Theoretical Study Of One-dimensional Isentropic Flow In Samples Under Ramp Wave Loading

Theoretical study on hydrodynamics is the basis of the research on high pressure and high density of material and is also an important content of extreme state physics and mechanics for its contribution to the exploration of the material structure and the physical and mechanical properties,which involves mathematics,physics and mechanics,statistics and other disciplines.As an important concept in physics and mathematics,the characteristic line can be an effective means for theoretical research of flow field.First of all,the ramp wave compression experiments and data processing methods are investigated.From the aspects of realization principle,typical experimental device,experimental ability and loading characteristics,two kinds of ramp wave compression experimental techniques(magnetic driven ramp wave compression experimental technique and laser driven ramp wave compression experimental technique)are introduced.Subsequently,based on the concepts of isentropic flow,simple wave flow field and characteristic method,the main data processing methods for ramp wave loading experiments are introduced emphatically from the aspects of method deduction process,method characteristics,approximation,citation hypothesis and application scope.Then the research background and main contents of this thesis are summarized.Secondly,the characteristic line method is sorted out.The meaning and expression method of characteristic line are introduced in general sense,and the image and physical characteristics of three commonly used models in one-dimensional flow field in ramp wave compression experiment is collated,which provides the basis for the following chapters.Thirdly,the optimal waveform of ramp wave compression is studied.Based on the simple wave theory,the analytic expression which described the transition of ramp wave to shock wave is deduced.This analytic expression allows us to establish the relationship between the history of loading pressure and the medium's internal flow field by using the characteristic line method.It has been shown that there is a threshold for the pressure rising rate which depends on the compression parameters and the thickness of the sample,and this threshold exists in every pressure value investigated.Shock wave would be created when the rate of pressure rising exceed the threshold.By comparing with the results in the literature,the relations in this article has more reasonable physical meaning,and it can accurately determine the position of shock wave transformation point.This work provides a solid theoretical basis for the parameter design and waveform optimization process in the experiment.Fourthly,the solution of ramp wave compression with free surface boundary condition is studied.Under the condition of the unknown EOS and the known free surface velocity history,the direct calculation method,which produces results with high accuracy in the data processing with no strength effect,is derived using the characteristic line method.By comparing with computing results from the commercial software and the experimental results in the literature,it is found that the method,as an approximate method,still produces results with considerable precision in the data processing with strength effect,and it also reflects the original compression properties of the material to some extent.In the end,the full thesis is summarized and prospected.The main conclusions and some problems to be further studied are given.