Hydroelasto-plasticity approach to predicting the post-ultimate strength behavior of a ship’s hull girder in waves

Dynamic collapse behavior of a ship’s hull girder in waves is investigated; post-ultimate strength behavior is the focus. Firstly, a simulation method is proposed. Assuming that a plastic hinge is formed during the collapse of the hull girder, the whole ship is modeled as two rigid bodies connected amidship via a nonlinear rotational spring. The post-ultimate strength behavior, such as the reduction of load carrying capacity due to buckling and yielding, is reflected in the model. Hydrodynamic loads are evaluated by using nonlinear strip theory to account for the effect of large plastic deformations on the loads. A scaled model for validation of the simulation is designed and fabricated. Then a series of tank tests is conducted using the scaled model to validate the simulation results. Post-ultimate strength behavior characteristics in waves are clarified by using the numerical and tank test results. It is shown that the hull girder collapses rapidly after reaching ultimate strength, and then the plastic deformation grows until unloading starts at the collapsed section. Finally, several parametric dependencies of the extent of the collapse behavior are discussed based on a series of the simulations.     

A consideration of the structural design of a large-scale floating structure

The land area of Japan, especially flat land, is very small compared with its economic size. Large-scale floating structures are one solution to satisfy the demand for space by utilizing the ocean. This paper presents a general view of the dynamic response characteristics of large-scale floating structures, pontoons and semi-submersibles. For example, it is shown that the natural frequencies of eigenmodes are higher than the natural frequency of heaving motion. The response of the outer framework of a structure is shown to be generally larger than the response of the central part. Within the limits of our present understanding of the general dynamic response characteristics of such structures, the design and analysis of semi-submersible, large-scale floating structures is discussed. For a pontoon-type large-scale floating structure, a type whose perimeter structure has been modified to become lighter and more rigid is proposed. With this modification, the dynamic response of the whole structure is imporved.     

Parametric dependencies of the post-ultimate strength behavior of a ship’s hull girder in waves

To rationally assess the consequence of a ship’s hull girder collapse, it is necessary to know the post-ultimate strength behavior of the hull girder including the global deformation and motions under extreme wave-induced loads. In the foregoing research, the authors proposed a numerical analysis system to predict the collapse behavior in waves including the post-ultimate strength behavior. The primary objective of the present paper is to clarify the parametric dependencies of the severity of the collapse in a rational manner. The parameters may include those related to load-carrying capacity and the extreme loads. To this end, an analytical solution to describe the post-ultimate strength behavior is derived. Assuming that a plastic hinge is formed at the midship during the collapse procedure, the whole ship is modeled as a two-rigid-bodies system connected to each other amidship via a nonlinear rotational spring, which represents the nonlinear relationship between the bending moment and the rotational angle. The relationship may be modeled as piece-wise linear curves. It is further assumed that large motions and elastic/plastic deformations of the hull girder may not affect the load evaluations, and that the hull girder is subjected to a large single wave. Some important parameters to predict the severity of the collapse are specified based on the analytical solution.     

An Advanced Steering System with Active Kinesthetic Feedback for Handling Qualities Improvement

Advanced Steering System with artificial steering wheel torque-active kinesthetic information feedback for improving handling qualities is discussed. Fundamentally the structure of the system may be considered to another form of model following control. In this system, a driver always remains in the control loop and receives steering control information which give him/her a direct hint to steer a steering wheel. This system works as a stability and control augmentation system of the vehicle to improve the vehicle handling qualities both in compensatory and pursuit control task, and is expected to reduce driver's workload. Effects of this system are analyzed in terms of man-machine system characteristics. Identification of driver dynamics was carried out to find why such improvement could be achieved. Availability of the proposed system is verified by analysis, simulator and proving ground tests.     

外资物流企业如何在中国开展业务

一、中日间贸易和运输的概要说明 ●现状 2004年,中国超越美国成为日本的最大贸易伙伴国.静观近年来中日贸易额,日本对中国的进出口的比率从20%增长到40%.同时,进入中国市场的日本企业也在逐年剧增.据统计,2004年在华投资的日籍公司大约有4,300家,比去年增加了16%,所以我们确信今后这个比例会进一步增加.     

Hydrogen adsorption by woodceramics produced from biomass

Hydrogen adsorption characteristics of woodceramics, made from radiata pine wood fiber boards carbonized at 1 473K after impregnation with phenolic resin, with and without chemical treatment in an alkaline (KOH) or an acid (H₂SO₄) solution were investigated The hydrogen adsorption capacity is improved by chemical treatment. The chemical treatment by KOH improves the adsorption capacity more than by H₂SO₄. The improvement of the capacity level, in any solution, is dependent on the type of chemical in the solution and its concentration. The maximum hydrogen capacity measured at 93K is mass fraction about w(H) = 2% for the woodceramics after chemical treatment in a volume fraction ?? = 50% KOH solution, although that is about w(H) = 0.7% for one without chemical treatment. The microscopic condition of pores in the woodceramics is thought to vary after chemical treatment.     

Theoretical,experimental and numerical investigations into nonlinear motion of a tethered-buoy system

In this paper, we discuss nonlinear motion of a buoy connected vertically to the seabed via a tensioned tether (tethered-buoy). A series of scaled model tests has been conducted and a significant nonlinear behavior of the buoy motion, sub-harmonic motion in particular, is observed. Taking account of the influence of time-varying tether tension on the buoy motion, theoretical explanation is made for the sub-harmonic response. The stability of the tethered-buoy system is focused based on Mathieu instability theory. A strongly coupled numerical model between the buoy motion and the tether behavior is established to clarify the mechanism of the nonlinear motion of the tethered-buoy system. A comparison between the experiment data and simulation results is presented not only for the linear but also for the sub-harmonic components. Influential factors for the sub-harmonic motion are discussed in detail. It turned out that the sub-harmonic motion is dominated by the nonlinear coupling effect of time-varying tension in the tether with the buoy motion. Finally, the influential factors to the sub-harmonic motion are indicated throughout the comparison between two different buoy models.     

HCCI combustion characteristics during operation on DME and methane fuels

The Homogeneous Charge Compression Ignition (HCCI) engine has attracted much interest because it can simultaneously achieve high efficiency and low emissions. However, the ignition timing is difficult to control because this engine has no physical ignition mechanism. In addition, combustion proceeds very rapidly because the premixed mixture ignites simultaneously at multiple locations in the cylinder, making it difficult to increase the operating load. In this study, an HCCI engine was operated using blended test fuels comprised of dimethyl ether (DME) and methane, each of which have different ignition characteristics. The effects of mixing ratios and absolute quantities of the two types of fuel on the ignition timing and rapidity of combustion were investigated. Cool flame reaction behavior, which significantly influences the ignition, was also analyzed in detail on the basis of in-cylinder spectroscopic measurements. The experimental results revealed that within the range of the experimental conditions used in this study, the quantity of DME supplied substantially influenced the ignition timing, whereas there was little observed effect from the quantity of methane supplied. Spectroscopic measurements of the behavior of a substance corresponding to HCHO also indicated that the quantity of DME supplied significantly influenced the cool flame behavior. However, the rapidity of combustion could not be controlled even by varying the mixing ratios of DME and methane. It was made clear that changes in the ignition timing substantially influence the rapidity of combustion.     

波浪中船体梁后极限强度特性的实验评估(英文)

Experimental investigations into the collapse behavior of a box-shape hull girder subjected to extreme wave-induced loads are presented.The experiment was performed using a scaled model in a tank.In the middle of the scaled model,sacrificial specimens with circular pillar and trough shapes which respectively show different bending moment-displacement characteristics were mounted to compare the dynamic collapse characteristics of the hull girder in waves.The specimens were designed by using finite element(FE)-analysis.Prior to the tank tests,static four-point-bending tests were conducted to detect the load-carrying capacity of the hull girder.It was shown that the load-carrying capacity of a ship including reduction of the capacity after the ultimate strength can be reproduced experimentally by employing the trough type specimens.Tank tests using these specimens were performed under a focused wave in which the hull girder collapses under once and repetitive focused waves.It was shown from the multiple collapse tests that the increase rate of collapse becomes higher once the load-carrying capacity enters the reduction path while the increase rate is lower before reaching the ultimate strength.