Predicting Mobility in MILITARY OPERATIONAL SCENARIOS
U.S. Army leads a seven-year, multinational effort to develop new off-road vehicle mobility analysis methodology.
On the battlefield, mobility is the key to survivability. It is crucial for commanders to know which vehicle(s) to deploy on what terrain(s). They need to have the ability to assess their own and opposing forces’ vehicle mobility in any area of operations, which increases confidence in mission planning and reduces the risk of mission failures due to compromised vehicles.
Unlike the commercial automotive industry, the military has unique mobility challenges and must operate in unknown and unstructured environments where roads may not exist. The U.S. Army requires the ability to validate/predict numerous operational scenarios; being able to predict mobility increases the survivability of soldiers and vehicles. As intelligence, surveillance, target acquisition, and reconnaissance capabilities are rapidly developing, assured mobility becomes even more important.
Existing mobility prediction tools are extensively based on the NATO Reference Mobility Model (NRMM), an empirically derived set of tools based on a stand-alone model that can be accessed by NATO nations to evaluate the mobility of tracked or wheeled military vehicles across various terrains. It still is accepted as the international standard for mobility modeling of ground combat and tactical vehicles traversing on- and off-road. It traditionally has been used to facilitate comparisons between vehicle design candidates and to assess the mobility of existing vehicles under specific scenarios. From an acquisition perspective, the Army needs to know how mobile a vehicle system is from an operations perspective and how well it can go from point A to point B.
NRMM was developed using decades-old data and technology. It is broadly understood to be theoretically limited and difficult to adapt to contemporary vehicle designs and to implement within modern vehicle dynamic simulations. The following is a chronology of actions and events describing exploration, development, testing and adoption of a new, modern mobility analysis methodology by the international community.
End-to-end mobility solver
Recognizing the need for an updated modeling approach, the U.S. Army’s DEVCOM Ground Vehicle Systems Center (GVSC) has led efforts to assemble the international community to consolidate various independent and often duplicative efforts into a collection of tools that meet Next-Generation NATO Reference Mobility Model (NG-NRMM) standards. Over the past seven years, GVSC researchers and engineers have partnered with a series of North Atlantic Treaty Organization (NATO) Research Task Groups (RTG) — consisting of as many as 70 members and up to 15 nations — to develop, validate, standardize and maintain the resulting NG-NRMM approach as a shared NATO resource.
NG-NRMM is a new methodology that brings a physics-based approach to the mobility problem. It is defined as any modeling and simulation (M&S) capability that predicts land and amphibious vehicle mobility through coordinated interoperation of Geographic Information Systems (GIS) software, in conjunction with multibody, physics-based, vehicle dynamics M&S software. By leveraging the latest advances in multibody physics, ever-expanding computing power and significant advancements in remote sensing GIS systems, NG-NRMM holds the potential to significantly improve mobility predictions, while supporting the latest ground interaction geometries (fully active suspensions, walking geometries, micro-sized platforms, etc.).
In the spring of 2014 during a NATO Applied Vehicle Technology (AVT) meeting in Copenhagen, Denmark, GVSC proposed an exploratory team (ET-148) to investigate the development of an improved, efficient, simulation-based NG-NRMM methodology to replace the aging NRMM. It was envisioned that the new capability would have enhanced capabilities in the following areas:
- Increased flexibility to support operations by assessing the operational mobility of different deployed platforms in different areas of operation and routes
- Increased functionality to assess operational issues, e.g., being able to model multi-pass mobility
- Improved flexibility as a design and procurement support tool through enhanced fidelity and the ability to model current and emerging off-road mobility technologies.
To understand what an end-to-end mobility solver would require, the group focused on key attributes such as methodologies, tool choices, input/output needs and stochastics. For instance, they identified scale-invariant terrain descriptions for representing topographic map data (obtained at various scales) within a suitable multibody dynamic simulator that will enable automated analysis of regions of interest, given heterogeneous map data products as inputs. The group also was able to identify efficient, automated, parallelizable experimental design methods (i.e., sampling methods) for extracting metrics of interest from a multibody dynamic simulator. These included mobility-related metrics and auxiliary metrics that can yield rich statistical mobility-related outputs in a computationally efficient manner, allowing the use of modern high-performance computing (HPC) resources.
ET-148 looked at the use of compact representations of vehicle dynamics (i.e., response surface methods or other approximation methods) within a multibody dynamic simulator, with a goal of further reducing computational cost that will yield an update to classical “Speed-Made-Good” or “GO/NOGO” maps. They are respectively defined as the effective maximum possible vehicle straight-line running speed from one location to another, and regions where the vehicle can and cannot traverse. In addition, a benchmarking exercise was conducted to understand the capabilities of physics-based tools available from commercial software developers.
The ET determined that a desirable set of new NG-NRMM requirements would encompass certain traits (see table). At the conclusion of the study, the committee felt confident that an adequate set of new requirements had been defined and that the necessary tools were available. The time was right to develop an improved vehicle mobility modeling capability appropriate to the needs of NATO nations, and they recommended the formation of a research task group (RTG) to develop a new NG-NRMM methodology.
Developing game-changing capabilities
The follow-on, three-year RTG (AVT-248) started work in January 2016 to research and develop an updated mobility modeling methodology that could yield a new paradigm for ground vehicles with the possibility to model and simulate complex off-road vehicle maneuvers in high fidelity anywhere in the world. The new RTG was organized around seven working groups: GIS terrain/mobility mapping, simple terramechanics, complex terramechanics, intelligent vehicles, uncertainty treatment, verification/validation (V&V), and data gaps/ operational readiness. The RTG was able to develop an NG-NRMM prototype approach that included many of the desired attributes en- visioned by the ET, such as the integration of GIS-based terrain data and implementation of mobility mapping metrics into mobility simulation software.
The RTG also was able to identify and implement vehicle-terrain interaction models — i.e., terramechanics models that balance fidelity with computational efficiency, which may be semi-empirical, or fully analytical, such as those based on discrete elements — and integrate those terramechanics models into modern vehicle dynamic simulation software. The goal was to place the physics-based mobility software at the center of the geospatial terrain data and soil maps so that mobility performance metrics such as GO/NOGO maps could be derived. This mobility metric can be used in the acquisition process and in operational planning as is done today using NRMM.
The group also was able to implement efficient, automated tools that enable the use of HPC techniques and develop in-situ and realtime measurement tools to identify required terrain parameters. Further, the RTG identified the type and form of desired responses, to yield rich mobility predictions and useful auxiliary outputs that included the development of stochastic mobility output by embedding stochastic terrain and vehicle data elements. The team investigated numerical algorithms that improved computational efficiency since the NG-NRMM methodology can be computationally intensive. The new NG-NRMM process is envisioned as an open-architecture NATO standard.
Finally, to demonstrate the prototype(s), the RTG developed and executed separate demonstrations in the areas of simple and complex terramechanics such that V&V exercises were conducted. As the RTG neared completion and with a working methodology in hand, two complementary RTGs were initiated as new activities. First, a Cooperative Demonstration of Technology (CDT), AVT-CDT-308, was formed to demonstrate the new NG-NRMM approach capabilities and showcase the differences between legacy and next-generation mobility prediction software. Subsequently, a new task group (AVT-327) was initiated to develop formal M&S standards applicable to the development of the new NG-NRMM methodology.
To demonstrate the differences between legacy NRMM and the NG-NRMM methodology, a CDT was held in the fall of 2018 at the Michigan Technological University, Keweenaw Research Center (MTU/KRC) in Houghton, MI. The goal was to demonstrate the enhanced capabilities of NG-NRMM on mobility prediction, highlight its architecture, technologies and methods, and their verification with a wheeled vehicle demonstrator on a real test site. It was conducted with a particular focus on mobility over soft and marginal terrains, typical of ground combat operations. The event consisted of collecting vehicle test data to calibrate computer-based models, conducting mobility simulation and analyses, comparing models to live test results, and presenting results to the participants.
The CDT demonstrated the following NG-NRMM software approach capabilities:
- A GIS-based Terrain and Mobility Mapping tool that implements and integrates existing valid mobility metrics (%NoGo and Speed-Made-Good) in an open architected environment
- A Simple Terramechanics methodology that supports NG-NRMM requirements and provides a means of correlating terrain characteristics to remotely sensed GIS data
- Establishment of a long-term vision for a complex terramechanics approach
- Identification of practical steps required to embed stochastic characteristics of vehicle and terrain data to extend and refine the current deterministic mobility metrics
- Implementation of near-term V&V vehicle-terrain interaction benchmarks for verification of candidate NG-NRMM M&S software solutions
- Refinement of the NG-NRMM operational requirements and identification of the data gaps and operational readiness needs.
Commercial software vendors as well as other interested developers were invited to participate in the event to gauge their software’s effectiveness and accuracy in modeling and simulating vehicles in off-road and soft soil environments. They compared their state-of-the-art, physics-based mobility models against actual test results as well as combined terrain and vehicle datasets on both paved surfaces and soft soil. This allowed them to evaluate and improve their models and provide predictions of live performance.
The MTU/KRC CDT showcased NG-NRMM’s enhanced approach to mobility prediction capabilities using advanced physics-based modeling and provided real-world demonstrations to highlight the complex mobility challenges faced by today’s land-based forces. A second CDT event (AVT-CDT-308-2) is scheduled in May 2022 at the Test Center for Vehicle Mobility (WTD41) in Trier, Germany, to demonstrate NG-NRMM’s expanded M&S capabilities to support military planners, acquisition and vehicle design.
The objectives of the event will be to demonstrate the extended usage of the NG-NRMM methodology for mobility prediction and to energize military mobility stakeholders to start utilizing the software tool for operational military needs according to NATO standards. The target audience will be military stakeholders (operations, procurement, logistics), vehicle manufacturers, software tool suppliers, and academia.
The need for a standard
By definition, NG-NRMM is not a specific computer code but any M&S solution that is compliant with NG-NRMM standards and benchmarks, and hence needs to be specified in a NATO STANREC (STANdardization RECommendation). It is defined as a land-vehicle mobility M&S open architectural specification that is applicable to all land-vehicle geometric scales, implements GIS-based M&S methods and mobility metrics, promotes modularity, interoperability and portability and embraces scalable M&S at multiple levels of resolution.
It also includes M&S verification and validation maturity scales and practical benchmarks, along with standards and databases for terramechanics experimental data measurement methods that support the terramechanics models and a soils database that should be applied to all physics-based simulations of operational land and amphibious mobility among the alliance. The STANREC was recently completed and promulgated in July 2021 as NATO’s M&S standard for mobility of off-road vehicle systems. Efforts currently are underway to have the NG-NRMM methodology approved as a U.S. Army standard.
Looking to the future
The U.S. Army is developing a tool that will be compliant with NG-NRMM standards and benchmarks, called Mercury, which is part of the Department of Defense’s High Performance Computing Modernization Program’s (HPCMP) CREATE Ground Vehicles (CREATE-GV) development program. Many of the commercial vendors that participated in these efforts are actively developing compliant models as well.
Modern methods such as NG-NRMM can significantly improve the ability to make more accurate mobility predictions and assessments that hold the promise of reducing prediction errors by an order of magnitude. The vision is to reach a point where nearly all virtual prototyping and operational effectiveness can be determined upfront, leading to the rapid fielding of new technologies with a clear understanding of the operational capability of the technology. The goal of M&S investments is to minimize the need to build physical prototypes and to fill the gaps in our mobility M&S capabilities especially for autonomous operations.
Operational mobility readiness demands that Allied nations take full advantage of mobility modeling summarized by the recommended NG-NRMM methodologies. The future of analytical soft-soil mobility analysis clearly rests with the NG-NRMM approach as it holds the promise of allowing manufacturers, planners and users the ability to model virtually any platform, over any soil and terrain type.
Although there has been significant progress in the NG-NRMM methodology development, further work and investment are needed to increase computational efficiency so that it runs faster but still is able to model and accurately simulate off-road — including autonomous — mobility. The near-term solution would be based on physics-based models such as Bekker-Wong rather than empirical assessment. The far-term solution would rely on more-advanced Discrete Element Method (DEM) models and Finite Element Models (FEM) requiring HPC. The NG-NRMM would include larger-scale terrains with variable resolutions dependent on the area covered. There would be a necessary tradeoff between computational efficiency and model fidelity.
Future off-road vehicle mobility may involve many different classes and sizes of vehicles such as wheeled/ tracked vehicles, small robots, legged robots, humanoid robots and other emerging technologies traversing a variety of environments that may include on-road, urban, off-road and building interiors. The mobility performance metric maps generated using this technology are key requisites for consideration of military missions that could succeed or fail depending on how accurately the performance maps are generated.
Dr. David Gorsich of the U.S. Army Ground Vehicle Systems Center, and Michael Letherwood, P.E., and Dr. Jean Dasch of Huntington Ingalls Industries wrote this article for SAE Truck & Off-Highway Engineering. Distribution A. Approved for public release; distribution unlimited. OPSEC #: 6066