Engineering topics

Morino, L.

Publications and source records attributed to Morino, L..

At least 19 records

NASA NTRS1986

Helmholtz decomposition revisited: Vorticity generation and trailing edge condition. I - Incompressible flows

Using the decomposition for the infinite-space, the issue of the nonuniqueness of the Helmholtz decomposition for the problem of the three-dimensional unsteady incompressible flow around a body is considered. A representation for the velocity that is valid for both the fluid region and the region inside the boundary surface is employed, and the motion of the boundary is described as the limiting case of a sequence of impulsive accelerations. At each instant of velocity discontinuity, vorticity is shown to be generated by the boundary condition on the normal component of the velocity, for both inviscid and viscous flows. In viscous flows, the vorticity is shown to diffuse into the surroundings, and the no-slip conditions are automatically satisfied. A trailing edge condition must be satisfied for the solution to the Euler equations to be the limit of the solution of the Navier-Stokes equations.

Morino, L.↗

NASA NTRS1986

A boundary element method for unsteady viscous flows

A potential vorticity method for the analysis of unsteady viscous incompressible flow past arbitrarily shaped objects is discussed which is based on the Helmholtz decomposition. It is found that the correct boundary condition to be imposed is on the normal component of the velocity for the cases of both inviscid and viscous flows. The no-slip condition is shown to be automatically satisfied for viscous flows. Numerical solutions for two-dimensional flow problems are given for attached flows in addition to those involving separation. The vorticity is confined, at least for the case of symmetric flows, to a small region in the immediate vicinity of the body, making possible the minimization of the number of node points in the field, and hence the computational time, without loss of accuracy.

Bharadvaj, B. K.↗

NASA NTRS1985

Scalar/Vector potential formulation for compressible viscous unsteady flows

A scalar/vector potential formulation for unsteady viscous compressible flows is presented. The scalar/vector potential formulation is based on the classical Helmholtz decomposition of any vector field into the sum of an irrotational and a solenoidal field. The formulation is derived from fundamental principles of mechanics and thermodynamics. The governing equations for the scalar potential and vector potential are obtained, without restrictive assumptions on either the equation of state or the constitutive relations or the stress tensor and the heat flux vector.

Morino, L.↗

NASA NTRS1982

Steady, Oscillatory, and Unsteady Subsonic and Supersonic Aerodynamics

Computer program SOUSSA-P (Steady, Oscillatory, and Unsteady Subsonic and Supersonic Aerodynamics--Production Version) accurately and efficiently evaluates steady and unsteady aerodynamic loads on aircraft having arbitrary shapes and motions, including structural deformations.

Desmarais, R. N.↗

NASA NTRS1982

Nonlinear Green's function method for unsteady transonic flows

Advantages to employing Green's function in describing unsteady three-dimensional transonic flows are explored. The development of the function for application to linear subsonic and supersonic unsteady aerodynamics is reviewed. It is shown that unique solutions are possible for external flows, with all functional expressions being defined in Prandtl-Glauert space. The development of methods of using the Green's function for transonic flows is traced, noting the necessity of including the effects of significant nonlinear terms. The steady-state problem is considered to demonstrate the shock-capturing ability of the method and the usefulness of the function in the incompressible, subsonic, transonic, and supersonic areas of potential unsteady three-dimensional flows around complex configurations. Computational time is asserted to be an order of magnitude less than with finite difference methods.

Tseng, K.↗

NASA NTRS1980

Steady, oscillatory, and unsteady subsonic Aerodynamics, production version 1.1 (SOUSSA-P1.1). Volume 2: User/programmer manual

A user/programmer manual for the computer program SOUSSA P 1.1 is presented. The program was designed to provide accurate and efficient evaluation of steady and unsteady loads on aircraft having arbitrary shapes and motions, including structural deformations. These design goals were in part achieved through the incorporation of the data handling capabilities of the SPAR finite element Structural Analysis computer program. As a further result, SOUSSA P possesses an extensive checkpoint/ restart facility. The programmer's portion of this manual includes overlay/subroutine hierarchy, logical flow of control, definition of SOUSSA P 1.1 FORTRAN variables, and definition of SOUSSA P 1.1 subroutines. Purpose of the SOUSSA P 1.1 modules, input data to the program, output of the program, hardware/software requirements, error detection and reporting capabilities, job control statements, a summary of the procedure for running the program and two test cases including input and output and listings are described in the user oriented portion of the manual.

Smolka, S. A.↗

NASA NTRS1980

Steady, Oscillatory, and Unsteady Subsonic and Supersonic Aerodynamics, production version (SOUSSA-P 1.1). Volume 1: Theoretical manual

Recent developments of the Green's function method and the computer program SOUSSA (Steady, Oscillatory, and Unsteady Subsonic and Supersonic Aerodynamics) are reviewed and summarized. Applying the Green's function method to the fully unsteady (transient) potential equation yields an integro-differential-delay equation. With spatial discretization by the finite-element method, this equation is approximated by a set of differential-delay equations in time. Time solution by Laplace transform yields a matrix relating the velocity potential to the normal wash. Premultiplying and postmultiplying by the matrices relating generalized forces to the potential and the normal wash to the generalized coordinates one obtains the matrix of the generalized aerodynamic forces. The frequency and mode-shape dependence of this matrix makes the program SOUSSA useful for multiple frequency and repeated mode-shape evaluations.

Morino, L.↗

NASA NTRS1978

Geometry requirements for unsteady aerodynamics in aeroelastic analysis and design

Aircraft geometry requirements for unsteady aerodynamic computations are discussed and differences between requirements for steady and unsteady flow are emphasized within the framework of a general potential-flow aerodynamic formulation. Its implementation in a computer program called SOUSSA (Steady, Oscillatory, and Unsteady Subsonic and Supersonic Aerodynamic is detailed.

Yates, E. C., Jr.↗

NASA NTRS1978

Time-domain Green's Function Method for three-dimensional nonlinear subsonic flows

The Green's Function Method for linearized 3D unsteady potential flow (embedded in the computer code SOUSSA P) is extended to include the time-domain analysis as well as the nonlinear term retained in the transonic small disturbance equation. The differential-delay equations in time, as obtained by applying the Green's Function Method (in a generalized sense) and the finite-element technique to the transonic equation, are solved directly in the time domain. Comparisons are made with both linearized frequency-domain calculations and existing nonlinear results.

Tseng, K.↗

NASA NTRS1978

Steady, Oscillatory and Unsteady, Subsonic and Supersonic Aerodynamics (SOUSSA) for complex aircraft configurations

The Green's function method and the computer program SOUSSA (Steady Oscillatory and Unsteady Subsonic and Supersonic Aerodynamics) are reviewed. The Green's function method is applied to the fully unsteady potential equation yielding an integro-differential-delay equation. This equation is approximated by a set of differential-delay equations in time using the finite element method. The Laplace transform is used to yield a matrix relating the velocity potential to the normal wash. The matrix of the generalized aerodynamic forces is obtained by premultiplying and postmultiplying the matrices relating generalized forces to the potential and the normal wash by the generalized coordinates. The program SOUSSA is compared with existing numerical results. Results indicate that the program is not only general, flexible, and easy to use, but also accurate and fast.

Morino, L.↗

NASA NTRS1977

Aerodynamic interference effects on tilting proprotor aircraft

The Green's function method was used to study tilting proprotor aircraft aerodynamics with particular application to the problem of the mutual interference of the wing-fuselage-tail-rotor wake configuration. While the formulation is valid for fully unsteady rotor aerodynamics, attention was directed to steady state aerodynamics, which was achieved by replacing the rotor with the actuator disk approximation. The use of an actuator disk analysis introduced a mathematical singularity into the formulation; this problem was studied and resolved. The pressure distribution, lift, and pitching moment were obtained for an XV-15 wing-fuselage-tail rotor configuration at various flight conditions. For the flight configurations explored, the effects of the rotor wake interference on the XV-15 tilt rotor aircraft yielded a reduction in the total lift and an increase in the nose-down pitching moment. This method provides an analytical capability that is simple to apply and can be used to investigate fuselage-tail rotor wake interference as well as to explore other rotor design problem areas.

Soohoo, P.↗

NASA NTRS1977

FCAP - A new tool for the performance and structural analysis for complex flexible aircraft with active control

A very general formulation has been developed for the analysis of complex flexible-aircraft configurations in presence of active control. The formulation is incorporated into a computer program, Flight Control Analysis Program (FCAP), which is designed in a modular fashion to incorporate aircraft dynamics and aerodynamics for complex configurations, as well as sensor, actuator and control logic element dynamics. Formulation of the total aircraft dynamic system is accomplished in matrix form by casting equations in state vector format. The system stability and performance are determined in either the frequency or time domain using classical analysis techniques. Fully unsteady aerodynamics is used for the evaluation of the flutter characteristics as well as the gust response of the aircraft.

Morino, L.↗

NASA NTRS1977

Recent developments in the Green's function method

A recent computational development on the Green's function method (the method used in the computer program SOUSSA: Steady, Oscillatory and Unsteady Subsonic and Supersonic Aerodynamics) is presented. A scheme consisting of combined numerical (Gaussian quadrature) and analytical procedures for the evaluation of the source and doublet integrals used in the program is presented. This combination results in 80 to 90% reduction in computer time.

Tseng, K.↗

NASA NTRS1977

Nonlinear steady incompressible lifting-surface analysis with wake roll-up

The problem of lifting surfaces in steady incompressible flow is considered in terms of an integral equation relating the potential discontinuity on wing and wake to the normal derivative of the potential (normal wash) on the lifting surface. The integral equation is approximated by a system of linear algebraic equations obtained by dividing the surfaces into small quadrilateral elements and by assuming the potential discontinuity and the normal wash to be constant within each element. The wake geometry is obtained through iteration by satisfying the condition that the velocity be tangent to the surface of the wake and that the potential discontinuity be constant along the streamlines. Numerical results are in good agreement with existing ones

Suciu, E. O.↗

NASA NTRS1977

State-space formulations for flutter analysis

Two state-space methods for true-damping flutter analysis are presented here. The aerodynamic matrix is assumed to be function of the complex reduced frequency p (off-the-imaginary axis aerodynamics) as the ones provided for instance by the computer code SOUSSA (Steady, Oscillatory and Unsteady, Subsonic and Supersonic Aerodynamics). This matrix is approximated by a third order polynomial or by a Pade's matrix approximant. Then the equations are cast into a suitable state space format including the Laplace transform of the space vector, a frequency-independent matrix, and the flight speed. The solution is then obtained by standard root-locus methods. Results are in good agreement with existing ones in a suitable range of the flutter reduced frequency. A discussion on spurious roots is also included.

Weiss, S. J.↗

NASA NTRS1977

Unsteady subsonic and supersonic potential aerodynamics for complex configurations

A recently developed general theory for unsteady compressible potential fluid dynamics for complex-configuration aircraft is reviewed. The method is based on a combination of the following techniques: Green's function method (to transform the differential equation into an integral differential-delay equation), finite element method (to transform the equation into a set of differential-delay equations in time), and the Laplace transform method (to transform the differential-delay equations into algebraic equations).

Morino, L.↗

NASA NTRS1976

Response analysis of flexible aircraft with active control

The small-perturbation equations of motion of a flexible aircraft with an active control technology (ACT) system are developed to evaluate the stability and performance of the controlled aircraft. The total aircraft system is formulated in state vector format and the system of equations is completed with fully unsteady and low-frequency aerodynamics for arbitrary, complex configurations based on a potential aerodynamic method. The ACT system equations are incorporated in the digital computer program FCAP (Flight Control Analysis Program) which can be used for the analysis of complete aircraft configurations, including control system, with either low-frequency or fully unsteady aerodynamics. The application of classical performance analyses including frequency response, poles and zeros, mean-square response, and time response in FCAP in state vector format is discussed.

Noll, R. B.↗

NASA NTRS1976

A new unified approach for analyzing wing-body-tail configurations with control surfaces

A general theory for steady and unsteady, subsonic and supersonic potential aerodynamics for complex configurations is presented. Special attention is given to the theoretical formulation and the corresponding numerical implementation for coplanar interfering surfaces. Applying the Green's function method to the equation of the velocity potential and discretizing the spatial problem by using the finite-element technique, yields a set of differential-delay equations in time relating the potential to the normal wash. For fully unsteady flow, the motion is assumed to consist of constant subsonic or supersonic speed for time t less than or equal to 0 (steady state) and of small perturbations around the steady state for time t greater than 0; the solution is obtained in the Laplace domain. From the potential, the aerodynamic pressure and the generalized forces are evaluated. The program SOUSSA (Steady, Oscillatory and Unsteady Subsonic and Supersonic Aerodynamics) is briefly described. Numerical results obtained with SOUSSA are presented.

Tseng, K.↗