作者：
COULOUVRAT, FY229)
Université Pierre et Marie Curie (Paris 6) Tour 66 4 place Jussieu 75252 Paris Cedex 05 France
The propagation of large nonlinear bounded sound beams in inviscid fluids is studied by means of the method of renormalization. Starting from a nonuiform quasilinear expansion of a solution of the Khokhlov-Zabolotskay...
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The propagation of large nonlinear bounded sound beams in inviscid fluids is studied by means of the method of renormalization. Starting from a nonuiform quasilinear expansion of a solution of the Khokhlov-Zabolotskaya equation for a Gaussian source, a straining of the retarded time is introduced, which leads to a uniform approximation. The main point is the choice of a nonlinear phase shift, which yields a single smooth continuous representation for the wave, both before and beyond the shock formation point. A computation of the harmonics shows the asymmetrical distortion of the wave profile due to the coupling between nonlinearity and diffraction. A comparison with the results of a finite-difference numerical algorithm turns out favorable. The method is then extended to general plane sources.
In Ref. 1, a perturbation theory for the linear least-squares problem with linear equality constraints is presented. In this paper, the condition numbers of a general formula given in Ref. 1 are examined in order to c...
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In Ref. 1, a perturbation theory for the linear least-squares problem with linear equality constraints is presented. In this paper, the condition numbers of a general formula given in Ref. 1 are examined in order to compare them with the condition numbers of the two matrices of the problem. A class of test problems is also defined to study experimentally the numerical stability of three algorithms.
作者：
ECKARDT, HSiemens AG
Zentralabteilung Forschung und Entwicklung Dept. ZFE F 2 SYS 3 Otto-Hahn-Ring 6 D-8000 München 83 FRG
In this paper the architecture of the bus-connected, hierarchical parallel computer system Parawell used in the Siemens research laboratories in Munich is presented. Benchmark results testing the individual nodes and ...
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In this paper the architecture of the bus-connected, hierarchical parallel computer system Parawell used in the Siemens research laboratories in Munich is presented. Benchmark results testing the individual nodes and the Parawell bus are given. A general model for the speedup of parallel algorithms on the Parawell is discussed. For the implementation of several numerical algorithms (Fourier transformation, Laplace equation, N -body problem, systems of linear equations) the Parawell was proven to be suitable as long as the size of the individual tasks was sufficiently large.
The advantages of using an analytical formulation describing a satellite's attitude as a function of time, in order to monitor its rotation, are presently assessed by comparison with numerical integration procedur...
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The advantages of using an analytical formulation describing a satellite's attitude as a function of time, in order to monitor its rotation, are presently assessed by comparison with numerical integration procedures. A second-order theory of satellite rotation is presented in the form of self- contained algorithms for the first- and second-order theories with respect to the magnitude of the disturbing torques. The theory, developed under the assumption that attitude variations consist of a fast rotation around a slowly moving axis, is valid for a period during which the displacement of the rotation axis remains small. The algorithms used for application of the theory are presented. (O.C.)
A numerical technique is presented to place the eigenvalues of the estimator in a positive real control environment. The estimator is based on a reduced-order model of the full system. The technique involves posing th...
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A numerical technique is presented to place the eigenvalues of the estimator in a positive real control environment. The estimator is based on a reduced-order model of the full system. The technique involves posing the problem as a constrained optimization problem. Two formulations are presented for solving the optimization problem that differ in their objective functions and in the way constraints are handled. Examples are given illustrating the pole placement for estimators based on an arbitrary second-order model, and on fourth- and sixth-order models of the DRAPER I tetrahedral truss structure. (Author)
This study presents a three-dimensional explicit, finite-difference, shock-capturing numerical algorithm applied to viscous hypersonic flows in thermochemical nonequilibrium. The algorithm employs a two-temperature ph...
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THIS paper presents a difficult flow problem for the numerical solution of the Euler equations: the inviscid flow past an ellipse. The basic result obtained here is a lifting solution for any combination of grid and/o...
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This paper presents a unified theory for the construction of steady-state and unsteady nonreflecting boundary conditions for the Euler equations. These allow calculations to be performed on truncated domains without t...
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This paper presents a unified theory for the construction of steady-state and unsteady nonreflecting boundary conditions for the Euler equations. These allow calculations to be performed on truncated domains without the generation of spurious nonphysical reflections at the far-field boundaries. The general theory, developed perviously by mathematicians, is presented in a more easily understood form based upon fundamental ideas of linear analysis. The application to the Euler equations is given, and the relation to standard "quasi-one-dimensional" boundary conditions is explained. Results for turbomachinery problems show the effectiveness of the new boundary conditions, particularly the steady-state nonreflecting boundary conditions.
A possible mechanism of the self-sustained shock-wave oscillation caused by unsteady transonic shock boundary-layer interaction on a supercritical airfoil with fully separated flow at the shock wave is illustrated. Th...
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A possible mechanism of the self-sustained shock-wave oscillation caused by unsteady transonic shock boundary-layer interaction on a supercritical airfoil with fully separated flow at the shock wave is illustrated. The case of a shock wave oscillating on the upper airfoil surface about a mean position is considered (corresponding to Tijdeman's type A shock motion). Because of the movement of the shock, pressure waves are formed which propagate downstream in the separated flow region at a velocity ap. On reaching the trailing edge, the disturbances generate upstream moving waves at velocity au. These waves will interact with the shock and impart energy to maintain its oscillation. The loop is then completed and the period of the shock wave oscillation should agree with the time it takes for a disturbance to propagate from the shock to the trailing edge plus the duration for an upstream moving wave to reach the shock from the trailing edge. In this Note, experimental results supporting this model for self-sustained shock oscillation are presented.
In this paper, a state-space formulation of the H(infinity) optimal-control problem is given. Assuming a finite interval of control, the problem of synthesizing a finite-interval H(infinity) controller is converted in...
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In this paper, a state-space formulation of the H(infinity) optimal-control problem is given. Assuming a finite interval of control, the problem of synthesizing a finite-interval H(infinity) controller is converted into an optimization problem in which a parameter occurring in a boundary-value problem needs to be maximized. An optimality condition for the maximization of this parameter is given. The proposed method makes use of the observer-based parameterization of all stabilizing controllers. An example is given. (Author)
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