Showing papers by "Saab AB published in 1998"

Recent advances in aerodynamics inside the nsmb (navier stokes multi block) consortium

Abstract: Since June 1992, a joint research project to develop a Multi Block Navier Stokes solver, called NSMB, is being carried out by two universities (IMHEF/EPFL, Lausanne, Switzerland and KTH, Stockholm, Sweden), one research establishment (CERFACS, Toulouse, France) and two industries (Aerospatiale, Toulouse, France and SAAB, Linkoping, Sweden) in Europe. This paper gives a short overview of the numerical and physical modelling available in NSMB. The structure of NSMB is discussed, and particular attention is given to the use of parallel computers. Examples of complex external flows calculated by the different NSMB partners are given. The paper is concluded with a summary of on going research activities.

On the hinge-finding algorithm for hingeing hyperplanes

Abstract: This correspondence concerns the estimation algorithm for hinging hyperplane (HH) models, a piecewise-linear model for approximating functions of several variables, suggested in Breiman (1993). The estimation algorithm is analyzed and it is shown that it is a special case of a Newton algorithm applied to a sum of squared error criterion. This insight is then used to suggest possible improvements of the algorithm so that convergence to a local minimum can be guaranteed. In addition, the way of updating the parameters in the HH model is discussed. In Breiman, a stepwise updating procedure is proposed where only a subset of the parameters are changed in each step. This connects closely to some previously suggested greedy algorithms and these greedy algorithms are discussed and compared to a simultaneous updating of all parameters.

Target type estimation in target tracking

Abstract: The present invention is in general related to target type estimation in target tracking systems. The invention enables a low complexity estimation of target type, using, e.g. ESM sensor data, by the introduction of an ambiguity restoring procedure in certain likelihood calculations. The invention further enables the systematic use of target type probability information in the calculation of strobe track crosses and their associated quality, which is particularly useful for deghosting purposes. Methods for utilisation of target type probability information in the processess of strobe tracking, association, track quality evaluation and multiple hypothesis tracking are also disclosed.

Multi target tracking initiation with passive angle measurements

Abstract: The present invention is in general related to tracking of multiple targets by means of measurements by various sensors. In particular the invention provides procedures for track initiation during multiple target tracking by means of measurements from passive sensors. The invention defines a quality measure for each tentative new target, by which the tentative targets are sorted and selected. The calculation of the parameters of possible targets and their covariance are preferably performed in a recursive manner. The track initiation comprises the steps of creating strobe tracks, calculating strobe track crosses, selecting a strobe track cross as a probable target and creating a target track.

Active and passive noise control in practice on the Saab 2000 high speed turboprop

Abstract: Low interior noise is an important comfort feature in all aircraft. Damping of propeller-generated noise in turboprop airliners has always been a major concern of aircraft manufacturers. Over the years different methods have been tried with varying levels of success. Active Noise Control(ANC) gives designers a potentially powerful tool for achieveing dramatic noise reduction. ANC systems are operational on both the Saab 340 and the high-speed turboprop Saab 2000 since 1994. In addition noise control measures in the Saab 2000 incorporates also a number of passive treatments and measures implemented already during the design stage. The resulting interior noise level is 76 dBA, averaged over all seats, at high cruise speed of 350 KTAS. This kind of interior noise level is compatible with turbo-fan powered aircraft of the same size.

Bias estimating method for a target tracking system

Abstract: The present invention is in general related to automatic alignment in multi-sensor target tracking. The process of the invention repeatedly generates estimates for sensor bias errors (b) by minimising a function, given on one hand by the magnitude of the discrepancy between measurements (M) and a measuring model, where the measuring model is a function of the unknown target location and unknown bias parameters, and on the other by the bias parameters and their predetermined statistical distributions (15). In a preferred embodiment of the present invention, the minimising step is performed by linearising components of the function around an approximate target position (normally obtained from the tracker (10)) and around nominal (typically zero) bias errors, and the function is subsequently minimised with respect to target positions as well as to the bias parameters (b). In addition, possible time dependence of the bias parameters are modelled by the incorporation of process noise.

Parallel Implicit Time-Accurate Navier-Stokes Computations Using Coarse Grid Correction

Abstract: A parallel implicit Navier ‐Stokes solver is constructed using a block-by-block inversion of the resulting linear system of equations followed by a global coarse grid correction to account for the block coupling. This solver is used to compute two different cases of vortex shedding e ows. The efe ciency of our method is compared to the efe ciency of the method based on pseudotime stepping and multigrid acceleration. This comparison is based on direct comparison of the two methods applied to identical test cases, as well as results reported in the literature. Emphasis is put on scalability as well as mesh sensitivity. It is concluded that the solver is not sensitive to grid stretching and scales well with both problem size and number of processors, and it is shown that measured CPU times compare well with the multigrid approach.

Method and apparatus for phase compensation in a vehicle control system

Abstract: The present invention relates to a method and a device for executing phase compensation in a control system of a motor-driven vehicle, in which the time derivative for an output signal (y) from a circuit (1) contained in the control system is limited relative to the time derivative for an input signal (u) to the circuit (1) if the time derivative for the input signal (u) exceeds a predetermined value. An error signal (e) is formed between the output signal (y) and a signal (x) present in the circuit (1), the time derivative of which is not limited in relation to the time derivative for the input signal (u). The error signal (e) is filtered via an asymptotically stable filter (3) to form a signal (δ), which is fed back and subtracted from the input signal (u) of the circuit (1) to form the signal (x). A conventional rate limiter may be used to form the output signal (y) from the signal (x).

Shell with multi-charges

Abstract: A joint for a shell with at least a first charge unit and a second charge unit arranged in series one after the other is provided. The charge units include one shaped charge each. The charges are designed to be detonated one after the other with a time separation between the detonations. In order to suppress the interference to an undetonated charge by a shock wave generated by the detonation of a previously detonated charge, the joint that connects the charge units has been designed in a special way. The joint includes a damping section parallel to the longitudinal axis of the device, that mechanically fastens together the two charge units. In addition a rigid support device is connected to the damping section and dimensioned so that when the damping section is in an unstressed state there is a clearance in the longitudinal axis of the device between the two charge units.

Ada in the JAS 39 Gripen Flight Control System

Abstract: The positive experiences from the usage of Ada in a safety critical flight control system are described in this paper. It states that preemptive scheduling implemented with tasking, can be combined with high requirements on reliability and a deterministic behaviour. How data consistency has been obtained between the periodic tasks is outlined. Also the exception handling in the system is mentioned.

Color for moving map cockpit displays

Abstract: Three color schemes (monochrome, dichrome, and polychrome) based on basic principles for color perceptionand cognition were optimized and applied to an electronic map in a horizontal-situation display. Principles forcolor discrimination, symbol coding, and color naming were applied for the super-imposed symbols (targets,waypoints etc) and for the map symbology (land, water, roads). The color codes were tested in a visual searchand detection experiment in a real-time simulation in an air-to-air mission with test pilots as subjects. Thesimulation task was as close as possible to a real-life situation. The pilots had to track a maneuvering targetwithin specified limits. Reaction times for target detection were recorded. After the simulation, the test pilotsgave a subjective estimation ofthe different color schemes. They also estimated them according to situationawareness using a rating technique on cognitive compatibility (CC-SART). All the results, both the objectiveand the subjective show that color schemes are advantageous in comparison to the monochrome code. Thereactions times were significantly lower for the chromatic color codes. The estimated situation awareness washigher for the chromatic schemes and the subjects gave higher preferences to the chromatic codes.Keywords: human factors, aviation, moving map cockpit displays, horizontal-situation displays, electronicmaps, color coding

Machining of MMC material

Abstract: A component made from a material of metal matrix composite, a so-called MMC material, is manufactured by High Speed Machining, so-called HSM machining, of a workpiece or blank of MMC material to provide a predetermined shape. HSM machining is characterized in that the cutting tool operates at a very high speed in relation to the machined work piece, especially as compared to what is normally the case when using conventional machining techniques.

Method and device for determining distances

Abstract: In determining distances using electro-magnetic waves, in particular when determining short distances in a radar installation, from a transmitter (1) a frequency modulated signal is issued, which can be modulated by a sinusoidal or triangular signal and the modulation of which in addition can have a frequency varying in time. In the receiver part (11) of the installation, in a mixer (9) a received echo signal is mixed with a leak signal (7) from the transmitter side (4). From the obtained spectrum signals are extracted around several different multiples of the modulation frequency by means of coherent detectors (19a, 19b) in different signal processing branches (a, b). After the mixing also a product modulation using a reference signal in the shape of a suitable sine signal can be executed. The signals from the signal processing branches (a, b) are conducted to a device (27), which executes a weighted production of a difference. The difference signal obtains, when using suitable control signals (vref,a, vref,b) to the coherent detectors (19a, 19b), a strongly increasing signal strength, when the installation increases the object, which causes the echo signal. The control signals to the detectors are selected, so that different special linear combinations are selected among tones in the incoming signal, whereby desired distance dependencies can be achieved.

Discussion of a new type of HMD symbology

Abstract: The use of a helmet mounted display system in a fixed-wing fighter will, without no doubt, increase the capabilities of that aircraft. Basic requirement of a helmet system could be fulfilled with a simple austere Helmet Mounted Sight. With new, more advanced, Helmet Mounted Displays that have greater possibilities to display a wide variety of information great emphasis must be made on the analysis of that information. The question of what kind of information that should be displayed in a HMD is certainly not a trivial one. This paper discusses a novel approach of trying to compress a lot of information into few symbols. The goal is to have a decluttered HMD and yet give the pilot superior situation awareness.

Display media for helmet-mounted displays

Abstract: The requirements on Helmet Mounted Displays regarding display media has historically been focused on brightness. The CRT has been the only technology available to fulfil that requirements. Today we see a number of new technologies where the brightness is not the major issue. But even when we find a display media that can handle sunshine on white clouds we still have other requirements that need to be managed. This paper will discuss some additional requirements and how new display media manage these requirements.

Cable protector for a remote controlled underwater craft

Abstract: The present invention relates to a cable protector for underwater craft remote-controlled by cable. The function of the cable protector is to protect the operating cable (1) of the underwater craft against wearing and catching on the surface mother-ship from which the craft is operated. The cable protector guides the operating cable (1) out to such a great depth that it runs clear of the ship at the same time as it allows the cable to run out in any chosen direction at the same time as it limits the deflection angle at which the operating cable leaves the cable protector. The cable protector according to the invention comprises a first, essentially vertical part in the form of telescopically acting helical springs and ends at the bottom in a link system (26-34) which prevents any too tight bending of the operating cable at the same time as it ensures that the operating cable always runs out in the direction of the craft. The solution using telescopically acting helical springs (12, 17) results in low flow resistance through the water and in it being simple to vary the length/depth of the cable protector continuously within a wide range.