Originally Posted by
DocGKR
EKE/AKE:
An outgrowth of the earlier KE theory, the Expected Kinetic Energy (EKE) model was developed by the U.S. military in 1975 to assess bullet lethality; in 1977 this new EKE model became the U.S. recommended method for the NATO small arms trials and also established it as the official Army Model. The EKE model estimated P(I/H) by correlating the weighted sum of experimentally determined, incremental kinetic energy deposits in 20% gelatin with existing estimates of P(I/H) from animal experiments. Note--although the notation “P(I/H)” was and is used in the literature, the meaning assigned was expected value of incapacitation given a hit; the preferred modern notation is E(I/H), expected level of incapacitation, in order to avoid the widespread misunderstanding that “P(I/H)” is a probability of incapacitation. EKE was later renamed AKE (ARRADCOM Kinetic Energy) and remains a current Army and NATO standard.
To compute the AKE of a particular projectile, ARL obtained the velocity decay curve by shooting into a 38 cm long block of 20% gelatin. The event is recorded with high seed cameras and the velocity versus distance kinetic energy decay curve is extracted by analyzing the camera footage on a frame by frame basis--this is called “dynamic” gel testing. From this decay curve, ARL can derive the energy deposit function within the gelatin medium. This function is then fed into a complex algorithm to calculate the expected level of incapacitation given a hit, or E (I/H). The AKE method for bullets is based upon summing the incremental kinetic energy lost in the gel block multiplied by the probability the projectile is still in the body at the same depth of penetration in the body component (thorax, abdomen, etc…) being evaluated. These probabilities have been generated for the whole body and for a number of specified major body components. The probabilities were estimated from horizontal shots on a number of shot-lines at different angles around a standing male body. This weighted value, AKE, is then inserted into an empirical correlation to predict a level of incapacitation given a hit. It is important to note that current dynamic testing (AKE and E(I/H)) actually measures the energy lost by the projectile, and NOT the damage done by that energy.
Unfortunately, like its KE predecessor, as well as the RII/COMPUTERMAN, EKE/AKE methodology has numerous flaws, including a continued reliance on kinetic energy deposit as a measure of wounding rather than assessing potential physiologic and anatomic damage potential, an overly simplistic and inaccurate COMPUTERMAN anatomic and physiological model that does not account for different tissue types along a shot-line through the body, an inability for the COMPUTERMAN model to assess shot-lines other than standing and account for intervening body sections, projectiles that in reality have quite distinct terminal performance end up have their reported performance blurred to “just about the same” as all other projectiles when the expected levels of incapacitation are computed using the erroneous COMPUTERMAN model, an overemphasis on temporary stretch effects over permanent crush injuries, an inability to assess the synergistic effects of fragmenting projectiles, and ignoring the requirement that projectiles must have adequate penetration to reach critical anatomic structures deep within the body from any angle and despite intervening objects. AKE also fails to account for projectile total penetration, yaw effects, and bullet fragmentation. Finally, the dynamic AKE method requires expensive test measurement equipment and extensive data reduction and analysis.
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COMPUTERMAN/ORCA:
U.S. Army Research Laboratory’s Survivability Lethality Analysis Directorate’s (ARL/SLAD) Operational Requirement-based Casualty Assessment (ORCA) computer modeling system was initiated in 1992 and has continued to the present. The COMPUTERMAN model of the human body is composed of a large number of horizontal cross-sections in which all tissues (muscles, organs, bones, blood vessels, and nerves) are dimensioned in detail. The limbs can be articulated to some degree (positions that cannot be created include arms or legs crossing in front of the body). Shot-lines through COMPUTERMAN are constrained to be straight lines between entry and exit points. A particular trajectory in the body is computed from the parameters of the fragment; and the determination of the resulting incapacitation is made from the hole size made in the various tissues encountered. COMPUTERMAN makes estimates of level of incapacitation based on the levels of functioning present in the four limbs at specified time intervals after wounding and on their importance to specific missions.
ORCA attempts to be a more comprehensive model for estimating incapacitation from a number of classes of body injury. ORCA does include a far wider range of injury mechanisms, extends the measure of incapacitation beyond the four limbs, and uses a more detailed model of the human body. Unfortunately, ORCA still contains as its ballistic insult subroutine, a refined version of the flawed COMPUTERMAN, because of this, the current ballistic wounding model is the same as COMPUTERMAN. The ORCA model proposes several metrics that attempt to evaluate the impairment caused by injuries to the body, for example, the Weighted Task Average Impairment (WTAI) metric provides the supposed percent reduction of impaired tasks relevant to a specific activity or job. Another metric, the Job Impairment (JI) is used to determine if an average human can successfully perform the totality of tasks that in aggregate constitute a specific job, for example infantry rifleman, vehicle crewman, helicopter pilot, etc... ORCA is compromised by a strong reliance on adaptation of previously flawed COMPUTERMAN models & EKE/AKE methodology, a failure to fully appreciate the infinite variety of stochastic variables inherent in trying to predict the potential incapacitation of a human, and an excessive averaging of measurements leading to loss of data fidelity (with too many fuzzy data points and gross averaging of physiological responses, a hit from a .22LR begins to look similar to a hit from a .338 Lap Mag).