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.     

Transformation Plasticity─The Effect on Metallo-Thermo-Mechanical Simulation of Carburized Quenching Process

IntroductionInelashcorhaersiblestrainaccompaniedbyslidingofcrystalsduetothermalandphasetransformationdilatationiswellknowntointensivelythethedistonionofworkpieceunderqUopching,andsomanynumericalsimulatonsll-7]havebeencAnedoutintheframeworkofmotallochermo-mechwhcsl1].Transformationplasticity(TP),anothekindofbeversiblestrain,isalsorecognizedasoneofdominantparwtersthechngthestr6ssanddistorton,andsomenumcricalcalculationaremadebytakingtheeffectintoconsideration.Figurelschematicallyillustraresthe…     

Tributyltin in marine sediments and Philippine green mussels (Perna viridis) in Manila Bay

Tributyltin (TBT) is a pollutant, mainly introduced to the environment as insecticides, fungicides, bactericides, wood preservatives and marine antifouling agent. Concentrations of TBT and its degradation products were isolated from the bivalve Perna viridis and marine sediments collected from selected coastal areas along Manila Bay. In all samples, the extremely toxic TBT compound was detected, calculated as Sn. In sediments, measured concentration ranged from the limit of detection of 0.5 to 9.0 ng Sn g^?1. Highest levels of TBT were observed at the inner and northern part of the bay, adjacent to coastal areas of varying land and water use (i.e., aquaculture, fishpond, mangrove forests, industrial establishments, and ports). However, the levels decrease near the bay entrance. Accumulation in this area can also be deduced from the movement of the prevailing wind and hydrodynamic behavior of the bay during the time of sampling, which transports suspended sediments from the eastern coast of Manila to the northern coast of Bulacan. In green mussels, the levels of TBT ranged from 2.1 to 8.9 ng Sn g^?1. While these values are relatively low, concentrations as low as 0.659 ng Sn g^?1 have been reported to be toxic to molluscs. The environmental levels of organotin species determined in the samples are comparatively low by global standards. Nevertheless, there is a need to estimate the levels of TBT in coastal waters and its associated uses, to evaluate the effectiveness of imposed regulation prohibiting the application of organotin compounds (OTs) as biocides in antifouling agents on ships and aquaculture facilities.     

跨临界CO_2热泵热水器的性能

为了研究跨临界CO2热泵热水器制冷剂充注量对制热系数的影响,通过调节变频压缩机频率与电子膨胀阀脉冲,在制热量与压缩机入口过热度一定的条件下,对制热系数、压缩比、吸气和排气压力等与制冷剂充注量的关系进行了实验研究.结果表明:随着制冷剂充注量的增加,压缩机的排气压力上升,气体冷却器出口制冷剂的温度下降;随着蒸发器中热源水入口温度的上升,吸气压力上升,压缩比和排气温度下降;最大制热系数随热源水入口温度的上升而增大.当热源水入口温度为15℃且压缩机入口过热度为5℃时,系统的最大制热系数为3.25,最佳制冷剂充注量为1.7 kg.     

The Japanese experience with mini‐cars

Despite the early appeal of the light vehicle, increases in the average annual income have allowed consumers to consider a broader range of vehicles so that the negative aspects of mini‐vehicles such as higher noise and vibration levels, the lack of horsepower and instability in certain driving conditions have made light vehicles less tolerable. The “oil shock” shattered economic projections, and people began to acknowledge that living in a world with limited resources was a harsh reality. Concurrently, congestion increased dramatically in urban areas as a result of the popularity of automobiles, and producers made a number of design changes to improve the safety and comfort limitations of light vehicles. Thus, in a world where fuel economy and ease of use gained a greater meaning, light vehicles slowly regained their original appeal.

Light vehicles may play a greater role in the future. Studies indicate that light vehicles tend to be driven by females and elderly people and current trends indicate that the number of female drivers is increasing and that the average age of the Japanese population is getting higher. Furthermore, migration patterns indicate that a greater number of people are moving to smaller cities and their outlying areas as a result of national decentralization policies. The migration pattern may popularize light vehicles because vehicle ownership rates are higher in these areas than in larger cities. Another development which may increase the popularity of light vehicles is that more families are owning more than one car and light vehicles are popular as second vehicles. Moreover, the prospects of low economic growth have tempered the importance of comfortable amenities, and the virtues of maneuverability and fuel economy have become more important.

     

Behavioral modeling of Pagrus major in the East Seto Inland Sea

Evaluation of the behaviors of fish that belong to higher levels of the food web is important from the viewpoint of resource management and other environmental issues. Especially for adult fish that can swim against the surrounding currents, it is quite important to consider migration effects when modeling fish behavior. In the present study, a model of fish behavior is developed that considers the migration effect by incorporating a preference for various environmental factors. The species to be modeled, Pagrus major, was chosen because its high value as a food makes it representative of an exploited fish species. In the developed model, the direction of the fish movement is determined by the strength of preference for environmental factors of water temperature, salinity, dissolved oxygen, and prey density. The model is coupled with a hydrodynamic model and a lower-trophic ecosystem model, which predict the physical environment and water quality of the target area. Numerical simulations are carried out to reproduce the spatial distribution and seasonal variations of the ecosystem in the East Seto Inland Sea. Proper parameters for fish behavior were obtained through the processes of model tuning. As a result of the simulations, we clarified that the environmental conditions have a sizeable influence on the migration and distribution of Pagrus major. The developed model is also able to reproduce the fish biomass variation in time and space, which will provide more detailed information for resource management of the fish.     

Comparison of simulation results and field data on currents and density in Tokyo Bay

A multilevel model was applied to the calculation of permanent current and density variation in Tokyo Bay, and the change of the state of stratification and the accompanying current field was simulated. In the numerical simulation, the observed field data such as wind conditions and atmospheric temperature were used as input to the calculation, and the results were compared with the observed values of currents, salinity, and sea temperature. Comparison of simulation results and observed data revealed that the numerical simulation could describe well the current and density field governed by wind under stratified conditions. In particular, the long-term variations of the vertical structure of salinity and temperature from summer to autumn could be predicted qualitatively, as could the long-term variations of the vertical structure of salinity and temperature from summer to autumn. Additionally, the effects of boundary conditions on the results of numerical simulations were examined. As a result, it was clarified that the simulation results of salinity stratification were strongly affected by the boundary conditions such as river discharge and the vertical structure of salinity at the open boundary adjacent to the outer ocean.     

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.     

Sea trial of prototype Vertical Weight Stabilizer (VWS) anti-rolling system for small ships

Anti-rolling is an important technique for safety and efficient ship operation. In the era of sailing ships, rolling motions were not so severe compared to those of modern ships running by prime mover without sails, because the sail itself had a damping effect on rolling motion. After propeller driven ships exceeded sailing ships in number and performance, namely, from the end of the nineteenth century, many types of anti-rolling–related techniques were invented and developed, of both passive and active types. Recently (2009, 2010), as sea trials, we carried out proto-type experiments on an anti-rolling system and confirmed its effectiveness. The new concept utilizes the so-called Corioli’s effect, which appears in the rotational coordinate system. Usually, this effect is considered as virtual, but the real effect appears when a mass moves in the radial direction in a rotating coordinate system. In the case of ship rolling, the vertical motion of a mass generates Corioli’s force to finally generate anti-rolling moment. This is the reason the system was named Vertical Weight Stabilizer (VWS). This new system was invented in 1998 by Hirayama, and confirmed by the model experiments in a towing tank. Numerical simulations were carried out by the Sea and Air Control System laboratory of Yokohama National University, but the actual system could not be realized, because we could not find an appropriate actuator. The key technology for the success of the current sea experiment is the powerful, high-speed, compact actuator for the vertical movement of the weight. In this paper, we introduce this new concept by adopting a simple experiment, the control system with new actuator used in an actual sea experiment, and report on the successful results.