OBJECTIVE:To investigate the risk and injury severity on the regional body (head, neck, and chest) of obese children in frontal motor vehicle crashes (MVCs). METHODS:No physical surrogates (i.e., crash dummies) for obese children were available, and experiments on pediatric cadavers were generally not feasible. Therefore, computational models of obese children using medical imaging processing and state-of-the-art modeling techniques were developed. A hybrid modeling technique was used to integrate the finite element model for torso fat layer into the standard multibody model to represent various levels of obese children for 3- and 6-year-old age groups. The models were used to investigate injury severity under various crash scenarios through model simulations. RESULTS:The head injury criterion and chest acceleration were observed to increase as body mass index (BMI) increased. Meanwhile, no such correlations were found between BMI and neck injury and chest deformation. Forward head and torso excursions were observed to increase as obesity increased, owing to the momentum effect of greater body mass. CONCLUSIONS:Obese children appeared to have greater risks for head and chest injuries than do their non-obese counterparts in frontal MVCs, owing to higher head and chest accelerations induced by greater body excursion.

According to current definitions [1], individuals ages 2 to 18 years are determined to be overweight (≥ 85th and < 95th percentile [of prior population distributions]) or obese (≥ 95th percentile) based on U.S. age- and sex-specific body mass index (BMI; kg/m 2) charts updated by the Centers for Disease Control and Prevention (CDC) in 2000 [2]. The prevalence of being obese among children has increased over the last several decades and is a major public health concern. A recent survey [3] indicated that 16.3% of children and adolescents aged 2 through 19 years were at or above the 95 th percentile of the BMI-for-age growth charts.

OBJECTIVE:To investigate the risk of bone fracture sustained by obese children exposed to falls. The bone fracture risk of obese children would be greater than that of their nonobese counterparts was hypothesized. DESIGN AND METHODS:Finite element-based computational models for children that reflected various levels of obesity by varying body mass and the thickness of the subcutaneous adipose tissue layer was developed. The models took account of both the momentum effect of variation of body mass and the cushion effect of variation of soft tissue thickness and examined these two contradictory effects on pelvic bone fracture risk through a set of sideways fall simulations with a range of impact speeds. RESULTS:The critical impact speed that yielded pelvic bone fracture decreased as the levels of obesity increased, which meant that the momentum effect of a greater body mass took precedence over the cushion effect of the soft tissue layer. CONCLUSIONS:The result suggests that obese children have a greater risk of pelvic bone fracture than do their nonobese counterparts in sideways falls. A further implication is that current child safety devices, systems, and regulations will need to be revisited as the prevalence of child obesity increases.

The University Hospital at the University of Alabama at Birmingham (UAB) is the only Level I Trauma Center in the state of Alabama. Roughly 3,500 patients are admitted each year from the Birmingham Regional Emergency Medical Services System (BREMSS) region, which has a population of approximately 1.3 million. The UAB Crash Injury Research Engineering Network (CIREN) Center has agreed to enroll cases and work with CIREN engineering resources to determine injury causation.

Reliable numerical simulation of failure is important for the design and planning of new solids and structures, as well as for the safety assessment of existing ones. In the past two decades, gradient and non-local models for regularizing loss of ellipticity due to material failure using non-standard finite element method and more recently the meshfree method have been the topic of considerable research. Alternatively, discontinuous partition of unity enrichments and meshfree visibility concepts were proposed and used in finite element method (also called extended finite element method XFEM) and meshfree method to model cracks. Due to the fact that the description of crack plane in XFEM using level set method still presents several difficulties in the three-dimensional simulation of solids, the meshfree method using visibility concept is tested for the solid failure analysis of reinforced concrete structure under impact loading. The current method incorporates the discontinuous field into the generalized meshfree approximation [1] by the introduction of visibility approach [2]. To determine the onset of fracture and subsequently the crack propagation, a stress-based initial-rigid cohesive cracking model was developed for the brittle and semi-brittle materials. After the insertion of new crack, the state variables are interpolated and transferred to the new stress point using second-order meshfree approximation [3]. To integrate the discrete equations involving the crack plane, the strain smoothing algorithm developed in SCNI method [4] was adopted in this development. A typical reinforced concrete structure under impact loading failure involving multi-cracks is modeled using the developed method and results are presented. Generalized Meshfree Approximation The generalized meshfree (GMF) approximation method can be used to construct a convex, nonconvex, or combined convex and non-convex approximation for meshfree computation. The GMF approximation has one unique feature. That is it naturally bears the weak Kronecker-delta property at boundaries regardless of its convexity or non-convexity. This property makes the imposition of essential boundary conditions in meshfree methods easier. The first-order GMF approximation in one dimension is described as follows: Simulation(1) 12 th International LS-DYNA ® Users Conference 2 1 (x; ) ( , ) (x, ) (x; ) ( , ) i a i i i i n a j j j j X X X X               for fixed x , (1)

Motor vehicle crashes (MVCs) are the most common cause of serious injury (Healthy People, 2010). Moffat et al. (1990) estimated that, in 1985 alone, 15,300 pelvic fractures occurred during MVCs in the United States. Since the early 1990’s, the incidence of pelvic fractures has significantly increased (Inaba et al., 2004), which is alarming since more patients die from pelvic fracture than from any other skeletal injury (Cryer, 1996).

Finite element modelling of musculoskeletal systems, with geometrical structures constructed from computed tomography (CT) scans, is a useful and powerful tool for biomechanical studies. The use of CT scans from living human subjects, however, is still limited. Accurate reconstruction of thin cortical bone structures from CT scans of living human subjects is especially problematic, due to low CT resolution that results from mandatory low radiation doses and/or involuntary movements of the subject. In this study, a new method for mapping cortical thickness is described. Using the method, cortical thickness measurements of a coxal (pelvis) bone obtained from CT scans of a cadaver were mapped to the coxal geometry as obtained through CT scans of a live human subject, resulting in accurate cortical thickness while maintaining geometric fidelity of the live subject. The mapping procedure includes shape-preserving parameterisation, mesh movement and interpolation of thickness using a search algorithm. The methodology is applicable to modelling of other bones where accurate cortical thickness is needed and for which such data exist.

A finite element (FE) model of the pelvis and lower limb was developed to improve understanding of injury mechanisms of the lower extremities during vehicle collisions and to aid in the design of injury countermeasures. The FE model was developed based on the reconstructed geometry of a male volunteer close to the anthropometry of a 50th percentile male and a commercial anatomical database. The model has more than 625,000 elements included in 285 distinct components (parts). The material and structural properties were selected based on a synthesis of current knowledge of the constitutive models for each tissue. The model was validated in seventeen loading conditions observed in frontal and side impact vehicle collisions. These validations include combined axial compression and bending (mid-shaft femur, distal third leg), compression/flexion/xversion/axial rotation (foot), and lateral loading (pelvis). In addition to very good predictions in terms of biomechanical response and injuries, the model showed stability at different severe loading conditions. Overall results obtained in the validation indicated improved biofidelity relative to previous FE models. The model may be used in future for improving the current injury criteria of lower extremity and anthropometric test devices. Furthermore, the present pelvis and lower limb was coupled together with other body region FE models into the state-of-art human FE model to be used in the field of automotive safety.

The objective of this study was to examine the role of body mass and subcutaneous fat in injury severity and pattern sustained by overweight drivers. Finite element models were created to represent the geometry and properties of subcutaneous adipose tissue in the torso with data obtained from reconstructed magnetic resonance imaging data-sets. The torso adipose tissue models were then integrated into the standard multibody dummy models together with increased inertial parameters and sizes of the limbs to represent overweight occupants. Frontal crash simulations were carried out considering a variety of occupant restraint systems and regional body injuries were measured. The results revealed that differences in body mass and fat distribution have an impact on injury severity and pattern. Even though the torso adipose tissue of overweight subjects contributed to reduce abdominal injury, the momentum effect of a greater body mass of overweight subjects was more dominant over the cushion effect of the adipose tissue, increasing risk of other regional body injuries except abdomen. Through statistical analysis of the results, strong correlations (p<0.01) were found between body mass index and regional body injuries except neck injury. The analysis also revealed that a greater momentum of overweight males leads to greater forward torso and pelvic excursions that account for higher risks (p<0.001) of head, thorax and lower extremity injury than observed in non-overweight males. The findings have important implications for improving the vehicle and occupant safety systems designed for the increasing global obese population.

Pelvis fracture and associated injuries from motor vehicle accidents or falls are often life threatening [1]. Cadaveric experiments and finite element (FE) models have been widely used to investigate biomechanical properties, structural responses, and injury tolerances of the pelvis. In FE model development, the geometry of the bone structures is commonly constructed from computed tomography (CT) scans of cadavers. The use of live human subjects, however, has been limited due to low CT resolution resulting from mandatory low radiation doses and involuntary movements of the subject. The Global Human Body Models Consortium (GHBMC) elected to use a living 50th percentile male for its full body FE model development; however, cortical bone thickness was not accurately imaged for the pelvis, where it is believed to play an important role in absorbing strain energy during lateral impact [2].

BACKGROUND:Men tend to have more upper body mass and fat than women, a physical characteristic that may predispose them to severe motor vehicle crash (MVC) injuries, particularly in certain body regions. This study examined MVC-related regional body injury and its association with the presence of driver obesity using both real-world data and computer crash simulation.METHODS AND FINDINGS:Real-world data were from the 2001 to 2005 National Automotive Sampling System Crashworthiness Data System. A total of 10,941 drivers who were aged 18 years or older involved in frontal collision crashes were eligible for the study. Sex-specific logistic regression models were developed to analyze the associations between MVC injury and the presence of driver obesity. In order to confirm the findings from real-world data, computer models of obese subjects were constructed and crash simulations were performed. According to real-world data, obese men had a substantially higher risk of injury, especially serious injury, to the upper body regions including head, face, thorax, and spine than normal weight men (all p<0.05). A U-shaped relation was found between body mass index (BMI) and serious injury in the abdominal region for both men and women (p<0.05 for both BMI and BMI(2)). In the high-BMI range, men were more likely to be seriously injured than were women for all body regions except the extremities and abdominal region (all p<0.05 for interaction between BMI and sex). The findings from the computer simulation were generally consistent with the real-world results in the present study.CONCLUSIONS:Obese men endured a much higher risk of injury to upper body regions during MVCs. This higher risk may be attributed to differences in body shape, fat distribution, and center of gravity between obese and normal-weight subjects, and between men and women. Please see later in the article for the Editors' Summary.

A finite element (FE) model of a 10-years-old child pelvis was developed and validated against experimental data from lateral impacts of pediatric pelves. The pelvic bone geometry was reconstructed from a set of computed tomography images, and a hexahedral mesh was generated using a new octree-based hexahedral meshing technique. Lateral impacts to the greater trochanter and iliac wing of the seated pelvis were simulated. Sensitivity analysis was conducted to identify material parameters that substantially affected the model response. An optimization-based material identification method was developed to obtain the most favorable material property set by minimizing differences in biomechanical responses between experimental and simulation results. This study represents a pilot effort in the development and validation of age-dependent musculoskeletal FE models for children, which may ultimately serve to evaluate injury mechanisms and means of protection for the pediatric population.

Although many efforts have been made to develop an aerodynamic shape optimization (ASO) framework, iterative grid generation of the complex configuration within the optimization loop has still been a critical barrier. In this paper, an efficient ASO framework is developed by integrating a parametric grid generator, an optimization toolkit, and a flow solver. A geometry-grid template toolkit is developed to address the need to produce a large number of grids in a timely manner for the parametric design study. An object-oriented optimization toolkit that allows a flexible and extensible interfacing with user-specific codes is used. An in-house full Navier–Stokes flow solver is developed and used in the framework. Code integration is achieved using a black-box interface with script files. Two ASO applications and their optimum solutions are presented to demonstrate the success of this framework.

The pediatric pelvis is vulnerable to injuries in motor vehicle collisions, sport activities, and fall accidents. Pelvic fractures and injury mechanisms in children differ substantially from those found in adults [1]. While the injury mechanisms and tolerances of the adult pelvis have been fairly well characterized through cadaveric experiments and computational models, efforts related to the pediatric pelvis have been limited due to difficulties in acquiring and testing pediatric cadavers. The objective of this study was to develop a finite element (FE) model of a 10-year-old (10YO) human pelvis to provide more comprehensive understanding of injury mechanisms experienced by children.

Atherosclerosis is widely accepted as the main causative factor in the development of lower limb peripheral arterial disease (PAD). Approximately 8 million Americans is affected by the PAD [1]. The atherosclerosis in PAD patients are frequently observed on the site at the femoral artery bifurcation [2].

The influence of wall motion on the hemodynamic characteristics of the human femoral bifurcation and its effects on the development of peripheral artery disease has not been previously investigated. This study aimed in investigating the hemodynamics of a compliant patient-specific femoral artery bifurcation model by a fluid structure interaction (FSI) scheme. The complex physiological geometry of the femoral artery bifurcation was reproduced from sequentially obtained transverse CT scan images. Velocity waveforms derived from phase contrast MR images were extracted and mapped to define boundary conditions. Equations governing blood flow and wall motion were solved using an FSI framework that utilizes commercial codes: FLUENT for computational fluid dynamics and ANSYS for computational structural dynamics. The results showed that wall compliance decreased flow velocities at the relatively high curvature geometries including common and superficial femoral artery (SFA), and it created strong recirculation in the profunda femoris artery close to the bifurcation. In the SFA region near the apex, time averaged wall shear stress (TAWSS) differences up to 25% between compliant and rigid models were observed. The compliant model also exhibited lower TAWSS and oscillatory shear at the superior section of the common femoral artery close to the bifurcation. The presence of wall motion, however, created minor differences in the general flow-field characteristics. We conclude that wall motion does not have significant influence on the global fluid dynamic characteristics of the femoral artery bifurcation. Longer arterial segments need to be simulated to see the effect of wall motion on tortuousity which was previously cited as an important factor in the development of atherosclerosis at the femoral artery.