Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 36 for “"friction velocity"”.
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Frictional vibrations in structural polymers
… investigated to determine their influence on the frictional behavior of the ABS materials. These parameters included: the time dependence of friction under static load, friction-normal load relationships, surface roughness, internal lubrication, friction-velocity relationships, and system …
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Comprehensive throughflow method for steam turbine development
… vertical pipe flow, using a coarse estimate of friction velocity. While the choice of friction velocity model is likely to have a strong impact on the deposition rates, most studies use flat-plate boundary layer equations whose flow assumptions strongly deviate from the flow in turbine blade …
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An investigation of momentum exchange parameterizations and atmospheric forcing for the Coastal Mixing and Optics Program
… A quantitative comparison of direct covariance friction velocity measurements to bulk aerodynamic and inertial dissipation estimates indicates that both indirect methods systematically underestimate the momentum flux into developing seas. To account for wave-induced processes and yield improved …
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An investigation of momentum exchange parameterizations and atmospheric forcing for the Coastal Mixing and Optics Program
… A quantitative comparison of direct covariance friction velocity measurements to bulk aerodynamic and inertial dissipation estimates indicates that both indirect methods systematically underestimate the momentum flux into developing seas. To account for wave-induced processes and yield improved …
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Frictional oscillations in elastomeric sliding
… 1. Steady state sliding where the sliding friction is constant; 2. A high frequency self-excited oscillation of the test structure superimposed on the mean value of friction; 3. Stick-slip, where the elastomeric specimen goes through alternating periods of no relative and relative motion to …
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Evaluation of the dynamic characteristics of the K-Gill anemometer
… 1964). The test results showed that mean wind velocity components can be measured with an error of 2%. To determine the Reynolds stress values, uw covariance and friction velocity from different methods were compared. When the stability conditions were unknown, the resulting Reynolds stress …
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A study of the static to kinetic friction transition of polymers
… the transition from static to kinetic friction for structural polymers and continues previous research conducted by Dr. N. S. Eiss, B. McCann, and R. Molique. A new test apparatus which simultaneously measures friction, normal load, and relative velocity was developed to study this …
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Pressure Fluctuations in a High-Reynolds-Number Turbulent Boundary Layer over Rough Surfaces of Different Configurations
… and hotwire measurements were made to obtain the velocity and turbulence field. Among the principal findings is the development of two scaling laws for the low frequency pressure fluctuations. Both of these are based on the idea that the defect between the edge velocity and some local boundary …
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Frictional behavior of polymers: the transition from static to kinetic conditions
… in squeaking dashboards is caused by the drop in friction force during the transition from static to kinetic conditions between the mating plastic components of the dashboard. The frictional behavior of a polymer determines whether there is a drop in friction force during this transition. This …
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Scale Interactions within a Perturbed Plane Wall Jet
… a range of large-scale forcing showed that the friction velocity Uτ decreased for all forcing wavelengths considered. The scaling behavior of this reduction in Uτ with respect to inner, outer and global (PWJ exit conditions) variables suggested that the responsible underlying mechanism was an …
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Definizione di una metodologia integrata per la stima delle emissioni di PM da superfici di materiali granulari esposte all’erosione eolica
… the experimental determination of the threshold friction velocity, and the CFD-based modelling of the wind field over the exposed surfaces. At its core is a physical–mathematical model implemented in MATLAB, which simulates the saltation, impact, and release of fine particles generated by the …
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The Rough Wall High Reynolds Number Turbulent Boundary Layer Surface Pressure Spectrum
… defined by viscosity, but controlled by the friction velocity adjusted to exclude the pressure drag on the roughness elements. Based on these three scaling regions an empirical model describing the wall pressure spectra for hydraulically smooth, traditionally rough, and fully rough flows was …
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Large-eddy simulation of turbulent wall-pressure fluctuations using the finite element method
… method, is used. In this method, the turbulent velocity profile from a specific plane within the computational domain is recycled and rescaled propriately, and re-introduced at the inlet of the domain at every time step iteration. In the proposed method, the mean velocity profile is fixed at the …
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The exchange of oxygen at the surface of open waters under wind forcing
… breaking are quantified with respect to friction velocity, wave steepness and an efficiency of microscale wave breaking. The parasitic capillary ripples are shown to have a negligible role in gas enhancement. A hybrid model is developed to estimate the gas flux based on both wind and wave …
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Fluid Dynamics and Surface Pressure Fluctuations of Turbulent Boundary Layers Over Sparse Roughness
… was used to measure all three components of velocity. The friction velocity was calculated using an integral momentum balance. Comparisons were made with various fitting methods that assume the von Kármán constant is appropriate for rough walls. Results indicate that this is not the case, …
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Development of a MEMS Sensor for sub-kPa Shear Stress Measurements
… flow up to a mean shear stress of 335Pa and a friction velocity Re value of 200,000. After numerical temperature compensation was implemented (required due to temperature-dependent material properties) the sensor gain was calculated as 0.16mV/Pa. The mean shear stress calibration was then used …
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An experimental study of a three-dimensional pressure-driven turbulent boundary layer
… sitting on a flat plate. The nominal reference velocity of the flow is 27 m/sec and the Reynolds number based on the momentum thickness at 0.75 chord upstream of the body on the centerline of the tunnel is ≃ 5936. The data presented include time-mean static pressure, skin friction magnitude and …
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Measurements, Modeling, and Analysis of Fluxes of Nitrogen Compounds
… near-surface winds (wind speed at 10m), friction velocity, turbulence, atmospheric stability, air temperature, surface heat flux and relative humidity, as well as the spatial distribution of sources. This research initiative has been prepared in response to the expressed need for a better …
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Effects of Surface Roughness on the Indoor Particle Deposition Rate Constant
… by using Particle Image Velocimetry (PIV). The friction velocities were determined by analyzing the experimental data and used as the input of an empirical model that describes deposition rate constant as a function of friction velocity, air kinematic viscosity, particle Brownian diffusivity, …
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Development and application of a dispersed two-phase flow capability in a general multi-block Navier Stokes solver
… 100 microns with response times (normalized by friction velocity and hydraulic diameter) of 0.06875, 1.71875, and 6.875 respectively are considered. The calculations are performed for a nominal bulk Reynolds number of 20,000 under fully developed conditions. The carrier phase was solved using …
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