Wilford Smith

Robust Control Techniques Enabling Duty Cycle Experiments Utilizing a 6-DOF Crewstation Motion Base, a Full Scale Combat Hybrid Electric Power System, and Long Distance Internet Communications

Abstract : The RemoteLink effort supports the U.S. Armys objective for developing and fielding next generation hybrid-electric combat vehicles. It is a distributed soldier-in-the-loop and hardware-in-the-loop environment with a 6-DOF motion base for operator realism, a full-scale combat hybrid electric power system, and an operational context provided by OneSAF. The driver/gunner crewstations rest on one of two 6-DOF motion bases at the U.S. Army TARDEC Simulation Laboratory (TSL). The hybrid power system is located 2,450 miles away at the TARDEC Power and Energy System Integration Laboratory (P&E SIL). The primary technical challenge in the RemoteLink is to operate both laboratories together in real time, coupled over the Internet, to generate a realistic power system duty cycle. A topology has been chosen such that the laboratories have real hardware interacting with simulated components at both locations to guarantee local closed loop stability. This layout is robust to Internet communication failures and ensures the long distance network delay does not enter the local feedback loops. The TSL states and P&E SIL states will diverge due to (1) significant communications delays and (2) unavoidable differences between the TSLs power system simulation and the P&E SILs real hardware-in-the-loop power system. Tightly coupled, bi-directional interactions exist among the various distributed simulations and software and hardware-in-the-loop components representing the driver, gunner, vehicle, and power system.

Robust Control Techniques for State Tracking in the Presence of Variable Time Delays

Abstract : In this paper, a distributed driver-in-the-Ioop and hardware-in-the-Ioop simulator is described with a driver on a motion simulator at the U.S. Army TARDEC Ground Vehicle Simulation Laboratory (GVSL). Realistic power system response is achieved by linking the driver in the GVSL with a full-sized hybrid electric power system located 2,450 miles away at the TARDEC Power and Energy Systems Integration Laboratory (P&E SIL), which is developed and maintained by Science Applications International Corporation (SAIC). The goal is to close the loop between the GVSL and P&E SIL over the Internet to provide a realistic driving experience in addition to realistic power system results. In order to preserve a valid and safe hardware-in-the-Ioop experiment, the states of the GVSL must track the states of the P&E SIL. In a distributed control system utilizing the open Internet, the communications channel is a primary source of uncertainty and delay that can degrade the overall system performance and stability. The presence of a cross-country network delay and the unavoidable differences between the P&E SIL hardware and GVSL model will cause the GVSL states and P&E SIL states to diverge without any additional action. Thus, two robust strategies for state convergence are developed and presented in this paper. The first strategy is a non-linear Sliding Mode control scheme. The second strategy is an H-infinity control scheme. Both schemes are implemented in simulation, and both schemes show promising results for state convergence in the presence of variable cross-country time delays.

Power and energy computational models for the design and simulation of hybrid-electric combat vehicles

This paper describes the work being performed under the RDECOM Power and Energy (P&E) program (formerly the Combat Hybrid Power System (CHPS) program) developing hybrid power system models and integrating them into larger simulations, such as OneSAF, that can be used to find duty cycles to feed designers of hybrid power systems. This paper also describes efforts underway to link the TARDEC P&E System Integration Lab (SIL) in San Jose CA to the TARDEC Ground Vehicle Simulation Lab (GVSL) in Warren, MI. This linkage is being performed to provide a methodology for generating detailed driver profiles for use in the development of vignettes and mission profiles for system design excursions.

Virtual Combat Vehicle Experimentation for Duty Cycle Measurement

Abstract : This paper describes a human-in-the-loop motion-based simulator which was designed, built and used to measure the duty cycle of a combat vehicle in a virtual simulation environment. The simulation environment integrates two advanced crew stations which implement both a drivers station and a gunners station of a simulated future tank. The simulated systems of the tank include a series hybrid-electric propulsion system and its main weapon systems. The simulated vehicle was placed in a virtual combat scenario which was then executed by the participating Soldiers. The duty cycle as measured includes the commands of the driver and gunner as well as external factors such as terrain and enemy contact. After introducing the project, the paper describes the simulation environment which was assembled to run the experiment. It emphasizes the design of the experiment as well as the approach, challenges and issues involved. It presents the experiment results and briefly discusses on-going and future work.

Gain models for source-flow chemical lasers

Four gain models are developed for use in analyzing source‐flow chemical laser resonators. The first is a rotational nonequilibrium (RNE) model which traces the evolution of each vibrational‐rotational state of the lasing molecule. The second is a less detailed model based on the assumption that each vibrational level is in rotational equilibrium (RE). In the third model, in addition to the rotational equilibrium assumption, the gain is assumed to be the same for all the vibrational transitions. The equations then become identical in form to those describing single‐line (SL) lasing from a two‐level system. The RE and RNE models solve the chemical kinetics equations for the gain self‐consistently with the gasdynamic equations describing the flow field. In the SL model coupling between the gasdynamics and the laser kinetics is eliminated by using the gasdynamics from a simple Fabry–Perot calculation at a representative value of the threshold gain to provide the flow field conditions for the resonator calcul...

Design of an agile unmanned combat vehicle: a product of the DARPA UGCV program

The unmanned ground compat vehicle (UGCV) design evolved by the SAIC team on the DARPA UGCV Program is summarized in this paper. This UGCV design provides exceptional performance against all of the program metrics and incorporates key attributes essential for high performance robotic combat vehicles. This performance includes protection against 7.62 mm threats, C130 and CH47 transportability, and the ability to accept several relevant weapons payloads, as well as advanced sensors and perception algorithms evolving from the PerceptOR program. The UGCV design incorporates a combination of technologies and design features, carefully selected through detailed trade studies, which provide optimum performance against mobility, payload, and endurance goals without sacrificing transportability, survivability, or life cycle cost. The design was optimized to maximize performance against all Category I metrics. In each case, the performance of this design was validated with detailed simulations, indicating that the vehicle exceeded the Category I metrics. Mobility metrics were analyzed using high fidelity VisualNastran vehicle models, which incorporate the suspension control algorithms and controller cycle times. DADS/Easy 5 3-D models and ADAMS simulations were also used to validate vehicle dynamics and control algorithms during obstacle negotiation.

Full-bore simulation for plasma-driven railguns

The authors have embarked on a program to develop a full-bore simulation of the railgun plasma armature. The simulation extends from the back of the projectile to the breech of the railgun, thereby treating explicitly the entire bore. The extent of the armature is unrestricted, and the armature is allowed to grow into the background gas as dictated by physical interactions. This paper documents their progress to date in achieving this full-bore simulation. Most of the activities have focused on formulating the defining equations and boundary conditions, and implementing (and then validating) a numerical technique capable of resolving the steep gradients that they expect to encounter in the simulation. >

Hydrogen fluoride (HF) overtone phase-step resonator

The low gain nature of HF overtone chemical lasers has heretofore limited the devices to low magnifications on the order of 1.5. In this paper analyses are presented that show a phase step mirror resonator can enhance modal feedback in these devices such that operation at magnifications of at least 3 is possible. The mechanism for this feedback enhancement is destructive interference of the output wave causing confinement of the beam around the resonator axis. It is shown that the radius of the phase step for optimum performance is directly related to the resonator geometry. It is also seen that the phase step technique increases sensitivity of the resonator to misalignments. The analyses include both two and three-dimensional physical optics calculations complete with rotational non-equilibrium chemical laser gain.

High-Q resonator design for an HF overtone chemical laser

In this study geometric and physical optics analyses were used to examine an HF overtone/UR90 design (OTR90). The geometric analyses were primarily used to calculate the physical optics parameters and to understand the misalignment sensitivities of the resonator. The physical optics calculations then provided information regarding output power, phase and intensity distributions, and mode control. The physical parameters used in the optical analyses were based on a rectangular resonator designed around the NACL, two-bank gain generator and facility; a likely candidate for a near-term HF overtone experiment. Also, the gain model was anchored to the small-signal gain (SSG) and spectrum of this device. These analyses show that indeed high power within a good mode can be extracted using this resonator and that the impact of mirror misalignment is greatly reduced.

Novel resonators for high-power HF overtone lasers

A variety of resonator designs that may be scalable to large high-power HF overtone lasers are discussed. Multipass resonators with multiple turning mirrors and with common turning mirrors are included in the discussion. Geometric optics are utilized in analyzing these concepts. Emphasis is placed on gain saturation, amplified-spontaneous-emission and parasitic control by gain segmentation, alignment tolerances, and diffractive beam spillage. It is concluded that for moderate powers, the multipass concept with separate turning mirrors is preferable, while for higher powers, a concept with common turning mirrors may be chosen.