Engineering topics

Rizzi, S. A.

Publications and source records attributed to Rizzi, S. A..

9 records

NASA NTRS2004

Effect of Transducer Flushness on Measured Surface Pressure Fluctuations in Flight

The procedure for investigating the effect of deviation from flush mounting of pressure transducers on the exterior of Tu-144LL in flight is described. Experimental data in the mach-number range 0.58 - 2.0 are presented for distortion of the measured wall-pressure fluctuation spectra of the turbulent boundary layer by recessed and protruding transducers. The results of flight experiments are compared with data of wind tunnel experiments. The distortion of measured turbulent boundary layer wall pressure fluctuations caused by transducer-surface deviation from the surrounding surface as a function of dimensionless parameters is predicted and presented on the basis of dimensional analysis.

Efimtsov, B. M.↗

NASA NTRS2004

Reduced Order Methods for Prediction of Thermal-Acoustic Fatigue

The goal of this investigation is to assess the quality of high-cycle-fatigue life estimation via a reduced order method, for structures undergoing random nonlinear vibrations in a presence of thermal loading. Modal reduction is performed with several different suites of basis functions. After numerically solving the reduced order system equations of motion, the physical displacement time history is obtained by an inverse transformation and stresses are recovered. Stress ranges obtained through the rainflow counting procedure are used in a linear damage accumulation method to yield fatigue estimates. Fatigue life estimates obtained using various basis functions in the reduced order method are compared with those obtained from numerical simulation in physical degrees-of-freedom.

Przekop, A.↗

NASA NTRS2004

Modelling Unsteady Wall Pressures Beneath Turbulent Boundary Layers

As a structural entity of turbulence, hairpin vortices are believed to play a major role in developing and sustaining the turbulence process in the near wall region of turbulent boundary layers and may be regarded as the simplest conceptual model that can account for the essential features of the wall pressure fluctuations. In this work we focus on fully developed typical hairpin vortices and estimate the associated surface pressure distributions and their corresponding spectra. On the basis of the attached eddy model, we develop a representation of the overall surface pressure spectra in terms of the eddy size distribution. Instantaneous wavenumber spectra and spatial correlations are readily derivable from this representation. The model is validated by comparison of predicted wavenumber spectra and cross-correlations with existing emperical models and experimental data.

Ahn, B-K.↗

NASA NTRS1994

Free vibration of thermally loaded panels including initial imperfections and post-buckling effects

A combined theoretical and experimental approach is developed to consider the small amplitude free vibration characteristics of fully clamped panels under the influence of uniform heating. Included in this study are the effects of higher modes, in-plane boundary elasticity, initial imperfections, and post-buckling. Comparisons between theory and experiment reveal excellent agreement.

Murphy, K. D.↗

NASA NTRS1993

Nonlinear random response prediction using MSC/NASTRAN

An equivalent linearization technique was incorporated into MSC/NASTRAN to predict the nonlinear random response of structures by means of Direct Matrix Abstract Programming (DMAP) modifications and inclusion of the nonlinear differential stiffness module inside the iteration loop. An iterative process was used to determine the rms displacements. Numerical results obtained for validation on simple plates and beams are in good agreement with existing solutions in both the linear and linearized regions. The versatility of the implementation will enable the analyst to determine the nonlinear random responses for complex structures under combined loads. The thermo-acoustic response of a hexagonal thermal protection system panel is used to highlight some of the features of the program.

Robinson, J. H.↗

NASA NTRS1992

A spectral element approach to wave motion in layered solids

A matrix methodology similar to that of the finite element method is developed for the analysis of stress waves in layered solids. Because the mass distribution is modeled exactly, the approach gives the exact frequency response of each layer. The fast Fourier transform and Fourier series are used for inversion to the time/space domain. The impact of a structured medium with multiple layers is used to demonstrate the method. Comparison with existing propagator and direct global matrix methods show the present approach to be computationally more efficient.

Rizzi, S. A.↗

NASA NTRS1992

Spectral analysis of wave motion in plane solids with boundaries

A spectral formulation is employed whereby in-plane stress waves are synthesized from the superposition of components at discrete frequencies and wavenumbers. The summations are performed using the fast Fourier transform and the Fourier series, respectively. Because the components are discrete, the solution to problems (over the entire field) with completely arbitrary loading, both in time and space, is made tractable. Waves generated from a line load acting on an infinite and semiinfinite plane are first considered. A cascade approach is then adopted for the treatment of these waves incident on a free, fixed, and elastic boundary. At each stage, the results are compared with those obtained from the available classical solutions and/or finite element results. These studies will form the basis for the investigation of in-plane stress waves in multiply layered media.

Rizzi, S. A.↗

NASA NTRS1992

Large deflection random response of flat and blade stiffened carbon-carbon panels

The large deflection random response of flat and blade-stiffened carbon-carbon panels is studied both experimentally and analytically. The experimental data was obtained from tests performed in the Thermal Acoustic Fatigue Apparatus at NASA Langley. The analytical results were generated using a numerical simulation program that used the measured acoustic pressure as input. Comparisons of the measured and simulated power spectral densities are presented for several locations on each panel. A comparison of the rms strains at various locations on each panel is also discussed. The measured rms strains were generally a factor of two larger than the predicted. The effect of the nonlinearity was overpredicted at higher sound spectrum levels.

Robinson, J. H.↗

NASA NTRS1992

Acoustic fatigue characterization of carbon/carbon panels

Data from a sonic fatigue test of a blade-stiffened carbon/carbon panel is analyzed to determine the progression of damage to failure. The reduction in stiffness, as observed from acceleration measurements taken during the test, is correlated with the physical damage. Damage was measured through visual inspection, thermographic measurements, and through the novel use of vibration data collected using a scanning laser vibrometer.

Rizzi, S. A.↗