Thrust

Abstract: Oscillating foils produce thrust through the development of a jet-like average flow. It is found that such jets are convectively unstable with a narrow range of frequencies of maximum amplification, resulting in the formation of a staggered array of vortices with direction opposite to that of the classical Karman street. A stable co-existence of the jet profile and the large-scale patterns is ensured only at the frequency of maximum amplification, hence at this frequency optimal efficiency is obtained, i.e., maximum thrust per unit input energy. The nondimensional frequency of maximum amplification (Strouhal number) is in the range of 0·25 to 0·35. Experiments confirms this results, while the analysis of a large number of data from observations on fish and cetaceans confirm that optimal fish propulsion is achieved within this range of Strouhal number.

Abstract: Fluid Mechanics Lift Drag Lift and Drag at High Mach Numbers The Production of Thrust Airplane Performance Helicopters and V/STOL Aircraft Static Stability and Control Open-Loop Dynamic Stability and Control Controlled Motion and Automatic Stability.

Abstract: Two-dimensional modeling of loading during the formation of the Idaho-Wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin. The flexural rigidity of the lithosphere is inferred to have been approximately 1023 Nm (1030 dyne cm), on the basis of palinspastic comparison of predicted downwarping, due to the thrust plate loads, to the shape of the sedimentary wedge on the west side of the Cretaceous Western Interior seaway. Erosion of part of the uplifted thrust plates redistributed the load, depositing it farther to the east, thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates. Paleotopography after major Cretaceous thrust events was calculated. The resulting mountainous terrain, gentle alluvial plain, and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the Andes of South America and to paleogeographic reconstructions in the western United States thrust belt. Topography is controlled by the subsurface geometry of the thrust faults, particularly the positions of ramp zones, and by isostatic subsidence.

Abstract: The results of cavitation tunnel and tank tests on an 800 mm diameter model of a marine current turbine (MCT) are presented. The tests were carried out in a 2.4 m×1.2 m cavitation tunnel and the 60 m towing tank. Results for power and thrust coefficients are presented for a range of tip speed ratio and pitch settings for various conditions. The results of this investigation provided an insight into the operation of a singe turbine in straight or yawed flow, the effect on performance of changes in the tip immersion of the rotor, the interference between twin rotors and the likely areas of cavitation inception. In addition, the analysed results presented provide useful information for the hydrodynamic design of MCTs and detailed data for the validation of numerical models.

Abstract: Nomenclature Ar = rotor disk area CD = sectional drag coefficient CD0 = zero-lift drag coefficient Clα = lift-curve slope CP = power coefficient CPi = induced power coefficient CP0 = profile power coefficient CT = thrust coefficient c = chord length D = drag force D.L . = disk loading L = lift force m = mass P.L . = power loading SF = separated flow T = rotor thrust V = local wind velocity perceived by flap W = weight W f = final weight Wo = gross takeoff weight α = blade section angle of attack η = efficiency μ = dynamic viscosity ρ = air density σ = rotor solidity = flapping amplitude (peak to peak)