Ken Yamamoto

Improving performance of DS/SS-IVC under shadowing environment using LMS adaptive circular array antenna

In this paper, an adaptive circular array antenna is applied to DS/SS (Direct Sequence / Spread Spectrum) IVC (Inter-Vehicle Communication) under shadowing environment. The DS/SS scheme is an attractive technique for the IVC system because it has advantages for CDMA (Code Division Multiple Access) capability and so on. However, the near-far problem is occurred in the DS/SS scheme. Shadowing the radio paths by large vehicles is also significant problem for the IVC system. To solve those problems, a LMS (Least Mean Square) adaptive circular array antenna is proposed. The array antenna can be controlled its directivity when the receiving vehicle knows the information of the target vehicle. The PER (Packet Error Rate) and the throughput performances are evaluated. And the performances are compared with the ordinary system by using omini-directional antenna. From the simulation results, the adaptive circular array antenna is effective for the near-far problem and influence of shadowing in the DS/SS TVC system.

Improving performance of Inter-Vehicle Communication using LMS adaptive circular array antenna

In this paper, LMS (Least Mean Square) adaptive array antenna is applied to IVC(Inter-Vehicle Communication) in order to reduce interference which is caused by surrounding vehicles. The LMS adaptive array antenna has a characteristic that the control of directivity is possible according to surrounding radio wave condition, if the receiving vehicle knows the information of the target vehicle. Under the case where the adaptive array antenna is used in IVC systems, packet error rate characteristic, throughput performance and improvement in near-far problem are evaluated by comparing with the performance of the IVC system using omni-directional antenna.

Initiation of the Worthington jet on the droplet impact

Deformation of liquid droplets by impingement induces Worthington jet in certain range of the impact velocity. Although the growth of the jet as well as its tip velocity is predicted from similar cases to the droplet impact, the mechanism of the jet generation is yet to be understood. In this study, high-speed visualization of the droplet impact on a superhydrophobic surface was conducted to understand the initiation of the jet generated by a collapse of an air cavity. Water droplets whose diameter are 2.0 mm and 3.0 mm were generated and the Weber number of the droplet was varied in a range of 2 to 20. The jet velocity was measured from the captured images and it was found that it has a peak at the Weber number equals to approximately seven. The resulting jet velocity at the peak was approximately 15 folds higher than the impact velocity. Moreover, we observed that surface waves were generated by a collision of the droplet on the solid and the waves induced an oscillation of the droplet cap as they propagate from the solid-liquid contact line to the top portion of the droplet. Furthermore, we found the phase of the oscillation is related to the Weber number and it influences the jet velocity significantly, as it determines the initial condition of the jet generation.

Near-hydrophobic-surface flow measurement by micro-3D PTV for evaluation of drag reduction

This study reports the estimation of drag reduction effect, which is obtained from slip flow measurement in hydrophobic microchannels by direct measurement of near-wall velocity distribution. To reveal laminar drag reduction effect of hydrophobic surfaces, it is necessary to investigate near-microstructured-surface flow. In this study, we employed a hydrophobic surface, which has longitudinal microribs and microgrooves oriented parallel to the water flow direction in a microchannel, and measured a near-microstructured-surface flow by astigmatism particle tracking velocimetry (APTV) that enables to obtain the three-dimensional and three-component velocity profile. From the flow measurement results, the curvature and profile of liquid–gas interfaces formed at the microgrooves were obtained. Additionally, since the APTV has the ability to measure the three-dimensional velocity distribution near interfaces, it is possible to determine the shear stress on the interfaces if the interface position is known. More...

A study on space division DS/SS Inter-Vehicle Communication system using circular array antenna

In this paper, a space division DS/SS IVC(Direct Sequence / Spread Spectrum, Inter-Vehicle Communication) scheme using a circular array antenna is studied. A circular array antenna can reduce the interference between PN codes due to the congestion of many vehicles. The circular array antenna which is used in this paper has a characteristic that the directivity of the antenna can be controlled easily when a direction of target vehicle is known. The scheme to control the directivity of a circular array antenna based on the information which is exchanged between each vehicle.