Flow visualization was made for water to broaden our fundamental understanding of the physical process of the confined circular jet impingement. Transition (with laminar wall jet) and turbulent regimes are identified. A correlation of boundary layer thickness was developed in terms of relevant parameters.

Fatigue crack propagation data of a batch of AISI 4340 steel specimens are released in the present paper. The statistical nature of the data is specially emphasized, and a probabilistic fracture mechanics model is introduced to analyze the data. The stochastic differential equation associated with the model is then solved. The solution gives us the crack exceedance probability as well as the probability distribution of the random time to reach a specified crack size. These quantities are useful in the reliability assessment of structures made of the tested material. Comparing the analytical result with the experimental result, it is found that the proposed probabilistic fracture mechanics model can reasonably explain the experimental data. For those data that cannot be fitted well by the proposed model, methods of improvement are proposed in the present paper as well.

This study investigates experimentally the velocity of the center of mass with respect to the base of support while subjects step on slippery flooring. The moments of the joints of both legs are also investigated to gain further insights into the source of any correlation found in reacting to slippery perturbation. Twenty-two healthy subjects dressed with safety harness walked first without and then with slippery perturbation, guided by a metronome at 120 steps/min and 90 steps/min cadence. Data were collected from a motion analysis system and force plates. Subjects falling had distinguishably slower velocity of center of mass with respect to the lead stance foot compared to the subjects maintaining balance at contralateral toe off. Larger knee flexion moment and ankle plantar flexion moment in the perturbed leg were found among subjects regaining balance. Faster velocity of center of mass with respect to base of support is noteworthy in subjects regaining balance from slippery perturbation. The response of lower extremities, especially about the thigh and leg in the lead stance limb, were important to improve the velocity of the center of mass with respect to base of support.

Laminar heat transfer for large ranges of Reynolds numbers, rotational Reynolds numbers, and Prandtl numbers are studied numerically for incompressible fully developed flow in a circular straight pipe, which is rotating constantly about an axis perpendicular to its own axis under the constant wall temperature gradient condition. There exist four types of local Nusselt number distributions associated with the four different flow regimes for different parameters depending on the relative importance of different forces. Correlations of the averaged Nusselt number are also provided. When the Prandtl number is sufficiently large, the temperature distribution in the core is determined essentially by the secondary flow. Scaling analyses are provided for understanding the essential physics of the problem.

The fractal properties of premixed transient flames propagating downwards through a near-isotropic turbulent flow field in a fan-stirred cruciform burner were investigated. The long vertical section of the cruciform burner was used to provide a downward propagating premixed flame at 1 atm. The large horizontal vessel equipped with a pair of counter-rotating fans and perforated plates at each end was used to generate near-isotropic turbulence. Turbulent flame front images were obtained using high-speed laser sheet imaging for both methane-air and propane-air mixtures. The nondimensional turbulent intensity (u′/SL), Reynolds number based on the integral length scale, and turbulent Karlovitz number were varied from 1 to 10, from 698 to 6032, and from 0.05 to 1.43, respectively. Hundreds of runs for each experimental condition were carried out to obtain sufficient images of these turbulent transient flame fronts just in the central uniform region. These images were then processed to extract fractal dimension, inner and outer cutoffs using both the circle and the caliper methods. It was found that the mean fractal dimension is only 2.18, nearly independent of u′/SL, in support of recent Bunsen-flame results found by Gülder and his co-workers. This contradicts the findings of many previous studies in which the fractal dimension may approach asymptotically to a value of 2.33 when u′/SL > 3. The inner (εi) and outer (ε0) cutoffs are found to be nearly constant for all flames studied, where ε0 is an order of magnitude greater than εi and it is smaller than the integral length scale of unreacted turbulence. Finally, the present fractal characteristics cannot predict turbulent burning velocities correctly when the available fractal closure model was used, indicating a limit of the fractal analysis on prediction of turbulent burning velocities.

A technique for inverting residual stress based on a theory of acoustoelasticity is presented. A general incremental constitutive relation is first derived for a pre-stressed material subjected to an additional infinitesimal elastic deformation. The theory is then employed on using ultrasonic means to evaluate residual stresses of residually stressed materials. The residual stresses are assumed to be homogeneous in materials as usual. The only major assumption in this formulation is that the additional deformations caused by ultrasonic evaluating process are infinitesimal and elastic. No assumption on the origin of residual stresses is needed, nor the assumption on the possible existence of “natural state” of the materials. Successful inversion of residual stresses are demonstrated through a preliminary numerical experiment.