Research On The Key Techniques Of The Hybrid Atomistic-continuum Coupling Parallel Simulation Framework For Microfluidics

With the increasing development of nanotechnology and micro-machining technology,the study of fluid properties has been extended from the macroscopic level to the microscopic level.The research on the phenomena and properties of microfluidics has important scientific significance and application value in the design and manufacture of bioengineering,pharmaceutical,chemical and high-throughput devices.Due to the smaller temporal-spatial scale and the high surface-volume ratio,the continuum assumption becomes invalid.The hybrid atomistic-continuum(HAC)coupling method is proposed to serve as a bridge to connect the macroscopic scale and the microscopic scale.However,there are still many challenges to achieve efficient large-scale parallel simulation of microfluidics: accurate HAC coupling method,efficient and scalable parallel numerical solver and parallel optimization method for HAC coupling simulation.In this thesis,aiming at the difficult development,simulation accuracy and computational efficiency problems faced by microfluidic simulation,we focus on the key techniques of large-scale parallel numerical simulation for microfluidics.The main contents and innovations of the thesis include:· The hybrid atomistic-continuum coupling simulation parallel framework for microfluidics is designed and implemented.(Chapter 2)We abstract the overall architecture of the hybrid atomistic-continuum coupling application framework for the first time and design the hierarchical framework for the cooperation of multiple research domains.Based on the open source software framework Open FOAM,LAMMPS,we design the kernel coupling simulation solver.Based on the open source software framework SALOME,we design and implement the easy-to-use pre-and post processing tool.These research provide a software platform for large-scale parallel simulations of microfluidics,reduce development complexity,achieve cross-domain collaboration,and guide the manufacture of microfluidics devices.· The coupling strategies of the hybrid atomistic-continuum coupling method for microfluidics are proposed and implemented.(Chapter 3)The effects of spatial coupling strategies,temporal coupling strategies,sampling strategies and correlation coefficients configuration of hybrid atomistic-continuum method on the accuracy and efficiency of coupling simulation are analyzed in detail.Taking full account of accuracy and computational efficiency of channel flow simulation,we design the following coupling strategies for straight side coupling geometry: the spatial coupling strategies with minimum width of the overlap region and fully data exchanging,the temporal coupling strategies with proper sampling numbers and data exchanging times,and the non-periodic boundary force model with the least fluctuation.These research provide a reference for the field researchers to select the coupling strategies for the simple geometric case,and provide the guidance for the coupling strategy setting of the complex geometric coupling case.· An efficient parallel particle insertion algorithm of the hybrid atomistic-continuum coupling method for microfluidics is proposed.(Chapter 4)Aiming at solving the time-consuming problem of the particle insertion algorithm,we propose a grid-based parallel particle insertion algorithm,White-Initial USHER(WI-USHER)for dense microfluidics.The WI-USHER algorithm slices the region to be inserted into finer grids with proper spacing scale,marks parts of finer grids in black according to three exclusive rules,and finds the target insertion point in the remained white grids.The WI-USHER algorithm performs lower averaged force evaluation times,which decreases from O(104)to O(103)compared to the USHER algorithm when the number density with value of 0.6 ? 1.0.The percentage of the total parallel simulation time processed by the particle insertion operation decreases from 23.5% to 3.2% compared to the USHER algorithm.The WI-USHER algorithm not only greatly enhance the performance of the original particle insertion algorithm,but also balance the particle insertion workload in the parallel computing framework.· The coupling oriented parallel optimization techniques for the hybrid atomisticcontinuum coupling method are designed and implemented.(Chapter 5)Based on the characteristics of the hybrid atomistic-continuum coupling simulation,taking account of the difference of the two scales,the additional computational load introduced by the coupling procedures,limited computing resources and the demand of noise elimination,we design the multi-communication world nested parallelism processes allocating and mapping mechanism for the hybrid atomisticcontinuum coupling simulation.At the same time,we design the smart sending mechanism with the minimum communication between processes.We design the load balancing evaluation index for coupling simulation and establish the load balancing model for the hybrid atomistic-continuum coupling method.The multicopy advancing method and the allocation decision mechanism are designed and the model of computing resource allocation is put forward.Experimental results show that the corresponding optimization technology can alleviate problems of the original load imbalance and improper resource allocation.Meanwhile,the hybrid atomistic-continuum coupling application framework designed in this thesis achieves good parallel scalability.