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Symposia
Abstract MULTI-SCALE MODELING OF MAGNETOMECHANICAL COUPLING 15
PHENOMENA
Understanding and simulating realistic human pulsations or arterial
pressure waveforms play an important role in training medical Bjoern Kiefer
professionals and developing advanced medical devices. Particularly, in Institute of Mechanics and Fluid Dynamics
the field of Oriental Medicine (OM), there exists a growing demand in TU Bergakademie Freiberg, Germany
developing mechanical pulse simulations to standardize the “subjective”
pulse diagnosis method with modern technologies. Currently, limited Abstract
blood pulsatile systems are available in the market, and they are bulky,
complex, and expensive. Moreover, there are no controllable pulsatile In this talk, the focus is placed on the computational continuum
systems that can simulate quantitatively distinct pulse patterns. Thus, this mechanics-based modeling of active materials exhibiting magneto-
project intends to develop a simple and cost-effective pulsatile simulator mechanical coupling, e.g. giant magnetostrictives, magnetic shape
using Magneto-Rheological (MR) fluids whose flow can be controlled by memory alloys, and magneto-active polymers. Great challenges in this
magnetic fields instantly. It also intends to evaluate its effectiveness in endeavor stem from the complex coupled, non-linear, and inelastic nature
generating various arterial blood pulsation patterns. To this end, a test set of the constitutive responses exhibited by these materials. Their
up consisting of tubing, an electromagnet, sensors, and MR fluids is macroscopic behavior is often driven by microstructural changes, such as
constructed. By using Pulse Width Modulation (PWM) techniques, the first and second-order phase transitions, twin-boundary and magnetic
electromagnet can produce control signals to regulate the flow motion, domain wall motion, or the interaction of embedded, magnetized particles.
and the output pressure changes (perceived human pulsation) are The presented work is concerned with capturing these mechanisms on
measured using pressure sensors. Using the test setup, a series of testing different length scales as well as establishing scale-bridging techniques to
was performed to measure arterial pulsations by varying the duty cycles compute effective properties. In addition to methods of direct
of PWM signals. The results show that the pulsatile system was capable of computational homogenization, novel ideas on energy relaxation-based
replicating various human pulsation waveforms. The results are further homogenization techniques for multi-phase magnetic materials are also
compared with published human pulsation wave patterns to assess the discussed. In particular, Taylor/Voigt and Reuss/Sachs-like energetic
performance of the MR pulsatile system. The findings of this project will be bounds—well known from micromechanics—are introduced for the
foundation for further advancement of human pulsation research and the magnetic case. In this context, a magnetic potential perturbation scheme
development of commercial pulsation systems using MR fluids. is proposed which yields relaxed effective free energy densities that
simultaneously satisfy magnetic induction and magnetic field strength
Biography compatibility requirements—i.e. the magnetostatic Maxwell equations—at
the phase boundary.
Dr. Koo is an associate professor of mechanical and manufacturing
engineering at Miami University in Oxford, Ohio. He earned his Ph.D. in Biography
Mechanical Engineering at Virginia Tech. He joined Miami University in
2005, after teaching one year at Rowan University in New Jersey. Dr. Dr. Kiefer holds the full professor chair of Applied Mechanics – Solid
Koo’s research focus lies in smart materials and systems. He performs Mechanics at the Institute of Mechanics and Fluid Dynamics of TU
fabrication, testing, modeling, and control research of various smart Bergakademie Freiberg, Germany. After completing a five-year
materials for development of novel actuators and sensors for engineering mechanical engineering program at the Ruhr-University of Bochum,
applications. Recently, his research focus has extended to Appropriate Germany, in 2001, he joined the Aerospace Engineering Department at
Technology or Development Engineering. Dr. Koo has established strong Texas A&M University as a Graduate Assistant Research, where he earned
international collaborations for scholarly activities and educational his Ph.D. degree under the guidance of Professor D. C. Lagoudas in 2006
partnerships for global programs. Since 2012, he has offered an and was honored with the Distinguished Graduate Student Award for
engineering summer study abroad program at KAIST for US and Korean Excellence in Doctoral Research in 2007. After returning to his native
engineering students. During the summer program, students form Germany, Dr. Kiefer was first employed as a postdoctoral research fellow
international capstone design teams and perform projects related to at the University of Stuttgart and from 2010-2016 held the position of
Appropriate Technology to offer innovative design solutions for the Juniorprofessor (Assistant Professor) for the Mechanics of Functional
improvement of human and economic development. Dr. Koo is actively Materials at the Institute of Mechanics, TU Dortmund, Germany.
involved in professional services. He has served as an officer in a various
role for the ASME Technical Committee on Modeling, Dynamics, and Dr. Kiefer’s research focusses on the computational mechanics-based
Control of Adaptive Structures. Moreover, he has served as an organizer modeling and simulation of coupling phenomena across length-scales,
and a program committee member for numerous international particularly in the context of active and multifunctional material behavior.
conferences in the area of vibrations and smart materials. Currently, he is Such couplings can arise from intrinsic multi-physical constitutive
serving as an (associate) editor for Journal of Vibration and Control, the interactions (thermal, electric, magnetic, mechanical), microstructural
Shock and Vibration journal, and Frontiers in Materials – Smart Materials. mechanisms (phase transformations, plasticity, damage), and coupled field
During his leisure time, he enjoys playing racquetball.
