• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1295
  • 528
  • 290
  • 217
  • 189
  • 57
  • 42
  • 37
  • 35
  • 35
  • 27
  • 21
  • 21
  • 21
  • 21
  • Tagged with
  • 3490
  • 708
  • 454
  • 441
  • 352
  • 346
  • 343
  • 245
  • 237
  • 236
  • 223
  • 213
  • 210
  • 207
  • 188
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Countermeasures against railway ground and track vibrations

Hildebrand, Robert January 2001 (has links)
Railway track and ground vibrations are considered, with anemphasis on methods of mitigation ("countermeasures"), forapplication to wayside disturbance problems. Original field measurements from two sites in Sweden, aswell as borrowed measurements from Norway, provide vibrationresults at many points on the track, on and underneath theground surface, for a variety of trains, both with and withoutcountermeasures in-place. Infinite periodic system theory is the basis of track-onlyand track-ground interaction models presented. The repeatingelement includes the sleeper, pad-fastener, rail, and either alocally-reacting ballast or a continuous ballast-soilwaveguide. The track-only model is even refined for nonlinearand high-frequency cases. The models are suitable for studyingcountermeasures in the track, or in the foundation(soil-stabilization). This latter countermeasure is shown to beeffective at low frequencies (of geotechnical interest), butsometimes counterproductive at audible frequencies (disturbanceproblems). An analytical model for hard seismic screens is alsopresented, to complement the treatment of ground vibrationcountermeasures; this is based on physical approximations whichare favored by "high" (i.e, audible)frequencies and softsoils. Notably, experimentally observed resonant behavior isexplained. <b>Keywords:</b>ground vibration, vibration screen, trackvibration, railway vibration
32

Vibration sensors utilizing fiber fabry-perot interferometers and permanent magnets

Conkey, Andrew P. 15 May 2009 (has links)
A unique set of vibration sensors was designed that incorporate the fiber Fabry-Perot interferometer (FFPI) and permanent magnets. Feasibility of the design and its advantages over traditional sensors were verified by experiments. The new sensors consist of one that monitors the motion of a body across an air gap with the other designed to respond to the motion while in contact with the vibrating body. The FFPI is the device used to transmit the vibrational response while permanent magnets are used to transfer the vibratory motion to the FFPI. In the non-contacting sensor, a permanent magnet was used as the motive to transfer the vibratory motion to be registered at the FFPI. Although the magnet resulted in a non-linear response, the effect of the non-linearity can be removed by signal processing. The fiber optic gap sensor (FOGS) developed has a sensitivity of 250 mV/mil for a 30 mil gap to 50 mV/mil for a 65 mil gap and a dynamic range up to 820 Hz. An advantage of the FOGS over traditional eddy current based gap sensors (ECP), for measuring rotor vibration, was demonstrated with a test rotor face that had brass strips attached to it. The FOGS response was not affected by the strips whereas the response of the traditional ECP was greatly affected by the strips. This demonstrated the potential of the FOGS for measuring the motion of a coated shaft. The fiber optic vibration sensor (FOVS) had a marginal response as its construction led to spurious signals. The feasibility of it to act as a vibration sensor, however, was demonstrated. Due to problems in maintaining the proper gap between the proof mass and sensor head during assembly the natural frequency of the FOVS was around 31 Hz and not the targeted 10 Hz. The sensors presented were meant to be a first generation. However, access to additional FFPI elements was restricted limiting further development. Improvements to the sensors would be to modify the sensing head, magnet size, and the embedment of the FFPI as well as to employ tighter machining precision and assembly practices.
33

Countermeasures against railway ground and track vibrations

Hildebrand, Robert January 2001 (has links)
<p>Railway track and ground vibrations are considered, with anemphasis on methods of mitigation ("countermeasures"), forapplication to wayside disturbance problems.</p><p>Original field measurements from two sites in Sweden, aswell as borrowed measurements from Norway, provide vibrationresults at many points on the track, on and underneath theground surface, for a variety of trains, both with and withoutcountermeasures in-place.</p><p>Infinite periodic system theory is the basis of track-onlyand track-ground interaction models presented. The repeatingelement includes the sleeper, pad-fastener, rail, and either alocally-reacting ballast or a continuous ballast-soilwaveguide. The track-only model is even refined for nonlinearand high-frequency cases. The models are suitable for studyingcountermeasures in the track, or in the foundation(soil-stabilization). This latter countermeasure is shown to beeffective at low frequencies (of geotechnical interest), butsometimes counterproductive at audible frequencies (disturbanceproblems).</p><p>An analytical model for hard seismic screens is alsopresented, to complement the treatment of ground vibrationcountermeasures; this is based on physical approximations whichare favored by "high" (i.e, audible)frequencies and softsoils. Notably, experimentally observed resonant behavior isexplained.</p><p><b>Keywords:</b>ground vibration, vibration screen, trackvibration, railway vibration</p>
34

The tactile perception of vibration frequencies

Joël, Walther D. January 1934 (has links)
Portions of a dissertation (Ph. D.)--University of Southern California. / Bibliography: p. 30.
35

Establishing a vibration threshold value, which ensures a negligible false alarm rate for each gear in CH-53 aircraft using the operational data /

Elyurek, Mehmet. January 2003 (has links) (PDF)
Thesis (M.S. in Operations Research)--Naval Postgraduate School, December 2003. / Thesis advisor(s): Samuel E. Buttrey, Robert Koyak. Includes bibliographical references (p. 77-78). Also available online.
36

The effects of vibration on human performance

Erskine, Julie Anne January 2013 (has links)
Vibration training has been reported to induce acute and chronic physiological adaptations to the skeletal, neuromuscular and central nervous systems, similar to those occurring after a period of resistance or explosive power training. This series of studies aimed to investigate the effects of a single session of vibration exercise, delivered either from a vibrating platform or via a vibrating dumbbell, on several physiological systems. A consistent finding across these studies is that vibration, be it whole body vibration (WBV) or upper-limb vibration, is a significant stressor to the neuromuscular system. Significant reductions in leg extensor muscle (Study I) and elbow flexor muscle (Study III) maximal voluntary isometric force (MVC) were observed following a session of WBV or upper-limb vibration exercise respectively. A single session of WBV however had no effect on bone turnover, endocrine status or voluntary muscle activation in healthy young adult males. The effect of altering the amplitude of vibration was investigated in a subsequent study. High amplitude WBV did not induce greater muscle activation compared to low amplitude WBV, with no significant effects on stretch shortening cycle, postural control, or hormonal status in healthy young adult males. In a similar fashion, a single session of VE with a vibrating dumbbell did not significantly alter maximal isometric force-generating capacity of elbow flexor muscles or the fluctuations in elbow flexion force in comparison to conventional isometric exercise. A novel finding from the research conducted in Study IV was that high speed ultrasonography could be used effectively to analyse vibration damping in-vivo. The results of this study suggest that transverse waves of vibration can be observed propagating along muscle fascicles when a vibratory stimulus is applied.
37

Natural frequencies of non-uniform beams

Ballen, Thomas Joseph, 1939- January 1964 (has links)
No description available.
38

The natural frequencies of vibration of slender uniform beams on elastic supports

Kaser, Raymond Victor, 1938- January 1961 (has links)
No description available.
39

An investigation of the practicability of tuned pendulum type vibration absorbers for use on rotary wing aircraft

Gray, R. B. (Robin Bryant) 08 1900 (has links)
No description available.
40

Ritz series analysis of rotating machinery

Zirkelback, Nicole Lisa 12 1900 (has links)
No description available.

Page generated in 0.1056 seconds