Studies on the optimization of stern hull form based on a potential flow solver

A hypothesis of the minimum energy of secondary flow, suggested by Bessho, is introduced here. According to this hypothesis, it can be expected that hull forms having frame lines with a minimum energy of secondary flow show less form drag. In the first part of this article, secondary flow energy is evaluated for the cases with and without a free-surface effect, and Bessho’s hypothesis is confirmed for practical hull forms. Then optimization methods for the stern hull form are suggested, in which a nonlinear optimization technique is introduced. Numerical examples are given for a practical tanker hull form and a practical container hull form. From these studies, the suggested optimization method can be confirmed as a simplified and practical design method to the select frame lines of stern hull forms.     

新西海桥的振动特性及舒适性评价研究

以日本首座公路钢管混凝土拱桥——新西海桥为对象,进行该桥的自由振动特性分析,采用考虑路面不平整的桥梁与车辆相互作用力学模型,分析了在移动车辆作用下该桥的动力特性,包括冲击系数和舒适度评价。研究结果表明,在移动车辆作用下钢管混凝土拱桥主跨的拱肋和桥面冲击系数都较小,钢管混凝土拱肋的振动小于主桥桥面的振动。从振动舒适性的观点看,采用纵横梁格构桥道体系的新西海桥在车辆荷载作用下拱肋、桥面和人行桥均满足舒适性要求,具有较好的行车性能。     

货物的时间价值的评估方法及应用研究

时间价值在分析交通行为，定量地评价交通项目的经济效益中都起到十分重要的作用。本研究的目的是提供一个货物时间价值的估计方法。本研究根据非集合行为模型建立货物时间价值的估计模型，运用日本的调查数据，探讨评估货物时间价值的应用问题，并估计时间价值。     

Design system for optimum contra-rotating propellers

A new type of contrarotating propeller (CRP) system has been developed through the cooperative research work of five shipbuilding companies in Japan (Hitachi Zosen Corporation; Kawasaki Heavy Industries, Ltd.; Mitsui Engineering and Shipbuilding Co., Ltd.; NKK Corporation; and Sumitomo Heavy Industries, Ltd.). This paper describes a design system for an optimum CRP, which is one of the numerous outcomes of this work. The optimum design system is composed of three theoretical programs: (1) the design program of the optimum CRP; (2) the steady lifting surface program of the CRP; (3) the unsteady lifting surface program of the CRP. These theoretical programs will be discussed in the first part of the paper, and the design system supported by these theoretical programs will then be verified by comparing calculated and experimental results.Translation of an article that appeared in the Journal of The Society of Naval Architects of Japan, vol. 180 (1996): The original article won the SNAJ prize, which is awarded annually to the best papers selected from the SNAJ Journal, JMST, or other quality journals in the field of naval architecture and ocean engineering.     

Two-dimensional numerical simulation of water splash phenomena with and without surface tension

Two-dimensional numerical analyses were conducted and analyzed to simulate water splash produced by free falling object models starting from the resting position. The equilateral prism-shaped object models were allowed to fall onto the free surface of the water. The moving-particle semi-implicit (MPS) method was used to solve the unsteady Navier-Stokes equation for incompressible fluid flows with and without the surface tension effect. Froude numbers of 0.75, 1.0, and 1.25 were used with different model sizes for the entry velocity at the free surface. Splashes obtained by numerical computation closely agreed with the experimental results. The surface tension force, the Froude number, and the Weber number were found in these calculations to play major roles in determining various types of splash shapes. Model size was found to influence splash phenomena, even if the Froude number remained the same. The dependencies on these two nondimensional numbers and the fundamental law of similarity on water splash with and without the surface tension effect were thoroughly investigated in this research. Several two-dimensional numerical simulations are presented in this article to describe the hydrodynamic behaviors of water splash with and without the surface tension effect.     

Hydrodynamic optimization of a catamaran hull with large bow and stern bulbs installed on the center plane of the catamaran

Here, a numerical optimization procedure is proposed for a fundamental study of a fast catamaran, and we compare the wave-making characteristics of a catamaran hull form with and without large bow and stern airship-type bulbs installed on the center plane of a catamaran operating at high speed. The method involves coupled ideas from two distinct research fields: numerical ship hydrodynamics and a nonlinear programming technique. The wave-making characteristics of catamaran hulls with and without bulbs were investigated using the panel method applied to free surface flow (PAFS), in which Morinos method for lifting bodies is extended to analyze the problem of free surface flow, and PAFS is linked to the optimization procedure of the sequential quadratic programming (SQP) technique. An optimum hull form for a catamaran can be obtained through a series of iterative computations, subject to some design constraints. Here, only the hull shape of a catamaran is optimized with and without center-plane bow and stern bulbs. The optimization is carried out at two Froude numbers, 0.45 and 0.5, which are around the last hump of the wave-making resistance curve. The numerical results show that a reduction in wave-making resistance is achieved around the design speed.     

Hydrodynamic optimization of ship hull forms in shallow water

A computational method for improving hull form in shallow water with respect to wave resistance is presented. The method involves coupling ideas from two distinct research fields: numerical ship hydrodynamics and nonlinear programming techniques. The wave resistance is estimated by means of Morinos panel method, which is extended to free surface flow and considers the influence of finite depth on the wave resistance of ships. This is linked to the optimization procedure of the sequential quadratic programming (SQP) technique, and an optimum hull form can be obtained through a series of iterations giving some design constraints. Sinkage is an important factor in shallow water, and this method considers sinkage as a hydrodynamic design constraint. The optimization procedure developed is demonstrated by selecting a Wigley (C _B = 0.444) hull and the Series 60 (C _B = 0.60) hull, and new hull forms are obtained at Froude number 0.316. The Froude number specified corresponds to a lower than critical speed since most of the ships operating in shallow water move below their critical speed. The numerical results of the optimization procedure indicate that the optimized hull forms yields a reduction in wave resistance.     

Socioeconomic Conditions and Perceptions of Environmental Risks in the Mekong Delta,Vietnam

This study investigates the effects of sociodemographic and economic status on the differences in environmental awareness, risk perception, and stewardship of the Mekong Delta residents based on a survey conducted in person with 1,006 households across the delta system. Spatial visualization and a multiple correspondence analysis (MCA) were performed on the survey results to discover underlying factors of the participants' responses. The study results revealed that public environmental awareness in the Mekong Delta is still limited. The level of environmental awareness, risk perception, and understanding of stewardship of local people varies by location. Furthermore, how the Mekong Delta dwellers perceive environmental risks and behave toward environmental protection is unlikely to be influenced by their demographic profiles. However, they are significantly affected by the economic status including income levels and sources. Poor economic status was found to significantly hamper pro-environmental behavior of Mekong Delta people regardless of their knowledge of environmental degradation and the related consequences. These findings provide key information to assist policymakers in developing a successful and sustainable disaster risk reduction mitigation plan for the Mekong Delta region. The implications may also be applicable for other coastal zones, which are composed of similar sociodemographic, economic, and environmental conditions.     

Measurement of intention to travel: Considering the effect of telecommunications on trips

Mobility, one of the key concepts to evaluate the effect of a transportation policy such as TDM and mobility management as well as to analyze the problems such as social exclusion, must be measured by how much of an intention to make a trip can be realized, not merely by how many trips are available. The advent of new communication tools such as the Internet and mobile phones has allowed one to accomplish certain tasks that previously required a trip. This new situation has brought up a discussion over the necessity to incorporate telecommunications as an aspect of mobility. Aware of such discussions, we analyzed the relationship between the number of trips and telecommunications based on the data we collected on trips, telecommunications, and activities, and found some significant correlations. Our study which used an ordered regression model found several significant relationships between the individual attributes and the number of trips/telecommunications. We formulated a model which assumes the latent factors among the trips and telecommunications. In addition, we found that the latent factors construable as intentions to trips and telecommunications could be measured better by e-mails than by trips. These results indicate that measuring mobility requires the inclusion of information about telecommunications.