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The different encoder/decoder strategies to digitally encode video using an adaptive delta modulation are described. The techniques employed are: (1) separately encoding the R, G, and B components; (2) separately encoding the I, Y, and Q components; and (3) encoding the picture in a line sequential manner.
A three-level, time-split, mixed spectral/finite difference method for the numerical solution of the three-dimensional, compressible Navier-Stokes equations has been developed and implemented on the Control Data Corporation (CDC) CYBER-203. This method uses a spectral representation for the flow variables in the streamwise and spanwise coordinates, and central differences in the normal direction. The five dependent variables are interleaved one horizontal plane at a time and the array of their values at the grid points of each horizontal plane is a typical vector in the computation. The code is organized so as to require, per time step, a single forward-backward pass through the entire data base. The one-and two-dimensional Fast Fourier Transforms are performed using software especially developed for the CYBER-203.
An existing method which solves the multi-dimensional ensemble-averaged compressible time-dependent Navier-Stokes equations in conjunction with mixing length turbulence model and shock capturing technique has been extended to include the shock-tracking adaptive grid systems. The numerical scheme for solving the governing equations is based on a linearized block implicit approach. The effects of grid-motion and grid-distribution on the calculated flow solutions have been studied in relative detail and this is carried out in the context of physically steady, shocked flows computed with non-stationary grids. Subsequently, the unsteady dynamics of the flows occurring in a supercritically operated transonic diffuser and a mixed compression supersonic inlet have been investigated with the adaptive grid systems by solving the Navier-Stokes equations.
The subject of rotordynamics and instability problems in high performance turbomachinery has been a topic of considerable industry discussion and debate over the last 15 or so years. This paper reviews an original equipment manufacturer's history of development of concepts and equipment as applicable to multistage centrifugal compressors. The variety of industry user compression requirements and resultant problematical situations tends to confound many of the theories and analytical techniques set forth. The experiences and examples described herein support the conclusion that the successful addressing of potential rotordynamics problems is best served by a fundamental knowledge of the specific equipment. This in addition to having the appropriate analytical tools. Also, that the final proof is in the doing.
A combined experimental and computational investigation of an axisymmetric turbulent shock-wave boundary-layer interaction flow is presented. Experimental measurements include both mean and fluctuating data obtained by LDV techniques and identify large scale unsteady motions associated with shock induced separation. Computations using the compressible Navier-Stokes equations, and a two-equation turbulence model are in relatively good agreement with experimental measurements. It is found that the large scale unsteady motions do not appear to have a critical impact on the ability to compute the mean properties of the flows investigated in this paper.
Composite materials remain extremely vulnerable to out-of-plane impact loads, which may lead to severe losses in strength and stiffness. Impact induced damage is often a complex mixture of transverse cracks, delaminations and fiber failures. An experimental investigation was undertaken to quantify damage tolerance and resistance in composite materials impacted using the drop-weight method. Tests were conducted on laminates of several different carbon-fiber composite systems such as epoxies, modified epoxies, and amorphous and semicrystalline thermoplastics. In this paper, impacted composite specimens have been examined using destructive and nondestructive techniques to establish the characteristic damage states. Specifically, optical microscopy, ultrasonic and scanning electron microscopy techniques have been used to identify impact induced damage mechanisms. Damage propagation during post impact compression was also studied.
A nonhydrostatic extension to the Pennsylvania State University-NCAR Mesoscale Model is presented, which employs reference pressure as the basis for a terrain-following vertical coordinate, and the fully compressible system of equations. It is shown that this model, combined with the existing initialization techniques and the physics of the current hydrostatic model, is capable of real-data simulations on any scale, limited only by data quality and resolution and by computer resources. An example of an explosive cyclone simulation is presented, demonstrating the capability of the nonhydrostatic model to reproduce the hydrostatic model results at large scales.
A system design for aeronautical audio broadcasting, with C-band uplink and L-band downlink, via Inmarsat space segments is presented. Near-transparent-quality compression of 5-kHz bandwidth audio at 20.5 kbit/s is achieved based on a hybrid technique employing linear predictive modeling and transform-domain residual quantization. Concatenated Reed-Solomon/convolutional codes with quadrature phase shift keying are selected for bandwidth and power efficiency. RF bandwidth at 25 kHz per channel, and a decoded bit error rate at 10(exp -6) with E(sub b)/N(sub o) at 3.75 dB are obtained. An interleaver, scrambler, modem synchronization, and frame format were designed, and frequency-division multiple access was selected over code-division multiple access. A link budget computation based on a worst-case scenario indicates sufficient system power margins. Transponder occupancy analysis for 72 audio channels demonstrates ample remaining capacity to accommodate emerging aeronautical services.
This is an introduction to numerical Particle-Mesh techniques, which are commonly used to model plasmas, gravitational N-body systems, and both compressible and incompressible fluids. The theory behind this approach is presented, and its practical implementation, both for serial and parallel machines, is discussed. This document is based on a four-hour lecture course presented by the author at the NASA Summer School for High Performance Computational Physics, held at Goddard Space Flight Center.
Design and analysis of the inlet for a rocket based combined cycle engine is discussed. Computational fluid dynamics was used in both the design and subsequent analysis. Reynolds averaged Navier-Stokes simulations were performed using both perfect gas and real gas assumptions. An inlet design that operates over the required Mach number range from 0 to 12 was produced. Performance data for cycle analysis was post processed using a stream thrust averaging technique. A detailed performance database for cycle analysis is presented. The effect ot vehicle forebody compression on air capture is also examined.
Glenn Research Center s Creek Road Cryogenic Complex, Small Multi-Purpose Research Facility (SMiRF) recently completed validation / checkout testing of a new liquid methane delivery system and liquid methane (LCH4) conditioning system. Facility checkout validation was conducted in preparation for a series of passive thermal control technology tests planned at SMiRF in FY10 using a flight-like propellant tank at simulated thermal environments from 140 to 350K. These tests will validate models and provide high quality data to support consideration of LCH4/LO2 propellant combination option for a lunar or planetary ascent stage.An infrastructure has been put in place which will support testing of large amounts of liquid methane at SMiRF. Extensive modifications were made to the test facility s existing liquid hydrogen system for compatibility with liquid methane. Also, a new liquid methane fluid conditioning system will enable liquid methane to be quickly densified (sub-cooled below normal boiling point) and to be quickly reheated to saturation conditions between 92 and 140 K. Fluid temperatures can be quickly adjusted to compress the overall test duration. A detailed trade study was conducted to determine an appropriate technique to liquid conditioning with regard to the SMiRF facility s existing infrastructure. In addition, a completely new roadable dewar has been procured for transportation and temporary storage of liquid methane. A new spherical, flight-representative tank has also been fabricated for integration into the vacuum chamber at SMiRF. The addition of this system to SMiRF marks the first time a large-scale liquid methane propellant test capability has been realized at Glenn.This work supports the Cryogenic Fluid Management Project being conducted under the auspices of the Exploration Technology Development Program, providing focused cryogenic fluid management technology efforts to support NASA s future robotic or human exploration missions.
Structural efficiency studies were made to determine the weight-saving potential of graphite/epoxy composite structures for compression panel applications. Minimum-weight hat-stiffened and open-corrugation configurations were synthesized using a nonlinear mathematical programing technique. Selected configurations were built and tested to study local and Euler buckling characteristics. Test results for 23 panels critical in local buckling and six panels critical in Euler buckling are compared with analytical results obtained using the BUCLASP-2 branched plate buckling program. A weight efficiency comparison is made between composite and aluminum compression panels using metal test data generated by the NACA. Theoretical studies indicate that potential weight savings of up to 50% are possible for composite hat-stiffened panels when compared with similar aluminum designs. Weight savings of 32% to 42% were experimentally achieved. Experience to date suggests that most of the theoretical weight-saving potential is available if design deficiencies are eliminated and strict fabrication control is exercised.
A new computer code to solve the time averaged Navier-Stokes equations is developed. Many of the state-of-the-art numerical techniques and algorithms have been tested and implemented in the program in order to achieve a better numerical accuracy and code efficiency. Various turbulence models are tested for a wide range of flows. The initial focus has been on two-equation eddy-viscosity models, which are the most advanced available in current compressible flow codes. The long term goal will be to test Reynolds-Stress models and to explore their performance in the high Mach number range. Although testing and improvement of turbulence models for supersonic and hypersonic flows is the primary objective of this research, part of the effort has been devoted to analyzing the vortex breakdown phenomena using new computer programs. Some preliminary results on the breakdown of a vortex flow in a tube are reported. Present calculations are restricted to two dimensional flow geometry.
The various techniques by which the goal of computational aeroacoustics (the calculation and noise prediction of a fluctuating fluid flow) may be achieved are reviewed. The governing equations for compressible fluid flow are presented. The direct numerical simulation approach is shown to be computationally intensive for high Reynolds number viscous flows. Therefore, other approaches, such as the acoustic analogy, vortex models and various perturbation techniques that aim to break the analysis into a viscous part and an acoustic part are presented. The choice of the approach is shown to be problem dependent.
This report describes the research work undertaken at the Massachusetts Institute of Technology. The aim of this research is to identify effective algorithms and methodologies for the efficient and routine solution of hypersonic viscous flows about re-entry vehicles. For over ten years we have received support from NASA to develop unstructured mesh methods for Computational Fluid Dynamics. As a result of this effort a methodology based on the use, of unstructured adapted meshes of tetrahedra and finite volume flow solvers has been developed. A number of gridding algorithms flow solvers, and adaptive strategies have been proposed. The most successful algorithms developed from the basis of the unstructured mesh system FELISA. The FELISA system has been extensively for the analysis of transonic and hypersonic flows about complete vehicle configurations. The system is highly automatic and allows for the routine aerodynamic analysis of complex configurations starting from CAD data. The code has been parallelized and utilizes efficient solution algorithms. For hypersonic flows, a version of the, code which incorporates real gas effects, has been produced. One of the latest developments before the start of this grant was to extend the system to include viscous effects. This required the development of viscous generators, capable of generating the anisotropic grids required to represent boundary layers, and viscous flow solvers. In figures I and 2, we show some sample hypersonic viscous computations using the developed viscous generators and solvers. Although these initial results were encouraging, it became apparent that in order to develop a fully functional capability for viscous flows, several advances in gridding, solution accuracy, robustness and efficiency were required. As part of this research we have developed: 1) automatic meshing techniques and the corresponding computer codes have been delivered to NASA and implemented into the GridEx system, 2) a finite element algorithm for the solution of the viscous compressible flow equations which can solve flows all the way down to the incompressible limit and that can use higher order (quadratic) approximations leading to highly accurate answers, and 3) and iterative algebraic multigrid solution techniques.
We have developed a down-the-hole (DTH) rotary-percussive drill prototype that could operate on compressed Mars atmospheric CO2 gas with a wireline drilling approach. This technology addresses a need for more aggressive sampling and drilling techniques, for both scientific purposes and to obtain In-Situ Resource Utilization (ISRU) resources for future NASA missions and human crew support. Using a spool of lightweight, high-pressure capillary, a DTH drill assembly would be moved in and out of the hole that could be a kilometer or more in depth. The CO2 drill is designed so that Mars atmospheric CO2 could be collected, compressed, and supplied down the hole and routed through microducts, valves, and reservoirs for the purpose of controlling miniature mechanical actuation in the assembly. By using compressed CO2, the drill system avoids the need for heavy electrical cabling and actuator systems or a liquid media for carrying away particulates as is typically used in terrestrial drilling systems. Instead, the liquid CO2 that powers the drill expands to a gas and could be channeled around the drill housing to carry cuttings to be collected in a bailing bucket. Where terrestrial systems often use drill depth vs time as a metric, a Mars drilling system would need to be extremely low mass, but would have no need to perform under tight schedules. In this paper, we will document our trade studies, progression for the design of microduct logic verified through multiple generations of prototypes, and provide predictive performance data on energy consumption, hole depth, and drill time.
We have developed a down-the-hole (DTH) rotary-percussive drill prototype that could operate on compressed Mars atmospheric CO2 gas with a wireline drilling approach. This technology addresses a need for more aggressive sampling and drilling techniques, for both scientific purposes and to obtain In-Situ Resource Utilization (ISRU) resources for future NASA missions and human crew support. Using a spool of lightweight, high-pressure capillary, a DTH drill assembly would be moved in and out of the hole that could be a kilometer or more in depth. The CO2 drill is designed so that Mars atmospheric CO2 could be collected, compressed, and supplied down the hole and routed through microducts, valves, and reservoirs for the purpose of controlling miniature mechanical actuation in the assembly. By using compressed CO2, the drill system avoids the need for heavy electrical cabling and actuator systems or a liquid media for carrying away particulates as is typically used in terrestrial drilling systems. Instead, the liquid CO2 that powers the drill expands to a gas and could be channeled around the drill housing to carry cuttings to be collected in a bailing bucket. Where terrestrial systems often use drill depth vs time as a metric, a Mars drilling system would need to be extremely low mass, but would have no need to perform under tight schedules. In this paper, we will document our trade studies, progression for the design of microduct logic verified through multiple generations of prototypes, and provide predictive performance data on energy consumption, hole depth, and drill time.
Static uniaxial compression effect measurement along /100/, /110/ and /111/ on electroreflectance spectrum of gallium arsenide, using electrolyte technique