Browsing by Subject "Acceleration"
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Item Development of an optimal impact energy absorber for highway crash cushions(Texas A&M University, 2005-11-01) Michalec, Christopher RyanThe objective of this research is to develop a new and efficient method of absorbing a vehicle??s kinetic energy for highway safety crash cushions. A vehicle that makes a direct impact with a rigid highway structure traveling at highway speeds can be fatal for its occupants. Crash cushions are implemented on roadways in front of these rigid structures with the intent to ??soften?? the impact. The cushion will bring a vehicle to a stop at safe rates before it impacts the rigid structure. The energy absorbing component of the crash cushion must meet four main requirements. The cushion must reduce the vehicles speed at a rate that does not allow the occupant to impact the vehicle interior at velocities greater than 12 m/s. The cushion must then bring the vehicle to a complete stop with deceleration rates below 20 g??s. A crash cushion must satisfy these requirements for an 820 kg vehicle and a 2000 kg vehicle traveling at 100 km/hr. Advanced design methodologies were applied to enable multiple, innovative design concepts. These concepts made use of the deformation of steel in structural pipe, structural angle, and structural plate to reduce the velocity of a vehicle at a safe rate. Critical design parameters were identified which allowed for efficient and effective numerical experiments to be conducted. The data collected from these experiments were then validated when compared to physical test data. After the data had been collected, each of the designs was compared to one another in order to decide upon the best design. The design selected was the deforming plate concept which makes use of steel plate mounted in a fashion that created two arms that acted similar to two cantilever beams. A wedge was forced beneath these arms deforming them upward. This design is effective because the deformation can be easily controlled by the thickness of the plate, the moment arm created by the wedge, and the geometry of the wedge. Steel plate is a readily available material that requires minimal manufacturing for installation preparation making it cost-effective, and easy to install. In the event of impact with the cushion, new parts will be inexpensive and readily available. Being reusable, easy to repair and low in cost, the energy absorbing concept presented herein is a cost effective alternative to existing energy absorbing technology. Due to replaceable parts being readily available, repair time and cost will be reduced compared to other designs that require new parts to be fabricated for replacement. This will make for a competitive design.Item Simulation and experimental analyses of human movement : application to post-stroke hemiparetic gait(2010-08) Peterson, Carrie Lynn, 1981-; Neptune, Richard R.; Abraham, Lawrence D.; Barr, Ronald E.; Kautz, Steven A.; Longoria, Raul G.Stroke is the leading cause of long term disability with improved walking being an important goal following stroke. Understanding deficits that result in reduced walking performance by hemiparetic subjects is important for the design of effective rehabilitation strategies. The goal of this research was to investigate muscle coordination and mechanical work in hemiparetic walking and mechanisms of acceleration and deceleration in nondisabled walking as a framework for investigating non-steady state walking in hemiparetic subjects. Musculoskeletal modeling and simulation analyses were used to compare individual muscle contributions to important walking subtasks and muscle mechanical work by representative hemiparetic subjects (limited community and community walkers) during pre-swing with a representative speed and age-matched control. Simulation analyses identified decreased paretic soleus and gastrocnemius contributions to forward propulsion and power generation as the primary impairment in the limited community walker compared to the control. Comparison of mechanical work showed that total paretic and non-paretic fiber work was increased in the limited community walker, which was primarily related to decreased fiber and tendon work by paretic soleus and gastrocnemius. The decreased output by the ankle plantar flexors required compensatory work by other muscles. Also, the experimental analyses of accelerated and decelerated walking showed that the ankle plantar flexor moment was positively related to braking and propulsive impulses, which increased with speed. Thus, deficits of the paretic plantar flexors limit forward propulsion and increase mechanical work during pre-swing, and would limit the ability of hemiparetic walkers to accelerate and decelerate, which are essential tasks in daily living activities. For the community walker, simulation analyses showed that deficits in paretic swing initiation are a primary impairment. Specifically, the paretic gastrocnemius and hip flexors contributed less to swing initiation in the community walker compared to the control subject. Total paretic and non-paretic fiber work was increased in the community walker, primarily due to increased work by the hip abductors and adductors. Because step length and step frequency were positively related to walking speed in accelerated and decelerated walking, impaired paretic swing initiation would likely limit the community walker’s ability to accelerate and decelerate.