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1.
I. V. Sturova 《Journal of Applied Mechanics and Technical Physics》2006,47(1):71-78
The effect of initial disturbances and unsteady external loading on an elastic beam of finite length which floats freely on
the surface of an ideal incompressible fluid is studied in a linear treatment. The fluid flow is considered potential. The
beam deflection is sought in the form of an expansion in the eigenfunctions of beam vibrations in vacuum with time-dependent
amplitudes. The problem reduces to solving an infinite system of integrodifferential equations for unknown amplitudes. The
memory functions entering this system are determined by solving the radiation problem. The beam behavior is studied for various
loads with and without allowance for the weight of the fluid. The effect of fluid depth on beam deformation was determined
by comparing with the previously obtained solutions of the unsteady problem for a beam floating in shallow water.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 85–94, January–February, 2006. 相似文献
2.
Andrew J. Dick Balakumar Balachandran Hiroshi Yabuno Masatoshi Numatsu Keiichi Hayashi Masaharu Kuroda Kiwamu Ashida 《Nonlinear dynamics》2009,57(3):335-349
Grazing behavior in soft impact dynamics of a harmonically based excited flexible cantilever beam is investigated. Numerical
and experimental methods are employed to study the dynamic behavior of macro- and micro-scale cantilever beam–impactor systems.
For off-resonance excitation at two and a half times the fundamental frequency, the response of the oscillating cantilever
experiences period doubling as the separation distance or clearance between the beam axis and the contact surface is decreased.
The nonlinear phenomenon is studied by using phase portraits, Poincaré sections, and spectral analysis. Motivated by atomic
force microscopy, this general dynamic behavior is studied as a means to locating the separation distance corresponding to
grazing where the contact force is minimized. 相似文献
3.
I. V. Sturova 《Journal of Applied Mechanics and Technical Physics》2002,43(3):415-423
A solution is derived for the twodimensional unsteady problem of the behavior of an elastic beam of finite dimensions floating on the free surface of water under external loading. It is assumed that the fluid is ideal and incompressible and its depth is well below the beam length. The simultaneous motion of the beam and the fluid is considered within the framework of linear theory, and the fluid flow is assumed to be potential. The behavior of the beam under various loadings with and without allowance for the inertia of the load is studied. 相似文献
4.
V. P. Zhukov I. V. Shvab A. V. Burdakov 《Journal of Applied Mechanics and Technical Physics》2007,48(6):779-788
Dynamics of the plasma in open magnetic traps with an electron beam, in particular, in a GOL-3 trap, is studied. The possibility of the formation of a resonant surface of the magnetic field and the development of helical
instability caused by the presence of this surface is studied numerically.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 6, pp. 3–14, November–December, 2007. 相似文献
5.
At present, the problems of unsteady waves initiated by surface perturbations in an elastic half-space have been studied sufficiently
well (see, e.g., [1–5]; a detailed bibliography on this problem can be found in [6]). At the same time, the analytical solutions
of the corresponding unsteady problems of bulk perturbations are practically absent. It is these questions as applied to the
plane problem that are considered in this paper. 相似文献
6.
The surface waves generated by unsteady concentrated disturbances in an initially quiescent fluid of infinite depth with an inertial surface are analytically investigated for two- and three-dimensional cases. The fluid is assumed to be inviscid, incompressible and homogenous. The inertial surface represents the effect of a thin uniform distribution of non-interacting floating matter. Four types of unsteady concentrated disturbances and two kinds of initial values are considered, namely an instantaneous/oscillating mass source immersed in the fluid, an instantaneous/oscillating impulse on the surface, an initial impulse on the surface of the fluid, and an initial displacement of the surface. The linearized initial-boundary-value problem is formulated within the framework of potential flow. The solutions in integral form for the surface elevation are obtained by means of a joint Laplace-Fourier transform. The asymptotic representations of the wave motion for large time with a fixed distance- to-time ratio are derived by using the method of stationary phase. The effect of the presence of an inertial surface on the wave motion is analyzed. It is found that the wavelengths of the transient dispersive waves increase while those of the steady-state progressive waves decrease. All the wave amplitudes decrease in comparison with those of conventional free-surface waves. The explicit expressions for the freesurface gravity waves can readily be recovered by the present results as the inertial surface disappears. 相似文献
7.
M. F. Ionina 《Journal of Applied Mechanics and Technical Physics》1999,40(6):1163-1172
The plane unsteady problem of impact of a thin elastic cylindrical shell on the surface of an ideal incompressible liquid
is considered. The initial stage of interaction between the body and the liquid when the stresses in the shell attain peak
values is studied. The problem is treated in a linearized formulation and is solved numerically by the normal modes method
within the framework of the Wagner approach. The numerical results agree with experimental data for various types of circular
cylindrical shells made from mild steel.
Lavrent'ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from
Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 6, pp. 186–197, November–December, 1999. 相似文献
8.
A. A. Chesnokov 《Journal of Applied Mechanics and Technical Physics》2006,47(6):800-811
The problem of the decay of an arbitrary discontinuity for the equations describing plane-parallel shear flows of an ideal
fluid in a narrow channel is considered. The class of particular solutions corresponding to fluid flows with piecewise constant
vorticity is studied. In this class, the existence of self-similar solutions describing all possible unsteady wave configurations
resulting from the nonlinear interaction of the specified shear flows is established.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 6, pp. 34–47, November–December, 2006. 相似文献
9.
The vibrations of a vessel strongly influence the behavior of the interface of the fluids in it. Thus, vertical vibrations
can lead both to the parametric excitation of waves (Faraday ripples) and to the suppression of the Rayleigh-Taylor instability
[1–2]. At the present time, the influence of vertical vibrations on the behavior of a fluid surface have been studied in sufficient
detail (see, for example, review [3]). The behavior of an interface of fluids in the case of horizontal vibrations has been
studied less. An interesting phenomenon has been revealed in the experimental papers [4, 5]: in the case of fairly strong
horizontal vibrations of a vessel containing a fluid with a free surface, the fluid collects near one of the vertical vessel
walls, the free surface being practically plane and stationary with respect to the vessel, while its angle of inclination
to the horizon depends on the vibration rate. But if there is a system of immiscible fluids with comparable but different
densities in the vessel, horizontal vibrations lead to the formation of a steady wave relief at the interface. An explanation
of the behavior of a fluid with a free boundary was given in [6] on the basis of averaged equations of fluid motion in a vibrational
field. The present paper is devoted to an analysis of the behavior of the interface of fluids with comparable densities in
a high-frequency vibrational field.
Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 8–13, November–December, 1986. 相似文献
10.
L. A. Tkacheva 《Journal of Applied Mechanics and Technical Physics》2008,49(5):853-863
Unsteady crack propagation is studied in the beam approximation. The Euler and Timoshenko models of beam theory are used.
Crack propagation is described using an energy balance equation.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 5, pp. 177–189, September–October, 2008. 相似文献
11.
For active materials such as piezoelectric stacks, which produce large force and small displacement, motion amplification
mechanisms are often necessary – not simply to trade force for displacement, but to increase the output work transferred through
a compliant structure. Here, a new concept for obtaining large rotations from small linear displacements produced by a piezoelectric
stack is proposed and analyzed. The concept uses elastic (buckling) and dynamic instabilities of an axially driven buckling
beam. The optimal design of the buckling beam end conditions was determined from a static analysis of the system using Euler's
elastica theory. This analysis was verified experimentally. A stack-driven, buckling beam prototype actuator consisting of
a pre-compressed PZT stack (140 mm long, 10 mm diameter) and a thin steel beam (60 mm× 12 mm× 0.508 mm) was constructed. The
buckling beam served as the motion amplifier, while the PZT stack provided the actuation. The experimental setup, measuring
instrumentation and method, the beam pre-loading condition, and the excitation are fully described in the paper. Frequency
responses of the system for three pre-loading levels and three stack driving amplitudes were obtained. A maximum 16∘ peak-to-peak rotation was measured when the stack was driven at an amplitude of 325 V and frequency of 39 Hz. The effects
of beam pre-load were also studied. 相似文献
12.
Characteristics of unsteady type IV shock/shock interaction 总被引:1,自引:0,他引:1
Characteristics of the unsteady type IV shock/shock interaction of hypersonic blunt body flows are investigated by solving
the Navier–Stokes equations with high-order numerical methods. The intrinsic relations of flow structures to shear, compression,
and heating processes are studied and the physical mechanisms of the unsteady flow evolution are revealed. It is found that
the instantaneous surface-heating peak is caused by the fluid in the “hot spot” generated by an oscillating and deforming
jet bow shock (JBS) just ahead of the body surface. The features of local shock/boundary layer interaction and vortex/boundary
layer interaction are clarified. Based on the analysis of flow evolution, it is identified that the upstream-propagating compression
waves are associated with the interaction of the JBS and the shear layers formed by a supersonic impinging jet, and then the
interaction of the freestream bow shocks and the compression waves results in entropy and vortical waves propagating to the
body surface. Further, the feedback mechanism of the inherent unsteadiness of the flow field is revealed to be related to
the impinging jet. A feedback model is proposed to reliably predict the dominant frequency of flow evolution. The results
obtained in this study provide physical insight into the understanding of the mechanisms relevant to this complex flow. 相似文献
13.
The research carried out in [1–8] is developed by considering the self-similar problem of the unsteady separated flow over
a plate expanding from a point with the constant velocity D of a plane-parallel stream of ideal fluid with velocity V∞. At infinity the flow is uniform, steady and normal to the surface of the plate. A wide range of values of the parameter
α=V∞/D is investigated. On the value of α there depends, in particular, the direction of shedding of the vortex sheets (VS) which,
in accordance with the Joukowsky-Chaplygin condition, occur in separated flow over a plate. A comparison is made with the
results obtained when the sheets are replaced by vortex filaments (VF). In accordance with [9] the choice of the intensity
of the VF ensures, like the introduction of VS, the finiteness of the flow velocity at the edges of the plate. Within the
framework of the unsteady analogy and the law of plane sections the problem of the flow over a delta wing at an angle of attack
reduces to the unsteady flow over an expanding plate investigated. In addition to [3, 9], this question was also examined
in [10–15]. In [11–15] and in [3] the analysis is based on VS and in [9, 10] on VF. Special attention is paid to the topology
of the flow, in particular, to the structure of the so-called conical streamlines and their points of convergence and divergence
(this was done in [3] for a special, nonlinear law of expansion of the plate and a variable free-stream velocity). The results
obtained for the models with VS and VF are compared over a broad range of values of α, not only with respect to the integral
characteristics, as in [12], but also with respect to the flow patterns.
Moscow. Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 62–69, September–October, 1988. 相似文献
14.
We found a solution of an unsteady two-dimensional heat conduction equation in a functionally gradient material (FGM) which
is subjected to a double thermal shock, namely, a local heating of a specimen by a power laser beam and cooling of a heated
surface by a water-air spray. We developed an analytical method whereby a coating is described as a laminated plate composed
of n layers with the constant material properties within a layer. Temperature distribution in a nonhomogeneous laminated plate
is obtained in a form of series using the Laplace–Hankel integral transforms. In order to extend the model of a laminated
plate to describe FGM where thermal physical characteristics are continuous functions of spatial coordinate, we considered
the limiting case of the obtained temperature distribution when the thickness of the layer iΔ
i
→ 0, and the number of layers n→∞. This allowed us to obtain the temperature distribution in an easy-to-use analytical form which can be used for determining
thermal stresses in FGM. The dependence of the temperature distribution in FGM on the operating parameters of a double thermal
shock method, e.g., a duration of heating, laser beam radius, the rate of a spray cooling, is discussed.
Received on 3 May 1999 相似文献
15.
O. Yu. Korotkov G. M. Shumskii 《Journal of Applied Mechanics and Technical Physics》2000,41(3):452-455
A mathematical model of an unsteady separated flow around an oscillating airfoil is considered. This model is based on a viscid-inviscid
approach. The points of separation and the intensity of vorticity displaced into the external flow are determined using boundary-layer
equations in an integral form. Dynamic stall on an oscillating airfoil is studied. The mechanism and nature of antidamping
are discovered.
Novosibirsk State Technical University, Novosibirsk 630092. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika,
Vol. 41, No. 3, pp. 81–85, May–June, 2000. 相似文献
16.
The coupled thermomechanical behavior of structurally inhomogeneous viscoplastic bodies under cyclic loading is investigated
by an example of the problem on harmonic bending and dissipative heat-up of a three-layer beam. Both the generalized thermomechanically
consistent flow theory (an exact formulation) and the scleronomic model (an approximated formulation) are used to solve the
problem. Aluminum alloy AMg-6 and steel 12KhN3A are chosen as the materials of the layers. The following two configurations
of the beam are considered: (i) the outer layers are aluminum and the inner layer is steel, and (ii) the outer layers are
steel and the inner layer is aluminum. The results obtained in solving the problem in the exact and approximate formulations
are compared for the amplitudes of the mechanical field characteristics, dissipated and accumulated energies, and the temperature
of dissipative heat-up. A good agreement between the results is pointed out. A comparative estimation of the absorption factor
of the beam for different arrangement of the layers is performed.
S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraines, Kiev. Translated from Prikladnaya Mekhanika,
Vol. 36, No. 2, pp. 135–143, February, 2000. 相似文献
17.
M. Abu-Hilal 《Archive of Applied Mechanics (Ingenieur Archiv)》2003,72(9):637-650
Summary The transverse vibrations of elastic homogeneous isotropic beams with general boundary conditions due to a moving random
force with constant mean value are analyzed. The boundary conditions considered are: pinned–pinned, fixed–fixed, pinned–fixed,
and fixed–free. Based on the Bernoulli beam theory, the problem is described by means of a partial differential equation.
Closed-form solutions for the variance and the coefficient of variation of the beam deflection are obtained and compared for
three types of force motion: accelerated, decelerated and uniform. The effects of beam damping and speed of the moving force
on the dynamic response of beams are studied in detail.
Received 3 December 2001; accepted for publication 30 April 2002 相似文献
18.
D. Q. Lu 《Archive of Applied Mechanics (Ingenieur Archiv)》2009,79(4):311-322
The interaction of unsteady Stokeslets with the free surface of an initially quiescent incompressible fluid of infinite depth
is investigated analytically for two- and three-dimensional cases. The disturbed flows are generated by an unsteady singular
force moving perpendicularly downwards away from the surface. The analysis is based on the assumption that the motion satisfies
the linearized unsteady Navier–Stokes equations with linear kinematic and dynamic boundary conditions. Firstly, the asymptotic
representation for the transient free-surface waves due to an instantaneous Stokeslet is derived for a large time with a fixed
distance-to-time ratio. As is well known, the corresponding inviscid waves predicted by the potential theory do not decay
to zero as the time goes to infinity. In the present study, the transient waves predicted by the viscous theory eventually
vanish due to the presence of viscosity, which is consistent with reality from the physical point of view. Secondly, the asymptotic
solutions are obtained for the unsteady free-surface waves due to a harmonically oscillating Stokeslet. It is found that the
unsteady waves can be decomposed into steady-state and transient responses. The steady state can be attained as time approaches
infinity. It is shown that the viscosity of the fluid plays an important role in the evolution of the singularity-induced
waves. 相似文献
19.
D. G. Arkhipov G. A. Khabakhpashev 《Journal of Applied Mechanics and Technical Physics》2007,48(4):508-518
The dynamics of disturbances of the interface between two layers of incompressible immiscible fluids of different densities
in the presence of a steady flow between the horizontal bottom and lid is studied analytically and numerically. A model integrodifferential
equation is derived, which takes into account long-wave contributions of inertial layers and surface tension of the fluids,
small but finite amplitude of disturbances, and unsteady shear stresses on all boundaries. Numerical solutions of this equation
are given for the most typical nonlinear problems of transformation of both plane waves of different lengths and solitary
waves.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 4, pp. 49–61, July–August, 2007. 相似文献
20.
Time-resolved stereo PIV measurements of shock–boundary layer interaction on a supercritical airfoil
Time-resolved stereo particle-image velocimetry (TR-SPIV) and unsteady pressure measurements are used to analyze the unsteady
flow over a supercritical DRA-2303 airfoil in transonic flow. The dynamic shock wave–boundary layer interaction is one of
the most essential features of this unsteady flow causing a distinct oscillation of the flow field. Results from wind-tunnel
experiments with a variation of the freestream Mach number at Reynolds numbers ranging from 2.55 to 2.79 × 106 are analyzed regarding the origin and nature of the unsteady shock–boundary layer interaction. Therefore, the TR-SPIV results
are analyzed for three buffet flows. One flow exhibits a sinusoidal streamwise oscillation of the shock wave only due to an
acoustic feedback loop formed by the shock wave and the trailing-edge noise. The other two buffet flows have been intentionally
influenced by an artificial acoustic source installed downstream of the test section to investigate the behavior of the interaction
to upstream-propagating disturbances generated by a defined source of noise. The results show that such upstream-propagating
disturbances could be identified to be responsible for the upstream displacement of the shock wave and that the feedback loop
is formed by a pulsating separation of the boundary layer dependent on the shock position and the sound pressure level at
the shock position. Thereby, the pulsation of the separation could be determined to be a reaction to the shock motion and
not vice versa. 相似文献