Slip-Angle Estimation for Vehicle Stability Control

Recently, some direct yaw-moment control systems have been in development. Obviously, such systems need accurate slip-angle information. This paper describes a strategy of vehicle slip angle estimation. The difficulty in slip angle estimation is due to nonlinear characteristics of tyres and influence of relative slant of the road surface. To solve this difficulty, a combined method of model observer and direct integration method is proposed. In this method, two kinds of values of the side forces of the wheels are provided, i.e., direct detected values by the G-sensor and values from a tyre model. Then those values are combined appropriately which results in the combination of model observer and direct integration. A feedback algorithm, redesigned to suppress the influence of tyre model error, is applied in the observer. Considering interference of road surface and its avoidance, road slant angle is estimated and consequently vehicle model is corrected. The estimated value of the road friction coefficient is given by the acceleration, and an adequate bias, depending on yaw-deviation, is added. The calculation method of reference yaw-velocity is improved, in order to avoid interference of road slant and variation of dynamic characteristic of vehicle.     

Quasisteady theory for the hydrodynamic forces on a circular cylinder undergoing vortex-induced vibration

Vortex-induced vibrations of a rigid circular cylinder were studied by constructing a theory based on a wake oscillator model under quasisteady approximations, thereby evaluating vortex-induced hydrodynamic forces acting on the cylinder. A lock-in limit line representing the boundary for the occurrence of frequency lock-in was also theoretically derived. Hydrodynamic forces in forced oscillation problems estimated by the theory were compared with measured ones. Although some discrepancies were found, particularly in cases with high-frequency oscillations, good agreement was achieved in most cases. Accordingly, we conclude that the present theory captures well real phenomena in the wake downstream of a cylinder subjected to a flow.     

日本FASTECH360主电路系统的开发

为新干线高速试验列车开发了3种主电路系统,并用E954型车辆进行了运行试验,来确认各种主电路系统的功能和性能,且在约60万km的耐用性试验运行后,进行了解体检测。     

Prediction methods for the surf-riding threshold and the wave-blocking threshold based on Melnikov’s method

A ship operating in following and/or quartering seas may be susceptible to broaching-to preceded by the surf-riding phenomenon. Therefore, for the safety assessment of fast vessels such as destroyers and patrol craft, the estimation of the surf-riding condition is important. As shown by previous research, there are two boundaries for ship motion in following and quartering seas. These are the surf-riding threshold and wave-blocking threshold. In this study, the theoretical methods to estimate both boundaries are obtained by making use of Melnikov’s method. In order to validate the formulae, free-running model experiments are conducted in the towing tank. Comparisons between the results obtained from calculations and experiments show good agreement. It is concluded that the formulae based on Melnikov’s method could be applicable to the safety assessment of surface ships.     

Fundamental research on resistance reduction of surface combatants due to stern flaps

It is well known that a decrease in ship resistance may be achieved due to the installation of a stern flap. Therefore, so far, a considerable amount of research on stern flaps has been conducted. Previous research has demonstrated that the primary mechanism by which a stern appendage reduces resistance is a change in the pressure distribution over the aft body of the hull, and secondly through effects on the running attitude, near and far field wave generation, and local transom flow among other phenomena. However, the change in pressure distribution is influenced by the other components. Hence, there is still room for argument about the relative contribution of each component to the pressure distribution. Therefore, as the first step of the research, by conducting the model experiment in towing tank and CFD (Computational Fluid Dynamics) analysis, we examined the effect of running attitudes and wave making at the after portion of the hull on resistance reduction. As a result, it is concluded that a flap affects a change in the wave generated at the transom part and it could lead to a decrease in wave-making resistance.     

Development of a renewable energy system utilizing vortex induced vibration of a cylinder and principle of leverage aiming for application in deep sea

This study carried out an experiment to develop a renewable energy system utilizing vortex induced vibration (VIV) that can drive generators even in weak flow conditions. In our experimental setup, the translation motions of a cylinder undergoing VIV and a linear-type generator (coil and magnet) are connected through a rotational machinery, which enables us to apply the principle of leverage, leading to power generation even by small excitation force acting on the cylinder. The measurement shows that the present system performs optimally under the lock-in and upper branch conditions, and that there exists an optimum length of the lever of electromagnetic moment on a center of the rotation. Efficiencies of primary (from flows to the VIV) and secondary (from the VIV to electricity) energy conversions are estimated to show that the primary one is not enough high. We thus propose a few directions to improve it.     

Analysis of the contribution of ice algae to the ice-covered ecosystem in Lake Saroma by means of a coupled ice–ocean ecosystem model

A new coupled ice–ocean ecosystem model that links the pelagic and ice ecosystems was used to clarify the role of ice algae in ice-covered ocean ecosystems. The model was applied to Lake Saroma (Hokkaido, Japan) in 1992. Comparison of the model's results with observational data confirmed that the model reproduced the behavior of the ecosystem with acceptable accuracy during the period from winter to spring. The primary production of the ice algae is effectively transported into the pelagic system by means of physical releasing effects: brine convection, ice melting and freezing, and diffusion generated at the bottom of the ice. Ice algae released from the ice are rapidly exported because of their high sinking speed and the shallow depth of Lake Saroma. For this reason, the zooplankton in Lake Saroma cannot graze these released algae. However, zooplankton actively graze the ice algae living along the bottom of the ice. These results show that, before their release, ice algae play an important role as a food source for overwintering zooplankton. A sensitivity analysis revealed a positive correlation between the sinking speed of the released ice algae and the magnitude of the spring bloom by pelagic phytoplankton, and that the time when secondary production becomes active is an important factor in the linkage between these two algal populations.