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In the applications of the Large eddy simulation (LES) to open-channel flows with roughness, water surface is usually treated as a fixed boundary by neglecting the effects of surface fluctuation generated by boil vortices or relatively large surface variations caused by the drag force at each roughness element. In the present study, in order to expand the applicability of LES to such general conditions, the bottom topography is treated by introducing the immersed boundary method and the free surface variation is simulated by introducing a density function. It was made clear that the developed model is capable to represent relatively large surface variations in the strip-roughness flows with various roughness spacings. The numerical results agreed fairly well with those obtained by PIV.

Water surface velocity field is affected by the three dimensional flow structures under the water. Typically, some of the separation vortices generated near the bottom ascend up to the water surface which causes the diversion of surface floating particles. These vortices, usually called the boil vortices in the field of river engineering, can be commonly observed in natural streams with relatively large roughness. In order to make clear the characteristics of such boil vortices appeared on the water surface, horizontal flow fields at the water surface of flows with several strip roughness are visualized by tracer particles. The visualized images are processed by multiply superposing the images viewed from a frame moving with the surface velocity. It is shown that superposed images clearly emphasize the flow features showing artistic patterns generated by floating tracers.

This paper describes the numerical simulation of a GM refrigerator operating at about 4 K. The simulation model is composed of a regenerator, an expansion space, and a cooling stage. The volumetric change of the expansion space and the actual thermophysical properties of the working fluid, helium are considered. The basic equations are mode up of one-dimensional fluid equations and an energy equation of the regenerator material and the cooling stage. The fluid equations are expressed in the general coordinate system of which a coordinate axis moves with time to take account of the volumetric change of the expansion space. These basic equations are differentiated by using the TVD MacCormack method. In order to verify the simulation model, the theoretical validity of the calculation results was checked and calculation results were compared with results of experiments. As a result it was confirmed that the simulation model is appropriate.

This paper describes analysis of transitional change in pressure after a quench of field windings in a superconducting generator. We constructed a calculation model by which it is possible to predict transitional changes in pressure after a quench in the helium vessel of a superconducting generator, and performed numerical calculation. To verify the calculation model, the calculated results were compared with tested results derived from the Model Rotor, and we could confirm the accuracy of the calculation model. Applying the calculation model to the 70-MW class superconducting generator, we found that the maximum pressure in the helium vessel of the 70-MW class superconducting generator reached 1. 7 MPa at the quench of the maximum field current.

We are now developing a 70MW class superconducting generator with low response excitation (hereafter we call it simply 70MW class machine). The field windings for the 70MW class machine require high current density to achieve low reactance and low a. c. losses to resist the magnetic flux variation at the power system fault. To develop such field windings with high current density and low a. c. losses, it is important to select proper superconducting cables and to find appropriate cable supporting and cooling system. Therefor we constructed model coils of the field windings for the 70MW class machine and investigated these performance. This paper describes at first the configuration of the model coils and then the test apparatus and the test method for these model coils. This paper also describes the test results and the applicability of these test results to the field windings for the 70MW class machine. We have found the superconducting cable and the cable supporting and cooling system which are applicable to the field windings for the 70MW class machine.

AC losses and critical currents of three types of superconductors were measured to evaluate the characteristics of the superconductors which are designed to meet the requirements for the field windings of a 70MW class superconducting generator with low response excitation system. The superconductors used for the test are compacted stranded cables composed of Cu-CuNi-NbTi strands, and have the same cable size. The cross sectional structure of the strands and matrix ratios for tested cables are different. This paper presents the results of the experiment and design concepts of the superconductor for the 70MW class generator.

Benkei, which was a large window frame conventional magnet at KEK has been converted to a superconducting magnet. In the conversion, the pole gap has been doubled from 0.5 m to 1.0 m retaining an analysing power at 2 T m. Several new techniques were applied to coil windings and cryostat fabrication. The superconducting Benkei has shown satisfactory performances for long term operation.

A 30 1/h helium liquefier for use in a 30 MVA superconducting synchronous condenser has been developed, and successfully tested in combination with a 6 MVA superconducting synchronous generator which had been previously developed and installed at MELC0 Central Research Laboratory. A 30 MVA superconducting synchronous condenser has already been installed and is going to be tested in combination with the 30 1/h helium liquefier. The principal design features of the liquefier are described and the test results are presented.

There has recently been much interest in spacecraft borne long lifetime mechanical coolers in Japan, because the cooling loads of IR detectors (IRCCD) for Earth observation instruments have become greater than the cooling capacity of radiant coolers. Therefore active development programs of several types of long lifetime mechanical coolers are in progress.The Vuilleumier cooler is one of the most feasible mechanical coolers for space craft system, because a cooler of this type has the potential advantages of long lifetime operation, small vibration, compactness and low weight. We have designed, built and successfully tested a feasibility model of the spacecraft borne Vuilleumier cooler for the first time in Japan.The major cooler performances are 1.8 watts of cooling capacity at 80 K, 52 K of no-load temperature, 28 minutes of cooldown time, and 130 watts of heater input power.