Simulation Test Bed Research Articles

Modeling and simulation in support of the design of a data fusion system

This paper uses a modeling and simulation approach in the engineering process of designing a data fusion system for military applications. Fundamental issues in the design of a data fusion system are the selection of appropriate architecture and efficient and dedicated real-time algorithms for the application of interest. Selection of data fusion algorithms is performed using a simulation test bed where realistic modeling of sensor performance is being performed. The test bed also allows the use of multiple algorithms in a dynamic sense based on the particular regime in which the fusion system is operating. This paper first presents the data fusion system engineering guidelines that are being used. Then the paper addresses the complex problem of the tactical picture compilation. Finally the paper shows a case study where the selection of data fusion algorithms is performed for an airborne platform.

Evaluation of Phase- and Element Distribution After Non-Traditional In Situ Vitrification (NTISV) at Los Alamos National Laboratory on a Simulated Adsorption Bed

A cold test demonstration of the Geosafe® Non-TraditionalIn-Situ Vitrification technology (NTISV) was performed at a simulated adsorption bed by using commercial-scale equipment. A successful demonstration of NTISV at Los Alamos National Laboratory (LANL) is expected to provide a useful technology for remediation needs of EM-40 in the U.S. Department of Energy (DOT) complex on legacy buried waste containing organics and radionuclides in geological environments. Therefore, a simulated test bed including surrogates was prepared to evaluate the impact this technology has on immobilizing radionuclides. The total volume of the cold demonstration vitrification was 3.1 m × 4.6 m × 4.9 m resulting in 176,667 kg of glass or glassy constituents. A drill core sample was removed from the glass monolith and divided into 13 samples to gain spatial (vertical) information about (a) vitrification progress, (b) phase distribution, and (c) element distribution. Based upon optical microscopy, least square and Rietveld refinement of the X-ray diffraction data, the phase constitution was determined and a temperature profile estimated. The glass compositions as well as the concentrations of surrogates and trace metals were analyzed by using X-ray Fluorescence Analysis, Electron-beam Microprobe Analysis, and Scanning Electron Microscopy. In the main melting zone, in the depth range 3.7 m to 6.3 m, NTISV successfully vitrified the geological formation (Bandelier Tuffl Unit 2/3 of Tshirege) and convert it mainly into 98-99 wt.-% silicate-based glass and 1-2 wt.-% iron-based metal inclusions. Within this zone the glass compositions have been found to be nearly constant and the surrogate elements (cerium and cesium) are distributed homogeneously.

3D Numerical Simulation of Black Hole Formation Using Collisionless Particles

We have constructed a numerical code for 3D numerical relativity with which we can investigate black hole formation processes for a wide variety of problems. We adopt a standard 3+1 formalism for the evolution of geometric variables incorporating a swarm of collisionless particles as a source of the energy momentum tensor. In order to determine black hole formation, we also incorporate an apparent horizon finder which was recently developed. Assuming triplane symmetries with respect to x-y, y-z and z-x planes, we have performed a variety of simulations for black hole formation, such as the collapse of triaxial ellipsoids, collapse of spheroids of co-rotating and counter-rotating particles, and head-on collision of two nearly equilibrium spherical clusters, as well as test-bed simulations including spherical symmetric dust collapse. We present numerical results and demonstrate that using our numerical code, we can investigate black hole formation in these problems fairly accurately.

Determining the optimal configuration for the zone routing protocol

The zone routing protocol (ZRP) is a hybrid routing protocol that proactively maintains routes within a local region of the network (which we refer to as the routing zone). Knowledge of this routing zone topology is leveraged by the ZRP to improve the efficiency of a reactive route query/reply mechanism. The ZRP can be configured for a particular network through adjustment of a single parameter, the routing zone radius. We address the issue of configuring the ZRP to provide the best performance for a particular network at any time. Previous work has demonstrated that an optimally configured ZRP operates at least as efficiently as traditional reactive flood-search or proactive distance vector/link state routing protocols (and in many cases, much more efficiently). Adaptation of the ZIP to changing network conditions requires both an understanding of how the ZRP reacts to changes in network behavior and a mechanism to allow individual nodes to identify these changes given only limited knowledge of the network behavior. We demonstrate the effects of relative node velocity, node density, network span, and user data activity on the performance of the ZRP. We then introduce two different schemes ("min searching" and "traffic adaptive") that allow individual nodes to identify and appropriately react to changes in network configuration, based only on information derived from the amount of received ZRP traffic. Through test-bed simulation, we demonstrate that these radius estimation techniques can allow the ZRP to operate within 2% of the control traffic resulting from perfect radius estimation.

Performance Analysis of a Horizontal Miss Distance Filter for TCAS II

This paper describes the performance of a filter for reducing unnecessary alerts from the Traffic Alert and Collision Avoidance System (TCAS). The filter uses range and bearing measurements to estimate miss distance for potential threat aircraft. When the estimated miss distance is high, TCAS resolution advisories are suppressed. The filter has been prototyped and extensively tested in MITRE’s TCAS simulation test bed. When implemented, the filter is expected to reduce TCAS resolution advisories by about 25% in US airspace and by about 40% in European airspace, while having a negligible effect on system safety. The filter will be included in the next fielded version of TCAS.

Deformable modeling of facial tissue for craniofacial surgery simulation.

While deformable object modeling has been studied by computer graphics specialists for more than two decades, only a few applications in the field of surgical simulation have been developed which provide both real-time and physically realistic modeling of complex, nonlinear tissue deformations. Particularly in craniofacial surgery, the prediction of soft-tissue changes--which result from alterations in the underlying bone structure--is critical to the surgical outcome. The prediction these tissue changes and, therefore, the prognosis of the postoperative appearance of the patient, is still based on empirical studies of the relationship between bone and tissue movements: There exists no physical model which takes into account the individual patient anatomy to simulate the resulting tissue changes during craniofacial surgery. In this article we present two different deformable tissue models which are intergrated in an interactive surgical simulation test bed. Both techniques allow precise preoperative simulation of the resulting soft tissue changes during craniofacial surgery and visualization of the patient's postoperative appearance. The different deformable models are described in detail and both are applied to the same craniofacial case study. The simulation results are shown and compared with regard to the speed and accuracy of the prediction of the patient's postoperative appearance.

The Performance of Two Phase Commit Protocols in the Presence of Site Failures

The two phase commit is an important protocol in distributed database systems. Much of the existing literature on the protocol is restricted to discussing and analyzing the protocol (and its variants) in the absence of failures. Very little, especially in quantitative terms, has been written about its performance in the presence of site failures. In this study, we use a simulation testbed of a distributed database system to quantify the differences in the performances of four widely known variants of the 2PC protocols (the generic 2PC, presumed commit, presumed abort, and early prepare). Our study covers both the no-failure case and the case of site failures. We present a number of interesting results based on our experiments. One is that the performance of these protocols is highly dependent on the message-processing latency at the transaction coordinator site. Another is that the presumed abort protocol does not necessarily yield better performance in the presence of site failures.

Test‐Bed Simulations of Collisionless, Self‐Gravitating Systems Using the Schrodinger Method

The Schrodinger method is a novel approach for modeling numerically self-gravitating, collisionless systems that may have certain advantages over N-body and phase-space methods. In particular, smoothing is part of the dynamics and not just the force calculation. This paper describes test-bed simulations which illustrate the viability of the Schrodinger method. We develop the techniques necessary to handle hot systems as well as spherically symmetric systems. A number of experiments are performed, and direct comparisons are made to results obtained using a simple shell code. We demonstrate that the method can adequately model a stable, equilibrium star cluster by constructing and then evolving a Plummer sphere. We also follow the evolution of a system from nonequilibrium initial conditions as it attempts to reach a state of virial equilibrium. Finally, we make a few remarks concerning the dynamics of axions and other bosonic dark matter candidates. The Schrodinger method, in principle, provides an exact treatment of these fields. However, such scalar field simulations are feasible and warranted only if the de Broglie wavelength of the particle is comparable to the size of the system of interest, a situation that is almost certainly not the case for axions in the Galaxy. The dynamics of axions is therefore no different from that of any other system of collisionless particles. We challenge recent claims in the literature that axions in the Galaxy form soliton stars.

Toward a more realistic performance evaluation of interconnection networks

lnterconnection network design plays a central role in the design of parallel systems. Most of the previous research has evaluated the performance of interconnection networks in isolation. In this study, we investigate the relationship between application program characteristics and interconnection network performance using an execution driven simulation test bed: the Reconfigurable Architecture Workbench (RAW). We simulate five topological configurations of a k-ary n-cube interconnect and four different network link models for a 4,096 node SIMD machine, and quantify the impact of the network on two application programs. We provide experimental evidence that such in-context simulation provides a better view of the impact of network design variables on system performance. We show that recent results, indicating that low-dimensional designs provide better ICN performance, ignore application requirements that may favor high-dimensional designs. Furthermore, applications that would appear to favor low dimensional designs may not, in fact, be significantly impacted by the network's dimensionality. We experimentally test the results of published performance models comparing the use of a synthetic load to that of a load generated by a typical application program.

Accuracy, Integrity, and Availability of GLS-Based Autopilot-Coupled Aircraft Landings

The project Integrity of Satellite Navigation (ISAN) investigates the potential of GNSS (GPS and/or GLONASS) as part of a hybrid GNSS Landing System (GLS) for precision approach and landing down to Category (CAT) III. Specifically, accuracy, integrity, continuity of function, and availability are considered. The accuracy and continuity of function of the GLS were demonstrated in more than 400 flight tests in a commuter aircraft, and landing trials with a Boeing 757 aircraft during the Boeing Autoland Program. These flight tests demonstrated that the navigation system provides sufficient accuracy to perform landings according to suggested FAA requirements of CAT I to III. The present objectives of ISAN are the analysis and improvement of the system availability and establishment of a method to approve system integrity standards. A combination of GPS/GLONASS is considered for the GLS availability improvement. For reasons of integrity monitoring, satellite anomalies, atmospheric effects, and multipath problems on the signal-in-space, as well as GPS receiver failures, are taken into account in a GLS Closed Loop Simulation Test Bed installation, including a GPS Simulator to validate the system integrity in defined test scenarios.

A MULTIPLE-CHANNEL FREE-ACCESS COLLISION RESOLUTION ALGORITHM BASED CONNECTION REQUEST PROCEDURE FOR LAND MOBILE SATELLITE NETWORKS

A new binary feedback multiple-channel free-access (MCFA) collision resolution algorithm (CRA) based random-access protocol (RAP) is devised to implement the connection request procedure for demand-assigned channel access protocols in land mobile satellite communications networks. The maximum stable throughput of this protocol is derived and is shown to be superior to a previously devised multiple-channel obvious blocked-access CRA based RAP as well as to slotted ALOHA. The throughput performance is also superior to the previously devised multiple-channel window blocked-access CRA based RAP for four or more channels. An exact analysis of the average packet delay for this MCFA CRA based RAP is given and shown to be in excellent agreement with computer simulation results. The protocol is shown to have smaller average delays than the best single-channel free access CRA based RAPs over a wide range of practically usable throughput rates with reasonable delays. This MCFA CRA based RAP was implemented on a channel request protocol test-bed simulator which incorporates the physical link characteristics of the MSAT-X land mobile satellite system. These test-bed simulation results also demonstrate the superiority of this protocol over slotted ALOHA for both error-free channel and mobile facing channel scenarios.

An Experimental Plan for the Evaluation of a Decision Support System

This paper describes an experimental plan for the evaluation of display modules that comprise an experimental decision support system (DSS) for combat information center (CIC) decision makers. A description of the test bed simulation known as the decision-making evaluation facility for tactical teams (DEFTT) is given. A rationale for the development of the test tasks (scenarios) is also given. The initial effort and rationale for developing the display modules is described along with a brief description of the performance measurement system. Data have been collected for subjects’ performance in the DEFTT system without the DSS and the results of these baseline runs are given.

Modeling Team Processes: Issues and a Specific Example

This paper develops a perspective to modeling team processes by drawing on concepts from team theory, and the informational processing and organizational paradigms. In such a perspective, humans and their interactions in a team are modeled as objects in a computerized environment. The behavior of the objects are specified in terms of the executable programs. A simulation testbed is described. Various information structures for team decision making in an example financial domain are examined. Questions regarding the relationship between information structure (who (knows) what, when, and how (the information is used)) and team performance are studied for the example. Thus this study can be seen as a step in the translation of behavioral and normative viewpoints of team decision making into a computational framework. The results indicate that there are complex relationships between information structure and team performance. The conventional wisdom relating improved performance to more information is not always true. The experiments demonstrate several situations of team interaction where more information can lead to dysfunctional effects.

Performance monitoring of long chains of optical amplifiers

The monitoring and fault location of long chains of optical amplifiers such as will be deployed in undersea cable systems is an important design consideration. The Letter describes two methods which have been proposed and one which has been evaluated on our test bed simulator of 3100 km with OAs spaced at 45 km and operating at 5 Gbit/s.

NEST: a network simulation and prototyping testbed

NEST: a network simulation and prototyping testbed

A case study of an adaptive load balancing algorithm

In this paper we present an effective load balancing algorithm for a multi-processor architecture designed for the real time switching of telephone calls. By modifying an algorithm developed for an abstract queueing model, which is of independent interest by itself, we propose a hybrid load balancing algorithm and study its performance in a simulation test-bed. This case study demonstrates how simple abstractions and theoretically intractable but intuitively appealing ideas can be combined to effectively solve a real problem.

Topologically Independent State Estimation: Part 2 — Test Bed and Results

The paper describes a simulated real-time test bed for the testing and comparison of programs implementing state estimation algorithms. The test bed is used to compare the performance of a program implementing a traditional Newton-Raphson weighted least-squares state estimation algorithm with that of a program implementing a novel state estimation algorithm.

Simulating Just‐in‐Time Systems

This paper describes the development and early use of a test bed for Just‐In‐Time GIT) control of Flexible Assembly Systems (FAS). JIT has, up to now, been used in repetitive manufacturing systems. However, increasingly, companies involved in batch production who frequently use Materials Requirements Planning (MRP) approaches, are seeking to achieve the benefits of JIT, and to use Kanban type control at the operational level. The test bed simulation can be configured by the user to model a range of assembly systems each of which can, within limits, be configured by the experimenter. It is built using the SLAM II simulation package. Kanban cards are modelled as resources, as are the individual assembly stations and the transportation devices which carry work between the assembly stations. The test bed can be used to experiment with batch sizes, set‐up times, assembly station breakdowns, various Kanban sequences, varying purchasing lead times, etc. It allows experimentation with the application of the Kanban system to manufacturing systems which are not purely repetitive in nature and more closely resemble batch manufacturing systems.

A sensor simulation and animation system

A shaded computer graphics system for sensor simulation and animation must possess extensive capabilities. Sensor simulation involves scenes that are viewed, environments that produce tones in the scenes, and sensors that image the scenes. Animation centers on image generation, but data input, motion specification, and tone specification routines are very important for an effective system. A unique system has been developed that models a variety of scenes, environments, and sensors. It possesses a balance of data input, motion and tone specification, and frame generation routines. The system possesses several user languages for data input. User defined sections of the scene can move. Visible, infrared, laser radar, and radar sensors have been modeled. The frame generator possesses advanced aliasing controls, textured shading, and a very fast list priority hidden surface algorithm. The system is used as a test bed for training simulators and sensor-based system simulation.