Timothy Patterson

Generalized center of compliance and stiffness

The elastic characteristics of many robot systems can be modeled by a 6*6 stiffness or compliance matrix. Three results are presented via screw theory. First, stationary values of compliance and stiffness are determined. Second, linear and rotational properties are characterized by dual ellipsoids in three-dimensional space. Third, a generalized center-of-elasticity (compliance and stiffness) is proposed. If a compliant axis exists, it is shown to pass through the center. These elements simplify the understanding of complex elastic properties.<<ETX>>

Pulsating Jet Impingement Heat Transfer Enhancement

This article presents results from a numerical study of pulsating jet impingement heat transfer. The motivation is to seek conditions offering a significant enhancement compared to steady flow impingement drying. The CFD software package FLUENT was used for simulating slot-type pulsating jet impingement flows with confinement. The parameter study included velocity amplitude ratio, mean jet velocity, and pulsation frequency. The distance from nozzle exit to surface was three times the hydraulic diameter of the nozzle. The Reynolds number based on the nozzle hydraulic diameter and jet temperature was 2,460 with a mean jet velocity of 30 m/s, which is the base case of the numerical experiments. Results showed that time-averaged surface heat transfer increased with increasing velocity amplitude for the same mean jet velocity. Large velocity amplitudes helped enhance heat transfer by two mechanisms: high jet velocity during the positive cycle and strong recirculating flows during the negative cycle. For the cases with different mean jet velocities but the same maximum velocity, time-averaged surface heat flux decreased with decreasing mean jet velocity. As for the effects of pulsation frequency, with high-velocity amplitude ratio, time-averaged surface heat fluxes were at the same level regardless of frequency. However, at low-velocity amplitude ratio, high frequency caused stronger recirculating flows resulting in greater heat transfer compared to the cases with a lower frequency.

Duality of constrained elastic manipulation

For unconstrained manipulation, the linear compliance and stiffness models are equivalent. The equivalence does not hold for constrained manipulation, but leads to two dual models. These are analyzed using screw theory and a novel duality is explicitly demonstrated. The eigenstructure of the singular compliance and singular stiffness matrices is determined and several new dual propositions are developed.<<ETX>>