| Smoothed Particle Hydrodynamics (SPH) discretizes the configuration by a set of particles with the properties of mass and volume. By tracing the motion of each particle, the variation history of the configuration could be derived. The mesh distortion, which occurs usually in the methods based on girds when they are applied to compute the large deformation in continuum mechanics, is thus avoided in SPH because of its meshless property. It also masters the high speed and hyperpressure problems in continuum mechanis well with a density-based algorithm.Supercavities are induced for the high speed underwater moving bodies. Two classes of methods based on the Euler formulation, i.e. potential theory and transportation equations with two kinds of cavitation models, are the two main ways for studying the supercavity flows. The potential theory neglects the vapor in the supercavity, because the mass in the cavity is so tiny that its inertial applies little effect on the dynamics of the water flow. Massive iterations are performed to seek the cavity surface in this method. The relationship between the vapor and water flows is included in the second type methods and it thus reveals much more characteristics in the cavity flows. Much more iterations are performed to derive the supercavity in the second type methods. The second type ones, which are mainly realized with the pressure-based algorithm, are relatively inconvenient, comparing with the ones with density-based algorithm, to process the flows with considerable compression.The supercavity surface, in fact, is the interface between mediums. Mediums'interface, in SPH, is regarded as a set of particles. Theoretically, SPH could conveniently and naturally provides the cavity's development, if it could realize the flows driven by the high speed underwater bodies. Because it is performed with a density-based algorithm, it thus treats the considerable compression well in the flows. The work in this thesis, which is performed to numerically study the low-subsonic and high-subsonic flows driven respectively by underwater high speed bodies with speeds of 100 m·s-1 and 1000 m·s-1 (for simplicity, we'll refrence it as high speed driven flows), is realized by the code developed by us with SPH. Along with the work, a basic problem, i.e. the stabitliy of SPH, is also studied, and two important techniques are proposed to implement the wall boundary conditions and to process the SPH data respectively. Especially, the supercavity surface could be easily extracted by the post-processing techniques proposed here.Complicate relative position between static and dynamic walls which have complex geometries exist in the computational models of the high speed driven flows. Too many walls with too many angles and relative motion between walls challenge the universality and simplicity of the implementation algorithm for the wall boudanry conditions. If the algorithm is restrict only to simple shape walls or changes for different shape walls, the universality of the complete SPH code is thus reduced rapidly. And the Boundary Deficience of SPH (BDS), i.e. the SPH approximation being truncated near the wall, requires a remedy when the boundary conditions are being implemented. However, the methods, i.e. the Ghost Particle Method (GPM) and Dummy Particle Method (DPM), which could remedy BDS, are neither inconvenient to be implemented on complex geometrical walls and neither universal for different shape walls. A Convenience and Universality Improved Ghost Particle Method (CUI-GPM) is thus proposed to universally treat the walls with angles or curvatures. Its applications in the fluids and heat conduction exhibit its feasibilities and reasonabilities. Regretfully, CUI-GPM encounters difficulties in the computations of high speed driven flows. Because the supercavity separates the fluid from the body, which arouse the errors in the interpolation of CUI-GPM, and re-entry jet at the tail of the supercavity could not be mastered well in SPH. Another boundary implementation algorithm, which combines the DPM and GPM, is thus advised. DPM realizes the non-slippery condition by directly assigning the body speed to the ghost particles, and GPM refreshes the density on ghost particles as that on fluid particles. With the latter route, the re-entry jets derived by SPH accords the practical ones.For extracting the supercavity surface and comparing it with the theoretical shape, the post-processing of SPH is studied. Traditional post-processing technique could not supply continuous color contours, continuous contour lines and streamlines, and slices of the datas, etc. A relatively new post-process technology is thus presented, which supplies a route to tansforme the SPH data into the FEM data, and the developed post-processing technology for FEM are employed for SPH. The Delaunay triangulation algorithm transforms the SPH particle sets into the meshes with a set of triangular elements. However, for the particle set on the non-convex domain, the Delaunay triangulation results some empty elements which contains no mass, these empty elements should be deleted from the original element set. Thus, a so called"Element Mass Weighting"Method (EMWM) is presented to delete those empty elements. And the rest elements with their nodes (particles) and the datas on them are employed as the FEM data to process the SPH data. The EMWM with Delaunay triangulation is very convenient to extract the supercavity's surface.The stability analysis with its results supplies the basis for the computation of the high speed driven flows. The matrix form of SPH is imported to study the stability of the SPH particle set. The intrinsic reason of the Tensile Instability (TI) is found to be caused by the Euler coordinates of particles, and the sufficient condition of TI, which was ever given by Swegle, is also derived here. The Tensile Stability Prerequisite (TSP) requires the smoothing length factor (the ratio of smoothing length to the particle interval) equals the extreme point of the first order derivative of the smoothing function. The value of the smoothing factor is also found to be equal to the smoothing function's extreme point with respect to the smoothing length, which also makes the Fourier tansformation of the smoothing function attain its extreme value.The TSP yields the value of the numerical sound speed. The TSP also requires that a correct and suitable physical model of the medium should be chosen for the flow otherwise the spurious compression occurs in the computation. Consequently, a proper state equation of the water is chosen in the computation of high speed driven flow. The implication of the TSP, i.e. the frequence of the error should be far smaller than that of the time integration, is also revealed and which yields the Courant number of CFL condition, which supplies the reasonable refrence to choose the time step size. It could consequently yield the flow compression that satisfies the stability prerequisite, which yields the empirical values of the flow compression from the studies of Monaghan[10] and Morris[95] for observing and checking the stability and reasonability of a computation case with weakly compression flows. This supplies the theoretical route to observe and check the reasonability of the computation case of the high speed driven flow.Based on the results derived above and with their application in the computation of the high speed driven flow, stable and reasonable computational cases are perfomed, during which the compression varies in a reasonable limit. The supercavity derived by SPH accords well with the ones given by the Principle of Independent Expansion of the Cross Sections of the Supercavity and experiments, which shows the feasibility of applying SPH to calculate the high speed driven flows. The numerical results also indicate that, the re-entry jet occurs obviously at the tails of the supercavities when the bodies start in the water, and that the re-entry jet is not obvious when the bodies start in a lauch canister and the cavity tail is almost perpendicular to the bodies's surface. It can also be found that the length of the caity is reduced for the body with a longer afterbody. The asymmetry along the axis of the supercavity is found to be induced by the compression in the flow which also futher enlarges the size of the supercavity.The numerical studies of the flows driven by high speed underwater bodies are realized by SPH. The implementation algorithms of the wall boundary, which was proposed as a technique to realize the work above, relatively enable SPH to be conveniently developed for complex shapes walls in engineering. And the post-processing algorithms advised above supplies a practical route to realize a universal post-processor of SPH. And the stability analysis of SPH provides the information to construct and perform a reasonable and stable computation case.
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