Takeshi Toi

Rotor vibration reduction with polymeric sectors

Abstract This work has been undertaken principally with an idea to improving the dynamic performance of rotor–shaft systems, which often suffer from two major problems (a) resonance and (b) loss of stability, resulting in excessive vibration of such systems. Polymeric material in the form of sectors has been considered in this work as bearing supports. Polymeric material has been considered in this work as both stiffness and loss factor of such materials varies with the frequency of excitation. Stiffness and loss factor have been found out for the proposed support system comprising of polymeric sectors. Depending upon the frequency of excitation the system matrix, in this case, changes and dynamic performance of the rotor–shaft system also changes accordingly. Here in this work avoidance of resonance and application of optimum damping in the support have been investigated by finding out the optimum dimension, i.e., the optimum thickness and optimum length of the sectors. It has been theoretically found that use of such sectors reduces the rotor unbalanced response, increases the stability limit speed for simple rotor–shaft systems and thus improves the dynamic characteristics. Parameters of the system have been presented in terms of non-dimensional quantities. Many examples have been presented in support of the conclusion. The life of such supports, particularly in the presence of chemicals and other reagents has not been investigated.

Sensitivity analysis and its application for dynamic improvement

In order to determine appropriate points where natural frequency or mode shape under consideration can be effectively modified by structural modification, the theoretical background of sensitivity analysis is described, followed by experimental verification with a simple structure. Then it can be extended to (1) operational deflection shape, where a problem arises at offresonance frequency, (2) relative motion, (3) transmitted force through connecting points between components, (4) servo system, which consists of electrical elements with mechanical elements, and (5) acoustics generated by the vibration of the structure. To illusrate its effectiveness, many actual examples are given.

Sound quality evaluation of transient sounds in precision information equipments

These days, sound quality in mechanical products has become a very important factor in addition to reduction of the sound pressure level. A new method is proposed for sound quality evaluation including the transient sound in precision information equipment taking MFP (multifunction peripheral), for example. The MFP has many functional parts and a lot of operational modes, so single copy mode and ten times continuous copies mode in monochrome are taken into account. Since the operational sound including the transient sound is changed with time in one cycle, it is necessary to identify high contribution sound section to decide the sound quality by pair comparison method and SD method with original, filtered, and edited sounds. As a result, sound quality of the transient sound is influenced by the cycle time, the rhythm, the sound pressure, and the frequency characteristics. As the single copy mode, main uncomfortable sound can be estimated at the steady‐state sound section caused by a rotational component. ...

Right/left asymmetricity of horizontal sound localization of younger people

To investigate the performance of horizontal sound localization of younger people, authors conducted a test using 12 young participants (11 males, 1 females; ages 21–24.) The stimuli were presented through headphones to their right and left ears with 4 interaural time differences (ITDs) (0.2, 0.4, 0.6, and 0.8 ms) and 4 interaural level differences (ILDs) (3, 6, 9, and 12 dB(A)) besides the same condition to both ears. Concerning the frequency, pure tones of 0.5, 1.0, and 2.0 kHz, and composite sound of 0.5 + 2.0 kHz were presented, which lasted one second for each trial. The participants answered “Right” or “Left” after each trial according to their own judgment. The results of ITD condition showed that a right-sided inferiority was recognized in case of 1.0 and 2.0 kHz. Concerning the ILD condition, no right/left asymmetricity was shown. This asymmetricity may be caused by the improper setting of the experiment apparatus. Therefore, we switched right/left of the headphones to carry out an additional test in the same way. The same tendency as the original test was obtained, which means that the asymmetricity is likely due to the native characteristics of the participants.To investigate the performance of horizontal sound localization of younger people, authors conducted a test using 12 young participants (11 males, 1 females; ages 21–24.) The stimuli were presented through headphones to their right and left ears with 4 interaural time differences (ITDs) (0.2, 0.4, 0.6, and 0.8 ms) and 4 interaural level differences (ILDs) (3, 6, 9, and 12 dB(A)) besides the same condition to both ears. Concerning the frequency, pure tones of 0.5, 1.0, and 2.0 kHz, and composite sound of 0.5 + 2.0 kHz were presented, which lasted one second for each trial. The participants answered “Right” or “Left” after each trial according to their own judgment. The results of ITD condition showed that a right-sided inferiority was recognized in case of 1.0 and 2.0 kHz. Concerning the ILD condition, no right/left asymmetricity was shown. This asymmetricity may be caused by the improper setting of the experiment apparatus. Therefore, we switched right/left of the headphones to carry out an additional tes...

Characteristics of horizontal sound localization of elderly people and analysis of its potential influential factors

To investigate the performance of horizontal sound localization of elderly people, authors conducted a test using 19 elderly participants (10 males, 9 females; ages 65-85; mean 71.5 years old.) The stimuli were presented through headphones to their right and left ears with 4 interaural time differences (ITDs) (0.2, 0.4, 0.6, and 0.8 ms) and 4 interaural level differences (ILDs) (3, 6, 9, and 12 dB(A)) besides the same condition to both ears. Concerning the frequency, pure tones of 1.0 and 2.0 kHz, and composite sound of 0.5 + 2.0 kHz were presented, which lasted one second for each trial. The participants answered “Right” or “Left” after each trial according to their own judgment. The results of ITD condition showed that in case of the pure tones a right-sided inferiority was recognized, which was poorer than the results of the younger participants. Meanwhile, no right/left difference was recognized with the composite sound. Concerning the ILD condition, no right/left asymmetricity was shown. Furthermore, no significant differences were recognized regarding the relationships between their sound localization performance and potential influential factors. The factors were Trail Making Test (TMT) results, their preferred ear, and their hearing loss difference between right/left ears.To investigate the performance of horizontal sound localization of elderly people, authors conducted a test using 19 elderly participants (10 males, 9 females; ages 65-85; mean 71.5 years old.) The stimuli were presented through headphones to their right and left ears with 4 interaural time differences (ITDs) (0.2, 0.4, 0.6, and 0.8 ms) and 4 interaural level differences (ILDs) (3, 6, 9, and 12 dB(A)) besides the same condition to both ears. Concerning the frequency, pure tones of 1.0 and 2.0 kHz, and composite sound of 0.5 + 2.0 kHz were presented, which lasted one second for each trial. The participants answered “Right” or “Left” after each trial according to their own judgment. The results of ITD condition showed that in case of the pure tones a right-sided inferiority was recognized, which was poorer than the results of the younger participants. Meanwhile, no right/left difference was recognized with the composite sound. Concerning the ILD condition, no right/left asymmetricity was shown. Furthermore,...

Vibration and Acoustic Analysis of Acoustic Guitar in Consideration of Transient Sound

The sound characteristic of an acoustic guitar is empirically designed for long time. The up to date vibration and acoustic analysis are applied to investigate the difference between typical guitars especially focused on transient vibration and sound just after picking a string at keynote and higher harmonic frequencies. By using a simplified front plate model of a guitar with bracings, structural modification method is utilized to realize the Operational Deflection Shape in order to meet the target sound characteristic.

Reduction of Radiating Sound from CFRP Laminated Plates with Orthotropy

CFRP is being positively introduced because of its light weight with sufficient stiffness for example in vehicle body but from acoustic aspect more investigations are needed. In order to grasp the vibration and acoustic feature of flat and curved CFRP laminated plates with orthotropy, the difference from isotropic material such as steel is clarified using experimental modal analysis. As a result CFRP is found to possess a dominant radiating sound mode shape at specific frequency. Then based on the FE model of the CFRP plate, a small CFRP patch with optimum anisotropy is designed to attach for effective reduction of the sound and finally its performance is verified in experiment.

Modification of impact sound by adjusting the excitation input for comfortable design of punch press machine sound

The effectiveness of adjusting the excitation input as a method for modifying impact sound was investigated. The radiation from the impact can be described using a convolution of an impulse response function for a vibro-acoustic system and the corresponding impact excitation function. Therefore, the radiated sound can be changed by modifying both the impact excitation function and the structural response. Excitation with complicate shapes of input which is required to make an arbitrary shape of wave form, such as selective excitation or rejection of a specific frequency component, is not easy for manually operated traditional system. However, the modification of excitation input is useful for the automated system with an electrically controlled impactor, such as a servo-motor. As a practical application, a punching process of a punch press machine was designed to not only reduce the overall sound pressure level but also improve the perceived sound quality. Sound from a punch press can be improved by dividing the punching process into several steps with different stroke speeds without substantially reducing the cutting surface quality.

Development of Vibration Damper for Energy Harvesting

In vibration engineering, unnecessary vibration energy can be dissipated by a damper into not only heat energy but also electric energy for energy harvesting. But a common damper for energy harvesting has to be tuned into a resonance in order to reserve large vibration and therefore for frequency varying case, the efficiency is very low and the application is limited. In this study a special damper system is so designed as to generate sufficient electric power even for frequency varying case based on two approaches: the resonance of the damper can be adjusted corresponding to the input frequency and the fixture of the damper has multiple resonances which coincide the structural resonances. The damper system consisted of permanent magnet and coil is verified to have variable resonance and the resonances of the damper fixture are found to have coincident resonances. Finally the damper system is applied to a motor bike where sufficient power is generated in case of varying engine rotation.

Vibration Reduction of Brush Cutter

Brush cutter powered by engine has been widely used on a daily basis for mowing of road shoulders and gardens. People who regularly operate brush cutter are at risk of developing Raynaoud’s disease due to large vibration. Such vibration disorder can be prevented by reducing the handle vibration by good use of structural modification. In this study we focused on rubber bushes which support the drive shaft in pipe to transmit the engine power to the cutting blade. First the dynamic characteristics of the brush cutter such as Operational Deflection Shape are grasped and then the hardness and the placement of rubber bushes are optimized to reduce the handle vibration effectively.