1. Department of Mechanical Engineering University of Chile Av. Beauchef 851 Santiago 8370456 Chile
2. Dipartimento di Matematica e Applicazioni Università di Milano‐Bicocca Milano 20153 Italy
3. Istituto di Matematica Applicata e Tecnologie Informatiche del CNR via Ferrata 1 Pavia 27100 Italy
4. Department of Civil and Environmental Engineering University of California Davis 95616 CA USA