Multiresolution modeling and simulation of an air-ground combat application

The High Level Architecture (HLA) establishes a common modeling and simulation framework facilitating interoperability and reuse of simulation components. Since 1996, ONERA (French Aeronautics and Space Research Centre) carries out several studies on HLA in order to gain a better understanding of the underlying mechanisms of HLA implementations. The first critical step of this initiative was to develop our own RTI from the HLA specifications. In order to evaluate the cost of making a transition from legacy simulations to HLA, we first developed an HLA federation simulating an air-ground combat involving a set of aircraft's engaged against a surface to air defense system. Current studies on HLA distributed simulation include security, WAN simulations and multiresolution. Conventional simulations represent entities at just one single level of resolution. Multiresolution representation of entities consists in maintaining multiple and concurrent representations of entities. In this paper we address the problem of how HLA services may allow to achieve multiresolution modeling and simulation. Our goal is not to provide a general framework as a basis for designing simulations of entities at different levels of resolution concurrently. We focus on experience feedback we have obtained by migrating a single level resolution HLA federation to a multi-level resolution federation. The selected application is an air-ground combat simulation involving aggregated patrols of aircraft's engaged against a surface to air defense system. In this paper, we briefly describe the air-ground combat simulation application. We then detail the multiresolution representation of entities (patrols and aircraft's), and discuss the chosen mechanisms allowing triggering aggregation from an entity-level representation, and conversely, triggering disaggregation from an aggregate representation. We focus on the HLA services we have selected to maintain several levels of representation concurrently and on methodological issues in designing multiresolution HLA simulations. We have tackled some difficulties and we propose a new HLA service that should make easier the user's task. This multiresolution management service can be added to our RTI or written by using existing HLA services. Finally, future trends are discussed

Towards an HLA Run-time Infrastructure with Hard Real-time Capabilities

Our work takes place in the context of the HLA standard and its application in real-time systems context. The HLA standard is inadequate for taking into consideration the different constraints involved in real-time computer systems. Many works have been invested in order to providing real-time capabilities to Run Time Infrastructures (RTI) to run real time simulation. Most of these initiatives focus on major issues including QoS guarantee, Worst Case Transit Time (WCTT) knowledge and scheduling services provided by the underlying operating systems. Even if our ultimate objective is to achieve real-time capabilities for distributed HLA federations executions, this paper describes a preliminary work focusing on achieving hard real-time properties for HLA federations running on a single computer under Linux operating systems. Our paper proposes a novel global bottom up approach for designing real-time Run time Infrastructures and a formal model for validation of uni processor to (then) distributed real-time simulation with CERTI

HLA high performance and real-time simulation studies with CERTI

Our work takes place in the context of the HLA standard and its application in real-time systems context. Indeed, current HLA standard is inadequate for taking into consideration the different constraints involved in real-time computer systems. Many works have been invested in order to provide real-time capabilities to Run Time Infrastructures (RTI). This paper describes our approach focusing on achieving hard real-time properties for HLA federations through a complete state of the art on the related domain. Our paper also proposes a global bottom up approach from basic hardware and software basic requirements to experimental tests for validation of distributed real-time simulation with CERTI

HP-CERTI: Towards a high performance, high availability open source RTI for composable simulations (04F-SIW-014)

Composing simulations of complex systems from already existing simulation components remains a challenging issue. Motivations for composable simulation include generation of a given federation driven by operational requirements provided "on the fly". The High Level Architecture, initially developed for designing fully distributed simulations, can be considered as an interoperability standard for composing simulations from existing components. Requirements for constructing such complex simulations are quite different from those discussed for distributed simulations. Although interoperability and reusability remain essential, both high performance and availability have also to be considered to fulfill the requirements of the end user. ONERA is currently designing a High Performance / High Availability HLA Run-time Infrastructure from its open source implementation of HLA 1.3 specifications. HP-CERTI is a software package including two main components: the first one, SHM-CERTI, provides an optimized version of CERTI based on a shared memory communication scheme; the second one, Kerrighed-CERTI, allows the deployment of CERTI through the control of the Kerrighed Single System Image operating system for clusters, currently designed by IRISA. This paper describes the design of both high performance and availability Runtime Infrastructures, focusing on the architecture of SHM-CERTI. This work is carried out in the context of the COCA (High Performance Distributed Simulation and Models Reuse) Project, sponsored by the DGA/STTC (Délégation Générale pour l'Armement/Service des Stratégies Techniques et des Technologies Communes) of the French Ministry of Defense

Real-time distributed simulations in an HLA framework: Application to aircraft simulation

This paper presents some ongoing research carried out in the context of the PRISE Project (Research Platform for Embedded Systems Engineering). This platform has been designed to evaluate and validate new embedded system concepts and techniques through a special hardware and software environment. Since much actual embedded equipment is not available, corresponding behavior is simulated within a high-level architecture (HLA) federation implemented with a run-time infrastructure (RTI) called CERTI and developed at ONERA. HLA is currently largely used in many simulation applications, but the limited performances of the RTIs raise doubts over the feasibility of HLA federations with real-time requirements. This paper addresses the problem of achieving real-time performances with the HLA standard. Several experiments are discussed using well-known aircraft simulators such as Microsoft Flight Simulator, FlightGear, and X-plane connected with the CERTI RTI. The added value of these activities is to demonstrate that according to a set of innovative solutions, HLA architecture is well suited to achieve hard real-time constraints. Finally, a formal model guaranteeing the schedulability of concurrent processes is also proposed

Analysis and Optimization of time-management services in CERTI 4.0

Time management services are one of the key features of the High Level Architecture (HLA) IEEE simulation standard. Several algorithms allow the implantation of HLA time management services ranging from the Chandy-Misra-Bryant (CMB) null message conservative algorithm up to optimistic Jefferson time warp one. For years now, we are interested in enhancing the high and/or real-time performance of our open source RTI (CERTI). In this paper, we precisely describe our updated conservative time management algorithm which, under some assumptions, limits the time creep problem inherent to the classical CMB algorithm. We will provide detailed analysis and experimental results for different implementations of HLA time management services using our new release version called CERTI 4.0

Real-time aircraft simulation using HLA standard

Distributed computing paradigm proposes a high performance solution thanks to advances in network technologies. Different programs located on several computers interact all together in order to achieve a global common goal. However, designers and developers of distributed software applications have to face several problems such as heterogeneity of the various hardware components as well as both operating systems and communication protocols. Development of middleware standards allows to consistently face these problems. Modern flight simulators techniques and implementations often result in many sophisticated and complex calculations that require a high level of computing power. Several flight simulator applications often require their services to be delivered with respect to a given period of time (deadline). This issue constitutes the problematic of real-time systems, which are defined as systems in which the correctness of the system not only depends on the logical results of computation, but also on the time at which these results are produced. Real-time systems are broadly classified into two categories based on the nature of the deadline, namely, hard real-time systems, in which the consequences of not executing a task before its deadline may be catastrophic and soft real-time systems, in which the utility of results produced by a task with a soft deadline decreases over time after the deadline expires. The main objective of our work is to use the HLA IEEE 1516-2000 standard in order to develop, to interconnect and to maintain a flight simulator. For years, the French Aerospace Laboratory (ONERA) has been developing his own Open-Source middleware RTI compliant with HLA standard called CERTI, running under several operating systems including Linux and Windows. We will use this RTI for interconnecting each part of our simulator. This RTI is recognizable through its original architecture of communicating processes. It is a distributed system involving two processes, a local one (RTIA) and a global one (RTIG), as well as a library (libRTI) linked with each federate. Each federate process interacts locally with an RTI Ambassador process (RTIA) through a Unix-domain socket. The RTIA processes exchange messages over the network, in particular with the RTIG process, via TCP (and also UDP) sockets, in order to run the distributed algorithms associated with the RTI services. Our work takes place in a global project named PRISE (Plate-forme de Recherche et d'Ingénierie des Systèmes Embarqués). The main focus of this project is to study new embedded systems concepts and techniques through a special hardware and software environment. However, works to include real-time specifications and properties to HLA standard are less advanced than other ones. This presentation explains how we proceed to implement and to test this flight simulator and how we validate real-time behavior on our computing platform. In our case, a key benefit of this architecture is to master the implementation of RTI used and thus facilitate the integration of changes in the source code to ensure temporal predictability of CERTI. Initial results, providing some answers about the suitability of CERTI to face with real-time constraints, came from ONERA/CNES satellites formation flying studies. These studies have shown that CERTI (in its original version) is able to manage multiple real-time federates with short period of time

How to solve ODEs in real-time HLA distributed simulation

In the context of the Research Platform for Embedded Systems Engineering (PRISE) Project, we are developing and maintaining a complete aircraft flight simulation using the High Level Architecture (HLA), an IEEE standard for distributed simulation. This complex distributed simulation is composed of different distributed HLA simulators (e.g., Flight Dynamics, Sensors), whose dynamic behaviors are implemented as Ordinary Differential Equations (ODEs). The resolution of these equations is done, locally for each simulator, by numerical integration with methods like Euler or Adams-Bashforth. The global behavior of this distributed simulation, where each component runs its own local resolution, is a key challenge. The main problem is to ensure the global simulation consistency and, in particular, the specific data flows between components with the correct temporal real-time behavior. This paper specifically addresses the problem of solving ODEs over an HLA distributed architecture and offers a complete study (specifications, implementation and validation) where several theoretical concepts and methods are discussed

High-throughput determination of Hubbard U and Hund J values for transition metal oxides via linear response formalism

DFT+U provides a convenient, cost-effective correction for the self-interaction error (SIE) that arises when describing correlated electronic states using conventional approximate density functional theory (DFT). The success of a DFT+U(+J) calculation hinges on the accurate determination of its Hubbard U and Hund's J parameters, and the linear response (LR) methodology has proven to be computationally effective and accurate for calculating these parameters. This study provides a high-throughput computational analysis of the U and J values for transition metal d-electron states in a representative set of over 2000 magnetic transition metal oxides (TMOs), providing a frame of reference for researchers who use DFT+U to study transition metal oxides. In order to perform this high-throughput study, an atomate workflow is developed for calculating U and J values automatically on massively parallel supercomputing architectures. To demonstrate an application of this workflow, the spin-canting magnetic structure and unit cell parameters of the multiferroic olivine LiNiPO4 are calculated using the computed Hubbard U and Hund J values for Ni-d and O-p states, and are compared with experiment. Both the Ni-d U and J corrections have a strong effect on the Ni-moment canting angle. Additionally, including a O-p U value results in a significantly improved agreement between the computed lattice parameters and experiment.Comment: 18 pages, 6 figure