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1.
Local strain data obtained throughout the entire weld region encompassing both the weld nugget and heat affected zones (HAZs)
are processed using two methodologies, uniform stress and virtual fields, to estimate specific heterogeneous material properties
throughout the weld zone. Results indicate that (a) the heterogeneous stress–strain behavior obtained by using a relatively
simple virtual fields model offers a theoretically sound approach for modeling stress–strain behavior in heterogeneous materials,
(b) the local stress–strain results obtained using both a uniform stress assumption and a simplified uniaxial virtual fields
model are in good agreement for strains ɛ
xx < 0.025, (c) the weld nugget region has a higher hardening coefficient, higher initial yield stress and a higher hardening
exponent, consistent with the fact that the steel weld is overmatched and (d) for ɛ
xx > 0.025, strain localization occurs in the HAZ region of the specimen, resulting in necking and structural effects that complicate
the extraction of local stress strain behavior using either of the relatively simple models.
相似文献
S. M. AdeebEmail: |
2.
In this paper, an implicit coupling algorithm for fluid–structure interaction problems with under-time steps for the solid
is presented. Its implementation on two configurations is achieved by using the CASTEM finite-elements code. First, the free
oscillations of a cylinder in an annular fluid domain where its movement is determined by the coupled fluid–solid action is
considered in the case of viscous fluid. It should be noted that the implicit coupling algorithm gives the best prediction
of the structure oscillations. The under-time steps for the solid are introduced in order to obtain better results. Then,
an application whose final objective is to model a floating barrage is studied. The main goal of this application is to predict
the displacements of a ring completely immersed and anchored by a cable to the lower boundary of the fluid domain. The finite-element
discretization of the Navier–Stokes equations in the ALE formulation is used 相似文献
3.
This paper presents the theoretical modeling and corresponding experimental results of the oblique incidence response of a
luminescent photoelastic coating (LPC) applied to a cylinder under load. LPC is a measurement technique to acquire full-field
maximum shear strain and its principal strain direction. The technique uses an absorption dye and a luminescent dye within
a photoelastic coating, and the coating is applied on the surface of the specimen using conventional aerosol techniques. On
3D objects, the response of the emission field is dependent on the excitation orientation due to the surface inclination of
the structural component and the out-of-plane strain component within the coating. Full-field strain separated results have
been previously demonstrated on a 2D specimen. The extension of the strain separation technique to a 3D specimen—a cylinder
in bending—is the focus of this investigation. Two different responses were obtained from normal and oblique excitation. As
a result, the principal strain was separated over ±56° of circumference of the cylinder with RMS error relative to the theoretical
result of 87 μɛ for maximum principal strain and 78 μɛ for minimum. 相似文献
4.
Flow-induced vibration of an elastic airfoil due to the wake propagating from an upstream cylinder at a Reynolds number of 10 000 based on cylinder diameter D was investigated. A laser vibrometer was employed to measure the bending and torsional vibration displacements at the mid-span of the airfoil and the cylinder. The dimensionless gap size S/D between the two structures was selected as the governing parameter of the flow-induced vibration problem. It is found that the vibration amplitudes of the elastic airfoil and the vortex shedding frequency of the coupled cylinder–airfoil system are strongly dependent on S/D, due to the different fluid–structure interaction experienced by the airfoil at various S/D. Strong vortex-induced vibration of the airfoil appears to be excited by the organized Karman-vortex-street (KVS) vortices in the cylinder wake for S/D>3 and becomes stabilized for S/D3. However, as a result of the shear-layer-induced vibration at an appropriate frequency, structural resonance is also found to occur even though the airfoil is located in the stabilizing range. The occurrence of structural resonance is further supported by a complementary experiment where the slender structure is an elastic flat plate. This phenomenon indicates that assuming the structures in any fluid–structure interaction problem to be rigid is not appropriate, even though they might appear to be highly stiff. The experimental results were used to validate a numerical model previously developed to estimate the structural responses in complicated fluid–structure interaction problems. 相似文献
5.
Experiments on a square-section cylinder fixed and forced to oscillate transversely in a uniform stream were conducted in
a water tank. The Reynolds number of the experiments is in the range of 3·103 to 104, the amplitude to side length ratioA/D is up to 0.7 and the range of reduced velocity is 4.5<V
r
<12. This study aims at investigating the lock-in phenomenon, the fluctuating lift and the phase shift between fluctuating
lift and displacement of the oscillating cylinder. The problems on the aeroelastic instability relating to present experimental
results have been discussed. The flow visualization clearly shows that there are drastic changes of vortex-shedding from cylinder
at the resonance point and the upper end of the lock-in range. The results of the flow visualization give better understanding
of the physical mechanism of the phase shift.
Project supported by National Natural Science Foundation of China 相似文献
6.
I. Yu. Tsvelodub 《Journal of Applied Mechanics and Technical Physics》2007,48(5):708-711
An elastic plate with a physically nonlinear inclusion of an arbitrary shape is considered. This plate is subjected to pure
bending under the action of transverse forces and bending moments applied at the external boundary of the plate. There are
no loads distributed over the surface. The problem of finding external actions that provide a necessary uniform moment state
in the inclusion, i.e., prescribed constant moments and curvatures, is formulated and solved.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 5, pp. 104–107, September–October, 2007. 相似文献
7.
Results of a numerical study of a laminar separated flow behind a rectangular step on a porous surface with uniform injection
or suction are described. Two cases are considered: an unconfined flow past a step and flow evolution in a confined channel
(duct). It is shown that mass transfer on the surface causes strong changes in the flow structure and substantially affects
the position of the reattachment point, as well as friction and heat transfer. More intense injection leads first to an increase
in the separation-zone length and then to its rapid vanishing due to boundary-layer displacement. Vice versa, suction at high
Reynolds numbers Re
s
> 100 reduces the separation-zone length. The duct flow has a complicated distribution of friction and heat-transfer coefficients
along the porous surface owing to the coupled effect of the transverse flow of the substance and changes in the main flow
velocity due to mass transfer.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 18–28, January–February, 2006. 相似文献
8.
Advances using optical fibres as sensors may represent an important contribution for development of minimally invasive techniques
in biomedical and biomechanical applications. Concerning spine injuries, intervertebral disc (IVD) degeneration is a major
clinical issue since it represents gross structural disruption and it is irreversible. Measuring biomechanical parameters
of the IVD should contribute for better understanding on its mechanical response to external applied forces. The purpose of
this study was to explore the potential of a Fibre Bragg Grating (FBG) sensor to measure strain caused by bulging of the intervertebral
disc under axial compression. Disc bulging is a consequence of IVD compression and a technique to register this behaviour
is addressed in this study. Needle-mounted sensors were already used to measure IVD pressure in cadaveric material. In this
study we also explored the possibility of using needles only for sensor guiding and positioning leaving sensor directly in
contact with the IVD material. An ex vivo porcine dorsal functional spinal unit was instrumented with a FBG sensor and submitted to axial compression. Results suggest
the sensor’s ability to measure strain response to load. Bulging of the annulus fibrosus as a consequence of axial compression
was confirmed using the FBG sensor. Hysteresis and viscoelastic behaviour were observable suggesting that energy is dissipated
by the deformation of the annulus and that unloading time was insufficient for disc recovery. Nevertheless the relatively
low strain sensitivity of the sensor as well as signal artefacts caused by transverse loading may constitute a problem in
the analysis and interpretation of strain data. The technique may not be suitable for measurement of physiologic bulging being
more indicative of the radial force exerted by the annulus. 相似文献
9.
The grating objective speckle method has been applied in whole-field strain analysis of carbon-fiber-woven polyimide-composite
materials. A sequence of rosette fringe patterns was obtained from one single specklegram, indicating displacement components
along four different directions with a 45-deg interval. The spatial frequencies, which represent the sensitivities of the
fringe intervals, were 2400 ℓ/mm forU
x
,U
y
and 1697 ℓ/mm forU
45 andU
135. Normal strain components, ɛ
x
, ɛ
y
, ɛ45, and ɛ135, were trasformed to quantitative topographic representations by coupling to a digital computer system. Shear strain can be
determined by the rosette equations. 相似文献
10.
The surface vorticity method (SVM), which is a fast and practical grid-free two-dimensional (2-D) method, and a fluid–structure interaction model incorporating the effects of cylinder motions and displacements is used to simulate the vortex-induced vibration of cylinder arrays at sub-critical Reynolds number Re=2.67×104. The SVM is found to be most suitable for simulating a 2-D cylinder row with large-amplitude vibrations where the vorticity field and the fluid forces of the cylinder row change drastically, and the effect of the stream on the transverse direction vibration is very significant. The fluidelastic instability of a flexible cylinder row at small pitch ratio is also investigated, and the critical reduced velocity of the cylinder row at a reduced damping parameter SG=1.29 is calculated, which is in good agreement with experimental and analytical results of the unsteady model. Vortex-induced vibration of a staggered cylinder array is simulated using different structural parameters. When the cylinders are relatively more flexible, the flow pattern changes dramatically and the fluid–structure interaction has a dominant impact on the flow field. Compared with grid-based methods, the grid-free SVM is a fast and practical method for the simulation of the FIV of cylinder arrays due to vortex shedding at sub-critical Reynolds numbers. 相似文献
11.
The turbulent fluid and particle interaction in the turbulent boundary layer for cross flow over a cylinder has been experimentally
studied. A phase-Doppler anemometer was used to measure the mean and fluctuating velocities of both phases. Two size ranges
of particles (30μm–60μm and 80μm–150μm) at certain concentrations were used for considering the effects of particle sizes
on the mean velocity profiles and on the turbulent intensity levels. The measurements clearly demonstrated that the larger
particles damped fluid turbulence. For the smaller particles, this damping effect was less noticeable. The measurements further
showed a delay in the separation point for two phase turbulent cross flow over a cylinder.
The project supported by the National Natural Science Foundation of China 相似文献
12.
The boundary layers developing on a single and two tandem circular cylinders were examined using multiple hot-film sensor
arrays for Re=2.4–5.1×104. Hot-wire and surface pressure measurements, and smoke-wire flow visualization were also made to better understand the flow
pattern and the evolution of the vortex street. The results show that, by use of the sensor arrays in conjunction with a bank
of constant-temperature anemometers, (i) the effects of the upstream cylinder on the boundary layer developing on the downstream
cylinder, (ii) the frequency of the vortex shedding, and (iii) the locations of flow separation and reattachment can be determined
non-intrusively and simultaneously. These measurement capabilities will provide a practical means for the characterization
and manipulation of unsteady flow phenomena.
Received: 27 October 1996 / Accepted: 13 February 1997 相似文献
13.
The stability of a surface-charged cylindrical jet in a longitudinal uniform electric field with respect to capillary pertubations
is investigated in the linear approximation. The evolution of both axisymmetric and azimuthal-periodic perturbations is analyzed.
In the latter case the first two modes among the azimuthal wavenumbers — bending and Bohr — are considered. Axisymmetric and
bending instabilities lead to the transverse disintegration of the jet into individual drops and the Bohr mode to the longitudinal
separation of the input jet into two parts. It is found that the axisymmetric and bending instabilities, respectively, can
be completely suppressed and significantly attenuated by means of an external longitudinal field. In this case the role of
the Bohr mode becomes more important leading under certain conditions to longitudinal longwave jet splitting. Events which
can be interpreted as manifestations of longitudinal partition of the jet (dumbbell-like cross-section, branching nodes) are
observed in experiments with evaporating polymer-solution microjets.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 29–40, March–April, 1998.
The work was carried out with support from the Russian Foundation for Fundamental Research (project No. 97-01-00153). 相似文献
14.
An innovative technique for measuring both the shape, the displacement, the strain and the temperature fields at the surface
of an object using a single stereovision sensor is proposed. The sensor is based on two off-the-shelf low-cost high-resolution
uncooled CCD cameras. To allow both dimensional and thermal measurements, the sensor operates in the visible and near infrared
(NIR) spectral band (0.7–1.1 μm), and a radiometric and geometric calibration of the sensor is required. This technique leads
to a low-cost camera-based simplified instrumentation that gives simultaneously dimensional/kinematical and thermal field
measurements. 相似文献
15.
Luan Thach Hoang 《Journal of Mathematical Fluid Mechanics》2010,12(3):435-472
This study is motivated by problems arising in oceanic dynamics. Our focus is the Navier–Stokes equations in a three-dimensional
domain Ωɛ, whose thickness is of order O(ɛ) as ɛ → 0, having non-trivial topography. The velocity field is subject to the Navier friction boundary conditions on the
bottom and top boundaries of Ωɛ, and to the periodicity condition on its sides. Assume that the friction coefficients are of order O(ɛ3/4) as ɛ → 0. It is shown that if the initial data, respectively, the body force, belongs to a large set of H1(Ωɛ), respectively, L2(Ωɛ), then the strong solution of the Navier–Stokes equations exists for all time. Our proofs rely on the study of the dependence
of the Stokes operator on ɛ, and the non-linear estimate in which the contributions of the boundary integrals are non-trivial. 相似文献
16.
This paper describes the measurement of average strain, strain distribution and vibration of a cantilever beam made of Carbon
Fiber Reinforced Plastics (CFRP), using a single Fibre Bragg Grating (FBG) sensor mounted on the beam surface. Average strain
is determined from the displacement of the peak wavelength of reflected spectrum from the FBG sensor. Two unstrained reference
FBG sensors were used to compensate for temperature drift. Measured strains agree with those measured by a resistance foil
strain gauge attached to the sample. Stress distributions are measured by monitoring the variation in the full width at half
maximum (FWHM) values of the reflected spectrum, using a proposed optical analytical model, described in the paper. FWHM values
were measured for both the cantilever test beam and for a reference beam, loaded using a four-point bending rig. The trend
of the stress distribution for the test beam matches with our analytical model, however with a relatively large noise present
in the experimentally determined data. The vibration of a cantilever beam was measured by temporal analysis of the peak reflection
wavelength. This technique is very stable as measurements are not affected by variations in the signal amplitude. Finally
an application of FBG sensors for damage detection of CFRP plates, by measuring the natural frequency, is demonstrated. With
small defects of different sizes applied to the CFRP plate, the natural frequency decreased with damage size. 相似文献
17.
M. A. Kulesh V. P. Matveenko M. V. Ulitin I. N. Shardakov 《Journal of Applied Mechanics and Technical Physics》2008,49(2):323-329
A study is made of waves in a Cosserat continuum, whose strain state is characterized by independent displacement and rotation
vectors. The propagation of longitudinal and transverse bulk waves is considered. Wave solutions are sought in the form of
wave trains specified by a Fourier spectrum of arbitrary shape. It is shown that if the solution is sought in the form of
three components of the displacement vector and three components of the rotation vector which depend on time and the longitudinal
coordinate, the initial system is split into two systems, one of which describes longitudinal waves, and the other transverse
waves. For waves of both types, dispersion relations and analytical solutions in displacement are obtained. The dispersion
characteristics of the solutions obtained differ from the dispersion characteristics of the corresponding classical elastic
solutions.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 2, pp. 196–203, March–April, 2008. 相似文献
18.
We consider a mixed boundary-value problem for the Poisson equation in a plane two-level junction Ω ɛ that is the union of a domain Ω0 and a large number 2N of thin rods with thickness of order ɛ =
(N
−1). Depending on their lengths, the thin rods are divided into two levels. In addition, the rods from each level are ɛ-periodically
alternated. Inhomogeneous Neumann boundary conditions are given on the vertical sides of the thin rods of the first level,
and homogeneous Dirichlet boundary conditions are given on the vertical sides of the rods of the second level. We investigate
the asymptotic behavior of a solution of this problem as ɛ → 0 and prove a convergence theorem and the convergence of the
energy integral.
__________
Translated from Neliniini Kolyvannya, Vol. 8, No. 2, pp. 241–257, April–June, 2005. 相似文献
19.
Matthieu Barrandon 《Journal of Mathematical Fluid Mechanics》2006,8(2):267-310
We consider bifurcations of a class of infinite dimensional reversible dynamical systems which possess a family of symmetric
equilibria near the origin. We also assume that the linearized operator at the origin Lɛ has an essential spectrum filling the entire real line, in addition to the simple eigenvalue at 0. Moreover, for parameter
values ɛ < 0 there is a pair of imaginary eigenvalues which meet in 0 for ɛ = 0, and which disappear for ɛ > 0. The
above situation occurs for example when one looks for travelling waves in a system of superposed perfect fluid layers, one
being infinitely deep. We give quite general assumptions which apply in such physical examples, under which one obtains a
family of bifurcating solutions homoclinic to every equilibrium near the origin. These homoclinics are symmetric and decay
algebraically at infinity, being approximated at main order by the Benjamin–Ono homoclinic. For the water wave example, this
corresponds to a family of solitary waves, such that at infinity the upper layer slides with a uniform velocity, over the
bottom layer (at rest). 相似文献
20.
This paper is concerned with the numerical simulation of the flow structure around a square cylinder in a uniform shear flow. The calculations were conducted by solving the unsteady 2D Navier–Stokes equations with a finite difference method. The effect of the shear parameter K of the approaching flow on the vortex-shedding Strouhal number and the force coefficients acting on the square cylinder is investigated in the range K=0·0–0·25 at various Reynolds numbers from 500 to 1500. The computational results are compared with some existing experimental data and previous studies. The effect of shear rate on the Strouhal number and the force acting on the cylinder has a tendency to reduce the oscillation. The Strouhal number, mean drag and amplitude of the fluctuating force tend to decrease as the shear rate increases, but show no significant change at low shear rate. Increasing the Reynolds number decreases the Strouhal number and increases the force acting on the cylinder. At high shear rate the shedding frequencies of the fluctuating drag and lift coefficients are identical. © 1997 John Wiley & Sons, Ltd. 相似文献