A quantitative understanding of thermal field evolution is vital for quality control in additive manufacturing (AM). Because of the unknown material parameters, high computational costs, and imperfect understanding of the underlying science, physically-based approaches alone are insufficient for component-scale thermal field prediction. Here, I present a new framework that integrates physically-based and data-driven approaches with quasi in situ thermal imaging to address this problem. The framework consists of (i) thermal modeling using 3D finite element analysis (FEA), (ii) surrogate modeling using functional Gaussian process, and (iii) Bayesian calibration using the thermal imaging data. Based on heat transfer laws, I first investigate the transient thermal behavior during AM using 3D FEA. A functional Gaussian process-based surrogate model is then constructed to reduce the computational costs from the high-fidelity, physically-based model. I finally employ a Bayesian calibration method, which incorporates the surrogate model and thermal measurements, to enable layer-to-layer thermal field prediction across the whole component. A case study on fused deposition modeling is conducted for components with 7 to 16 layers. The cross-validation results show that the proposed framework allows for accurate and fast thermal field prediction for components with different process settings and geometric designs. / Master of Science / This paper aims to achieve the layer to layer temperature monitoring and consequently predict the temperature distribution for any new freeform geometry. An engineering statistical synergistic model is proposed to integrate the pure statistical methods and finite element modeling (FEM), which is physically meaningful as well as accurate for temperature prediction. Besides, this proposed synergistic model contains geometry information, which can be applied to any freeform geometry. This paper serves to enable a holistic cyber physical systems-based approach for the additive manufacturing (AM) not only restricted in fused deposition modeling (FDM) process but also can be extended to powder-based process like laser engineered net shaping (LENS) and selective laser sintering (SLS). This paper as well as the scheduled future works will make it affordable for customized AM including customized geometries and materials, which will greatly accelerate the transition from rapid prototyping to rapid manufacturing. This article demonstrates a first evaluation of engineering statistical synergistic model in AM technology, which gives a perspective on future researches about online quality monitoring and control of AM based data fusion principles.

Numerical simulations of incompressible, two-dimensional, monochromatically and bichromatically forced laminar free shear layers are performed on the basis of a vorticity-velocity formulation of the complete Navier-Stokes equations employing central finite differences. Spatially periodic shear layers developing in time (temporal model) are compared with shear layers developing in the stream-wise direction (spatial model). The regimes of linear growth and saturation of the fundamental are quantitatively scrutinized, the saturation of the subharmonic and vortex merging are investigated, and the effects of a forcing phase-shift between fundamental and subharmonic. For the spatial model the appearance of an unforced subharmonic was also examined. It was found that contrary to temporal shear layers a significant control of vortex merging by means of a forcing phase-shift and vortex shredding are not possible in spatial shear layers due to strong dispersion.

Detailed current profiles between the sediment-water interface and 20 cm above it reveal a viscous sublayer in the bottom boundary layer on the Oregon continental shelf. Data from three field experiments are used to test fundamental assumptions about boundary layer flow in the ocean. The first study, discussed in Chapter 1, evaluates the hypothesis that, in the absence of the obvious influence of topographic irregularities, the flow behaves like a universally similar, neutrally-buoyant flow over a smooth wall. The second study, discussed in Chapter 2, evaluates the influence which irregular small-scale topography may have on the near-bed flow, while the third, discussed in Chapter 3, examines streamwise velocity fluctuations in the viscous Sublayer and buffer layer and evaluates the hypothesis that spectra from the viscous sublayer and buffer layer of laboratory and geophysical boundary layer flows can be reduced to universal forms. although the thickness of the viscous sublayer scales with v/u, as required by universal similarity, the non-dimensional sublayer thickness is not as constant as in neutrally-buoyant laboratory flows. Even in the absence of the obvious effects of bottom irregularities, the near-bed flow is not as simple as smooth-walled boundarylayer flows in the laboratory. In the second study, it is shown that when the near-bed flow experiences resistance due to form drag as well as skin friction, the constant stress boundary layer assumption is not valid close to the sediment-water interface. Th the third study, it is shown that non-dimensionalized spectra of streamwise velocity fluctuations in the viscous sublayer and buffer layer at the ocean floor are very similar to those found in the laboratory. / Graduation date: 1982

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An experimental investigation of transition in boundary layer flows under the influence of various freestream conditions is described. Velocity profiles are obtained automatically by means of a stepper-motor driven traverse mechanism which carries a hot wire probe connected to a constant temperature anemometer and associated instrumentation. This was achieved by use of a data acquisition and control facility centred around a microcomputer with a Eurocard rack mounted extension. The automatic boundary layer traverse is software controlled and the data obtained is stored in a disc file for subsequent analysis and graphical display. As an integral part of this facility a successful method of obtaining reliable intermittency values from a hot wire signal was developed. The influence of freestream turbulence and pressure gradient upon transition within a boundary layer developing on a flat plate is elucidated by a series of controlled experiments. From the data accumulated, the concept of statistical similarity in transition regions is extended to include moderate non-zero pressure gradients, with the streamwise mean intermittency distribution described by the normal distribution function. An original correlation which accounts for the influence of freestream turbulence in zero pressure gradient flows, and the combined influence of freestream turbulence and pressure gradient in adverse pressure gradient flows, on the transition length Reynolds number R, is presented. (The limited amount of favourable pressure gradient data precluded the extension of the correlation to include favourable pressure gradient flows). A further original contribution was the derivation of an intermittency weighted function which describes the development of the boundary layer energy thickness through the transition region. A general boundary layer integral prediction scheme based on existing established integral techniques for the laminar and turbulent boundary layers with an intermittency modelled transition region, has been developed and applied successfully to a range of test data.

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No description available.

No description available.

No description available.