Numerical simulation of wave-induced nonlinear motions of a two-dimensional floating body by the moving particle semi-implicit method

The moving particle semi-implicit (MPS) method was applied to compute nonlinear motions of a floating body influenced by the water on deck. To compute the motions of a rigid body, the fluid pressure at the position of each particle on the body surface was directly integrated in space and the equations of translational and rotational motions were integrated in time to determine the correct position of the rigid-body surface at each time step of the time-domain calculation. The performance of this method was validated through a comparison with measured results in an experiment that was newly conducted using a model of a box-shaped floating body with a small freeboard. Although the overall agreement was good, some discrepancies were observed for a shorter wave period, especially for the drift motion in sway. The effect of numerical resolution on the results was checked by changing the number of particles. With a higher number of particles, no obvious improvement was seen in the global body motions, but the resolution of the local free-surface profile, including the water on deck, was improved.     

Decisions on truck parking place and time on expressways: an analysis using digital tachograph data

With the objective of deriving useful insights into measures against traffic congestion at service areas (SAs) and parking areas (PAs) on expressways and ensuring efficient use of SAs/PAs, this study investigated the decisions on where a truck is parked (i.e., choice of an SA or a PA), how long it is parked (i.e., parking time), and their influential factors. To this end, this study used the trajectory data of 1600 trucks recorded in 6-min intervals by in-vehicle digital tachographs on the Sanyo and Chugoku Expressways in Japan from October 2013 to March 2014. First, the aspect of repeated choice of each truck (i.e., habitual behavior) toward a specific SA/PA was clarified. Next, a multilevel discrete–continuous model (Type II Tobit model) was developed to reveal the factors affecting the above decisions. The modeling results confirmed the existence of habitual behavior and showed that trucks were more likely to be parked a longer time at an SA/PA when it is closer to the destination. It appears that truck drivers may adjust their time at the SA/PA close to the destination to comply with the arrival time, which is often predetermined by the owner of the transported goods. Furthermore, the availability of restaurants and shops, and the number of parking spaces available for trucks and trailers are important determinants of parking time, whereas the existence of a convenience store is important to the choice of the SA/PA. Parking experience has an extremely strong positive effect on the parking choice and use. Moreover, increasing the number of parking lots may induce its longer use.

     

Motion response prediction by hybrid panel-stick models for a semi-submersible with bracings

A diffraction-radiation analysis is usually required when the hydrodynamic interactions between structural members occur in short waves. For bracings or small cylindrical members, which play important roles in the vicinity of the natural frequency of a floating platform, special care should be taken into account for the effect of viscous damping. Two hybrid panel-stick models are, therefore, developed, through the combination of the standard diffraction-radiation method and the Morison’s formulae, considering the effect of small members differently. The fluid velocity is obtained directly by the panel model. The viscous fluid force is calculated for individual members by the stick model. A semi-submersible type platform with a number of fine cylindrical structures, which is designed as a floating foundation for multiple wind turbines, is analyzed as a numerical example. The results show that viscous force has significant influence on the hydrodynamic behavior of the floating body and can successfully be considered by the proposed hybrid models.     

溃坝问题的数值仿真和实验(英文)

In this paper, two novel numerical computation methods are introduced which have been recently developed at Research Institute for Applied Mechanics ( RIAM ), Kyushu University, for strongly nonlinear wave-body interaction problems, such as ship motions in rough seas and resulting green-water impact on deck. The first method is the CIP-based Cartesian grid method, in which the free surface flow is treated as a multi-phase flow which is solved using a Cartesian grid. The second method is the MPS method, which is a so-called particle method and hence no grid is used. The features and calculation procedures of these numerical methods are described. One validation computation against a newly conducted experiment on a dam break problem, which is also described in this paper, is presented.     

A study on improving the course-keeping ability of a pure car carrier in windy conditions

The course-keeping ability of a pure car carrier (PCC) in windy conditions is discussed in this article. Numerical simulations of two PCCs were carried out to compare their course-keeping abilities in wind. The two PCCs had the same hull form but different types of rudder. One PCC was fitted with a semispade rudder (hereinafter, the normal rudder), whereas the other was fitted with a spade-type Schilling rudder (hereinafter, the Schilling rudder). Both PCCs were designed to a new concept for the accommodation structure and hull form above the load water line. In this new design concept, there are no sharp corners in the superstructure so as to reduce wind resistance and improve steering performance. The limits of course keeping for the two PCCs were investigated through simulations. The course-keeping abilities of the two PCCs, each with two different types of autopilot system, were also investigated in wind. To develop the numerical simulation, the hydrodynamic coefficients of the two PCCs were predicted based on the data published for a third PCC having similar principal particulars. The numerical model of the two PCCs was validated by comparing its behavior with the respective full-scale trial results. Wind resistance coefficients were predicted by combining the results of wind tunnel experiments of the object PCCs and a regression model. Numerical simulations under steady wind conditions were also carried out and the results compared with some full-scale experiments to validate the mathematical model of the PCC.     

Study of Ecological Impact Regionalization of Expressway Construction in Guangxi

在综合分析广西公路建设生态影响特点的基础上,探讨了生态影响区划的原则和依据,建立了各级生态影响区单元划分的指标体系.本区划采用二级区划,即地貌侵蚀动力大区和生态敏感区.其中各级区划指标包括:海拔高度、年暴雨天数、年干旱天数、公路隔离效应指数、植被类型、土地石漠化程度和自然保护区分布等.本区划共分为4个一级区和11个二级区,便于在公路设计、建设和营运管理中采取目标明确的影响抑制措施.     

A genetic algorithm for the hub-and-spoke problem applied to containerized cargo transport

A genetic algorithm for the hub-and-spoke problem (GAHP) is proposed in this work. The GAHP configures a hub-and-spoke network with shuttle services for containerized cargo transport. For a fixed number of hubs, it determines the best network configuration of hub locations and spoke allocations that minimizes the total costs of the system. The GAHP has a simple individual structure with integer number representation, where spokes, their allocations, and hub locations are easily recognized. Due to the characteristics of the problem, which has fixed number of hubs, rearrangements should be performed after every process. The GAHP rearrangement process includes improvements of individual structures, resulting in an improved population. Before applying the GAHP to the container transport network problem, the algorithm is validated using the Civil Aeronautics Board data set, which is extensively used in the literature to benchmark heuristics of hub location problems. To illustrate an example of a hub-and-spoke network with shuttle services, a study case with 18 ports is analyzed.     

Hydrodynamics of a body floating in a two-layer fluid of finite depth. Part 2. Diffraction problem and wave-induced motions

A linearized two-dimensional diffraction problem in a two-layer fluid of finite depth was solved for a general floating body and relevant wave-induced motions were studied. In a two-layer fluid, for a prescribed frequency, incident waves propagate with two different wave modes. Thus the wave-exciting forces and resulting motions must be computed separately for each mode of the incident wave. The boundary integral equation method developed by the authors in the Part-1 article was applied to directly obtain the diffraction potential (pressure) on the body surface. With the computed results, an investigation was carried out on the effects of the fluid density ratio and the interface position on the wave-exciting forces on the body and the motions of the body, including the case in which the body intersects the interface. By a systematic derivation using Green's theorem, all the possible reciprocity relations were derived theoretically in explicit forms for a system of finite depth; these relations were confirmed to be satisfied numerically with very good accuracy. Experiments were also carried out using water and isoparaffin oil as the two fluids and a Lewis-form body. Measured results for the sway- and heave-exciting forces and the heave motion were compared with the computed results, and a favorable agreement was found.     

Dispersion of spilled oil by a cavitating jet at sea

This article presents the possibility of using a high-speed water jet for the dispersion of spilled oil at sea. Laboratory experiments showed that a high-speed water jet is very effective in dispersing heavy oil. Two methods were examined and compared using freshwater. The first method was to disperse an oil layer on the water surface using a cavitating jet ejected upward at an angle of 45°. A target plate was placed at the interface of the water and oil layer to enhance the collapse of cavitating bubbles. The second method was to eject a high-speed water jet vertically downward from the air. A guide plate with a guide hole was placed under the oil layer with no target plate as such. The second method showed an improved dispersion ability and thus its effectiveness was examined using an oil layer on seawater. The dispersion of oil was better in seawater than in freshwater, probably because seawater contains natural surfactants.     

半干旱地区公路岩质边坡植被恢复技术工程试验——以内蒙古赤峰-通辽高速公路为例

针对半干旱地区公路岩质边坡的生态恢复难题,以内蒙古赤峰-通辽高速公路某岩质边坡为例,采用保育块技术与客土喷播技术相结合的方法构建以木本(灌木)为主、草本植物为辅的坡面植物群落。试验结果表明,此方法可使木本植物成活率达到60%以上且长势良好;草本植物生长茂盛,地上部生物量达自然阴坡生物量水平;物种构成以木本植物和多年生草本植物为主,群落稳定且植被覆盖度高于70%;移植的保育块树苗的根系结构与天然树木相似,具有主根发达、侧根不多但较强壮、根系呈网络状深入土中等特征。