To stay competitive, new products require faster development time at low cost and good quality. Defense as well as commercial industries are forced to use analytical tools to stay competitive in a tough market. The use of simulation tools and approximation techniques in evaluating product performance during the early stages of the product development has a major impart on the product development efficiency, effectiveness, and lead time. Building physical prototypes of complex systems is expensive and it is difficult and time consuming to develop them. It is extremely beneficial to know as much as possible about the product performance and to optimize its dynamic characteristics before the first physical prototype is built. Without the need for physical prototypes, it takes the use of simulation tools and approximation techniques throughout the product development cycle to analyze product performance, conduct trade-off studies, guide the direction of the design to optimally satisfy performance, structural integrity, reliability, durability, cost and other requirements.