Virtual prototyping often reduces the cost of overall development of a product, as well as the time required to develop it, and can increase innovation as well. The physically accurate simulation of a mechanical system enables the designer to investigate, explore, and experience the performance and behavior of an evolving product, and thus reduce the number of physical prototypes needed. For the sake of better support for designers to manipulate the simulation, we have developed a dynamic simulation package of a mechanical system considering its environment effect. The package incorporates physical behavior modeled by multi-body dynamics, fluid and contact dynamics with environment and user input. The main contribution of the simulator is in providing support that allows the usersʼ interactive manipulation in terms of a specific environment parameter configuration in the simulation loop online as opposed to the traditional offline.