Experimental investigation on the influence of liner non-uniformities on prevailing modes

From the in-flight measured circumferential modal spectra of the Rolls-Royce Tay 650 engine mounted on the Fokker 100, it was found that the sound field propagating upstream in the inlet is strongly modulated by intercostal hard-walled strips in the lined area, the non-cylindrical geometry of the duct, and the non-axisjnmnetric flow velocity...

Theory of sound propagation in a flow duct lined with annular segments of porous material

A theory is presented to calculate acoustic modes in a circular flow duct lined with porous material. The porous material is divided into annular segments by a rigid structure, which prevents axial sound propagation from one segment into the other. Single modes cannot exist in such a configuration, but it is shown that approximate solutions of...

Multimedia tele-education - PC based real-time narrowband applications

After surveying tele-education systems and technology, this study describes the design of a tele-education system which is particularly suitable for the extension of the educational facilities of universities to remote communities. The study is focused on the application of third-world small-scale institutes like the University of the...

A study on focusing in telescience using the TELEPODI breadboard

Microgravity experiments operated using telescience concepts face certain constraints. The effect of these constraints on the focusing task are identified. Four types of focusing strategy, which provide a natural means of focusing in the presence of these constraints, are described. Three specific strategies are implemented as part of the...

Meetfouten bij intensiteitsmetingen, toegepast op de bepaling van geluidsisolatie

A study has been carried out on the errors, connected with acoustic intensity measurements, measuring the sound transmission loss of panels with the intensity method. The magnitude of some measuring errors can be estimated from available publications. From measurements in a standing wave tube and on a flat plate the measuring errors have been...

De netwerkvoorzieningen op het NLR ten behoeve van het supercomputergebruik - Data communication network at NLR for supercomputer usage

For the development of methods for aerospace research and development at NLR large computer facilities are available, among which a NEC SX-2 supercomputer, a Control Data Cyber 180-855 mainframe and various minicomputers and workstation. To provide users a good access to the various systems a high speed computer network is defined, existing of a...

Implementation aspects of a decompressor for compressed METEOSAT data on a VME/68000 system

This report describes the results of a feasibility study into some aspects of a proposed METEOSAT image data compression unit. The study was performed to support the preparation of a proposal for ESOC. For the considered algorithms (ESTEC 1 & MEANDER 1) an estimate of the needed processing power based on the 68000 instruction set was made. This...

Data compression in computational fluid dynamics

Computations in numerical fluid dynamics create large sets of data. Transmission of these datasets requires a high speed communication link or, alternatively, the use of data compression techniques. This report describes the results of a study to the applicability of data compression techniques. An algorithm is designed that yields favourable...

Error correcting coding for satellite communications

This report describes the most relevant block- and convolutional codes to be used in satellite communication systems. Design trade-offs are given for the choice of coding techniques in SCPC, TDMA and SS-TDMA communication system,

Study of NAVSAT control segment characteristics: part III: executive summary

On the proposed satellite-based navigation system NAVSAT, a study has been performed concerning the characteristics of the control segment. Starting from the outcome of earlier preliminary studies of ESA, this study shows that the concept is feasible.

Channel coding with the (255,255-2T) Reed-Solomon codes over CF(256)

The class of (255, 255-2T) Reed-Solomon codes over CF(256) is studied in detail. In particular the encoding and decoding algorithms are elaborated. Main computational elements are the discrete Fourier transform for syndrome and error locator computation, Euclid's algorithm for solving the key equation and Horner's scheme for determining the...

Het gebruik van glasvezels in de vliegtuiginstrumentatie

Fiber optics, a rapidly advancing new technology, seems very well suited for use as data transmission medium in aircraft. The advantages are substantial: galvanic isolation, electromagnetic compatibility, savings in volume and weight, and superior transmission qualities. In this report possibilities and limitations are discussed for using...

The NLR/NGTE joint programme on the measurement of attenuation and impedance in acoustic flow duct facilities.

The National Aerospace Laboratory NLR in the Netherlands and the National Gas Turbine Establishment NOTE operate similar acoustic flow duct facilities but with differences in their respective approaches to the measurement of attenuation and impedance of duct linings. A joint exercise was arranged with the object of comparing methods and results,...

Dissemination of ERS-a low bitrate data and the use od L-band receiving stations

The dissemination of ERS-1 real-time thematic products via the Global Telecommunication System, the ECS satellite telecom system or the Eiuronet packet switching network is analysed and evaluated against the use of direct-receive L-band stations as used for NOAA weather image reception.

Trends in airline avionics

Modern avionics are an integral part of the aircraft. They provide the functions of communication, navigation, energy management, identification, weather, terrain, and collision avoidance, the presentation of flight and warning data as well as aircraft guidance and stabilization. New developments in micro-electronics and display technology...

Computer aided EMC analysis: A review of available tools

A review is given of methods for the analysis of intrasystem electromagnetic compatibility. Emphasis is placed on pocket calculator programs and on the SEMCAP computer program. Taking into account the applications at NLR, we conclude that both tools can be very useful for such an analysis. As far as antenna-to-antenna coupling is considered, the...

Image data security in the concept of the agricultural real time imaging satellite system (artiss)

The study on image data security is directed to the requirement for exclusive access to satellite imagery in the concept of the Agricultiiral Real Time Imaging Satellite System (ARTISS). The security assessment indicates that user survey requests are handled confidentially and it shows the access vulnerability of the transmission of image data...

Calculation of acoustic modes in an infinite duct with shear flow and sound absorbing walls

The sound field in an infinitely long duct with shear flow and sound absorbing walls, but with the sound source unspecified, is analysed into its constituents, the acoustic duct modes. The equations, wave numbers, and various properties of the modes are discussed. Some calculated results are used to show the effects of shear flow and absorbing...