D.J. Taunton

Impact of a free-falling wedge with water: synchronized visualization, pressure and acceleration measurements

A fixed 25deg 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

Kayak blade–hull interactions: A body force approach for self-propelled simulations

A sprint kayak experiences an unsteady flow regime due to the local influence of the paddle. However, kayak designs are usually optimised for steady-state, naked hull resistance. To determine whether unsteady paddle effects need to be included in kayak design, the hydrodynamic interactions between a kayak paddle and a hull are assessed using computational fluid dynamics. A body force model of a drag-based paddle stroke is developed using a blade element approach and validated against experimental data. This allows the paddle-induced local velocities to be simulated without the need to fully resolve the detailed flow around a moving paddle geometry. The increase in computational cost, compared to the naked hull simulation, is 8%. A case study investigating the impact of different paddle techniques on the hydrodynamic forces acting on a self-propelled kayak is conducted. A 0.23% difference in self-propelled resistance was observed, while an estimated 0.5% additional increase can be attributed to paddle-induced draught increases. An estimate of small changes in resistance on race times indicates that reductions of even a fraction of a percent are worth pursuing, indicating that the developed methodology may provide a useful design tool in the future.

Repeatable techniques for assessing changes in passive swimming resistance

Two different methods of measuring the passive resistance of swimmers are used to compare system accuracy and repeatability. Method I uses a submerged glide tow, and Method II, a novel, simpler approach, is based on measuring deceleration during a submerged push-off glide. The comparison of each method is made for specific changes in passive resistance. A set of three male and three female swimmers compare the use of drag shorts to make swimmer-specific increases in drag. In a second study, the effect of hair removal is quantified on a single male swimmer (Method I 9.7% reduction and Method II 9.4% reduction). For five repeat tests, a 1.8% difference in resistance can be resolved with 95% and 70% confidence levels for the passive tow and push-off glide experiments, respectively.

Aircraft Ditching Loads Simulation Tool

The present work presents a novel methodology developed for calculating the steady loads acting on aircraft structures in the event of ditching in water. It represents the preliminary result of Stirling Dynamics as part of a NATEP research project. The overall objective of the project is to expand the capabilities of the Stirling Dynamics proprietary software SD-GLOAD (originally designed for ground and crash loads dynamic simulations) to aircraft ditching simulations. The methodology presented in this paper employs a Doublet Lattice Method (DLM) to calculate the steady pressure distribution acting on the submerged parts of the ditching aircraft. The proposed methodology is validated against a higher-fidelity CFD multi-phase model for a selected test-case and several ditching conditions.