Model and parameter identification through Bayesian inference in solid mechanics Hussein Rappel h.rappel@gmail.com September 07, 2018 Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 1 / 69
Introduction: Probabilistic modelling y 4 3 y = -ax + b 2 a 1 1 x 1 2 3 4 Introduction to Gaussian Processes, Neil Lawrence Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 2 / 69
Introduction: Probabilistic modelling y 4 3 2 1 x 1 2 3 4 Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 3 / 69
Introduction: Probabilistic modelling y 4 3 2 1 x 1 2 3 4 Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 4 / 69
Introduction: Probabilistic modelling y 4 3 2 1 x 1 2 3 4 Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 5 / 69
Introduction: Probabilistic modelling Each point can be written as the model+ a corruption: y 1 = ax + c + ω 1 y 2 = ax + c + ω 2 y 3 = ax + c + ω 3 Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 6 / 69
Introduction: Probabilistic modelling The corruption term can be presented with a probability distribution Pierre-Simon Laplace 1749-1827 (source wikipedia) Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 7 / 69
Introduction: Probabilistic modelling y 4 How can we fit the y = ax + b line, having 3 only one point? 2 1 x 1 2 3 4 Introduction to Gaussian Processes, Neil Lawrence Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 8 / 69
Introduction: Probabilistic modelling y 4 If b is fixed ⇒ a = y-b 3 = x 2 1 x 1 2 3 4 Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 9 / 69
Introduction: Probabilistic modelling y 4 3 2 1 x 1 2 3 4 Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 10 / 69
Introduction: Probabilistic modelling y 4 b ∼ π 1 = ⇒ a ∼ π 2 3 2 1 x 1 2 3 4 Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 11 / 69
Introduction: Probabilistic modelling This is called Bayesian treatment. The model parameters are treated as random variables. Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 12 / 69
Introduction: Bayesian perspective Original belief New belief Observations Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 13 / 69
Introduction: Bayesian formula (inverse probability) likelihood prior posterior � �� � � �� � � �� � π (x) × π (y|x) π (x|y) = π (y) � �� � evidence y := observation x := parameter π (x) := original belief π (y|x) := given by the mathematical model that relates y to x π (y) := is a constant number Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 14 / 69
Introduction: Bayesian formula (inverse probability) π (x|y) ∝ π (x) × π (y|x) Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 15 / 69
BI in computational mechanics σ ε Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 16 / 69
Linear elasticity σ σ = E ε E 1 ε Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 17 / 69
Linear elasticity y = E ε + ω Ω ∼ π ω ( ω ) Capital letters denote a random variable Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 18 / 69
Linear elasticity σ ( ) - ω 2 1 π ω ( ω ) = 2 π s ω exp √ 2 s 2 ω ε Noise PDF is modelled through calibration test. Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 19 / 69
Linear elasticity Bayes’ formula: π (E|y) = π (E) π (y|E) = π (E) π (y|E) π (y) k π (E|y) ∝ π (E) π (y|E) Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 20 / 69
Linear elasticity y = E ε + ω Ω ∼ N( 0 , s 2 ω ) Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 21 / 69
Linear elasticity - (y - E ε ) 2 1 ( ) π (y|E) = √ exp 2 s 2 2 π s ω ω Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 22 / 69
Linear elasticity Posterior: ( ) ( ) - (E-E) 2 - (y-E ε ) 2 π (E|y) ∝ exp exp 2 s 2 2 s 2 E ω Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 23 / 69
Linear elasticity Prediction interval: An estimate of an interval in which an observation will fall, with a certain probability. Credible region: A region of a distribution in which it is believed that a random variable lie with a certain probability. Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 24 / 69
Linear elasticity Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 25 / 69
Prior effect Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 26 / 69
Model uncertainty and input error y = f( x , ε ) + ω Ω ∼ π ω ( ω ) ε is the input variable and x is the parameter vector Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 27 / 69
Model uncertainty and input error Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 28 / 69
Model uncertainty and input error Kennedy-O’Hagan (KOH) framework: y = f( x , ε ) + d( x d , ε ) + ω � �� � y true ε is the input variable and x is the parameter vector Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 29 / 69
Model uncertainty and input error Constant number d 0 Deterministic function ∑ l i= 0 a i ε i Random variable from normal distribution d ∼ N(m, s 2 d ) Random variable from a normal distribution with input dependent mean and variance d ∼ N(m( ε ), s 2 d ( ε )) Gaussian process (GP) ... Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 30 / 69
Model uncertainty and input error Bayes’ formula: π ( x , x d |y) ∝ π ( x ) π ( x d ) π (y| x , x d ) Both material and model error parameters must be inferred. If d( x d , ε ) is deterministic (for simplicity): π ( x , x d |y) ∝ π ( x ) π ( x d ) π ω (y - f( x , ε ) - d( x d , ε )) x d parameter vector of model uncertainty Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 31 / 69
Model uncertainty and input error Bayes’ formula: π ( x , x d |y) ∝ π ( x ) π ( x d ) π (y| x , x d ) Both material and model error parameters must be inferred. If d( x d , ε ) is deterministic (for simplicity): π ( x , x d |y) ∝ π ( x ) π ( x d ) π ω (y - f( x , ε ) - d( x d , ε )) x d parameter vector of model uncertainty Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 31 / 69
Model uncertainty and input error But what about the input error? Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 32 / 69
Model uncertainty and input error y = f( x , ε ) + d( x d , ε ) + ω ε ∗ = ε + ω ε Ω ∼ π ( ω ) Ω ε ∼ π ( ω ε ) Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 33 / 69
Model uncertainty and input error Bayes’ formula: π ( x , x d , ε |y, ε ∗ ) ∝ π (y| x , x d , ε ) π ( ε | ε ∗ ) π ( x ) π ( x d ) ∫ b π ( x , x d |y, ε ∗ ) ∝ 0 π (y| x , x d , ε ) π ( ε | ε ∗ )d ε π ( x ) π ( x d ) π (y| x , x d , ε ) = π ω (y - f( x , ε ) - d( x d , ε )) π ( ε | ε ∗ ) = π ω ε ( ε ∗ - ε ) Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 34 / 69
Model uncertainty and input error Bayes’ formula: π ( x , x d , ε |y, ε ∗ ) ∝ π (y| x , x d , ε ) π ( ε | ε ∗ ) π ( x ) π ( x d ) ∫ b π ( x , x d |y, ε ∗ ) ∝ 0 π (y| x , x d , ε ) π ( ε | ε ∗ )d ε π ( x ) π ( x d ) π (y| x , x d , ε ) = π ω (y - f( x , ε ) - d( x d , ε )) π ( ε | ε ∗ ) = π ω ε ( ε ∗ - ε ) Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 34 / 69
Model uncertainty and input error: Linear elasticity Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 35 / 69
Model uncertainty and input error: Effect of model uncertainty Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 36 / 69
Model uncertainty and input error: Effect of model uncertainty as well as input error Normal distribution with constant parameters Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 37 / 69
Model uncertainty and input error: Effect of model uncertainty as well as input error Normal distribution with an input-dependent mean Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 38 / 69
Model uncertainty and input error: Effect of model uncertainty as well as input error Gaussian process Hussein Rappel (UL-ULg) BI for parameter identification September 07, 2018 39 / 69
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