Parametric Design And Simulation Of Fractal Voronoi Bimodal Porosity Structure

Porous structure significantly affects performance of porous materials,wherein bimodal porosity structure is a mesoscale structure deriving from pore size bimodal distribution of porous materials.By adjusting pore sizes and proportion in each scale,optimization of transport and reactive performance of porous materials can be achieved.This work suggests a bimodal porous structure with independently controlled pore size distribution and even spacing via iterating Voronoi stochastic geometry process.By establishing the framework of adapting the mesoscale bimodal pore structure to various governing equations and numeric methods,complete ion transport dynamics simulations is made feasible,thus enabling more comprehensive design on bimodal pore structure and optimization on materials performance.The self-resemblance of the structure is from fractal feature by iteration,and the structure is applicable to modelling of bimodal porous materials due to its advantages over other Voronoi processes.Research process and results as following(1)Based on stochastic and fractal geometry,this work details the theory of independently forming bimodal pores by devising a bimodal pore structure controlled by 4 parameters.This work shows the geometry features including porosity,specific area,fractal dimension and lacunarity determined by control parameters in analytic or semi-analytic approachs,among which cylindrical space diameter has the most numerical weight.(2)To provide geometry inputs to simulation,this work designs algorithm and program for geometry files generation both in 2D and 3D.The algorithms are in time complexity as O(n~2(log)~2n) and storage complexity as O(n~2).eeanwhile,programs are designed with optimizations regarding implicit parallelism,robustness for geometry file output in voxel scale beyond 5000 and interactivity with considerations on inherited data structure and demands of simulation.(3)With computing domain from geometry files of bimodal porous structure,this work simulates the transport performance of bimodal porous structure.Permeability simulation and 3D lattice model methodsare developed in combination with lattice Boltzmann method.(4)To enable inspection on reactive performance of the structure,this work develops a simulation method on charge transfer dynamics between bimodal porous electrode and electrolyte.For a detailed characterization of actual performance in hydrogen evolution reaction,this work discusses the concentration dependent dynamics of electrochemical simulation.As a reference to pore structure design under fiexed radius ratio between pores,a computation example is implemented to demonstrate the configuration method for optimizing porous electrode’s structure by considering both permeability and specific area,in which pore ratio as 1:5.70 demonstrats best reactivity among all presented ratios under constant pore scale 2:1.