45,138 research outputs found
The use of FEA packages in the simulation of a drawing operation with springback, in the presence of random uncertainty
No full textThe springback response on a stamped part, calculated by finite element analysis has been evaluated taking into account the uncertainty of some process conditions. In fact, in the simulation of sheet metal forming and springback, a traditional deterministic approach is not able to take into account the uncertain physical variations related to material characteristics, friction conditions, tools active surfaces status, etc.
During sheet metal forming operations many different sources of non-controllable process variations usually display their effect leading to a degree of uncertainty in the final parts’ quality. For this reason, statistical tools and methods are increasingly being used in combination with FE numerical simulation. Then, if one of the purposes of process design is to study and model robustness or reliability of a given process in aleatory conditions, a CAE study might become a feasible way to do it.
Today, the evaluation of the performances of a sheet metal stamping process, under uncertainty of the main variables, is possible using several commercial FEA packages. These software tools automatically allow the pre-emptive evaluation of the robustness of technological decisions and the process sensitivity to a random variation of uncontrollable parameters or conditions. For accurate calculations these innovative numerical approaches usually require a considerable amount of computational work both in terms of CPU time and in terms of number of CPUs. A specific experimental and numerical activity has been developed in order to better understand the technical capabilities in terms of process simulation in stochastic conditions
Carbon nanotube-guided thermopower waves
No full textThermopower waves are a new concept for the direct conversion of chemical to electrical energy. A nanowire with large axial thermal diffusivity can accelerate a self-propagating reaction wave using a fuel coated along its length. The reaction wave drives electrical carriers in a thermopower wave, creating a high-power pulse of as much as 7 kW/kg in experiments using carbon nanotubes. We review nanomaterials designed to overcome limitations of thermoelectricity and explore the emerging scientific and practical outlook for devices using thermopower waves
Rapid surface quality assessment of green 3D printed metal-binder parts
No full textMixtures made of a solid metal powder and a viscous polymeric binder are increasingly used in material Extrusion Additive Manufacturing (EAM) processes. The EAM process adopts the relative movement of an extruder head to a build table, to deposit thin strands of the mixture and build a 3D object layer by layer. In this study, EAM process was applied to produce 3D printed square plate-shaped parts of stainless steel 316 L at the green state, i.e. before debinding and sintering. The 3D printing experiments were designed by considering various independent process parameters: extrusion velocity v e , table velocity v t , layer height h and hatch spacing D a . The surface characteristics of as printed (green) square plate-shaped parts were investigated by a rapid, high-resolution optical imaging technique. The obtained images were analyzed to model the effect of the process parameters on the surface uniformity Ui and space filling Fi. The proposed methodology can be also used as a process monitoring technique. The study has demonstrated that the layer height h has the most relevant effect on the infill quality and should be set at a low value for good quality. However, a combination of the other parameters can be found that yields a compromise between infill surface quality and build up rate
Settling of finite-size particles in isotropically forced, homogeneous turbulence: interface-resolved simulations
No full textWe have simulated the gravity-induced settling of finite-size particles in a turbulent background flow which is forced in a statistically-stationary fashion. The simulations are accurately resolving the solid-fluid interface with the aid of an immersed boundary technique [1]. The parameters of the simulation are (apart from background turbulence) identical to those of reference [2], where particle clustering was observed at a Galileo number of 178 and a solid volume fraction of 0.005. In the present case, it is found that a relative turbulence intensity of 0.24 leads to the disappearance of the clusters; as a consequence, the increase in average particle settling velocity found in [2] also vanishes. [1] M. Uhlmann. An immersed boundary method with direct forcing for the simulation of particulate flows. J. Comput. Phys., 209(2):448–476, 2005. [2] M. Uhlmann and T. Doychev. Sedimentation of a dilute suspension of rigid spheres at intermediate Galileo numbers: the effect of clustering upon the particle motion. J. Fluid Mech., 752:310–348, 2014
Rotary draw bending of small diameter copper tubes: predicting the quality of the cross-section
No full textThe purpose of the present work is to study the correlation between the main geometrical tube parameters of the rotary draw bending process and the resulting quality of the cross-section of small hydraulic pipings. The method of choice, named free rotary draw bending, is a rotary draw bending process where no internal support from an internal mandrel or plug is
possible, because hydraulic tubes cannot be lubricated on their internal diameter. Furthermore, no axial boosting of the tube or of the pressure die is applied. Free bending is mainly used when
small-diameter tubes are involved, with high length and relatively thin wall.
A unique quality estimator QCS of the cross-section geometry of bent tubes has been developed, which is able to synthetically represent the main functional and aesthetical properties of tubes:
the maximum ovalization, the minimum hydraulic diameter, and so on. In the case of copper tubes for hydraulic applications a strongly deformed cross-section after bending means a poor
quality of the product, since it delivers an increase of head losses and of pressure drops. The deformation occurring in the cross-section of the tube has been studied through a set of FEM simulations, run with an explicit code with shell elements, and the model has been validated by comparing the experimental and numerical results of specific cases, in terms of geometry of
the cross-section in a 90 bend. The plan of simulations has been designed using the typical copper tube dimensions for hydro-thermo-sanitary applications and a few runs have been added with modified parameters with the aim of completing the plan for evaluating the sensitivity to a change either in geometrical variables (thickness t, outer diameter OD, mean bending radius RM) or in the tube material. An indicator (bending factor) is proposed, able to reliably estimate the difficulty of a bending process with respect to tendency to ovalization and collapse of the crosssection.
Some design guidelines of the bending tools are provided
A Multi-Year Study of Forchlorfenuron’s Effects on Physical Fruit Quality Parameters in A. chinensis var. chinensis
No full textCPPU, N-(2-Chloro-4-pyridyl)-N-phenylurea, is a synthetic cytokinin extensively used to enhance fruit size and overall quality in several crops, including kiwifruit. This study aimed to investigate the effects of three different CPPU application strategies (2.3, 3.0, and 4.6 ppm) and two crop load levels on key fruit quality parameters at harvest, as well as on post-harvest storage performance. Our results demonstrate that two applications of CPPU (4.6 ppm) significantly increased fruit weight, especially under standard crop-load conditions, likely due to more efficient resource allocation. Additionally, fruit firmness improved with two or three CPPU applications, probably because of enhanced cell wall development. Crop load consistently influenced fruit firmness, with lower loads resulting in softer fruits. The soluble solids content was not significantly affected by the two CPPU applications; however, it was notably influenced by crop load, with fruits from the standard crop load showing higher sugar accumulation. A similar trend was observed in fruit dry weight, where CPPU had a greater impact under standard crop loads. Regarding post-harvest performance, CPPU applications showed a limited effect on maintaining fruit firmness during the first five months of storage. Overall, CPPU can be a potential strategy to enhance fruit quality, but its effectiveness depends heavily on field management practices. Therefore, controlling field variables is essential to fully realize the benefits of CPPU and to avoid interference with the plant’s physiological responses
Mesophilic-hydrothermal-thermophilic (M-H-T) digestion of green corn straw
No full textMesophilic-hydrothermal (80-160 degrees C, 30 min)-thermophilic (M-H-T) digestion and control tests of mesophilic (M), thermophilic (T), hydrothermal-mesophilic (H-M), and mesophilic-thermophilic digestion (M-T) of green corn straw were conducted for a 20-day fermentation period. The results indicate that M-H-T is an efficient method to improve methane production. A maximum methane yield of 371.74 mL/g volatile solid was obtained by the M (3 days)-H (140 degrees C)-T (17 days) process, which was 20.44%, 16.55%, 31.44%, and 14.31% higher than the yields of the M, T, 140-M, and M-T processes. The enhanced methane production was attributed to (1) the improved hemicellulose degradation and lignin disorganization; (2) prevention of the degradation of soluble sugar, easily hydrolyzed hemicellulose and cellulose into furfural and methylfurfural; and (3) lack of formation of Maillard reaction products during initial hydrothermal treatment. (C) 2015 Elsevier Ltd. All rights reserved
Dr. Glendon Swarthout
No full textHosted by Roger M. Busfield, MSU Assistant Professor of Speech and Theater, Meet the Author is designed to introduce a general audience to a contemporary author and their work through in-depth interviews. This episode features a conversation between Dr. Glendon Swarthout, prolific author and English professor at MSU, and assistant professors Sam S. Baskett and Theodore B. Strandness
The maternal immune system during pregnancy and its influence on fetal development
No full textThe maternal immune system plays a critical role in the establishment, maintenance, and completion of a healthy pregnancy. However, the specific mechanisms utilized to achieve these goals are not well understood. Various cells and molecules of the immune system are key players in the development and function of the placenta and the fetus. Effector cells of the immune system act to promote and yet limit placental development. The T helper 1 (Th1)/T helper 2 (Th2) immune shift during pregnancy is well established. A fine balance between proinflammatory and anti-inflammatory influences is required. We herein review the evidence regarding maternal tolerance of fetal tissues and the underlying cell-mediated immune and humoral (hormones and cytokines) mechanisms. We also note the many unanswered questions in our understanding of these mechanisms. In addition, we summarize the clinical manifestations of an altered maternal immune system during pregnancy related to susceptibility to common viral, bacterial, and parasitic infections, as well as to autoimmune diseases.Peer reviewe
Erosie door open taludbekledingen. Samenvattend verslag + Bijlage A t/m D
No full textOpen taludbekledingen die bestaan uit in verband geplaatste betonblokken met gaten, bieden de mogelijkheid vegetatie te doen groeien, waardoor mogelijk een milieuvriendelijke oever kan worden verkregen. In het pioniersstadium van de vegetatie is het evenwel ongewenst dat de gatvulling uitspoelt. Teneinde de relatie tussen waterbeweging en erosie van de gatvulling vast te stellen, is door de Dienst Weg- en Waterbouwkunde van Rijkswaterstaat per brief d.d. 16 maart 1987 (kenmerk WB 570), opdracht verleend aan het Waterloopkundig Laboratorium tot het uitvoeren van onderzoek naar de erosie door open taludbekledingen. Het doel van het onderzoek is het ontwikkelen van ontwerprichtlijnen voor taludbekledingen met gaten die groter zijn dan de zand- of filterkorrels eronder. Hiertoe dient de kritieke waterbeweging bij een oever- of dijkbekleding te worden vastgesteld, waarbij nog toelaatbare erosie is te verwachten. De toelaatbare erosie mag daarbij maximaal gelijk zijn aan de hoeveelheid sediment in de gaten. Filter- of basismateriaal gelegen onder de elementen mag dus niet uitspoelen. Bij oeverbekledingen waar vegetatie een rol moet gaan spelen, is de toelaatbare erosie kleiner, dat wil zeggen in de gaten dient sediment achter te blijven.Steenzettingen - TAW/EN
- …
