Hidemi Mutsuda

Kinematics of overturning solitary waves and their relations to breaker types

Abstract Numerical simulations using a full-nonlinear BIM (Boundary Integral Method) potential-theory wave model are carried out to study the internal velocity and acceleration fields of an solitary wave overturning on a reef with vertical face (submerged breakwater) and their relation to breaker type. The simulations make it clear that the jet size normalized by the incident wave height is uniquely governed by the crown height of the reef, while the jet shape is similar and independent of the size. Further, they reveal that the overall internal kinematics of overturning waves is clearly related to the jet size. As the jet size increases and the breaker type changes from spilling to plunging, the kinematics thus become increasingly different from those of steady waves. Water particles with the greatest velocities or accelerations within the wave converge towards the jet. After the breaking, both of the velocities and accelerations almost simultaneously reach extreme values near locations beneath the jet. Some of the extreme values are closely related to the breaker type and can be uniquely determined by substituting the breaker type index into the regression equations suggested here.

An experimental study of power generation and storage using a flexible piezoelectric device

An experimental study of a small, efficient and flexible piezoelectric power generator is presented herein. Forced vibration experiments were performed and the results show linearity between amplitude of output voltage and maximum vibration velocity. Experiments for storage of the power generated were also performed. These confirmed that the power can be stored in capacitors with the time derivative of the stored energy being independent of the capacitance value.

RELATIONSHIPS OF PLUNGING JET SIZE TO KINEMATICS OF BREAKING WAVES WITH SPRAY AND ENTRAINED AIR BUBBLES

Wave breaking processes inducing violent transition of wave shapes and internal kinematics are investigated through laboratory experiments using flow visualization techniques, and through numerical...

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

Forced vibration experiments on flexible piezoelectric devices operating in air and water environments

In this paper, forced vibration experiments on flexible piezoelectric devices operating in both air and water environ- ments are discussed. Validation of the theoretical analysis method for such devices, via experimental means, is needed in order to achieve future cost effective design optimisations. In aim of this, numerous devices of differing dimensions are manufactured and tested, in various operating conditions, with comparison and discussion to simulation results provided.

CAUSE AND CHARACTERISTICS OF IMPACT PRESSURE EXERTED BY SPILLING AND PLUNGING BREAKERS ON A VERTICAL WALL

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

Wind Energy Harvesting Using Flexible Piezoelectric Device

We have developed a flexible piezoelectric device (FPED) composed of polyvinylidene fluoride (PVDF) and functional resin to generate electric power from wind energy with wide range in frequency. We made clear electrical characteristics of the FPED generated by wind power and availability of an attached bluff body in uniform wind. Moreover, we also validated electric performance of the FPED which is laminated with a stretching resin and has a roughness surface such as woolen and small hemisphere. We showed that both a force caused by breeze and wind energy with wide range of spectrum could be harvested effectively using the FPED.

Simply-supported multi-layered beams for energy harvesting:

This paper develops an analytical model for predicting the performance of simply-supported multi-layered piezoelectric vibrating energy harvesters. The model includes the effects of material and geometric non-linearities, as well as axial pre-tension/compression, and is validated against experimental devices for a large range of base accelerations. Numerical and experimental investigations are performed to understand the benefits of using simply-supported devices compared to cantilevered devices. Comparisons are made in an unbiased manner by tuning the resonant frequency to the same value by modifying the geometry, and the results obtained indicate that simply-supported devices are capable of generating higher voltage levels than cantilever devices. The model is also used to investigate the benefits of using multi-layered devices to improve power density. Depending on harvester composition, power-per-unit-volume of piezoelectric material for a device is increased through the stacking of layers.