Axial flow through gaps between aligned straight yarns with realistic cross-sectional shapes, described by power-ellipses, was analysed numerically. At a given fibre volume fraction, equivalent gap ...permeabilities have a maximum at minimum size of elongated tapering parts of the gap cross-section and a ratio of gap width to height near 1. When the yarn spacing is given in addition to the fibre volume fraction, calculated maximum and minimum values for the equivalent permeability of inter-yarn gaps, which occur at near-rectangular and lenticular cross-sections, differ by factors of up to 3.3. Novel approximations for the shape factor and the hydraulic diameter in Poiseuille flow were derived as a function of the fibre volume fraction, the yarn cross-sectional aspect ratio and the geometrical parameter describing the shape of the power-elliptical yarn cross-section. This allows the equivalent gap permeability to be predicted with good accuracy for any fibre volume fraction and yarn cross-section.
Scatter in composite mechanical properties is related to variabilities occurring at different scales. This work attempts to analyse fibre strength variability numerically from micro to macro-scale ...taking into account the size effect and its transition between scales. Two micro-mechanical models based on the Weibull distribution were used within meso-scale finite element models of fibre bundles which were validated against experimental results. These models were then implemented in a meso-scale model of an AS4 carbon fibre plain weave/vinyl ester textile composite. Monte Carlo simulations showed that fibre strength variability has a limited effect on the strength of the textile composite at the meso-scale and introduces variability of less than 2% from the mean value. Macro-scale strength based on the predicted meso-scale distribution was lower than the strength of the composite without variability by 1–4% depending on the model. The presented multi-scale approach demonstrates that a wide fibre strength distribution leads to a narrow distribution of composite strength and a shift to lower mean values.
Hyperon II: Properties of excited hyperons Sarantsev, A. V.; Matveev, M.; Nikonov, V. A. ...
The European physical journal. A, Hadrons and nuclei,
10/2019, Letnik:
55, Številka:
10
Journal Article
Recenzirano
Odprti dostop
.
We report properties of
Λ
and
Σ
hyperon resonances formed in
K
-
induced reactions. Special emphasis is laid on the analysis of the three-body final states
2
π
0
Λ
and
2
π
0
Σ
and of the ...quasi-two-body final states
π
Λ
(
1520
)
,
K
¯
Δ
(
1232
)
,
π
Σ
(
1385
)
,
K
¯
*
N
, and
ω
Λ
. We give pole positions of
Λ
and
Σ
hyperon resonances and transition residues from the
K
-
p
initial to various final states as well as Breit-Wigner masses and widths and decay branching ratios. Twenty resonances and “bumps” reported in the Review of Particle Physics are not required in our fits, evidence for five new resonances is reported. The observed mass spectrum is compared to the spectrum calculated in the Bonn quark model. Three spin doublets, six
Λ
hyperons, are tentatively assigned to the
SU
(3) singlet system.
Modelling the mechanical performance of textile composites is typically based on idealised unit cell geometry. However, 3D woven composites feature more complex textile architecture then 2D woven ...materials, and in reality nominally straight warp and weft yarns can also possess significant waviness. For such textiles, idealising yarns as straight entities becomes an oversimplification. In this study, the voxel method and a continuum damage model are used in a finite element analysis to compute stress–strain curves for an orthogonal 3D woven composite under tensile loading. The main goal of this study was to compare results produced using idealised geometry with realistic geometry obtained from detailed simulation of the preform during weaving and compaction. Significant variation in predictions was obtained using the different geometrical models. The idealised model lead to an overestimation of stiffness and strength compared to experiment due to the neglecting of yarn waviness, whereas the simulated geometry models produced more conservative results closer to experiment.
Abstract
The problem of bias of OLS estimates arises when solving the problem of parametric identification of distributed dynamic processes. There are various possible solutions to this problem. If ...the time series is trend-stationary, then these may be “ostationation” methods, which are generally difficult to apply. It is possible to use dimensionality reduction methods, but in this case we will still get biased estimates. In our previous works, it was shown that the problem of biased estimates can be solved using the conservativeness condition. The aim of this work was to investigate the possibility of using the conservativeness condition to improve the quality of estimates of the parametric identification problem, as well as to compare these results with the solution of the problem, in the case of applying a filter to it, as well as ridge regression.
A kinetic approach is used in the study of the conditions for instability of a low-voltage beam discharge in inert gases versus electron beam temperature, velocity dispersion of beam electrons along ...the discharge axis, and electron energy distribution function (EEDF). Regimes in which the interelectrode distance is on the order of the electron mean free path with respect to elastic collisions with inert-gas atoms are considered. It is shown that beam temperature
T
b
that is determined in the low-voltage beam discharge by the cathode temperature, which is no greater than 1500 K, and energy dispersion of beam electrons, which can be significantly greater than
kT
b
in such a discharge and amount to 1–2 eV, weakly affect the conditions for stability loss and an increment of perturbation growth at frequencies of up to the plasma frequency. It is found that the EEDF that monotonically decreases with increasing electron energy also does not affect parameters of perturbations that propagate in the low-voltage beam discharge at a beam energy that is significantly greater than the mean energy of electrons in plasma. The results obtained for the specified discharge can also be used for alternative self-sustained beam discharges.
This work is devoted to analysis and research of OLS-estimates properties when identifying parameters of distributed dynamic processes. The study showed that at a low level of observation errors (1% ...and lower), the use of direct OLS estimates to identify parameters of distributed dynamic processes gives satisfactory results. At the same time, the displacement value is always slightly higher than the value of the standard deviation of the parameter estimate, which does not allow to neglect the displacement, especially at a high and average level of observation errors. The method of obtaining so-called alternative OLS-estimates is also proposed, which allows to reduce multicollinearity in sample statistics and at any level of observation errors significantly reduce standard error of parameter estimation.
The behavior of low-carbon pipe steel containing 2 and 6 vol.% martensitic-austenitic component in the structure is studied under step forming, expanding and unbending of the pipe using the method of ...finite-element simulation. The effect of martensitic transformation in the MA-component on the ductility of the steel after processing and unbending of the pipe depending on the volume fraction of the MA-particles in the structure and on the test conditions (the direction of cutting of the samples and the stresses at the start of martensitic transformation) is studied. It is shown that the presence of untransformed austenite in the MA-component can restore partially the ductility of the steel lost due to the plastic deformation during processing of the pipe.
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