导图社区 Very Large Floating Structures
- 45
- 4
- 0
- 举报
Very Large Floating Structures
”Very Large Floating Structures: Applications, Research and Development“（C.M. Wanga, Z.Y. Taya）漂浮结构的应用、研究及发展，读书笔记
编辑于2020-07-08 14:21:03- 漂浮结构
- 相似推荐
- 大纲
Very Large Floating Structures
1. Introduction
focus on the pontoon-type VLFS
1.1. Types
Semisubmersibel-type
a raised platform above sea level by using column tubes
in high sea with large waves
Pontoon-type
in calm water
cove, lagoon, harbor
1.2. History
propose
in circa 1920
Edward Armstrong
a seadrome as stepping stones for aircraft flying across the oceans
dampen
1927
the extraordinary non-stop flight of Charles Lindbergh from New York to Paris
military use
WWII
construct a floating pontoon flight deck measuring 552m x 83m x 1.5m with a draft of 0.5m for use by Great Britain
Laycock, 1943
pre-cold war era
The US navy
mobile offshore bases (MOB)
Suzuki et al. 2006
develop further
1970s
a floating airport
the Kansai International Airport
floating city
the Okinawa International Ocean Exhibition - Aquapolis
1995
the Mega-Float in Tokyo Bay
a test floating runway
understanding the hydroelastic behavior, the mooring systems, the connector system, the anticorrosion system and its effect on seawaves, currents, water quality and marine eco-system
validate hydroelasticity codes, the performance of the rubber-fender-dolphin mooring system, the performance of welded connections and the effect of wave action
1. environmentally friendly as they do not damage the marine eco-system, or silt up deep harbor or disrupt the ocean currents; 2. easy and fast to construct; 3. can be easily removed or expanded; 4. not affected by seismic shocks since they are inherently base isolated
2. Applications
2.1. the Mega-Float in Tokyo bay
a 1 km long floating test runway
feasible even with the stringent requirement that the radius of curvature of the runway be kept at 30,000 m.
2.2. the floating fuel storage bases at the Shirashima island and Kamigoto island
2.3. floating ferry piers at Ujina port Hiroshima
2.4. floating bridges
the 2013m long Lacey V. Murrow Bridge
the Third Washington Bridge over Lake Washington in Seattle
the one over the Dubai Creek and it is 300m long
2.5. floating performance stage
2.6. floating fuel storage facility
increase oil storage capacity
relieve traffic congestion in harbour
decrease the turnaround time for ships
Singapore
2.7. floating islands
for entertainment and convention centres
2.8. floating cruise terminal for Seoul
hotel rooms and CIQ(customs, immigration and quarantine), and a floating mobile quay system
South Korea
2.9. the sustainable engineering science barge
urban agriculture on floating structure
NY, USA
2.10. marine salmon farms
ensure continuous supply of fresh fish
salmon producing countries
2.11. the Lilypad Floating Ecopolis
2.12. floating town comprising greenhouses, commercial centre and residential area
the Dutch
3. Research studies
focus on the hydro-elastic response, the structural integrity and the steady drift forces
3.1. Hydroelastic response
the frequency domin approach
simplicity and ability to capture the pertinent response parameters in a steady state condition
the Laplace equation for the velocity potential is converted into a boundary value problem when solving for the motion of the floating body
the time domain approach
obtain transient response
the direct time integration method
the equations of motion are discretized for both the structure and the fluid domain.
the Fourier transform method
obtain the frequency domain solutions for the fluid domain and then Fourier transforms the results for substitution into the differential equations for elastic motions. The equations are then solved directly in the time domain analysis by using the finite element method or other suitable computational methods
the computational fluid dynamic (CFD) method
involves solving the Navier Stokes equation
handle vortex formations when wave is diffracted by sharp edges or attachment
3.2. Structural integrity(Functionality and Safety Criteria)
dominate the structural design
3.3. Drift forces for mooring system design
methods for computing the wave drift forces
the near-field method
based on the direct pressure integration method
the far-field method
based on the momentum-conservation principle
not suitable for two or more floating modules adjacent to each other
only the total forces acting are given, can't obtain individual force
4. Development of VLFS technology
4.1. mooring systems
function
keep in position
facilities can be reliably operated
prevent from drifting away under critical sea conditions and storms
freely drifting VLFS may lead to
damage to surrounding facilities
loss of human lift id it collides with ships
types
the mooring lines type
use chains, wire ropes, synthetic ropes, chemical fiber ropes, steel pipe piles, and hollow pillar links
used in deep sea such as the tension leg floating wind farm and the floating salmon farm
large motion when length is long
adopt the tension leg system
apply pretension to the mooring line to restrain motion
difficult to restrain the horizontal motion and usually the mooring lines experience significant tension forces
the caisson or pile-type dolphins with rubber fender system
first adopted for the two floating oil storage bases at Kamigoto and Shirashima islands in Japan
effective in restraining the horizontal displacement
be able to undergo a large deformation (of up to approximately one-third of their lengths)
absorb kinetic energy
4.2. mitigation of hydroelastic response
breakwater
construct bottom-founded breakwater
reduce the hydroelastic response and drift forces
drawbacks
massive construction material requirements
difficulty in construction
occupy precious sea space
remove difficult if relocated
not environmentally friendly
the reflected waves could result in coastal erosion
the floating box-like breakwater moored with mooring lines
do not disrupt the ocean flow
cause lithe damage to the seabed
could function as collision and oil spill barriers
expensive and requires more time for construction
submerged horizontal or vertical plate
attached to the fore-end of the VLFS
generate breaking wave, wave fission, vortices
dissipate the incident wave energy
reduce the incident wave length
oscillating water column(owc) anti-motion device
the owc air chamber could absorb wave energe
reduce more hydroelastic response
but increase the drift forces
air-cushion
reduce dispalcements and drift forces due to wave slamming or air-craft take-off/landing load
hybird type
4.3. connector designs
hinge or semi-rigid connectors instead of rigid connectors
reduce the hydroelastic response
4.4. other developments
shape
edge shape
notched edge could reduce the propagation of deformation
VLFS with moon-pools and different stiffness
innovative gill cells
5. Conclusion
5.1. Summary of the current applications, research and development
Various existing VLFSs are presented and some potential applications of VLFS as urban agriculture and future human habitation are highlighted. The research developments of the VLFS are also presented with main emphasis on the hydroelastic response, structural integrity and steady drift forces. The conventional method in performing the hydroelastic analysis by using the frequency and time-domain approaches and a more recent method based on cfd are briefly discussed. Research studies on functionality and safety criteria that affect the structural integrity of the VLFS as well as the near-field and far-field method used to obtain the steady drift forces of the VLFS are also presented.
5.2. Technological developments
The technological developments on the mooring system, anti-motion devices and connector designs of VLFS over the past decades are highlighted. Two different types of mooring system are used for the VLFS, i.e. The mooring lines type and the caisson/dolphin type. The mooring lines type is usually used for VLFS deployed in deep water whereas the caisson/dolphin type for VLFS in shallow water. Methods used for mitigating the hydroelastic responses include the bottom-founded and floating breakwaters, submerged and owc anti-motion devices, air cushion, and the hybrid type anti-motion devices. Connectors used to join modules of VLFS have also evolved from fixed type to semi-rigid and hinge type. The semi-rigid and hinged type connectors are also found to be effective in reducing the hydroelastic response of the VLFS.
5.3. Future research
the effect of variable water depth and/or wave shortcrestedness on hydroelastic response of VLFS equipped with anti-motion devices
on-sea experiment for validation of the effectiveness of anti-motion devices in real environmental conditions
the effect of slowly varying drift forces on the hydroelastic response of VLFS equipped with anti-motion devices
the boundary conditions
earlier works consider as a rigid body 1990s, hydro-elastic analysis was used
the Neumann condition at the seabed and the wetted surfaces of the floating body
the linearised free surface condition
the radiation conditions at infinity
hydroelasticity
term: fluid-structure interaction
pontoon-type VLFS
large surface area
relatively small depth