Showing papers in "Journal of Ship Research in 1965"

Elastic Vibration Characteristics of Cantilever Plates in Water

Abstract: : The presence of the liquid free surface has a significant effect upon the dynamic plate characteristics (frequencies) only when the surface is less than about one-half span length from the plate. The effect of the liquid free surface on the resonant frequency of a vertical surface peircing plate is highly dependent upon the relationship between the depth of immersion of the plate and the mode of vibration. The overall damping of cantilever plate vibration is increased significantly in water as compared with air. The results of this study would indicate that for those problem areas in the field of Naval dynamics wherein elastic plate vibrations are involved, and for which predictions of resonant frequencies and damping factors are derived, knowledge is either inadequate or unavailable. For cantilever plates, the present results should enable one to predict resonant frequencies in practical applications with some degree of confidence; but damping factors have been obtained only to within order-of-magnitude and to show trends. Clearly, similar information is very much needed for other plate geometries (i.e., skewed) and support conditions.

On the Role of Corrosion in Cavitation Damage

Abstract: : The interacting influence of corrosion on cavitation damage was studied quantitatively using a magnetostrictive device The relationship between the rate of weight loss and the amplitude of oscillation for 1020 mild steel became modified as the NaC1 concentration was increased When 1100-F aluminum was used, this relationship was not affected An attempt was made to estimate the contribution of electrochemical corrosion to total damage by means of (1) static polarization measurements, (2) dynamic polarization measurements, (3) short-duration pulsing technique, and (4) long duration pulsing technique (Author)

Pressure measurement on flapped hydrofoils in cavity flows and wake flows

Abstract: : The purpose of the present experiments is to obtain a detailed information about the flow field, such as the pressure distribution, at the surface of a flapped hydrofoil in full cavity or wake flows. The model and the experimental procedure are described. The experimental results obtained have been used to compare with the theoretical predictions, to investigate the tunnel wall effect and to estimate the viscous effect at a sharp corner. An empirical method for correcting the tunnel wall effect is developed here, the validity of which is supported by tests with models of three different sizes. An appreciable viscous effect has been found near the hinge of a deflected flap. Except for this effect, the theory and experiments are found to be in good agreement.

Forces on a submarine hull induced by the propeller

Abstract: : The induced-flow field generated by a propeller operating in the wake of a submarine can exert forces on the submarine in some arbitrary made of motion in two ways: Either by pressures applied to the propeller blades and resulting in the conventional propeller thrust or by pressures applied to the hull surface. The ratio of these forces is shown, by theoretical analysis, to depend most strongly on the flow velocity which the particular hull mode of motion would generate at the propeller, to be slightly dependent on the shape of the propeller, and to be negligibly dependent on the magnitude or distribution of the submarine wake. The derived relations are valid for both the inertial and quasi-steady components of the induced-pressure field. The predominant factor in the force ratio is evaluated by a numerical technique which is applicable to any surface of revolution moving in almost any pattern of motion. As one application, it is shown that the steady longitudinal force on the hull is 8 to 12 percent of the steady component of the propeller thrust, in good agreement with measurements of the thrust-deduction factor. As another application, it is shown that a particular vibratory component of the hull force, tending to vibrate the hull in the accordion-vibration mode, is 6 to 8 percent of the same component of the propeller thrust. (Author)

Unsteady Lifting Surface Theory for a Marine Propeller of Low Pitch Angle With Chordwise Loading Distribution

Abstract: : This study is third in a series of investigations applying the unsteady lifting surface theory to the marine propeller case In this investigation, the surface integral equation is solved for a mathematical model where the chordwise loading is taken as the first term of Birnbaum's lift distribution (flat-plate chordwise distribution), in conjunction with Glauert's lift operator, which, in essence, satisfies the chordwise boundary conditions by a weighted average It is shown that this model is an improvement over the modified Weissinger model used previously in this series, because it contains as a nucleus the exact two-dimensional solution, and thus it provides a sounder basis for dtermining the three-dimensional effects The blade-loading is determined for a propeller operating in flow disturbanccs induced by the presence of a hull and by the blade-camber effect The stationary loading obtained by the present model is about 10% less than that obtained by the modified Weissinger model, whereas the nonstationary loading is slightly larger (Author)

Some New Measurements On the Drag of Cavitating Disks

Abstract: As part of an experiment on unsteady flow past a cavitating circular disk, it was necessary to make calibrating measurements of the drag on disks in steady flow. The measurements were made for greater cavitation numbers than have been previously recorded, and show that the drag coefficient is essentially linearly dependent upon cavitation number up to values of this parameter as high as 1.3.

Unified Lifting-Line Theory of Fully Wetted Hydrofoils

Abstract: Unified lifting-line theory is developed for the hydrofoil of fully submerged and surface piercing type. The indirect and direct problems are discussed in some details in relation with the effect of the Froude number.The disturbing velocity potential is derived from the linearized boundary condition on the free water surface. Then, from the boundary condition on the foil, a basic integral equation is obtained for the distribution of circulation over the span, from which the lift and resistance can be readily computed, and also the optimum condition is clarified.Some numerical examples of practical interest are shown for the characteristics, and optimum circulation and minimum resistance in a specified condition of operation for the fully submerged and surface piercing hydrofoils.

Two-Dimensional Supercavitating Plate Oscillating Under a Free-Surface

Abstract: Bureau of Ships Fundamental Hydromechanics Research Program SR-009-01-01; Office of Naval Research Contract Nonr 710(51)

Uniform Oval Reinforcing Rings—Power-Series Expansions

Abstract: : Power series expansions are employed in the analysis of oval reinforcing rings which are arbitrarily located on the inside or outside of oval cylindrical shells of prescribed cross section. The expansions are in terms of two small geometric parameters which are fixed by specifying the cross section of the ring and the major and minor axis lengths of the oval. Analytical solutions are presented for the case of a uniform radial load. A graphical comparison is made with the results of a relatively lengthy energy solution. In addition, the effect of inside or outside rings is displayed in graphs, where the results are plotted versus the major-to-minor axis ratio. (Author)