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1.
《Particuology》2016
Journal bearings operating in hot environments and at high temperatures experience accelerated degradation of lubricating oils. In such situations, dry granular particulates have emerged as potential media for providing lubrication in journal bearings in place of lubricating oils. Granular particulates do not degrade thermally, even at considerably high temperatures. This work explores the static and dynamic performance characteristics of elliptical-bore journal bearings lubricated with granular particulates. It is found that a bearing lubricated with a larger size (2 μm) particles offers better performance compared with that using smaller size (1 μm) particles. Bore ellipticity reduces the load-carrying capacity and increases side leakage and the coefficient of friction; however, rotor stability is marginally improved at low eccentricity ratios (<0.6), followed by significant improvement at high eccentricity ratios (>0.6). 相似文献
2.
The mechanical model was established for the anti-plane fracture problem of a functionally graded coating–substrate system
with a coating crack inclined to the weak/micro-discontinuous interface. The Cauchy singular integral equation for the crack
was derived using Fourier integral transform, and the Lobatto–Chebyshev collocation method put up by Erdogan and Gupta was
used to get its numerical solution. Finally, the effects of the weak/micro-discontinuity of the interface on SIFs were analyzed,
the “affected regions” corresponding to the two crack tips have been obtained and their engineering significance was discussed.
It was indicated that, for the crack tip in the corresponding “affected region”, to reduce the weak-discontinuity of the interface
and to make the interface micro-discontinuous are the two effective ways to reduce the SIF, and the latter way always has
more remarkable SIF-reduction effect. For the crack tip outside the “affected region”, its SIF is mainly influenced by material
stiffness, and to prevent such a tip from growing toward the interface “softer coating and stiffer substrate” is a more advantageous
combination than “stiffer coating and softer substrate”. 相似文献
3.
Qian Jian 《Acta Mechanica Sinica》1994,10(1):12-15
Using nonequilibrium statistical mechanics closure method, it is shown that the skewness factor of the velocity derivative
of isotropic turbulence approaches a constant −0.515 when the Reynolds number is very high, which is in agreement with the
DNS (direct numerical simulation) result of Vincent and Meneguzzi (1991).
The project supported by the National Basic Research Program “Non-linear Science” 相似文献
4.
Robert M. Lewis 《Archive for Rational Mechanics and Analysis》1960,5(1):355-381
The basic formulas of classical equilibrium statistical mechanics are derived from well-known theorems in measure theory and
ergodic theory. The method used is a generalization of the methods of Khinchin and Grad and deals with several, in fact a “complete set”, of “invariants” or “integrals of the motion”. Most of the results are simple
corollaries of Birkhoff's ergodic theorem, and since time-averages are used, the whole approach is characterized by an absence of statistical “ensembles”
and probability notions. In the course of the development a “generalized temperature” is introduced, and a generalization
of the second law of thermodynamics is derived. Formulas for the “microcanonical”, “canonical”, and “grand canonical” distributions
appear as special cases of the general theory. 相似文献
5.
This paper presents an operator‐splitting method (OSM) for the solution of the universal Reynolds equation. Jakobsson–Floberg–Olsson (JFO) pressure conditions are used to study cavitation in liquid‐lubricated journal bearings. The shear flow component of the oil film is first solved by a modified upwind finite difference method. The solution of the pressure gradient flow component is computed by the Galerkin finite element method. Present OSM solutions for slider bearings are in good agreement with available analytical and experimental results. OSM is then applied to herringbone grooved journal bearings. The film pressure, cavitation areas, load capacity and attitude angle are obtained with JFO pressure conditions. The calculated load capacities are in agreement with available experimental data. However, a detailed comparison of the present results with those predicted using Reynolds pressure conditions shows some differences. The numerical results showed that the load capacity and the critical mass of the journal (linear stability indicator) are higher and the attitude angle is lower than those predicted by Reynolds pressure conditions for cases of high eccentricities. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
6.
基于油膜内屈服面位置可能出现的4种情况,Tichy提出了用于Bingham流体滑动轴承特性及其屈服面位置的计算方法,在将该计算方法推广到电流变液滑动轴承的计算时,发现随着外加电场强度的变形,出现了轴承风屈服面位置不变的非物理结果,而且Tichy的方法只能适用于无限宽滑动轴承,为了对有限宽度的电流变液滑动轴承进行数值研究,采用了类Bingham模型,通过差分离散和超松驰迭代的方法对雷诺方程进行求解,计算结果表明:电流变流滑动轴承内的压力分布可以通过外加电场强度来控制,轴承间隙内屈服面位置随电场强度变化而产生的移动是使轴承润滑性能得以改变的重要力学机制;在轴承以高剪切速率运转时,由于电流变液表观黏度随电场强度的变化已经很小,该机制在轴承的设计中尤为重要。 相似文献
7.
Manufacturing tolerant topology optimization 总被引:6,自引:0,他引:6
Ole Sigmund 《Acta Mechanica Sinica》2009,25(2):227-239
In this paper we present an extension of the topology optimization method to include uncertainties during the fabrication of macro, micro and nano structures. More specifically, we consider devices that are manufactured using processes which may result in (uniformly) too thin (eroded) or too thick (dilated) structures compared to the intended topology. Examples are MEMS devices manufactured using etching processes, nano-devices manufactured using e-beam lithography or laser micro-machining and macro structures manufactured using milling processes. In the suggested robust topology optimization approach, under- and over-etching is modelled by image processing-based "erode" and "dilate" operators and the optimization problem is formulated as a worst case design problem. Applications of the method to the design of macro structures for minimum compliance and micro compliant mechanisms show that the method provides manufacturing tolerant designs with little decrease in performance. As a positive side effect the robust design formulation also eliminates the longstanding problem of one-node connected hinges in compliant mechanism design using topology optimization. 相似文献
8.
Numerical investigation on the flowfield of "swallowtail" cavity for supersonic mixing enhancement 总被引:1,自引:0,他引:1
A "swallowtail" cavity for the supersonic combustor was proposed to serve as an efficient flame holder for scramjets by enhancing the mass exchange between the cavity and the main flow. A numerical study on the "swallow- tail" cavity was conducted by solving the three-dimensional Reynolds-averaged Navier-Stokes equations implemented with a k-e turbulence model in a multi-block mesh. Turbu- lence model and numerical algorithms were validated first, and then test cases were calculated to investigate into the mechanism of cavity flows. Numerical results demonstrated that the certain mass in the supersonic main flow was sucked into the cavity and moved spirally toward the combustor walls. After that, the flow went out of the cavity at its lateral end, and finally was efficiently mixed with the main flow. The comparison between the "swallowtail" cavity and the conventional one showed that the mass exchanged between the cavity and the main flow was enhanced by the lateral flow that was induced due to the pressure gradient inside the cavity and was driven by the three-dimensional vortex ring generated from the "swallowtail" cavity structure. 相似文献
9.
An isotropic flexible shaft, acted by nonlinear fluid-induced forces generated from oil-lubricated journal bearings and hydrodynamic
seal, is considered in this paper. Dimension reductions of the rotor system were carried out by both the standard Galerkin
method and the nonlinear Galerkin method. Numerical simulations provide bifurcation diagrams, spectrum cascade, orbits of
the disk center and Poincaré maps, to demonstrate the dynamical behaviors of the system. The results reveal transitions, or
bifurcations, of the rotor whirl from being synchronous to non-synchronous as the unstable speed is exceeded. The non-synchronous
oil/seal whirl is a quasi-periodic motion. In the regime of quasi-periodic motion, the “windows” of multi-periodic motion
were found. The investigation shows that the nonlinear Galerkin method has an advantage over the standard one with the same
order of truncations, because the influences of higher modes are considered by the former. 相似文献
10.
The three-dimensional H-type nonlinear evolution process for the problem of boundary layer stability is studied by using a newly developed method called parabolic stability equations (PSE). The key initial conditions for sub-harmonic disturbances are obtained by means of the secondaryinstability theory. The initial solutions of two-dimensional harmonic waves are expressed in Landau expansions. The numerical techniques developed in this paper, including the higher order spectrum method and the more effective algebraic mapping for dealing with the problem of an infinite region, increase the numerical accuracy and the rate of convergence greatly. With the predictor-corrector approach in the marching procedure, the normalization, which is very important for PSE method, is satisfied and the stability of the numerical calculation can be assured. The effects of different pressure gradients, including the favorable and adverse pressure gradients of the basic flow, on the “H-type“ evolution are studied in detail. The results of the three-dimensional nonlinear “H-type“ evolution are given accurately and show good agreement with the data of the experiment and the results of the DNS from the curves of the amplitude variation, disturbance velocity profile and the evolution of velocity. 相似文献
11.
A numerical model developed on the basis of the level set method is proposed. This makes it possible to describe both the
nonlinear oscillations of a single viscous-fluid droplet and the fragmentation and coalescence processes. The Navier-Stokes
equations written in “velocity-pressure” variables on a rectangular uniform grid in cylindrical coordinates are solved using
the method of splitting into physical processes. Non-oscillating solutions for two-phase media with a characteristic density
ratio of less than 10−3 and Re > 1000 are obtained. The possibilities of the approach proposed are demonstrated with the reference to the problem
of a droplet falling from a capillary (detachment from the capillary, formation of a “Plato ball”, droplet motion, collision
with a plane wall, droplet oscillations on the wall, and droplet spreading). A comparison of the numerical results with the
known calculation models and experimental data shows satisfactory agreement with respect to both the phases and the shape
of the droplet. 相似文献
12.
V. V. Alekhin 《Journal of Applied Mechanics and Technical Physics》2007,48(4):556-561
The problem of optimal design of a transversely layered cantilever beam of minimum mass composed of a finite set of elastic
homogeneous isotropic materials is considered for the case where a constraint is imposed on the maximum deflection of the
beam and information on the loads applied to the beam is incomplete. It is shown that, among these loads, there exists the
“worst” point load whose magnitude is equal to the resultant of the forces applied to the beam, for which the deflection is
maximal for any material distribution along the beam. The necessary optimality conditions are obtained for the mass-minimization
problem of the beam under the “worst” loading, a numerical algorithm is developed for the synthesis of the optimal cantilever,
and a numerical example is given.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 4, pp. 104–110, July–August, 2007. 相似文献
13.
The classical mechanical problem on the motion on a system of two or several bodies is stated in terms of parameters of the 13-parameter extended Galilean group (translations, rotations, boosts, and gravitational transformations) without using such traditional notions as “point” and “force.” 相似文献
14.
According to constructal theory, the “generation of flow configuration” is a universal phenomenon in physics. This phenomenon is covered by the constructal law: “For a finite-size flow system to persist in time (to live)
it must evolve such that it provides greater and greater access to the currents that flow through it.” This paper shows how
the constructal law can be used to (1) predict and explain features of “design” in nature, and (2) design effective strategies
and configurations for engineering. Many natural flow designs rely on two flow mechanisms: channels with relatively low resistivity,
interwoven with diffusion across the interstices. The “design” is the balance between the two mechanisms. The flow from line
to line (or plane to plane) through a sufficiently fine porous medium encounters less resistance than the flow through parallel
channels when it is configured as trees that alternate with upside down trees: from this follows the prediction that natural
porous media (e.g., hill slope) should be multiscale (bidisperse) and non-uniformly distributed. A porous medium contaminated
with ionic species is decontaminated the fastest when the ionic flow is configured as two flow mechanisms in balance: “channeling”
driven by potential differences between optimally positioned electrodes, and diffusion driven by concentration differences
across the interstices between the channels. 相似文献
15.
High-speed liquid “curtains” have been proposed to protect solid structures in fusion energy applications. Minimizing free-surface
waves and spray formation in such flows is important for effective protection in this application. In this work, free-surface
waves and turbulent breakup were studied experimentally in jets of water issuing from a rectangular nozzle into ambient air
at a Reynolds number of 1.2 × 105. Laser-Doppler anemometry was used to characterize the streamwise and transverse velocity components in the nozzle for two
different flow calming section designs. Planar laser-induced fluorescence was used to measure the free-stream position in
the near-field of the sheet. The results suggest that transverse velocity fluctuations in the nozzle are the primary factor
in determining the amplitudes of free-surface waves. Removing a small amount of low-speed fluid immediately downstream of
the nozzle exit (“boundary-layer cutting”) is shown to both significantly reduce free-surface waves and the amount of spray
due to turbulent breakup. Overall, boundary-layer cutting appears to have the greatest benefit when used on a “well-conditioned”
turbulent liquid sheet. 相似文献
16.
Alberto Cecchi 《Meccanica》2010,45(6):829-833
This paper is a historical re-visitation of the work of C. Hutton, a mathematician of the XVIII century, who wrote an innovative
essay on the shape of arches, whose intrados he identifies with the curve of pressure, that he names “arch of equilibration”. His solution was mostly ignored by his contemporaries and after the middle of the XIX century forgotten. But Hutton’s problem
is important, also because it offers the first example of an inverse problem in structural mechanics. 相似文献
17.
In this paper, the “FLIC” difference method with triangular mesh is adopted to numerically simulate the regular and Mach reflections
that occur when a shock wave pass around a wedge. The compuational result is compared with the shock tube experimental results
of G. Ben-Dor and I. I. Glass. The comparison shows that the position, shape of shock wave and height of Mach stem all show
a good agreement. Consequently, the “FLIC” difference method with triangular mesh is quite satisfactory in numerical simulation
of the regular and Mach reflections. 相似文献
18.
19.
陈宜周 《应用数学和力学(英文版)》2004,25(11):1298-1303
Stress analysis for an infinite stripcracks were assumed in a horizontal position,weakened by periodic cracks is studied. The and the strip was applied by tension “p“ in y-direction. The boundary value problem can be reduced into a complex mixed one. It is found that the EEVM ( eigenfunction expansion variational method) is efficient to solve the problem. The stress intensity factor at the crack tip and the T-stress were evaluated. From the deformation response under tension the cracked strip can be equivalent to an orthotropic strip without cracks. The elastic properties in the equivalent orthotropic strip were also investigated. Finally, numerical examples and results were given. 相似文献
20.
V. A. Seleznev V. Ya. Prinz V. M. Aniskin A. A. Maslov 《Journal of Applied Mechanics and Technical Physics》2009,50(2):291-296
A new method is proposed for creating “smart” surfaces for suppressing turbulence and retaining a laminar supersonic flow.
Methods of formation of super-fast-response sensors and actuators for such surfaces are developed. Such sensors and actuators
are structurally designed as microtubes made of SiO
2
/Si
3
N
4
/Au and InGaAs/GaAs/Au heterofilms and suspended above a substrate; the wall thickness of these tubes is in the nanometer range; the tubes are connected
to electrical contacts. Models of distributed arrays of tubular microsensors and microactuators are fabricated in a single
technological process, which involves the well-established planar technology and the technology of rolling of stressed heterofilms.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 2, pp. 145–151, March–April, 2009. 相似文献