Trajectory Model of Occupants Ejected in Rollover Crashes

Funk, James R.; Luepke, Peter

doi:10.4271/2007-01-0742

Cited by 7 publications

(2 citation statements)

References 9 publications

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“…The rotational acceleration rate (α) of the vehicle is obtained by summing the moments about the center of gravity of the vehicle and setting them equal to zero: (6) where (I) is the roll moment of inertia of the vehicle about its center of gravity, which can also be expressed in terms of the vehicle's mass (m) and radius of gyration (k):…”

Section: Figure 1 Free Body Diagram Of a Rolling Vehiclementioning

confidence: 99%

An Integrated Model of Rolling and Sliding in Rollover Crashes

Funk¹,

Wirth²,

Bonugli³

et al. 2012

SAE Technical Paper Series

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Rollover crashes are often difficult to reconstruct in detail because of their chaotic nature. Historically, vehicle speeds in rollover crashes have been calculated using a simple slide-tostop formula with empirically derived drag factors. Roll rates are typically calculated in an average sense over the entire rollover or a segment of it in which vehicle roll angles are known at various positions. A unified model to describe the translational and rotational vehicle dynamics throughout the rollover sequence is lacking. We propose a pseudocylindrical model of a rolling vehicle in which the rotational and translational dynamics are coupled to each other based on the average frictional forces developed during ground contacts. We describe the model as pseudo-cylindrical because vertical motion is ignored but the ground reaction force is not constrained to act directly underneath the center of gravity of the vehicle. The tumbling phase of a rollover is modeled in three distinct phases: an initial brief airborne phase between roll initiation and the first ground contact, an early phase in which relative sliding between the perimeter of the vehicle and the ground causes the roll rate to increase, and a later phase in which the vehicle rolls without sliding and the roll rate decreases. In the early phase, the average vehicle deceleration is higher and is governed by sliding friction. In the later phase, the average vehicle deceleration is lower and is governed by geometric factors. Model predictions were fit to data from 12 well-documented rollover crashes in order to derive empirical values for the model parameters. In 11 out of the 12 rollovers studied, the model predictions matched the actual results with good accuracy. The results validate the underlying physical principles of the model and provide data that can be used to apply the model to real world rollovers. The proposed model provides a physical basis for understanding vehicle dynamics in rollovers and may be used in certain cases to improve the accuracy of a rollover reconstruction.

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Section: Figure 1 Free Body Diagram Of a Rolling Vehiclementioning

confidence: 99%

An Integrated Model of Rolling and Sliding in Rollover Crashes

Funk¹,

Wirth²,

Bonugli³

et al. 2012

SAE Technical Paper Series

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“…where v v is the vertical component of the occupant's velocity at ground impact and f s is the sliding drag factor for the occupant. One study cited a value of 0.66 for the sliding drag factor in testing involving anthropomorphic test devices (ATDs or crash test dummies) 4 . For the sliding phase of the occupant's motion following impact, the students assumed a constant deceleration of a = f s g.…”

Section: Impact Of Ejected Occupant and Ground And Sliding Phasementioning

confidence: 99%

Reconstruction of an Actual Vehicle Rollover as a Special Project in an Undergraduate Dynamics Course

Ashby¹,

Asay²

2011 ASEE Annual Conference &Amp; Exposition Proceedings

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The reconstruction of a vehicle rollover was assigned as a special group project in an undergraduate course in dynamics at Grand Valley State University. The students were provided with a diagram documenting the path of an actual vehicle rollover. Using the principles learned in the dynamics course, the students were tasked with determining the translational velocity of the vehicle throughout the event, including the pre-trip, trip, and tumbling phases. The project also required the students to calculate the yaw rate prior to trip and the roll rate during the tumbling phase of the event. With the translational and rotational velocities along with the relevant geometry of the vehicle, the students were able to determine the trajectories of a hypothetical occupant ejected from the vehicle at different points in time throughout the rollover and estimate the locations where the occupants would come to rest. The data for this rollover came from a test conducted on a rural highway by Woolley Engineering Research Corporation. A 1994 Nissan Pathfinder was towed to highway speed before being released, at which point an automated steering controller steered the vehicle through a series of maneuvers that resulted in rollover. The test was documented with on-board high-speed instrumentation and two off-board high-speed video cameras. This instrumented test allowed for the direct comparison of the students' reconstructions of the rollover event with what actually occurred. This course project gave the students the opportunity to demonstrate that the principles taught in their undergraduate dynamics course can be used to effectively and accurately analyze a real-world event. In a student survey conducted at the end of the course, 95% of the students reported that they felt that completing this project enhanced their understanding of the principles of kinematics and dynamics that were taught in the class. OverviewOne of the key challenges in undergraduate engineering education is helping students understand how the theoretical principles they learn in their coursework can be applied to solving real-world engineering problems. This can be especially challenging in a core mechanical engineering course like dynamics. As the students work through problem set after problem set, they can find it difficult to see how solving the contrived, simplified problems from the book actually relates to analyzing dynamics in the "real world." To help the students begin to see how dynamics is applied by practicing engineers, a special group project was assigned to two sections of an undergraduate dynamics course taught at Grand Valley State University. In groups of two or three, the students were given the opportunity to demonstrate that the principles taught in this dynamics course can be used to effectively and accurately analyze a real-world event such as an actual on-road vehicle rollover.

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