A fixed 25 • deadrise angle wedge is allowed to fall from a range of heights into static water. A high-speed (up to 5000 frames s −1 ) camera is used to visualize the impact and subsequent formation of jet flows and droplets. Unsteady pressure measurements at six locations across the wedge surface are measured at 10 kHz. Two accelerometers (10g, 100g) are mounted above the apex of the wedge and measure the vertical acceleration. A purpose-built position gauge and analysis of the synchronized video allows the wedge motion to be captured. The synchronization of these data with the digital images of the impact makes it particularly suitable for the validation of computational fluid dynamics simulations as well as theoretical studies. A detailed experimental uncertainty analysis is presented. The repeatability of the test process is demonstrated and the measured pressures are comparable to previous studies. A ∼2.5 ms time delay is identified between the point of impact observed from the video and the onset of actual wedge deceleration. The clear definition of the free surface provides insight into jet formation, its evolution and eventual breakdown, further assisting with the development of numerical predictions.
In order to understand the physical origin of passive resistance in swimming the resistance breakdown for a swimmer is investigated. A combination of empirical methods and theoretical analysis is used to predict passive resistance in the speed range 0 – 2 ms-1 and is shown to provide similar results to those from experimental testing. Typical magnitudes of wave, viscous pressure and skin friction resistance contribute 59%, 33% and 8% of total passive resistance respectively at free swim speed. A comparison is made between the widely used Velocity Perturbation Method and a Naval Architecture based approach in predicting active drag. For the swimmer investigated the two approaches predict active drag of 131.4 N and 133.9 N for a swimming speed of 1.53 ms-1. However, the results predicted from the Velocity Perturbation Method have a much higher uncertainty and the Naval Architecture based approach is suggested as a more robust method of predicting active drag
Behavior in visual search tasks is influenced by the proportion of trials on which a target is presented (the target prevalence). Previous research has shown that when target prevalence is low (2 % prevalence), participants tend to miss targets, as compared with higher prevalence levels (e.g., 50 % prevalence). There is an ongoing debate regarding the relative contributions of target repetition and the expectation that a target will occur in the emergence of prevalence effects. In order to disentangle these two factors, we went beyond previous studies by directly manipulating participants’ expectations regarding how likely a target was to appear on a given trial. This we achieved without using cues or feedback. Our results indicated that both target repetition and target expectation contribute to the emergence of the prevalence effect.Electronic supplementary materialThe online version of this article (doi:10.3758/s13423-015-0970-9) contains supplementary material, which is available to authorized users.
High-Speed planing Craft (HSC) expose their crew to levels of vibration that regularly exceed the daily exposure limit set out by European directive 2002/44/EU. The human exposure to vibration can cause many effects, from chronic and acute, to physiological and psychological. Many reduction methods are currently being researched, such as suspension seats, but Coats et al. (2003) and Coe et al. (2013) concluded that a combination of methods will be required to reduce the level sufficiently to meet the legislation. The highest levels of acceleration occur during the slamming of HSC. This paper describes an experimental investigation to determine whether hydroelasticity can affect the slamming characteristics and Whole Body Vibration (WBV) of a HSC using quasi-2D and full-scale drop tests. The quasi-2D drop tests revealed that hydroelasticity can affect the peak acceleration and Vibration Dosage Value (VDV), and that a wooden hull generated higher magnitude WBV than fabric hulls. The full-scale drop tests were performed on a RNLI D-class inflatable lifeboat. Hydroelasticity was controlled using the internal pressures of the sponson and keel. The full-scale results show that the peak acceleration and VDV can be reduced by decreasing the internal pressures and structural stiffness at the transom and crew locations; however, this lead to an increase at the bow. This indicates that the WBV experienced by the crew can be reduced by considering hydroelasticity. Incorporating an element of hydroelasticity shows great potential, alongside other reduction strategies, to alleviate the human exposure to vibration on board HSC.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.