# UDF srivastava and sundaresan friction model - divergence of the solutor

 Register Blogs Members List Search Today's Posts Mark Forums Read June 7, 2016, 08:06 UDF srivastava and sundaresan friction model - divergence of the solutor #1 New Member   Luca Panariello Join Date: May 2016 Posts: 1 Rep Power: 0 Hi everybody I am trying to implement the srivastava and sundaresan model for friction pressure and viscosity via UDF in fluent. My problem consist in a fluidized bed where air is injected through a jet. Johnson&Jsckson and Schaeffer models, available in fluent, failed to predict the bubbling of the bed. I am now trying to implement this model, but the UDF I write causes the divergence of the solver. You can find the UDF code below. Is there anyone who knows what's wrong? DEFINE_PROPERTY(frictional_pressure, cell_s, thread_s) { real es, dudx, dudy, dvdx, dvdy, div, S11, S12, S21, S22, SS, theta, pc, pf, n, den, exponent, Fr; /* find velocity gradient for solid phase, solid volume fraction and granular temperature */ es = C_VOF(cell_s, thread_s); /*solid volume fraction */ dudx = C_DUDX(cell_s, thread_s); /* velocity gradient components */ dudy = C_DUDY(cell_s, thread_s); /* velocity gradient components */ dvdx = C_DVDX(cell_s, thread_s); /* velocity gradient components */ dvdy = C_DVDY(cell_s, thread_s); /* velocity gradient components */ theta = C_GT(cell_s, thread_s); /* granular temperature 8/ /* define divergence and compute S:S */ div = dudx+dvdy; /* divergence of solid velocity */ S11 = 2/3*dudx-1/3*dvdy; /* component 11 of the strain rate tensor */ S12 = 0.5*(dudy+dvdx); /* component 12 of the strain rate tensor */ S21 = S12; /* component 21 of the strain rate tensor */ S22 = 2/3*dvdy-1/3*dudx; /* component 22 of the strain rate tensor */ SS = abs(pow(S11,2)+2*S12+pow(S22,2)); /* S:S */ /* compute pc, Johnson&Jacskon model */ Fr = 0.1*es; if(es > esmin) pc = Fr*(pow((es-esmin),r)/pow((esmax-es),s)); else pc = 0; /* compute n */ if(div >= 0) n = sqrt(3)/(2*sin(fi)); else n = 1.03; /* compute and return pf */ den = n*sqrt(2)*sin(fi)*sqrt(SS+theta/(pow(ds,2))); exponent = 1/(n-1); if (den == 0) pf = pc; else pf = pc*(pow((1-div/den),exponent)); return pf; } DEFINE_PROPERTY(frictional_viscosity, cell_s, thread_s) { real es, dudx, dudy, dvdx, dvdy, div, S11, S12, S21, S22, SS, theta, pc, pf, n, den1, den2, exponent, Fr, muf; /* find velocity gradient for solid phase, solid volume fraction and granular temperature */ es = C_VOF(cell_s, thread_s); /*solid volume fraction */ dudx = C_DUDX(cell_s, thread_s); /* velocity gradient components */ dudy = C_DUDY(cell_s, thread_s); /* velocity gradient components */ dvdx = C_DVDX(cell_s, thread_s); /* velocity gradient components */ dvdy = C_DVDY(cell_s, thread_s); /* velocity gradient components */ theta = C_GT(cell_s, thread_s); /* granular temperature 8/ /* define divergence and compute S:S */ div = dudx+dvdy; /* divergence of solid velocity */ S11 = 2/3*dudx-1/3*dvdy; /* component 11 of the strain rate tensor */ S12 = 0.5*(dudy+dvdx); /* component 12 of the strain rate tensor */ S21 = S12; /* component 21 of the strain rate tensor */ S22 = 2/3*dvdy-1/3*dudx; /* component 22 of the strain rate tensor */ SS = abs(pow(S11,2)+2*S12+pow(S22,2)); /* S:S */ /* compute pc, Johnson&Jacskon model */ Fr = 0.1*es; if(es > esmin) pc = Fr*(pow((es-esmin),r)/pow((esmax-es),s)); else pc = 0; /* compute n */ if(div >= 0) n = sqrt(3)/(2*sin(fi)); else n = 1.03; /* compute pf */ den1 = n*sqrt(2)*sin(fi)*sqrt(SS+theta/(pow(ds,2))); exponent = 1/(n-1); if (den1 == 0) pf = pc; else pf = pc*(pow((1-div/den1),exponent)); /* compute and return muf */ den2 = sqrt(SS+theta/(pow(ds,2))); if((den2 == 0) && (pc != 0)) muf = pf*sin(fi); if (pc == 0) muf = 0; else muf = sqrt(2)*pf*sin(fi)/den2*(n-(n-1)*pow(pf/pc, exponent)); return muf; }   January 18, 2017, 11:07 #2 New Member   Tommaso Join Date: Jan 2016 Posts: 1 Rep Power: 0 Shouldn't be the in the S:S calculation: pow(S11,2)+2*pow(S12,2)+pow(S22,2) instead of pow(S11,2)+2*S12+pow(S22,2) ?  Thread Tools Search this Thread Show Printable Version Email this Page Search this Thread: Advanced Search Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules Similar Threads Thread Thread Starter Forum Replies Last Post Musa FLUENT 1 March 14, 2014 03:42

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