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Numerical meshing issues for three-dimensional flow simulation in journal bearings
This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Hydrodynamic journal bearings are widely used in technical and industrial applications due to their favourable wearing quality and operating characteristics. In the recent years, various experimental and numerical analyses were carried out on the design layout, the load capacity and the durability of the bearing. For typical applications the two-dimensional Reynolds differential equation is solved numerically to calculate the pressure distribution in the oil film, which is essential to simulate the dynamic behavior of the bearing. This approach however, does not allow any detailed predictions of the local three-dimensional flow structures. To understand the mechanisms, which are driven by local flow phenomena, it is necessary to solve the full Navier-Stokes-Equations in 3D together with the conservation of mass. An accurate computation of a three-dimensional flow field requires a careful discretisation of the model. Moreover, only a deliberately chosen meshing based on the optimum number of cells across the gap achieves a sufficient numerical accuracy with acceptable computational effort. This work presents variations of the mesh generation of small gaps in journal bearing models and the computed flow fields, respectively. The threedimensional calculations are validated with measured experimental data done by Laser-Doppler-Velocimetry (LDV). In conclusion of this process the comparison of the velocity profiles of the flow field across the gap yield the necessary numerical discretisation limit applicable to the computation of the flow in journal bearings
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Three dimensional flow structures in journal bearings
This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.In general, the fluid flow in journal bearings can be described by the Navier-Stokes Equations and the conservation of mass. The application of the small gap criterion allows a simplification of these equations yielding the Reynolds Equation, which links the local gap size with the pressure gradient resulting in a powerful tool for the designing process of journal bearings. Typically, the Reynolds Equation is used in EHD-design software based on FE-methods, which is used to compute pressure distributions, forces, deformations and many more parameters needed for the selection of the right bearing geometry. However, there are regions in the journal bearing where the Reynolds Equation must fail, because either the small gap criterion or the Couette flow assumption is violated. There are pockets, grooves and holes, which are necessary to distribute the oil supply across the gap. Moreover, the oil feed represents a cross flow perpendicular to the circumferential main flow. In these regions three dimensional flow structures replace the
undisturbed Couette flow, which are strongly affected by vortices, but are non-turbulent due to the Re-scale. This work presents experimental data obtained from a cylinder apparatus with moderate gap sizes, which
features independently rotating cylinders and a cross flow through a hole in the sidewall. LDV-measurements of velocity profiles and visualization methods to animate the three dimensional nature of the
flow are presented. The experimental data are used to validate 3D-CFD calculations, which are expanded towards smaller gap sizes in the range of typical journal bearings in automotive applications
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Three-dimensional simulation of cavitating flow in real journal bearing geometry
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Hydrodynamic journal bearings are commonly used in many technical applications because they provide low friction and minimal wear. In general, flow simulation during the engineering design process is carried out by means of the Reynolds equation. The Reynolds equation is a non-linear two-dimensional differential equation, which is based on the pressure and the gap between shaft and bushing in relation to bearing clearance, eccentricity, bushing deformation and load. However, due its two-dimensional nature it is inaccurate where the lubricant flow inside the bearing becomes three-dimensional e.g., in the vicinity of feed holes or grooves. The work on hand presents the numerical approach and the cavitation model based on the Rayleigh-Plesset equation. Moreover, a bearing flow experiment was designed and constructed with the goal to validate numerical results. Finally, the validated 3D simulation model is applied on a real bearing, which was subject to an experimental investigation targeting cavitation. The numerical results include images of complex three-dimensional flow structures, vortices and vapor distributions. In comparison of 2D and 3D simulation, the two-dimensional approach gives wrong information in 2 out of 6 critical regions pertaining cavitation failing in both, over- and under-prediction of cavitation. In summary, a new numerical model expands the scope for the numerical simulation of the lubricant flow in hydrodynamic journal bearings and improves the prediction of cavitation
Quantifier-Free Interpolation of a Theory of Arrays
The use of interpolants in model checking is becoming an enabling technology
to allow fast and robust verification of hardware and software. The application
of encodings based on the theory of arrays, however, is limited by the
impossibility of deriving quantifier- free interpolants in general. In this
paper, we show that it is possible to obtain quantifier-free interpolants for a
Skolemized version of the extensional theory of arrays. We prove this in two
ways: (1) non-constructively, by using the model theoretic notion of
amalgamation, which is known to be equivalent to admit quantifier-free
interpolation for universal theories; and (2) constructively, by designing an
interpolating procedure, based on solving equations between array updates.
(Interestingly, rewriting techniques are used in the key steps of the solver
and its proof of correctness.) To the best of our knowledge, this is the first
successful attempt of computing quantifier- free interpolants for a variant of
the theory of arrays with extensionality
Automated Synthesis of Tableau Calculi
This paper presents a method for synthesising sound and complete tableau
calculi. Given a specification of the formal semantics of a logic, the method
generates a set of tableau inference rules that can then be used to reason
within the logic. The method guarantees that the generated rules form a
calculus which is sound and constructively complete. If the logic can be shown
to admit finite filtration with respect to a well-defined first-order semantics
then adding a general blocking mechanism provides a terminating tableau
calculus. The process of generating tableau rules can be completely automated
and produces, together with the blocking mechanism, an automated procedure for
generating tableau decision procedures. For illustration we show the
workability of the approach for a description logic with transitive roles and
propositional intuitionistic logic.Comment: 32 page
Measurement of the fraction of t-tbar production via gluon-gluon fusion in p-pbar collisions at sqrt(s)=1.96 TeV
We present a measurement of the ratio of t-tbar production cross section via
gluon-gluon fusion to the total t-tbar production cross section in p-pbar
collisions at sqrt{s}=1.96 TeV at the Tevatron. Using a data sample with an
integrated luminosity of 955/pb recorded by the CDF II detector at Fermilab, we
select events based on the t-tbar decay to lepton+jets. Using an artificial
neural network technique we discriminate between t-tbar events produced via
q-qbar annihilation and gluon-gluon fusion, and find
Cf=(gg->ttbar)/(pp->ttbar)<0.33 at the 68% confidence level. This result is
combined with a previous measurement to obtain the most precise measurement of
this quantity, Cf=0.07+0.15-0.07.Comment: submitted to Phys. Rev.
Measurement of Resonance Parameters of Orbitally Excited Narrow B^0 Mesons
We report a measurement of resonance parameters of the orbitally excited
(L=1) narrow B^0 mesons in decays to B^{(*)+}\pi^- using 1.7/fb of data
collected by the CDF II detector at the Fermilab Tevatron. The mass and width
of the B^{*0}_2 state are measured to be m(B^{*0}_2) =
5740.2^{+1.7}_{-1.8}(stat.) ^{+0.9}_{-0.8}(syst.) MeV/c^2 and \Gamma(B^{*0}_2)
= 22.7^{+3.8}_{-3.2}(stat.) ^{+3.2}_{-10.2}(syst.) MeV/c^2. The mass difference
between the B^{*0}_2 and B^0_1 states is measured to be
14.9^{+2.2}_{-2.5}(stat.) ^{+1.2}_{-1.4}(syst.) MeV/c^2, resulting in a B^0_1
mass of 5725.3^{+1.6}_{-2.2}(stat.) ^{+1.4}_{-1.5}(syst.) MeV/c^2. This is
currently the most precise measurement of the masses of these states and the
first measurement of the B^{*0}_2 width.Comment: 7 pages, 1 figure, 1 table. Submitted to Phys.Rev.Let
Search for lepton flavor violating decays of a heavy neutral particle in p-pbar collisions at root(s)=1.8 TeV
We report on a search for a high mass, narrow width particle that decays
directly to e+mu, e+tau, or mu+tau. We use approximately 110 pb^-1 of data
collected with the Collider Detector at Fermilab from 1992 to 1995. No evidence
of lepton flavor violating decays is found. Limits are set on the production
and decay of sneutrinos with R-parity violating interactions.Comment: Figure 2 fixed. Reference 4 fixed. Minor changes to tex
Search for Long-Lived Massive Charged Particles in 1.96 TeV \bar{p}p} Collisions
16 pages, 2 figures; Revision to fix PDF errors on some displays/printersWe performed a signature-based search for long-lived charged massive particles (CHAMPs) produced in 1.0 of collisions at TeV, collected with the CDF II detector using a high transverse-momentum () muon trigger. The search used time-of-flight to isolate slowly moving, high- particles. One event passed our selection cuts with an expected background of events. We set an upper bound on the production cross section, and, interpreting this result within the context of a stable scalar top quark model, set a lower limit on the particle mass of 249 GeV/ at 95% C.L.We performed a signature-based search for long-lived charged massive particles produced in 1.0 fb-1 of pp̅ collisions at √s=1.96 TeV, collected with the CDF II detector using a high transverse-momentum (pT) muon trigger. The search used time of flight to isolate slowly moving, high-pT particles. One event passed our selection cuts with an expected background of 1.9±0.2 events. We set an upper bound on the production cross section and, interpreting this result within the context of a stable scalar top-quark model, set a lower limit on the particle mass of 249 GeV/c2 at 95% C.L.Peer reviewe
Search for a Higgs Boson Decaying to Two W Bosons at CDF
We present a search for a Higgs boson decaying to two W bosons in ppbar collisions at sqrt(s)=1.96 TeV center-of-mass energy. The data sample corresponds to an integrated luminosity of 3.0 fb-1 collected with the CDF II detector. We find no evidence for production of a Higgs boson with mass between 110 and 200 GeV/c^2, and determine upper limits on the production cross section. For the mass of 160 GeV/c^2, where the analysis is most sensitive, the observed (expected) limit is 0.7 pb (0.9 pb) at 95% Bayesian credibility level which is 1.7 (2.2) times the standard model cross section
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