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Technical Paper

“Motion in FEA”: An Innovative Approach for More Physical and More Accurate Vehicle Dynamics Simulation

Vehicle dynamics is a discipline of mechanical engineering that benefited of significant improvements thanks to the progress of computational engineering. Vehicle dynamics engineers are using CAE for the development of a vehicle with MBS and FEA. The concurrent use of these two technologies is a standard in the automotive industry. However the current simulation process is not fully efficient because local geometrical and material nonlinearities are not accurately modeled in classical MBS software. This paper introduces a methodology for vehicle dynamics simulation integrating MBS capabilities in one single nonlinear FEA environment enabling an accurate modeling of nonlinearity in vehicles.
Technical Paper

Yaw/Roll Stability Modeling and Control of HeavyTractor-SemiTrailer

This paper sets up a simplified dynamic model for simulating the yaw/roll stability of heavy tractor-semitrailer using Matlab/Simulink. A linear quadratic regulator (LQR) based on partial-state feedback controller is used to optimize the roll stability of the vehicle. The control objective for optimizing roll stability is to be reducing the lateral load transfer rate while keeping the suspension angle less than the maximum allowable angle. The simulation result shows that the LQR controller is effective in the active roll stability control of the heavy tractor-semitrailer.
Technical Paper

Yaw Testing of an Instrumented Vehicle with and without Braking

Two methods for calculating speed from curved tire marks were investigated. The commonly used critical speed formula and a computer simulation program were evaluated based on their ability to reproduce the results of full-scale yaw tests. The effects of vehicle braking and friction coefficient were studied. Twenty-two yaw tests were conducted at speeds between 70 and 120 km/h. For half of the tests, about 30% braking was applied. Using the measured sliding coefficient of friction, both the critical speed formula and the computer simulations under-predicted the actual speed of the vehicle. Using the measured peak coefficient of friction, both methods over-estimated the actual speed. There was less variance in the computer simulation results. Braking tended to increase the speeds calculated by the critical speed formula.
Technical Paper

Yaw Stability Control of Tractor Semi-Trailers

Tractor semi-trailer stability during emergency braking and steering maneuvers has been an issue that was improved through implementation of Anti-lock Braking Systems (ABS). Although some improvements have been achieved, the need for new control methodologies is evident from the number of accidents reported by NHTSA involving tractor semi-trailers. In this paper, a new control algorithm has been developed for improving the tractor semi-trailer stability through utilization of yaw moment, i.e., tire differential braking strategy. This new, multifaceted, adaptive control algorithm which allows the estimation of the unknown vehicle parameters through use of the adaptation laws is based on the Lyapunov Direct Method. A tractor semi-trailer model with four degrees of freedom was used to develop the control algorithm and the adaptation laws. The controller was implemented on a 2-axle tractor 1-axle van trailer in TruckSim 7©.
Technical Paper

Yaw Moment Control of the Vehicle by Means of a Magnetorheological Semi-Active Differential

A new controllable limited slip differential is proposed and tested in software environment. It is characterized by the employment of a magnetorheological fluid, which presents the property of changing its rheology thanks to an applied magnetic field. A vehicle model has been designed and employed for the synthesis of a sliding controller. The control is based on a double level scheme: the upper controller aims to generate the target locking torque, while the lower controller generates, as control action, the supply current for the controllable limited slip differential. The obtained results show the effectiveness of the device in terms of vehicle dynamics improvement. Indeed, the results reached by the vehicle in presence of the new differential confirm the improved performances for both steady and unsteady state manoeuvres.
Technical Paper

Yaw Instability Due to Longitudinal Load Transfer During Braking in a Curve

Active vehicle dynamics control ensures improved safety. So far, yaw instability is mostly associated with transient steering manoeuvres when driving at a constant speed. However, braking related load transfer affects yaw stability. Intense braking at high friction combined with elevated and forwarded CG amplifies this influence on unloaded tractors. Designing a dynamic stability system to enhance active safety requires fresh insight into braking related yaw instability. This investigation covers a theoretical analysis of braking influence on yaw stability on unloaded 4×2 tractors, being applicable to vehicle braking while cornering, including steering induced by other asymmetrical forces, since it focuses essentially on small steering angles.
Technical Paper

Yaw Dynamics of Command Steered Multi Axle Semitrailer

Abstract This paper investigates the yaw dynamic behaviour of a seven axle tractor semitrailer combination vehicle developed by VRDE (Vehicle Research & Development). The semitrailer has four steerable axles which follow command steering law i.e. all axles of semitrailer are steered in a particular relation with articulation of tractor. A 4 dof (degree of freedom) linear yaw plane model was developed for this combination vehicle. Yaw response characteristics such as lateral acceleration, yaw rate and articulation angle for step and sine steer is obtained from this model. Effects of speed on the above parameters are also studied to the same steering inputs. Lateral tyre forces due to semitrailer steering at various speeds are estimated to understand its distribution on each axle. Steady state yaw rate and articulation angle gain are obtained to predict the understeer / oversteer behaviour of combination vehicle.
Technical Paper

Worst Case Scenarios Generation and Its Application on Driving

The current test methods are insufficient to evaluate and ensure the safety and reliability of vehicle system for all possible dynamic situations including the worst cases such as rollover, spin-out and so on. Although the known NHTSA J-turn and Fish-hook steering maneuvers are applied for the vehicle performance assessment, they are not enough to predict other possible worst case scenarios. Therefore, it is crucial to search for the various worst cases including the existing severe steering maneuvers. This paper includes the procedure to search for other useful worst case based upon the existing worst case scenarios in terms of rollover and its application in simulation basis. The human steering angle is selected as a design variable and optimized to maximize the index function to be expressed in terms of vehicle roll angle. The obtained scenarios were enough to generate the worse cases than NHTSA ones.
Technical Paper

Workload Analysis Method via Optimal Driver Model

Race car design requires precise estimation of car behavior under aggressive driving conditions. Ground vehicles are highly complicated man-machine systems, in which driver operation plays a great role. Thus, analysis based on a driver model is advantageous. In this research, an H∞ optimal driver model is formulated, and the cost index of the operation workload, which is derived from the lead operation of the driver, is developed. In addition, sensitivity to disturbances, such as bumps on the road, is evaluated using control theory. The proposed method can estimate workload and the effects of disturbances on man-machine systems. This is especially valuable for First Order Analysis. Several parametric studies have contributed to the development of guidelines for high-performance car design to guarantee a good workload level, high tracking performance, and low disturbance sensitivity.
Technical Paper

Wiper System Dynamic Behavior

In this paper are presented some results about the dynamic of the wiper systems, vibratory phenomena and some influences of the friction, the weight and the clearances.
Journal Article

Window Buffeting Measurements of a Full Scale Vehicle and Simplified Small Scale Models

Window buffeting is a major source of flow induced sound and vibration. This paper will describe window buffeting measurements acquired on a full scale vehicle as well as two different simplified small scale models. The experimental data sets included microphone and phase averaged Particle Image Velocimetry (PIV) measurements both of which show that the flow physics are qualitatively and quantitatively similar in all cases. The implication of this result is that simplified laboratory models of a vehicle are sufficient to study the various aspects of window buffeting in full scale vehicles.
Technical Paper

Wind-Tunnel Investigation of Commercial Transport Aircraft Aerodynamics at Extreme Flight Conditions

A series of low-speed static and dynamic wind tunnel tests of a commercial transport configuration over an extended angle of attack/sideslip envelope was conducted at NASA Langley Research Center. The test results are intended for use in the development of an aerodynamic simulation database for determining aircraft flight characteristics at extreme and loss-of-control conditions. This database will be used for the development of loss-of-control prevention or mitigation systems, pilot training for recovery from such conditions, and accident investigations. An overview of the wind-tunnel tests is presented and the results of the tests are evaluated with respect to traditional simulation database development techniques for modeling extreme conditions to identify regions where simulation fidelity should be addressed.
Technical Paper

Wind Tunnel Testing of an Advanced Flying Automobile Concept

A 1:12 scale model based on the Sokol A350 Advanced Flying Automobile Concept was examined in the San Diego State University Low Speed Wind Tunnel for performance and stability characteristics. Observation showed that the model stalled at angles of attack above 12 degrees, corresponding to a maximum coefficient of lift of 1.54 and a drag coefficient of .284 for the wing center position. Analysis of the moments revealed that the test model was unstable with the current design specifications, however varying the wing location provided additional insight on the stability of the model. With design changes based on moving the center of gravity forward, the prototype vehicle is capable of creating enough lift to fly safely.
Technical Paper

Wind Tunnel Investigation of an Inflatable Aerodynamic Boattail for Tractor-Trailers

The objective of this research was to initiate the development of a design procedure to optimize the shape of a drag reducing device to obtain a significant drag reduction on the rear end of a trailer of a tractor-trailer rig. To meet this objective, four wind tunnel experiments were conducted. An optimized shape has not been determined as of yet; however, it was found that the aerodynamic drag could be reduced as much as 17.4 percent, and that there are several important parameters that influence the drag reduction, such as: device length, device edge curvature, and the device-to-trailer attachment angles.
Journal Article

Wind Noise Measurements for Automotive Mirrors

In order to understand the flow and wind noise characteristics generated by the outside rearview (OSRV) mirror, a series of wind noise measurements for two production mirrors was conducted at the GM Aerodynamics Lab (GMAL) wind tunnel. These measurements included the time-averaged static pressures, surface noise sources, and far field propagation noise. The data obtained in this investigation will be used for future CFD numerical validations. The two mirrors chosen for the test are the GMT360 (a truck mirror) and the GMX320 (a sedan mirror). The test mirror was mounted on an elevated table which was specially designed for the current project to avoid any significant flow boundary layer buildup on the wind tunnel floor. The test conditions reported in this paper include four inlet speeds of 30, 50, 70 and 90 mph at 0 yaw angle. To record the wind noise sources, nine surface flush-mount microphones were used.
Technical Paper

Wide Tires, Narrow Tires

Tractive performance comparisons among five different size tires were made on two different surface conditions, a wheat stubble field and a tilled wheat stubble field. Radial 18.4R46, 20.8R42 and 710/70R38 radial tires; and bias 750/65-38 and 850/55-42 tires were used. Instrumentation to evaluate tractive performance was installed on a two-wheel drive and a mechanical front wheel drive agricultural tractor. Axle torques, drawbar pull, travel speed, and engine rpm were recorded for a series of drawbar pulls on the two soil surfaces. Tractive performance evaluations among the tires were made by comparing the relationships of dynamic traction ratio to slip, tractive efficiency to slip, and tractive efficiency to dynamic traction ratio. In general, narrower tires exhibited performance advantages over wider tires.
Technical Paper

Why Simulators are More Difficult to Fly Than Aircraft

Simulators are typically more difficult to fly than the aircraft they represent. The factors involved include limited field of view, degraded visual acuity, scene distortion, absence of depth perception, attenuation or absence of motion cues, and response delays that are often inconsistent among visual, motion, and instruments. It is suggested that for most training tasks the added difficulty because of these factors is not a drawback, and should not be alleviated at the expense of dynamic fidelity.
Technical Paper

Why Simulation? An Interesting Case Study

Abstract This paper presents an example application for vehicle dynamics simulation software. This example investigates the validity of the vehicle motion presented in the famous car chase scene from the 1968 movie Bullitt. In this car chase, a 1968 Ford Mustang, driven by Det. Frank Bullitt of the San Francisco Police Department, is chasing a criminal driving a 1968 Dodge Charger through the streets of the Russian Hill district of San Francisco. The purpose of the simulation was to reconstruct the chase scene to determine the level of realism in the movie, in terms of conformance to Newton’s Laws of motion. To produce the simulation, several city blocks of the pertinent area of the city were surveyed and exemplar vehicles were measured and inspected. Three-dimensional computer models of the scene and vehicles were built. The movie footage was analyzed to determine vehicle speeds and driver inputs.
Technical Paper

What Happens to a Passenger When Traveling in a car

WHY one gets that aching neck and those tired eyes after driving for long stretches is explained in this paper. A brief qualitative study of the motion of the driver and passenger in the front seat of an automobile is given here. The author provides a reasonable explanation for some of the commonly observed kinds of driver fatigue and points the way for some improvement in the dynamic comfort of automobile seats.
Technical Paper

Wet Handling Track: Design, Execution and Analysis of a High Performance Asphalt Mixture

Abstract Asphalt specifications for a Wet Handling Track (WHT) are very stringent regarding coefficient of adherence and homogeneity of this coefficient over time. Currently, asphalt mixture pavements used in wet conditions have a very limited useful life and continue degrading following different patterns depending on the asphalt mixtures used. This is due to many reasons, but mainly as a consequence of supporting big strains and the extreme conditions during its useful life. During its lifetime, the asphalt is constantly immersed in water and submitted to adverse weather conditions. Moreover, Wet Handling pavements should provide very specific and stable adherence values for vehicle testing during the asphalt aging evolution. Consequently, the study, execution and testing of the new asphalt concrete mixture for the pavements and the materials used for WHT is necessary to reach durable, homogenous in time and cost effective pavements with very low adherence parameters.