Control experiments with a semi-axisymmetric supercavity and a supercavity-piercing fin

Supercavitation can significantly reduce skin-friction drag on an underwater body, thus enabling a dramatic increase in attainable velocity. The control of a High-Speed Supercavitating Vehicle (HSSV) poses unique challenges, since only small regions at the nose (cavitator) and on the afterbody (fins) are in contact with water and can be used as control surfaces. The interaction between supercavity dynamics and control surface actuation is complex and nonlinear. Experiments were conducted with a semi-axisymmetric, ventilated supercavity and a single wedge-shaped, 45 degree swept, cavitypiercing fin in the high-speed water tunnel at St. Anthony Falls Laboratory. Motion control was combined with water tunnel testing to create a hardware-in-the-loop system that can (a) provide critical hydrodynamic parameters for control models and (b) serve as a test bed for fin control strategies. Through a series of experiments, control surfacecavity interaction, cavity stability and hysteresis effects were studied. Fin torque (lift) was measured for different angles of attack with varying cavitation numbers. Closed-loop fin control experiments simulating simple maneuvers were carried out.http://deepblue.lib.umich.edu/bitstream/2027.42/84319/1/CAV2009-final146.pd

DNS study of a pipe flow following a step increase in flow rate

Direct numerical simulation (DNS) is conducted to study the transient flow in a pipe following a near-step increase of flow rate from an initial turbulent flow. The results are compared with those of the transient flow in a channel reported in He and Seddighi (2013). It is shown that the flow again exhibits a laminar–turbulent transition, similar to that in a channel. The behaviours of the flow in a pipe and a channel are the same in the near-wall region, but there are significant differences in the centre of the flow. The correlation between the critical Reynolds number and free stream turbulence previously established for a channel flow has been shown to be applicable to the pipe flow. The responses of turbulent viscosity, vorticity Reynolds number, and budget terms are analysed. Some significant differences have been found to exist between the developments of the vorticity Reynolds number in the pipe and channel flows

An Energy-Water Corridor Along the US/Mexico Border: Changing the \u27Conversation\u27

Over the last decade, migration has become a divisive issue around the world. A large number of countries have erected barriers along their borders to prevent migration, leading to geopolitical tension. Climate change effects will likely exacerbate migration tensions, which will require bold and creative solutions to this difficult social predicament. Here we detail a plan to construct an energy-water corridor along a border that has been the focus of much attention recently: The U.S.-Mexico border. Our proposed solution helps to alleviate some of the negative effects of climate change, while providing energy and economic stimulus to an area that begs for sustainable development. The energy-water corridor will take advantage of the unique renewable energy resources along the border states and will use state-of-the-art water desalination and treatment systems to provide the resources for economic development in the region

Design of a mooring system for an inertia tube wave energy collector

The dynamics of a point absorber wave energy collector (WEC) were investigated using the University of New Hampshire (UNH) developed finite element computer program Aqua-FE and tank testing. The WEC design considered here makes use of a buoy rigidly connected to a long, vertical inertia tube which is open at the top and bottom. A piston-rod assembly is enclosed and connected to the power take-off (PTO) mechanism. Due to inertia of water within the tube, relative motion between the piston and buoy-inertia tube structure occurs, and this drives the PTO. The Aqua-FE model was then used to design a slack mooring system sufficient for holding the WEC on station while minimizing interference with its energy absorption function. The Aqua-FE model was created and validated by comparison to wave tank measurements made using a 1/9.4 scale physical model in experiments conducted in the UNH 36.6 m long by 3.66 m wide by 2.44 m deep wave tank. The mathematical model was then applied to predict full scale response to seas representing extreme storms expected at UNH\u27s offshore test site south of the Isles of Shoals, NH. Predicted mooring loads were used to specify mooring system hardware. The Aqua-FE model for this system was evaluated using scale model results for free-release tests in heave (vertical displacement), pitch (angular motion), as well as heave in a series of single frequency waves. Wave periods, Froude-scaled to full size, spanned the range of periods observed at the UNH site

Streamwise velocity statistics in turbulent boundary layers that spatially develop to high Reynolds number

Well-resolved measurements of the streamwise velocity in zero pressure gradient turbulent boundary layers are presented for friction Reynolds numbers up to 19,670. Distinct from most studies, the present boundary layers undergo nearly a decade increase in Reynolds number solely owing to streamwise development. The profiles of the mean and variance of the streamwise velocity exhibit logarithmic behavior in accord with other recently reported findings at high Reynolds number. The inner and mid-layer peaks of the variance profile are evidenced to increase at different rates with increasing Reynolds number. A number of statistical features are shown to correlate with the position where the viscous force in the mean momentum equation loses leading order importance, or similarly, where the mean effect of turbulent inertia changes sign from positive to negative. The near-wall peak region in the 2-D spectrogram of the fluctuations is captured down to wall-normal positions near the edge of the viscous sublayer at all Reynolds numbers. The spatial extent of this near-wall peak region is approximately invariant under inner normalization, while its large wavelength portion is seen to increase in scale in accord with the position of the mid-layer peak, which resides at a streamwise wavelength that scales with the boundary layer thickness

Communication skills of medical students during the OSCE: Gender-specific differences in a longitudinal trend study

Background: Communication skills are essential in a patient-centred health service and therefore in medical teaching. Although significant differences in communication behaviour of male and female students are known, gender differences in the performance of students are still under-reported. The aim of this study was to analyse gender differences in communication skills of medical students in the context of an OSCE exam (OSCE = Objective Structured Clinical Examination).Methods: In a longitudinal trend study based on seven semester-cohorts, it was analysed if there are gender differences in medical students' communication skills. The students (self-perception) and standardized patients (SP) (external perception) were asked to rate the communication skills using uniform questionnaires. Statistical analysis was performed by using frequency analyses and t-tests in SPSS 21.Results: Across all ratings in the self-and the external perception, there was a significant gender difference in favour of female students performing better in the dimensions of empathy, structure, verbal expression and non-verbal expression. The results of male students deteriorated across all dimensions in the external perception between 2011 and 2014.Discussion & conclusion: It is important to consider if gender-specific teaching should be developed, considering the reported differences between female and male students.peer-reviewe