<H1>INTRODUCTION</H1>
      
      While the simulation of wind is an area of vast interest in aerodynamic engineering, computational fluid dynamics (CFD), and animation/visualisation of fluids in computer graphics, it has been a rather abandoned subject in simulation of deformable objects such as cloth simulation. This is mostly due to the fact that conventional CFD applications require enormous computational power. However, aerodynamic effects are obviously capable of enhancing the realism of an animated scene and thus are an important part of a cloth simulation system. For example, air resistance is a vital component which cannot be neglected if realistic animation is desired [ BTH + 03 ]. In this work we discuss two different approaches to
      model force fields describing air motion and show how these forces can be applied to generate aerodynamic effects on textiles. The first method is based on modelling air flows with the Navier-Stokes equations. With this model, the effect of wind fields on smoke has already been investigated 
[FSJ01], and in this paper we extend this approach to wind effects on textiles. However, the solution of the sophisticated NavierStokes equations is not desired and not necessary in all situations where wind effects shall be integrated into cloth simulations. For this case, we present a much simpler model based on tracing wind particles that move along a global force field. During the simulation, the wind field is evaluated for each wind particle at its current position. The so determined flow field is used to compute the wind force which is added to the forces that act on the textiles. By detecting collisions between the wind particles and objects in the scene, we are able to simulate the important effect of lee even with this straightforward method. Of course, both approaches have different characteristics and aim at different applications for wind simulation. In this work, we compare the models’ advantages and disadvantages and show practical results of the described methods. The rest of this paper is organized as follows. After giving an overview of related work in section 2, we describe the aerodynamic force model applied in this work in section 3. In section 4 we discuss the two wind field models, namely the one based on the Navier-Stokes equations in 4.1, and the one based on tracing wind particles in 4.2. Finally, we show some practical results of the implemented algorithms in section 5, before we conclude the paper in section 6.
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