Search

In the present study, the free fall impact test in accordance with the EN1078 standard for certification of bicycle helmets is replicated using numerical simulations. The impact scenario is simulated using an experimentally validated, patient-specific head model equipped with and without a bicycle helmet. Head accelerations and intracranial biomechanical injury metrics during the impacts are recorded. It is demonstrated that wearing the bicycle helmet during the impact reduces biomechanical injury metrics, with the biggest reduction seen in the metric for skull fracture.

Structural and functional disorders of pulmonary cilia may result from genetic disorders and acquired insults. A two-dimensional numerical model based on the immersed boundary method coupled with the projection method is used to study the flow physics of muco-ciliary transport of the human respiratory tract under various abnormalities of cilia. The effects of the cilia beat pattern (CBP), ciliary length, immotile cilia, beating amplitude and uncoordinated beating of cilia are investigated. As expected, the mucus velocity decreases as the beating amplitude reduces. The windscreen wiper motion and rigid planar motion, which are two abnormal CBPs owing to genetic disorders, greatly reduce or almost stop the mucus transport. If the ciliary length varies from its standard length, the mucus velocity would decrease. The mucus velocity decreases rather linearly if the number of uniformly distributed immotile cilia increases. The numerical results show that the mucus velocity would be further reduced marginally when the uniformly distributed immotile cilia are rearranged as a cluster of immotile cilia. Furthermore, if half of the cilia are immotile and uniformly distributed and motile cilia beat at reduced amplitude, the incoordination between the active motile cilia would not significantly affect the mucus velocity.

This study employs both the traditional and the complex modal analyses of a detailed finite element model of human head-neck system to determine modal responses in terms of resonant frequencies and mode shapes. It compares both modal responses without ignoring mode shapes, and these results are reasonably in agreement with the literature. Increasing displacement contour loops within the brain in higher frequency modes probably exhibits the shearing and twisting modes of the brain. Additional and rarely reported modal responses such as 'mastication' mode of the mandible and flipping mode of nasal lateral cartilages are identified. This suggests a need for detailed modelling to identify all the additional frequencies of each individual part. Moreover, it is found that a damping factor of above 0.2 has amplifying effect in reducing higher frequency modes, while a diminishing effect in lowering peak biomechanical responses, indicating the importance of identifying the appropriate optimised damping factor.

In this study, a methodology for studying porous structures was proposed. The extended finite element method (XFEM) in conjunction with a penalty approach was used to model the porous structures. The holes were considered to have very small Young's modulus, thus they could be treated as inclusions in a matrix. The level set method was applied to describe the internal boundaries of the holes. Various porous structures were investigated. A practical example of the porous structures, which was the microstructure of a trabecular bone, was examined to show the capability of the proposed methodology. The aim of the study was to demonstrate that various complicated porous structures can be modelled efficiently by the XFEM without any major modification to the existing formula.

This study attempts to evaluate the effects of deviation of external nose to nasal airflow patterns. Four typical subjects were chosen for model reconstruction based on computed tomography images of undeviated, S-shaped deviated, C-shaped deviated and slanted deviated noses. To study the hypothetical influence of deviation of external nasal wall on nasal airflow (without internal blockage), the collapsed region along the turbinate was artificially reopened in all the three cases with deviated noses. Computational fluid dynamics simulations were carried out in models of undeviated, original deviated and reopened nasal cavities at both flow rates of 167 and 500 ml/s. The shape of the anterior nasal roof was found to be collapsed on one side of the nasal airways in all the deviated noses. High wall shear stress region was found around the collapsed anterior nasal roof. The nasal resistances in cavities with deviated noses were considerably larger than healthy nasal cavity. Patterns of path-line distribution and wall shear stress distribution were similar between original deviated and reopened models. In conclusion, the deviation of an external nose is associated with the collapse of one anterior nasal roof. The crooked external nose induced a larger nasal resistance compared to the undeviated case, while the internal blockage of the airway along the turbinates further increased it.

Partial inferior turbinectomy is typically performed on patients suffering from chronic nasal obstruction due to hypertrophy of inferior turbinates and is refractory to other more conservative treatments. The effects of the various options of incision performed on the inferior turbinate in terms of the resulting nasal airflow pattern are examined using computational fluid mechanics. The pressure drops across the severely blocked nose and healthy nose models were found to be 32.3 and 12.3 Pa, respectively, whereas the pressure drops across the nasal cavity following one-third turbinate resection, total turbinate resection and front-end resection were obtained as 5.8, 6.1 and 30.5 Pa correspondingly. Based on the total pressure drop results, the one-third resection option seems to be better than the front-end surgery and the total turbinate resection.

A parametric study to investigate the compressive and the shear stress distributions for various edge shapes created during penetrating keratoplasty (PK) using femtosecond laser is reported. The finite element analysis has been implemented using ABAQUS to study the cornea with various edge shapes, namely the standard edge shape, the zigzag edge shape, the top hat edge shape and the mushroom edge shape for PK. The ratio of maximum compressive stress to maximum shear stress is used as the main factor to assess the relative merits of wound healing rate for different edge shapes. For the typical values of tissue mechanical properties, the zigzag edge shape has the highest ratio of maximum compressive stress to maximum shear stress (11.1 in the xy-direction and 3.7 in the yz-direction), followed by the mushroom edge shape (7.7 in the xy-direction and 3.2 in the yz-direction). The ratios for the top hat and the standard edge shapes are even lower in both directions. A sensitivity analysis of the model has been done to demonstrate that the zigzag edge shape always results in the highest ratios of stresses regardless of the difference in the tissue mechanical properties. The zigzag edge shape also gives the lowest dioptric power D = 45.4. The present results imply that the zigzag edge shape provides the best wound healing rate and optical outcome among the four edge shapes models for PK.

The ballistic impact of a human head model protected by a Personnel Armor System Ground Troops Kevlar® helmet is analysed using the finite element method. The emphasis is to examine the effect of the interior cushioning system as a shock absorber in mitigating ballistic impact to the head. The simulations of the frontal and side impacts of the full metal jacket (FMJ) and fragment-simulating projectile (FSP) were carried out using LS-DYNA. It was found that the Kevlar® helmet with its interior nylon and leather strap was able to defeat both the FMJ and FSP without the projectiles penetrating the helmet. However, the head injuries caused by the FMJ impact can be fatal due to the high stiffness of the interior strap. The bulge section at the side of the Kevlar® helmet had more room for deformation that resulted in less serious head injuries.

Head trauma injury due to impact by a flying golf ball is one of the most severe possible injury accidents on the golf course. Numerical simulations based on the finite element method are presented to investigate head injury in children due to impact by a flying golf ball. The stress and energy flow patterns in a head model during the golf ball impact are computed for various combinations of striking speed, falling angle of the golf ball before impact, and impact location. It is found that a child is more prone to head injury due to golf ball impact on the frontal and side/temporal areas. The simulated results are found to conform to the clinical reports on children's head injuries from flying golf balls.