In this paper we propose a new method to design a reinforcement for a given thin shell structure such as body structure of a vehicle by utilizing a structural optimization method based on the level set method. In this method the allowed design space is defined around the given structure and the optimal reinforcement is created utilizing the level set based optimization method. The proposed method can give a designer more useful information of topology and shape of the reinforcement than the conventional topology or shape structural optimization methods. We demonstrate the efficiency of the method by showing a result where the optimal reinforcement is found for a simple given structure made by thin shell.
