All Publications

  • On analysis and stochastic modeling of the particle kinetic energy equation in particle-laden isotropic turbulent flows PHYSICS OF FLUIDS Pietrzyk, K., Horwitz, J. K., Najjar, F. M., Minich, R. W. 2022; 34 (1)

    View details for DOI 10.1063/5.0075650

    View details for Web of Science ID 000747691700014

  • Upscaling and Automation: Pushing the Boundaries of Multiscale Modeling through Symbolic Computing An Introduction to Symbolica TRANSPORT IN POROUS MEDIA Pietrzyk, K., Korneev, S., Behandish, M., Battiato, I. 2021
  • Swimming efficiency in a shear-thinning fluid PHYSICAL REVIEW E Nganguia, H., Pietrzyk, K., Pak, O. 2017; 96 (6): 062606


    Micro-organisms expend energy moving through complex media. While propulsion speed is an important property of locomotion, efficiency is another factor that may determine the swimming gait adopted by a micro-organism in order to locomote in an energetically favorable manner. The efficiency of swimming in a Newtonian fluid is well characterized for different biological and artificial swimmers. However, these swimmers often encounter biological fluids displaying shear-thinning viscosities. Little is known about how this nonlinear rheology influences the efficiency of locomotion. Does the shear-thinning rheology render swimming more efficient or less? How does the swimming efficiency depend on the propulsion mechanism of a swimmer and rheological properties of the surrounding shear-thinning fluid? In this work, we address these fundamental questions on the efficiency of locomotion in a shear-thinning fluid by considering the squirmer model as a general locomotion model to represent different types of swimmers. Our analysis reveals how the choice of surface velocity distribution on a squirmer may reduce or enhance the swimming efficiency. We determine optimal shear rates at which the swimming efficiency can be substantially enhanced compared with the Newtonian case. The nontrivial variations of swimming efficiency prompt questions on how micro-organisms may tune their swimming gaits to exploit the shear-thinning rheology. The findings also provide insights into how artificial swimmers should be designed to move through complex media efficiently.

    View details for DOI 10.1103/PhysRevE.96.062606

    View details for Web of Science ID 000417691400010

    View details for PubMedID 29347300

  • Propulsion via flexible flapping in granular media PHYSICAL REVIEW E Peng, Z., Ding, Y., Pietrzyk, K., Elfring, G. J., Pak, O. 2017; 96 (1): 012907


    Biological locomotion in nature is often achieved by the interaction between a flexible body and its surrounding medium. The interaction of a flexible body with granular media is less understood compared with viscous fluids partially due to its complex rheological properties. In this work, we explore the effect of flexibility on granular propulsion by considering a simple mechanical model in which a rigid rod is connected to a torsional spring that is under a displacement actuation using a granular resistive force theory. Through a combined numerical and asymptotic investigation, we characterize the propulsive dynamics of such a flexible flapper in relation to the actuation amplitude and spring stiffness, and we compare these dynamics with those observed in a viscous fluid. In addition, we demonstrate that the maximum possible propulsive force can be obtained in the steady propulsion limit with a finite spring stiffness and large actuation amplitude. These results may apply to the development of synthetic locomotive systems that exploit flexibility to move through complex terrestrial media.

    View details for DOI 10.1103/PhysRevE.96.012907

    View details for Web of Science ID 000406642400013

    View details for PubMedID 29347182

  • Power generation modeling for a wearable thermoelectric energy harvester with practical limitations APPLIED ENERGY Pietrzyk, K., Soares, J., Ohara, B., Lee, H. 2016; 183: 218–28
  • Thermoelectric module design strategy for solid-state refrigeration ENERGY Pietrzyk, K., Ohara, B., Watson, T., Gee, M., Avalos, D., Lee, H. 2016; 114: 823–32
  • Quantification of a Latex Agglutination Assay for Bacterial Pathogen Detection in a Low-Cost Capillary-Driven Fluidic Platform Pak, O., Pietrzyk, K., Ly, A., Maldonado-Liu, A., Fukuoka, S., Kim, U., IEEE IEEE. 2016: 765–69