A Shake Table Frequency-Time Control Method Based on Inverse Model Identification and Servoactuator Feedback-Linearization

Shake tables are one of the most widespread means to perform vibration testing due to their ability to capture structural dynamic behavior. The shake table acceleration control problem represents a challenging task due to the inherent non-linearities associated to hydraulic servoactuators, their low hydraulic resonance frequencies and the high frequency content of the target signals, among other factors. In this work, a new shake table control method is presented. The procedure relies on identifying the Frequency Response Function between the time derivative of pressure force exerted on the actuator’s piston rod and the resultant acceleration at the control point. Then, the Impedance Function is calculated, and the required pressure force time variation is estimated by multiplying the impedance by the target acceleration profile in frequency domain. The pressure force time derivative profile can be directly imposed on an actuator’s piston by means of a feedback linearization scheme, which approximately cancels out the actuator’s non-linearities leaving only those related to structure under test present in the control loop. The previous architecture is completed with a parallel Three Variable Controller to deal with disturbances. The effectiveness of the proposed method is demonstrated via simulations carried over a non-linear model of a one degree of freedom shake table, both in electrical noise free and contaminated scenarios. Numerical experiments results show an accurate tracking of the target acceleration profile and better performance than traditional control approaches, thus confirming the potential of the proposed method for its implementation in actual systems.

Lane Change Dynamics of a Commercial Tractor-Trailer

A number of vehicle-to-vehicle accidents occur as a result of significant differentials in speed and lane changes between traffic in laterally offset lane positions. These analyses can include many scenarios. One typical scenario is the merging of an articulated commercial vehicle from a roadway shoulder or on-ramp into a travel lane at a relatively low speed compared to the posted speed limit and/or actual travel speed of established lane traffic. Collisions arising during such events often involve less than full engagement between the vehicles and are complicated by the extended length (20 meters (m) (65.6 feet (ft)) or more) of most combination units and its effect on the time and distance it takes the unit to transition from one lane to another. Vehicle dynamics is used to analyze and understand the lane change dynamics in order to assess causes of accidents, as well as aide engineers in creating safeguards to avoid such accidents. A review of currently available analytical models finds that most are based on an analysis of a single-point object or a standard, non-articulated passenger vehicle. Additionally, many of these models consider either a constant lateral acceleration profile or a half-sine acceleration profile with specified peak lateral acceleration resulting in a constant lane change time regardless of vehicle longitudinal speed. When considering the actual lane change dynamics of a tractor-trailer, the typically applied predictive models are limited to predicting the dynamics of a singular point on the tractor-trailer during the lane change as opposed to more specific dynamics of the tractor and trailer combined effect. Testing in this study was completed using a conventional truck-tractor with sleeper berth, coupled to an unloaded 40-foot trailer chassis with a container. A total of 23 tests were completed, including (a) constant speed maneuvers for travel speeds ranging from 8.0 to 67.6 kilometers per hour (kph) (5.0 to 42.0 miles per hour (mph)) and (b) continuously accelerating travel speeds with lane changes initiated at 10.5 to 27.4 kph (6.5 to 17.0 mph). Two-dimensional time dependent tracking of the corners (tractor front left and right, trailer rear left and right) of the vehicle was documented and an imaging of the Detroit Diesel engine electronic control module (ECM) was collected after each test. Results of this study show that above speed ranges of 48 to 56 kph (30–35 mph), the timing involved in a constant-speed lane change maneuver tends to converge toward a constant; however, at lower speeds a clear inverse relation exists between speed and lane change timing. Empirical relationships were developed to more accurately predict the lane change dynamics of multiple points and the overall profile of an articulated commercial vehicle. Overall, this study provides data and relationships for consideration in lane change dynamics as well as the ability to distinguish timing of when a tractor-trailer would become perceivable versus its position in the roadway.

The Quantification of Hop Landing Balance Using Trunk-Mounted Accelerometry

Context:Balance is important for injury prediction, prevention, and rehabilitation. Clinical measurement of higher level balance function such as hop landing is necessary. Currently, no method exists to quantify balance performance following hopping in the clinic.Objective:To quantify the sacral acceleration profile and test–retest reliability during hop landing.Participants:A total of 17 university undergraduates (age 27.6 [5.7] y, height 1.73 [0.11] m, weight 74.1 [13.9] kg).Main Outcome Measure:A trunk-mounted accelerometer captured the acceleration profile following landing from hopping forward, medially, and laterally. The path length of the acceleration traces were computed to quantify balance following landing.Results:Moderate to excellent reliability (intraclass correlation coefficient .67–.93) for hop landing was established with low to moderate SEM (4%–16%) and minimal detectable change values (13%–44%) for each of the hop directions. Significant differences were determined in balance following hop landing from the different directions.Conclusion:The results suggest that hop landing balance can be quantified by trunk-mounted accelerometry.