Yasuaki Doi

Numerical Simulation of Dynamic Response of Structure Caused by Wave Impact Pressure Using an Eulerian Scheme With Lagrangian Particles

This study focuses on the development of computational techniques for computing fluid-structure interaction with wave breaking. This is of practical relevance in both ocean, and ship hydrodynamics. This paper also presents a prediction of the local highly pressure load impacting on a rigid and elastic structure caused by fluid force including impact pressure. We have developed a new numerical scheme that combines a Eulerian scheme with Lagrangian particles, i.e. free surface particles and SPH particles, to compute fluid-structure interaction caused by impact pressure. In this model, we employed two kinds of particles. One is free surface particle located near the free surface to capture air-water interface accurately. The other one is SPH particle to compute solid motion and elastic deformation. The air-water mixing flow is treated on a fixed Eulerian grid with the free surface particles to rebuild the density function for capturing the interface in filamentary regions that are under-resolved. Conversely, the structure is solved using the particle method, SPH. These Lagrangian particles are useful and available to capture the interface between different phases. In this paper, the proposed method was applied to the water entry problems of a V-shaped wedge, a horizontal flat-plate, a circular cylinder, an elastic cylindrical shell and impact pressure acting on an elastic wall caused by wave breaking. The free surface and elastic deformation are compared with both numerical and experimental results. The pressure and strain predictions are also compared with experimental results obtained by other researchers.Copyright

Ocean Power Generator Using Flexible Piezoelectric Device

We have developed a way of harvesting electrical energy from ocean power, e.g. tide, current wave, breaking wave and vortex, using a Flexible PiezoElectric Device (FPED) consisting of polyvinyledene fluoride (PVDF) and elastic material such as rubber, silicon and resin. The proposed FPED has a multi-layered structure with a distance δ between FPEDs located away from centerline of the FPED. When the FPED can be easily deformed by ocean power, the PVDF laminated in the FPED can be expanded and compressed and then the internal strain energy can be stored in the FPED. The electric power is generated when the electric polarization occurs in the PVDF.In this study, we have proposed an ocean power generator of EFHAS (Elastic Floating unit with HAnging Structures) consisting of floating unit and hanging unit using the FPEDs to obtain electric power from ocean energy. We investigated a structure of the EFHAS and also examined characteristics of motion and electric performance of the EFHAS (1/50–1/75 scale model. We made clear that the EFHAS could be useful as ocean power generator.Copyright

Elastic Floating Unit With Piezoelectric Device for Harvesting Ocean Wave Energy

The purpose of this study is to improve FPED (Flexible PiEzoelectric Device) we have developed. The FPED consisting of piezo-electric polymer film (PVDF) is a way of harvesting electrical energy from ocean power, e.g. tide, current, wave, breaking wave and vortex. We also propose an Elastic Floating unit with HAanging Structures (EFHAS) using FPED. The EFHAS consists of floating unit and hanging unit. In this study, we investigated electric performance of FPED and EFHAS and also modified internal structure of FPED to increase electrical efficiency. As a result, Electric performance is increasing with increasing number of PVDFs laminated in FPED. Multilayer type of FPED can rapidly increase electric efficiency. Electric power can be improved by FPED attached a bluff body with relative density. Electric performance of floating type for floating unit of EFHAS is better than that of submerged type. Distance L/λ = 0.4 between floaters of floating unit is suitable for highly electric performance. In hanging unit of EFHAS, it is possible to increase electric power per unit area with increasing number of stairs. In conclusion, we showed the EFHAS with the FPED could be useful for harvesting ocean wave energy.Copyright

Coupled Analysis of Unsteady Aerodynamics and Vehicle Motion of a Heavy Duty Truck in Wind Gusts

In the present study, unsteady aerodynamic forces acting on a simplified heavy duty truck in strong wind gust and their effects on the truck’s motion were investigated by using a coupled analysis. Unsteady fluid dynamics simulation was applied to numerically reproduce unsteady aerodynamic forces acting on the truck under sudden crosswind condition. Taking account of vehicle’s motion, moving boundary techniques were introduced. Motions of the truck were simulated by a vehicle dynamics simulation including a driver’s reaction. The equations of motion of the truck in longitudinal, lateral, and yaw-rotational directions were numerically solved. These aerodynamics and vehicle dynamics simulations were coupled by exchanging the aerodynamic forces and the vehicle’s motion. In order to investigate effects of the unsteady vehicle aerodynamics on the vehicle’s motion, conventional analysis of the vehicle’s motion using quasi-steady aerodynamic forces and one-way coupled analysis with fixed vehicle attitude were also conducted. The numerical results of these simulations were compared with each other, and the effects of the two kinds of unsteady aerodynamics were discussed separately and totally. In the sudden crosswind condition, the unsteady aerodynamics effected significantly on the truck’s motion. An effect of transient aerodynamics as the truck ran into a sudden crosswind was greater than an effect of unsteady aerodynamics caused by unsteady vehicle’s motion, while both of the effects showed significance.Copyright

Unsteady Aerodynamics Simulation of a Heavy-Duty Truck in Wind Gusts Coupled With Vehicle Motion Analysis in Six Degrees of Freedom

A one-way coupled analysis was used to investigate both the unsteady aerodynamic forces on a simplified heavy-duty truck in strong wind gusts and their effects on its motion. The vehicle model for the dynamics simulation was extended to six degrees of freedom (6DoF). First, a transitional aerodynamics simulation was conducted for the simplified truck with a fixed vehicle attitude but subject to a sudden crosswind. Based on the visualized results of this aerodynamics simulation, flow phenomena generating transitional aerodynamic forces and moments are discussed, especially those acting in the vertical direction. While the truck was running into the crosswind region, the growth and breakdown of a large-scale vortex above the container generated a transitional behavior of aerodynamic lift and pitching moment. Next, time series of the six components of the aerodynamic forces and moments were input into the vehicle dynamics simulation. By comparing the results with those of a quasi-steady aerodynamics simulation, the effect of transitional aerodynamics on vertical motions was clarified, with the largest difference found in a rolling motion. Moreover, the effect of considering 6DoF was investigated by also conducting the vehicle dynamics simulation with 3DoF. The consideration of dynamics in the vertical direction changed the estimation of tire forces, which were related to a vertical load on the tire. Finally, the effects of considering 6DoF were also identified for horizontal motions.Copyright

A Technology of Electrical Energy Generated From Ocean Power Using Flexible Piezoelectric Device

We have developed a way of harvesting electrical energy from the ocean power, e.g. tide, current, wave, breaking wave and vortex, using a flexible piezoelectric device consisting of piezo-electric polymer film (PVDF), silicon and natural rubber. The flexible piezoelectric device (FPED) is a hydro-electric ocean energy converter designed to convert renewable energy harnessed from ocean energy into usable electricity. The basic concept generating electric power using FPED is to utilize fluid structure interaction, e.g. flattering, flapping and periodic bending, caused by ocean energy. The FPED deformed by kinetic energy of the ocean power stores elastic energy and also converts it to the electric energy. We carried out some experiments using wave tank and the water tunnel with a bluff body. We have confirmed the electricity generated by wave, current and vortex using the FPED. The developed FPED could be a new technology of harvesting electrical energy from the ocean power. A floating platform attached FPED could be coupled with an offshore wind turbine as a hybrid energy system in ocean space.Copyright

Coupled Analysis of Unsteady Aerodynamics and 6DOF Motion of a Heavy Duty Truck in Strong Wind Gusts

In this study, a one-way coupled simulation of unsteady aerodynamics and vehicle dynamics has been applied to a heavy duty truck subject to a sudden crosswind. Transient aerodynamic forces and moments were predicted by a large-eddy simulation (LES) technique assuming that the truck was in a straight running with fixed attitude. In the numerical result, overshooting profiles of aerodynamic forces and moments were observed. Then, they were input to a vehicle dynamics simulation for the coupled analysis. In order to investigate bouncing, pitching and rolling motions of the vehicle, the vehicle dynamics simulation method has been extended to the six degrees of freedom (6DOF) motion. The result indicated that the vertical motions could change a clearance under the truck’s body significantly. The numerical results were compared with a vehicle dynamics simulation with three degrees of freedom (3DOF) in the horizontal directions. The yaw rate, which strongly relates to driver’s feeling of stability, showed quantitatively different behaviors though the trajectory of the truck was almost similar to each other simulation. The effect of transient aerodynamic forces and moments were also discussed. Additional vehicle dynamics simulation based on a quasi-steady aerodynamics assumption was conducted and the result was also compared with the coupled simulation. Effect of the transient aerodynamic forces and moments, which appeared only in the one-way coupled simulation were clarified for the vehicle motions in all directions.

HIGHLY ACCURATE FREE SURFACE CAPTURING TECHNIQUE FOR WAVE BREAKING

We developed a new fluid solver that combines the advantages of both a Lagrangian scheme and an Eulerian scheme. The massless Lagrangian marker particles are put into the Eulerian grid and advected to capture accurately the free surface. The applicability of the present method was demonstrated for dam breaking, wave breaking in shallow water, impact pressure acting on a vertical wall. The efficiency and the accuracy were also investigated. The numerical results showed good agreement with numerical and experimental results performed by other researchers.

Numerical investigation into the restoration of ocean environments using steelmaking slag

Steelmaking slag has been utilized in shore protection and to improve ocean environments of sea bottom sediments in semi-enclosed areas and coastal regions. This is achieved by reducing dissolved sulphide concentration. In this study, a numerical model is proposed and developed using a Eulerian-Lagrangian model coupled with an ocean circulation model to compute advection-diffusion of dissolved sulphides and fluid-particle interactions between ocean circulation and steelmaking slag. We applied the model to the Fukuyama inner harbour in the Seto Inland Sea and Tokyo Bay and compared our results with field data. The numerical results show good agreement with the field results. We demonstrate that steelmaking slag can control advection-diffusion with regard to concentration of hydrogen sulphide. The steelmaking slag could be a useful material in restoration of ocean environments at enclosed sea areas.

SEASONAL CHANGE OF OYSTER RAFT PLACEMENT AND SEAWATER EXCHAGE IN ETAJIMA BAY

To evaluate impacts of oyster raft placement on tidal current and seawater exchange in Etajima Bay, northern part of Hiroshima Bay, we have developed a coastal circulation model incorporating the drag force of the oyster raft in Etajima Bay. We found that the number of oyster rafts in summer season is twice as large as that in winter season. In Etajima Bay, the seawater exchange is relatively large in the northwest part, whereas the term of the seawater exchange is about one year in the southern part. Moreover, we computed some scenarios which the oyster rafts are reduced at each zone, and then it could be desirable to reduce 40% of the total number of oyster rafts in order to make a plane for reducing organic matter load from the oyster culture.