Fatigue strength improvement for ship structures by Ultrasonic Peening

Ultrasonic Peening has attracted recent attention as a fatigue strength improvement method. The main features of Ultrasonic Peening are generation of compressive residual stress and smoothing of weld toe radius. However, for ship structures, various loads act on the hull structure over a ship??s life, including the construction period, and the compressive stress field of structural members generated by Ultrasonic Peening may change. In order to verify the technique's benefits to ship structures, the influence of load history on the improvement effects on fatigue strength by Ultrasonic Peening needs to be clarified. In this paper, the improvement effects on fatigue strength by Ultrasonic Peening for welding joints were confirmed by experiments with several joint type specimens. In addition, fatigue tests modeling launching, when the stress conditions of a ship's structure changes significantly, were carried out in order to clarify the influence of load history in a ship??s life. Consequently, some cases that have the possibility of decreasing or increasing the improvement effects on fatigue strength by Ultrasonic Peening were clarified, and some efficient methods of Ultrasonic Peening for ship structures were suggested.     

消石灰稳定土用于路基材料时的耐久性研究

根据路基主要承受长期反复交通荷载作用的特征，通过室内试验，探讨了消石灰稳定土用于路基材料时，在反复动荷载作用下的变形和强度特征，并分析了对路基耐久性产生影响的塑性变形量与荷载应力间的关系。     

Reduction of preview distance in lane-keeping control

Lane marker detection is indispensable for a lane-keeping-control algorithm. However, it is impossible to detect lane markers when the curvature of the lane the vehicle is travelling on is large or when there is another car in front of the vehicle with short distance. For lane marker detection, it is desirable to set a preview point close to the vehicle. Therefore, by analyzing the block diagram of driver-vehicle system, we propose a method to reduce preview distance without lane tracking performance deterioration by increasing preview points from the conventional one point to two points. Furthermore, it is revealed that driving along a corner with constant curvature without steady-state deviation and arbitrary design of tracking dynamic characteristics become possible by increasing preview points.     

A CIP-based method for numerical simulations of violent free-surface flows

A CFD model is proposed for numerical simulations of extremely nonlinear free-surface flows such as wave impact phenomena and violent wave–body interactions. The constrained interpolation profile (CIP) method is adopted as the base scheme for the model. The wave–body interaction is treated as a multiphase problem, which has liquid (water), gas (air), and solid (wave-maker and floating body) phases. The flow is represented by one set of governing equations, which are solved numerically on a nonuniform, staggered Cartesian grid by a finite-difference method. The free surface as well as the body boundary are immersed in the computation domain and captured by different methods. In this article, the proposed numerical model is first described. Then to validate the accuracy and demonstrate the capability, several two-dimensional numerical simulations are presented, and compared with experiments and with computations by other numerical methods. The numerical results show that the present computation model is both robust and accurate for violent free-surface flows.     

Time-domain strip method with memory-effect function considering the body nonlinearity of ships in large waves (second report)

In the previous paper, one of the authors proposed a new time-domain nonlinear strip method for a rigid body, in which hydrodynamic forces are evaluated by a convolution integral with the memory function computed for the instantaneous submerged part of the transverse sections, and the Froude–Krylov and hydrostatic forces are evaluated on the instantaneous wetted hull surface. In this paper, first, that nonlinear strip method is extended for an elastic body using a method of superposition of elastic mode functions, which enabled us to investigate whipping phenomena due to impulsive large waves. Second, the influence of different approximations of the pressure above the still-water surface is investigated, and then the results calculated by the proposed nonlinear strip method are compared with the experimental ones. Third, whipping phenomena observed for an elastic body at higher Froude numbers are studied through a comparison between computed and measured results. Higher-frequency vibrations in the vertical bending moment due to slamming are discussed. Furthermore, the wave load due to green water on deck is calculated by introducing a practical model, and the effects of the green water on responses of both rigid and elastic bodies are investigated.