شبيه سازي پديده كاويتاسيون به روش عددي DPD

چكيده انگليسي :

A Study on the Cavitation Phenomena using Dissipative Particle Dynamics Simulations Siavash Sandooghdar s sandooghdar@me iut ac ir Date of Submission 2012 25 2 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Ahmad Reza Pishevar Email apishe@cc iut ac irAbstractCavitation is one of the fundamental phenomena in fluid mechanics This phenomenon can be observed influids in an acoustic field Cavitation is essentially a multi scale and multi process phenomenon In thisthesis we investigate the dynamic aspect of the nucleation growth shrinkage and collapse process usingdissipative particle dynamics DPD simulations Dissipative particle dynamics DPD is a mesoscopic simulation method that can be used to simulate thebehavior of fluids In DPD a coarse graining is employed at the molecular level to discard the excessivedetail at smaller length and time scales Hence each DPD particle implies a cluster of real molecules whichallows one to study of larger scale systems for longer times as compared to purely atomistic simulationssuch as Molecular Dynamics MD The method has proven to be useful in the simulation of complex liquids such as polymer suspensions colloids and surfactants However It is important that the coarse grained mesoscopic model be able toprovide properly the thermodynamic and hydrodynamic properties of a real system beyond certain lengthand time scales On the other hand some of the observed phenomena may have a purely thermodynamicorigin due to the modification of equations of state For example the prediction of thermodynamicproperties for metastable liquid is important in the research on liquid structure and phase transition So itseems to be necessary to consider the thermodynamic properties of fluid during the simulation Furthermore accurately matching the phase behavior of a model system a static property to that of a realfluid allows one to focus on the dynamical aspects during the study of the phase separation and provides thelinks to reality necessary for quantitative simulation Therefore the ability to specify beforehand thethermodynamic behavior of coarsegrained systems is an important point Unfortunately the conventional DPD method is not flexible enough to correctly reproduce thethermodynamic behavior of a real system Owing the soft interaction forces in the method the DPD EOShas rigid quadratic density which is quite different from the EOS of a real fluid To overcome this problemmany body DPD method invented by Pagonabarraga and Frenkel They assume that the conservative forcedepends on the instantaneous local particle density which allows one to obtain a much wider range ofpossibilities for the EOS Also Trofimov investigated multibody DPD MDPD which they improved thethermodynamic consistency by employing different density calculation schemes Thus improved MDPDmethod obtained In this work we have developed improved MDPD in which the standard DPD model combined as a long range attractive force with improved MDPD conservative force This form of conservative Force based ondifferent influence ranges for attractive and repulsive forces is similar in concept to the model proposed byWarren The combination of repulsive behavior within short range and attractive behavior for long rangereflects the microscopic physical origins of coexisting liquid and gas phases in single component fluids By examining our model on the coarse grained Lennard Jones fluid below the critical point we have shown

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شبيه سازي پديده كاويتاسيون به روش عددي DPD

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