Distributed mass/discrete floe model for pack ice rheology computation

A new model, called the distributed mass/discrete floe model, is proposed for performing practical computations of mesoscale pack ice rheology. This model possesses the advantages of both the continuum and the discrete element models: it can express the discrete nature of pack ice, for which it is difficult to use a continuum model, and requires a much shorter computation time than a discrete element model. The pack ice is divided into ice bunches in which the floes, assumed to be distributed uniformly, are modeled as inelastic disks or rectangles floating on the water. The ice interaction forces are formulated from the relationship between the impulse on the bunch and the variation of momentum in the bunch. The ocean flow is calculated simultaneously with the floe movement using a multilayer model. In a circulating water channel, drift tests of physical model floes were performed in order to investigate the characteristics of their motion and interaction with ocean structure models. Near the structure, the floe motion depends on the floe shape. Disk floes show a lateral motion in front of the structure. They flow out around both sides of the structure and the number of floes in front of the structure decreases with the lapse of time. On the other hand, rectangular floes scarcely flow laterally. The number of floes in front of the structure remains constant over time. These experiments indicate that when the motion of pack ice around a structure is simulated, it is important to consider the floe shape. The disk floe motion and the rectangular floe motion can be regarded as extreme cases of pack ice motion. Actual pack ice motion may be between these two extremes. Computations were carried out using the distributed mass/discrete floe (DMDF) model. Simulation results were compared with the circulating water channel experiment results and sea ice motion in the southern part of the Sea of Okhotsk. The DMDF model predicted the circulating water channel drift test results quite closely. The DMDF model results also compared quite well with the sea ice motion.     

Experimental Study of System Optimization for Suppression of Vehicle Vibration

The improvements of ride comfort and vehicle maneuverability in the vehicle design can be achieved by using an active suspension. However, the problems in such a control are the complex control logic because of the control laws incompatible with the improvements of ride comfort and maneuverability, and the cost increase because of various sensors to be attached. Therefore, we examined the control abilities of ride comfort and maneuverability on a unique control law using frequency shaped LQ, and controlled the characteristic of the contact between tire and road without a road displacement sensor     

Measurement and computation of the acoustic field in a cavitation tunnel

Sound pressure distribution around a monotone sound source was measured inside a marine propeller cavitation tunnel and compared with the calculated result by a two-dimensional boundary element method. The measured sound pressure distribution showed some peaks due to the reflection effect of the tunnel test section boundary. As the frequency increased, the sound pressure distribution became more complicated, showing more peaks. The tunnel reverberant effect should be taken into account when the noise data measured in the tunnel are converted into full-scale values. In the boundary element method calculation, the boundary condition at the acrylic observation window of the tunnel was examined in detail. The calculated sound pressure distribution pattern in the tunnel transverse section agreed well with the measured distribution when a reasonable boundary condition was adopted. The boundary element method is an effective method for theoretically predicting the acoustic field inside the cavitation tunnel if the precise boundary condition is adopted.     

On the mechanism of the bursting phenomena of propeller tip vortex cavitation

 The bursting phenomenon of tip vortex cavitation of a propeller sometimes causes severe high-frequency vibration, but its mechanism has not yet been elucidated. In this study, we carried out model experiments by changing the propellers, wake distributions, thrust coefficients, and cavitation numbers parametrically, examined the bursting phenomenon with a high-speed video camera, and measured the pressure fluctuations caused by the phenomenon. We also measured flow distribution around the tip vortex. As a result, we found that in the bursting phenomenon, large pressure fluctuations occurred twice, and that they strongly depended on the wake distribution. Two means were suggested to suppress the bursting phenomenon, other than changing the wake distribution: stabilizing tip vortex cavitation or reducing the cavity volume. Numerical fluid simulations around a propeller in noncavitating, unsteady conditions were also conducted, and the strength of the tip vortex along the circumference and its derivative were examined. As a result, the phenomena were parameterized by the time derivative of the strength of the tip vortex, and if it was higher than a threshold value, the tip vortex cavitation burst. Therefore, it is possible to predict the occurrence of the bursting phenomenon by numerical analysis. Received: November 6, 2001 / Accepted: January 24, 2002     

Hydrodynamic loads on ice-class propellers during propeller-ice interaction

Hydrodynamic loads on a propeller blocked with simulated ice were studied using a cavitation tunnel. Comparative predictions were made using a panel method. The propeller was a model of the Canadian Coast Guard's R-class icebreake propeller, and the ice block was simulated using a solid blockage. Experimental results show the open water performance of the propeller, its performance behind a blockage, and the effects of cavitation in these conditions, as well as the loading on the simulated ice block. Panel method predictions were made of the time series propeller performance in the blocked flow. Cavitation during propellerice interaction resulted in a reduction of mean suction load on the ice block. Block load measurements indicated an increase in the oscillation about the mean value of the loads, with a variation in the phase of the loading with respect to blade position as compared with the non-cavitating results. Comparisons of panel method results with the measured block loads support the reliability of the dynamic measurements.List of symbols D propeller diameter - F block drag load - K _T thrust coefficient,T/(n ² D ⁴) - K _B block load coefficient,F/(n ² D ⁴) - K _Q torque coefficient,Q/(n ² D ⁵) - Q propeller torque - T propeller thrust - n propeller rotational speed - J propeller advance coefficientV _A/(nD) - P _A ambient pressure at propeller - P _ATM atmospheric pressure - P _V vapour pressure of water - V _A propeller advance speed - dissolved gas content - _s saturated dissolved gas content at atmospheric pressure - _o open water propeller efficiency - cavitation number, (P _A –P _V )/(0.5(nD)²) - density of water     

The need for building role models for motorcycle riders' education in the kingdom of Cambodia

In Cambodia, a rider's license is not required for motorcycles below 125?cc. and 73% of traffic accident fatalities among persons aged 15–19?years involve unlicensed riders. Motorcycle riding differs from automobile driving in that motorcycle riding reflects the rider's skill to a much greater degree, so unskilled riding is much more highly correlated with accidents. Going forward, in addition to gaining knowledge from traffic safety education, motorcycle riders should also learn basic specific motorcycle techniques. In particular, having riders learn and practice the three key tasks in motorcycle riding (breaking, leaning, and exiting) is effective at curbing the number of motorcycle accidents. In a new initiative aimed at improving riding skill, university students, instructors, and police officers were given practical riding instruction on a course using pylons. Program participants were able to learn riding techniques in an enjoyable setting, while seeing the potential for becoming motorcycle riding role models.     

New Control Technique for Maximizing Braking Force on Antilock Braking System

In this paper, we propose a new control strategy for an antilock braking system (ABS) to maintain the braking force at maximum. The popularization of the ABS that prevents the wheels from locking has resulted in an improvement of the vehicle stability and shortening of the braking distance. Further improvement is anticipated if the maximization of the braking force is realized. We found an interesting phenomenon in which the characteristics of the resonance system composed of the vehicle body and the wheel and road surface reflects the slip condition of the road surface. Using this phenomenon, we realized a control method for maintaining the maximum value of the braking force.     

Study on the design of propeller blade sections using the optimization algorithm

A new method for designing propeller blade sections is presented. A vortex lattice method is used to evaluate the performance and the time-dependent pressure distribution on the blade surface in a non-uniform flow, while efficient optimization algorithms are used to modify the blade sections. Two different designs were carried out in this study. The first was a design to realize a target pressure distribution in a rotating three-dimensional flow. A two-dimensional wing theory was used to obtain the target pressure distribution. The predicted increase in efficiency and the reduction in the cavity volume were confirmed by model experiments. The second was a design to maximize the propeller efficiency. By this method, the propeller efficiency was improved by 1.2% under the constrains of constant thrust and a prescribed margin for face cavitation.     

止裂韧度值Kca的实尺模型试验研究

对船用钢进行长裂纹止裂特性研究表明:它们的脆性裂纹止裂能力不够。TMCP钢有足够的脆性裂纹止裂能力。对船用钢进行了两种实尺(actual-scale)模型试验,明确了脆性裂纹扩展的条件。根据试验结果提出了止裂韧度值Kca,已经归纳在"脆性裂纹止裂设计指导性文件"中。     

Identifying variations and co-variations in discrete choice models

This study introduces an extended version of a standard multilevel cross-classified logit model which takes co-variations into account, i.e., variations jointly caused by two or more unobserved factors. Whilst focusing on mode choice behavior, this study deals with four different types of variation: spatial variations, inter-individual variations, intra-individual variations and co-variations between inter-individual and spatial variations. Such co-variations represent individual-specific spatial effects, reflecting different responses to the same space among individuals, which may for example be due to differences in their spatial perceptions. In our empirical analysis, we use data from Mobidrive (a continuous six-week travel survey) to clarify the existence of co-variation effects by comparing two models with and without co-variation terms. The results of this analysis indicate that co-variations certainly exist, especially for utility differences in bicycle and public transport use in comparison with car use. We then sequentially introduce four further sets of explanatory variables, examine the sources of behavioral variations and determine what types of influential factors are dominant in mode choice behavior.