This paper describes programs to reduce a nonsymmetric matrix to tridiagonal form, to compute the eigenvalues of the tridiagonal matrix, to improve the accuracy of an eigenvalue, and to compute the corresponding eigen...
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This paper describes programs to reduce a nonsymmetric matrix to tridiagonal form, to compute the eigenvalues of the tridiagonal matrix, to improve the accuracy of an eigenvalue, and to compute the corresponding eigenvector. The intended purpose of the software is to find a few eigenpairs of a dense nonsymmetric matrix faster and more accurately than previous methods. The performance and accuracy of the new routines are compared to two EISPACK paths: RG and HQR-INVIT. The results show that the new routines are more accurate and also faster if less than 20 percent of the eigenpairs are needed.
The authors present a numerical method for determining a dynamic output feedback controller. Such a controller has the capability of stabilizing systems where static output feedback fails while being simpler in struct...
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The authors present a numerical method for determining a dynamic output feedback controller. Such a controller has the capability of stabilizing systems where static output feedback fails while being simpler in structure than the control based on the separation theorem, where one first designs the controller gains assuming the complete state can be measured and then uses the same gains with an estimated state. The procedure is extended to the problem of simultaneously stabilizing several plants by a single controller.
The increasing number of research opportunities in a microgravity environment will benefit not only fundamental studies in fluid dynamics, but also technological applications such as those involving materials processi...
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The increasing number of research opportunities in a microgravity environment will benefit not only fundamental studies in fluid dynamics, but also technological applications such as those involving materials processing. In particular, fluid configurations that involve fluid-fluid interfaces would occur in a variety of experimental investigations. This work investigates the stability of a configuration involving fluid-fluid interfaces in the presence of a time-dependent (periodic) forcing. The fluid configuration is multilayered and infinite in extent. The analysis is linear and inviscid, and the acceleration vector is oriented perpendicular to each interface. A Floquet analysis is employed, and the resulting algebraic eigensystem is truncated. Nondimensional parameters appear in the algebraic system. A numerical study is performed to elucidate the regions of instability and the effect of parameter variation on the fluid configuration stability.
Active structural members with built-in sensing, feedback control, and actuation functions are used herein, along with passively damped members, to augment the inherent damping in truss structures. The effective use o...
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Active structural members with built-in sensing, feedback control, and actuation functions are used herein, along with passively damped members, to augment the inherent damping in truss structures. The effective use of such members makes it desirable to distribute them optimally throughout the structure. For simple structural systems, it is possible to place these members with some degree of optimality on the basis of engineering judgment. However, for more complex systems, the number of possible choices is so large that one may have to rely on a more formal optimization technique. This paper deals with the optimal placement of active and passive members in complex truss structures. The problem falls in the class of combinatorial optimization, for which the solution becomes exceedingly intractable as the problem size increases. This difficulty is overcome herein by use of the simulated annealing technique. We adopt the maximization of the cumulative energy dissipated over a finite time interval as the measure of optimality. The selection of nearly optimal locations for both passive and active members is consistently treated through the use of the finite-time energy dissipation criterion within the framework of the simulated annealing algorithm. numerical examples are used to illustrate the effectiveness of this methodology.
A computational procedure for the analysis of loads due to steady and oscillatory control surface deflections is presented. The numerical algorithm is based on a time accurate solution of the transonic full potential ...
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A computational procedure for the analysis of loads due to steady and oscillatory control surface deflections is presented. The numerical algorithm is based on a time accurate solution of the transonic full potential equation in a body-fitted coordinate system. Control surface deflection and motion are modeled using an equivalent body velocity that circumvents the need for generating time-dependent grids and interpolation between planes and discontinuity. Viscous effects, including mild separation, are modeled using an interactive inverse boundary layer and the transpiration velocity approach. numerical results are presented for a three-dimensional transport aircraft wing with supercritical sections, for control surfaces located at the trailing edge and the leading edge, for steady as well as oscillatory deflections. Results are compared with experimental data as well as with linear theory.
The convergence of inviscid and viscous hypersonic flow calculations using a two-dimensional flux-vector-splitting code is accelerated by applying a Richardson-type overrelaxation method. Successful results are presen...
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The convergence of inviscid and viscous hypersonic flow calculations using a two-dimensional flux-vector-splitting code is accelerated by applying a Richardson-type overrelaxation method. Successful results are presented for various cases, and a 50% savings in computer time (convergence rate is increased by a factor of 2) is usually achieved. An analytical formula for the overrelaxation factor is derived, and the performance of this scheme is confirmed numerically. Moreover, application of this overrelaxation scheme produces a favorable preconditioning for Wynne's epsilon-algorithm. Both techniques have been extended to viscous three-dimensional flows and applied to accelerate the convergence of the compressible Navier-Stokes code. A savings of 40% in computer time is achieved in this case.
A critical examination of the use of higher-order viscous-now equations in the computation or airfoil flowfields with a viscid-inviscid interaction scheme is presented. Comparisons are made between experimental data a...
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A critical examination of the use of higher-order viscous-now equations in the computation or airfoil flowfields with a viscid-inviscid interaction scheme is presented. Comparisons are made between experimental data and interactive solutions obtained using the boundary-layer equations, the second-order boundary-layer equations, and the Navier-Stokes equations, with corresponding approximations (o the viscid-inviscid matching conditions, for flows about symmetric and aft-loaded airfoils. In all cases, the viscous solution is coupled with a potential-flow solution. The results are restricted to attached, incompressible flow. An important feature of the comparisons is that the numerical algorithm, computational grid, and turbulence model are the same for all of the computations. Consequently, the effects of the higher-order terms can be studied separately from the influence or these factors. Detailed comparisons of computed and experimental results show that normal pressure gradients can be significant in the shear layers near the airfoil trailing edge and that the boundary-layer equations underestimate the boundary-layer growth in this region. The higher-order terms in the viscous-flow equations do not affect the lift and moment predictions but lead to significantly higher predictions of drag.
A finite-difference method for the characteristic equations of gasdynamics is developed. The method is based on a directed discretization of the characteristic compatibility conditions. The choice of wave propagation ...
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A finite-difference method for the characteristic equations of gasdynamics is developed. The method is based on a directed discretization of the characteristic compatibility conditions. The choice of wave propagation directions is arbitrary, and there is no need to fit interpolating functions to the initial data. The proposed method is not conservative and therefore must be used with a shock-fitting procedure in regions wherever the flow is discontinuous. numerical results are presented for sample two-dimensional problems.
The inconvenience of supercritical aerofoils is the narrowness of the optimum Mach number and incidence range. When the region of the aerofoil surface where the shock waves occur is perforated, the pressure jump inten...
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The inconvenience of supercritical aerofoils is the narrowness of the optimum Mach number and incidence range. When the region of the aerofoil surface where the shock waves occur is perforated, the pressure jump intensity across the shock wave on aerofoil can be reduced by using a secondary flow through the porous surface. numerical algorithms to compute the unsteady form of full potential equation are still in a developmental stage, and the progress in the area has recently been made by several researchers. In the present approach, a calculation procedure combining the internal integral equation method7 and the finite-difference technique is adopted to compute full potential solution with large embedded supersonic regions and strong shocks. The integral equation method is integrated via Green's theorem to show that the velocity at any point in the field space can be expressed as the effects of distributions of source and vorticity on the mean camberline of aerofoil.
作者：
JOSHI, SMNASA
Langley Research Center Hampton VA
The present consideration of the design of online computation-saving second- order state estimators for second-order vector-matrix differential systems proposes a class of such estimators which is proven to possess gu...
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The present consideration of the design of online computation-saving second- order state estimators for second-order vector-matrix differential systems proposes a class of such estimators which is proven to possess guaranteed convergence. A class of optimal second-order estimators is then obtained, and the conditions required for optimality are identified. The estimator proposed offers high performance in conjunction with online computation reductions sufficiently great to allow the estimation of the large number of state variables associated with control of large, flexible space structures represented by high-dimensional second-order systems. (O.C.)
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