Permanent URI for this community
Browse
1359 results
Search results
Publication COMBUSTION AND EMISSIONS FORMATION IN DIESEL ENGINE FUELED BY POLYOXYMETHYLENE DIMETHYL ETHER AND ITS BLENDS(2021-05-07) LIN QINJIE; MECHANICAL ENGINEERING; Yang WenmingThe use of alternative oxygenated fuels is imperative for reducing harmful emissions, especially soot particles. Amongst the various oxygenates, polyoxymethylene dimethyl ether, or PODEn, has the highest potential largely due to its high oxygen content and cetane number. A highly compact and reliable PODE3 mechanism consisting of 61 species and 190 reactions has been developed based on decoupling methodology. The major reaction pathway of the PODE3 sub-mechanism, consists of only 11 species and 17 reactions. Another PODE3 mechanism consisting of 120 species and 560 reactions has also been developed for soot prediction. Furthermore, an engine experiment has been conducted using realistic PODE3/diesel blends to ascertain the characteristics of PODE3 combustion in a practical setting. It has been found that PODE3 addition generally leads to decrements in soot and the usage of PODE3 has minimal impact on fuel economy due to the high density of PODE3.Publication Thermosyphon flow for cooling of compact devices(2011-07-04) FILIAN ARBIYANI; MECHANICAL ENGINEERING; YAP, CHRISTOPHER ROBERT; NG KIM CHOONThe challenge of power dissipation in compact devices requires advanced cooling systems. In the present study, three novel cooling systems with essential attributes of compactness, low-cost, high cooling capacity, and orientation-free design are developed. A two-phase thermosyphon water-cooled condenser system was built and used in an experiment and numerical investigation of the effect of heat load on chip temperature. The effect of heat load on temperature difference between chip and inlet cooling water, and the heat load vs heat dissipation were also studied. A new designed of a helical-grooved heat pipe was then fabricated for an experimental study in obtaining the operating temperature as well as temperature distribution along the heat pipe axis for varying conditions, and the thermal resistance and overall heat transfer coefficient over a range of temperatures. Finally, a new design of a sintered heat pipe was fabricated for experiments to obtain a comparison with previous studies of a helical-grooved heat pipe.Publication Micromechanical Properties and Domain Structures of PZN-PT Piezoelectric Single Crystals(2011-01-18) WONG MENG FEI; MECHANICAL ENGINEERING; ZENG KAIYANGRelaxor ferroelectric single crystals of Pb(Zn1/3Nb2/3)O3-(6-7)%PbTiO3 solid solution have recently attracted considerable attention due to their superior dielectric and piezoelectric properties. This has spurred remarkable motivation to study their deformation and domain phenomena since mechanical properties directly pertain to the crystals? reliability in piezoelectric device applications. Nanoindentation and Piezoresponse Force Microscopy (PFM) revealed the effects of mechanical pop-in events on structural and domain distortion due to a surface deformed layer, produced during the crystal fabrication process. However, this layer could be removed by an additional polishing procedure to mirror finish. Overall quantitative analysis shows that the unpoled PZN-PT single crystals have an elastic modulus of ~110 ? 120 GPa, which can be better enhanced by a poling process, especially for (011)-oriented crystals. Despite better mechanical properties, the (011)-oriented crystals were more susceptible to frequency effects during Continuous Stiffness Measurement (CSM) compared with their (001)-oriented counterparts. On the other hand, domain studies suggested that the {110} planes were the domain switching planes for the PZN-PT single crystals, while the {100} planes could be special cleavage planes caused by tensile hoop stress. All these finding are of considerable importance for a better understanding of PZN-PT single crystals behaviors in piezoelectric device applications.Publication Design and Development of an Autonomous Omni-Directional Mobile Robot(2011-08-19) SEAN EFREM SABASTIAN; MECHANICAL ENGINEERING; ANG, MARCELO JR. H.The objective of this M Eng work is the design and development of a low-cost omnidirectional mobile robot that has specific required abilities that will aid it in its safe autonomous navigation in an unknown environment. Some of the abilities are omni-directional motion capability that allows it to be holonomic, ground edge detection capabilities that will prevent the robot from experiencing a fall, obstacle avoidance which is essential as it moves to a goal location, carry a note book that will serve as a higher level control which will allow wireless communication, navigation computation and a platform for further developments (such as the attachment of a camera for vision processing) and collision detection so that the robot will be aware that it has collided into an obstacle. A microcontroller has been custom designed for the low-level control of the mobile robot architecture. It consists of three ARM Cortex-M processors that will communicate with the three actuators and sensors on the robot. The two Slave processors on board have also been programmed to communicate reliably with a Master processor which will be the gateway for communication to the notebook for higher-level control. The communication protocol between the microcontroller and the notebook has also been set up. It will send data which will be used in the navigation computation, writing to file and be displayed on a Graphical User Interface (GUI) which has also been written. With the aim of this project to be low cost, reliable working components were obtained where possible and fabrication was done in-house by the author. The robot?s mechanical design is built from scratch and having three wheels, the kinematics of motion that relates the overall robot?s velocity and the individual wheel?s velocities has been derived. A control algorithm of the actuator has been implemented and shows good performance. A navigation algorithm has also been implemented and efficacy has been demonstrated. Performance analysis has been performed and drawbacks to both the control and navigation algorithm are discussed. This autonomous holonomic robot is also meant to serve as a platform for future developments and it is described in this thesis.Publication INVESTIGATION ON THE COMBUSTION PROCESS AND EMISSIONS FORMATION IN THE GRATE BOILER BY COUPLING THREE-DIMENSIONAL FULL-SCALE GAS PHASE SIMULATION WITH DYNAMIC PACKED FUEL CONVERSION MODEL(2020-05-20) ZHOU ANQI; MECHANICAL ENGINEERING; Wenming YangPublication CYCLOPROP - A NOVEL FLYING MODE(2019-09-23) BRIAN SHOHEI TEO; MECHANICAL ENGINEERING; Teo Chiang Juay; Lim Kah BinCyclorotors have inherent thrust vectoring capabilities which make them ideally suited for VTOL aircraft. They have mainly been used in smaller unmanned aircraft with limited capability. Thus, we will be exploring the use of a larger scale prototype along with their associated characterization. A series of equations were proposed to characterize the performance of a larger Cyclorotor. Following the generation of these equations, a prototype was built to validate these equations. The prototype Cyclorotor was divided into several major sub-assemblies and designed accordingly. The main mechanisms included planetary gears and a blade control system. During testing, a number of difficulties were encountered. These difficulties were related to the design of the system and were eventually overcome. The results of the testing were inconclusive. However, a number of important lessons were learnt about how to better approach the design of a future Cyclorotor prototype.Publication Lubrication and Tribological Performance Optimizations for Micro-Electro-Mechanical Systems(2012-10-18) LEONG YONGHUI, JONATHAN; MECHANICAL ENGINEERING; SINHA, SUJEET KUMAR; HUGH SPIKESTwo approaches to solving MEMS tribology problems have been pursued. In the first approach, a direct lubrication method using well-known lubricants such as perfluoropolyether (PFPE) and multiply alkylated cyclopentane (MAC) was developed. Extensive tribological tests using reciprocating sliding and actual MEMS tribometry were conducted. The second approach utilized the concept of hydrodynamic lubrication and selective surface modification for MEMS. In the interests of fluid-film liquid lubrication of MEMS, MAC was found to reduce the hydrodynamic friction of high-sliding MEMS when included as an additive in hexadecane at an optimum concentration. This phenomenon is believed to be due to the ?half wetted bearing? effect and not due to the change in viscosity. A compound blend of octadecylamine and MAC additives in hexadecane was found to reduce both boundary and hydrodynamic friction. Anti spreading methods using additives were finally investigated to prevent starvation.Publication A FRAMEWORK FOR CONCEPT VALIDATION IN DESIGN USING DIGITAL PROTOTYPING(2015-08-17) SOHEIL ARASTEHFAR; MECHANICAL ENGINEERING; LU WEN-FENGValidation of product concepts to fulfill user needs is of great importance to develop a successful product. The objective of this thesis was to develop a framework for concept validation by using digital prototyping and quantitative feedback. The framework aims to identify the best product concept by using user feedback on specification values and design solutions at conceptual design. The framework involves users at two stages (1) before concept generation to identify the best target specifications from product design specification so as to produce better design solutions, and (2) at concept selection to identify the best solutions to develop a product concept complying better with user needs. Conclusive evidence was provided that the concept validation based on the developed framework can deal with a large number of specifications and solutions, and yields the product concepts that effectively fulfill user needs. We focused on hand-held electronic consumer products such as smartphones.Publication A STUDY OF HEAT GENERATION AND CYCLING PERFORMANCE OF SODIUM-ION CELLS(2020-01-22) LIHIL UTHPALA SUBASINGHE; MECHANICAL ENGINEERING; Palani BalayaThis thesis reveals heat generation and impedance characteristics of different 18650-sized sodium-ion cells with monoclinic Na2Fe2(CN)6·2H2O (MPB), rhombohedral Na2Fe2(CN)6 (RPB), pristine Na3V2(PO4)3 (P-NVP), and modified Na3.2V1.8Zn0.2(PO4)3 (M-NVP) as cathodes and hard carbon (HC) as anode, filled with non-flammable electrolyte: 1 M NaBF4 in tetraglyme. Comparison of calorimetric studies performed on 18650 cells reveals lower heat generation in MNVP vs. HC among all the tested cells. Internal resistance, which is the major contributor to heat generation, is assessed by analysing the impedance spectra of the cells. Furthermore, variation in subcomponents of internal resistance across different depths of discharge is determined by equivalent circuit fitting and distribution of relaxation times (DRT) analysis. Moreover, a long-term cycling study is conducted on M-NVP vs. HC coin cells filled with 1 M NaBF4 in tetraglyme to evaluate the effect of different operating conditions on cycle life and to determine capacity degradation mechanisms in sodium-ion cells.Publication PHYSICS-BASED AND DATA-DRIVEN DEEP LEARNING MODELS FOR FLOW FIELD PREDICTION AND AIRFOIL DESIGN(2020-11-24) VINOTHKUMAR SEKAR; MECHANICAL ENGINEERING; Shu Chang; Khoo Boo CheongComputational Fluid Dynamics (CFD) techniques have emerged as powerful tools for exploring and solving real engineering problems in mechanical and aerospace industries. However, it is still relatively time-consuming for tasks such as optimization and fluid-structure interaction, where there is a requirement of large iterations. Hence, the current work develops data-driven deep learning models, which are fast yet accurate. First, the current work develops a deep learning-based framework for obtaining flow field over variable geometries. Further, a surrogate model-based approach is developed to perform fast optimization of airfoils. In addition, an approach is presented to perform inverse design of airfoil using deep learning. Besides, the current work explores Physics Informed Neural Networks (PINN) for obtaining flow solutions near the wall accurately with measurements (or sampling points) away from the wall. From the obtained results, it is observed that the developed methods are efficient and accurate.