Parallel Discrete Element Simulation and Its Application to the Study of Solid-Liquid Flow Behavior

自離散元素法(Discrete Element Method，簡稱DEM)問世以來，至今已經被用於各項工程領域之中。隨著計算技術的快速發展，離散元素法今日也被用來描述更為複雜的物理現象或解決更困難的工程問題，流固混合流(solid-liquid flow)之流動行為即為離散元素法的其中一項應用，該現象常見於自然界或工業中，卻因流固介面的互動機制甚為複雜使得其行為不易預測，亦需耗費大量的計算。計算需求實為以離散元素法模擬流固混合流之流動行為時無法避免的課題，工程界有必要發展更有效率的離散元素模擬(Discrete Element Simulation，簡稱DES)系統。本研究之目的即在發展一套平行離散元素模擬系統以應用於自充填混凝土(Self-Compacting Concrete，簡稱SCC)與濕顆粒流(wet granular flow)等兩種流固混合流之行為模擬。 本研究針對離散元素模擬程序實作三種策略以增進其效率，針對流固混合流之模擬發展出一套名為KNIGHT&ANNE/IRIS 2.0的模擬系統，在經由分散式與共享式記憶體等兩種計算平臺上進行多個數值案例以評估及效能，確認前述各項策略對離散元素模擬效率之增進確有其貢獻。 對於自充填混凝土的流動行為，本研究採用異質模型描述之，並以離散元素模擬數個質流(rheology)實驗：類型包括V形漏斗與L箱形試驗，模擬過程則涵蓋充填(packing)乃至其流動行為。結果顯示所提出的離散元素模型足以描述自充填混凝土之流動現象，亦對模擬所需之參數及其範圍提出適當的建議。本研究另行提出一種將流體特性導入以修正元素間互動行為(interaction)之模型用於模擬濕顆粒流，並以一乾、濕顆粒傾斜流動之案例進行測試，結果顯示該模型確可描述濕顆粒流之物理現象，且模擬與實驗之結果亦相當一致。In recent years the widespread use of the Discrete Element Method (DEM) in engineering has generated increasing research interest across a variety of fields. As a result of rapid and continuing developments in computer science, DEM is now being applied to the modeling of physical phenomena and engineering problems of ever-increasing complexity. Solid-liquid flow behavior simulation is one ubiquitous application. However, dynamic behavior in such systems is difficult to predict due to complex interactions at the solid-liquid interface, which invoke considerable computational overhead. Since the method is constrained by contemporary processing power, an efficient Discrete Element Simulation (DES) system is needed for solving large-scale solid-liquid interaction problems. This paper undertakes to develop and apply such a system in the simulation of both Self-Compacting Concrete (SCC) and wet granular flow behavior. Three strategies are implemented to optimize existing DES procedures for computational speed; the result is an in-housed parallel DES system, KNIGHT&ANNE/IRIS 2.0 developed specifically for accelerated performance in solid-liquid flow simulation. Several numerical benchmarks are applied to both shared and distributed-memory platforms, indicating substantial performance improvements. A two-phase model is then developed for simulating SCC flow behavior. Various rheological experiments - the V-funnel flow test and the L-shaped box test - are modeled from packing to flowing, and DES handling of the simulation is shown to provide an adequate representation of empirical data. This comparison is also used to propose corresponding DES parameter values and ranges for simulation of SCC and mortar flow. A liquid-modified interaction model is proposed for the simulation of wet granular systems, and tested on both wet and dry particulate flows down an inclined channel. The level of congruence found between simulated and empirical data sets confirms the physical model to be reasonably accurate.誌謝(Acknowledgement) ibstract iii要 vable of Contents viiist of Figures xiist of Tables xvhapter 1 Introduction 1.1 Background 1.2 Objectives 2.3 Scope 3.3.1 Parallel Discrete Element Simulation System 3.3.2 Modeling of Solid-liquid Flow Behavior 4.3.3 Discrete Element Simulation of SCC Flow Behavior 6.3.4 Discrete Element Simulation of Wet Granular Flow 9.4 Organization 11hapter 2 Parallel Discrete Element Simulation 13.1 Parallel Discrete Element Procedure 14.2 Parallel Computing Environment 18.3 Strategies 23.3.1 Zone of Interest 23.3.2 Zoning 25.3.3 Partitioning 26.5 Load Balance Index 33hapter 3 Self-Compacting Concrete Flow Behavior Simulation 35.1 Rheology 35.1.1 Viscosity Index 36.1.2 Flowability Index 37.1.3 Workability Index Diagram 39.2 Numerical Model 40.2.1 Mortar Element 41.2.2 Coarse Aggregate Element 42.2.3 Elastic Force 43.2.4 Energy Dissipation 45.2.5 Friction 45.2.6 Bond 45.2.7 Density Control 46.3 Numerical Examples and Verification 47.3.1 Initialization 47.3.2 Mortar Flow 53.3.3 SCC Flow 61hapter 4 Benchmark of Parallel Discrete Element Simulation System 67.1 Examples 67.1.1 SCC V-funnel Packing and Test 67.1.2 SCC L-shaped Box Test 69.2 Verification 70.3 Evaluations 71.3.1 Evaluation of the Zone of Interest and Zoning Strategies 71.3.2 Parallel DES system 71.3.3 Partitioning Strategy with Variable Direction SCC Flow 75hapter 5 Wet Granular Flow Simulation 79.1 Modeling of Interactions between Wet Particles in DEM 79.1.1 Elastic Contact 79.1.2 Equivalent Normal Viscous Damper 81.1.3 Coulomb friction 83.1.4 Mass of liquid 84.2 Implementation of Wet-particles Interaction Model in VEDO 84.3 Numerical Examples and Verification 85hapter 6 Conclusions and Future Work 97.1 Conclusions 97.1.1 Parallel Discrete Element Simulation System 97.1.2 Discrete Element Simulation of SCC Flow Behavior 99.1.3 Discrete Element Simulation of Wet Granular Flow 101.2 Future Work 102eferences 105ppendix: dosXML Schema 2.0 117omenclature 12