Hesam Moghaddam, Ph.D.
Postdoctoral Research Scholar
VA Medical Center
UC San Francisco
Computational Biomechanics of Blast-Induced Traumatic Brain Injury: Role of Loading Directionality, Head Protection, and Blast Flow Mechanics
Traumatic brain injury (TBI) is defined as a type of acquired brain injury that occurs upon an assault exerted by an external force. The high mortality rate and TBI-related disabilities, make it necessary for the fundamental studies to clearly understand the mechanisms leading to brain injuries. Accordingly, in this research, both impact and blast induced TBIs are studied with respect to the injury mechanisms, as well as the protective methods for preventing them using the main injury predictors: tissue responses of the brain in terms of the intracranial pressure (ICP), shear stress, and the brain kinematics in terms of the linear brain acceleration. Using a validated finite element (FE) model of the real human head and neck, Mr. Moghaddam developed a transient, nonlinear, and explicit FE approach to study the mechanical response of the head to dynamic loads. It was found that due to the differences in the shape, function, and tolerance of different head components, the response of the head/brain varies with the direction of the assault. To this end, first the directional dependence of the head mechanical response was examined through impacting the head against a rigid wall in frontal, backward, and lateral directions. Moreover, due to the different injury mechanism of the head when it is exposed to blast shockwaves, the mechanical response of the head was also evaluated under blast. To study the directionality effect, the head was exposed to an identical blast loading in frontal, backward, upward, and downward orientations. In the final part of the study, a parametric study was conducted to delineate the efficiency of Personal Protective Equipment (PPE) such as ballistic faceshields and Advanced Combat Helmets (ACH) under blast. Unprotected, helmeted and fully-protected head models were examined in the aforementioned blast scenarios. In terms of the blast modeling, the propagation of blast waves and their interactions with the head were modeled using a multi-material arbitrary Lagrangian–Eulerian (ALE) method and a fluid-structure interaction (FSI) coupling algorithm. Depending on blast waves’ orientation, the mitigation potential of the PPE was observed to be different in terms of attenuating the blast-induced loads on the brain. As an adverse effect of PPE, the travel of high pressure blast waves inside the helmet’s subspace may form an elevated pressure region at the countercoup site of the head, known as the underwash effect. A major part of our work was dedicated to development of a novel computational algorithm to study the underwash effect and analyze the behavior of high-pressure fluid flows around the head through a Computational Fluid Dynamic (CFD) approach using Ansys-CFX. Interaction of traveling pressure waves in the helmet gap, followed by the momentum change in the helmet curvature were perceived as the main reasons for this effect. The outcomes of Hesam Moghaddam’s research is believed to have a remarkable impact on the modification and improvement of the current protective tools, as well as development of new brain injury criteria using computational methods to better assess the risk of injury.
Dr. Moghaddam is currently a Postdoctoral Fellow in the Department of Surgery at University of California, San Francisco. He received his PhD in Mechanical Engineering from North Dakota State University (NDSU). He received his MS in Aerospace Engineering from Tarbiat Modares University in 2010, and BS degree with Honors in Mechanical Engineering from Shahrood University of Technology in Iran in 2007. Dr. Moghaddam’s current research is on the computational biomechanics of cardiovascular diseases such as aortic aneurysms using finite element (FE) methods. His Ph.D. research primarily focused on the development of innovative FE and CFD approaches for the assessment of the mechanical response of the human head to dynamic loads such as high speed impacts and blast waves. In his research, he developed novel solutions for the evaluation of the brain injury risks through computational algorithms. A major part of Dr. Moghaddam’s Ph.D. research was devoted to determine the effect of protective tools such military helmets and faceshields in protection of head against explosion and greatly contributes to the development and improvement of advanced military helmets to better protect the servicemen. During his doctorate and master’s researches, he has published 6 peer-reviewed publications with more than 4 under revision as well as 4 conference papers presented in the biomechanical engineering field. Dr. Moghaddam is a member of American Society for Mechanical Engineers (ASME) and North American Brain Injury Association (NABIS). His research was funded by US Department of Defense (DoD) and Army Research Office (ARO). He received Charles W. Haynes "Pay It Forward" Brain Injury Fellowship from NABIS, Graduate Student Research and Teaching awards from Mechanical Engineerign department at NDSU, best poster presentation award from NDSU, as well as the Young Investigator Travel award from National Neurotrauma Society for the recognition of his research on brain injury. His research interests include computational biomechanics, traumatic brain injury, nonlinear finite element modeling, computational fluid dynamics, and fluid-structure interaction studies.