Effects of Aircushion Division to Hydroelastic Responses of an Aircushion Type Very Large Floating Structure

2003 ◽  
Author(s):  
Tomoki Ikoma ◽  
Koichi Masuda ◽  
Hisaaki Maeda ◽  
Chang-Kyu Rheem
Keyword(s):  
Water Waves ◽  
Final Section ◽  
Three Dimensional ◽  
Offshore Structure ◽  
Floating Structure ◽  
Distribution Method ◽  
Steady Wave ◽  
Elastic Deflection ◽  
Momentum Theory ◽  
Very Large Floating Structure

A target offshore structure in this study is an aircushion supported very large floating structure. The aircushion type VLFSs behave elastically in water waves. Corresponding aircushions are very large or relatively small size. The VLFSs considered in this study are supported by a large aircushion, two aircushions, or several module aircushions. The zero-draft theory is applied to the prediction of the hydrodynamic forces. The zero-draft theory is based on the pressure distribution method. The elastic deflection predicted by the zero-draft method is compared with that by another three-dimensional method in order to confirm the validity of it. In addition, the steady wave drifting forces on VLFSs with the aircushion are shown and their characteristics are examined. Then, the momentum theory is applied to the prediction. In the final section, effects of aircushion division to the elastic deflection and the wave drifting force are investigated. From the results, it is confirmed that the elastic deflection is can be reduced in the specification relation between the wavelength and the length of a module aircushion. In addition, it is possible to ajust the aircushion setting in order to simultaneously reduce the elastic deflection and the steady wave drifting force of the aircushion type VLFS on the case.

scholarly journals Surface and Internal Waves due to a Moving Load on a Very Large Floating Structure

2012 ◽  
Vol 2012 ◽  
pp. 1-14 ◽  
Author(s):  
Taro Kakinuma ◽  
Kei Yamashita ◽  
Keisuke Nakayama
Keyword(s):  
Thin Plate ◽  
Internal Waves ◽  
Water Waves ◽  
Moving Load ◽  
Fluid Motion ◽  
Point Load ◽  
Internal Mode ◽  
Floating Platform ◽  
Floating Structure ◽  
Very Large Floating Structure

Interaction of surface/internal water waves with a floating platform is discussed with nonlinearity of fluid motion and flexibility of oscillating structure. The set of governing equations based on a variational principle is applied to a one- or two-layer fluid interacting with a horizontally very large and elastic thin plate floating on the water surface. Calculation results of surface displacements are compared with the existing experimental data, where a tsunami, in terms of a solitary wave, propagates across one-layer water with a floating thin plate. We also simulate surface and internal waves due to a point load, such as an airplane, moving on a very large floating structure in shallow water. The wave height of the surface or internal mode is amplified when the velocity of moving point load is equal to the surface- or internal-mode celerity, respectively.

Three-Dimensional Analysis of Hydroelastic Behaviors of an Aircushion Type Large Floating Structure

2005 ◽  
Author(s):  
Tomoki Ikoma ◽  
Koichi Masuda ◽  
Chang-Kyu Rheem ◽  
Hisaaki Maeda
Keyword(s):  
Integral Method ◽  
Three Dimensional ◽  
Present Theory ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Floating Structure ◽  
Program Code ◽  
Distribution Method ◽  
Point Distribution ◽  
Method Effect

This paper describes theoretical formulations for a prediction of hydrodynamic forces on the aircushion type large floating structure and shows corresponding results. Therefore, a new program code is developed. The structure is supported by large mono-aircushion. The present theory is based on the three-dimensional singular point distribution method. Effect of the aircushion is considered in this. Then, a processing of a singular integral of the boundary integral method is shown and its validity is confirmed. In conclusion, the draft effect to the pressure within the aircushion is discussed. As a result, when width of the skirt is thin, the draft effect is little. However, in case that the width is large, the draft effect is enlarged.

scholarly journals The Numerical Modeling of Coupled Motions of a Moored Floating Body in Waves

Water ◽  
2018 ◽  
Vol 10 (12) ◽  
pp. 1748 ◽  
Author(s):  
Lin Cheng ◽  
Pengzhi Lin
Keyword(s):  
Numerical Model ◽  
Water Waves ◽  
Three Dimensional ◽  
Numerical Results ◽  
Floating Body ◽  
Mooring Line ◽  
Floating Structure ◽  
Structure Interaction ◽  
Coupling Procedure ◽  
Boundary Force

Nonlinear interactions between water waves and a moored floating body are investigated using the virtual boundary force (VBF) method. The paper first introduces an in-house three-dimensional viscous incompressible flow model (NEWTANK), which is used to simulate wave-floating structure interaction by using the VBF method. Then the coupling procedure between the mooring line model and the floater model is described. Some validation cases of the developed model, including the motions of a free-floating box in two different water waves, are presented. The present numerical results will be compared with the available experimental data and other numerical results from the published literature. After that, the validity of the mooring line in the numerical model is simulated by simulating the motions of a floating box in still water. Finally, the verified model is applied to analyze the wave-induced motions of a catenary moored floating structure, investigating the motion responses and mooring forces responses. The numerical results agree well with the experimental measurements on the whole. This indicates that the present numerical model can correctly capture the main features of the wave-moored floating structure interaction.

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.

Hydroelastic Responses of Pontoon and Semi-Submersible Types of Very Large Floating Structure in Regular Head Waves

2002 ◽  
Author(s):  
T. S. Phan ◽  
P. Temarel
Keyword(s):  
Three Dimensional ◽  
Source Distribution ◽  
Mode Shapes ◽  
Floating Structure ◽  
Floating Structures ◽  
Hydrodynamic Damping ◽  
Very Large Floating Structure ◽  
Head Waves ◽  
Interaction Problem ◽  
Regular Head Waves

The symmetric dynamic behaviour of two types of Very Large Floating Structure (VLFS) is investigated. The structures are of pontoon (or mat like) and semi-submersible type and have the same beam, length and displacement. The responses for these stationary and free-floating structures in regular head waves are investigated using the three-dimensional hydroelasticity theory, applicable to structures with arbitrary shape. The “dry analysis” is carried out by discretising the structures using beam and shell finite elements, as appropriate. The solution of the fluid-structure interaction problem is achieved through a pulsating source distribution whereby the mean wetted surface of either structure is discretised using four-cornered panels. The symmetric dynamic characteristics of both structures are compared, both in vacuo (e.g. natural frequencies and mode shapes) and in water (e.g. generalised added mass and hydrodynamic damping). Predicted responses such as vertical deflections and direct stresses, in regular head waves, are also discussed and compared.

scholarly journals NUMERICAL SIMULATION FOR TSUNAMI-HEIGHT REDUCTION USING A VERY LARGE FLOATING STRUCTURE

2017 ◽  
pp. 24
Author(s):  
Taro Kakinuma ◽  
Tatsuya Nakahira ◽  
Takatsugu Kamba ◽  
Takahiro Murakami ◽  
Keisuke Nakayama
Keyword(s):  
Water Waves ◽  
Flexural Rigidity ◽  
Reduction Rate ◽  
Two Dimensional ◽  
Floating Structure ◽  
Tsunami Height ◽  
Tsunami Propagation ◽  
Height Reduction ◽  
Very Large Floating Structure ◽  
Crest Line

The tsunami-height reduction using a very large floating structure, i.e., VLFS, is discussed, with the water waves, interacting with a floating thin-plate, simulated numerically. The final tsunami-height reduction rate increases, as VLFS length, VLFS flexural rigidity, or the wave height of an incident tsunami, is increased. If two VLFSs are utilized, the final tsunami-height reduction rate, also depends on the distance between the VLFSs. In two-dimensional tsunami propagation, another wave propagates to the outside, along the crest line of the main wave, leading to an additional tsunami-height reduction.

scholarly journals A Proof-of-Concept Algorithm for the Retrieval of Total Column Amount of Trace Gases in a Multi-Dimensional Atmosphere

2021 ◽  
Vol 13 (2) ◽  
pp. 270
Author(s):  
Adrian Doicu ◽  
Dmitry S. Efremenko ◽  
Thomas Trautmann
Keyword(s):  
Trace Gases ◽  
Three Dimensional ◽  
Principal Component ◽  
Radiative Transfer Model ◽  
Computational Time ◽  
Transfer Model ◽  
Proof Of Concept ◽  
Discrete Ordinate ◽  
Distribution Method ◽  
Total Column

An algorithm for the retrieval of total column amount of trace gases in a multi-dimensional atmosphere is designed. The algorithm uses (i) certain differential radiance models with internal and external closures as inversion models, (ii) the iteratively regularized Gauss–Newton method as a regularization tool, and (iii) the spherical harmonics discrete ordinate method (SHDOM) as linearized radiative transfer model. For efficiency reasons, SHDOM is equipped with a spectral acceleration approach that combines the correlated k-distribution method with the principal component analysis. The algorithm is used to retrieve the total column amount of nitrogen for two- and three-dimensional cloudy scenes. Although for three-dimensional geometries, the computational time is high, the main concepts of the algorithm are correct and the retrieval results are accurate.

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