430 research outputs found
Time-dependent calculation of the velocity of a yarn launched by the main nozzle of an air-jet loom
In air-jet weaving looms the yarn is initially accelerated by the main nozzle. To obtain a high yarn velocity a high air velocity is required which results in complex flow patterns. Consequently, predicting the influence of a change in geometry or inlet pressure on the yarn velocity is not straightforward. In this research a fast time-dependent fluid-structure interaction framework is used to model the acceleration of a yarn during launch. Initially, the performance of the framework is assessed by considering a smooth monofilament yarn. A suggestion is also madeand tested to deal with the surface texture of hairy/multifilament yarns
Three-dimensional fluid-structure interaction simulations of a yarn subjected to the main nozzle flow of an air-jet weaving loom using a Chimera technique
In air-jet weaving looms, the main nozzle pulls the yarn from the prewinder by means of a high velocity air flow. The flexible yarn is excited by the flow and exhibits high amplitude oscillations. The motion of the yarn is important for the reliability and the attainable speed of the insertion. Fluid-structure interaction simulations calculate the interaction between the air flow and the yarn motion and could provide additional insight into yarn behavior. However, the use of an arbitrary LagrangianâEulerian approach for the deforming fluid domain around a flexible yarn typically results in severe mesh degradation, vastly reducing the accuracy of the calculations or limiting the physical time that can be simulated. In this research, the feasibility of using a Chimera technique to simulate the motion of a yarn interacting with the air flow from a main nozzle was investigated. This methodology combines a fixed background grid with a moving component grid deforming along with the yarn. The component grid is, however, not constrained by the boundaries of the flow domain allowing for large deformations with limited mesh degradation. Two separate cases were investigated. In the first case, the yarn was considered to be clamped at the main nozzle inlet. For the second case, the yarn was allowed to move axially as the main nozzle pulled it from a drum storage system
Development of an iterative procedure with a flow solver for optimizing the yarn speed in a main nozzle of an air jet loom
In this research, a fluid-structure interaction (FSI) framework was established to estimate the velocity of a yarn as it is propelled by the main nozzle. To allow the methodology to be used in an optimization context, the computational time was limited as much as possible. The methodology was first validated on polymer coated yarns to avoid any influence of yarn hairiness. Results from the calculations were compared to experiments and adequate agreement was found without tuning. Subsequently, an extension to hairy yarns was made by representing the hairiness as a wall roughness. The roughness height was determined by matching the simulated to the experimental velocity for a single case. The approach was validated by applying the obtained roughness height to different setups and comparing the simulations to the corresponding experiments. Taking into account some limitations, the methodology can be applied for optimization purposes using either smooth or hairy yarns
Dense gas in IRAS 20343+4129: an ultracompact HII region caught in the act of creating a cavity
The intermediate- to high-mass star-forming region IRAS 20343+4129 is an
excellent laboratory to study the influence of high- and intermediate-mass
young stellar objects on nearby starless dense cores, and investigate for
possible implications in the clustered star formation process. We present 3 mm
observations of continuum and rotational transitions of several molecular
species (C2H, c-C3H2, N2H+, NH2D) obtained with the Combined Array for Research
in Millimetre-wave Astronomy, as well as 1.3 cm continuum and NH3 observations
carried out with the Very Large Array, to reveal the properties of the dense
gas. We confirm undoubtedly previous claims of an expanding cavity created by
an ultracompact HII region associated with a young B2 zero-age main sequence
(ZAMS) star. The dense gas surrounding the cavity is distributed in a filament
that seems squeezed in between the cavity and a collimated outflow associated
with an intermediate-mass protostar. We have identified 5 millimeter continuum
condensations in the filament. All of them show column densities consistent
with potentially being the birthplace of intermediate- to high-mass objects.
These cores appear different from those observed in low-mass clustered
environments in sereval observational aspects (kinematics, temperature,
chemical gradients), indicating a strong influence of the most massive and
evolved members of the protocluster. We suggest a possible scenario in which
the B2 ZAMS star driving the cavity has compressed the surrounding gas,
perturbed its properties and induced the star formation in its immediate
surroundings.Comment: 17 pages, 13 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Society (Main Journal
Agreement between physical therapists and radiologists of stratifying patients with shoulder pain into new treatment related categories using ultrasound; an exploratory study
© 2019 Elsevier Ltd Study design: A systematic overview of the literature and an agreement study. Objectives: The aim of this study is to explore the inter-professional agreement of diagnostic musculoskeletal ultrasound (DMUS) between physical therapists (PT) and radiologists, using a new classification strategy based upon the therapeutic consequences in patients with shoulder pain. Background: DMUS is frequently used by PTs, although the agreement regarding traditional diagnostic labels between PTs and radiologists is only fair. Nevertheless, DMUS could be useful when used as a stratifying-tool. Methods: First, a systematic overview of current evidence was performed to assess which traditional diagnostic labels could be recoded into new treatment related categories (referral to secondary care, corticosteroid injections, physical therapy, watchful waiting). Next, kappa values were calculated for these categories between PTs and radiologists. Results: Only three categories were extracted, as none of the traditional diagnostic labels were classified into the âcorticosteroid injectionâ category. Overall, we found moderate agreement to stratify patients into treatment related categories and substantial agreement for the category âreferral to secondary careâ. Both categories âwatchful waitingâ and âindication for physical therapyâ showed moderate agreement between the two professions. Conclusion: Our results indicate that the agreement between radiologists and PTs is moderate to substantial when labelling is based on treatment consequences. DMUS might be able to help the PT to guide treatment, especially for the category âreferral to secondary careâ as this showed the highest agreement. However, as this is just an explorative study, more research is needed, to validate and assess the consequences of this stratification classification for clinical care
Proton and Li-Ion Permeation through Graphene with Eight-Atom-Ring Defects
Defect-free graphene is impermeable to gases and liquids but highly permeable
to thermal protons. Atomic-scale defects such as vacancies, grain boundaries
and Stone-Wales defects are predicted to enhance graphene's proton permeability
and may even allow small ions through, whereas larger species such as gas
molecules should remain blocked. These expectations have so far remained
untested in experiment. Here we show that atomically thin carbon films with a
high density of atomic-scale defects continue blocking all molecular transport,
but their proton permeability becomes ~1,000 times higher than that of
defect-free graphene. Lithium ions can also permeate through such disordered
graphene. The enhanced proton and ion permeability is attributed to a high
density of 8-carbon-atom rings. The latter pose approximately twice lower
energy barriers for incoming protons compared to the 6-atom rings of graphene
and a relatively low barrier of ~0.6 eV for Li ions. Our findings suggest that
disordered graphene could be of interest as membranes and protective barriers
in various Li-ion and hydrogen technologies
- âŠ