This proposal sets out a programme of work that, if successful, will lead to a change in the way that computational tools are used to provide engineering simulations. The approach will bring considerably more interactivity into the process, so that the engineer/designer is continuously interacting with the analysis and receiving immediate feedback of solutions from which he/she can assess the durability, life and fatigue resistance of the component being designed. The reader is asked to imagine a computer showing contours of stresses on the surface of a solid body, and next imagine the engineer making some geometric change to the design, e.g. increasing a fillet radius. Such an operation might normally be performed by a click-and-drag mouse operation. Next, imagine the stress contours updating on the screen in real time as the mouse is dragged and the geometry is being deformed. Further geometric changes using different dynamic operations also cause stresses to update in real time. Thus the stress analysis evolves along with the geometry, and guides the design rather than validates it after its completion. This is the vision for the output of the proposed work.This level of interactivity is no longer a vision, but instead a reality, for 2D simulations. Previous work at Durham has led to the development of a system Concept Analyst, and readers are invited to view the web site http://www.conceptanalyst.com to view screen captures of typical interactive design analysis sessions. It is the aim of the proposed work to bring the same level of interactivity to 3D simulations. This will present several technical challenges, but promises to have considerable impact.We request funding from EPSRC to support a post-doctoral research associate and a postgraduate student, to provide for appropriate computational facilities, and to fund collaboration and dissemination through conferences and academic publications. The duration of the proposed project is three years.