Norihiko Ozaki

A hybrid locomotion vehicle for nuclear power plants

A hybrid locomotion vehicle for use in remote maintenance of a nuclear power plant is proposed. The vehicle has five locomotion devices, each consisting of a supporting leg and a driving wheel. Each device has three degrees of freedom: leg lifting, wheel revolution, and wheel steering. These degrees of freedom and the inclusion of touch sensors for obstacle detection enable flexible locomotion such as stepping over rises and going up and down stairs in the plant. Two slope sensors set at orthogonal directions maintain vehicle posture through vertical leg motion. The control system, based on a microcomputer, supervises all of these motions. Laboratory tests with a prototype vehicle demonstrate successful locomotion.

Luminous Efficiency of the High‐Pressure Sodium Lamp

The luminous efficiency of the high‐pressure sodium lamps (one sodium‐xenon lamp and four sodium‐mercury‐xenon lamps) is measured as a function of the vapor pressure of sodium and of the discharge current. The vapor pressure of sodium is determined from the self‐reversal width, which is defined as the distance between both lateral peaks of the self‐reversed resonance line of sodium. The self‐reversal width becomes large when the vapor pressure increases at a constant discharge current, and when the discharge current decreases at a constant vapor pressure. It is attributed to elevation of the plasma temperature that the luminous efficiency becomes high when the discharge current increases at a constant vapor pressure and when mercury is added to the sodium‐xenon plasma. When the discharge current is kept constant, there is an optimum pressure at which the luminous efficiency takes its maximum value. The optimum pressure depends on the discharge current, and it corresponds to the self‐reversal width of abou...

Temperature distribution of the high-pressure sodium vapour discharge plasma

Abstract The temperature distribution of the high-pressure sodium vapour discharge plasma (sodium-mercury-xenon plasma) whose optical depth is much larger than unity has been measured by using the spectroscopic method developed by H. Bartels. The measured temperature distribution is expressed approximately as T(r) = 4100−1·4 × 10 4 . r 2 , where T is the temperature in °K and r is the radial distance from the axis in cm. The temperature distribution of the plasma is also obtained from the electrical conductivity of the plasma and the wall temperature of the discharge tube on the assumption that the temperature distribution of the plasma is parabolic. The temperature distribution thus obtained is given by T(r) = 4120−1·9 × 10 4 . r 2 . The agreement between these temperature distributions is satisfactory.

A heuristic planner and an executive for mobile robot control

A path planner and an execution system are proposed for automatic indoor guidance. The planner creates a route plan in two levels of hierarchy. The first level selects doors to pass through, minimizing the total number of doors, and the other generates a near shortest trajectory inside a room. In order to reduce search space and computation time for the planning, heuristic pruning strategies are used in a path search procedure. The execution system performs hierarchical plan repair with regard to the plan levels against unexpected events by detecting obstacles. Simulation tests are conducted to evaluate its execution behaviour with various representations of terrain, unknown obstacles, and an omnidirectional vehicle robot equipped with a sonic range finder for obstacle detection. The results exhibit the effectiveness of simple heuristics in combination with a sonic range finder that provides an adequate amount of data from multiple viewpoints.

A Numerical Study of Source-Sink Flows in a Rotating Cylinder

Numerical investigations are made on the source-sink flows in a rotating cylinder. A finite difference method is used to solve the time-dependent full Navier-Stokes equations to an incompressible, viscous and axisymmetric flow. Computations are carried out for three cases with different Ekman numbers and a fixed aspect ratio. Transient aspects of flows are discussed focusing on the developments of the Ekman layers on both disks, and the E 1/4 layers vertically formed at the radii of a source and sink located on the upper and lower disk, respectively. Numerical results based on a similarity analysis of the nonlinear E 1/4 layer agree well with the experimental ones.

Measurements of velocity profiles of gas in a rapidly rotating cylinder

The azimuthal and axial velocity of the source‐sink flow in a rapidly rotating cylinder were measured by using the back scattered mode of the laser‐Doppler velocimeter. A rotating optical system was devised for measuring the gas flow with a high angular velocity of 5.2×102 rad/s. The incident laser beams were introduced into the cylinder through the rotating optical system which synchronously, but independently, rotating with the cylinder. The Doppler‐shifted signal was observed from the light back‐scattered by small paraffin mist particles of about 1 μm in diameter. The accuracies of the measurements were within ±5% for the azimuthal flow‐velocity component and ±8% for the axial one. The E1/4 layers formed on the sidewall and the feed radius were clearly observed due to the small Ekman number E=2.2×10−5. The theoretical results (boundary layer theory and numerical calculation) agree quantitatively with the experimental ones, except in the case of the feed radius.

Cost analyses of uranium enrichment by laser isotope separation process

The probability of the selective two-step photoionisation of 235U atoms by laser and ultraviolet radiations is estimated from the rate equations for uranium atoms with two isotopes with three levels. The population of 235U ions is obtained by linearising the rate equations. We have calculated the ion production rates for three cases in which the laser and ultraviolet powers are changed while the atom density is kept constant. The power consumption and the capital investment required for the large-scale laser enrichment plant conceptionally designed based upon the above results, and consequently the unit cost of separative work, are estimated. It is concluded that the laser isotope separation process could be competitive with the conventional gaseous diffusion and gas centrifugal methods.

Optimum operating conditions for a laser uranium enrichment plant

Operating conditions of the laser uranium enrichment plant to obtain cheaper enriched uranium are optimised by using the standard optimisation procedure. A simple kinetic model is given to obtain the ion production rate as a function of the laser energy density, ultraviolet light energy density, atomic density and depth and height of the reaction region. The unit cost of enriched uranium is chosen as a value function instead of the unit cost of the separative work. The construction cost is expressed by means of an exponential function to take the scale merit into account. Two numerical results are given. In case 1, the laser power and efficiency are subject to the restraints determined by the present technical levels and in case 2, they are free. The unit cost of the enriched uranium is higher than those of the gaseous diffusion and gas centrifuge methods by a factor of 2 ~ 11. Results indicate that laser uranium enrichment is probably competitive with the other uranium enrichment methods, provided that the laser efficiency is improved by up to 1% and the laser lifetime is extended several times.