10,658 research outputs found
A Generic Conceptual Model for Risk Analysis in a Multi-agent Based Collaborative Design Environment
Organised by: Cranfield UniversityThis paper presents a generic conceptual model of risk evaluation in order to manage the risk through
related constraints and variables under a multi-agent collaborative design environment. Initially, a hierarchy
constraint network is developed to mapping constraints and variables. Then, an effective approximation
technique named Risk Assessment Matrix is adopted to evaluate risk level and rank priority after probability
quantification and consequence validation. Additionally, an Intelligent Data based Reasoning Methodology
is expanded to deal with risk mitigation by combining inductive learning methods and reasoning
consistency algorithms with feasible solution strategies. Finally, two empirical studies were conducted to
validate the effectiveness and feasibility of the conceptual model.Mori Seiki – The Machine Tool Compan
Newtonian Flow in Converging-Diverging Capillaries
The one-dimensional Navier-Stokes equations are used to derive analytical
expressions for the relation between pressure and volumetric flow rate in
capillaries of five different converging-diverging axisymmetric geometries for
Newtonian fluids. The results are compared to previously-derived expressions
for the same geometries using the lubrication approximation. The results of the
one-dimensional Navier-Stokes are identical to those obtained from the
lubrication approximation within a non-dimensional numerical factor. The
derived flow expressions have also been validated by comparison to numerical
solutions obtained from discretization with numerical integration. Moreover,
they have been certified by testing the convergence of solutions as the
converging-diverging geometries approach the limiting straight geometry.Comment: 23 pages, 5 figures, 1 table. This is an extended and improved
version. arXiv admin note: substantial text overlap with arXiv:1006.151
Emission Optics of the Steigerwald Type Electron Gun
The emission optics of a Steigerwald type electron gun is re-examined. The
virtual and real points of divergence, divergence angles and beam-widths of the
electron beams at different telefocusing strength are measured in detail for
first time . Two different Wehnelt cylinders are used to establish a
contrasting viewpoint. The original `focusing' curves measured by Braucks are
reconstructed and will be explained only through a `new' interpretation which
is different from the conventional views. While the image of the emitting
surface in front of the filament is indeed telefocused beyond the anode, the
envelope of the beam does not `focus' as expected. A new model for the emission
mechanism is established based on our results.Comment: 14 pages, 10 figure
Bottom Boundary Potential Vorticity Injection from an Oscillating Flow: A PV Pump
Oceanic boundary currents over the continental slope exhibit variability with a range of time scales. Numerical studies of steady, along-slope currents over a sloping bathymetry have shown that cross-slope Ekman transport can advect buoyancy surfaces in a bottom boundary layer (BBL) so as to produce vertically sheared geostrophic flows that bring the total flow to rest: a process known as buoyancy shutdown of Ekman transport or Ekman arrest. This study considers the generation and evolution of near-bottom flows due to a barotropic, oscillating, and laterally sheared flow over a slope. The sensitivity of the boundary circulation to changes in oscillation frequency ω, background flow amplitude, bottom slope, and background stratification is explored. When ω/f ≪ 1, where f is the Coriolis frequency, oscillations allow the system to escape from the steady buoyancy shutdown scenario. The BBL is responsible for generating a secondary overturning circulation that produces vertical velocities that, combined with the potential vorticity (PV) anomalies of the imposed barotropic flow, give rise to a time-mean, rectified, vertical eddy PV flux into the ocean interior: a “PV pump.” In these idealized simulations, the PV anomalies in the BBL make a secondary contribution to the time-averaged PV flux. Numerical results show the domain-averaged eddy PV flux increases nonlinearly with ω with a peak near the inertial frequency, followed by a sharp decay for ω/f > 1. Different physical mechanisms are discussed that could give rise to the temporal variability of boundary currents
Analytical and experimental study of vibrations in a gear transmission
An analytical simulation of the dynamics of a gear transmission system is presented and compared to experimental results from a gear noise test rig at the NASA Lewis Research Center. The analytical procedure developed couples the dynamic behaviors of the rotor-bearing-gear system with the response of the gearbox structure. The modal synthesis method is used in solving the overall dynamics of the system. Locally each rotor-gear stage is modeled as an individual rotor-bearing system using the matrix transfer technique. The dynamics of each individual rotor are coupled with other rotor stages through the nonlinear gear mesh forces and with the gearbox structure through bearing support systems. The modal characteristics of the gearbox structure are evaluated using the finite element procedure. A variable time steping integration routine is used to calculate the overall time transient behavior of the system in modal coordinates. The global dynamic behavior of the system is expressed in a generalized coordinate system. Transient and steady state vibrations of the gearbox system are presented in the time and frequency domains. The vibration characteristics of a simple single mesh gear noise test rig is modeled. The numerical simulations are compared to experimental data measured under typical operating conditions. The comparison of system natural frequencies, peak vibration amplitudes, and gear mesh frequencies are generally in good agreement
Modal analysis of multistage gear systems coupled with gearbox vibrations
An analytical procedure to simulate vibrations in gear transmission systems is presented. This procedure couples the dynamics of the rotor-bearing gear system with the vibration in the gear box structure. The model synthesis method is used in solving the overall dynamics of the system, and a variable time-stepping integration scheme is used in evaluating the global transient vibration of the system. Locally each gear stage is modeled as a multimass rotor-bearing system using a discrete model. The modal characteristics are calculated using the matrix-transfer technique. The gearbox structure is represented by a finite element models, and modal parameters are solved by using NASTRAN. The rotor-gear stages are coupled through nonlinear compliance in the gear mesh while the gearbox structure is coupled through the bearing supports of the rotor system. Transient and steady state vibrations of the coupled system are examined in both time and frequency domains. A typical three-geared system is used as an example for demonstration of the developed procedure
Correlation between electrons and vortices in quantum dots
Exact many-body wave functions for quantum dots containing up to four
interacting electrons are computed and we investigated the distribution of the
wave function nodes, also called vortices. For this purpose, we evaluate the
reduced wave function by fixing the positions of all but one electron and
determine the locations of its zeros. We find that the zeros are strongly
correlated with respect to each other and with respect to the position of the
electrons and formulate rules describing their distribution. No multiple zeros
are found, i.e. vortices with vorticity larger than one. Our exact calculations
are compared to results extracted from the recently proposed rotating electron
molecule (REM) wave functions
Modal simulation of gearbox vibration with experimental correlation
A newly developed global dynamic model was used to simulate the dynamics of a gear noise rig at NASA Lewis Research Center. Experimental results from the test rig were used to verify the analytical model. In this global dynamic model, the number of degrees of freedom of the system are reduced by transforming the system equations of motion into modal coordinates. The vibration of the individual gear-shaft system are coupled through the gear mesh forces. A three-dimensional, axial-lateral coupled, bearing model was used to couple the casing structural vibration to the gear-rotor dynamics. The coupled system of modal equations is solved to predict the resulting vibration at several locations on the test rig. Experimental vibration data was compared to the predictions of the global dynamic model. There is excellent agreement between the vibration results from analysis and experiment
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