Raul G. Longoria

Coordinated and Reconfigurable Vehicle Dynamics Control

A coordinated reconfigurable vehicle dynamics control (CRVDC) system is achieved by high-level control of generalized forces/moment, distributed to the slip and slip angle of each tire by an innovative control allocation (CA) scheme. Utilizing control of individual tire slip and slip angles helps resolve the inherent tire force nonlinear constraints that otherwise may make the system more complex and computationally expensive. This in turn enables a real-time adaptable, computationally efficient accelerated fixed-point (AFP) method to improve the CA convergence rate when actuation saturates. Evaluation of the overall system is accomplished by simulation testing with a full-vehicle CarSim model under various adverse driving conditions, including scenarios where vehicle actuator failures occur. Comparison with several other vehicle control system approaches shows how the system operational envelope for CRVDC is significantly expanded in terms of vehicle global trajectory and planar motion responses.

CAVITY DYNAMICS IN HIGH-SPEED WATER ENTRY

A method is presented for modeling the cavity formation and collapse induced by high-speed impact and penetration of a rigid projectile into water. The approach proposes that high-speed water-entry is characterized by a cavity that experiences a deep closure prior to closure at the surface. This sequence in the physical events of the induced cavity dynamics is suggested by the most recent high-speed water-entry experimental data, by results from numerical experiments using a hydrocode, and by an understanding of the fundamental physics of the processes that govern surface closure. The analytical model, which specifies the energy transfer for cavity production as equivalent to the energy dissipated by velocity-dependent drag on the projectile, provides accurate estimates for variables that are important in characterizing the cavity dynamics, and reveals useful knowledge regarding magnitudes and trends. In particular, it is found that the time of deep closure is essentially constant and independent of the i...

Coordinated vehicle dynamics control with control distribution

This paper investigates a hierarchically coordinated vehicle dynamics control approach with individual wheel torque and steering actuation. A high-level robust nonlinear sliding mode controller is designed to determine the generalized forces/moments required to achieve vehicle motion objectives. A weighted pseudo-inverse based control allocation method is employed for computationally efficient distribution of control effort to the slip and slip angle of each wheel. To avoid saturation, tire-road friction estimation is an essential part of the control distribution scheme. Two adverse driving scenario simulations are used to evaluate the effectiveness of this control system

On the Control Allocation for Coordinated Ground Vehicle Dynamics Control Systems

This paper presents a new control allocation scheme for advanced coordinated vehicle dynamics control (CVDC) that takes into account vehicle operating condition and tire-surface friction coefficient. Individual tire slip and slip angles are selected as the control variables to resolve the inherent tire force nonlinear constraints. A real-time adaptable accelerated fixed-point (AFP) method is proposed to solve the magnitude and rate constrained quadratic programming control allocation (CA) problem. It could achieve faster convergence rates when control variable saturations occur. The performance of this control allocation approach is evaluated for adverse driving conditions simulated using the CarSimreg vehicle simulation package.

A framework for planning comfortable and customizable motion of an assistive mobile robot

Assistive mobile robots that can navigate autonomously can greatly benefit people with mobility impairments. Since an assistive mobile robot transports a human user from one place to another, its motion should be comfortable for human users. Moreover, it should be possible for users to customize the motion according to their comfort. While there exists a large body of work on motion planning for mobile robots, very little attention has been paid to characterizing comfort and planning comfortable trajectories.

Utilization of Optimal Control Law to Size Grid-Level Flywheel Energy Storage

This paper presents a method for sizing grid-level flywheel energy storage systems using optimal control. This method allows the loss dynamics of the flywheel system to be incorporated into the sizing procedure, and allows data-driven trade studies to be performed which trade peak grid power requirements and flywheel storage capacity. A demonstration of the sizing methodology will be illustrated through a case study based on home consumption and solar generation data collected from the largest smart grid in Austin, Texas, USA.

Low Cost Flywheel Energy Storage for a Fuel Cell Powered Transit Bus

This paper presents work that was performed to design a compact flywheel energy storage solution for a fuel cell powered transit bus with a focus on commercialization requirements. For hybrid vehicle applications, flywheels offer much higher power densities than conventional batteries. The presented design attempts to maximize the use of lower-cost technologies. The rotor relies primarily on steel for the flywheel structure, and emphasis is placed on size reduction for vehicle packaging advantages Simulations of bus configurations on measured routes was performed using PSAT to correctly size the flywheel energy storage system.

Combined Tire Slip and Slip Angle Tracking Control for Advanced Vehicle Dynamics Control Systems

This paper describes a combined tire longitudinal slip and lateral slip angle tracking control approach as part of an overall advanced vehicle dynamics control system. Nonlinear sliding mode control is used to manipulate the driving/braking/steering of each wheel to track slip and slip angles specified by a higher-level controller and a control allocation algorithm. Controlling slip and slip angles, which depend on individual wheel and vehicle dynamic states, relies on a tire model to estimate the induced tire longitudinal and lateral forces as well as self-aligning moment. Further, vehicle body states are treated here as exogenous signals independent of the slip/slip angle controller in order to isolate and simplify the control design. The performance of this control approach is evaluated and compared against results for conventional vehicle control systems in a full-vehicle CarSimreg model simulation. Improved performance is observed under an adverse split-mu hard braking scenario

Verification of a computational cardiovascular system model comparing the hemodynamics of a continuous flow to a synchronous valveless pulsatile flow left ventricular assist device.

The purpose of this investigation is to use a computational model to compare a synchronized valveless pulsatile left ventricular assist device with continuous flow left ventricular assist devices at the same level of device flow, and to verify the model with in vivo porcine data. A dynamic system model of the human cardiovascular system was developed to simulate the support of a healthy or failing native heart from a continuous flow left ventricular assist device or a synchronous pulsatile valveless dual-piston positive displacement pump. These results were compared with measurements made during in vivo porcine experiments. Results from the simulation model and from the in vivo counterpart show that the pulsatile pump provides higher cardiac output, left ventricular unloading, cardiac pulsatility, and aortic valve flow as compared with the continuous flow model at the same level of support. The dynamic system model developed for this investigation can effectively simulate human cardiovascular support by a synchronous pulsatile or continuous flow ventricular assist device.

Modeling and evaluation of a plug-in hybrid fuel cell shuttle bus

The Center for Electromechanics at The University of Texas at Austin acquired a plug-in hybrid fuel cell bus for demonstration and model development under a program funded through the USDOT-FTA. The purpose of this program was to evaluate the performance and use of the bus while developing a model that could predict overall performance and energy consumption on daily driving routes. A model of the fuel cell bus was developed using PSAT (Powertrain Analysis Toolkit). The model development involved verifying component characteristics and a parametric study of drivetrain efficiencies to relate predicted to measured vehicle energy consumption data from on-road testing. The PSAT model was able to predict net energy consumption to within 5% over varying route profiles and vehicle conditions. Further investigations with advanced energy storage were performed to evaluate the benefits of ultracapacitor assisted batteries by using the correlated PSAT model. Ultracapacitors act as an additional load leveling device in the hybrid vehicle for peak propulsion and braking vehicle loads, thereby reducing stress on the batteries. The model simulation results show that ultracapacitors can increase overall vehicle economy by 2 to 4% and deliver a net increase in battery efficiency of 3 to 4%.