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1.
An investigation into varying the spatial density of three-dimensional (3D) modes in order to accurately tune a finite element
(FE) model to larger numbers of modes is conducted. This FE model tuning approach is evaluated on a 60,000+ FE degree of freedom
(DOF) model of the United States Air Force Academy’s fifth small satellite, FalconSAT-5 (FS-5), structural engineering model
(SEM). The evaluation of this FE model tuning approach starts with the collection of natural frequencies and 3D modes extracted
from scanning laser Doppler velocimeter (LDV) frequency response function measurements at 2,165 closely-spaced points on the
surface of the test article. The measured modes and their associated natural frequencies serve as target values in a gradient-based
tuning approach. The FE model is tuned to have differences with the measured natural frequencies less than 2% and in many
cases cross-orthogonality values greater than 0.90. Using both a QR-decomposition and the Triaxial Effective Independence
(EfI3 + ) sensor selection strategies, the effect of adding more tuning points on tuning accuracy is studied. This study demonstrates
that increasing the number of experimental data points using the EfI3 + sensor selection strategy for FE model optimization results in increased tuning accuracy. 相似文献
2.
In the present study, a novel evaluation method involving rapid prototyped (RP) technology and finite element (FE) analysis
was used to study the elastic mechanical characteristics of human vertebral trabecular bone. Three-dimensional (3D) geometries
of the RP and FE models were obtained from the central area of vertebral bones of female cadavers, age 70 and 85. RP and FE
models were generated from the same high-resolution micro-computed tomography (μCT) scan data. We utilized RP technology along
with FE analysis based on μCT for high-resolution vertebral trabecular bone specimens. RP models were used to fabricate complex
3D objects of vertebral trabecular bone that were created in a fused deposition modeling machine. RP models of vertebral trabecular
bone are advantageous, particularly considering the repetition, risks, and ethical issues involved in using real bone from
cadaveric specimens. A cubic specimen with a side length of 6.5 mm or a cylindrical specimen with a 7 mm diameter and 5 mm
length proved better than a universal cubic specimen with a side length of 4 mm for the evaluation of elastic mechanical characteristics
of vertebral trabecular bones through experimental and simulated compression tests. The results from the experimental compression
tests of RP models closely matched those predicted by the FE models, and thus provided substantive corroboration of all three
approaches (experimental tests using RP models and simulated tests using FE models with ABS and trabecular bone material properties).
The RP technique combined with FE analysis has potential for widespread biomechanical use, such as the fabrication of dummy
human skeleton systems for the investigation of elastic mechanical characteristics of various bones. 相似文献
3.
4.
TheT
ε
*
integral was calculated on the surface of single edge notched, three-point bend (SE(B)) specimens using experimentally obtained
displacements. Comparison was made withT
ε
*
calculated with the measured surface displacements andT
ε
*
calculated at several points through the thickness of a finite element (FE) model of the SE(B) specimen. Good comparison
was found between the surfaceT
ε
*
calculated from displacements extracted from the FE model and the surfaceT
ε
*
calculated from experimentally obtained displacements. The computedT
ε
*
integral was also observed to decrease as the crack front was traversed from the surface to the mid-plane of the specimen.
Mid-planeT
ε
*
values tend to be approximately 10% of the surface values. 相似文献
5.
Matthew Dobson Mitchell Luskin Christoph Ortner 《Archive for Rational Mechanics and Analysis》2010,197(1):179-202
Due to their algorithmic simplicity and high accuracy, force-based model coupling techniques are popular tools in computational
physics. For example, the force-based quasicontinuum (QCF) approximation is the only known pointwise consistent quasicontinuum
approximation for coupling a general atomistic model with a finite element continuum model. In this paper, we present a detailed
stability and error analysis of this method. Our optimal order error estimates provide a theoretical justification for the
high accuracy of the QCF approximation: they clearly demonstrate that the computational efficiency of continuum modeling can
be utilized without a significant loss of accuracy if defects are captured in the atomistic region. The main challenge we
need to overcome is the fact that the linearized QCF operator is typically not positive definite. Moreover, we prove that no uniform inf-sup stability condition holds for discrete versions of the W
1,p
-W
1,q
“duality pairing” with 1/p + 1/q = 1, if 1 ≤ p < ∞. However, we were able to establish an inf-sup stability condition for a discrete version of the W
1,∞-W
1,1 “duality pairing” which leads to optimal order error estimates in a discrete W
1,∞-norm. 相似文献
6.
A. Alper Ozalp 《Heat and Mass Transfer》2008,45(1):31-46
Variable fluid property continuity, Navier–Stokes and energy equations are solved for roughness induced forced convective
laminar-transitional flow in a micropipe. Influences of Reynolds number, heat flux and surface roughness, on the momentum-energy
transport mechanisms and second-law of thermodynamics, are investigated for the ranges of Re = 1–2,000, Q = 5–100 W/m2 and ε = 1–50 μm. Numerical investigations put forward that surface roughness accelerates transition with flatter velocity profiles
and increased intermittency values (γ); such that a high roughness of ε = 50 μm resulted in transitional character at Re
tra = 450 with γ = 0.136. Normalized friction coefficient (C
f*) values showed augmentation with Re, as the evaluated C
f* are 1.006, 1.028 and 1.088 for Re = 100, 500 and 1,500, respectively, at ε = 1 μm, the corresponding values rise to C
f* = 1.021, 1.116 and 1.350 at ε = 50 μm. Heat transfer rates are also recorded to rise with Re and ε; moreover the growing influence of ε on Nusselt number with Re is determined by the Nu
ε=50 μm/Nu
ε=1 μm ratios of 1.086, 1.168 and 1.259 at Re = 500, 1,000 and 1,500. Thermal volumetric entropy generation values decrease with Re and ε in heating; however the contrary is recorded for frictional volumetric entropy generation data, where the augmentations in are more considerable when compared with the decrease rates of 相似文献
7.
M.Z. Tekeste E.W. Tollner R.L. Raper T.R. Way C.E. Johnson 《Journal of Terramechanics》2009,46(5):229-239
Axisymmetric finite element (FE) method was developed to simulate cone penetration process in layered granular soil. The FE was modeled using ABAQUS/Explicit, a commercially available package. Soil was considered as a non-linear elastic plastic material which was modeled using variable elastic parameters of Young’s Modulus and Poisson’s ratio and Drucker–Prager criterion with yield stress dependent material hardening property. The material hardening parameters of the model were estimated from the USDA-ARS National Soil Dynamics Laboratory – Auburn University (NSDL-AU) soil compaction model. The stress–strain relationship in the NSDLAU compaction model was modified to account for the different soil moisture conditions and the influence of precompression stress states of the soil layers. A surface contact pair (‘slave-master’) algorithm in ABAQUS/Explicit was used to simulate the insertion of a rigid cone (RAX2 ABAQUS element) into deformable and layered soil medium (CAX4R ABAQUS element). The FE formulation was verified using cone penetration data collected on a soil chamber of Norfolk sandy loam soil which was prepared in two compaction treatments that varied in bulk density in the hardpan layer of (1) 1.64 Mg m−3 and (2) 1.71 Mg m−3. The FE model successfully simulated the trend of cone penetration in layered soils indicating the location of the sub-soil compacted (hardpan) layer and peak cone penetration resistance. Modification of the NSDL-AU model to account for the actual soil moisture content and inclusion of the influence of precompression stress into the strain behavior of the NSDL-AU model improved the performance of FE in predicting the peak cone penetration resistance. Modification of the NSDL-AU model resulted in an improvement of about 42% in the finite element-predicted soil cone penetration forces compared with the FE results that used the NSDL-AU ‘virgin’ model. 相似文献
8.
Particle tracer response across shocks measured by PIV 总被引:1,自引:0,他引:1
The experimental approach used for the evaluation of the particle response time across a stationary shock wave is assessed
by means of PIV measurements. The study focuses on the experimental requirements for a reliable and unbiased measurement of
the particle response time τ
p
and length ξ
p
based on a single-exponent decaying law. A numerical simulation of the particle response experiment returns the parameters
governing the measurement: namely the normalized spatial and temporal resolution, shock strength, and digital resolution.
Representing the velocity decay in logarithmic coordinates it is shown that measurements performed with laser pulse separation
time up to τ
p
and interrogation window up to ξ
p
still yield unbiased results for the particle response. A set of experiments on the particle response across a planar oblique
shock wave was conducted to verify the results from the numerical assessment. Liquid droplets of DEHS and solid tracer particles
of silicon and titanium dioxide with different primary crystal size are compared. The resulting temporal response ranges from
2 to 3 μs, corresponding to values commonly reported in literature, to almost 0.3 μs when particles are properly dehydrated
and a filter is applied before injection into the wind tunnel. It is the first experimental evidence of particle tracers with
a measured response time lower than 0.4 μs. The same procedure is applied to attempt the measurement of individual particle
tracers by particle tracking velocimetry to estimate the spread in the distribution of tracer time response. The latter analysis
is limited by the particle image tracking precision error, which biases the results introducing a wider broadening of the
particle velocity distribution. 相似文献
9.
Hamed Ashraf M. Shabana Ahmed A. Jayakumar Paramsothy Letherwood Michael D. 《Nonlinear dynamics》2011,66(4):809-824
Existing multibody system (MBS) algorithms treat articulated system components that are not rigidly connected as separate
bodies connected by joints that are governed by nonlinear algebraic equations. As a consequence, these MBS algorithms lead
to a highly nonlinear system of coupled differential and algebraic equations. Existing finite element (FE) algorithms, on
the other hand, do not lead to a constant mesh inertia matrix in the case of arbitrarily large relative rigid body rotations.
In this paper, new FE/MBS meshes that employ linear connectivity conditions and allow for arbitrarily large rigid body displacements
between the finite elements are introduced. The large displacement FE absolute nodal coordinate formulation (ANCF) is used to obtain linear element connectivity conditions in the case of large relative rotations between the finite
elements of a mesh. It is shown in this paper that a linear formulation of pin (revolute) joints that allow for finite relative
rotations between two elements connected by the joint can be systematically obtained using ANCF finite elements. The algebraic
joint constraint equations, which can be introduced at a preprocessing stage to efficiently eliminate redundant position coordinates,
allow for deformation modes at the pin joint definition point, and therefore, this new joint formulation can be considered
as a generalization of the pin joint formulation used in rigid MBS analysis. The new pin joint deformation modes that are
the result of C
0 continuity conditions, allow for the calculations of the pin joint strains which can be discontinuous as the result of the
finite relative rotation between the elements. This type of discontinuity is referred to in this paper as nonstructural discontinuity in order to distinguish it from the case of structural discontinuity in which the elements are rigidly connected. Because ANCF finite elements lead to a constant mass matrix, an identity generalized
mass matrix can be obtained for the FE mesh despite the fact that the finite elements of the mesh are not rigidly connected.
The relationship between the nonrational ANCF finite elements and the B-spline representation is used to shed light on the
potential of using ANCF as the basis for the integration of computer aided design and analysis (I-CAD-A). When cubic interpolation
is used in the FE/ANCF representation, C
0 continuity is equivalent to a knot multiplicity of three when computational geometry methods such as B-splines are used.
C
2 ANCF models which ensure the continuity of the curvature and correspond to B-spline knot multiplicity of one can also be
obtained. Nonetheless, B-spline and NURBS representations cannot be used to effectively model T-junctions that can be systematically
modeled using ANCF finite elements which employ gradient coordinates that can be conveniently used to define element orientations
in the reference configuration. Numerical results are presented in order to demonstrate the use of the new formulation in
developing new chain models. 相似文献
10.
In the present study, peel tests and inverse analysis were performed to determine the interracial mechanical parameters for the metal film/ceramic system with an epoxy interface layer between film and ceramic. Al films with a series of thicknesses between 20 and 250 μm and three peel angles of 90°, 135° and 180° were considered. A finite element model with the cohesive zone elements was used to simulate the peeling process. The finite element results were taken as the training data of a neural network in the inverse analysis. The interracial cohesive energy and the separation strength can be determined based on the inverse analysis and peel experimental result 相似文献
11.
Natural convection in a fluid saturated porous medium has been numerically investigated using a generalized non-Darcy approach.
The governing equations are solved by using Finite Volume approach. First order upwind scheme is employed for convective formulation
and SIMPLE algorithm for pressure velocity coupling. Numerical results are presented to study the influence of parameters
such as Rayleigh number (106 ≤Ra ≤108), Darcy number (10−5 ≤ Da ≤ 10−2), porosity (0.4 ≤ ɛ ≤ 0.9) and Prandtl number (0.01 ≤ Pr ≤ 10) on the flow behavior and heat transfer. By combining the method of matched asymptotic expansions with computational
fluid dynamics (CFD), so called asymptotic computational fluid dynamics (ACFD) technique has been employed to generate correlation
for average Nusselt number. The technique is found to be an attractive option for generating correlation and also in the analysis
of natural convection in porous medium over a fairly wide range of parameters with fewer simulations for numerical solutions. 相似文献
12.
Saint-Venant's torsion of symmetric cylindrical bars consisting of two or four homogeneous phases is studied. A symmetric
section is meant that the cross section of the cylindrical bar possesses reflectional symmetry with respect to one or more
axes. Each constituent region may have different shear modulus. The idea of the analysis is to superimpose suitably reflected
potentials to obtain the torsion solution of the same composite section but with different moduli. For two-phase sections,
we show that, if the warping fields for a given symmetric section with phase shear moduli μ1 and μ2 are known a priori, then the warping fields for the same configuration but with a different set of constituent moduli μ1
′ and μ2
′ are readily found through simple linear superpositions. Further, suppose that the torsional rigidities T(μ1,μ2) and T(μ1
′,μ2
′) for any two sets of phase moduli can be measured by some experimental tests or evaluated through numerical procedures, then
the torsional rigidity for any other combinations of constituent moduli T(μ1
′′,μ2
′′) can be exactly determined without any recourse to the field solutions of governing differential equations. Similar procedures
can be applied to a 4-phase symmetric section. But the coefficients of superposition are only found for a few branches. Specifically,
we find that depending on the conditions of μ and μ′, admissible solutions can be divided into three categories. When the correspondence between the warping field is known to
exist, a link between the torsional rigidities can be established as well.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
13.
The aim of this work is to carry out an experimental investigation into the generation of airborne microparticles when millimetric
droplets of aqueous solutions impact onto a liquid film. Impact experiments using 3.9 mm diameter droplets were carried out
for Weber numbers between 159 and 808, with a fixed Ohnesorge number of 2 × 10−3 and film parameters S
f (the ratio between the thickness of the liquid film h
film and the diameter of the impacting droplet d
i) between 0.3 and 1. Observed results show that the deposition/splashing threshold is independent of the parameter S
f in agreement with the data in the literature. The aerosol measurement results demonstrate the production of solid particles
from the evaporation of secondary microdroplets with diameters less than 30 μm formed when splash occurs. The median diameter
of these microdroplets is around 20 μm, corresponding to a value of d
50/d
i = 5 × 10−3. Taken together, the results show that the mass and the number of particles emitted increase as the Weber number increases.
Moreover, at a Weber number of 808, the results show that the mass and number of particles emitted increases as the parameter
S
f decreases. In this case, the mean number of microdroplets emitted per impact is equal to 14 for S
f = 1 and equal to 76 for S
f = 0.3. 相似文献
14.
In this paper a finite element (FE) based unitcell model has been devised with periodic boundary conditions to calculate the effective tan δ of a composite as a function of frequency. Using this method, it is demonstrated that the tan δ of the nano-composite manifests important information about the extent and properties of the interphase region that surrounds each nano-particle. Thus we imply that tan δ measurements provide a simple yet useful experimental tool to understand more about the interphase. However, severe agglomeration or wide size distribution of the nano-particles may introduce errors in measurement. 相似文献
15.
Bernard Ducomet ?��rka Ne?asov�� Alexis Vasseur 《Journal of Mathematical Fluid Mechanics》2011,13(2):191-211
We consider the Cauchy problem for the equations of spherically symmetric motions in
\mathbb R3{\mathbb {R}^3}, of a selfgravitating barotropic gas, with possibly non monotone pressure law, in two different situations: in the first
one we suppose that the viscosities μ(ρ), and λ(ρ) are density-dependent and satisfy the Bresch–Desjardins condition, in the second one we consider constant densities. In
the two cases, we prove that the problem admits a global weak solution, provided that the polytropic index γ satisfy γ > 1. 相似文献
16.
Wassim Kriaa Kamel Abderrazak Hatem Mhiri Georges Le Palec Philippe Bournot 《Heat and Mass Transfer》2008,44(9):1051-1063
In this work, we propose to study non isothermal air–air coaxial jets with two different approaches: parabolic and elliptic
approaches. The standard k−ε model and the RSM model were applied in this study. The numerical resolution of the equations governing this flow type was
carried out for: the parabolic approach, by a “home-made” CFD code based on a finite difference method, and the elliptic approach
by an industrial code (FLUENT) based on a finite volume method. In forced convection mode (Fr = ∞), the two turbulence models are valid for the prediction of the mean flow. But for turbulent sizes, k−ε model gives results closer to those achieved in experiments compared to RSM Model. Concerning the limit of validity of the
parabolic and elliptic approaches, we showed that for velocities ratio r lower than 1, the results of the two approaches were satisfactory. On the other hand, for r > 1, the difference between the results became increasingly significant. In mixed convection mode (Fr ≅ 20), the results obtained by the two turbulence models for the mean axial velocity were very different even in the plume
region. For the temperature and the turbulent sizes the two models give satisfactory results which agree well with the correlations
suggested by the experimenters for X ≥ 20. Thus, the second order model with σ
t = 0.85 is more effective for a coaxial jet study in a mixed convection mode. 相似文献
17.
High-speed tomographic PIV was used to investigate the coalescence of drops placed on a liquid/liquid interface; the coalescence
of a single drop and of a drop in the presence of an adjacent drop (side-by-side drops) was investigated. The viscosity ratio
between the drop and surrounding fluids was 0.14, the Ohnesorge number (Oh = μd/(ρdσD)1/2) was 0.011, and Bond numbers (Bo = (ρ
d
− ρ
s
)gD
2/σ) were 3.1–7.5. Evolving volumetric velocity fields of the full coalescence process allowed for quantification of the velocity
scales occurring over different time scales. For both single and side-by-side drops, the coalescence initiates with an off-axis
film rupture and film retraction speeds an order of magnitude larger than the collapse speed of the drop fluid. This is followed
by the formation and propagation of an outward surface wave along the coalescing interface with wavelength of approximately
2D. For side-by-side drops, the collapse of the first drop is asymmetric due to the presence of the second drop and associated
interface deformation. Overall, tomographic PIV provides insight into the flow physics and inherent three-dimensionalities
in the coalescence process that would not be achievable with flow visualization or planar PIV only. 相似文献
18.
P. Ortwein W. Woiwode S. Fleck M. Eberhard T. Kolb S. Wagner M. Gisi V. Ebert 《Experiments in fluids》2010,49(4):961-968
The release of HCl is an important parameter for industrial combustion and gasification processes, which must be determined
in the ppm range for active process control and optimization. Based on a low power vertical-cavity surface-emitting laser
(VCSEL) at 1.74 μm, we developed a new tuneable diode laser absorption spectrometer for calibration-free, absolute in situ
HCl detection using the H35Cl (2 ← 0) R(3) absorption line with minimized cross-sensitivity to CO2 and H2O. The spectrometer was applied to in situ measurements in a gasification process (T = 1,130°C, P = 1 atm, L = 28 cm) and yielded an optical resolution of 2.3·10−4, i.e. a HCl sensitivity of 45 ppm (13 ppm·m). 相似文献
19.
Transient elongational viscosities of aqueous polyacrylamide solutions measured with an optical rheometer 总被引:1,自引:1,他引:0
An anionic polyacrylamide solution was characterized in elongational flow by combining laser-Doppler velocimetry to determine
the strain rate in the flow direction and the two-color flow-induced birefringence method to measure the first normal stress
difference along the axial centerline of a hyperbolic die. The elongational rate was constant along the axial centerline of
the planar hyperbolic die as long as vortices at the die entrance did not occur. The transient elongational viscosity μ
+ was determined as a function of the elongational rate. The parameters varied are the Hencky strain rate and the polymer concentration.
μ
+ showed a pronounced increase over the linear viscoelastic behavior above critical Hencky strains of 1.2 to 1.5; that is, a significant strain hardening could be observed for polyacrylamide
solutions. This strain hardening is stronger the higher the elongational rate. A slight enhancement of strain hardening was
found by increasing the concentration from 0.5 to 1 g/l. The stress optical coefficient was determined as 1.8 × 10−7 Pa−1 (0.5 g/l) and 1.2 × 10−7 Pa−1 (1 g/l).
相似文献
Helmut MünstedtEmail: |
20.
Non-Newtonian fluid flow through porous media is of considerable interest in several fields, ranging from environmental sciences
to chemical and petroleum engineering. In this article, we consider an infinite porous domain of uniform permeability k and porosity f{\phi} , saturated by a weakly compressible non-Newtonian fluid, and analyze the dynamics of the pressure variation generated within
the domain by an instantaneous mass injection in its origin. The pressure is taken initially to be constant in the porous
domain. The fluid is described by a rheological power-law model of given consistency index H and flow behavior index n; n, < 1 describes shear-thinning behavior, n > 1 shear-thickening behavior; for n = 1, the Newtonian case is recovered. The law of motion for the fluid is a modified Darcy’s law based on the effective viscosity μ
ef
, in turn a function of f, H, n{\phi, H, n} . Coupling the flow law with the mass balance equation yields the nonlinear partial differential equation governing the pressure
field; an analytical solution is then derived as a function of a self-similar variable η = rt
β
(the exponent β being a suitable function of n), combining spatial coordinate r and time t. We revisit and expand the work in previous papers by providing a dimensionless general formulation and solution to the problem
depending on a geometrical parameter d, valid for plane (d = 1), cylindrical (d = 2), and semi-spherical (d = 3) geometry. When a shear-thinning fluid is considered, the analytical solution exhibits traveling wave characteristics,
in variance with Newtonian fluids; the front velocity is proportional to t
(n-2)/2 in plane geometry, t
(2n-3)/(3−n) in cylindrical geometry, and t
(3n-4)/[2(2−n)] in semi-spherical geometry. To reflect the uncertainty inherent in the value of the problem parameters, we consider selected
properties of fluid and matrix as independent random variables with an associated probability distribution. The influence
of the uncertain parameters on the front position and the pressure field is investigated via a global sensitivity analysis
evaluating the associated Sobol’ indices. The analysis reveals that compressibility coefficient and flow behavior index are
the most influential variables affecting the front position; when the excess pressure is considered, compressibility and permeability
coefficients contribute most to the total response variance. For both output variables the influence of the uncertainty in
the porosity is decidedly lower. 相似文献