The model will display the resulting acceleration-time history, the peak linear acceleration and the pulse duration for the unknown fall scenario under investigation. So I composite all of the experimental model results into a single, composite model by fixing the computed “a,” “b” and “c” parameters, and then I input the desired “a” parameter (the impact velocity corresponding the fall height I want to investigate). Ultimately I want to determine the peak linear acceleration and pulse duration for a particular fall height. For example, the data I have fit are for falls from various heights onto a particular impact surface, with the head contacting that surface as the primary point of contact. This approach is mush more accurate than assuming a more simplified pulse shape and permits the assembly of an average, or “typical” response based on data that can then be used to model an unknown impact condition. Then I can adjust “b” to get the response that fits the experiment. With each modeled pulse, I can use the published (or computed, based on free-fall calculations) impact velocity as input (“c”) and fix “a” to set the beginning of the pulse at time t=0. Here, “c” is the initial velocity of the head at impact, “a” modulates the offset of the history along the time axis, and “b” changes the slope of the linear portion of the velocity-time curve, which changes the peak linear acceleration and acceleration-time pulse duration. I can visualize in real time, through live Differentiation of the velocity function, the resulting linear head acceleration history and match its peak value and pulse duration to each test published in the experimental literature or within my own test data. It turns out that a sigmoid function is a really good approximation of how the head changes its velocity during an impact.ĭataGraph permits me to assign Values with sliders for a, b and c to modulate the velocity as a function of time. From some unrelated analysis I have performed I fit sigmoid functions with DataGraph to make differentiating the data smoother. By accumulating and analyzing each impact test, a composite data set can be developed to reflect the average, or composite response of the infant head for a particular age/developmental stage.ĭataGraph has been really useful in visualizing the typical impact response data and fitting these data to an analytical model of the velocity and acceleration histories of the head during an impact. There are various sources of impact data in the literature and through my own testing that characterize the impact response for well-defined tests, utilizing both ATDs (“crash dummies”) and post-mortem human surrogates (cadavers). I regularly perform forensic analysis of incidents that involve infant head impact, which includes reconstructing the impact event to determine the potential for various types of cranial and intracranial injury. It does not store any personal data.My background is in biomechanics, specifically related to the impact response of the infant’s head as the mechanical and biological properties of the head, skull and brain change as a function of age.
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