Air Supported Structures and their response to Wind Loading

Abstract

In the presented work, we have developed a method to analyse the interaction between the wind and membrane structures. The complex behaviour of light weighted membrane structures can induce dynamic and wind effects, so this requires an appropriate method to analyse the structure. When the deformation of membrane structures is large, it becomes necessary to consider the interaction between wind flow and membrane. This interaction leads to aeroelastic problems.
The necessary properties to be considered for the aeroelastic coupled problem are considered and presented. The major focus of the thesis is to simulate the geometric non-linear behaviour of the membrane structures when subjected to wind loading. To derive the initial equilibrium shape, the method of form finding is applied. To properly simulate the wind flow around the structure, existing research regarding wind tunnel testing of a hemispherical air dome model is used. First, hemispherical model similar to existing research was made to verify the boundary conditions. The results are compared to the wind-tunnel testing results to get proper boundary conditions in Computational Fluid Dynamics models. In order to keep the simulation simple, the wind velocity is considered constant with height and constant wind flow with respect to time.
Partitioned analysis is used to simulate the physics behind the wind-membrane interaction simulation. By using this method, the multi-physics problem is separated into individual fields. Considering the wind-membrane interaction, the problem is separated into fluid domain and structural domain.
The structural and fluid domain mechanics are discussed in detail. For the single field solvers, methods are introduced based on the fundamentals. Finite Element method is used for the form-finding as well as numerical simulation of the structural field and SOFiSTiK software is used. For the fluid simulation, ANSYS CFX is used.
The strong physical coupling is done between the fluid and the structural domain. For this, the partitioned coupling simulation is used. The requirements and methods for the partitioned analysis are presented as well. For the coupling of separate solvers, a central coupling tool is made using Grasshopper. The transfer of coupling data such as displacement and wind pressure on the membrane structure is done using the developed coupling tool. In the development of this coupling method using Grasshopper, Python programming language is used. The developed method was used in iterations to analyse the effect of geometric non-linearity.
In order to make the developed method reusable for the air-supported membrane structures, the whole process is made parametric using grasshopper. This enables us to analyse the membrane structures with known base shape, internal air pressure. Ultimately this method can be used to analyse the effect of geometric non-linearity on membrane structures when subjected to wind loading. To show the use case of developed method, two different models are developed to analyse the fluid structure interaction. First model has been considered with a circular base shape and the second one has been considered with a square base shape. In order to analyse the effect of geometric non-linearity on these structures, the results such as maximum wind pressure on the membrane structure and maximum structural displacement are compared to the results without considering the geometric non-linearity.
Moreover, wind variation analysis is done to analyse the extent to which geometric non-linearity is dependent on the wind speed. Similarly, size variation analysis is also done to analyse the extent to which geometric non-linearity is dependent on the structure size, keeping the wind velocity constant.