We present a simulation and design framework for simultaneously designing and modeling electromechanical systems. By instantiating component objects and connecting them to each other via ports, a designer can configure complex systems. This configuration information is then used to automatically generate a corresponding system-level simulation model. The building block of our framework is the component object. It encapsulates design data and behavioral models and their inter-relationships. Component objects are composed into systems by connecting their ports. However, when converting a system configuration into a corresponding simulation model, the corresponding models for the component objects do not capture the physical phenomena at the component interfaces>the interactions. To obtain an accurate composition, the interaction dynamics must also be captured in behavioral models. In this paper, we introduce the concept of an interaction model that captures the dynamics of the interaction. When two ports are connected, there is an intended interaction between the two components. For composition of component objects to work, an interaction model must be introduced between each pair of connected behavioral models. We illustrate these ideas using an example.