Analysis of Modal Parameters of Adhesively Bonded Double-Strap Joints by the Modal Strain Energy Method

This paper presents the analysis of modal parameters (natural frequencies, damping ratios and mode shapes) of a simply supported beam with adhesively bonded double-strap joint by the finite-element based Modal Strain Energy (MSE) method using ANSYS 4.4A software. The results obtained by the MSE method are compared with closed form analytical solutions previously obtained by the first author for flexural vibration of the same system. Good agreement has been obtained between the two methods for both the natural frequencies and system loss factors. The effects of structural parameters and material properties of the adhesive on the modal properties of the joint system are also studied which are useful in the design of the joint system for passive vibration and noise control. In order to evaluate the MSE and analytical results, some experiments were conducted using aluminum double-strap joint with 3M ISD112 damping material. The experimental results agreed well with both analytical and MSE results indicating the validity of both analytical and MSE methods. Finally, a comparative study has been conducted using various commercially available damping materials to evaluate their relative merits for use in the design of these joints.

A Forced Response Analysis and Application of Impact Dampers to Rotordynamic Vibration Suppression in a Cryogenic Environment

A high speed damper test rig has been assembled at Texas A&M University to develop rotordynamic dampers for rocket engine turbopumps that operate at cryogenic temperatures, such as those used in the Space Shuttle Main Engines (SSMEs). Damping is difficult to obtain in this class of turbomachinery due to the low temperature and viscosity of the operating fluid. An impact damper has been designed and tested as a means to obtain effective damping in a rotorbearing system. The performance and behavior of the impact damper is verified experimentally in a cryogenic test rig at Texas A&M. Analytical investigations indicate a strong amplitude dependence on the performance of the impact damper. An optimum operating amplitude exists and is determined both analytically and experimentally. In addition, the damper performance is characterized by an equivalent viscous damping coefficient. The test results prove the impact damper to be a viable means to suppress vibration in a cryogenic rotorbearing system.

Parametric Studies on Muffler Design With Applications to a Vacuum Pump

A computer simulation was employed to perform parametric studies on muffler design. Engine exhaust system parameters such as muffler diameter, source-muffler pipe length, number of mufflers, series and parallel installation of mufflers, and the source and termination impedances were considered during the studies. The muffler insertion loss and radiated sound pressure level were predicted for several values of each parameter. An acoustic model consisting of a lumped source-muffler-termination system was used. A scheme was developed using the pressure source model to predict the radiated sound pressure and a simplified expression for the predicted quantity was obtained as a sum of the measured, plane wave and monopole terms. The relationship between the insertion loss and radiated sound pressure level was established for a given set of conditions. A vacuum pump was used as the sound source. An expansion chamber was used as a muffler.

A Numerical Approach for the Prediction and Reduction of Structure-Borne Noise During the Design Stage of Ground Vehicles

During the design stage of ground vehicles it is important to reduce the noise emitted from structural components. In commercial applications the reduction of the interior noise for passenger comfort is a concern with increased significance. In military applications noise radiated from the exterior of the vehicle is of primary importance for the survivability of the vehicle. Numerical acoustic prediction software can be used during the design stage to predict and reduce the radiated noise. Two formulations, the Rayleigh integral equation1 and the direct boundary element method2,3 were implemented into software for acoustic prediction. The developed code can accept information from a finite element model with a known input forcing function. Specifically, the predicted velocities on the structural surfaces can be used as input to the acoustic code for predicting the noise emitted from a vibrating structure. Computation of acoustic sensitivities4 was also implemented in the code. This information can identify the portions of the boundary that effect the radiated noise most, and it can be used in an optimization process to reduce the noise radiated from a vibrating structure.

Comparison of Finite Element Models for Predicting Structural Vibration

Three structural finite-element models of a small aluminum box with moderately thick walls, representative of a powertrain casting structure, are assessed by comparisons with measured vibration data. The finite element models are: (1) a plate element model, (2) a solid element model, and (3) a hybrid model consisting of plate, beam, and rigid elements. Both lumped- and consistent-mass formulations are evaluated. Comparisons are made with the measured velocity vibration response to shaker excitation. The consistent-mass plate model and the lumped-mass solid model are found to be comparable in accuracy, while the hybrid model can be tuned to achieve the greatest accuracy by matching the measured mode frequencies. The study illustrates the difficulty in accurately predicting the narrow-band vibration response of even a relatively simple structure. However, it is shown that all three models predict a similar one-third octave-band response, which is a vibration measure commonly used in practice.

Multi-Mass Absorbers Effective in Wide Frequency Band

One of the most efficient method of vibration control is the method of dynamic damping. Most existing theory enables a design of a dynamics damper for a one degree-of-freedom system. Here the theory is extended to allow for a design of dynamic mass dampers with viscous friction suitable for a systems with multiple degrees-of-freedom. Effective method of multi-mass absorbers in a wide angular frequency band was designed and developed. Finally, by inspection of the frequencies for the amplitudes of vibrations of the essential masses within the vibratory system are reduced or decreased to zero. One may optimize the various designs of dynamic systems containing mass-damping elements. Detailed numerical analysis and specific calculations are performed in this publication.

Putting Statistics Into the Statistical Energy Analysis of Automotive Vehicles

Sound and vibration transmission modeling methods are important to the design process for high quality automotive vehicles. Statistical Energy Analysis (SEA) is an emerging design tool for the automotive industry that was initially developed in the 1960’s to estimate root-mean-square sound and vibration levels in structures and interior spaces. Although developed to estimate statistical mean values, automotive design application of SEA needs the additional ability to predict statistical variances of the predicted mean values of sound and vibration. This analytical ability would allow analysis of vehicle sound and vibration response sensitivity to changes in vehicle design specifications and their statistical distributions. This paper will present an algorithm to extend the design application of the SEA method through prediction of the variances of RMS responses of vibro-acoustic automobile structures and interior spaces from variances in SEA automotive model physical parameters. The variance analysis is applied to both a simple, complete illustrative example and a more complex automotive vehicle example. Example variance results are verified through comparison with a Monte Carlo test of 2,000 SEA responses whose physical parameters were given Gaussian distributions with means at design values. Analytical predictions of the response statistics agree with the statistics generated by the Monte Carlo method but only require about 1/300 of the computational effort.

Development of a Houde Damper Using Magnetic Damping

This paper presents experimental results that demonstrate the vibration suppression effectiveness of a Houde damper, a type of dynamic absorber that contains an auxiliary mass and a damping element. The damper that was developed uses an eddy current brake consisting of a pair of permanent magnets and a copper plate which acts as a conductor. A vibration test using a straight piping model was used to show that the Houde damper is effective not only in reducing small amplitude vibrations, but large amplitude vibrations as well. Analytical calculations were used to establish that the precise tuning required for effective vibration suppression using a conventional dynamic absorber (that is, a passively tuned mass damper) is not necessary for the Houde damper.

A Variational Method for Solving Vibration Problems

Rayleigh-Ritz and Galerkin methods are frequently used in engineering to solve boundary value and eigenvalue problems. The success in applying these methods depends entirely on the construction of a variational entity called the functional, and the choice of a system of elements known as the basis functions. This in some cases greatly narrows down the class of problems to which the above methods may be applied. Here, we present a specific but sufficiently general method known as the Methods of Moments for constructing the elements going into the expansion of the approximate solution. The Method of Moments has been shown to posses the capability of generating the basis functions successfully. The Method of Moments in its various forms has been widely used in electromagnetism. Due to generality involved in the construction of these basis functions, the Method of Moments may be readily used to solve a large variety of problems arising in discrete as well as continuous vibrating systems. This idea forms the central theme of this article.

Reduction of Precision Spindle Vibration by Radial Shear-Layer Damping

A damping technique is proposed as a simple method for reducing non-repeatable radial runout (NRR) in magnetic disk file assemblies. Using finite element methods, the behavior of a typical system is investigated using eigenvalue and steady state response analyses to assess the benefits and shortcomings of the proposed technique. Simple impact response experiments are then performed to verify the analytical results. It is seen both in the numerical analysis and experimentation that the overall magnitudes of the radial response can be reduced using the proposed technique, and topics for continued investigation of the subject are discussed.