## 1 Introduction  
The main cabins in offshore platforms are very different from ordinary ship cabins or building rooms [1, 2]. The uniqueness of the main cabins in offshore platforms is found in the presence of a set of mechanical equipment such as main engines, pumps, boilers, and heat exchangers in the cabins [3]. Oxygen is essential for both the cabin personnel and power machineries. It is crucial to supply sufficient fresh air to the cabins in order to ensure full oxygen combustion and personnel safety. Furthermore, the normal operation of mechanical equipment will generate a large amount of heat [4], which is difficult to discharge from the relatively narrow and well-sealed cabin structure. More importantly, a small amount of flammable gases will emit from the diesel engines. Therefore, it is necessary to optimally design the ventilation system for the main cabins in order to supply fresh air and take away the heat and flammable gases.  
Optimal design of the ventilation system for buildings is always an important task [5]. Many researches have investigated the effectiveness of different ventilation systems for building rooms, but very limited work has been done for ship cabins, let alone to the design of a ventilation system for offshore platforms. Theoretical modelling and numerical simulation have been widely used in optimizing the ventilation systems in various applications. The theoretical modelling often requires mathematical simplification of the cabins. [PERSON] et al. [6] optimized the ventilation system for an airliner cabin to improve the contaminant removal efficiency and to enhance the cabin thermal comfort. [PERSON] et al. [7] optimized the air distribution of an aircraft cabin using simulation analysis. [PERSON] [8] improved the thermal comfort in an aircraft cabin using computational fluid dynamics (CFD) simulation, and [PERSON] et al. [9] discussed the passengers' comfort for an aircraft cabin by analyzing empirical data. [PERSON] et al. [10] managed the cabin heat in an electric car. Experimental evaluation was carried out to investigate the temperature distribution on the car roof. Literature review indicates that great progress has been made in the ventilation optimization for aircraft cabins, building rooms, and vehicle cabins. However, very limited work has been done to address the ventilation optimization for ships and offshore platforms. [PERSON] et al. [11] simulated the thermal behaviors in a manned submersible, and [PERSON] et al. [12] modeled a ship main cabin. To our best knowledge, ventilation optimization for offshore platforms has not been found in literature.  
In order to bridge the research gap in ventilation optimization of offshore platforms, this work proposes a novel thermodynamics model of a main cabin in a JU-2000E jack-up offshore platform. To that avail, a 1:1 scaling model of the main cabin was established using the SolidWorks software (SolidWorks 2016, SolidWorks Corporation, Waltham, MA, USA). Different influence factors were then investigated in ANSYS FLUENT (Ansys15.0 2016, Ansys Inc., Canonsburg, PA, USA) based on the SolidWorks model to calculate the thermodynamics of the ventilation system of the main cabin. The temperature field, velocity field, and vector diagram of the airflow [6] in the main cabin were compared using different ventilation designs. The optimal ventilation design scheme was obtained based on a reasonable trade-off between different impact factors. The contribution of this work is that a quantitative analysis of the significance of the impact factors, such as ventilation temperature, volume and humidity, is presented for the ventilation system design of offshore platform cabins.