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Error in Jacobian

Posted Feb 23, 2013, 12:50 a.m. EST Fluid & Heat, Heat Transfer & Phase Change, Computational Fluid Dynamics (CFD) Version 4.3a 3 Replies

Nithin
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Can I know what the error means??

"Failed to find consistent initial values.
Segregated group 1

Failed to evaluate operator Jacobian.
Operator: nif, Geometry: 1, Boundary: 12 13 14 15 17 18 19 20 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 81 82 85 86 87 88 90 91 92 93 95 96 97 98 100 101 102 103 105 106 107 108 110 111 112 113 115 116 117 118 120 121 122 123 125 126 127 128 130 131 132 133 135 136 137 138 140 141 142 143 145 146 147 148 150 151 152 153 155 156 157 158 160 161 163 164 166 167 169 170 172 173 174 175 177 178 179 180 182 183 184 185 187 188 189 190 192 193 194 195 197 198 199 200 202 203 204 205 207 208 209 210 212 213 214 215 217 218 219 220 222 223 224 225 227 228 229 230 232 233 234 235 237 238 239 240 242 243 244 245
Last time step is not converged."
3 Replies Last Post Feb 23, 2013, 2:41 p.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Feb 23, 2013, 7:43 a.m. EST
Hi

it means that for those boundaries you have defined a BC in such a way that the expression cannot be derived, and the Jacobian, used by the solver for the solving algorithm cannot be evaluated

ift en it comes from Dirac shape functions, or sharp step functions, you should rather use Heavyside smoothing (or step/rect type functions) than Boolean expressions

It's related that all functions ahall be derivable once or twice (or more) depending on your discretization

--
Good luck
Ivar
Hi it means that for those boundaries you have defined a BC in such a way that the expression cannot be derived, and the Jacobian, used by the solver for the solving algorithm cannot be evaluated ift en it comes from Dirac shape functions, or sharp step functions, you should rather use Heavyside smoothing (or step/rect type functions) than Boolean expressions It's related that all functions ahall be derivable once or twice (or more) depending on your discretization -- Good luck Ivar
Nithin
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Posted: 1 decade ago Feb 23, 2013, 10:21 a.m. EST

Hi

it means that for those boundaries you have defined a BC in sich a way that the expression cannot be derived, and the jacobian, used by the solver for the solvinf algorithm cannot be evaluated

iften it comes from Dirac shape functions, or sharp step functions, you should rather use Heavyside smoothing (or step/rect type functins) than Boolean expressions

It's related that all funcions ahall be derivable once or twice (or more) depending on your discretization

--
Good luck
Ivar


I was not able to get what you are saying sir... Can you elaborate it a little bit, please??
[QUOTE] Hi it means that for those boundaries you have defined a BC in sich a way that the expression cannot be derived, and the jacobian, used by the solver for the solvinf algorithm cannot be evaluated iften it comes from Dirac shape functions, or sharp step functions, you should rather use Heavyside smoothing (or step/rect type functins) than Boolean expressions It's related that all funcions ahall be derivable once or twice (or more) depending on your discretization -- Good luck Ivar [/QUOTE] I was not able to get what you are saying sir... Can you elaborate it a little bit, please??
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Feb 23, 2013, 2:41 p.m. EST
Hi

the error message says you have an operator named "nif" (probably something you have defined in the model Definition nodes, that apply to geometry 1 boundaries ...

This operator is defined with expressions such that it cannot be derived, hence COMSOL cannot estimate the Jacobian of the model equations and it cannot solve

I guess that your operator is used some-way with for example Boolean equations or even it might have a typo, but it is not "smooth", hence no unique derivative

For the need and use of the Jacobian, check the solver doc

--
Good luck
Ivar
Hi the error message says you have an operator named "nif" (probably something you have defined in the model Definition nodes, that apply to geometry 1 boundaries ... This operator is defined with expressions such that it cannot be derived, hence COMSOL cannot estimate the Jacobian of the model equations and it cannot solve I guess that your operator is used some-way with for example Boolean equations or even it might have a typo, but it is not "smooth", hence no unique derivative For the need and use of the Jacobian, check the solver doc -- Good luck Ivar

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