Feasibility Study of Deploying Floating Houses in Metropolitan Coastal Cities Under Near-shore and Off-shore Conditions


Student thesis: Doctoral Thesis

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Awarding Institution
Award date31 Aug 2021


Coastal areas have long been appealed to human beings due to their comfortable climates, rich food resources, and convenient transportation. These regions often urbanize faster than the hinterlands, and thus, are more densely populated, facing challenges like overpopulation and land scarcity. Moreover, in recent times, sea level rise caused by global warming is further diminishing the usable land along the coastline. When combined with the increasing frequency of extreme weather events, housing issues in coastal areas are predicted to worsen in the future. A new type of housing product – the floating house – might provide a solution to the existing and forthcoming problems in coastal areas, by developing the sea space for residential or commercial use in an environmentally friendly way. This study aims to systematically explore the feasibility of deploying the floating house in metropolitan coastal cities under nearshore and offshore conditions, from the viewpoints of finance, comfort, and safety.

To identify the threats posed by global climate change to coastal cities, a geographic information system was used to quantify the impacts of future coastal flooding which could be intensified by rising sea levels. Hong Kong, a typical metropolitan coastal city troubled by severe housing problems such as small living space and high cost of housing, is selected as the target city. The return period of future extreme coastal disasters was predicted based on projected sea level rise and a probability distribution analysis of historical sea level records. The consequent land loss, affected facilities, exposed assets, etc. were estimated accordingly.

A preliminary study conducted locally in Hong Kong disclosed the fact that price is a major concern when people look for a new home. Consequently, the value obtained for money invested in the floating house concept was first computed and compared through a value management approach with investing in the traditional land-based counterpart. Questionnaire surveys were carried out to collect public opinions on the performance of various building functions; the performance was then normalized by the cost to yield true function values. The results indicate that though the floating house shows some weakness in living-related functions, it brings interesting opportunities to solve environmental and tourism related issues.

As Hong Kong is frequently exposed to tropical cyclones, the critical issues of comfort and safety (structural stability) for occupants of the floating house were also inspected. Several continuum models mimicking the dynamic responses of the floating houses deployed in offshore and nearshore waters were constructed in the finite element analysis tool Abaqus. Based on real wind and wave records, irregular wave fields were produced following a wave spectrum approach. The fluid-structure interaction was handled with a coupled Eulerian-Lagrangian technique. Comfort of living in the floating house was quantified by a motion sickness theory depending upon the acceleration of the floor, while structural stability was evaluated based on the interstory drift ratio. The simulation results indicate that the floating house performs well in nearshore waters that are isolated from offshore waves. On the contrary, deploying the floating house in offshore waters is a challenging issue for both comfort and safety concerns, even with the protection of breakwaters.

Lastly, an analytical model was developed that efficiently solves the coupled heave and pitch motions and superstructure deformation of the floating house when subjected to sea waves. The formulation of the said model was modified from the sway-rocking model commonly applied in earthquake engineering and wind engineering, with the original soil-structure interaction replaced by the fluid-structure interaction. To save computational cost, the potential flow theory was applied, where the complex fluid-solid interaction was captured using added mass and equivalent dashpots and springs. The added mass and damping coefficients, which are required to predict the radiation and diffraction forces, can be either approximated by integrating the two-dimensional analytical solutions or directly computed in three-dimensional continuum simulation using the boundary element method. When integrated with the instantaneous restoring and Froude-Krylov forces, the overall response becomes weakly nonlinear and can be solved in the time domain. Ultimately, the dynamic response of the floating house in real, irregular sea states can be obtained via superimposing multiple constituent regular wave force components. The proposed analytical model was validated against the finite element simulation results and showed satisfactory agreement.