Noriyuki Sadaoka

Skeleton surface generation from volumetric models of thin plate structures for industrial applications

Computed Tomography (CT) is a powerful non-destructive measurement technology to generate cross-sectional X-ray images of objects, fromwhich three-dimensional volumetricmodels can be constructed. In this study, we focus on industrial applications for X-ray CT in the analysis of thin plate structures, and propose in particular a method to generate sufficiently accurate skeleton meshes from a volumetric model of a thin plate structure. We use a geodesic-based skeletonization algorithm to extract skeleton cells, which can then be contoured to generate a skeleton surface. Since the thin plate structure has junctions, the skeleton surface is non-manifold around these areas. Because of this, the Marching Cubes algorithm is extended to enable handling ofmultiple labels (signs) to generate non-manifoldmeshes. The generatedmesh is optimized to pass through the mid of the plate by interpolating mapping. Some experimental results for industrial samples are shown using our implemented prototype system, and it is proven that the accuracy of the generated mesh is sufficient for industrial applications.

Experimental Study on Acoustic Energy Absorbers to Suppress Acoustic Resonance in Tube Bundles of Boiler Plants

The present paper deals with acoustic resonance in tube bundles which occurred in actual boiler plants. A practical method to suppress the resonant noise is proposed based on scale model tests. In those experiments, besides the transverse modes which are relatively well-known, longitudinal modes which are known to be difficult to suppress, were realized. The relation of both kinds of acoustic modes to vortex shedding frequency was clarified. In the following step, a design method of the acoustic energy absorbers is proposed based on the feedback system stability theory. According to this theory, acoustic energy absorbers were equipped in the duct of the test model, and remarkable increase of the critical flow velocity was confirmed for both types of resonant mode. Based on these results, this method was applied to the actual boiler plants and it was confirmed that the proposed method is the effective countermeasure for both types of acoustic resonant modes.Copyright

Casting Defects Analysis Making the Best Use of High-Energy X-Ray CT

A novel method of analyzing casting defects such as shrinkage cavities by utilizing high-energy x-ray computed tomography (CT) has been developed. The method was realized as the module of three-dimensional (3-D) bitmap CAD software StereoCooker for utilizing x-ray CT images. The cavity measurement method was based on the defocusing feature of an x-ray CT image. The authors assumed the defocusing to Gaussian, and therefore the diameter of the cavity could be calculated from the summation of the voxel value profile of the cavity and the circumference. The Gaussian defocusing hypothesis was confirmed by the CT reconstruction simulation with an accuracy higher than 10% for the conditions of the actual x-ray CT apparatus. The cavity measurement method was verified by applying it to cavity test pieces. The test pieces had cavity diameters of 0.5, 0.6, 0.7, 0.8 and 1.0mm. Using the rotate-only mode of the 6MeV x-ray CT, cavities of 0.6mm or greater in diameter could be detected. The accuracy of the cavity size is higher than 0.1mm for diameters of 0.7mm and greater. The verification of simulation by a comparison of the defects predicted by a simulation and those measured by this method has been proposed.Copyright

Vectorized Calculations and Use of Fast Semiconductor Memories in the Dv-Xα Method

Two types of vectorized programs of the discrete varia tional Xα method with the basis set of Slater-type or bitals have been developed. The first type calculates a basis function every time that it is used and the second type reads a basis function from outside memories. They are examined for the most efficient way of per forming calculations with the HITAC S-810/20 supercom puter (630 MFLOPS at peak) and its available outside memory devices. The acceleration factor of computation by the first type of program over scalar processing is more than 12. The second type of program has no ad vantage over the first in small electron systems of atomic clusters with primitive basis functions. But in larger systems such as Si2O7H6 with complex basis functions, the second type of program, used with semi conductor memories, results in 11 times less CPU time than the first type of program.