The Influence of Surface Proximity on Photoswitching Activity of Stilbene-Functionalized N-Heterocyclic Carbene Monolayers

Self-assembly of photo-responsive molecules is a robust technology for reversibly tuning the properties of functional materials. Herein, we probed the crucial role of surface-adsorbate interactions on the adsorption geometry of...

On Blockage Effects for a Tidal Turbine in Free Surface Proximity

Experiments with a three-bladed, constant chord tidal turbine were undertaken to understand the influence of free surface proximity on blockage effects and near-wake flow field. The turbine was placed at various depths as rotational speeds were varied; thrust and torque data were acquired through a submerged sensor. Blockage effects were quantified in terms of changes in power coefficient and were found to be dependent on tip speed ratio and free surface to blade tip clearance. Flow acceleration near turbine rotation plane was attributed to blockage offered by the rotor, wake, and free surface deformation. In addition, particle image velocimetry was carried out in the turbine near-wake using time- and phase-averaged techniques to understand the mechanism responsible for the variation of power coefficient with rotational speed and free surface proximity. Slower wake propagation for higher rotational velocities and increased asymmetry in the wake with increasing free surface proximity was observed. Improved performance at high rotational speed was attributed to enhanced wake blockage, and performance enhancement with free surface proximity was due to the additional blockage effects caused by the free surface deformation. Proper orthogonal decomposition analysis revealed a downward moving wake for the turbine placed in near free surface proximity.

Stress Intensity Factor Interaction for Subsurface to Surface Flaw Transformations Under Stress Concentration Fields

If a single subsurface flaw is detected that is close to a component's free surface, a flaw-to-surface proximity rule is used to determine whether the flaw should be treated as a subsurface flaw, or transformed to a surface flaw. The transformation from subsurface to surface flaw is adopted as flaw-to-surface proximity rules in all fitness-for-service (FFS) codes. These proximity rules are applicable when the component's free surface is without a stress concentration. On the other hand, subsurface flaws have been found under notches, such as roots of bolts, toes in welded joints, or geometrical discontinuities of components. The stress intensity factors of the subsurface flaws are affected by the stress concentrations caused by the notches. The stress intensity factor of the subsurface flaw increases with increasing stress concentration factor of the notch and decreasing ligament distance between tip of the subsurface flaws and the notch, for a given notch width. Such subsurface flaws are transformed to surface flaws at a distance from the notch tip for conservative evaluations. This paper shows the interactions of stress intensity factors of subsurface flaws under stress concentration fields. Based on the interaction, a flaw-to-surface proximity criterion is proposed for a circular flaw under the stress concentration field induced by a notch.

Stress Intensity Factors for Transformed Surface Flaws and Remaining Fatigue Lives Based on Flaw-to-Surface Proximity Rules

Subsurface flaws are sometimes found as blowholes near free surfaces of structural components. Net-section stress at the ligament between the free component surface and the subsurface flaw increases when the ligament size is short. It can be easily expected that the stress intensity factor at the tip of the subsurface flaw increases with decreasing the ligament size. Fitness-for-service (FFS) codes provide flaw-to-surface proximity rules, which are transformation from subsurface to surface flaw. Although the concepts of the proximity rules of the FFS codes are the same, the specific criteria for the rules on transforming subsurface flaws to surface flaws are significantly different among FFS codes. This study demonstrates the proximity criteria provided by the FFS codes and indicates that the increment of the stress intensity factors before and after the transformation depends on the flaw aspect ratio and the ligament size at the transformation from subsurface to surface flaws. In addition, it is shown that remaining fatigue lives for pipes with flaws are strongly affected by the ligament size at the transformation from subsurface to surface flaws.