The author is Professor emeritus at Norwegian University of Science and Technology (NTNU) since 2005. His major field is Continuum Mechanics. He obtained a M.Sc degree in Theoretical and Applied Mechanics from Iowa State University in 1960, on leave from NTNU, and completed the degree in Civil Engineering, majoring in Structural Engineering at NTNU in 1960. He started his academic carrier as Assistant and Associate Professor in Mechanics at NTNU in 1963 and was appointed Professor in Solid Mechanics in 2003 at NTNU. He has been visiting Professor at University of Connecticut and University of Colorado. The author has been involved in a variety of projects in which fluids and fluid-like materials have been modeled as non-Newtonian fluids, such as avalanching snow, granular materials in landslides, extrusion of aluminium, modeling of biomaterials as bone, modeling of viscoplastic modeling of paper in simulation of the calendaring process. He is author or coauthor of 26 papers and 11 conference presentations in Mechanics and Biomechanics. He has published the following textbooks in the Norwegian language: Statics 7 editions, Strength of Materials 7 editions, Dynamics 4 editions, Continuum Mechanics, and Tensor Analysis. In 2008 his book Continuum Mechanics was published by Springer Verlag. At NTNU the author has lectured on elementary and advanced topic in the whole field of theoretical and applied mechanics: Engineering Mechanic, Dynamics, Fluid Mechanics, Biomechanics,  Rheology, Continuum Mechanics and Tensor Analysis. For NTNU he has developed new courses in Continuum Mechanics, Tensor Analysis, Rheology and Non-Newtonian Fluids, and Biomechanics. Professor Irgens has been major adviser to 9 Ph. D. students and member in 11 Adjudication committees at NTNU, University of Oslo, and Lund University, Sweden.