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Vibration modeling and supression in tennis racquets.

Description: The size of the 'sweet spot' is one measure of tennis racquet performance. In terms of vibration, the sweet spot is determined by the placement of nodal lines across the racquet head. In this studx the vibrational characteristics of a tennis racquet are explorod to discover the size and location of the sweet spot. A numerical model of the racquet is developed using finite element analysis and the model is verified using the results from an experimental modal analysis. The affects of string tension on the racquet's sweet spot and mode shapes are then quantified. An investigation is also carried out to determine how add-on vibrational datnpers affect the sweet spot.
Date: January 1, 2003
Creator: Farrar, C. R. (Charles R.); Buechler, M. A. (Miles A.); Espino, Luis & Thompson, G. A. (Gordon A.)
Partner: UNT Libraries Government Documents Department

Nonlinearity in modal and vibration testing.

Description: This set of slides describes some aspects of nonlinear Vibration analysis thru use of analytical fromulas and Examples from real or simulated test systems . The Systems are drawn from a set of examples based on Years of vibration testing experience . Both traditional and new methods are used to describe nonlinear vibration.
Date: January 1, 2003
Creator: Hunter, N. F. (Norman F.)
Partner: UNT Libraries Government Documents Department

Active vibration damping in the presence of uncertainties.

Description: Several control design techniques including PlD, LQG, and PPF are investigated For adive vibration damping of a cantilever beam with uncertain boundary conditions. Step disturbances were used to evaluate the performance of the designed controllers.
Date: January 1, 2002
Creator: Farrar, C. R. (Charles R.); Eisenhour, T. A. (Travis A.); Hatchett, S. (Sam) & Salazar, I. (Isaac)
Partner: UNT Libraries Government Documents Department

FORTE spacecraft vibration mitigation. Final report

Description: This report documents work that was performed by CSA Engineering, Inc., for Los Alamos National Laboratory (LANL), to reduce vibrations of the FORTE spacecraft by retrofitting damped structural components into the spacecraft structure. The technical objective of the work was reduction of response at the location of payload components when the structure is subjected to the dynamic loading associated with launch and proto-qualification testing. FORTE is a small satellite that will be placed in orbit in 1996. The structure weighs approximately 425 lb, and is roughly 80 inches high and 40 inches in diameter. It was developed and built by LANL in conjunction with Sandia National Laboratories Albuquerque for the United States Department of Energy. The FORTE primary structure was fabricated primarily with graphite epoxy, using aluminum honeycomb core material for equipment decks and solar panel substrates. Equipment decks were bonded and bolted through aluminum mounting blocks to adjoining structure.
Date: February 1, 1996
Creator: Maly, J.R.
Partner: UNT Libraries Government Documents Department

Shaker force measurements using voltage and current

Description: In a previous paper (Smallwood and Coleman, 1993), equations were developed which would allow the force into a test item during a vibration test to be measured using voltage and current measurements from the input to an electrodynamic shaker. To accomplish this, the voltage and current required to drive the shaker with no load and with a known mass were required. In this paper, the equations are generalized to cover the case where the measurements are made with several (at least 2) load conditions. It is not required that one of the conditions be the no load condition. The equations are written in a form where the known loads are not required to be a simple mass, but can be a complex impedance. For the case of more than two load conditions, a least squares solution is found.
Date: October 1, 1996
Creator: Smallwood, D.O.
Partner: UNT Libraries Government Documents Department

Theoretical model of granular compaction

Description: Experimental studies show that the density of a vibrated granular material evolves from a low density initial state into a higher density final steady state. The relaxation towards the final density follows an inverse logarithmic law. As the system approaches its final state, a growing number of beads have to be rearranged to enable a local density increase. A free volume argument shows that this number grows as N = {rho}/(1 {minus} {rho}). The time scale associated with such events increases exponentially e{sup {minus}N}, and as a result a logarithmically slow approach to the final state is found {rho} {infinity} {minus}{rho}(t) {approx_equal} 1/lnt.
Date: November 1, 1997
Creator: Ben-Naim, E.; Knight, J.B.; Nowak, E.R.; Jaeger, H.M. & Nagel, S.R.
Partner: UNT Libraries Government Documents Department


Description: The vibration data obtained from ambient, drop-weight, and shaker excitation tests of the Z24 Bridge in Switzerland are analyzed to extract modal parameters such as natural frequencies, damping ratios, and mode shapes. Two system identification techniques including Frequency Domain Decomposition and Eigensystem Realization Algorithm are employed for the extraction of modal parameters and the stationarity of the bridge is also investigated using time-frequency analysis.
Date: October 1, 2000
Creator: Luscher, D.J. & Borwnjohn, J.M.
Partner: UNT Libraries Government Documents Department


Description: Equations describing the hoop stresses in a pipe due to water hammer have been presented in the literature in a series of papers, and this paper discusses the complete derivation of the pertinent equation. The derivation considers the pipe wall response to a water hammer induced shock wave moving along the inner wall of the pipe. Factors such as fluid properties, pipe wall materials, pipe dimensions, and damping are considered. These factors are combined to present a single, albeit rather complicated, equation to describe the pipe wall vibrations and hoop stresses as a function of time. This equation is also compared to another theoretical prediction for hoop stresses, which is also derived herein. Specifically, the two theories predict different maximum stresses, and the differences between these predictions are graphically displayed.
Date: April 30, 2007
Creator: Leishear, R
Partner: UNT Libraries Government Documents Department

Energy scavenging from environmental vibration.

Description: The goal of this project is to develop an efficient energy scavenger for converting ambient low-frequency vibrations into electrical power. In order to achieve this a novel inertial micro power generator architecture has been developed that utilizes the bi-stable motion of a mechanical mass to convert a broad range of low-frequency (< 30Hz), and large-deflection (>250 {micro}m) ambient vibrations into high-frequency electrical output energy. The generator incorporates a bi-stable mechanical structure to initiate high-frequency mechanical oscillations in an electromagnetic scavenger. This frequency up-conversion technique enhances the electromechanical coupling and increases the generated power. This architecture is called the Parametric Frequency Increased Generator (PFIG). Three generations of the device have been fabricated. It was first demonstrated using a larger bench-top prototype that had a functional volume of 3.7cm3. It generated a peak power of 558{micro}W and an average power of 39.5{micro}W at an input acceleration of 1g applied at 10 Hz. The performance of this device has still not been matched by any other reported work. It yielded the best power density and efficiency for any scavenger operating from low-frequency (<10Hz) vibrations. A second-generation device was then fabricated. It generated a peak power of 288{micro}W and an average power of 5.8{micro}W from an input acceleration of 9.8m/s{sup 2} at 10Hz. The device operates over a frequency range of 20Hz. The internal volume of the generator is 2.1cm{sup 3} (3.7cm{sup 3} including casing), half of a standard AA battery. Lastly, a piezoelectric version of the PFIG is currently being developed. This device clearly demonstrates one of the key features of the PFIG architecture, namely that it is suitable for MEMS integration, more so than resonant generators, by incorporating a brittle bulk piezoelectric ceramic. This is the first micro-scale piezoelectric generator capable of <10Hz operation. The fabricated device currently generates a peak power ...
Date: October 1, 2009
Creator: Galchev, Tzeno (University of Michigan); Apblett, Christopher Alan & Najafi, Khalil (University of Michigan)
Partner: UNT Libraries Government Documents Department

Vibration response for a multilayer cylinder

Description: Consider a circular cylinder composed of N concentric layers of materials. Each layer is characterized by its material density {rho}{sub n}, and elastic moduli {lambda}{sub n} and {mu}{sub n} (n = 1,...,N). The interfaces between layers are specified by the radii R{sub 0}, R{sub 1},..., R{sub n}, with R{sub 0} the inner surface and R{sub N} the outer surface of the cylinder.
Date: February 28, 2007
Creator: Chambers, D H
Partner: UNT Libraries Government Documents Department

Downhole Vibration Monitoring and Control System

Description: The objective of this program is to develop a system to both monitor the vibration of a bottomhole assembly, and to adjust the properties of an active damper in response to these measured vibrations. The key feature of this system is its use of a magnetorheological fluid (MRF) to allow the damping coefficient to be changed extensively, rapidly and reversibly without the use of mechanical valves, but only by the application of a current. Phase I of this program, which entailed modeling and design of the necessary subsystems and design, manufacture and test of a full laboratory prototype, was completed on May 31, 2004. Much of the effort was devoted to the design and testing of the MRF damper, itself. The principal objectives of Phase II were: more extensive laboratory testing, including the evaluation of different feedback algorithms for control of the damper; design and manufacture of a field prototype system; and, testing of the field prototype in a drilling laboratory. Phase II concluded on January 31, 2006, and a final report was issued. Work on Phase III of the project began during the first quarter, 2006, with the objectives of building precommercial prototypes, testing them in a drilling laboratory and the field; developing and implementing a commercialization plan. All of these have been accomplished. The Downhole Vibration Monitoring & Control System (DVMCS) prototypes have been successfully proven in testing at the TerraTek drilling facility and at the Rocky Mountain Oilfield Test Center (RMOTC.) Based on the results of these tests, we have signed a definitive development and distribution agreement with Smith, and commercial deployment is underway. This current version of the DVMCS monitors and controls axial vibrations. Due to time and budget constraints of this program, it was not possible to complete a system that would also deal with ...
Date: September 30, 2007
Creator: Cobern, Martin E.
Partner: UNT Libraries Government Documents Department


Description: The objective of this program is to develop a system to both monitor the vibration of a bottomhole assembly, and to adjust the properties of an active damper in response to these measured vibrations. Phase I of this program, which entailed modeling and design of the necessary subsystems and design, manufacture and test of a full laboratory prototype, was completed on May 31, 2004. The principal objectives of Phase II are: more extensive laboratory testing, including the evaluation of different feedback algorithms for control of the damper; design and manufacture of a field prototype system; and, testing of the field prototype in drilling laboratories and test wells. Work during this quarter centered on the testing of the rebuilt laboratory prototype and its conversion into a version that will be operable in the drilling tests at TerraTek Laboratories. In addition, formations for use in these tests were designed and constructed, and a test protocol was developed. The change in scope and no-cost extension of Phase II to January, 2006, described in our last report, were approved. The tests are scheduled to be run during the week of January 23, and should be completed before the end of the month.
Date: January 17, 2006
Creator: Cobern, Martin E.
Partner: UNT Libraries Government Documents Department


Description: The complexities of resonance in multi-degree of freedom systems (multi-DOF) may be clarified using graphic presentations. Multi-DOF systems represent actual systems, such as beams or springs, where multiple, higher order, natural frequencies occur. Resonance occurs when a cyclic load is applied to a structure, and the frequency of the applied load equals one of the natural frequencies. Both equations and graphic presentations are available in the literature for single degree of freedom (SDOF) systems, which describe the response of spring-mass-damper systems to harmonically applied, or cyclic, loads. Loads may be forces, moments, or forced displacements applied to one end of a structure. Multi-DOF systems are typically described only by equations in the literature, and while equations certainly permit a case by case analysis for specific conditions, graphs provide an overall comprehension not gleaned from single equations. In fact, this collection of graphed equations provides novel results, which describe the interactions between multiple natural frequencies, as well as a comprehensive description of increased vibrations near resonance.
Date: May 2, 2010
Creator: Leishear, R.
Partner: UNT Libraries Government Documents Department


Description: One of the concerns in using compact superconducting magnets in the final focus region of the ILC is the influence of the cryogen flow on the vibration characteristics. As a first step towards characterizing such motion at nanometer levels, a project was undertaken at BNL to measure the vibrations in a spare RHIC quadrupole under cryogenic conditions. Given the constraints of cryogenic operation, and limited space available, it was decided to use a dual head laser Doppler vibrometer for this work. The performance of the laser vibrometer was tested in a series of room temperature tests and compared with results from Mark L4 geophones. The laser system was then used to measure the vibration of the cold mass of the quadrupole with respect to the outside warm enclosure. These measurements were carried out both with and without the flow of cold helium through the magnet. The results indicate only a minor increase in motion in the horizontal direction (where the cold mass is relatively free to move).
Date: October 17, 2005
Creator: JAIN, A.; AYDIN, S.; HE, P.; ANERELLA, M.; GANETIS, G.; HARRISON, M. et al.
Partner: UNT Libraries Government Documents Department


Description: To compensate modulated beam-beam offsets caused by mechanical vibrations of IR triplet quadrupoles at frequencies around 10 Hz, a fast IR orbit feedback system has been developed. We report design considerations and recent status of the system.
Date: June 26, 2006
Partner: UNT Libraries Government Documents Department

Investigation of Pipelines Integrity Associated With Pump Modules Vibration for Pumping Station 9 of Alyeska Pipeline Service Company

Description: Since the operation of PS09 SR module in 2007, it has been observed that there is vibration in various parts of the structures, on various segments of piping, and on appurtenance items. At DOT Pipeline and Hazardous Materials Safety Administration (PHMSA) request, ORNL Subject Matter Experts support PHMSA in its review and analysis of the observed vibration phenomenon. The review and analysis consider possible effects of pipeline design features, vibration characteristics, machinery configuration, and operating practices on the structural capacity and leak tight integrity of the pipeline. Emphasis is placed on protection of welded joints and machinery against failure from cyclic loading. A series of vibration measurements were carried out by the author during the site visit to PS09, the power of the operating pump during the data collection is at about 2970KW, which is less than that of APSC's vibration data collected at 3900KW. Thus, a first order proportional factor of 4900/2970 was used to project the measured velocity data to that of APSC's measurement of the velocity data. It is also noted here that the average or the peak-hold value of the measured velocity data was used in the author's reported data, and only the maximum peak-hold data was used in APSC's reported data. Therefore, in some cases APSC's data is higher than the author's projective estimates that using the average data. In general the projected velocity data are consistent with APSC's measurements; the examples of comparison at various locations are illustrated in the Table 1. This exercise validates and confirms the report vibration data stated in APSC's summary report. After the reinforcement project for PS09 Station, a significant reduction of vibration intensity was observed for the associated pipelines at the SR Modules. EDI Co. provided a detailed vibration intensity investigation for the newly reinforced Pump Module structures ...
Date: September 1, 2009
Creator: Wang, Jy-An John
Partner: UNT Libraries Government Documents Department