a 84-2 Similarity Principle When we design or manufacture some complex and huge hydraulic machines built water power engineering as well as search some complicated hydraulic phenomena, we often design and made a model which is reduced size according to similarity principle. Carrying out simulation experiment, deduce the flow situation and relative data of practicality through observing the flow situation of model defination: The basic theory which analyze and study the similitude relation between model and real object is called similarity pI rinciple Real object is called prototype too 77 §4-2 Similarity Principle When we design or manufacture some complex and huge hydraulic machines ,built water power engineering as well as search some complicated hydraulic phenomena ,we often design and made a model which is reduced size according to similarity principle. Carrying out simulation experiment, deduce the flow situation and relative data of practicality through observing the flow situation of model. The basic theory which analyze and study the similitude relation between model and real object is called similarity principle Real object is called prototype too. defination：