Advanc ances s in STAR-CCM CCM+ DEM m models for simulating - PowerPoint PPT Presentation

Advanc ances s in STAR-CCM CCM+ DEM m models for simulating ulating deformatio mation, n, breakag age, , and d flow of solids Satish sh Bonthu thu

Out utli line ne Overvie view of DEM EM in STAR AR-CC CCM+ M+ Recen cent t DEM EM imp mprovem ements nts – Parallel Bonds in STAR-CCM+ – Constant Rate Damage Model – Maximum Packing Random Injector – Particle Depletion Model – Abrasive Wear Model Simulat ation ion st studies udies – Compression of brittle material – Rock drilling – Erosion in a pipe bend – Erosion due to water jet Sum umma mary 2

Discre Di crete e Element ement Modeling ling (DE DEM) M) - Overvie view DEM EM is us used d to mode del particles ticles of differe erent nt sizes es and shapes pes • DEM resolves the collisions between particles • Particles can be bonded together to form deformable / breakable material 3

DEM Go DE Governing erning Equat uations ns Moment mentum m conser nservat ation ion 𝑒𝑤 𝑗 𝑛 𝑗 𝑒𝑢 = 𝐺 𝑗𝑘 + 𝐺 𝑕 + 𝐺 𝑔𝑚𝑣𝑗𝑒 𝑘 𝑛 𝑗 and 𝑤 𝑗 are mass and velocity of particle 𝑗 , 𝐺 𝑕 = 𝑛 𝑗 𝑕 is gravity force, 𝐺 𝑗𝑘 is contact force between particle 𝑗 and element 𝑘 - DEM is a meshless method - DEM is computationally intensive method Conse nservati tion on of angul ular r mome mentum ntum 𝑒 𝑒𝑢 𝐽 𝑗 𝜕 𝑗 = 𝑈 𝑗𝑘 𝑘 – 𝑗, 𝐽 𝑗 and 𝜕 𝑗 are the momentum on inertia and rotational velocity of particle 𝑗 . 𝑈 𝑗𝑘 = 𝑠 𝑗𝑘 (𝐺 𝑗𝑘 + 𝐺 𝑠 ) is the torque produced at the point of contact and it is the function of the rolling friction force 𝐺 𝑠 4

Cont ntact act forces es Normal l component ponent of cont ntac act t force Particle icle A Young’s modulus ulus (stiffnes fness) Normal l restit itut ution ion Particle icle B Tangent gential ial component ponent of cont ntac act t force Fricti tion on Tangent gential ial restit itution ution 5

Cont ntact act models els in n STAR-CCM+ CM+ Basic ic models ls Hertz-Mindlin Classical nonlinear contact force model for rigid bodies Walton-Braun Linear model for deformable particles Linear Spring Linear model for rigid bodies Optional nal models ls Rolling Resistance Three models for resisting rolling Linear Cohesion Constant attractive force Artificial Viscosity Velocity dependent damping model Heat Conduction Heat flow through contact Parallel Bonds Bonds resisting to tension, bending, twist 6

Pa Parallel rallel bo bond nds s in n STAR-CC CCM+ Massless less bar, subject ject to break aking ing under er load Two o STAR AR-CC CCM+ M+ models odels us use same me bond nd physi sics – Parallel bond contact model • Bonds are formed after injection at each new contact • User specifies time interval of bonding – Bonded particle model • Used to create clumped particles: • Bonds are formed at the moment of injection Recen cent t imp mproveme ments nts – Bond strength distribution, visualization, and… 7

Bond nd Failur lure e Models ls in n STAR AR-CCM+ CCM+ Simple Failure Model F t t+dt Constant Rate Damage Model New in version 10.04 F F F F t t+dt t + n dt 8

Consta nstant nt Rate e Da Damage age Model A 0 Stress on bond M σ m A σ l B 0 B ε f k r ε f O Bond tensile strain k r is the fracture softening modulus, model parameter 9

Exam ample ple of Brazilian azilian compression pression test st Standar ndard d test t to det etermine ermine the e strength rength of britt ttle le mater erial ial Solid id materi erial al is modeled odeled as particles cles bon onded ded togeth ther er 10

Sample ple preparati paration on New Maximu ximum Pa Packing ing option on in Random ndom Inject ector – Particles “grow from seeds” until whole region is fully packed – Resulting configuration has no overlaps between particles 200 seeds 10000 seeds 11

Run unni ning ng compress ression ion test st Geome ometr try y invol olves es stati tion onary y bott ottom om wall and moving ving down wn top platen en – Particles are injected using table injector with “Allow overlap” option • Particle diameters are “inflated” by factor 1.01 to ensure small overlaps – Bonds are set to form for first 0.1 s before starting compression 12

Ani nimation mation of compression pression test st 13

Crac ack k formati mation on Both “Simple Failure” and “Constant Rate Damage” models were re tested: d: – Only “Constant Rate Damage” model reproduced the vertical crack observed in experiment Bonds nds mode del parame meters s (Normal ormal and Tangen ential tial strength rength of bon onds ds, , its s dist stributi ribution on) ) were re calibra brated ed to reprod oduc uce e the e target t materi erial al – Soft sandstone in our tests 14

Exam ample ple of rock drilling illing Rock ck is perme meable ble with h void d fracti tion on =0.4 Ov Overset t mesh is s us used d to rot otat ate e and advanc nce e the e drill-bit bit down wn Soluti tion on for drilling ing flui uid d flow w was obtaine tained d us using 2-way y coup upli ling ng model odel Jet et flow w form rm nozzl zzles es results ults in large e drag g forces ces on bonde nded d grains ns (jett etted ed erosi osion on) 15

Erosion osion and Wear r in Solids ids Processing cessing Equipm ipmen ent Drilling rock Slurr rry y flow w in pip ipes erosion ion Sedimen ent t flow, , Gravel el Pa Pack cking ing 16

Abr brasi sive e Wear Model l in n STAR-CCM CM+ New w in versi sion on 10.04 .04 Relevant ant for flow w regimes imes – With high solids loading – Prolonged “sliding” contact between particles and geometry 17

Abr brasi sive e Wear Formulat mulation ion motion Archar chard Model: l: 𝑵 𝒇 = 𝑫 𝑮 𝒅𝒐 𝒘 𝑑𝒖 𝒆𝒖 is mass 𝒅𝒑𝒐𝒖𝒃𝒅𝒖𝒕 eroded from single surface cell 𝐺 𝑑𝑜 – 𝑫 is abrasive wear coefficient in units of kg/J (model parameter) Surface cell Contact path – 𝐺 𝑑𝑜 is normal component of particle-cell contact force 𝒆𝒖 At the e end d of each h times estep ep, , for – 𝒘 𝑑𝒖 is tangential component of each h sur urfa face ce cell, l, particle-cell relative velocity at the point of contact – Erosion rate calculated as 𝐹 𝑠 = 1 1 – 𝒆𝒖 i s DEM timestep 𝑁 𝑓 𝑈 𝐵 𝑑𝑓𝑚𝑚 Field Func nction tion option: on: • 𝑈 is the timestep • 𝐵 𝑑𝑓𝑚𝑚 is the area of surface cell 𝑵 𝒇 = 𝑫 𝐺(𝑑)𝒆𝒖 – 𝑁 𝑓 is reset to zero 𝒅𝒑𝒐𝒖𝒃𝒅𝒖𝒕 – 𝐹 𝑠 is available for postprocessing – 𝐺(𝑑) is user field function 18

Abr brasi sive e wear formulation mulation summa ummary Model del proper perly ly accounts ounts for – All contacts during timestep – Variation of contact force strength and relative velocity for single particle during prolonged “sliding contact” Abrasi sive e wea ear r coef efficient cient is often n related to “hardness” of boundary Abrasiv ive e wear ear model odel is s compati patible ble Best t for flows ws when hen harde der r with h coarse se grain n model odel partic icles les are sliding ing along ng sof ofter er boundar ndary 19

Elbo bow w pipe exam ample, ple, top view 2 m 0.4 m Inlet 1 m Mean Parcel Diameter = 10 mm Mesh size 20 mm Outlet 20

Pa Partic icle le Inj nject ection gravity Injection Volume Rando dom m inject ctor or – Uses “Maximum Independent Set” Algorithm to provide High Solid Loading flow – Fast, mesh independent – Initial particle velocity: • Horizontal component = inlet fluid velocity • Small “down component” 21

Ini nitial tial Results sults for Elbo bow w flow 22

DE DEM Postpr stproc ocessing essing View from bottom 23

Erosion osion due ue to water er jet et exam ample ple Segme gment nt of pipe (or r solids ids bui uildu dup inside ide pipe) can be modeled odeled us using g DEM EM particles cles bonde nded d togeth ther 0.4 m – D_inner = 0.3 m – D_outer = 0.4 m Water er flow w is set et with th inlet t at one e end d of DEM EM pipe and out utle let t at anoth ther end Inle let t veloci ocity ty is tilted ed 10 deg deg with th respect pect to inlet et norma rmal – One side of pipe should experience more erosion 24

Ini nitial tial Results sults with h Const nstant ant Rate e Da Damage age Model Inle let t veloci ocity ty in aggres essively y ramped mped from om 0 till 20 m/s over r simula ulated d time me Ful ully y 2-way y coup upling ing bet etwee een n DEM EM and CFD 25

DE DEM Post st-pr proc ocessing essing 26