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A Theoretical Approach towards the Modeling of Vibrothermography Using Finite Element Methods
No full textA Master of Science thesis in Mechanical Engineering by Vibhor Bhargava entitled, “A Theoretical Approach towards the Modeling of Vibrothermography Using Finite Element Methods”, submitted in April 2019. Thesis advisor is Dr. Bassam Abu-Nabah and thesis co-advisor Dr. Maen Alkhader. Soft and hard copy available.The demand for preventive maintenance in the aerospace industry has been growing as part of life extension programs. Due to its reduced inspection time, part preparation requirements, floor space, and environmental concerns, vibrothermography has become an attractive solution to these programs as a potential replacement to conventional surface inspection methods. It offers the capability to detect surface cracks mainly through capturing vibration-induced frictional heat generation of contacting crack surfaces. The multidisciplinary nature of this inspection technology makes it rather difficult to theoretically capture the system response without the proper application of finite element (FE) methods. It requires relating the material mechanical and thermal properties in a coupled finite element model to properly address wave propagation, contact mechanics, fracture mechanics, friction heat generation and heat diffusion in simulated inspections. In this study, a theoretical model is developed to estimate the dynamic strain response at any location in commonly used cantilever beams oscillating at a given frequency. This model is utilized to assess the convergence of FE-based dynamic system response while determining the element size requirements to realistically model elastic wave propagation throughout the sample. Three different meshing criteria are assessed to properly capture the singularity at the crack tip. It is demonstrated that the use of solid element circular meshing criteria converges to singular quarter-node solid element solution and allows coupling it with heat generation and diffusion around the vicinity of a crack to deliver the most effective approach for modelling vibrothermography. Any deviation from the optimized meshing criteria and element size requirements will adversely affect the relative motion of crack surfaces and frictional heat generation. This effort brings FE modeling of vibrothermography a step closer towards realistic inspection simulation in the future.College of EngineeringDepartment of Mechanical EngineeringMaster of Science in Mechanical Engineering (MSME
Challenges of retrofitting affordable housing to net-zero carbon in the United Arab Emirates
No full textFollowing the Paris Agreement, several governmental bodies in the United Arab Emirates (UAE) started working on further initiatives to improve the energy efficiency of buildings. Some of these hope to target net-zero carbon for new and existing buildings. As in most countries, the stock of existing buildings represents the bigger challenge for this target. In particular, existing affordable housing is the most challenging segment of the building stock. The limited access to expertise and financial resources makes it more difficult for owners of these buildings to retrofit them. Therefore, there need to be appropriate guidelines on how to achieve net-zero carbon in such building typology. This paper identifies both the technical and the financial challenges when trying to develop such guidelines within the context of the UAE. It also discusses the possible solutions that can be used to overcome some of these challenges. The technical challenges include the variation in construction systems, and the quality of construction for these buildings. It also includes energy modelling challenges such as selecting relevant weather data, and defining the patterns of using electricity for the different functions. The financial challenges include the subsidized price for electricity, the cost estimation for various energy conservation methods, and the payback for installing local renewable energy sources. Finally, the paper suggests a path for research activities to address these challenges and to develop the guidelines
Lipophilic Metabolites and Anatomical Acclimatization of Cleome amblyocarpa in the Drought and Extra-Water Areas of the Arid Desert of UAE
No full textPlants adapt to different environmental conditions by developing structural and metabolic mechanisms. In this study, anatomical features and lipophilic metabolites were investigated in Cleome amblyocarpa Barr. & Murb., Cleomaceae plants growing in the arid desert of United Arab Emirates (UAE) in either low-water or extra-water areas, which were caused by the surrounding road run-o . The plant showed the presence of shaggy-like trichomes. The plant also developed special mechanisms to ensure its survival via release of lipophilic metabolites. The lipophilic metabolites, stained red with Sudan III, were apparently released by glandular trichomes and idioblasts of the shoot and roots, respectively. The identified lipophilic metabolites included those required for drought tolerance, protection against pathogens invasion, and detoxification. Plants growing in the low-water area caused an increase in the production of lipophilic metabolites—in particular, hydrocarbons and terpenoids. The lipophilic metabolites are known to provide the plant with unique waxy surfaces that reduce water loss and avoid penetration by pathogens. The release of lipid metabolites and the presence of shaggy-like trichomes represented unique features of the species that have never been reported. The provided chemical ecology information can be extended for several plant-related applications, particularly including drought tolerance
Effect of Basalt Microfiber on the Shear Response of RC Short Beams
No full textA Master of Science thesis in Civil Engineering by Mohamad Kusay Ahmad Rabee Sabbagh entitled, “Effect of Basalt Microfiber on the Shear Response of RC Short Beams”, submitted in December 2019. Thesis advisor is Dr. Farid Abed. Soft copy is available (Thesis, Approval Signatures, Completion Certificate, and AUS Archives Consent Form).Basalt composites are known for their high strength, lightweight and corrosion-resistance features. Basalt microfibers in fiber reinforced concrete mixes (FRC) can enhance the tensile strength, toughness and ductility as well as the post-cracking behavior of concrete members. This research investigates experimentally and analytically the effects of using basalt microfibers on the shear response of (FRC) short beams reinforced with basalt fiber reinforced polymers bars (BFRP), and compares the results with the strut-and-tie modeling (STM) according to ACI-318-14. The experimental program consists of performing four-point bending tests on eight BFRPFRC short beams that are 2000 mm long with 150 mm x 260 mm cross-section each. The test parameters include shear span-to-depth ratio, reinforcement ratio, concrete compressive strength and the type of microfibers used in the concrete mix. Experimental results showed that the presence of basalt microfibers has a significant influence in enhancing the overall beam stiffness and ultimate shear strength of tested beams. The maximum load carrying capacity increased by 42.1% and 38.2% with addition of basalt and synthetic microfibers, respectively. The capability of basalt microfibers in improving the shear responses of tested beams is attributed to their ability in bridging the micro-cracks by the efficient transfer of the stresses from tips of those cracks to the surrounding concrete. Hence, the propagation of more cracks is eliminated and the failure in the beam is delayed, which results in a greater load-carrying capacity. The constructed STM model as per ACI 318-14 resulted in a conservative prediction of the ultimate shear strength of tested beams compared to the experimental results.College of EngineeringDepartment of Civil EngineeringMaster of Science in Civil Engineering (MSCE
Outcomes and Key Factors of Success for ISO 14001 Certification: Evidence from an Emerging Arab Gulf Country
No full textThe objectives of this research were: (1) To examine the outcomes and key factors of success (KFS) related to ISO 14001 certification, (2) to compare and contrast these in private organizations (PRIVOs) and public organizations (PUBOs), and (3) in the under-explored context of an Arab Gulf country with an emerging economy: The United Arab Emirates. We used an exploratory, qualitative research approach, based on semi-structured interviews with the environmental managers of 14 UAE organizations from the private and public sector. The five major outcomes of ISO 14001 certification were improved: (1) Environmental performance, (2) organizational reputation and relationships with stakeholders, (3) organizational efficiency, (4) environmental management (EM) practices, and (5) environmental awareness. These outcomes were shared by PRIVOs and PUBOs, although improved resource management, improved relations with stakeholders, and improved EM practices were more common in PUBOs, and improved organizational efficiency was more common in PRIVOs. The six KFS for implementation were: (1) Senior management’s support, (2) employees’ awareness, involvement and competence, (3) government initiatives and commitment, (4) sufficient organizational resources, (5) adoption of a continuous, integrative, and collaborative approach, and (6) the use of external consultants. These KFS were shared by PRIVOs and PUBOs, although government initiatives and commitment were more common in PUBOs, and sufficient resources were more common in PRIVOs. Our study contributes to a better understanding of environmental management system implementation in emerging countries in general, and in Arab Gulf countries particularly. Our study has implications for business leaders, policy makers, EMS professionals, and educators in the UAE and other emerging countries
Conserved-Mass Metastructures For Vibration Suppression
No full textA Master of Science thesis in Mechanical Engineering by Ehab Emad Basta entitled, “Conserved-Mass Metastructures for Vibration Suppression”, submitted in April 2019. Thesis advisor is Dr. Samir Emam and thesis co-advisor is Dr. Mehdi Ghommem . Soft and hard copy available.Vibration suppression, cancellation or absorption is an expansive field of research, which has been the focus of numerous studies performed by scientists and engineers for decades. Metamaterials are a new class of semi-active composites that can be deployed to reduce vibration of the host structure (beam) within a desired frequency. In this thesis, we investigate the nonlinear vibrations of a metamaterial structure that consists of an Euler-Bernoulli beam host attached to a periodic array of spring-mass-damper subsystems deployed for vibration absorption. The governing equations of motion of the coupled system are derived and solved numerically. A mathematical model is first utilized to perform the linear free and forced vibration analyses. The effect of the local resonators on the suppression of the oscillations of the host beam is studied. The ability to mitigate the vibration of the host structure at a desired resonant frequency is achieved by tuning the resonant frequencies of the local absorbers. More interestingly, the results show that the simultaneous suppression of several modes is possible by tuning and properly placing each absorber along the host structure. More importantly, the results show that simply adding bulk mass to the host structure barely suppresses the vibration. The comparison between metastructure and adding bulk mass confirmed that the added mass using the metastructure assembly is essentially the reason for the mitigation and not the extra mass. Furthermore, the mathematical model is used to investigate the effect of the resonators (local absorbers) on the nonlinear behavior of the main structure when being subject to external forcing over an extended frequency range. The numerical study reveals that proper tuning of the local resonators allows significant vibration suppression of the metamaterial beam when being excited in the neighborhood of any of the first three natural frequencies. We demonstrate the capability of the metamaterial structure to withstand to external loading even when operating near resonance. Finally, we combine the nonlinear mathematical model with an optimizer to identify the number and tuning frequencies of the absorbers that maximize the vibration suppression. The optimization results show that significant mitigation can be achieved by tuning properly the absorbers in the vicinity of the host structure’s natural frequencies.College of EngineeringDepartment of Mechanical EngineeringMaster of Science in Mechanical Engineering (MSME
Motion-Based Gait Recognition for Recognizing People in Traditional Gulf Clothing
No full textGait recognition is gaining popularity as it can recognize people in a non-intrusive and a non-contact manner. However, gait recognition is known for its susceptibility to clothing conditions. In this paper, we propose a solution specific to clothing conditions in the Gulf region where Abaya and Kandura are considered traditional clothing. The paper proposes a solution capable of training users based on traditional clothing and recognizing them in Western style clothing and vice-a-versa. The solution uses depth imaging, optical flow, accumulated motion and Discrete Cosine Transformation (DCT). Motion is calculated from consecutive images where the magnitudes and phases of motion vectors are accumulated into separate matrices. DCT and zonal coding is then applied to these matrices to form one concise feature vector that represents a walk. Experimental results, with 38 participants, showed that the proposed method is suitable for gait recognizing with such clothing constraints. The average classification accuracy is 88%. In comparison to an existing method, it is shown that the proposed method results in much more accurate recognition results yet at a higher computational cost
Shear Strength of Concrete Beams Reinforced with Steel Welded Wire Fabric
No full textA Master of Science thesis in Civil Engineering by Yazan L. Alhoubi entitled, “Shear Strength of Concrete Beams Reinforced with Steel Welded Wire Fabric”, submitted in November 2019. Thesis advisor is Dr. Sami Tabsh. Soft copy is available (Thesis, Approval Signatures, Completion Certificate, and AUS Archives Consent Form).Reinforced concrete (RC) beams are typically reinforced transversely with steel stirrups to resist shear. However, this form of reinforcement requires extended time and considerable labor to make and place the stirrups, and results in large tolerances. Such shortcomings have encouraged researchers to seek alternatives methods of shear reinforcement. This study aims at researching the viability of using welded wire fabric (WWF), cold formed into the shape of a steel cage as shear reinforcement. A comprehensive literature review on this topic revealed scarce research about the use of WWF as shear reinforcement in RC beams. To accomplish the objective of the study, 23 half-scale beams that are 1900 mm or 2050 mm long with 200 mm x 300 mm cross- section are tested at AUS under a single-load configuration with consideration of different wire diameters (4, 6 and 8 mm), grid openings (25, 50 and 100 mm, concrete compressive strengths (30 and 35 MPa), shear span-to-thickness ratios (2.5 and 3.0), and transverse steel reinforcement ratios (251 and 505 N/mm). A comparison is carried out between the test results of WWF reinforced beams and corresponding stirrup reinforced beams in terms of the shear strength and ductility. The experimental study was complemented by a theoretical investigation utilizing the shear design provisions I n North American and European structural design codes. Results of the study showed that not all the vertical shear reinforcement in the WWF and stirrup reinforced beams reach yielding at ultimate and the shear span-to-depth ratio has no impact on the shear strength of such beams. The WWF reinforced beams possess 2-17% higher shear strength than corresponding stirrup reinforced beams and the ductility index of WWF reinforced beams matches the ductility index of corresponding stirrup reinforced beams. Beams containing WWF cages that consist of smaller diameter wires at narrow spacing exhibit slightly higher shear strength than corresponding ones containing larger diameter wires at wide spacing. The predicted shear strength by the ACI 318, Eurocode2, CSA23.3 and BS 8110 is within 6% of the strength obtained by the experiments. This shows that the current approaches for computing the shear strength of stirrup reinforced beams can be reliably used for WWF reinforced beams.College of EngineeringDepartment of Civil EngineeringMaster of Science in Civil Engineering (MSCE
Prediction of the Backwater Level Due to Bridge Constriction in Waterways
No full textA Master of Science thesis in Civil Engineering by Kimia Haji Amou Assar entitled, “Prediction of the Backwater Level Due to Bridge Constriction in Waterways”, submitted in May 2019. Thesis advisor is Dr. Serter Atabay. Soft and hard copy available.Worldwide, bridges and culverts built across rivers are obstacles to the flow which cause an increase in water depth at the upstream of the structure that significantly intensifies flooding of land and property upstream. Therefore, it is important to understand the effects of bridges and culverts on water levels for flood damage reduction, flood risk management, scour evaluation, flood risk mapping, and maintenance of rivers and channels. Moreover, the methods available in the literature are generally not convenient for engineers due to the complexity of the equations and procedures of each method. On the other hand, the simple methods available in the literature do not contain a high level of accuracy. Hence, acquiring a simple accurate empirical method for computing backwater is necessary. In this study, a series of parametric studies is conducted to examine the influence of different factors on backwater. The results of the parametric studies along with multiple regression analysis are used in deriving a simple accurate mathematical model for computing backwater. The proposed method is firstly compared with the most commonly used method, energy method, for different skew angles and roughness cases. The comparison of the results of the proposed and energy methods indicates high correlations between the two methods. Furthermore, the proposed method is validated by comparing its results with experimental data for normal (at 0º), and skewed crossings at 30º and 45º. The overall absolute average percentage difference between the proposed method and experimental data is found to be 5.1%, while the overall root-mean-square error is found to be 0.008. Thus, the empirical method proposed by this study is considered highly accurate as well as simple in comparison with available methods in the literature. Additionally, the proposed method is applicable for rectangular and arch bridges, multiple opening bridges, and any type of crossings (normal and skewed) in compound channels.College of EngineeringDepartment of Civil EngineeringMaster of Science in Civil Engineering (MSCE
Multi Agent Reinforcement Learning Approach for Autonomous Fleet Management
No full textA Master of Science thesis in Computer Engineering by Mohammed Omer Alamin Alhusin entitled, “Multi Agent Reinforcement Learning Approach for Autonomous Fleet Management”, submitted in December 2019. Thesis advisor is Dr. Michel Pasquier and thesis co-advisor is Dr. Gerassimos Barlas. Soft copy is available (Thesis, Approval Signatures, Completion Certificate, and AUS Archives Consent Form).The Taxi Dispatch problem is a well-known and important problem in the field of transportation and logistics, that has many similarities with other fleet management problems. The objective of the taxi dispatch system is to assign idle taxis to passengers waiting at different geographical locations in a way that maximizes resource utilization while minimizing their operating cost. Traditionally, heuristic rules are used in dispatch problems, mainly because of the simplicity and scalability of the approach. However, at high demand rates, rule-based approaches perform poorly. This encouraged many researchers to build more complex models to tackle the dispatch problem, but most of these models are computationally expensive and cannot scale to handle large fleets. Additionally, most of these approaches are not robust enough for a stochastic environment, which is usually the case with real-world traffic. In this work we model the problem as a Markov Game and solve it using Model-Free Multi-Agent Deep Reinforcement Learning, which is the best approach when the environment is stochastic and there is otherwise no good model for it. The main drawback of reinforcement learning is that it requires too much time and data to learn the optimal policy. In this work we address this issue and strive to improve the efficiency of this algorithm. The curse of dimensionality was broken by representing the state variable as an image which made the complexity independent from the number of taxis and requests and only dependent on the size of the map thus allowing the algorithm to handle large fleets with ease. Using a residual convolutional neural network as Q function approximator allowed the agents to learn complex spatial patterns while seeing only few training samples. We have also found that we can reduce the resolution of the state variable by more than half while losing only 3% of the performance. The proposed algorithm was validated against a rule-based heuristic under different supply-demand ratios, and found to outperform the rule-based technique by a large margin when there is a lack of supply.College of EngineeringDepartment of Computer Science and EngineeringMaster of Science in Computer Engineering (MSCoE