Commodity Trading Advisors (CTAs), which has grown in the past 35 years and highlighted by its diversification benefit to traditional asset classes. I will study the risk-taking, market timing and market capacity of this type of hedge fund. I study the volatility of an extensive sample of live and defunct Commodity Trading Advisor funds from 1994 to 2013. Utilizing the gross-of-fee return, I document significant mean-reversion in volatility in the time series of CTA funds. I further examine the impact of performance on volatility shift, and find consistent evidence of risk tournament behavior, especially when the CTA industry is performing well. Moreover, the risk shifting of CTA managers depend upon both relative and absolute fund performance. The practice of this conditional risk shifting has benefitted the fund managers at the cost of fund investors. I estimate the average benefit to manager's return income and the average cost to investor's Sharpe ratio. My findings provide a first comprehensive evidence on the risk strategy of CTA funds, suggesting that managerial career concerns do not eliminate the moral hazard problem in the CTA space. The asymmetric nature of performance-based compensation in hedge funds produces a strong incentive for risk-shifting, but empirical research presents mixed evidence of risk-seeking behavior. The driver of the change in risk can also be related to other reasons other than incentive fees. I introduce a behavioral regime-switching model of fund manager sentiment in which Bayesian learning is used to update beliefs about market environment in an effort to predict future performance and anticipate market moves. I use a subset of hedge funds in the managed futures industry between 1994 and 2014 and find that the risk-taking behavior of fund managers is influenced by human emotions but in two distinctly different ways. The capital flow to hedge funds has well-known price pressure and smart money effect. This paper studies the capital flows impact on CTA future performance. It had been observed both in mutual funds and hedge funds that mangers scale their existing holding up or down by using new capital inflow rather than trade new positions. This strategy will generate positive returns for the funds due to the price pressure effect. It is interesting whether it will exist in managed future space. I use Vector auto-regression (VAR) to evaluate a system of 2 variables: capital inflow and future performance. If the relationship is negative, one possible reason could be the market impact that erodes the profit generated by price pressure. Therefore, I will implement a market impact test that investigate the market capacity in terms of Sharpe ratio and t-statistics of alpha.
Ph.D. in Management Science, May 2017
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Title: MEAN-VARIANCE HEDGING WITH TIME CHANGED LEVY PROCESS
Creator: Liu, J Ingran
Date: 2012-11-17, 2012-12
Description: The goal of this thesis is to consider asset pricing model which driven by an exponential time changed process: Brownian motion with time...
Show moreThe goal of this thesis is to consider asset pricing model which driven by an exponential time changed process: Brownian motion with time changing process{ Poisson process. We rst present the characteristic function of the time change exponential Brown motion and its ltration. Second we exhibit the explicit European call pricing formula then discuss the mean-variance hedging method in this thesis.
M.S. in Applied Mathematics, December 2012
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Title: EFFICIENT ALGORITHMS FOR POWER ASSIGNMENT PROBLEMS
Creator: Qiao, Kan
Date: 2015, 2015-05
Description: Power assignment problems take as input a directed simple graph G = (V;E) and a cost function c : E ! R+. A solution to this problem assigns...
Show morePower assignment problems take as input a directed simple graph G = (V;E) and a cost function c : E ! R+. A solution to this problem assigns every vertex a nonnegative power, p(v). We use H = (V;B(p)) to denote the spanning subgraph of G created by this power assignment. Let B(p) denote the set of all the links established between pairs of nodes in V under the power assignment p. The minimization problem then is to find the minimum power assignment, Pp(v), subject to H satisfying a specific property. 4 variants of this problem are discussed in this paper (a) Min-Power Strong Connectivity: H = (V;B(p)) is strongly connected. (b) Min-Power Broadcast: H = (V;B(p)) has a path from the fixed source z to every other vertex. (c) Min-Power Connectivity with 2-level power (Symmetric): c : E ! f0; 1g and H = (V;B(p)) is connected. (d) Min- Power Strong Connectivity with 2-level power (Asymmetric): c : E ! f0; 1g and H = (V;B(p)) is strongly connected. We give the exact solution using an improved integer linear program for problem (a) and (b) (We do not have a section for the integer linear program of Min-Power Broadcast problem since it is very similar to Min-Power Strong connectivity). Then we try to speedup current best approximation algorithms while preserving their approximation ratio. For problem (a), we give a fast variant of 1:85-approximation algorithm with running time O(n2 log2 n). For problem (b), we give a fast variant of 2(1 + ln n)-approximation algorithm for the most general cost model with running time O(n3) and a fast variant of 4:2- approximation algorithm for 2-dimensional cost model with running time O(nm), where n = jV j and m = jEj. For both problem (c) and (d), We give 5 3-approximation algorithms that run in O(m (n)), where (n) is the inverse Ackermann function.
Ph.D. in Computer Science, May 2015
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Title: MODELING, ANALYSIS AND DESIGN OF MULTI-CHANNEL BONDING FOR IEEE 802.11 WLANS
Creator: Khairy, Sami
Date: 2016, 2016-12
Description: The aim of this dissertation is to study the performance of distributed and opportunistic multi-channel bonding protocol in IEEE 802.11ac...
Show moreThe aim of this dissertation is to study the performance of distributed and opportunistic multi-channel bonding protocol in IEEE 802.11ac WLANs, and design channel bonding strategies to efficiently utilize the available spectrum. To this end, we first develop an analytical framework to study the throughput performance of WLANs with co-existing ac users and legacy users, characterizing the contentions among ac and legacy users in both primary and secondary channels. By modeling the transmissions of legacy users and ac users with and without bonding as a twolevel renewal process, the channel bonding probability of ac users in each secondary channel can be derived. Based on the bonding probability, MAC throughput of ac and legacy users can be analyzed respectively. Our analysis show that in a homogeneous multi-channel WLAN where only ac users are present, the contention probability of ac users is the same as that in a single channel with the same number of users; and in a heterogeneous WLAN with both ac and legacy users, an ac user can achieve a higher throughput than a legacy user, although the overall throughput decreases due to the increased contention level imposed by ac users in secondary channels. Based on the analysis, we further propose a channel selection strategy for ac users to select the best primary channel, in order to mitigate the contentions in the network and attain the maximal throughput. Analytical results show that primary channel selection is indifferent in a homogeneous network, whereas in a heterogeneous network, ac users should select the least congested channel as the primary channel to attain the maximal throughput. To evaluate the performance of a multi-channel WLAN, we develop an event-driven simulator based on network simulator-3 (NS-3). Extensive simulations validate our analyses and the efficiency of the proposed channel selection strategy.
M.S. in Electrical Engineering, December 2016
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Title: DEVELOPMENT OF A PREDICIlVE FRAMEWORK TO FORECAST VENOUS STENOSIS
Creator: Mahmoudzadeh Akherat, S.m. Javid
Date: 2016, 2016-12
Description: The end stage renal disease (ESRD) patient population is growing at a troubling rate, calling for a focused attention to investigate the...
Show moreThe end stage renal disease (ESRD) patient population is growing at a troubling rate, calling for a focused attention to investigate the chronic kidney diseases, their characteristics and our lines of defense against them. One major medical treatment for ESRD patients is hemodialysis which is facilitated through vascular access (VA). The vascular access of particular interest in this investigation as well as the medical community is the brachiocephalic fistula (BCF), which is a form of arteriovenous fistula (AVF), created surgically by connecting the brachial artery and the cephalic vein. It is commonly used for elderly patients and for those with poor circulation systems, e.g. diabetics. The extreme hemodynamic environment that BCF creates triggers the onset of neointimal hyperplasia (NH) in most of these patients which leads to access failure and a high morbidity and mortality rate. This process happens in a matter of months, providing an excellent translational medicine experimental stage to observe as the vessel walls react and adapt to the new hemodynamically violent conditions. Through extensive analysis of the venous deformation and subsequent hemodynamics of a patient cohort of 160, a prognosticative framework to predict the vein deformation in these patients prior to the occurrence of the failure has been developed. The obtained results are the consequence of the integration of clinical practice and computational science. The proposed method was first based on our hypothesis which roots the NH in non-physiological wall shear stresses (WSS), and was then improved and modified using rigorous optimization and numerical approaches. This finding is essential to the modification of the current VA techniques to increase the patency of the AVFs, to prevent the diminishing functionality of the access, and to increase the life expectancy of ESRD patients. Moreover, this finding will further assist us in comprehension of the human vasculature growth and remodeling (G&R) through bypassing the analysis of unknown biological phenomena, as it is achieved purely by juxtaposing well-defined mathematical, physical, and medical concepts.
Ph.D. in Mechanical and Aerospace Engineering, December 2016
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Title: NUMERICAL ANALYSIS OF NON-DUCTILE BRACED FRAME DUE TO DYNAMIC LOADS
Creator: Keivan Esfahani, Ashkan
Date: 2014, 2014-05
Description: In recent years, typical steel construction in regions of high seismic risk has shifted from moment-resisting frames to concentrically braced...
Show moreIn recent years, typical steel construction in regions of high seismic risk has shifted from moment-resisting frames to concentrically braced frames. As a result of the increased popularity of braced frames, the poor performance of some conventionally braced frames in past earthquakes, and the limited experimental data available on the inelastic response and the failure characteristics of braced-frame systems, a series of experimental and analytical investigations were initiated. Steel concentrically braced frames are common lateral force resisting systems in both new construction and existing buildings. However, the seismic behavior of braced frames designed prior to the adoption of capacity design principles in the 1980s is generally not well understood despite their widespread presence. These older braced frames, termed non-seismic concentrically braced frames (NCBFs) are the subject of a research project titled “NEESR: Collaborative Developments for Seismic Rehabilitation of Vulnerable Braced Frames” that seeks to evaluate NCBFs and determine retrofit strategies. In this project two tests were conducted. First Test examined a full scale two story NCBF in the inverted V configuration subjected to quasistatic cyclic load and this specimen contained a bottom story beam that is considered weak in capacity design. Second Test examined a post-earthquake repair scenario using the damaged NCBF-INV-1 frame in which the bottom story braces and gusset plates were removed and replaced with seismically compact braces with connection designed for in plane buckling. In this work, finite element models developed in Abaqus were validated using data collected from these tests. The outcomes of this research will be a greater understanding of seismic performance of NCBFs, the development of rehabilitation strategies for vulnerable NCBFs, and a robust technique for modeling NCBFs.
M.S. in Civil Engineering, May 2014
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Title: NUMERICAL ANALYSIS OF NON-DUCTILE BRACE FRAME WITH KNIFE PLATE DUE TO DYNAMIC LOADS
Creator: Keivan Esfahani, Arshia
Date: 2014, 2014-05
Description: In recent years, typical steel construction in regions of high seismic risk has shifted from moment-resisting frames to concentrically braced...
Show moreIn recent years, typical steel construction in regions of high seismic risk has shifted from moment-resisting frames to concentrically braced frames. As a result of the increased popularity of braced frames, the poor performance of some conventionally braced frames in past earthquakes, and the limited experimental data available on the inelastic response and the failure characteristics of braced-frame systems, a series of experimental and analytical investigations were initiated. Steel concentrically braced frames are common lateral force resisting systems in both new construction and existing buildings. However, the seismic behavior of braced frames designed prior to the adoption of capacity design principles in the 1980s is generally not well understood despite their widespread presence. These older braced frames, termed non-seismic concentrically braced frames (NCBFs) are the subject of a research project titled “NEESR: Collaborative Developments for Seismic Rehabilitation of Vulnerable Braced Frames” that seeks to evaluate NCBFs and determine retrofit strategies. In this project two tests were conducted. First Test examined a full scale two story NCBF in the inverted V configuration subjected to quasistatic cyclic load and this specimen contained a bottom story beam that is considered weak in capacity design. Second Test examined a post-earthquake repair scenario using the damaged NCBF-INV-1 frame in which the bottom story braces and gusset plates were removed and replaced with seismically compact braces with connection designed for in plane buckling. In this work, finite element models developed in Abaqus were validated using data collected from these tests. The outcomes of this research will be a greater understanding of seismic performance of NCBFs, the development of rehabilitation strategies for vulnerable NCBFs, and a robust technique for modeling NCBFs.
M.S. in Civil Engineering, May 2014
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Title: POWER TAKE-OFF AND GRID SUPPORT IN HYBRID VEHICLES USING WOUND FIELD SYNCHRONOUS MACHINES
Creator: Dong, Weizhen
Date: 2016, 2016-07
Description: Energy sectors are undergoing revolutionary changes. Due to environmental concerns and customer desires, a considerable increase of Electric...
Show moreEnergy sectors are undergoing revolutionary changes. Due to environmental concerns and customer desires, a considerable increase of Electric Vehicles (EVs) and Plug-in Hybrid Electric Vehicles (PHEVs) is expected. A technology of Vehicle to Grid (V2G) is emerging in the electric power industry. This technology provides connections between PHEVs and microgrids, and utilize PHEVs as distributed generators for grid support or as backup power sources. With the development of Electric Vehicles, wound field synchronous machines (WFSM) have been used and studied in EV traction motors and generators. For the application of EV technology, WFSMs have several advantages over permanent magnet synchronous machines (IPMSM) and induction machines (IM) including the complete control of the field excitation from the rotor side, higher system and machine efficiencies, and reduced cost due to the absence of rare earth permanent magnets. At the same time, WFSMs can work as generators to realize power take-off and microgrid support for EV tractions. Due to the several advantages of WFSMs in EVs application, this research focuses on the control of the WFSM in PHEVs for power take-off and grid support as a generator. PHEVs internal combustion (IC) engine is considered as a prime mover and would couple to the shaft which is connected to the WFSM. Such PHEVs applications would be used as power supplies for nearby loads and microgrids. This system is able to reduce cost of power electronics converters and directly provides desired AC voltage. This work aims to study the power take-off from hybrid electric vehicles using wound field synchronous machines and operation in microgrids. The feasible HEVs configurations to realize this purpose is studied. The modeling of IC engine, wound field synchronous machine, brushless exciter and distributed generators (DGs) in microgrid is demonstrated. One disadvantage of this application is the time delay during the combustion progress in the IC engine. This delay could affect the stability and dynamic response of the system. At the same time, the IC engine based generators have slower dynamic response compared with power electronic based sources. A state variable voltage regulator and a rotor speed controller are designed to improve the performance of the system. These controllers enable wound field synchronous machines provide desired voltage frequency and voltage magnitude. A real power - frequency droop controller and a reactive power – voltage droop controller are also studied. The droop controllers would keep the stability and better power quality of the system for islanded mode operation and grid-connected mode operation. The droop controllers enable EVs system share loads in a desire portion of power with other DGs in the grid and this reactive power – voltage droop controller would eliminate the circulating reactive power in the whole grid system. The EV’s isolated power take-off operation, islanded mode operation in microgrid with other DGs, and grid connected mode operation in microgrid are discussed. Stabilities, disturbance responses, and load sharing abilities are shown in simulation studies. The results are presented and discussed.
M.S. in Electrical Engineering, July 2016
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Title: IMAGING TISSUE SCAFFOLDS WITH X-RAY PHASE CONTRAST IMAGING
Creator: Doe, Frederick
Date: 2014, 2014-12
Description: A major challenge in tissue engineering is imaging within scaffolds. Biomaterials commonly used in tissue engineering have similar x-ray...
Show moreA major challenge in tissue engineering is imaging within scaffolds. Biomaterials commonly used in tissue engineering have similar x-ray absorption properties to native tissue, so they provide poor contrast in radiography. X-ray phase contrast imaging (XPCI) is an imaging modality that measures light/matter interactions other than absorption. By providing insight into these interactions, x-ray phase contrast imaging has the potential to allow imaging of materials used in biomedical applications. In this thesis, a technique for imaging explanted poly(ethylene glycol) (PEG) hydrogels is presented. PEG is a highly biocompatible polymer with widespread use in biomedical applications. Porous PEG hydrogels were synthesized with 100-150 μm pore size through a salt-leaching technique and loaded with fibrin, a natural protein known to stimulate vascularized tissue formation. The hydrogels were formed in the shape of disks and implanted subcutaneously in the backs of rodent animal models for 1, 2 and 3 weeks. The hydrogels and surrounding tissue were harvested at 1, 2, and 3 weeks. After explanation, the hydrogels were placed in formaldehyde and imaged at the National Light Source at Brookhaven National Laboratory using a multiple image radiography (MIR) technique. Five hundred angles were captured of each sample over 180°, and computed tomography was performed. The samples were compared to histological stains to identify specific tissue features that could be identified in the XPCI images. XPCI allowed imaging of hydrogels and identification of interfaces between native tissue and the PEG material. In addition, tissue invasion into the pores of the scaffold could be identified and could be used to quantify the depth of invasion. Muscle tissue could also be seen, and within muscle fibers were visible. With computed tomography, 3D volumes were constructed, enabling analysis throughout the samples.
M.S. in Biomedical Engineering, December 2014
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Title: ENGINEERING OF CLINICAL-SCALE, IN VITRO VASCULARIZED BONE TISSUE FOR IMPLANTATION
Creator: Gandhi, Jarel K.
Date: 2016, 2016-05
Description: Tissue engineering has been a rapidly expanding field dedicated to regeneration of tissue. The field has focused on application through...
Show moreTissue engineering has been a rapidly expanding field dedicated to regeneration of tissue. The field has focused on application through combinations of 3 key components: cells, signals, and scaffolds. One ambitious combination of all three is the desire to engineer functional tissues in vitro to meet the clinical-demand of organ replacement. While major advances have been made, a critical obstacle that has yet to be overcome is the need to grow large volumes of complex 3D tissue. In this proposal, this issue is addresed in two ways: the use of a perfusion bioreactor system to culture 3D scaffolds to enhance mass transport, and engineering of a vascular network withing the scaffold for rapid perfusion once implanted in vivo. This thesis aims to address both aspects for bone tissue engineering by engineering pre-vascularized, mineralizing scaffolds that can be scaled up to clinically-relevant volumes by using a tubular perfusion bioreactor system (TPS). To address this, 3 aims were addressed. First, 3D culture of endothelial colony forming cells (ECFCs), a clinically-relevant cell population, was demonstrated utilizing fibrin gels within the TPS. The TPS allowed for viable culture of ECFCs within fibrin bead scaffold up to 1 week without a reduction in cell amount or genomic quality of the cells. Second, a co-culture model of angiogenesis utilizing ECFCs and mesenchymal stem cells (MSCs) was demonstrated to reproducibly form pre-formed vessel networks within a mineralizing fibrin scaffold. Data shows that MSC suspension concentration and fibrinogen concentration modulate the angiogenic response. Mineralization is demonstrated without the use of osteogenic media utilizing shear stress within the TPS. Finally, functionality of the pre-formed vessels is demonstrated following implantation to a SCID mouse model. Engineered human vessels showed anastasmosis to the host vasculature, with evidence of interconnected host and human vessel networks as well as formation of hybrid vessels. Additionally, evidence of mineralization within the scaffolds is maintained in TPS-cultured samples. In demonstrating these aims, future work should focus on fortifying the scaffold material to enable addressing implantation and persistence of clinically-relevant tissue volumes. In conclusion, pre-vascularization within bioreactor-cultured scaffolds represents a promising solution for future tissue engineering application.
Ph.D. in Biomedical Engineering, May 2016
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Title: OPERATION ANALYSIS AND LOSS REDUCTION OF MAGNETIC GEAR
Creator: Feng, Yanjun
Date: 2015, 2015-12
Description: In the first part of this thesis, analysis of magnetic gears which includes operation analysis and loss analysis is introduced. With these...
Show moreIn the first part of this thesis, analysis of magnetic gears which includes operation analysis and loss analysis is introduced. With these analysis, the behavior of magnetic gears are deeply studied for their advantages and disadvantages. Their performance in terms of torque transfer, speed transfer, and the loss are the main focus. With different properties setting for magnetic gear, the influence of these properties to the final performance are also studied. By comparing results from different simulation software and different methods, the results are analyzed more accuracy and detailed. For loss analysis, FFT are utilized for harmonics analysis. This analysis was done by Matlab. All these analysis processes and results lead to the next part of this thesis which is optimization for magnetic gear. The second portion of this thesis focuses on core loss reduction in magnetic gears. Pole shaping similar to what is used in electric machines to reduce electromagnetic torque ripple is introduced to attempt to reduce higher order harmonic flux components in the magnetic gears without reducing power density. In this part, lots of simulation shows the work analysis of magnetic gear to verify the working principle and optimizations results. Large ripple problems of magnetic gear are also found during this part.
M.S. in Electrical Engineering, December 2015
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Title: A 4-Phase Flow Model for Methane Production from an Unconsolidated Hydrate Reservoir
Creator: Hinz, Deniz
Date: 2019
Description: Natural gas from hydrates is extremely abundant as an energy resource; US resource-grade hydrate deposits are estimated to be over 20 times...
Show moreNatural gas from hydrates is extremely abundant as an energy resource; US resource-grade hydrate deposits are estimated to be over 20 times the domestic proved natural gas resources, at approximately 7000 trillion cubic feet (tcf). The theoretical potential of hydrates is immense, but production testing and research remain lacking, which has led to the development of numerous hydrate production numerical simulators for consolidated porous media hydrate reservoirs. However, due to the onset of unconsolidated flow behavior upon significant hydrate dissociation, numerical models haven’t agreed well with the experimental data from the Mallik production tests. Hydrate contributes substantially to the strength of the sediment matrix, such that hydrate-bearing sediment ultimately falls apart exhibiting 4-phase unconsolidated flow behavior of gas, water, hydrate, and sand. In order to better capture the multiphase flow characteristics of gas, water, hydrate, and sand in an unconsolidated gas hydrate reservoir, we have developed a novel 4-phase flow model coupled with numerical simulation of the Mallik 2007/2008 production tests. The model is able to capture the coupled 4-phase hydrodynamics, mass transfer, and heat transfer physics inherent to the unconsolidated hydrate reservoir. Solid deformation is modeled by extending multiphase and granular flow theory to hydrate-bearing sediment. Constitutive models for the solid viscosity and solid pressure are developed to model the change in strength of the sediment as hydrate dissociates and the solid deforms. The solid viscosity is a composite of frictional contributions from the solid normal stress and cohesive contributions from the hydrate. The interphase momentum exchange between the fluid phases (gas and water) and solid phases (hydrate and sand) modeled based on a volume-averaged approach that considers the formation and closure of high-permeability volumes due to dilation and compaction of hydrate-bearing sediment as it deforms. By considering the deformation of solids and the subsequent effect on the permeability, the 4-phase simulations showed good agreement with the experimental data from the Mallik 2007/2008 production phases. The 4-phase modeling approach serves as a proof of concept for the application of granular flow theory to hydrate-bearing sediment. An unconsolidated hydrate reservoir with sustained sand production essentially behaves like a naturally fracking reservoir, exhibiting a dramatic increase in permeability induced solely by depressurization. Conversely, preventing sand production with a sand screen ultimately leads to significant throttling of the gas production rate due to the compaction and accumulation of sand at the sand screen.
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