An efficient built-in self test method for robust path delay fault testing

Single Input Change (SIG) testing has been proposed for robust path delay fault testing. In this letter a new Built-In Self Test (BIST) method for SIC vector generation is presented. The proposed method compares favourably to the previously proposed methods for SIC pattern generation with respect to hardware overhead and time required for completion of the test

Accumulator-based BIST approach for two-pattern testing

Two-pattern tests target the detection of most common failure mechanisms in CMOS VLSI circuits, which are modeled as stuck-open or delay faults. In this paper the Accumulator-Based Two-pattern generation (ABT) algorithm is presented, that generates an exhaustive n-bit two-pattern test within exactly 2n×(2n-1)+1 clock cycles, i.e. within the theoretically minimum time. The ABT algorithm is implemented in hardware utilizing an accumulator whose inputs are driven by either a binary counter (counter-based implementation) or a Linear Feedback Shift Register (LFSR-based implementation). With the counter-based implementation different modules, having different number of inputs, can be efficiently tested using the same generator. For circuits that do not contain counters, the LFSR-based implementation can be implemented, since registers (that typically drive the accumulator inputs into datapath cores) can be easily modified to LFSRS with small increase in the hardware overhead. The great advantage of the presented scheme is that it can be implemented by augmenting existing datapath components, rather than building a new pattern generation structure

Roll control of unmanned aerial vehicles using fuzzy logic

Abstract:- This paper presents an effective methodology for the simplified representation of the kinematics and the horizontal flight control of Unmanned Aerial Vehicles (UAVs). A real UAV has been used as a model in this project. The flight behavior of the UAV has been modeled in terms of simple analytic relationships, which proved very helpful in representing UAV’s actual horizontal motion. A fuzzy controller for the autonomous navigation of UAVs on the horizontal plane, has been developed. The controller inputs are the heading error of the aircraft and its current roll angle, whereas the output is the change command of the roll angle. Despite its simple design, the controller achieved the desired performance as evidenced from various simulated test flights

Daedalus – A software package for the design and analysis of airfoils

Summarization: A software package named Daedalus is presented for the design and analysis of airfoils. Daedalus is a collection of integrated geometry, analysis, optimization and visualization tools, which provide the ability to interactively construct and analyze standard airfoils using the NACA analytical equations and non-standard airfoils using the NURBS equations. Additionally, a database incorporating hundreds of airfoils is linked to Daedalus. Computational Fluid Dynamics (CFD) and mesh generation tools have been integrated, providing the ability to produce fast flow field calculations. Additionally, a Differential Evolution algorithm is embedded, in order to iteratively solve the inverse airfoil design problem, using a prescribed pressure (or velocity) distribution. Concerning the standard airfoil profiles, Daedalus supports various NACA-series and symmetrical biconvex airfoils. Airfoils are produced in the form of a distribution of points with variable density, in order to provide densely spaced points near the leading and trailing edges. Furthermore, by providing the coordinates and weights of the corresponding control points, the user can design non-standard section profiles using the NURBS equations. Additionally, the proposed software incorporates the ability of interpolating an existing airfoil using B-Splines polynomials. In this way a section described with a small number of surface points can be reconstructed with a desired density of points for producing acceptable computational meshes. Moreover, a new airfoil can be produced by slightly modifying an existing standard airfoil, by displacing the corresponding B-Splines control points of the interpolated initial airfoil. Besides the geometrical tools, Daedalus provides the capability of calculating the flow field around any airfoil, under prescribed flow conditions, using embedded mesh generation and analysis tools. By incorporating the geometrical design, the mesh generation and the flow analysis tools within the same software package, the airfoil design and evaluation procedure becomes automated, without the need of interaction and data transfer between different software packages. The above mentioned tools can be used in conjunction with a Differential Evolution optimizer, integrated within the software package, in order to solve the inverse airfoil design problem. The cost function to be minimized is the area of the difference between the target pressure distribution and the calculated one for each candidate solution.Παρουσιάστηκε στο: First South-East European Conference on Computational Mechanic

Freeform deformation vs. B-Spline representation in inverse airfoil design

Summarization: In this work FFD technique is compared to the classical parameterization technique using B-Spline curves by performing inverse airfoil design tests, with a Differential Evolution (DE) algorithm to serve as the optimizer. The criteria of the comparison between the two techniques are the achieved accuracy in the approximation of the reference pressure distribution and the convergence behavior of the optimization algorithm. Experiments are presented, comparing FFD to B-Spline techniques under the same flow conditions, for various numbers of design variables.Παρουσιάστηκε στο: 8th Biennial Conference on Engineering Systems Design and Analysi

Structural optimization of a centrifugal impeller using differential evolution in CATIA™ environment

Summarization: A Differential Evolution (DE) algorithm is used to optimize the backface geometry of a centrifugal impeller, with respect to the calculated maximum stress, in order to extend its overspeed limits. A detailed fully parametric 3D model of the impeller was initially constructed using CATIA V5; the backface geometry is defined using a Bezier curve with its parameters used as design variables for the present optimization procedure. The stress analysis is performed using the Generative Structural Analysis workbench of CATIA. Two different versions of the same DE algorithm are utilized in this work. The first one was developed in order to cooperate with different analysis software, in the form of executables or batch files, which are automatically called to evaluate each candidate solution; for the problem at hand, CATIA software is used to analyze each solution in a batch optimization procedure. The values of the independent design variables of each solution are provided to CATIA by using specific macro commands in batch mode, thus automatically updating the geometry, along with the corresponding mesh and the following stress calculation, in an automated manner. As an alternative approach to the same optimization problem, a DE plug-in, fully compatible with CATIA has been developed, utilizing exposed objects of CATIA (open CAA V5 automation architecture), which provide all the necessary properties and methods to interact directly with a part or analysis document through the VBA programming language. This plug-in also features a friendly and ‘easy to use’ graphical interface, which enables the user to manipulate the part’s design and analysis parameters, as well as the objective function, in order to specify the problem as suited. Optimization results are presented and compared with the results provided by the Simulated Annealing (SA) optimizer embedded in CATIA. The advantages of the proposed procedures are discussed with respect to the alternative approach.Presented on: Operational Research, An International Journa

Prediction of losses due to the tip clearance presence in axial flow machines

Μη διαθέσιμη περίληψηNot available summarizationΠαρουσιάστηκε στο: AGARD Conferenc

A method for the calculation of the tip clearance flow effects in axial flow compressors. Part I: Description of basic models

Summarization: Theoretical models for the investigation of the phenomena connected with the tip clearance are presented. The mass flow rate through the gap, the formation and evolution of the leakage vortex and the losses occurring inside and downstream of the gap are considered. Firstly, a model was developed for the description of the flow through the gap, which uses different simple velocity profiles at the gap exit. The model recognizes the basic flow characteristics inside the gap. A new method is proposed for the calculation of the shed vorticity and the formation of the leakage vortex. The moment of momentum equation is used along with the conservation of mass, in order to provide the circulation of the leakage vortex. A diffusion model for the vorticity distribution is used for the calculation of the pressure deficit field, so that the total pressure losses due to the presence of the leakage vortex, are derived. Theoretical results are compared to experimental ones for compressor and turbine cascades as well as for single rotors. The agreement between theory and experiment is good.Παρουσιάστηκε στο: ASME 1993 International Gas Turbine and Aeroengine Congress and Expositio