# Numerical Study on Hydrodynamic Performance of a New Semi-Submersible Aquaculture Platform
## 1 Introduction
[32] presented a semi-submersible offshore fish farm similar to ShenLan 1 with a pontoon, main frame system, net system, and upper building and developed a hybrid method that combined the direct time domain and indirect time domain to analyze the motion responses of the cage. Physical model tests in the wave basin verified the numerical model. South China Sea Fisheries Research Institute and Zhuhai Desai Marine Fishery Technology Co., Ltd. (Zhuhai, China) co-designed a semi-submersible fish farm named Dehai Farm 1. It consists of the truss-work system and ballast tanks with dimensions of 91.3 m in length, 27.6 m in width, and 10.3 m in height. [PERSON] et al. [33] investigated the mooring forces and motion response of Dehai Farm 1 in waves and currents through a series of physical model tests. [PERSON] and [PERSON] [34] presented a novel offshore fish farm consisting of a deep draught floating spar and an octagonal net steel cage (named COSPAR) and performed the hydrodynamic response analysis of free-floating COSPAR and the coupled analysis involving COSPAR and mooring lines using the software Design Modeler R2012 and Aqwa R2017 owned by Ansys, Inc. (Canonsburg, PA, USA) [35,36]. Guangzhou Institute of Energy Conversion (GIEC) of the Chinese Academy of Sciences designed a semi-submersible aquaculture platform by combining Sharp Eagle WEC technology and offshore aqua-culture. This innovative design led to the successful deployment of the world's first semi-submersible wave energy aquaculture platform named \"Penghu\" (Figure 1) in Zhuhai, China, in 2019 [37]. The invention belongs to the team of the authors of this paper. By utilizing this platform, the challenges encountered by traditional aquaculture cages in offshore environments, including poor performance, limited energy supply, and inability to accommodate modern farming equipment, can be effectively addressed. GIEC continues to develop a series of semi-submersible aquaculture platforms to further promote industrial applications. Systematic numerical or experimental analyses are essential for the design of these offshore structures to assess their performance in complicated environmental conditions. However, open publications on the detailed hydrodynamic and structural analysis of these concepts are rare, to the authors' knowledge. In this paper, we aim to fill the gap in the understanding of the hydrodynamic performance of a semi-submersible aquaculture platform, which is newly designed by GIEC and put into operation. While [PERSON] et al. [38] developed a numerical model to analyze the structural response of this type of platform, their model did not consider the mooring system and nets and only evaluated the platform under pure wave action. In contrast, our study proposes a comprehensive numerical model that takes into account the semi-submersible main structure, net system, and mooring system and further analyzes the mooring line tension and motion response of the platform under wave, wind, and current conditions. The rest of this paper is organized as follows: Section 2 provides a description of the new aquaculture platform. Section 3 presents a coupled numerical model of the platform under the combined action of waves, winds, and currents. Section 4 validates the numerical results and analyzes the hydrodynamic performance of the platform in regular waves and the dynamic responses of the platform with and without nets in waves, winds, and currents. Section 5 summarizes the main conclusions and the prospects for future study.