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Vaicaitis, R.

Publications and source records attributed to Vaicaitis, R..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Vibrations and structureborne noise in space station

Analytical models were developed to predict vibrations and structureborne noise generation of cylindrical and rectangular acoustic enclosures. These models are then used to determine structural vibration levels and interior noise to random point input forces. The guidelines developed could provide preliminary information on acoustical and vibrational environments in space station habitability modules under orbital operations. The structural models include single wall monocoque shell, double wall shell, stiffened orthotropic shell, descretely stiffened flat panels, and a coupled system composed of a cantilever beam structure and a stiffened sidewall. Aluminum and fiber reinforced composite materials are considered for single and double wall shells. The end caps of the cylindrical enclosures are modeled either as single or double wall circular plates. Sound generation in the interior space is calculated by coupling the structural vibrations to the acoustic field in the enclosure. Modal methods and transfer matrix techniques are used to obtain structural vibrations. Parametric studies are performed to determine the sensitivity of interior noise environment to changes in input, geometric and structural conditions.

Vaicaitis, R.↗
NASA NTRS1987

Response of stiffened panels for applications to acoustic fatigue

The surface protection systems of aerospace and aircraft structures are often constructed from discretely stiffened panels. This paper presents an analytical study on dynamic stress response of these structures to random surface flow and acoustic loads. To account for aerodynamic heating of high speed flow, thermal effects are included in the structural model. A generalized transfer matrix procedure is developed to obtain the required dynamic response solutions. Numerical results include spectral densities of stress, response root mean square values and fatigue damage for a variety of loading and thermal conditions.

Vaicaitis, R.↗
NASA NTRS1987

Response of discretely stiffened structures

This paper presents a theoretical study on dynamic response of complex discretely stiffened and interconnected structures to random loads. Modal and transfer matrix techniques are utilized to analyze these multidimensional structures. Application of this formulation for response and noise generation studies in space station and fuselage-wing design is discussed. The response spectral densities are calculated for several typical discretely stiffened and interconnected structural systems. It is found that this approach allows for easy parametric evaluation and that by proper selection of structural parameters and loading conditions, the vibration response can be reduced.

Vaicaitis, R.↗
NASA NTRS1987

Acoustic fatigue - A Monte Carlo approach

The present paper reviews the basic concepts of nonlinear structural response to surface flow and acoustic pressure inputs. A time domain solution and the Monte Carlo method are utilized to estimate the required statistics of the nonlinear response. Simulation procedures of multi-dimensional and multi-variate random processes are discussed. Application of these procedures to acoustic fatigue of flight structures are considered. Numerical examples are included to illustrate the applicability of this method for the solution of nonlinear problems.

Vaicaitis, R.↗
NASA NTRS1986

Nonlinear response - A time domain approach

The present paper reviews the basic concepts of nonlinear response of panels to surface flow and acoustic pressures, simulation of random processes, time domain solutions and the Monte Carlo Method. Applications of this procedure to the orbit-on-demand space vehicles, acoustic fatigue and composite materials are discussed. Numerical examples are included for a variety of nonlinear problems to illustrate the applicability of this method.

Vaicaitis, R.↗
NASA NTRS1986

Vibro-acoustics for Space Station applications

An analytical procedure has been developed to study noise generation in a double wall and single wall cylindrical shell due to mechanical point loads. The objective of this study is to develop theoretical procedures for parametetric evaluation of noise generation andd noise transmission for the habitability modules of the proposed Space Station operation. The solutions of the governing acoustic-structural equations are obtained utilizing modal decomposition. The numerical results include modal frequencies, deflection response spectral densities and interior noise sound pressure levels.

Vaicaitis, R.↗
NASA NTRS1986

Vibration and structureborne noise in space station

Analytical models and computer programs for structural response calculations under action of mechanical point loads were developed for single wall shells (composite or aluminum), double wall shells (composite or aluminum), and single wall or double wall circular plates (aluminum). The design configuration of the habitability modules of the space station concept are expected to be discretely stiffened cylindrical shells with truncated cone type end caps or flat but stiffened circular end plates. Analytical formulations and response calculations were performed for the case where the stiffened shell is represented by an orthotropic shell model. The natural frequencies can be calculated. For application to low frequency (below 1000Hz) vibrations and noise generation, such a model might be adequate to evaluate vibration and noise transmission characteristics of space station habitability modules. Parametric studies are now being performed to assess interior noise environment inside a habitability module to mechanically induced vibrations.

Vaicaitis, R.↗
NASA NTRS1986

Noise transmission into enclosures

This paper describes analytical and experimental studies of noise transmission into rectangular and cylindrical enclosures. The solutions of the governing acoustic-structural equations are developed by modal decomposition of structural vibrations and the interior acoustic field. Particular attention is directed toward the low frequencies, that is, frequencies up through the first few structural and cavity resonant modes. The structural vibrations are driven by the external acoustic and/or mechanical point loads which are taken to be Gaussian stationary random processes. The structural models include rectangular panels and cylindrical shells.

Vaicaitis, R.↗
NASA NTRS1985

Vibrations and structureborne noise in space station

Theoretical models were developed capable of predicting structural response and noise transmission to random point mechanical loads. Fiber reinforced composite and aluminum materials were considered. Cylindrical shells and circular plates were taken as typical representatives of structural components for space station habitability modules. Analytical formulations include double wall and single wall constructions. Pressurized and unpressurized models were considered. Parametric studies were conducted to determine the effect on structural response and noise transmission due to fiber orientation, point load location, damping in the core and the main load carrying structure, pressurization, interior acoustic absorption, etc. These analytical models could serve as preliminary tools for assessing noise related problems, for space station applications.

Vaicaitis, R.↗
NASA NTRS1985

Aircraft cabin noise prediction and optimization

Theoretical and experimental studies were conducted to determine the noise transmission into acoustic enclosures ranging from simple rectangular box models to full scale light aircraft in flight. The structural models include simple, stiffened, curved stiffened, and orthotropic panels and double wall windows. The theoretical solutions were obtained by model analysis. Transfer matrix and finite element procedures were utilized. Good agreement between theory and experiment has been achieved. An efficient acoustic add-on treatment was developed for interior noise control in a twin engine light aircraft.

Vaicaitis, R.↗
NASA NTRS1985

Vibrations and structureborne noise in space station

The related literature was reviewed and a preliminary analytical model was developed for simplified acoustic and structural geometries for pressurized and unpressurized space station modules. In addition to the analytical work, an experimental program on structureborne noise generation and transmission was started. A brief review of those accomplishments is given.

Vaicaitis, R.↗
NASA NTRS1985

Response of double wall composite shells

This paper presents an analytical study of double wall laminate cylindrical shell response to random loads. A soft viscoelastic core with dilatational modes included is used. The theory of laminate shells is simplified by assumptions similar to those in the Donnell-Mushtari development for isotropic shells. Modal solutions of simply supported shells are obtained. Modal frequencies and deflection response spectral densities are determined. It is found that this approach allows for easy parametric evaluation and that by proper selection of dynamic parameters, viscoelastic core characteristics and fiber reinforcement orientation, vibration response can be reduced.

Vaicaitis, R.↗
NASA NTRS1985

Review of research on structureborne noise

Publications on the topic of structureborne noise are reviewed. Recent accomplishments, including representative results, are presented for aircraft, rotorcraft, space structures, automotive vehicles, ship and building technology. Special attention is given to propeller-driven aircraft. This review demonstrates that substantial progress has been made in understanding the characteristics of structureborne noise. Possible future research efforts and development of technology for control of structureborne noise are discussed.

Vaicaitis, R.↗
NASA NTRS1985

Noise transmission of double wall composite shells

This paper describes analytical studies of noise transmission of double wall laminated composite cylindrical shells of finite extent. The main objective is to estimate structureborne noise generated by the concentrated random forces. The theoretical solutions of the governing acoustic-structural equations are obtained utilizing modal decomposition. Results indicate that from the viewpoint of noise attenuation the composite shell does not seem to offer advantage over an aluminum shell. However, the orientation of the fibers and the material characteristics of the soft viscoelastic core can be tailored to meet the specific needs of noise attenuation.

Vaicaitis, R.↗
NASA NTRS1984

Theoretical design of acoustic treatment for cabin noise control of a light aircraft

An analytical procedure has been used to design an acoustic treatment for cabin noise control of a light aircraft. Using this approach acoustic add-on treatments capable of reducing the average noise levels in the cabin by about 17 dB from the untreated condition are developed. The added weight of the noise control package is about 2 percent of the total gross take-off weight of the aircraft. The analytical model uses modal solutions wherein the structural modes of the sidewall and the acoustic modes of the receiving space are accounted for. The additional noise losses due to add-on treatments are calculated by the impedance transfer method. The input noise spectral levels are selected utilizing experimental flight data. The add-on treatments considered for cabin noise control include aluminum honeycomb panels, constrained layer damping tape, porous acoustic materials, noise barriers and limp trim panels. To reduce the noise transmitted through the double wall aircraft windows to acceptable levels, changes in the design of the aircraft window are recommended.

Vaicaitis, R.↗