2.4.1　Physical simulation

The physical simulation refers to the simulation that the physical essence of the artificially manufactured model is the same with that of the actual research object.The physical simulation must meet the following conditions.First,the geometric size of the model is reduced or enlarged in proportion to the geometric size of the original content,in other words,the model and the original content are completely similar in shape.This is called the geometric similarity condition.Second,the model and the original content are required to comply with the same physical laws.Only under this condition can the model be used to test and research within the scope of physical laws instead of the original content,which is physical similarity.(https://www.daowen.com)

For example,in order to develop the dynamic characteristics of a new type of aircraft flying at high speed in the air,a model similar to the actual aircraft geometry needs to be created,and then placed in a wind tunnel(high-speed airflow device)to create a similar researching environment to that of the original aircraft in the air.Through the force test of the aircraft model,we can easily obtain reliable data in a short time at a small cost.