Hisaichi Ohnabe

Turning characteristics and stability of manual wheelchairs on a slope

Wheelchairs will be in ever greater demand in a rapidly aging society. Because of the special needs of aging users, due to frailty and reduced reflexes in many cases, it is important to give careful consideration to rather fundamental design properties. Inter alia it is very important to define, clarify and design running, turning and stability properties of the highest standards in manual wheelchairs. In particular we discuss these matters in regard to wheelchair behavior on sloping surfaces. In the present paper we report on an analytical model for a 4 wheel manual wheelchair which shows good correlation with the existing experimental data relating to torque and speed when the wheelchair is moving on a level plane and when climbing a 3 degree slope. The rolling stability of the wheelchair on a slope is also discussed.

Measurement of Orthotropic Elastic Constants of Ceramic Matrix Composites from Impact Sound

The isotropic and/or orthotropic elastic constants of ceramic matrix composites are measured from the impact sound of a small rectangular bar specimen which is suspended by thin ceramic threads in a furnace. The natural frequencies at high temperatures of the flexural and torsional vibration modes are measured from the impact sound using a fast Fourier transform analyzer and elastic constants are computed from these frequencies using Timoshenkos beam theory and Saint-Venants torsion theory. The natural frequencies of a rectangular silicon carbide/silicon carbide (SiC/SiC) plate are also measured at high temperatures and its elastic constants are determined using an iteration technique employing a finite element method. This technique is extended to measure the natural frequencies of a jet engine nozzle flap made of SiC/SiC composite panel from the impact sound before and after engine operation, and thus the damage of the flap is evaluated as the reduction of the Youngs modulus of the material.

Transient vibration of lightweight rotor due to sudden imbalance.

The transient vibration due to imbalance of a lightweight rotor that comprises flexible blades, disk, shaft, and rigid bearings is analyzed by a finite element method. The dimensions of matrices used in the computation are reduced by representing the shaft and blades by beam elements, and the disk by annular elements. The computed results are compared with the experimental data obtained by a test conducted on a small model rotor with a blade loss simulator. A fairly good agreement was obtained between the computed and experimental results.