Downloads & Free Reading Options - Results

Two computational procedures for analyzing complex structural systems for their natural modes and frequencies of vibration are presented. Both procedures are based on a substructures methodology and both employ the finite-element stiffness method to model the constituent substructures. The first procedure is a direct method based on solving the eigenvalue problem associated with a finite-element representation of the complete structure. The second procedure is a component-mode synthesis scheme in which the vibration modes of the complete structure are synthesized from modes of substructures into which the structure is divided. The analytical basis of the methods contains a combination of features which enhance the generality of the procedures. The computational procedures exhibit a unique utilitarian character with respect to the versatility, computational convenience, and ease of computer implementation. The computational procedures were implemented in two special-purpose computer programs. The results of the application of these programs to several structural configurations are shown and comparisons are made with experiment.

This research report is presented in three parts. In the first part, acoustical analyses were performed on modes of vibration of the housing of a transmission of a gear test rig developed by NASA. The modes of vibration of the transmission housing were measured using experimental modal analysis. The boundary element method (BEM) was used to calculate the sound pressure and sound intensity on the surface of the housing and the radiation efficiency of each mode. The radiation efficiency of each of the transmission housing modes was then compared to theoretical results for a finite baffled plate. In the second part, analytical and experimental validation of methods to predict structural vibration and radiated noise are presented. A rectangular box excited by a mechanical shaker was used as a vibrating structure. Combined finite element method (FEM) and boundary element method (BEM) models of the apparatus were used to predict the noise level radiated from the box. The FEM was used to predict the vibration, while the BEM was used to predict the sound intensity and total radiated sound power using surface vibration as the input data. Vibration predicted by the FEM model was validated by experimental modal analysis; noise predicted by the BEM was validated by measurements of sound intensity. Three types of results are presented for the total radiated sound power: sound power predicted by the BEM model using vibration data measured on the surface of the box; sound power predicted by the FEM/BEM model; and sound power measured by an acoustic intensity scan. In the third part, the structure used in part two was modified. A rib was attached to the top plate of the structure. The FEM and BEM were then used to predict structural vibration and radiated noise respectively. The predicted vibration and radiated noise were then validated through experimentation.

Vibration response of OGO spacecraft full-scale structural model to simulated launch acoustic environment

Mariner 5 forced vibration test program

The correlation achieved with each program provides the material for a discussion of modeling techniques developed for general application to finite-element dynamic analyses of helicopter airframes. Included are the selection of static and dynamic degrees of freedom, cockpit structural modeling, and the extent of flexible-frame modeling in the transmission support region and in the vicinity of large cut-outs. The sensitivity of predicted results to these modeling assumptions are discussed. Both the Sikorsky Finite-Element Airframe Vibration analysis Program (FRAN/Vibration Analysis) and the NASA Structural Analysis Program (NASTRAN) have been correlated with data taken in full-scale vibration tests of a modified CH-53A helicopter.

Structural Vibration Analysis And Damping C. E Beards

Structural Vibration Analysis And Damping C. E Beards

A theoretical investigation of structural vibration characteristics of rotor blades was carried out. Coupled equations of motion for flapwise bending and torsion were formulated for rotor blades with noncollinear elastic and mass axes. The finite element method was applied for a detailed representation of blade structural properties. Coupled structural mass and stiffness coefficients were evaluated. The range of validity of a set of coupled equations of motion linearized with respect to eccentricity between elastic and mass axes was investigated. The sensitivity of blade vibration characteristics to torsion were evaluated by varying blade geometric properties, boundary conditions, and eccentricities between mass and elastic axes.

Previous analyses of the design of vibration-isolating mounts for a rear-mounted engine to decouple linear and rotational oscillations are extended to take into account flexibility of the engine-mount structure. Equations and curves are presented to allow the design of mount systems and to illustrate the results for a range of design conditions.

The structural test unit of the electron-proton spectrometer was tested to a random vibration spectra and to a sinusoidal resonant search to comply with the requirements of a verification plan for the spectrometer. The test item consisted of mass simulated electronic and printed circuit boards mounted in a flight type electronic housing. The arrangement, center of gravity, and weight were as proposed for flight units.

The present study is a simulation of a machine shaft. The study will be done on FEM simulation software called Ansys 14.5, where a modal would be developed which will undergo a process of meshing. Meshing will divide the modal in extremely small units without changing the shape of actual geometry which will help the software to study the change at every small unit of the model. Then the of the modal would be defined in terms of inlet and outlet thereafter the boundary condition and design equation would be applied to get the desired result. Syed Minal Hussian Jafri | Prof Amit Kaimkuriya "Structural and Vibration Analysis of a Machine Shaft using Finite Element Analysis" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-4 , June 2019, URL: https://www.ijtsrd.com/papers/ijtsrd23844.pdf Paper URL: https://www.ijtsrd.com/engineering/mechanical-engineering/23844/structural-and-vibration-analysis-of-a-machine-shaft-using-finite-element-analysis/syed-minal-hussian-jafri

Thesis advisor, Joshua H. Gordis

Thesis advisor, Joshua H. Gordis

Thesis advisor, Joshua H. Gordis

This article is from Sensors (Basel, Switzerland) , volume 12 . Abstract In structural vibration tests, one of the main factors which disturb the reliability and accuracy of the results are the noise signals encountered. To overcome this deficiency, this paper presents a discrete wavelet transform (DWT) approach to denoise the measured signals. The denoising performance of DWT is discussed by several processing parameters, including the type of wavelet, decomposition level, thresholding method, and threshold selection rules. To overcome the disadvantages of the traditional hard- and soft-thresholding methods, an improved thresholding technique called the sigmoid function-based thresholding scheme is presented. The procedure is validated by using four benchmarks signals with three degrees of degradation as well as a real measured signal obtained from a three-story reinforced concrete scale model shaking table experiment. The performance of the proposed method is evaluated by computing the signal-to-noise ratio (SNR) and the root-mean-square error (RMSE) after denoising. Results reveal that the proposed method offers superior performance than the traditional methods no matter whether the signals have heavy or light noises embedded.

Vibracion estructural

In order to promote public education and public safety, equal justice for all, a better informed citizenry, the rule of law, world trade and world peace, this legal document is hereby made available on a noncommercial basis, as it is the right of all humans to know and speak the laws that govern them. (For more information: 12 Tables of Code ) Name of Standards Organization: Bureau of Indian Standards (BIS) Division Name: Mechanical Engineering Section Name: Mechanical Vibration and Shock (MED 28) Designator of Legally Binding Document: IS/ISO 20283-2 Title of Legally Binding Document: Mechanical Vibration – Measurement of Vibration on Ships, Part 2: Measurement of Structural Vibration Number of Amendments: Equivalence: ISO 20283-2:2008 Superceding: IS 14728 : 1999, IS 14729:1999 Superceded by: LEGALLY BINDING DOCUMENT Step Out From the Old to the New --Jawaharlal Nehru Invent a new India using knowledge. --Satyanarayan Gangaram Pitroda

In order to promote public education and public safety, equal justice for all, a better informed citizenry, the rule of law, world trade and world peace, this legal document is hereby made available on a noncommercial basis, as it is the right of all humans to know and speak the laws that govern them. (For more information: 12 Tables of Code ) Name of Standards Organization: Bureau of Indian Standards (BIS) Division Name: Mechanical Engineering Section Name: Mechanical Vibration and Shock (MED 28) Designator of Legally Binding Document: IS/ISO 20283-2 Title of Legally Binding Document: Mechanical Vibration – Measurement of Vibration on Ships, Part 2: Measurement of Structural Vibration Number of Amendments: Equivalence: ISO 20283-2:2008 Superceding: IS 14728 : 1999, IS 14729:1999 Superceded by: LEGALLY BINDING DOCUMENT Step Out From the Old to the New --Jawaharlal Nehru Invent a new India using knowledge. --Satyanarayan Gangaram Pitroda

Described is the transmission of vibration in dynamical systems, and a particular example is studied in detail. This consists of two freely supported elastic plates, connected by a rigid link. It is shown that the addition of a dynamic absorber to such a system can significantly attenuate the transmitted velocities over a chosen narrow band of frequency.

A design procedure for minimizing propeller-induced vibration in hull structural elements is recommended. This procedure begins when the ship's vibration specifications are defined and continues through the design and construction process until the vibration levels measured during sea trials are compared with the specifications. Consideration is given to the hydrodynamic excitation and structural response of the propeller-induced vibration problem, with both analytical and experimental techniques being used in the design process. The recommended procedure is presented and discussed in the form of a flow diagram with 27 separate design steps. The process also contains five evaluation milestones. At these points, the design is assessed, and, if deficiencies are found, corrective action can be taken before the design proceeds. The recommended complete procedure is presented in this report for the first time. Many of the aspects of this procedure are still being developed, in particular, the influence of propeller cavitation on hull pressures and a simple but accurate treatment of water inertia. These indefinite aspects have to be treated empirically using judgement and experimental data. The portions of the procedure which are available are illustrated in an example using a single-screw, containerized and unitized cargo ship. (Author)

Symposium topics include: An Integrated Gear System Dynamics Analysis over a Broad Frequency Range; Coupled Torsional-flexural Vibration of a Geared Shaft System Using Finite Element Analysis; Influence of an Axial Torque on the Dynamic Behavior of Rotors in Bending; Sensitivity Analysis of the Locations of the Balancing Planes of an Unbalanced Rotor-Bearing System using Dynamic Condensation Technique; Structural Damage Detection by the System Identification Technique; Time Domain Modal Analysis of a Slotted Cylindrical Shell; Application of the Ibrahim Time Domain (ITD) Algorithm to LANDSAT Transient Responses; Identification Matrix and Convergence of Parameters in Off-line System Identification; Model Evaluation of Spinal Injury Likelihood for Various Ejection System Parameter Variations; Time Domain Mathematical Modeling of Elastic Instabilities and Large Elastic-plastic Deflections; Low Order Dynamic Models of Indian Remote Sensing Satellite; A Direct Method for Estimating Lower and Upper Bounds of the Fundamental Frequency; and Approximating Dynamic Response in Small Arrays using Polynomial Parameterizations and Response Surface Methodology.

This final report documents the development of an experimental buffet load alleviation (BLA) system that utilizes distributed piezoelectric actuators in conjunction with a closed-loop rudder control system to reduce the structural dynamic response of fighter aircraft vertical tails to buffet loads. The BLA system was defined analytically with a detailed finite element model of the tail structure and piezoelectric actuators. Oscillatory aerodynamics were included along with a buffet forcing function to complete the aeroservoelastic model of the tail with rudder control surface. Two single-input single-output (SISO) controllers were designed one for the active rudder and one for the active piezoelectric actuators. The results from the analytical open- and closed-loop simulation were used to predict the system performance.

Structural response predictions have been made for two important areas of STOL-type aircraft. The method was developed to significantly improve environmental prediction methods that have been used in the past. A mathematically rigorous spectral analysis approach was developed that simulated the structure with a finite element model and used correlated and calculated acoustic input data for the forcing function.

Structural response predictions have been made for two important areas of STOL-type aircraft. The method was developed to significantly improve environmental prediction methods that have been used in the past. A mathematically rigorous spectral analysis approach was developed that simulated the structure with a finite element model and used correlated and calculated acoustic input data for the forcing function.

The design of fatigue resistant structures for high speed aircraft and aerospace vehicles depends largely on the prediction of realistic acoustic, fluctuating aerodynamic, and engine vibration environments and on the estimation of the attendant vibration levels of structural components and attached equipment. The practical engineering limitations on the mathematical and numerical analyses required to treat such structures rigorously by classical dynamics necessitate studies of alternate, approximate methods. In the report, a definitive statement is presented of the empirical approach for determining correlations between the excitation environment and the vibration response of typical flight vehicle structures by means of statistical analyses of measured vibration data. The various aspects of the vibration prediction problem and the general philosophy motivating research in the area of empirical correlation are discussed. Specific treatment is given to the effects of bandwidth, modal density, and surface pressure spacecorrelation on the crosscorrelation of energy transmitted along various structural transmission paths in complex linear structures.

The design of fatigue resistant structures for high speed aircraft and aerospace vehicles depends largely on the prediction of realistic acoustic, fluctuating aerodynamic, and engine vibration environments and on the estimation of the attendant vibration levels of structural components and attached equipment. The practical engineering limitations on the mathematical and numerical analyses required to treat such structures rigorously by classical dynamics necessitate studies of alternate, approximate methods. In the report, a definitive statement is presented of the empirical approach for determining correlations between the excitation environment and the vibration response of typical flight vehicle structures by means of statistical analyses of measured vibration data. The various aspects of the vibration prediction problem and the general philosophy motivating research in the area of empirical correlation are discussed. Specific treatment is given to the effects of bandwidth, modal density, and surface pressure spacecorrelation on the crosscorrelation of energy transmitted along various structural transmission paths in complex linear structures.

Described is the transmission of vibration in dynamical systems, and a particular example is studied in detail. This consists of two freely supported elastic plates, connected by a rigid link. It is shown that the addition of a dynamic absorber to such a system can significantly attenuate the transmitted velocities over a chosen narrow band of frequency.

Described is the transmission of vibration in dynamical systems, and a particular example is studied in detail. This consists of two freely supported elastic plates, connected by a rigid link. It is shown that the addition of a dynamic absorber to such a system can significantly attenuate the transmitted velocities over a chosen narrow band of frequency.

In this paper, the bending and free flexural vibration behaviour of sandwich plates with carbon nanotube (CNT) reinforced facesheets are investigated using QUAD-8 shear flexible element developed based on higher-order structural theory. This theory accounts for the realistic variation of the displacements through the thickness, and the possible discontinuity in slope at the interface, and the thickness stretch affecting the transverse deflection. The in-plane and rotary inertia terms are considered in the formulation. The governing equations obtained using Lagrange's equation of motions are solved for static and dynamic analyses considering a sandwich plate with homogeneous core and CNT reinforced face sheets. The accuracy of the present formulation is tested considering the problems for which solutions are available. A detailed numerical study is carried out based on various higher-order models deduced from the present theory to examine the influence of the volume fraction of the CNT, core-to-face sheet thickness and the plate thickness ratio on the global/local response of different sandwich plates.

This article is from Sensors (Basel, Switzerland) , volume 14 . Abstract This work presents a hybrid (experimental-computational) application for improving the vibration behavior of structural components using a lightweight multilayer composite. The vibration behavior of a flat steel plate has been improved by the gluing of a lightweight composite formed by a core of polyurethane foam and two paper mats placed on its faces. This composite enables the natural frequencies to be increased and the modal density of the plate to be reduced, moving about the natural frequencies of the plate out of excitation range, thereby improving the vibration behavior of the plate. A specific experimental model for measuring the Operating Deflection Shape (ODS) has been developed, which enables an evaluation of the goodness of the natural frequencies obtained with the computational model simulated by the finite element method (FEM). The model of composite + flat steel plate determined by FEM was used to conduct parametric study, and the most influential factors for 1st, 2nd and 3rd mode were identified using a multifactor analysis of variance (Multifactor-ANOVA). The presented results can be easily particularized for other cases, as it may be used in cycles of continuous improvement as well as in the product development at the material, piece, and complete-system levels.

A piloted simulation experiment has been conducted in the NASA Langley Visual/Motion Simulator facility to address the impact of dynamic aeroelastic effects on flying qualities of a supersonic transport. The intent of this experiment was to determine the effectiveness of several measures that may be taken to reduce the impact of aircraft flexibility on piloting tasks. Potential solutions that were examined included structural stiffening, active vibration suppression, and elimination of visual cues associated with the elastic modes. A series of parametric configurations was evaluated by six test pilots for several types of maneuver tasks. During the investigation, several incidents were encountered in which cockpit vibrations due to elastic modes fed back into the control stick through involuntary motions of the pilot's upper body and arm. The phenomenon, referred to as biodynamic coupling, is evidenced by a resonant peak in the power spectrum of the pilot's stick inputs at a structural mode frequency. The results of the investigation indicate that structural stiffening and compensation of the visual display were of little benefit in alleviating the impact of elastic dynamics on the piloting tasks, while increased damping and elimination of control-effector excitation of the lowest frequency modes offered great improvements when applied in sufficient degree.

A structural vibration response prediction method was developed for STOL type aircraft. The method was developed to significantly improve environmental prediction methods that have been used in the past. A mathematically rigorous spectral analysis approach was developed that simulated the structure with a finite element model which used correlated and calculated acoustic input data for a forcing function. The structural vibration predictions adequately described the operating levels and spectral frequency content of chosen locations on two STOL aircraft. Comparisons of predicted and measured data show that the method developed may be used for a precise way to predict complex structural response to jet engine excitation. The development of prediction method for determination of external acoustic levels for STOL aircraft was accomplished in a concise manner. The method is described in detail with successful comparisons of actual measurements to predictions. The method is seen to give good results and represents a significant improvement in acoustic prediction methods for STOL aircraft.

Significant levels of undesired vibration and noise are inherent in transport and combat vehicles, particularly in helicopters and propeller aircraft. Therefore, it is important to investigate techniques that reduce vibration and noise in the cabin to improve habitability, effectiveness, and safety for passengers. In addition, continuous exposure may lead to long-term physiological effects. In contrast to passive approaches, active techniques have the potential to suppress low frequency vibration and noise over a broadband of frequencies. Various smart structure based techniques using active materials have been studied for vibration and noise suppression applications. These include active helicopters blades, variable twist propeller blades, adaptive damper, etc. Use of these techniques promises vast improvements in vibration and noise levels. However, full-scale implementations of these techniques have been hindered by electromechanical limitations of active materials. The Smart Spring is a novel approach to control combinations of impedance properties of a structure, such as stiffness, damping, and effective mass. It uses stacked piezoceramic actuators to adaptively vary structural impedance at strategic locations to suppress mechanical vibration. The Smart Spring is a versatile approach that can be implemented in a variety of applications. For example, an adaptive Smart Spring mount can be used to reduce vibration on vehicle seats, mitigate vibratory loads transmitted from engines, or suppress rotor vibration in helicopters. It is a unique concept that overcomes some of the difficulties encountered with other piezoceramic based vibration control approaches.

This technical report presents part of the results and findings from the Structural Vibration Modeling and Validation in-house research effort conducted by the Large Deployable Optics program in collaboration with General Dynamics. This effort was part of a larger program involving two contractors, Lockheed Martin and ITT. This report focuses on model uncertainty and robust control analysis and techniques available in the open literature and how these methods are applicable to the SVMV paradigm. The literature review presented here provides a starting point for future analyses.

Contents: Qualification by analysis of Inertial Upper Stage Plume deflectors; Analysis of reinforced concrete structures under the effects of localized detonations; Reinforced concrete arches under blast and shock environment; Dynamic stress at critical locations of a structure as a criterion for mathematical model modification; Optimized structure design using reanalysis techniques; Reliability of structures with stiffness and strength degradation; New look at the use of linear methods to predict aircraft dynamic response to taxi over bomb-damaged and repaired airfields; Frequency response functions of a nonlinear system; System characterization in nonlinear random vibration; Interactive-graphics method for dynamic system modelling applying consistency rules; Dynamic response of a geared train of rotors subjected to random support excitations; Dynamics of an oscillating four-bar linkage: Modal test and analysis -- Centaur G modal test.

To reduce energy consumption, emissions, and noise, NASA is exploring the use of high aspect ratio wings on subsonic aircraft. Because high aspect ratio wings are susceptible to flutter events, NASA is also investigating methods of flutter detection and suppression. In support of that work a new remote, non-contact method for measuring flutter-induced vibrations has been developed. The new sensing scheme utilizes a microwave reflectometer to monitor the reflected response from an aeroelastic structure to ultimately characterize structural vibrations. To demonstrate the ability of microwaves to detect flutter vibrations, a carbon fiber-reinforced polymer (CFRP) composite panel was vibrated at various frequencies from 1Hz to 130Hz. The reflectometer response was found to closely resemble the sinusoidal response as measured with an accelerometer up to 100 Hz. The data presented demonstrate that microwaves can be used to measure flutter-induced aircraft vibrations.

NASA is currently investigating methods to reduce the boil-off rate on large cryogenic upper stages. Two such methods to reduce the total heat load on existing upper stages are vapor cooling of the cryogenic tank support structure and integration of thick multilayer insulation systems to the upper stage of a launch vehicle. Previous efforts have flown a 2-layer MLI blanket and shown an improved thermal performance, and other efforts have ground-tested blankets up to 70 layers thick on tanks with diameters between 2 3 meters. However, thick multilayer insulation installation and testing in both thermal and structural modes has not been completed on a large scale tank. Similarly, multiple vapor cooled shields are common place on science payload helium dewars; however, minimal effort has gone into intercepting heat on large structural surfaces associated with rocket stages. A majority of the vapor cooling effort focuses on metallic cylinders called skirts, which are the most common structural components for launch vehicles. In order to provide test data for comparison with analytical models, a representative test tank is currently being designed to include skirt structural systems with integral vapor cooling. The tank is 4 m in diameter and 6.8 m tall to contain 5000 kg of liquid hydrogen. A multilayer insulation system will be designed to insulate the tank and structure while being installed in a representative manner that can be extended to tanks up to 10 meters in diameter. In order to prove that the insulation system and vapor cooling attachment methods are structurally sound, acoustic testing will also be performed on the system. The test tank with insulation and vapor cooled shield installed will be tested thermally in the B2 test facility at NASAs Plumbrook Station both before and after being vibration tested at Plumbrooks Space Power Facility.

The focus of the study was in three areas: (1) Development of new and efficient models for accurate prediction of structural damping ability; (2) Development and application of new strategies to the associated optimization problem, i.e., damping layer redistribution for maximizing damping subject to static stiffness, stress, weight and frequency constraints and (3) experimental quantification for comparison with analytical predictions.

Described is the transmission of vibration in dynamical systems, and a particular example is studied in detail. This consists of two freely supported elastic plates, connected by a rigid link. It is shown that the addition of a dynamic absorber to such a system can significantly attenuate the transmitted velocities over a chosen narrow band of frequency.

Partial contents: Multiple tests concept for improved validation of large space structure mathematical models; Algorithms and application of a new multi-input-multi-ouput modal parameter identification method; Modal parameter identification using adaptive digital filters; SAFE/DAE (Solar Array Flight Experiment Dynamics Augmentation Experiment): Modal test in space; Random variation of modal frequencies experiments and analysis; Structural degradation of impacted graphite/expoxy laminates; Updating rail impact test methods; Prediction of natural frequencies of flexible shaft-disc system; Implementation of action force control for robots subject to dynamic loading; Force magnitude and angular velocity fluctuation reduction in a spring-restrained; flexibility- supported four-bar mechanical linkage; Blade damping measurements in a spin rig with nozzle passing excitation simulated by electromagnets; New approach for gearbox modelling in-finite element analyses of torsional vibration of gear- branched propulsion systems; Temperature shift considerations for damping materials; Prediction of Metal Fatigue using Miner rule; Optimizing aerospace structures subjected to random vibration and fatigue constraints; Evaluation of vibration specifications for static and dynamic material allowables; and Supersonic flow induced cavity acoustics.

Partial Contents: Prediction of Gas Dynamic Laser Mounting Forces Using Admittance Testing Techniques; Influence of fluid on the Dynamic Plastic Response of a Pipe; Theoretical Analysis of the Dynamic Response of Construction Cableway Systems; Empirical Investigation of Water-Shock Loading of a Concrete Half-Space; Effect of Earth Cover on the Dynamic Response of Hardened Reinforced Concrete Structures; Dynamic Responses of a Soil Covered Concrete Arch to Impact and Blast Loadings; Instructure Shock Environment of Buried Structures Subjected to Blast Induced Ground Shock; Crack Pattern of an Underground Cylindrical, Reinforced Concrete Structure under an Axial Blast Load; Failure of Aluminum Cylindrical Shells Subjected to Transverse Blast Loadings; Extended Transfer Matrix Method for Free Vibration of Shells of Revolution; Practical Scheme for Including Shear Wall (or Floor) Stiffness in Frame Analysis; Rail Overturning; Application of Modern Parameter Estimation Methods to Vibrating Structures; Analysis of Vibration Records by ata Dependent Systems; Method of System Identification with an Experimental Investigation; Method for the Direct Identification of Vibration Parameters from the Free Response; and Laboratory Identification of the Patriot Launchers Structure.

Internal loads and stresses caused by space vehicle vibration resulting from induced or natural environments

The effects of tilt and structural asymmetry on the vibration characteristics of partly liquid-filled thin-wall cylinders were experimentally studied. It was found that tilting the longitudinal axis of a partly filled axisymmetric cylinder from the vertical could markedly reduce its resonant frequencies and change significantly the shape of the circumferential modes. For the minimum frequency modes, vibratory motion occurred only on that side of the cylinder where the liquid was deepest. An empirical equation was derived that gives the equivalent liquid depth of an untilted cylinder having the same minimum resonant frequency as a tilted, partly filled cylinder. Circumferential mode shapes of an untilted asymmetric cylinder were similar to those of the tilted, partly filled axisymmetric cylinder. Vibratory motion in the minimum frequency modes occurred in most instances only on the side of minimum thickness. Correlation between test data and results from a reformulated NASTRAN hydroelastic analysis was excellent.

The effects of tilt and structural asymmetry on the vibration characteristics of partly liquid-filled thin-wall cylinders were experimentally studied. It was found that tilting the longitudinal axis of a partly filled axisymmetric cylinder from the vertical could markedly reduce its resonant frequencies and change significantly the shape of the circumferential modes. For the minimum frequency modes, vibratory motion occurred only on that side of the cylinder where the liquid was deepest. An empirical equation was derived that gives the equivalent liquid depth of an untilted cylinder having the same minimum resonant frequency as a tilted, partly filled cylinder. Circumferential mode shapes of an untilted asymmetric cylinder were similar to those of the tilted, partly filled axisymmetric cylinder. Vibratory motion in the minimum frequency modes occurred in most instances only on the side of minimum thickness. Correlation between test data and results from a reformulated NASTRAN hydroelastic analysis was excellent.

The drones for aerodynamic and structural testing (DAST) project was designed to control flutter actively at high subsonic speeds. Accurate knowledge of the structural model was critical for the successful design of the control system. A ground vibration test was conducted on the DAST vehicle to determine the structural model characteristics. This report presents and discusses the vibration and test equipment, the test setup and procedures, and the antisymmetric and symmetric mode shape results. The modal characteristics were subsequently used to update the structural model employed in the control law design process.

This SERDP SEED Project was focused on extending the applicability of the NRL-developed structural acoustic fault monitoring technique using laser measured surface vibration to the materials and fabrics associated with historic buildings. In this regard, flexural wave inversion was successfully demonstrated numerically on thin plates of plaster, steel, and concrete and on thick plaster and steel plates with flaws at different depths. A new orthotropic inversion algorithm was developed and demonstrated on a similarly generated numerical data base on a wood slab. Two novel adaptive inversion approaches were developed and demonstrated, one using the flexural wave and generalized force algorithms sequentially, and the other based on high order equations of motion with unknown coefficients. A finite element-based study of a plaster dome ceiling with a detached section and a deconsolidated inclusion was carried out using acoustic speaker excitation. A model was developed for predicting flaw size detectability and for generalizing to other ceiling conditions. A new conformal spatial transform was developed and applied to the elliptical dome ceiling showing marked differences in the wave-number spectra associated with the two flaw types. Finally, a laboratory demonstration was carried out on a large wooden ceiling support beam in whose interior was created a small, thin cavity filled with sawdust. Direct observation of the band-averaged SLDV scans clearly detected and localized the defect. The orthotropic inversions indicated very large spatial variations in the wood beam elastic properties.

A piloted simulation experiment has been conducted in the NASA Langley Visual/Motion Simulator facility to address the impact of dynamic aeroelastic effects on flying qualities of a supersonic transport. The intent of this experiment was to determine the effectiveness of several measures that may be taken to reduce the impact of aircraft flexibility on piloting tasks. Potential solutions that were examined included structural stiffening, active vibration suppression, and elimination of visual cues associated with the elastic modes. A series of parametric configurations was evaluated by six test pilots for several types of maneuver tasks. During the investigation, several incidents were encountered in which cockpit vibrations due to elastic modes fed back into the control stick through involuntary motions of the pilot's upper body and arm. The phenomenon, referred to as biodynamic coupling, is evidenced by a resonant peak in the power spectrum of the pilot's stick inputs at a structural mode frequency. The results of the investigation indicate that structural stiffening and compensation of the visual display were of little benefit in alleviating the impact of elastic dynamics on the piloting tasks, while increased damping and elimination of control-effector excitation of the lowest frequency modes offered great improvements when applied in sufficient degree.

The report is a compilation of papers relative to structural and dynamic response of structures exposed to shock and vibration environments.

The use of the SUDAN computer program for analyzing structural systems for their natural modes and frequencies of vibration is described. SUDAN is intended for structures which can be represented as an equivalent system of beam, spring, and rigid-body substructures. User-written constraint equations are used to analytically join the mass and stiffness matrices of the substructures to form the mass and stiffness matrices of the complete structure from which all the frequencies and modes of the system are determined. The SUDAN program can treat the case in which both the mass and stiffness matrices of the coupled system may be singular simultaneously. A general description of the FORTRAN IV program is given, the computer hardware and software specifications are indicated, and the input required by the program is described.

Spacecraft are susceptible to structural damage over their operating life from impact, environmental loads, and fatigue. Structural damage that is not detected and not corrected may potentially cause more damage and eventually catastrophic structural failure. NASA's current fleet of reusable spacecraft, namely the Space Shuttle, has been flown on several missions. In addition, configurations of future NASA space structures, e.g. Space Station Freedom, are larger and more complex than current structures, making them more susceptible to damage as well as being more difficult to inspect. Consequently, a reliable structural damage detection capability is essential to maintain the flight safety of these structures. Visual inspections alone can not locate impending material failure (fatigue cracks, yielding); it can only observe post-failure situations. An alternative approach is to develop an inspection and monitoring system based on vibration characterization that assesses the integrity of structural and mechanical components. A methodology for detecting structural damage is presented. This methodology is based on utilizing modal test data in conjunction with a correlated analytical model of the structure to: (1) identify the structural dynamic characteristics (resonant frequencies and mode shapes) from measurements of ambient motions and/or force excitation; (2) calculate modal residual force vectors to identify the location of structural damage; and (3) conduct a weighted sensitivity analysis in order to assess the extent of mass and stiffness variations, where structural damage is characterized by stiffness reductions. The approach is unique from other existing approaches in that varying system mass and stiffness, mass center locations, the perturbation of both the natural frequencies and mode shapes, and statistical confidence factors for structural parameters and experimental instrumentation are all accounted for directly.