Abstract: A method for reducing frictional-resistance at a hull (2) of a ship (1), characterized in that the method comprising a step of ejecting micro-bubbles (8) having predetermined diameters; wherein the micro-bubbles (8) are ejected into water from a position adjacent to the starting point of desired stream line (F.L.) of water and from the position where the static pressure is low; the stream line (F.L.) being directed, from the submerged shallow position at a stem portion (4) of the ship's hull (2), to the ship's bottom (5) along both side surfaces of the ship's hull (2), so that the ejected micro-bubbles (8) are transferred to the ship's bottom (5) along the stream line (F.L.); whereby the micro-bubbles (8) are distributed at at least a part of the circumferential area of the submerged portion of the hull (2), thus reducing frictional-resistance at a hull (2) of a ship (1) while cruising.

Abstract: A method is provided for reducing skin-friction of a ship moving through bubbly flow fields generated in proximity of hull surfaces by jetting gas through a plurality of jet nozzles provided on hull surfaces of the ship. The gas flow rate is controlled so as to establish a peak void fraction in a turbulent boundary layer, by applying an observation that the location of a peak void fraction shifts away in a direction normal to the hull surface with increasing gas flow rate through the jet nozzles.

Abstract: A magnetic sensor in which magnetic leakage flaw detection can be performed with high accuracy without so reducing liftoff, and a magnetic flaw detection method and apparatus to which the magnetic sensor is applied. The magnetic sensor 50 for detecting magnetic flux generated due to a defect portion of a magnetized subject to be inspected has an E-shaped core 51 having magnetic poles (51a, 51b and 51c) arranged in the neighborhood of a steel plate (13) to be inspected, and a search coil (52) wound on the center magnetic pole (51b) of the E-shaped core for detecting the magnetic flux. An external magnetic field floating in the circumference of the E-shaped magnetic sensor passes through the opposite side magnetic poles (51a and 51c) of the E-shaped core 51 but does not cross the center magnetic pole (51b) of the E-shaped core. Accordingly, no voltage due to the external magnetic field is induced in the search coil (52), so that only the magnetic flux caused by the defect portion is detected.

Abstract: Distribution pattern of bubbles produced from a bubble jet of a ship is analyzed by approximating the bubbly flow as a continuous flow of a gas phase and treating the bubbles as diffusing particles dispersing in a flow of the gas phase.

Abstract: A method for reducing the frictional resistance of a navigating vehicle, and a method for generating micro-bubbles for reducing the friction of the navigating vehicle and an apparatus therefor. The friction reduction is achieved with the expenditure of a small amount of energy, thereby improving the overall energy efficiency for operating the ship. An air bubble/water mixture is injected towards the stern of the ship, at an inclined angle to the underwater surface, into a boundary layer formed in the vicinity of the underwater surface of the ship. The friction reduction is effectively performed because of the dynamic energy of the water, being a larger mass than air, enables the gas-including mixture to be injected over a longer distance into the boundary layer than in the case of air bubbles alone.

Abstract: The plating amount and composition of a plated steel plate are measured by determining a theoretical relation for an intensity at two different light-receiving angles of K-series fluorescent X-rays of analysis target elements reflected by the plate when monochromatized X-rays are radiated onto the plate at two incident angles, measuring a fluorescent X-ray intensity by using standard samples having known plating amounts and compositions, under the same conditions as for obtaining the theoretical relation, and calculating a conversion coefficient for converting the measured value into a theoretical value by the theoretical relation, measuring a fluorescent X-ray intensity obtained from a plated steel plate to be measured having unknown plating amount and composition under the same conditions for obtaining the theoretical relation, and converting the measured fluorescent X-ray intensity into a theoretical intensity by using the conversion coefficient, and calculating a plating amount and composition as paramete

Abstract: A low-resistant hydrofoil comprises at least one concave step arranged backwardly in the direction of a chord of blade of the hydrofoil in parallel with the leading edge of the hydrofoil to form a lamellar cavitation layer on the negative pressure surface of the hydrofoil moving under water. The concave step has depth .DELTA.t and .DELTA.t/C is more than 0.001 and less than 0.01, being a chord length. The concave step is 0<x.sub.1 /C<0.1, x.sub.1 being a distance from the leading edge of said hydrofoil and C being a chord length.