Abstract : Cloth and hair are representative flexible bodies that exhibit large deformation, delayed motion, localized fluttering, and curvature variation under wind. However, coupling explicit air-flow simulation with cloth and hair simulation requires high computational cost and a complex pipeline, making it difficult to apply in real-time or iterative animation production environments. In this paper, we propose a method for generating dynamic wind responses in XPBD-based cloth and hair animation by combining procedural wind fields with a geometry-aware aerodynamic model without explicit fluid simulation. The proposed method constructs temporally varying rotating and swirling wind fields and couples them with lift–drag forces that are adaptively modulated according to surface orientation, relative velocity, wind exposure, wrinkle state, and curvature state. For cloth, angle-dependent lift and drag are computed based on triangle area and normal direction, and different aerodynamic responses are generated in folded and boundary regions by incorporating local wrinkle intensity and wind-direction-dependent exposure attenuation. For hair, the relative velocity component perpendicular to the wind-facing strand direction is extracted using segment-level tangent direction and curvature information, and wind-induced separation and fluttering motions are represented by reflecting the response difference between exposed and shielded strands. As a result, the proposed method generates more spatially localized cloth fluttering and more directional hair flow than a simple fixed-direction wind model, while being stably integrated into the XPBD framework without a separate fluid solver. Experiments on various cloth and hair scenes demonstrate that the proposed geometry-aware lift–drag model can generate differentiated flexible-body deformation according to wind direction, surface geometry, and curvature variation at low computational cost.

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