6,251 research outputs found
Effect of curing conditions and harvesting stage of maturity on Ethiopian onion bulb drying properties
The study was conducted to investigate the impact of curing conditions and harvesting stageson the drying quality of onion bulbs. The onion bulbs (Bombay Red cultivar) were harvested at three harvesting stages (early, optimum, and late maturity) and cured at three different temperatures (30, 40 and 50 oC) and relative humidity (30, 50 and 70%). The results revealed that curing temperature, RH, and maturity stage had significant effects on all measuredattributesexcept total soluble solids
Marshall Space Flight Center Research and Technology Report 2019
Today, our calling to explore is greater than ever before, and here at Marshall Space Flight Centerwe make human deep space exploration possible. A key goal for Artemis is demonstrating and perfecting capabilities on the Moon for technologies needed for humans to get to Mars. This years report features 10 of the Agencys 16 Technology Areas, and I am proud of Marshalls role in creating solutions for so many of these daunting technical challenges. Many of these projects will lead to sustainable in-space architecture for human space exploration that will allow us to travel to the Moon, on to Mars, and beyond. Others are developing new scientific instruments capable of providing an unprecedented glimpse into our universe. NASA has led the charge in space exploration for more than six decades, and through the Artemis program we will help build on our work in low Earth orbit and pave the way to the Moon and Mars. At Marshall, we leverage the skills and interest of the international community to conduct scientific research, develop and demonstrate technology, and train international crews to operate further from Earth for longer periods of time than ever before first at the lunar surface, then on to our next giant leap, human exploration of Mars. While each project in this report seeks to advance new technology and challenge conventions, it is important to recognize the diversity of activities and people supporting our mission. This report not only showcases the Centers capabilities and our partnerships, it also highlights the progress our people have achieved in the past year. These scientists, researchers and innovators are why Marshall and NASA will continue to be a leader in innovation, exploration, and discovery for years to come
SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES
Crack propagation in thin shell structures due to cutting is conveniently simulated
using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell
elements are usually preferred for the discretization in the presence of complex material
behavior and degradation phenomena such as delamination, since they allow for a correct
representation of the thickness geometry. However, in solid-shell elements the small thickness
leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new
selective mass scaling technique is proposed to increase the time-step size without affecting
accuracy. New ”directional” cohesive interface elements are used in conjunction with selective
mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile
shells
Rheological Model for Wood
Wood as the most important natural and renewable building material plays an
important role in the construction sector. Nevertheless, its hygroscopic
character basically affects all related mechanical properties leading to
degradation of material stiffness and strength over the service life.
Accordingly, to attain reliable design of the timber structures, the influence
of moisture evolution and the role of time- and moisture-dependent behaviors
have to be taken into account. For this purpose, in the current study a 3D
orthotropic elasto-plastic, visco-elastic, mechano-sorptive constitutive model
for wood, with all material constants being defined as a function of moisture
content, is presented. The corresponding numerical integration approach, with
additive decomposition of the total strain is developed and implemented within
the framework of the finite element method (FEM). Moreover to preserve a
quadratic rate of asymptotic convergence the consistent tangent operator for
the whole model is derived.
Functionality and capability of the presented material model are evaluated by
performing several numerical verification simulations of wood components under
different combinations of mechanical loading and moisture variation.
Additionally, the flexibility and universality of the introduced model to
predict the mechanical behavior of different species are demonstrated by the
analysis of a hybrid wood element. Furthermore, the proposed numerical approach
is validated by comparisons of computational evaluations with experimental
results.Comment: 37 pages, 13 figures, 10 table
The Latest Scientific Problems Related to the Implementation and Diagnostics of Construction Objects
This book contains publications related to the special topic entitled: "The Latest Scientific Problems Related to the Implementation and Diagnostics of Construction Objects". Construction is a sector of the economy that is characterized by a very high variability of execution conditions and a large variety of building structures. In a period of very rapid economic development, this high variability and diversity generates many new scientific problems that must be solved in order to further improve the quality of production, as well as to reduce the cost and time of construction. The purpose of the issue is to present and discuss the results of the latest research in the broad field of construction engineering, particularly concerning: modification of the composition of construction materials using various micro- and nanomaterials, by-products or wastes; modern methods of controlling construction processes; methods of planning and effective management in construction, as well as methods of diagnosing construction objects. The articles published in this issue deal with theoretical, experimental, applied and modeling research conducted worldwide in the above-mentioned scientific areas
Tracing back the source of contamination
From the time a contaminant is detected in an observation well, the question of where and when the contaminant was introduced in the aquifer needs an answer. Many techniques have been proposed to answer this question, but virtually all of them assume that the aquifer and its dynamics are perfectly known. This work discusses a new approach for the simultaneous identification of the contaminant source location and the spatial variability of hydraulic conductivity in an aquifer which has been validated on synthetic and laboratory experiments and which is in the process of being validated on a real aquifer
Advanced Topics in Mass Transfer
This book introduces a number of selected advanced topics in mass transfer phenomenon and covers its theoretical, numerical, modeling and experimental aspects. The 26 chapters of this book are divided into five parts. The first is devoted to the study of some problems of mass transfer in microchannels, turbulence, waves and plasma, while chapters regarding mass transfer with hydro-, magnetohydro- and electro- dynamics are collected in the second part. The third part deals with mass transfer in food, such as rice, cheese, fruits and vegetables, and the fourth focuses on mass transfer in some large-scale applications such as geomorphologic studies. The last part introduces several issues of combined heat and mass transfer phenomena. The book can be considered as a rich reference for researchers and engineers working in the field of mass transfer and its related topics
Advanced Manufacturing of Multilayer Ceramic Composites for Application in Solid Oxide Fuel Cells
This thesis investigates advanced techniques to control multilayer ceramic composite (MCC) 3D geometry and layer architecture. MCCs have tremendous potential to significantly change a variety of fields due to their ability to withstand extreme environments. However, our limited ability to shape them into complex objects impedes these efforts. To address this issue, two techniques have been introduced: fill coating and bilayer shrinkage driven self-shaping. Central to both techniques is the control of residual stresses experienced by MCCs during sintering. In the case of fill coating and the control of layer architecture, these residual stresses needed to be reduced to prevent the fracture of the novel internal cathode tubular solid oxide fuel cell (IC-tSOFC). This was achieved with the adoption of extended sintering procedures which promoted plastic deformation processes like creep stress relaxation. The novel fill coating technique used to produce IC-tSOFCs was then investigated using scanning electron microscopy (SEM) to ensure that the deposited films were highly uniform and comparable to films deposited using the more mature dip coating technique. The electrochemical performance of the IC-tSOFC was then thoroughly evaluated on a variety of fuel streams including pure hydrogen, dilute hydrogen, simulated exhaust from a boiler, and simulated exhaust from a two-stroke internal combustion engine. The second focus of this thesis takes advantage of the residual stresses that complicated IC-tSOFC development rather than dissipating them. By using the mismatch in the thermal expansion coefficient between adjacent layers within planar MCCs, curvature may be introduced. Substrates were produced using tape casting and a thin film was then added to this substrate using aerosol spray deposition. By controlling the thickness of the substrate and film, as well as the 2D shape of the substrate and pattern of the applied film, the curvature and shape of the final self-formed part was controlled. Beyond demonstration of this novel manufacturing technique, investigation into curvature and shape prediction using analytical and finite element method (FEM) modeling enabled the development of a methodology to design parts using self-shaping. Initial investigations focused on predicting curvature. Though a disagreement between modeling and experiment was observed, an experimental TEC was introduced to replicate experimental results in FEM modeling. This understanding of the 2D curvature was then extended to three dimensions to analyze shape. Predictions regarding bifurcation between cap-like and tube-like deformation modes was applied to the ceramic system using FEM modeling and experiment. These predictions were shown to be consistent with theoretical understanding. Similarly, bending direction for tube-like deformation was shown to be generally consistent with theoretical understanding, but here FEM modeling struggled to reliably predict the final 3D geometry of shapes with high degrees of symmetry, and experimental samples experienced misorientation of bending, indicating that models may need to be expanded to include a greater variety of forces controlling deformation. Overall, this thesis shows successful development of novel manufacturing techniques to enable wider application of ceramic materials. While the IC-tSOFC introduces new combined heat and power-SOFC systems to be explored, self-shaping ceramics introduces a variety of fundamental questions regarding the underlying mechanism driving bilayer shrinkage within MCCs as well as full understanding of the interaction between 2D substrate shape and film pattern at any scale
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