Dynamic Brake Control for a Wearable Impulsive Force Display by a String and a Brake System

In recent years, it has become possible to experience sports in the virtual reality (VR) space. Although many haptic displays in the VR environment currently use vibrators as the mainstream, the vibrators’ presentation is not suitable to express ball-receiving in the VR sports experience. Therefore, we have developed a novel haptic display that reproduces an impulsive force by instantaneously applying traction to the palm using a string and wearable brake system. This paper proposes a method to present various reaction forces by dynamic control of the braking system and report the quantitative evaluation of the device’s physical and psychological usability.

Experimental force reconstruction on plates of arbitrary shape using neural networks

Measuring the forces that excite a structure into vibration is an important tool in modeling the system and investigating ways to reduce the vibration. However, determining the forces that have been applied to a vibrating structure can be a challenging inverse problem, even when the structure is instrumented with a large number of sensors. Previously, an artificial neural network was developed to identify the location of an impulsive force on a rectangular plate. In this research, the techniques were extended to plates of arbitrary shape. The principal challenge of arbitrary shapes is that some combinations of network outputs (x- and y-coordinates) are invalid. For example, for a plate with a hole in the middle, the network should not output that the force was applied in the center of the hole. Different methods of accommodating arbitrary shapes were investigated, including output space quantization and selecting the closest valid region.

A possible physical mechanism of the torque generation of the bacterial flagellar motor

The torque required for the rotation of the rotor of a bacterial flagellar motor (BFM) can be generated from an impulsive force resulting from the collision between the stator and the rotor. The asymmetry in the fluctuations of the tilting angle of the rotor determines the direction of rotation. The expressions of the torque and the step size can be derived from a Langevin equation of motion. The drag coefficient of BFM derived from the Langevin equation and the measured torque–speed (τ-ω) relation is notably high; the viscous force from the environment cannot account for it. The drag force may be caused by the frictional interaction between the bearing-like L- and P-rings of BFM and the cell membrane. Order-of-magnitude estimations of the torque and the step size are consistent with previous experimental observations. The slope of the linear dependence of the rotational frequency on the temperature was estimated and was consistent with the observed value. A simulation device having the structural characteristics of BFM was designed to demonstrate the applicability of the proposed mechanism. Many observations for the actual BFM, such as the bidirectional rotation and the τ-ω relations of the clockwise and counterclockwise rotations, were reproduced in the simulation experiments.ImportanceThe concept that the torque required for the rotation of the rotor of a bacterial flagellar motor (BFM) can be generated from an impulsive force resulting from the collision between the stator and the rotor is new and effective. The magnitude of the torque and the size of the step derived from the proposed mechanism are consistent with the observed values. The torque-speed (τ-ω) relation might be explained by the frequency-dependent drag force caused by the frictional interaction between the bearing-like L- and P-rings of BFM and the cell membrane. The slope of the linear dependence of the rotational frequency on the temperature is consistent with the observed value, which has not been achieved previously.

Experimental simulation of tsunami surge and its interaction with coastal structure

Following the tsunamis occurred in Japan (2011) and Indian Ocean (2004), investigating interaction between coastal structures and tsunamis became necessary. Although several attempts have been made to estimate the tsunami forces acting on the coastal structures, there still remain inconsistencies among the published design guidelines. This research includes an experimental study to investigate the interaction between a tsunami surge and a coastal structure. The tsunami surge was generated using a novel dam-break system, capable of generating higher tsunami surges than the previous simulations. The relations between surge velocity, surge depth, and surge-induced pressure on the structure were presented. In the surge-induced pressure–time histories, there were three identified force components, namely, run-up, impulsive and quasi-steady hydrodynamics. Furthermore, this research presents a comparison made between the experimental results and existing tsunami guidelines. The ratio of impulsive force to hydrodynamic force was found around 2.4 for each tsunami surge. The hydrodynamic forces were found to be higher with respect to those determined using the ‘Federal Emergency Management Agency’ FEMA P646 guidelines, whereas they were approximately in agreement with those obtained by FEMA 55. Moreover, the results showed that the ‘Structural Design Method of Building for Tsunami Resistance’ overestimates the impulsive force.