Showing papers on "Performance prediction published in 1991"

Expanding the Performance Envelope of GPS-Based Attitude Determination

Abstract: The advent of GPS-based attitude determination offers the potential for significant cost savings in applications where inertial guidance has traditionally been the standard approach We report new experimental results supporting advances in expanding the performance of attitude determination based on GPS Attitude is measured by differential measurements of GPS carrier phase between two or more antermas The performance envelope may be characterized in terms of accuracy and bandwidth, both functions of application-specific parameters such as antenna spacing and carrier-to-noise ratio The goals of the research reported here are to uantitatively identify the factors ultimately limiting performance ‘and to offer approaches and techniques through which the theoretical limits of the performance envelope may be reached Experimental results are included Factors limiting performance are multipath, carrier-to-noise ratio, and integer resolution Techniques are described for ameliorating multipath and increasing the bandwidth of differential carrier phase tracking A family of new ‘Eigenaxis” methods for resolving the integer ambiguities is presented Real time processing techniques are described which make possible survey-level accuracy attitude determination in high dynamic applications (such as high performance jet aircraft) based exclusively on GPS

An Analytic Performance Model of Disk Arrays And Its Application

Abstract: As disk arrays become widely used, tools for understanding and analyzing their performance become increasingly important. In particular, performance models can be invaluable in both configuring and designing disk arrays. Accurate analytic performance models are desirable over other types of models because they can be quickly evaluated, are applicable under a wide range of system and workload parameters, and can be manipulated by a range of mathematical techniques. Unfortunately, analytic performance models of disk arrays are difficult to formulate due to the presence of queuing and fork-join synchronization: a disk array request is broken up into independent disk requests which must all complete to satisfy the original request. In this paper, we develop, validate and apply an analytic performance model for disk arrays. We derive simple equations for approximating their utilization, response time and throughput. We then validate the analytic model via simulation and investigate the accuracy of each approximation used in deriving the analytic model. Finally, we apply the analytic model to derive an equation of the optimal unit of data striping in disk arrays.

Mechanical Performance and Lifetime Prediction

Abstract: Publisher Summary This chapter discusses the mechanical performance and lifetime prediction for parts made from metals. In the temperature range of technical interest, dislocations are relatively inactive and dislocation-induced plasticity is not found. This is the basis for the inherent brittleness of ceramics. Special care must be taken when components made from ceramics are used with constrained shape loading and the limited fracture strain makes this a more dangerous condition than constant force loading. The lack of ductility also implies the need for careful design of critical parts, for more precise tolerances, and for very careful use of those parts. Strength testing is more complicated for ceramics than for metals because problems arising from any misalignment of specimens can be severe. The statistical nature of the fracture strength of ceramics arises from the brittleness and from the high yield strength and therefore, performance prediction has to be approached statistically. It is found that the Weibull distribution is sometimes used with the argument that it is one of the three asymptotic solutions of extreme-value statistics that can be used to describe the brittle failure.

Performance prediction for parallel numerical algorithms

Abstract: In this paper, we discuss the performance prediction of Fortran constructs commonly found in numerical scientific computing. Although the approach appears applicable to multi-processors in general, within the scope of the paper we will concentrate on the Alliant FX/8 multiprocessor. The techniques proposed involve a combination of empirical observations, architectural models and analytical techniques, and exploit earlier work on data locality analysis and empirical characterization of memory system behavior. The Lawrence Livermore Loops are used as a test-case to verify the approach. Our results indicate that a prediction approach developed for a target architecture following the strategy proposed can successfully predict the performance of numerical codes.

User's manual for rocket combustor interactive design (ROCCID) and analysis computer program. Volume 1: User's manual

Abstract: The user's manual for the rocket combustor interactive design (ROCCID) computer program is presented. The program, written in Fortran 77, provides a standardized methodology using state of the art codes and procedures for the analysis of a liquid rocket engine combustor's steady state combustion performance and combustion stability. The ROCCID is currently capable of analyzing mixed element injector patterns containing impinging like doublet or unlike triplet, showerhead, shear coaxial, and swirl coaxial elements as long as only one element type exists in each injector core, baffle, or barrier zone. Real propellant properties of oxygen, hydrogen, methane, propane, and RP-1 are included in ROCCID. The properties of other propellants can easily be added. The analysis model in ROCCID can account for the influence of acoustic cavities, helmholtz resonators, and radial thrust chamber baffles on combustion stability. ROCCID also contains the logic to interactively create a combustor design which meets input performance and stability goals. A preliminary design results from the application of historical correlations to the input design requirements. The steady state performance and combustion stability of this design is evaluated using the analysis models, and ROCCID guides the user as to the design changes required to satisfy the user's performance and stability goals, including the design of stability aids. Output from ROCCID includes a formatted input file for the standardized JANNAF engine performance prediction procedure.

Large liquid rocket engine transient performance simulation system

Abstract: A simulation system, ROCETS, was designed and developed to allow cost-effective computer predictions of liquid rocket engine transient performance. The system allows a user to generate a simulation of any rocket engine configuration using component modules stored in a library through high-level input commands. The system library currently contains 24 component modules, 57 sub-modules and maps, and 33 system routines and utilities. FORTRAN models from other sources can be operated in the system upon inclusion of interface information on comment cards. Operation of the simulation is simplified for the user by run, execution, and output processors. The simulation system makes available steady-state trim balance, transient operation, and linear partial generation. The system utilizes a modern equation solver for efficient operation of the simulations. Transient integration methods include integral and differential forms for the trapezoidal, first order Gear, and second order Gear corrector equations. A detailed technology test bed engine (TTBE) model was generated to be used as the acceptance test of the simulation system. The general level of model detail was that reflected in the Space Shuttle Main Engine DTM. The model successfully obtained steady-state balance in main stage operation and simulated throttle transients, including engine starts and shutdown. A NASA FORTRAN control model was obtained, ROCETS interface installed in comment cards, and operated with the TTBE model in closed-loop transient mode.

Optimization of rotor performance in hover using a free wake analysis

Abstract: The aim of this research was to demonstrate that a free wake hover performance prediction code could be coupled to a numerical optimization algorithm. The hover code, dubbed EHPIC (evaluation of hover performance using influence coefficients), uses a quasilinear wake relaxation to solve for the rotor performance and is well suited to optimization applications

Update on the C2NVEO FLIR90 and ACQUIRE sensor performance models

Abstract: The C2NVEO FLIR90 thermal imaging systems model released in June 1990 has become the community standard model for evaluating tactical FLIR systems. This model, which successfully predicts MRTD performance for first- and second-generation thermal imagers, differs from the 1975 NVEOL thermal model in three critical areas: sampling, noise, and two-dimensional MRTD. This paper explains how each of these effects is modeled in FLIR90. First, the paper discusses how the model incorporates sampling effects by imposing Nyquist frequency limits and using pre- and postsampling MTFs. Second, the treatment of directional noise and modifications to the NETD prediction is discussed. Third, the paper discusses the two-dimensional MRTD methodology and the adjustments it imposes on the Johnson range performance prediction methodology modeled in ACQUIRE. Additionally, changes and additions in forthcoming upgrades to both FLIR90 and the ACQUIRE range performance model are described.

System for performance prediction and performance diagnosis

Abstract: PURPOSE: To provide the system for predicting and diagnosing performance by automatically and continuously performing the system performance diagnosis and the system performance prediction of a computer system. CONSTITUTION: The system consists of an external storage device 7 storing system operating state recording data 8 of the computer system, a main storage device 9 reading and storing the system operating state recording data required for predicting and diagnosing the performance from outer storage device 7 and a performance prediction and diagnosis device 1 providing the computer system without bottle neck by automatically continuing the performance evaluation diagnosing the performance of the computer system based on the system operating state recording data stored in the main storage device 9 to provide the improved plan and predicting the performance of the plan. COPYRIGHT: (C)1993,JPO&Japio

Computer simulation of staring-array thermal imagers

Abstract: The recent advances in infrared technology have led to large two-dimensional detector arrays in a range of materials including cadmium mercury telluride, platinum silicide, and ceramic pyroelectric materials. The relatively high temperature sensitivity of these arrays compared with scanned detectors is being exploited in advanced electro-optic equipment either directly or by trading off against other parameters. A major difficulty which faces system designers is that of system performance prediction prior to expensive build and trial phases. In the past, this has been overcome using a number of established computer models which were developed for conventional scanned imagers. However, the principle of operation of staring imagers is so different that a new approach is required. This paper describes a modular computer simulation of staring array imagers.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

User's manual for rocket combustor interactive design (ROCCID) and analysis computer program. Volume 2: Appendixes A-K

Abstract: The appendices A-K to the user's manual for the rocket combustor interactive design (ROCCID) computer program are presented. This includes installation instructions, flow charts, subroutine model documentation, and sample output files. The ROCCID program, written in Fortran 77, provides a standardized methodology using state of the art codes and procedures for the analysis of a liquid rocket engine combustor's steady state combustion performance and combustion stability. The ROCCID is currently capable of analyzing mixed element injector patterns containing impinging like doublet or unlike triplet, showerhead, shear coaxial and swirl coaxial elements as long as only one element type exists in each injector core, baffle, or barrier zone. Real propellant properties of oxygen, hydrogen, methane, propane, and RP-1 are included in ROCCID. The properties of other propellants can be easily added. The analysis models in ROCCID can account for the influences of acoustic cavities, helmholtz resonators, and radial thrust chamber baffles on combustion stability. ROCCID also contains the logic to interactively create a combustor design which meets input performance and stability goals. A preliminary design results from the application of historical correlations to the input design requirements. The steady state performance and combustion stability of this design is evaluated using the analysis models, and ROCCID guides the user as to the design changes required to satisfy the user's performance and stability goals, including the design of stability aids. Output from ROCCID includes a formatted input file for the standardized JANNAF engine performance prediction procedure.

On the Performance Prediction of PRAM Simulating Models

Abstract: This paper considers performance prediction for various computer networks in terms of the number of references made to the memory. Analytical solutions were obtained for the models with multiple requests to the memory and parallel access to one memory bank with a Negative Exponential distribution of requests generated by CPUs. Numerical simulation was carried out for Hyper-cube, Cube Connected Cycle and Torus processor networks. The distributed parallel architectures investigated could be viewed as PRAM simulating models. The analytical solutions are compared to numerical simulation results.

Performance Prediction For An Advanced Multipolarisation SAR

Abstract: It is generally accepted that the next generation of Advanced Spacebome SAR systems will be based on ,the concept of an active distributed arra!y antenna. Such systems will be able to provide vasty increased coverage, better image quality and also offer the possibility of being able to transmit and receive signals in both horizontal and vertical planes of polarisation. The ability to achieve such performance places stringent requirements on the instrument design. An advanced SAR design concept intended to achieve such performance was described in the Reference and, in the current paper, the more important constraints will be discussed in greater detail. Among tlhe topics addressed and quantified will be the folllowing. The problem associated with maintaining the temperature of an active array antenna within acceptable limits. This is particularly significant for an Advanced SAR deployed on a Polar Platform; as in addition to the prloblem of heat generated within the antenna itself, heat may only be radiated via the earth facing surface. The mechanical structure of the instrument and the overall mass are subject to stringent constraints.

Development of a computer algorithm for the analysis of variable-frequency AC drives: Case studies included

Abstract: The development of computer software for performance prediction and analysis of voltage-fed, variable-frequency AC drives for space power applications is discussed. The AC drives discussed include the pulse width modulated inverter (PWMI), a six-step inverter and the pulse density modulated inverter (PDMI), each individually connected to a wound-rotor induction motor. Various d-q transformation models of the induction motor are incorporated for user-selection of the most applicable model for the intended purpose. Simulation results of selected AC drives correlate satisfactorily with published results. Future additions to the algorithm are indicated. These improvements should enhance the applicability of the computer program to the design and analysis of space power systems.