Microstructural evolution along the build height of laser melting deposited TA15 alloy

This study emphasizes the TA15 alloy microstructural distribution fabricated by the laser melting deposition (LMD) technique. The motivation of the study is to analyze the microstructural features, such as grain or laths thickness, phase fraction, and porosity occurrence in the different regions along the build height, due to the complex thermal-solidification history during the laser melting deposition. During laser deposition of titanium alloy, the laser beam forms a melt pool, where the near-α and α+β alloys transform into a single β-phase, followed by rapid solidification. This process is repeated when a successive layer is deposited, where the previously deposited layers are re-melted. These thermal cycles can affect the parent microstructure in the previously deposited layers. It was identified from the results that the width of α-laths was larger in the regions near the top of the build component. In comparison, the bottom region near to substrate contained fine laths due to a steep thermal gradient and repeated thermal effect. The volume fraction of β-phase was higher in the bottom region, which could be regarded as the transformed β matrix due to the successive thermal effect in the α+β field. The results also showed shallow porosity existence in the top and near to top regions. According to the morphology and size, the formation of these pores can be attributed to the gas entrapment during the deposition process.

Derivation of a Viscous Serre–Green–Naghdi Equation: An Impasse?

In this article, we present the current status of the derivation of a viscous Serre–Green–Naghdi system. For this goal, the flow domain is separated into two regions. The upper region is governed by inviscid Euler equations, while the bottom region (the so-called boundary layer) is described by Navier–Stokes equations. We consider a particular regime binding the Reynolds number and the shallowness parameter. The computations presented in this article are performed in the fully nonlinear regime. The boundary layer flow reduces to a Prandtl-like equation that we claim to be irreducible. Further approximations are necessary to obtain a tractable model.

Метод управления аэродинамическим сопротивлением цилиндра с газопроницаемыми пористыми вставками путем регулирования донного давления

The results of an experimental and numerical study of a supersonic (M = 7) flow around a hollow cylinder with gas-permeable porous inserts located along the flow are presented. The possibility of controlling the aerodynamic drag of the model by passing a part of the incident flow into the bottom area through gas-permeable porous inserts is shown. The flow rate of air directed to the bottom region to control the resistance was controlled by heating the porous inserts with an electric glow discharge.

Experimental Study of Entrainment and Mixing of Renewable Active Particles in Fluidized Beds

Fluidized bed combustors were initially designed and built basically for the utilization of fossil fuels, mostly coal. The actual worldwide trend of transitioning from fossil fuels to renewables requires sufficient knowledge on the fluid mechanics of these new particle types because of the significant differences in their shapes, sizes, densities, and homogeneities. This article presents experimental results on the particle entrainment and mixing of some industrially relevant fuels such as solid refused fuel/refuse derived fuel (SRF/RDF), bark, sunflower shell, and wheat shell. The measurements were performed on a lab-scale fluidized bed experimental facility. The results show that sunflower shell is entrained in the highest degree; however, at very low velocity, the entrainment of wheat shell is the most intensive. The entrainment behaviors of the investigated SRF and bark samples are similar. On the other hand, the mixing results showed that the SRF has relatively high mass fractions in the bottom and centeral regions of the fluidized bed at low superficial velocities, while at elevated velocities, the entire mass of this fuel is shifted upwards. Interestingly, just the opposite tendency can be observed in cases of all other investigated biomass fuels. Finally, the nonspherical renewable active particles have markedly higher concentrations in the bottom region of the bed compared to spherical ones.

Isotopic Confirmation of the Timing and Intensity of Maize Consumption in Greater Cahokia

The history of maize (Zea mays L.) in the eastern Woodlands remains an important study topic. As currently understood, these histories appear to vary regionally and include scenarios positing an early introduction and an increase in use over hundreds of, if not a thousand, years. In this article, we address the history of maize in the American Bottom region of Illinois and its importance in the development of regional Mississippian societies, specifically in the Cahokian polity located in the central Mississippi River valley. We present new lines of evidence that confirm subsistence-level maize use at Cahokia was introduced rather abruptly at about AD 900 and increased rapidly over the following centuries. Directly dated archaeobotanical maize remains, human and dog skeletal carbon isotope values, and a revised interpretation of the archaeological record support this interpretation. Our results suggest that population increases and the nucleation associated with Cahokia were facilitated by the newly introduced practices of maize cultivation and consumption. Maize should be recognized as having had a key role in providing subsistence security that—combined with social, political, and religious changes—fueled the emergence of Cahokia in AD 1050.

The Cahokian Crucible: Burning Ritual and the Emergence of Cahokian Power in the Mississippian Midwest

Much of what is known about the Indigenous city of Cahokia, located in and influential on the North American midcontinent during the eleventh through fourteenth centuries AD, derives from decades of salvage, research, and CRM excavations in the surrounding American Bottom region. We use this robust dataset to explore patterns of building conflagration that suggest these practices of burning were part of pre-Mississippian traditions that were bundled into new Cahokian landscapes during the early consolidation of the city. These bundled practices entangled sources of power that were at once political and religious, thus transforming the practices and meanings associated with terminating building use via fire.

Investigation of the riser cross-sectional aspect ratio effect on the flow dynamics in circulating fluidized beds by electrical capacitance tomography

With the increase of capacity, most of the circulating fluidized beds (CFB) risers are constricted to have rectangular cross section. Therefore, it is important to find out the cross-sectional aspect ratio effect on the gas-solids flow characteristics. In this study, a lab-scale CFB with two rectangular risers, which have the aspect ratio of 1:1 and 3:1, respectively, were studied by the electrical capacitance tomography (ECT), with the aided of pressure measurements and computational particle fluid dynamics (CPFD) simulation. Key issues related with ECT sensor design and image reconstruction, such as sensitivity map and excitation frequency, are also discussed. The results show that ECT image quality is affected by the sensitivity map and excitation frequency, and high excitation frequency and voltage are not equivalent of high image quality. In the riser bottom region, cross-sectional aspect ratio has big effect on ECT measured particle distribution and pressure drop, fewer particles are brought away from the bottom when the aspect ratio is larger. Multiple bubbles exist in the bottom region at Ve= 2.7 m/s, and bubble size decreases in the rectangular riser with larger cross-sectional aspect ratio. Static bed height influences the bubble behaviour that bubbles with smaller size scattered around and behave collapse or coalescence in the moving process when the static bed height is high.

Cutting of a Thick Glass Plate by Using Hot Wire

A thick glass plate was cut by using hot wire. Crack growing was stopped when wire temperature was low. Ligament length decreased with increase in temperature of hot wire and full-cutting was achieved at the temperature of 650°C. The center region in the thickness direction seemed to propagate earlier compared to surfaces regions when the crack propagation was stopped. Finite element thermal stress analysis was carried out. According to distribution of thermal stress inside a glass plate, higher stress was generated in the bottom region at the beginning of the process but occurred in the center region in the later stage as matching with the experimental result.