As the power of computational Grids increases, there is a corresponding need for better usability in PSE community. In this paper, we describe our experiences on design of project GridPSi, a Grid-enabled PSE for physical simulation. GridPSi provides a rich suite of functions that facilitate the composition of computational scripts to automate physical simulations by design domain-specific templates for a verity of research fields. The generic functionality provided by it includes problem modeling, mesh file conversion, computational script generation, solution scheme specification and access to Grid resources. GridPSi offers a simple interface that is intuitive to users in the human-PSE interactions and ways of thinking. Furthermore, we developed higher-level graphical components named PDE wizards that build upon the core functions to guide users through problem modeling process with minimum effort. By using Unicore as Grid middleware, we are lowering the barriers to entry for users wishing to exploit Grid technologies.