Browsing by Subject "Damping (Mechanics)"
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Item Absorption characteristics of impact vibration absorbers(Texas Tech University, 2002-05) Ozerdim, CaglarThis research deals with passive vibration control of a primary mass using impact vibration absorbers (IVA). Primary mass is the structure for which the vibrations are to be mitigated. Different types of IVAs have been proposed, studied and used in practical applications. This research is on two types of IVAs, namely, simple IVA and compound IVA. In simple IVA the impact mass hangs from a pendulum not connected to the primary mass. In compound IVA the impact mass hangs from a pendulum connected to the primary mass. The first objective of this research was to compare the effect of the pendulum arm length on the absorption characteristics of the simple and compound IVA. The second objective was to determine the effect of the mass ratio, excitation amplitude, and clearance between impact walls on absorber efficiency of the compound IVA model. For transient vibration involving compound IVAs it was shown that the longest pendulum was more efficient than the shortest pendulum. The largest clearance was more efficient than the smallest clearance. For the largest initial displacement the vibrations were attenuated faster than for the smallest initial displacement. For forced vibrations, the simple IVA (compare to the compound IVA) has a more pronounced inefficient absorption region. This is due to the apparent shift of the resonance point. On the other hand the compound IVA hardly has a clear inefficient absorption region. In the respective absorption region, it is noted that the single IVA has a more prominent vibration absorption level. It was also noted that for the simple IVA the shortest pendulum length is the most efficient, while for the compound IVA the shortest pendulum length is the least efficient.Item Controlled electrodynamic suspension vehicle damping(2006-05) Knierim, Glenn Auld, 1970-; Driga, Mircea D.Commercial application linear motion magnetically levitated, maglev, bodies are inherently unstable owing to minimal large magnitude or prolonged oscillating disturbance natural damping. Induced vibrations into large inertial, magnetically levitated bodies experience resonance under certain operating conditions. Maglev vehicles typically incorporate a non-magnetic ancillary damping suspension system as compensation. Maglev designers desire an efficient, solely magnetic based damping system without auxiliary compensation for these large inertial vehicles, but no effective system has presented itself. This paper investigates the unstable nature of a maglev electrodynamic suspension, E.D.S., system. Electromagnetic solenoid coils operating in concert with an appropriate control law offer this solution. A hierarchy of controlled, electromagnetic damping suspension systems is theorized and analyzed and in one case designed, fabricated, and tested. These designs range from a single degree of freedom, D.O.F., maglev suspension to a dynamically coupled six D.O.F. maglev suspension. Solenoid coils form the electromagnetic damping prime mover hardware. Soft computing optimal nonlinear control forms the final electromagnetic damping control kernel for this proof of concept paper whereas soft computing adaptive nonlinear control forms the final electromagnetic damping control kernel for a proposed final system solution.Item Dynamic characteristics of municipal solid waste (MSW) in the linear and nonlinear strain ranges(2007-12) Lee, Jung Jae, 1973-; Stokoe, Kenneth H.A series of resonant column and torsional shear (RCTS) and large scale resonant column (LSRC) tests were performed to investigate the dynamic properties (shear modulus and material damping ratio) of municipal solid waste (MSW). the MSW materials were recovered from the Tri-Cities landfill adjacent to the San Francisco Bay in California. A total of 30 specimens 2.8-in. (71.1-mm) and 6.0-in. (152.4-mm) of old, fresh, and mixed MSW were reconstituted in accordance with established sample preparation procedures. Ten of specimens were small-diameter (2.8-in. (71.1-mm)) RCTS specimen and 20 specimens were larger (6.0-in. (152.4-mm)) LSRC specimens. Dynamic laboratory measurements were performed in the linear and nonlinear strain ranges. Test parameters affecting the dynamic properties in the linear range included: (1) duration of confinement, (2) isotropic total confining pressure, [sigma]o, (3) excitation frequency, f, and (4) specimen size. Other test parameters affecting dynamic properties in the nonlinear strain range were: (1) shearing strain amplitude, [gamma], (2) isotropic total confining pressure, (3) overconsolidation ratio, (4) number of loading cycles, and (5) excitation frequency. In addition, the effects on dynamic properties of MSW specimens of material parameters such as (1) waste composition, (2) water content, (3) unit weight of waste, and (4) particle size were evaluated. The total unit weights of old, fresh, and mixed MSW specimens were estimated during testing in the RCTS and LSRC devices. These estimated total unit weights in the laboratory were compared with those measured at other MSW landfills and were found to generally be less than the field measurements. At a given [sigma]o, Gmax decreases with decreasing weight percentage of soil-size (passing the 3/4-in. (19.1-mm) sieve) material. However, Dmin increases slightly with decreasing weight percentage of soil-size material. Another relationship was developed between estimated total unit weight, [gamma]t, and confining pressure, including weigh percentage of soil-size material. The Vs profiles of old, fresh, and mixed MSW specimens obtained in the laboratory tests were compared with those measured at other MSW landfills in situ. The 62 to 76% soil-size material groups are in good agreement with in-situ Vs profiles. The variation in normalized shear modulus and material damping ratio curves were patterned after the Darendeli model (2001) for different weight percentages of soilsize material. An empirical relationship between normalized shear modulus (G/Gmax) and modified material damping ratio (D-Dmin) was developed in the nonlinear strain range. As part of collaborative research project, nonlinear shear modulus reduction and material damping curves generated by The University of Texas at Austin (UT) and The University of California at Berkeley (UCB) were compared according to different weight percentages of soil-size material. Furthermore, nonlinear shear modulus reduction and material damping ratio curves generated by UT were also compared with ones previously proposed by other researchers.Item Lubrication as a damping force in the model of eye rotation under listing's constraint(2012-05) Karsli, Neslihan; Aulisa, Eugenio; Ibragimov, Akif; Ghosh, Bijoy K.In this work, the effect of lubrication forces to the rotation of the eye is investigated where the eye is modeled as a perfect sphere and the movement is restricted to Listing's Law. For the lubrication forces, the nondimensional forms of Navier-Stokes and continuity equations are found, the boundary conditions are applied and the torques are derived. Then, Listing's constraint is introduced to the model and a potential function and lubrication as a damping force has been added. Using lubrication as a damping force, an optimum potential function for the model is derived.Item Propagation and damping of the fast Alfven wave in the Texas Tech Tokamak(Texas Tech University, 1983-08) Coleman, Phillip DalePropagation and damping of the fast Alfven wave has been investigated for a deuterium-hydrogen plasma in a small research Tokamak. Magnetic probes served as the principle diagnostic in studying the waves* dispersion characteristics, the eigenmode Q's and the radial profiles of the electrical field polarization. Results indicate that a simple cylindrical model is sufficient for predicting the waves* dispersion properties, Q measurements supply strong evidence that the fast wave damping is dependent on resonance layers in the plasma. The dependence of Q on percentage hydrogen in the predominantly deuterium plasma suggests that mode conversion of the fast wave to the ion Bernstein wave at the ion-ion hybrid resonance layer may be occurring. The measured field patterns differed substantially from theoretical expectations and no localized resonance layer effect was detected in the polarization profiles. However, a more quiescent plasma and better spatial resolution of the probe measurements may help in resolving some mode conversion effects.Item Response of a rotating machine supported on nonlinear springs(Texas Tech University, 1988-05) Chew, Eng KeongThe dynamic response of a two-degree-of-freedom rotating machine supported on hardening springs and viscous dampers is investigated. The rotating machine is subjected to internal forces caused by the eccentricity of the center of mass of the rotor. The equations of motion of the system were determined from Lagrange's equation. The system has cubic nonlinearities. The method of multiple scales was then used to determine the response of the system. The method predicts that primary resonance occurs when the excitation frequency Q is near the first modal frequecy o)i, and the second modal frequency 0)2. The method also predicts that the system can have internal resonance when o)2~3o)i. The response of the system was determined when the excitation frequency is near the first and the second modal frequency under noninternal resonance and internal resonance conditions. The system exhibits the jump phenomena near the mode frequencies of the system. Unimodal response was also observed under internal resonance conditions when Ω≈~W2.Item Wave propagation and damping in a hot, bounded plasma(Texas Tech University, 1971-08) Cato, James EarlNot available