# Wind-Load Response and Evacuation Efficiency Analysis of Marine Evacuation Inflatable Slide
## 2 Wind-Load Response Analysis Method of Inflatable Slide and Establishment of Numerical Model
### Establishment of Numerical Models for Wind Field Domain and Structure Domain of Inflatable Slide  
In order to establish the numerical model of wind field, boundary conditions should be set first. The boundary conditions of wind field include inlet, outlet, opening boundary, walls and  
Figure 3: Basic scheme of weak coupling solution method.  
symmetry [13]. The establishment criterion of calculation area is to approximate the actual situation as much as possible, and to minimize the influence of the simulation solution on calculation results [14]. It should be ensured that the boundary of the simulated wind field is far enough from the inflatable film slide, and the calculation area should not be too small. According to the size specifications of the inflatable slide, the sea surface wind field size is 150 m \(\times\) 100 m \(\times\) 50 m, as shown in Figure 4. The injected fluid is set to be 20 m/s subsonic fluid with turbulence intensity of 0.05 and temperature of 25 \({}^{\circ}\)C. The mass and momentum of the ejected fluid are set at 0 Pa of average static pressure and 0.05 of turbulence intensity, and the wall is set as a forbidden boundary for the fluid in the fluid field, which is passable for heat transfer and other additional variables.  
Next, the numerical model of the structure domain of the inflatable slide is established. The length of the inflatable slide surface is 14 m, the total width of the slide is 1.8 m, and the width of the unilateral slide surface is 0.8 m. The angle between the film surface and the sea surface is 35\({}^{\circ}\), and the diameter of the boarding platform is 6 m. The PVDF (polyvinylidene fluoride) membrane material with a thickness of 1 mm is selected as the membrane material. Its advantages are high mechanical strength and toughness, high wear resistance, high permeability to gases and liquids, good anti-ultraviolet and anti-impact properties [15]. It is suitable for use in complex marine environments. The material density of the model is 1250 kg/m\({}^{3}\), the modulus of elasticity is \(5.0\times 109\) Pa and Poisson's ratio is 0.35. Because the inflatable slide is composed of multi-compartments, it is necessary to add air pressure to each compartment independently in the simulation environment, and the internal pressure is set to 4000 Pa.  
During mesh generation, five inflation layers are set for the FSI surface, and the mesh is refined. The purpose of this setting is that when the wind acts on the surface of the inflatable membrane, the gas velocity decreases near the FSI surface, and the flow is relatively stable. The fluid viscosity at this time will appear. Therefore, the mesh near the surface should be finely divided to make the calculation process converge as soon as possible. The structure domain numerical model of the inflatable slide is shown in Figure 5.  
After checking the mesh quality, most of the mesh topology quality is greater than 0.5, and the mesh skew coefficient values are all close to 1. The mesh quality is good. The quadrilateral element is used as the structural mesh for the mesh generation of wind field domain. The mesh of the inflatable slide domain also uses quadrilateral elements as the structural mesh, as shown in Figure 6a. The area with poor quality after mesh division is shown in Figure 6b.  
Figure 4: The schematic diagram of boundary conditions setting of sea surface wind field.  
It can be seen from the partition results that the poor quality area of the mesh appears at the top connection of the inflatable slide. In the simulation process, the fixed constraint is applied to this part, and the analysis of the FSI surface will not be affected, so the quality of the mesh partition meets the requirements.