Kumbakonam Ramamani Rajagopal

Kumbakonam Ramamani Rajagopal (November 24, 1950 – March 20, 2025), also known as K. R. Rajagopal or Kumbakonam R. Rajagopal, was an Indian-American mechanical engineer, applied mathematician, and academic known for his work in continuum mechanics, rheology, and non-Newtonian fluid mechanics. He held several academic positions across various disciplines, including mechanical engineering, mathematics, and biomedical engineering.

Early life and education Rajagopal was born in Delhi, India, on November 24, 1950. His mother's father, V. S. Sundaram, was a Government Civil Servant who authored the first book on Indian taxation laws, titled The Law of Income Tax in India.

Rajagopal also held honorary and adjunct positions at several institutions worldwide, including Charles University (Czech Republic), the University of Pretoria (South Africa), and the University of Witwatersrand (South Africa), and IIT Madras (India). Some of his research work in collaboration with a number of colleagues include: focusing on materials whose viscosity changes with applied stress. His work included developing constitutive models to describe the behavior of such fluids, including shear-thinning and viscoelastic materials. He also investigated the flow of non-Newtonian fluids between rotating disks, providing insights into their rheological properties.

Thermodynamic frameworks He developed thermodynamic frameworks for rate-type fluid models, particularly for viscoelastic fluids lacking instantaneous elasticity. These models aimed to capture the creep and stress relaxation behaviors observed in such materials.

Electrorheological materials Rajagopal explored the mathematical modeling of electrorheological materials, which exhibit changes in rheological properties under electric fields. His work provided a theoretical basis for understanding the behavior of these materials under different conditions.

Biomechanics In biomechanics, he modeled the behavior of blood

Implicit constitutive theories Rajagopal introduced implicit constitutive theories to generalize classical fluid models, such as the Euler and Korteweg fluids. These theories aimed to describe phenomena such as capillarity and provided a framework for analyzing complex fluid behaviors.

Pressure-dependent viscosity He investigated fluids with pressure-dependent viscosities, analyzing the global existence of solutions for flows of such fluids. This research addressed the mathematical challenges associated with modeling fluids whose viscosity changes with pressure.

Rheologically nonstationary fluids Rajagopal's work also included the development of differential models for rheologically nonstationary fluids, focusing on materials whose rheological properties change over time or under different conditions.

Awards and honors Rajagopal received several awards, including the Eringen Medal from the Society of Engineering Science (2004), the Werner Medal from the American Society of Mechanical Engineers (2022), and the Genesis Award from Texas A&M University (2024). He was a fellow of the American Society of Mechanical Engineers and the Indian National Academy of Engineering.