The direction of the water force on a rowing blade and its effect on efficiency (original) (raw)
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Numerical modelling of rowing blade hydrodynamics
Sports Engineering, 2009
The highly unsteady flow around a rowing blade in motion is examined using a three-dimensional computational fluid dynamics (CFD) model which accounts for the interaction of the blade with the free surface of the water. The model is validated using previous experimental results for quarter-scale blades held stationary near the surface in a water flume. Steady-state drag and lift coefficients from the quarter-scale blade flume simulation are compared to those from a simulation of the more realistic case of a full-scale blade in open water. The model is then modified to accommodate blade motion by simulating the unsteady motion of the rowing shell moving through the water, and the sweep of the oar blade with respect to the shell. Qualitatively, the motion of the free surface around the blade during a stroke shows a realistic agreement with the actual deformation encountered during rowing. Drag and lift coefficients calculated for the blade during a stroke show that the transient hydrodynamic behaviour of the blade in motion differs substantially from the stationary case.
Procedia Engineering, 2010
A hydrodynamics-based model of the highly complex flow around a rowing oar blade during a rowing stroke, consisting of an analytical shell velocity model fully coupled with a computational fluid dynamics (CFD) model, is presented. A temporal examination of the resulting blade force for a standard blade, decomposed into propulsive, drag, and lift components, illustrates the flow mechanisms responsible for shell propulsion and a blade propulsive efficiency term is defined. A comparison of blades with modified cant angles reveals that a-3° cant blade has a higher efficiency than the standard (-6° cant) blade.
Fluid Mechanics in Rowing: The Case of the Flow Around the Blades
Procedia Engineering, 2014
The aim of this research is to develop hydrodynamic models to enhance the knowledge of the propulsion efficiency in rowing. The flow around a rowing blade is a complex phenomenon characterised by an unsteady 3D behaviour, with violent free surface deformation including breakup and with a flexible shaft driven by a 6-DOF movement. The study uses experimental results obtained on an instrumented boat to perform CFD computations. All parameters are considered except the minor role played by the spin rotation of the shaft. The numerical results fit fairly well with experimental data given a high number of uncertainties. Once CFD computations fully validated, more accurate parametric models could be built and integrated in a rowing simulator which will help coaching staff in analysing and improving performance and training of athletes. Another considered possibility is the direct coupling between the rowing simulator and the CFD code.
Improving rowing performance by adjusting oar blade size and angle
Frontiers in Sports and Active Living
The principal aim of the work presented here is to investigate and demonstrate that a forward tilted rowing blade would result in a more efficient and effective motion of the blade through the water that would result in a higher boat speed when an equal input power is provided. A 1:5 scaled rowing boat is used to determine the performance of rowing blades with different sizes and blade angles. This is used to validate the results of a previous study where the optimal blade angle of 15o with respect to the oar shaft was determined ( 1). The input power and speed of the rowing boat can be compared between original and modified oar blades. Measurements in a towing tank demonstrate that a modified rowing blade result in faster rowing by 0.4% at the same input power. Maintaining the same stroke rate, the improvement of the blade efficiency is compensated by using a 4–6% increased blade area to yield the same input power.
Propulsive efficiency of rowing oars
2006
Is the common folklore, that oars are less efficient at propulsion than propellers, correct? Here we examine the propulsive efficiency of the oars used in competitive rowing. We take the propulsive efficiency η of rowing to be the ratio of the energetic benefit, the energy D b dissipated by boat drag, to the energetic cost, the work Wr performed by the rower. Air drag is neglected as is the energetic cost of raising and lowering the oar out of and into the water. We calculate η first by directly using extensive data from an instrumented single scull and again using less data and extrapolating on the basis of a simple rowing model. From the data, we estimate that η ≈ 0.84. That is, about 84% of the rower's energy dissipated during a stroke is due to boat drag and the remaining 16% of the energy dissipated is due to oar drag. The best marine propellers have efficiencies of about 80%. We also point out some subtleties in energetic calculations in rowing, discuss the essential differences between oars and propellers, and discuss how oars might be made still more efficient.
Detailed On-Water Measurements of Blade Forces and Stroke Efficiencies in Sprint Canoe
Proceedings, 2018
Measurements of blade forces are made using a load cell mounted between the blade and shaft of a modified paddle. All six force components and moments are measured simultaneously to give a full picture of blade hydrodynamic forces as the centre of pressure on the blade varies throughout the stroke. Blade orientation was also measured using inertial measurement units, one on the blade shaft, and the other on the canoe giving the relative position of blade with respect to the boat, as well as boat speed, acceleration and motion. Testing of the instrumented paddle was undertaken by one of the authors, an ex-national team athlete. The measured forces (and propulsive/vertical forces) are analyzed in detail through the stroke and as stroke averages. Various measures of propulsive efficiency are proposed using either the input force and propulsive force, or using input force and boat speed, and can be used for stroke analysis, or as training tools/targets.
Sprint Canoe Blade Hydrodynamics - Modeling and On-water Measurement
Procedia Engineering, 2016
A computational fluid dynamics model of the transient flow around a sprint canoe blade has been developed including the full blade motion in the catch and draw phases of the stroke, with the translational and rotational path of the blade is obtained from video analysis of a national team athlete. Examination of the blade path and associated flow patterns around the blade reveals the development of tip and side vortices and their interaction with the blade. An interval of reversed flow and pressure at the top of the blade late in the catch is seen and results in a braking pressure field on the blade surface. On-water measurements have also been made using a new instrumented paddle with multiple strain gauge full bridges. This level of bending moment measurement then allows the tracking of the real centre of pressure of the blade force and the determination of the real blade force (and its components) through the stroke.
Validated biomechanical model for efficiency and speed of rowing
Journal of biomechanics, 2014
The speed of a competitive rowing crew depends on the number of crew members, their body mass, sex and the type of rowing-sweep rowing or sculling. The time-averaged speed is proportional to the rower's body mass to the 1/36th power, to the number of crew members to the 1/9th power and to the physiological efficiency (accounted for by the rower's sex) to the 1/3rd power. The quality of the rowing shell and propulsion system is captured by one dimensionless parameter that takes the mechanical efficiency, the shape and drag coefficient of the shell and the Froude propulsion efficiency into account. We derive the biomechanical equation for the speed of rowing by two independent methods and further validate it by successfully predicting race times. We derive the theoretical upper limit of the Froude propulsion efficiency for low viscous flows. This upper limit is shown to be a function solely of the velocity ratio of blade to boat speed (i.e., it is completely independent of the...
Energy efficiency of the rowing oar from catch to square-off
2008
The mechanical efficiency of a rowing oar during the drive phrase may be defined as that proportion of the energy put into the oar by the rower which is 'usefully' dissipated in overcoming hull and aerodynamic drag as the boat is propelled forwards. Ignoring friction in the oar gate/pivot, the remaining energy is 'uselessly' dissipated by the blade as it shifts and churns water. As an example of energy analysis of propulsion systems, the energy efficiency for a slipping and a non-slipping car wheel is derived. The same method applied to the oar, shows that the efficiency of the oar is inextricably related to the direction of the water reaction force on the blade. If, as is usually assumed, the force is normal to the oar-shaft direction, the efficiency of the oar can be expressed as V sin ψ/ (ω), where V is the hull speed through the water, ω is the rotational speed of the oar, is the distance from the gate to the centre of force on the blade, and ψ is the angle of the oarshaft to the boat forward direction. We consider the efficiency of the oar from catch to square-off, using data gathered from an elite eight rowing at the Australian Institute of Sport. We show that, except for a degree or two of oar-sweep at the catch, when the force is negligible, the efficiency is greatest towards square-off, where a greater portion of the blade force is directed forward, which agrees with the results of Affeld et al. (Int. J. Sports Medicine, 14:S39-S41, 1993). Correlations of force profile shape with average efficiency show that a later application of the maximum force, nearer square-off, is generally more efficient than an earlier application. However, since the oar efficiency increases with boat speed, less efficient oars, for which the maximum force is applied near the catch, cause a greater increase of the boat speed early in the stroke, and this tends to enhance the efficiency of all the oars later in the stroke. 1. Introduction. 2. Example: Propulsive efficiency of a car wheel. 3. Efficiency and 'wheel slip'. 4. Energy flows in rowing propulsion. 5. Slipping and sliding. 6. No-slip rowing. 7. Blade slip and oar efficiency. 8. The hydrofoil theory. 9. Oar efficiency from catch to square-off. 10. Effect of the force profile. 11. Discussion. 1 The 'force curve' shows how the force applied to the handle varies with time. The varying force could also be shown as a function of oar angle through the sweep. During the drive, a 'sweep' oar rotates through about 90 • starting at about 35 • to the forward direction; the 'mid-point' of the drive is ahead of square-off by about 10 •. In the second reference [16], Mallory depicts his ideal force curve as an (inverted) parabola, symmetric about the middle of the stroke. We have no special information about what sequence of muscle activation by the rower produces a particular shape of force curve, or whether similar force curves could be produced by different means. Mallory's views (mentioned later) about how to produce different force curves at least seem plausible.