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Domain |
Explanation |
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Abstract |
- The presentation will consist of three parts. Part 1 involves a video presentation on the overall introduction of the concepts of VLFS (the video is produced by the Mega-Float Association of Japan). Part 2 presents a linear wave response analysis of VLFS using the accelerated boundary element method that was recently developed at Kyoto University. Finally, Part 3 deals with a feasibility study on the construction of VLFS in a reef sea, conducted as a national project in the financial year 2001, and the future developments that are needed in this area
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Author |
- A/Prof T. Utsunomiya obtained his B.Eng., M.Eng. and Ph.D. in Architectural Engineering from Kyoto University in 1985, 1987 and 1990, respectively. He worked as a research fellow at the Japan Society for the Promotion of Science before joining the Department of Civil Engineering in Kyoto University. His primary research interest is on floating structures. Over the last ten years, he has published over 20 papers on very large floating structures and floating bridges
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People involved |
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VLFS |
- Very Large Floating Structure (VLFS) for shallow or deep seas
- Present project: Mega-Float conducted between 1990-2000
- Concerns: design, analysis, computation, construction period, EQ-resistant, environmental-friendliness, conservation
- Location: shallow sea (reef, bay, near harbour with breakwaters to lower wave excitations)
- Structure: 1600x400x4, steel (durability, construction, welding), thin flat plate in calm waters for loads, protected by breakwaters, moored (held) by mooring systems (piles anchored), with access to mainland
- Analysis: higher-order boundary element method (HOBEM), Hamilton’s principle, fluid-structure coupled interaction (decoupled analysis using Graf’s theorem) , assumption (linear hydro-dynamics), modal analysis
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Questions |
- Need prompted by: no land available through politics or reclamation, ecology, material/technology
- Steel: high durability, rippling with hydro-elastic responses (assumed)
- Potential: serviceability limits (edges: ~30% of incoming wave height; center: ~10% of incoming wave height), high seas (pontoons with floating piles for stability)
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Design |
- Mega-Float is actually a large assembled plate comprising of welded hollow-core steel panels of length d, towed to location by tug-boats & assembled on-site
- Anchored by mooring system: also serves to limit wave-excited deflections (possibility of active control – since Watanabe)
- Breakwaters along transverse (y-axis) & if needed, along longitudinal (x-axis)
- Response: deflections along edges (~30% wave ht) > deflections @ center (~10% wave ht), possibly due to center mooring
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Analysis |
- Coupled fluid-structure analysis with Laplace equation & relevant BC of VLFS, breakwater & moors
- Assume: linearity, plate on uniform elastic foundation, BC for free edges
- Modal expansion:
 , along x- & y-axes
- Modal analysis for wave diffraction & radiation
- Mesh: recommended
 , where wave length is four times of panel length
- HOBEM: for VLFS & breakwaters
- Hamilton’s principle:
- Damping
using Galerkin’s method |
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Computation algorithm |
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Implications |
- Amplitude of wave-excited deflections < w/o breakwaters
- Constant sea depth < ampl. with varying sea depth
- d
lower, more assembly
- Plot deflection ampl. vs w: for resonance (frequency analysis)
- Higher wave eccentricity, higher uncertainty of wave height around VLFS & deflection responses
- Lower EQ, lower rigidity of mooring system, lower ampl.
- Higher wave ht: higher BM along edges > higher BM @ center
- Uncertainty/errors: linear (sometimes 100%) > nonlinear
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Possibilities |
- Emergencies, extended port (airport / harbour), storage, evacuation, EQ-resistance
- Research directions: uneven bottoms, steep waves in shallow waters, wave breaking, nonlinear analysis (computations critical), fictitious BC for BEM region
- Singapore: good test-bed due to scarcity of land, surrounded by seas, calm waters, increased land-usage, might be cheaper
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Sites |
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