Impact Resistance of Fiber-Reinforced Composites Using Computational Simulations

Composite materials are widely used in aerospace, automotive and wind power industries due to their high strength-to-weight and stiffness-to-weight ratios and their improved mechanical properties compared to metals. The damage resistance of composite materials due to low velocity impact depends on fiber breakage, matrix cracking and delamination between the interfaces. In this research, a numerical investigation of low velocity impact response of a multidirectional symmetric carbon-epoxy composite laminate is carried out and presented. Two different finite element models are developed for composite laminates made of non-crimp fabric to investigate their behavior under different levels of impact energy. In the first approach, a finite element homogeneous ply model is generated wherein the heterogeneous plies are replaced by equivalent homogeneous anisotropic plies. In the second approach, a finite element mesoscale model that captures the individual constituents of the composite (i.e., the tows and matrix) has been developed. Different failure criteria have been presented in the literature to predict the damage modes of the composites during and after impact events. The 3D Hashin failure criteria is implemented to predict the intralaminar failure and the surface-based cohesive behavior is implemented to capture the delamination between the plies. Following the low velocity impact investigation, the finite element models are subjected to axial compression to investigate the compressive residual strength after impact, which is a measure of damage tolerance. The numerical predictions, the low velocity impact response as well as the compressive residual strength after impact, are validated with experimental data. The homogeneous ply laminate impacted up to 50 J is seen to be capable of predicting the impact response as well as the compressive residual strength after impact

Flexural Behavior of Scaled-Down Cross-Laminated Timber Beams Under Short- and Long-Term Loadings: Experimental & Numerical Investigations

Cross-laminated timber (CLT), a product in the mass timber family, is an innovative engineered wood product that enables the construction of mid- and high-rise timber buildings. CLT has been used extensively in timber construction. A typical use of CLT panels is in the construction of walls, floors, and roofs which can carry a continuous load. This load can impact the long-term performance of the CLT structure and must be considered in the design phase. The primary goal of this research was to better understand the long-term creep behavior of CLT beams and contribute to the development of numerical approaches. The creep performance of CLT beams was assessed under elevated relative humidities using computational simulation and validated against experimental investigation. This study consists of two parts. In the first part, the flexural response of CLT beams was assessed. Material characterization experiments were conducted on spruce to provide the necessary material data for the numerical models. Flexural tests of CLT beams were performed to determine the modulus of elasticity (MOE) and modulus of rupture (MOR) of the CLT beams. In addition to the experimental work, a computational model was developed to predict the flexural response of CLT beam. The 3D Hashin failure criterion was adopted to predict the intralaminar failure of the CLT beam. The mean experimental and numerical values of MOE of the CLT beam were 9.14 GPa and 8.69 GPa, respectively with a difference of 5.10 %. In terms of the MOR, the mean experimental value and numerical value were 39.16 MPa and 40.11 MPa, respectively with a difference of less than 3 %. The second part of this study was focused on the assessment of creep performance of the CLT beam. A finite element creep model was developed to predict the interaction between the stress and moisture content change in the CLT beam simultaneously loaded under a constant dead load and subject to an elevated relative humidity condition, 30%, 60%, and 90%. ABAQUS user-defined UMAT and DFLUX subroutines were used to evaluate the material behavior and the elevated relative humidity loadings, respectively. The numerical model showed a well prediction of the moisture content distribution in the CLT model. Also, the numerical deflection result had shown a good agreement when compared to the experimental creep deflection. The results of this study showed that the current computational model can be used to predict the long-term creep behavior of such beams, and it can easily be adapted to account for different timber and geometry once the appropriate material properties are available

A Feature Modelling Language Based on Product Family Algebra

Feature modelling is an emerging software engineering paradigm, which helps organizations to develop products from core assets. Products are organized into families that share common core features. Feature modelling involves capturing, into a feature model, the commonality and variability of product families and several relationships among features or products. This thesis is about proposing a language for specifying feature models that is based on product family algebra (PFA). The language is intended to encompass the constructs found in early feature modelling graphical notations and languages. The thesis gives the syntax and the semantics of the proposed language. It discusses the design of its compiler that takes a feature model specification and generates its corresponding PFA, which can be analyzed using the tool Jory. The thesis uses a quite extensive case study to illustrate the use of the proposed language and its compiler.Master of Applied Science (MASc

Quantum Mechanics Investigation of the Photophysical Properties of Ruthenium(II)-Based Complexes Combined with the Development of their Force Field Parameters Using Molecular Mechanics and Molecular Dynamics Simulation

The focus of this study is to develop a theoretical strategy that can help guide the design of novel organometallics with desirable photophysical properties for molecular engineering. This computational study includes proposed complexes and others for which experimental data are available. The agreement between the computational results and the experimental observations confirms the validity of our procedure and the level of theory we applied in this study. The ground singlet (S0) and excited triplet (T1) electronic states and corresponding optical spectra of a series of cationic complexes —[RuH(CO)L(PPh3)2]+ (L=2,2´-bipyridyl) (Rubpy), 4,4´-dicarboxylic-2,2´-bipyridyl (Rudcbpy), bis-4,4’-(N-methylamide)-2,2´-bipyridyl (Rudamidebpy), bis-4,4’-(methyl)-2,2´-bipyridyl (RudMebpy), [Ru(CO)2dcbpy(PPh3)2]2+ (Ru(2CO)dcbpy), [Ru(H)2dcbpy(PPh3)2] (Ru(2H)dcbpy), and a series of cationic complexes [RuLL(phen)(PPh3)2]+ (phen= 1,10-phenanthroline , L= H, CO, Cl, TFA) — have been studied by combined Density Functional/Time-Dependent Density Functional (DFT/TDDFT) techniques using different combinations of DFT exchange-correlation functionals and basis sets. We demonstrate a correlation between HOMO-LUMO energy gap, Stokes shift, and T1 distortion, which reflects the effects of parent ligand and electron-withdrawing and donating groups. The results of this study of Ru-phen complexes revealed that this correlation is valid only when the metal-to-ligand charge-transfer (MLCT) transition is not isoenergetic with other transitions. In addition, we successfully developed new force field parameters for Ru-bpy based complexes, using molecular mechanics (MM) combined with molecular dynamics (MD), which can help to explain critical aspects of the optical phenomena of Ru-bpy based complex in solution and biological systems

Experimental investigation of geomechanical aspects of hydraulic fracturing unconventional formations

textUnderstanding the mechanisms that govern hydraulic fracturing applications in unconventional formations, such as gas-bearing shales, is of increasing interest to the petroleum upstream industry. Among such mechanisms, the geomechanical interactions between hydraulic fractures and pre-existing fractures on one hand, and simultaneous multiple hydraulic fractures on the other hand are seen of high importance. Although the petroleum engineering and related literature contains a number of studies that discusses such topics of hydraulic fracture interactions, there still remain some aspects that require answers, validations, or further supporting data. Particularly, experimental evidence is fairly scarce and keenly needed to solidify the understanding of such complex applications. In this work, the investigation methodology uses a series of hydraulic fracturing laboratory tests performed on synthetic rocks made of gypsum-based cements such as hydrostone and plaster in various experimental set ups. Those laboratory tests aim to closely investigate hydraulic fracture intersection with pre-existing fractures by assessing some factors that govern its outcomes. Specifically, the roles of the pre-existing fracture cementation, aperture, and relative height on the intersection mode are examined. The results show dominant effect of the cement-fill type relative to the host-rock matrix in determining whether hydraulic fracture crossing the pre-existing interface may occur. Similarly, hydraulic fracture height relative to the height of the pre-existing fracture may dictate the intersection results. However, the intersection mode seems to be insensitive of the pre-existing fracture aperture. Moreover, simultaneous multi-fracture propagation is examined and found to be impacted by the interference of the stresses induced from each fracturing source on neighboring fracturing sources. Such stress interference increases as the number of the propagating hydraulic fractures increase. While hydraulic fractures initiating from fracturing sources located in the middle of the fracturing stage seem to have inhibited propagation, outer hydraulic fractures may continue propagating with outward curvatures. Overall, the experimental results and analyses offer more insights for understanding hydraulic fracture complexity in unconventional formations.Petroleum and Geosystems Engineerin

A study of school attendance and exclusions in secondary schools in England

This study explores the links between school attendance, exclusions, and subsequent academic attainment at age 16 in mainstream schools in England. For this research, school attendance is defined as school-aged children attending school regularly. School exclusion is the removal of school-aged children from school either for fixed terms or permanently. Academic attainment for this research refers to the final exam results at the end of Key Stages 2, 3, and 4. Three different approaches were used. A detailed longitudinal approach, modelling the course of one age cohort of 554,145 pupils from the National Pupil Database (NPD), through their entire schooling to the age of 16 in different analytical steps using cross-tabulations, ‘effect’ sizes, correlations, and regression models. The analysis draws on secondary data in which indicators from the NPD were included to explain the outcomes. The main outcomes were the school attendance rate, exclusion pattern, and academic attainment for Key Stage 4. A systematic review was conducted of the evidence published over the last 20 years on school attendance interventions that have targeted disadvantaged pupils. This began by rating the obtained evidence from the included studies, following a well-developed sieve to judge the quality of evidence. The subsequent descriptive analysis includes a description of the included studies. The included interventions were also described in terms of their implementation protocols and categorised into financial interventions, counselling and mentoring, out of school educational programmes, health, school reforms, parental involvement, and school engagement for the disadvantaged children. Following this, the evidence obtained from these studies was complemented through semi-structured interviews with 10 primary and secondary school teachers that have lengthy experience of dealing with school attendance challenges. The robust analysis of the NPD showed that eligibility for Free School Meals (FSM), a measure of poverty, is the main predictor of school attendance, exclusions, and academic attainment. Prior academic attainment (KS2 and KS3 Maths and English attainment) are more strongly associated with academic attainment at KS4 (GCSEs results) than school attendance. The interview results confirmed this finding. The review results suggest that financial interventions that support parents of disadvantaged children with regular stipends could promote school attendance among the disadvantaged. The findings of this study entail a number of implications for policy and practice. Addressing the needs of disadvantaged groups of pupils through effective interventions, including regular cash payments to parents or carers, could promote the school attendance of these pupils and inspire their families to become more engaged with their children’s education, thereby enhancing their academic attainment. In terms of school exclusions, the current school data seems ineffective in illustrating the issue of school exclusions. Therefore, school exclusions data should be developed in a way that enables researchers to investigate the possible gaps in how schools conceive and implement exclusions

OUTCROP-SCALE STUDY OF THE PERMIAN BONE SPRING FORMATION, BONE SPRING CANYON, GUADALUPE MOUNTAINS, TEXAS: FRACTURE CHARACTERIZATION

A light detection and ranging- (LiDAR) focused outcrop study was conducted on Upper Leonardian Bone Spring limestone in the Bone Canyon, Delaware Basin of West Texas. LiDAR technology is very useful in modeling fracture systems from outcrop data. It provides several advantages such as accessibility to regions where hand measurements are not possible, a greater density of data, and a convenient PC-powered platform for interpretation. Using LiDAR data, a population of 7449 fracture planes was delineated and characterized. Fracture planes represented 3 major sets: E-W trending Fracture Set-1, N-S trending Fracture Set-2, and NE-SW trending Fracture Set-3. Fracture sets were used to delineate stress fields within the Bone Canyon. Fracture Set-1 is more systematic (containing closely spaced fractures and is characterized with uniform strikes) and older corresponding to a N-S sigma 3. Fracture Set-2 and Set-3 is less systematic (containing variably spaced fractures and is characterized with less uniform strike) and are younger corresponding to present day stress field that corresponds to a general E-W and NW-SE sigma 3, respectively. Statistics of fractures planes across rock units on the north and south canyon walls showed some variations indicating that parameters such as bed thickness and bedding pattern (whether a rock unit is thinly or thickly bedded) can influence the distribution of fractures, their density, and intensity. The north wall has an average fracture density of 2.6 fractures/m2 while the south wall has an average fracture density of 1.23 fracture/m2

A Formal Approach to Secure the Segmentation and Configuration of Dynamic Networks

Network segmentation and layered protection are critical strategies used in building and designing secure networks. Although they are recommended by security practitioners and agencies, they are defined vaguely and lack precise formal treatment. Implementing these strategies might be achievable for a small network with few resources; however, it is nearly an impossible task for a large network with a large number of resources and complex policies. The challenge is even harder for dynamic networks, where resources frequently join and leave the network. This case requires an adaptive approach for maintaining the implementation of these strategies. In this thesis, we provide a formalism for the strategies of layered protection and network segmentation. The formalism is based on Product Family Algebra (PFA) and guarded commands. We use this formalism to assess whether a network satisfies these strategies. Furthermore, we articulate two implementation schemes for the layered protection strategy. Moreover, based on the introduced formalism, we propose two algorithms for structuring and configuring robust and secure networks. We then extend the formalism and the algorithms to handle networks with several entry points, where each entry point is intended to give access to a certain subnetwork. We employ the algorithms for the dynamic configuration and governance of Software Defined Networks (SDN). In addition to SDN data and control planes, we propose a plane in charge of the configuration and governance of SDN data planes. We call it the Dynamic Configuration and Governance (DCG) plane and it is intended to give agility to dynamic networks. Moreover, we propose and assess three architectures that use the DCG plane. The assessment results identify an architecture that is suitable for dynamic networks and another for networks that are more stable regarding changes to policy and network topology. The formalism presented in this thesis provides an automatic and adaptive approach for the segmentation and configuration of networks. It takes into consideration the security requirements of local resources as well as the global security situation. It constitutes a foundational framework for automated security solutions applicable to computer networks that use any type of connecting technology or topology.ThesisDoctor of Philosophy (PhD

Preferences for health-related quality of life: do they vary by age? A systematic literature review on the EQ-5D measure

IntroductionCost-utility analysis (CUA) is a commonly used method in Health technology assessment (HTA) that utilises generic metrics such as quality-adjusted life years (QALYs). QALY is a measure derived from individuals’ preferences for different health states, with these preferences represented as utility values. However, utility values may differ by age, raising equity concerns in healthcare allocation. Given the globally ageing demographic, understanding the age-utility relationship becomes essential.ObjectivesThis systematic review aimed to explore the impact of age on utility values derived from the EQ-5D, a widely used instrument in CUA that contributes to calculating QALYs by assessing five dimensions of health: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression.MethodsOur search used the comprehensive pearl growing approach and database searching. We included studies that analysed the effect of age on EQ-5D utility values in the general population. We excluded qualitative, non-English, and non-EQ-5D instrument studies. Quality was appraised using the Joanna Briggs Institute tool, and a narrative synthesis was used.ResultsOf the 28 studies reviewed, primarily from Europe and the Americas, the average age of participants ranged from 34.1 and 47.7 years. Around 46% (n = 13) associated older age with lower utility values; 28% (n = 8) with higher utility; and 25% (n = 7) found no consistent relationship between age and utility.DiscussionAge was identified as a critical factor affecting EQ-5D-derived utility values, with implications for the equitable distribution of healthcare resources. These findings corroborate previous research on utility measurement across different instruments, highlighting the ethical and policy issues due to age-related utility differences

Decomposition of the unitary representation of SU(1,1) on the unit disk into irreducible components

In this thesis, we decompose the representation of SU(1,1) on the unit disk into ir reducible components. We start with the decomposition over the maximal compact subgroup K, we identify the modules of eigenfunctions which are square integrable with respect to the quasi invariant measure on the unit disk. These modules rep resent the discrete series representations. Then, we use the induction in stages method to find the principal series representation. The matrix coefficient with the principal series and a K-invariant vector turns to be an important function which is called a spherical function. There is a nice function (Harish Chandra’s function) controlling the decay of the spherical function at infinity. Finally, we use a new approach to find the inversion formula which is equivalent to decomposition into irreducible representations using the geometry of cycles with dual numbers and the covariant transform