An Overview of Hydrodynamic Performance of the Multi Purpose Floating Structures MPFS
Authors: Liu Xiao , Zhang Chi , Magee Allan Ross , Ang Kok Keng 
Published: November 2020

Two innovative concepts under the Multi-purpose Floating Structures (MPFS) project has been proposed recently. The two concepts are Floating Hydrocarbon Storage Facility (FHSF) and Modular Multi-purpose Floating Structures (MMFS). Both concepts are based on modular design and are proposed to utilize sea space for different purposes. The FHSF is aiming specifically to store different hydrocarbon products in the nearshore area, while the MMFS is developed to create "land on the sea" by connecting a few standardized modular units with rigid or flexible connectors. Both concepts can be extended to broader applications. For example, the FHSF can be extended as a floating fish farm and floating LNG system, while the MMFS can be used as a floating aggregate storage facility and floating flatted factory. The overall conceptual design of the two floating systems is described and compared in this paper. The innovation in these two concepts is highlighted. In addition to the conceptual design, extensive research studies have been conducted to verify the performance of both concepts to realize the concept in practice. The verified performance includes structural integrity, hydrodynamic behaviors under given sea conditions, ship collision, etc. In this paper, we mainly concentrate on their hydrodynamic performance.

To investigate the hydrodynamic performance of both concepts, experimental and numerical simulations have been conducted. In these studies, we followed a procedure that starts from local components to the global system. Based on this procedure, experimental and numerical studies are divided into different stages with different focuses. Three-stage experimental studies for the FHSF were carried out in the coastal basin of National University of Singapore (NUS) Hydraulic Lab, and in the ocean basin at SINTEF Ocean. Similar three-stage experiments on a model system of MMFS were performed. The model scale of 1:49 and 1:50 was adopted in the FHSF and MMFS tests, respectively. Decay tests, regular wave and random waves tests in the 1-year and 100-year storm at a particular coastal area were performed to evaluate their hydrodynamic performance. For the FHSF, the focus of the experiment is on the motions of single FHSF, the connection forces and the sloshing of the internal liquid. For the MMFS, the focus of the experiment is on the connection forces under various configurations and the reduction of motions of the modules.

Following the experimental studies, comprehensive numerical studies were conducted, and the numerical models were verified through experimental results. These numerical models are mostly based on both linear potential flow theory. According to the verified numerical model, the optimized design of the floating structures was further proposed. An additional numerical model is built to study the viscous effect induced by current by computational fluid dynamics. Very good agreements were found from the comparison of experimental and numerical results of both concepts. The comparison studies also demonstrate a very promising performance of the two concepts even in extreme sea conditions. The motions of the system are mild, and the hydrodynamic loads are small. These verify that the conceptual design of both the FHSF and MMFS is feasible in the practice.

This paper delivers an overview of the research work on the conceptual design of FHSF and MMFS and their hydrodynamic performance. The major findings through the numerical and experimental work may provide a useful reference for floating structures design in the nearshore region. In addition, we also found that the present numerical tools have limited capability to calculate the hydrodynamic responses of multi-module floating structures, especially when the body number becomes large, and a numerical tool with higher efficiency is under developing.