Numerical study on active wave devouring propulsion

The possibility of extracting energy from gravity waves for marine propulsion was numerically studied by a two-dimensional oscillating hydrofoil in this study. The commercially available computational fluid dynamics software FLUENT was used for the unstructured grid based on the Reynolds-average Navier?CStokes equation. The free surface waves and motion of the flapping foil were implemented by customizing the FLUENT solver using a user-defined function technique. In addition, dynamic mesh technology and post processing capabilities were fully utilized. The validation of the model was carried out using experimental data for an oscillation hydrofoil under the waves. The results of the simulation were investigated in detail in order to explain the increase of propeller efficiency in gravity waves. Eight design parameters were identified and it was found that some of them greatly affected the performance of wave energy extraction by the active oscillating hydrofoil. Finally, the overall results suggested that when the design parameters are correctly maintained, the present approach can increase the performance of the oscillating hydrofoil by absorbing energy from sea waves.     

A novel physiological index for Driver’s Activation State derived from simulated monotonous driving studies

Automobile driving in monotonous situations such as driving for long periods and/or travelling a familiar route may cause the lowering of the driver’s awareness level or what we term here as a Driver’s Activation State (DAS), resulting in an increased risk of an accident. We propose here to develop means with which to create an in-car environment so as to allow active driving, hopefully thus avoiding potentially dangerous situations. In order ultimately to develop a validated activation method, we firstly set out to examine physiological variables, including cardiovascular parameters, during simulated monotonous driving. Subsequently, we investigated the derivation of a suitable DAS index. During the experiment, a momentary electrical test stimulus of 0.5 s duration was applied at a rate of approximately once per 10 min to the subject’s shoulder to evoke a physiological responses. In 11 healthy male volunteers we successfully monitored physiological variables during the experiment and found particular patterns in the beat-by-beat changes of blood pressure in response to the electrical test stimulus. This finding, explained by autonomic activity balance, suggests that the patterns may be used as an appropriate and practicable index relevant to the Driver’s Activation State.     

Decisions on truck parking place and time on expressways: an analysis using digital tachograph data

With the objective of deriving useful insights into measures against traffic congestion at service areas (SAs) and parking areas (PAs) on expressways and ensuring efficient use of SAs/PAs, this study investigated the decisions on where a truck is parked (i.e., choice of an SA or a PA), how long it is parked (i.e., parking time), and their influential factors. To this end, this study used the trajectory data of 1600 trucks recorded in 6-min intervals by in-vehicle digital tachographs on the Sanyo and Chugoku Expressways in Japan from October 2013 to March 2014. First, the aspect of repeated choice of each truck (i.e., habitual behavior) toward a specific SA/PA was clarified. Next, a multilevel discrete–continuous model (Type II Tobit model) was developed to reveal the factors affecting the above decisions. The modeling results confirmed the existence of habitual behavior and showed that trucks were more likely to be parked a longer time at an SA/PA when it is closer to the destination. It appears that truck drivers may adjust their time at the SA/PA close to the destination to comply with the arrival time, which is often predetermined by the owner of the transported goods. Furthermore, the availability of restaurants and shops, and the number of parking spaces available for trucks and trailers are important determinants of parking time, whereas the existence of a convenience store is important to the choice of the SA/PA. Parking experience has an extremely strong positive effect on the parking choice and use. Moreover, increasing the number of parking lots may induce its longer use.

     

Reduction of skin friction by microbubbles and its relation with near-wall bubble concentration in a channel

Determination of the flow structure near the wall is essential for a clear insight into the phenomenon of skin friction reduction by microbubbles in a turbulent boundary layer. An important parameter, is the bubble concentration or void fraction in the wall region in drag-reducing conditions. The purpose of this paper is to show drag-reducing effects due to microbubbles in a water channel and, more importantly, to show the dependence of the drag-reduction values on the near-wall void fraction. A two-dimensional channel with an aspect ratio of 10 was specially built for this purpose with provisions for air injection through porous plates. Skin friction was directly measured by a miniature floating element transducer with a 5-mm circular sensing disk mounted flush on the top wall 67 channel-heights downstream of the injector. The wall friction in the presence of air bubbles was found to be reduced under the same bulk velocity when compared with the value without air. Detailed void fraction profiles across the channel were obtained by a sampling probe and a fiber-optic probe. Better collapse of the drag reduction data, independent of different profile shapes, was found when plotted against the near-wall void fraction than against a cross-sectional mean void fraction. While this dependence reconfirms that the phenomena are essentially inner-region dependent, the lack of influence of the bubble distribution patterns away from the wall implies lack of outer region influence.     

A new functional optimization method applied to the pitch distribution of a marine propeller

Based on Hilbert space theory, an infinite-dimensional optimization method to find the optimal pitch distribution of marine propellers was developed. Thereby, the three-dimensional effect of induced velocity could effectively be controlled in an optimal way; i.e., an investigation was carried out to learn whether the present method is applicable to the design of marine propellers, especially pitch distributions, by maximizing the propeller efficiency functional. In addition, with the help of Hilbert space theory, it was successfully shown that the optimization method developed has a unique mathematical solution. In this work, only the pitch distribution was optimized, while other parameters such as the camber and thickness of the trial propeller remained as in the original. With a numerical study, it is shown that the present optimization method gives an optimal pitch distribution, the open-water characteristic curve being superior to the original curve. Received: August 24, 2000 / Accepted: July 16, 2001     

Low-cost carriers in Asia: Deregulation, regional liberalization and secondary airports

While the demand for low-cost air transportation is potentially huge in Asia, development of low-cost carriers (LCCs) lags behind the region's overall aviation development, and certainly lags behind the LCC development in North America and Europe. It has been noted that market conditions and the regulatory environment of Asia are different from those of North America and Europe. What are the main differences here; and how do these differences impact market entry and success of Asian LCCs? This paper describes salient features of Asian LCCs and their developments. It examines the impact of Asia's domestic and international airline regulations and airport infrastructure on the performance of its LCCs. We find that the “Southwest effect” may also exist in Asia and that the development of low-cost terminals may compensate, at least partly, the scarcity of secondary airports in the region. The experiences of Thailand and China are investigated as case studies.     

GIS-aided prediction for sea-ice distribution

A method of applying the geographic information system (GIS) to predict sea-ice distribution is proposed. The prediction computations are performed using the distributed mass/discrete floe (DMDF) model. The GIS is used to prepare the initial data for the DMDF model, and to display the simulation results together with a digital map and observational data for evaluation and further use. Two areas in the Arctic Ocean were selected to test the computations in this study. The results of the case studies show that this method can help with (1) free-area and free-scale prediction fitting for various purposes, (2) a high-resolution output to provide more detailed data, and (3) a reasonable combination of different data sets to make the best use of the information obtained. The results also suggest that the DMDF model is a good simulation of the ice motion not only for large-scale but also for local-scale predictions. Received: March 19, 2002 / Accepted: June 20, 2002 Acknowledgments. This study was financially supported by the Japan Science and Technology Corporation. The SSM/I sea-ice data were obtained from the EOSDIS NSIDC Distributed Active Archive Center (NSIDC DAAC), University of Colorado at Boulder. The authors thank the persons concerned. Address correspondence to: H. Yamaguchi (yama@fluidlab.naoe.t.u-tokyo.ac.jp)     

Experimental study on microbubble ejection method for frictional drag reduction

The formation of air bubbles ejected through a single hole in a flat plate was observed in uniform flow of 2–10 m/s It was confirmed that the size of the air bubbles was governed by main flow velocity and air flow rate. According to previous experiments, the size of the bubbles is an important factor in frictional drag reduction by microbubble ejection. Usually bubbles larger than a certain diameter (for example 1 mm) have no effect on frictional drag reduction. Three different methods were proposed and tested to generate smaller bubbles. Among them, a 2D convex (half body of an NACA 64-021 section) with ejection holes at the top was the best and most promising. The diameter of the bubbles became about one-third the size of the reference ejection on a flat plate. Moreover, the bubble size did not increase with increasing flow rate. This is a favorable characteristic for practical purposes. The skin friction force was measured directly with a miniature floating element transducer, and decreased drastically by microbubble ejection from the top of the 2D convex shape.     

Effect of microbubbles on the structure of turbulence in a turbulent boundary layer

The time-averaged velocity and turbulence intensity distributions were measured by a laser Doppler velocimeter in a turbulent boundary layer filled with microbubbles. The void fraction distribution was also measured using a fiber-optic probe. The velocity decreased in the region below 100 wall units with an increase in bubble density. This led to a decrease in the velocity gradient at the wall, which was consistent with a decrease in shearing stress on the wall. The turbulence intensity in the buffer layer increased at a low microbubble density, and then began to decrease with an increasing microbubble density. Based on the present measurements, the mechanism of turbulence reduction by microbubbles is discussed and a model is proposed. Received for publication on Dec. 3, 1999; accepted on April 18, 2000     

Development of ocean carriers' behaviour model focusing on their 'cost and tariff' based on the spatial general equilibrium

Spatial computable general equilibrium (SCGE) theory has been applied to an international trade model to evaluate tariff and fiscal policies of a country. Those models can not be applied for the evaluation of transport policies such as port development and tax/subsidy policy against transportation sectors, since they do not deal with ocean freight and ocean carriers explicitly in the model. Ocean freight often varies with the changes of competitive conditions and/or demand/ supply balances in the short run, while it should reflect the actual expenditure of the carriers in the long run. The model proposed here considers the profit maximization behaviour of ocean carriers, and deals with ocean freight explicitly. The model is applied to four major economic regions; Japan, USA, EU and Asia. A multi-level function composed of the Cobb-Douglas function is adopted to produce reliable parameters of the production function for many industries.