Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones

Observation of keyhole-mode laser melting in laser powder-bed fusion additive manufacturing

Space and airborne sensors have been used to map area burned, assess characteristics of active fires, and characterize post-fire ecological effects. Confusion about fire intensity, fire severity, burn severity, and related terms can result in the potential misuse of the inferred information by land managers and remote sensing practitioners who require unambiguous remote sensing products for fire management. The objective of the present paper is to provide a comprehensive review of current and potential remote sensing methods used to assess fire behavior and effects and ecological responses to fire. We clarify the terminology to facilitate development and interpretation of comprehensible and defensible remote sensing products, present the potential and limitations of a variety of approaches for remotely measuring active fires and their post-fire ecological effects, and discuss challenges and future directions of fire-related remote sensing research.

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Remote sensing techniques to assess active fire characteristics and post-fire effects

Localized fluid flow measurements with an He-Ne laser spectrometer

On the limitations of Volumetric Energy Density as a design parameter for Selective Laser Melting

In laser material processing, understanding the laser interaction and the effect of processing parameters on this interaction is fundamental to any process if the system is to be optimized. Expanding this to different materials or other laser systems with different beam characteristics makes this interaction more complex and difficult to resolve. This work presents a relatively simple physical model to understand these interactions in terms of mean surface enthalpy values derived from both material parameters and laser parameters. From these fundamental properties the melt depth and width for any material can be predicted using a simple theory. By considering the mean enthalpy of the surface, the transition from conduction limited melting to keyholing can also be accurately predicted. The theory is compared to experimental results and the predicted and observed data are shown to correspond well for these experimental results as well as for published results for stainless steel and for a range of metals. The results suggest that it is important to keep the Fourier number of the weld much smaller than one to make it efficient. It is also discussed that the surface enthalpy could be used to prodict other effects in the weld such as porosity and material expulsion.

https://iopscience.iop.org/article/10.1088/0022-3727/44/44/445401/pdf

A simple methodology for predicting laser-weld properties from material and laser parameters

Wavelet analysis represents a powerful set of image processing techniques that have considerable potential to quantify ecologically relevant patterns at multiple scales. This paper provides a preliminary assessment of whether two‐dimensional wavelets convolved with 1 m panchromatic aerial photography can be used to detect automatically the location and crown diameters of western juniper (Juniperus occidentalis) plants as they encroach upon a sagebrush (Artemisia spp.) steppe landscape. The juniper crown diameters derived from wavelet analysis produced a strong correlation with crown diameters measured via comparable hand‐digitizing in a geographic information system (r = 0.96, n = 69) with a 5% commission and an 8% omission error. Through comparison with historical photography, we found that juniper plant cover increased 2.7 fold (from 2.7% to 7.3% total cover) during the period from 1939 to 1998 within the 15 ha study area. This approach has considerable potential for the long‐term monitoring of vegetation change via aerial photograph and other remotely sensed imagery.

Wavelet Estimation of Plant Spatial Patterns in Multi-temporal Aerial Photography

Wavelet analysis represents a powerful set of image processing techniques that have considerable potential to quantify ecologically relevant patterns at multiple scales. This paper provides a preliminary assessment of whether two‐dimensional wavelets convolved with 1 m panchromatic aerial photography can be used to detect automatically the location and crown diameters of western juniper (Juniperus occidentalis) plants as they encroach upon a sagebrush (Artemisia spp.) steppe landscape. The juniper crown diameters derived from wavelet analysis produced a strong correlation with crown diameters measured via comparable hand‐digitizing in a geographic information system (r = 0.96, n = 69) with a 5% commission and an 8% omission error. Through comparison with historical photography, we found that juniper plant cover increased 2.7 fold (from 2.7% to 7.3% total cover) during the period from 1939 to 1998 within the 15 ha study area. This approach has considerable potential for the long‐term monitoring of vegetati...

/pdf/wavelet-estimation-of-plant-spatial-patterns-in-uvh5ynd0iu.pdf

Wavelet estimation of plant spatial patterns in multitemporal aerial photography

https://nottingham-repository.worktribe.com/preview/741637/Study%20of%20gas-sheared%20liquid%20film%20in%20horizontal%20rectangular%20duct%20using%20high-speed%20LIF%20technique-%20three-dimensional%20wavy%20structure%20and%20its%20relation%20to%20li.pdf

Study of gas-sheared liquid film in horizontal rectangular duct using high-speed LIF technique: Three-dimensional wavy structure and its relation to liquid entrainment

Investigations of the impact regimes for a liquid droplet impacting onto horizontal moving liquid films are presented here for the first time. The aim of this study is to show the main impact outcomes and to highlight the effect the movement of films has upon these outcomes. The droplet diameters used in this experiment were 2.47 and 3.86 mm with impact Weber number of between 0.6 and 460. The Reynolds number of the moving film was between 351 and 1,818 depending on the flow rate (1–5.5 L/min) with changes in the film height of between 4.3 and 9.4 mm. The results showed that the impact outcomes exhibit the same regimes established for the impact on static liquids but with different transition boundaries. Moreover, the shape of the impact outcomes is unsymmetrical similar to the inclined impact on static liquids. The impact outcomes are shown to undergo a transition as the Reynolds number of the film increases, this occurs at a threshold value close to the expected transition between laminar and turbulent flow.

David Hann

Papers

A simple methodology for predicting laser-weld properties from material and laser parameters

Wavelet Estimation of Plant Spatial Patterns in Multi-temporal Aerial Photography

Wavelet estimation of plant spatial patterns in multitemporal aerial photography

Study of gas-sheared liquid film in horizontal rectangular duct using high-speed LIF technique: Three-dimensional wavy structure and its relation to liquid entrainment

Normal droplet impact on horizontal moving films: an investigation of impact behaviour and regimes