Atsuhiko Shintani

Axial Leakage Flow-Induced Vibration of the Elastic Rod as the Axisymmetric Continuous Flexible Beam

The evaluation methodologies for the flow-induced vibration instability of a long flexible rod due to axial leakage-flow are reported. In the previous papers, the axisymmetric rods are regarded as rigid bodies, not as continuous bodies. In this paper, we deal with the rod as a continuous flexible body. The equations for the fluid and the structure are coupled analytically and the added mass, added damping, and added stiffness are derived by considering unsteady pressure acting on the rod. The relation between the axial velocity and the unstable phenomena is clarified. Concerning the critical flow velocity, the root locus (Argand diagram) is shown. We compared our results with the experimental results which one of the authors reported before.

Axial Leakage Flow-Induced Vibration of a Thin Cylindrical Shell With Respect to Lateral Vibration

In this paper, the stability of a thin cylindrical shell subjected to axial leakage flow is discussed. In this paper, the second part of a study of the axial leakage flow-induced vibration of a thin cylindrical shell, we focus on lateral vibration, that is, the beamlike vibration of a shell. The coupled equations between a shell and a fluid are obtained by using the Donnells shell theory and the Navier-Stokes equation as same as the former paper. The influence of the axial velocity on the unstable vibration phenomena is clarified concerning the beamlike vibration mode of a shell. The numerical results on shell theory are compared with the ones on beam theory which have been already reported by the authors; and the numerical parameter studies are done for various dimensions of a shell and a fluid.

Evaluation of the Effects of a Personal Mobility Vehicle on Multiple Pedestrians Using Personal Space

Personal mobility vehicles (PMVs) have increasingly attracted research interest as new individual transportation vehicles that are environmentally friendly, compact, and convenient to use. It is important to ensure the safety and comfort of pedestrians sharing space with PMVs. In this paper, we developed a simulation model considering the interaction between a PMV and pedestrians, and investigated the effects of a PMV in pedestrian flows using the concept of personal space (PS), which is the space in which invasion by others induces a psychological strain. To estimate the mutual effects of a PMV and nearby pedestrians, the invasion ratio and crossing time are introduced as indexes. Furthermore, to ensure pedestrians are comfortable in the presence of a PMV, we proposed an assistance system for a PMV. Simulation results revealed that the invasion of PS increases with increasing pedestrian density. Additionally, experimental results showed that the levels of discomfort and fear that pedestrians felt toward a PMV are also affected by pedestrian density. Finally, the effectiveness of the assistance system was confirmed, particularly for low pedestrian densities.

Individually specialized feedback interface for assistance robots in standing-up motion

We present a navigational interface for users of assistance robots. The interface suggests a motion that places low body load at the lower joints, carries a low risk of falls, and requires high voluntary activation of muscles. We describe an application that uses animations to provide feedback on a users sit-to-stand motion in order to demonstrate the potential benefits of such an interface.

Influence of the Size of a Personal Mobility Vehicle on the Affinity With a Pedestrian

Personal mobility vehicles (PMVs) as new individual transportation vehicles have been proposed around the world. It is important to ensure the safe operation of a PMV, especially when a PMV shares the space with a pedestrian. In this paper, in order to evaluate the influence of the size of a PMV on pedestrians, we measured the personal space of the pedestrians who walked against the PMV user. From the experimental results, it was shown that the width of the PMV and height of the step of the PMV significantly affected the personal space of pedestrians. Especially when the width and height becomes larger, the front personal space of the pedestrians expanded. In the simulation introducing the idea of personal space, the affinity between the PMV and pedestrians was quantitatively analyzed. It was found that the size of PMV affects to the affinity toward pedestrians.Copyright

Axial Leakage Flow-Induced Vibration of Thin Cylindrical Shell With Respect to Circumferential Vibration

In this paper, the dynamic stability of a thin cylindrical shell subjected to axial leakage flow is discussed. In this paper, the third part of a study of the axial leakage flow-induced vibration of a thin cylindrical shell, we focus on circumferential vibration, that is, the ovaling vibration of a shell. The coupled equations of motion between shell and liquid are obtained by using Donnell’s shell theory and the Navier-Stokes equation. The added mass, added damping and added stiffness in the coupled equations of motion are described by utilizing the unsteady fluid pressure acting on the shell. The relations between axial velocity and the unstable vibration phenomena are clarified concerning the circumferential vibration of a shell. Numerical parametric studies are done for various dimensions of a shell and an axial leakage flow.Copyright

Adaptive control method for an undulatory robot inspired from a Leech's nervous system

Many mobile robots using undulatory locomotion have been developed for search or rescue operations in narrow or dangerous places where people cannot enter, because undulatory locomotion can be employed for locomotion in various environments. However, an environmental change will require a mobile robot to change the pattern of undulatory locomotion. Recent studies showed that a leech changes its undulatory locomotion pattern depending on changes in the environment, and this is derived from sensory feedback from the muscle strain to the central nervous system. We propose an adaptive control method for a mobile robot that is inspired by the leechs adaptive locomotion. First, we make clear the role of this adaptive behavior of a leech by using the numerical leech model proposed in the preceding study. After that, we construct the simplified adaptive control method that simulates the leechs adaptive nervous system. Finally, we evaluate the effectiveness of our proposed control method with a numerical model. Our study showed that the proposed adaptive control method achieves regulation of body load due to the fluid despite a change in the fluid viscosity. Moreover, our control method reproduced the adaptive behavior of a living leech to changes in the fluid viscosity.

Sliding and Rocking Motion Mitigation of a Rigid Body Subjected to Seismic Excitation due to High-Viscous Liquid

After the accident at the Fukushima Daiichi Nuclear Power Plant in Japan, it has steadily become more important to ensure the structural integrity of cask systems containing spent fuels or radioactive debris during seismic events. These cask systems are free-standing cylindrical structures and are believed to show rocking and sliding motions at huge seismic excitations. In the worst case, these cask systems can possibly overturn or collide with each other. Therefore, it is very important to reduce the sliding and rocking motions of the cask system in order to avoid subsequent contamination due to radioactive substances.To date, the authors have been studying the response behaviors of these motions, and have developed some types of methods that are effective at mitigating sliding or rocking motions, and confirmed the effectiveness of these methods. A system utilizing coaxial circular cylinders and high-viscosity liquid filled into the annular spaces was developed for the suppression of sliding motion. This system was installed at the bottom end of the rigid body. Previous studies show that liquids with high-viscosity provide a very large added damping effect that causes sliding motion to be suppressed significantly. For the suppression of rocking motion, the authors developed a system that utilizes a gyro system, and confirmed it’s effectiveness both analytically and experimentally.However, the gyro system is slightly complex and requires electric power even during a seismic event. Thus, some passive suppression method is required. On the other hand, the above-mentioned coaxial circular cylindrical system filled with high-viscosity liquid is thought to have a high damping effect on rocking motion, along with suppression of sliding motion.This study investigated the effect of rocking motion suppression due to the above-mentioned coaxial circular cylindrical system that is utilized for the suppression of sliding motion. First, an analytical model that can account for the coupled rocking and sliding motion was established, and then the rocking behavior of a rigid structure coupled with its sliding motion was studied. Next, shaking table tests were conducted by using a fundamental test model. By comparing the analytically obtained rocking motion with that obtained by the test results, the validity of the analytical model was confirmed. Finally, the analytical model was modified for cask systems equipped with a rocking suppression system, and the rocking motion was analyzed to evaluate its effectiveness.The proposed rocking suppression system was found to be very effective in suppressing the rocking motion of the rigid body when subjected to base excitations.Copyright

Basic study of power reduction for shape memory alloy actuator drive

Use of shape memory alloy (SMA) for a moving body has some merits against use of the other conventional actuators in view of high specific power, downsizing and simplification of actuators. On the other hand, large power consumption of SMA prevents to put to practical use. This paper shows optimization of input voltage into SMA actuators. First of all, a numerical actuator model is identified from measured data. After that, input voltage waves are optimized under three evaluation functions by using multi-objective optimization; maximum input voltage, time averaged input power and time averaged bending moment as output from SMA actuator. Obtained numerical results showed that high input maximum voltage reduced power consumption.

Effects of Connecting Damper on Rocking Motion of Multiple Cabinets Subjected to Seismic Excitation

In various industrial plants such as thermal power plants, nuclear power plants and chemical plants, numerous cabinets are used for storing the electronic circuits and devices used for controlling the plants. These cabinets are very important for maintaining stable plant operation. Some of these cabinets are simply placed on the floor as free-standing structures, and in many cases, they cannot be connected to the floor using bolts or other means for various reasons. Thus, if these cabinets are subjected to very strong seismic excitations, they will experience very large rocking motions. In the worst case, they will overturn, and the installed electronic circuits or devices will collapse which will cause a loss of plant control and could result in significant accidents. Thus, rocking motion suppression methods have been proposed for these free-standing structures. The authors have also been investigating a method that utilizes a gyro system. Connecting adjacent buildings by damping devices is a well-known architectural mitigation method that is very effective at mitigating their seismic response. The effectiveness of this method was confirmed during the Great East Japan Earthquake in 2011.In this paper, we apply the above-mentioned connecting method to free-standing cabinets in order to suppress rocking motion. There are various types of connecting devices, such as a viscous damper. In this paper, considering the characteristics of these dampers, an elasto-plastic damper is adopted as a connecting device. Analytical models of the rocking motions of control cabinets are established, and the connecting devices are expressed as dampers with a bilinear-type force-displacement characteristic. The rocking motions of the cabinets are analyzed for sinusoidal and seismic excitations by changing the aspect ratio of the cabinets, along with the yield force in the bilinear hysteretic curve. The effects of connecting devices and various parameters are evaluated and discussed in comparison with the rocking motion of a single cabinet.It is found that the proposed connecting method is very effective in suppressing the rocking motion of the free-standing cabinets subjected to base excitations when the hysteretic characteristics are properly adjusted.Copyright