To enable the simulation of shape formation of an inflatable structure.

In the computing method for expressing a membrane as an assembly of triangular elements formed by beam elements, a processing part reads an inside-outside pressure difference from a storage part (S100). The processing part determines a surface force acting on triangular elements and node points based on the pressure difference and the coordinates of the node points in reference to a file storing the relation among node points, beam elements and triangular elements (S101 and S103). The processing part determines a tension acting on each beam element (S105). The processing part determines, for each node point, the speed of node point based on the tension and the surface force (S107). The processing part determines convergence of the tension and the speed (S109), and determines a new time coordinate based on the speed of node point (S111 and S113). The processing part divides each beam element which receives compression (S115 and S131). The processing part determines whether all the speeds of the nodes are close to 0 or not and stores the coordinate and the tension in a storage part to perform a display on a display part or the like (S117).

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