A Prediction Method of Hydroelastic Motion of Aircushion Type Floating Structures Considering With Draft Effect Into Hydrodynamic Forces

2008 ◽  
Author(s):  
Tomoki Ikoma ◽  
Masato Kobayashi ◽  
Koichi Masuda ◽  
Chang-Kyu Rheem ◽  
Hisaaki Maeda
Keyword(s):  
Potential Theory ◽  
Water Waves ◽  
Large Scale ◽  
Prediction Method ◽  
Linear Potential ◽  
Wave Loads ◽  
Floating Structure ◽  
Model Experiments ◽  
Very Large Floating Structure ◽  
Linear Potential Theory

An aircushion type floating structure can prevent to enlarge the wave drifting force restraining the hydroelastic response of it in water waves. The floating structure should be large scale to incident waves in order to make the best use of such advantages, i.e. it is a very large floating structure. The linear potential theory is useful to easily handle the wave force etc. on the aircushion type floating structure theoretically because it is predicted that its theory can give good results of behaviors of water elevation within aircushions and pressure and of wave loads on the structure qualitatively. The authors have confirmed from our past model experiments that non-linear effect does not always increase but for some exceptions. A prediction method of hydroelastic responses for the aircushion type very large floating structure by using the three-dimensional linear potential theory is shown in this paper. The validity of the method is proven and the application of the method is investigated by comparing the theoretical results with the results of the past model experiments.

Primary Conversion Efficiency of OWC Type WECs Installed on a Large Floating Structure

2012 ◽  
Author(s):  
Tomoki Ikoma ◽  
Koichi Masuda ◽  
Chang-Kyu Rheem ◽  
Hisaaki Maeda ◽  
Yuka Watanabe
Keyword(s):  
Boundary Condition ◽  
Wave Energy ◽  
Large Scale ◽  
Prediction Method ◽  
Free Water ◽  
Wave Power ◽  
Linear Potential ◽  
Floating Structure ◽  
Distribution Method ◽  
Point Distribution

This paper describes the performance of wave power conversion. A large scale floating system on which oscillating water column type wave energy convertors installed is proposed and the efficiency of primary conversion of wave power is estimated. In this paper, a boundary condition due to OWC is theoretically modeled in order to consider influence of wave energy absorption to hydrodynamic forces on the floating structure into the three-dimensional singular point distribution method based on the linear potential theory. In the modeling, a boundary condition on a free water surface and an equation of state within an air-chamber above OWC are mathematically and linearly formulated. Air-pressures and variation of water elevation within OWC areas can be simultaneously and directly solved by setting both the variables and by solving the simultaneously equations of the air-pressure and the vertical displacement. The damper effect of OWC devices is taken into account. The validity of the prediction method proposed is proven by comparing with experimental results. There are three types of large scale wave energy platform which is a pontoon type in the paper. Each performance of the efficiency of primary conversion of wave power is estimated. It is shown that the performance is very good.

Hydroelastic Motion of Aircushion Type Large Floating Structures With Several Aircushions Using a Three-Dimensional Theory

2009 ◽  
Author(s):  
Tomoki Ikoma ◽  
Koichi Masuda ◽  
Chang-Kyu Rheem ◽  
Hisaaki Maeda ◽  
Mayumi Togane
Keyword(s):  
Theoretical Calculations ◽  
Three Dimensional ◽  
Prediction Method ◽  
Free Water ◽  
Bending Moment ◽  
Linear Potential ◽  
Floating Structures ◽  
Wide Wavelength Range ◽  
Linear Potential Theory ◽  
Vertical Bending Moment

This paper describes hydroelastic motion and effect of motion reduction of aircushion supported large floating structures. Motion reduction effects due to presence of aircushions have been confirmed from theoretical calculations with the zero-draft assumption. A three-dimensional prediction method has been developed for considering draft influence of division walls of aircushions. It is investigated that hydroelastic motion reduction is possible or not by using the three-dimensional theoretical calculations. In addition, the aircushion types are supported by many aircushions which are small related to wavelengths. The Green’s function method is applied to the prediction method with the linear potential theory in which effect of free water surfaces within aircushions are considered. Hydroelastic responses are estimated as not only elastic motion but also a vertical bending moment. From the results, the response reduction is confirmed, in particular, to the vertical bending moment in wide wavelength range and in whole structure area.

A Study on Predictions of Fully Nonlinear Motion Aircushion Type Floating Structures Using 2D MPS Method

2008 ◽  
Author(s):  
Mitsuhiro Masuda ◽  
Tomoki Ikoma ◽  
Koichi Masuda ◽  
Hisaaki Maeda
Keyword(s):  
Water Waves ◽  
Theoretical Calculations ◽  
Numerical Technique ◽  
Ocean Waves ◽  
Nonlinear Phenomena ◽  
Linear Potential ◽  
Floating Structure ◽  
Fully Nonlinear ◽  
Floating Structures ◽  
Mps Method

Very large floating structures (VLFSs) have been proposed for new ocean space utilization and many researches have been carried out. VLFSs are elastically deformed due to ocean waves because the rigidity of the structure decreases relatively. The authors examine the aircushion type floating structure in order to reduce hydroelastic motion. An aircushion type floating structure to which air-chambers are installed can reduce the wave drifting force and hydroelastic motion at the same time. Most theoretical calculations of motion of aircushion type floating structures in water waves have been done based on a linear potential theory so far. As a result, the utility of the aircushion has been proved. However fully nonlinear phenomena such as deck wetness, slamming and air-leakage cannot be investigated by using existing calculations based on the linear theory. In this study, a computer program code of the two-dimensional MPS method that can consider fully nonlinear influence is developed and then the air layer inside an aircushion is expressed with particles of the MPS. Moreover, the numerical technique for introducing directly the mooring force into the motion equation of the particle is developed. Motion response of aircushion type floating structures in a billow is computed. As a result, the usefulness of this numerical calculation method is confirmed.

Characteristics of OWC Type WEC Dampers Installed on a Very Large Floating Structure

2020 ◽  
Author(s):  
Tomoki Ikoma ◽  
Shoichiro Furuya ◽  
Yasuhiro Aida ◽  
Koichi Masuda ◽  
Hiroaki Eto
Keyword(s):  
Wave Energy ◽  
Sea Water ◽  
Prediction Method ◽  
Hydrodynamic Performance ◽  
Floating Body ◽  
Hydrodynamic Characteristics ◽  
Linear Potential ◽  
Floating Structure ◽  
Combined System ◽  
Floating System

Abstract Oscillating water column (OWC) type wave energy converters (WECs) have been researched and developed. OWC WECs are relatively friendly to maintain them in operation because all of mechanical units are set above a sea water surface. In addition, a feature of an OWC device is similar to an air dumper system. Thus, it should be possible not only to harvest wave energy but also to reduce motion of a floating system at the same time. As well as WEC system should be used with other ocean renewable energies as a combined system. This paper describes hydrodynamic characteristics of OWC devices and wave fields around them of multi-OWC devices equipped large floating structures. For this research, the linear potential theory based in-house programme code was applied to calculate hydrodynamic performance of OWC regions and elastic motion behaviours of the structures. Besides, calculation results were compared with some experimental results of characteristics of OWC devices on reference papers published. Then we proved validity of the calculation method. We have quantitatively summarized how much the reduction effect can be seen according to the aircushion placement and the number of aircushions on the floating body. the paper investigated arrangement of OWC devices on the floating structure with several variations. Using the prediction method, effects of arrangement of OWC devices on the performances are investigated.

Improvement of Wave Power Take-Off Performance due to the Projecting Walls for OWC Type WEC

2013 ◽  
Author(s):  
Tomoki Ikoma ◽  
Koichi Masuda ◽  
Hikaru Omori ◽  
Hiroyuki Osawa ◽  
Hisaaki Maeda
Keyword(s):  
Prediction Method ◽  
Air Pressure ◽  
Wave Power ◽  
Linear Potential ◽  
Oscillating Water Column ◽  
Air Chamber ◽  
Pressure Water ◽  
Linear Potential Theory ◽  
Hydrodynamic Behaviors ◽  
Water Elevation

This paper describes a method in order to improve the performance of the primary conversion of wave power take-off. A corresponding wave energy convertor (WEC) is an oscillating water column (OWC) type. The method of the improvement has been proposed and its usefulness has been confirmed in past researches. In the method, projecting walls were attached onto front of inlet-outlet of OWC. The prediction method of hydrodynamic behaviors for the projecting walls installed OWC type WEC is explained in the paper. The boundary element method with the Green’s function is applied and influence of air pressure and free surface within every an air-chamber was directly taken into consideration in the prediction method based on a linear potential theory. Validity of the prediction method was proved comparing with results of model experiments. Series calculations are performed with the prediction method. Behaviors of air pressure, water elevation and the efficiency of primary conversion of wave power are investigated. From the calculations, length of the projecting walls was shown to affect the efficiency of primary conversion. It was available to equip the projecting walls for the improvement in oblique waves to beam sea condition as well as head sea condition. As well as only the projecting walls, application and effects of the end walls with the slit were investigated in the paper. The end walls were very useful to improve the efficiency.

Linear potential theory of steady internal supersonic flow with quasi-cylindrical geometry. Part 1. Flow in ducts

1994 ◽  
Vol 281 ◽  
pp. 159-191 ◽  
Author(s):  
Andreas Dillmann
Keyword(s):  
Supersonic Flow ◽  
Potential Theory ◽  
Broad Class ◽  
Three Dimensional ◽  
Double Series ◽  
Initial Boundary ◽  
Initial Boundary Value Problem ◽  
Linear Potential ◽  
Linear Potential Theory ◽  
Initial Boundary Value

Based on linear potential theory, the general three-dimensional problem of steady supersonic flow inside quasi-cylindrical ducts is formulated as an initial-boundary-value problem for the wave equation, whose general solution arises as an infinite double series of the Fourier–Bessel type. For a broad class of solutions including the general axisymmetric case, it is shown that the presence of a discontinuity in wall slope leads to a periodic singularity pattern associated with non-uniform convergence of the corresponding series solutions, which thus are unsuitable for direct numerical computation. This practical difficulty is overcome by extending a classical analytical method, viz. Kummer's series transformation. A variety of elementary flow fields is presented, whose complex cellular structure can be qualitatively explained by asymptotic laws governing the propagation of small perturbations on characteristic surfaces.

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