The models used for modeling the airflow in the human airways are either 0-dimensional compartmental or full 3-dimensional (3D) computational fluid dynamics (CFD) models. In the former, airways are treated as compartments, and the computations are performed with several assumptions, thereby generating a low-fidelity solution. The CFD method displays extremely high fidelity since the solution is obtained by solving the conservation equations in a physiologically consistent geometry. However, CFD models (1) require millions of degrees of freedom to accurately describe the geometry and to reduce the discretization errors, (2) have convergence problems, and (3) require several days to simulate a few breathing cycles. In this paper, we present a novel, fast-running, and robust quasi-3D wire model for modeling the airflow in the human lung airway. The wire mesh is obtained by contracting the high-fidelity lung airway surface mesh to a system of connected wires, with well-defined radii. The conservation equations are then solved in each wire. These wire meshes have around O(1000) degrees of freedom and hence are 3000 to 25 000 times faster than their CFD counterparts. The 3D spatial nature is also preserved since these wires are contracted out of the actual lung STL surface. The pressure readings between the 2 approaches showed minor difference (maximum error = 15%). In general, this formulation is fast and robust, allows geometric changes, and delivers high-fidelity solutions. Hence, this approach has great potential for more complicated problems including modeling of constricted/diseased lung sections and for calibrating the lung flow resistances through parameter inversion.

No abstract

Explosive devices are the main weapon of terrorist attacks and a cause of major injuries to Soldiers and civilians. Recent military medical statistics show that a significant percentage of Soldiers injured in explosion events endures blast wave traumatic brain injury (BW-TBI). In the last few years, better understandings of BW-TBI mechanisms and of improved injury protection have become of paramount importance. Most studies have taken the conventional approach of animal testing, in vitro brain tissue study, and analysis of clinical data. These, while useful and necessary, are slow, expensive, and often non-conclusive. Physiology-based mathematical modeling tools of blast wave brain injury will provide a complementary capability to study both BW-TBI mechanisms and the effectiveness of protective armor.

Bone conduction (BC) hearing is the process of transmitting sound energy through vibrations of the skull, cerebrospinal fluid (CSF) and brain, which results in an auditory sensation (Stenfelt and Goode 2005). BC communication is attractive for military operations because the transducers are lightweight, inconspicuous, and easily integrated into military headgear. Bone conduction (BC) headsets can present audio when ambient sounds must be either blocked by hearing protection or preserved to maintain situational awareness, and they can provide necessary radio communication in quiet and high noise environments, especially when combined with an appropriate hearing protection system (McBride et al. 2005, Henry and Letowski, 2007). The overall objective of this research is to develop, validate, and deliver anatomy and physics based modeling tools and experimental procedures for analysis and design of cranial bone conduction (BC) communication systems. The modeling tools will be used to optimize the design, attachment, and anatomical location of BC speakers and microphones for best communication clarity in various military environments.

Generally a helmet comprises two main components: the shell and the fitting system. Despite the variations in designs due to the different usage requirements, typically helmets are intended to protect the user’s head through an energy absorption mechanism. The weight and volume are important factors in helmet design since both may alter the injury risk to the head and neck. The helmet outer shell is usually made of hard material that will deform when it is hit by hard objects. This action disperses energy from the impact to lessen the force before it reaches the head. The fitting system frequently includes a dense layer that cushions and absorbs the energy as a result of relative motion between the helmet and the head. A balance needs to be achieved on how strong and how stiff a helmet should be to provide the best possible protection. If a helmet is too stiff it can be less able to prevent brain injury in the kinds of impacts that may occur. If it is too flexible or soft, it might not protect the user in a violent, high-energy crash. For military applications, the requirements for helmet performance may be even more demanding. Not only do helmets have to protect a Soldier’s head from blunt impacts, but helmets also are expected to provide mounting platforms for ancillary devices and to function in ballistic and blast events as well.