Fill Time Optimization Analysis In Flow Simulation Of Injection Molding Using Response Surface Method

This study focuses on the analysis of fill time by optimizing the injection molding parameters to reduce the defects that are always found on the plastics part such as poor weld line and part not completely filling which can contribute to mechanical properties of the plastic part. The parameters selected for this study are melting temperature, mold temperature, injection time,and the number of gate positions. Response Surface Method (RSM) was used to determine the most significant and optimum parameters on the fill time. From the result analysis, it is found that the injection time is the most significant parameter that affected the fill time with a 99% contribution. The result shows that there is no interaction between process parameters toward fill time which the injection time is the only major factor that affects the fill time. The improvement increases by 0.07% after the optimization process from 4.278s to 4.281s. The most optimum parameters to longer the injection time are mold temperature at 60°C, injection time at 4s, and the number of the gate with two gates position. Thus, the longer the injection time, it can reduce the defect of molded part in the injection molding process

Friction stir processing of aluminium-silicon alloys

Friction Stir Processing (FSP) has the potential for locally enhancing the properties of Al-Si alloy castings, for demanding applications within the automotive industry. In this thesis, the effect of FSP has been examined on three different cast Al-Si alloys:i) A Hypoeutectic Al-8.9wt%Si Alloyii) A Hypereutectic Al-12.1wt%Si Alloyiii) A Hypereutectic Al-12.1wt%Si-2.4wt%Ni AlloyThe influence of different processing parameters has been investigated at a fundamental level. Image analysis of particle size distributions and growth method of tessellation were used to quantify the level of particle refinement and the homogeneity of the second phase spatial distribution. Stop-action experiments were also carried out, to allow the microstructural changes around the tool during FSP to be studied. Two computer models have been explored, in order to predict the temperature distribution and the material flow behaviour. Furthermore, the stability of the microstructure of the friction stir processed material was studied after being heat treated at elevated temperatures. The changes in particle size and grain structure were examined, hardness measurements were taken across the PZ, and tensile testing were carried out at room and elevated temperatures.After FSP, the microstructure of the cast Al-Si alloys was greatly refined. However, differences in microstructure have been observed throughout the PZ, which tended to be better refined and distributed on the advancing side, than the retreating side of the PZ. Changing the processing parameters also influenced the size and spatial distribution of the second phase particles. By studying the changes in microstructure around the tool from the stop-action experiments, and comparing the results to the thermal distribution and material flow behaviour predicted by the computer models, it has been shown that the flow stress, pitch, and temperature of processing, all needed to be considered, when determining the effects that FSP have on the microstructure. FSP caused very little changes to the hardness of the material, while tensile properties were greatly improved, due to the elimination of porosity and refinement of large flawed particles. In terms of the stability of the microstructure after FSP, particle coarsening and abnormal grain growth has been observed during high temperatures heat treatment. Furthermore, the Al2Cu phase was found to dissolve into solid solution at elevated temperatures, so GPZs and solute clustering can then develop within the alloy during natural ageing.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Advanced geometries for dryout mitigation in temhd-driven liquid lithium systems

The promise of nuclear fusion as an energy source is unparalleled, but the technological challenge is arguably the most difficult humanity has faced. As progress continues toward bringing sustained fusion power production to the grid, the conditions inside fusion devices are becoming more extreme. A common method of producing sustained fusion reactions is by heating isotopes of hydrogen until they are a plasma and confining them magnetically in a toroidal vacuum system. High plasma density, long confinement time, and extremely high plasma temperatures must be achieved in order to create efficient fusion. Plasma facing components (PFCs) must bear the brunt of these extreme conditions, which can result in a myriad of damage mechanisms on even the most resilient materials. One method of mitigating the damage in solid PFCs is through the use of liquid metals, specifically liquid lithium. Liquid lithium PFCs reduce erosion and thermal stress damage, prolonging device lifetime, and have been shown to enhance plasma performance, decrease edge recycling, and reduce impurities. Flowing open surface liquid metal concepts utilize flowing liquid lithium to provide a constantly refreshing PFC surface and can remove impurities from the device, though potential concerns include surface stability, wetting control, hydrogen retention, and heat flux handling. The Liquid Metal Infused Trench (LiMIT) concept pioneered at the University of Illinois harnesses the heat and magnetic fields already present in fusion devices to drive lithium flow via thermoelectric magnetohydrodynamics (TEMHD). Proof of concept testing at the Center for Plasma Material Interactions and larger scale testing in the HT-7 and EAST tokamaks and the Magnum PSI linear plasma device have shown sustained flow and improved plasma performance. Continued development of the system has focused on mitigating potential concerns, including defining stability criteria, enhancing ability to control lithium wetting and flow, and designing systems to recover the hydrogenic fuel species from lithium. Under high localized heat fluxes present in fusion devices, TEMHD forces can cause a depression of the lithium surface below the solid structures, minimizing the benefits of the flowing liquid system and risking damage. This is known as the lithium dryout phenomenon. This work adapts the standard LiMIT trench design to improve heat flux handling and eliminate the presence of lithium dryout on the free surface. Improvements to the design focus on extending the 1-D trench design to 2-D and 3-D flow channels, which result in post and foam structures. Using extensive COMSOL Multiphysics modeling and experimental testing, the propensity for TEMHD flow and the resistance to dryout in the face of high localized heat flux is investigated. The 3 post TEMHD designs exhibit effective TEMHD drive with maximum velocities on the order of 0.2 to 0.9 m/s, depending on the geometry and the peak heat flux applied. The addition of secondary flow channels improves dryout resistance, though swirling flow and eddies develop around the posts. Experimental testing verifies the usefulness of the crosstalk to distribute flow, and velocities match numerical modeling of the system. A disordered foam geometry and 3 ordered foam geometries are tested as concepts to improve capillary action and surface stability while still allowing TEMHD flow. While the internal structure of the disordered foam as manufactured did not prove compatible with liquid lithium, a new pipeline was developed to incorporate arbitrary geometries into TEMHD modeling. The ordered designs exhibit sustained TEMHD flow of slower maximum magnitude than the post geometries, between 0.05 and 0.35 m/s. This reduction in flow speed comes with improved resistance to dryout. Experimental testing of proof of concept cases showed velocities that matched numerical modeling. Electron beam testing of the foam proves heat flux handling capabilities of the designs and increases the operating regime of the LiMIT system by 127%, to 6.8 MW/m2, with no signs of dryout or impending damage. New capabilities of multiphysics modeling of the TEMHD systems were developed to capture the motion of the free surface. Using a level set multiphase model, TEMHD flow under low heat flux proof of concept conditions was replicated. Applying a high heat flux stripe to the free surface resulted in lithium dryout and pileup in the trench domain, which was reduced in the post and foam designs. The inclusion of surface tension in the model steadies the free surface against dryout. Surface tension values near that of liquid lithium, up to 0.3 N/m, were applied. The surface tension simulations displayed successful elimination of dryout in a 3 MW/m2 peak heat flux scenario, but the large surface forces induced spurious wave motion in the free surface

High-Fidelity Simulation of Small-Body Lander/Rover Spacecraft

The scientific return of spacecraft missions that explore solar system small bodies can be increased through the inclusion of surface exploration with deployed probes. In this dissertation, a methodology is presented that allows for fast, parallel simulation of bouncing trajectories of arbitrary-shaped ballistic probes in the small-body environment. This enables planning of probe deployment and operation, and supports their inclusion on future missions.The coarse small-body shape is modeled using an implicit signed distance field (SDF) that allows for fast collision detection. Statistical features are included onto the SDF using procedural generation techniques. The small-body gravity field is captured using a voxelization of the classical constant-density polyhedron. Surface interactions between a probe and the surface are accounted for using a hard contact model that takes into account restitution and friction. These models are implemented in a GPU environment to allow for the parallel execution of multiple trajectories.The developed simulation framework is applied to perform parametric investigations of probe deployment, which quantify the effects of relevant properties of a probe and its target small body. The probe shape and internal mass distribution are found to strongly affect its deployment dynamics, with near-spherical probes dispersing over greater regions than more distorted shapes. The effect of the surface interactions coefficients on the different shapes variants is quantified. The presence of statistical surface features is also shown to further influence probe dynamics.Finally, the framework is applied to perform a pre-arrival deployment analysis of the MINERVA-II rovers onboard the Hayabusa-2 spacecraft. This analysis identified challenges in the rover deployment and was used to redesign aspects of the nominal rover release sequence. These models will be used to inform the target site selection and follow-on analysis for the Hayabusa-2 mission rover deployments

Automated calibration of multi-sensor optical shape measurement system

A multi-sensor optical shape measurement system (SMS) based on the fringe projection method and temporal phase unwrapping has recently been commercialised as a result of its easy implementation, computer control using a spatial light modulator, and fast full-field measurement. The main advantage of a multi-sensor SMS is the ability to make measurements for 360° coverage without the requirement for mounting the measured component on translation and/or rotation stages. However, for greater acceptance in industry, issues relating to a user-friendly calibration of the multi-sensor SMS in an industrial environment for presentation of the measured data in a single coordinate system need to be addressed. The calibration of multi-sensor SMSs typically requires a calibration artefact, which consequently leads to significant user input for the processing of calibration data, in order to obtain the respective sensor's optimal imaging geometry parameters. The imaging geometry parameters provide a mapping from the acquired shape data to real world Cartesian coordinates. However, the process of obtaining optimal sensor imaging geometry parameters (which involves a nonlinear numerical optimization process known as bundle adjustment), requires labelling regions within each point cloud as belonging to known features of the calibration artefact. This thesis describes an automated calibration procedure which ensures that calibration data is processed through automated feature detection of the calibration artefact, artefact pose estimation, automated control point selection, and finally bundle adjustment itself. [Continues.

A hydrodynamical perspective on the turbulent transport of bacteria in rivers

The transport of bacteria in river systems is a phenomenon which occurs on a multitude of length scales ranging from the size of individual microbes up to the size of an entire estuary. At the same time the understanding of the spreading of microbial populations after a localised contamination event such as a combined sewer overflow is crucial for the prediction of the water quality downstream of the source, which is in turn essential to managing public health. It is well-established that microbial populations in fluvial systems may preferably be found on the surface of small particles rather than solely freely suspended in the water body. The attachment to particles provides an environment beneficial to the survival of bacteria due to the improved access to nutrients and the shielding from environmental stressors, but also alters their dispersion characteristics as the transport of bacteria is then coupled to the trajectories of heavy particles. The importance in the distinction between the particle-attached and the freely-suspended mode of transport has been recognised in the mechanistic modelling of bacteria fate and transport. However, due to the multiscale nature of the problem, the mechanisms which govern the transport of particles in river-like flows are never resolved explicitly, and hence, the models profoundly rely upon the availability of accurate descriptions thereof. The associated problem of particles settling in a turbulent carrier flow is an active topic of research by itself, and is rich in emerging phenomena such as the emergence of spatial inhomogeneities or non-trivial modifications of the settling characteristics compared to quiescent environments. In particular, the transient settling of particles in horizontal open channels, which serves as an abstraction of particle-attached bacteria transport in rivers, has hitherto received only little attention in the literature. As a consequence, the knowledge on the impact of its defining features such as boundedness, anisotropy and vertical inhomogeneity on the settling characteristics is limited and needs to be addressed to enable the formulation of reliable models thereof. The aim of this thesis is to fill the knowledge gap on the transport characteristics of heavy particles in turbulent horizontal open channel flows, and to identify phenomena which may be of importance in the context of bacteria transport modelling. For this purpose, the incompressible Navier--Stokes equations and the momentum balance equations for dispersed particles are solved using direct numerical simulations and the immersed boundary method. This approach resolves all relevant scales of turbulence and the microscopic flow around each particle explicitly, and thus, describes the particle-fluid interaction from fundamental principles of physics without the need of additional modelling. Apart from the contaminated particles, which are introduced near the free surface of the flow, the simulation domain includes approximately 100,000 fully resolved particles at the bottom of the domain, which form a realistic sediment bed, and enable the examination of the interaction between contaminated particles and mobile sediments. Concerning the parameter space, the value of the friction Reynolds number is varied within the range $Re_{\tau} \in [241,838]$, while the contaminant parameter space is chosen such that the resulting relative turbulence intensities---defined as the ratio between the friction velocity and the undisturbed terminal velocity---lie within the range $I_{\tau} \in [0.47,2.88]$. Moreover, two types of sediment bedforms are investigated in order to assess their effect on contaminant transport, namely a macroscopically flat bed and a bed featuring ripples. The analysis of the simulation data shows that the settling velocity of the contaminant particles is enhanced in the ensemble-averaged sense, yet, the time from beginning of the settling until the initial deposition is prolonged when compared to the ratio between the channel height and the terminal velocity. The enhancement is demonstrated to be a result of the preferential sampling of turbulent sweep events, which also implies that the streamwise component of the particle velocity is increased compared to the mean fluid velocity at the same position. A closer examination of the spatial organisation of contaminated particles reveals that they tend to accumulate in large-scale high-speed velocity streaks in the outer region of turbulence. Due to this focusing mechanism, the mean-squared lateral displacement of the settling particles stagnates in the lower half of the channel such that contaminants are not further dispersed in cross-stream direction until shortly before deposition. The same behaviour could be reproduced using a time-invariant exact coherent flow state resembling a hairpin vortex as a proxy for turbulence, and an extended parameter sweep in this setup suggests that this transport barrier effect persists even at high relative turbulence intensities. It is speculated that this phenomenon might confine contaminated particles to a region close to the river bank over a considerable downstream distance in the aftermath of a combined sewer overflow event, which might seriously impact decisions regarding public health measures. Near the sediment bed, the barrier effect of the large-scale motions is inactive and contaminants are found to disperse laterally at a rate which presumably depends on the Shields parameter. The interaction between the sediment and the contaminants is distinct for the two bed topologies under investigation. In the case of macroscopically flat beds, the contaminated particles are transported towards sediment ridges which are in turn known to be a result of the action of large-scale fluid motions, and the mixing of contaminants and sediment particles is restricted to the thin layer of sediment near the interface. In contrast, the presence of ripples leads to a capturing effect where contaminated particles are preferentially deposited in the trough of the ripple, and subsequently buried by a thick layer of sediment due to the propagation of the bed feature. This mechanism temporarily immobilises a large share of all contaminated particles until the displacement of the ripple has sufficiently progressed for them to be eroded on the windward side. During the immobilisation, the associated bacteria are shielded from solar radiation to a substantial degree, which likely has a significant impact on their inactivation, especially in shallow waters. Moreover, the cyclic nature of this phenomenon may provide one of many explanations for bacteria storages which are known to exist in river sediments and may cause bursts in fecal bacteria indicator levels even in absence of immediate contamination events. It is concluded that direct numerical simulation can be a valuable tool for the analysis of bacteria transport, and recommendations are made on how the conjectures compiled in this thesis can be targeted in laboratory experiments to examine their relevance

A hydrodynamical perspective on the turbulent transport of bacteria in rivers

The transport of bacteria in turbulent river-like environments is addressed, where bacterial populations are frequently encountered attached to solids. This transport mode is investigated by studying the transient settling of heavy particles in turbulent channel flows featuring sediment beds. A numerical method is used to fully resolve turbulence and finite-size particles, which enables the assessment of the complex interplay between flow structures, suspended solids and river sediment

Association of Architecture Schools in Australasia

"Techniques and Technologies: Transfer and Transformation", proceedings of the 2007 AASA Conference held September 27-29, 2007, at the School of Architecture, UTS