Chathuri Silva

Physics (S&T/UMSL Cooperative Program)

DATE: Friday, July 23, 2021

TIME: 11 am

LOCATION: https://umsystem.zoom.us/j/92511105560?pwd=UnNldjArdHUwTFBvVUdLMTAxRlFwQT09

ADVISOR(S): Dr. Philip Fraundorf, Julia Medvedeva (co-advisor)

DISSERTATION TITLE: COMPUTATIONAL STUDIES OF CARBON NANOCLUSTER SOLIDIFICATION

ABSTRACT:

A subset of micron-size meteoritic carbon particles formed in red giant atmospheres show a core-rim structure, likely condensed from a vapor phase into super-cooled carbon droplets that nucleated graphene sheets (~40) on randomly oriented 5-atom loops during solidification, followed by coating with a graphite rim. Similar particles form during slow cooling of carbon vapor in the lab.

Here we investigate the nucleation and growth of carbon rings and graphene sheets using density functional theory (DFT). Our objectives: (1). explore different computational techniques in DFT-VASP for various carbon structures and compare the results with literature, (2). investigate the nucleation and growth of carbon rings and graphene sheets at the experimental 1.8 g/cc density estimate, by supercell relaxation of randomized liquid-like carbon atom clusters, and (3). Compare carbon cluster energies for combinations of DFT-VASP and long-range carbon bond order potential (LCBOP) relaxations. Observations show: (a) that 29 atom diamond clusters relax into the C28 fullerene with a central carbon atom, (b) new evidence for the instability of an Fm3m carbon phase with the diamond unit cell, and (c) that pent-loop formation is energetically favored over hex-loop formation in a relaxed melt. Literature work on the effectiveness of pent-loops as nucleation seed for graphene structures, plus the fact that each pent-loop can give rise to 5 differently oriented sheets, helps explain electron-microscope data on graphene-sheet number densities and provides guidance for nucleation/growth models being developed.

Wenyu Liao

Civil Engineering

DATE: Thursday, July 29, 2021

TIME: 10 - 12 pm

LOCATION: https://umsystem.zoom.us/j/91083960962?pwd=dGIwVWVnNXFZMDdBREp3THVRWXRDZz09#success

ADVISOR(S): Dr. Hongyan Ma

DISSERTATION TITLE: EXPERIMENTAL AND NUMERICAL STUDIES OF NOVEL THERMAL ENERGY STORAGE MATERIALS FOR APPLICATIONS IN CONCRETE AND ENERGY STORAGE SYSTEMS

ABSTRACT:

          For the sake of energy saving and green energy deployment, thermal energy storage (TES) - in view of supplementing energy consumption of buildings and improving demand flexibility and overall resilience of grid - is desired. In this study, several types of novel thermal energy storage (TES) materials and composites are explored, and a series of numerical simulation models and experimental protocols are developed to evaluate the potentials of these materials to be applied in concrete, pavement, and thermal energy storage systems.

          TES materials studied include phase change material (PCM) and thermochemical material (TCM). The first two type of novel TES materials/composites are at the micro-scale, which use micro diatomite (DE) and cenosphere (Ceno) as carriers of PCM (i.e., n-octadecane), respectively. Both DE-PCM composite (30wt% PCM, latent heat of 68 J/g) and CenoPCM composite (46wt%, latent heat of 109 J/g) have been proved to have pozzolanic reactivity, which prevents leakage of PCM and maintains the mechanical properties of the functional construction materials incorporated with PCM. The third type of novel TES material is at the macro-scale, utilizing lightweight sand (LWS) and lightweight coarse aggregate as carriers to load PCM. Mortar prepared with PCM loaded LWS has comparable compressive strength to that of reference mortar using normal rive sand and 63% smaller autogenous shrinkage, along with an abatement of apparent hydration heat as well as a delay of peak temperature. The last two types of novel TES materials are solid-solid PCM (SSPCM, i.e., PEG-PMDI-Graphite composite) and TCM (i.e., struvite-K). Their phase change mechanisms/properties and thermal stabilities/reliabilities are revealed. The results suggest high potentials of them in specific TES applications.

          The above multi-scale TES materials and composites can be used independently or in combination, according to application scenarios. To evaluate performance of TES materials in various scenarios, numerical simulation frameworks and experimental protocols have been developed and implemented.  Three representative scenarios (i.e., thermal cracking control for concrete, thermal curling mitigation for pavement, and TES enhancement for geothermal energy storage systems) have been selected for study in this dissertation. The studies presented in this thesis show that TES materials (i.e., PCMs and TCMs) are technically feasible in mitigating thermal degradations of concrete and enhancing efficiencies of TES systems. They have promising marketability upon they can be economically available.

Amr Elsayegh

Civil Engineering

DATE: Wednesday, August 11, 2021

TIME: 11 am

LOCATION: https://umsystem.zoom.us/j/93437365168?pwd=WmN4WkhkcGt1RWZvMExlT3p6UkZ0QT09

ADVISOR(S): Dr. Islam H. El-adaway

DISSERTATION TITLE: COLLABORATIVE PLANNING IN THE CONSTRUCTION INDUSTRY: A HOLISTIC FRAMEWORK FOR ASSESSING COLLABORATIVE PLANNING PRACTICES AND PREDICTING PROJECT PERFORMANCE

ABSTRACT:

The fragmentation of the construction industry prompted developing novel methods such as collaborative planning, lean construction, advancements in technology, integrated project delivery, and relational contracting. Current research focused on specific facets of collaborative planning without presenting a comprehensive analysis of its factors. As such, the goal of this research is to develop a holistic framework that studies and evaluates collaborative planning practices in construction projects. This research offers significant addition to the body of knowledge through various theoretical and practical contributions. In relation to that, this research developed a comprehensive framework by (1) identifying a comprehensive list of factors influencing construction collaborative planning; (2) conducting a social network analysis on the identified factors; (3) introducing a novel index for measuring the effectiveness of collaborative planning; (4) developing prediction models for the cost and schedule performance of construction projects in relation to collaborative planning risks; and (5) offering recommended strategies to enhance the application of construction collaborative planning. The research objectives were achieved by using analytical and modeling techniques including social network analysis, analytical hierarchy process, mathematical and risk modeling, industry expert and project-based surveys, and validation of its applicability in construction projects. Ultimately, this research aims to expand the application of construction collaborative planning. This will enable and facilitate reliable planning and management practices that should lead to improved project performance.