With rapid technological advances in network infrastructure, programming languages, compatible component interfaces and so many more areas, today the computational Grid has evolved with the potential of seamless aggregation, integration and interactions. This has made it possible to conceive a new generation of realistic, scientific and engineering simulations of complex physical phenomenon. These applications will symbiotically and opportunistically combine computations, experiments, observations, and real-time data, and will provide important insights into complex phenomena. However, the phenomena being modeled are inherently complex, multi-phased, multi-scaled, dynamic and heterogeneous (in time space and state). Furthermore, their implementations involve multiple researchers with scores of models, hundreds of components and dynamic compositions and interactions between these components. The underlying Grid infrastructure is similarly heterogeneous and dynamic, globally aggregating...